Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session N30: Polymer - Inorganic Composites II |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Joao Cabral, Imperial College Room: LACC 505 |
Wednesday, March 23, 2005 8:00AM - 8:12AM |
N30.00001: Control of the Dynamic Behavior of The Particle-Copolymer Nanocomposites Gang He, Anna Balazs Nanocomposites of linear copolymers and various kinds of particles have long been of great interest to researchers because of their attractive industrial applications. The microphase separation of copolymers can be used to template the particles into regular structure to gain needed optical/magnetical/electrical properties. On the other hand, clustering of the particles can be utilized to influence the morphology of the polymer to improve the properties of the polymer matrix. Theoretical studies on these phenomena have focused mostly on the cases where one of the self-organizing process dominates the behavior of the system. In this computatoinal study, we will focus more on the interplay/competition of two different self assembly processes. Our model combines the cell dynamical equations for the diblock polymers and Langevin dynamics for particles interacting with various potentials. We study particles with different magnetic/electrical properties. The aggregation behavior of these particles can be controlled through external fields and consequently make the behavior of the whole composite controllable through the interplay of the two competing self assembly processes. The results of these studies can potentially pose new avenues to the fabrication and application of the particle-polymer nanocomposites. [Preview Abstract] |
Wednesday, March 23, 2005 8:12AM - 8:24AM |
N30.00002: Network formation in sheared polymer nanocomposites Eihab Jaber, Haobin Luo, Wentao Li, Dilip Gersappe We use Molecular Dynamics simulations to study the effects of shear on polymer nanocomposites. Our studies show the formation of a transient network at concentrations exceeding 5\% by vol of filler particles. The structure of this network under shear is investigated. We find at lower shear rates the network significantly enhances the viscosity of the polymer, but at higher shear rates it contributes to an acceleration in shear thinning, resulting in a viscosity that is close to the orginal viscosity of the unfilled polymer system. Our results also show an unexpected effect of fillers on chain orientation under shear. We find that even before a transient network exists in the system, small concentration of filler particles induce a large orientation effect on the polymer chains. Possible implications of this effect will be discussed. [Preview Abstract] |
Wednesday, March 23, 2005 8:24AM - 8:36AM |
N30.00003: Phase Separation Dynamics of Polymer Blend Films Containing Polymer-Grafted Nanoparticles H.-J. Chung, R.J. Composto, K. Ohno, T. Fukuda Polymer blends containing nanoparticles (NP) are important in advanced technologies including opto-electronic and biosensor devices. Upon adding methyl-terminated silica NP's [22nm (NP$_{A})$] at dilute concentrations, PMMA:SAN (50:50) films (650nm) undergo early, intermediate and late stages of morphology development, similar to a PMMA:SAN film (Wang {\&} Composto, JCP (2000)). NP's partition into the PMMA-rich phase, and slow down the kinetics of domain growth. This result is consistent with a coalescence model that predicts $\xi \quad \sim $ (1 / $\eta )^{1/3}$ t$^{1/3}$, where $\xi $ and $\eta $ are the correlation length and PMMA viscosity, respectively (Chung \textit{et al}., EPL (2004)). Although the bulk $\eta $ agrees with this model, a microscopic understanding of the phase separation mechanism requires knowledge of polymer-NP and NP-NP interactions. To address this issue, well-characterized silica NP's (15 nm) with densely grafted PMMA [M$_{w}$ = 1.8K (NP$_{B})$ and 21K (NP$_{C})$] are employed as non-interacting fillers in the PMMA-rich phase. The impact of PMMA-grafted NP on the phase separation dynamics in films, as well as the rheology of PMMA/NP composites, is investigated. Specifically, phase separation was slowest for NP$_{B}$ relative to films containing NP$_{A}$ and NP$_{C}$. These studies show that wetting and domain coarsening in polymer blend films can be controlled by the judicial addition of surface modified NP. [Preview Abstract] |
Wednesday, March 23, 2005 8:36AM - 8:48AM |
N30.00004: Thermally Induced Lateral Motion of $\alpha$-Zirconium Phosphate Layers Intercalated with Hexadecylamines Kookheon Char, Bongwoo Ha Well-defined intercalated structure, either interdigitated layers or bilayers, of hexadecylamines (HDAs) in a confined space of a highly-functionalized layered material, $\alpha$- zirconium phosphate ($\alpha$-ZrP), was prepared and these two distinct intercalated structures can serve as model systems to investigate the interaction of the two monolayers whose amphiphilic tails are adjacent to each other. Acidic functional groups (-POH) on the $\alpha$-ZrP are in well-ordered array and the number of functional group is quite high (i.e., cationic exchange capacity (CEC) = 664 mmole/100 g, area per one charge site = 0.24 nm$^{2}$) enough to realize the bilayers (i.e., discrete two monolayers) of HDAs within the $\alpha$-ZrP interlayer. We employed the two-step intercalation mechanism for the preparation of well- ordered interdigitated layers as well as the bilayers of alkyl chains attached to both sides of the $\alpha$-ZrP intergallery. An intriguing lateral motion of the $\alpha$-ZrP sheets was observed with in-situ SAXS measurements for the interdigitated layer during heating and cooling cycle and verified with TEM. This lateral motion is believed to be due to the transition from the tilted to the untilted conformation of the interdigitated HDA chains and this transition is found to be thermally reversible. [Preview Abstract] |
Wednesday, March 23, 2005 8:48AM - 9:00AM |
N30.00005: Molecular Dynamics Simulations of Poly(dimethylsiloxane) - Silica Interfaces James Smith, Oleg Borodin, Grant Smith Molecular Dynamics simulations using new quantum chemistry based interactions between Poly(dimethylsiloxane) (PDMS) and silica surfaces were conducted to explore the chain behavior near the interface between 300 and 500 K. The effects of surface chemistry particularly the presence of hydroxyl and trimethyl-silyl groups at the interface were examined. The PDMS chain dynamics, as measured by the mean squared displacement of backbone atoms, were strongly affected by the surface chemistry and intermolecular interactions. The PDMS structure near the interface depended upon the type of surface group on the silica surface and its concentration. The significance of intermolecular forces such as hydrogen bonding, electrostatics etc. will be discussed. [Preview Abstract] |
Wednesday, March 23, 2005 9:00AM - 9:12AM |
N30.00006: First Observation of an ``Anomalous Mullins Effect'' in Silica Filled PDMS Marilyn Hawley, Debra Wrobleski, E. Bruce Orler, Robert Houlton, Kiran Chitanvis, Geoffrey Brown, David Hanson We proposed a predictive model to explain the Mullins Effect (stress softening) and a new phenomenon we refer to as the ``Anomalous Mullins Effect'' in silica filled polydimethysiloxane (PDMS). The mechanism we propose is based on surface interaction between polymer chains and filler particles. The ``Anomalous Mullins Effect'' is the dependence of stress ``softening'' on the direction of a second pull relative to an initial strain axis. We will present experimental data to support this model. Atomic force microscopy (AFM) phase imaging was used to characterize filler size and distribution. A tensile stage was used to measure stress-strain properties using model samples with various filler content. Samples were not pulled to break in order to study stress softening as a function of elongation and second strain direction. As predicted by our model, we observed a clear Mullins Effect only when the second strain axis was parallel to the initial one but not when it was perpendicular. No change was seen in mechanical behavior over 26 weeks or with heat-treatment. [Preview Abstract] |
Wednesday, March 23, 2005 9:12AM - 9:24AM |
N30.00007: A physical mechanism for the Mullins Effect in silica-filled polydimethylsiloxane David Hanson, Marilyn Hawley The Mullins Effect pertains to the reduction in tensile stress, or ``softening,'' that is observed between the first and subsequent extensions of filled polymer materials. First reported by W. L. Holt in 1938 and later studied in detail by L. Mullins, it is considered by many to be a major unsolved mystery of polymer physics. We propose a physical mechanism to explain this effect that is based on surface interactions between polymer chains and filler particles. Its predictions are consistent with most experimental results including the integrated strain energy and the shape of the tensile stress/strain curve. The proposed mechanism also predicts that stress softening should \underline {not} occur if a previously strained sample is stretched at right angles to the original strain axis. This effect, which we are calling ``The Anomalous Mullins Effect,'' has now been confirmed experimentally. We will present a description of the mechanism. [Preview Abstract] |
Wednesday, March 23, 2005 9:24AM - 9:36AM |
N30.00008: SANS studies of polymer chain conformation in the presence of nanofillers Sanat Kumar, Rebecca Godlaski, Sudeepto Sen, Yuping Xie We will present the results from recent and ongoing SANS experiments on polystyrene nanocomposites containing silica nanofillers. Recent simulation results for the role of nanofiller on chain dimensions have been controversial. Nanocomposite samples corresponding to combinations of different weight percentages of the nanoparticles (highest being 5) and five matrix polymer molecular weight (highest being 550k g/mol) have been studied. We will report on chain dimensions and how they are altered by the presence of filler. [Preview Abstract] |
Wednesday, March 23, 2005 9:36AM - 9:48AM |
N30.00009: Nanosphere Embedment into Polymer Surfaces: A Viscoelastic Contact Mechanics Analysis Stephen Hutcheson, Gregory McKenna Teichroeb and Forrest (\textit{Phys. Rev. Lett.}, \textbf{91}, 1, 016104-1(2003)) image gold nanosphere embedment into a polystyrene surface and imply the existence of a liquid surface layer. We use a viscoelastic contact mechanics model of their results to give a contrary interpretation. The surface interactions between gold and polystyrene and the indentation depth determine the loads on the nanospheres. Using bulk properties, quantitative agreement between the model and the data is obtained, implying little or no, depression in the glass temperature or existence of a liquid layer at the polystyrene surface. An important aspect of the present analysis is that it is the first to solve the problem for the time dependent Poisson's ratio. The fact that this varies from 0.33 to 0.5 upon traversing the glass transition (time) flattens the nanosphere embedment profile with increasing time. [Preview Abstract] |
Wednesday, March 23, 2005 9:48AM - 10:00AM |
N30.00010: Influence of Nanoparticles on the Miscibility in Binary Polymer Blends – A Simple Theory Valeriy Ginzburg We propose a simple theory describing the influence of nanoparticles on thermodynamics of binary polymer mixture. In particular, we consider the case in which nanoparticles preferentially segregate into one of the polymeric components. Depending on the particle radius \textit{Rp }and the polymer degree of polymerization $N$, addition of nanoparticles can either promote or hinder mixing of the polymers. We calculate how the addition of nanoparticles shifts the spinodal of the polymer blend. Results are compared with recent experimental data of Nesterov and Lipatov, and satisfactory qualitative agreement is found. [Preview Abstract] |
Wednesday, March 23, 2005 10:00AM - 10:12AM |
N30.00011: Surfaces of Fluoroelastomer Nanocomposites David Pan Stiffening or reinforcement of elastomer with a second hard particle phase to produce a networked or crosslinked composite is common in applications of high-performance elastomers. The average size of reinforcing particle is frequently in the range of a few tenths to several microns, the shape from spheres to cylinders of high aspect ratio, and the particle concentration can be as high as about 50{\%} by weight partly because of ease of dispersing a small number of large particles. One of the main problems with micro-filled fluoroelastomer surfaces is the continuous removal of large particles by abrasion and wear resulting in large pits or surface defects. Furthermore, these large pits can lead to a roughened surface. The aim of this work is to investigate the influence of nano-particles versus micro-particles on the surface defect size and density of filled fluoroelastomer. We applied scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), and surface roughness measurement to examine the surfaces of paper abraded fluoroelastomer nanocomposites. Qualitatively, SEM images show the surface defect size or density of nanocomposites is generally reduced, as compared to that of fluoroelastomer microcomposites. On a somewhat larger scale, it is found that the surface roughness (Ra) of paper abraded nanocomposites can be controlled to less than 0.2 to 0.3 microns. [Preview Abstract] |
Wednesday, March 23, 2005 10:12AM - 10:24AM |
N30.00012: Bulk and Interfacial Behavior of Nano\-particle/Polymer Blends A.L. Frischknecht, R.S. Krishnan, A. Tuteja, M.A. Holmes, M.E. Mackay We have investigated a model athermal system consisting of polystyrene (PS) nanoparticles (NPs) in PS melts. Neutron scattering shows that the chain dimensions expand in the presence of the NPs. We investigate this result theoretically using self-consistent PRISM theory, and also find an expansion in chain dimensions as a function of NP volume fraction. Recently it has been shown that nanoparticles can suppress dewetting in thin polymer films, a counterintuitive result since particles usually induce dewetting. Neutron reflectivity measurements have shown that the NPs phase separate to the surface, so one proposed mechanism for the inhibition of dewetting is that this segregation changes the surface energies. We calculate the density profiles for dilute NPs in polymer melts near a substrate using classical density functional theory, which shows that the NPs do indeed segregate to the surface. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE- AC04-94AL85000. [Preview Abstract] |
Wednesday, March 23, 2005 10:24AM - 10:36AM |
N30.00013: Interactions between nano-particles in solutions of adsorbing polymers Megha Surve, Victor Pryamitsyn, Venkat Ganesan Adsorption of polymer on colloidal surfaces plays an important role in many practical applications like bridging flocculation, steric stabilization, protein crystallization and polymer nanocomposites. In the present talk, we present a multiscale approach that examines the phase behavior of colloidal suspensions in adsorbing polymeric solutions. We use generalized McMillan Mayer theory to coarse-grain the polymeric component. This leads to a framework wherein the effective interactions between the colloids can be computed quite accurately using polymer self-consistent field theory. By solving the self-consistent field theory equations numerically in bispherical coordinates we account for possible size disparities between the colloids and polymers. Here, we present our results on the effective interactions and phase behavior of colloids in solutions of reversibly and irreversibly adsorbing polymers. Our results suggest that specific interactions between polymers and colloids can lead to significant changes in both the interactions and the resulting phase behavior of the system. Further, we extend the self-consistent framework to characterize the structure of adsorbed polymer layers in terms of conformational statistics of bridges, loops and tails. We present a comparison between polymer adsorption on planar surface and that on a spherical particle and our results show a strong dependence of structure of adsorbed layer on surface curvature [Preview Abstract] |
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N30.00014: Models of the viscoelasticity of polymer nanocomposites Catalin Picu, Alireza Sarvestani, Abhik Rakshit A family of models is developed to represent the viscoelasticity of polymers filled with nanoparticles. This includes discrete modeling and simulation, as well as rheological molecular modeling. Discrete coarse-grained models are used at various spatial and temporal scales to inform the rheological models as well as to validate their output. The main objective is to capture the mechanisms relevant for the chain dynamics such as chain-filler interactions, entanglements, tube fluctuations and constraint release. These are incorporated in the constitutive model whose predictions are then compared with relevant published experimental data. [Preview Abstract] |
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N30.00015: Magnetic Investigations of Titanium Doped Gamma Iron Oxides Dispersed in Polymers Mircea Chipara, Ioan Morjan, Rodica Alexandrescu, Jeffrey Zaleski, David Baxter, Nicholas Remmes Titanium doped gamma iron oxide nanoparticles were prepared by laser pyrolisis. X-Ray studies indicated the presence of $\gamma $ Fe$_{2}$O$_{3}$ and $\beta $ FeO(OH). Small amounts of $\gamma $ titanium maghemite were observed. The average particle size is 5 nm (Transmission Electron Microscopy). Magnetic nanoparticles were dispersed by sonicating a solution of styrene-isoprene-styrene blockcopolymer. The solvent was evaporated by heating at 75 $^{0}$C for 24 hours. The as obtained films were studied by SQUID and ferromagnetic resonance (FMR). The temperature dependence of the magnetization and of hysteresis loops in the temperature range 4 K -- 300 K is reported. The temperature dependence of FMR line parameters in then range 100 K to 450 K is reported. A weak matrix effect within the glass transition range of the polymeric matrix has been observed. [Preview Abstract] |
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N30.00016: Nucleation and Growth in Poly(L-lactic acid)/clay nanocomposites Vahik Krikorian, Darrin Pochan We have investigated the crystallization behavior of semicrystalline poly (L-lactic acid) (PLLA) upon addition of organically modified montmorillonite clay. The real-time crystallization was probed by Polarized Optical Microscopy (POM), Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR) techniques. The exfoliation-adsorption technique was employed to fabricate the nanocomposites from solution. Crystallization studies were performed on cast nanocomposite films, which were isothermally recrystallized at different temperatures from the quiescent melt. The radial spherulite growth rate measurements and isothermal bulk crystallization kinetics indicate that the silicate layers, in the case of the fully miscible organic modifier, did not act as a nucleating agent. However, the less miscible clay acted as a good nucleating agent and significantly decreased the spherulite sizes. Interestingly, spherulite growth rates were significantly increased by the addition of organoclays, being the highest in the fully exfoliated case. Despite the increase in spherulite growth rate, the overall bulk crystallization rate was retarded in the exfoliated nanocomposites. The bulk crystallization rate was increased in the intercalated case in which clay acted as a good nucleating agent. In-situ FTIR studies revealed a valuable insight into the chain configurations, which are in good accordance with the DSC and POM experiments [Preview Abstract] |
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