Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session J25: Focus Session: Hybrid Organic, Inorganic Nanomaterials: Synthesis, Assembly |
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Sponsoring Units: DPOLY Chair: Rich Vaia, Air Force Research Laboratory Room: Colorado Convention Center 203 |
Tuesday, March 6, 2007 11:15AM - 11:51AM |
J25.00001: Directing and Orienting Nanoparticles and Nanorods at Fluid Interfaces, within Templates, and on Substrates Invited Speaker: This presentation will center on the functionalization of nanoparticles and nanorods with organic and polymer ligands that influence the behavior of such particles in solution, at interfaces, and on substrates. When nanoparticles, whether quantum dots, gold nanoparticles, or bionanoparticles (such as tobacco mosaic virus or ferritin), are surface-functionalized with reactive ligands, they not only can form interesting assemblies, but also can be converted to robust structures through performing chemistry on the ligands. Nanoparticle-based capsules and sheets arise from such chemistries, which can be considered for potential applications in for example functional membranes and coatings. [Preview Abstract] |
Tuesday, March 6, 2007 11:51AM - 12:03PM |
J25.00002: Formation of Giant Meso-Polymers from Magnetic Nanoparticles Using Fossilized Liquid Assembly Jason Benkoski, Steven Bowles, Ronald Jones, Jack Douglas, Jeffrey Pyun, Alamgir Karim We report the ability to directly image the self-organization of polymer-coated ferromagnetic nanoparticles into one-dimensional mesostructures at a liquid-liquid interface. When polystyrene-coated Co nanoparticles (15 nm) are deposited at an oil/water interface under zero-field conditions, long ($\sim$ 5 $\mu$m) chain-like assemblies spontaneously form, where the precise morphology depends upon particle concentration, temperature, and assembly time. The assembly process was examined using ``Fossilized Liquid Assembly,'' a recently developed platform consisting of a biphasic oil/water system in which the oil phase can be flash-cured upon ultraviolet light exposure. The nanoparticle assemblies embedded in the crosslinked phase were then imaged using atomic force microscopy. Noting the dependence of chain length on the assembly conditions, we observed striking similarities between nanoparticle self-assembly and polymer synthesis. Previous reports on the mechanism and kinetics of equilibrium polymerization provide a useful framework for performing quantitative image analysis on the AFM-visualized mesostructures. [Preview Abstract] |
Tuesday, March 6, 2007 12:03PM - 12:15PM |
J25.00003: Nanoparticle Alignment and Repulsion During Failure of Glassy Polymer Nanocomposites Alfred Crosby, Jong-Young Lee, Qingling Zhang, Todd Emrick We investigate crazing and failure in a model nanocomposite of surface modified nanoparticles (cadmium selenide, diameter is 5 nm) blended into polystyrene. We demonstrate that nanoparticles undergo three stages of rearrangement during craze formation and propagation in glassy polymer nanocomposites: 1) Alignment along the precraze, 2) Expulsion from craze fibrils, and 3) Assembly into clusters entrapped between craze fibrils. At an optimal volume fraction of nanoparticles, the failure strain of the nanocomposite is increased by nearly 100{\%} relative to unfilled polystyrene. This optimal volume fraction is related to the balance of two mechanisms: 1) the decrease in cross-tie fibril density for craze structures, and 2) the decrease in the probability of craze widening at higher tensile strain by decreasing the number of polymer entanglements at small interparticle lengths. These results offer a clear and detailed understanding of failure mechanism of glassy polymer-nanoparticle composites, and provide predictions for the future design of nanoparticle-based materials. [Preview Abstract] |
Tuesday, March 6, 2007 12:15PM - 12:27PM |
J25.00004: Solvent-Mediated Plasmon-Tuning in a Nanoparticle-Poly(Ionic Liquid) Organogels and Hydrogels Millicent Firestone, Dolly Batra, Soenke Seifert The design, synthesis and characterization of hierarchically ordered composites whose structure and optical properties can be reversibly switched by adjustment of solvent conditions are described. Solvent-induced swelling and deswelling is shown to provide control over the internal packing arrangement and hence, optical properties of \textit{in situ} synthesized metal nanoparticles. Specifically, metal nanoparticle-containing ionic liquid-derived polymers are synthesized in a single step by UV irradiation of a metal ion precursor-doped, self-assembled ionic liquids, 1-decyl-3-vinylimidazolium chloride or 1-(8-(acryloyloxy)octyl)-3-methylimidazolium chloride, physical gels. Small-angle X-ray scattering (SAXS) studies are used to monitor the nanostructure of the polymers in the deswollen and swollen states. Optical spectroscopy of the dried composites reveals plasmon resonances positioned in the near-infrared. Upon swelling in alcohol or water, the materials undergoes a structural conversion to a disordered structure, which is accompanied by a color change and a blue shift in the surface plasmon resonance. These results demonstrate the far-field tuning of the plasmonic spectrum of gold nanoparticles by solvent-mediated changes in its encapsulating matrix, offering a straightforward, low-cost strategy for the fabrication of nanophotonic materials. [Preview Abstract] |
Tuesday, March 6, 2007 12:27PM - 12:39PM |
J25.00005: Immobilizing Au Nanoparticles with Polymer Single Crystals, Patterning and Asymmetric Functionalization Bing Li, Christopher Li Considerable attention has been paid to nanoparticle (NP) research due to their fascinating properties and potential applications in nanotechnology and biotechnology. Asymmetrically functionalizing NP is of particular interest since it could directly lead to controlled patterning of NPs into complex structures for a variety of applications. Here we report, for the first time, using 2-dimensional polymer lamellar single crystals as the solid substrate to create patterned functional (thiol) surface and immobilize AuNPs. We demonstrated that patterning of AuNPs could be achieved and the AuNP area density could be easily controlled by polymer molecular weight. Furthermore, this unique technique also enables asymmetric functionalization of AuNPs. Bilayer AuNPs/polymer hybrids were obtained. Dissolving PEO single crystals led to free asymmetric binary AuNP complexes. This approach provides a novel means to pattern AuNPs and synthesize asymmetrically functionalized AuNPs. We also anticipate that this methodology could be applied to other metallic or semiconducting NPs. [Preview Abstract] |
Tuesday, March 6, 2007 12:39PM - 12:51PM |
J25.00006: High-Energy Density Capacitors using Nanoparticle-Polymer Composite Dielelectrics Kristin Kraemer, Jiangyu Li, Lei Zhang, D.J. Sellmyer, X. Wei, Stephen Ducharme By combining a polymer with a high dielectric strength and nanoparticles with an even higher dielectric constant, we can to explore exchange coupling between the two materials that will result in a material with an optimized dielectric constant and dielectric strength. [J. Li, \textit{Phys. Rev. Lett.} \textbf{90}, 217601 (2003)] We report the results of dielectric characterization of composites consisting of barium titanate and other dielectric nanoparticles embedded in a matrix of copolymers of vinylidene fluoride with trifluoroethylene. Basic measurements are made by creating parallel plate capacitors with aluminum electrodes on glass substrates. Capacitors made by solvent spin coating contain 0{\%} to 50{\%} nanoparticles by weight and have thickness of approximately 100 nm. Dielectric studies examine the relationship between capacitance and electric field, capacitance and temperature, and the pyroelectric response. This work is supported by the Office of Naval Research and the Nebraska Research Initiative. [Preview Abstract] |
Tuesday, March 6, 2007 12:51PM - 1:03PM |
J25.00007: Fabrication of Patterned Mesoporous Silica Films Templated From Chemically Amplified Block Copolymers Sivakumar Nagarajan, Joan Bosworth, Christopher Ober, James Watkins, Thomas Russell Mesoporous metal oxide films have been the subject of intense research, for numerous applications including sensors, microfluidics, microelectronics, optoelectronics, microelectromechanical systems and catalysis. Many applications require precise patterning of the films to incorporate device features necessary for intended application. Here, patterned mesoporous silica films are obtained by performing domain selective condensation of precursors within self-assembled block copolymer templates by using supercritical CO$_{2}$ as a delivery medium. The domain selectivity is imparted by the segregation of acid catalyst into hydrophilic domains. Further, by using a photo acid generator, the presence of acid within the film can be controlled spatially via photolithography. Thus patterns at two different length scales i.e., at nanoscale from self-assembled block copolymer and microscale from photolithography can be generated simultaneously. Chemically amplifiable polymers, including poly (tertiary-butoxy carbonyloxy styrene-b-styrene), were used as block copolymer templates. Triphenyl sulfonium triflate was used as a photo acid generator. [Preview Abstract] |
Tuesday, March 6, 2007 1:03PM - 1:15PM |
J25.00008: Metal nanocrystals incorporated within pH-responsive microgel particles Maria Vamvakaki, D. Palioura, S.H. Anastasiadis, S.P. Armes Cross-linked latexes of approximately 250 nm in diameter are synthesized by emulsion polymerization of 2-(diethylamino)ethyl methacrylate using a PEO-based macromonomer as the stabilizer at pH 9. These particles exhibit reversible swelling properties in water by adjusting the solution pH: at low pH they exist as swollen microgels due to protonation of the tertiary amine units whereas deswelling occurs above pH 7. The swollen microgels can be used as nanoreactors for the in situ synthesis of Pt nanoparticles. The effects of the method of Pt nanoparticle formation on the size of the microgel particles are studied by DLS. Polymer-metal interactions are investigated by UV-visible absorption spectroscopy, which confirms that the Pt salt is completely reduced to zero-valent Pt using NaBH$_{4} $. TEM and XRD verify the formation of nanometer-sized Pt nanocrystals within the microgels, which can be used as recoverable colloidal catalyst supports for various organic reactions. [Preview Abstract] |
Tuesday, March 6, 2007 1:15PM - 1:27PM |
J25.00009: Self-Assembly of Magnetic Nanoparticles at the Surface and Within Block Copolymer Films Chen Xu, Kohji Ohno, Russell Composto We investigate the self-assembly of magnetic Fe$_{3}$O$_{4}$ nanoparticles in thin films of a symmetric block copolymer of poly(styrene-$b$-methyl methacrylate), PS-$b$-PMMA (75 kg/mol). The Fe$_{3}$O$_{4}$ nanoparticles (4nm) are grafted by poly(methyl methacrylate) (PMMA) (2.7 kg/mol) brushes to improve their compatibility. The weight percent of Fe$_{3}$O$_{4 }$in PS-$b$-PMMA is 1, 4 and 10. The Fe$_{3}$O$_{4 }$reside at the intermaterial dividing surface and also form small disk-like aggregates within the PMMA phase. The addition of Fe$_{3}$O$_{4}$ slows down the transition from perpendicular to parallel lamellae morphology at the surface and slowing down increases as weight percent Fe$_{3}$O$_{4 }$increases. Using cross-sectional TEM, nanoparticles are found to be rejected from the parallel lamellae and gather preferentially within the perpendicular lamellae. These studies demonstrate that the Fe$_{3}$O$_{4}$ particles influence thin film morphology and visa versa. Because of widespread interest in nanodevices, this study shows that arrays of functional nanoparticles can be formed using block copolymer templates. [Preview Abstract] |
Tuesday, March 6, 2007 1:27PM - 1:39PM |
J25.00010: Effect of Nanoparticles on the Phase Morphology of Block copolymers. David Bucknall, Deepali Palta In this study we show that addition of nanoparticulates to copolymer self-assembling molecular templates causes variations in the phase morphologies. We report the results of the bulk phase behavior of poly(styrene-dimethyl siloxane) (PS-PDMS) and poly(styrene-butadiene-styrene) (SBS) block copolymer systems with inclusion of different percent loadings of 1-50 nm particles of gold and endohedral fullerenes. The copolymer samples (both with and without nanoparticles) have been prepared and characterized using AFM, TEM, SAXS and $^{13}$C-NMR measurements. We present results which show that even at relatively low concentrations nanoparticle inclusions (less than 2 wt./vol.{\%}) the block copolymer phase morphology is altered from that of the native copolymer. [Preview Abstract] |
Tuesday, March 6, 2007 1:39PM - 1:51PM |
J25.00011: Limitations of electric field assisted patterning of nanoparticle filled polymers. Hilmar Koerner, Richard Vaia, Wei Lu, Evangelos Manias Among the many challenges as Polymer Nanocomposites move beyond commodity plastic applications, hierarchical morphology control is paramount as random arrangements of nanoparticles (NPs) will not provide optimized electrical, thermal or optical performance for many potential high-tech applications. Two general approaches to this challenge are emerging, i.e.: external-in (directed patterning of NP dispersions) and internal-out (mesophase assembly of NPs). To better understand limitations of electric field assisted patterning of NPs, the impact of inherent (particle shape, matrix viscosity, complex dielectric properties of the constituents) and external (temperature, frequency and magnitude of applied field) parameters on the torque generated on an isolated NP in a uniform electric field is calculated. An applied electric field induces a dipole in a dielectric particle when it has different permittivity from that of the media. When the particle shape is anisotropic, orientation of the induced dipole does not necessarily coincide with the applied field. The tendency of the dipole to align along the field causes a torque for the particle to rotate. Similarly, conductivity difference of particle and medium causes charges to build up at the interface. This free charge dipole can also generate a torque. These theoretical predictions are compared to experimental observations. [Preview Abstract] |
Tuesday, March 6, 2007 1:51PM - 2:03PM |
J25.00012: Separation of Ionic Solutes Using Nanoparticle-Crosslinked Polymer Hydrogels Peter Thomas, Bani Cipriano, Srinivasa Raghavan Polymer hydrogels are usually made by crosslinking a monomer such as N-isopropylacrylamide (NIPAAm) with a multifunctional crosslinker. Recently, gels have been shown to be formed even in the absence of monomer by using clay nanoparticles as crosslinkers. These particle-crosslinked gels tend to have larger pore sizes and higher gel strengths compared to conventional NIPAAm gels. In this talk, we will show that particle-crosslinked gels are also suited for use as separation matrices. In particular, we will describe the extraordinary ability of these gels to soak up a cationic solute from a solution. We speculate that cationic molecules can be adsorbed on the anionic surface of the clay platelets inside the gel, akin to a process of ion exchange. An additional unique property of these gels is that they can be disassembled in the presence of organic solvents -- due to the non-covalent interaction between polymer and particles (there is no counterpart for this behavior in conventional covalently-linked gels). By exploiting this property, cationic solutes adsorbed on the particles within our gel can be released and recovered. [Preview Abstract] |
Tuesday, March 6, 2007 2:03PM - 2:15PM |
J25.00013: Molecular Dynamics Simulations of Cubic Phases in Pluronics Systems and Their Role in Templating Nanoparticles Joshua Anderson, Alex Travesset, Chris Lorenz We discuss molecular dynamics simulations aimed at predicting phase diagrams in Pluronic systems. Crystalline phases with cubic symmetries are particularly challenging to simulate. A general method that is able to obtain these phases is presented. As an example, we show our results for a system of ABA triblock polymers where each hydrophilic A block contains 10 beads and the hydrophobic block B contains 7 beads. These values match the ratio of PEO to PPO in Pluronic F127. Numerous simulation runs are carried out with differing initial conditions, which consistently produce textbook bcc and fcc lattices of micelles along with two other distorted bcc lattices. We find that the formation of a lattice is sensitive to the system's preparation and depends mainly on the kinetic temperature and equilibration time. Examination of the distorted lattices shows that they are related to the finite size of the simulation box. We conclude with some discussion on using these crystals as a template for nanoparticles or biomineralization. [Preview Abstract] |
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