11:30 AM - **KK3.6
Electrical Properties of High Volume Fraction Composites from Polymers Filled with Carbon Nanotubes and Graphene.
Jonathan Coleman 1 Show Abstract
1 Sch Physics, Trinity College Dublin, Dublin Ireland
We have used advances in nanotube dispersion and solubilisation to produce polymer-nanotube composites with high volume fractions (0.2
12:00 PM - KK3.7
Tailoring the Microstructure of Latex-based Ccarbon Nanotube Composites Using Poly(acrylic acid).
Yeon Seok Kim 1 , Jaime Grunlan 1 Show Abstract
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States
In an effort to enhance the microstructural tailorability of composites using a pH-responsive polymer, carbon nanotubes (CNTs) predispersed with poly(acrylic acid) (PAA) were added to a poly(vinyl acetate) polymer emulsion. Microscopic images reveal significant changes in the composite microstructure depending on the mixture’s pH. Segregated networks of CNTs are clearly observed at both high and low pH. Composites at a high pH exhibit the typical microstructure for a latex-based composite that has an obvious boundary between the polymer particles and suspended CNTs between them. At low pH (intrinsic pH of the PAA solution), polymer particles are better coalesced, creating softer boundaries. The affinity between CNTs and polymer particles is also increased at lower pH. These distinct microstructures lead to differences in electrical and mechanical properties of the dried composite films. The low pH composite has a higher percolation threshold due to greater disruption of the CNT network in the matrix. The storage moduli for both composites show remarkable changes, with the low pH composite (containing 7wt% CNT) increasing more than two orders of magnitude over the neat polymer films above the glass transition temperature.
12:15 PM - KK3.8
Direct Comparison of Epoxy Composites Containing Covalently and Noncovalently Functionalized Carbon Nanotubes.
Lei Liu 1 , Kang-Shyang Liao 2 , Andrew Stephenson 1 , David Bergbreiter 2 , Jaime Grunlan 1 Show Abstract
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 2 Chemistry, Texas A&M University, College Station, Texas, United States
Epoxy composites containing a physical mixture of multi-walled carbon nanotubes (MWNT) and polyethylenimine (PEI) were compared to composites containing MWNT with PEI molecules covalently attached their surfaces. PEI with two different molecular weights (10,000 g/mol and 600 g/mol) was used and the final functionalized tubes contained 6 wt% and 1.5 wt% PEI, respectively. For comparison, composites containing noncovalently functionalized MWNT had the same PEI-MWNT ratio. The composites containing noncovalently functionalized nanotubes show similar electrical conductivity to composites containing nanotubes without any PEI, while the composites with covalently functionalized nanotubes exhibit decreased electrical conductivity. This result is likely due to deteriorated nanotube exfoliation after PEI attachment and disruption of the conjugated chemistry along the nanotube surface. Mechanical properties of the composites were improved after the introduction of covalently functionalized nanotubes, which can be attributed to the improved nanotube/epoxy interaction. On the contrary, composites with noncovalently functionalized nanotubes showed decreased mechanical properties, even as compared to composites with only nanotubes (i.e., without PEI). Direct comparison of the contribution from covalently and noncovalently functionalized nanotubes in these composites is necessary for a better understanding of nanotube-polymer interaction and property tailoring in nanocomposites.
12:30 PM - KK3.9
Novel All Carbon-Based, UV-Curable Conductive Composites for Printed Microelectronics Applications.
Samali Datta 1 , Maung Htet 2 , Dean Webster 1 2 Show Abstract
1 Coatings and Polymeric Materials, North Dakota State University, Fargo, North Dakota, United States, 2 Center for Nanoscale Science and Engineering, North Dakota State University, Fargo, North Dakota, United States
Electrically conductive, UV-curable formulations were made with cycloaliphatic epoxy resins, different types of hyperbranched polyols and exfoliated graphite nanoplates. Exfoliated graphite was prepared by acid treatment of natural flake graphite followed by rapid thermal expansion. Graphite nanoplates were prepared either through sonication of expanded graphite or by ball milling. Characterization of the graphite nanoplates was done using scanning electron microscopy (SEM). The binder system was based on cycloaliphatic epoxy resin and hyperbranched polyols, plus a cationic photoinitiator, which can rapidly photopolymerize through cationic mechanism. Thus, this is a solventless system and is environmentally friendly. Electrical resistivity of the composite films was determined by a four-point probe method and the morphology of the composite films was revealed by electron microscopy. It was found that the electrical properties of the system depends both on the amount of conductive filler in the system as well as on the composition of the binder system. Binder formulations containing hyperbranched polyols showed lower resistivity i.e. lower percolation threshold compared to the binder without the hyperbranched polyol. Possible application areas of such systems are in printed microelectronics.
12:45 PM - KK3.10
Direct Imaging of Current Paths in Multi-walled Carbon Nanotube Polymer Nanocomposites Using Conducting-Tip AFM.
A. Trionfi 1 , D. Scymgeour 1 , J. P. Hsu 1 , M. Arlen 2 , D. Jacobs 2 , D. Wang 2 , L. Tan 2 Show Abstract
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , Air Force Research Lab, Wright-Patterson AFB, Ohio, United States
Carbon nanotube/ polymer composites have been commonly suggested as an alternative material in a multitude of electrical applications. Using conducting-tip atomic force microscopy (C-AFM), we clearly show that electrical transport in a multi-walled carbon nanotube/polymer nanocomposite is confined to the conducting network formed by the carbon nanotubes. Previous studies of similar systems were hindered by a polymer-rich skin layer that exists at the nanocomposite surfaces. We present an experimental technique using oxygen plasma etching to remove this polymer skin layer at the surface of carbon nanotube/polyimide nanocomposites. After this treatment, we can directly probe the microscopic transport characteristics of the nanocomposite using C-AFM. High-resolution C-AFM maps also suggest the presence of polymer wrapping around nanotubes. Local two probe conductivity measurements in which one electrode (the C-AFM tip) is contacting a single constituent conducting particle were performed to investigate potential damage to the nanotubes caused by the oxygen plasma. Finally, a comparison between C-AFM conducting area fraction vs. nanotube loading and the standard bulk conductivity vs. loading measurement is made. Suggestions of how the comparison relates microscopic electrical properties to macroscopic properties are discussed.This work was performed in part at the US Department of Energy, Center for Integrated Nanotechnologies, at Los Alamos and Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the U. S. Department of Energy under Contract No. DE-AC04-94AL85000.
KK4: Nanocomposite Membranes
Tuesday PM, December 02, 2008
Room 300 (Hynes)
2:45 PM - KK4.2
Permeation of Small Molecules through Membranes Containing Second Phase Particles.
Reiner Kirchheim 1 Show Abstract
1 Institut fuer Materialphysik, University of Goettingen, Goettingen Germany
3:00 PM - **KK4.3
Gas Transport Properties in Oriented Single-Walled Carbon Nanotube Membranes.
Eva Marand 1 , Sangil Kim 2 Show Abstract
1 Chemical Engineering, Virginia Tech, Blacksburg, Virginia, United States, 2 Biosciences & Biotechnology Division (BBTD), Lawrence Livermore National Laboratory, L-233, Livermore, California, United States
3:30 PM - KK4.4
Barrier Properties of Polyurethane/Clay Nanocomposites.
Jose Herrera-Alonso 1 , Eva Marand 1 , John Little 2 , Steven Cox 2 Show Abstract
1 Chemical Engineering, Virginia Tech, Blacksburg, Virginia, United States, 2 Civil Engineering, Virginia Tech, Blacksburg, Virginia, United States
3:45 PM - KK4.5
Nanocomposites based on Polyethylene and on Lamellar Nanofillers : Influence of the Clay Dispersion State and of the Polymer/Clay Interface on the Barrier Properties.
Eliane Espuche 1 , Emilie Picard 1 , Jean-Francois Gerard 2 Show Abstract
1 , Laboratoire des Matériaux Polymères et des Biomatériaux/IMP UMR CNRS 5223, Université de Lyon, Université Lyon 1, Villeurbanne France, 2 , Laboratoire des Matériaux Macromoléculaires/ IMP UMR CNRS 5223, Villeurbanne France
4:00 PM - KK4: Membranes
4:30 PM - **KK4.6
Improved Gas Barrier from Confined Crystallization of PEO in Nanolayered Films.
Anne Hiltner 1 , Haopeng Wang 1 , Jong Keum 1 , Chuanya Lai 1 , Benny Freeman 2 , Eric Baer 1 Show Abstract
1 Department of Macromolecular Science and Enginneering, Case Western Reserve University, Cleveland, Ohio, United States, 2 Department of Chemical Engineering, University of Texas at Austin, Austin, Texas, United States
When polyethylene oxide (PEO) is confined in nanolayer assemblies, it crystallizes as single lamellae, resembling very large, single crystals. The impermeable crystals impart two orders of magnitude reduction in PEO gas permeability. The nanolayer polymer assembly, consisting of thousands of alternating PEO and ethylene-co-acrylic acid (EAA) nanolayers, was achieved by the innovative layer-multiplying coextrusion or “forced assembly”. Direct observation by atomic force microscopy, complemented with wide and small angle X-ray scattering, revealed that when the PEO layer thickness was in the micron scale (1-4μm), the PEO lamellar crystal orientation was isotropic. As a result, the gas barrier of PEO layer matched the non-layered PEO control film. The layer confinement effect was progressively shown upon decreasing the PEO layer thickness to around 100nm. The long PEO lamellar crystals were observed to be stacked between EAA layer confinements and were aligned parallel to the layer direction. When the thickness confinement occurred on the 20 nm size scale, the PEO layers crystallize as single, high aspect ratio lamellae that resemble large, impermeable single crystals. The unique PEO crystalline structure imparted two orders of magnitude reduction in oxygen and carbon dioxide permeability. This was attributed to the dramatic increase in the gas diffusion tortuosity in the PEO layer as reflected by the low gas diffusion coefficient in the nanolayered films. The conventional Cussler model for a polymer composite showed good agreement with the lamellar crystal dimension. Interestingly, aligned PEO lamellar crystals effectively reinforced the nanolayered film by showing two fold increase in tensile modulus. Compared with the nano-confinement achieved by self-assembly of block copolymers, the facile “forced assembly” process offers the potential of making high barrier films from conventional polymeric materials.
5:00 PM - **KK4.7
Gas Transport in Poly(dimethylsiloxane)-SiOx Composite Films: Effects of Filler Size Variation from Micro- to Nanoscale.
Nancy Lape 1 , Lupita Bermudez 1 , Georgi Dinolov 1 , Jonathan Hubbard 1 , Michael Mayeda 1 , Daniel O'Neil 1 Show Abstract
1 Engineering, Harvey Mudd College, Claremont, California, United States
Recent research has shown that the addition of impermeable inorganic nanoparticles to ultra-high free volume glassy polymers enhances gas permeability in these membranes with no detrimental effects on membrane selectivity. This trend, attributed to increased free volume, defies the expected behavior described by the Maxwell relation: decreasing permeability upon the addition of impermeable spheres. We are investigating both the filler size at which deviation from the Maxwell behavior appears (nano- to microscale) and the range of polymers for which this anomalous behavior occurs (rubbery polymers and traditional glassy polymers to ultra-high free volume glassy polymers). In this work, we examine the permeability of He, N2, and CO2 through pure and SiOx-composite Sylgard 184 Elastomer poly(dimethylsiloxane) (PDMS) films. All PDMS membranes were prepared via cold solution casting; SiOx particles of size ranging from 10 nm to 10 microns were added at approximately 10 wt % to create the composite films. Composite films will be characterized using TEM, positron annihilation spectroscopy (PALS), and density measurements. Additionally, molecular modeling simulations using Materials Studio 4.2 are being carried out to examine interfacial interactions and free volume distribution at a molecular level.
5:30 PM - KK4.8
Evaluation of Electrospun Biopolymer Nanocomposite Filtration Membranes.
Jessica Schiffman 1 , Caroline Schauer 1 Show Abstract
1 Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States
After cellulose, chitin is the most abundant organic material (produced by biosynthesis). The nitrogen-rich polysaccharide is a high-molecular weight linear polymer composed of N-acetyl-D-glucosamine (N-acetyl-2-amino-2deoxy-D-glucopryanose) units linked by β-D (1→4) bonds. When chitin is N-deacetylated, the polyelectrolyte chitosan, with a –NH2 functionality on the C-2 of the D-glucosamine repeat unit, is obtained. These renewable biopolymers are abundant waste products of the sea food industry as they are primarily derived from the shells of crustaceans. The inherent properties of chitin and chitosan such antibacterial activity, biodegradability, biocompatibility, and chelation capabilities make them ideal for use in a wide variety of membrane applications such as, medical sutures, alternatives to agricultural pesticides, functional textiles, such as protective clothing, coatings, air and water filters, and sensing devices. We have electrospun these two materials into nanofibrous polymer and polymer-composite membranes. The membranes are composed of randomly oriented cylindrical nanofibers and have large surface area-to-volume ratios. The mechanical properties of these membranes were evaluated utilizing a uniaxial tensile tester. For many applications, the creation of composite membranes would yield more desirable properties; therefore, organic molecules (glutaraldehyde), clays (diatomaceous earth), and nanoparticles (carbon black) were incorporated into the chitosan membranes. The creation of composite mats was confirmed using Fourier transform infrared spectroscopy (FTIR), solubility testing, and a Zeiss Supra 50/VP field emission scanning electron microscopy (FESEM). We intend to tailor these membranes for water purification applications. Hence, flux capacity and chelation capabilities were tested and the resulting microstructure and presence of metal ions analyzed with a FESEM combined with energy dispersive spectroscopy (EDS). Finally, the crystalline domains of the chitin and chitosan membranes were confirmed using X-ray diffraction (XRD) since filtration capability is a function of amorphous and crystalline domains. As a result of their intrinsic properties, as well as nanoscale fibers and pores, chitin and chitosan composite membranes offer unique properties that can be tailored to suit a variety of applications.
5:45 PM - KK4.9
Polymer Zeolite Nanocomposites for Gas Separation Applications.
Sudeep Maheshwari 1 , Jungkyu Choi 1 , Frank Bates 1 , Michael Tsapatsis 1 Show Abstract
1 Department of Chemical Engineering and Material Science, University of Minnesota, Minneapolis, Minnesota, United States
Polymer-zeolite mixed matrix materials are promising as future membrane material with high separation capability due to molecular sieving capability of zeolites. However, they suffer from the drawback of low productivity due to increase in the membrane thickness by incorporation of micron sized zeolites. Nanocomposite materials consisting of thin zeolite layers (~2 nm) can overcome this problem and provide a membrane material with high selectivity and high productivity.
In this talk, the fabrication and properties of nanocomposites containing 2.5 nm exfoliated MCM-22 layers will be presented and compared with the composite membranes containing ~50-100 nm thick MCM-22 crystals. Composites with MCM-22 crystals were prepared by depositing alternate layers of a matrix phase and oriented MCM-22 crystals and, for a certain appropriately selected matrix; they exhibit high hydrogen/nitrogen and carbon dioxide/nitrogen selectivities. Polymer nanocomposites were prepared by swelling MCM-22(P) layers by surfactant intercalation and employing melt-processing techniques to separate the layers. A major challenge during nanocomposite processing, layered structure preservation, was successfully addressed as revealed by Small Angle X-Ray Scattering and Transmission Electron Miocroscopy. The potential use of the nanocomposite films as easily processable, high-flux, high-selectivity gas separation membranes will be discussed.
KK5: Poster Session: Polymer Nanocomposite Transport Properties
Wednesday AM, December 03, 2008
Exhibition Hall D (Hynes)
9:00 PM - KK5.1
Controllable Nanocomposite Interface Microstructure via Polymer Crystallization-induced Wrapping of Carbon Nanotubes.
Gaurav Mago 1 , Dilhan Kalyon 2 , Frank Fisher 1 Show Abstract
1 Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, New Jersey, United States, 2 Department of Chemical Engineering and Materials Science, Stevens Institute of Technology, Hoboken, New Jersey, United States
Carbon nanotubes (CNTs) have attracted notable interest due to their excellent mechanical, electrical, and physical properties. The properties of CNT-polymer nanocomposites significantly depend on the level of dispersion of CNTs in the matrix. The physical properties and dispersion of CNTs in a polymer can be significantly affected by the attachment of organic, inorganic and biological entities to the CNT surface. For example, covalent chemical functionalization and non-covalent wrapping techniques are being used to improve the CNTs dispersion. In this study, we utilized a polymer crystallization (non-covalent functionalization) technique to functionalize the surface of multi-walled carbon nanotubes (MWNTs) and carbon nanofibers (CNFs). A solution crystallization technique was used to coat MWNTs and CNFs with various semi-crystalline polymers, such as Nylon-11, Nylon-6 and poly (butylene terephthalate) (PBT). The samples obtained after crystallization were analyzed under scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that the crystals are formed with a periodicity, and resembled the typical shish-kebab structure found in semicrystalline polymers due to deformation-induced crystallization. Such structures with a period patterning of polymer crystals on the surface of CNTs are referred to as nano-hybrid shish-kebabs (NHSKs). Here the nanoparticles act as nucleating agents in the process, facilitating the growth of the polymer crystals grow on its surface. The crystal size depends on the polymer solution concentration, with higher polymer solution concentration yielding large crystals (spherulites) on the surface of the nanofillers. This work illustrates how nanocomposite processing can be used to generate polymer nanocomposites with unique and controllable interface microstructure to tune the multifunctional and transport properties of these materials.
9:00 PM - KK5.10
Surface Segregation of Nanoparticles in Polymer Nanocomposite Thin Films Induced by Supercritical Carbon Dioxide.
Mitsunori Asada 1 2 , Miriam Rafailovich 1 , Tadanori Koga 1 Show Abstract
1 Dept of Mat. Sci. & Eng., Stony Brook University, Stony Brook, New York, United States, 2 Kurashiki Research Laboratories, Kuraray Co., Ltd., Kurashiki, Okayama, Japan
The surface segregation (i.e., preferential segregation of one component to the surface in multicomponent systems) is common to all materials classes and is typically driven by a reduction in surface energy which more than compensates for the entropy loss and/or energy gain associated with the demixing of the components. However, the conventional surface segregation requires high temperatures, typically close to 200°C, and long annealing time, in order to ensure enough polymer mobility. This process consumes energy and can cause substantial degradation of polymers. Here we show a new “green”, and “polymer-friendly” means to preferentially migrate inorganic nanoparticles into the surface regions where large degree of molecular scale porosity is produced by using supercritical carbon dioxide process. In addition, the scCO2 process may be a general phenomenon regardless of a choice of nanoparticles and polymers. The detailed structure analysis using atomic force microscopy and X-ray reflectivity measurements will be presented.
9:00 PM - KK5.11
Effect of the Polarity of Silver Nanoparticles Induced by Ionic Liquids on Separation of Olefin/Paraffin Mixtures.
Sang Wook Kang 1 , Kookheon Char 1 , Jong Hak Kim 2 , Yong Soo Kang 3 Show Abstract
1 , Seoul National University, Seoul Korea (the Republic of), 2 , Yonsei University, Seoul Korea (the Republic of), 3 , Hanyang University, Seoul Korea (the Republic of)
Previous study showed that the polarized silver nanopartices by p-benzoquinone and ionic liquid could be olefin carrier for separation of propylene/propane mixtures. In this paper we reported the effect of an ionic liquid on the formation of a partial positive charge on the surface of silver nanoparticle and its subsequent effect on facilitated olefin transport. Three different ionic liquids of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM+BF4-), 1-butyl-3-methylimidazolium triflate (BMIM+Tf-), and 1-butyl-3-methylimidazolium nitrate (BMIM+NO3-) were employed to control the positive charge density of the surface of silver nanoparticles. The positive charge density of the silver nanoparticles, as characterized by the binding energy of the silver atom, was in the following order: BMIM+BF4-/Ag >> BMIM+Tf-/Ag > BMIM+NO3-/Ag. This order was consistent with the tendency of ionic liquids to form free ions, confirmed by FT-Raman spectroscopy. The best separation performance for the propylene/propane mixtures was a mixed gas selectivity of 17 and a permeance of 7 GPU through a composite membrane consisting of BMIM+BF4-/Ag. A better separation performance for olefin/paraffin mixtures was observed with a higher positive charge density of the silver nanoparticles. It was therefore concluded that facilitated olefin transport was a direct consequence of the surface positive charge of the silver nanoparticles induced by ionic liquids.
9:00 PM - KK5.12
Novel Surface Modification to Control Microstructure Development in Nanocomposites: Application to Xerographic Chemical Toners.
Angelos Kyrlidis 1 , Eilidh Bedford 1 , David Reynolds 1 Show Abstract
1 Performance Products, Cabot Corporation, Billerica, Massachusetts, United States
The static and dynamic properties of nanocomposites are governed by the dispersion and organization of the nanoparticle in the surrounding matrix. We have developed novel surface modification technology to enable the tailoring of particle surface chemistry to match the properties of the surrounding matrix. In this approach surface energy or solubility parameter calculations are used to assist design of specific nanoparticle surface coating and microstructural image analysis is used to quantify the evolution of microstructures so obtained. In this paper we illustrate the approach using the example of Chemical Toners. These are complex nanocomposites formed from polymer resin and pigment such as carbon black. Chemical toners enable very small uniform toner particles to be created, as needed in high speed printing. The static and dynamic properties of this nanocomposite influence some of the key performance attributes of the toner, including the printed image density and the toner's electrical characteristics. In these new processes, carbon black and the other pigments are typically first dispersed into a liquid matrix (aqueous or organic solvent or monomer) and are then incorporated into the toner particle either by chemical assembly processes, such as emulsion aggregation, or direct polymerization. Throughout the various process steps the carbon black needs to remain dispersed in the matrix to optimize the performance. Even after the toner is produced, the carbon black dispersion needs to be controlled to ensure the proper toner performance characteristics. In this paper we describe approaches to specifically design nanocomposite systems for this dynamic application.
9:00 PM - KK5.13
Fiber Direction Effect on Thermal Conductivity of PEEK Composites.
Sung-Ryong Kim 1 , Seung-won Yim 1 , Dong-Bum Seo 1 , Won-Ho Kim 1 , Eun-Sun Chnung 1 , Joung-Man Park 2 Show Abstract
1 , Chungju National University, Chungju Korea (the Republic of), 2 , Gyeongsang National University, Jinju Korea (the Republic of)
We have studied thermal conductivity of conductive materials filled polyetheretherketone(PEEK) composites with various direction, processing method, fiber aspect and polymer grain size. Thermal conductivity of composites was increased to 6.78 W/m-K for hybrid filler of (CFDKD+SiC) 7:1 ratio system, whereas that of hybrid filler 1:1 filler ratio was 4.8 W/m-K at 40 vol%.Fiber aligned composites parallel to incident laser beam gave a higher thermal conductivity than those of perpendicular to incident beam. The electrical resistance of PEEK/CF (40 vol. %) at parallel direction was lower than that of perpendicular direction. However, the electrical resistance of CF/SiC (30 vol. %/10 vol. %) hybrid filler composites were 2.9 × 10^6 Ω-cm and 1.5 × 10^7 Ω-cm for perpendicular and parallel fiber direction, respectively. It is speculated that the non-conducting SiC particles may inhibit easy electron conduction at parallel direction.
9:00 PM - KK5.14
Thermo- and Chemo-electrical Behavior of Carbon Nanotube Filled Co-continuous Conductive Polymer Nanocomposites (CPC) to Develop Amperometric Sensors.
Jianbo Lu 1 , Mickaël Castro 1 , Bijandra Kumar 1 , Jean-François Feller 1 Show Abstract
1 Laboratory of Materials Engineering of Brittany , European University of Brittany , Lorient France
The development of electrically Conductive Polymer nanoComposites (CPC) has attracted a lot of attention in the last decade due to their variety of application like self regulated heating or vapor sensing. CPC heterogeneous by nature, combine the insulting character of the polymer matrix and the high level of electrical conductivity of carbon nanofillers. At suitable composition CPC can be sensitive to their environment, essentially temperature, vapor, and strain. Their response is characterized by a sharp increase in resistivity upon exposure to heat or organic vapors, leading respectively to the so called positive temperature coefficient effect (PTC) or positive vapor coefficient effect (PVC).Two different kinds of co-continuous CPC, i.e., PP/PCL-CNT and PA12/PCL-CNT were prepared by melt mixing process. Their thermo- and chemo-electrical properties have been investigated independently to determine possible interactions between them. Results show that PP/PCL-CNT CPC is more suitable for temperature sensor than for vapor sensor. In fact, PP phase prevents the diffusion of vapor molecules within PCL conductive phase. In contrast, PA12/PCL-CNT exhibits good vapor sensing capability. It is assumed that PP external matrix provides the CPC with higher barrier effects than PA12.
9:00 PM - KK5.15
The Influence of Particle Size and Surface Chemistry on the Morphology and Properties of Silica-Nafion® Nanocomposite Membranes.
Beatrice Muriithi 1 , Douglas Loy 1 Show Abstract
1 Materials Science and Engineering, University of Arizona, Tucson, Arizona, United States
High temperature (100-200C) operation of fuel cells alleviates the CO poisoning of the electrocatalysts and thermal-management problems associated with current proton exchange membrane (PEM) fuel cell technology. Perfluorosulfonic acid-based membranes have high proton conductivity at low temperatures (< 80C), but at higher temperatures conductivity and fuel cell performance rapidly dwindle. Incorporation of inorganic fillers into the PEM has been shown to increase its working temperature range and improve its mechanical properties. These include composite materials prepared by sol-gel methods from Nafion® and tetralkoxysilanes. However, these studies did not examine the effects of particle size and the surface chemistry of the filler (silica) on processing and composite properties. In this work, we prepared and characterized a family of composites of Nafion® with monodisperse silica spheres with varied particle size and surface chemistry. Silica particles with controlled sizes (20-200 nm diameter) were prepared from tetraethoxysilane by the Stober method. Modification of silica particles with silane coupling agents afforded hydrophobic mercaptopropylsilane- and hydrophilic sulfonic acid modified particles in addition to the original hydrophilic silica. Considerable effort was directed at developing procedures for homogeneously dispersing the particles in Nafion® to make 80-100µm thick nanocomposite membranes. Atomic force microscopy and scanning electron microscopy were used to determine the distribution of the silica particles in the membranes and how it is affected by their size and surface chemistry. The results of our morphological studies and the influence of the size and chemical modification of the well-defined silica particles on the properties of the composite membranes, such as water uptake and proton conductivity at high temperatures, will be presented.
9:00 PM - KK5.16
Water Vapor Transport Properties of Sulfonated Block Copolymers Neutralized with Inorganic Cations.
Eugene Napadensky 1 , James Sloan 1 Show Abstract
1 Multifunctional Materials Brunch, U. S. Army Research Laboratory, Aberdeen, Maryland, United States
Polystyrene-block-polyisobutylene–block-polystyrene (SIBS) block copolymers are materials that are known to have excellent barrier properties to hazardous vapors and liquids. However, when these block copolymers are sulfonated, water and small polar molecules are allowed to be transported through the polymer film. In some instances, this could be beneficial and allow the film to be used as a separation membrane.In this paper, we compare the vapor transport properties of polymer membranes that have been neutralized with +1 (Na, K, Cs) and +2 (Mg, Ca, Ba) cations to form irreversible crosslinks. Results show that water permeation is slightly reduced, however the permeation of toxins is significantly reduced. The elastomeric character of the tri-block copolymer, coupled with its selectively–permeable characteristics, gives rise to a polymeric membrane with potential for use as breathable membranes.
9:00 PM - KK5.18
Direct-Write Fabrication of Polymer Nanocomposite Fibers.
Scott Berry 1 , Santosh Pabba 2 , Scott Cambron 3 , Robert Cohn 2 , Robert Keynton 1 2 3 Show Abstract
1 Department of Mechanical Engineering, University of Louisville, Louisville, Kentucky, United States, 2 ElectroOptics Research Institute and Nanotechnology Center, University of Louisville, Louisville, Kentucky, United States, 3 Department of Bioengineering, University of Louisville, Louisville, Kentucky, United States
The unique properties of carbon-nanotube (CNT)-doped polymers have generated several promising applications including gas sensors, high-strength/light-weight materials, and electromagnetic interference shielding. The ability to process CNT-doped materials into complex architectures may enable further advancement of these devices. We have developed a direct-write technique for processing CNT-doped poly(methyl methacrylate) (PMMA) into 3D arrays of precisely-positioned fibers with micro- and sub-microscale diameters. In this method, a programmable micromanipulator-controlled syringe was loaded with solvated CNT/PMMA and utilized to draw an array of freely-suspended solution filaments on a substrate in a “connect-the-dots” fashion. As the filaments are drawn, they are thinned by surface tension-driven necking as they dry and form solid fibers. The degree of thinning can be controlled by varying the viscosity of the solution, which acts to resist the necking while the volatile solvent evaporates and solidification occurs. Multiple fibers were drawn to investigate the effects of several variables on fiber diameter and process yield. These variables included fiber length (4, 8, and 18 mm), fiber drawing velocity (5 and 20 mm/s), polymer concentration in solution (22 and 24% by wt.), and CNT concentration in solution (0, 0.5, 1, and 1.5% by wt.), with the latter two of these variables strongly influencing solution viscosity. Measurement of the fibers via scanning electron microscopy (SEM) revealed several trends: Fiber diameter was not influenced by CNT concentration, but increased with increasing PMMA concentration (P<0.001), increasing drawing rate (P<0.01), and decreasing fiber length (P<0.001), with fiber diameter ranging from 538 nm to >100 μm. Furthermore, fiber yield exceeded 75% for all tested solutions except for the lowest viscosity CNT-doped solution (24% PMMA/0.5% CNT, η=50.1 Pa*s), which experienced capillary breakup prior to solidification.The conductivities of direct-write PMMA/CNT fibers ranged from <10-7 to 0.15 S/m, with shorter fibers having higher conductivities (P<0.005). Also, fibers drawn from solutions with 1.0% CNTs had higher conductivities that those drawn from solutions with 0.5% or 1.5% CNTs (P<0.01). This nonlinear trend was further investigated by cleaving fibers in liquid N2 and imaging their cross-sections with an SEM. This analysis illustrated that the CNTs, which were functionalized to remain dispersed in the solvent, tended to randomly aggregate within the polymer-fiber matrix, particularly for fibers drawn from solutions containing 1.5% CNTs. In conclusion, CNT/PMMA fibers were successfully drawn with the direct-write technique and CNT doping had no significant influence on fiber diameter or yield compared with fibers drawn from PMMA homopolymer. However, the CNTs were found to strongly aggregate when drawn from solutions loaded at high concentrations (1.5%), thereby hindering electrical transport.
9:00 PM - KK5.19
A New Class of Biodegradable Flame Retardant Nanocomposites.
Seongchan Pack 1 , Ezra Bobo 3 , Alan Deroine 6 , Kimberly Leonard 4 , Joshua Rosenbaum 5 , Takashi Kashiwagi 2 , Miriam Rafailovich 1 Show Abstract
1 , Stony Brook University, Stony Brook, New York, United States, 3 , University of Pennsylvania, Philadelphia , Pennsylvania, United States, 6 , School of Polytech, Nantes France, 4 , Dix Hills High School, Dix Hills, New York, United States, 5 , Yeshiva of Flatbush HS, Brooklyn, New York, United States, 2 , Materials Fire Research Group, NIST,, Gaithersburg, Maryland, United States
There is interest in making a thermoplastic starch (TPS) composite since the starch is completely biodegradable. However, since starch is brittle is must be mixed with other polymers. Hence a bio-compatiblizer is needed in order to increase a degree of compatibilization, which leads to improved material properties. We have developed a nanotube based compatiblizer which can also be imprgnated wiht non-halogenated flame retadant formulations. Addition of as little as 5% increased the Young's Modulus and impact toughness siginificanlty. Flame tests also indicated that the compounds would pass with a UL-94V0 rating. The procecure for producing these compounds can be generalized and shows how one can produce new bio degradable, yet flame retardant compounds.
9:00 PM - KK5.2
Electrospinning and Characterization of the Stable and ``Metastable" Self-Assembled Poly(ethylene oxide)-Urea Complexes.
Yang Liu 1 , Helene Antaya 1 , Christian Pellerin 1 Show Abstract
1 Department of Chemistry, University of Montreal, Montreal, Quebec, Canada
9:00 PM - KK5.20
Effect of Transformation to Nanotube-like Clays from Organoclays on Self-extinguishing Polymer Blends.
Seongchan Pack 1 , Takashi Kashiwagi 2 , Miriam Rafailovich 1 Show Abstract
1 , Stony Brook University, Stony Brook, New York, United States, 2 , Materials Fire Research Group, NIST,, Gaithersburg, Maryland, United States
We have showed that self-extinguishing polymer blends is attributed to not only of intercalation and/or exfoliation of modified organoclays but also good dispersion traditional halogen FR agents. It has been proven that small amount of the clays enhance in degree of dispersion of the FR compound due to strong interactions between the clays and the FR agents during melting mixing. This fact resulted in high reduction of HRR and MLR in the PS/PMMA polymer blend with the clays due to a formation of firm solid residues, which consisted of a lot of nanotubes-like clay platelets, onto polymer blends during decomposing and burning. In particular, only addition of the 5 % and 10% clays eliminated Peak of HRR in the cone calormetry test. It was believed that disappearance of the peak was affected by the relationship between combustion efficiency and amount of char yield. In additional to the relationship, a good quality of char formation could be a factor to determine the flammability during combustion. The X-ray scattering data proved that the clays, highly intercalated and partly exfoliated in polymer blends, could be retained at high temperatures and then produce enough amount of char yield to penetrate the heat flux into the polymer matrix. Furthermore, the clay platelet could be transformed into nanotubes-like rods during combustion, which led to increase of the thermal diffusivity in polymer blends. This is a good evidence to explain the synergy of combination FR particles and the clays, where the clay not only could act as a heat sinker but also a good heat transfer. However, the fact that the organically the fact that modified clays yield char formation could not applied to polymer blends where at least one highly charring polymer existed. We discovered the fact in PC/SAN24 blend in which PC was a good char former. Even if the clay was intercalated and partly exfoliated in the blend with the bromine-based compounds, the clay could not produce enough amount of char yield because it might disturb chain scission of the PC polymer. Nevertheless, combination the modified organoclays with the FR agents in non-charring thermalplastic polymer blends could be a new method of improving flammability and mechanical property. Moreover, this method could reduce amount of traditional FR agents at industry markets, which also meant that self-extinguishing polymers could be accomplished in some FR formula.
9:00 PM - KK5.22
Functionalized Clay Vinyl Ester Nanocomposites.
Dharmaraj Raghavan 1 Show Abstract
1 Department of Chemistry, Howard University , Washington, District of Columbia, United States
In recent years, the area of nanoclay filled polymer nanocomposites has received considerable attention with the expectation that nanoclay filled polymers can be useful as matrix material for composite applications. To achieve significant improvement in the properties of polymer nanocomposite, dispersion of clay platelets at the nanometer scale in the polymer matrix is desired. The primary objective of this study is to examine the role of reactive and nonreactive organic modifiers in exfoliation and dispersion of clay platelets in vinyl ester matrix and evaluate the susceptibility of nanocomposites to alkali medium. Medium chain length reactive onium salt (undecenyl amine hydrochloride) and medium chain length nonreactive onium salt (undecyl amine chloride) were synthesized and characterized by NMR and MALDI techniques. When the clay was ion-exchanged with a mixture of reactive and non-reactive onium salts an aggregated vinyl ester resin polymer nanocomposite was formulated. Addition of a co-monomer styrene and use of high intensity ultrasonic mixing produces a partially exfoliated vinyl ester nanocomposite The extent of clay platelet separation and aggregation were found to depend on composition of clay and processing conditions. We also investigated the alkali degradation of clay filled and unfilled polyester film. Tapping mode AFM was used to examine the microstructural changes of vinyl ester film and mass loss analysis was used to follow physical changes of vinyl ester film as a function of degradation time and temperature. The addition of nanoclay to vinyl ester resin reduces the susceptibility of polyester film to alkali medium as evidenced by mass loss data. Funding Agency : AFOSR
9:00 PM - KK5.3
Dielectric and Thermal Measurements on Polystyrene Coated SBA-15 Mesoporous Silica.
Joseph Lomax 1 , John Fontanella 2 , Charles Edmondson 2 Show Abstract
1 Chemistry, U.S. Naval Academy, Annapolis, Maryland, United States, 2 Physics, U.S. Naval Academy, Annapolis, Maryland, United States
Mesoporous silica, SBA-15, was be made by decomposing silica onto the non-ionic surfactant Pluronic 123. Calcining removes the surfactant and creates a somewhat spherical nanoparticle which is about 10 nm across, with a 7 nm mesopore in the center which is accessed by 2 nm complementary holes. The thickness of the silica shell is determined by the ratio of the tetraethylorthosilicate (TEOS) to triblock polymer and can be between 45 and 75 (R=45 to 75). SBA-15 (with a range of R values) was impregnated with an 80% styrene and a 20% divinylbenzene solution and then polymerized. The cross-linked polystyrene coated the SBA-15 to a thickness in the range of 2-4 nm. This system allows for materials with very thin polystyrene that has three environments - outer shell, inner shell and pores. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) suggest subtle differences in environment for the polystyrene on the SBA-15. As many as three glass transition temperatures are observed in DSC at temperatures consistent with thin layer polystyrene (300-320 K), and the decomposition of the polystyrene upon heating occurs in at least two overlapping steps in the TGA. Variable temperature (120 – 350 K) and variable frequency (10 – 105 Hz) dielectric measurements have been also been carried out. All results are discussed in the light of what is known about nano-confined polystyrene. Much of the recent work has been reviewed by M. Alcoutlabi and G. B. McKenna (J. Phys: Condens. Mattter 17 (2005) R461-R524). One model that is frequently used to describe the first- and second-order transitions of polymers in confined geometries attributes the physical properties to three, distinct layers (bulk, dead and liquid-like). As the thickness of the layer decreases, the bulk layer decreases and the thermal and dielectric properties change. The extent to which the present data can be explained by this model and others is discussed in the present work.
9:00 PM - KK5.4
Influence of Clay on Electrical and Mechanical Behavior of Carbon Black Filled Epoxy.
Krishna Etika 1 , Lance Hess 1 , Jaime Grunlan 1 Show Abstract
1 Department of Mechanical Engineering, Texas A&M University, College Station, Texas, United States
In order to investigate the efficiency of clay in dispersing carbon black and its influence on enhancing electrical and mechanical properties, carbon black – epoxy nanocomposites were prepared with various concentrations of carbon black and clay. Epoxy-carbon black composites have better mechanical and electrical properties as compared to neat epoxy. Electrical percolation of these composites was observed at 4 wt% carbon black. Addition of 0.1 wt clay lowers the percolation threshold to 2.5 wt% of carbon black. This lowered percolation threshold is likely the result of a positive interaction between these two types of particles, something akin to clay acting as a rigid surfactant. Composites with a clay-carbon black ratio around 1 revealed poor electrical properties, but superior mechanical properties. This may be due to the better dispersion of carbon black at elevated concentrations of clay. Composites with clay to carbon black ratio greater than 1 revealed simultaneously better electrical and mechanical properties. The observance of a critical ratio in enhancing electrical and mechanical properties signifies a tradeoff for harnessing the synergistic effects of clay on carbon black filled polymer composites. Conductive epoxy composites with a low percolation threshold could be used as an EMI shielding material, while improved mechanical behavior could be useful for structural applications.
9:00 PM - KK5.5
Electrospun Fibers of Poly(ethylene terephthalate) with Carbon Nanotubes.
Huipeng Chen 1 , Zhen Liu 1 , Lei Yu 1 , Peggy Cebe 1 Show Abstract
1 Physics and Astronomy, Tufts University, Medford, Massachusetts, United States
To improve the electrical and thermal properties of poly(ethylene terephthalate), PET, nanocomposite materials have been prepared with multi-walled carbon nanotubes (MWCNT), using high voltage electrospinning. Solutions were prepared in hexafluoro-2-propanol, with MWCNT to PET ratios of 0, 0.1, 0.5, 1.0, and 2.0 wt.%. After sonication, solutions containing 10% (w/v) PET were electrospun at 15kV using a 6cm working distance between electrodes. Using scanning electron microscopy, diameter of electrospun fibers was found to range from 200-300nm. Fourier transform infrared spectroscopy showed that the MWCNTs did not alter the chain conformation of the amorphous, as-spun fibers. Annealing at 130C was used to cold-crystallize the spun fibers. Presence of MWCNTs was found to induce more trans conformation into the amorphous portions of crystalline PET. Using temperature modulated differential scanning calorimetry, the specific reversing heat capacity of crystalline fibers was investigated. MWCNTs caused mobility restriction within the PET, leading to reduction in the heat capacity increment at the glass transition. Dielectric relaxation properties of electrospun fiber mats have also been investigated as a function of frequency (10Hz-1MHz) and temperature (-50C to 150C) to elucidate the glass transition relaxation process. (Research supported by the National Science Foundation, Division of Materials Research, Polymers Program, through and DMR-0602473 and DMR-0704056.)
9:00 PM - KK5.6
Microstructure of Adsorbable Polymer Suspension and Its Flow Properties.
So Youn Kim 1 , Charles Zukoski 1 Show Abstract
1 Chemical and biomolecular engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
The microstructural stability and phase behavior of colloidal-polymer mixtures are explored. The degree of dispersion plays an important role in the transport behavior of the polymer nanocomposite. When suspended in a solvent and non adsorbing polymer is added, particles experience a net attraction. This depletion attraction leads to liquid/liquid phase separation or gelation depending on the polymer to particle size rations and the polymer concentration. In a polymer melt where the polymer adsorbs to the particle surface, the particles are again stable and experience essentially hard sphere repulsions. Here we study the effect of adding adsorbing polymer to dilute suspensions of particles when the polymer adsorbs to the particle surface. Our interest is to explore how adsorption impacts the depletion forces and how these forces change as polymer concentration increases towards that of the polymer melt. We study these phenomena by measuring the second virial coefficient of the particles in suspension. In the present study, we focus on a tertiary system composed of 44nm diameter silica particles, poly(ethylene glycol) (PEG) and ethanol and investigate the second virial coefficient from low polymer concentration up to polymer melt. In addition, we vary the polymer molecular weight. In our studies we discuss how adsorption of the polymer changes the magnitude of the depletion interaction and thus the phase behavior of the suspensions.
9:00 PM - KK5.7
Covalently Bonded Polyurethane Gold Nanoparticle Composite Films of High Conductivity.
Muhammad Iqbal 1 , Stephan Eichhorn 1 Show Abstract
1 Chemistry and Biochemistry, University of Windsor , Windsor, Ontario, Canada
Dodecyl amine stabilized gold nanoparticles were synthesized in high yields using a single phase approach.1 Exchange reactions with 1-mercapto-11-undecanol produced gold nanoparticles that contain different mole ratios of dodecyl amine to 1-mercapto-11-undecanol as determined by Energy Dispersive X-ray analysis. Their size is 3.1 ± 0.6 nm and shape was spherical based on Transmission Electron Microscopy (TEM) analysis and their purity was confirmed by thermal analysis and 1H-NMR. Gold nanoparticles protected exclusively by 1-mercapto-11-undecanol as well as mixtures of dodecyl amine and 1-mercapto-11-undecanol were incorporated into polyurethane networks by reacting them with commercial polyisocyanates. Conductive thin films (lowest resistivity of 10-5 Ohm-m (Ω-m)) were obtained after heat treatment due to a spatially confined coagulation of the metal cores. The degree of coagulation can be varied by changing the compositions of the organic protective coating of the nanoparticles and the overall composition of the polymer composite. The morphology of the films and nanoparticle distributions were studied by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Mechanical properties were determined by Dynamic Mechanical Analysis (DMA). Conductive polyurethanes nanocomposites may have applications as conductive adhesives. 1. N. R. Jana and X. Peng, J. Am. Chem. Soc., 125, 14280, (2003).
9:00 PM - KK5.8
Influence of Polymer Modulus on the Percolation Threshold of Latex-Based Composites.
Yeon Seok Kim 1 , Jaime Grunlan 1 Show Abstract
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States
Monodispersed copolymer emulsions with different glass transition temperatures were synthesized to investigate the effect of room temperature polymer matrix modulus on the electrical conductivity of carbon black (CB) filled segregated network composites. The emulsion with the highest modulus at room temperature produced composites with the lowest percolation threshold. The threshold for a composite made from a copolymer latex containing equal quantities of butyl acrylate and methyl methacrylate (BA5) is 1.5 vol%, while the percolation threshold for the much lower modulus BA7 (7:3 BA:MMA ratio) is 4.9 vol %. The microstructure of each composite shows significant differences in the level of CB dispersion within the polymer matrix. Higher modulus polymer particles push the CB more efficiently into the interstitial space between them, resulting in a lower percolation threshold. This influence of modulus was confirmed by increasing the drying temperature, where the modulus of the latexes (BA5, BA5.5, and BA6) were more similar and the percolation thresholds for three composites also became closer to one another.
9:00 PM - KK5.9
Improved Dispersion of Single-walled Carbon Nanotubes in Epoxy with the Introduction of Clay.
Lei Liu 1 , Jaime Grunlan 1 Show Abstract
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States
Natural sodium montmorrilonite clay was introduced into single-walled carbon nanotube (SWNT)/epoxy composites to improve nanotube dispersion. Unlike other surfactant or polymer dispersants, clay is mechanically rigid and well known for its ability to improve the properties (e.g., modulus, gas barrier, and flame retardation) of polymer composites. Composites containing clay exhibit improved nanotube dispersion, along with electrical and mechanical behavior. The percolation threshold for the composites containing nanotubes is 0.05 wt% SWNT, while composites containing 2 wt% clay had a percolation threshold of 0.01 wt% SWNT. For the composite with 0.05 wt% SWNT, more than four orders of magnitude increase in electrical conductivity was observed with the addition of 0.2 wt% clay. This improvement in conductivity is accompanied by an increase in storage modulus. Clay also makes it possible to stably suspend nanotubes in water. SWNTs appear to have an affinity toward clay that causes them to become more exfoliated and better networked in these composites. The synergy observed between nanotubes and clay may lead to improved performance for these multifunctional polymer nanocomposites.
Jaime Grunlan Texas A&M University
Mark Ellsworth Tyco Electronics
Sergei Nazarenko The University of Southern Mississippi
Jean-Francois Feller University of South Brittany
Bryan Pivovar Hydrogen Technologies and Systems Center
Wednesday AM, December 03, 2008
Room 300 (Hynes)
9:30 AM - KK6.1
Polymer/Metal Nanocomposites: from In Situ Nanostructuration Process to Functional Properties.
Eliane Espuche 1 , Sandra Clemenson 1 , Laurent David 1 Show Abstract
1 , Laboratoire des Materiaux Polymères et des Biomateriaux/IMP UMR CNRS 5223, Université de Lyon, Université Lyon 1, Villeurbanne France
9:45 AM - KK6.2
Designing Self Assembly Strategies for Polymeric Nanocomposites.
Lorena Ruiz-Perez 1 , Anthony Ryan 1 Show Abstract
1 Department of Chemistry, University of Sheffield, Sheffield, South Yorkshire, United Kingdom
Block copolymer modified epoxy resins have generated considerable interest since it was demonstrated that the combination could form nanostructured thermosets through self-assembly. The modified thermosets experience an improvement in their mechanical properties via toughening depending on the morphology adopted by the copolymers. Over moderate to high polymer concentration the system behaves as expected for a block copolymer in a solvent selective for one block. In this fashion, a block copolymer self assembles in the pre-cure stage via a block copolymer core (resinophobe) and a corona (resinophile) immiscible and miscible with the resin respectively. As in aqueous solution, morphologies such as micelles (spherical or worm-like) and vesicles can be formed in the resin pre-cured stage via self assembly. The polymerization of the resin (typically an epoxy resin but the principles apply universally) causes the high molecular weight crosslinking mixture to become a poorer solvent. This can cause macrophase separation or a change in the particle morphology. If the solubilities are selected appropriately then the crosslinking of the resin causes debonding between the micelles and thermoset leading to optimum toughness.Poly (ethylene oxide)-co-poly (butylene oxide) diblock copolymers (PEO-PBO) were used as modifiers of Bisphenol A diglycidyl ether ( BADGE ) resin. The morphology adopted by the block copolymers in the epoxy system could be varied depending on various parameters. Resinophilic/resinophobic block ratio, polarity of the solvent (i.e. aromatic versus aliphatic hardeners) and kinetics of cure were the mechanisms employed to design well-defined morphologies at the nanometer size scale. Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) provided local real-space images in 2 dimensions. Differential Scanning Calorimetry (DSC) and time-resolved Small Angle X-ray Scattering (SAXS) were used to monitor the overall structure changes with temperature. These studies provide a good example of how epoxy resins can be templated into well-defined nanostructures using amphiphilic diblock copolymers.
10:00 AM - **KK6.3
Effects of Filler Size and Shape on Compatibility in Lyotropic Liquid Crystalline Matrix: SWNT and MWNT, Carbon clack and Fullerene.
Einat Nativ-Roth 1 , Rachel Yerushalmi-Rozen 1 , Oren Regev 1 Show Abstract
1 Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva Israel
The effect of single walled carbon nanotubes (SWNT) on the phase behavior of cationic surfactant cetyltrimethylammonium bromide (CTAB) in aqueous solutions was investigated. We found that dispersion of SWNT at surfactant concentration below the lyotropic liquid-crystalline (LC) region of the native surfactant induces de-mixing and macroscopic phase separation in otherwise homogeneous surfactant solution. Two coexisting liquid phases of similar surfactant concentrations were observed, with the SWNT residing within the lower phase. We investigated nanometrically thin films of the lower phase under external shear and revealed shear-induced structural elongation of micelles along the SWNT vector (cryogenic-transmission electron microscopy (cryo-TEM)). The effect was found to be exclusive to SWNT and did not occur in dispersions of other carbonaceous additives (multi-walled carbon nanotubes, carbon black or fullerene).1 At higher surfactant concentrations (LC region) the SWNTs were found to incorporate into the ordered lyotropic LC phase while preserving the native d-spacing (small-angle x-ray scattering (SAXS)). The results are discussed in light of the filler geometrical similarity with the micelles. The inclusion of SWNT within lyotropic LC phases would open a wealth of possibilities as LC phases are important in a variety of applications, ranging from cosmetics, paints, to molecular sensors.1. Nativ-Rot et al. Chem. Comm. 17, 2037 (2008) and Small (2008, in press).
10:30 AM - KK6.4
Effect of Supramolecular Structureon Polymer Nanocomposite Mechanical Properties.
Eyal Zussman 1 Show Abstract
1 Mechanical Engineering, Technion, Haifa Israel
10:45 AM - KK6.5
Visualization of Single Wall Carbon Nanotube Networks in Polyimide Composites by Microscopic Imaging.
Jae-Woo Kim 1 , Peter Lillehei 2 , Cheol Park 1 Show Abstract
1 , National Institute of Aerospace, Hampton, Virginia, United States, 2 , NASA Langley Research Center, Hampton, Virginia, United States
The development of effective characterization tools to assess single wall carbon nanotube (SWCNT) networks in polymer matrices is a significant step towards predicting nanocomposite performance non-destructively. An accurate assessment of SWCNT dispersion is the most critical factor in correlating the performance of the final nanotube polymer composites to the nanostructure. Spectroscopic tools such as UV-VIS, IR, and Raman could aid the characterization by providing information of carbon nanotube structure, functionalization, charge transfer between the polymer and the nanotubes, and even alignment of the nanotubes within the matrix. However, these techniques are optically based and thus measure an ensemble of nanotubes because the minimum spot size is on the order of a few microns even in state-of-the-art instruments. While this information is useful and necessary to help to understand the electrical, mechanical, and thermal data collected on the composites, additional information on how the nanotube networks are actually distributed within the polymer matrices is required to better understand nanocomposite morphologies. In this talk, we will present the framework for a systematic study to assess SWCNT networks in polymer matrices and compare applications of various microscopic techniques such as electron microscopy, magnetic force microscopy, and current sensing atomic force microscopy. These tools allow one to visualize SWCNT networks deep within the composite through the polymer matrix.
11:00 AM - KK6: Structure
KK7: Thermally Conductive Nanocomposites
Wednesday PM, December 03, 2008
Room 300 (Hynes)
11:30 AM - KK7.1
Thermal Conductivity of Carbon Nanotube/Epoxy Resin Composites with Covalent Nanotube-Matrix Bonding.
Michael Jakubinek 1 2 , Mary Anne White 1 2 , Jingwen Guan 3 , Benoit Simard 3 Show Abstract
1 Departments of Physics and Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada, 2 Institute for Research in Materials, Dalhousie University, Halifax, Nova Scotia, Canada, 3 Steacie Institute for Molecular Sciences, National Research Council, Ottawa, Ontario, Canada
Carbon nanotubes (CNTs) have received particular attention as fillers in polymer composites because of their exceptional properties and high aspect ratios, which suggest that significant improvements in the polymer properties might be achieved with low CNT content. The high thermal conductivity of individual CNTs makes CNT materials potential candidates for new thermal interface materials. Advances in CNT synthesis and the availability of commercial supplies of CNTs are removing one practical obstacle to the development of such composites, but the thermal conductivity enhancements achieved for CNT/polymer composites are poor in comparison to early predictions. It has been demonstrated that the interfacial thermal resistance associated with the CNT/matrix interfaces is an important factor in limiting the observed thermal conductivity enhancements and the introduction of covalent bonding between CNTs and the matrix has been suggested as the most promising route to improve thermal conductivity. Here we report experimental measurements for composites containing single walled CNTs that are covalently bonded, to varying degrees, to an epoxy matrix.
11:45 AM - KK7.2
Effect of Interfacial Thermal Resistance on Thermal Conductivity of CNT Filled Polymer Nanocomposites.
Chandra Singh 1 , Tapas Dey 1 Show Abstract
1 Cryogenic Engineering Centre, Indian Institute of Technology Kharagpur, Kharagpur, west bengal, India