### Session D30: Multiphase Polymer Materials

 Monday, March 13, 2006 2:30PM - 2:42PM D30.00001: Phonon Propagation in Dry and Wet Polystyrene Opals George Fytas , Wei Cheng , Jian Jun Wang , Ulrich Jonas The phononic properties of fabricated soft opals consisting of closely packed spherical submicrometer polystyrene particles were investigated by Brillouin light scattering in the GHz frequency range. In air, the numerous modes found in the dry opal are theoretically identified as the particle eigenmodes using the two elastic constants for the bulk polystyrene. The line shape of the low-frequency modes can be utilized as an index of the particle size polydispersity and a sensitive probe for monitoring the latex film formation. Unlike for the dry opal, the study of the propagation of acoustic waves in the infiltrated (by silicon oil) opal for wave vector k$_{\vert \vert }$ parallel to the fcc (111) planes of the slab has revealed two modes: an effective medium mode with linear dispersion over the examined k$_{\vert \vert }$ range and a second mode the dispersion of which depends on the direction of k$_{\vert \vert }$ relatively to the symmetry lines of the Brillouin zone. The experimental dispersion will be compared with phononic band structure calculations. Monday, March 13, 2006 2:42PM - 2:54PM D30.00002: Kinetics of phase separation in a dilute short-ranged square-well system: a molecular dynamics study Hongjun Liu , Shekhar Garde , Sanat Kumar We report on a molecular simulation study of the phase separation in a dilute short-ranged square-well system. The phase diagram of model displays solid-fluid equilibrium, with a metastable fluid-fluid separation. Equilibrium fluid configuration are quenched along the isochore at a sequence of temperatures and followed during the time evolution. We present the clear evidence of the metastable fluid-fluid separation, of the homogeneous crystallization and of the kinetically arrested gel. We also discuss the relevance of our simulation to the crystallization slot''. Monday, March 13, 2006 2:54PM - 3:06PM D30.00003: Styrene-Hydroxystyrene Gradient and Block Copolymers: Comparisions of Behavior as Compatibilizers of Immiscible, Crystallizable Polymer Blends and in the Neat and Solution States. Jungki Kim , John M. Torkelson Styrene-hydroxystyrene (S-SOH) gradient and block copolymers are made by semi-batch nitroxide-mediated controlled radical polymerization of styrene and acetoxystyrene followed by hydrolysis of the acetoxystyrene repeat units to SOH. These copolymers are investigated as compatibilizers for polystyrene (PS)/polycaprolactone (PCL) blends made by melt mixing; the hydroxyl groups on the SOH units undergo attractive hydrogen-bonding interactions with the ester groups on PCL. Gradient copolymers of a wide composition range are effective compatibilizers of PS/PCL blends, with the dispersed phase (PCL) domain size being a function of gradient copolymer composition. Block copolymers are also effective compatibilizers, resulting in very small dispersed-phase domain sizes ($\sim$ 200 nm average diameter). In addition, block copolymer addition has major effects on the crystallizability of the PCL domains; in contrast, only small effects on PCL crystallizability are observed upon addition of gradient copolymer to the blend. The different effects of block and graft copolymers are likely due to greater hydrogen bonding of the PCL with the block copolymer, which impedes crystallization. The properties of the block and gradient copolymers in the neat state and their micellization in solvent and in homopolymer will also be discussed. Monday, March 13, 2006 3:06PM - 3:18PM D30.00004: An off-lattice Wang-Landau simulation of the coil-globule and solid-liquid transitions of flexible homopolymers. Drew Parsons , David Williams The temperature-independent Wang-Landau Monte Carlo approach is implemented for an off-lattice model of flexible homopolymers and applied to the study of the coil-globule and solidification transitions. Transition temperatures are calculated and the thermodynamic limit of the two transitions is compared. We address the issue of obtaining crystal structure in the low energy solid globules, and raise the question of whether a glass-like state rather than crystalline is a correct description of the solid state. Monday, March 13, 2006 3:18PM - 3:30PM D30.00005: Exploring the Effects of Deuteration on Polymer Blends Michael Tambasco , Jane Lipson , Julia Higgins Deuterium labeling is a requirement of neutron scattering experiments, but the extent to which the H-D switch affects the thermodynamic properties of the mixture under investigation has not been widely examined. In order to explore this, we apply a simple lattice theory to the analysis of a fairly complete set of experimental data on blends of polystyrene(PS)/polybutadiene(PB), in which all permutations of PS, dPS, PB, and dPB are of interest. Available data include cloud point curves, neutron scattering intensities, and pressure-volume-temperature surfaces. In this talk we discuss what we have learned regarding the consequences of deuterium substitution on the properties of this blend, and draw some broader conclusions. Monday, March 13, 2006 3:30PM - 3:42PM D30.00006: Coarse-Grained Simulations of PEO/PMMA Blends Praveen Depa , Chunxia Chen , Janna Maranas Coarse-graining involves mapping successive atoms along a polymer chain to larger coarse-grained beads, which are then simulated using conventional molecular dynamics techniques. The interaction between the coarse-grained [CG] beads is parameterized so as to reproduce static properties observed in the underlying atomistic simulations. We extend this methodology to blends by developing CG models for poly(ethylene oxide) [PEO], poly(methylmethacrylate) (PMMA) and PEO/PMMA blends. In the case of PEO, six united atoms were mapped to a CG bead with the center at every other oxygen atom and for PMMA, each monomer was replaced with two CG beads, one centered along the main chain and the other centered at the ester-oxygen on the side group. The CG models reproduce static properties for both components. Dynamic properties evolve correctly if rescaled by a constant factor, specific to each component. The CG model is then used to simulate larger system for longer times such that whole chain dynamics can be accessed and compared to local dynamics. Monday, March 13, 2006 3:42PM - 3:54PM D30.00007: Relationship between Fluctuation and Stress Relaxation in a Block Copolymer Melt Amish Patel , Nitash Balsara , Suresh Narayanan , Alec Sandy , Simon Mochrie , Bruce Garetz , Hiroshi Watanabe The relationship between microscopic fluctuation relaxation and macroscopic stress relaxation was explored in a disordered block copolymer melt containing disordered micelles. Experiments conducted near the order-to-disorder transition, show that the fluctuation relaxation time, measured by X-ray photon correlation spectroscopy is larger than the terminal stress relaxation time, measured by rheology, by factors as large as 100. These observations are in qualitative agreement with predictions of the Fredrickson-Larson theory. The lack of quantitative agreement suggests the need for a comprehensive theory that predicts stress relaxation in systems with complex free energy landscapes, such as those containing micelles and disordered fluctuations. Monday, March 13, 2006 3:54PM - 4:06PM D30.00008: Self-consistent field theoretic calculations of stress in diblock Panagiotis Maniadis , Kim O. Rasmussen , Turab Lookman , Edward M. Kober The elastic properties of diblock copolymers are studied using self-consistent field theoretical calculations. Our starting point is the approach of Fredrickson (J. Chem. Phys. 117, 6810, 2002) in which microscopic expressions of the elastic energy and stress of polymer chains are self-consistently incorporated into the free energy expression for a homopolymer. We extend this theory to phase separating diblock copolymers and calculate numerically the complete stress tensor in the presence of external strain. Our numerical method can be easily generalized to multi-block copolymers, and our method can be used to study the elastic properties of phase separating polymer materials in general. Monday, March 13, 2006 4:06PM - 4:18PM D30.00009: Coarse-Grained Modeling of the Mechanical Properties of Entangled Polymer Systems Brian Pasquini , Fernando Escobedo , Yong L. Joo The complexity of entangled polymer interactions is a promising area for simulation studies to build upon polymer physics theories; however, it is necessary to use a coarse-grained approach to simulate the dynamic response of large polymer systems. Such studies have been done by treating the entanglement interactions as a set of entanglement points, which serve as the ends for the coarse-grained simulation unit. One method from literature (Smith and Termonia) formulates the free energy of an entanglement network based exclusively on neighboring entanglement points and uses temporary bonds which break as the simulation progresses. Another method (Terzis, Theodorou and Stroeks) treats the coarse-grained units as delocalized polymer density clouds, and formulates an expression for the free energy based on local polymer density. The first method has been extended to three dimensions for direct comparison to the second in tensile strain experiments. These models also show promise to understanding microstructure effects on mechanical properties in materials such as spider silk. Monday, March 13, 2006 4:18PM - 4:30PM D30.00010: Flame Retardant Homopolymer and Polymer Blend Composites Miriam Rafailovich , Mayu Si , Jonathan Sokolov , Tohru Araki , Harald Ade , Daniel Hefter , Aryeh Sokolov We investigated the flame retardant performance of homopolymer, EVA, PMMA, PP, and PS, and polymer blends, PS/PMMA, PC/SAN, with organoclay and conventional flame retardant agents such as decabromodiphenyl ether (DB) and phosphorus compounds. These materials were characterized by TEM, STXM, LOI and UL 94 V-0. TEM and STXM photographs show that the addition of organoclays into polymer blends drastically slows down the phase separation and accelerates the decompose of bromine compounds during the combustion. Further, UL 94 V-0 results indicate that PS/PMMA blend with DB can not achieve self-extinguishing in the absence of clay. The amounts of flame retardants and clay used were varied to try to achieve the optimal formula to pass UL 94 V-0. The synergism of clay and flame retardant agents were completely studied by various measurements, time dependence burning (TEM, Ion Chromatography), GC-MS, and cone calorimeter. Monday, March 13, 2006 4:30PM - 4:42PM D30.00011: Ellipsometry studies of nanofilled polymer thin films. Ufuk Karabiyik , Alan Esker Thermal properties of polymer thin films and polymer/nanofiller blends are crucial and expected to be different from their corresponding bulk properties because of the large surface area/volume ratio and the greater fractional free volume in confined geometries. Langmuir-Blodgett thin films of trisilanolphenyl-POSS (TPP) and poly(t-butyl acrylate) (PtBA) blends were prepared by Y-type deposition. The films have been characterized by x-ray reflectivity and ellipsometry. Ellipsometry is able to measure thermally induced structural changes and can be used to monitor surface glass transition temperatures as well as layer deformation in multilayer thin films. The results show that TPP depresses the glass transition temperature(Tg) of PtBA LB-films like a plasticizer at low TPP concentrations less than 3 wt. percent TPP and that Tg increases for TPP concentrations greater than 3 wt. percent. A speculative mechanism for this cross-over is an increase in TPP aggregation that pins PtBA chains leading to lower chain mobility at higher wt. percent TPP. Monday, March 13, 2006 4:42PM - 4:54PM D30.00012: Charge dissipation measurement on the surface of polymeric materials using modified surface potential electric force microscopy Michael Reagan , Sergei Lyuksyutov , Ivan Dolog , Robert Mallik , Shane Juhl , Richard Vaia , Michael Durstock , John Ferguson The AFMEN technique when combined with surface potential electric force microscopy (SP-EFM) reveals the pattern of electric charge build-up and dissipation in polymeric and organic materials. This information can be used to develop an adequate description of nanoconductivity in these materials. The description includes effects due to local electric field variations and charge transport mechanisms. Charge evolution was estimated by measuring electric currents using AFM. In addition to the SP-EFM and AFM work outlined above, we also use Inelastic Electron Tunneling Spectroscopy (IETS) to characterize the electronic and vibrational properties of polymer and composite materials. IETS has been used in the past by one of the authors to investigate ultra-thin (roughly 1 nm) polymer films, including PMMA. The films were deposited either by spin coating from or by plasma polymerization. This work is being extended to study the adsorption of spin-coated PMMA on photovoltaic materials such as CdS. Temperature dependent current-voltage and conductance voltage data obtained from tunnel diodes containing CdS/PMMA heterolayers can be used to determine the conduction mechanisms in these layers. Monday, March 13, 2006 4:54PM - 5:06PM D30.00013: Preparation and Characterization of a Superparamagnetic Polymer Nanocomposite N. Brenner , R. Isseroff , M. Rafailovich , G. Rudomen , R. Gambino , S.S. Liang , D. Sunil , M. Si , L. Collazo , N. Pernodet , X. Fang Fe(CO)$_{5}$ decomposition produced ferro- and superparamagnetic polymer nanocomposites. Fe(CO)$_{5}$ and Cloisite 20A clay were combined in a closed vial for 12 hours, then opened to air for 2 hours. M\"{o}ssbauer analysis indicated formation of Fe$_{2}$O$_{3}$ on clay; mass analysis indicated 12{\%} Fe in clay. A Brabender mixed Fe$_{2}$O$_{3}$/clays with PMMA and EVA at ratios by mass of 9:4:36 and 1:1:4 respectively (Fe(CO)$_{5}$:clay:polymer). TEM displayed Fe$_{2}$O$_{3}$ nanoparticles, 3.3 $^{+}$ 0.8 nm in diameter, adsorbed on exfoliated clay platelet surfaces in polymer matrices. VSM data indicated superparamagnetism with moments of 510.3 emu/g$_{(Fe2O3)}$ (PMMA) and 8.46 emu/g$_{(Fe2O3)}$ (EVA). DMA showed 37{\%} decreased dynamic modulus (EVA) and 11{\%} (PMMA) due to Fe$_{2}$O$_{3}$. TGA indicated PMMA stability to 400$^{o}$C (9.3{\%} mass residual) and EVA to 435$^{o}$C (11{\%} mass residual). Cell adhesion tests showed Fe$_{2}$O$_{3}$/clay enhanced proliferation, promising applications in bone implants. Monday, March 13, 2006 5:06PM - 5:18PM D30.00014: Molecular Simulation of the intercrystalline region in isotactic polypropylene Vikram Kuppa , Gregory C. Rutledge Monte Carlo (MC) computer simulations are used to study the crystal-amorphous interlamellar phase in semi-crystalline isotactic polypropylene. This represents the first such study of the detailed atomic level structure of the interlamellar phase for a polymer with side groups. The polymer is modeled using a united atom force-field model. Replica exchange in energy space is required in addition to local conformation and topology altering MC moves to achieve effective sampling of phase space. The simulations reveal the temperature dependence of structural features such as mass and energy density profiles as well as population distributions of tails, loops and bridges associated with the fold surface. These results for polypropylene are compared and contrasted with previous results for the prototypical linear polymer, polyethylene, in order to study the effect of architectural complexity on structure and properties of semi-crystalline polymers Monday, March 13, 2006 5:18PM - 5:30PM D30.00015: Phase Transition Behavior of Isotactic Polypropylene Crystallized from a Homogeneous Melt Xiaofeng Chen , Sanat K. Kumar , Rahmi Ozisik The equilibrium melting behavior of helical structures in isotactic polypropylene (iPP) was studied by a Monte Carlo simulation. It was found that the melting of iPP helical structure was an exponential process at high temperatures (T $>$ 470 K), whereas it becomes highly stretched at low temperatures (T $<$ 400 K). An estimate of the melting temperature was obtained from a novel application of the second moment of the waiting time distribution for helix melting as described by Odagaki (T. Odagaki, \textit{Phys. Rev. Lett.} \textbf{1995}, 75, 3701). The calculated melting temperature was approximately 455 K, which is in surprisingly good agreement with experimental values. A second transition temperature was also observed at a lower temperature (T $\sim$390 K), which we can not explain by equilibrium considerations. We suggest that at this temperature, once a helix forms, it does not melt within the time scale studied.