Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session A38: Polymer Nanocomposites, Active Particles and ApplicationsFocus Industry
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Sponsoring Units: DPOLY FIAP GSOFT Chair: Michael Hore, Case Western Reserve University Room: 341 |
Monday, March 14, 2016 8:00AM - 8:12AM |
A38.00001: Plasmonic Gold Nanorod Dispersions with Electrical and Optical Tunability Christopher Grabowski, Clare Mahoney, Kyoungweon Park, Ali Jawaid, Timothy White, Richard Vaia The transmissive, absorptive, electrical, and thermal properties of plasmonic gold nanorods (NRs) have led to their employment in a broad range of applications. These electro-optical properties - governed by their size, shape, and composition - are widely and precisely tunable during synthesis. Gold NRs show promise for large scale optical elements as they have been demonstrated to align faster than liquid crystal films ($\mu $s) at low fields (1 V/$\mu $m). Successfully dispersing a high volume fraction of gold NRs requires a strategy to control particle-particle separation and thus avoid aggregation. Herein, we discuss the role of theta temperature and the ability to swell or collapse the chains of polymer-grafted gold NRs to alter the interaction potential between particles. UV-Vis spectroscopy, scattering, and electrical susceptibility characterization methods were employed to determine nanoparticle dispersion along with the degree of gold NR alignment. The development of new agile photonic materials, controllable with both light and electric fields, will help address emerging needs in laser hardening (agile filters) and variable transmission visors. [Preview Abstract] |
Monday, March 14, 2016 8:12AM - 8:24AM |
A38.00002: Molecular dynamics study of reversible thermal stiffening in viscoelastic polymer blends and nanocomposites Wei Peng, Raghavan Ranganathan, Fiona Kine, Rahmi Ozisik, Pawel Keblinski We use non-equilibrium molecular dynamics simulations to model stiffening mechanisms in viscoelastic polymer blends and nanocomposites with the overarching goal to understand the mechanisms for reversible thermal stiffening (stiffening while heating and softening up on cooling). The blend is comprised of two kinds of polymer chains with differing stiffness and glass transition temperatures (Tg) and the nanocomposite consists of nanoparticles grafted to the high Tg polymer phase in addition to the soft matrix phase. We employ both constant shear-rate and oscillatory shear deformations to characterize stiffening. Upon heating above the Tg of both polymeric phases, we show that significant stiffening arises due to the coupled relaxation and dynamics of both polymeric phases. The effects of shear rate, interaction strength between phases and the corresponding structural changes and dynamics leading to reversible stiffening are studied and are corroborated with experimental findings. [Preview Abstract] |
Monday, March 14, 2016 8:24AM - 8:36AM |
A38.00003: Role of bound polymer mobility on multiscale dynamics of PEO in attractive nanocomposites Erkan Senses, Antonio Faraone, Pinar Akcora We study intermediate and large scale chain dynamics in nanocomposites where particle-bound polymer (PMMA) and matrix (PEO) chains are chemically different, miscible, and have very large T$_{g}$ difference ($\Delta $T$_{g} \quad \approx $ 200 K). These nanocomposites with dynamically asymmetric `polymer blend interphases' were shown to exhibit an unusual reversible thermal-stiffening accompanied by vitreous-to-rubbery transition of PMMA.* Using quasi-elastic neutron scattering, this work examines the impact of mobility of the bound-polymer on segmental and collective dynamics of the matrix chains at sub-ns to 100 ns range. While bare silica particles appear to slow down the segmental relaxation, in the composites with PMMA coated particles the Rouse dynamics of PEO is identical to its bulk behavior, possibly due to the negligible enthalpic interaction inherent to this blend system. On larger scale, we observed $\approx $25{\%} increase in the apparent tube diameter of PEO when PMMA is glassy. Remarkably, the tube size recovers its bulk value as PMMA softens at elevated temperatures. The resulting disentanglement-entanglement transition of PEO under hard and soft confinement well relates to the macroscopic softening-stiffening transition of these composites as evidenced from the bulk rheology. (*ACS Appl. Mater. Interfaces$,~$2015,~7~(27), pp 14682--14689) [Preview Abstract] |
Monday, March 14, 2016 8:36AM - 9:12AM |
A38.00004: Hierarchical Nanocomposites for Device Applications Invited Speaker: James Watkins We have outlined templating strategies for electronic and optical device fabrication that include self-assembly of well-ordered polymer/nanoparticle hybrids and nanoimprint lithography using novel materials sets. Using additive-driven self-assembly, for example, we demonstrate the formation of periodic nanocomposites with tunable magnetic and optical characteristics containing up to 70 wt. {\%} of metal, metal oxide and/or semiconducting nanoparticles through phase specific interactions of the particles with either linear block copolymer or brush block copolymer (BBCP) templates. The BBCP templates provide direct access to large domain spacings for optical applications and spontaneous alignment within large volume elements. We have further developed highly filled nanoparticle/polymer hybrids for applications that require tailored dielectric constant or refractive index and a new imprinting process that allows direct printing of patterned 2-D and 3-D crystalline metal oxide films and composites with feature sizes of less than 100 nm. Applications in flexible electronics, light and energy management, and sensors and will be discussed. [Preview Abstract] |
Monday, March 14, 2016 9:12AM - 9:24AM |
A38.00005: Driving degradation within biodegradable polymers with embedded nanoparticles Russell Gorga, Gabriel Firestone, Daniela Fontecha, Jason Bochinski, Laura Clarke The ability to controllably trigger breaking of chemical bonds enables a substance that has robust material properties during use but can be re-worked or deteriorated upon command.~~Photothermal heating creates intense local heat at isolated nanoparticle locations within a sample and can result in very different material responses than those achievable with conventional (uniform) heating.~~In this process, irradiation with visible light resonant with the nanoparticle's surface plasmon resonance results in dramatic local heating of the particles and the surrounding material.~~This work studies intentional thermal degradation of poly ethyl cyanoacrylate-starch composites doped with metal nanoparticles, and explores differences in degradation speed, efficiency, and resultant mechanical properties when heated via the photothermal effect.~ [Preview Abstract] |
Monday, March 14, 2016 9:24AM - 9:36AM |
A38.00006: Waveguiding Actuators Based on Photothermally Responsive Hydrogels Ying Zhou, Adam Hauser, Nakul Bende, Mark Kuzyk, Ryan Hayward A simple means to achieve rapid and highly reversible photo-responsiveness in a hydrogel is to combine a thermally-responsive gel such as poly(N-isopropyl acrylamide) (PNIPAM), with the photothermal effect of gold nanoparticles. Relying on such composite gels, we fabricate micro-scale bilayer photoactuators by photolithographic patterning, and demonstrate their controlled bending/unbending behavior in response to visible light. In addition to actuation by flood exposure, 532 nm laser light can be waveguided through a plastic optical fiber to direct it into the photoactuator, providing the possibility for remotely controllable actuators that do not require line-of-sight access. The actuators show large magnitude responses within time-scales of \textasciitilde 1 s, consistent with the small dimensions of the actuators, but also exhibit smaller-scale responses over much longer times, suggesting the possibility of slow internal relaxations within the network. Based on our study on this bilayer system, we further explore fabrication methods for cylindrical actuators that are able to bend in arbitrary directions. [Preview Abstract] |
Monday, March 14, 2016 9:36AM - 9:48AM |
A38.00007: In-situ curing of liquid epoxy via gold-nanoparticle mediated photothermal heating Gabriel Firestone, Ju Dong, Jason Bochinski, Russell Gorga, Laura Clarke The ability to selectively alter material properties in-situ is important for many biological applications where an initially flexible part (needed for ease of placement) would ideally be rigidified once in position (for instance, within a broken bone as a tissue scaffold). Thermoset epoxies harden from viscous liquids into solid materials when heated. In this work, metal nanoparticle-epoxy-hardener composites are formed and utilized to enable in-situ crosslinking by drawing a pattern on a shallow bath of liquid epoxy with a laser. This approach capitalizes on the phothothermal effect of metal nanoparticles where irradiation with light resonant with the nanoparticle surface plasmon resonance leads to dramatic local heating. We discuss challenges to incorporating metal particles into epoxy-hardener, observation of changes in the heat profile within the epoxy due to the intensity and rastering speed of the laser, and show that the mechanical properties of internally cured epoxy are the same as those cured conventionally. The ability to selectively fabricate a part from a liquid (with no mold or waste) may be an important alternative manufacturing approach. [Preview Abstract] |
Monday, March 14, 2016 9:48AM - 10:00AM |
A38.00008: High Thermal Conductivity Aligned Polyethylene-Graphene Nanocomposites Jivtesh Garg, Mortaza Saeidijavash We investigate enhancement of thermal conductivity in polyethylene-graphene nanocomposites. The effect of alignment of both the polymer chains and the dispersed graphene flakes on thermal conductivity enhancement will be reported. In this work nanocomposites are prepared through microextrusion of polyethylene pellets and graphene nanopowder. Alignment is achieved through mechanical stretching of the nanocomposites. Thermal conductivity is measured using both Angstrom method and Laser flash. Variables involved in the study are the draw ratio and the weight percentage of graphene nanopowder. Results will shed light on the role of alignment of graphene flakes on enhancing thermal transport and provide new avenues to achieve ultra-high thermal conductivity in polymeric materials. [Preview Abstract] |
Monday, March 14, 2016 10:00AM - 10:12AM |
A38.00009: Mechanical Properties of Polymeric Nanocomposites with Liquid Inclusions Heyi Liang, Zhen Cao, Andrey Dobrynin We study mechanical properties of polymeric nanocomposites of liquid inclusions in network matrix using molecular dynamics simulations and analytical calculations. The shear modulus of nanocomposite is shown to be a non-monotonic function of the elastocapillary number $\gamma _{\mathrm{SL}}$/($G_{\mathrm{N}}R)$, where $\gamma_{\mathrm{SL}}$is the interfacial energy network/liquid interface, $G_{\mathrm{N}}$is the shear modulus of network and $R$is the initial size of liquid inclusion. First, in the range of elastocapillary numbers, $\gamma _{\mathrm{SL}}$/($G_{\mathrm{N}}R)$ \textless \textless 1, the composite shear modulus increases with increasing this parameter value. In this interval of elastocapillary numbers, a liquid inclusion softens the network such that the composite modulus $G_{\mathrm{comp}}$is smaller than $G_{N}.$This is in agreement with the classical Eshelby theory. However, for elastocapillary numbers $\gamma_{\mathrm{SL}}$/($G_{\mathrm{N}}R) \quad \approx $ 1, the liquid inclusions reinforces the network, $G_{\mathrm{comp}}$\textgreater $G_{N}$. In this range of parameters the surface energy of the deformed liquid inclusions strengthens the composite. When the elastocapillary number increases further, $\gamma _{\mathrm{SL}}$/($G_{\mathrm{N}}R)$ \textgreater \textgreater 1, the interfacial energy of network/liquid interface dominates the mechanical response of the composite resulting in composite weakening. Analysis of the elongation ratio of the liquid inclusion shows that it decreases with increasing elastocapillary number $\gamma _{\mathrm{SL}}$/($G_{\mathrm{N}}R)$. The classical Eshelby's theory of inclusions fails to explain this phenomenon. We develop a new linear elasticity model of this class of nanocomposite materials capable to explain this unusual mechanical response of nanocomposite materials. [Preview Abstract] |
Monday, March 14, 2016 10:12AM - 10:24AM |
A38.00010: Tailoring the Structure of Polymer Networks with Photo-Controlled Radical Polymerization Awaneesh Singh, Olga Kuksenok, Jeremiah A. Johnson, Anna C. Balazs Using dissipative particle dynamics (DPD) approach, we developed a novel computational model to study the photo-controlled radical polymerization (photo-CRP) within polymer networks with embedded iniferters.~The polymerization process can be turned ``on'' or ``off'' in response to light and the polymerization rate can be modulated by altering the light intensity. This ``photo-growth'' approach allows us to impart changes in the gel network pore size and composition to form photo-tunable smart materials. For example, our approach allows us to design gel composites that are comprised of two distinct layers made of two compatible components at low photo-iniferter concentrations or gel composites that are comprised of two incompatible components that are relatively well intermixed at high photo-iniferter concentration. [Preview Abstract] |
Monday, March 14, 2016 10:24AM - 10:36AM |
A38.00011: Use Electrospinning to Introduce Graphene into Poly(4-Vinylpridine) (P4VP) Polymer Fibers and Their Biocompatibility with Dental Pulp Stem Cells (DPSCs) Linxi Zhang, Chung-chueh Chang, Miriam Rafailovich Graphene-polymer composite materials have been popularized in tissue engineering due to the outstanding thermal, electrical and mechanical properties of graphene. Most of the current studies, however, focus on 2-D structured films which hardly represent the real conditions of scaffolds in vivo environment and dispersion of graphene in polymer matrix has always been challenging since the graphene tends to aggregate. In our study, we have successfully introduced graphene nanoplatelets (GNPs) into poly(4-vinphylpridine) (P4VP) matrix and fabricated nano- and micro-scale size fibers by using electrospinning technique. SEM and TEM reveal uniform defect-free fiber structures and good dispersion of graphene; DSC and AFM indicate the enhancement of physical properties. The biocompatibility of the electrospun 3-D scaffolds with dental pulp stem cells (DPSCs) has been examined. Our results show that the cells can accelerate proliferation to respond to the existence of GNPs. SEM with EDAX reveals a deposition of mineralized calcium matrix on the fibers after 35-day incubation, which has possibly been caused by cell differentiation induced by fibrous scaffolds. [Preview Abstract] |
Monday, March 14, 2016 10:36AM - 10:48AM |
A38.00012: Studies of a new class of high electro-thermal performing Polyimide embedded with 3D scaffold in the harsh environment of outer space Manuela Loeblein, Asaf Bolker, Siu Hon Tsang, Nurit Atar, Cecile Uzan-Saguy, Ronen Verker, Irina Gouzman, Eitan Grossman, Edwin Hang Tong Teo The polymer class of Polyimides (PIs) has been wide-spread in the use of outer space coatings due to their chemical stability and flexibility. Nevertheless, their poor thermal conductivity and completely electrically insulating characteristics have caused severe limitations, such as thermal management challenges and spacecraft electrostatic charging, which forces the use of additional materials such as brittle ITO in order to completely resist the harsh environment of space. For this reason, we developed a new composite material via infiltration of PI with a 3D scaffold which improves PIs performance and resilience and enables the use of only a single flexible material to protect spacecraft. Here we present a study of this new material based on outer-space environment simulated on ground. It includes an exhaustive range of tests simulating space environments in accordance with European Cooperation for Space Standard (ECSS), which includes atomic oxygen (AO) etching, Gamma-ray exposure and outgassing properties over extended periods of time and under strenuous mechanical bending and thermal annealing cycles. Measurement methods for the harsh environment of space and the obtained results will be presented. [Preview Abstract] |
Monday, March 14, 2016 10:48AM - 11:00AM |
A38.00013: Biocompatible Silk-Poly(Pyrrole) Composite Trilayer Actuators Carly Fengel, Nathan Bradshaw, Sean Severt, Amanda Murphy, Janelle Leger Biocompatible materials capable of controlled actuation are in high demand for use in biomedical applications such as dynamic tissue scaffolding, valves, and steerable surgical tools. Conducting polymers (CPs) have some desirable traits for use as an actuator, such as the ability to operate in biologically relevant fluids and responsiveness to low voltages. However CPs alone are limited due to their brittle nature and poor solubility. Recently we have shown that a composite material of silk and the CP poly(pyrrole) (PPy) shows promising characteristics as an actuator; it is mechanically robust as well as fully biocompatible. Initial proof-of-concept experiments demonstrated that these composites bend under an applied voltage (or current) using a simple bilayer device. Here we present trilayer devices composed of two silk-PPy composite layers separated by an insulating silk layer. This configuration results in more charge is passed in comparison to the analogous bilayer system, as well as a more sustainable current response through cycling, resulting in a larger angle of deflection per volt applied. In addition, the motion of the trilayer devices is more symmetric than that of the bilayer analogs, resulting in a more repeatable movement. We will discuss the fabrication and characterization of these devices, as well as their performance and future applications of this technology. [Preview Abstract] |
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