Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session T41: Polymer Nanocomposites I |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Praveen Agarwal, Dow Chemical Company Room: 214A |
Thursday, March 5, 2015 11:15AM - 11:27AM |
T41.00001: Self-Assembly of Grafted Nanoparticles for Transport Channels in Membranes Connor Bilchak, Ellie Buenning, Christopher Durning, Sanat Kumar Polymer membranes have seen increased application for vapor separations, particularly for natural gas processing and purification. The addition of nanoparticles to such membranes has led to conflicting findings; conventional (Maxwell) composite theory predicts the addition of inert filler to hinder membrane transport properties. However, our research using silica nanoparticles grafted with Poly (Methacrylate) has shown these grafted systems to possess permeabilities similar to those of a pure polymer system increasing penetrant solubility without compromising diffusivity. This is counterintuitive to Maxwell theory. We propose that the grafted nanoparticles self-assemble into an ordered crystal lattice containing low-density ``channels'' which facilitate penetrant uptake. Atomic force microscopy and small-angle neutron scattering experiments appear to confirm this theory. Varying polymer grafting density and chain length is also predicted to alter transport properties, allowing for the fabrication of membrane with tunable diffusivity and selectivity. These grafted nanocomposite systems therefore represent a means of creating robust membranes with transport properties similar to those of conventional polymeric films that may be easily adapted for various separations processes. [Preview Abstract] |
Thursday, March 5, 2015 11:27AM - 11:39AM |
T41.00002: Effects of temperature on structure and mechanical properties of alkanethiol coated gold nanoparticle membranes K. Michael Salerno, Gary Grest Single-nanoparticle-thick membranes have a variety of potential uses due to unique mechanical properties. While these membranes have been studied experimentally and computationally at 300K, the effects of thermal annealing on structure and properties have not been investigated. We present atomistic molecular dynamics simulations that study the effects of temperature on nanoparticle membrane properties. Nanoparticles are made of a gold core coated with organic oligomer ligands. At high grafting density, ligands with CH$_3$ end groups exhibit local crystallinity at 300K while those with COOH end groups orient to form dimers due to electrostatics. Both features influence membrane mechanical properties. As temperature increases ligand crystallinity and COOH affinity are disrupted, and mechanical strength is reduced. Immediately after cooling back to 300K, membranes are weaker and measures of ligand interdigitation and COOH affinity are reduced. Over time, interdigitation and end-group interactions rejuvenate and samples that undergo high-temperature annealing have mechanical properties comparable to the original membranes. The structure/property temperature dependence points to ways that membranes could be tailored for temperature-dependent/resistant properties. [Preview Abstract] |
Thursday, March 5, 2015 11:39AM - 11:51AM |
T41.00003: Quantitative Analogy Between Polymer Grafted Nanoparticles and Patchy Particles Makoto Asai, Angelo Cacciuto, Sanat Kumar We establish a quantitative analogy between polymer grafted nanoparticles (PGNPs) and patchy nanoparticles (NPs). Over much of the experimentally relevant parameter space, we show that PGNPs behave quantitatively like Janus NPs, with the patch size having a universal dependence on the number of grafted chains and the ratio of the size the NPs to the grafted chain size. The widely observed anisotropic self-assembly of PGNPs into superstructures can thus be understood through simple geometric considerations of single patch model, in the same spirit as the geometry-based surfactant models of Israelachvili [Preview Abstract] |
Thursday, March 5, 2015 11:51AM - 12:03PM |
T41.00004: Reversible Thermal-Stiffening in Polymer Nanocomposites Erkan Senses, Pinar Akcora Silica nanoparticles adsorbed with a high glass-transition temperature polymer, PMMA (T$_{\mathrm{g}}$: 130 $^{\circ}$C) are shown to uniformly disperse in a low-T$_{\mathrm{g}}$ polymer matrix, PEO (T$_{\mathrm{g}}$: -60 $^{\circ}$C). These nanocomposites exhibit an unusual reversible liquid-to-solid transition at temperatures above T$_{\mathrm{g}}$'s of both polymers. Mechanical adaptivity of PEO nanocomposites to temperatures underlies the existence of dynamically asymmetric bound layers on particles, and more importantly their impact on mechanical behavior, which sets these materials apart from conventional polymer composites that soften upon heating. Moreover, the growth rate of elastic moduli at temperatures above T$_{\mathrm{g}}$ of PMMA presents an Arrhenius-type relaxation with activation energy well-matching with the $\alpha $-$\beta $ merging region of PMMA. These results suggest that the mobility of the surface-bound polymer is essential for reinforcement contrary to commonly accepted glassy-layer hypothesis. [Preview Abstract] |
Thursday, March 5, 2015 12:03PM - 12:15PM |
T41.00005: SANS Study on the Behaviors of Polymeric Ligands on the Nanoparticle Surfaces Seyong Kim, Soo-Hyung Choi, June Huh, Joona Bang In this work, we employed small angle neutron scattering (SANS) and contrast variation technique to characterize the behaviors of polymer ligands on the nanoparticle (NPs) surfaces. The Janus-type Au NPs were coated with a mixture of two different ligands, PMMA-SH and deuterated PS-SH, and the Au NPs coated only with P(MMA-r-dS)-SH were also prepared for the control case of NPs with homogeneous ligands. From the SANS analysis, it was observed that the ligands become phase separated with increasing the molecular weight of ligands. Furthermore, computational simulation was performed to examine how ligands are phase separated on the curved NPs surfaces. [Preview Abstract] |
Thursday, March 5, 2015 12:15PM - 12:27PM |
T41.00006: Semi-crystalline polymer nanocomposites: interplay of matrix crystallization and nanoparticle self-assembly Dan Zhao, Jacques Jestin, Longxi Zhao, Sanat K. Kumar, Mohammad Mohammadkhani, Brian C. Benicewicz We investigate a new class of nanocomposite materials made of semi-crystalline poly(ethylene oxide) and poly(methyl methacrylate) grafted silica nanoparticles (NPs). The results indicate that NPs do not act as nucleating agents as indicated from the lowering of the onset of crystallization temperature with addition of NPs. Although the crystal sizes and rate of crystallization are reduced in the presence of NPs, the equilibrium melting temperature seems to be unaffected. Furthermore, no remarkable change was observed in the spatial dispersion of NPs upon fast crystallization. However, for slow crystallization, both TEM and X-ray scattering reveal that the system starts to be organized in a ``layer-by-layer'' architecture, where the NPs are aligned in the amorphous phases intercalated by the crystalline lamellar phases. [Preview Abstract] |
Thursday, March 5, 2015 12:27PM - 12:39PM |
T41.00007: Chemically Designed Molecular Interfaces in Cross-Linked Poly(ethylene glycol)/Silica Nanocomposites Reveal Strong Size-Dependent Trends in Gas Permeability Norman Su, Jeffrey Urban Polymer nanocomposite membranes can exhibit gas separation performance that surpasses conventional polymeric membranes. While promising, the optimization of nanocomposite membranes requires a fundamental understanding of the transport mechanism and interfacial effects between the inorganic and polymer phase that is currently limited to empirical relationships. Synthesized nanocomposites often consist of poorly distributed and polydisperse inorganic nanomaterials. It is known that polymer dynamics can change drastically upon introduction of an inorganic phase, which can dramatically alter molecular transport behavior. Here, we systematically explore the role of nanoparticle sizes from 12 to 130 nm on polymer dynamics and permeability in a series of cross-linked poly(ethylene glycol)/silica nanocomposite membranes. The nanocomposites are well-dispersed and display excellent homogeneity throughout. Size-dependent broadening of the T$_{\mathrm{g}}$ indicates strong attractive interactions especially at high surface area loadings, which lead to deviations in permeability not captured by Maxwell's model. Chemical modifications of silica at this interface can yield significantly different polymer dynamics than previously observed with enhanced transport and mechanical properties. [Preview Abstract] |
Thursday, March 5, 2015 12:39PM - 12:51PM |
T41.00008: Interactions between Nanoparticles and Polymer Brushes: Molecular Dynamics Simulations and Self-consistent Field Theory Calculations Shengfeng Cheng, Chengyuan Wen, Sergei Egorov Molecular dynamics simulations and self-consistent field theory calculations are employed to study the interactions between a nanoparticle and a polymer brush at various densities of chains grafted to a plane. Simulations with both implicit and explicit solvent are performed. In either case the nanoparticle is loaded to the brush at a constant velocity. Then a series of simulations are performed to compute the force exerted on the nanoparticle that is fixed at various distances from the grafting plane. The potential of mean force is calculated and compared to the prediction based on a self-consistent field theory. Our simulations show that the explicit solvent leads to effects that are not captured in simulations with implicit solvent, indicating the importance of including explicit solvent in molecular simulations of such systems. Our results also demonstrate an interesting correlation between the force on the nanoparticle and the density profile of the brush. [Preview Abstract] |
Thursday, March 5, 2015 12:51PM - 1:03PM |
T41.00009: Dispersion/Aggregation of polymer grafted nanorods in a polymer matrix studied by Dissipative Particle Dynamics Joao Maia, Shaghayegh Khani Nanorods are incorporated into polymer matrices for fabricating composite materials with enhanced physical and mechanical properties.The final macroscopic properties of the composites are directly related to the dispersion and organization of the nanoparticles in the matrix. For instance, a significant improvement in the mechanical properties of the nanorod-polymer composites is observed upon formation of a percolating network. One way of controlling the assembly of nanorods in the polymer medium is adjusting the chemical interactions which is done through grafting polymer chains on the surface of the rods. The recent developments in the computational techniques have paved the road for further understanding of the controlled dispersion and aggregation of nanorods in polymer matrices. In this study, Dissipative Particle Dynamics (DPD) is employed in order to investigate the effect of enthalpic and entopic variables on the phase behavior of the abovementioned nanocomposites. In DPD, the interaction parameter between the components of the systems can be mapped onto the Flory-Huggins $\chi $-parameter via well-known Groot-Warren expression. This works studies the effect of the enthalpic and entropic variables on phase transitions. The main goal is to provide a phase diagram than can be used to guide the experiments in designing new materials. [Preview Abstract] |
Thursday, March 5, 2015 1:03PM - 1:15PM |
T41.00010: Phase Behavior of Polymer-Grafted Nanoparticles in a Polymer Matrix Katrina Irene Mongcopa, Rana Ashkar, Paul Butler, Ramanan Krishnamoorti We examine the thermodynamic interactions of polystyrene (PS) grafted onto spherical silica nanoparticles blended with a poly(vinyl methyl ether) (PVME) matrix using light, x-ray and neutron scattering techniques. PS/PVME systems are known to exhibit a lower critical solution temperature, with blending thermodynamics greatly affected by the chain length of the components. Thus, we study how enthalpic and entropic effects play a role in the dispersion of PS-grafted nanoparticles in a chemically-distinct matrix, especially as the system approaches a phase boundary. Scattering techniques are used to examine the effect of molecular weight on the blend thermodynamics and concentration fluctuations for such strongly interacting polymer blends. X-ray scattering data and analysis of the structure factor reveal that for a grafted deuterated polystyrene brush (33,000 Da) in a PVME matrix (226,000 Da), an initial dispersion of nanoparticles occurs at low temperatures. The system then gradually transitions to an aggregated state as temperature is increased, suggesting the presence of strong inter-particle interactions that lead to fractal formation as the system approaches a phase boundary. Complementary neutron scattering experiments confirm this phenomenon. [Preview Abstract] |
Thursday, March 5, 2015 1:15PM - 1:27PM |
T41.00011: Study of Polymer/Graphene Nanocomposites through Atomistic Molecular Dynamics Simulations Anastassia Rissanou, Vagelis Harmandaris Polymer/graphene nanostructured systems have attracted great attention the last years both for scientific and technological reasons. A main challenge in the study of graphene based polymer nanocomposites is to predict their properties at the molecular level. In the current study the effect of the weight fraction of graphene in a polymer matrix, as well as the size of the graphene sheet, on the properties of polymer chains are examined. Density profiles, structural and conformational characteristics as well as mobility aspects are studied. All the above properties are examined, as a function of the distance from the substrate. Results are compared with the interfacial properties of polymer chains confined between two periodic (i.e., ``infinite'') frozen graphene layers. In addition dynamical and conformational properties of the graphene sheet are studied as a function of the size and the weight fraction of the sheet in the polymer matrix. Furthermore, thermal as well as matrix induced fluctuations (i.e. wrinkling) of graphene sheets are examined. The extent of the fluctuations and the frequency of conformation interchange between crests and troughs are computed. All above properties are presented for different polymeric systems. [Preview Abstract] |
Thursday, March 5, 2015 1:27PM - 1:39PM |
T41.00012: Thermally Tunable Metallodielectric Photonic Crystals from Self-assembly of Brush Block Copolymers and Gold Nanoparticles Dongpo Song, Cheng Li, Nicholas Colella, Xuemin Lu, James Watkins Photonic crystals (PCs) based on the self-assembly of block copolymers (BCPs) are under intense investigations, providing new opportunities for simple fabrication of flexible photonic devices or coatings in an inexpensive and scalable way.$^{\mathrm{\thinspace }}$The precise control and selective incorporation of inorganic nanoparticles (NPs) into specific domains of the microphase separated BCPs can be used to tune the optical constant of the target domains and create hybrid materials with unique optical properties. In this work, we demonstrate a simple strategy for rapid fabrication of well-ordered metallodielectric 1-D PCs using PS-$b$-PEO brush BCPs as the templates and H-bonding as the driving force for selective incorporation of phenol-coated gold nanoparticles (NPs) into PEO domains. By varying gold NP loading or molecular weight of the brush BCP, periodic layered metallodielectric structures with the domain spacing controlled from 120 nm to 261 nm were readily created resulting in reflection of light widely tunable from the visible to near IR regions (458-1010 nm). The control over size as well as the distribution of the gold NPs in the well-ordered structure was realized through simple thermal treatment, showing significant effects on the optical properties. [Preview Abstract] |
Thursday, March 5, 2015 1:39PM - 1:51PM |
T41.00013: Design and organization of nanoparticles in thin film copolymer/homopolymer hosts Junnan Zhao, Peter Green The organization of polystyrene (PS) grafted gold (Au) nanoparticles (NPs) in supported thin film mixtures of polystyrene-$b$-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymers (BCP) with PS homopolymers was examined. The copolymer chains formed micelles, composed of inner cores of P2VP blocks and outer coronae of PS blocks, within the PS hosts. The spatial distribution of nanoparticles within this thin film BCP/homopolymer system is characterized by a morphological diagram of the curvature of the Au cores, 1/$R_{C}$, vs. the degree of polymerization N of the grafted PS-chains. The distribution is quantified by five basic regimes, largely dictated by competing entropic and enthalpic intermolecular interactions. The NP distributions range from predominantly residing at external interfaces (free surface and substrate) to primarily ``decorating'' the surface of micelles. The phase behavior of PS-Au/BCP/homopolymer (PS) systems is necessarily more intriguing than PS-Au/homopolymer (PS) systems, as the relative roles of specific intermolecular interactions on local NP distributions become more apparent. [Preview Abstract] |
Thursday, March 5, 2015 1:51PM - 2:03PM |
T41.00014: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 2:03PM - 2:15PM |
T41.00015: Directed Phase Separation of Brush-coated Nanoparticles in Miscible and Immiscible Polymeric Thin Films Ren Zhang, Bongjoon Lee, Jack Douglas, Sanat Kumar, Michael Bockstaller, Alamgir Karim Fascinating as the combined properties of polymer/inorganic nanoparticle composite system, it is challenging to manipulate the distribution and assembly structures of the nanofillers at nanoscale with high loading fraction. Inspired by polymer blend phase separation, we expect similar behavior for blend of brush-coated nanoparticles and a polymer matrix with unfavorable enthalpic interactions. We confirm this relationship in blend thin films of polystyrene (PS) grafted gold nanoparticles (AuPS) in immiscible poly (methyl methacrylate) (PMMA). We show that application of soft-shear dynamic thermal zone annealing (DZA-SS) generates tunable directional aligned anisotropic nanoparticle structures. Alternatively, the phase-separated nanoparticle domains can also be organized into periodic nanostructures with well-defined shape and order with a simple geometric patterned elastomer confinement. These simple yet powerful strategies to fabricate nanopatterned NP arrays can be exploited for many nanotechnology applications. [Preview Abstract] |
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