Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E49: Polymer Nanocomposites I: Matrix-Free Nanoparticle SystemsFocus
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Sponsoring Units: DPOLY Chair: Francisco Buitrago, University of Pennsylvania Room: BCEC 252A |
Tuesday, March 5, 2019 8:00AM - 8:36AM |
E49.00001: E49 POLYMER PHYSICS PRIZE BREAK
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Tuesday, March 5, 2019 8:36AM - 8:48AM |
E49.00002: Single-Component Semi-Crystalline Nanocomposite Materials Jacob LaNasa, Robert Hickey Polymer nanocomposites possess the potential to enhance thermal, mechanical, and dielectric properties of soft materials compared to their neat polymer counterparts. In order to develop high-performance nanocomposite materials, traditionally immiscible nanoparticles need to maintain adequate dispersion at sufficiently high volume fractions. The work presented here highlights the development of semi-crystalline polymer-particle nanocomposites and the ensuing investigation on the thermal and mechanical effects of constraining one end of the polymeric chain to a particle surface. Poly(cyclooctadiene)-grafted silica nanoparticles are synthesized through surface-initiated ring opening metathesis polymerization, and characterized using transmission electron microscopy, size exclusion chromatography, and optical light scattering. The unsaturated polymer backbone is then hydrogenated to form silica nanoparticles grafted with poly(ethylene). The mechanical properties and the crystallization processes are then measured for the single-component nanocomposites and compared their neat polymer equivalent. The work presented provides a route to semi-crystalline nanocomposite synthesis and provides insight into the phase behavior of a novel class of materials. |
Tuesday, March 5, 2019 8:48AM - 9:00AM |
E49.00003: Multiscale dynamics in matrix-free polymer grafted nanoparticle systems Mayank Jhalaria, Eileen N Buenning, yu cang, Yucheng Huang, Madhusudan Tygai, Victoria Garcia-Sakai, Reiner Zorn, George Fytas, Brian C Benicewicz, Sanat Kumar Recent work has shown that gas separation membranes constructed using only polymer grafted nanoparticles exhibit enhanced transport properties compared to the bulk. Additionally, this behavior is non-monotonic with increasing chain length (at constant grafting density). Macroscopic rheological measurements reveal a glass to liquid transition with increasing chain lengths, with the transition occurring at the point where the permeability goes through a maximum. This implies a possible connection between the two behaviors although they operate at different scales. Using techniques that allow for more spatially sensitive probes, we explore the effective medium sound velocity, particle relaxation and local polymeric dynamics across a variety of timescales. The key takeaways are i)Different sound velocity behaviors in the glass and liquid like regimes, ii)Kinetic jamming at of the particles governs long time relaxation and iii)Faster local dynamics in the polymer grafts as compared to the neat polymer. These results extend the understanding of how dynamics manifest in such systems and provide a scaffold to develop newer materials with desirable properties. |
Tuesday, March 5, 2019 9:00AM - 9:12AM |
E49.00004: Mechanical Properties and Crazing Behavior in Model Polymer-Grafted Nanoparticle Thin Films Jeffrey Ethier, Lisa Hall Thin films comprised of inorganic-organic polymer-grafted nanoparticles (PGNs) show promise for use in flexible electronics and high energy density materials. Recently, there has been significant interest in tuning the properties of the polymer-grafted layers to optimize entanglement formation between neighboring PGNs and improve mechanical performance. In this work, we show how graft density and polymer length affect inter-PGN entanglements and mechanical properties using coarse-grained molecular dynamics (MD) simulations. Specifically, we simulate twelve PGNs organized in a hexagonal spacing on a smooth, attractive surface. We rigidly attach the first monomer of every chain to the surface of a nanoparticle (using rigid body constraints) and model the polymers as bead-spring chains. We first quantify the number of interparticle entanglements between PGNs and show that moderate graft density particles have increased interparticle entanglements per chain and better mechanical toughness compared to high graft density particles in the melt state. We then cool the monolayer below the glass transition and compare the crazing behavior of PGN thin films to their analogous homopolymer thin films. |
Tuesday, March 5, 2019 9:12AM - 9:48AM |
E49.00005: Microscopic origins of caging and hyperdiffusive relaxations in hairy nanoparticle fluids Invited Speaker: Lynden Archer Nanocomposites formed from well-dispersed suspensions of solvent-free silica nanoparticles tethered with flexible polymers are known to exhibit jamming behavior due to interpenetrated chains in the confined space between nanoparticle cores. This talk discusses equilibration processes in such materials by means of small-angle X-ray scattering (SAXS), dielectric relaxation, and rheology measurements. In so doing the talk we explore the microscopic processes responsible for caging and show how cages emerge on the nanoparticle cores. The talk also considers consequences of caging, including hyperdiffusive particle dynamics and yielding. A simple microscopic model for caging and particle clustering is shown to explain both the yielding transition and onset of hyperdiffusive relaxations. |
Tuesday, March 5, 2019 9:48AM - 10:00AM |
E49.00006: Polymer-Grafted Nanoparticle (PGN) Assemblies: Supramolecular Dynamic Bonds for Enhanced Toughness Andrew Tibbits, Ali Jawaid, Jason Streit, Lawrence Drummy, Richard Vaia The targeted design of PGNs has significant ramifications in the design of scalable and tough coatings, flexible electronics, and functional inks. Studies of the nanomechanics of polystyrene grafted nanoparticles have shown a strong dependence of PGN architecture on plasticity. Nonetheless, toughness at high NP fraction is impeded by the inherently high entanglement molecular weight (MWe) of amorphous polymer grafts. The incorporation of supramolecular dynamic bonds (e.g. hydrogen bonding) into the canopy provides dynamic crosslinks that enhance viscoelasticity and dissipative processes at lower molecular weights. The modification of pendant olefins in poly(1,2-butadiene) with supramolecular dynamic bonds and subsequent grafting onto gold nanoparticles permits directed self-assembly into ordered superlattice structures at high core volume fraction (>30 vol%). The modular chemistry and grafting approach facilitates development of a comprehensive phase space correlating PGN architecture, dynamic bond strength and content, morphology, and nanomechanics to direct optimal engineered canopy designs to maximize robustness in PGN assemblies. |
Tuesday, March 5, 2019 10:00AM - 10:12AM |
E49.00007: Structure and dynamics of architecturally engineered all-polymer nanocomposites Erkan Senses, Madhusudan Tygai, Antonio Faraone We present nanocomposites formed by using glassy star-shaped polymers as nanofillers and dispersing them in soft matrices. The resulting ‘architecturally engineered’ nanocomposites structurally reside between the linear homopolymer blends and the conventional polymer nanocomposites with solid fillers. We observed that the star polymers can induce reinforcement that can be as strong as that of solid nanoparticles, or softening depending on the compactness and concentration of the nanoparticles. We showed that the remarkable influence of filler architecture on the rheological properties can be traced back to the dynamical features at the segmental and the chain level which we investigated using neutron scattering over a wide range of time and lenghts scales in the glassy and melt states of the nanocomposites. The local and segmental dynamics as well as chain-chain entanglements are all modified by polymer architecture, offering a novel approach for tuning the physical properties of all-polymer based composites. |
Tuesday, March 5, 2019 10:12AM - 10:24AM |
E49.00008: Entropy-Enthalpy Compensation (EEC) Behavior in Relaxation of Nanoparticle-Brush Filled Imprinted Polymer Films Sonal Bhadauriya, Xiaoteng Wang, Christopher M Stafford, Jack Douglas, Alamgir Karim Entropy-enthalpy compensation (EEC) effect signifies a linear correlation between the activation parameters of a relaxation process and is routinely observed in the dynamics of many condensed materials such as molecular additives and glass-forming materials. Herein we present relaxation behaviour of nanoparticle-brush filled imprinted polymer films showing similar compensation effect leading to slower decay kinetics above the compensation temperature (Tcomp) compared to the neat polymer film. The compensation of the activation enthalpy with the entropy of activation led to the observed increase in the relaxation time constant with concentration above Tcomp. Kinetics of structural decay in imprinted thin films of polymethyl methacrylate (PMMA) matrix with different nanoparticle-brush systems (PMMA-grafted TiO2 and PMMA-grafted SiO2) were investigated and EEC was robustly observed for both the systems. This is the first experimental study of structural decay (“slumping”) of a patterned nanocomposite film and the relaxation behaviour witnessed here is similar to relaxation dynamics of ultrathin wrinkled polymer films. Our results suggest a common origin of EEC behaviour in patterned thin films and provides a simple nanoparticle additive strategy to tune the structural stability. |
Tuesday, March 5, 2019 10:24AM - 10:36AM |
E49.00009: Deformation Mechanism of Mechanochromic Polymer Nanocomposites Fabricated by Self-Assembly of Colloidal Particles Chao-Hung Cheng, Shuhei Nozaki, Shiori Masuda, Nattanee Dechnarong, Kazutaka Kamitani, Tomoyasu Hirai, Ken Kojio, Atsushi Takahara A novel polymer nanocomposite consisting of polymer-grafted nanoparticles have attracted great attention due to their properties of self-assembling to an ordered colloidal crystal structure. However, the deformation mechanism of this colloidal crystal has not been clarified yet. In this study, the structural evolution of a colloidal crystal with rubbery/glassy block copolymer-grafted silica particles (BCP-g-SiO2) was investigated by in situ ultra small-angle X-ray scattering (USAXS) under deformation. Poly(butyl acrylate) (PBA) and poly (methyl methacrylate) (PMMA) were chosen as inner and outer layers of BCP-g-SiO2, respectively. |
Tuesday, March 5, 2019 10:36AM - 10:48AM |
E49.00010: Polymer-grafted Nanoparticle Membranes with Exceptional Gas Separation Performance Connor Bilchak, Sanat Kumar, Christopher James Durning, Yucheng Huang, Brian C Benicewicz, Jacques Jestin There is considerable interest in developing novel gas separation membranes that improve on current, pure polymer-based technologies. Pure polymer grafted nanoparticle based membranes offer the exciting opportunity to tunable small gas permeabilities but are still limited compared to current exotic polymers. Here, we discuss gas transport in GNPs incorporating small amounts of ungrafted polymer chains with judiciously chosen chain lengths. We find that the addition of homopolymer allows us to almost independently increase membrane gas selectivity, and thus exceed the Upper Bound representing the best currently available membrane materials. X-Ray and neutron scattering suggest that gas transport in GNPs is spatially inhomogeneous with solutes bigger than a critical size being moved primarily through the interstitial spaces between the NPs, while small solutes are carried more homogeneously through the whole layer. High molecular weight free chains segregate into these interstitial regions and preferentially hinder large solute motion, thus greatly improving selectivity. Controllably manipulating transport in these inhomogeneous materials thus offers the opportunity to construct gas-separation membranes with exceptional performance. |
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