Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Z21: Polymer Composites: Nanocomposites |
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Sponsoring Units: DPOLY Chair: Laura Clarke, North Carolina State University Room: 406 |
Friday, March 7, 2014 11:15AM - 11:27AM |
Z21.00001: Molecular Simulation and Microstructure Characterization of Poly(p-phenylene/m-phenylene) Copolymers Robert Bubeck, Steven Keinath Molecular simulation and characterization of the molecular structure and microstructure of poly(p-phenylene/m-phenylene) copolymers were carried out. Tensile modulus, yield stress, and entanglement molecular weight were modeled as amorphous polymers as a function of m-phenylene content. Significant biphasic character, however, was observed for two copolymers in the melt (environs of 300$^{\circ}$C) using variable temperature synchrotron-based WAXS. Precise experimental determinations of entanglement molecular weights were frustrated by the occurrence of significant amounts of nematic mesophasic order in the rubbery and melt regimes of two commercial poly(p-phenylene/m-phenylene) examples. Nonetheless, entanglement molecular weights obtained by molecular modeling are useful for future experimental guidance because the level of order in the glassy phase near ambient temperature was found to be low (approx. 5{\%}) regardless of melt processing history. The biphasic nature of the melt may also be a contributor to more difficult melt processing. Based on both the modeling and WAXS measurements, it is believed that increasing m-phenylene content might improve toughness and processibility relative to the interrogated samples. [Preview Abstract] |
Friday, March 7, 2014 11:27AM - 11:39AM |
Z21.00002: Synergy, Effect and Mechanism on Different Scale of organoclay Filled an Elastomer Blends by Rheological Method Xia Dong, Xianggui Liu, Charles C. Han, Dujin Wang The influence of organoclay on the phase separation temperature and phase separation kinetics of solution polymerized styrene butadiene rubber (SSBR)/low vinyl content polyisoprene (LPI) blends was investigated by rheological methods. The WAXD and the dynamic rheological test showed that the two components had similar interaction with the organoclay and could partially penetrate into the silicate layers. The intercalated clay could restrict the movement of polymer chains and act as a compatibilizer to reduce the phase separation temperature. The intercalated clays localized at the interface could act as an interface agent to reduce the interfacial tension, and also could act as a physical barrier to restrict the coarsening of the domains. Those two effects could slow down the phase separation kinetics and reduce the phase domain size. This effect became more obvious with increasing organoclay concentration. In addition, the addition of 3wt{\%} clay could form a rigid three-dimensional clay network which could dominant the rheological properties of the blend samples and stabilize the phase morphology permanently. [Preview Abstract] |
Friday, March 7, 2014 11:39AM - 11:51AM |
Z21.00003: Polymer-polymer and hybrid clay-polymer complexes at liquid-liquid interfaces Yuhao Wang, Svetlana Sukhishvili We report on polymer-polymer and hybrid clay-polymer complex formation at oil-water interfaces. The complexes were composed of poly(methacrylic acid) (PMAA) and poly(N-isopropylacrylamide) (PNIPAM) or PNIPAM modified Laponite (L@PN). Interfacial surface tension, confocal laser scanning microscopy (CLSM) and cryogenic scanning electron microscopy (cryo-SEM) measurements were performed at various ratios of complex components and as a function of solution pH. The results reveal that interfacial PNIPAM/PMAA and L@PN/PMAA complexes are significantly more stable across the pH scale than their solution counterparts, probably because of the suppressed ionization of PMAA at the oil-water interface. In addition, we will discuss the effect of interfacial complex formation on PMAA chain dynamics, as measured by fluorescence-correlation spectroscopy (FCS), and demonstrate the use of these systems to control emulsion stability via changes in solution pH or temperature. [Preview Abstract] |
Friday, March 7, 2014 11:51AM - 12:03PM |
Z21.00004: Controlled assembly of nanorods in block copolymer thin films Huikuan Chao, Dongliang Wang, Russell Composto, Robert Riggleman Block copolymers can be used as a template to order nanoparticles to obtain functional polymer nanocomposites. While progress has been made in understanding the distribution of spherical particles in the block copolymer, significantly less work has focused on the distribution of nanorods in block copolymers. Nanocomposites containing anisotropic particles could have enhanced mechanic, electrical and optical properties and become candidates for numerous applications such as conductive membranes or coatings with controlled optical properties. Understanding the thermodynamic origins that regulate the distribution of nanorods in block copolymers is of central importance in obtaining desired structures, and molecular modeling could be a powerful tool to guide experiments. In the talk, I will first introduce our extension of polymer field theory that enables the study of the equilibrium properties of block copolymer thin films containing nanorods. Then I will present how the geometry of the nanorod, including its aspect ratio and size, affects the distribution of nanorods in thin films. Finally, we will examine the role of surface wetting on the distribution of nanorods. We find the rods segregate to defects in the block copolymer structure, which agrees well with ongoing experiment. [Preview Abstract] |
Friday, March 7, 2014 12:03PM - 12:15PM |
Z21.00005: Block copolymer templated growth of ZnO nanorod arrays with controlled size and spatial density Candice Pelligra, Chinedum Osuji The ability to control the diameter and spatial density of substrate-supported ZnO nanorods is critical for leveraging these nanomaterials in emerging applications. Specifically, in polymer-based photovoltaics (PV), there is a need to fabricate ZnO arrays with control over nanorod diameter and spacing to optimize device active area and to maximize exciton harvesting by matching the nanorod spacing to the exciton diffusion length in the polymer matrix. Self-assembly of block copolymers (BCPs) is well-suited to ordering nanoscopic domains over macroscopic areas with high levels of control in a low-cost, scalable manner. We present here a simple and robust method for templating the growth of vertically oriented ZnO nanorods with controlled diameter and spatial density based on the self-assembly of close-packed BCP micelles on pre-seeded substrates. Templating is accomplished using a wide range of BCP molecular weights and compositions to provide control of the ultimate nanowire diameter and areal density, respectively. Because the method relies on selective infiltration of nanorod precursor species through a hydrophobic micelle corona, it is readily extensible to a wide variety of block copolymers and nanomaterials. [Preview Abstract] |
Friday, March 7, 2014 12:15PM - 12:27PM |
Z21.00006: Hybrid Thin Films Based Upon Polyoxometalates-Polymer Assembly Na Qi, Benxin Jing, Yingxi Zhu Block copolymers (BCPs) and polyoxometalates (POMs) have been used individually as building blocks for design and synthesis of novel functional materials. POM nanoclusters, the assemblies of transition metal oxides with well-defined atomic coordination structure, have been recently explored as novel nanomaterials... for catalysis, semiconductors, and even anti-cancer treatment due to their unique chemical, optical and electrical characteristics. We have explored the blending of inorganic POM nanocluster with BCPs into hierarchaically structured inorganic-organic hybrid nanocomposites. Using polystyrene-b-poly(ethylene oxide) (PS-b-PEO) thin films as the template, we have observed that the spatial organization of BCP thin films is modified by molybdenum based POM nanocluster to form 2D in-plane hexagonal ordered or 3D ordered network of POM-BCP assemblies, depending on the concentration ratio of POM to PS-b-PEO. The dielectric properties of such hybrid thin films can be enhanced by embedded POMs but show a strong dependence on the supramolecular structures of POM-polymer complexes. The assembly of nanoclusters in BCP-templated thin films could pave a new path to design new hybrid nanocomposites with uniquely combined functionality and material properties. [Preview Abstract] |
Friday, March 7, 2014 12:27PM - 12:39PM |
Z21.00007: Two-dimensional networks of nanowires with large-scale continuity and connectivity patterned by the self-assembly of block copolymers Mark Stoykovich, Ian Campbell Self-assembled block copolymers in thin films have advantages for nanolithography including tunable and scalable feature sizes below 50 nm, and parallel patterning over large areas. Here we characterize the interconnectedness of two-dimensional networks self-assembled by a lamellar-forming diblock copolymer of polystyrene and poly(methyl methacrylate) in thin films. The topology of the network (its connectivity and large-scale continuity) was explored as a function of the copolymer composition and processing (i.e., solvent versus thermal annealing, film thickness, annealing temperature, annealing time). The block copolymer templates have then been used to fabricate metal and Si nanowires (less than 25 nm diameters) in the structure of the two-dimensional networks. The electrical and optical properties of the networks were measured over macroscopic areas, and were comparable to theoretical calculations based on the characteristic dimensions and network structure. Furthermore these two-dimensional nanowire networks have exciting mechanical properties; they can be stretched, compressed, twisted or folded with no significant changes in their optoelectronic characteristics, making such materials attractive for application in flexible or stretchable electronics. [Preview Abstract] |
Friday, March 7, 2014 12:39PM - 12:51PM |
Z21.00008: Preparation of Low Band Gap Fibrillar Structures by Solvent Induced Crystallization Hsin-Wei Wang, Emily Pentzer, Todd Emerick, Thomas Russell Solution-induced crystallization of the low band gap polymer poly[$N$-9''-heptadecanyl-2,7-carbazole-\textit{alt}-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) was shown to give fibril-like structures of 40-60 nm width and $\sim$ 0.5 $\mu$m length. These structures, formed by heating and cooling PCDTBT in a marginal solvent, were characterized by AFM, TEM, GI-WAXS, and steady state absorption and emission spectroscopy. The width of the PCDTBT structures suggests that the polymer chains are oriented perpendicular to the fiber axis, while the observed undulated structures, as revealed by AFM, suggest that the nanostructures may be composed of smaller crystalline units, suggesting a crystal face-specific assembly. Surprisingly, no spectroscopic signatures in either absorption or emission were observed upon crystallization of PCDTBT, in sharp contrast to the well-known conjugated polymer poly(3-hexyl thiophene) (P3HT). The solution-based crystallization of PCDTBT offers insight into the self-assembly of conjugated polymers and a better understanding of their role in photovoltaic devices [Preview Abstract] |
Friday, March 7, 2014 12:51PM - 1:03PM |
Z21.00009: Controlling the thermomechanical behavior of nanoparticle/polymer films Dan Zhao, Dirk Schneider, George Fytas, Sanat K. Kumar Using Brillouin light scattering, we show that the thermomechanical properties of polymer nanocomposite films consisting of silica nanoparticles (NPs) and poly (2-vinylpyridine) (P2VP) critically depend on the casting solvent and thermal annealing. The composite films are solvent cast in either methylethylketone (MEK) or pyridine. In the MEK as-cast films, no remarkable dependence of elastic modulus on particle loading has been found, which suggests poor adhesion between the bound polymer chains and those in the bulk. Further, when the particle loading exceeds 20 wt{\%}, we observe another independently propagating phonon due to local bridging of silica NPs by P2VP chains. In contrast, when pyridine is used, the sound velocity vs. silica contents can be described by effective medium predictions. This implies that, at a mesoscopic scale, silica NPs are homogeneously dispersed in the P2VP matrices, preserving their potential attractions with P2VP. However, after thermal annealing, the solvent effect disappears. Additionally, we study the effect of the presence of NPs on the glass transition temperature (T$_{\mathrm{g}})$ of the resulting nanocomposites and find only a slight increase (5 K) in T$_{\mathrm{g}}$ for composites with a loading of 45 wt{\%}. [Preview Abstract] |
Friday, March 7, 2014 1:03PM - 1:15PM |
Z21.00010: Synthesis of Biomimetic Branched Polymer Architectures Amanda Marciel, Danielle Mai, Charles Schroeder Development of sequence-defined or structurally-precise polymers as high-performance materials is a major challenge in materials science. In this work, we report a facile synthesis platform to produce monodisperse and stereochemically precise nucleotidomimetic polymers. Based on a top-down approach, we are able to precisely incorporate a wide-variety of functional group modifications in a simple two-step process. First, we utilize the natural ability of DNA polymerase to enzymatically incorporate chemically-modified monomers (e.g., C5-dibenzocyclooctyl dUTP) in a template-directed fashion. Second, we employ copper-free click chemistry to integrate the desired chemical functionality at precise locations along the polymer chain. In this way, we produced a variety of branched DNA homopolymer architectures including 3-arm star, symmetric H, and block-brush. Overall, this synthetic strategy allows for the systematic variation of oligomer length, stoichiometry, concentration, and environmental conditions to rapidly explore nucleotidomimetic polymer phase behavior for materials discovery. [Preview Abstract] |
Friday, March 7, 2014 1:15PM - 1:27PM |
Z21.00011: Nanoscale phase separation in ultra-tough hydrogels Ryan Nixon, Jan Bart ten Hove, Adrian Orozco, W. Gregory Sawyer, Thomas Angelini Soft, wettable, water permeable materials that resist protein adsorption are essential to countless biomaterials, adaptive optics and microfluidics technologies. Hydrogels would be ideal for these applications, but are notoriously brittle and weak. For example, hydrogel coatings of synovial joint prosthetics exhibit irrecoverable damage after a single cycle of wear. The development of elastomer-like hydrogels that are tough, soft, and mechanically resilient would improve their versatility and create opportunities for a wide range of new applications. Here we present studies of an ultra-tough hydrogel, synthesized by the co-polymerization of two monomer species that polymerize at different rates and have strongly differing degrees of solvation. The resulting blended hydrogel network forms with both covalent and labile adhesive bonds, greatly improving recoverable energy dissipation and reducing fatigue relative to networks made from either constituent alone. We have studied the structural origins of the strengthening behavior using small angle x-ray scattering (SAXS) and found that the constituent polymers phase separate into nanoscale domains, which may prevent crack nucleation and propagation. [Preview Abstract] |
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