Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session Q18: Polymer Nanocomposites II |
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Sponsoring Units: DPOLY Chair: Erik Hobbie, National Institute of Standards and Technology Room: Morial Convention Center 210 |
Wednesday, March 12, 2008 11:15AM - 11:27AM |
Q18.00001: Cluster Dominated Rheology of SWNTs based Polymer Nanocomposites Tirtha Chatterjee, Ramanan Krishnamoorti An outstanding issue in the field of polymer nanocomposite has been to separate and quantify the roles of polymer-particle, particle-particle and polymer mediated particle-particle interactions in controlling properties of such systems. In this study, we have attempted to understand the linear and non-linear rheological properties of the nanocomposites in terms of their structure and the underlying polymer-particle interactions. The network structure of single walled carbon nanotube in polymeric matrices is investigated using SANS and USANS(The neutron scattering work utilized facilities supported in by the NSF under Agreement No. DMR-0454672). In their quiescent state, a hierarchical fractal network made of aggregated flocs or clusters inside which tubes overlap each other to form dense mesh, dominates the nanoparticle structure. We have identified that the floc-floc interactions provides the stress bearing capacity and are responsible for strong modulus scaling of these systems. The interaction is inversely related to the particle dispersion state which influences the absolute values of the viscoelastic parameters. More interestingly, under steady shear these nanocomposites show network independent behavior. [Preview Abstract] |
Wednesday, March 12, 2008 11:27AM - 11:39AM |
Q18.00002: Preparation and Characterization of Polypropylene / MWCNT Dispersions Saswati Pujari, Wesley Burghardt, Thillaiyan Ramanathan, L. Catherine Brinson, Kosmas Kasimatis, John Torkelson Dispersions of multiwall carbon nanotubes in polypropylene are prepared via melt batch mixing and solid-state shear pulverization, and characterized via linear viscoelastic measurements, SEM, polypropylene crystallization kinetics, electrical conductivity and dynamic mechanical analysis. Increasing the intensity or duration of the melt mixing leads to higher dispersion, evidenced by increases in a low-frequency elastic plateau and accelerated PP crystallization kinetics attributed to more effective heterogeneous nucleation. The sample prepared by pulverization exhibits faster crystallization kinetics than any of the melt blended samples, but in contrast shows no measurable low frequency elastic plateau. Electrical conductivity measurements similarly show higher conductivity in melt blended samples. This may be attributable to scission of the nanotubes during pulverization, such that even well dispersed tubes cannot form an entangled network at a given concentration. At the same time, pulverized composites show marked increase in stiffness at low loadings, indicating that tube scission due to pulverization is not catastrophic. Conversely, long mixing times required in melt blending cause substantial thermal degradation of the polymer matrix with a corresponding loss of mechanical properties. [Preview Abstract] |
Wednesday, March 12, 2008 11:39AM - 11:51AM |
Q18.00003: Improving the Dispersion and Interfaces in Polymer-Carbon Nanotube Nanocomposites by Sample Preparation Choice Chang-Uk Lee, Mark Dadmun Polymer nanocomposites composed of poly(styrene-\textit{ran-}vinyl phenol) (PSVPh) copolymers and 5 wt {\%} multi-walled carbon nanotubes (MWNTs) were prepared by three different methods, including melt-mixing and solution casting. The MWNTs were either oxidized to incorporate oxygenated defects or utilized as received. The mechanical properties of the nanocomposites were measured by DMA, and the extent of intermolecular hydrogen bonding between MWNTs and PSVPh was quantified by IR. Our DMA results suggest that melt-mixing leads to more stable morphologies of the final nanocomposites than solution casting. Additionally, the IR analysis of the nanocomposites indicates melt-mixing can result in the formation of more intermolecular hydrogen bonding between the MWNTs and PSVPh than solution casting, and thus suggests that melt-mixing leads to nanocomposites with more reproducible mechanical properties than solution casting. Our results thus provide guidelines to realize improved morphologies and properties of polymer carbon nanotube nanocomposites by optimizing intermolecular interactions between MWNTs and polymers using processing. [Preview Abstract] |
Wednesday, March 12, 2008 11:51AM - 12:03PM |
Q18.00004: Enhancing Dispersion and Properties of SWNT-polymer Nanocomposites by Controlled Non-covalent Interactions Dias Linton The enhancement of the dispersion and properties of singlewalled carbon nanotubes in a polymer nanocomposite via non-covalent interaction is studied. 1{\%} w/w SWNT are dispersed in random copolymers of methyl methacrylate and 2-(dimethylamino)ethyl methacrylate (DMAEMA), where the composition of the copolymer varies from 0{\%} to 50{\%} DMAEMA. The resulting nanocomposites indicate the existence of interactions between the carbon nanotube and polymer matrix by a shift of the D* peak position ($\sim $2600-2700 cm$^{-1})$ of the polymer nanocomposite. The copolymer with 30{\%} DMAEMA shows the smallest shift, suggesting that the nanotubes are debundled, where it is expected that this non-covalent interaction originate from the tertiary amino group in DMAEMA by formation of an electron-donor interaction with the SWNT. [Preview Abstract] |
Wednesday, March 12, 2008 12:03PM - 12:15PM |
Q18.00005: Spectroscopic Investigations on Polypropylene -- Carbon Nanofibers Composites Mircea Chipara, Jones Brian, Karen Lozano, John R. Villareal, Alin Cristian Chipara, Anna Hernandez, Magdalena Dorina Chipara, David J. Sellmyer Nanocomposites were obtained by high-shear mixing of isotactic polypropylene (Marlex HLN-120-01; Philips Sumika Polypropylene Company) with various amounts of vapor grown carbon nanofibers (PR-24AG; Pyrograf Products, Inc) by utilizing a HAAKE Rheomix at 65 rpm and 180 $^{\circ}$C for 9 min followed by an additional mixing at 90 rpm for 5 min. Composites loaded with various amounts of vapor grown carbon nanofibers have been prepared. Wide angle X-Ray scattering investigations focus on the effect of carbon nanofibers on the crystalline phases of polypropylene and on the overall crystallinity degree of the polymeric matrix. Raman spectroscopy analysis concentrates on D and G bands. X-band electron spin resonance investigations aim at a better understanding of the purity of carbon nanofibers and of the ratio between conducting and paramagnetic. [Preview Abstract] |
Wednesday, March 12, 2008 12:15PM - 12:27PM |
Q18.00006: Simulation of Electrical Conductivity of Composites Containing Uniaxially-Aligned, Finite Rods above the Percolation Threshold Sadie White, Brian Didonna, Lai-Ching Chou, Tom Lubensky, Karen Winey Simulations probed the percolation behavior of composites containing isotropic and uniaxially aligned, conductive, cylindrical fillers with aspect ratios of 10, 20, and 80. In addition, the random resistor network model was used to calculate the electrical conductivity of these composites at concentrations above the percolation threshold. The observed trends compare favorably with our experimental results in carbon nanotube and carbon nanofiber polymer nanocomposites. For example, the electrical conductivity is highest when the fillers are slightly uniaxially aligned in both simulation and experimental results. In addition, the critical degree of filler orientational order at which the electrical conductivity abruptly decreases was found to depend on rod aspect ratio along the same trends noted for experimental data. This work represents the first simulations of electrical conductivity above the filler percolation threshold for oriented and isotropic composites containing permeable, conductive, finite-sized rods, and is pertinent to the rapidly expanding field of polymer nanocomposites. [Preview Abstract] |
Wednesday, March 12, 2008 12:27PM - 12:39PM |
Q18.00007: Polymer Dynamics in Single Wall Carbon Nanotube / Polystyrene Nanocomposites Minfang Mu, Russell Composto, Nigel Clarke, Karen Winey Polymer nanocomposites provide access to new regimes of polymer dynamics in which the impenetrable filler particles are comparable to and frequently smaller than the end-to-end distances of the polymer. In this study, single wall carbon nanotubes (SWCNTs) / polystyrene (PS) nanocomposite was prepared by a coagulation method. Rheological properties were measured in the linear viscoelastic regime and tracer diffusion coefficients were determined using an elastic recoil detection (ERD) method. The tracer diffusion coefficient first decreases and then increases with increasing SWCNT loading. Across this same range of filler concentration, the plateau modulus and the cross-over frequency are approximately constant. The transition from decreasing to increasing tracer diffusion corresponds approximately with the onset to rheological percolation and appears to increase with decreasing matrix molecular weight. A model is under development to describe the polymer dynamics is polymer nanocomposites. [Preview Abstract] |
Wednesday, March 12, 2008 12:39PM - 12:51PM |
Q18.00008: Periodic Patterning of Polyethylene Block Copolymers Directed by Carbon Nanotubes Bing Li, Lingyu Li, Christopher Li Periodic patterning on one-dimensional carbon nanotubes (CNTs) is of great interest from both scientific and technological points of view. Although both chemical and noncovalent CNT functionalization have attracted extensive attention during the past decades, very few efforts have been dedicated to periodic patterning on individual CNTs. Recently, we demonstrated using a controlled polymer solution crystallization method to achieve periodically decorated CNTs. Polyethylene (PE) and Nylon 6,6 single crystals were controlled to grow on CNTs, forming a unique nanohybrid shish kebab (NHSK) structure. The periodicity was, however, not uniform because the concentration governed growth mechanism. Here we report improving the regularity of the periodic NHSK structures by employing block copolymers (BCPs), poly(ethylene-b-ethylene oxide) (PE-b-PEO), to produce NHSKs on CNTs. By crystallizing BCP on CNTs via thin film crystallization, periodic structures were generated along CNTs. The characteristic microphase separation of BCP was clearly observed, forming the striking alternating stripes perpendicular to the axes of individual CNTs. Furthermore, by functionalizing the PEO blocks with thiol groups, Au nanoparticles were subsequently immobilized on the PEO domains of the hybrid nanomaterial, replicating the periodic patterns. [Preview Abstract] |
Wednesday, March 12, 2008 12:51PM - 1:03PM |
Q18.00009: Clay dispersion and interaction effects in supercritical CO2 processed polystyrene-clay nanocomposites. R. Kannan, R. Bellair, M. Manitou, S. Horsch, E. Gulari The major challenges in producing high performance nanocomposites are in effectively dispersing the clay layers in the matrix and in promoting interactions at the polymer-clay interface. A novel process exploiting the properties of supercritical CO2 (scCO2) has recently been shown to be an effective means to delaminate clay platelets with or without a polymer matrix present. In this study we demonstrate the ability of scCO2 to exfoliate commercial, organically modified clay and to produce nanocomposites with significantly improved properties. Rheology shows solid-like behavior in loadings as low at 2wt{\%}, and elastic modulus improvements as high as 2.5 orders of magnitude in 5wt{\%} nanocomposites. TEM images indicate a rich morphology for scCO2 processed composites, with a large fraction of dispersed platelets. In contrast, solution blended control samples display much larger tactoids and a lack of individual clay sheets. Unexpectedly, XRD shows a strong intercalation peak that is unchanged between solvent blended and scCO2 processed composites even though TEM and rheology show large differences in the samples. Effects of scCO2 soaking, depressurization rate, solvent, and clay dispersion are investigated to better understand the mechanisms behind the significant rheological enhancements. The degree of enhancement in the properties appears to be not only dependant on the degree of dispersion, but also on how polymer-clay interactions are promoted by the supercritical fluid. [Preview Abstract] |
Wednesday, March 12, 2008 1:03PM - 1:15PM |
Q18.00010: Surface characterization of Laponite-Poly(ethylene oxide) nanocomposite films Eduard A. Stefanescu, Ioan I. Negulescu, William H. Daly, Bogdan C. Donose, Anh V. Nguyen The aim of the present work is to understand how ionic strength of precursor polymer-clay gels influences the final structure of multilayered nanocomposite films fabricated from such gels. We have prepared three aqueous precursor gels containing 3wt\% LRD, 2wt\% PEO and 95wt\% water, in which the salt concentrations were kept at 0X, 1X and 3X with X = 5.57 *~10$^{- 5}$ g NaCl/mL. The Laponite (LRD) - PEO multilayered films (LRD60\%-PEO40\%) were fabricated by manually spreading and drying each gel on a glass slide. Prior to the AFM measurements the polymer-clay composite films where freeze-dried by immersion in liquid nitrogen until they were totally degassed. Frozen samples where then fractured and left for additional drying for 24 hours in a desiccator. The imaging procedure employed here was tapping-mode AFM. Distinct features were identified on the layered transversal surface of the films, and were attributed to the different salt concentrations in the samples. Addition of salt increases the adhesion and compactness properties of the nanoparticles, as a more uniform side surface can be observed after freeze-fracturing the materials. [Preview Abstract] |
Wednesday, March 12, 2008 1:15PM - 1:27PM |
Q18.00011: Viscoelastic Behavior of Polyhedral Oligomeric Silsequioxane (POSS)-Filled Epoxy Matrices Qingxiu Li, Stephen Hutcheson, Gregory McKenna, Kadine Mohomed, Sindee Simon Large residual stress in fiber-filled thermosetting resin composites is a major technological problem encountered during the development and applications of these materials. Strategies to reduce the residual stress of the composites include lowering the thermal stress coefficient by lowering the product of coefficient of thermal expansion and shear modulus ($\alpha $G) and/or lowering the thermal pressure coefficient by lowering the product of coefficient of thermal expansion and bulk modulus ($\alpha $K). Nanoparticles are unique fillers for resins used in composites and generally result in improved moduli and reduced linear thermal expansion coefficient (CTE); however, the effect on the thermal residual stresses has not been addressed. This paper develops epoxy/polyhedral oligomeric silsequioxane (POSS) nanocomposites with mitigated residual stress. The effect of functionalized POSS loading on the viscoelastic properties, linear coefficient of thermal expansion, and glass transition temperature of epoxy/POSS nanocomposites is investigated. The outcome of the current study provides fundamental knowledge to the design criteria for nanoparticle-filled polymer matrix composites with mitigated residual stress and high shear properties. [Preview Abstract] |
Wednesday, March 12, 2008 1:27PM - 1:39PM |
Q18.00012: Spectacular Improvements in Toughness of Poly(lactide-co- glycolide), PLG, Nanocomposites Haris Retsos Poly(lactide-co-glycolide) (PLG), a biocompatible, biodegradable polymer, was toughened by adding small amounts of surface modified clay nanoparticles. The elongation of nanocomposite during tensile tests is highly increased in comparison with that of the pure polymer, while we observed also an increase in modulus. Electron microscopy, X-ray scattering, rheometry and dielectric spectroscopy were used to investigate the toughening mechanism. It is revealed that multiple crazing occurs in the clay nanocomposite right after the yield point. The fibrils in the crazes have the ability to be significantly extended before fracture, which translates into a dramatic increase in elongation before failure. Rheological studies show that the nanoclay particles act as physical crosslinks that increase the fracture strength of the polymer. Small angle x-ray scattering used to investigate any orientation of nanoparticles during deformation and their mobility provided by the polymer matrix. [Preview Abstract] |
Wednesday, March 12, 2008 1:39PM - 1:51PM |
Q18.00013: ABSTRACT WITHDRAWN |
Wednesday, March 12, 2008 1:51PM - 2:03PM |
Q18.00014: Rheological Studies on the Quasi-quiescent Crystallization of Polypropylene Nanocomposites Xia Dong, Tongchen Sun, Fenghua Chen, Ke Wang, Qiang Fu, Charles C. Han Isothermal crystallization of isotactic polypropylene/organic modified montmorillonite binary nanocomposite (iPP/OMMT) and iPP/OMMT/PEOc (poly(ethylene-co-octene)) ternary nanocomposites were investigated by polarized optical microscope, rheometer and scanning electron microscope. The modulus change which accompanying the crystallization growth process can be clearly divided into three stages. It was found that there were different effects due to different nucleation processes (heterogeneous nucleation effect due to the presence of OMMT and the concentration fluctuation assisted nucleation effect due to the liquid-liquid phase separation), entanglement effect of iPP and PEOc chains in the ternary nanocomposite and hydrodynamic flowing effect of the amorphous phase in the three stages. [Preview Abstract] |
Wednesday, March 12, 2008 2:03PM - 2:15PM |
Q18.00015: Effect of additive particles on the crystallization of homopolymers Ashok Dasmahapatra, Guruswamy Kumaraswamy, Hemant Nanavati The effect of additive particles on polymer crystallization has been investigated using lattice dynamic Monte Carlo simulation. Additives are compatible with the polymer matrix (viz. there is an attractive ``sticky'' interaction between additives and monomers) and, additive particles have the same size as a monomer. Polymer crystallization is strongly influenced by both additive fraction, x and the additive-monomer interaction strength, $\lambda $. With increase in x or $\lambda $, the diffusivity of the polymer chain decreases dramatically. The decrease in chain mobility correlates with lower crystallinity and smaller crystallite sizes. Further, the presence of additive particles also dramatically suppresses the peak in specific heat during crystallization. Structural analysis shows that the additive particles are well-dispersed in the polymer matrix -- they are surrounded by both crystalline and non-crystalline chain segments, the relative proportions of which depend on x and $\lambda $. We show that sticky additive particles suppress crystallization. [Preview Abstract] |
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