Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session P19: The Physics of Polymer Nanocomposites: Properties |
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Sponsoring Units: DPOLY Chair: Jan Obrzut, National Institute of Standards and Technology Room: 320 |
Wednesday, March 18, 2009 8:00AM - 8:12AM |
P19.00001: Tuning optical properties of gold nanorods in polymer films through thermal reshaping Russell Composto, Eric Mills, Yu Liu The thermal reshaping of gold nanorods (NRs) in a poly(methyl methacrylate) (PMMA) nanocomposite film is investigated by UV-vis and TEM. To ensure dispersion, the NRs are modified with PEG brushes, and then dispersed in PMMA. Thermal annealing of the PMMA:NR film results in a blue shift of the longitudinal plasmon resonance, caused by a decrease in the length of the NR. The rate of the blue shift increases as temperature increases from 100 $^{\circ}$C to 200 $^{\circ}$C, and the longitudinal absorption peak approaches a constant value that scales linearly with temperature. We demonstrate a potential application by fabricating a device with a gradient in optical properties. [Preview Abstract] |
Wednesday, March 18, 2009 8:12AM - 8:24AM |
P19.00002: Quenching Photoluminescence in Single-Walled Carbon Nanotube/Copolymer Composite Materials Andrew Schoch, L. Catherine Brinson, Kenneth R. Shull Single-walled carbon nanotubes (SWNTs) stabilized by A-B diblock and A-B-A triblock copolymers are excellent model systems for studying the relationship between nanotube dispersion and mechanical response. The SWNTs cannot be dispersed in the alcoholic solvent used here without the addition of copolymer. However, the B blocks are in good solvent conditions for all temperatures and the A blocks solvent quality decreases with decreasing temperature. This solvent quality difference drives the formation of micelles with A block cores at low temperatures. As verified by AFM, the micelles form heterogeneous micelles in solutions by incorporating the SWNTs. The dispersion has also been verified with near-IR photoluminescence spectroscopy (NIR-PLS) and the mechanical properties of these materials have been examined with rheological methods. The elastic contribution to the shear modulus increases while at high temperatures which we attribute to an increase in the number of NT-NT contacts. We have attempted to verify this observation by simulating the high temperature environment in the NIR-PLS measurements and looking for quenching. [Preview Abstract] |
Wednesday, March 18, 2009 8:24AM - 8:36AM |
P19.00003: Temperature measurements of inverse micelles coated in gold nanoparticles using fluorescence Chad Daley, James A. Forrest, Ryan Speller, Toews William, Patrick McVeigh, Todd Emrick When nanoparticles are subject to laser radiation they have the ability to efficiently absorb energy from the beam and transform this energy into heat. Photothermal therapy uses this phenomenon to irreparably damage tissue surrounding nanoparticle conjugates. Despite the promise of this technique, there is no concensus on the damage mechanism or even the local heating. Here we present an experiment designed to measure local temperatures achieved in such processes. Ligand covered Gold nanoparticles are used to stabalize inverse micelles containing fluorescence dye in the water component. The fluorescence intensity being temperature dependent provides us with a means of measuring the temperature of the micelles as a function of time immediately following a laser pulse. [Preview Abstract] |
Wednesday, March 18, 2009 8:36AM - 8:48AM |
P19.00004: Magnetic and Optical anisotropy thiol-capped Au NPs embedded into a polymer Jose de la Venta, Miguel Angel Garcia, Virginia Bouzas, Andrea Pucci, Giacomo Ruggeri The anisotropy at the nanoscale is achieved when the shape of the objects is not spherical such as in the case of nanorods, nanotubes or nanowires. However, when they are embedded in a macroscopic matrix, the random distribution destroys the anisotropy. In this work we study the possibility of induce optical and magnetic anisotropy in a system consisting of spherical thiol capped Au NPs embedded in a polymeric matrix. The ferromagnetic-like behavior arises from the bond between the Au-S atoms and the optical response is also highly dependent on these bonds. So, modifications in the environment and in these bonds could alter the behavior of the whole system. When the NPs are embedded in a polymeric matrix, which is stretched even 40 times in one direction, SQUID and UV/Vis measurements show that arise a macroscopic anisotropy in spite of the spherical shape of the NPs. EXAFS measurements confirm that there are modifications in the Au-S bonds along the stretched direction that are responsible of the induced macroscopic anisotropy. [Preview Abstract] |
Wednesday, March 18, 2009 8:48AM - 9:00AM |
P19.00005: Stability of the double gyroid phase to nanoparticle polydispersity in polymer tethered nanosphere systems Carolyn Phillips, Christopher Iacovella, Sharon Glotzer Recent simulations have shown that aggregating nanospheres functionalized with polymer ``tethers'' can self-assemble to form the double gyroid phase also seen in block copolymer and surfactant systems. Within the gyroid domain, the nanoparticles pack in icosahedral motifs, stabilizing the gyroid phase in a small region of the phase diagram[1]. We study the impact of nanoparticle polydispersity on the properties of the double gyroid phase [2]. Here we show that a low amount of polydispersity lowers the energy of the phase. A large amount of polydispersity raises the potential energy of the system, disrupts the icosahedral packing, and eventually, destabilizes the gyroid. A study of binary gyroids indicates that the inclusion of a small population of either smaller or larger nanospheres encourages low-energy icosahedral clusters. Using a new measure for determining the volume of a component in a microphase-separated system based on the Voronoi-tessellation, we show that polydispersity compacts the gyroid domain and lowers the average coordination of the nanospheres. [1] Iacovella, et al., PRE, 2007 [2] Phillips, et al., ``Stability of the double gyroid phase to nanoparticle polydispersity in polymer tethered nanosphere systems, preprint. [Preview Abstract] |
Wednesday, March 18, 2009 9:00AM - 9:12AM |
P19.00006: Experimental and computational investigation of percolation in complex polymer nanocomposites Derrick Stevens, Lori Downen, Russell Gorga, Laura Clarke The continuing development of polymer nanocomposites has led to increasingly complex morphology, such as the mats of composite nanofibers formed from electrospinning. The formation of particle networks within the composite volume that leads to enhanced properties, such as electrical conductivity, may be influenced by this complex sample geometry. In this work, experimental and computational efforts are utilized to understand and predict the percolation threshold (critical volume fraction) for two cases: single ultra-high aspect ratio fibers (where fiber diameter can be similar to the particle dimensions) and these same fibers arranged in a random mat with up to 80{\%} porosity. 2D and 3D Monte Carlo simulations, modeled on the actual parameters of our experimental system [1], are utilized and the results are compared with our experimental findings. In particular, confinement to fibers increases the percolation threshold; however the multi-fiber pathways available in mats partially reduce this constraint [2]. [1] S.S. Ojha, D.R. Stevens, K. Stano, T. Hoffman, L.I. Clarke, R.E. Gorga, \textit{Macromolecules} \textbf{41}, 2509 (2008). [2] D.R. Stevens, L.N. Downen, L.I. Clarke, \textit{Phys. Rev. B} \textbf{in press }(2008). [Preview Abstract] |
Wednesday, March 18, 2009 9:12AM - 9:24AM |
P19.00007: Influence on Thermal Diffusivity through a Transformation of Nanotube-like Clay Platelets in Polymer Blends Seongchan Pack, Takashi Kashiwagi, Tadanori Koga, Jonathan Sokolov, Miriam Rafailovich We have previously demonstrated that large aspect ratio nanoparticles such as clays or nanotubes can form in-situ grafts which become universal compatiblizing agents for polymer blends. Here we show how the same mechanism could be applied to producing flame retardant materials in the polymer matrix. In particular, the large aspect nanoclays prevent thermally induced phase segregation and disperse the flame retardants, which greatly decrease flammability and increase efficiency of the flame retardants during combustion due to a formation of ribbons-like structures. These structures could produce a lager thermal differential gradient between the two polymer phases, which could change a heat specific of the system during combustion. Therefore, a small addition of the nanoclays affects the huge reduction on heat release rate and the mass loss rates. Furthermore, using a small angle X-ray scattering (SAXS), a transmission electron microscopy (TEM), and a scanning electron microscopy (SEM) shows that the clay platelets could be transformed into tubular-like rods during combustion, which would increase of the thermal diffusivity in the polymer blend. [Preview Abstract] |
Wednesday, March 18, 2009 9:24AM - 9:36AM |
P19.00008: Electrical Conductivity in Polymer Composites Containing Metal Nanowires: Simulation and Experiment Sadie White, Tarun Vemulkar, John Fischer, Karen Winey The study of rod percolation behavior has resurfaced in recent years, because it explains electrical conductivity in polymer nanocomposites containing carbon nanotubes and metal nanowires. Common processing techniques result in fillers with L/D $<$ 50, so traditional models, which are only strictly correct in the limit of L/D $\sim \quad \infty $, are ineffective at predicting percolation in these systems. We present a simulation that constructs percolated networks of finite-aspect ratio rods and calculates their electrical conductivity. We will compare our simulation results with polymer composites containing silver nanowires with aspect ratios of $\sim $10 and $\sim $30. Finally, we will present the temperature-dependent electrical conductivity of these composites and interpret the results using the thermal expansion coefficients of polystyrene and silver. These materials act as ``thermal switches,'' wherein electrical conductivity of certain composites can be manipulated by several orders of magnitude over the temperature range from 80K-425 K. [Preview Abstract] |
Wednesday, March 18, 2009 9:36AM - 9:48AM |
P19.00009: Polymer Nanocomposites Made with Unmodified Graphite or Carbon Nanotubes: Role of Dispersion in Optimizing Mechanical and Thermal Properties and Electrical Conductivity Junichi Masuda, Katsuyuki Wakabayashi, Philip Brunner, Cynthia Pierre, John Torkelson Polymer nanocomposites made with carbon-based nanofiller have the potential to achieve unprecedented, multifunctional property enhancements in comparison with other nanocomposite systems. Here, we describe research in which we prepare nanocomposites with polymers that are not amenable to solution-based processing, such as polypropylene and poly(ethylene terephthalate). Solid-state shear pulverization is used singly or in conjunction with melt processing to obtain well-dispersed polymer/graphite and polymer/carbon nanotube nanocomposites. We report record improvements in properties of unoriented films of polypropylene nanocomposites, including Young's modulus, crystallization rate, and thermal degradation temperature. We also characterize electrical conductivity of such nanocomposites and note that the dispersion characteristics necessary to achieve maximum mechanical and thermal properties differ from those needed to maximize electrical conductivity. The potential of and challenges with using unmodified graphite as a filler in polymer nanocomposites will be discussed. [Preview Abstract] |
Wednesday, March 18, 2009 9:48AM - 10:00AM |
P19.00010: Conductive Paper by LBL Assembly of PSS and ITO onto Wood Fibers and its Electrical Properties through Impedance Spectroscopy and I-AFM Chunqing Peng, Yonathan Thio, Rosario Gerhardt Conductive paper has been fabricated by layer-by-layer (LBL) assembly of polyelectrolytes and indium tin oxide (ITO) nanoparticles onto wood fibers, followed by traditional paper making method. The wood fibers were first coated with polyethyleneimine (PEI) and then LBL assembled with poly(sodium 4-styrenesulfonate) (PSS) and ITO for several bilayers. The AC electrical properties, measured for frequencies ranging from 0.01 Hz to 1 MHz, will be reported for the in-plane (IP) and through-the-thickness (TT) directions. With 10 bilayers of PSS/ITO assembly on wood fibers, the conductivity of as-prepared paper was improved by more than six orders of magnitude and reach to 5.2$\times $10$^{-6}$ S cm$^{-1}$ in IP direction and 1.9$\times $10$^{-8}$ S cm$^{-1}$ in TT direction. The percolation phenomenon of ITO nanoparticles through the handsheet in both directions was observed through current atomic force microscopy (I-AFM). By applying a bias voltage, either on one end of the paper stripes or on one side of the paper handsheet, the current can be detected on the other end of the paper stripes or on the other side of the paper handsheet. PEI can be used to modify the ITO suspension and significantly improve the LBL procedure. The mechanism of PEI modifying ITO colloidal suspension will be discussed. [Preview Abstract] |
Wednesday, March 18, 2009 10:00AM - 10:12AM |
P19.00011: Placement Control of Nanomaterial Arrays on Surface-Reconstructed Block Copolymer Thin Films Jeong Gon Son, Wan Ki Bae, Huiman Kang, Paul F. Nealey, Kookheon Char Nanomaterials such as nanoparticles, quantum dots and nanorods/wires have recently attracted considerable attention not only because of their unique electronic, optical, and magnetic properties depending on their size and chemical structure but also due to their possible applications to optoelectronic devices, next-generation memory devices, and biological sensors. In order to take full advantage of these useful properties for highly integrated fabrication, precise control of such nanomaterials on patterned substrates is inevitably required. In this presentation, we demonstrate a straightforward and reproducible method for the placement of nanomaterials such as nanoparticles and nanorods on patterned PS-$b$-PMMA block copolymer (BCP) thin films. This concept is based on the properties of surface-reconstructed BCP thin films, which could induce topographical nanopatterns induced by selective solvent vapor treatment without any etching process. The deposition conditions for high density nanomaterial patterns in the grooves of BCP nanopatterns were optimized. By treating the surface under electron beam irradiation, the pattern inversion of nanomaterial-containing BCP nanopatterns was also observed, which can be further processed to realize the dual nanomaterial patterning. [Preview Abstract] |
Wednesday, March 18, 2009 10:12AM - 10:24AM |
P19.00012: Confinement and Ordering of Au Nanorods in Polymer Films Michael J. A. Hore, Eric Mills, Yu Liu, Russell J. Composto Ordered arrays of gold nanorods (Au NRs) possess interesting optical properties that might be utilized in future devices. Au NRs functionalized with a poly(ethylene glycol)-thiol brush are incorporated into homopolymer or block copolymer (BCP) films. NR distribution and orientational correlations are studied as a function of nanorod concentration and spacial confinement via Rutherford backscattering spectrometry (RBS) and transmission electron microscopy, respectively. In particular, differences in the degree of nanorod ordering are presented for PMMA homopolymer films ($d \quad \sim $ 45 nm) versus PS-$b$-PMMA BCP films (L/2 $\sim $ 40 nm), where higher ordering is seen in the case of BCP films. At moderate volume fractions of NRs, $\phi $ = 1{\%} to 10{\%}, the degree of ordering is moderate, and increases with increasing $\phi $ . However, coexistence between regions of higher ordering and isotropic orientations is observed. In addition to the planar confinement considered above, orientation of Au NRs confined to cylindrical P2VP domains is studied in PS-$b$-P2VP BCP films. [Preview Abstract] |
Wednesday, March 18, 2009 10:24AM - 10:36AM |
P19.00013: Carbon nanotubes nucleate the growth of graphitic layers during carbonization.of electrospun poly(acrylonitrile) nanofibers. Sabina Prilutsky, Yachin Cohen, Eyal Zussman Hybrid nanofibers with varying concentration of multiwalled carbon nanotubes (MWCNTs) in polyacrylonitrile (PAN) were fabricated using the electrospinning technique and subsequently carbonized. The morphology of the fabricated carbon nanofibers (CNFs) at different stages of the carbonization process was characterized by high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. In-situ morphological changes during heating were followed by HRTEM using a heated stage. The polycrystalline nature of the CNFs was shown, with increasing content of ordered crystalline regions having enhanced orientation with increasing content of MWCNTs. The results indicate that MWCNTs embedded within the PAN nanofibers nucleate the growth of graphitic layers during PAN carbonization. [Preview Abstract] |
Wednesday, March 18, 2009 10:36AM - 10:48AM |
P19.00014: Crystallization and melting behavior of isotactic polypropylene and carbon nanotube nanocomposites Georgi Georgiev, Yaniel Cabrera, Lauren Wielgus, Zarnab Iftikhar, Michael Mattera, Peter Gati, Austin Potter, Peggy Cebe Polymer nanocomposites (PNCs) are the most recent development in the field of polymer science and technology. Geared toward creating novel polymer based materials, PNCs are the largest commercial application for nanotubes. Spherulitic polymer crystal growth was changed by inducing new fibrillar crystals on the surface of carbon nanotubes. Upon isothermal melt crystallization at 135$^{o}$C, CNTs lead to monoclinic crystal growth perpendicularly to the long axis of the nanotubes, explained by the multiple nucleation centers formed at the interface of the carbon nanotube and the polymer chains. Using Microscopic Transmission Ellipsometry (MTE), the sign of the alpha crystallographic phase was determined as positive. Using Differential Scanning Calorimetry (DSC), a decrease in the Avrami exponent was measured with increase of concentration of nanotubes. [Preview Abstract] |
Wednesday, March 18, 2009 10:48AM - 11:00AM |
P19.00015: Crystallization kinetics in poly(ethylene oxide) / layered silicates nanocomposites Eleni Pavlopoulou, Sapfo Fotiadou$^{1}$, Eleni Papananou, Kiriaki Chrissopoulou, Spiros H. Anastasiadis, Giuseppe Portale, Wim Bras We investigate the effect of inorganic clay on the crystalline characteristics and the crystallization kinetics of PEO in its intercalated nanocomposites with natural montmorillonite (Na+- MMT). The structure of the hybrids was investigated over multiple length scales by X-ray diffraction, small-angle X-ray scattering (SAXS) and polarizing optical microscopy (POM) as well as by DSC. The PEO within the galleries is completely amorphous whereas only the excess polymer outside the completely full galleries can crystallize at high PEO concentrations. The time resolved measurements reveal the effect of clay on crystallization. Even very small amount of the inorganic can cause a significant decrease of the spherulite size. The crystallization mechanism varies from sporadic nucleation for pure PEO to two-dimensional growth with predetermined nuclei at 10wt\% clay with a higher activation barrier for low clay concentration. Sponsored by NATO's Scientific Affairs Division, by the Greek GSRT and by the EU. [Preview Abstract] |
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