Symposium Organizers
Jaime Grunlan Texas A&M University
Dibakar Bhattacharyya University of Kentucky
Eva Marand Virginia Polytechnic Institute and State University
Oren Regev Ben-Gurion University of the Negev
Anna Balazs University of Pittsburgh
R1: Electrically Conductive Polymeric Materials
Session Chairs
Tuesday PM, April 10, 2007
Room 2000 (Moscone West)
9:45 AM - **R1.2
Carbon Nanotube – Polymer Composites: Application as Field Emission Cathodes.
David Carey 1
1 , University of Surrey, Guildford United Kingdom
Show AbstractCarbon nanotube – polymer composites offer the potential of producing a large area cold cathode material in which the nanotube content, as the emitter material, can be carefully controlled. Efficient emission from these materials is controlled by the carbon nanotube (CNT) density and dispersion. Factors such as the field enhancement factor, usually derived from the Fowler-Nordheim formulism, and transport through the film contribute to the efficiency of cathode. At high CNT concentrations the effects of electrostatic field screening and surface conductivity are found to be important. We show that efficient emission can be observed from arc discharge carbon nanotube – conjugated polymer composites. The effects of disorder and fluctuation induced tunnelling within the composite network on the field emission characteristics along with prospects for applications are also discussed.
10:15 AM - R1.3
Influence of Polymer Modulus on Electrical Conductivity of Latex-Based Nanocomposites.
Yeon Seok Kim 1 3 , Jaime Grunlan 1 2 3
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 3 Polymer Technology Center, Texas A&M University, College Station, Texas, United States, 2 Materials Science and Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractIn an effort to reduce the concentration of conductive particles required to achieve significant electrical conductivity in a polymer composite, latex has been used as the polymer matrix starting material. Latexes, or polymer emulsions, exist as solid polymer particles suspended in water. When combined with conductive particles (e.g., carbon black, carbon nanotubes, etc.) these aqueous mixtures produce segregated networks upon drying. This non-random distribution of conductive particles dramatically reduces the percolation threshold (i.e., minimum particle concentration required to impart conductivity) of the final composite. Significant electrical and mechanical property tailoring can be achieved in these composites by simply altering the modulus of the polymer matrix. This concept is demonstrated here using carbon black and copolymer emulsions made with methyl methacrylate and butyl acrylate. Changing the relative monomer concentration changes the glass transition temperature and room temperature modulus of the resulting polymer. These types of composites are useful for a variety of sensing (temperature, pressure, chemical, etc.), dissipation and shielding applications.
10:30 AM - **R1.4
Nanorod-Filled Polymer Composites
Thomas Russell 1
1 Polymer Science & Engineering Department, University of Massachusetts-Amherst, Amherst, Massachusetts, United States
Show Abstract11:00 AM - R1: Electric
Break
11:15 AM - **R1.5
Electrical Conductivity in Nanotube-Polymer Composites.
Karen Winey 1
1 Materials Science and Engineering, Univ. of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractElectrical conductivity in polymer nanocomposites with carbon nanotubes is understood in terms of percolation due to the many orders of magnitude differences in electrical conductivity between typical polymers and nanotubes. Consequently, percolation conductivity depends on the nanotube loading and the extent of nanotube dispersion. We have recently reported the importance of nanotube orientation on electrical conductivity, where we control the alignment using various extensional flow conditions and quantify the alignment by analyzing the form factor scattering from the highly anisotropic nanotube bundles. As with nanotube loading, the electrical conductivity increases dramatically as the orientation of the nanotubes transition from very well aligned to isotropic and is fit with a power law. We are now exploring this phenomenon by modeling an assembly of rods with various levels of alignment in three dimensions and calculating the resulting electrical conductivity. Furthermore, we are extending our work to include other high aspect ratio, highly electrically conductive fillers is polymers including multi wall carbon nanotubes. The nanocomposites discussed above were prepared by our coagulation method that combines bare nanotubes in a solvent with a thermoplastic in a similar solvent and then rapidly co-precipitates the two components. Nanotube dispersion using this method is comparable to their dispersion in the solvent, namely small bundles. An alternative method will be described that intentionally produces a heterogeneous nanotube distribution in which the nanotubes are confined to an interconnected, cellular structure, with the intention of achieving good electrical conductivities at lower loadings.
11:45 AM - **R1.6
Carbon-Nanotube/Polymer Composites: Starting Wetter, Conducting Better.
Cor Koning 1 5 , Nadia Grossiord 1 , Joachim Loos 2 , Jan Meuldijk 3 , Oren Regev 4 , Hans Miltner 5 , Bruno Van Mele 5
1 Laboratory of Polymer Chemistry, Eindhoven University of Technology, Eindhoven Netherlands, 5 Department of Polymer Science and Structural Chemistry, Free University of Brussels, Brussels Belgium, 2 Laboratories of Polymer Technology and Materials and Interface Chemistry, Eindhoven University of Technology, Eindhoven Netherlands, 3 Process Development Group, Eindhoven University of Technology, Eindhoven Netherlands, 4 Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva Israel
Show AbstractA recently developed, versatile, latex-based concept for dispersing Single and Multi Wall Carbon Nanotubes (S/MWNTs) in a highly viscous polymer matrix is described. The first, crucial step of the concept is the ultrasound-driven exfoliation of the as produced SWNT and MWNT bundles in water, containing sodium dodecylsulfate (SDS) for the stabilization of the obtained dispersion. By applying UV/Vis spectroscopy, the minimum required energy input for obtaining the maximum attainable degree of exfoliation of the nanotubes could be determined. The exfoliation process was also directly visualized with cryo-TEM and SEM images, which were in agreement with the collected UV/Vis data. The minimum amount of surfactant required to achieve maximum exfoliation of a given amount of CNTs in water was determined by thermogravimetric analysis, UV-Vis spectroscopy, surface tension measurements and a variant of Maron’s titration. All four methods, applied to aqueous mixtures of carbon nanotubes and the surfactant SDS, consistently yield a surface coverage of slightly more than two SDS molecules per square nanometer, which is comparable to the known maximum packing density of SDS at the air-water interface and in agreement with the theoretical value calculated with the Gibbs equation for surface excess. The second step of the concept is mixing the stable aqueous CNT dispersions with a polymer latex, preferably stabilized by the same surfactant as the CNT dispersion. The third step implies freeze-drying, followed by compression molding of the powder into a polymer film.The extremely high aspect ratio of the CNTs, along with the very efficient way of dispersing them, generates a percolating network of the SWNTs in a highly viscous polystyrene (PS) matrix, which accordingly becomes semi-conductive for SWNT amounts as low as 0.2-0.3 wt %. For the MWNTs the percolation threshold in a PS matrix is around 1.8-2.0 wt%.Depending on the molar mass distribution of the PS matrix in the PS/SWNT nanocomposites, the well-dispersed CNTs significantly raise the Tg of the PS. A low molar mass PS fraction, probably acting as a wetting agent for the SWNTs, seems to be required for an improved PS/SWNT interaction. Surprisingly, this enhanced interaction also raises the conductivity level of these composites. We believe that this latter phenomenon is caused by a change of the electronic structure of the CNTs, resulting from π-π interactions between the phenyl rings of the PS and the surface of the CNTs.Finally, the versatility of the ’latex concept’ is demonstrated for semi-crystalline polypropylene (PP)/CNT nanocomposites, prepared from aqueous PP emulsions. For this system, a low percolation threshold was found, and the extremely well-dispersed CNTs proved to be excellent nucleating agents for PP, raising the crystallization temperature by ca. 20 degrees.
12:15 PM - R1.7
Clay-Assisted Dispersion of Carbon Nanotubes in Conductive Epoxy Nanocomposites.
Lei Liu 2 3 , Jaime Grunlan 1 2 3
2 Materials Science and Engineering, Texas A&M University, College Station, Texas, United States, 3 Polymer Technology Center, Texas A&M University, College Station, Texas, United States, 1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractClay was introduced into single-walled carbon nanotube (SWNT)/epoxy composites to improve nanotube dispersion without harming electrical conductivity or mechanical performance. Unlike surfactant or polymer dispersants, clay is mechanically strong and known to exhibit good dispersion/load transfer characteristics in polymer composites. Combining nanotubes and clay allows both electrical and mechanical behavior to be simultaneously enhanced. With just 0.05 wt% SWNT, electrical conductivity is increased by more than four orders of magnitude with the addition of 0.2 wt% clay. This improvement in conductivity is accompanied by an increase in storage modulus. Furthermore, the percolation threshold of these nanocomposites is reduced from 0.5 wt% SWNT to 0.1 wt% with the addition of clay. SWNTs appear to have an affinity for clay that causes them to become more exfoliated and better networked in these composites. It is possible that adding clay may impart other properties, such as flame retardancy or gas barrier that will make these composites useful for a wide variety of applications.
12:30 PM - R1.8
Fabrication and Electrical Characterization of Polymer based Hexaaztrinaphthylene nanofibers: A possible substitute for Polyaniline nanofibers
Saima Khan 1 , Jeffery Rack 2 , Martin Kordesch 1
1 Physics and Astronomy and CMSS Program, Ohio University, athens, Ohio, United States, 2 Chemistry and Bio-Chemistry, Ohio University, athens, Ohio, United States
Show AbstractNanofibers have been fabricated from Hexaaztrinaphthylene (HATN)/Polyethylene blend using the electrospinning technique. The morphology of the fibers was studied using the SEM, TEM and Optical microscope. The electrical conductivity of the fibers was measured using the four-point-probe method. A preliminary value of 0.86 S/cm was obtained. These fibers present a possible substitute for the conducting polyaniline (PAni) nanofibers .The ease of processing and accuracy in determining the chemical composition give these fibers an advantage over the PAni fibers.
12:45 PM - R1.9
Synthesis of Nickel-Coated Carbon Nanopaper Sheets by Pulse Laser Deposition
Jihua Gou 1 , Roy Blanco 1 , Aurangzeb Khan 2 , Aditya Appalla 2
1 Department of Mechanical Engineering, University of South Alabama, Mobile, Alabama, United States, 2 Department of Electrical & Computer Engineering, University of South Alabama, Mobile, Alabama, United States
Show AbstractR2: Electrically Conductive Polymeric Materials II
Session Chairs
Tuesday PM, April 10, 2007
Room 2000 (Moscone West)
2:30 PM - **R2.1
Nanocomposites Based on Cellulose Whiskers and (Semi)Conducting Conjugated Polymers.
Otto van den Berg 1 , Michael Schroeter 1 , Jeffrey Capadona 1 2 , Christoph Weder 1 2
1 Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 2 Advanced Platform Technology Center, L. Stokes Cleveland VA Hospital, Cleveland, Ohio, United States
Show Abstract3:00 PM - **R2.2
Layered Nanoscale Composites by Layer-by-Layer Assembly: Molecular Engineering of Tensile Strength, Toughness and Electronic Properties
Nicholas Kotov 1 3 4 , Paul Podsiadlo 1 , Bong Shim 1 , Ellen Arruda 2 , Amit Kaushik 2 , Anthony Waas 2
1 Chemical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 4 Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show Abstract3:30 PM - **R2.3
Thermoelectrical and Chemoelectrical Properties of Conductive Polymer NanoComposites (CPC): Different Strategies for Conducting Network Structuring.
Jean-Francois Feller 1
1 Laboratory of Polymers, Properties at Interfaces & Composites, University of South Brittany, Lorient, Bretagne, France
Show Abstract4:00 PM - R2: Electrical
BREAK
R3: Dielectric and Piezoelectric Behavior
Session Chairs
Tuesday PM, April 10, 2007
Room 2000 (Moscone West)
4:30 PM - **R3.1
Polymer Nanocomposites as Active Materials: Piezo-Resistivity and Pyro-Resistivity
Michael Arlen 1 , David Wang 1 , Loon-Seng Tan 1 , Aaron Trionfi 2 , Michael Lilly 2 , Julia Hsu 2 , Richard Vaia 1
1 Materials Directorate, Air Force Research Laboratory, WPAFB, Ohio, United States, 2 Center for Integrated Nanotechnologies (CINT), Sandia National Laboratory, Albuquerque, New Mexico, United States
Show AbstractActive materials undergo a reversible, predicable and controllable shape or property change in response to an external stimulus, such as stress, temperature, light, or pH. Technological uses range from temperature sensitive switches to tunable stiffeners for mechanical damping and morphing of aerospace structures. Nanoparticle additions to polymers offer at least two new design paradigms for active, soft materials – enhancement of the inherent active response of the polymer via local field enhancement (e.g. strain or electric) or creation of new active response associated with the nanoparticle distribution (i.e. percolation network) or nanoparticle-polymer coupling (i.e. interface). For example, by considering the dispersion of carbon nanotubes within a polymer as a ‘compliant-network’ consisting of ‘semi-rigid-struts’ (nanoparticles) and ‘weak-joints’ (nanoparticle-nanoparticle interactions), numerous ‘active’ characteristics can be envisioned based on thermomechanical modulation of this nanoparticle network, including pyro-resistivity and piezo-resistivity.
5:00 PM - R3.2
Electrical Characterization of Polyimide Nanocomposites by Atomic Force Microscopy.
Ricardo Perez 1 , Zoubeida Ounaies 1
1 Aerospace, TAMU, College Station, Texas, United States
Show Abstract5:15 PM - R3.3
Low Dielectric Constant Nanocomposite Thin Films Based on Silica Nanoparticle and Organic Thermosets
Qinghuang Lin 1 , Stephen Cohen 1 , Lynne Gignac 1 , Brian Herbst 1 , David Klaus 1 , Eva Simonyi 1 , Jeff Hedrick 1 , John Warlaumont 1 , Hae-Jeong Lee 2 , Wen-li Wu 2
1 , IBM Watson Research Center, Yorktown Heights, New York, United States, 2 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractLow dielectric constant (low-k) nanocomposite thin films have been prepared by spin coating and thermal cure of solution mixtures of two organic low-k thermoset pre-polymers and a silica nanoparticle with an average diameter of about 8 nm. The electrical, the mechanical, and the thermo-mechanical properties of these low-k nanocomposite thin films have been characterized with 4-point probe electrical measurements, nanoindentation measurements with an atomic force microscope (AFM), and specular X-ray reflectivity. Addition of the silica nanoparticle to the low-k organic thermosets enhances both the modulus and the hardness and reduces the coefficient of thermal expansion of the resultant nanocomposites. The enhancements in the modulus of the nanocomposites are less than those predicted by the Halphin-Tsai equations presumably due to the relatively poor interfacial adhesion and/or the aggregation of the hydrophilic silica nanoparticles in the hydrophobic organic thermoset matrices. The addition of the silica nanoparticle to the low-k organic thermoset matrices does not alter significantly the dielectric constant of the resultant nanocomposite thin films at lower concentrations of the silica nanoparticle. Its addition, however, increases the dielectric constant of the resultant nanocomposite thin films at higher concentrations of the silica nanoparticle. The dielectric constant of the nanocomposite thin films has been found to agree fairly well with an additive formula based on the Debye equation.
5:30 PM - R3.4
Ionic Liquid Enhanced Electrochemical Characterization of Transport Phenomena in Metal Particle - Polymer Matrix Composite Coatings.
Gordon Bierwagen 1 , Brian Hinderliter 1 , Kerry Allahar 1 , Dennis Tallman 1 , Stuart Croll 1
1 Coatings & Polymeric Materials, North Dakota State University, Fargo, North Dakota, United States
Show AbstractMetallic additives provide sacrificial protection and complement the barrier protection afforded by heterogeneous organic coatings to metallic substrates. The transport of materials, water in particular, into, out, and within a coating has a significant impact on the effectiveness of the coating as a barrier and as a medium for sacrificial protection additives. Recent papers from our group have introduced the methodology whereby room temperature ionic liquids (RTILs) in conjunction with capacitance monitoring via electrochemical impedance spectroscopy (EIS) can be used to determine the diffusion coefficient of water out of a non-pigmented, additive free coating.(ref. 1-4) This methodology is extended in this effort to a Zn-rich epoxy that is used as a primer for Army vehicles. The RTILs can be used to investigate the electrochemical properties of coatings in a non-aqueous medium, and for hydrophilic RTILs, can be used to extract water from a wet coating. An experiment was conducted to simulate the alternate wetting and drying of the Zn-rich epoxy. The capacitance evolution associated with the exposure of the coating on a steel substrate to cycles comprising of 0.05 M NaCl wetting and RTIL drying is presented as follows: Capacitance data as a function of immersion time associated with the test area exposed to (a) cyclic NaCl wetting and (b) RTIL drying conditions with cycle number as a parameter. The capacitance data obtained from these experiments were analyzed using models to separate the Fickian transport of water into and out the coating from the percolation of water through pores. The wet-dry cycling procedure resulted in the leaching of zinc containing species from the coating. The experimental results were analyzed to determine the dielectric response, void fraction changes, and dissolution rate of the zinc containing species associated with the coating. References:1.K. Allahar, et al., “Simulation of Wet-Dry Cycling of Organic Coatings using Ionic Liquids,” submitted to the J. Electrochem. Soc., Oct. 2006.2.Brian Hinderliter, et al., “Using ionic liquids to measure coating properties via electrochemical impedance spectroscopy,” submitted to the 2006 International Coatings Exposition (FSCT), New Orleans, LA., Oct. 20063.K. Allahar, et al., “Simulation of Wet-Dry Cycling of Organic Coatings using Ionic Liquids,” Trans. of the 209th Meeting of the Electrochem. Soc., Denver CO., May 2006.4.A.M. Simões, D. Tallman, G.P. Bierwagen, “The use of ionic liquids for the electrochemical characterization of water transport in organic coatings,” Electrochem. Solid-State Lett., 8, 60 (2005).
5:45 PM - R3.5
Three-Dimensionally Ordered Polymer Nanocomposite Formed by Spin-Coating.
Peng Jiang 1
1 Chemical Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractWe describe a simple spin-coating technology for rapidly fabricating wafer-scale (up to 8-inch diameter) polymer nanocomposite with 3D highly ordered microstructures. Dispersion of monodisperse silica colloids in triacrylate monomers is spin-coated onto a variety of substrates, including silicon, glass, and PMMA plates. Shear-induced ordering and subsequent photopolymerization lead to the formation of three-dimensionally (3D) ordered colloidal crystals trapped inside a polymer matrix. Using the spin-coating technique, monodisperse silica colloids with a wide diameter range from ~30 nm to 2 μm can be cast to form 3D ordered nanocomposite films. The thickness of as-synthesized colloidal crystal-polymer nanocomposite is highly uniform and can be controlled simply by changing the spin speed and time. The wafer-scale process is compatible with standard microfabrication, enabling the construction of complex micropatterns using proximity photolithography and reactive ion etching (RIE). Selective removal of silica spheres leads to the formation of large-area macroporous polymers with crystallization arrays of air cavities, which have important technological applications in DNA separation, biosensors, and low-k materials for interconnects in integrated circuits. Besides spherical colloids, plate-like zeolite particles have also been aligned using the spin-coating technique. The resulting 3D zeolite assembly mimics the microstructures of natural nacre.
Symposium Organizers
Jaime Grunlan Texas A&M University
Dibakar Bhattacharyya University of Kentucky
Eva Marand Virginia Polytechnic Institute and State University
Oren Regev Ben-Gurion University of the Negev
Anna Balazs University of Pittsburgh
R4: Mixed Matrix Membranes
Session Chairs
Dibakar Bhattacharyya
Eva Marand
Wednesday AM, April 11, 2007
Room 2000 (Moscone West)
10:00 AM - **R4.1
Hierarchically Structured Nanocomposites: Assembly and Properties
Emmanuel Giannelis 1
1 Materials Science and Engineering, Cornell Univeristy, Ithaca, New York, United States
Show AbstractPolymer nanocomposites have attracted considerable attention in recent years. The goal is to develop lightweight composites with potentially superior mechanical and transport properties. Challenges with poor dispersion and poor interfacial strength, however, have prevented nanocomposites from realizing their full potential. In this talk I will present our recent efforts to synthesize hierarchically structured nanocomposites using directed assembly of nanoparticles in a polymer matrix and I will discuss their properties.
10:30 AM - R4.2
Ordered Carbon Nanotube/Polymer Nano-composite Membranes for Gas Separations
Sangil Kim 1 , Eva Marand 1
1 Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States
Show AbstractRecent molecular simulation and theoretical studies of single walled carbon nanotubes (SWNT) have indicated that these materials are predicted to have both high selectivities and very high fluxes for gas transport. Oriented multi-walled carbon nanotube (MWNT) and double-walled carbon nanotube (DWNT) membrane have been fabricated by several research groups. The gas permeabilities and water flux of DWNT membranes with a 1.6 nm pore diameter were higher than those of commercial polycarbonate membranes having 15 nm pore size by several orders of magnitude. However, these reported carbon nanotubes (CNTs) membranes are not commercially attractive because of complex and costly fabrication procedure and limited surface area. In this study, in order to overcome disadvantages of chemically grown CNTs membranes, we have developed fabrication techniques to prepare CNTs/polymer nano-composite membranes with large surface area. Mixed matrix membranes containing randomly oriented CNTs showed that addition of nanotubes to a polymer matrix could improve its selectivity properties as well as permeability by increasing diffusivity. Overall increases in permeance and diffusivity for all tested gases suggested that carbon nanotubes can provide high diffusivity tunnels in the SWNTs within the polymer matrix agreed well with molecular simulation estimation. In order to prepare ordered CNTs membranes, we have developed a simple, fast, commercially attractive, and scalable method. The oriented single-walled carbon nanotube (SWNT) membrane sample showed higher permeability by one order of magnitude than the value predicted by the Knudsen model. Another unique feature of these membranes is that various functional groups can be attached to CNTs end tips. The various amino groups (-NH2) on the nanotube pore entrance provide the sites for CO2 adsorption and facilitate its separation from N2 and CH4. Selectivities of CO2/CH4 mixtures through SWNT membranes were higher than the ideal separation values calculated from single gas permeation and Knudsen model. This amine functionalized SWNT membrane showed higher selectivities of CO2 over other gas molecules because of preferential interaction of CO2 with the nanotubes demonstrating practical applications in gas separations.
10:45 AM - R4.3
Crosslinking High Free Volume Polymers - Effect on Gas Separation Properties
Lei Shao 1 , Jon Samseth 2 , May-Britt Hägg 1
1 Department of Chemical Engineering, Norwegian University of Science and Technology, Trondheim Norway, 2 , SINTEF Materials and Chemistry, Trondheim Norway
Show AbstractPoly(4-methyl-2-pentyne)[PMP] is an amorphous, glassy, disubstituted acetylene-based polymer and one of the most permeable hydrocarbon-based polymers known. However, when PMP is used for gas separations, its selectivity is relatively low and the high gas permeability is unstable over time. For example nitrogen permeability in PMP has been reported to decrease by 25% over 29 days. Gas permeability in PMP is sensitive to processing history and time. PMP undergoes significant physical aging which is caused by the gradual relaxation of non-equilibrium excess free volume in glassy polymers. PMP is also soluble in some organic compounds. These phenomena may compromise the practical use of PMP. The current study investigates the effect of crosslinking PMP on transport properties and physical aging. The PMP membranes were crosslinked using bis azides, which have been shown to be successful in crosslinking PTMSP. The resulting membranes were transparent and homogeneous and further cross-linked by using UV irradiation at room temperature. When PMP is crosslinked it becomes insoluble in common PMP solvents such as cyclohexane and methylcyclohexane. Thus, the effect is a significant increase in the chemical stability due to crosslinking. The reaction between the bis azide crosslinker and PMP was observed using FT-IR analysis. The initial permeability of PMP decreased with increasing crosslinking due to the loss in fractional free volume (FFV). The selectivities of O2/N2, H2/N2, CO2/N2, CH4/N2 increased as the FFV decreased, showing that crosslinked PMP is more size selective to gases than uncrosslinked PMP. The permeability stability of crosslinked PMP for the gases is clearly improved. The increased stability may be caused by crosslink constraining the PMP chains and not allowing relaxation of the excess, non-equilibrium FFV that is inherent in PMP. For all gases considered permeability decreased as amount of crosslinking agent increased. The permeability decrease can be correlated with the FFV decrease. The sorption levels of N2 and CH4 were measured and found to be independent of crosslinker content, within typical sample variability and experimental uncertainty. Therefore gas solubility in PMP does not seem to be affected by the FFV decrease accompanying the increase in crosslinker content. The permeability (P) may be described as the product of the gas diffusivity (D) and solubility (S), hence the decrease in permeability in crosslinked PMP is most likely due to a decrease in the diffusivity.Nanoparticles such as fumed silica were added to uncrosslinked and crosslinked PMP films, and permeability increased substantially in both cases. Crosslinking is successful in maintaining the permeability and selectivity of PMP over time. The permeability of PMP-membranes without nanoparticles added, were not stable over time. A systematic study of the effect of type, shape and amount of nanoparticle added to crosslinked PMP is being conducted.
11:30 AM - **R4.4
In Search of Selective Nano-flakes for Mixed Matrix Membranes
Michael Tsapatsis 1
1 Chemical Eng & Mater Sci, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractPolymer and other composites incorporating oriented molecular sieve plate-like particles (selective flakes) have been proposed as membrane materials combining process-ability and easy scale-up with improved performance. Molecular sieve crystals with one thin and two extended dimensions with selective micropores running across the thin dimension are needed for this application. Despite some limited success, it has been proven difficult to synthesize flake-like zeolite crystals for many important structure types. Alternative candidates are layered silicate and aluminophosphate materials synthesized under solvothermal conditions that are similar to the ones used to make molecular sieve frameworks. Often, these layered materials are synthetic and/or structural precursors of zeolites and other molecular sieve frameworks. For many of them, the structure of the layer includes micropores running across and/or within the layer and can be used as additives in polymers or other matrices to form perm-selective nanocomposite membranes provided that the pore structure is retained during nanocomposite processing. In comparison with swelling, delamination and exfoliation of typical layered silicates, similar treatments for zeolite layered precursors are less well developed and appear to be more challenging. The synthesis of plate-like molecular sieve crystals and the ion exchange and swelling of layered silicates with microporous layers will be described along with their incorporation in polymer and silicate matrix composites. Performance in gas separation applications will be discussed and a mathematical model that highlights the materials design challenge ahead will be presented.
12:00 PM - R4.5
Novel Carbon Fiber Composite Materials for Gas Separations.
Elisa Vogel 1 , Glenn Lipscomb 1 , Maria Coleman 1
1 Chemical and Environmental Engineering, The University of Toledo, Toledo, Ohio, United States
Show AbstractInterest in mixed matrix materials for separations continues to grow at a feverish pace. We report on the transport properties of a new group of carbon fiber composite materials based on the Pyrograf© fiber produced by Applied Science, Inc. This fiber is produced in commercial quantities by vapor phase decomposition of a hydrocarbon source. Mixed matrix composites are produced by either mechanically blending the as-received fiber or surface functionalizing the fiber to improve interfacial adhesion between the fiber and the polymer matrix. The properties of polyolefin and polyamide composites are reported.
12:15 PM - R4.6
Mixed Matrix Polymer-aluminophosphate Composites for Gas Separations.
Benjamin Vaughan 1 , Eva Marand 1
1 Chemical Engineering, Virginia Tech, Blacksburg , Virginia, United States
Show Abstract12:30 PM - R4.7
Mesoporous Nanoparticles and Polymer Nano-composite Membranes:High flux and Permeability
Sangil Kim 1 , Eva Marand 1
1 Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States
Show AbstractPolymeric membranes have been widely used in industrial gas separation processes. The inherent limitations of polymers, however, prevent them from being extended to new applications. In order to enhance gas separation membrane performances, recent work has focused on enhancing polymer selectivity and permeability by fabricating mixed matrix membranes (MMMs). The incorporation of various inorganic materials, such as zeolites, carbon molecular sieves, or mesoporous molecular sieves, into a polymer matrix has been investigated. Mesoporous molecular sieves have been used in MMMs to primarily enhance permeability. For example, it has been shown that mesoporous materials offered the favorable effect of increasing the permeability of polysulfone MMMs without decreasing selectivity. While the compatibility of the silica with the polymer matrix was good, the micrometer scale of the particle sizes caused the composite membrane to be extremely brittle and to crack at higher silica loading. In this study, we have developed fabrication techniques to prepare MMMs containing mesoporous MCM-41 nanoparticles with ~50 nm particle size. These smaller nanoparticles lead to a higher polymer/particle interfacial area and provide more opportunity to synthesize composites containing up to 80 vol% of molecular sieve loading in the polymer matrix. At 80 vol% of nano-sized MCM-41 silica loading, gas permeability of the membranes increased dramatically up to 300 %. Despite these increases in permeability, the separation factor of the MMMs changed only slightly. Another unique feature of the mesoprous silica, is that various functional groups can be easily attached to the surface of silica to increase its selectivity. The incorporation of amine-modified mesoporous silica, for example, not only increased the permeability, but also enhanced the CO2 selectivity of the mixed matrix membrane. This particular MMM is suitable for coal gasification applications such as CO2/N2 separation from flue gas. Therefore, these nanoscale molecular sieves are more suitable for commercialization of MMMs with very thin selective layer than micro-sized zeolite or molecular sieves.
R5: Ionic Transport for Batteries and Fuel Cells
Session Chairs
Wednesday PM, April 11, 2007
Room 2000 (Moscone West)
2:30 PM - R5.1
Ionic Complexation: a Route to Enhanced Block Copolymer Alignment with Electric Fields
Jia-Yu Wang 1 , Ting Xu 2 , Julie Leiston-Belanger 1 , Suresh Gupta 1 , Thomas Russell 1
1 Polymer Science and Engineering, University of Massachusetts, Amherst, Amherst, Massachusetts, United States, 2 Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractBlock copolymers (BCPs) self-assemble into periodic arrays of nanoscopic domains that are emerging as ideal candidates for the generation of templates and scaffolds for the fabrication of nanoscopic structures [1]. External electric fields have been shown to be an effective means of orienting the BCP microdomains in a desired direction. It remains a challenge to achieve the complete alignment of microdomains in BCP thin films due to the preferential interactions of one of the blocks with the interfaces of the electrodes confining the film. Recently, both experimental and theoretical studies suggested that lithium ionic impurities remaining from the synthesis of copolymers may influence the alignment of BCP microdomains under the applied electric field [2]. Questions persist, however, in terms of the direct evidence that lithium ions improve the microdomains alignment, the nature of the interactions of the lithium ions with the BCP chains, and the origin of the enhanced alignment. In this study, lithium ions were successfully introduced into purified polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) to form lithium-PMMA complexes that markedly enhanced the alignment of BCP microdomains under a DC electric field, even adjacent to the two interfaces. The origin of improved alignment arises from the increased dielectric constant difference between the PS and PMMA blocks which reduces the critical field strength required to overcome interfacial interactions of the blocks [3]. Furthermore, χ was significantly increased with the formation of the lithium-PMMA complexes, resulting in a transition in the orientation mechanism of the lamellar microdomains from a disruption and re-formation of the microdomains to a grain rotation mediated by movement of defects [4]. The formation of large grains amplifies the ability of the external electric field to overcome preferential interfacial interactions and eliminate defects. Consequently, complete alignment of BCP microdomains can be achieved. By controlling the number of lithium-PMMA complexes, the microdomain alignment can be regulated in PS-b-PMMA thin films.Reference:1. Hawker, C. J.; Russell, T. P. MRS Bull. 2005, 30, 952.2. (a) Xu T.; Goldbach J. T.; Leiston-Belanger J.; Russell T. P. Colloid Polym. Sci., 2004, 282, 927. (b) Tsori, Y.; Tournilhac, F.; Andelman, D.; Leiber, L. Phys. ReV. Lett. 2003, 90, 145504.3. Wang, J. Y.; Xu, T.; Leiston-Belanger, J. M.; Gupta, S.; Russell, T. P. Phys. ReV. Lett. 2006, 96, 128301.4. Wang, J. Y.; Leiston-Belanger, J.; Sievert, J. D.; Russell, T. P. Macromolecules 2006, in press.
2:45 PM - R5.2
Development of a New Li-ion Composite Polymer Electrolyte
Gilles Toussaint 1 , Catherine Henrist 1 , Rudi Cloots 1 , Christophe Detrembleur 2
1 Laboratory of Inorganic Structural Chemistry, University of Liege, Liege Belgium, 2 Center for Education and Research on Macromolecules , University of Liege, Liege Belgium
Show AbstractThe aim of this work is to develop a new composite polymer electrolyte for energy storage application. This research deals with the synthesis of a polymer composite made of a PEO matrix and various nanofillers, offering both electrochemical performance and mechanical stability of the battery under use. Different inorganic nanofillers were dispersed in various amounts in this polymer using different strategies in order to decrease the crystallinity level of PEO and thus, to increase its ionic conductivity. Modified lamellar natural clays, such as montmorillonite, snake-like structure silica and synthetic lamellar silica made by liquid crystal templating have been used as nanofillers. The snake-like structure and lamellar synthetic silica have been modified by grafting lithium-complexating molecule containing ether groups. The influence of these grafting on the dispersion of the particles inside the matrix and on the electrochemical and mechanical properties of the polymer have been investigated.
3:00 PM - R5.3
Time-of-flight Technique with Polymeric Charge Blocking Layer for Measuring Charge Carrier Mobility of poly(3-hexylthiophene) with High Dark Currents.
Daesung Chung 1 , Sangyoon Yang 1 , Chan Im 2 , Chaneon Park 1
1 Chemical engineering, Postech, Pohang, Kyungbuk, Korea (the Republic of), 2 Chemistry, Konkuk university, Seoul Korea (the Republic of)
Show Abstract3:15 PM - R5.4
Morphology Of Sulfonated Polyarylene Membranes As A Function Of Sulfonation, Processing And Molecular Weight.
Beatrice Muriithi 1 , Douglas Loy 1 , Chris Cornelius 2
1 Material science and engineering, University of Arizona, Tucson, Arizona, United States, 2 Sandia, National labs, Albuquerque, New Mexico, United States
Show AbstractPolymer membranes that can operate at high temperatures and have good proton conductivity are required for high performance PEM fuel cells. Perfluorosulfonic acid based membranes have high proton conductivity at low temperatures (< 80 °C), but at higher temperature conductivity and fuel cell performance rapidly dwindle. The high proton conductivity of these materials is associated with the ability of these materials to phase separate into the hydrophobic and hydrophilic region and this ability is lost at high temperatures. In contrast, sulfonated polyarylenes have been demonstrated to have high proton conductivity and can function in fuel cells at high temperatures. These materials are cheap, can be easily processed, oxidatively stable, have high proton conductivity, thermally stable (high glass transition temperature) and tailorable gas permeabilities. This study focuses on using atomic force microscopy to understand the relationship between polyarylene morphology and the thin films ion conductivity and mechanical properties. Our analyses with atomic force microscopy suggest that these materials phase segregate into larger hydrophilic domains than perfluorosulfonic acid based membranes. The mechanism for this phase separation is currently under investigation. In addition, we have looked at the solvent dependent morphology of these new membranes, the changes in morphology with increases in sulfonation, the effect of molecular weight of the polymer and how this correlates with their mechanical strength as well as the proton conductivity at different temperatures.
3:30 PM - R5.5
Anisotropic Charge Transport in the Polymer Blend PEDOT:PSS.
Alexandre Nardes 1 , Martijn Kemerink 1 , Rene A.J. Janssen 1 , Jolanda A.M. Bastiaansen 2 , Nicole M.M. Kiggen 2 , Bea M.W. Langeveld 2 , Albert J.J.M. van Breemen 2 , Margreet M. Kok 3
1 Applied Physics, Eindhoven University of Technology, Eindhoven Netherlands, 2 , TNO Science and Industry, Eindhoven Netherlands, 3 , Philips Research Laboratories, Eindhoven Netherlands
Show Abstract3:45 PM - R5.6
Novel Polymeric Blend Membranes Based on Acid-Base Interactions for Direct Methanol Fuel Cells
Yongzhu Fu 1 , Arumugam Manthiram 1
1 Materials Science and Engineering Program, The University of Texas at Austin, Austin, Texas, United States
Show AbstractDirect Methanol Fuel Cells (DMFC) currently use the sulfonated fluoropolymer membrane, Nafion. The high methanol permeability through the Nafion membrane from the anode to the cathode (methanol crossover) leads to a poisoning of the cathode Pt catalyst and a consequent performance loss in DMFC. Design and development of alternative polymeric membranes with high proton conductivity as well as low methanol permeability can suppress or eliminate these problems and enhance the commercialization feasibility of the DMFC technology for portable applications. In this regard, fluorine-free, aromatic polymer membranes like sulfonated poly(ether ether ketone) (SPEEK) have been pursued as a replacement for Nafion. These materials generally exhibit lower methanol crossover and are less expensive than Nafion. However, high degrees of sulfonation to maximize the proton conductivity often lead to undesirable swelling of the membrane and mechanical integrity problems. We present here a novel polymer blend membrane strategy, consisting of an aromatic acidic polymer and an aromatic basic polymer, which provide proton conduction due to acid-base interactions with much reduced methanol permeability.The basic polymer is synthesized by tethering N-heterocycles like benzimidazole or 2-amino-benzimidazole to polysulfone by a condensation reaction between the carboxylic acid groups of carboxylated polysulfone and 1,2-diaminobenzene or 2-amino-benzimidazole. The basic polymer is then blended with SPEEK. Our strategy in selecting these type of systems is based on the following: (i) N-heterocycles are easy to synthesize or tether to polymer networks by condensation reactions, (ii) carboxylated polymers are used as precursors, which can be readily synthesized with a wide variation in the degree of carboxylation, offering the flexibility to tune the content of N-heterocycle units in the polymer, (iii) the acidic and basic polymers in the blend are expected to have good compatibility with each other due to their structural similarity and offer good long-term stability, (iv) the pendant N-heterocycles could ‘insert’ into the sulfonic acid domains of SPEEK, promoting proton conduction through acid-base interactions, and (v) the polysulfone and PEEK precursors are inexpensive industrial polymers with excellent mechanical and thermal properties. Blend membranes fabricated with polysulfone-benzimidazole (PSf-BIm) or polysulfone-amide-benzimidazole (PSf-ABIm) (basic polymers) and SPEEK (acid polymer) show higher performance in DMFC compared to plain SPEEK or Nafion 115 membranes due to higher proton conductivity and lower methanol crossover. The blend membranes exhibit a stable performance without any noticeable degradation with time due to suppressed methanol crossover. The blend membranes have the potential to accelerate the commercialization prospects of DMFC.
4:00 PM - R5.7
Local Photocurrent Spectroscopy on Blended Organic Solar Cells.
Klara Maturova 1 , Martijn Kemerink 1 , Rene Janssen 1
1 Molecular Materials and Nanosystems, Eindhoven University of Technology, Eindhoven Netherlands
Show Abstract4:15 PM - R5: Ionic
Break
R6: Modeling and Biology
Session Chairs
Wednesday PM, April 11, 2007
Room 2000 (Moscone West)
4:30 PM - R6.1
Healing Substrates with Mobile, Particle-Filled Microcapsules: Designing a ``Repair and Go" System.
Anna Balazs 1
1 Chemical Engineering Dept., University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show Abstract4:45 PM - R6.2
On Nature of Supercooled Liquids.
Vacheslav Yasnovsky 1
1 , Rheology Associates, San Francisco, California, United States
Show Abstract5:00 PM - R6.3
Poly(lactic-co-glycolic acid) Hollow Fibre Membranes as Tissue Engineering Scaffolds: Tayloring the Characteristics for Controlled Tissue Culture
Xujun Wu 1 2 3 , Sarah Waters 4 , Matthew Davidson 3 , Julian Chaudhuri 1 2 , Marianne Ellis 1 2
1 Centre for Regenerative Medicine, University of Bath, Bath United Kingdom, 2 Chemical Engineering, University of Bath, Bath United Kingdom, 3 Chemistry, University of Bath, Bath United Kingdom, 4 Mathematical Sciences, University of Nottingham, Nottingham United Kingdom
Show AbstractWithin the human body there is a complex blood supply in every tissue type and each cell is within 200μm of a blood capillary in order to prevent cell death (necrosis). Blood capillaries supply cells with nutrients, remove waste products and deliver chemical signals to other parts of the body. When cells are cultured in the lab (in vitro), such nutrient supply is easily achievable in a 2D monolayer, but in 3D, factors such as diffusion limitations and fluid shear adversely affect cell culture and have meant that a major hurdle to overcome in tissue engineering is the mass transport to and from cells in the 3D ‘scaffold’. Biodegradable Poly(lactic-co-glycolic acid) hollow fiber membranes address this tissue engineering scaffold design problem. The fibers provide a system of ‘pseudovascularisation’; the lumen mimic the blood capillaries that would feed cells in the body, and the membrane wall provides the surface necessary for adherent cells to grow on while allowing nutrients to pass through and be received by the cells. A hollow fiber membrane bioreactor (HFB) provides a single unit for both cell expansion and then differentiation towards a given mature tissue type. Because of the large surface area to volume ratio of a HFB and the superior mass transfer properties of hollow fibre membranes compared to other architectures, this system can aid tissue regeneration on a larger scale than has previously been possible.The required physical and mechanical properties of the scaffold will vary with the cell type being expanded or the targeted mature tissue type. This paper reports how the fiber properties can be tailored at every stage of manufacture from polymer synthesis to membrane spin casting. We have demonstrated control of polymer microstructrure (stereocontrol) and molecular weight which effects crystallinity and inherent viscosity. Lactic acid isomer selection was shown to have significant effect on mean pore diameter and effective porosity, surface roughness and human bone derived cell proliferation. A mean pore size of 0.16±0.006 μm and effective porosity of 190±110 m-1 and a surface roughness of 2.385±0.969 nm was seen for the fibres prepared from the mixture of d- and l-isomer. For the l-isomer only, a mean pore size of 0.54±0.019 μm, and effective porosity of 2640±1500 m-1 and a surface roughness of 6.214±2.517 nm was seen. Twice as many cells were seen on membranes made with the l-isomer after 1 week in culture. Membrane spinning conditions were selected to control membrane morphology, for example air gap and nonsolvent composition used to control skin thickness. Mathematical modelling of the mass transfer mechanism further aids the selection of the manufacturing conditions.The results suggest that biodegradable hollow fibre membranes can be tailor-made to fine tune physical and mechanical properties so providing an extremely versatile scaffold for a variety of tissue types.
R7: Poster Session
Session Chairs
Thursday AM, April 12, 2007
Salon Level (Marriott)
9:00 PM - R7.1
Conductive Thin Films on Functionalized Polyethylene Particles.
Yeon Seok Kim 2 3 , Jaime Grunlan 1 2 3
2 Materials Science and Engineering, Texas A&M University, College Station, Texas, United States, 3 Polymer Technology Center, Texas A&M University, College Station, Texas, United States, 1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractHyperbranched polyethylenimine (PEI) is covalently grafted to the surface of polyethylene (PE) particles in an effort to promote the growth of conductive thin films deposited using layer-by-layer (LbL) assembly. Layer-by-layer films are then deposited using dilute aqueous mixtures containing carbon black stabilized with polyethylenimine or poly(acrylic acid). Deposition of carbon black-filled bilayers on PEI-grafted PE shows uniform surface coverage and strong bonding after just 2-bilayers, while neat polyethylene shows patchy film growth and poor adhesion, requiring 8-bilayers to achieve full surface coverage. Acid-oxidized PE shows intermediate behavior with regard to deposition, but shows weak bonding like neat polyethylene. LbL films are characterized using electron microscopy and thermogravimetric analysis, which show linear growth for PEI-grafted particles and non-linear growth for neat and acid-oxidized particles. Following carbon black deposition, the electrical conductivities of films made by compressing the coated particles were compared. No conductivity can be measured for films made with neat PE particles containing 2 and 4-bilayers, but acid-oxidized and PEI-grafted systems exhibit conductivities of 0.0000045 and 0.01 S/cm, respectively. Plotting conductivity as a function of carbon black concentration reveals a percolation threshold below 0.01 wt% and a conductivity of 0.2 S/cm with just 6 wt%. This combination of covalent polyelectrolyte grafting and layer-by-layer deposition could potentially be used to impart useful properties to a variety of polyolefin surfaces.
9:00 PM - R7.10
Electrical Transport Behavior in Phenolic Resin-based Composites Doped with Multi-walled Carbon Nanotubes.
Renato Minamisawa 1 , Bopha Chhay 1 , Daryush Ila 1
1 Center for Irradiation of Materials, Alabama A&M University, Huntsville, Alabama, United States
Show Abstract9:00 PM - R7.11
Sorption and Diffusion of Supercritical Carbon Dioxide in Poly(vinyl fluoride)
Muoi Tang 1 , Yan-Ping Chen 2
1 Chemical Engineering, Chinese Culture University, Taipei Taiwan, 2 Dept. of Chemical Engineering, National Taiwan University, Taipei Taiwan
Show AbstractSorption and diffusion of supercritical carbon dioxide (SCCO2) in poly (vinyl fluoride) (PVF) at 40 C and 20 MPa are shown in this study. The saturated sorption in the PVF specimen with 3.8 μm thickness has been observed at 40 C and 20MPa for 3 h. A gravimetric method was used to measure the mass gain of CO2 in the PVF specimen under ambient conditions. Fick’s diffusion model has been applied to calculate the sorption amount (Ms) and the desorption diffusivity (Dd) of CO2 in the PVF specimen. The sorption amount (Ms) of CO2 in the PVF specimen is 5.66 wt%. The diffusivity of CO2 in PVF specimen is 7.7x10-13 m2/s for short time period and 1.1x10-13 m2/s for long time period. The interaction between CO2 and the PVF specimen has also been investigated by the FTIR spectrum. According to the spectra of the different time periods at the bending mode (ν2) of CO2 near 660 cm-1, the desorption of CO2 in the PVF specimen completely finished about 1 h venting from high-pressure SCCO2 cell. The wide split of IR bands at the antisymmetric stretching mode (ν3) of CO2 near 2340 cm-1 in the PVF specimen indicates that there are bonding forces between CO2 and C-F group of PVF specimen. The peak at 2340 cm-1 vanished after 2 to 4 h venting from high-pressure SCCO2 cell. Compare with the untreated PVF specimen, the stretching mode of C-F group near 828 cm-1 of the treated PVF specimen has a shift of 1.5 cm-1. It can show that there is the weak dipole-dipole interaction between C-F group and CO2. Furthermore, the glass transition temperature (Tg) is measured by LT-DSC. The Tg of the treated PVF specimen has a shift of about 5.3 C to lower temperature, and this result indicates that plasticization phenomenon has occurred in the treated PVF specimen.
9:00 PM - R7.12
Polarized Silver Nanoparticles by Ionic Liquid and Its Application to Facilitated Olefin Transport Membranes
Sang Wook Kang 1 , Kookheon Char 1 , Yong Kang 2
1 Chemical and Biological Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Department of Chemical Engineering, Hanyang University, Seoul Korea (the Republic of)
Show AbstractPartially polarized silver nanoparticles induced by ionic liquid have been prepared and their applicability for facilitated olefin transport membrane has been explored. Previous study showed that the polarized silver nanopartices by p-benzoquinone played an olefin carrier for separation of propylene/propane mixtures. Here, the highly charged nature of ILs has been utilized to polarize the surface of silver nanoparticles, resulting in the facilitated olefin transport. The presence of the silver nanoparticles in BMIM+BF4- resulted in an increase in propylene permeance while the propane permeance remained constant. In particular, above 0.1 weight ratio of silver nanoparticles, the facilitated olefin transport was observed in separation performance of propylene/propane mixtures. The improved separation performance is due to the facilitated olefin transport, resulting from the carrier activity of polarized Ag metal surface induced by the ionic liquid. The mixed gas selectivity was about 0.9 for the BMIM+BF4- membrane without silver nanoparticles with a permeance of about 0.5 GPU. However, the addition of silver nanoparticles significantly improves the separation performance; the selectivity of the BMIM+BF4-/Ag metal composite membrane was found to be 17, with mixed gas permeances of 2.7 GPU. The stability of the long-term separation performances of the BMIM+BF4-/Ag metal composite membrane was also tested, and exhibited stable separation performance throughout continuous operation for 120 hours.The interaction in BMIM+BF4-/Ag metal composite between the Ag metal and BF4- ions was investigated using FT-Raman spectroscopy. Raman results suggest the following interaction scheme: 1) BMIM+BF4- exists as the forms of ion pairs and ion aggregates, and 2) BF4- ions interact with the surface of Ag metal to some degree, resulting in a weakening of the interaction between BF4- and BMIM+. Thus it was concluded that the interaction between Ag metal and BF4- caused the surface of Ag metal to be partially polarized as positive charge, presumably making the silver metal more active in silver-olefin complexation.
9:00 PM - R7.13
Evolution of the Thermal and Electrical Transport Properties of GPC:CNT Composites versus Concentration.
Bopha Chhay 1 , Renato Minamisawa 1 , Bangke Zheng 1 , Satilmis Budak 1 , Daryush Ila 1
1 Center for Irradiation of Materials, Alabama A&M University, Normal, Alabama, United States
Show Abstract9:00 PM - R7.14
Rheology of Nanofiber Suspensions: Effect of Concentration and Fiber Aspect Ratio.
Manish Tiwari 1 , Alexander Bazilevsky 1 , Alexander Yarin 1 , Constantine Megaridis 1
1 Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, Illinois, United States
Show Abstract9:00 PM - R7.2
Tailoring Carbon Nanotube Dispersion and Conductivity with Weak Polyelectrolytes.
Lei Liu 2 3 , Jaime Grunlan 1 2 3
2 Materials Science and Engineering, Texas A&M University, College Station, Texas, United States, 3 Polymer Technology Center, Texas A&M University, College Station, Texas, United States, 1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractCarbon nanotubes are an exciting material due to their small size, high modulus, and high intrinsic conductivity. As a result, nanotubes hold significant promise for imparting electrical conductivity, mechanical strength, and thermal conductivity to polymeric materials. Despite this potential, the ability to stabilize nanotubes in solution remains a significant hurdle to their widespread use. This has led to significant research efforts on the use of stabilizing agents and chemical modification of the nanotubes to impart solubility. The present work demonstrates a method to control the dispersion of carbon nanotubes in aqueous solution and the microstructure of composite films using poly(acrylic acid) and poly(allylamine hydrochloride). As the pH of an aqueous mixture containing 1 wt% polymer and 0.1 wt% nanotube is altered, a significant change in viscosity is observed that suggests changing dispersion state of the nanotubes. Drying these aqueous suspensions into composite films reveals pH-dependent microstructural differences that influence electrical conductivity. These microstructural changes are reversible. This behavior has significant implications for the processing of carbon nanotubes and tailoring of composite properties. Many of the relationships uncovered here could be applied to other types of hydrophobic nanotubes and nanowires.
9:00 PM - R7.3
The Impact of Bentonite Extrusion on Radionuclide Migration in a Saturated Planar Fracture.
Robert Angelo Borrelli 1 , Joonhong Ahn 1
1 Department of Nuclear Engineering, University of California - Berkeley, Berkeley, California, United States
Show AbstractThis paper presents results of numerical explorations for radionuclide transport in bentonite extruding in rock fractures that intersect the bulk bentonite in the Engineered Barrier System (EBS) for the saturated repository. In the EBS, bentonite will be utilized for the buffer primarily due to favorable characteristics: low permeability, high sorption capacity, and high swelling capacity. Bentonite particles possess an overall negative charge and high surface area and thus exhibit a high sorption capacity and swelling capability greatly beyond its initial volume when in contact with water. This effect results in extrusion of the buffer into fractures in the surrounding rock, which can seal intersecting fractures and reduce releases of radionuclides.
Previous studies of radionuclide transport in the EBS and its vicinity do not consider the effects of the bentonite swelling and extrusion into rock fractures. This paper will present a radionuclide migration model that incorporates bentonite extrusion into a radionuclide transport study. The model consists of two parts: one for movement of water and bentonite in a planar fracture and the other for radionuclide transport in the same planar fracture by taking into account advection, diffusion, sorption onto moving bentonite, and decay. Movement of water and bentonite is quantified by obtaining space-time-dependent porosity and tip location of the extruding bentonite. The radionuclide transport model is unique in that a solid phase movement is included and in that water will flow in a direction countercurrent to the direction of bentonite extrusion.
For this analysis, a planar fracture assumed to be initially filled with water intersects water-saturated bulk bentonite. The bulk bentonite has a cylindrical shape, and extrusion occurs in a radial direction into the intersecting planar fracture. A radionuclide source is located at the intersection between the bulk bentonite and the fracture. A constant concentration is assumed at the source. Beyond the tip of the extruding bentonite, it is assumed that only water fills the fracture. Finite element solutions have been derived for the porosity and for the radionuclide concentration.
Numerical results for a strongly sorbing radionuclide indicate that concentration exceeds the constant concentration at the source, and that radionuclides are contained completely within the region of bentonite extrusion. Due to assumed strong sorption, radionuclides are primarily transported in the fracture by the solid phase movement. Containment is also affected by the water flow countercurrent to bentonite-particle movement. These observations suggest importance of the region in the vicinity of buffer/rock interface, especially for short lived radionuclides. Validation of this radionuclide transport model can allow for more long term analyses and eventual inclusion of the model into future repository performance assessments.
9:00 PM - R7.4
Preparation and Characterization of the Polycarbonate Based Composite Gas Separation Membranes.
Levent Yilmaz 1 , Halil Kalipcilar 1 , Deger Sen 1
1 Chemical Engineering, METU, Ankara Turkey
Show AbstractPolymeric membranes for gas separations have been known to have an upper bound trade-off curve between permeability and selectivity. The incorporation of zeolites into polymer matrix has been examined as a promising way to overcome this limitation by modifying the membrane morphology. Due to their partial incompatibility, non-selective voids may form reducing membrane performance. Better interaction can be provided by modifying the matrix polymer with low molecular-weight additives (LMWA). These additives should have multifunctional groups that are capable of interacting both with polymer and zeolite.In this study, the matrix polymer, poly(bisphenol-A-)carbonate (PC), was modified with a LMWA (p-nitroaniline, pNA) for performance improvement by better interaction of polymer chains with zeolite 4A particles. PC based composite membranes were prepared by solvent-evaporation method using dichloromethane as solvent. Suitable zeolite range for workable membranes was determined by the preparation of PC/zeolite 4A membranes, and it was found as 10-30% (w/w). The concentration of PC in the membrane preparation solution was kept constant at 12% (w/v), and the pNA concentration was varied in between 1-5% (w/w) of PC. Single gas permeability measurements of nitrogen, hydrogen, oxygen, carbondioxide and methane were done. Characterization of the membranes was revealed from DSC thermograms and SEM micrographs.PC/pNA and PC/zeolite 4A membranes showed lower permeabilities and higher selectivities compared to pure PC membrane. The nitrogen permeabilities through PC membrane, PC/zeolite 4A (20% w/w) membrane and PC/pNA (5% w/w) membrane were 0.27, 0.20 and 0.08 Barrer, respectively. The H2/N2 selectivities were 57.3, 66.2 and 91.0 for these membranes. These results indicated that the incorporation of zeolite and pNA into PC matrix improved the performance values. On the other hand, the permeability and selectivity values of pNA containing PC/zeolite 4A membranes were in between those of PC/pNA and PC/zeolite 4A membranes. These values are close to the performance values of PC/pNA (5% w/w) membranes, indicating the effect of pNA was more significant than zeolite. DSC analysis of the PC/zeolite 4A MMMs showed that the addition of zeolite 4A particles into PC matrix has no effect on the glass transition temperature, Tg, of PC membrane, indicating the no significant interaction between PC and zeolite. On the other hand, the incorporation of zeolite 4A into pNA modified PC membranes increased the Tg of PC/pNA membranes. Increase in Tg of PC/pNA/4A MMMs could be related to the pNA content of the membranes. SEM images of the PC/zeolite 4A MMMs showed voids around zeolite particles, which are believed to occur due to weak interaction between polymer chains and zeolite particles. In PC/pNA/zeolite 4A MMMs, this structure was slightly intensified. Therefore,it can be concluded that pNA acts as a facilitator to improve interaction between PC and zeolite.
9:00 PM - R7.5
Thermal Ttransport Mechanism in Inorganic and Polymeric Glasses.
Sergei Shenogin 1 , Arun Bodapati 1 , Pawel Keblinski 1 , Alan McGaughey 2
1 Nanotechnology Center, RPI, Troy, New York, United States, 2 Mechanical Engineering Department, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show Abstract9:00 PM - R7.6
Carbon Nanofiber Induced Bubble Growth Suppression in Liquid Crystalline Hydrocarbon Precursor for Carbon Composite
Chris Calebrese 1 , Linda Schadler 1 , Glenn Eisman 1
1 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractMesophase pitch (MP) is a discotic liquid crystalline hydrocarbon used as a precursor in producing carbon fibers and carbon composites. During carbon composite processing MP is injected in the melt into a fiber perform, then oxidized in the solid state over a period of hours, days, or weeks to form oxygen crosslinks resulting in a thermoset MP. Finally, the composite is pyrolized above 1000 °C in an inert environment to remove hydrogen and oxygen from the structure. These elements are removed as volatiles such as H2, H2O, CO2, and low molecular weight hydrocarbons. Incomplete oxidation of the composite will lead to foaming of the thermoplastic MP as gaseous products are released during pyrolysis. It has been found that the addition of carbon nanofiber to MP can reduce foaming (measured by the change in volume) by over 1000 % compared to unfilled MP, without the use of a time consuming oxidation step. Currently, we are investigating this phenomenon in terms of volatile gas transport and isotropic bubble growth. Large reductions in swelling are observed as the percolation limit is approached, and the presence of carbon nanofibers may ease the release of products gases during pyrolysis, reducing volume of gas available for bubble nucleation and growth. Volumetric loadings of 3 to 13 % carbon nanofiber increase the bulk viscosity by a factor of 5 to 50, providing a mechanism of bubble growth retardation, where the bubble growth rate is inversely proportional to the melt viscosity. The current work is being investigated for possible use in making injection moldable carbon bipolar plates for proton exchange membrane fuel cells.
9:00 PM - R7.7
Characterization of Electromechanical Transduction in Polyelectrolyte Gels for Mechanical Sensor Applications
Katsiaryna Prudnikova 1 , Marcel Utz 1
1 Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia, United States
Show AbstractWe report a new experimental method for the characterization of the electromechanical properties of polyelectrolyte gels (PG). PGs have been studied extensively, but with limited success, as mechanical actuators. However, they show substantial promise as biocompatible mechanical sensors. However, in order to integrate them into actual devices, their electromechanical transduction properties need to be characterized in a reproducible manner. We have therefore developed a technique to measure the mechanically induced change in electrostatic potential in PGs. The polyelectrolyte gel is subjected to a well-defined pressure gradient by placing a thin, flat sample on a substrate with integrated electrodes and indenting it with a soft sphere. The potential values at the electrodes were measured using a CMOS operational amplifier circuit with input impedance of 1014 Ω. This method was utilized to quantify the electromechanical coupling in poly(acrylic acid-co-acrylamide) gels swollen in water and various concentrations of NaCl solution.
9:00 PM - R7.8
Fabrication of AlPO4-zeolites Filled Polymer Composite Membranes and their Properties.
K. Byrappa 1 , Byrappa Shayan 2 , B. Suresh Kumar 1 , B. Siddaramaiah 2 , C. Ranganathaiah 3 , Gummididala Narasimha Rao 1
1 DOS in Geology, University of Mysore, Mysore, KARNATAKA, India, 2 Department of Polymer Science and Technology, V.T.U. SJCE Manasagangogtri, Mysore, Karnataka, India, 3 International Advanced Research Center for Powder Metallurgy & New Materials, ARCI, Hyderabad, Andhra Pradesh, India
Show Abstract9:00 PM - R7.9
Effects of Al2O3 Nanopowder Filler Size on Glassy Polymeric Carbon Electrical Transport Behavior.
Renato Minamisawa 1 , Bopha Chhay 1 , Daryush Ila 1
1 Center for Irradiation of Materials, Alabama A&M University, Huntsville, Alabama, United States
Show Abstract
Symposium Organizers
Jaime Grunlan Texas A&M University
Dibakar Bhattacharyya University of Kentucky
Eva Marand Virginia Polytechnic Institute and State University
Oren Regev Ben-Gurion University of the Negev
Anna Balazs University of Pittsburgh
R8: Barrier and Separation Membranes
Session Chairs
Glenn Lipscomb
Michael Tsapatsis
Thursday AM, April 12, 2007
Room 2000 (Moscone West)
9:30 AM - **R8.1
Polymer-Inorganic Membrane Materials for Energy Efficient Separations
William Koros 1
1 Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractEnergy and environmental challenges caused by global development are attractive targets for membranes as population expands and emerging economies compete for resources. Reverse osmosis purification of water was the first large scale commercially viable membrane fractionation of low molecular weight liquid mixtures. Like all cases involving fractionation of low molecular weight using membranes, RO purification of potable water from brine relies upon “partitioning selectivity” and “mobility selectivity” contributions. Optimization of membrane materials and structures for this application took place over two decades, but these membranes are now rapidly displacing thermal desalting. By understanding how and why RO has displaced thermally intensive distillation in this large scale application, one can see how to help expand the energy-efficient membrane paradigm more broadly. Conventional solution-processable polymers and inorganic materials each have limitations that currently prevent their use across the full spectrum of membrane-based separation applications. For instance, for polymers, penetrant size and shape-discriminating ability is often lower than desired; however, for pure inorganic membranes, brittleness and high manufacturing cost are drawbacks. Ideally, hybrid materials comprising blends of organic and inorganic materials can be formulated to combine the best characteristics of each of the components. Besides offering technical advantages, hybrid materials are compatible with existing economical processes for membrane formation. This compatibility is valuable, since maintaining attractive economics is crucial to compete successfully with other separation technologies. Material science and processing technology appear to be the keys to overcoming the challenges to introducing this next generation of membranes. These advanced membrane materials and structures push the state of the art in terms of theory and characterization techniques in the materials science and engineering fields. Some examples of these types of materials that offer the greatest promised will be discussed to illustrate the above issues, challenges and opportunities.
10:00 AM - **R8.2
Gas Permeation Properties of Polymer Nanocomposite Films.
Donald Paul 1 , Rhutesh Shah 1
1 Chemical Engineering, University of Texas at Austin, Austin, Texas, United States
Show AbstractImprovement of barrier properties is one of the frequent reasons for creating polymer nanocomposites. This presentation will focus on the permeation of gases in nanocomposites based on polyolefins containing particles consisting of layered silicate platelets in various states of exfoliation. Where possible, experimental results will be compared with applicable theories. Key issues affecting the reduction of the gas permeability of these composites include particle aspect ratio (related to the degree of exfoliation and the intrinsic size of the particles) and particle orientation (related to method of film formation). Low density polyethylene nanocomposites formed from organoclays were converted into films by compression molding and by a blown film process; these results will be compared. Similar nanocomposites were also formed from an ethylene-based ionomer which interacts much more favorably with the organoclay and, thus, leads to a higher level of exfoliation. Other physical and rheological properties of these materials and their morphological characterization will be described. In addition, the gas barrier propeties of butyl rubber nanocomposite films containing vermiculite made by a latex process will be discussed. This process leads to extremely high barrier improvement owing to the much higher filler contents that can be achieved and to the very high aspect ratio of vermiculite platelets compared to montmorillonite.
10:30 AM - R8.3
Layer-by-Layer assembled Carbon Nanotube Membranes for Ethane/Ethylene Separation
Szushen Ho 1 , Nicholas Kotov 1
1 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractEthane/Ethylene separation has long been a challenge because of their similarity in size, mass, geometry, and interaction parameters. The most successful approach by using the interaction of the double bond of ethylene with transition metal ions, such as Ag+, Ni2+, Fe3+ and Fe2+, introduces sulfur and other impurity that poison the feedstocks. Instead of transition ions, single-walled carbon nanotubes are used. They are assembled into polymeric membranes using layer-by-layer technique. Carbon nanotubes and related nanostructures are proven to have high electron affinity and are confirmed to demonstrate strong adsorption of ethylene. The small thickness of the LBL membranes contributes to high permeation flux, while the selectivity adsorption of ethylene on carbon nanotubes suggests high selectivity.
10:45 AM - R8.4
Nanoporous Membranes for Virus Filtration with high flux
Seung Yun Yang 1 , Incheol Ryu 2 , Sung Key Jang 2 , Jin Kon Kim 1 , Thomas P. Russell 3
1 Environmental Science and Engineering & Chemical Engineering, POSTECH, Pohang Korea (the Republic of), 2 Life sciences, POSTECH, Pohang Korea (the Republic of), 3 Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts, United States
Show AbstractNanoporous templates prepared by block copolymer thin films with cylindrical domains have been employed for biomaterial separation with high selectivity.1) The thickness of block copolymer film in nanoporous membrane was less than ~ 100 nm, because the perpendicular porous structures are not extended for thick films. Therefore, thin film could not be maintained mechanically at higher pressures, which is necessary for high flux. In this study, we introduce a new double layered nanoporous membrane suitable for virus filtration with high flux maintaining high selectivity. The upper layer is nanoporous block copolymer film with a thickness of ~ 160 nm, which is suitable even at high pressure. But, in this situation, the orientation of nanopores was not completely perpendicular. Namely, only nanopores located near top and bottom of the film are vertically oriented, whereas the nanopores inside the film are randomly oriented. This block copolymer thin film floated on conventional micro-filtration membrane. It is found that a new double layered nanoporous membrane showed high mechanical stability even at a pressure of 2 bar, while maintaining high selectivity for the separation of human rhinovirus type 14 which has a diameter of ~ 30 nm and is a major pathogen of the common cold in humans.1) Adv. Mater. 18, 709 (2006)
11:00 AM - R8: Barrier
BREAK
11:30 AM - **R8.5
Gas Barrier Behavior of Polystyrene/Montmorrilonite Clay Nanocomposites: Effect of Mineral Layer Aggregation
Sergei Nazarenko 1 , Syed Qutubuddin 2
1 Polymer Science, The University of Southern Mississippi, Hattiesburg , Mississippi, United States, 2 Chemical Engineering, Case Western Reserve University, Cleveland, Ohio, United States
Show AbstractThree model PS/clay hybrid systems, with dissimilar layer morphologies, have been prepared in this work in order to develop fundamental understanding of the effect of mineral layer aggregation on gas barrier behavior of layered silicate nanocomposites (LSNs). All the composites were prepared via in- situ polymerization of styrene in the presence of three different clays: unmodified montmorrilonite (MMT) and MMT modified with zwitterionic cationic surfactant octadecyldimethyl betaine (C18DMB), and with polymerizable cationic surfactant vinylbenzyldimethyldodecylammonium chloride (VDAC). WAXS and TEM was used to probe mineral layer organization and to expose the morphology of these systems. Polymerization using unmodified MMT led to formation of conventional composite structure consisting of unintercalated, randomly oriented and homogeneously dispersed in the PS matrix primary clay particles. Polymerization using C18DMB –MMT clay led to formation of intercalated nanocomposite structure consisting of randomly oriented and homogeneously dispersed in the PS matrix ordered layer stacks. Finally, polymerization using PS/VDAC-MMT led to formation of transitional (disordered intercalated) nanocomposite structure consisting of randomly oriented, homogeneously dispersed in the PS matrix disordered layer stacks.Oxygen barrier properties of PS/MMT clay nanocomposites was determined as a function of mineral composition and compared with that for conventional composite PS system containing unmodified MMT. Both PS/VDAC-MMT and PS/C18DMB-MMT nanocomposites displayed relative oxygen permeability (diffusivity) noticeably smaller than that found for the conventional composite PS/Na-MMT system. In turn, PS/C18DMB-MMT LSN system showed lower permeability than PS/VDAC-MMT LSNs. Yet, the reduction of permeability for the nanocomposites was considerably smaller than that anticipated assuming that individual mineral layers were homogeneously dispersed in PS matrix. Lower oxygen barrier found for the nanocomposites in this work was attributed to the effect layer aggregation. The layer morphology of all the hybrids, in particular LSNs, was studied. Systematic statistical analysis of the layer aggregate parameters such as characteristic width, length, number of layers per aggregates enabled to develop the representative morphological models for nanocomposite structures.It was possible to expand the Nielsen equation, originally derived to describe relative permeability in the fully delaminated composite structure containing homogeneously dispersed layers, so it can be used to predict relative permeability for nanocomposite structure which consists of a polymer matrix with homogeneously dispersed ordered layer stacks (aligned or randomly oriented) comprised of equal number of layers (disks) N. Fairly good agreement was found between the new approach predictions the results of oxygen barrier measurements and morphological observations for all studied nanocomposites.
12:00 PM - R8.6
Fluorescent Nanoparticles as Probes of Porosity and Defects in Membranes.
Wade Richardson 1 , Kelly Milani 1 , Douglas Loy 1
1 Materials Science and Engineering, University of Arizona, Tucson, Arizona, United States
Show Abstract12:15 PM - R8.7
Interactions of the Partially Polarized Surface of Silver Nanoparticles by p-Benzoquinone with Olefin and Its Implication to Facilitated Olefin Transport
Yong Kang 1 , Sang Kang 2
1 Department of Chemical Engineering, Hanyang University, Seoul Korea (the Republic of), 2 Chemical nad Biological Engineering, Seoul Natonal University, Seoul Korea (the Republic of)
Show AbstractA new application of metallic silver nanoparticles as a novel olefin carrier for facilitated olefin transport membranes has been explored. The surfaces of silver nanoparticles were chemically activated to induce partial positive charge using an electron acceptor, p-benzoquinone. It is thus expected that the chemically activated surface of the silver nanoparticles reversibly interacts with olefin molecules, resulting in facilitated olefin transport. The nanocomposite membranes containing silver nanoparticles in poly(ethylene-co-propylene) (EPR) were prepared and applied for separation of olefin/paraffin mixtures such as propylene/propane mixtures. The separation performance of the 50/50 (v/v) propylene/propane mixture was tested through the 1/1/0.85 EPR/AgO/ p-benzoquinone membrane with time for up to 105 hrs. The selectivity and permeance were nearly invariant for the duration of the experiment up to 105 hrs after reaching the steady state, suggesting stable carrier action of the surface of the silver nanoparticles.XPS was used to observe the change of the chemical environment around the silver nanoparticles in EPR/Ago composite membranes upon the incorporation of p-benzoquinone. The binding energy of the d5/2 orbital of the silver particle in the EPR/Ago/p-benzoquinone system increased gradually with increasing p-benzoquinone content. This indicates that the binding energy of the valence electrons in the silver atoms increased due to the interactions between the silver atoms and p-benzoquinone, and that the surface of the silver nanoparticles was partially positively charged.The complexation of propylene with the surface of the silver nanoparticles was investigated using FT-IR spectroscopy. Upon exposure to propylene, the EPR/Ago/p-benzoquinone composite showed new shoulder peaks at 1664 and 1640 cm-1 representing the C=C stretching vibration of propylene. The intensities of both peaks at 1664 and 1640 cm-1 decreased and a new peak at 1649 cm-1 became dominant with increasing propylene exposure time. In other words, the free propylene peaks at 1664 and 1640 cm-1 shift to 1649 cm-1 presumably due to the partial electron transfer from the C=C bond of propylene to the partially positively charged surface of the silver nanoparticles.This is the first attempt to use silver nanoparticles activated by electron acceptors such as p-benzoquinone as olefin carriers for facilitated olefin transport. The partially positively charged surface, confirmed by XPS, may cause its interactions or complexation with olefin molecules, such as propylene and ethylene, as supported by FT-IR spectroscopy and ab-initio calculations.
12:30 PM - R8.8
WITHDRAWN 04/02/07 Studies on Moisture Diffusion Phenomenon in CNT-modified Epoxy Composites
Gopala Krishna Rao Raja Manuri Vankata 1 , Shylaja Srihari 1 , Vanaja Avadhanam 1
1 Fibre Reinforced Plastics (FRP) Division, National Aerospace Laboratories (NAL), Bangalore, India, Bangalore, Karnataka, India
Show AbstractThursday, April 12Withdrawn-oralR8.8 @ 11:30 am
R9: Thermal Behavior of Polymeric Materials
Session Chairs
Thursday PM, April 12, 2007
Room 2000 (Moscone West)
2:30 PM - **R9.1
From Atoms and Vibrations to Thermal Transport Properties of Polymer Nanocomposites
Pawel Keblinski 1
1 , Resselaer Polytechnic Institute, troy, New York, United States
Show AbstractTransport measurements on carbon-nanotube (CN) polymer composites demonstrate that electrical conductivity increases sharply when the percolation threshold is crossed due to development of continuous conductive paths for the electric current. By contrast, thermal transport shows no signatures percolations. Furthermore, even below the percolations threshold, thermal conductivity increases are much lower than that predicted by engineering rule of mixtures. Using atomistic simulations we demonstrate that a limiting factor for the heat flow in CN composites is significant interfacial thermal resistance arising from poor thermal coupling between the tubes and the matrix. Our results on the interfacial thermal resistance are in agreement with those obtained from femtosecond laser based thermal characterization of the CN-matrix interface. Based on the predictions of a homogenization theory accounting for the interfacial thermal resistance we suggest design routes towards increasing thermal conductivity of carbon nanotube (fiber) as well as particulate polymer nanocomposites. Finally we will discuss the issue of localized heating due to radiation induced heat generation by optically active nanofibes and nanoparticles embedded in soft materials, Such localized heating can be used for proposed for selective thermal control of chemical reactivity or biofunctionality.
3:00 PM - R9.2
Thermal Transport Through a Clay-Based Aerogel with Embedded Polymer
Stephen Hostler 1 , Matthew Gawryla 2 , Alexis Abramson 1 , David Schiraldi 2
1 Mechanical and Aerospace Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 2 Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio, United States
Show AbstractAerogel materials exhibit superior thermal insulation characteristics due largely to their highly porous internal structure. A recently developed class of montmorillonite clay-based aerogels provides the attractive thermal properties of traditional aerogel materials using constituents that are both chemically benign and abundantly available. These clay-based materials have an internal structure dominated by thin, minimally connected sheets. We report results for the thermal conductivity of clay-based aerogels with sheets both parallel and perpendicular to the direction of heat flow. Results are compared for aerogels made from clay alone and those with polyvinyl alcohol introduced during processing. The incorporation of the polymer, which forms a thin layer on the clay walls within the structure, improves the mechanical rigidity of the aerogel. Preliminary results demonstrate that as well as strength advantages, the addition of the polymer also leads to a reduction in the thermal conductivity. Experimental thermal conductivity data as well as a model to describe the mechanisms involved in impeding thermal transport will be presented.
3:15 PM - R9.3
Effect of Nnetwork Formation of Nanoparticles on the Processing and Flammability of Polymer Nanocomposites.
Sameer Rahatekar 1 , Mauro Zammarano 1 , Andrea Panara 1 , K. Koziol 2 , A. Windle 2 , J. Gilman 1
1 Materials and Products Group, Fire Research Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Show Abstract