Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Y40: Focus Session: Nanocomposite Physics II-Polymer Dynamics |
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Sponsoring Units: DPOLY Chair: Jim Watkins, University of Massachusetts--Amherst Room: A122/123 |
Friday, March 25, 2011 8:00AM - 8:36AM |
Y40.00001: Particles Bridge the Gap -- Relevance of Polymer Graft Architecture on the Properties of Particle Brush Assemblies Invited Speaker: Current interest in the assembly of ligand-coated nanoparticles into 2D and 3D array structures is driven by the opportunities for novel material technologies that derive from the interactions within nanoparticle superlattice structures. A common challenge in the solution-based assembly of particle superlattice structures is the propensity of hard-sphere type particle assemblies to crack formation and brittle fracture during solvent evaporation. Recent progress in controlled radical polymerization offers novel opportunities for polymer-stabilized particle systems (particle brushes) as building blocks of particle superlattice structures. This contribution will discuss synthetic strategies to realize particle brush systems with well defined polymer graft-architecture in the dense or semi-dilute brush regime and discuss the effect of polymer grafting on the structure formation and cohesive interactions in particle brush assemblies. In particular, it will be demonstrated chain entanglements between surface-grafted chains give rise to fracture through polymer-like crazing thus dramatically increasing the toughness and flexibility of the particle assembly. The modulus and toughness of polymer nanocomposites synthesized by self-assembly of particle brush systems will be shown to exceed those of ``conventional'' particle-filled polymer composites -- a result that will be interpreted as a consequence of the particular conformational constraints of surface grafted chains. [Preview Abstract] |
Friday, March 25, 2011 8:36AM - 8:48AM |
Y40.00002: How do Macromolecules Diffuse Through Pathways imposed by Nanoparticles? Russell Composto, Karen Winey, Nigel Clarke, Sangah Gam, Jeff Meth Macromolecular motion slows down in crowded biological and engineered systems. Polymer nanocomposites (PNC) containing nanotubes and nanospheres are ideal systems for probing the underlying mechanisms of diffusion in a crowded system. Here, we review the current experimental studies of tracer diffusion in PNC. For silica nanospheres (12nm and 28nm), the normalized diffusion coefficients fall on a master curve when plotted against the interparticle separation divided by the probe size. The entropic barrier model accounts for the reduced diffusion by the loss of chain entropy due to the constrictive bottlenecks between nanoparticles. A new flux-based model depicts confined chains as diffusing along narrow pathways arranged by the NPs. This model captures experimental results while accounting for the distribution of particle separations inherent to real PNC. [Preview Abstract] |
Friday, March 25, 2011 8:48AM - 9:00AM |
Y40.00003: Macromolecular Diffusion in Polymer Nanocomposites Sangah Gam, Jeff Meth, Steve Zane, Karen Winey, Nigel Clarke, Russell Composto Macromolecular diffusion in crowded systems is important in biological and engineered systems. We have studied macromolecular diffusion through a model polymer nanocomposite (PNC) containing phenyl grafted silica nanoparticles (NPs), randomly distributed in a polystyrene matrix. Over a wide range of NP loading and tracer molecular weight (M), the scaling of the diffusion coefficient with M is in excellent agreement with the entropic barrier model (EBM) previously used to describe diffusion of DNA through confined media (e.g., gels and nanopores). To investigate the effect of NP size, diffusion was measured in PNC's with silica NPs having diameters of 28 and 12 nm. The normalized diffusion coefficients ($D$/$D_{0})$ plotted against the interparticle separation relative to probe size (i.e., \textit{ID}/2$R_{g})$ collapse on a master curve. Diffusion in a poly(methyl methacrylate):silica NP system was also investigated to understand how attractive interactions (i.e., enthalpy) perturb motion relative to the polystyrene and phenyl-silica NP system which is athermal. Finally, a flux-based model is proposed and compared with experimental results. [Preview Abstract] |
Friday, March 25, 2011 9:00AM - 9:12AM |
Y40.00004: Role of Particle -- Polymer Interactions on the Dynamics of Polymer Nanocomposites Guglielmo Capuano, Ramakrishna Ponnapati, Domenico Acierno, Ramanan Krishnamoorti Understanding the physics of polymers in the presence of nanoparticle fillers is of crucial importance, since it can lead to the formulation of truly engineered, functional nanocomposites with unique features and broad commercial utilization. The thermomechanical behavior of polymer nanocomposites qualitatively resembles those of polymer films confined to the nanoscale. It has been recently hypothesized that the suppression of physical aging in PMMA/silica nanocomposites is primarily due to hindered mobility of polymer molecules resulting from hydrogen bonding with hydroxyl units on the silica. Further, when solid nanoparticles are dispersed in polymer melts adsorption of polymer chains on the surface of nanoparticles alters the mobility of the chains far into the bulk, and several non-continuum effects are observed. We therefore investigate the effects of polymer-particle interactions on the relaxation dynamics and viscoelastic properties of a model nanocomposite based on a mixture of silica nanoparticles and poly(methyl acrylate). Narrow molecular weight distribution PMA was synthesized using ATRP and mixed with nanoparticles at different concentrations. Alterations in the viscoelastic behavior are attributed to filler structuring and interactions with the host polymer. [Preview Abstract] |
Friday, March 25, 2011 9:12AM - 9:24AM |
Y40.00005: The relationship between the $T_{g}$ depression and the speeding up of physical aging in polystyrene/gold nanocomposites Virginie M. Boucher, Daniele Cangialosi, Angel Alegria, Juan Colmenero The effect of gold nanoparticles on the segmental dynamics, glass transition ($T_{g})$ and physical aging of polystyrene (PS) was studied in PS/Gold nanocomposites samples containing 5 and 15 wt.{\%} of 60 nm spherical gold nanoparticles, surface-treated with thiolated-PS. While the segmental dynamics of PS, as assessed by broadband dielectric spectroscopy (BDS), was found to be unchanged in presence of gold nanoparticles, the calorimetric $T_{g}$ of PS was shown to decrease with increasing the amount of nanoparticles in the samples. Furthermore, the physical aging of PS, monitored by measuring the enthalpy relaxation below $T_{g }$ by means of DSC, was shown to speed up with increasing the nanoparticles weight fraction, i.e. the amount of PS/Gold interface in the hybrid material. Thus, the main conclusion of our work is that PS molecular mobility and out-of-equilibrium dynamics are decoupled in these nanocomposites. The significant effect of the amount of PS/Gold interface on both the physical aging rate of PS and the calorimetric $T_{g}$ depression are quantitatively accounted for by a model based on the diffusion of free volume holes towards polymer interfaces, with a diffusion coefficient depending only on the molecular mobility. [Preview Abstract] |
Friday, March 25, 2011 9:24AM - 10:00AM |
Y40.00006: Nanoparticle-directed self-assembly of amphiphilic block-copolymers Invited Speaker: The self-assembly of nanoparticles and amphiphilic polymers provides a powerful tool for the fabrication of functional composite materials for a range of applications spanning from nanofabrication to medicine. Here, we present how the incorporation of nanoparticles affects the self-assembly behavior of amphiphilic block-copolymers and how to control the morphology of nanoparticle-encapsulating polymer assemblies. Based on the approach, we have prepared various types of well-defined nanoparticle-encapsulating polymeric nanostructures, including polymersomes packed with magnetic nanoparticles and unique cavity-like quantum dot assembles. We found that the incorporation of nanoparticles drastically affects the self-assembly structure of block-copolymers by modifying the relative volume ratio between the hydrophobic block and the hydrophilic block. In addition, the nanoparticle-polymer and nanoparticle-solvent interactions impact the arrangement and the hybridization of nanoparticles in polymer matrix. These findings should form the basis for the design rules of the self-assembly of nanoparticles and polymer amphiphiles, which will allow one to create new hybrid structures with predesigned morphology and properties. Furthermore, we demonstrated that the morphology of nanoparticle-encapsulating polymer assemblies significantly affects their properties such as magnetic relaxation properties, underscoring the importance of the overall self-assembly structure and the nanoparticle arrangement in polymer matrixes. [Preview Abstract] |
Friday, March 25, 2011 10:00AM - 10:12AM |
Y40.00007: Isothermal Crystallization of Poly(ethylene oxide) / Single Walled Carbon Nanotube Nanocomposites Arnaldo Lorenzo, Tirtha Chatterjee, Ramanan Krishnamoorti The isothermal crystallization behavior of poly(ethylene oxide)/single walled carbon nanotubes (PEO/SWNT) nanocomposites were studied with a focus on the \textit{overall crystallization kinetics} and the \textit{morphological} evolution of PEO using differential scanning calorimetry and in-situ small angle x-ray scattering measurements, respectively. The overall crystallization process of the PEO was strongly affected by lithium dodecyl sulfate (LDS) stabilized carbon nanotubes. Further, analysis of the overall crystallization kinetics showed that the PEO chains were topologically constrained by the presence of LDS with an increased energy barrier associated with nucleation and crystal growth, and the nanotubes further act as a barrier to chain transport or enhance the LDS action on the PEO chains. The energy penalty and diffusional barrier to chain transport in the nanocomposites disrupt the PEO crystal helical conformation. This destabilization leads to formation of thinner crystal lamellae and suggests that the crystallization kinetics is primarily controlled by the growth process. This study is particularly interesting considering the suppression of the PEO crystallinity in presence of small amounts of Lithium ion based surfactant and carbon nanotubes. [Preview Abstract] |
Friday, March 25, 2011 10:12AM - 10:24AM |
Y40.00008: MD Simulations of DNA-Programmable Nanoparticle Self-Assembly Christopher Knorowski, Alex Travesset Self-assembly through linker mediated hybridization is a powerful technique to control self-assembly at the nanoscale. Recent experiments with complementary ssDNA attached to Au nanoparticles have shown crystallization into BCC and FCC crystals. We give a brief overview of a coarse grained model and present molecular dynamics simulations of the model. We discuss its static and dynamical properties. [Preview Abstract] |
Friday, March 25, 2011 10:24AM - 10:36AM |
Y40.00009: Hierarchical Superstructures from the Self-assembly of Giant Surfactants in Condensed State Wen-Bin Zhang, Xinfei Yu, Xuehui Dong, Yiwen Li, Kan Yue, Jinlin He, Stephen Cheng Giant surfactants are a class of tadpole-shaped hybrid nanomaterials with a functional nanoparticle as the head group and a polymer chain as the tail, such as perfluorochain-functionalized polyhedral oligomeric silsesquioxane end-capped poly($\varepsilon $-caprolactone) (FPOSS-PCL). The self-assembly of FPOSS-PCL with different composition in bulk were studied using DSC, SAXS, WAXD, and TEM. The compact arranagement of the perfluorochains on the POSS nanoparticles clearly distinguishes them from the polymer chain, leading to the formation of nanophase-separated supramolecular structures such as spheres, cylinders, and bilayered lamellaes. This physical picture is rather unusual and quite reminescent to that observed in the aggregates of small-molecule surfactants. The striking similarity indicates the importance in tuning the interactions to control the hierarchical structure formation in hybrid nanomaterials. [Preview Abstract] |
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