Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session G19: Polymer Composites |
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Sponsoring Units: DPOLY Chair: Mircea Chipara, University of Texas Pan American Room: 404 |
Tuesday, March 4, 2014 11:15AM - 11:27AM |
G19.00001: Critical Effect of Segmental Dynamics in Polybutadiene / Clay Nanocomposites Characterized by Solid State 1H NMR Spectroscopy Xiaoliang Wang, Rongchun Zhang, Pingchuan Sun, H. Henning Winter, Gi Xue The segmental dynamics of rigid, intermediate, and mobile molecular components in end-functionalized polybutadiene (PB) / organo-clay systems was characterized by fully refocused 1H NMR FID. In addition, 1H DQ NMR experiments allowed to semi- quantitatively monitor changes in segmental dynamics near the interface. Both methods suggested a critical concentration of end-functionalized polybutadiene, indicating a saturation effect for the surface-adsorbed polymer. The critical concentration depended on molecular weight of PB and PB-clay interaction. Based on the 1H NMR results, a tentative model was proposed to illustrate the evolution of the structure and segmental dynamics in PB/organo-clay nanocomposites. [Preview Abstract] |
Tuesday, March 4, 2014 11:27AM - 11:39AM |
G19.00002: Percolation Threshold in Polycarbonate Nanocomposites Suresh Ahuja Nanocomposites have unique mechanical, electrical, magnetic, optical and thermal properties. Many methods could be applied to prepare polymer-inorganic nanocomposites, such as sol-gel processing, in-situ polymerization, particle in-situ formation, blending, and radiation synthesis. The analytical composite models that have been put forth include Voigt and Reuss bounds, Polymer nanocomposites offer the possibility of substantial improvements in material properties such as shear and bulk modulus, yield strength, toughness, film scratch resistance, optical properties, electrical conductivity, gas and solvent transport, with only very small amounts of nanoparticles Experimental results are compared against composite models of Hashin and Shtrikman bounds, Halpin--Tsai model, Cox model, and various Mori and Tanaka models. Examples of numerical modeling are molecular dynamics modeling and finite element modeling of reduced modulus and hardness that takes into account the modulus of the components and the effect of the interface between the hard filler and relatively soft polymer, polycarbonate. Higher nanoparticle concentration results in poor dispersion and adhesion to polymer matrix which results in lower modulus and hardness and departure from the existing composite models. As the level of silica increases beyond a threshold level, aggregates form which results in weakening of the structure. Polymer silica interface is found to be weak as silica is non-interacting promoting interfacial slip at silica-matrix junctions. Our experimental results compare favorably with those of nanocomposites of polyesters where the effect of nanoclay on composite hardness and modulus depended on dispersion of nanoclay in polyester. [Preview Abstract] |
Tuesday, March 4, 2014 11:39AM - 11:51AM |
G19.00003: Path-Integration Computation of the Transport Properties of Nanoparticles Jack Douglas There is need for effective computational methods for calculating the transport properties of polymers and complex-shaped particle aggregates arising in materials science and biology as a foundation for rational material design and the design of well-defined measurements assessing the environmental impact of nanoparticles. We focus on the problem of calculating basic solution transport properties (translational diffusion coefficient, intrinsic viscosity) of isolated particles having essentially any geometry using a novel computational method involving path integration developed by Mansfield and Douglas. The basic concepts behind the method are described and the method is validated in cases where exact analytic, or at least highly accurate numerical estimates, are known for comparison. After defining and validating our method, some applications of the program are given to some non-trivial problems illustrating the use of the program for charactering such as nanoparticles with grafted DNA brush layers, DNA orgami, carbon nanotubes, etc. The path-integration method is evidently a powerful tool for computing basic transport properties of complex-shaped objects and should find wide application in polymer science, nanotechnological applications and biology. [Preview Abstract] |
Tuesday, March 4, 2014 11:51AM - 12:27PM |
G19.00004: N/A Invited Speaker: TBD TBD |
Tuesday, March 4, 2014 12:27PM - 12:39PM |
G19.00005: Field-theoretic simulations of polymer nanocomposites containing grafted nanoparticles Robert Riggleman, Huikuan Chao, Jason Koski As polymer nanocomposite materials have found their way into an ever-growing number of applications, it has become clear that the dispersion state of the nanoparticles can play a key role in the resulting material properties. In some instances, it is ideal to have well-dispersed nanoparticles in a polymer matrix to facilitate high loading, while in other cases, self-assembled structures are preferred. A common route for controlling the dispersion state of the nanoparticles is to graft the particles with polymer chains, and efficient computational methods capable of predicting the limits of dispersion, aggregation, and the structure of any self-assembled particles could go a long way towards enabling the design of future polymer nanocomposite devices. To that end, we have extended the field-theoretic simulations framework to include grafted nanoparticles, where polymer chains can be grafted to the surface of hard nanoparticles. Our method is compatible with both self-consistent field theory and fully-fluctuating field theoretic simulations. Calculations will be shown for the distribution of grafted nanoparticles in homopolymer thin films as well as binary homopolymer blends, where our results agree very well with recent experiments. [Preview Abstract] |
Tuesday, March 4, 2014 12:39PM - 12:51PM |
G19.00006: Effect of interfacial entanglement density on the melt and glassy properties of attractive polymer nanocomposites Erkan Senses, Pinar Akcora Individual dispersion of silica nanoparticles of 13 nm and 56 nm sizes in poly(methyl methacrylate) is achieved by the right choice of a solvent.By using this well-defined model attractive system, it was shown in our previous work that the conformation of PMMA on attractive silica surfaces can be dynamically altered by applying large amplitude oscillatory shear (LAOS) well above the Tg of the polymer[1].Correspondingly, the entanglement density of polymer is increased due to dynamic heterogeneities between the matrix and the adsorbed polymer. Here, we investigate, on the same system, the effect of different interfacial entanglement densities on the melt and glassy properties (Tg, fragility and physical aging).Instead of surface modification of particles, which leads to poor control over the dispersion, we tuned the interfaces by applying LAOS above Tg of the composites and by using binary blends of short (Mw< |
Tuesday, March 4, 2014 12:51PM - 1:03PM |
G19.00007: Dynamics of nanoparticles in an entangled polymer matrix Subas Dhakal, Radhakrishna Sureshkumar Quantitative description of the dynamics and rheology of the extracellular polymeric substance (EPS) of bacterial biofilms is still a major challenge due to their structural complexity. Recent experiments suggest that the viscoelasticity of EPS is not governed by entanglements in the polymer matrix. Here, we investigate the microstructure, dynamics and rheology of a Dextran EPS by probing the motion of nanoparticles embedded in the matrix using coarse-grained molecular dynamics simulations. Specifically, these simulations show that for particle diameter D \textgreater entanglement length $l_{e}$, the probe particles exhibit normal diffusion, while for D \textless $l_{e}$ sub-diffusive motion modulated by the polymer chain dynamics is observed. Results will be discussed in the context of micro-rheology experiments. [Preview Abstract] |
Tuesday, March 4, 2014 1:03PM - 1:15PM |
G19.00008: Field Theoretic Simulations of Polymer Nanocomposites Jason Koski, Huikuan Chao, Rob Riggleman Polymer nanocomposites (PNCs) are materials comprised of nanoparticles immersed in a polymer matrix. PNCs are used in a broad range of industries due to the enhanced properties achieved from the coexistence between the polymer and nanoparticle. A global understanding of the physical principles that dictate the equilibrium morphologies of these systems would greatly assist further development of PNCs. While polymer field theory has long been an efficient method to model equilibrium morphologies of inhomogeneous polymer systems, extensions to incorporate nanoparticles are often limited by their accuracy, computational expense, or their restriction to mean-field descriptions. In this talk, I will present a method in which nanoparticles are incorporated into a polymer matrix using a pure field theoretic approach. I provide results that indicate our approach captures correlations in the particle positions that agree identically with particle-based simulations of the same model. Additionally, our method can be applied in a fully-fluctuating field theoretic simulation where the field fluctuations are sampled using complex Langevin dynamics. Finally, I will show demonstrative calculations of the distribution of spherical and cylindrical particles embedded in a diblock copolymer melt. [Preview Abstract] |
Tuesday, March 4, 2014 1:15PM - 1:27PM |
G19.00009: Micro-Scale Polymer Matrix Elastic Properties in Composites using Inelastic Light Scattering Measurements and Molecular Dynamics Simulations Michael Aldridge, Katherine Sebeck, Anthony Waas, John Kieffer Polymer matrix composites with carbon fiber reinforcement are used in a wide range of aerospace and industrial applications. Composite behavior predictions based on continuum mechanics have been inaccurate, and required empirical corrections, due to the lack of polymer materials property information. The involved length scales make measurement of the elastic properties within fiber tows and near to individual fibers difficult. Micro-Brillouin and Raman light scattering provide sufficiently high spatial resolution to probe the mechanical properties and chemical composition of the matrix, without interfering with the thermo-mechanical equilibrium of the material. Elastic properties of an epoxy resin have been measured between and within the fiber tows of a composite with this technique, and compared to a bulk epoxy resin. These experimental results are complemented with molecular dynamics simulations of the interface, allowing extrapolation of findings to nanometer length scales. A diminished elastic modulus is observed in close proximity to fibers. We identify the extent to which residual stresses, chemical inhomogeneities, or structural rearrangements near the interface contribute to this effect in order to explain the underlying reason for this finding. [Preview Abstract] |
Tuesday, March 4, 2014 1:27PM - 1:39PM |
G19.00010: Reinforcement in Natural Rubber Elastomer Nanocomposites: Breakdown of Entropic Elasticity Paul Sotta, Roberto Perez-Aparicio, Arnaud Vieyres, Pierre-Antoine Albouy, Loic Vanel, Didier R. Long, Olivier Sanseau Understanding reinforcement mechanisms, which are responsible for the remarkable mechanical properties of elastomers filled with nanometric particles, implies combining complementary techniques. Here, we propose an approach based on the combination of different experiments in order to discriminate various reinforcement effects in elastomers filled with carbon black or silica: mechanical response, independent measurements of the crosslink density by multiple-quantum proton NMR and of chain segment orientation under stretching by X-ray scattering, in unfilled and filled vulcanized natural rubbers with various crosslink densities. In unfilled materials, all measurements are nicely correlated, in agreement with rubber elasticity theory. In filled materials, analyzing the deviations with respect to the behavior of the pure unfilled elastomer matrix allows discriminating various physical mechanisms. We demonstrate that the mechanical response at medium/large strains is essentially driven by strain amplification effects, while, in the linear regime, there is a strong additional reinforcement which is not related to the properties of the elastomer matrix. [R. Perez-Aparicio et al., Macromolecules 2013]. [Preview Abstract] |
Tuesday, March 4, 2014 1:39PM - 1:51PM |
G19.00011: ABSTRACT WITHDRAWN |
Tuesday, March 4, 2014 1:51PM - 2:03PM |
G19.00012: Thermal Investigations on PVDF-BaTiO$_{3}$ Nanocomposites Mircea Chipara, David Garza, Dorina M. Chipara, Armando Salinas, Steven C. Tidrow, Jerry Contreras Nanocomposites of polyvinylidene fluoride (PVDF) and barium titatanate (BaTiO3) were obtained by melt. BaTiO3 with cubic structure and average size of 100 nm was purchased from Nanostructured {\&} Amorphous Materials, Inc. The mixing consisted of 3 segments at 190 $^{\circ}$C and 60 rotations per minute (rpm) for 30 minutes, 210 $^{\circ}$C and 80 rpm for 15 minutes, and 180 $^{\circ}$C and 6o rpm for 30 minutes. Nanocomposites loaded with various amounts of BaTiO3 ranging from 0 to 15 {\%} wt. were synthesized. Differential Scanning Calorimetry measurements were performed by using a DSC Q-100 TA Instruments equipment. Isothermal crystallization rates were recorded for 100 minutes in the temperature range 130 $^{\circ}$C to 150 $^{\circ}$C. Prior crystallization, the samples were annealed at 175 $^{\circ}$C for 10 minutes. Experimental results were analyzed within the Avrami model including subsequent improvements. The effect of the nanofiller on melting temperature, crystallization temperature, and degree of crystallization was investigated. Wide Angle X-Ray scattering data are also reported. Electron microscopy confirmed the dispersion of BaTiO3 nanoparticles within PVDF. [Preview Abstract] |
Tuesday, March 4, 2014 2:03PM - 2:15PM |
G19.00013: Dielectric Performance of Polymer Nanocomposites: Matrix Free, Hairy Nanoparticle Assemblies and Amorphous Polymer-Nanoparticle Blends Christopher Grabowski, Elizabeth Opsitnick, Hilmar Koerner, Jeffrey Meth, Michael Bockstaller, Michael Durstock, Richard Vaia Over the past decade, polymer nanocomposites (PNCs) have been developed for electrical insulation and capacitor films to achieve extreme energy-power storage. The quality of nanoparticle dispersion has been shown to greatly affect dielectric performance. Nanoparticle aggregates function as defect sites and dramatically reduce dielectric strength. It is unclear, however, to what extent enhanced nanoparticle order (or perfect dispersion) can improve energy storage properties. Uniform dispersions of silica colloids (15 and 29 nm diam.) in polystyrene (PS) and polymethyl methacrylate (PMMA) have been achieved by two methods: (1) solvent-annealed, two-component, polymer-nanoparticle blends and (2) single-component matrix free, hairy nanoparticle assemblies. The dielectric strength, permittivity, and energy storage over a wide range of silica loadings (0-50{\%} v/v) will be discussed. Our findings indicate PS NCs have comparable breakdown strength for blend and hairy nanoparticle assemblies, while at intermediate silica loadings ($\sim$ 15{\%} v/v) PMMA grafted silica assemblies show enhanced breakdown strength compared to simple blends. Dielectric permittivity follows the Bruggeman effective medium model for all materials. [Preview Abstract] |
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