Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session A19: The Physics of Polymer Nanocomposites: Polymer Nanoparticle Interactions |
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Sponsoring Units: DPOLY Chair: Amalie Frischknecht, Sandia National Laboratories Room: 320 |
Monday, March 16, 2009 8:00AM - 8:12AM |
A19.00001: Functional polymer colloids stabilized by type-purified single-wall carbon nanotubes. Erik K. Hobbie, Jeffrey A. Fagan, Jan Obrzut Emulsion polymerization of a methacrylate monomer in aqueous biological suspensions of type-purified single-wall carbon nanotubes (SWNTs) is used to synthesize polymer colloids coated by nearly pure metallic or semiconducting SWNTs. The polymer-nanocomposite spherical particles are 1-100 micrometers in diameter, are marginally stable in ethanol, and retain the color and unique optical characteristics of the purified SWNT coating in the absence of any surfactant. By assembling these functional polymer colloids on microelectronic circuits, we characterize the electronic properties of the SWNT-polymer nanocomposite microspheres and relate this to the band structure of the purified SWNT coating, demonstrating their potential use as microscopic optical and electronic components that can be easily manipulated using standard methods of colloidal self-assembly. [Preview Abstract] |
Monday, March 16, 2009 8:12AM - 8:24AM |
A19.00002: Theoretical analysis of dispersing of aggregated nanorods in shear flow in presence of AC electric or magnetic fields Victor Pryamitsyn, Venkat Ganesan Efficient dispersion of nanotubes in polymeric matrices is a critical problem confronting the development of modern polymer nanocomposites. The nanotube-nanotube interactions usually promote aggregation, which also depends on factors such as the chemical makeup of the polymer matrix and the size of nanotubes. High intensity mechanical mixing such shear pulverization are commonly used for dispesion of nanotubes. The main disadvantage of such processes is the degradation of polymer matrix, which may downgrade the final properties of PNC's. In this work, we theoretically explore a novel strategy to reduce the shear stresses required for dispersion of rodlike fillers. Explicitly, we found that simultaneous applications shear flow and AC electric field oriented at an angle to each other may cause rotational instabilities of the rods suspension and lead to the dispersion of the rods. We demonstrate this idea through Brownian dynamics simulations of aggregating nanorods and a complementary theoretical analysis using a 2D Smoluchowski equation. Our results suggest that an optimal dispersion may be achieved at an shear-E field orientation of $\beta=-45^{\circ} $ with an optimal amplitude of AC electric field which is proportional to the rotation Peclet number of nanorods suspension. [Preview Abstract] |
Monday, March 16, 2009 8:24AM - 8:36AM |
A19.00003: Effective Interactions, Structure and Phase Behavior of Polymer Nanocomposites with Nonspherical Fillers Lisa M. Hall, Kenneth S. Schweizer The Polymer Reference Interaction Site Model is applied to study polymer-mediated inter-nanoparticle interactions, fluid structure, and miscibility of nonspherical filler particles in a melt of adsorbing freely-jointed chains. The behavior of hard rod, disk, and cube-like nanoparticles are compared. The depletion contact aggregation, dispersed, and polymer bridging mediated nanoparticle network states of organization are sensitive to filler shape. A detailed study of thin rod fillers, including the rod-rod potential of mean force and second virial coefficient, B$_{2}$, as a function of polymer-rod and rod-rod attraction strengths, has also been performed. A primary goal is to identify design rules for dispersing nanotubes in polymer melts. Shortening the spatial range of rod-rod attraction compared to polymer-rod attraction increases miscibility. The transition from positive to negative B$_{2}$ at low polymer-rod interfacial attraction (entropic depletion) occurs more readily (at higher attraction strength) as rod-rod attraction is increased. However, the transition to negative B$_{2}$ at high polymer-rod attraction strength, driven by polymer-induced enthalpic bridging of rods, is relatively invariant to inter-rod attraction strength. Increasing rod length reduces the stabilizing consequences of polymer adsorption and the attendant steric repulsion. [Preview Abstract] |
Monday, March 16, 2009 8:36AM - 9:12AM |
A19.00004: Polymer-tethered nanoparticle ``shape amphiphiles": A new class of macromolecular building block for self-assembly Invited Speaker: Fabricating complex ordered structures from nanoparticles requires controlling nanoparticle interactions for self-assembly over multiple length scales. Here we exploit both building block shape and interaction anisotropy for self-assembly, and explore the use of polymer ``tails'' attached to nanoparticle ``head groups'' to create a new kind of amphiphile that self assembles into structures like those seen in surfactant and block copolymer systems, but with important differences arising from nanoparticle shape, and tethered nanoparticle geometry and topology. We investigate the impact of nanoparticle size polydispersity and show that it can both help and hinder formation of certain complex phases. Using simulation, we investigate tethered spheres, rods, cubes, triangles, and other shapes, and provide design rules for the predicted self-assembly of a range of chiral and achiral structures, including helical scrolls, gyroid, square arrays, and ionic crystal-like structures. [Preview Abstract] |
Monday, March 16, 2009 9:12AM - 9:24AM |
A19.00005: Control of the Spatial Distribution of Nanoparticles in Fluorescent Polymer Nanocomposites Chelsea Chen, Peter Green In a brush-coated nanoparticle (NP) / polymer nanocomposite system, the spatial distribution of the NPs is largely determined by the entropic and enthalpic interactions between the brush and polymer host chains. We examined the miscibility between polystyrene (PS) homopolymer chains and a fluorescent polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]~(MEH-PPV) and found that in thin films, low molecular weight (MW) PS and MEH-PPV are miscible, whereas high MW mixtures exhibit phase separation. Consequences of this behavior were examined with regard to the effect on the morphology of nanocomposite thin films composed of MEH-PPV and thiol terminated polystyrene grafted Au nanoparticles of varying sizes. We were able to achieve complete dispersion, as well as interfacial segregation, of the Au-PS nanoparticles within MEH-PPV hosts. Through control of the morphology, we were able to ``tune'' the optical properties of the MEH-PV/Au-PS nanocomoposites. [Preview Abstract] |
Monday, March 16, 2009 9:24AM - 9:36AM |
A19.00006: Importance of Chain Connectivity in the Formation of Non-covalent Interactions between Polymers and Single-Walled Carbon Nanotubes Dias Linton, Brad C. Miller, Huimin Li, Charles Feigerle, Bobby G. Sumpter, Mark D. Dadmun Our work is focused on understanding and utilizing non-covalent electron donor-acceptor (EDA) interactions between polymers and SWNT to optimize interfacial adhesion and homogeneity of nanocomposites without modifying the SWNT native surface. Nanocomposites with polymer bound electron donating 2-(dimethylamino)ethyl methacrylate or electron accepting acrylonitrile and cyanostyrene moieties leads to improved SWNT dispersion if the interacting functional group is a minor component of a copolymer matrix. Correlation of experimental (Raman mapping, Raman D* band peak shifts, and optical microscopy) and computational results indicates that chain connectivity is critical in controlling the accessibility of the functional groups to form EDA interactions. Thus, controlling the amount of e$^{-}$ donating or withdrawing moieties throughout the polymer chain will direct the extent of EDA interaction, which enables tuning the SWNT dispersion. [Preview Abstract] |
Monday, March 16, 2009 9:36AM - 9:48AM |
A19.00007: The Structure of Amphiphilic Polymers Interacting with Carbon Nanotubes Yachin Cohen, Meirav Granite, Wim Pyckhout-Hintzen, Aurel Radulescu Dispersion of single-walled carbon nanotubes, necessary for their beneficial utilization, is often based on amphiphilic copolymers. We have successfully utilized the following systems: an alternating copolymer of styrene and sodium maleate, exhibiting alternating hydrophobic and hydrophilic groups, amphiphilic block copolymers such as Pluronic F108 and a synthetic short polypeptide (FFDD)$_{6}$, containing alternating hydrophobic blocks of two phenylalanine (FF) and hydrophilic block of two aspartic acid (DD). Cryo-transmission electron microscopy images reveal isolated, very small bundles of carbon nanotubes, with diameters range from 1 to 5 nm and approximately 500 nm length. Small-angle neutron scattering experiments were conducted at different D$_{2}$O/H$_{2}$O content of the dispersing medium. The scattering patterns suggest a complex entity with an heterogeneous structure. For the alternating copolymer, loose adsorption of polymer coils is indicated, contrary to published ideas on ``polymer wrapping'' of nanotubes. For the Pluronic block copolymers, the data suggest that even below the critical micellization temperature there is a dense coating on the nanotube surface and the hydrophilic blocks are highly extended. The polypeptide also forms a dense coating with an apparently ``spongy'' structure. [Preview Abstract] |
Monday, March 16, 2009 9:48AM - 10:00AM |
A19.00008: Chain Expansion in Polymer-Nanoparticle Melts A. L. Frischknecht, E. S. McGarrity, M. E. Mackay We apply a self-consistent version of the polymer reference interaction site model (PRISM) theory to a model of spherical nanoparticles in a polymer melt. The average radius of gyration of the chains in the blend clearly increases (over that from chains in a neat melt at the same density) with increasing nanoparticle volume fraction. The amount of chain expansion also depends on the magnitudes of the attractive interactions in the system. The bulk modulus of the blend decreases with increasing nanoparticle volume fraction. We compare our theoretical results to experimental scattering data from polystyrene blended with various nanoparticles and to previous simulation results. (This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. Department of Energy, Office of Basic Energy Sciences user facility. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the U. S. Department of Energy under Contract No. DE-AC04-94AL85000.) [Preview Abstract] |
Monday, March 16, 2009 10:00AM - 10:12AM |
A19.00009: Effects of nanoparticles on chain dynamics and glass transition in athermal polymer nanocomposites Hyun Joon Oh, Peter Green Chain relaxation dynamics and the glass transition of mixtures of polystyrene (PS) homopolymer with PS-grafted gold nanoparticles were examined using broadband dielectric spectroscopy, differential scanning calorimetry and capacitive scanning dilatometry. Through changes in the nanoparticle core size, D, grafting density, $\sigma $, degree of polymerization of grafted chains, N, and the nanoparticle concentration, $\phi $, both the chain relaxation time, $\tau $, and the T$_{g}$ could be induced to undergo significant changes, increases or decreases, in magnitude. These results will be discussed in light of dynamics in other polymer/nanoparticle systems. In addition, the role of particle size and the role of the melt/brush interfacial interactions on the dynamics will be discussed. [Preview Abstract] |
Monday, March 16, 2009 10:12AM - 10:24AM |
A19.00010: Dynamics in Nanoparticle Liquids Peter Mirau, Michael Jespersen, Richard Vaia, Robert Rodriguez, Emmanuel Giannelis Nanoscale Ionic Materials (NIMS) are organic-inorganic hybrids in which a nanometer-sized core is functionalized with a covalently attached corona and an ionically tethered canopy. NIMS can be engineered to be liquids at ambient temperature in the absence of solvent and are of interest for a variety of applications. We have used NMR relaxation and pulse-field gradient NMR to measure the dynamics of NIMS made from a 20 nm silica core modified with propyl sulfonic acid groups and amino-terminated ethylene oxide/propylene oxide block copolymers. Carbon NMR studies show that the block copolymer canopy is quite mobile both in the bulk and the nanoparticle liquid. The carbon spin-lattice relaxation times as a function of temperature are fit to a model with rapid librational motions and slower reorientation of the copolymer. Neither the correlation times for reorientation of the block copolymer nor the self-diffusion coefficient are influenced by the presence of the silica nanoparticle core. These data suggest that the liquid-like behavior in NIMS is due to rapid exchange of the block copolymer canopy between the ionically modified nanoparticles. [Preview Abstract] |
Monday, March 16, 2009 10:24AM - 10:36AM |
A19.00011: Hierarchically Structured Block Copolymer $\backslash $ Silicate Nanocomposites Ross Behling, Eric Cochran In this contribution we functionalized MMT with a bromine terminated alkylamine and subsequently polymerized polystyrene-$b$-poly(tert-butyl acrylate) via graft-from atom transfer radical polymerization. Hierarchical assembly of these composites was facilitated through targeted graft density, polymer block size, and MMT intrinsic properties. The high graft density on the MMT surface results in confinement effects which force growing polymer chains into highly extended conformations. Block copolymer (BCP) brushes were chosen because they inherently offer an easily tunable method for producing self-assembled structures on the order of tens of nanometer. Montmorillonite (MMT) in its raw state is composed of negatively charged tactoid stacks 100-300 nm in diameter and 1-2 nm thick resulting in BCP$\backslash $silicate nanocomposites particles arranged under shear into structures spanning several hundreds of nanometers. The equilibrium structures were influenced by the MMT platelet curvature and the BCP interaction parameter, $\chi $. BCP nanocomposites were observed via transmission electron microscopy to display novel morphologies with multiple systems exhibiting interpenetrating networks reminiscent of ``worm micelles''. [Preview Abstract] |
Monday, March 16, 2009 10:36AM - 10:48AM |
A19.00012: Effect of Copolymer-Nanoclay Interactions on Intercalation Kinetics Loan Vo, Haris Retsos, Emmanuel Giannelis We use X-ray diffraction to measure the melt intercalation kinetics of a series of surface-modified clay nanoparticles (nanoclay) with styrene-butadiene-rubber (SBR). Since SBR is a copolymer, both the styrene and the butadiene components interact with the nanoparticles contributing to the nanoclay miscibility and the intercalation kinetics. We are able to directly measure the butadiene-nanoclay interaction strength by using dielectric relaxation spectroscopy to probe the butadiene-nanoclay interfacial relaxation mode, and by varying the nanoclay surfactant and copolymer composition, we can indirectly measure the styrene-nanoclay interaction strength. We will present the spectroscopy results and discuss the relation to the intercalation kinetics. [Preview Abstract] |
Monday, March 16, 2009 10:48AM - 11:00AM |
A19.00013: Polymer Nanocomposites Containing Carbon Nanotubes and Exfoliated Nanoplatelets Hung-Jue Sue, Dazhi Sun We report a simple and efficient method to disperse carbon nanotubes (CNTs) into an epoxy matrix through exfoliated nanoplatelets. Pre-oxidized CNTs were first dispersed in the presence of exfoliated nanoplatelets in water, followed by re-dispersion in epoxy matrix. Both individual CNTs and nanoplatelets are exfoliated and well dispersed in epoxy, which is confirmed by high-resolution transmission electron microscopy. The possible mechanisms responsible for the CNT dispersion in polymers are proposed. The epoxy nanocomposites containing CNTs and nanoplatelets show exceptional mechanical properties: significant improvements in both modulus and strength without reduction in ductility have been found from tensile testing. The implication of the present findings for the engineering applications of the CNT-based polymer nanocomposites is also discussed. [Preview Abstract] |
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