Symposium Organizers
Mircea Chipara The University of Texas Pan American
Pulickel M. Ajayan Rice University
Ali Nasar CNC Coatings
Alan Kin-Tak Lau The Hong Kong Polytechnic University
II3: Poster Session: Polymer-Based Nanocomposites
Session Chairs
Tuesday AM, November 30, 2010
Exhibition Hall D (Hynes)
II2: Modeling of Polymer-Based Nanocomposites
Session Chairs
Monday PM, November 29, 2010
Republic B (Sheraton)
2:30 PM - II2.1
Nanoscale Visualization and Multiscale Mechanical Implications of the Bound Rubber Interphase in Rubber-carbon Black Composites.
Meng Qu 1 , Fei Deng 1 , Agathe Robisson 2 , Krystyn Van Vliet 1
1 , MIT, Cambridge, Massachusetts, United States, 2 , Schlumberger-Doll Research and Development , Cambridge, Massachusetts, United States
Show AbstractThe concept of a “bound rubber” phase extending over nanometer-scale distances from the interface of rubber-particle nanocomposites is generally accepted. However, the thickness and elastic properties of this interphase have not been confirmed by direct experimental observation. Here, we demonstrate the existence of bound rubber in hydrogenated nitrile butadiene rubber (HNBR)-carbon black composites, through direct visualization and measurement of elastic properties. Both macro- and nanoscale mechanical analyses show that the bound rubber exhibits an elastic modulus distinct from that of the rubber matrix and of the particles. Direct visualization of this bound rubber via scanning probe microscopy-based imaging shows that the bound rubber content decreases with increasing temperature, and that this bound rubber stiffness exceeds that of the rubber matrix by approximately one order of magnitude. The measured thickness and elastic moduli of this bound rubber are consistent with that predicted by our numerical model of a matrix-interphase-particle composite. Together, these experiments and model demonstrate that the mechanical properties of nanocomposite interphases of less than 20 nm thickness can be directly interrogated.
3:00 PM - II2.3
Waviness Dominated Controlled Morphology Nanocomposite Modeling with Experimental Correlation.
Hulya Cebeci 1 2 , Halit Turkmen 2 , Brian Wardle 1
1 Aeronautics and Astronautics, MIT, Cambridge, Massachusetts, United States, 2 Aeronautical Engineering, ITU, Istanbul Turkey Turkey
Show AbstractControlled morphology of a nanocomposite is critical to realizing the potential of carbon nanotubes (CNTs) as structural reinforcement. As opposed to filler-like concepts in the literature, CNTs in this study have a morphology similar to fibers in advanced composites; aligned, high volume fraction (exceeding 20%), collimated, continuous, high graphitic quality and homogeneously dispersed in a surrounding matrix without voids or inclusions. Aligned polymer nanocomposites (A-PNCs) are fabricated using capillarity-driven wetting, avoiding dispersion issues and then mechanically densified [1] to obtain desired volume fractions so that the CNTs can dominate composite properties and so that non-istotropic properties can be assessed, such as electrical conductivity.Overall, the A-PNC properties show a volumetric effect from the CNTs, and CNT waviness is noted as a dominant morphological effect controlling modulus by comparing the experimental results to standard composite theories modified to account for CNT waviness [2]. Prior wavy PNC analysis [3] had several assumptions that can be improved: appropriate elastic modulus assumptions and bending of the CNT are not considered due to symmetric boundary conditions invoked. In the current work, an improved FE model is developed to understand the importance of those parameters and investigate the tension vs. compression behavior of the PNC as compared to experimental data obtained via nanoindentation. Implications for the realization of CNT potential in polymer matrices such as advanced composite applications are elucidated. 1. Wardle, B.L., Saito, D.S., Garcia, E.J., Hart, A.J., deVilloria, R.G.,, Fabrication and Characterization of Ultra-High Volume Fraction Aligned Carbon-Nanotube-Polymer Composites, Advanced Materials, Vol. 20, 2008, pp. 2707-27142. Cebeci, H., de Villoria, R. G., Hart, A. J., Wardle, B. L., Multifunctional properties of high volume fraction aligned carbon nanotube polymer composites with controlled morphology", Composites Science and Technology (2009), Vol. 69, pp. 2649-26563. Fisher, FT, Bradshaw, RD, and LC Brinson (2002). “Effects of nanotube waviness on the modulus of nanotube-reinforced polymers”, Applied Physics Letters, Vol. 80, pp. 4647-4649
3:15 PM - **II2.4
Multiscale Modelling of Polymer-Based Carbon Nanocomposites.
James Elliott 1
1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom
Show AbstractPolymer-based carbon nanocomposites, usually containing filler materials such as multi-wall carbon nanotubes (MWCNTs), graphene, carbon black, or mixtures thereof, are now widely employed to enhance the electrical, mechanical and thermal properties of a polymer matrix. However, difficulties with achieving uniform dispersion or adequate coupling of the filler-matrix interface can limit or even degrade overall performance, leading to a wide range of experimental results in the literature. In this talk, a multiscale computational modelling framework is presented to generate atomistic morphologies for polymer-based carbon nanocomposites from mesoscale simulations, and use these to investigate their elastic properties, electrical conductivity and thermal conductivity. The polymer matrix was prepared using a coarse-grained lattice model to fully relax the chain conformation near the nanotube-polymer interface, followed by reverse-mapping of an atomistic structure (polyethylene, PE). Calculation of elastic modulus revealed deviations from rule-of-mixtures behaviour due to structuring of the polymer at the filler-matrix interface. On the other hand, using a mesoscale model for geometric packing of filler particles, the electrical conductivity was found to be dominated by network percolation effects related to shape, orientation and distribution of filler particles and relatively insensitive to tunnelling effects at the interface. For this reason, mixtures of particles of small and high aspect ratios were generally found to give superior properties to monodisperse mixtures at high degrees of filler orientation, such as may occur during processing or shear mixing. By contrast, thermal conductivity is mainly determined by the thermal boundary or Kapitza resistance (TBR), which was calculated for the CNT-PE composite system via a lumped heat capacity method using the temperature difference between the CNT and PE matrix obtained from non-equilibrium molecular dynamics simulations. The results show that the TBR increases with stiffness of the CNT, indicating elastic heat transport at the interface. On the other hand, TBR decreases with increasing temperature, indicating an increasing contribution of inelastic heat transport. This may indicate the possibility of intrinsic interfacial resistance coupling by tuning the structure of polymer at the interface. In summary, an improved understanding of the morphology of polymer-based carbon nanocomposites at multiple length scales obtained by modelling gives helpful insights into improving their performance.
3:45 PM - II2.5
Microstructural and Mechanical Properties of Polyester/Nanoclay Nanocomposites: Microstructure-mixing Strategy Correlation.
Hamid Dalir 1 , Vireya Nhim 1 , Benjamin Samson 1 , Martin Levesque 1 , Daniel Therriault 1
1 Mechanical Engineering, Ecole Polytechnique de Montreal, Montreal, Quebec, Canada
Show AbstractResearch in nanoclay related polymer composites has been a hot topic in past few years, because the use of this material in fabrication of nanocomposites enables us to enhance the mechanical, thermal and electrical properties of polyester resins such as polylactic acid (PLA) and polyethylene terephthalate (PET). However, these composites have only achieved a small modulus, strength and stiffness increment that is below expected potential. The difficulties are on how to produce uniformly-dispersed polyester/nanoclay composites and avoid clustering effect. In this report, different nanoclay mixing strategies using a three-roll mill and ultrasonication for different weight percentages up to 6 wt% was proposed to obtain the optimal polyester/nanoclay dispersion. The best dispersion of the modified nanoclay in polymer with 4 wt% loading was confirmed from X-ray diffraction, and high magnification scanning electron microscopy (SEM). The mechanical properties of the clay-reinforced polyester nanocomposites were found by means of a dynamic mechanical analyzer (DMA), tensile test machine and three point bending and were observed to be a function of nature and the content of nanoclay in the matrix. The nanocomposite containing 4 wt% modified nanoclay exhibits excellent improvement in tensile strength (by ~27%), thermal stability (6 °C higher), and storage modulus at 25 °C (by ~42%). These mechanical enhancements are a consequence of the successful dispersion of the nanoclays inside the polyester matrix which will make them ideal materials for potential applications in transportation and packaging industry.
4:00 PM - II2:MODEL
BREAK
4:15 PM - II2.6
Simulations of Carbon Nanotube/Polymer Composites.
Ali Eken 1 , Emilio Tozzi 2 , Daniel Klingenberg 3 , Wolfgang Bauhofer 1
1 , Institute of Optical and Microelectronic Materials, Technische Universität Hamburg- Harburg, Hamburg Germany, 2 Department of Chemical Engineering and Materials Science, University of California, Davis, California, United States, 3 Department of Chemical and Biological Engineering, University of Wisconsin, Madison, Wisconsin, United States
Show AbstractWe used particle level simulations to simulate carbon nanotube (CNT)/polymer suspensions. A resistor network algorithm was developed to measure the electrical conductivity of these composites. Our method is suitable to study effects of different parameters such as nanotube shape, nanotube aspect ratio and flow fields on the suspension conductivity. Simulations showed that concentrations above the percolation threshold follow a power-law dependence of conductivity on concentration, and imposed shear flow can decrease the electrical percolation threshold. Effects of nanotube aspect ratio and shape were investigated. In order to achieve a percolating conductive network with low nanotube fractions, nanotubes with high aspect ratio should be used. Our results showed that using curved nanotubes in sheared suspensions assists agglomeration which reduces the percolation threshold, whereas in randomly distributed suspensions, using straight nanotubes instead of curved ones gives lower percolation thresholds. These two different behaviors are attributed to different agglomeration behaviors of the systems. The conductivity evolution during shearing for different concentrations was also investigated. We showed that at low concentration, percolating clusters form and break simultaneously which causes large conductivity fluctuations during the simulations. When sufficiently large concentrations are reached, percolating clusters persist during shearing and the conductivity fluctuations decrease. Finally, effects of shearing on structure and electrical conductivity were investigated. As previously shown in many experimental studies, increasing shear stresses cause complete dispersion and aligning of the nanotubes in the flow direction which causes a reduction in conductivity.
4:30 PM - **II2.7
Multiscale Simulation Study of Nano-reinforced Epoxy.
Kelvin Suggs 1
1 Physics, Clark Atlanta University, Atlanta, Georgia, United States
Show Abstract Nanocomposites are of increasing interest due to their unique structural, electronic, and thermal properties. Simultaneously, multiscale molecular modeling is becoming more robust in accordance with Moore’s Law as computing memory, power, and speed continue to improve. Therefore computational models are able to be examined with increased accuracy, complexity, and dimension. Graphene based molecules are lauded for their conductive properties as well as their architecture-like geometry which may allow bottom up nanoscale fabrication of nanoscopic structures. Furthermore, these macrocycled molecules allow high interactivity with other molecules including highly tensiled polymers that yield other novel supramolecular structures when intereacted. These supramolecular structures are being investigated in lieu of a variety of potential military and commercial applications. A fundamental issue is how the self-organized dynamic structure of functional molecular systems affects the interactions of the nano-reinforced composites. To this end we employ a combination of force-field based molecular dynamics and local density-functional calculations. Force-field based molecular dynamics was used to pre-select molecular geometries, and first-principles calculations were employed to determine the electronic structure of the nano-reinforced composites.Our results show that the stacking between the aromatic macrocycle and the surface of the SWNTs manifests itself via increased interfacial binding. First-principles calculations on the electronic structures further reveal that there exists distinct level hybridization behavior for metallic and semiconducting nanotubes. In addition, there is a monotonic increase in binding energy with an increase in the nanotube diameter. Our simulation studies suggest that graphene nanoplatelets are potentially the best fillers of epoxy matrices.
5:00 PM - II2.8
Predicting Macroscale Elastic Properties of Nanocomposite Materials Exhibiting a Particle-matrix Interphase.
Fei Deng 1 , Krystyn Van Vliet 1
1 material science and engineering, massachusetts institute of technology, Cambridge, Massachusetts, United States
Show AbstractPolymer composites comprising nanoscale particles often exhibit macroscale mechanical properties that are described poorly by micromechanical homogenization models including only the particle and matrix phases. The existence of an interfacial region between the particle and matrix, termed the interphase, has been posited and indirectly demonstrated to account for elastic properties of such nanocomposites. Here, we present a facile analytical approach to estimate the effective elastic properties of composites, for cases when these composites comprise particles encapsulated by an interphase of finite thickness and distinct elastic properties. We show that the predicted elastic properties of particle reinforced nanocomposite agree well with a range of reported experiments for epoxy-based composites comprising either metal or oxide nanoparticles. Finally, we demonstrate the relative influence of particle-polymer interphase thickness and stiffness, in order to identify maximum possible changes in macroscale elastic properties.
5:15 PM - **II2.9
Length Scales of Interactions in Multifunctional Nanocomposites.
Ralph Skomski 1 , Balamurugan Balasubramanian 1 , Eva Schubert 2 , Axel Enders 1 , D. Sellmyer 1
1 Physics and Astronomy, University of Nebraska, Lincoln, Nebraska, United States, 2 Department of Electrical Engineering, University of Nebraska, Lincoln, Nebraska, United States
Show AbstractThe development of multifunctional and multiferroic nanostructures constitutes an important trend in materials science, and a key question is the range of the involved electric, magnetic, and elastic interactions. Many interaction mechanisms are long-range and described, for example, by Maxwell's equations or continuum mechanics, but some have ranges from 1 or 2 nm to about 100 nm and can be specifically exploited in nanostructures. We discuss these length scales for a number of composites with mechanical, dielectric, and/or magnetic degrees of freedom. Emphasis is on magnet-polymer nanocomposites [1], such as barium ferrite in styrene-butadiene-styrene and Fe in polypyrrole. The magnetic regions have different shapes, from nanoparticles to slanted columns and nanospirals produced by glancing-angle deposition onto a rotating substrate. For each system, there are typically two different length scales, depending on whether one considers volume-averaged or extrinsic or defect-related physical properties. The former are often, but not always, proportional to the relative interface area between the phases. The latter include fracture, breakdown, and hysteresis in mechanical, dielectric, and magnetic composites, respectively, and typically show a logarithmically weak dependence on the macroscopic system size. Nanoscale interaction lengths reflect competing interactions of atomic origin, such as exchange and spin-orbit coupling, complemented by statistical segment lengths and gyration radii in polymers. One example is multiferroic crystal-field interactions between ferroelectric and ferromagnetic phases. The coupling between magnetic and electric degrees of freedom is usually discussed in terms of elastic interactions and electronic-structure effects near interfaces. However, if the ferromagnetic phase is a rare-earth oxide, then there is a long-range crystal-field interaction between the ferroelectric (FE) and ferromagnetic (FM) phases. The effect involves spin-orbit coupling, and its magnitude is given by the electrostatic interaction between the FE dipole moments and the quadrupole moments of the rare-earth 4f shells, similar to crystal-field-controlled anisotropy mechanism in rare-earth magnets [2]. Aside from a relatively small screening contribution, the interaction is proportional to dipole-field gradient and therefore decreases as 1/D4 with increasing distance D between 4f ions and the ferroelectric dipole moments. By comparison, uniaxial and cubic rare-earth anisotropies involve 1/D3 and 1/D5 power laws, respectively. Our examples show how well-known fundamental interactions yield intriguing new physics when applied to complex nanostructures. — This research is supported by NSF-MRSEC and NCMN. — [1] M. Chipara, D. Hul, J. Sankar, D. Leslie-Pelecky, A. Bender, L. Yue, R. Skomski, and D. J. Sellmyer, Composites Part B-Engineering 35, 235 (2004). [2] R. Skomski, Simple Models of Magnetism, University Press, Oxford 2008.
5:45 PM - II2.10
Hierarchical Structured Nanocomposite of Liquid Crystalline Block Copolymer and Magnetic Nanoparticles.
Yuxiang Zhou 1 , Rubinder Kaur Lakhman 2 , Rajeswari Kasi 1 2
1 Department of Chemistry, University of Connecticut, Storrs, Connecticut, United States, 2 Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States
Show AbstractSelf-assembled microsegregation of block copolymers provides an important approach of the “bottom-up” techniques to build up materials with hierarchical structures. Further introduction of different functional groups or nanoparticles into the microphase separated block copolymers can produce smart materials/nanocomposites which are capable of being responsive to multiple types of stimuli and undergo conformational or structural change at different length scales.In the present study, we design and synthesized a well-defined pentablock copolymer with poly(acrylic acid) (PAA), polymethacrylate with side chain cholesterols via methylene spacers (PCnMA) and poly(ethylene glycol) (PEG), in the sequence as PAA-PCnMA-PEG-PCnMA-PAA. This polymer can stabilize the Fe3O4 magnetic nanoparticles (MNPs) in aqueous solution through the coordination bonding between acid groups and the surface of the MNPs. The resulted ferrofluid can be cast to produce films, which undergo microphase separation while annealing. The annealed films contain hierarchical structures with liquid crystalline (LC) ordering of cholesterols at the length scale of ~5 nm as well as microphase separation at the length scale of ~40 nm, with the MNPs confined at particular microsegregated domain. Due to the LC, acidic functional groups and MNPs, this material can be responsive to temperature, pH and magnetic field, respectively. Currently we are working on preparing devices such as magnetic field triggered actuators with this nanocomposite.
II3: Poster Session: Polymer-Based Nanocomposites
Session Chairs
Tuesday AM, November 30, 2010
Exhibition Hall D (Hynes)
9:00 PM - II3.1
Study ITO@PMMA Composites by Transmission Electron Microscopy.
Marcelo Orlandi 1 , Elen Arlindo 1
1 Physical-Chemistry, São Paulo State University, Araraquara, São Paulo, Brazil
Show AbstractNanocomposites are materials that have two or more solid phases, and at least one of them should present one dimension below 100 nm. They are known as multifunctional materials because they have, usually, more than one property increased for some special application. Up to now, a great effort has been done by researches to achieve multifunctional polymer-matrix nanocomposites filled with metallic, ceramic or inorganic phases, and in this work we studied the influence of conductive ITO (Indium Tin Oxide) nanowires on the electrical and the optical properties of Polymethyl methacrylate (PMMA) polymer. PMMA is a polar polymer which is extensively commercially used because of its excellent transparence in the visible range of electromagnetic radiation, good mechanical properties and light weight. However, the extremely low conductivity of the PMMA can be a drawback depending of the application. By other hand ITO nanowires can have good conductivity and transparence in the visible range depending on the In:Sn ratio in their structure. The ITO nanowires were synthesized by carbothermal reduction process, using a co-evaporation method, and have controlled size, shape, and chemical composition. The electrical measurements of nanowires showed they have about a 10^2 Ω resistance. In order to produce nanocomposites films, nanowires were dispersed in toluene using an ultrasonic cleaner, so the PMMA polymer was added, and the system was kept under agitation up to obtain a clear suspension. The PMMA polymer was filled with 1, 2, 5 and 10 wt% of wires, and films were obtained by tape casting. The results showed that the UV-Vis spectra in the visible range did not change significantly after the addition of nanobelts, although the transmittance decreased as the amount of wires increased. In the other way, the electrical resistance of nanocomposites changed by over 7 orders of magnitude by increasing the amount of filler, and using 5 wt% of filler the composite resistance decreased from 10^10 Ω to about 10^4 Ω, which means that percolation threshold of wires occurred at this concentration. This is an interesting result once for nanocomposites filled with ITO nanoparticles it is necessary about 18% in weight to obtain percolation. The addition of filler up to 10 wt% decreased the resistance of the composite to 10^3 Ω, which is a value close to the resistance of wires. The composites were also analyzed by transmission electron microscopy (TEM), and the TEM results are in agreement with the electrical ones about percolation of nanobelts. These results are promising once indicates that is possible to produce conductive and transparent in the visible range films by the addition of ITO nanobelts in a polymeric matrix using a simple route.
9:00 PM - II3.10
Gold Nanoparticles with a Narrow Distribution Synthesized in Hydrogen Bonded Multilayer Film.
Sung-Ho Park 1 , Sung Yun Yang 1
1 , Chungnam National University, Daejeon Korea (the Republic of)
Show AbstractThe optical properties of gold nanoparticles (AuNPs) are of great interest for nano-scale science and practical sensing applications. The fabrication of three-dimensional arrays of AuNPs on flat substrates or thin films can be employed to tune and manipulate their optical properties. We have studied hybrid films containing AuNP with polyelectrolyte multilayers (PEMs) which may stabilize AuNP. These polymer thin films made by layer-by-layer deposition enables to create gold nanoparticles in-situ. Especially the multilayers formed by using weak polyelectrolytes or polymers with hydrogen-bonding capacity exhibited interesting stimuli-responsive behaviors in addition to chemical functionalities. We also studied bio-molecular detection of the hybrid fulms using their SPR properties.
9:00 PM - II3.11
Formation of Hybrid Film Using Gold Colloid/Polyelectrolyte for Biosensor Application.
Byoung-soo Park 1 , Sung yun Yang 1
1 , Chungnam National University, Daejeon Korea (the Republic of)
Show AbstractGold has many poperties which is strong optical properties, bio-compatible, various size-shape and stable. Especially, the optical properties of gold nanoparticles (AuNP) are of great interest for nano-scale science and practical sensing applications. The fabrication of three-dimensional arrays of AuNP on flat substrates or thin films can be employed to tune and manipulate their optical properties.1 This also allows for characterization using surface sensitive spectroscopic and microscopic analytical methods. Because the excitation of surface plasmon resonance (SPR) 2 at the surface can largely enhance the local optical field, they also have the potential for sensor applications. Patterning also is used to confirm potential of biosensor application. We fabricate Gold nanoparticle-polyelectrolyte hybrid films using layer-by-layer process. Non-spherical gold nanoparticles which have functionalized with carboxyl groups were assembled with a polymer having the opposite charges. First of all, we studied to find better condition of AuNP which was concentration and pH. We try to detect bio-molecule using SPR measurement and stamp patterning using PDMS. As a result, we have the potential of biosensor application.[1] H.-J. Heong, W. -H. Pyunn, S. Y. Yang, Macromol. Rapid Comm. 30, 1109 (2009)[2] R. J. Green, J. Davies, M. C. Davies, C. J. Roberts, S. J. B. Tendler, Biomaterials, 18, 405 (1997)
9:00 PM - II3.13
Investigation of Fiber Mats of Poly(ethylene terephthalate) with Silicon Dioxide Nanoparticles via Electrospinning: Morphology and Phase Structure.
Qian Ma 1 , Bin Mao 1 , Peggy Cebe 1
1 Physics, Tufts Unversity, Medford, Massachusetts, United States
Show AbstractPoly(ethylene terephthalate), PET, nanofibers containing silicon dioxide nanoparticles were electrospun from solution in hexafluoro-2-propanol (HFIP). Various fill fractions of silicon dioxide nanoparticles in PET were used, ranging from 0-1.0% by weight. The influences of solution properties and processing conditions on the morphology of ES fiber were studied to obtain fibers with highly regular diameter, and containing no beads. The morphologies of both the electrospun (ES) nanofibers and the SiO2 powders were investigated by scanning and transmission electron microscopies. The phase structure of the non-woven, nanofibrous, composite mats has been investigated with temperature-modulated differential scanning calorimetry, real-time wide-angle X-ray scattering and real-time FTIR. The growth of the crystalline lamellae is manifested by the emergence of Bragg peaks in the time-resolved WAXS profiles. The amount of immobilized layer, the rigid amorphous fraction (RAF), is obtained based on the measurement of the specific reversing heat capacity for PET nanocomposite samples with different amounts of SiO2. Neat PET as-spun fibers contain 0.18 RAF and 0.25 crystal fraction. RAF increased to 0.32 and crystallinity increased to 0.29 when 1% SiO2 was incorporated into the PET electrospun fibers. The interaction between the filler and polymer matrix is also investigated.
9:00 PM - II3.14
Shape Memory Biodegradable Polyurethane/Montmorillonite Nanocomposites for Periodontal Regeneration.
Iaci Pereira 2 , Rodrigo Orefice 1
2 , Federal Center of Technological Education of Minas Gerais, Timoteo, Minas Gerais, Brazil, 1 Department of Metallurgical and Materials Engineering, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil
Show AbstractBiodegradable polymers that display shape memory behavior can be very useful to guide tissue regeneration to treat periodontal diseases. In this work, montmorillonite (MMT) nanoparticles were incorporated into biodegradable polyurethanes to tailor mechanical and shape memory properties to allow the fabrication of membranes that can be used to treat periodontal diseases. The nanocomposites were produced by introducing MMT in an aqueous dispersion of biodegradable polyurethane based on polycaprolactone soft segments. The shape memory properties were determined using mechanical tests and changes in morphology during the shape memory cycles were investigated mainly using synchrotron small angle x-ray scattering (SAXS). Moreover, the feasibility of using the obtained nanocomposites as membranes for guiding periodontal regeneration was tested by culturing cementoblasts derived from rats in contact with the nanocomposites. SAXS results showed that the temporary shape was stored by the polyurethane metastable structure formed during deformation, while shape recovery was triggered by the melting of the soft segment crystallites and the formation of strong hydrogen bonds among hard domains. SAXS results also demonstrated that the nanoparticles affect the changes in morphology during shape memory cycles. In vitro tests showed that cementoblasts can attach and proliferate on the obtained nanocomposites. Therefore, the produced shape memory biodegradable nanocomposites can be considered suitable biomaterials for participating in procedures associated with periodontal regeneration.
9:00 PM - II3.15
Enhancement of the Electrical Properties of PDMS by Conducting Polymer Nanowire Composites.
Ping Du 1 , Zhiyong Gu 2 , Xin Zhang 1
1 Mechanical Engineering, Boston University, Boston, Massachusetts, United States, 2 Chemical Engineering, University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractPolydimethylsiloxane (PDMS) plays an essential role in chemical and biological applications due to its optical transparency, mechanical compliance, chemical stability, bio-compatibility, and easy of fabrication. However, as a non-conductive elastomer, PDMS has been limited to a structural material in most applications. Hence there is an increasing demand to enhance the electrical properties of PDMS. A common approach is through adding other inorganic or organic material as fillers. Silver or carbon black powder have been added in PDMS to form conducting composites, but they suffered high threshold concentrations and the composites became stiff and easy to break. Conducting polymer nanowires (CPNWs) become a promising filler candidate because of the mechanical flexibility, elongated shape and much lower threshold concentration. In this work, polypyrrole (PPy) nanowires were synthesized and added in PDMS to form the composites. The enhancement of dielectric constant and AC conductivity of the composites were characterized.Anopore porous alumina membranes (Whatman) with a pore diameter of 200 nm were used as the template to electrochemically synthesize CPNWs. The synthesis was carried out at a constant potential of 0.55 V (versus Ag/AgCl reference electrode) for 2 hr. After that the alumina membrane was etched in phosphoric acid to free the nanowires. The average length of the CPNWs was 20 μm. Subsequently the seed layer was also etched, followed by centrifuge and ultrasonic stirring for several times to replace the etchant solution by ethanol and obtain evenly distributed CPNW dispersion. After ultrasonic the CPNWs tended to break into shorter wires, which average length was reduced to 7.11 μm. This dispersion was then mixed with PDMS and thermal cured to form the composites.To evaluate the effect of CPNW on the electrical properties of PDMS composites, the dielectric constant and dissipation factor were measured in the frequency range of 20 Hz ~ 1 MHz using a HP 4284A LCR meter. A parallel capacitor setup was used to extract the dielectric constant from the capacitance data. In this work the pure PDMS and PDMS with 0.1 vol% CPNW composite were used as the test specimens. The dielectric constants are relative constant, but the addition of CPNWs indeed increases the dielectric constant from 20 to 30. The AC conductivity shows strong frequency dependence, increasing from 10-8 S/m to 10-4 S/m.In summary, CPNWs is an economic and efficient approach to enhance the electrical properties of PDMS. More works need to be conducted on other effects of CPNW composites, such as the mechanical stiffness and optical transmittance, etc.
9:00 PM - II3.17
Atomic Force Microscopy Examination of Polymeric Nanocomposite Layers.
Bernadette Peace 1 , Michael Topka 2 , Kenneth Skorenko 2 , Adam Kowalski 2 , Michael Hagerman 2 , Rebecca Cortez 1
1 Mechanical Engineering Department, Union College, Schenectady, New York, United States, 2 Chemistry Department, Union College, Schenectady, New York, United States
Show AbstractAtomic force microscopy has been used to examine the relationship between the synthesis of multiple layers for a polymer based nanocomposite and the resulting morphology. Understanding the relationship between the processing of the layers and their resultant topography and interfacial features is critical to designing inorganic-organic hybrid bilayer and bulk heterojunction solar materials. We will highlight several synthesis techniques and the resulting film morphologies. The three synthesis approaches discussed will include films generated by mechanochemical grinding, solution based drop casting, and vapor phase loading. Specific films to be discussed include layers of aniline/Laponite clay, PEDOT: PSS, aniline solution processed with V2O5 catalyst, and ice templated polyaniline blended with Laponite.
9:00 PM - II3.18
Degradation Behaviour and Thermal Stability Properties of Epoxy Resin/Carbon Black Nanocomposites.
Athanasios Kanapitsas 1 , Zois Haris 1 , Costas Delides 2
1 Electronics, Technological Educational Institute of Lamia, Lamia Greece, 2 Laboratories of Physics and Materials Technology, Technological Educational Institute of West Macedonia, Kila, Kozani Greece
Show AbstractThe thermomechanical properties and thermal stability of a nanocomposite system, which consist of epoxy resin (ER) as matrix and carbon black particles(CB) as filler, were investigated by Thermogravimetric/Differential Thermal Analysis (TGA/DTA) and Dynamic Mechanical Analysis (DMA). The dependence of the thermal properties (i.e. weight loss rate, decomposition temperature, residual mass) of the nanocomposites is associated with the filler content. The addition of carbon black nanoparticles improves generally, the thermal behavior of the epoxy matrix. The results were discussed in terms of the epoxy resin-CB interactions. The interactions between the polymer matrix and the filler nanoparticles seem to play an important role, especially for the higher CB concentration.
9:00 PM - II3.19
Nylon 6 Reinforced with Acrylic Polymer Nanoparticles. Thermal Properties and Nano Structure.
Estefania Huitron-Rattinger 1 2 , Bonifacio Alvarado-Tenorio 1 2 , Angel Romo-Uribe 2
1 Posgrado de Ingenieria, Facultad de Quimica, Universidad Nacional Autonoma de Mexico, D. F. Mexico, 2 Instituto de Ciencias Fisicas, Universidad Nacional Autonoma de Mexico, Cuernavaca, Morelos, Mexico
Show AbstractThe correlation of thermal properties and nanostructure of nylon 6 (denoted PA6) reinforced with polymer nanoparticles (denoted PNP, size~8 nm) has been investigated. The PNPs are highly crosslinked acrylic-based polymers, synthesized and kindly provided by the Rohm and Haas Co. PNPs and those grafted with maleic anhydride (denoted PNP-g-MA) were each one dispersed into a commercial PA6 matrix by melt extrusion, at a concentration of 3 wt%. Thermal analysis showed that the PNPs increased the thermal stability of PA6 but did not influence the melting and crystallization temperatures. Small-angle light scattering showed that the polymer nanocomposites crystallize into a spherulitic morphology, typical of PA6. Isothermal crystallization studies showed that the PNPs act as nucleating agents, accelerating the rate of crystallization relative to the neat PA6. Wide-angle X-ray scattering showed that the composites crystallize in the alpha-form, and the degree of crystallinity was reduced. On the other hand, small-angle X-ray scattering showed that the long range spacing was decreased by the presence of the PNPs. The investigations of the spatial arrangement at the molecular and nano- scales will be discussed in the context of the rheological behavior (shear and extensional) of these materials where strain hardening behavior has been observed for the nanocomposites.
9:00 PM - II3.2
Influence of the Cellulose Substrate on the Electrochemical Properties of Paper Based Polypyrrole Composites.
Henrik Olsson 1 , Gustav Nystrom 1 , Martin Sjodin 1 , Daniel Carlsson 1 , Albert Mihranyan 1 , Leif Nyholm 2 , Maria Stromme 1
1 Department of Engineering Sciences, Division of Nanotechnology and Functional Materials, The Angstrom Laboratory, Uppsala University, Uppsala Sweden, 2 Department of Materials Chemistry, The Angstrom Laboratory, Uppsala University, Uppsala Sweden
Show AbstractThere is currently significant interest in the manufacturing of flexible batteries and supercapacitors that can be utilized in novel applications [1-2]. In a recently published paper [3], it was shown that commercial Xerox paper can be coated with single-walled carbon nanotubes to create a versatile energy storage device. In addition, we have previously reported a composite battery based on a high surface area cellulose coated with a 50 nm thin layer of conductive polymer, polypyrrole [4]. An increased amount of polypyrrole does not always lead to an increase in charge capacity. The reason for this is that the charge capacity in polypyrrole is highly dependent on film porosity and thickness [5], since the mass transport through dense thick layers will be slow. This may give rise to an inactive innermost layer. The cellulose we use in our composite battery is extracted from the Cladophora sp. algae that has a very porous structure [6]. This makes it possible to obtain a high energy storage capacity even with very thin layers of polypyrrole on the cellulose substrate. In this work, the relationship between structure, surface area and electrochemical properties will be discussed for different cellulose substrates coated with polypyrrole. [1] Scrosati, B., Nanomaterials - paper powers battery breakthrough. Nature Nanotechnology, 2007, 2, p. 598-599. [2] Nishide, H. and K. Oyaizu, Materials science - toward flexible batteries. Science, 2008, 319, p. 737-738. [3] Hu, L.B., J.W. Choi, Y. Yang, S. Jeong, F. La Mantia, L.F. Cui, and Y. Cui, Highly conductive paper for energy-storage devices. Proceedings of the National Academy of Sciences of the United States of America, 2009, 106, p. 21490-21494. [4] Nystrom, G., A. Razaq, M. Stromme, L. Nyholm, and A. Mihranyan, Ultrafast all-polymer paper-based batteries. Nano Letters, 2009, 9, p. 3635-3639. [5] Osaka, T., K. Naoi, S. Ogano, and S. Nakamura, Dependence of film thickness on electrochemical kinetics of polypyrrole and on properties of lithium-polypyrrole battery. Journal of the Electrochemical Society, 1987, 134, p. 2096-2102. [6] Mihranyan, A., A.P. Llagostera, R. Karmhag, M. Stromme, and R. Ek, Moisture sorption by cellulose powders of varying crystallinity. International Journal of Pharmaceutics, 2004, 269, p. 433-442.
9:00 PM - II3.20
Correlation between Rheology of Nano-particles Integrated Polymeric Non-Newtonian Fluids and Colloidal Interactions.
Burcu Ozel 1 , Mehmet Yildiz 1 , Yusuf Ziya Menceloglu 1
1 , Sabanci University, Istanbul Turkey
Show AbstractMost of the manufacturing process encountered non-newtonian flow behavior; namely shear thinning and shear thickening. The use of shear-thickening fluids has resulted in a tremendous amount of industrial and commercial innovations, as an example, fluid filled dampers that include seismic protectors for buildings and shock absorbers for automotive industry, design of biomedical, sports wear and military applications. Different explanations have been given for the origin of the shear thickening; namely, the hydrodynamic clustering and order-to-disorder transition which were concluded from light/neutron scattering experiments as well as from Stokesian Dynamic simulations. Although a large body of study has been published, exact conditions and the driving forces behind the shear thickening behavior of these complex fluids have not been clearly understood yet. Therefore, the aim of the present study is to systematical investigation of physicochemical parameters (particle size, concentration, surface chemistry, continuous phases, molecular weight and polarity of polymeric phase) influence on the rheology of shear thickening/shear thinning behaviour of nano particles integrated polymeric fluids (CNS) to shed a light on the mechanism behind the thickening behaviour, which is an ongoing controversial issue in the relevant literature. In the first part of the study, we have studied the effect of constituent parameters and it is obvious from the results that the most important parameter for the shear thickening behavior is the colloidal interactions. In this regard, we have studied the rheological response of suspensions under steady and dynamic shear. In dynamic rheology, elastic modulus (G’) and viscous modulus (G’’) provides a signature of microstructure and intermolecular interaction. Viscoelastic characterization indicate that interaction strenght can be tailored by modifying the surface chemistry of silica particles or changing the polarity of the continuous phase. Hydrodynamic clustering and order disorder transition theories are not reasonable model to explain our results because most of the studies in literature investigate the rheology of suspensions that are composed of monodisperse/nonagglomerated sphere particle. In our case, primary flow units are composed of flocs which are polydisperse, irregular and anisotropic structures, floc structure was observed in cryoscopic transmission electron micrographs and observed hydrodynamic radius was supported by dynamic light analysis. In this part of the preliminary study, conductivity of mixture composed of conductive polymer and insulating particles was measured during viscosity analysis and decrease in conductivity of system at critical shear rate give a clue about the mechanism of shear thickening behaviour.
9:00 PM - II3.21
Optical Polarization Properties of Uniaxially Aligned Single-wall Carbon Nanotubes in Polyvinyl Alcohol.
Satoru Shoji 1 , Thomas Rodgers 1 , Shota Ushiba 1 , Satoshi Kawata 1
1 Department of Applied Physics, Osaka University, Suita, Osaka Japan
Show AbstractDue to its one-dimensional crystal structure, single-wall carbon nanotubes (SWCNTs) show unique characteristics for a variety of physical properties including electronic, thermal, and mechanical properties. It is known that the optical properties of individual SWCNTs also show distinctive behavior, especially in terms of optical anisotropy. However, because of the nature of SWCNT production, they immediately attract and tightly adhere each other to form a random entanglement, so that as-grown SWCNTs do not exhibit any anisotropic optical property. In this presentation, we show polarized Raman spectroscopy and polarized absorption/transmission spectroscopy of uniaxially aligned SWCNTs, where alignment is achieved in a polymer matrix. This alignment of SWCNT was prepared by stretching a polyvinyl alcohol (PVA) film by mechanical tension. We untangled SWCNTs in ionic surfactant aqueous solution and suspended in PVA by means of ultrasonication. The shearing fore of the polymer molecules in stretched PVA forced SWCNTs to lie along the stretching direction. We measured polarized Raman spectra of the SWCNTs at the radial breathing mode (RBM) and the G-band by rotating the SWCNTs film respect to the polarization of the laser light. The RBM and the G-band showed clear angular dependence in proportion to the fourth power of cosine of the rotation angle, which is the same behavior as the resonant Raman scattering of isolated single SWCNTs. Both the RBM and the G-band completely disappeared when the polarization of excitation light was perpendicular to the SWCNTs. The disappearance of Raman peaks indicates that we achieved an excellent alignment of SWCNTs by mechanical tension. Such well-aligned SWCNTs also showed strong optical anisotropy in absorption/transmission spectra. In polarized transmission spectra, we clearly observed a disappearance of the van Hove-like absorption peaks when the light polarization is perpendicular to the direction along the SWCNTs. From these spectra, we observed that the film exhibits the degree of polarization of more than 95 % with the transmission of about 20 % through a wide wavelength range from 350 nm to 1600 nm. The results indicate the potential application of SWCNT for wide-band optical polarizer from ultraviolet to near infrared light. Additionally, we discuss the origin of the background absorption and bundle-effect of SWCNTs observed in our polarized Raman and transmission spectra. Reference : S. Shoji, R. P. Zaccaria, Z. Sekkat, and S. Kawata, Phys. Rev. B 77, 153407 (2008).
9:00 PM - II3.23
Novel Aster-like ZnO Nanowire Clusters for Nanocomposites.
Mikhail Ladanov 1 2 3 , Garrett Matthews 4 , Manoj Ram 2 3 , Ashok Kumar 2 3
1 Department of Electrical Engineering, University of South Florida, Tampa, Florida, United States, 2 Department of Mechanical Engineering, University of South Florida, Tampa, Florida, United States, 3 Nanotechnology Research and Education Center, University of South Florida, Tampa, Florida, United States, 4 Department of Physics, University of South Florida, Tampa, Florida, United States
Show AbstractZnO nanostructures have attracted a great deal of interest because of their biocompatibility and outstanding optical and piezoelectric properties. Their uses are widely varying, including incorporation in sensors, solar cells, and nanogenerators. Biological systems are yet another area of application of ZnO nanowires. Apart from their electrical and optical properties, ZnO nanostructures can be used for the mechanical reinforcement of existing biomimetic scaffolds such as collagen and/or other biodegradable polymers. In this work we have demonstrated a cheap and comparatively facile hydrothermal growth method for the bulk production of ZnO nanostructures exhibiting an aster-like geometry. These novel nanostructures can be used as reinforced material to biopolymer. The aster shape presented an increased surface area, providing a means for enhancing the stabilization of the gels and\or polymers. With controllable growth the method allows the geometry of presented nanostructures to be tuned for maximal coupling between the two phases of composite and increased mechanical strength.
9:00 PM - II3.24
Transparent Polymer Composites Enhanced by Bioderived Nanacrystalline Cellulose Nanofibers.
Hong Dong 1 , James Snyder 1 , Joshua Orlicki 1 , Kenneth Strawhecker 1 , Richard Reiner 2 , Alan Rudie 2
1 , U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland, United States, 2 , USDA Forest Service, Forest Products Laboratory, Madison, Wisconsin, United States
Show AbstractThe demand for lighter and stronger materials is fueling the development of lightweight composites reinforced with a wide variety of high performance nanofillers. Cellulose nanocrystals (CNC), which possess high specific strengths and moduli, may be derived from wood, plant or other high feedstock bioresources. In contrast to other reinforcement materials such as carbon, clays, ceramics and glasses, CNC are renewable, easily modified, low cost, consume little energy to process, and exhibit low densities and high sound attenuation. We are advancing a multiscale research program for low cost, high performance reinforcement of transparent composites that includes both preparation and application of cellulose-based nanomaterials. The current focus is on the production of cellulose-polymer composite nanofibers of varying composition using electrospinning to disperse and control the orientation of CNC in polymer. Uniform nanofibers of various weight ratios of poly(methyl methacrylate)/cellulose nanocrystals (PMMA/CNC) and nylon 6/CNC have been developed that have diameters in the ranges of 200nm-300nm and 100 nm, respectively. Uniform dispersion of CNC in nanofibers was evident via electron microscopy and one-dimensional alignment of CNC along the nanofiber axis was also observed. Transparent PMMA/CNC nanocomposites were prepared by thermal compression of layers of PMMA/CNC nanofibers with PMMA powder. In this manner the polymer from the nanofibers was being used to probe and improve cellulose-matrix interactions. Integration of nylon 6/CNC nanofibers into polymer matrices such as PMMA is also being investigated to take advantage of both flexibility and high modulus of nanofibers. Chemical modification of the cellulosic structures is being investigated as a means toward facilitating dispersion and CNC-matrix interactions. Mechanical property studies include nanoindentation of the nanofibers and conventional mechanical tests of the bulk materials. Our results indicate that cellulose reinforcement of transparent materials is feasible, which would enable a potential route to low cost, scalable composite structures using these bioderived resources.
9:00 PM - II3.25
In-situ Multiaxial Deformation Studies of Polyethylene/Clay Nanocomposites via Simultaneous Synchrotron Small and Wide Angle X-ray Scattering (SAXS/WAXS).
Bilge Gurun 1 , Chin Teoh 2 , Eileen Harkin-Jones 2 , Yonathan Thio 1 , David Bucknall 1
1 MSE, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 School of Mechanical and Aerospace Engineering, Queen’s University Belfast, Belfast United Kingdom
Show AbstractA recent development in polymer science has been in the area of polymer-matrix nanoclay composites (PNCs), which exhibits dramatic improvements in base material performance for small loadings. Among the extensive research on PNCs, the use of combined SAXS/WAXS measurements has been shown to be a very powerful method for in-situ measurements of polymer structures during processing operations such as uniaxial stretching and fiber formation. These studies have elucidated the influence of parameters such as strain, strain rate, and temperature on the polymer fundamental behavior and morphological evolution. However, under many processing conditions, such as blow molding and film blowing, the deformation is more complex and often multiaxial. In order to predict the properties of polymers prior to and after processing, it is essential to study the morphological development of the polymers in situ under multiaxial deformation. A unique in-situ multiaxial deformation device (IMDD) has been designed and built specifically for simultaneous synchrotron SAXS and WAXS measurements. High-density poly(ethylene) (HDPE) and HDPE/clay sheets were prepared using melt mixing and film extrusion techniques. SAXS and WAXS patterns of HDPE and HDPE/clay nanocomposites were measured in real time during in-situ multiaxial deformation at room temperature and at 55C. The morphological evolution of polyethylene was affected by the existence of clay platelets as well as the temperature and the strain rate of deformation. Martensitic transformation of orthorhombic HDPE crystal planes into monoclinic crystal planes was observed under strain, which was delayed at higher temperature and hindered in the presence of clay nanoplatelets due to the confinement effects of the nanoclays. The thickness of the interlamellar amorphous domain, as measured in SAXS, increased with increasing strain at room temperature. The increase was slightly higher for nanocomposites compared to the pure polymer. At 55C, no increase was observed in the characteristic repeat distance due to the faster relaxations of amorphous chains at this increased temperature.
9:00 PM - II3.3
Nanocomposites of Polypyrrole Stabilized by Amphiphilic Block Copolymers of Poly(ethylene)-b-Poly(ethylene oxide): A Chemometric Study.
Helinando de Oliveira 1 , Jacques Rieumont 2 , Clara Nogueiras 2 , Ruben Sanchez 3
1 Materials Science, Universidade Federal do Vale do São Francisco, Juazeiro, Bahia, Brazil, 2 Quimica, Universidad de la Habana, Habana Cuba, 3 Ciência dos Materiais, Universidade Estadual do Norte Fluminense, Rio de Janeiro Brazil
Show AbstractThe use of amphiphilic block copolymers of poly(ehtylene)-b-poly(ehtylene oxide) (PE-b-PEO) as stabilizers of nanocomposites of polypyrrole and gold nanoparticles (PPy/ AuNPs) is analyzed from the results of a chemometric study in which the concentration of both polymers is varied. The progressive introduction of PE-b-PEO in the nanocomposites is characterized on the basis of the electrical impedance of colloids, the measurement of size of particles, absorbance in the UV-vis region and the TEM microscopies. The results indicate that at optimized concentrations it is possible to obtain organic cylindrical structures connected by gold nanoparticles. The reduction in the of aggregation is observed, in an indication that new current pathways are created in the process of interaction between aggregates and the PE-b-PEO copolymers promoting the minimization in the impedance levels of colloidal dispersion. The appropriate ratio of PE-b-PEO/ PPy improves the porosity of nanocomposites, optimizing the selectivity of devices applied as active cells in electronic nose systems.
9:00 PM - II3.4
Thermal, Mechanical and Ablation Properties of Hydroxyl-terminated Polybutadiene-based Polyurethane/Polyhedral Oligomeric Silsesquioxane Nanocomposites.
Ho-Joong Kim 1 , Chang Kee Kim 2 , Younghwan Kwon 1
1 Chemical Engineering, Daegu University, Gyeongsan, Gyeongbuk, Korea (the Republic of), 2 , ADD, Daejeon Korea (the Republic of)
Show AbstractResearch into organic–inorganic hybrid nanocomposites has recently become popular, particularly the development of new polymer nanocomposites. Compared to pristine polymers or conventional composites, these hybrid nanocomposites exhibit improved properties. Therefore, this method delivers new materials with significantly improved thermal and mechanical properties, while still permitting the use of existing commercial processes. Currently, a new class of materials has been used to investigate the behavior of nanoparticles, called polyhedral oligomeric silsesquioxanes (POSS). These are a class of three dimensional organic–inorganic hybrid silicon–oxygen particles with the generic formula of (RSiO1.5)n. These molecules contain an inner inorganic framework covered by inert and/or reactive organic substituents. POSS molecules with well defined shapes and sizes ranging from 1 to 3 nm have been described as the smallest version of colloidal silica. When there is covalent bonding between the POSS and polymeric matrix, reinforcement is favored. In this study, effect of incorporation of functionalized POSS molecular particles covalently into thermoplastic PUs on its thermal, mechanical and ablation properties was investigated by means of DMTA, TGA, tensile measurement, and oxy-acetylene torch test. The results showed that thermal/mechanical properties of the nanocomposites were linearly related with the POSS content. The ablation performance of the POSS hybrid nanocomposites was evaluated by taking into considering the rate of weight loss during thermal degradation and the mechanical strength of the char formed during the oxy-acetylene torch test. The thermal stability and ablation performance of POSS hybrid nanocomposites were improved significantly under the experimental conditions employed.
9:00 PM - II3.5
Polymer Assisted Exfoliation of Graphene and Polymer-graphene Composite Formation Using Low Boiling Point Solvents: The Role of Solubility Parameters.
Peter May 1 , Umar Khan 1 , Jonathan Coleman 1
1 School of Physics, Trinity College Dublin, Dublin Ireland
Show AbstractLiquid phase exfoliation of graphene has been reported in literature, often in high boiling point (BP) solvents and at low concentrations. High BP solvents can be difficult to evaporate/remove from the systems while lack of high concentration dispersions hinders applications such as composite formation. In this paper we demonstrated polymer assisted exfoliation of graphene with reasonable concentrations (up to 0.14 mg/ml) by low power ultrasonication of graphite flakes in the low BP solvent tetrahydrofuran (THF). THF alone is a poor solvent for graphene exfoliation. However in combination with certain polymers very good graphene exfoliation is observed. Various polymer dispersants with a range of solubility parameters were used in this work. The study reveals that exfoliation is maximised for polymers with certain solubility parameters. TEM analysis showed populations of monolayer and few layer graphene flakes. Thermogravimetric analysis showed that solvent can be completely removed on drying. These polymer stabilised dispersions an easily be formed into composite films. Mechanical data showed good reinforcement, particularly for composites prepared from polymers with certain solubility parameters.
9:00 PM - II3.6
Nucleophilic Substitution Reaction-induced Magnetic Multilayer Films with Highly Improved Nonvolatile Memory Properties.
Younghoon Kim 1 , Yongmin Ko 1 , Jinhan Cho 1
1 , Kookmin Univ., Seoul Korea (the Republic of)
Show AbstractWe introduce a facile and robust approach for the preparation of superparamagnetic nanocomposite multilayers, which allows the highly enhanced magnetic and electronic properties as well as the dense and homogeneous adsorption of nanoparticles. Superparamagnetic iron oxide nanoparticles (SPMNP) of about size 12 nm (or 7 nm) synthesized with oleic acid (OA) in nonpolar solvent could be converted into 2-bromo-2-methylpropionic acid (BMPA)-stabilized iron oxide nanoparticles (BMPA-SPMNP) by stabilizer exchange without change of solvent polarity. In addition, bromo groups of BMPA-SPMNP could be connected with highly branched amine groups of poly (amidoamine) dendrimer (PAMA) in ethanol by nucleophilic substitution reactions of between bromo and amine groups. Based on these results, nanocomposite multilayers using layer-by-layer (LbL) assembly could be fabricated in nonpolar solvent by nucleophilic substitution reactions of between BMPA-SPMNP and PAMA without any additional phase transfer of SPMNP for conventional LbL assembly. These resulting superparamagnetic multilayers displayed highly improved magnetic properties in comparison with those of multilayers based on water-dispersible SPMNP. Furthermore, we demonstrate that 7 nm BMPA-SPMNP superparamagnetic multilayers using nucleophilic substitution reactions could be used as an active layer for nonvolatile resistive switching memory (NRSM) devices at room temperature comparable to that of conventional inorganic NRSM devices produced by vacuum deposition. Two different currents states by resistive switching property of BMPA-SPMNP multilayers were maintained for up to at least 5 months with ON/OFF ratio of 1E+2 ~ 1E+3.
9:00 PM - II3.8
Optical Coating by Hybrid Sol.
Wei-Hong Wang 1 , Lih-Yue Chen 1
1 Chemical System Research division, Chemical Engineering Section, Chung-Shan Institute of Science and Technology, Tao-Yuan Taiwan
Show Abstract Optical Coating can be made by hybrid sol. Nano hybrid sol is prepared by the requirement of coating condition and refraction. Most optical coating is made by low and high refraction sol with thermal or UV curing within quarter wave by light interference for antireflection coating. To prepare the hybrid sol with low and high refraction, first synthesis the nano SiO2 and TiO2 sol, then hybrid with polymeric organic. After coating, it can be harden by thermal and UV to get transparence optical film on subtract. The low refraction sol is important for antireflection coating. It can be prepare by TEOS and fluorocarbon derivative at acid process to get the SiO2 hybrid sol. It can decrease the coating refraction by increase the fluorocarbon/SiO2 ratio in sol preparing. The TiO2 hybrid sol is prepared by nano TiO2 sol with silane derivative to get the TiO2 hybrid sol, its coating refraction depend on the ratio of TiO2/silane. This hybrid sol could be applied on glass and plastic for optical coating. By the fluorocarbon/SiO2 hybrid sol ( n ≒ 1.38) with single layer quarter wave by dip coating, 2 .0 % reflection coating glass can be made. Less reflection can be made by two layers with high refraction TiO2 hybrid sol ( n ≒ 1.70) and low refraction SiO2 hybrid sol ( n ≒ 1.38), design with 2H/L coating thickness. This coating glass will be got the reflection less than 0.5 % with hardness in 3H, scratch resistance about 500g and contact angle about 107°. Those two kinds anti-reflection coating have good anti-stain effect, it could be applied on the surface of notebook and mobile phone with touching screen.
Symposium Organizers
Mircea Chipara The University of Texas Pan American
Pulickel M. Ajayan Rice University
Ali Nasar CNC Coatings
Alan Kin-Tak Lau The Hong Kong Polytechnic University
II4: Effect of Nanoparticles on the Thermal Features, Thermal Stability, and Flammability of Polymeric Materials
Session Chairs
Tuesday AM, November 30, 2010
Republic B (Sheraton)
9:00 AM - II4.1
Wide Temperature Polyimide/ZrO2 Nanodielectric Capacitor Film with Enhanced Lifetime.
Chen Zou 1 , Doug Kushner 2 , Xin Zhou 2 , Shihai Zhang 2 , Raj Pathak 2 , Brian Zellers 2
1 MRI, PSU, University Park, Pennsylvania, United States, 2 , Strategic Polymer Sciences, Inc., State College, Pennsylvania, United States
Show AbstractPower electronics are critical components in many electric drive and electricity transportation systems. In many power electronic devices, the DC bus capacitors occupies more than 25% of volume and weight, and contributes to over 25% of the inverter cost. The continuous increase in power density in power electronics demands DC bus capacitors with wide operating temperature, compact size, low equivalent series resistance, and long lifetime. We report our recent progress in developing of polyimide/ZrO2 nanodielectric capacitor film. It was found that the introduction of ZrO2 can increase the lifetime of the capacitor film by 10-100 times under high electric field of 500 MV/m. The nanodielectric film also has a very stable dielectric constant, high dielectric breakdown strength, low dielectric loss, and low leakage current in a wide temperature range from -55 degree C to 400 degree C. Graceful failure behavior was also observed in the capacitor film sample which formed an open circuit after local breakdown. The advanced nanodielectric film capacitors can alleviate thermal management challenges, reduce the size and cost, and enhance the reliability of more robust power electronics in harsh environment.
9:15 AM - **II4.2
Smart Shape Memory Polymer Nanocomposites: Design and Characterization.
B. Xu 1 , Y. Fu 2 , Y. Pei 2 , Z. Chen 2 , W. Huang 3 , J. Lu 4 , Jeff De Hosson 2
1 Department of Mechanical Engineering, Heriot-Watt University, Edinburgh United Kingdom, 2 Applied Physics, Un. of Groningen, Groningen Netherlands, 3 School of Mechanical and Aerospace Engineering, Nanyang Technological University, Edinburgh Singapore, 4 Centre for Materials Research & Innovation, University of Bolton, Bolton United Kingdom
Show AbstractTo enhance mechanical, shape memory and functional properties of shape memory polymer, nanocomposites were fabricated using polystyrene and polyurethane polymer as matrix and different nanofillers (including alumina, silica, clay, carbon powder and carbon nanofibre) as the reinforcing agents. Their thermo-mechanical properties, shape memory effects and electrical properties were characterized. Thermal mechanical experiments demonstrated good mechanical and shape memory effects of the nanocomposites. Experimental results revealed that the nanofillers provide significant reinforcement of the PS and PU, and the nanocomposites exhibit better thermal and mechanical properties, including shape memory properties. Both experimental and theoretical analysis have shown that the rod-shaped clay nanofillers offered better reinforcement than spherical nanoparticles because of their high aspect ratio and ability to reinforce in multiple directions. Electrical and dielectric properties of shape memory polymers have been modified by using polymer nanocomposites with incorporation of conductive nanofillers such as carbon powders and carbon nanofibers. The conductivity and dielectric constants changed dramatically as a function of frequency, temperature and nanofiller concentration.
9:45 AM - II4.3
The Role of Surface Interactions between Polymers/Flame Retardants in Functionalized Nanocomposites.
Seongchan Pack 1 , Su Jung Han 1 , Chad Korach 1 , Takashi Kashiwagi 2 , Miriam Rafailovich 1
1 , Stony Brook University, Stony Brook, New York, United States, 2 , NIST, Gaithersburg, Maryland, United States
Show AbstractThe absorption of resorcinol di(phenyl phosphate) (RDP) oligmoers on nanometer-scale clays has been proposed as a replacement for di-tallow molecules commonly used in functionalizing clays. Using SAXS, we showed that RDP can be adsorbed on the sodium montmorillonite (MMT) clays surfaces, thereby increasing the interlayer spacing to 2.23 nm. We then demonstrated, using SAXS and TEM that these RDP-coated clays can be exfoliated in styrenic polymers: HIPS and ABS. We also produced single layers of the RDP-coated clays, using the LB technique and measured the contact angle of polymers on the surface, which were consistent with the ability to exfoliate. We found that the contact angle for between PS/RDP coated clays substrate was ~ 2.5°, whereas the angle for PS/Cloisite 20A clays substrate was ~ 32°. Therefore, the RDP coated clays were more compatible to the styrene groups compared to the Cloisite clays, which could lead to the exfoliation of HIPS and ABS. The ability of RDP coated clays to compatibilize polymer blends was also probed. We showed that RDP coated clays segregated to the interfaces between the phase domains in the PC/SAN24 blend, while they segregated inside the PMMA domains in the PS/PMMA blend. This different morphology between the two blends could be explained by the interfacial energy. Since the interfacial tension for either PMMA/RDP or PS/RDP clays (~ 2.8 mN/m at 180 °C) was higher than that for PS/PMMA interfaces (~ 1.2 mN/m at 180 °C) the segregations of RDP coated clays could not reduce the interfacial energy of the system. However, the interfacial energy for PC/SAN24 blend (~ 2.8 mN/m at 200 °C) was much higher than the interfacial tension for PC/RDP clays (~ 0.5 mN/m if S=0). Hence segregation of the RDP clays to the interfaces resulted in a significant reduction of the overall energy and increased compatibilization. We also compared the effects of RDP coated clays on the flame retardant properties of the PC/SAN24 blend; We found that the addition of the RDP clays could reduce the heat release rate (HRR) and mass loss rate (MLR) for the blends in which they were interfacial active. In addition, the quality of chars is another important criterion for flame retardance. We show that elasticity is an important consideration in intumescing chars, which have to expand in order to contain the gases formed by the advancing heat front. TEM images indicated that the Cloisite clays segregated to the surfaces of the chars, while the RDP coated clays remained in the interior. Nanoindentation measurements showed that the clay rich surface crust resulted in the chars of the nanocomposites containing Cloisite 20A to be 400 % more brittle than those resulting from the compounds with the RDP or Na+ clays. These results show that surfaces, as well as interfacial energies have to be considered in engineering the optimal properties of nanocomposites.
10:00 AM - II4.4
Do Filler Nanoparticles Always Act as Synergists in Flame Retardant Polymers? Investigations on Potentials of Functionally-filled Novel Polymer Nanocomposites.
Nihat Isitman 1 , Cevdet Kaynak 1
1 Metallurgical and Materials Eng. Dept., Middle East Technical University, Ankara Turkey
Show AbstractMost polymers ignite easily, burn rapidly producing large heats, exhibit flaming drips, and sustain combustion even under the oxygen-deficient environments characteristic of fires. Therefore, flame retardancy of polymers should effectively be improved in order to broaden the field of applications where polymeric materials are suitable. In view of the current restrictions imposed by environmental regulations on widely used halogenated flame retardant additives, there is a growing need for environmentally friendly halogen-free flame retardants. In this respect, filler nanoparticles have been reported to synergistically enhance the flame retardancy of polymeric materials when used in combination with conventional flame retardant additives. Up to now, some progress has been made with filler nanoparticles such as organically modified layered-silicate clay minerals referred to as nanoclays, extended carbon nanostructures, layered double hydroxides, polyhedral oligomeric silsesquioxanes, and oxide ceramic nanoparticles. However, since there have been many cases reporting no synergism or even strong anti-synergism of filler nanoparticles and conventional flame retardants, it appears as an important task to reveal the synergistic combinations of filler nanoparticles and conventional flame retardants among the great many types of both.This study explores whether nanoclays and multi-walled carbon nanotubes function effectively as synergists of an organophosphorus flame retardant when incorporated in poly(methyl methacrylate). Specific to each filler nanoparticle, nanocomposites were prepared either with twin screw extrusion melt mixing or high-power sonication assisted solution mixing to attain satisfactory dispersion of filler nanoparticles. Characterization of nanomorphology was done by wide-angle X-ray diffraction and transmission electron microscopy techniques. Flame retardancy was evaluated by cone calorimeter analysis and limiting oxygen index measurements. Fire residues were analyzed by infrared spectroscopy whereas the thermal degradation of samples was studied by thermogravimetric analysis.On the basis of heat release and mass loss rates, amounts of solid fire residues and fire growth indices, nanoclays were shown to outperform carbon nanotubes in improving the fire properties of intumescent formulations assessed by cone calorimeter analysis. In fact, carbon nanotubes eventually failed to act as a synergistic filler nanoparticle for use in combination with a conventional phosphorus-based flame retardant as opposed to common expectations. An intriguing explanation for the observed behavior was the restriction of intumescence by strong carbon nanotube networks formed on the flaming surfaces during combustion contrary to enhanced intumescent chars by nanoclays.
10:15 AM - **II4.5
Polyhedral Oligomeric Silsesquioxane Based Self-assembled Nano-composites.
Melvina Leolukman 1 , Tomoyasu Hirai 2 , Teruaki Hayakawa 2 , Padma Gopalan 1
1 Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Tokyo Japan
Show AbstractOrganic-inorganic hybrid materials are of interest to enhance the thermal, dielectric and mechanical properties. When combined with concepts of self-assembly hybrid materials with multiple length scales of ordering can be created. We have primarily focused on an inorganic precursor based on polyhedral oligomeric silsesquioxane (POSS). POSS segments in a polymer are known to form nanometer size crystalline or glassy aggregates which are converted to silica on exposure to oxygen plasma. One approach to create a truly hierarchical structure where the POSS cages are ordered into sheets within the microphase-separated domains is to synthesize block copolymers from monomers containing POSS cage hence allowing tunable sheet length. We present studies on self-assembly in bulk and thin-film of a unique class of very well-defined diblock copolymers namely PS-b-PMAPOSS and PMMA-b-PMAPOSS which contains POSS. Detailed structural characterization of these hierarchical structures in bulk and thin films was carried out by a combination of transmission electron microscopy, and synchrotron-X-ray scattering. The excellent self-assembling characteristics both in bulk and thin-films, good etch selectivity between the blocks and access to a wide range of domain sizes and morphologies make these POSS based BCPs as an ideal candidate for BCP lithography. We also present an alternate approach based on non-covalent functionalization of POSS units selectively into one of the blocks to create these hybrid structures.
10:45 AM - II4:THERM
BREAK
11:00 AM - II4.6
Tailored Flame Retardancy via Nano-filler Dispersion State: Nanomorphology and Reaction to Fire of High-impact Polystyrene/Aluminum Tri-Hydroxide/Organoclay Nanocomposites.
Nihat Isitman 1 , Cevdet Kaynak 1
1 Metallurgical and Materials Eng. Dept., Middle East Technical University, Ankara Turkey
Show AbstractConventional flame retardant additives containing halogens are currently being enforced by legal obligations to be replaced by halogen-free counterparts such as phosphorus- and nitrogen-based compounds or metal hydroxides. The primary concern with the use of these new halogen-free compounds, especially with metal hydroxides, is usually that large filler loadings are required to attain satisfactory flame retardancy which in tern causes the deterioration of mechanical properties and processing characteristics.Polymer/organoclay nanocomposites attract great research interest owing to the modification of polymer properties in an exceptional manner with the use of very low filler loadings usually less than 5 wt%. Property modifications typically take place in mechanical properties, thermal stability, barrier properties and flame retardancy. However, the flame retardancy effect of organoclays is usually not sufficient to obtain satisfactory results from stringent legitimate flammability tests. Therefore, the current trend is to utilize organoclays in combination with a conventional flame retardant additive where they act as char enhancer.In this study, we will comparatively discuss the influence of micro- and nano-composite formation on the synergistic action between organoclays and an environmentally friendly flame retardant additive, namely aluminum tri-hydroxide. High power ultrasound assisted solution mixing and twin screw extrusion melt mixing techniques were utilized to disperse organoclays in the polymer matrix. Morphologies of the prepared samples were revealed by transmission electron microscopy and wide angle X-ray diffraction. Influence of the state of organoclay dispersion on the reaction of fire was monitored on the basis of fire behavior assessment by cone calorimeter analysis together with limiting oxygen index and burning rate measurements.Solution mixed samples demonstrated polymer intercalated clay nanomorphology and nanodispersion of clay layers throughout the matrix. On the other hand, melt mixing results in the phase separation of nano-filler and polymer matrix and thus leads to a conventional micro-composite morphology with poor dispersion. Cone calorimetry indicated that intercalated clay nanocomposites show considerable char enhancement and remarkably lower rates of mass loss and heat release compared to phase separated clay microcomposites. In addition, intercalated clay nanocomposites proved superior limiting oxygen indices and lower burning rates. Improved fire retardancy of nanocomposites was attributed to retarded volatilization under the influence of the barrier effect imposed by nano-dispersed clay layers having large interaction area with the polymer. Increased amounts of solid residue for nanocomposites allowed for the establishment of thicker and more consolidated protective carbonaceous layers that effectively shields the underlying polymer during combustion.
11:15 AM - II4.7
Transient Thermal Stability of Polymer Nanocomposite Materials.
Jeffrey Warrender 1 , Stephen Bartolucci 1 , Mark Johnson 1
1 , US Army ARDEC - Benet Laboratories, Watervliet, New York, United States
Show AbstractIncorporation of nanoscale materials, including nanoclays and carbon nanotubes, into polymers such as polystyrene, polymethyl methacrylate, and polypropylene, has been extensively studied, with such nanocomposites commonly exhibiting improved mechanical properties, increased thermal stability, and reduced flammability compared to unmodified polymers. However, characterization of the materials’ thermal degradation behavior generally occurs at low heating rates of at most 50°C/minute. In this work, we report on investigations of transient heating of polymer nanocomposites. Using a pulsed laser with a millisecond pulse duration, we achieve rates as high as 1 x106°C/minute, five orders of magnitude higher than conventional techniques such as thermogravimetric analysis. We study the influence of the loading of the nanoscale species on the optical and thermal stability of the materials. We find that for certain materials, such as 25 wt. % Al2O3 in epoxy, the nanocomposite shows stronger optical absorption and, exhibits less change in its surface morphology compared to the epoxy alone. We will report on our efforts to quantify the degradation processes operative in these materials during rapid heating, by obtaining or calculating chemical, temperature, and mass information during the laser pulse. These studies could lead to implementation of nanocomposite materials as insulators or lightweight structural materials in applications in which the materials are routinely subjected to transient heating.
11:30 AM - II4.8
High thermal Conductance Thermal Interface Materials Based on Nanostructured Metallic Network-polymer Composites.
Joel Plawsky 1 , Theodorian Borca-Tasciuc 3 , Hafez Fard 3 , Fengyuan Lai 2 , Kamyar Pashayi 2
1 Chemical and BiologicalEngineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractIn this work, a novel approach to the design of a Thermal Interface Material (TIM) is introduced. A thermal interface material (TIM) is a material used to minimize the contact thermal resistance between surfaces and to provide a low resistance path to spreading and removing heat. Our novel technology is based on a highly connected, nanostructured metallic network in a polymer matrix. The metal network is formed after dispersion of metallic nanoparticles in the matrix and before the polymer is cured. The thermal conductivity of the epoxy, filled with 20 nm, 80 nm, 1.8 micron and 4.2 micron diameter silver particles, was investigated. It was found that at the same volume fraction the nanoparticle-based composites have orders of magnitude higher thermal conductivities than the microparticle-based composites. The best performance was observed for the 20nm diameter silver nanoparticle materials. For these materials, the thermal conductivity ranged from 0.185 W/mK to 19.25 W/mK when the silver nanoparticle volume fraction was increased from 0 to 20%. The Maxwell-Garnett-type effective medium approach (EMA) and the Maxwell–Eucken model predictions agreed well with the experimental data for thermal conductivities of nanoparticle and microparticle composites respectively. SEM pictures of polymer nanocomposites proved that morphological changes induced by the sintering of silver nanoparticles construct a network between nanoparticles in the epoxy matrix, increasing the nanocomposite thermal conductivity.
11:45 AM - II4.9
Nanoscale Infrared Spectroscopic Analysis of ABS-polycarbonate Plastic Blends.
Michael Lo 1 , Jiping Ye 2 , Craig Prater 1 , Kevin Kjoller 1
1 , Anasys Instruments Corp., Santa Barbara, California, United States, 2 , Nissan ARC, LTD, Material Sciene Group, Kanagawa, Japan
Show AbstractInfrared spectroscopy is one of the most widely used techniques in materials characterization, but the spatial resolution is constrained to the micron scale due to diffraction limits. We have developed instrumentation based on atomic force microscopy that allows measurements of infrared absorption on the micro and nanoscale. Absorption of radiation by the sample generates local heating that is detected by the cantilever tip of an atomic force microscope. Local absorption spectra can be created by plotting this heat signal as a function of wavenumber as well as in space. In this presentation, samples containing domains of polycarbonate and ABS are identified and the corresponding IR spectra are interpreted. Further, nanometer-sized chemical features can be mapped within the ABS domains using this technique. The stiffness of the materials is also obtained concurrently in the form of varying contact frequencies, which compliment and assist the interpretation of the IR image maps.
12:00 PM - II4.10
Polyaniline/Organically Modified Layered Silicate (OMLS) Nanocomposites.
Basudam Adhikari 1 , Muktikanta Panigrahi 1 , Subhasish Majumder 1
1 Materials Science Centre, Indian Institute of Technology, Kharagpur, West Bengal, India
Show AbstractPolyaniline (PANI)/layered silicate nanocomposites have been successfully prepared. The nanostructure, as observed from wide angle X-ray diffraction, indicates exfoliation hybrid. X-ray diffraction patterns also suggest that PANI nanocomposite have higher crystallinity than its pristine polyaniline. The crystallinity of the nanocomposite has increased in comparison to neat polymer suggesting some sort of interaction between organically modified nanoclay and polymer and also can attribute to the smaller dopant HCl. The nanohybrids show significant improvement in the thermal properties of the matrix as compared to pristine polymer. This certainly indicates that PANI nanocomposites are stable than neat PANI due to the exfoliation nature of the clay tactoids of the PANI matrix. Here, the exfoliated nature of clay particles act as barrier to heat flow due to their high aspect ratio and hindered degradation process. The morphology of the nanocomposite sample was studied by HR-TEM, shows that the clay tactoides are dispersed in as exfoliated clay structure. FE-SEM analysis shows that clay particles participate in the nucleation process. As a result, the crystallinity of the nanocomposites increases. UV-Visible spectra indicate increase in charge carrier within the PANI-cloisite 20A nanocomposite. Electrical conductivity of polyaniline and its corresponding nanocomposite has been studied by four probe techniques which indicate an increasing conductivity by loading nano particles due to the interaction between anionic part of clay platelet and cationic part of emeraldine salt of polyaniline.
12:15 PM - **II4.11
Processs-characterization-analysis of Nanoreinforced Polymer Composite Nanofibers.
Karen Lozano 1 , Haidy Soto 1 , Steve Zambrano 1 , Carlos Gomez 1 , Andrea Arguellea 1 , Richard Patlan 1
1 Mechanical Engineering, The University of Texas Pan American, Edinburg, Texas, United States
Show AbstractNanofibers have become an attractive system for a vast number of promising applications and have been the center of a new wave of materials science research. The potential applications of nonwoven nanofibers are vast and can be broadly divided in biomedical, filtration, energy, smart textiles, sensors and structural applications. Therefore, research and development in the area of nanofiber production have recently intensified. Several processing techniques for nanofiber development are available such as: template synthesis, phase separation, self assembly, and spinning methods (wet, dry and melt spinning). This presentation will focus on the development of high yield nanoreinforced polymer composites nanofibers processed through the ForceSpinning system (based on the use of centrifugal forces rather than electrostatic forces). Polylactic acid, polyethylene oxide, and polyvinyl alcohol were chosen as the matrices. Carbon nanofiber and carbon nanotubes were used as reinforcements. Microscopy analysis as well as X-ray diffraction and Raman spectroscopy analysis will be presented together with electrical and mechanical characterization of the developed nonwoven nanofiber composites.
12:45 PM - II4.12
Thermal and Mechanical Characterization of Jute-Biopol Nanophased Green Composite.
Mohammad Hossain 1 , Mohammad Dewan 1 , Mahesh Hosur 1 , Shaik Jeelani 1
1 Mechanical Engineering & T-CAM, Tuskegee University, Tuskegee, Alabama, United States
Show AbstractWith growing environmental awareness research on green materials becoming a great motivating factor for materials scientists. Many of the renewable materials obtained from the agricultural products as a source of raw materials might be a great source of economic development for farming and rural areas in developing countries. Jute-based green composites can be used in consumer goods, low-cost housing, interior of cars, civil structures, and biomedical applications due to their ease of availability, echo-friendliness, low cost, and good specific properties that are comparable to the synthetic fibers. Biodegradable nanophased jute composites are manufactured using chemically treated jute fabrics, biodegradable polymer poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (biopol), and nanoclay for this study. 2%, 3%, 4%, and 5% Montmorillonite K10 nanoclay were infused into the nanophased jute biopol composites using solution inclusion techniques. The conventional and nanophased green composites were fabricated using the compression molding method. The melting temperature, crystallization temperature and degree of crystallinity of neat biopol and nanoclay infused biopol were calculated using differential scanning calorimetry (DSC). As nanoclay acts as a nucleating agent in the nano infused biopol, higher degree of crystallinity was observed in the nanoclay infused biopol. The decomposition temperature of treated and untreated jute fibers, biopol, and jute based nanophased composites were studied using thermogravimetric analysis (TGA). Better decomposition temperature was observed in nanophased jute-biopol composites compared to conventional ones. The mechanical characteristics of the treated and untreated jute fibers were studied using the tensile test of the fiber bundle as well as the single fiber. The diameter of the single fibers was measured using optical microscope. It was noticed that good tensile properties were attributed to the finally treated fibers, as compared to the untreated jute fibers due to the increment of the percentage of celluloses in the treated jute fibers. The mechanical properties of the conventional and nanophased jute biopol composites were evaluated using flexure test (3 point bending test) and dynamic mechanical analysis (DMA). Improved flexural properties and storage modulus were found in nanophased jute-biopol composites compared to conventional jute-biopol composites.
II5: Polymer-Based Nanocomposites: Mechanical Properties
Session Chairs
Tuesday PM, November 30, 2010
Republic B (Sheraton)
2:30 PM - II5.1
Influence of Amino Functionalized MWCNT Reinforcement on the Mechanical and Thermo-mechanical Properties of E-glass/ Epoxy Nanocomposites.
Shaik Zainuddin 1 , Mahesh Hosur 1 , Shaik Jeelani 1 , Rajib Barua 1
1 Materials Sci & Engg, Tuskegee University, Tuskegee, Alabama, United States
Show AbstractThis paper presents experimental studies aimed to evaluate mechanical and thermo-mechanical properties of e-glass/epoxy composites by the reinforcement of amino functionalized multi-walled carbon nanotubes (MWCNTs). A combination of shear mixing and sonication methods was used to effectively disperse 0.1-0.3 wt. % MWCNTs in SC-15 epoxy resin system through acetone solvent media. E-glass/epoxy nanocomposites were fabricated using compression molding process. In addition, control e-glass/epoxy composites without any MWCNTs reinforcement were also fabricated for baseline consideration. Static flexure and dynamic mechanical analysis (DMA) results demonstrated maximum improvement in 0.2 wt. % MWCNTs reinforced e-glass/epoxy composites. Transmission and scanning electron microscopic images revealed homogenous dispersion of MWCNTs in epoxy resin and better interfacial bonding in 0.2 wt. % samples.
2:45 PM - II5.2
In-situ WAXS Characterization of the Strain-induced Structural Evolution of Poly(D,L-Lactide) Based Nanocomposites.
Gregory Stoclet 1 , Jean-Marc Lefebvre 1 , Roland Seguela 1 , Cyrille Rochas 2
1 , Unite Materiaux Et Transformation, Universite Lille1, Villeneuve d'Ascq France, 2 , Centre de Recherche sur les Macromolécules Végétales - CNRS, Grenoble France
Show AbstractIncorporation of nanofillers in polymer matrices has resulted in a new class of multifunctional materials with specific behaviors, owing to the fact that the drastic reduction in filler size both dramatically enhances surface to volume ratio and in the meantime results in interparticle distances of the order of macromolecular dimensions, yet at small filler content. In the same manner, bio-based polymers have received an increasing interest in recent years as these polymers offer a potential alternative for the partial replacement of petroleum based polymers.As a consequence, bio-based polymers nanocomposites appear rather promising for a wide variety of applicationsOngoing research efforts worldwide have allowed to identify some key parameters of the micro/nanostructure, in relation to processing conditions. The characteristic nanoscale of these hybrid organic/inorganic systems clearly impact on local molecular dynamics and spatial arrangement, with a remarkable influence on macroscopic properties.The present work is focused on PLA based nanocomposites with special attention paid to:- the structural organization induced by the presence of clay platelets and its influence on the drawing behavior beyond Tg, as compared to the case of pure PLA,- the influence of both nature and filler content on the structural evolution- the plastic deformation behavior in the glassy state, regarding the interplay between shear banding and craze-like cavitational deformation modes.This study was carried out using appropriate and complementary tools comprising Electron microscopies, AFM, WAXS and SAXS, including in situ analysis under drawing using synchrotron radiation.
3:00 PM - II5.3
Study on the Mechanical Properties and Creep Behaviour of Carbon Fiber Nano-composites.
Yi Luen Li 1 , Wei-Jen Chen 1 , Chin-Lung Chiang 2 , Ming-Chuen Yip 1
1 Department of Power Mechanical Engineering, National Tsing-Hua University, Hsin-Chu Taiwan, 2 Department of Safety, Health and Environmental Engineering, Hung-Kuang University, Taichung Taiwan
Show AbstractAbstractRecently, it has been observed that surface modification of carbon nanotubes(CNTs)influences on CNT’s distribution among epoxy resin and affects the mechanical properties and electrical conductivities of CNTs. Owing to above-mentioned effects, carbon nanotubes treated with oxidizing in organic acids, a kind of surface modification, generates functional groups on the surface of CNTs is a major investigation in this study to enhance mechanical properties and retard the creep strain rate of CNT/ carbon fiber(CF)/epoxy resin thermosetting composites. The influence of the different proportion contents of CNTs added into epoxy resin on mechanical properties of composites is investigated, and strength of material tested under various environments is also observed. Moreover, the creep behavior of CF/epoxy resin composites and CNT/CF/ epoxy resin composites tested under various circumstances and conditions is concerned to be analyzed. The test results exhibit that mechanical strength increases with the increase of CNTs content added into composites and adding proper amount of CNTs also can retard creep strain rate. From observation of the fracture surface by SEM image, the debonding occurs and longitudinal fibers are pulled out due to poor interfacial bonding of fiber and matrix, which also results in entire strength degeneration.
3:15 PM - II5.4
Study of Mechanical Responses and Thermal Expansion of Different Mixing Systems Used CNF-modified Polyester Nanocomposites.
Muhammad Hossain 1 , Mohammad Hossain 1 , Mahesh Hosur 1 , Shaik Jeelani 1
1 Center for Advanced Materials (T-CAM), Tuskegee University, Tuskegee, Alabama, United States
Show AbstractPolymer-based composites have appeared into reality due to the need for high specific strength materials. These composites reinforced with a small percentage of strong fillers can significantly improve the mechanical, thermal, and barrier properties of the pure polymer matrix. In the nanocomposites field, dispersion of nanoparticles into matrix is a great challenge for researchers. In this study, high intensity ultrasonic, mechanical, and magnetic stirring mixing methods were employed to infuse carbon nanofibers (CNFs) into the polyester matrix that was then mixed with accelerator using a high speed mechanical agitator. The trapped air and reaction volatiles were removed from the mixture using a high vacuum. The controlled, 0.1 wt.%, 0.2 wt.%, 0.3 wt.%, and 0.4 wt.% CNFs modified polyester nanocomposites were fabricated in this investigation. Sonication mixing samples showed the better performance than other mixing systems. 0.2 wt.% CNFs infused polyester sample using sonication mixing showed about 88% and 16% increase in flexural strength and modulus, respectively, over the controlled samples. Quasi-static compression tests also showed the similar increasing trend with the addition of CNFs into the polyester matrix. Based on mechanical responses, thermal mechanical analysis (TMA) was performed on the neat and 0.2 wt.% CNF modified polyester samples, and exhibited decreasing trend of co-efficient of thermal expansion (CTE) due to the infusion of CNFs. Fracture morphology of tested specimens examined under scanning electron microscope (SEM) revealed relatively rougher surface in the CNFs modified polyester as compared to the neat due to the better adhesion associated to the CNFs presence. Excellent dispersion was observed in 0.2 wt.% CNFs incorporated polyester using sonication resulting enhanced performance. On the other hand, some agglomerations were seen using other mixing samples.*Contact author, Presenter and advisor,
[email protected]3:30 PM - II5.5
Enhancing the Mechanical And Electrical Properties of Epoxy Composites Using Clay Carbon Black Synergy.
Krishna Etika 1 , Jaime Grunlan 1 2 3
1 Materials Science and Engineering, Texas A&M University , College Station, Texas, United States, 2 Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 3 Chemical Engineering, Texas A&M University , College Station, Texas, United States
Show AbstractStudies of acetone-based suspensions suggest a synergistic stabilization of clay by carbon black (CB) that involves a haloing effect (i.e., CB surrounding clay). This synergy results in unique microstructure development that ultimately influences the electrical and mechanical properties of epoxy composites containing both particles. With the addition of 0.5 wt% clay, electrical conductivity increases by an order of magnitude for CB-filled epoxy (relative to composites containing no clay), but no significant improvement is observed in storage modulus. Composites containing equal concentrations of CB and clay show reduced electrical conductivity, but significant improvement in storage modulus (relative to composites containing equal amount (wt%) of either CB or clay alone). Both electrical conductivity and storage modulus improve in composites containing a 1:2 clay:CB (wt/wt) ratio. This synergy between CB and clay is a useful tool for simultaneously improving the electrical and mechanical properties of solution processed composites. Similar synergy has also been observed with carbon nanotubes and clay, which resulted in a dramatic reduction in percolation threshold.
3:45 PM - II5:MECHANICAL
BREAK
4:00 PM - **II5.6
Cooperative Adhesion and Friction of Aligned Carbon Nanotubes.
Liehui Ge 1 , Anubha Goyal 2 , L. Mahadevan 3 , Pulickel Ajayan 2 , Ali Dhinojwala 1
1 Polymer Science, University of Akron, Akron, Ohio, United States, 2 , Rice University, Houston, Texas, United States, 3 , Harvard, Boston, Massachusetts, United States
Show AbstractThe adhesion and friction behavior of soft materials, including compliant brushes and hairs, depends on the temporal and spatial evolution of the interfaces in contact. For compliant nanofibrous materials, the actual contact area of individual fibers make with surfaces depends on the preload applied upon contact. Using in-situ microscopy observations of preloaded nanotube hairs, we show how nanotubes make cooperative contact with a surface by buckling and conforming to the surface topography. The overall adhesion of compliant nanohairs increases with increasing preload as nanotubes deform and continuously add new side-wall contacts with the surface. Electrical resistance measurements indicate significant hysteresis in the relative contact area. Contact area increases with preload (or stress) and decreases suddenly during unloading, consistent with strong adhesion observed for these complaint
4:30 PM - II5.7
The Effect of Nanotube Content and Drawing on the Mechanical Properties of Coagulation-spun Polymer-nanotube Composite Fibres.
Karen Young 1 , Fiona Blighe 1 , Ian Kinloch 2 , Libo Deng 2 , Robert Young 2 , Jonathan Coleman 1
1 School of Physics, Trinity College Dublin, Dublin 2 Ireland, 2 North West Composite Science Centre and School of Materials, University of Manchester, Manchester M13 9PL United Kingdom
Show AbstractPolyvinyl alcohol-SWNT coagulation-spun fibres with a range of mass fractions were prepared using nanotube dispersions of varying concentration. Tensile measurements were made of these fibres and an additional set of fibres were prepared and drawn by varying degrees prior to testing in order to investigate the effect of nanotube orientation on the mechanical properties of the composites. The dY/dVf value of the drawn fibres was significantly higher than that of the undrawn fibres. Raman spectroscopy was then carried out to quantify nanotube orientation in the drawn fibres and find the effective modulus of the nanotubes within the composite. Comparing the effective modulus from Raman spectroscopy to dY/dVf values of the drawn fibres suggests the nanotubes are not solely responsible for reinforcement and that crystallinity of the PVA is also a factor.
4:45 PM - II5.8
Failure Mechanisms of Polymer/Oxide Nano Hybrid Permeation Barriers in Flexible Electronics.
Zheng Jia 1 , Matthew Tucker 1 , Teng Li 1 2
1 Department of Mechanical Engineering, University of Maryland, College Park, Maryland, United States, 2 Maryland NanoCenter, University of Maryland, College Park, Maryland, United States
Show AbstractFlexible electronics have potential applications, such as paper-like displays, printable solar cells, and smart electronic skins, which can revolutionize the way we can utilize electronics in the future. The functional organic materials used in flexible electronics are extremely vulnerable to the attack of environmental water vapor. Developing high performance permeation barrier for flexible electronics has been a significant challenge. A new design of permeation barrier that consists of multilayers of alternating nanoscale inorganic (i.e., Al2O3) and organic (i.e., polymers) thin films, is emerging as a possible solution. Flexible electronics are subject to cyclic, large deformation during their service life. While the polymer layers in a multilayer permeation barrier can sustain large deformation, the brittle oxide thin layers fractures at small strains. The fracture of the brittle oxide layers substantially increases the water vapor permeation through the barrier, leading to the degraded device function. Here we report a systematic study of the failure analysis of the polymer-oxide nano hybrid permeation barriers using finite element method. Our focus is placed on the debonding along the polymer/oxide interfaces as well as the fracture of the oxide layers. The parametric study leads to quantitative understanding of the structure/materials design of the nano hybrid barriers to achieve better performance. We also show that adding a thin protective layer on the top of the nano hybrid permeation barrier can significantly enhance the deformability of the barrier.
5:00 PM - **II5.9
Advanced Composite Technology and Multifunctional Structures in Reusable Launch Vehicle (RLV).
Leo Daniel 1
1 Aeronautics & Astronautics, MIT, Cambridge, Massachusetts, United States
Show AbstractThe need for ever-increased performance of space equipment has driven the space industries into developing extremely high-performance composites that are pushing their operating envelope in terms of strength-to-weight ratios, durability, and several other key aspects towards outstanding improvements. This paper describes the research development in composites for future reusable launch vehicle primary structures, which is seen in the experimental vehicle’s study under the European Space Agency Future Launcher Preparatory Program (FLPP) and NASA future Space Exploration systems. Specific aspects related to the level of advanced composite technology performance in RLV and ELV application are described. A series of trade studies are also undertaken to identify materials capability of meeting the requirements for a high propellant mass fraction, high thrust to weigh propulsion and extended reusability. The overall economic impacts of composites in spacecraft architecture for future space exploration systems.The second part of this paper looks at the structural behavior of multifunctional structures in RLV. Over the past decade, the term “smart or multifunctional structures” has been adapted to include a capability to sense, measure, process, and diagnose at critical location changes occurring in selected variables in order to command an appropriate action and to preserve the structural integrity of the system as required to perform the intended functions. This paper describes the current research initiative that addresses the aforementioned.
5:30 PM - II5.10
Structure & Strength of Silica-PDMS Nanocomposites.
Adrian Camenzind 1 , Thomas Schweizer 2 , Michael Sztucki 3 , Sotiris Pratsinis 1
1 ETH Zurich, Particle Technology Laboratory, Zurich Switzerland, 2 ETH Zurich, Institute of Polymers, Zurich Switzerland, 3 , European Synchrotron Radiation Facility , Grenoble France
Show AbstractA key issue in nanocomposites is the state of nanofiller aggregation. Agglomerates (nanoparticles held together by weak physical forces) can be readily dispersed in polymers assuring nanocomposite uniformity and excellent optical properties. On the other hand, fractal-like aggregates (nanoparticles that are held together by chemical (sinter) forces) are attractive for reinforcing as they influence much more nanocomposite volume than their own solid equivalent. As a result, less aggregate filler is needed that is, however, hard to disperse in the polymer matrix. Today the nanocomposite industry operates with flame-made carbon black and simple oxide nanofillers that have been developed by rather Edisonian research with notable commodity products such as tires and silicones [1]. The goal of this research is to understand the reinforcing of PDMS-based nanocomposites by commercially-available, more (e.g. Aerosil 150, 200, 300) or less aggregated (e.g. OX50) SiO2 fillers through detailed investigation of filler structure in nanocomposites by non-intrusive small and ultra small angle X-ray scattering. These measurements are compared to nitrogen adsorption data (BET) for primary particle size, and microscopic (TEM) images of nanocomposites at various SiO2 loadings [2]. The swelling ability of cured samples is investigated to determine the optimum crosslinker concentration. The mechanical strength of such composites is measured as a function of component mixing duration and compared to structural characteristics of the fillers. Mechanical properties of these nanocomposites are analyzed focusing on their Young’s modulus and elongation at break from tensile strength measurements. Finally, the potential of classic “bound rubber” theory, originally developed for carbon black filled rubbers [3], is explored here for describing the strength of silica/PDMS nanocomposites focusing on the relationship between Young’s modulus of the nanocomposites and filler volume fraction.1. A. Camenzind, W. Caseri, S.E. Pratsinis, “Flame-made nanoparticles for nanocomposites", Nano Today, 5, 48-65 (2010).2. A. Camenzind, T. Schweizer; M. Sztucki, S.E. Pratsinis, “Structure & Strength of Silica-PDMS Nanocomposites", Polymer, 51, 1796-1804 (2010).3. A. I. Medalia,”Effect of carbon-black on dynamic properties of rubber vulcanizates” Rubber Chem. Technol. 51, 437-523 (1978).
II6: Polymer-Based Nanocomposites: Rheology
Session Chairs
Wednesday AM, December 01, 2010
Republic B (Sheraton)
7:00 PM - II6.1
Rheological and Thermo-oxidative Behavior of Carbon Nanofiber-polyetheretherketone Nanocomposites.
Stephen Bartolucci 1 , Shriraj Modi 2 , Halil Gevgilili 2 , Kimberly Dikovics 2 , Frank Fisher 3 , Dilhan Kalyon 2
1 Benét Laboratories, US Army Armaments Research Development and Engineering Center, Watervliet, New York, United States, 2 Highly Filled Materials Institute, Stevens Institute of Technology, Hoboken, New Jersey, United States, 3 Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, New Jersey, United States
Show AbstractPoly(ether ether ketone), PEEK, is a widely-used engineering polymer that is especially suitable for high temperature applications. The compounding of PEEK with carbon nanofibers (CNF) has the potential of increasing its utilization even further. We have studied composites of CNF and PEEK that were fabricated using both a novel polymer crystallization technique at intermediate temperatures and a melt-mixing process at elevated temperatures. A comparison of the nanocomposite samples generated from each of these two techniques was then conducted, including differences in crystallization behavior and rheological properties. The contrasting fabrication methods allowed us to study the thermo-oxidative behavior of the PEEK macromolecules in the presence of the carbon nanofibers. Our research has shown that the carbon nanofibers play a major role in reducing the rate of thermo-oxidative crosslinking of the macromolecules due to a steric hindrance effect by the nanofibers. Small-amplitude oscillatory shear investigations were performed in the 360-400°C temperature range under air and nitrogen atmospheric conditions. The studies show that there is a strong dependence of the crosslinking behavior on nanofiber concentration, as well as time and temperature. Spectroscopic analysis was also performed in order to complement the rheological data. This study provides a major step in the understanding of how nanospecies affect oxidation and crosslinking in polymers.
7:15 PM - II6.2
Influence of Preparation Method and Molecular parameters on the Rheology of Model PEO/ Laponite Polymer Nanocomposites.
Jesmy Jose 1 , Omar Abakar Adam 1 , Guillame Brotons 2 , Jean-Francois Tassin 1
1 Polymeres, Colloides, Interfaces, UMR CNRS 6120, Université du Maine, Le Mans France, 2 Laboratoire de Physique de l'Etat Condense, UMR CNRS 6087, Université du Maine, Le Mans France
Show AbstractThe viscoelastic properties of polymer melts filled with a small concentration of nanometric particles such as clays have been the subject of numerous investigations. The transition, in the molten state of the polymer, from a viscoelastic liquid to a viscoelastic solid, characterized by a zero frequency modulus is well established, although to the best of our knowledge the parameters controlling this modulus have not been clearly tackled. We tried to move in this direction, focusing on the relationship between rheology and filler dispersion using two experimental parameters, namely preparation method and PEO matrix molecular weight.Model polymer nanocomposites based on geometrically well defined and protected Laponite particles dispersed in Poly(ethylene oxide) of widely varying molecular weights were prepared by two common techniques, i.e., from solution, and by melt processing. Laponite protection was carried out by adsorbing PEO chains in solution and the protected particles were eventually recovered by freeze-drying. For preparation via solution mixing, the protected Laponite dispersion in water was feeded with a PEO solution in water and the nanocomposites were finally recovered by freeze-drying, which ensured homogeneous dispersion of the Laponite. The melt mixing procedure involves the dispersion of a concentrated nanocomposite obtained from solution technique in neat PEO by melt blending in a laboratory scale twin-screw extruder. The linear viscoelastic data of the compressed nanocomposite disks were studied in the molten state of the matrix. The transition to solid like response for the shear moduli was observed at Laponite weight fractions as low as 0.1%, dramatically lower than the percolation threshold so far reported for such kind of systems.We show that sample preparation by melt, although leading to dispersed particles, does not achieve the same levels of modulus as compared to solution prepared mixtures. We propose a qualitative interpretation of this phenomenon, based on the mixture between a liquid and a dispersed phase of rather solid character. Further experiments using SAXS show that the modulus level is not necessarily related to the height of the correlation peak, characteristic of the laponite stacks. However, for samples prepared with varying PEO matrix molecular weight the fraction of laponite stacks decreases with increasing PEO molecular weight. Master curve analysis from rheology show that confinements of polymer chains arising from high concentrations of particles and high molecular weight matrix chains do not impact the level of the low frequency modulus. However, a slower polymer dynamics, as observed for higher molecular weights, leads to an increase of the modulus at low particle loadings.
7:30 PM - II6.3
Rheological Behavior of a Nanofluid Comprising High Aspect Ratio Nanoparticles.
YuanQiao Rao 1 , Jeffrey Munro 1
1 Core R&D, the Dow Chemical Company, Freeport, Texas, United States
Show AbstractThe incorporation of high aspect ratio nanofillers into an organic medium is desirable for its potential for creating high performance hybrid materials. One important aspect is the rheological behavior of a nanofluid comprising nanofillers. In this paper a synthetic hectorite, Laponite®, with a disc shape of 20 nm in diameter and 1 nm in thickness, is used as a model nanoparticle and its dispersion in different organic media ranging from organic solvents to oligmeric species is explored. The key factors in controlling the morphology of the nanofiller in the medium and the effect of this morphology on the rheological behavior will be discussed.
7:45 PM - II6.4
Water Wettability and Ice Adhesion of Fluorodecyl POSS-containing Polymer Nanocomposites.
Adam Meuler 1 3 , J. David Smith 2 , Kripa Varanasi 2 , Joseph Mabry 3 , Gareth McKinley 2 , Robert Cohen 1
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Air Force Research Laboratory, Edwards Air Force Base, Edwards Air Force Base, California, United States, 2 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractIce formation and accretion may hinder the operation of, for example, airplanes, power lines, windmills, ships, and telecommunications equipment. Yet despite the pervasiveness of the icing problem, the fundamentals of ice adhesion have received relatively little attention in the literature, and it is not widely understood which attributes must be tuned to design icephobic surfaces. Here we probe the relationships between advancing/receding water contact angles and the strength of ice adhesion to a range of test coatings. Contact angles are measured using a commercial goniometer while the ice adhesion strengths are evaluated with a custom-built laboratory-scale apparatus. The nanocomposite coatings investigated consist of commercially available homopolymers blended with fluorodecyl polyhedral oligomeric silsesquioxane (Fluoro POSS), a low surface energy additive known to enhance liquid repellency. Addition of Fluoro POSS to polymers provides a means of tuning nanocomposite surface energy and wettability, and we find that high receding water contact angles correlate strongly with reduced ice adhesion. We believe these results allow us to estimate the minimum strength of ice adhesion that is attainable on smooth surfaces using known low surface energy coatings. Current investigations are focused on incorporating surface texture (including reentrant topographical features) into the design of icephobic surfaces.
8:00 PM - II6.5
Ionic Liquid (IL) Electromechanical Bending Actuators Fabricated by Layer-by-layer Technique with Fast Response.
Dong Wang 1 , Reza Montazami 2 , Vaibhav Jain 3 , James Heflin 1 2 , Yang Liu 4 , Sheng Liu 4 , Minren Lin 5 , Qiming Zhang 4 6
1 Department of Physics, Virginia Tech, Blacksburg, Virginia, United States, 2 Department of Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia, United States, 3 Macromolecular Science and Engineering, Virginia Tech, Blacksburg, Virginia, United States, 4 Department of Electrical Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 5 Materials Research Institution, Pennsylvania State University, University Park, Pennsylvania, United States, 6 Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractElectromechanical bending actuators were fabricated by the layer-by-layer (LbL) technique with Nafion as a polymer membrane and conductive network composite (CNC) layers composed of different organic and inorganic materials were coated on both sides of the Nafion film. The ionic liquid (IL) EMI-Tf was selected as electrolyte in the actuator, because it has a high electrochemical stability window (>4 V), high thermal stability (>400 °C), high ionic conductivity, and long device lifetime due to its negligible vapor pressure. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) reveal that the CNC layers are evenly deposited with the LbL technique and have porous structure. The polycation used in this study is poly(allylamine hydrochloride) (PAH), while the anionic materials employed are gold nanoparticles (Au NPs, 3 nm from Purest Colloid Inc., and 5 nm, 30 nm, 100 nm from Ted Pella Inc.) and functionlized single-wall carbon nanotube (SWCNT, from Carbon Solutions Inc.). For LbL film deposition, the Nafion membranes were held in a “Zip-Loc” style frame provides a uniform stretch of the Nafion film, which results in a more homogenous coating of CNC layers. The actuators were soaked in EMI-Tf ILs to 38%~40% wt. before testing. Under 4 V input, the bending response times and curvatures of the actuators were obtained and compared as a function of LbL film thickness and components. Very fast responses (RC time constants of ~100 ms) and large curvatures (0.6 mm-1) were founded. The intrinsic strain generated by the actuator decreases as the number of CNC bilayers increases while the response speed and curvature are relatively independent of the number of CNC bilayers. Bending responses to 4V square wave input with different frequencies were also tested and the longest bending durability was observed at a frequency of 0.3 Hz.
8:15 PM - II6.6
Dielectric Properties of Electrospun Barium Titanate Fibers-silicone Rubber Composites.
Zepu Wang 1 , Jianjun Miao 1 , Henrik Hillborg 2 , Su Zhao 2 , Robert Linhardt 1 , J.Keith Nelson 1 , Linda Schadler 1
1 , Rensselaer Polytechnic Institute, Troy, New York, United States, 2 , ABB Corporate Research, Västerås Sweden
Show AbstractHigh dielectric constant ceramic fillers have been widely used to increase the dielectric constant of polymer composites. However, the ability of traditional spherical particles to increase the dielectric constant is limited at low volume fraction as described by the rule of mixtures. High aspect ratio fillers are predicted to increase the dielectric constant more efficiently than spherical fillers. In this work, barium titanate fibers were synthesized by electrospinning a sol-gel, followed by heat treatment to obtain a perovskite crystal structure. The influence of heat treatment on: fiber morphology, microstructure and crystal structure was investigated by X-ray diffraction and scanning electron microscopy. The relationship between crystal structure and dielectric constant of the fibers was explored. It was found that more rapid heating resulted in larger grains. Dielectric spectroscopy showed that the dielectric constant increased as predicted for whisker like fillers, and that the increase in dielectric loss over the pure matrix was small. This is a promising route for creating high dielectric constant, low loss materials, which have potential usage in electrical applications.
8:30 PM - II6.7
A Liquid Crystal Elastomer Modified by Carbon Nanotubes.
Chensha Li 1 , Ye Liu 1 , Chi-wei Lo 2 , Hongrui Jiang 1 2
1 Department of Electrical and Computer Engineering, University of Wisconsin, Madison, Wisconsin, United States, 2 Materials Science Program, University of Wisconsin, Madison, Wisconsin, United States
Show AbstractLiquid crystal elastomers (LCE) are currently of great interest due to the conjoining of mesogenic ordering and rubber elasticity, exhibited in their large spontaneous thermally stimulated changes in shape. Nematic co-elastomer was synthesized, which consists of a combination of nematic side- polymers and main-chain siloxane polymers. The side-chain siloxane LCE has mesogenic phenyl-benzoate side groups and flexible aliphatic cross links miscible with mesogenic side chain groups. By applying a mechanical field during the crosslinking process, the direction of the nematic phase becomes macroscopically and uniformly aligned, and liquid single crystal elastomers are obtained. At about 80 centigrade degree, the transformation from nematic phase to isotropic phase results in great change in shape in one dimension of these networks. It has been shown that nanoparticles can be incorporated into the LCE networks to create a more sensitive network to external stimuli. In principle, dispersing nanofillers with unique characteristics in polymer matrix can not only provide superb enhancement of performance but also afford novel actuators. Carbon nanotubes, for instance, can provide such superior performances in the realm of nanocomposites. Here, by using a new method, we fabricated such nematic liquid-crystalline elastomers filled with a much higher concentration of carbon nanotubes previously reported, amounting to 1 wt % with homogeneous dispersion. Significant improvement in mechanical properties, such as Young modulus, strength and anisotropic stress-strain response, was obtained for these nanocomposites, which increase the potential of their application as artificial muscles or mechanical actuators.
8:45 PM - II6.8
Shear-nanospinning of Polymer and Composite Fibers from Sheared Solutions.
Stoyan Smoukov 1 , Manuel Marquez 2 , Orlin Velev 1
1 , North Carolina State University, Raleigh, North Carolina, United States, 2 , YNano, LLC, Midlothian, Virginia, United States
Show AbstractEfficient production of nanofibers would enable their wider application in filters, protein purification, tissue engineering scaffolds, smart textiles, catalysts and photovoltaics. The biggest current limitation is the absence of scalable methods that can achieve high-volume nanofiber production. We will present a “shear nanospinning” technique that allows scalable fabrication of sub-micron diameter fibers by antisolvent-induced polymer precipitation under shear stress. The fibers are formed in the bulk liquid without the use of nozzles or spinnerets, by the combined action of shear and phase separation. The process is especially suitable for the fabrication of composite fibers with various particle additives because it eliminates the extrusion of fibers through nozzles which can be clogged. We report the fundamental influence of polymer molecular weight on the formations of fibers or rod-like particles by this process. We also demonstrate the ability to control the resulting fiber diameters by changing the antisolvent concentration and shearing medium viscosity. The method can be used in the fabrication of nanofibers from many classes of materials, including hydrophilic, chemically or biologically active polymers. We demonstrate the technique’s versatility by making fibers from cellulose acetate, poly-lactic acid, magnetic nanoparticle-containing fibers. We focus on incorporation of nanoparticles and processing needed to create inorganic and polymer-inorganic nanocomposite fibers with potential applications in photovoltaic energy production.
9:00 PM - **II6.9
Development of Bacterial Cellulose Nanocomposites.
Roberto Benson 1 , H. O'Neill 2 , B. Evans 2 , S. Hutchens 1 , C. Stephens 1 , R. Hammonds 1
1 Materials Science and Engineering, University of Tennessee - Knoxville, Knoxville, Tennessee, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractBacterial cellulose (BC) is a highly versatile nanostructured biomaterial with a wide variety of biomedical and environmental remediation applications as well as industrial uses in electronic and acoustic devices. In this presentation, we will discuss ongoing studies towards the development of a bacterial cellulose nanocomposite designed to support mammalian cell growth. Composites of native (BC) and degradable BC-and calcium deficient hydroxyapatite (CdHAP) were used in the study. The ability of native BC and a degradable BC- calcium-deficient hydroxyapatite (CdHAP) composite to act as scaffolds for growth of osteoblasts, the cells responsible for bone formation in the body was tested. The results show the cells grow well on both materials but adhere more strongly to CdHAP BC compared to the native material. Finally, we will discuss recent studies attempts to modulate the properties of BC during its synthesis to improve its ability to direct mammalian cell proliferation and growth.
Symposium Organizers
Mircea Chipara The University of Texas Pan American
Pulickel M. Ajayan Rice University
Ali Nasar CNC Coatings
Alan Kin-Tak Lau The Hong Kong Polytechnic University
II7: Polymer-Based Nanocomposites: Electrical Properties
Session Chairs
Wednesday AM, December 01, 2010
Republic B (Sheraton)
9:00 AM - II7.1
Self-assembled Nano-needles of Polyaniline, Efficient Structures in Controlling Electrical Conductivity.
Michael Ibrahim 1 2 , Maria Bassil 1 , Vincent Salles 2 , Umit Demirci 2 , Georges El Haj Moussa 1 , Mario El Tahchi 1 , Philippe Miele 2
1 LPA-GBMI, Department of Physics, Lebanese University, Jdeidet Lebanon, 2 LMI, University of Claude Bernard Lyon 1, Lyon France
Show AbstractPolyaniline (PANI) is one of the most interesting conducting polymers with a wide and controllable conductivity range, synthesized easily via chemical or electrical route, stable chemically and environmentally, having high absorption in the visible range and high mobility of charge carriers. With these properties PANI is used in many applications such as electrochromic devices, hybrid solar cells, corrosion protection and many other applications. Many have reported the formation of highly crystalline PANI with controllable morphologies [1]. For example Zhang et al. have used dicarboxylic acids for the formation of highly crystalline PANI nanostructures [2]. Under different conditions, PANI morphology can be controlled yielding to the creation of nano-tubes [3], belts, rods, fibers [4] and particles. The most used chemical formation of hydrochloric acid doped PANI is the chemical oxidative polymerization which consists of mixing aniline hydrochloride (A-HCl) with ammonium peroxydisulfate (APS). Fixing the weight ratio A-HCl/APS defined by the IUPAC while varying their quantities in a constant solution volume leads to the formation of PANI nanoparticles with variable diameters ranging between 100 and 400 nm. In addition, PANI nano-needles of 60 nm average diameter at the center are also obtained. The size and morphology of different structures obtained under different polymerization conditions such as monomer quantity and solution temperature are studied. The electrical conductivity of bulk PANI pellets is measured using the four-point probe technique. Other characteristics of the PANI particles and nano-needles such as their absorption in the visible range and their bonding types are determined using FTIR and UV-Vis spectroscopy. XRD analysis was performed on all the samples to study the effect of PANI particle size and morphology on the crystallinity of the powder. The co-existence of self-assembled PANI nano-needles and particles controls the direction of conduction and thus increases in the charge hopping mechanism. Such polymerization could enter in the fabrication of high efficiency hybrid solar cell based on PANI and metal oxide coatings.[1] S. Bhadra, D. Khastgir, N. Singha and J. Lee, Progress in Polymer Science 34, 783 (2009).[2] Z. Zhang, M. Wan and Y. Wei, Advanced Functional Materials 16, 1100 (2006).[3] J. Stejskal, I. Sapurina, M. Trchova, E. Konyushenko and P. Holler, Polymer 47, 8253 (2006).[4] Y. Wang and X. Jing, Journal of Physical Chemistry B 112, 1157 (2008).
9:15 AM - **II7.2
Dielectric TiO2-paraffin and TiO2-VDF Oligomer Nanocomposites.
Balamurugan Balasubramanian 1 , Kristin Kraemer 1 , Ralph Skomski 1 , Stephen Ducharme 1 , David Sellmyer 1
1 Nebraska Center for Materials and Nanoscience and Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska, United States
Show AbstractThe embedding of oxide nanoparticles in polymer matrices with high breakdown field is a promising approach to high energy-density capacitor applications, such as the replacement of batteries in mobile electronic devices, hybrid electric vehicles, and stationary power systems [1, 2]. This class of nanocomposites combines the high dielectric strength and low loss of suitable host polymers with the high electric polarizability of nanoparticles to produce a greatly enhanced dielectric response. Since oxide nanoparticles require high growth temperatures (≥ 300 °C), larger than the melting and decomposition temperatures of the host polymers (≤ 150 °C), wet chemical techniques have been generally adapted to fabricate nanocomposites by simply mixing commercially available oxide nanoparticles of much bigger sizes (about 30 to 70 nm) with polymers. A major impediment, however, is poor control of the size and size-distribution of the nanoparticles and their tendency to agglomerate even at a relatively low loading of 10 vol% in a polymer matrix, leading to poor film quality and device characteristics. In our presentation, we discuss a new synthetic process to grow oxide-organic core-shell nanoparticles at high vacuum conditions by means of a hybrid experimental technique. Monodisperse and spherical TiO2 nanoparticles having an average particle size of 13 nm were produced at room temperature as a collimated cluster beam in the gas-phase using a cluster-deposition source. Subsequently, the particles were coated with uniform molecular coatings using in-situ thermal evaporation, for example alkanes (paraffin) or vinylidene fluoride (VDF) oligomers, to form core-shell structures [3]. The molecular coatings on the dielectric nanoparticles serve two purposes, namely to prevent the TiO2 nanoparticles from contacting each other and to couple the nanoparticle polarization to the matrix. The thickness of the molecular coating (δ) was varied between 1 and 4 nm to tailor the dielectric properties of the core-shell nanoparticles. For example, the effective dielectric constant of TiO2-paraffin core-shell nanoparticles is varied from 4 to 58 on decreasing δ from 3.5 to 0 nm. The capacitors made of core-shell nanoparticles also reveal a minimum dielectric dispersion with low dielectric loss of about 5% in the frequency range of 100 Hz to 1 MHz, which are highly desirable for exploiting these core-shell nanoparticles in future applications.This research is supported by ONR (Grant No: N00014-06-1-0604), NSF-MRSEC (Grant No: DMR-0820521), and NCMN.References [1] P. Kim, S.C. Jones, P.J. Hotchkiss J.N. Haddock, and B. Kippelen, Adv. Mater. 19, 1001 (2007).[2] P. Kim, N.M. Doss, J.P. Tillotson, P.J. Hotchkiss, M.J. Pan, S.R. Marder, J. Li, J.P. Calame, and J.W. Perry,. ACS Nano 3, 2581 (2009).[3] B. Balasubramanian, K.L. Kraemer, N.A. Redding, R. Skomski, S. Ducharme, and D.J. Sellmyer, ACS Nano 4, 1893-1900 (2010).
9:45 AM - II7.3
Electroactive Properties of Boron Nitride Nanotube Polymer Composites.
Jin Ho Kang 1 , Cheol Park 1 4 , Godfrey Sauti 1 , Jae-Woo Kim 1 , Joycelyn Harrison 2 , Michael Smith 2 , Sharon Lowther 2 , Robert Bryant 2 , Peter Lillehei 2 , Kevin Jordan 3
1 , National Institute of Aerospace, Hampton, Virginia, United States, 4 Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia, United States, 2 Advanced Materials and Processing Branch, NASA Langley Research Center, Hampton, Virginia, United States, 3 , Jefferson Science Associates, Newport News, Virginia, United States
Show AbstractNovel electroactive materials have been required for increasing electroactive performance while reducing power consumption for many applications in the aerospace field and beyond. Although many electroactive materials have been proposed, they still have problems of poor mechanical/thermal properties or unsatisfactory electroacitve performance. Recently, boron nitride nanotubes (BNNTs) have been successfully synthesized. These nanotubes exhibit excellent mechanical, electronic, optical, and thermal properties. BNNTs are thought to possess high strength-to-weight ratio, high temperature resistance (about 800°C in air), and radiation shielding capabilities. Furthermore, intrinsic piezoelectricity of BNNTs has been theoretically predicted. However, no experimental result of the piezoelectric properties of BNNTs or BNNT composites has been reported until now. In this presentation, we demonstrate electroactive characteristics of novel BNNT based materials. A series of BNNT based electroactive materials including BNNT/polyimide composites and BNNT films were prepared. The BNNT based electroactive materials showed high piezoelectric coefficients (d33) as well as high electrostrictive coefficients (M33). It is anticipated that the BNNT based electroactive materials can be used for sensors, actuators, and energy harvesting devices in high temperature environments.
10:00 AM - II7.4
Preparation of Conducting Polymer Composite for Efficient Oxygen Reduction.
Rishi Parajuli 1 , Huixin He 1
1 Chemistry, Rutgers University, Newark, New Jersey, United States
Show AbstractPoly (3,4-ethylenedioxythiophene) (PEDOT) modified electrodes have been reported to catalytically reduce oxygen, which shows great potential to replace Pt based electrode in a fuel cell. The mechanism of the efficient electrocatalytic capability was ascribed to the unique electrochemical behavior of the vapor deposited PEDOT. It can be momentarily reduced by the action of the electrochemical cell, which is different from traditional solution phase produced PEDOT. Oxygen molecules absorb on the reduced PEDOT surface and rapidly re-oxidize the PEDOT to its preferred oxidized state. Oxygen itself is reduced in the process. Most of the bulk conducting-polymer systems, including PEDOT produced by various traditional methods, contain highly crystalline regions and low conductive amorphous regions. The existence of amorphous regions increased potentials to switch the conducting polymer from insulating to conducting states. We hypothesized that the production of PEDOT with highly crystalline structures can largely decrease the reduction potential to switch PEDOT to its reduced states, therefore facilitate oxygen reduction. Recently, water-soluble self-doped polyaniline nanocomposites were fabricated by in-situ polymerization of 3-aminophenylboronic acid monomers in the presence of single-walled carbon nanotubes dispersed by single stranded DNA (the ss-DNA/SWNTs). We found that the ss-DNA/SWNTs acted as catalytic molecular templates during in-situ polymerization of 3-aminophenylboronic acid hemisulfate salt (ABA). Not only was the polymerization speed greatly increased, but also the quality of the resulting poly(aniline boronic acid) (PABA) was remarkably improved, demonstrated that fewer short oligomers and more crystalline structures were produced. The backbone of the self-doped polyaniline had longer conjugated length and existed in the more stable and conductive emeraldine state. In this work, we report our efforts to optimize the parameters to produce PEDOT composites with highly crystalline structures for efficient oxygen reduction. We will share with you how the electronic structure, and surface functionality of carbon nanotubes, and graphene sheets dispersed by different methods impact on the in-situ polymerization speed, crystalline structure of the resulted PEDOT, and their capability in electrocatalytic reduction of oxygen.
10:15 AM - II7.5
Development of High Electrical Conductivity Nanocomposites, through Uniform Dispersion of Carbon Nanotubes (CNTs) in Polymers, with Multifunctional Applications in Electromagnetic Interference (EMI) Shielding, Thermoelectrics, Solar Cell Electrodes, and Structural Usage.
Sunghoon Park 1 , Paul Theilmann 2 , Peter Asbeck 2 , Prabhakar Bandaru 3
1 Materials Research Center, Samsung Advanced Institute of Technology, Samsun Electronics, Seoul Korea (the Republic of), 2 Electrical Engineering, University of California at San Diego, La Jolla, California, United States, 3 Mechanical Engineering, University of California at San Diego, La Jolla, California, United States
Show AbstractWe report on a new type of carbon nanotube-polymer nanocomposites with enhanced electrical and electromagnetic properties. Such composites were synthesized through a new methodology for integrating carbon nanotubes (CNTs) with polymers, where functional groups on CNTs were made to interact with select polymer groups, e.g., epoxy linkages, enabling uniform dispersion over a very wide range of CNT loading. Such composites, e.g., single-walled CNT- RET (reactive ethylene terpolymer), incorporate good dispersion with low electrical percolation volume fractions (~ 0.1 volume %), yielding outstanding microwave shielding efficiency, SE (~ 30 dB) for electromagnetic interference (EMI) applications. The SE was characterized for both single-walled and multi-walled CNTs and was much enhanced in the former. The specific roles of absorption and reflection in determining the total shielding, as a function of the CNT filling fraction, will also be discussed. It was also seen that CNT-RET composites possess a complex dielectric permittivity twenty times larger than composites composed of pristine single walled CNTs and three hundred times larger than functionalized multi-walled CNT-RET composites. We understand such an enhancement, both in terms of uniform nanotube dispersion and through a parallel resistor-capacitor model. We subsequently show that the AC electrical conductivity is a good predictor of the electromagnetic interference (EMI) shielding effectiveness of nanocomposites. We have also used, for the first time, novel CNT morphologies incorporating helical nanostructures, which have yielded even better performance. The above achievements are expected to lay a strong foundation for the widespread use of CNT composites for a whole host of applications including electromagnetic interference shielding, solar cell electrodes, thermoelectric materials, and for structural usage.
10:30 AM - II7.6
The Experimental Determination of the Onset of Electrical and Thermal Conductivity Percolation Thresholds in Carbon Nanotube-polymer Composites.
Byung-wook Kim 1 , Steve Pfeifer 2 , Prabhakar Bandaru 2
1 Department of Electrical Engineering, University of California, San Diego, La Jolla, California, United States, 2 Department of Mechanical Engineering, Material Science Program, University of California, San Diego, La Joll, California, United States
Show AbstractIt is of scientific and technological interest to analyze the minimal concentration of carbon nanotubes (CNTs) necessary to form a percolating network. For example, CNT networks have been proposed as constituents of thin film transistors for electronics and biosensors, polymer composites for electromagnetic interference shielding, etc. CNTs are attractive candidates for filler materials in polymers, primarily due to their large aspect ratio and tunable electrical conductivity, which enables electrical percolation to be achieved with very small amounts of nanotubes, e.g., we have calculated from the excluded-volume percolation theory, that single walled CNTs (SWNTs) with an aspect ratio of ~ 5000 (which corresponds to a length of 5 μm and a diameter of ~ 1 nm), when dispersed uniformly into a non-conducting polymer enable a conducting pathway at a volume fraction of ~ 0.1 %. Our experimental results yield values very close to the optimal considerations for both SWNTs and multi-walled nanotubes (MWNTs). We have synthesized CNT-Reactive ethylene terpolymer (RET) composites, where uniform dispersion of the CNTs was accomplished through intimate chemical reaction between functional groups on the CNTs with the epoxide group on the RET polymer. Subsequent DC and AC electrical conductivity measurements on the composites indicated a percolation like transition, at ~ 0.1 vol% for SWNTs (and 2 vol% for MWNTs) with an enhancement of electrical conductivity of the composites by 10 orders of magnitude. A similar percolation phenomena was observed, at ~ 2 vol%, in the thermal conductivity (determined through both the 3 omega and steady state methods) of MWNT dispersed composites, with an increase from 0.7 W/mK for the pristine polymer to 1.1 W/mK for a 5 vol% polymer-composite. The above experimental results, along with the theoretical justification, along with the practical implications of our results to CNT networks will be discussed.
10:45 AM - II7.7
Effect of Silica Particles Concentration and Particle Size on the Electrical Conductivity and Thermomechanical Property of Epoxy/Silver Nanocomposites.
Seungwoong Nam 1 2 , Hyunwoo Cho 3 , Daeheum Kim 2 , Bong June Sung 3 , Soonho Lim 1 , Heesuk Kim 1
1 Polymer Hybrids Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 Chemical Engineering, Kwangwoon Univiersity, Seoul Korea (the Republic of), 3 Chemistry, Sogang University, Seoul Korea (the Republic of)
Show AbstractIsotropical conductive adhesives (ICAs) have been studied extensively to replace the eutectic Sn/Pb solder in various electronic product interconnects. However, there have been limitations of these materials such as low electrical conductivity, unstable contact resistance and poor mechanical strength (such as adhesion, mechanical strength, impact strength) in various environmental conditions. Various approaches to get a high conductivity at low filler content without poor mechanical properties have been tried in many years. For example, 1-dimensional conductive fillers such as metal wires and carbon nanotubes have been used to reduce the contact resistance, thereby decreasing the electrical percolation threshold concentration. Another approach for high conductivity is to incorporate transient liquid-phase metallic fillers in ICA formulations and to sinter the nano-sized silver particles at curing temperature of ICAs.In this study, novel approach to decrease the contact resistance and coefficient of thermal expansion(CTE) of epoxy/Ag nanocomposites using silica particles has been introduced. Silver nanoparticles used as conductive fillers were replaced with silica particles because silica has been known to control the rheology of organic/inorganic hybrids and the reinforcement of polymer matrices. Recently, it has been reported that silica was involved in the generation of conductive polymer composites in order to control the rheological properties of the composites to improve the processability for various applications. This study described herein concerns the effect of silica concentration and silica particle size on electrical resistivity, rheological property and thermomechanical property such as coefficient of thermal expansion (CTE) of epoxy/Ag nanocomposites. The effect of silica particles on electrical resistivity through percolation threshold concentration is also studied using molecular simulation. Adding silica particles to epoxy/silver nanocomposites leads to reduced electrical percolation threshold and enhanced coefficient of thermal expansion (CTE) of nanocomposites. While the electrical resistivity of epoxy/Ag nanocomposite including 23vol% Ag nanoparticles is 1.9×10-4Ωcm, epoxy/Ag nanocomposite with 18vol% Ag nanoparticles shows 4.7×10-4 Ωcm after addition of 12vol% silica particles to this nanocomposite. In the thermomechanical study, neat epoxy composites containing no filler have high CTE, because of the characteristics of epoxy resin. But, CTE of the nanocomposites containing the silver nanoparticles of 23 vol% was improved up to 45μm/m*°C. By adding silica particles to the epoxy/silver nanoparticles composite, CTE of nanocomposites was decreased to 32.9 μm/m*°C. Because the silica has lower CTE than that of silver, increasing of silica content to silver content CTE of nanocomposites is improved to 32.9 μm/m*°C.
11:00 AM - II7:ELECTRIC
BREAK
11:15 AM - **II7.8
Electrical Conductivity and Switching in Polymer Nanocomposites.
Karen Winey 1
1 Materials Science and Engineering, Univ. of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractWe describe the design and preparation of isotropic silver nanowire-polystyrene composites, in which the nanowires have finite L/D (< 35) and narrow L/D distribution. These model composites allow us to isolate the L/D dependence of the electrical percolation threshold, φc, for finite-L/D particles. Our experimental φc values decrease with increasing L/D, as predicted qualitatively by analytical percolation models. However, quantitative agreement between our experimental data and both soft-core and core-shell analytical models is not achieved, because both models are strictly accurate only in the infinite-L/D limit. To address this analytical limitation, we have developed a soft-core simulation method to calculate φc and network conductivity for cylinders with finite L/D. (We have previously used this simulation method to explore the effect of orientation on electrical conductivity.) Our simulated φc results agree strongly with our experimental data, suggesting (1) that the infinite-aspect-ratio assumption cannot safely be made for experimental networks of particles with L/D < 35 and (2) in predicting φc, the soft-core model makes a less significant assumption than the infinite-L/D models do. The demonstrated capability of our simulations to predict φc in the finite-L/D regime will allow researchers to optimize the electrical properties of polymer nanocomposites of finite-L/D particles.Traditionally, bulk nanocomposites of electrically conducting particles and insulating polymers have been categorized as either insulating or conducting when the nanoparticle concentration is below or above the percolation threshold, respectively. Meanwhile, thin-film polymer nanocomposites can exhibit resistive switching behavior appropriate for digital memory applications. Here, we present reversible resistive switching in bulk, glassy polymer nanocomposites. At compositions close to the electrical percolation threshold, silver nanowire-polystyrene nanocomposites demonstrate reversible resistive switching at room temperature. Nanocomposites with compositions outside of this range exhibit either irreversible switching, or no switching at all. We propose that resistive switching in these materials is the result of the field-induced formation of silver filaments that bridge adjacent nanowire clusters, extending the percolation network and decreasing the sample’s bulk resistivity. These findings break from the usual dichotomy of insulating or conducting properties and could inspire new devices that capitalize on this responsive behavior in these versatile polymer nanocomposites.
11:45 AM - II7.9
In Situ Synthesis and Integration of Polymer Electrolytes in Nanostructured Electrodes for Photovoltaic Applications.
Siamak Nejati 1 , Kenneth Lau 1
1 Chemical and Biological Engineering, Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractSusceptible to leakage and corrosion, the use of a liquid electrolyte in the conventional dye sensitized solar cell (DSSC) remains a major challenge in limiting cell operability and performance. Efforts to replace the liquid with a solid equivalent have been met with difficulties in penetrating a solid material inside the tiny (17-25 nm) pore spaces of the nanostructured titanium dioxide photoanode, especially with using liquid processing techniques like spin coating. Here, we successfully applied initiated chemical vapor deposition (iCVD) to synthesize polymers and completely fill the pores of the mesoporous TiO2 electrode up to 12 µm in thickness. iCVD is a solvent-free one-step polymerization and deposition technique that involves the delivery of monomer and initiator vapors into a vacuum chamber where the initiator is selectively activated by thermal means to induce polymer growth on a substrate surface. Uniquely, the substrate is kept cooled as iCVD has been found to be an adsorption-limited process. In addition, the selective reaction pathway results in stoichiometric polymers without a loss of chemical functionality often associated with CVD-type polymer growth. Thus, iCVD allows for materials design analogous to liquid-based polymerization (including crosslinking and copolymerization) while also taking advantage of the liquid-free, low pressure growth environment to facilitate mass transport inside nanostructures. Specifically, we have incorporated iCVD polymers, including poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(glycidyl methacrylate) (PGMA), as polymer electrolytes in DSSCs. iCVD parameters were used to control diffusion (gas and surface) as well as polymerization kinetics to enable complete pore filling. FTIR, NMR, GPC, and electrochemical impedance spectroscopy (EIS) were used to determine polymer structure, molecular weight and ion conductivity. Cross sectional SEM was used to determine the degree of pore filling. The integrated polymer and inorganic nanostructure photovoltaic device was evaluated under simulated solar illumination (AM 1.5, 100 mW/cm2) to obtain current-voltage behavior and cell efficiency, and compared with standard liquid electrolyte cells containing acetonitrile. At all TiO2 electrode thicknesses investigated, the open circuit voltage (Voc) was found to be significantly higher in the polymer cells. By performing EIS at their respective Voc, we observed a shift to a higher electron recombination time constant when replacing the liquid with the polymers. We therefore attribute the increase in Voc to the complete filling of the mesoporous electrode with the polymers that reduced charge recombination losses at the electrode-electrolyte interface. Significantly, the power conversion efficiency of the polymer cells has been found to be higher than the liquid electrolyte ones. iCVD therefore represents a viable engineering pathway for achieving tight integration in polymer nanocomposite structures.
12:00 PM - **II7.10
Linear Carbon Chains/metal Nanoparticles Nanocomposite Systems: Aggregation Phenomena and Electromagnetic Amplification Properties.
Orazio Puglisi 1 , D'Urso Luisa 1 , Messina Elena 1 , Compagnini Giuseppe 1
1 Dipartimento di Scienze Chimiche, University of Catania, Catania Italy
Show AbstractThe aggregation control of metal nanoparticles is a topic of great interest and complexity, that involves surface physical-chemical properties of nanostructures and greatly influences their functional properties. In the last few years the growing interest for “plasmonics” lead to the knowledge and development of new “nano-photonic” concepts and applications in extremely advanced fields. Recent experimental and theoretical work on electromagnetic amplification phenomena allowed to amplify non-linear optical processes such as Raman scattering of single-molecules (SM-SERS) located in close proximity of plasmonic structures (so called hot-spot). The focus is to find new strategies to obtain pure and hybrid systems (metal/molecule nanostructures) both through controlled direct welding and by the interlinking of conductive units which preserve metal nanoparticles properties. In this work organic/inorganic structures of nanometric size were prepared by laser ablation in water with a nanosecond pulsed laser using 1064 and 532 nm radiation and deposited on suitable substrates. The possible presence of chemical bonds with organic molecules will be exploited to study metal nanoparticle ability to amplify localized electro-magnetic fields, which lead to an enhancement of several order of magnitude of vibrational features based on the “surface-enhanced Raman scattering (SERS)”. Linear Carbon Chains (LCCs) seem to be good candidates to create carbon shells around the nanoparticles, therefore allowing the formation of extended networks of stable metal nanoparticles connected by π- electron rich carbon nanowires. The interaction between the nanoparticles and LCC has been studied by UV-Vis and Raman spectroscopy. A strong dependence of the optical extinction after the interaction was detected. The observations are correlated to a plasmon coupling of the particles induced by the nanowires. Mass spectra measurements and XPS analysis were employed also to investigate possible oxidation states and charging on the surface of nanoparticles and to explain the surface state effect on electromagnetic amplification phenomena.
12:30 PM - II7.11
Characterizing Charge Transfer States at Electrodeposited Poly(3-hexylthiophene) (e-P3HT)/C60 Interfaces as a Function of Polymer Oxidative Doping Using X-ray and UV Photoelectron Spectroscopies.
Judtih Jenkins 1 , Paul Lee 1 , Ken Nebesney 1 , Erin Ratcliff 1 , Neal Armstrong 1
1 Chemistry & Biochemistry, University of Arizona, Tucson, Arizona, United States
Show AbstractThe poly(3-hexylthiophene) (P3HT)/C60 interface plays a critical role in the separation of photogenerated charges in organic photovoltaics. Recent reports within the literature have suggested that upon formation of the P3HT/C60 or P3HT/PCBM interface, there is a charge transfer event from the donor polymer to the PCBM acceptor. We have recently developed a unique method for electrodepositing P3HT (e-P3HT) using a multi-potential step process. By controlling the degree of oxidative doping of the e-P3HT film using chronoamperometry, we are able to lock the e-P3HT film in its neutral, polaronic, and biopolaronic forms. We can control the work function and ionization potentials of these films, with the work function varying between 3.9 eV for the neutral form to 4.8 eV for the bipolaronic form of the polymer using electrochemical doping. This systematic control of ionization potential is necessary for providing insight into the fundamental chemical processes occurring at the interface, as the degree of oxidation within the polymer layer may facilitate or hinder the formation of a P3HT/C60 charge transfer state. The charge transfer states were characterized using photoelectron spectroscopy as a function of polymer oxidation state. Thin layers of C60 (which has a higher electron affinity than PCBM) were thermally deposited onto e-P3HT films and ultraviolet photoelectron spectroscopy (UPS) was used to evaluate the energetic barriers and resulting work functions and ionization potentials before and after C60 depositions. The films were also characterized using monochromatic X-ray photoelectron spectroscopy (XPS). When the e-P3HT was forced into its bipolaronic form, the interface maintained distinct oxidized polymer and C60 characteristics, but spectra of the neutral polymer/C60 suggest some degree of energetic mixing between the two materials. The ability to turn this charge transfer state on and off with oxidative doping has significant implications for the donor/acceptor interface and may provide a unique understanding of not only charge separation states but also a systematic control of sites for charge recombination. Implications for reverse saturation current and open circuit voltages will be discussed. The ability to influence the presence and nature of charge transfer states demonstrated here through oxidative polymer doping should ultimately enable more strategic development of charge separation materials and interfaces.
12:45 PM - II7.12
Nanocomposites of Conducting Polymers and Carbon Nanotubes as Electrodes of High-performance Dye-sensitized Solar Cells and Polymer Photovoltaic Cells.
Benhu Fan 1 , Xiaoguang Mei 1 , Ouyang Jianyong 1
1 Materials Science and Engineering, National University of Singapore, Singapore Singapore
Show AbstractDye-sensitized solar cells and polymer photovoltaic cells are regarded as the next-generation solar cell technologies. However, there are some problems for both of them in the practical application. One problem for dye-sensitized solar cells is related to the counter electrode, which usually use Pt. Pt is expense and need to be fabricated through a high-temperature pyrolysis. On the other hand, polymer photovoltaic cells have a problem related to the transparent electrode. The traditional transparent electrode is indium tin oxide (ITO). ITO is facing problems of limited indium resource in earth and being mechanically brittle. Here, we report the development of nanocomposites of conducting polymers and carbon nanotubes. These nanocomposites were used as the counter electrode of high-performance dye-sensitized solar cells and transparent electrode of high-performance polymer photovoltaic cells.
II8: Polymer-Based Nanocomposites: Electromagnetic Features
Session Chairs
Wednesday PM, December 01, 2010
Republic B (Sheraton)
2:30 PM - II8.1
Magnetic Properties of Free-photoinitiator Acrylic UV-cured Films Containing Magnetite Nanoparticles.
Alessandro Chiolerio 1 , Lorenzo Vescovo 2 , Paolo Allia 2 , Paola Tiberto 3 , Lorenza Suber 4 , Giada Marchegiani 4 , Marco Sangermano 2
1 Physics, Politecnico di Torino, Turin Italy, 2 Materials Science and Chemical Engineering, Politecnico di Torino, Turin Italy, 3 Electromagnetism Division, INRiM, Turin Italy, 4 CNR-Area della Ricerca di Roma 1, Istituto di Struttura della Materia, Turin Italy
Show AbstractAcrylic based films containing thermo-chemically synthesized magnetite nanoparticles (NPs) were prepared by UV-curing. A stable dispersion of Fe3O4 NPs in n-hexane was added to polyethylene glycol diacrylate (PEGDA) oligomer or to hexanediol diacrylate (HDDA) oligomer, producing a blend whose viscosity matches the processing requirements for inkjet printing technology. Morphologic characterization included X-ray powder Diffraction of the NPs and Field Effect SEM on nanocomposite sections.By real-time FT-IR analysis it was shown that Fe3O4 NPs are able to initiate radical chain-grown polymerization under UV light. Tight cross-linked transparent polymeric films were obtained after 1 minute of UV irradiation. The thermal and dynamo-mechanical properties of cured films were characterized.The magnetic properties of the produced films were studied by means of an Alternating-Gradient Force Magnetometer in the temperature range 10 – 300 K and up to 18 kOe. The isothermal magnetization curves of both HDDA and PEGDA -based nanocomposites showed that these hybrid systems must be described as interacting superparamagnets [1] characterized by inter-particle magnetic interactions dominating over intra-particle effects.A Finite Element Method simulation allowed to better understand the thermo-mechanical stresses undergone by the NPs during sample cooling.[1] P. Allia et al. Phys. Rev. B 64 (2001) 144420
2:45 PM - II8.2
Magnetic Polypropylene Nanocomposites Filled with In-situ Synthesized Iron Nanoparticles.
Zhanhu Guo 1 , Jiahua Zhu 1 , Suying Wei 2
1 Dan F. Smith Department of Chemical Engineering, Lamar University, Beaumont, Texas, United States, 2 Chemistry and Physics, Lamar University, Beaumont, Texas, United States
Show AbstractMagnetic nanoparticles with a size close to the single domain are of tremendous interest in different fields of chemistry and physics due to their unique magnetic properties such as enhanced coercivity, superparamagnetism and chemical catalytic properties inherent with their small size and high specific surface area [1-3]. Therefore, polymer nanocomposites incorporated magnetic nanoparticles have shown promise in various potential applications [4-6]. To achieve uniform dispersion of nanofillers in the polymer matrix is a challenge [7-8].In this talk, we will present the results on the magnetic polypropylene (PP) nanocomposites. The PP nanocomposites with various loadings of iron nanoparticles are fabricated via an in-situ thermo-decomposition nanoparticle synthesis approach. To stabilize the formed iron nanoparticles and to improve the interfacial compatibility between the organic polymer phase and inorganic iron phase, two different species of propylene based surfactants are used to coat the iron nanoparticles. The morphology and dispersion quality of the iron nanoparticles in the PP matrix at different length scales are investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The magnetic property, electrical conductivity and linear viscoelastic behavior of these nanocomposites are investigated. A percolation threshold is obtained and the electrical conductivity of PP is increased significantly. The storage modulus (G’) versus frequency curves approaches a plateau above the percolation threshold with the formation of an interconnected particle network structure, indicative of ‘pseudo-solid-like’ behavior. The temperature of crystallization (Tc) and fraction of PP that is crystalline (Fc) are modified by incorporating iron nanoparticles. The thermal decomposition temperature of PP is significantly enhanced upon addition of various contents of iron nanoparticles.References:[1] Z. Guo, H. Lin, A. B.Karki, S. Wei, D. P.Young, S. Park, J. Willis, T. H.Hahn. Facile monomer stabilization approach to fabricate iron/vinyl ester resin nanocomposites. Composite science and Technology, 2008, 68:2551-2556 [2] D. Zhang; R. Chung; A. B. Karki; F. Li; D. Young; Z. Guo. Journal of Physical Chemistry C, 114, 212-219 (2010) [3] J. Zhu, S. Wei, X. Chen, A. B. Karki, D. Rutman, D. P. Young and Z. Guo. Electrospun Polyimide Nanocomposite Fibers Reinforced With Core-Shell Fe-FeO Nanoparticles, Journal of Physical Chemistry C, 114(19) 8844-8850, 2010[4] Z. Guo; H. T. Hahn; H. Lin; A. B. Karki; D. P. Young. Magnetic and Magnetoresistance Behaviors of Particulate Iron/Vinyl Ester Resin Nanocomposites, Journal of Applied Physics, 104, 014314 (2008).[5] Z. Guo; S. Park; H. T. Hahn; S. Wei; M. Moldovan; A. B. Karki; D. P. Young. Magnetic and Electromagnetic Evaluation of the Magnetic Nanoparticle Filled Polyurethane Nanocomposites, Journal of Applied Physics, 10, 09M511 (2007) [6] J. Zhu, S. Wei, J. Ryu, L. Sun, Z. Luo and Z. Guo. Magnetic Epoxy Resin Nanocomposites Reinforced with Core-Shell Structured Fe@FeO Nanoparticles: Fabrication and Property Analysis; ACS Applied Materials & Interfaces, accepted (2010)[7] Z. Guo; S. Park; S. Wei; T. Pereira; M. Moldovan; A. B. Karki; D. P. Young; H. T. Hahn. Flexible High-loading Particle Reinforced Polyurethane Magnetic Nanocomposite Fabrication through Particle Surface Initiated Polymerization; Nanotechnology, 18, 335704 (2007).[8] Z. Guo; T. Pereira; O. Choi; Y. Wang; H. T. Hahn. Surface Functionalized Alumina Nanoparticle Filled Polymeric Nanocomposite with Enhanced Mechanical Properties; Journal of Materials Chemistry, 16, 2800-2808 (2006).
3:00 PM - II8.3
Gelation, Electrical Conductivity and Elasticity of PAM- MWNT.
Gulsen Akin Evingur 1 , Onder Pekcan 2
1 Physics Engineering, Istanbul Technical University, Istanbul Turkey, 2 , Kadir Has University, Istanbul Turkey
Show AbstractPolymer composites with carbon nanotube additions are one of the research subjects which have attracted a lot of attention in recent years. The first polymer nanocomposites using carbon nanotubes as filler were reported in 1994 by Ajayan et al. [1]. The gelation, AC electrical conductivity and elasticity of nanocomposites from doped multiwalled carbon nanotubes(MWNTs) with Polyacrylamide(PAM) were measured.PAM-MWNT was prepared via free radical crosslinking copolymerization with different amounts of MWNTs varying in the range between 0.1 and 15 wt%. PAM-MWNT composite gels were characterized by fluorescence, dielectric spectroscopy and the tensile testing technique. A small content of doped nanotubes dramatically changed gelation time, conductivity and young modulus, respectively.The gel fraction exponent, β of PAM-MWNTs composite gels were investigated for various monomer and MWNTs concentrations and observed that the gel fraction exponent β agrees best with the percolation theory [2] for various amounts of PAM-MWNTs as shown in Table 1.In conclusion, if polymer systems which are initially of an isolator character are doped with carbon nanotubes of nano dimensions and when the amount of this addition exceeds a critical value known as the percolation threshold, then composite gel systems with carbon nanotubes added become electrically conducting structures after 1% MWNT and elasticity are decreasing after 3%MWNTs[4].[1] P. M. Ajayan, O. Stephan, C. Colliex, D. Trauth, Science, 265, 1212- 1214 (1994).[2] A. Aharony, Phys. Rev. B.22, 400- 414, (1980).[3] D. K. Aktas, G. A. Evingur, Ö. Pekcan, Composite Interfaces, 17, 301- 318, (2010). [4] G. A. Evingur, Ö. Pekcan, Carbon Symposium, 18- 19 March 2010,Istanbul Technical University, Istanbul.
3:15 PM - **II8.4
Microwave Metamaterials Containing Magnetically Soft Microwires.
Julian Estevez 1 , Larissa Panina 1 , Mihail Ipatov 1 , Valentina Zhukova 1 , Arkady Zhukov 1
1 Materials Physics, University of the Basque Country, San Sebastian, Guipuzcoa, Spain
Show AbstractComposites containing long parallel wires can be characterised by plasma-like dispersion of Ref [1] with a negative value of the real part of the permittivity below the characteristic plasma frequency, fp. A number of experimental studies confirmed a negative permittivity in the GHz region for wire media. Surface impedance Z may change under applied magnetic field, Hex, as a result of the MI effect [2]. Then, the permittivity spectra will depend on Hex. We studied composites containing amorphous ferromagnetic Co66 Fe3.5B16Si11Cr3.5 microwires with radius of 20 microns exhibiting large MI effect (up to 300% at 500 MHz) by free space methods. Large MI effect makes them very promising for engineering artificial dielectrics with tuneable microwave properties. The S-parameters were measured at 0.9-17 GHz in the presence of external field ranging up to 3000A/m. The effective permittivity spectra were deduced from S-parameters with the help of Reflection/Transmission Epsilon Fast Model. We report on magnetic field dependence of the dielectric response in composites with arrays of parallel magnetic wires, continuous and short-cut, in the frequency region of 0.9-17 GHz. Both the real and imaginary parts of εef show strong variations with increasing Hex owing to the MI effect which controls the losses in the dielectric response. Long-wire composite has a plasmonic type dispersion of εef with negative values of its real part below the plasma frequency ( GHz range) for wire spacing of about 1 cm and wire diameter of few microns. The presence of Hex suppresses low-frequency plasmons increasing the value of the real part of the permittivity. For cut-wire composites we confirmed a resonance type of εef dispersion due to the dipole resonance in wires at half wavelength condition. Application of Hex broadens the resonance and shifts it towards the higher frequencies. Therefore, both types of wire composites exhibit strong εef (Hex) dependence suitable for applications. Acknowledgements. We acknowledge support under projects MAT2007-66798-CO3-01 (MEC) and Saiotek 08 METAMAT (SPRI).REFERENCES1.Pendry, J. B., A. J. Holden, W. J. Stewart, and I. Youngs, “Extremely Low Frequency Plasmons in Metallic Mesostructures,” Phys. Rev. Lett., Vol. 76, No. 25, 4773-4776, 1996. 2.Makhnovskiy D. P., L. V. Panina, “Field dependent permittivity of composite materials containing ferromagnetic wires,” J. Appl. Phys. 93 4120, 2003.
3:45 PM - II8:ELECTROMAG
BREAK
4:00 PM - **II8.5
Large Tunneling Magnetoresistance in Fe3O4/Polymer Nanocomposites with Polymers Acting as the Intergranular Tunnel Barrier.
Jinke Tang 1 , Wendong Wang 1
1 Physics & Astronomy, University of Wyoming, Laramie, Wyoming, United States
Show AbstractMagnetite Fe3O4 is predicted to be a half metal with high spin polarization. This feature in combination with its high Curie temperature make it attractive for spintronic applications. However, since the magnetite surface in a typical environment is partially oxidized (i.e., enriched with Fe3+), the minority spin states at the Fermi level are mixed with the majority spin states, which lowers the spin polarization and thus the magnetoresistance (MR). Our investigation has found that a coating of very thin layer of polymer on the surface of Fe3O4 can effectively protect samples from the surface oxidation and results in improved MR. Both oxygen-free insulating polymers (Teflon and polystyrene) and oxygen containing insulating polymers (PMMA and polycarbonate) were chosen as the tunnel barrier material in an Fe3O4 intergranular tunneling experiment. Powders of polymer with average particle size in the order of microns and Fe2O3 nanoparticles were mixed together by ball milling. The mixture were annealed at 250 - 300 degree C in pure hydrogen flow and then pressed into pellets under a pressure of 5 x 10^8 N/m^2. The pellets were again annealed in hydrogen flow. X-ray diffraction (XRD) patterns indicated that there was a complete phase transformation from Fe2O3 to Fe3O4 after the samples were annealed under such conditions. Transmission electron microscopy study revealed that Fe3O4 nanoparticles ~10 nm in size were coated and separated by a thin layer of the polymer. The temperature dependence of the resistivity exhibits features characteristic of intergranular tunneling in these Fe3O4/polymer nanocomposites. Giant negative MR was observed at room temperature and the highest MR ratio is about 17 % in an applied field H = 5 T and about 23% for H = 14 T. Noticing that the MR ratio of pure Fe3O4 powder is typically only 4-5 % or lower at room temperature, large enhancement of the MR ratio in the Fe3O4/polymer nanocomposites is obvious. This is attributed to that the polymers act as barrier material and, more importantly, prevent the oxidation of the surface of Fe3O4, which is believed to alter the half-metallic state at the surface. Magnetotransport data further indicate that the oxygen-free polymers are better at the prevention of the oxidation than the oxygen-containing polymers. Our results suggest that there is a high degree of spin polarization for Fe3O4 (54% and 83% at room temperature and 110 K, respectively), making it still desirable for spintronic applications such as spin injectors. The higher melting point of Teflon than polystyrene may make it better suited for insulating barrier in spintronics devices.
4:30 PM - II8.6
Study of Thermo-physical Properties for Increased Efficiency of Hybrid Polymer-PbS Nanocrystals Photovoltaic Devices.
Ram Thapa 1 , Karen Lozano 1 , Mircea Chipara 2
1 Department of Mechanical Engineering, University of Texas - Pan American, Edinburg, Texas, United States, 2 Department of Physics and Geology, University of Texas - Pan American, Edinburg, Texas, United States
Show AbstractPower conversion efficiency of photovoltaic cells is not governed only by optical and electronic properties of the matrix but also by thermo-physical properties such as crystallization of the films, glass transition, and melting temperatures because thermo-physical properties governs the mobility of the charge carriers within the matrix. In this study, thermo-physical properties of binary mixture of poly(3-hexylthiophene) (P3HT) and lead sulfide (PbS) nanoparticles were studied using Differential Scanning Calorimetry (DSC), Thermogravimetric analysis (TGA), and Dynamical Mechanical Analysis (DMA). Additional experimental techniques such as Wide Angle X-ray Scattering and Raman Spectroscopy were used to further analyze the crystallization process in P3HT-PbS nanocomposites. DSC and X-ray data showed the change of crystallization behavior of the organic-inorganic hybrid nanocomposite from that of the individual components. Distinguishable shift in the crystallization temperature and multiple crystallization peaks were observed in the case of nanocomposite. The detail thermo-physical study of the P3HT-PbS nanocomposites provides the range of temperature within which the devices have to be annealed for maximum power conversion efficiency of the photovoltaic devices fabricated from these blends.Acknowledgement: This material is based on research sponsored by Air Force Research Laboratory under agreement number FA8650-07-2-5061.
4:45 PM - II8.7
Controlling the Spatial Positioning of Magnetic Nanoparticles in Electrospun Microfibers.
Kristen Roskov 1 , Jessie Atkinson 3 , Lyudmila Bronstein 3 , Richard Spontak 1 2
1 Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States, 3 Chemistry, Indiana University Bloomington, Bloomington, Indiana, United States, 2 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractIncorporation of nanoparticles (NPs) into polymer matrices has become a routine method by which to controllably alter the properties of the resultant nanocomposite. Recent studies of polymer blends and block copolymers have demonstrated that the spatial position of NPs can be controlled via surface selectivity. In this work, we explore the incorporation of magnetic NPs into electrospun microfibers composed of two chemically dissimilar polymers so that the NPs locate preferentially within the nanofibers. The NPs were also added to bulk samples of the blend to establish a relationship between the NPs positioning and both the crystallinity and phase separation of the constituent polymers. Magnetic iron oxide NPs with diameters ranging from 12 to 28 nm were prepared via thermal decomposition of iron oleate in the presence of oleic acid as a capping agent in high boiling hydrocarbons (docosane and eicosane). X-ray diffractometry confirmed that the NPs are crystalline and contain mostly wüstite (Fe(1-x)O) and some spinel (most likely Fe3O4). These NPs were further oxidized to maghemite (γ-Fe2O3). Initially, polycaprolactone (PCL) and poly(2-vinylpyridine) (P2VP) were chosen due to the hydrophobic nature of the NPs. Concentration, plate distance, and voltage were carefully tuned during electrospinning to yield fiber diameters in the range of 100-500 nm to permit investigation by transmission electron microscopy so that the fiber interior could be visually interrogated. The hydrophobic polymers with larger fiber diameters possess a better distribution and less aggregation of NPs. Complementary field-emission scanning electron microscopy and energy dispersive x-ray spectroscopy demonstrated that relatively few NPs locate on the external fiber surface. Blends of a hydrophobic and hydrophilic polymer were likewise prepared ex vivo of the NP solution to determine if it is possible to control the spatial location of the NPs within the fibers. In this case, poly(ethylene oxide) (PEO) and P2VP were blended at various ratios up to 70 wt% PEO. At concentrations higher than this, the PEO crystallized, hindering both NP migration and phase separation. We found that, depending on the PEO:P2VP ratio, it is possible to achieve an even distribution of circular, phase-separated domains of PEO along the edges of a P2VP matrix, as well as a core-sheath structure. It was also possible to control the NP location, since the NPs prefer to reside in the hydrophobic P2VP phase, which can be selectively stained for identification purposes. Analysis of the bulk blend morphology demonstrates that the size of the phase domains decreases upon addition of the NPs. In addition, alignment of the NPs within electrospun polymer microfibers was also achieved using an electromagnetic field in conjunction with the electric field applied during electrospinning.
5:00 PM - **II8.8
Conjugated Polymer/Nanoparticle Nanocomposites for Optoelectronic Applications.
Kung-Hwa Wei 1
1 Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan
Show AbstractIn this talk, I will present to you on various ways for binding colloidal nanoparticles to conjugated polymers for forming thin films for optoelectronic devices’ application such as in light emitting diode or photovoltaic devices. Conjugated polymers and colloidal nanoparticles can be designed or modifiedthrough altering molecular structure and using different ligands, respectively, for undergoing solution processing routes to fabricating large-area or flexible thin films for device applications. Two kinds of cases will be discussed. The first kind involves using the size of oxide or metal nanoparticles that were covalently bounded to the side chain of polyfluorene or MEH-poly(phenylenevinylene) for increasing the steric hindrance between polymer chains. Alternatively, adopting pi-pi stacking for binding surface ligands modified CdS nanoparticles to the dendritic side chain of polyfluorene for reducing the formation of excimers and thereby enhancing the efficiency or color purity of polymer light emitting diode. The second kind of cases is concerned with bulk heterojunction solar cells, in which an electron withdrawing conjugated species was tethered to the side chain of polythiophene for enhancing charge transfer and blending with fullerene derivatives. This approach results in the more balanced electron and hole mobility and the power conversion efficiency of the device as well.
5:30 PM - II8.9
A Gold Nanorods Nanocomposite with Macroscopically Anisotropic Linear and Nonlinear Optical Properties.
Jiafang Li 1 , Siyun Liu 1 , Fei Zhou 1 , Zhi-Yuan Li 1
1 Chinese Academy of Sciences, Laboratory of Optical Physics, Institute of Physics, Beijing China
Show AbstractGold nanorods (GNRs) have attracted great interest due to their anisotropic splitting of the surface plasmon resonance (SPR) into two polarization-dependent components, i.e. the transverse and the longitudinal component. Compared with the weak transverse SPR around 530 nm, the longitudinal SPR of GNRs induces strong absorption, scattering, local-field enhancement and photoluminescence. Consequently, GNRs have appealing applications in surface enhanced Raman spectroscopy, biological imaging and sensing, photothermal therapy, optical data encoding, etc. However, in most applications, only a portion of the GNRs with certain orientations was utilized because GNRs are naturally randomly oriented and their longitudinal SPR can not be excited in the direction perpendicular to their longitudinal axes. Moreover, the random distribution averages the microscopic anisotropy of the single GNR and the assembled GNRs behave like macroscopically isotropic materials. Therefore, macroscopically representing or constructively amplifying the anisotropic optical properties of a single GNR could be very preferable to improve the efficiency of GNR applications. Here we demonstrate the anisotropic and enhanced nonlinear absorption from aligned GNRs in a poly(vinyl alcohol) (PVA) film. The alignment of the GNRs was realized by utilizing a well-developed stretched-film method, in which the GNR-doped PVA film was stretched under heating at a temperature of 65 oC. After the alignment, the film showed strong macroscopic anisotropy in both linear and nonlinear absorption (NLA). Specifically, the stretch process directly enhanced the NLA coefficient by ~9 times. It was further observed that the absorptive nonlinearities of the aligned GNRs in PVA films were more than the linear summation of the nonlinearities of individual GNRs. Compared with a non-stretched film, an increase in the GNR concentration by 4 times in the stretched GNRs/PVA film could enhance the NLA coefficient by ~91 times.
II9: Poster Session: Polymer - Based Nanocomposites II
Session Chairs
Thursday AM, December 02, 2010
Republic B (Sheraton)
9:00 PM - II9.1
Alternating Conductivity and Investigations of Thick Polyaniline/Indium-tin Oxide Nanocomposite Films.
Gislayne Goncalves 1 2 , Mirela Santos 1 3 , Juliana Couto 1 , Sukarno Ferreira 3 , Maximiliano Munford 3 , Rodrigo Bianchi 1
1 Department of Physics, Federal University of Ouro Preto, Ouro Preto, MG, Brazil, 2 , Insitute Federal of Minas Gerais - Campus Ouro Preto, Ouro Preto, Minas Gerais, Brazil, 3 Physics Department, Federal University of Viçosa, Viçosa, Minas Gerais, Brazil
Show AbstractSince the discovery of semiconducting polymers in 1977, many authors have pointed out the use of conjugated polymers in several electronic devices, but a major drawback of these polymers has been their modest air stability, which has made their conventional processing into useful products difficult. Nowadays, it has attracted renewed interest from recent researchers as it is transparent and highly conducting to be used as hole transport layers in several lighting emitting displays in such a way that organic-inorganic composites are a novel class of materials for which the threshold voltage for light-emitting diodes can be reduced to values well below that required for commercial applications. Among various inorganic materials and conjugated polymer, indium tin oxide (ITO) and polyaniline (PANI) are widely used as transparent electrode for transparent and high work function materiais of lighting displays. In this work we investigated the electrical properties of thin ITO/PANI nanocomposites films under vacuum at room temperature. PANI was chemically obtained while ITO nanoparticles (c.a. 50 nm) were obtained from Sigma Aldrich. Alternating conductivity measurements, σ*(σ) = σ' (σ) + iσ”(σ), were carried out on ITO/PANI films in the 1–100 KHz frequency range, while atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS) were obtained at room temperature. The ac results are typical of a disordered medium in which the logarithm of the real component, σ' (σ) exhibits two frequency regions, one plateau at low frequencies (the dc plateau) followed by a region of increasing conductivity, obeying the relation σ’ (σ) α σn, where 0σ n σ1, for higher frequencies values. In order to interpret both the real and the imaginary components of σ* (σ), we developed a model which considers the doped PANI as a semiconductor matrix, sprinkled with conductive ITO nanoparticles. Analysis of SAXS and AFM results confirm this evidence showing that the nanoparticles are uniformly distributed among the polymer bulk and it is consistent with the characterization of polymers thin films using integral-geometry morphological image analysis. The conduction through the insulating matrix obeys the random free energy barrier model, while ITO nanoparticles a metallic frequency independent conductivity is considered. From the fittings is possible to obtain the activation energy value of the maximum energy barrier of the doping mechanism and to estimate the concentration of hopping sites. This work was sponsored by Capes, CNPq, LNLS, INEO/CNPq and Fapemig.
9:00 PM - II9.10
Fabrication and Characterization of Silver/PVDF Nanocomposite Fibers Using In-situ Synthesis Method.
Wenqiong Tang 1 , D. Chase 1 , John Rabolt 1
1 Department of Materials Science and Engineering, University of Delaware, Newark, Delaware, United States
Show AbstractIn situ synthesis of silver nanoparticles in polyvinylidene fluoride (PVDF) films has been achieved by using silver trifluoroacetate (AgTFA) as the metal precursor followed by a thermal treatment, as reported by E. Espuche et al*. However, no work on fabricating Ag/PVDF nanocomposite fibers by electrospinning using the similar method has ever been reported. In our work, the results in E. Espuche’s paper have been successfully reproduced and fabrication of Ag/PVDF nanocomposite fibers has been achieved. Electrospinning parameters for PVDF/DMAc (dimethylacetamide) solutions with AgTFA incorporated have been optimized. SEM is utilized to characterize the fiber morphology. Formation of silver nanoparticles has been confirmed by WAXS, UV-vis and TEM. FT-IR is also employed to study the change in crystalline structure of PVDF throughout each of the processing steps.*E. Espuche et al. Macromolecular Symposium 2005,228,155-165.
9:00 PM - II9.11
Fabrication of Silicon Nanoparticle Arrays-encapsulated Core/Shell Nanofibers via Coaxial Electrospinning.
Wenwen Liu 1 , D, Bruce Chase 1 , John F. Rabolt 1
1 Department of Materials Science and Engineering, University of Delaware, Newark, Delaware, United States
Show AbstractElectrospinning is a technique to process polymer solution or melts into continuous nanofibers by the application of a strong electric field. Si nanoparticle-incorporated polycaprolactone (PCL) nanofibers were prepared using the coaxial electrospinning method. The core-shell structure nanofibers were characterized by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Fourier transform infrared (FTIR) measurement was carried out as a means to characterize the structure of the PCL/Si composite fibers. The surface morphologies, thermal properties, and crystal structures were studied using various analytic techniques. The results provide a basis for the further study of the preparation of multistructured nanofibers, and illustrate the potential for the application of electrospinning to composite nanomaterial with inorganic nanoparticles.
9:00 PM - II9.12
Electroluminescence Enhancement in Polymer Light-emitting Diodes through Hole Injection Layer Insertion.
Sheng Li 1
1 , Zhejiang Normal University, Jinhua, Zhejiang Province , China
Show AbstractAfter a hole injection layer is inserted into a polymer light-emitting diode _PLED_, the positive polaron is easily injected into the polymer layer. An applied electrical field drives the positive polaron to approach and collide with the nonemissive triplet exciton. The collision between the positive polaron and neutral triplet exciton induces the exciton to emit light. Based on this physical picture, the maximum quantum efficiency of the PLEDs, 61.6%, is consistent with the experimental result of 60%. With the help of an external magnetic field, a structure of PLEDs with high electroluminescent efficiency is designed.
9:00 PM - II9.13
Coating Individual Single-walled Carbon Nanotubes with a Thin Skin of Polymers.
Prakash Aanand Sugumaran 1 , Ingrid Lin 1 , Carlos A Silvera Batista 1 , Kirk Ziegler 1
1 Chemical Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractSurfactants are typically used to disperse single-walled carbon nanotubes (SWNTs) in aqueous suspensions. The hydrophobic end of the surfactant shell attaches to the sidewall while the hydrophilic end extends into the aqueous phase, providing the needed repulsive barrier to disperse the SWNTs. Here, we will show that mixing aqueous SWNT suspensions with immiscible solvents swells the hydrophobic region between the surfactant and the nanotube. Both spectroscopy and SANS studies show that small regions of the solvent encase the SWNTs. These solvent-swelled systems provide a controlled microreactor around the nanotube to conduct emulsion polymerization. These microenvironments are first used to encapsulate the SWNTs with the monomer. A co-monomer or catalyst is then injected into the aqueous phase so the formation of a polymer is restricted to the interface between the microenvironment and water. This emulsion polymerization process results in a thin polymer skin around individual SWNTs. This method provides a general approach to coat nanotubes with various polymers, which can then be integrated into bulk-scale composites.KEYWORDS: carbon nanotubes; emulsion polymerization; encapsulate; composites
9:00 PM - II9.14
Melt-quench Formed iPP/CNT Nanocomposites Smectic Phase and Its Re-crystallization.
Georgi Georgiev 1 2 , Scott Schoen 2 , Devin Ivy 2 , Peggy Cebe 2
1 Natural Sicences, Assumption College, Worcester, Massachusetts, United States, 2 Physics and Astronomy, Tufts University, Medford, Massachusetts, United States
Show AbstractThe largest commercial application of carbon nanotubes (CNT) are their polymer nanocomposites (PNCs). This motivates detailed studies of the interactions between CNTs and polymers and the ways the CNTs influence the crystallization behavior of polymers. We have chosen Isotactic polypropylene (iPP) as one of the best model systems. We studied iPP/CNT nanocomposites with CNT concentrations ranging 0.01 - 5% per weight. Films were prepared by compression molding and quenching in a mixture of isopropyl alcohol and dry ice. The smectic liquid crystalline (LC) phase of iPP/CNT PNCs persisted to temperatures higher than the last melting temperature for iPP crystals. By means of differential scanning calorimetry we corroborated the existence of the LC phase and studied the impact of multi-walled carbon nanotubes on its formation and transition to a crystalline phase. POM and a home build Two Dimensional Microscopic Transmission Ellipsometer (2D-MTE) were used for analyzing the impact of the CNTs on the crystal structure. The authors thank for support Assumption College for a Faculty Development Grant, funding for students’ stipends, instrumentation and supplies. The NSF Polymers Program of the DME, grant (DMR-0602473) and NASA grant (NAG8-1167).
9:00 PM - II9.15
The Nanoclay Effects on the Lightweight Structural Biocomposites.
Seong Ok Han 1 , I Na Sim 1
1 Nano Materials Research Center, Korea Institute of Energy Research, Daejeon Korea (the Republic of)
Show AbstractNanoclay has shown promising results in polymers in terms of enhancing properties of thermal stability, stiffness, dimensional stability and barrier properties to moisture, gases, solvent, and vapors. Nanoclay consists of organically modified nanometer scale, layered magnesium aluminum silicate platelets and has ‘platelet’ structure. The platelets are surface modified with an organic chemistry to allow complete dispersion into and provide miscibility with the thermoplastic systems. Thermoplastic biocomposites reinforced with natural fiber have been actively used in automobile industry as door panel, headliner, etc and also enlarging their application to electronic, construction, and aerospace industries. In these areas the thermal and mechanical properties are especially important for credibility of materials. The nanoclay has been proven to enhance flexural and tensile modulus while lowering CTE of thermoplastic composites and the surface char formation of composites have also been improved by incorporating the nanoparticles into the structure. To improve the mechanical, thermal and dimensional stability of thermoplastic biocomposites reinforced with natural fiber such as hardwood pulp and red algae fiber, the nanoclay was used as a second reinforcement of biocomposites. The improvement of mechanical properties with addition of nanoclay on polypropylene biocomposites reinforced with hardwood pulp or red algae fiber were observed by tensile, flexural modulus and thermomechanical properties. The improvement of mechanical properties of biocomposites was observed with 5 wt% of the nanoclay loadings. The improvement of mechanical properties of biocomposites could be explained with better dispersion and interaction between cellulosic fibers and nanoclay.These results show that the lightweight biocomposites with environmentally friendliness, higher mechanical and thermal properties can be developed by applying nanoclay as a second reinforcement of polymer composites.
9:00 PM - II9.16
Molecular Dynamics Study of Thermal Expansion of Polymer/Silica Hybrid Dielectric Material for Printed Circuit Board.
Jihye Shim 1 , Soo-Young Ji 1 , Seong Hyun Yoo 1 , Keun Yong Lee 1 , Jinyoung Kim 1
1 Corporate R&D Institute, Samsung Electro-Mechanics, Suwon Korea (the Republic of)
Show AbstractIn order to guarantee the reliability of printed circuit boards (PCB), it is critical to lower the thermal expansion coefficients (CTE) of dielectric materials which are usually composed of epoxy-based polymers. If the CTE of laminated polymer resin is much larger than that of plated Cu circuit, the assembled PCB would easily warp and fail to work by rapid thermal change. Traditionally, the CTE of resin is lowered by blending silica fillers by rule of sum, however, the performance of post-processes and surface properties are worsen as the amount of fillers increases. In this study we designed hybrid composite in which well dispersed nano-scaled silica structures are directly bonded to epoxy polymer. The silica structures were formed by condensation of tetraethyl orthosilane (TEOS) and methyl triethoxysilane (MTES) and linked to polymer chain through the multifunctional hydrocarboxy silanes which can play a role of hardener. The composite structures were determined by reaction modeling of amorphously mixed monomers and precursors based on close proximity as a criterion. Molecular dynamics (MD) simulations were carried out to predict thermal and structural properties of the fully cured systems. We optimized the ratio of constituents and reaction condition for lowest CTE. The thermal resistivity of the hybrid composite was raised. Especially, the CTE of high temperature (above Tg) dropped down dramatically. It is thought that the long-range movement of polymer chains tethered through covalent bonds is significantly restricted by strong inorganic networks. The simulated results were compared with experimental values and they showed a good agreement.
9:00 PM - II9.17
Significant Increases in Strength and Stiffness on the Addition of Solvent Exfoliated Graphene to Polyurethane.
Umar Khan 1 , Peter May 1 , Arlene O'Neill 1
1 School of Pyhsics, Trinity College Dublin, Dublin, Dublin, Ireland
Show AbstractWe have prepared dispersions of graphene, stabilised by polyurethane in the solvents tetrahydrafuran and dimethylformamide. These dispersions can be drop cast to produce free-standing composite films. The graphene mass fraction is controlled by the concentration of dispersed graphene and can be controllably varied from 0% to 90%. Raman spectroscopy and Helium ion microscopy show the graphene to well dispersed and well exfoliated in the composites, even at mass fractions of 55%. On addition of graphene, the Young’s modulus and stress at 3% strain increase by ×100, saturating at values of 1 GPa and 25 MPa respectively for mass fractions above 50wt%. While the ultimate tensile strength does not vary significantly with graphene content, the strain at break and toughness degrade significantly on graphene addition. Both these properties fall by three orders of magnitude as the graphene content is increased to 90wt%. However, the rate of increase of Young’s modulus and stress at 3% strain with mass fraction is greater than the rate of decrease of ductility and toughness. This makes it possible to prepare composites with high modulus, stress at low strain and ultimate tensile strength as well as relatively high toughness and ductility. This could lead to new materials that are stiff, strong and tough.
9:00 PM - II9.18
Bioresorbable, Elastomeric Nanocomposites for Tissue Reconstruction.
Tabitha Rosenbalm 1 2 , Nicole Levi-Polyachenko 1 2 , Louis Argenta 2 , William Wagner 1 2
1 Biomedical Engineering Department, Wake Forest University, Winston-Salem, North Carolina, United States, 2 Department of Plastic and Reconstructive Surgery, Wake Forest University, Winston-Salem, North Carolina, United States
Show AbstractMechanically-customized, bioresorbable elastomers can potentially reduce operations for patients with cleft palates and craniosynostosis (prematurely fused skulls). Further, resorbable elastomers can be used to develop repair devices for pediatric patients experiencing tracheal collapse. For all three applications, the target polymer resorbtion is 3-12 months but the mechanical properties for the tissues differ. Tensile strengths and elastic moduli of polymers can be increased by incorporation of ceramic nanoparticles, such as nano-hydroxyapatite (nHA). Poly (glycerol sebacate) (PGS) and poly (diol citrate) family members (such as, poly (1,8 octanediol citrate) (POC)) are elastomeric polymers presently available with the desired degradation time. Key differences in the polymers are: 1) POC forms longer polymer chains than PGS; 2) POC has higher tensile strength and elastic modulus than PGS; 3) PGS degrades into neutral byproducts but POC has acidic degradation products. The degradative properties of PGS result in its preference over POC for biological applications. This work compares the previously developed POC nanocomposites to recently developed PGS nanocomposites. Our hypothesis is that PGS can be modified with nHA to achieve mechanical properties similar to those achieved with POC composites, namely tensile strength 2 - 20 N and elastic modulus 0.2 – 5N.PGS was synthesized by melting sebacic acid followed by dropwise addition glycerol under vacuum. POC was synthesized by melting equimolar amounts of citric acid and 1,8 octanediol. POC was dissolved in acetone and PGS was melted. Both polymers were doped with 0, 3, and 5% nHA. Spherical nHA particles with average diameter of 200 nm (Sigma) were used in these experiments. Composites were heat polymerized at 80°C for 72 hours (for POC) and 150°C for 6 hours followed by 120°C for 24-40 hours (for PGS). Since glass transition temperature (Tg) is directly correlated to extent of polymer chain crosslinking, each polymer was analyzed by differential scanning calorimetry to confirm similar Tg (-25 ± 1 °C) for all samples. ASTM D-638-IV standard shapes were assessed for tensile strength, elongation to break, and elasticity using an Instron mechanical tester. The results demonstrated that undoped PGS has a much lower tensile strength and elastic modulus than the undoped POC. Significant differences were observed when interfacing nHA and PGS compared to the POC/nHA interaction. Differences in polymerization time and final polymer thicknesses suggested the nHA and PGS prevented expected crosslinking. Both POC and PGS nanocomposites have mechanical properties in the range desired for cleft palate repair. Further modification is necessary to achieve PGS nanocomposites suitable for tracheal and craniosynostosis repair, which require higher tensile strength and elongation to break.
9:00 PM - II9.19
Raman and FTIR Investigations on Polystyrene-anatase Nanocomposites.
Thomas Mion 1 , Alin Cristian Chipara 2 , Hailan Xu 3 , Yun Zhai 3 , Steven Tidrow 1 , David Hui 3 , Karen Lozano 2 , Mircea Chipara 1
1 Physics and Geology, The University of Texas Pan American, Edinburg, Texas, United States, 2 Mechanical Engineering, The University of Texas Pan American, Edinburg, Texas, United States, 3 Mechanical Engineering, University of New Orleans, New Orleans, Missouri, United States
Show AbstractAnatase nanoparticles with a size of about 15 nm have been dispersed into polystyrene by solution sonication. The formation of the interface between nanometer-sized fillers and polymer has been investigated by Raman spectroscopy and FTIR spectroscopy (in the total attenuation reflectivity mode). Additional information regarding anatase crystallites has been obtained by X-Ray spectrometry.The as obtained complements the thermal investigation done on the same system and provides a refined image of the polymer-nanofiller interface and of the stress exerted by macromolecular chains on anatase nanoparticles. The as obtained spectra were carefully deconvoluted and simulated.The research performed at the University of New Orleans has been supported by DARPA under grant HR0011-08-1-0084 to AMRI- University of New Orleans. The research at The University of Texas Pan-American has been supported by US Army Research Office (AMSRD-ARL-RO-SI Proposal Number: 54498-MS-ISP).
9:00 PM - II9.2
Stability of Cladophora Cellulose Polypyrrole Nanocomposites in Aqueous Solutions.
Daniel Carlsson 1 , Gustav Nystrom 1 , Henrik Olsson 1 , Martin Sjodin 1 , Albert Mihranyan 1 , Leif Nyholm 2 , Maria Stromme 1
1 Department of Engineering Sciences, Division of Nanotechnology & Functional Materials, The Angstrom Laboratory, Uppsala University, Uppsala Sweden, 2 Department of Materials Chemistry, The Angstrom Laboratory, Uppsala University, Uppsala Sweden
Show AbstractIntrinsically conducting polymers, such as polypyrrole, have over the last decades attracted much attention for their potential use in various applications, including energy-storage, separation, and sensor applications. We have previously reported on a conducting high surface area nanocomposite material, composed of polypyrrole and cellulose from the green algae Cladophora [1]. The composite synthesis comprises a chemical oxidation and polymerization step of pyrrole in the presence of the cellulose fibres with FeCl3 as the oxidant. The synthesis is terminated by a washing step, in which unreacted species and impurities are removed. More recently, we have demonstrated the use of this composite, a paper material, in an environmentally friendly battery, employing composite sheets as electrodes [2]. So far, the research has mainly been concerned with the intrinsic properties of the battery, rather than attaining fundamental knowledge concerning the nanocomposite itself. To further improve battery properties as well as to evaluate the feasibility of other applications it is, however, of uttermost importance to also gain such knowledge. One key concern is the potential degradation of the material in aqueous solutions as water has been suggested to be involved in nucleophilic attacks on polypyrrole resulting in irreversible changes (degradation). This is manifested as structural changes and subsequent dedoping as well as loss of conductivity and electroactivity, as summarized in ref [3]. In the present investigation, it is shown that composite degradation occurs during the washing step ending the synthesis. This has been studied by washing the composite with various amounts of water and aqueous NaCl. The results indicate that degradation occurs with both water and aqueous NaCl, although there is significantly less degradation with the NaCl solutions. The degree of degradation is also dependent on the amount of liquid used in the washing step. It is further shown that composite material, that has been rendered significantly less electroactive during washing, to some extent can be reactivated by electrochemical cycling of the material in NaCl solutions. References: 1. Mihranyan, A., L. Nyholm, A.E.G. Bennett, and M. Stromme, Novel high specific surface area conducting paper material composed of polypyrrole and cladophora cellulose. Journal of Physical Chemistry B, 2008. 112(39): p. 12249-12255.2. Nystrom, G., A. Razaq, M. Stromme, L. Nyholm, and A. Mihranyan, Ultrafast all-polymer paper-based batteries. Nano Letters, 2009. 9(10): p. 3635-3639.3. Maksymiuk, K., Chemical reactivity of polypyrrole and its relevance to polypyrrole based electrochemical sensors. Electroanalysis, 2006. 18(16): p. 1537-1551 and references therein.
9:00 PM - II9.20
On Polyvinylchloride - Single Walled Carbon Nanotube Composites.
Alin Cristian Chipara 2 , Thomas Mion 1 , Edgar Vega 2 , John Hamilton 3 , Hailan Xu 4 , Yun Zhai 4 , Magdalena Dorina Chipara 1 , Elamin Ibrahim 3 , Karen Lozano 2 , Steven Tidrow 1 , David Hui 4 , Mircea Chipara 1
2 Mechanical Engineering, The University of Texas Pan American, Edinburg, Texas, United States, 1 Physics and Geology, The University of Texas Pan American, Edinburg, Texas, United States, 3 Chemistry, The University of Texas Pan American, Edinburg, Texas, United States, 4 Mechanical Engineering, University of New Orleans, New Orleans, Missouri, United States
Show AbstractPolyvinylchloride-Single Walled Carbon Nanotube composites have been obtained by solution sonication. The solvent was removed in a vacuum oven after a thermal heating at 150 oC for three hours. Thermogravimetric data confirmed the full removal of the solvent.Various spectroscopic measurements (TGA, DSC, Raman, FTIR in the ATR mode, and WAXS) have been use to assess and characterize the interactions between macromolecular chains and single walled carbon nanotubes. Attention has been paid to the thermal and thermooxidative degradation of these composites. A detailed analysis of the polymer-single walled carbon nanotube interface is reported.Acknowledgments: This material is based on research sponsored by US Army Research Office (AMSRD-ARL-RO-SI Proposal Number: 54498-MS-ISP) and by NSF PREM (DMR 0934157).
9:00 PM - II9.21
Irradiation Effects of Polypropylene-carbon Nanofibers Composites.
Margareta Cherestes 2 , Livia Constantinescu 3 , Magdalena Dorina Chipara 1 , Karen Lozano 4 , Mircea Chipara 1
2 , Dozimed, Bucharest Romania, 3 Physics, University of Bucharest, Bucharest Romania, 1 Physics and Geology, The University of Texas Pan American, Edinburg, Texas, United States, 4 Mechanical Engineering, The University of Texas Pan_american, Edinburg, Texas, United States
Show AbstractThe radiation-behavior of polymers filled with carbon nanotubes and carbon nanofibers is still under debate. The reported experimental data are rather scattered; the radiation behavior of carbon nanotubes and nanofibers is rather complex. Under the effect of high energy electron beams, carbon nanotubes are welded together. Complex modifications were also reported in carbon nanotubes exposed to ions or microwaves.Polypropylene-carbon nanofibers (PP-CNF) composites containing 0 to 25 % wt. carbon nanofibers have been prepared by extrusion. The effect of ionizing radiation (gamma rays from a Co60 source) are investigated in detail by using thermoluminescence. The irradiation has been performed in air, at room temperature, at integral doses ranging from 0 to 30 kGy.Additional experiments are in course, in order to provide a better picture of radiation-induced modifications in these nanocomposites and to assess their potential lifetime in radiation environments (such as the space environment).ACKNOWLEDGMENTS: This material is based on research sponsored by US Army Research Office (AMSRD-ARL-RO-SI Proposal Number: 54498-MS-ISP).
9:00 PM - II9.22
Polymer-self Healing.
Maritza Flores 1 , Nancy Puente 3 , Magdalena Dorina Chipara 2 , Karen Lozano 3 , Mircea Chipara 2
1 Chemistry, The University of Texas Pan American, Edinburg, Texas, United States, 3 Mechanical Engineering, The University of Texas Pan American, Edinburg, Texas, United States, 2 Physics and Geology, The University of Texas Pan American, Edinburg, Texas, United States
Show AbstractPolymeric materials are subjected to deterioration and degradation during their use. A simple self-healing system, triggered by mechanical stresses has been imagined and successfully tested on resins. Such self-healing system implies the dispersion within the resin matrix two components; a catalyst (typically first generation Grubbs catalysts) and a polyurea formaldehyde microcapsule filled with a monomer (typically cyclopentadiene). In plastics (resins) crack propagation generates sufficient shear stress to rupture microcapsules and to release the monomer, which will initiate a polymerization reaction upon the contact with catalyst's particles.This contribution describes the efforts of our research team to go beyond the classical picture, adding self-healing features to polymers rather than to resins and extending the limits of the self-healing process. Recent data on the possibility to add self-healing features to plastic materials and high elasticity block copolymers will be discussed in detail.ACKNOWLEDGMENTS. This research was supported by NSF PREM (DMR 0934157).
9:00 PM - II9.24
In Silico Layer-by-layer Assembly and Mesoscale Mechanical Characterization of Polyelectrolytes Multilayers.
Steven Cranford 1 2 , Christine Ortiz 2 3 , Markus Buehler 1 2
1 Department of Civil and Environmental Engineeirng, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Center for Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractLayer-by-layer (LbL) deposition of charged polymers, in which a substrate is sequentially exposed to solutions of oppositely charged polyelectrolytes is a promising technique for fabrication of layered nanocomposites. The mechanical properties of such assembled materials can be varied by the assembly procedure and the solution environment, illustrating a new class of “mechanomutable materials”. Full atomistic molecular dynamics investigations show a range of achievable adhesion strengths of short complexes of poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) via manipulation of ionization, demonstrating a potential fivefold increase in adhesion strength (Cranford et al., Soft Matter, 2010).Predictive modeling of such materials is, however, hindered by the molecular dependence of the polymeric interactions combined with the relatively large scale of the composite system which is too large for full atomistic simulation. To overcome these limitations here we develop, validate and apply a novel multi-scale approach to develop a coarse-grain representation of long polyelectrolytes. Full atomistic tests are performed to determine inter-polymer interactions, providing the required parameters for mesoscale representation via a bottom-up “fine-trains-coarse” approach. The coarse-grain model is then implemented to assemble hundreds of polymer chains in an in silico layer-by-layer process, with direct control of polymer density and ionization, replicating physical synthesis procedures in experimental studies. Assigned ionization densities are reflective of in situ pH conditions, taken from previous empirical studies and approximated protonation/deprotonation behavior of the implemented polyelectrolytes (PAA and PAH). The assembled composite is then subjected to nanomechanical characterization via in silico nanoindentation, and the potential variation of structural and mechanical properties is investigated as a function of relative charge distribution as a function of pH. Our work provides a novel bottom-up perspective on LbL deposited films, and results in insight that span length- and time-scales across several orders of magnitude.
9:00 PM - II9.27
Polymer-like Chain Structures in Fluids Subjected to Electric Fields: An Analogy between Electrorheology and the Rheology of Macromolecular Solutions.
Ram Thapa 1 , Steven French 1 , Carlos Ramos 2 , Jose Gutierrez 2 , Mircea Chipara 3 , Karen Lozano 1
1 Department of Mechanical Engineering, University of Texas - Pan American, Edinburg, Texas, United States, 2 Department of Chemistry, University of Texas - Pan American, Edinburg, Texas, United States, 3 Department of Physics and Geology, University of Texas - Pan American, Edinburg, Texas, United States
Show AbstractThe research on the electrorheological properties of fluids was fueled by the need for a fast, quick, and reversible actuation. The possibility to achieve actuation in oil suspensions of various particles revealed the alignment of such particles in a quasi-one dimensional chain under the effect of the applied external electric field. This suggests that silicone oil suspensions start to behave as polymeric solutions upon the application of the external electric field. The fine differences between the electrorheology of silicone oil suspensions in external fields and polymeric solutions can provide unique details about electrorheology and polymer’s rheology.The detailed analysis of the electrorheological features of various suspensions (small quasi-spherical particles and rod like particles) in silicone oil aims to a better understanding of the electrical interactions between the particles dispersed within silicone oil. Carbon nanofibers (CNF) showed promising behavior given their dielectrophoretic effect. Suspensions of CNF-silicone oil (0.01wt%-5wt% CNF) were tested and it was found that the fibers actuated at 40 V/mm, significantly lower electric fields than those used in conventional ER fluids (>2,000 V/mm). The response (yield stress and elastic modulus) though was not large and the system short circuited at 200 V/mm due to the high electrical conductivity of CNF. Chemical functionalization of the nanofibers was conducted and these were coated with macromolecular chains. Viscosity and storage modulus increased but still not significant. To overcome the problem of short circuit, non-conducting Al2O3 nanotubes in silicone oil were tested and compared to CNF systems. Electrorheological measurements on these systems have been performed at various applied electric fields for different concentrations using a HAAKE RheoStress RS-150 rheometer.Acknowledgement: This material is based on research sponsored by Air Force Research Laboratory under agreement number FA8650-07-2-5061.
9:00 PM - II9.28
Remote Controlled Bending Actuation of Alternating Magnetic Field-sensitive Hydrogels.
Santaneel Ghosh 1 , Somesree GhoshMitra 2 , Tong Cai 3
1 Department of Physics and Engineering Physics, Southeast Missouri State University, Cape Girardeau, Missouri, United States, 2 Departmet of Biology, Texas Woman's University, Denton, Texas, United States, 3 Department of Physics, University of North Texas, Denton, Texas, United States
Show AbstractMagnetically tunable hydrogel nano-structures hold great therapeutic potential for receptor specific targeting, intracellular delivery, sequential release of drug molecules and flow path regulation in micro-fluidic devices. Smart polymers, conventionally poly(N-isopropylacrylamide) (PNIPAM) or polyethylene glycol (PEG) analogue-based systems are attractive for device fabrication because of their perceived intelligence to external stimuli, i.e., possession of lower critical solution transition (LCST) behavior at ~33C, close to normal physiological temperature. Alternating magnetic field can be applied to change the phase of the nano-magnet doped polymeric structures as the magnetic nano-particles act as nano sources of heat when exposed to the oscillating magnetic field. Efficiency of the induced heat generation inside the medium can be controlled intrinsically by changing the size, concentration and composition of the nano-particles or extrinsically by tuning the frequency and intensity of the applied magnetic fields. Recent studies have reported magnetic hydrogel nano-structures and temperature regulation induced by remotely applied ac magnetic excitations. DC magnetic field induced bending has also been investigated. However, although, dc field initiates bending, it is not possible to change the phase of the polymer monolith, i.e., bending and shrinkage are not simultaneous. Furthermore, we are unaware of any study that assesses ac field induced controlled bending actuation of the magnetic hydrogel films. As ac magnetic field induced controlled modulation can directly transform the absorbed energy into bending and shrinkage simultaneously, this novel approach may lead to a new category of magnetically responsive polymeric structures for potential applications in the field of smart gel based devices, such as sensors, artificial muscles, drug delivery systems, and film separation devices. In this study, ferromagnetic properties of the embedded nano-magnets within PNIPAM networks are tuned to achieve controlled bending of the doped polymer film. The PNIPAM films are synthesized in the shape of cylinders. Conformal changes of the magneto-active PNIPAM hydrogel (MPNIPAM) consisting of over 90% water is performed under the influence of an alternating magnetic field by tuning the field induced nano-scale heating and relative humidity (RH) of the surroundings. Inside ac magnetic field (25-70 Oe, 150-280 kHz), the polymer monolith quickly bends along the longitudinal axis. In addition, we found that micro-scale monolith exhibited significantly faster actuation response through nano-scale heating and the bending behavior is completely reversible. Both de-swelling efficiency and volumetric transition temperature were not affected due to the nano-magnet incorporation. To our knowledge, this is the first time that quantitative oscillating field modulated bending actuation has been investigated for a tunable nano-composite system.
9:00 PM - II9.29
Nanocomposites Based on Polyaniline and Carbon / Silicon Nanostructures for Supercapacitor Applications.
Siu-Tung Yau 1 , Osama Nayfeh 2 , Munir Nayfeh 3 , Qiang Liu 1
1 Electrical and Computer Engineering, Cleveland State University, Cleveland, Ohio, United States, 2 , US Army Research Laboratory, Adelphi, Maryland, United States, 3 Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractA nano-composite material formed by dispersing carbon- or silicon-based nanomaterials, including ultrasmall silicon nanoparticles, carbon nanotubes, and grapheme, in polyaniline has been used as the electrode material for constructing supercapacitors. Electrochemical characterization of electrodes made of the composite material indicated that polyaniline produces pseudocapacitance while the nanomaterials give rise to double-layer capacitance. The composite material showed significantly improved capacitance compared to that of pure polyaniline. The specific capacitances were found to be 85.07F/g and 409.27F/g for the polyaniline electrode and the composite electrode, respectively. We have constructed flexible supercapacitors by painting sheets of flexible plastic electrolyte with the composite material. We have observed the effects of the constituents of the composite material on the performance of the capacitor. Charging/discharging measurements showed that the operating voltage of the supercapacitors can be increased with increasing amounts of carbon nanotubes in the composite material. Ragone plots and impedance spectra of the composite materials have been obtained. Stacks of the capacitor sheets were used to light up a system of light-emitting diodes.
9:00 PM - II9.3
Photopolymerizable Gold Nanorods / Methy Methacrylate Composite for Plasmonic Optical Application.
Kyoko Masui 1 2 , Satoru Shoji 1 , Xuan-Ming Duan 2 , Satoshi Kawata 1
1 Department of Applied Physics, Osaka University, Suita, Osaka Japan, 2 Technical Institute of Physics and Chemistry, Chinese Academy of Science, Beijing China
Show AbstractNanoparticles of noble metal exhibit strong resonant scattering of light by the oscillation of free electrons at optical frequencies. This so called “plasmonics” feature is of interest as a key factor for the creation of artificial nano-light sources, as well as metamaterials which exhibit uncommon dielectric and magnetic properties. Since the oscillation mode of free electrons confined in the nano-sized volume of the particles is very sensitive to geometry, ie the shape, distance, and orientation of the particles, the control and the arrangement of the metal nanoparticles is critical to engineer desired optical properties. We present a gold nanorods / methyl methacrylate (MMA) composite, which makes it possible to fix gold nanorods with arbitrary three-dimensional arrangements into a polymer matrix. The gold nanorods were prepared by the seed-mediated method. The synthesis started from small gold seeds, and by the anisotropic protection of the surface of the gold particles by the surfactant hexadecyltrimethylammonium bromide (CTAB), the individual gold particle grew in aqueous solution anisotropically as a rod shape with the thickness of 10 nm and the length of 60 nm. In order to disperse the gold nanorods into MMA, we performed hydrophobation of the CTAB-wrapped gold nanorods by using mercaptopropyltrimethoxysilane (MPS) and octadecyltrimethoxysilane (ODS). The nanorods were then dispersed in chloroform, and thereby mixed with MMA and photo-initiator. We successfully made a suspension of gold nanorods into MMA without aggregation. The absorption spectrum of the composite showed clear peaks at 500 nm and 800 nm, corresponding to the transverse and longitudinal local plasmon resonance mode of isolated individual gold nanorods, respectively. We performed two-photon polymerization of MMA using a femtosecond Ti:Sapphire laser with the emission wavelength of 780 nm. Since the transverse plasmon mode of the gold nanorods is located at around 800 nm, the laser light is absorbed not only by photo-initiator but also the gold nanorods. By controlling the intensity and the exposure time of the laser light, we found an optimal condition to induce dominant polymerization of MMA without causing thermal damage and aggregation of gold nanorods. By this method, we fabricated several microstructures of gold nanorods / polymethyl methacrylate (PMMA) composite. Our approach offers a flexible method to fabricate novel plasmonic photonic devices and metamaterials.
9:00 PM - II9.31
Miscibility and Nanostructure of Advanced Polymer Structural Composites Prepared from Bio-based Components1.
Giorgiana Giancola 1 , Richard Lehman 1
1 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States
Show AbstractImmiscible polymer blends are formulated with the goal of creating new materials with synergistic performance. These types of blends are an attractive approach since there is the ability to create a novel material that is engineered to yield specific end-use properties without resorting to synthesis of new monomers and polymers. Furthermore, the combination of dissimilar materials enables synergistic performance whereby the properties of the composite are superior to those of the individual components. Polymers prepared from bio-based raw materials are of increasing interest in the scientific community as a way to minimize dependence on traditional petroleum resources. These bio-based polymers, or polymer precursors, have the potential to lower cost, increase supply, and reduce dependence on scarce raw materials. The ultimate goal is to increase the renewable content of the composite while simultaneously yielding similar or increased engineering properties. The further addition of non-polymer additives has two functionalities. These particles act as reinforcement to existing components and also displace petroleum, thus increasing the sustainability of the blend. In this work we studied a new blend, one consisting of polyamide 6,10 and polytrimethyleneterephthalate1 in various ratios in an attempt to produce a high-level engineering polymer with a high fraction of bio-based precursors. The technical goal of this work is to create an immiscible blend with intimate interlocking and co-continuous morphology such that the properties of the blend meet or exceed the properties of neat polytrimethyleneterephthalate, but with an increased bio-based fraction. A range of blends around the estimated co-continuous composition were prepared and extruded in a single screw laboratory extruder. The renewable content of these blends is increased substantially over that of neat polytrimethyleneterephthalate since the polyamide 6,10 is prepared in part from castor oil and has a bio-based fraction of nearly 60%, whereas the polytrimethyleneterephthalate used in this work has bio-based content of only 36%. Samples were analyzed using electron microscopy in order to access the nano-scale morphology of the components and the potential for these blends to produce valuable and useful properties. 1 Both polymers from E. I. duPont de Nemours & Co., Wilmington, DE 19898
9:00 PM - II9.32
Physically Cross-linked Hyaluronic Acid-clay Based Novel Hydrogels.
Divya Bhatnagar 1 , Miriam Rafailovich 1 , Mary Cowman 2
1 Materials Science and Engineering, Stony Brook University, Stony Brook, New York, United States, 2 Department of Biochemistry, Polytechnic Institute of New York University, Brooklyn, New York, United States
Show AbstractThis work investigates the rheological properties of Hyaluronic acid (HA)-Clay hydrogels prepared by physically crosslinking non-modified HA with inorganic clay. Resulting hydrogels were transparent and mechanically stable. To investigate their mechanical properties the hydrogels were subjected to oscialltory shear rheometry which allows the evaluation and comparison of the shear storage moduli (G'), an index of the stiffness of the hydrogels. The stress sweep measured G' as a function of shear stress and the results suggested the formation of a stable, three dimensional network. In this study, we were able to create hydrogels of variable stiffness by modifying the amount of clay. Cell cultivation, proliferation and migration on the surface of a novel HA (Hyaluronic Acid)-clay hydrogel was studied using human dermal fibroblasts. To enhance the attachment of cells, gelatin was used to coat the surface of HA- Clay hydrogels producing a more biocompatible hydrogel. It was found that the cells could be cultured efficiently on the surfaces of HA-clay hydrogels . This study presents the synthesis of HA-clay hydrogels with no chemical additives which will aid in the design of biomaterials targeted for biomedical or pharmaceutical purposes, including rigid cell scaffold structures.
9:00 PM - II9.33
In Situ Quantitative Localized Characterization of Interfaces in Multi-wall Carbon Nanotube Reinforced Polymer Nanocomposites
Yogeeswaran Ganesan 1 , Cheng Peng 1 , Yang Lu 1 , Philip Loya 1 , Roberto Ballarini 2 , Valery Khabashesku 3 , Boris Yakobson 1 , James Tour 1 , Jun Lou 1
1 MEMS, Rice University, Houston, Texas, United States, 2 , The University of Minnesota, Minneapolis, Minnesota, United States, 3 , The University of Houston, Houston, Texas, United States
Show AbstractThe knowledge of the fundamental mechanisms that govern mechanical behavior at the nanotube-matrix interface are critical for CNT reinforced nanocomposite development i.e. in order to realize the theoretically and computationally predicted potential of CNTs as reinforcements for high performance composites. The single fiber pullout experiment has been used since the 1950s by researchers to perform the localized characterization of filler-matrix interfaces in composites. Recently we developed a simple micro-fabricated device, that works in conjunction with a quantitative nanoindenter, that can be used to perform in situ nanomechanical tests within an SEM chamber. The device was used to perform single fiber pullout experiments on pristine and functionalized MWNTs embedded in an epoxy matrix. The maximum pullout loads corresponding to a wide range of embedded length values were used to compute the interfacial shear strength values as a function of embedded length and to accurately ascertain the interfacial fracture energy, Gc, for the MWNT-epoxy interface.
9:00 PM - II9.34
Nucleation of the Electroactive Phase of Poly(vinylidene fluoride) by Ferrite Nanoparticles: Surface Versus Size Effects.
P. Martins 1 , C. Costa 2 , M. Benelmekki 1 , Senentxu Lanceros-Mendez 1
1 Center of Physics, University of Minho, Braga Portugal, 2 , 2Centre for Nanotechnology and Smart Materials, Famalicão Portugal
Show AbstractMultiferroics and magnetoelectric materials are gaining increasing attention due to their technnologial applications as well as for the scientific issues involved [1, 2]. There have been intensive research efforts in order to obtain composites with increased magnetoelectric coupling, being polymer based composites promising candidates for outstanding performance [2, 3]. Nano-size ferrites such as CoFe2O4, NiFe2O4 or NiZnFe2O4 can be incorporated into a poly(vinilidene fluoride), PVDF, matrix and have the ability to nucleate the electroactive beta phase of the polymer, providing in this way an easy route for the preparation of magnetoelectric particulate composites. Further, it is also an interesting system for the study of the polymer-nanoparticle interaction leading to the nucleation of the electroactive phase of ther polymer. Nanocomposites of CoFe2O4, NiFe2O4 and NiZnFe2O4 have been prepared by solution casting using funtionalized (surface modification by dispersion in water using citric acid as a surfactant) and non-funtionalized nanoparticles. Far infrared spectroscopy was used to determine the polymer phase and differential scanning calorimetry to calculate the degree of crystallinity. SEM, AFM and TEM were used to investigate nanoparticle dispersion and polymer/nanoparticle interface characteristics. All nonfunctionalized ferrite nanoparticles nucleated the electroactive phase of PVDF, but at a different rate: whereas beta phase contents larger than 80% are obtained for 5%wt of CoFe2O4, 50%wt of NiFe2O4 is needed for obtaining those values of beta-PVDF. This fact indicates that filler size is not the most important parameter determining phase nucleation but the filler-matrix chemical interaction. These results do not support the theory of nanoparticles promoting phase nucleation when their radius is less than the radius of gyration, Rg of the polymer [4]. The Rg value for PVDF is 27,5 nm, and the average radius of nanoparticles is 45 nm for CoFe2O4 and 25nm for NiFe2O4. The ferrite nanoparticles are either nucleating β-phase epitaxially on their surfaces or are interrupting the chain mobility during crystallization, so that more extended-chain beta-phase crystals are formed. TEM images clearly support the first hypothesis by the formation of an interlayer responsible for the nucleation of the electroactive phase. Nanoparticle funtionalization, on the other hand, promotes dispersion but prevents beta-phase nucleation. References:[1] N. Ortega, A. Kumar, R. Katiyar, IEEE, (2008) 336-337[2] N. A. Spaldin, M. Fiebig, Science 5733-309 (2005) 391-392[3] W. Eerenstein, M. D. Mathur, J. F. Scott, Nature, 7104-442 (2006) 759-765[4] J. Andrew, D. Clarke, Langmuir, 2008, 24, 8435ACKNOWLEDGMENTS We acknowledge the Portuguese FCT (projects PTDC/CTM/69316/2006, NANO/NMed-SD/0156/2007 and SFRH/BD/45265/2008 (PM))
9:00 PM - II9.4
Thermal Conductivity of Carbon-based Filler/PMMA Nanocomposites.
Gi-Moon Yoo 1 , Ju Ho Kim 1 , Sung Goo Lee 2 , Sung Ryong Kim 1
1 Polymer Sci. & Eng., Chungju National University, Chungju Korea (the Republic of), 2 Infomation & Electronics Polymer Research Center, Korea Research Institute of Chemical Technology, Daejon Korea (the Republic of)
Show AbstractThermal conductivities of carbon nanotube (CNT) and graphene filled poly (methylmethacrylate) (PMMA) nanocomposites were investigated. CNT/PMMA nanocomposites were prepared by coagulation and atom transfer radical polymerization method and the latter gave a higher thermal conductivity. Thermal conductivities of MWNT/PMMA, SWNT/PMMA and graphene/PMMA nanocomposites at 1 wt. % of filler loading were 0.32 W/mK, 0.39 W/mK, and 0.60 W/mK, respectively. The high thermal conductivity suggests that the good dispersion and functionalization of fillers in the polymer matrix. The morphologis of nanocomposite were correlated with the thermal conductivity.
9:00 PM - II9.5
Mechanical Properties of Carbon Nanotube/Glassy Polymeric Carbon Composite.
Bopha Chhay 1 , Cyrus English 2 , Samuel Uba 1 , Ryan Givens 1 , Stefon Lewis 1 , Daryush Ila 1
1 Center for Irradiaon of Materials, Alabama A&M University Research Institute, Normal, Alabama, United States, 2 Electrical engineering, Alabama A&M University, Normal, Alabama, United States
Show AbstractPyrolysis of phenolic resin GP5236 manufactured by Georgia Pacific leads to Glassy Polymeric Carbon (GPC). The fabrication of GPC is already complicated because of the high production rate of gaseous products in critical temperature ranges where out-diffusion is relatively slow. As we introduced carbon nanotubes (CNT) in the GPC precursor, we had to change our sample preparation procedure to include CNT in order to obtain a homogeneous final product without kilning faults or voids in it.Indeed, previous results showed that when CNT were present in GPC not only the Young’s modulus and the strain to fracture increased but also the degree of graphitization (when compared to pure GPC).In this paper we compared different processes to prepare the precursor of GPC/CNT nanocomposite and showed theirs impacts on the dispersion of the CNT in the gelled phenolic resin.We analyzed the structure with Raman spectroscopy and measured the Young’s modulus, the tensile strength and the hardness of the GPC/CNT composite.
9:00 PM - II9.6
Conjugated Polymer:TiO2 Nanocomposite Solar Cells Based on P3HT Nanoparticles.
Harihara Venkatraman Balasubramanian 1 , Soumitra Satapathi 2 , Jayant Kumar 2 , Dhandapani Venkataraman 1
1 Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts, United States, 2 Physics and Applied Physics , University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractRecently, a lot of research is devoted in constructing efficient solar cells from conjugated polymer:TiO2 nanocomposite based hybrid solar cell, since TiO2 is abundant and lowcost. However, infiltration of conjugated polymer (CP) onto porous titania is a major issue since it poses lot of constraint for the macromolecule to penetrate into the TiO2 pores. Here, we report a novel and facile approach of using conjugated polymer nanoparticles to make conjugated polymer:TiO2 nanocomposite based solar cell. Because the nanoparticle size is smaller than the pore size of TiO2, infiltration becomes easy. In this work, nanoparticles were made from P3HT (poly-3-hexylthiophene), a widely used conjugated polymer. Nanoparticles of different sizes (15-100 nm) with narrow size distribution was synthesized by mini-emulsion technique using anionic (sodium dodecyl sulfate) surfactant. These nanoparticles showed no change in the electronic properties such as UV-vis absortion and photoluminescence from the bulk material. The possibility of using these nanoparticles as both solar sensitizer and hole transport material in dye-sensitized and solid state heterojunction solar cell have been explored. The photovoltaic metrics made from this P3HT nanoparticles:TiO2 device will be presented. Nanoparticles made from cationic (cetyl trimethyl ammonium bromide) and neutral (Tween-80) surfactant have also been used for a comparative study.
9:00 PM - II9.7
Epoxy-MWNT for Enhanced Adhesives.
Stefanie Sydlik 1 2 , Joseph Walish 3 2 , Timothy Swager 1 2 , Edwin Thomas 3 2
1 Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Institute for Soldier Nanotechnologies, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Material Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractMulti-walled carbon nanotubes (MWNT) were covalently functionalized with epoxy resin-like moieties using novel chemistry. These Epoxy-MWNT were found to enhance the adhesive properties of epoxy in metal to metal bonds. Adding 1 weight % Epoxy-MWNT to an Epon 862- Epicure epoxy adhesive results in a 63% improvement in lap shear strength over neat epoxy; significantly better than the 10% with non-functionalized MWNT. The covalent functionalization also allows for a stable, homogenious dispersion. It is hypothesized that the carbon nanotubes increase the strength of the bond by preventing crack propagation through the adhesive. Scanning electron microscopy (SEM) will be used confirm this. Several functionalization motifs were applied for the novel covalent functionalization of MWNT including a zwitterionic functionalization method,“click” chemistry, and a 1,3-dipolar cycloaddition functionalization method. Covalent functionalization was confirmed by Thermogravimetric Analysis (TGA), Raman, and Infrared Spectroscopy (IR). It is expected that MWNT-enhanced adhesives will have improved thermal and electrical conductivity, which will further broaden their utility in high performance applications.
9:00 PM - II9.8
Spectroscopic Investigations on the Interfacial Excited States Related to the Energy Transfer in Polymer Blends.
Fei Dou 1 , Xinping Zhang 1
1 Dept. of Applied Science, Beijing Univ. of Technology, Beijing China
Show AbstractThe spectroscopic investigations on the photophysical properties of the exciplex in different types of heterojunction structures formed in the polymer blends of (poly(9,9’-dioctylfluorene-co- benzothiadiazole) (F8BT):poly(N,N’-bis(1-ethylpropyl)-3,4,9,10-perylenebis(dicarboximide)(perylene)) and (F8BT: poly (9,9’-dioctylfluorene-co- bis-N,N’-(4-butylphenyl)-bis-N,N'-phenyl-l,4–phenylenediamine)(PFB)), respectively, are demonstrated in this contribution. The dependence of the exciplex emission on the excitation wavelengths and on the phase-separation features in the blend film reveals how the energy transfer and exciton diffusion mechanisms play important roles in the formation of the exciplex. The modulation of the exciplex emission by particle plasmon resonance of the gold nanostructures enables further understanding of the interfacial excited states.
9:00 PM - II9.9
Thermal Properties of Silylated Apophyllite Filled Epoxy Nanocomposite.
Chenggang Chen 2 , Joseph Langat 1 , Dharmaraj Raghavan 1
2 , University of Dayton Research Institute, Dayton, Ohio, United States, 1 Department of Chemistry, Howard University, Washington, District of Columbia, United States
Show AbstractSeveral silylated apophyllites with different grafting degrees were synthesized by controlling the ratio of the apophyllite and chlorosilane reagent and characterized by XRD, TGA, & FTIR techniques. TGA measurements showed that the onset decomposition temperature of silylated apophyllite (~ 420.0 C) was significantly greater than the conventional organoclay. Epoxy-clay nanocomposites have been prepared by shear mixing silylated apophyllite with MY720/DER 661 (1:1 ratio) mixture and curing with dimethyl diphenyl sulfone (DDS). Chemorheological measurements of 2 wt% silylated apophyllite filled epoxy have shown that the addition of the silylated apophyllite does not much alter the cure chemistry of the resin and provides a processing window of nearly 40 min. XRD & TEM results reveal the presence of far fewer bundle of clay in the sheared nanocomposite. The char yield of epoxy nanocomposite seems to be influenced by the addition of clay in the epoxy system. Additionally, we observed the decomposition temperature of sonicated cyanopropyldimethylsiloxy-apophllite epoxy nanocomposite to be greater than that of pure epoxy.
Symposium Organizers
Mircea Chipara The University of Texas Pan American
Pulickel M. Ajayan Rice University
Ali Nasar CNC Coatings
Alan Kin-Tak Lau The Hong Kong Polytechnic University
II10: Polymer-Based Nanocomposites: Synthesis and Fabrication
Session Chairs
Thursday AM, December 02, 2010
Republic B (Sheraton)
9:30 AM - II10.3
Segregated-network Polymer Nanocomposites for Thermoelectric Energy Conversion.
Jaime Grunlan 1 2 3 , Choongho Yu 1
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 2 Chemical Engineering, Texas A&M University, College Station, Texas, United States, 3 Materials Science and Engineering Program, Texas A&M University, College Station, Texas, United States
Show AbstractPolymers are intrinsically poor thermal conductors, which are ideal for thermoelectrics, but low electrical conductivity (σ) and Seebeck coefficient (S) have excluded them as feasible candidates for thermoelectric applications. By adding single-walled carbon nanotubes (SWNT) to a polymer emulsion, a set of polymer nanocomposites that exhibit true thermoelectric behavior (i.e., generate electricity via a thermal gradient) have been created. As the polymer emulsion is drying, the relatively large polymer particles (100 – 1000+ nm) force the nanotubes to reside in the interstitial space between them. This creates a segregated network of carbon nanotubes with high electrical conductivity. This high electrical conductivity is accompanied by low thermal conductivity (k ~ 0.35 W/m-K). Electrical conductivity is further increased (> 300 S/cm with 20 wt% SWNT) when the nanotubes are stabilized in water using intrinsically-conductive poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) [PEDOT-PSS]. At the present time, segregated network composites are being produced with a thermoelectric figure of merit (ZT = S2σ/k) greater than 0.1 at room temperature (on par with best semiconductor thermoelectrics at RT), which is among the highest values ever reported for an all-carbon thermoelectric material. Further work with these nanocomposites is expected to result in low cost, easy to process polymer-based devices capable of converting waste heat to useful energy.
9:45 AM - II10.4
Compatibilizing Biodegradable Polymer Blends Using Flame Retardant-coated Biocompaibilizers.
Seongchan Pack 1 , Ezra Bobo 3 , Su Jung Han 1 , Takashi Kashiwagi 2 , Miriam Rafailovich 1
1 , Stony Brook University, Stony Brook, New York, United States, 3 , University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 , NIST, Gaithersburg, Maryland, United States
Show AbstractSince starch is not only inexpensive but completely biodegradable, starch-based polymers are a new class of biodegradable nanocomposites with nanofillers. Despite the benefits of using the starch, it is difficult for the starch-based nanocomposites to form thermoplastic polymers because it is very brittle. Furthermore, melt-blending starch with other biodegradable polymers is difficult since very few polymers are compatible with starches. In this paper, we have successfully synthesized the resorcinol diphenyl phosphates (RDP)-coated starch by the simple absorption method and then we have shown that the addition of the RDP-coated starch can improve the compatibility to either Ecoflex or polylactic acid (PLA). The increased compatibility of the blends could enhance the tensile properties, such as yield strength. In particular, we focused on the effect of the addition of RDP-coated starch at UL-94 V0 flammable test. We found that over 60 % RDP-coated starch could render the blend of 40 % Ecoflex self-extinguishing without any nanoparticles. By examining the scanning transmission X-ray microscopy (STXM) image of the blends, the RDP-coated starch phases were well dispersed in the Ecoflex matrix. However, too much the RDP-coated starch added in the Ecoflex matrix significantly decreased the impact toughness. In order to improve the toughness properties and to obtain the UL-94-V0 at the same time, we have demonstrated that the addition of Halloysite nanotube (HNTs) clay can achieve the goals due to the increased interfacial areas of the RDP-coated starch by being attached the HNTs clays, which could decrease the interfacial tension between the two biodegradable polymers. Hence the RDP-coated biodegradable polymer blends would become a new type of eco-friendly materials, which has the good flame retardant and mechanical properties as well as biodegradability.
10:00 AM - II10.5
Catalytic Behavior of Surface Functionalized BaTiO3 on the Cure of Bisphenol E Cyanate Ester.
J. Eliseo De Leon 1 , Eduard Stefanescu 1 , Michael Kessler 1
1 Materials Science & Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractMulti-functional materials are essential to the future of aerospace design given that every component that is placed aboard a satellite, air or space craft, adds to the cost of lifting the craft off the ground. Payload reduction, by developing materials that perform more than one function, improves not only the design efficiency of the craft, but has the inherent advantage of reducing cost. Bisphenol E cyanate ester, BECy, exhibits attractive structural properties that make it suitable for lightweight, high strength and high temperature applications. Barium titanate, BaTiO3, is a well known and widely used ferroelectric material utilized in the manufacturing of electronic components, including capacitors. Employing these constituents in the production of a capacitive-structural polymer matrix composite renders an attractive system that meets the lightweight, multifunctional demand of aerospace applications, (in this case structural load carrying capability coupled with dielectric energy storage). However, the effect of BaTiO3 nano-fillers on the cure behavior of cyanate ester is not well understood and is thus the motivation for this work.We investigate the cure kinetics of BaTiO3/BECy suspensions using dynamic differential scanning calorimetry, DSC. The experiment studies the cure behavior of BECy as affected by nano-particle loading and surface-functionality of BaTiO3, modified with γ-glycidoxypropyl trimethoxysilane, GPS, a covalent bond promoter. The DSC measurements are used to determine the kinetic parameters of the cure reaction and to probe the ability of phenomenological reaction models to describe the cure behavior. Preliminary results indicate that untreated BaTiO3 nano-particles have a dramatic catalytic effect on the cure of the BECy resin, exhibiting a reduction of the cure onset on the order of 85°C. Investigation of the onset cure behavior of BECy in the presence of GPS functionalized BaTiO3 is ongoing.
10:15 AM - II10.6
Selective Polymerization of Polypyrrole in Silica Mesopores Using an In-Situ Generated Oxidizing Agent on a Silica Surface.
Ryan Spray 1 3 , Youngju Jung 1 4 , Jin Hoe Kim 2 , Ji Man Kim 2 , Kyoung-Shin Choi 1
1 Department of Chemistry, Purdue University, West Lafayette, Indiana, United States, 3 Mechanical Engineering and Material Science Practice, Exponent Failure Analysis Associates, Natick, Massachusetts, United States, 4 Department of Applied Chemical Engineering, Korea University of Technology and Education, Cheonan Korea (the Republic of), 2 Department of Chemistry, Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractA novel method that selectively polymerizes the conducting polymer pyrrole on a silica surface without inducing polymerization in bulk solution will be presented. The method utilizes a mechanism where the acidic silanol groups on the mesoporous silica surface react with nitrite ions in solution to create a strong oxidizing agent (NO+) in-situ that polymerizes pyrrole monomer as a uniform polypyrrole (ppy) layer on the silica surface. The synthesis effectively avoids bulk polymerization since NO+ ions are available only on the silica surface, and no extra effort to localize monomers or oxidizing agents into the pores is needed. The resulting silica-polymer composite material was characterized using electron microscopy (TEM, SEM/EDS), powder X-ray diffraction (XRD), nitrogen adsorption (BET), thermal gravimetric analysis (TGA), and electrical conductivity, and the results will be presented. This method allows for facile synthesis of high-quality mesoporous silica-ppy composites containing a thin, uniform ppy coating on the silica walls, and adds the property of electrical conductivity to the surface of the mesoporous silica. Due to its simplicity for achieving a site-selective, conductive ppy coating on the silica surface, this method will provide a practical route to form a wide variety of silica/conducting polymer-based composite materials for use in sorption, catalysis, sensing and drug delivery applications.
10:30 AM - II10.7
Laser Assisted Fabrication of Porous Polymer MEMS With Nano Structured Additives.
Igor Shishkovsky 1 , Yuri Morozov 2
1 , Lebedev Physics Institute of Russian Academy of Sciences, Samara branch, Samara, Samara, Russian Federation, 2 , Institute of Structural Macrokinetics and Materials Science (ISMMS), RAS, Chernogolovka, Moscow, Russian Federation
Show AbstractNanoparticles are promising candidate as the solid lubricant, in conducting and magnetic materials, and in pressure cells and hydrogen storage devices also. Multilayers with giant magnetoresistance, which could be realized in the layers interleaving ferromagnetic and non-magnetic metals, have attractive applications. With the decrease of particle sizes from the micro- to the nano- level, the specific surface area to volume ratios grows and, consequently, the chemical activity of nanoparticles follows to this behavior. The direct multilayer fabrication of the nanoparticles is a difficult task. To stabilize the nanoparticles in the polymeric matrix is attractive, because of this makes possible the organization of beforehand determined distribution of nanoparticles by porous polymer structure. It is allow to protect them from the undesirable oxidation and even to attempt the functional graded structures design on this way. It is known, that the sintering is the thermally activated process, which compulsorily must be accompanied by the nanoparticle coagulation in the micrometer conglomerations. Therefore, the polymer mixture sintering is represented as more optimum due to the temperature for the polymer sintering is deliberately lower than temperatures under which the nanoparticles will begin actively to consolidate. Nano size core/polymer shell structure can change hydrophobic properties of the filter porous structure, ensure its colloidal stability also. Selective laser sintering (SLS) as technique for functional-graded structure fabrication with nano impurities is appropriate step in this direction. Actually, it is possible to realize the “bottom-up” paradigm of nanotechnologies by the layerwise synthesis of the smart nano- objects (NEMS devices). Earlier [1,2], we showed the possibility of the laser sintering of the functional- graded filters from metal (nickel or brass) - polymer (polycarbonate /PC/ or polyamide /PA/) powder compositions. At present paper, the possibilities of a layer-by-layer laser sintering of the porous devices from powder polycarbonate with interleaving nano - nickel and copper additives and laser parameter optimization are discussed. Phase-structural and magnetoresistive properties of Cu-PC-Ni-PC layers were investigated. 1. I. Shishkovsky, V. Sherbakov, A. Pitrov Optimization of fine structure and flow behavior of anisotropic porous filters, synthesized by SLS method. // Proc. of SPIE, Vol. 6732 - International Conference on Lasers, Applications, and Technologies 2007: Laser-assisted Micro- and Nanotechnologies, V.Y. Panchenkoand etc, Editors, (Jun. 28, 2007). 2. I. Yadroitsev, I. Shishkovsky, P. Bertrand, I. Smurov Manufacturing of fine-structured 3D porous filter elements by selective laser melting. // Applied Surface Science, Vol 255, Iss. 10, 1 March 2009, P. 5523-5527.
10:45 AM - II10:SYNTHE
BREAK
11:00 AM - **II10.8
Fluid Phases of Nano-carbon.
Matteo Pasquali 1
1 Chemical & Biomolecular Eng., Chemistry, Rice University, Houston, Texas, United States
Show AbstractNanoscale carbon—including Single-Walled Carbon Nanotubes (SWNTs) as well as graphene, i.e., graphite in its single layered form—has remarkable electrical, thermal, and mechanical properties, more so than previously known polymer molecules or colloidal particles. Realizing these properties in applications requires understanding and controlling the behavior fluid phases of nano-carbon. Biological and environmental applications are likely to require dilute phases of nano-carbon; material processing, e.g., production of coatings and fibers, will require more concentrated phases.Difficult fluid handling is one of the most important frontiers of applied research in SWNTs and graphene. Nano-carbon fluids are almost considered an oxymoron because dispersing or dissolving SWNTs and graphene into fluid phases is exceedingly difficult.In this lecture, I will discuss how SWNTs as well as graphene can and should be viewed as hybrids between polymer molecules and colloidal particles. Even at low concentrations (few parts per million), SWNTs form complex fluid phases with intriguing properties. Their interaction can be mediated by polymers and surfactants to produce complex individual architectures. In superacids, SWNTs as well as graphene dissolve spontaneously. At low concentration, these fluids can be used for making transparent, conducting films and coatings. At sufficiently high concentrations, they form liquid crystals that can be spun into well-aligned, macroscopic fibers. Intriguingly, the self-assembly of SWNTs into liquid crystalline phases can be understood by “hybridizing” Onsager’s theory for colloidal rods with Flory’s theory for rod-like polymers.The work on graphene is done in collaboration with the research group of Prof. James Tour (Rice University); cryo-microscopy of nano-carbon fluids is done in collaboration with the research groups of Profs. Yeshayahu Talmon and Yachin Cohen (Technion).
11:30 AM - II10.9
The Effects of Fluorine-contained Molecules on Improving the Anomalous Photocurrent Caused by the PEDOT:PSS Deterioration for the Organic Photovoltaic Devices.
Ching-Chun Chang 1 , Hsieh-Cheng Han 2 , Chi-Ang Tseng 3 , Kuei-Hsien Chen 1 , Li-Chyong Chen 2
1 , Institute of Atomic and Molecular Sciences, Taipei Taiwan, 2 , Center for Condensed Matter Sciences, Taipei Taiwan, 3 Department of Chemistry, National Taiwan Normal University, Taipei Taiwan
Show AbstractIn this study, we investigate the effects of the fluorinated poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) buffer layer on the performance of polymer photovoltaic cells based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blends. The results of humidity-controlled experiments show that the degradation of the device performance can be recovered simply by the interfacial modification, even though the PEDOT:PSS layer has been seriously deteriorated by the exposure to the air ambient. The anomalous S-shape photocurrent owing to the deterioration of the PEDOT:PSS layer can be rectified significantly as an ideal diode behavior by the surface treatments with fluorine-contained materials. Accordingly, the great enhancements of Voc from 0.51 to 0.64 V, and Fill factor from 22% to 57% can be achieved, where the efficiency is improved from 0.98% to 3.46%. It indicates that the deterioration of the PEDOT:PSS layer due to the moisture absorption occurred at the surface primarily. Meanwhile, the recovery of the performance can be achieved easily, without any additional thermal- treatments. This phenomenon is investigated and reported for the first time. Furthermore, the electrical properties at the PEDOT:PSS/active materials interfaces and the overall device performance are also enhanced by 10% or above as compared with the control device. The role of fluorine-related materials and the recovery mechanisms behind will be discussed in this study.
11:45 AM - II10.10
Synthesis of Luminescent Nanoparticle Embedded Polymer Nanocomposites for Scintillation Applications.
Thomas Rogers 1 , Chenlu Han 3 , Brent Wagner 2 , Jason Nadler 2 , Zhitao Kang 2 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Electro/Optical Systems Laboratory, Georgia Tech Research Institute, Atalanta, Georgia, United States
Show AbstractGamma ray detection from radionuclides in imported shipment containers and in other scenarios is a significant concern to national security. This detection is currently accomplished with the use of scintillating materials such as NaI:Tl, LaBr3:Ce single crystals. However, the use of these high quality single crystals limits the functionality of detectors due to the materials' high cost and scalability issues. Therefore, the development of more durable, more easily manufactured, and more cost effective scintillating materials is required. The incorporation of nanophosphors or Quantum Dots (QDs) into a polymer matrix to produce a transparent nanocomposite could potentially provide an alternative method to fabricate scintillating materials. Embedded in a suitable polymer matrix, nanocomposite detectors can be made desirably large for portal monitors with greater ease and lower expense than conventional means. Preparation of suitable particle size and/or doping will permit selection of a photon wavelength that optimally matches the photodetector response curve. This match increases the number of photons collected per pulse and in turn improves output resolution. In this paper a series of LaF3:Ce nanophosphors with varying doping concentrations (1-30mol%Ce) were synthesized using a chemical precipitation method. Photoluminescence and photoluminescence excitation characterizations indicated that the highest luminescent intensity was obtained from the 20%Ce doped sample with a peak emission at 325 nm. These nanoparticles' refractive index was identified by index matching measurements. Then an index matched epoxy was selected for incorporation of the nanoparticles to prepare transparent nanocomposite scintillators. In addition, colloidal solutions of CdTe QDs with various emitting colors were synthesized and incorporated into Polymethyl-methacrylate (PMMA) matrix to make transparent nanocomposite. The scintillation behavior and intensity of these nanocomposites was evaluated for gamma ray detection.
12:00 PM - II10.11
WITHDRAWN 12/27/10 Cobalt Nanoparticles Obtained from an Hybrid Material of Carboxymethylcellulose - CoC12.
Edgar Reyes-Melo 1 2 , Juan Luna-Martinez 1 2 , Virgilio Gonzalez-Gonzalez 1 2 , Alejandro Torres Castro 1 2 , Carlos Guerrero 1 2 , Ubaldo Ortiz 1 2
1 Programa Doctoral en Ingeniería de Material FIME-UANL, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, Nuevo León, Nuevo León, Mexico, 2 Centro de Innovación, Investigación y Desarrollo en Ingeniería y Tecnología, Universidad Autónoma de Nuevo León, Apodaca, Nuevo León, Mexico
Show AbstractIn this work, cobalt nanoparticles were synthesized in carboxymethylcellulose (CMC) matrix. In order to obtain this nanostructured material, first a composite of CMC-CoCl2 was prepared. Cobalt nanoparticles were obtained by treating the composite with a reducing agent, hydracine. The resulting nanoparticles are embedded and stabilized in the CMC. The morphological and structural analyses were performed by High Resolution Transmission Electron Microscopy (HRTEM). The nanoparticle size was about 7 nm; which was obtained from the direct measurement in the HRTEM images. The magnetic characterization was performed by magnetometry. It was observed that the magnetic behaviour of nanoparticles is superparamagnetic at room temperature, whereas, at very low temperature (1.8K) the nanoparticles showed a ferromagnetic behavior with magnetic remanence of 0.44 emu/g and coercitivity field of 0.34 kOe.
12:15 PM - **II10.12
Directing the Assembly of Semiconductors for OPV Applications.
Dhandapani Venkataraman 1 , Serkan Yurt 1 , Thomas Russell 2 , Dian Chen 2
1 Chemistry, University of Massachuetts Amherst, Amherst, Massachusetts, United States, 2 Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts, United States
Show AbstractNanoscale segregated structures for photovoltaic devices are currently created by the use of lamination techniques or by the controlled multi-step layer deposition of the semiconductors by vacuum processing techniques. Most organic conjugated materials have low vapor pressure and are not easy to vacuum process. Therefore, there is a need to use self-assembly based techiques to direct the packing of semiconductors. This talk will focus on two questions: How we can obtain segregated structures of electron rich and electron poor semiconductors through self-assembly? and (2) within the segregate stacks, what packing is needed for high mobility of the charges?
II11: Polymer-Based Nanocomposites: Applications I
Session Chairs
Thursday PM, December 02, 2010
Republic B (Sheraton)
2:30 PM - II11.1
Patterning of Elastomer Nanocomposite via Laser Ablation for Sensor Applications.
Chao-Xuan Liu 1 , Jin-Woo Choi 1 2
1 Department of Electrical and Computer Engineering, Louisiana State University, Baton Rouge, Louisiana, United States, 2 Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, Louisiana, United States
Show AbstractConductive nanocomposites composed of elastomer and carbon nanotubes possess distinct properties, such as piezoresistivity, flexibility and biocompatibility, which make them an attractive candidate for sensor applications as well as building blocks for MEMS devices. Microstructures have been so far fabricated by lithography and microcontact printing methods. Lithography involves elaborate processing steps including wet chemical etching that may undermine the functional performance of nanocomposites. Microcontact printing, on the other hand, requires a new machined printing stamp for every different pattern design which is inconvenient for prototyping purposes. Here, we introduce a novel patterning method that circumvents these issues. Geometries are defined by laser ablation of a thin tape or polyester film using a focused laser beam (KrF 248 nm). Customized in its shape, size and intensity, the laser beam ablates through the thin film cleanly following a path that is programmed through a computer. Nanocomposite is directly filled into the open grooves with excessive amount removed together with the film screen. The conductive patterns are then embedded in bulk elastomer and cured to form a conformal sensing device. To characterize patterning quality, uniformity in the width and thickness of nanocomposite lines are measured as well as their repeatability across samples. Attempts to optimize laser ablation conditions (screen material, beam focus, and pulse numbers) have lowered spatial patterning resolution of a 50 µm-thick tape down to ~35 µm with room for further improvement. In this method, different patterns can be generated in minutes with laser ablation, therefore the device fabrication process is greatly expedited—ideal for preliminary testing in a laboratory where many sensor designs can be compared in their performances over a short time. Based on the piezoresistive response of nanocomposite under strain or stress, various physical sensors are realized, for instance, to monitor large-range (>42%) tensile strains and ultra-sensitive (order of Pascal) air pressure change. Other applications are also under development which will be included in the report. Furthermore, the technique of patterning via laser ablation is not bound with a specific nanocomposite but is generally applicable to a wide variety of curable polymers and resins.
2:45 PM - II11.2
High Performance Rapid Prototyped PCL/TCP Composite Scaffolds for Bone Tissue Engineering Application.
Xu Li 1 , M Tarik Arafat 2 , Christopher X F Lam 2 , Siew Yee Wong 1 , Chaobin He 1 , Ian Gibson 2
1 Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), Singapore Singapore, 2 Department of Mechanical Engineering, National University of Singapore, Singapore Singapore
Show AbstractScaffold-based bone tissue engineering aims to aid in the repair and/or regeneration of bone defects by using scaffold as a platform for carrying cells or therapeutic agents to the site of interest. Recently, rapid prototyping (RP) technologies are fast becoming the technologies of choice for fabricating polymer/ceramic composite scaffolds for bone tissue engineering. However, the application of RP polymer composite scaffolds for bone tissue engineering is hindered by their relatively lower mechanical property and biological activity, especially for cancellous bone tissue engineering. In the present study, tricalcium phosphate (TCP) was surface treated with 3-glycidoxypropyltrimethoxyasilane (GPTMS) to increase the interfacial interaction between TCP and PCL matrix to fabricate RP PCL/si-TCP composite scaffolds with enhanced mechanical property. Compressive mechanical testing revealed that, the compressive modulus and strength of PCL/si-TCP composite scaffolds are more than four times and two times higher than those of PCL/TCP scaffolds, respectively. With this significant improvement in mechanical properties, the compressive modulus and strength of the PCL/si-TCP scaffolds match well with those of cancellous bone, while PCL/TCP scaffolds are notably weaker. The fabricated PCL/si-TCP scaffolds were further coated with carbonated hydroxyapatites (CHA)-gelatin composite via biomimetic coprecipitation to improve their osteoinductive/osteaoconductive property. The structure of the prepared composite coating was verified by SEM, XRD and FTIR. The cell-scaffold interaction was studied by culturing porcine bone marrow stromal cells (BMSCs) on the scaffolds, and assessing proliferation, bone related gene and protein expression capabilities of BMSCs. Confocal laser microscopy and SEM images of the cell-scaffold constructs showed uniform distribution of cell-sheet and accumulation of extracellular matrix at the interior of CHA-gelatin composite coated PCL/si-TCP scaffolds. The proliferation rate of BMSCs on CHA-gelatin composite coated PCL/si-TCP scaffolds was about 2.3 times higher than that on the PCL/si-TCP scaffolds by day 10. Furthermore, reverse transcription polymerase chain reaction and western blot analysis revealed that CHA-gelatin composite coated PCL/si-TCP scaffolds stimulate osteogenic differentiation of BMSCs the most, compared to PCL/si-TCP scaffolds and CHA coated PCL/si-TCP scaffolds. These results demonstrate that thin CHA-gelatin composite coated RP PCL/si-TCP composite scaffolds are promising for bone tissue engineering.
3:00 PM - **II11.3
Polymer Nanocomposites for Electric Energy Storage.
Junjun Li 1 , Paisan Khanchaitit 1 , Kuo Han 1 , Qing Wang 1
1 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractThe development of new materials to store electrical charges is of considerable current interest. Electrical energy storage not only plays an important role in portable electronic devices but also enables future transportation and renewable energy. Polymers offer an attractive alternative to traditional ceramics as dielectric materials for high energy density capacitors, owing to their great processability, low cost, and light weight. More recently, polymer nanocomposites have also emerged as a promising route to dielectric thin films. The idea underlying this approach is to integrate complementary elements, such as high dielectric permittivity from the inorganic dopants and high breakdown strength from the polymer matrix, for a substantially enhanced energy density. We report the preparation and characterization of the polymer nanocomposites based on the surface-functionalized BaTiO3 nanoparticles and ferroelectric polymers. The presence of organic surface layers on the particle affords excellent compatibility between the fillers and the polymer matrix and ensures uniform composite films even at higher filler concentrations. The dominant role of dielectric permittivity of the polymer matrix in determining the energy density of the nanocomposite has been demonstrated. This study suggests that the polymer matrix must be properly selected for the nanocomposites to realize significantly enhanced energy density. We have also prepared novel dielectric nanocomposites composed of ferroelectric polymers and surface-functionalized TiO2 nanoparticles with comparable dielectric permittivities and homogeneous nanoparticle dispersions. It was found that the presence of the nano-scale filler favors the formation of smaller crystalline domains and a higher degree of crystallinity in the polymer. In stark contrast to their weak-field dielectric behavior, substantial enhancements in electric displacement and energy density at high electric fields have been demonstrated in the nanocomposites, which has been attributed to the interfacial coupling effect. The presence of the interface between the filler and the matrix is evident in the dielectric spectra of the nanocomposites.
3:30 PM - II11.4
Poly(3-hexylthiophene) Wrapped Carbon Nanotube / Poly(dimethylsiloxane) Composites for Use in Finger-sensing Piezoresistive Pressure Sensors.
Jihun Hwang 1 , Jaeyoung Jang 1 , Kipyo Hong 1 , Jong Han 2 , Kun-Nyun Kim 2 , Kwonwoo Shin 2 , Chan Park 1
1 , Pohang University of Science and Technology, Pohang Korea (the Republic of), 2 , Korea Electronics Technology Institute , Seongnam Korea (the Republic of)
Show AbstractWe fabricated a piezoresistive composite using multi-walled carbon nanotubes (MWCNTs) as a conductive filler and polydimethylsiloxane (PDMS) as a polymer matrix, which operated in the extremely small pressure range required for finger sensing. To achieve a homogeneous dispersion of MWCNTs in PDMS, the MWCNTs were modified by a polymer wrapping method using poly(3-hexylthiophene) (P3HT). The percolation threshold of the composites was significantly lowered by the presence of P3HT. The electrical conductivity and piezoresistive sensitivity of the composite were found to strongly depend on the P3HT concentration. The well-dispersed P3HT-MWCNT/PDMS composite showed good piezoresistive characteristics in the 0~0.12 MPa pressure range.
3:45 PM - II11: APPLICAT
BREAK
4:00 PM - **II11.5
Processability of Nanotube-Polymer-based Nanocomposites.
Enrique Barrera 1
1 Mechanical Engineering and Materials Science, Rice University, Houston, Texas, United States
Show AbstractMuch of the focus of processing carbon nanotube reinforced polymer based nanocomposites steps from four key areas that include: starting nanotube conditions, nanotube dispersion, interfacial conditions and nanotube alignment. The range of conditions from reactive to miscible mixing exists and this can play a significant role in producing useful nanotube reinforced polymers. Furthermore, the nanotube type and origin play a role that suggests that one processing route does not fit all sources of nanotubes. The idea of nanotube insertion is related to the role they play and the properties that will be produced. Designing for multifunctionality is therefore an important factor in nanotube management and the role of nanotubes as templates can play a vital role. This presentation will focus on the nano to macro issues of processing nanotubes in polymer based composites and will give insight to navigating the issues that tend to limit the property enhancements.
4:30 PM - II11.6
Nanocrystal-polymer Hybrid Materials as Calibration Standard for Confocal Laser Scanning Microscopy.
Michael Krueger 1 2 , Frank Riehle 1 2 , Ying Yuan 1 2 , Roland Nitschke 3
1 Freiburg Materials Research Centre (FMF), University of Freiburg, Freiburg Germany, 2 Microsystems Technology, University of Freiburg, Freiburg Germany, 3 Centre od Systems Biology, Life imaging centre, University of Freiburg, Freiburg Germany
Show AbstractThe resolution of three dimensional fluorescent microscopical imaging strongly depends on the calibration of the instrument. This requires highly photostable fluorophores, therefore standard organic dyes cannot be utilized.Semiconductor nanocrystals are promising fluorophores due to their high brightness, photostability and quantum yield. We present novel CdSe NC-polymer hybrid materials with high quantum yields based on CdSe core quantum dots (QDs). Highly luminescent core NCs are incorporated in-situ into the polymer network during the polymerization reaction. The NCs are fixed and “frozen” into the polymeric network leading to a homogeneous distribution within the polymer maintaining their excellent photoluminescent properties. The hybrid materials can be further processed from the liquid phase leading to various desired forms and shapes. Laser scanning microscopical investigations revealed a high photostability of various polymer hybrids with different emission colors over a wide range of light exposure conditions such as time, laser power etc.. They were superior compared to polymer hybrids based on commercially available core shell CdSe/ZnS QDs which were unstable under the same experimental conditions. The potential of CdSe polymer hybrid materials for the establishment of a calibration standard for confocal laser scanning microscopy will be demonstrated and highlighted.
4:45 PM - II11.7
Mechanical and Gas Sensing Properties of Carbon Nanotube-polyaniline Nanofibre Composite Films.
Fiona Blighe 1 2 3 , Jonathan Coleman 2 3 , Dermot Diamond 1 , Emer Lahiff 1
1 CLARITY Centre for Web Technologies, Dublin City University, Dublin Ireland, 2 Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College Dublin, Dublin Ireland, 3 School of Physics, Trinity College Dublin, Dublin Ireland
Show AbstractOne-dimensional materials offer a route to addressing some of the problems facing the development of future sensor and actuator based technologies, namely those of improved selectivity and sensitivity through vastly increased active surfaces. A high surface area responsive composite material has been prepared by filtration from dilute dispersions of single-walled carbon nanotubes and the nanowire form of the conducting polmer polyaniline. The resulting structures are an adaptation of traditional bucky papers. Bucky papers have extremely high surface areas, low densities, are highly conductive and possess the mechanical properties of a typical thermoplastic. They have the ability to provide a scaffold-like structure suitable for the inclusion of a sensing material like polyaniline. Polyaniline (PAni) is an inherently conducting polymer whose conductivity can be controlled over ten orders of magnitude through changes in its surrounding environment. PAni nanofibre structures can be synthesised in a simple one-step process by interfacial polymerisation. This form of the polymer dramatically increases the exposed area available to react to its environment. It however exists as a powder like-substance and suffers from poor electrical stability and impractically low mechanical strengths. It so requires some form of mechanical reinforcement if it is to offer itself as a viable material for sensing applications. The use of a traditional bulk polymer for reinforcement of the nanofibers must be avoided as this would swamp and drastically decrease the available surface area of the sensing polymer.Nanotube-Polyaniline Nanofibre Composite Films unlike PAni-fibres alone exhibit mechanical stability while maintaining a large intractable surface of 371m^2/g. The properties of these films are easily reproduced by controlling the volume and quality of dispersion used in their preparation. Both composite, CNT reference and PAni reference films (supported) were exposed to a range of target gases. The composite exhibits a change in conductivity in the presence of a target gas at room temperature. Unlike PAni nanofibre films the composite continues to responds steadily after a large number of cycles. Raman spectroscopy on doped and dedoped states of PAni along with the composite helps explain why this is the case.
5:00 PM - II11.8
Transparent Polymeric Composite Reinforced by Carbon Nanotube Yarns.
Mei Zhang 1 2 , Hang Zhang 1 , Richard Liang 1 2 , Chuck Zhang 1 2 , Ben Wang 1 2
1 Industrial and Manufacturing Engineering, FAMU-FSU College of Engineering, Tallahassee, Florida, United States, 2 High-Performance Materials Institute, Florida State University, Tallahassee, Florida, United States
Show AbstractCarbon nanotubes (CNTs) belong to a class of nanomaterial that has remarkable physical and mechanical properties. Their superlative mechanical properties make them the filler material of choice for composite reinforcement. The reinforcement of the CNT-polymer composites is mainly influenced by three factors: dispersion of the CNTs in the polymer matrix, interfacial bonding between CNTs and polymer, and alignment of the CNTs in the polymer matrix. In this work, we developed processing methods to fabricate CNT-polymer composites. Instead of dispersing CNTs into a polymer matrix, we used solid-state processes: twist spinning CNTs from CNT forests to form a CNT yarn, making a CNT yarn array, and immersing the yarn array into a polymer matrix through a hot-press process. Twist spinning assembles the CNTs into a highly organized structure without damaging them or lowering their aspect ratio. Our approaches allow us to form well designed CNT networks inside polymer matrices and it meets the fundamental requirements for filler: high aspect ratio, good distribution in polymer matrix, good alignment and better interfacial stress transfer. When we use polymethylmethacrylate (PMMA) to make the PMMA/CNT composites, we found that the composite with 10 wt% CNT yarns showed an increase of 250% and 500% in tensile strength and modulus respectively with a little deduction in elongation. This approach also keeps over 50% transparency of the composite. Since the yarn’s strength is over 1 GPa, it is expected that the properties of the PMMA/CNT composite would be dramatically improved by further increasing the content of CNT yarns and this approach can be applied to other polymeric composites.
5:15 PM - II11.9
Thermal and Viscoelastic Behaviors of Nanotube-reinforced Polyethylene Composites.
Ananta Adhikari 1 , Mircea Chipara 2 , Karen Lozano 3
1 Department of Natural Sciences, Assumption College, Worcester, Massachusetts, United States, 2 Department of Physics and Geology, University of Texas Pan American, Edinburg, Texas, United States, 3 Department of Mechanical Engineering, University of Texas Pan American, Edinburg, Texas, United States
Show AbstractThe effect of processing (shear) time during melt mixing in twin miniextruder on the thermal stability and mechanical behavior of multiwalled nanotube reinforced polyethylene was investigated. It was found that a 45min processed composite exhibited better mechanical properties (storage modulus, loss modulus) compared to an 11min processed composite. The increase in thermal and mechanical behavior is attributed to a stronger interface between the nanotube and the polymer matrix.
5:30 PM - II11.10
PS-TiO2 Nanocomposites: Thermal Investigations.
Rafael Villegas 2 , Yun Zhai 3 , Hailan Xu 3 , Magdalena Dorina Chipara 1 , David Hui 3 , Karen Lozano 2 , Mircea Chipara 1
2 Mechanical Engineering, The University of Texas Pan American, Edinburg, Texas, United States, 3 Mechanical Engineering, University of New Orleans, New Orleans, Missouri, United States, 1 Physics and Geology, The University of Texas Pan American, Edinburg, Texas, United States
Show AbstractPolystyrene-anatase (PS-TiO2) nanocomposites loaded with various amounts of anatase ranging between 0 % wt. and 20 % wt., have been obtained by dispersing the polystyrene into cyclohexane followed by the addition of TiO2 nanoparticles and the subsequent sonication of the mixture at 1 kW for 100 minutes by using a Hielscher sonicator. The as obtained homogeneous solution was cast on microscope glass slides. The solvent has been completely removed by thermal treatment in a vacuum oven at 150 oC, for 3 hours.The thermal characteristics of the as obtained nanocomposites were investigated by using thermogravimetric analysis and differential scanning calorimetry.Acknowledgments: This research has been supported by DARPA under grant HR0011-08-1-0084 to AMRI- University of New Orleans. The research done at UTPA was supported by NSF PREM (DMR 0934157).
5:45 PM - II11.11
Image Analysis Optimization for Quantifying Nanoparticle Dispersions in Polymer-based Nanocomposites Using Transmission Electron Microscopy (TEM).
Anand Badami 1 , Mark Beach 1 , Stewart Wood 1 , Steve Rozeveld 1 , William Heeschen 1
1 Analytical Sciences, The Dow Chemical Company, Midland, Michigan, United States
Show AbstractTransmission electron microscopy (TEM) micrographs are routinely used to evaluate the dispersion of insoluble additives in polymer-based nanocomposite systems. When comparing large numbers of TEM micrographs, the ability to determine or estimate the dispersion quality (i.e. uniformity of size and/or spatial distribution) is often difficult. The objective of this study was to develop a method to quantify dispersions observed in TEM micrographs that enables both a numerical “ranking” to be assigned to individual dispersions as well as tabulation of a multitude of images acquired over time. Several methods were reviewed and applied to a set of TEM dispersion images acquired of an insoluble additive in polystyrene. Projected area diameter, particle area, and Euclidean distance between particle centroids were chosen from all the particle size distribution and spatial distribution parameters present in the literature to evaluate their effectiveness in yielding a numerical value useful in ranking dispersion quality. However, these three methods did not successfully yield a quantitative indicator of dispersion quality for the micrographs in this study. Their inability to generate a “ranking” value suggested that a different parameter is needed, one which quantifies size and distribution differently than these three methods. It appeared that this different parameter should be a three dimensional parameter, considering that Euclidean distance between centroids is a linear parameter, and equivalent circular diameter and particle area both incorporate two dimensions. It followed that a volume distribution may offer a better ability to quantitatively rank TEM micrograph dispersions. This was confirmed by calculating cumulative volume percent curves for the micrographs in this study. Generating cumulative volume percent curves for different samples appears to be a preferred method of quantifying and comparing dispersions in TEM micrographs. The volume diameter values obtained by this method can be used for “ranking” and tabulation of dispersion quality. This method proved much more successful in quantifying dispersion quality than equivalent circular diameter, particle area, or Euclidean distance between particle centroids, providing a method to account for both “good” additive dispersions (i.e. those with small domains of a narrow size range around 1 µm or less) and “bad” additive dispersions (i.e. those with non-uniform domains ranging in size by several microns or more). As a result, the numerical values generated by this method can be used to quantitatively determine correlations between the dispersion quality of nanoparticles in polymer-based nanocomposite materials and various macroscale physical and/or performance properties of such materials. A robust statistical evaluation of the precision of this quantification method will also be discussed.
II12: Polymer-Based Nanocomposites: Graphene
Session Chairs
Friday AM, December 03, 2010
Republic B (Sheraton)
7:00 PM - **II12.1
Graphene-based Nanocomposite Materials.
Nikhil Koratkar 1
1 , Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractGraphene is a single-atom-thick sheet of sp2 hybridized carbon atoms. Recent advances in the production of bulk quantities of exfoliated graphene sheets from graphite have enabled the fabrication of graphene polymer composites. Such composites show tremendous potential for mechanical properties enhancement due to their combination of high specific surface area, two-dimensional sheet geometry, strong nanofiller-matrix adhesion and the outstanding mechanical properties of the sp2 carbon bonding network in graphene.In this talk, I will describe the processes that can be used to synthesize bulk quantities of exfoliated graphene sheets from graphite and the processing techniques used to disperse them in polymer based matrices. I will discuss various mechanical properties of these composites including Young’s modulus, ultimate tensile strength, fracture toughness, fracture energy, buckling stability and fatigue resistance. I will show that graphene can match the performance of other competing nanofillers such as carbon nanotubes, nano-particles and nanoclays, at one to two orders of magnitude lower nanofiller weight fraction. I will discuss the reasons for the superiority of graphene over other forms of nanofiller reinforcement. Finally I will end by discussing some potential high impact applications of this enabling materials technology.Related Publications:(1) M. A. Rafiee, J. Rafiee, Z. Wang, H. Song, Z.-Z. Yu and N. Koratkar, ACS Nano 3, 3884-3890 (2009).(2) M. A. Rafiee, J. Rafiee, Z.-Z. Yu and N. Koratkar, Applied Physics Letters 95, 223103 (2009).(3) M. A. Rafiee, J. Rafiee, I. Srivastava, Z. Wang, H. Song, Z.-Z. Yu and N. Koratkar, Small 6, 179–183 (2010).(4) J. Rafiee, M. A. Rafiee, Z.-Z. Yu & N. Koratkar, Advanced Materials 22, 2151–2154 (2010).
7:30 PM - II12.2
Self-healable Graphene Polymer Composites.
Xingcheng Xiao 1 , Tao Xie 1 , Yang-Tse Cheng 2
1 , General Motors Global R&D Center, Warren, Michigan, United States, 2 , University of Kentucky, Lexington, Kentucky, United States
Show AbstractGraphene, a single planar layer of sp2-bonded carbon atoms, has attracted considerable attention owing to its extraordinary mechanical properties, high thermal and electronic conductivity. We demonstrate a simple and scalable method to fabricate graphene polymer nanocomposites, without the need for filler chemical treatment. The graphene material used is nanolayered graphene (NLG) obtained by a scalable chemical vapor deposition (CVD) method. The NLG, in its pristine state, is dispersed directly into the precursor for an epoxy shape memory polymer (SMP). The shape memory properties of the cured epoxy polymer matrix impart a heat triggered the self-healing capability and scratch resistance into the nanocomposites, which are significantly enhanced by the NLG fillers at ultralow contents (0.0026 vol% and 0.0124 vol.%, respectively).
7:45 PM - II12.3
Toughening Mechanisms in Graphene-epoxy and Carbon Nanotube-epoxy Nanocomposites.
Ardavan Zandiatashbar 1 , Catalin Picu 1 , Nikhil Koratkar 1
1 , Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractSignificant toughening was observed in this work in epoxy-based nanocomposites with graphene or carbon nanotubes (CNT) as nanoscale fillers. The fracture toughness increases by approximately 20% and 50% upon the addition of only 0.1 wt% of CNTs and functionalized graphene sheets, respectively. In cyclic loading the crack growth rate decreases by an order of magnitude relative to the unfilled epoxy. The mechanism leading to the enhancement in CNT-epoxy composites is crack bridging, as demonstrated by direct observations and modeling. The toughening mechanism active in graphene-epoxy is still a matter of debate. Nanoindentation, atomic force microscopy and electron probing are used to probe material behavior on the local scale in pure epoxy and in nanocomposites. This provides information about the presence of characteristic length scales induced by the microstructure (in nanocomposites), which control the mechanical behavior. The influence of these local fluctuations on the macroscopic behavior is determined using modeling and by the direct comparison with macroscopic properties of the filled materials.
8:00 PM - II12.4
Raman Study of Interfacial Load Transfer in Graphene-polymer Nanocomposites.
Iti Srivastava 1 , Rutvik Mehta 1 , Linda Schadler 1 , Nikhil Koratkar 2
1 Material Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractCharacteristic Raman band shifts have proven to be a valuable technique to study load transfer mechanisms in polymer nanocomposites. The stress transfer to the reinforcing filler imposes elastic strains in the filler materials, proportionally shifting their characteristic Raman bands. Tracking the strain-sensitive filler Raman band shifts with respect to the stress state applied to the nanocomposite reveals insights regarding the filler-matrix interactions at the micro-mechanical level. We use the sensitivity of these strain-induced filler Raman band shifts to probe the extent of graphene-polymer interfacial interactions and determine the basis for strengthening. In our previous work, we have demonstrated greatly improved mechanical properties in polymer nanocomposites using very small quantities (<0.1 wt.%) of graphene platelets. The enhanced bulk mechanical properties of the graphene-polymer composites are attributed to the strong bonding/interlocking of graphene with the polymer matrix. We relate the macroscopic mechanical behavior to the nanoscopic mechanisms at the graphene-polymer interface by studying the strain-induced Raman bands shifts in graphene-polymer nanocomposites. We monitored shift in the first order characteristic G band at 1596 cm-1 in the Raman spectrum of graphene in a thermoset and an silicone matrix. We synthesize graphene nanoplatelets (comprised of ~3-4 individual graphene sheets on average) by a thermal exfoliation process and prepared composites with PDMS (Polydimethylsiloxane) and epoxy resins by solvent dispersion techniques. We obtain significant peak shifts in both compression and tension of the nanocomposites due to the large elastic deformations in the graphene indicating efficient load transfer.A comparison between single-walled carbon nanotube and graphene-polymer composites reveal much larger debonding strains for graphene nanocomposites, as high as ~10% for PDMS with the rate of peak shift with strain being as large as 0.4 cm-1/strain %. We performed thermo-mechanical experiments to verify the strong filler-matrix interface bonding. The increase in the glass transition temperature by 10 C for the nanocomposite verified the strong bonding between graphene platelets and polymer matrix. We highlight filler orientation effects on stress transfer to graphene through polarized Raman scattering and detail the creation of compressive and tensile stress in the graphene on load transfer by the polymer. Finally we utilize Raman scattering in conjunction with atomic force microscopy, nanoindentation and diffraction studies to unravel the micro-mechanisms of stress transfer between graphene and polymer matrix in nanocomposites. The insights of the stress transfer mechanism would enable rational design of strategies to circumvent existing failure mechanisms through graphene-polymer interfacial engineering and enable potentially larger gains in nanocomposite strengthening.
8:15 PM - II12.5
Graphene-conducting Polymer Nanocomposite as Novel Electrode for Supercapacitor.
Humberto Gomez 1 2 5 , Farah Alvi 1 2 3 , Pedro Villalba 1 4 5 , Manoj Ram 1 2 , Ashok Kumar 1 2
1 Department of Mechanical Engineering, University of South Florida, Tampa, Florida, United States, 2 Nanotechnology Research and Education Center, University of South Florida, Tampa, Florida, United States, 5 Departamento de Ingenieria Mecanica, Universidad del Norte, Barranquilla Colombia, 3 Department of Electrical Engineering, University of South Florida, Tampa, Florida, United States, 4 Department of Chemical and Biomedical Engineering, University of South Florida, Tampa, Florida, United States
Show AbstractThe industry as well as research centers around globe are coping to address the world-wide energy demand, and competing with all available alternate technologies. In fact, the growing demand of portable systems and hybrid electric vehicles, memory protection in CMOS, logic circuit, VCRs, CD players, PCs, UPS in security alarm systems, remote sensing, smoke detectors, etc. require high power in short-term pulses. So, last 25 years, the electrochemical capacitors are required for the development of large to small devices driven by electrical power. We know that supercapacitor is well compared to the secondary battery which exhibits faster and higher power capability, long life, wide thermal operating range, and cost effective in the maintenance of the power devices. The supercapacitors have been made using highly conducting lightweight conducting polymers such as polyanilines (PANIs), polypyrroles, and polythiophenes. However, high power supercapacitors are a challenge to build from simply using conducting polymer because the conducting polymers exhibit poor stabilities during the charge/discharge process. The activated carbon and carbon nanotubes (CNTs) in recent days have been used to fabricate supercapacitors due to their good stability but these microstructures limit the value of the capacitance. The CNTs-PANI have been tested as supercapacitor electrodes and high capacitances and improved stability. However, the use of CNTs have been restricted from achieving electric double-layered capacitance for active devices. The graphene-polyaniline nanocomposite materials were synthesized using chemical precipitation technique. The graphene –polyaniline nanocomposite film was characterized using Raman, X-ray, SEM, TEM and cyclic voltammetric, techniques. The interesting composite structure could be observed using different ratio of graphene with aniline monomer. The supercapacitor was fabricated using graphene-PANI in N-methyl pyrrolidinone and graphene-PANI-nafion on graphite electrodes. A specific capacitance of 300 to 500 F/g at a current density of 0.1A/g was observed over PANI–graphene nanocomposite materials. We have aimed at tailoring properties optimization of the proposed capacitors through optimization of their components and packaging towards qualification for supercapacitor application. Based on experimental data shown in this work, we believe conducting polymer conjugated capacitor technology could be viable, and could surpass existing technologies when such novel materials approach will be taken.
8:30 PM - II12.6
Thermomechanical Behavior of Filled Thermoplastics: Role of Filler vs. Crystallinity.
Gowri Dorairaju 2 , Saurabh Toshniwal 2 , Kunal Tulsyan 2 , Daniel Schmidt 2 , Emmanuelle Reynaud 1
2 Plastics Engineering, UMass Lowell, Lowell, Massachusetts, United States, 1 Mechanical engineering, UMass Lowell, Lowell, Massachusetts, United States
Show AbstractMost industrial nanocomposites are based on semi-crystalline polymers (e.g. polyamides, polypropylene). While nanofillers affect the microstructure of semi-crystalline polymers, the effects of microstructural changes and nanofiller content on macroscopic properties have not been separated, nor their relative importance defined. With this in mind, our work focuses on the collection of straightforward experimental data on thermoplastic / layered silicate nanocomposites with high levels of nanofiller dispersion in analogous amorphous and semi-crystalline matrices.A polyamide 12 was chosen as the semi-crystalline matrix, while a cycloaliphatic polyamide 12 copolymer served as the amorphous analog. Southern Clay’s Cloisite 30B, an organically modified montmorillonite clay with excellent polyamide compatibility, served as the nanofiller in both cases. Nanocomposites were compounded via twin-screw extrusion and injection-molded to form test bars to achieve filler concentrations up to 1 vol% inorganic matter (~4 wt% Cloisite 30B). X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed partial nanofiller exfoliation in these nanocomposites. DSC analysis indicated no change in the amorphous character of the nanocomposites based on the amorphous polyamide. In the case of the semi-crystalline polyamide, crystallinity was observed to increase at low filler content, then decrease to the level of the pure polymer at higher filler content. Only the gamma crystalline phase was observed via XRD in the latter materials.Regarding mechanical properties, the amorphous nanocomposites were characterized by a ~30% increase in modulus at the highest nanofiller loading vs. an increase of only ~15% at the same inorganic content in the semi-crystalline matrix. On the other hand, the strain at failure decreased by ~60% at the highest nanofiller loading level in both systems.Maximum sample surface temperatures were recorded during selected tensile tests using a FLIR ThermoVision A20M/Researcher infrared camera. In all cases, plastic deformation was accompanied by adiabatic heating, and work of fracture and the heat of deformation were calculated and compared. In the amorphous nanocomposites, there is a fundamental shift in behavior as the nanofiller is introduced, with a greater propensity for dissipating mechanical energy in the form of heat as nanofiller content is increased. For the semi-crystalline nanocomposites, the trend is less straightforward. The introduction of a limited amount of filler (to 0.25 vol% inorganic) significantly decreases the amount of work converted to heat, but the conversion efficiency is recovered at higher filler loadings. This is consistent with the crystallinity trends observed in DSC, implying that reduced crystallinity (or perhaps the presence of smaller, less perfect crystallites) plays a key role in enhancing the conversion of mechanical energy to heat in this system.
8:45 PM - II12.7
Quantitative Measurement of the Interactions between Individual Graphene Sheets and Polymers.
Minzhen Cai 1 , Arthur Glover 2 , David Kranbuehl 2 , Hannes Schniepp 1
1 Department of Applied Science, The College of William and Mary, Williamsburg, Virginia, United States, 2 Department of Chemistry, The College of William and Mary, Williamsburg, Virginia, United States
Show AbstractThe filler–matrix interactions are vital in graphene–polymer nanocomposites. Only if large amounts of stress are transferred from the polymer matrix to the graphene sheets will it be possible to make full use of graphene’s outstanding mechanical properties. However, quantitative measurements of these interactions are challenging for such small particles. We believe that this experimental difficulty limits systematic analysis of nanocomposites. We present two novel methods to directly characterize the interfacial adhesion between individual single-layer graphene sheets and polymers using Atomic Force Microscopy (AFM). We have applied these methods for a broad range of polymers and for graphene sheets with different degrees of surface functionalization. We find that the sheet–polymer interactions vary greatly for the different systems. We observe the largest interactions between highly functionalized graphene sheets (C:O ratio 2:1) and strongly polar polymers such as polyvinyl alcohol. Some sheet–polymer combinations show surprisingly low interactions. In order to further understand these findings we complement our studies by traditional approaches to adhesion, including contact angle measurements on our materials. In order to understand the relationship between the filler–matrix interactions at the single sheet level on one hand and macroscopic nanocomposite properties on the other, we also carried out tensile testing and rheometric analysis on macroscopic nanocomposite specimens. We see this work as a contribution towards a rigorous understanding of the nanocomposite behavior across the length scales.
9:00 PM - II12.8
Facile Synthesis of Polypyrrole/Graphene Nanosheet-based Nanocomposites as Catalyst Support for Fuel Cells.
Burcu Saner 1 , Selmiye Alkan-Gursel 1 , Yuda Yurum 1
1 Materials Science and Engineering, Sabanci University, Istanbul Turkey
Show AbstractGraphene is a single flat monolayer of sp2-carbon atoms in two dimensional crystal structure. There are several chemical treatments for the separation of graphene sheets from graphite. Graphite oxidation is one of the widely used method to reduce the strong bonding between sheets in graphite and to receive monolayer graphene sheet. In addition, graphite oxide nanoplatelets having exceptional in-plane mechanical, structural, thermal, and electrical properties as graphite have been recently used as cheap fillers in polymer nanocomposites.Conducting polymers, such as polypyrrole (PPy), are extensively preferred for fuel cell operations due to the characteristics of good electronic and proton conductivity, dispensability and special nanometer structure. PPy-modification can increase the electrochemical surface area and enhance the electrocatalysis ability of Pt/carbon catalyst.Catalyst has a great effect on both the cost and durability of polymer electrolyte membrane fuel cells (PEMFCs). At this point, the support material has great importance to achieve high catalytic activity of fuel cell catalyst by lowering the catalyst loadings. The incorporation of metals into the graphene layers can be a bright opportunity to ensure thermal and electronic conductivities of the membrane electrolyte for the use as catalyst support in PEMFCs.In this work, PPy/graphene nanosheets-based nanocomposites having enhanced thermal stability and electrical conductivity, and high surface area were produced to be used as catalyst support in fuel cells. At first, graphene nanosheets were synthesized via a mild chemical route including three major steps: graphite oxidation by chromic acid, ultrasonic treatment and chemical reduction by hydroquinone. Then, PPy was deposited on graphene nanosheets by in-situ polymerization with different feed ratios of pyrrole to graphene nanosheets. The effect of pyrrole amount on the characteristics of nanocomposites were investigated by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Thermal Gravimetric Analyzer (TGA), Atomic Force Microscopy (AFM), Raman Spectroscopy and surface area analyzer.
9:15 PM - II12.9
Kinetic Monte Carlo and Optical T-matrix Modeling of Nanostructured Planar Heterojunction Solar Cells.
Paulus Geraldine 1 , Moon-Ho Ham 1 , Michael Strano 1
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractDue to their simple geometry and design, planar heterojunction (PHJ) solar cells have advantages both as potential photovoltaics with more efficient charge extraction than their bulk heterojunction (BHJ) counterpart, and as idealized interfaces to study basic device operation. In this work, we use a combination of both an optical T-matrix model and a kinetic Monte Carlo model to investigate the photocurrent generation in PHJ photovoltaics. The model takes into account the rates of exciton generation, transport, recombination and dissociation using literature values. By including the optical, electronic and structural properties of the different materials, we are able to predict the short-circuit current of an in lab constructed P3HT/SWNT PHJ and of a previously developed P3HT/PCBM PHJ solar cell. The experimental data for each of these devices show a maximum photocurrent output at a P3HT thickness of 60-65 nm, in contradiction to the expected value equal to the diffusion length of excitons in P3HT (8.5nm). The model demonstrates how bulk exciton dissociation is responsible for this shifted maximum in the P3HT/SWNT case, whereas the maximum is mainly determined by PCBM interdiffusing in P3HT in the P3HT/PCBM case. Based upon the results of this model it will be possible to more intelligently design polymer hybrid solar cells (both planar and bulk) and optimize them towards higher efficiencies.
Symposium Organizers
Mircea Chipara The University of Texas Pan American
Pulickel M. Ajayan Rice University
Ali Nasar CNC Coatings
Alan Kin-Tak Lau The Hong Kong Polytechnic University
II13: Polymer-Based Nanocomposites: Applications II
Session Chairs
Friday AM, December 03, 2010
Republic B (Sheraton)
9:00 AM - II13.1
Evaluating Nanocomposite Materials via Nuclear Magnetic Resonance.
Christopher Klug 1
1 Chemistry Division, Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractThe addition of carbon nanotubes to polymeric materials has the potential of resulting in light weight high strength materials with a wide variety of applications. However, achieving the desired material properties will require improvements in the dispersion of the carbon nanotubes within the polymer matrix and in the bonding between the carbon nanotubes and the polymer matrix. Maximizing the controlled interfacial contact between the phases of the composite requires a thorough understanding of the nanotube-polymer interaction which occurs at a buried interface ideal for study via solid state NMR. We have demonstrated: i) the ability to obtain NMR signals for a wide range of samples despite the presence of residual catalyst; ii) the effects of water absorption on NMR properties relevant to aging; iii) the correlation between NMR relaxation properties and nanotube loading; and iv) the correlation between NMR signal sizes and nanotube dispersion.
9:15 AM - II13.2
Electron Microscopy of Modular Layer-by-layer PAH/PSS-Au Nanocomposite Structures.
Nabil Bassim 1 , Walter Dressick 1 , Kenan Fears 1 , Rhonda Stroud 1 , Thomas Clark 1 , Andrew Herzing 2 , Dmitri Petrovykh 1
1 , U.S. Naval Research Laboratory, Washington, District of Columbia, United States, 2 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractWe synthesized modular nanocomposites of polyelectrolyte polymers and gold nanoparticles, and characterized the morphology with cross-sectional transmission electron microscopy (TEM) and electron tomography. These imaging techniques allowed us to directly measure the structural characteristics of heterogeneous nanocomposites that are typically examined indirectly, e.g., using UV-vis spectroscopy and X-ray reflectometry. Our synthesis procedure was layer-by-layer (LbL) assembly of alternating polyelectrolyte layers, polyallylamine hydrochloride (PAH) and sodium polystyrene sulfonate (PSS), with the addition of regularly interspaced layers of ~15-nm Au-citrate nanoparticles following the method of Johannes Schmitt et al., [Adv. Mater. 9, 61 (1997)]. Cross-sections of the PAH/PSS-Au LbL assemblies for TEM and tomography were prepared using a low-damage, focused ion beam technique. The electron microscopy analysis allowed us to elucidate from direct measurement of the nanocomposite structure the details of assembly mechanisms that previously had to be inferred or hypothesized. We find that ionic strength and metal counter ions present in the deposition and rinsing solutions control the morphology of the assembled nanocomposites. The lateral distribution of gold nanoparticles and the morphology of polyelectrolyte layers in these nanocomposites can be determined quantitatively from electron tomograms reconstructed from tilt-series imaging of the cross-sectioned samples. The ability to control and directly image the structure and morphology of modular LbL nanocomposites will allow us to design customized materials for potential plasmonic, mechanical, or optically-responsive applications.
9:30 AM - II13.3
Enhanced Stability of Conducting Polymer Composites Against UV Irradiation: The Role of Carbon Nanotubes.
William Cheung 1 , Yufeng Ma 1 , Guangru Mao 1 , Richard Mendelsohn 1 , Huixin He 1
1 , Rutgers University, Newark, New Jersey, United States
Show AbstractShort lifetime has been a thorny problem for devices consisting of conjugated polymer materials. Studies to improve the stability of the conjugated polymer are important for both academic interest and practical applications. In this work, water-soluble self-doped polyaniline nanocomposites were fabricated by in-situ polymerization of 3-aminophenylboronic acid monomers in the presence of single-walled carbon nanotubes (SWNTs) dispersed by different methods. We found that single stranded DNA dispersed and functionalized SWNT, not only dramatically speeded up the polymerization, it also remarkable enhanced stabilization of the resulting conducting polymer composite against UV irradiation. This is possibly due to the electronic structure of the DNA functionalized SWNTs: SWNTs becomes electron rich due to the DNA functionalization, which can catalytically reduce the polyaniline backbone from the unstable, degradable, fully oxidized pernigraniline state to the stable, conducting emeraldine states. Surprisingly, we found that microwave dispersed and functionalized SWNTs, which are known to be electron deficient, exhibited stronger photostabilization effect, protecting the polyaniline backbone from photodegradation under harsh laser irradiation; even though it did not increase the polymerization speed like DNA functionalized SWNTs. A different stabilization mechanism is proposed.
9:45 AM - **II13.4
Permeability of Polymer/Clay Nanocomposites.
Georgios Choudalakis 1 , Alexandros Gotsis 1
1 Sciences, Technical University of Crete, Chania Greece
Show AbstractThe presentation focuses on the barrier properties of polymer nanocomposites. The basic ideas on permeability reduction due to the inorganic nanoparticles are presented, as well as some of the existing theoretical models. The predictions are tested with the available experimental results, where it seems that the Nielsen model is sufficient for most cases. Deviations from the expected/predicted results are reported and explained on the basis of alterations of the free volume in the polymer matrix due to the presence of the clay particles. These features concern not only the total free volume variations but also its distribution over the free volume hole sizes. Experimental data that support the above arguments are reported. It seems that the barrier properties of polymer nanocomposites are affected not only by the difficulties of particle exfoliation but also by their interactions with the matrix, which may alter physical features of the polymer and in some cases they may lead to barrier properties deterioration.
10:15 AM - II13.5
Probing Polymer/Fullerene Interactions Using Wide Angle X-ray Scattering and Density Functional Theory: A Comparison of Experiment and Theory.
Katie Campbell 1 , Bilge Gurun 1 , Leah Nation 3 , Bobby Sumpter 2 , Yonathan Thio 1 , David Bucknall 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 Materials Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Center for Nanophase Materials Sciences, Oak Ridge National Lab, Oak Ridge, Tennessee, United States
Show AbstractC60 fullerenes have been shown to have limited solubility in common organic solvents and to form charge-transfer (CT) complexes with a variety of small molecules. Electron donating capability, atoms much larger than carbon such as chlorine, and aromaticity have all been shown to improve solubility and promote CT complex formation with C60. However, C60 miscibility studies with polymers have been limited. We previously showed C60 has a miscibility limit of ~0.5wt% with polystyrene (PS) via wide angle x-ray scattering (WAXS) and molecular dynamics simulations. We have undertaken a systematic study of the effects of increased aromaticity in the side group of vinyl polymers and their ability to disperse fullerenes in a polymer matrix of PS, poly(2-vinylnaphthalene) (P2VN), and poly(9-vinylphenanthrene) (P9VP). In addition, we have examined the effects of molecular weight on the dispersion limit using three different molecular weights of PS. WAXS was used to determine the dispersion limit of C60 in each polymer based on the point at which C60 associated crystalline peaks in the WAXS patterns are first observed. Density functional theory (DFT) calculations for binding energy between these molecules were also undertaken to determine the interaction between C60 and oligomers of each polymer system for comparison, as well as to explore the optimized geometries for the formation of the underlying interactions. WAXS results indicate that the dispersion limit increases with increasing aromaticity with limits of 0.5wt%, 2wt%, and 12wt% C60 for PS, P2VN, and P9VP respectively. DFT calculated binding energies are in good agreement with the WAXS behavior as binding energy also increases with increasing aromaticity. Because the molecular weight of the P9VP used was low compared to both the PS and P2VN systems investigated, additional PS systems with molecular weights similar to P2VN and P9VP were used to determine whether molecular weight was a contributing factor. The results indicated that molecular weight effects are not responsible for the magnitude of the miscibility increase seen with the C60/P9VP blends. More likely, the increased interaction can be attributed to the orientation of the vinyl side group relative to the C60 cage as a shift from limited parallel orientation with PS systems to more perpendicular orientation with P9VP systems is noted from DFT simulations. Similar investigations were also conducted for PCBM/polymer systems using both WAXS and DSC as characterization tools. Preliminary results indicate that PCBM, commonly used in organic solar cell applications, shows significantly improved miscibility with both PS and P2VN systems as compared to pure C60 as expected. The results of both C60 and PCBM studies have a wide range of potential application ranging from nanoparticle templating to photovoltaic applications.
10:30 AM - II13: APPL 2
BREAK
11:00 AM - II13.6
Morphological Investigations of Organic/Inorganic Nanocomposites Fabricated to Achieve Controlled Dispersion at High Loadings.
Andrew Duncan 1 , Andrew Schoch 1 , Michael Berg 1 , Kristoffer Stokes 1 , Christopher Gold 1 , Joseph Lenhart 1 , Frederick Beyer 1
1 Macromolecular Science and Technology Branch, U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland, United States
Show AbstractMost research efforts to realize the multifunctional benefits of polymeric nancomposites have focused primarily on low volume percent loadings and precise control of functional nanoparticle placement in polymer hosts. Our goal is to maximize loading of the functional particulate in the polymer template with minimal or controlled variation of the morphological structure. Coincident dispersion of the nanoparticle and stability of the polymer morphology provide hierarchically structured functional materials. Local aggregation extends the hierarchical structure and influences the composite similar to microscopic fillers. Bulk processing techniques have been employed to create scalable functional materials that retain the benefits of nanofillers and nanostructure. The initial approach tailors non-specific interactions between the particulate and polymeric host. Aliphatic or aromatic ligands were grafted with high areal density onto the surface of nano-SiO2 to tailor the miscibility of the nanoparticle to a targeted domain of poly(styrene-b-ethylene-co-butylene-b-styrene). The second approach employed a block-specific diluent to swell the target domain and allow increased loading of the miscible particulate during fabrication. Processing was facilitated with a twin-screw compounder/extruder. Post-extrusion the polymeric nanocomposites were annealed and examined in two states: with and without diluent extraction. Removal of the diluent creates artificially high loadings locally in the target domain of the block copolymer. A third approach employs reactive blending of the block copolymer with a homopolymer to achieve a co-continuous morphological structure capable of hosting the target nanoparticles. Variation in loading levels, diluent volume, particulate size, ligand composition, and MW of the block copolymer allowed for identification of critical parameters to achieve controlled dispersion at high loadings without extended disruption of the polymer morphology. The primary methods employed to characterize the polymer morphology and particle distribution of the nanocomposites were transmission electron microscopy (TEM), synchrotron-based ultra small-angle X-ray scattering (USAXS), and selective chemical etching. Aromatic ligand functionalization led to better dispersion of the particulates at high loadings than particulates modified with the aliphatic ligands. USAXS revealed that varied loadings resulted in minimal changes in aggregation compared to miscibility controlled by particulate functionalization. Electron energy loss spectroscopy (EELS) combined with energy filtered TEM allowed for imaging of the nano-SiO2 within the block copolymer morphology and correlation with scattering experiments.
11:15 AM - II13.7
Long Cycle Life Nanocellulose Polypyrrole Electrodes.
Gustav Nystrom 1 , Henrik Olsson 1 , Martin Sjodin 1 , Daniel Carlsson 1 , Albert Mihranyan 1 , Leif Nyholm 2 , Maria Stromme 1
1 Department of Engineering Sciences, Division of Nanotechnology and Functional Materials, The Angstrom Laboratory, Uppsala University, Uppsala Sweden, 2 Department of Materials Chemistry, The Angstrom Laboratory, Uppsala University, Uppsala Sweden
Show AbstractWe have recently reported on an electrode material consisting of nanostructured cellulose extracted from the green algae Cladophora subsequently coated with a 50 nm layer of polypyrrole [1]. This composite conductive paper material has a nitrogen BET surface area of 80 m2/g and has shown to be compatible with very high charging currents, up to 600 mA/cm2, when used as electrode material in aqueous electrolyte all-polymer batteries [2]. Limited cycling stability has long been considered one of the main drawbacks for conducting polymer based electrodes [3]. In this contribution, it is however, shown that very long cycle life times can be obtained with the present nanocomposite electrodes in aqueous electrolytes. References:1. Mihranyan, A.; Nyholm, L.; Garcia Bennett, A. E.; Stromme M. A novel high specific surface area conducting paper material composed of polypyrrole and Cladophora cellulose. J. Phys. Chem. B, 2008, 112, 12249-12255.2. Nystrom, G.; Razaq A.; Stromme M.; Nyholm L.; Mihranyan A. Ultrafast All-Polymer Paper-Based Batteries. Nano Letters, 2009, 9, 3635-3639.3. Naoi, K.; P. Simon, New Materials and New Configurations for Advanced Electrochemical Capacitors. Electrochem. Soc. Interface, 2008, 17, 34-37.
11:30 AM - II13.8
The Role of Chemical Interactions on the Diffusion of Phenyl-C61-Butyric Acid (PCBM) in Poly(3-HexylThiophene) (P3HT): Molecular Dynamics Simulations.
Rakhee Pani 1 , Evan Keresi 1 , Yaroslava Yingling 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractOrganic photovoltaic devices, which are usually based on a blend of a conjugated polymer and a fullerene derivative, offer a promise of creating lightweight and low-cost solar cells. However, there are many unsolved problems such as low power conversion efficiency and poor operational stability. It is widely accepted that polymer film morphology is the key that determines photovoltaic properties and controls the efficient charge transport and device efficiency of the solar cell. Further improvements in the performance of organic solar cells requires a better understanding of the mechanisms of diffusion and molecular rearrangement. We applied molecular dynamics simulations to the model system of poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), as this material combination has lead to the highest reported power conversion efficiency in bulk-heterojunction solar cells. The results from our simulations show that the diffusion of PCBM is faster in amorphous P3HT than in crystalline P3HT matrix, which agrees with the experimental observations. Simulations reveal that the decrease of the PCBM diffusion is mainly attributed to the efficient interactions between PCBMs and aromatic P3HT backbone. Also PCBM has a higher diffusion coefficient in crystalline P3HT as compared to C60, due to the decrease in binding energy of PCBM to P3HTs. A thorough understanding of the diffusion factors will promote better morphological control in polymer solar cells leading to improvements in efficiency.
11:45 AM - **II13.9
Polymer-Ceria Nanocomposites for Biomedical Applications.
Sudipta Seal 1 2 3 , Ajay Karakoti 1 , Jessica King 1 , Sanjay Singh 5 , William Self 4 5 , Peter Brenneisen 6 , Lirija Alili 6
1 Advanced Materials Processing and Analysis Center, University of Central Florida, Orlando, Florida, United States, 2 Nanoscience and Technology Center, University of Central Florida, Orlando, Florida, United States, 3 Mechanical Materials and Aerospace Engineering, University of Central Florida, Orlando, Florida, United States, 5 Department of Molecular Biology and Microbiology, University of Central Florida, Orlando, Florida, United States, 4 Burnett School of Biomedical Sciences, University of Central Florida, Orlando, Florida, United States, 6 Institute of Biochemistry & Molecular Biology , Heinrich Heine University, Dusseldorf Germany
Show AbstractThe ever increasing demand for energy efficiency, environmental sustainability and health care (treatment and disease control) has resulted in the development of various functional materials in nanoscale dimensions. Nanoscale materials are making a mark in a gamut of applications including sensors, energy generation and storage, and biomedical applications. Specifically in biomedical applications the nanoscale materials engineered from metals, metal oxides and polymers have opened a new dimension for efficient drug delivery and treatment of diseases. Polymeric nanocomposites containing metals and metal oxides is making a slow and steady progress towards the application of these materials in treatment of diseases and minimizing the toxic effects of the nanoparticles.The current talk will focus on the biomedical applications of polymeric cerium oxide nanocomposites. Cerium oxide nanoparticles have shown tremendous potential in radical scavenging antioxidant properties. Recently CNPs have been demonstrated to protect biological tissues against; radiation induced damage, scavenging of superoxide anions, prevention of laser induced retinal damage, reduction of spinal injury in a tissue culture model, prevention of cardiovascular myopathy and other inflammatory diseases. The tailor made 3-5nm CNPs show predominant Ce3+ oxidation state and are unstable at alkaline pH. Nanocomposites of nanoceria with polyethylene glycol (PEG) and dextran increase the stability in neutral to alkaline medium and the effect of such biocompatible composites on the redox properties of nanoceria will be discussed. Polymeric composites of ceria such as dextran-nanoceria is stable in alkaline pH range and demonstrate unique tumor killing properties in addition to its antioxidant properties to normal cells. It will be shown how the PEG –CNP composites can tune the redox properties of nanoceria and result in accelerated regeneration of Ce3+ valence state. The effect of PEG concentration and molecular weight on the size, shape and properties of CNPs will be discussed. The biological activity was tested using a classical SOD mimic model (competition with ferricytochrome C for reduction by superoxide) and a catalase activity model (reaction with hydrogen peroxide). Initial results showed no decrease in activity of CNPs with increasing concentration of PEG.
12:15 PM - II13.10
Stretchable Carbon-based Nanocomposite Electrodes.
Denis McCarthy 1 , Sebastian Risse 1 , Remi Wache 1 , Guggi Kofod 1
1 Institute of Physics & Astronomy, University of Potsdam, Potsdam, Brandenburg, Germany
Show AbstractFlexible and stretchable conductors are currently a major focus for electronics research to allow new devices such as wearable electronics and flexible displays. Similar materials are required for dielectric elastomer actuators (DEAs), which are soft capacitor-like "artificial muscles" consist of an insulating dielectric elastomer material between two soft, stretchable electrodes. These devices can be used actively, where an applied voltage can result in actuation strains up to 100% and actuation stresses of 1 MPa, or passively for energy harvesting or sensing. DEA operate by the Maxwell's stress where an applied voltage results in an attractive force between the electrodes causing a perpendicular actuation.DEA require electrode materials which can reach the strains without losing conductivity and which do not hinder the actuator motion, so they must remain conductive up to high strains for multiple cycles and be softer than the dielectric elastomer itself over this range. This is a demanding requirement which has yet to be fulfilled satisfactorily. Carbon-based electrodes and carbon-based composites, with materials such as carbon nanotubes and graphite, are ideal candidates where weak interaction forces between individual nanotubes and graphene sheets, respectively allow conduction to be maintained at high strains without mechanical stiffening.Electrode materials based on these systems are investigated to achieve these goals. High conductivities (10^3 S/m) were achieved, but compatibility with the elastomer surface has been observed to be important for long term conductivity performance of the electrode materials. Over repeated cycling the electrode material can become detached from the dielectric elastomer surface leading to large decreases in conductivity and eventually destruction of the electrode. Elastomer composite films with carbon-based fillers ensure compatibility with the dielectric elastomer and still maintain the high performance necessary for DEA. Carbon nanotube films without a polymer matrix have previously been shown to be self-healing, allowing the DEA to continue operating after a local electrical breakdown. Functionalisation of the carbon nanotubes allows a boarder range of solvents to be used for electrode processing and the greater control over compatibility with the dielectric elastomer. The composite and nanotube electrodes will be compared for DEA and their suitability for other applications will be discussed.