Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session X45: Focus Session: Nanocomposite Physics I-Dispersions and Physical Properties |
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Sponsoring Units: DPOLY Chair: Frederick Beyer, Army Research Laboratory Room: A310 |
Thursday, March 24, 2011 2:30PM - 2:42PM |
X45.00001: Dynamical Aspects of Percolation Networks of Carbon Nanotubes in Polymer Composites Gyemin Kwon, Bong June Sung Carbon nanotubes (CNTs) form a percolating network easily in polymer nanocomposites due to their high aspect ratios, thus improving both electrical and mechanical properties of composites. However, poor dispersion of CNTs has been a stumbling block to their application in industry. Therefore, extensive studies on the structure and thermodynamics of CNTs have been carried out to enhance the dispersion of CNTs in composites and find optimal conditions for better electrical and mechanical properties. But little attention has been paid to the dynamic aspects of percolation networks of CNTs, which should be also a critical factor to determine physical properties of composites. In this study, we investigate the 1st order survival rate, the assortative coefficients, and the bond connectivity time correlation function of percolation networks by using molecular dynamics simulations. We find that the CNT network dynamics becomes significantly slow and the CNT networks become dynamically stable as the concentration of CNTs increases beyond the percolation threshold concentration. We also investigate the effect of intermolecular interaction between CNTs and polymers on the dynamic behaviors of CNT networks. [Preview Abstract] |
Thursday, March 24, 2011 2:42PM - 2:54PM |
X45.00002: Langevin Approach to Optimizing Thermal Conductivity in Composite Materials Abdellah Ait Moussa, K.G.S.H. Gunawardana, Kieran Mullen The quest for high thermal conductivity materials has lead to nano-composites incorporating materials with excellent thermal conductivity in a matrix of poorer thermal conductivity. To minimize the interface thermal resistance the stiff, incorporated materials can be chemically functionalized with various side chains. We report here an efficient theoretical method to evaluate different choices for functionalization. We use this method to examine how effective different alkane chains improve the heat flux through a graphene nano-sheet. [Preview Abstract] |
Thursday, March 24, 2011 2:54PM - 3:06PM |
X45.00003: Use of embedded metal nanoparticles as photothermal heaters in polymer nanocomposites Somsubhra Maity, Jason Bochinski, Laura Clarke ~Embedded metallic nanoparticles within polymer nanofibers can internally heat and thus thermally-modify (soften, melt, or bond) polymer composites when irradiated with visible light via excitation and non-radiative relaxation of the nanoparticle surface plasmon resonance. ~Because the heating originates at the nanoparticle surface and propagates outward, a strong spatial temperature gradient exists. ~We discuss a non-contact, temperature-sensitive fluorescence technique to determine local temperature within the composite, which utilizes changes in the emission spectrum of perylene......,\footnote{Bur, A. J.; Vangel, M. G.; Roth, S. \textit{Applied Spectroscopy }\textbf{2002,} 56, (2), 174-181.} in addition to determining temperature from changes in polymer morphology. The efficacy of plasmonic heating in different morphologies (nanofibers/films) as well as its effect on material mechanical properties when heated between T$_{g}$ and T$_{m}$ is discussed. The spatial specificity of the photothermal heating as determined by the nanoparticle location represents a unique nanoprocessing tool. [Preview Abstract] |
Thursday, March 24, 2011 3:06PM - 3:18PM |
X45.00004: Resistive switching in bulk polymer nanocomposites containing silver nanowires Karen Winey, Sadie White, Patrick Vora, Jay Kikkawa, Rose Mutiso Traditionally, bulk nanocomposites of electrically conducting particles and insulating polymers have been categorized as either insulating or conducting when the nanoparticle concentration is below or above the percolation threshold, respectively. We present the first examples of reversible resistive switching in bulk, glassy polymer nanocomposites. At compositions close to the electrical percolation threshold, silver nanowire-polystyrene nanocomposites demonstrate reversible resistive switching upon increase voltage at room temperature. Nanocomposites with compositions outside of this range exhibit either irreversible switching, or no switching at all. We propose that resistive switching in these materials is the result of the field-induced formation of silver filaments that bridge adjacent nanowire clusters, extending the percolation network and decreasing the sample's bulk resistivity. We also describe the temperature-dependent characterization of resistive switching in these nanocomposites between 10 and 300K. These findings break from the usual dichotomy of insulating or conducting properties in polymer nanocomposites and could inspire new devices that capitalize on this responsive behavior in these versatile materials. [Preview Abstract] |
Thursday, March 24, 2011 3:18PM - 3:30PM |
X45.00005: The Development of Structure in Nanoscale Colloidal Silica -- Polymer Nanocomposites Jeff Meth, J. David Londono, Changzai Chi, Barbara Wood, Patricia Cotts, Sangah Gam, Karen Winey, Russell Composto Controlling the state of dispersion or agglomeration in polymeric nanocomposites has a profound impact on their properties. Many nanocomposites are manufactured by a solution process. In such processes, colloidal silica dispersed in a formulation possesses a certain interparticle structure, and this structure changes as the coating formulation dries. In this work, we have measured the structure of colloidal silica -- PMMA formulations as a function of solvent content using small angle X-ray scattering (SAXS). We found that the formulations dried in two stages: concentration and neutralization. In the concentrating stage, the charged colloid structure prevails, and the formulation simply concentrated down. In the neutralization stage, the colloid gradually lost its charge. Controlling the matrix viscosity enables one to control the final state of dispersion. These findings explain how and why it is possible to create good nanodispersions in some material systems. These general findings are applicable to a wide range of material systems. [Preview Abstract] |
Thursday, March 24, 2011 3:30PM - 3:42PM |
X45.00006: Dispersion Behavior of Au Nanorods in Polymer Thin Films Mediated by Brush-Matrix Interactions Michael J.A. Hore, Russell J. Composto Moderate volume fractions ($\sim $5 v{\%}) of poly(ethylene glycol) or polystyrene-functionalized Au nanorods are incorporated into poly(ethylene oxide), poly(methyl methacrylate), or polystyrene thin films (thickness $\sim $30 nm). Their dispersion is characterized via TEM, AFM, and x-ray reflectivity. When the chemical species of the brush is identical to that of the matrix, nanorod dispersion is dominated primarily by entropy and controlled by the ratio of the chain lengths of the brush and matrix. When there is a favorable enthalpic interaction between the brush and matrix, the dispersion is independent of the molecular weights of the brush and matrix. These experimental data are compared to Monte Carlo simulations. [Preview Abstract] |
Thursday, March 24, 2011 3:42PM - 3:54PM |
X45.00007: Particle networks through aggregation in polymer nanocomposites Meisha Shofner, Jasmeet Kaur, Ji Hoon Lee Structure-property research in polymer nanocomposites has often focused on producing systems that are homogeneously dispersed in order to capitalize on the large amount of specific surface area available from nanoparticles. However, inhomogeneous dispersion is often obtained and in some cases has been deliberately sought to enhance functional properties through the formation of particle networks. In this research, we are seeking to understand how particle aggregation impacts network formation in polymer nanocomposites as a function of native particle shape. Specifically, we are characterizing nanocomposites comprised of calcium phosphate particles with different shapes and a polyhydroxybutyrate matrix. Experimental results concerning the effect of particle aggregation and shape on polymer crystalline structure, thermal transitions and mechanical properties are presented to correlate particle aggregation to network formation and understand structure-property relationships in these materials. [Preview Abstract] |
Thursday, March 24, 2011 3:54PM - 4:06PM |
X45.00008: A silica nanoparticle based ionic material Nikhil Fernandes, Zubair Azad, Emmanuel Giannelis We report an ionic fluid consisting of silica nanoparticles as the anion, and amine-terminated polyethylene glycol as the cation. Unlike previous work that has required chemical functionalization of the silica surface, the charge on the nanoparticle anion is carried by the intrinsic surface hydroxyls, simplifying the synthesis, and thus making this a simple test system to probe the physics of these nanoscale ionic materials. Charge and steric factors result in excellent dispersion of the nanoparticles in the polymer matrix. The resulting material is a soft glass that has thermal and rheological properties that depend on the silica:polymer ratio. In particular, at a critical silica:polymer ratio, the ionic material shows a significant depression of the normalized heat of melting and the melting temperature compared to samples with higher or lower silica content (showing eutectic-like behaviour), and to controls without the ionic interaction between the polymer and the particle. [Preview Abstract] |
Thursday, March 24, 2011 4:06PM - 4:18PM |
X45.00009: Structure-Properties Relationship in Segmented Polyurethane/Silica Nanoparticle Composites Matthew Hood, James Sands, John La Scala, Frederick Beyer, Christopher Li Segmented polyurethanes (SPUs) phase separate into hard and soft domains due to differences in segment composition, resulting in extraordinary mechanical properties. We have synthesized a set of SPU/nanoparticle composites possessing 25, 35 or 45wt.{\%} hard segment content and loaded with less than 5wt.{\%} silica nanoparticles (SiNPs). SiNPs were added either during SPU synthesis or blended after. Drastic effects on morphology and mechanical properties were observed. Blended composites, due to their destabilizing of the hard domain, showed decreased mechanical robustness. When particles are added, at very low SiNP concentrations, during SPU synthesis the SiNPs are covalently attached to the SPU matrix and hard domains are intact which enhanced elongation to break and tensile strength considerably. With increasing SiNP concentration this effect was reversed and hard domain crystallization was hindered. Thermal, mechanical and diffraction experiments were used to correlate the relationship between interfacial chemistry of the SiNP and SPU matrix and the mechanical properties of the composites. [Preview Abstract] |
Thursday, March 24, 2011 4:18PM - 4:30PM |
X45.00010: Polyurethane Nanocomposites Reinforced with Core-shell Magnetic Particles for Microwave Absorption Applications Zhanhu Guo, Jiahua Zhu, Rahul Patil, Neel Haldolaarachchige, David Young, Suying Wei Iron-silica core-shell particles with controlled shell thickness are fabricated using a sol-gel method. Polyurethane nanocomposites are fabricated with a surface initialized polymerization (SIP) method. The thermal stability of iron-silica NPs and its corresponding PNCs is significantly enhanced due to the barrier effect of silica shell. The anti-corrosive property of the core-shell particle is dramatically improved which is able to keep stable in 1M acid solutions. Salt fog exposure tests on PNCs reveal a better anti-corrosive performance with the incorporation of core-shell particles. By embedding different NPs, unique physical properties such as enlarged coercivity and dielectric constant (real permittivity) are observed. After coating a silica layer on iron NPs, the PNCs show lower real permittivity as compared to the PNCs filled with pure NPs. However, it is interesting to observe that only slight difference in real permeability is observed in both samples at the same loading. The permittivity and permeability of the PNCs are investigated with frequency ranging from 2-18 GHz. Results indicate that the PNCs reinforced with core-shell NPs exhibit a reflection loss in a wider frequency ranges. The maximum reflection loss is around -20 dB. [Preview Abstract] |
Thursday, March 24, 2011 4:30PM - 4:42PM |
X45.00011: Studies of Microwave Absorption Properties of Carbon Nanotubes-Epoxy Composites Z. Ye, Z. Li, J.A. Roberts, G.L. Zhao Less weight, excellent mechanical properties, and high efficiency in absorbing electromagnetic (EM) wave make carbon nanotubes (CNTs) composites attractive for microwave technology applications. Six groups of multi-walled carbon nanotube (MWCNT)-epoxy composite samples with various outside diameter (OD) distributions were fabricated. The weight percentages of MWCNTs in the polymer composites were controlled in the range from 1 to 10{\%}. A microwave resonant cavity technique was utilized to measure the microwave absorption properties of all the sixty samples near a central frequency of 9.968 GHz. The results show that the maxima of EM wave absorptions for the six groups of samples were all around 7{\%} MWCNTs weight percentage. In general, the MWCNTs with smaller diameters have higher microwave absorption at 9.968 GHz. However, the sample group M5 (OD$<$8nm) shows unusual results, a lower microwave absorption than other samples. SEM was used to study the morphologies of the MWCNT samples. Based on the SEM analysis and microwave absorption measurements, it was found that the efficiency of the microwave absorption of MWCNT-Epoxy composites is also affected by the morphologies/structures of MWCNTs in individual bundles. *The work is funded in part by AFOSR, NSF, and Louisiana Board of Regents. [Preview Abstract] |
Thursday, March 24, 2011 4:42PM - 5:18PM |
X45.00012: Ecobionanocomposites: a new class of green materials Invited Speaker: This abstract not available. [Preview Abstract] |
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