Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session A11: Invited Session: Directed Assembly of Hybrid Materials |
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Sponsoring Units: DPOLY Chair: Richard Vaia, Air Force Research Laboratory Room: 310 |
Monday, March 18, 2013 8:00AM - 8:36AM |
A11.00001: Engineered Self-Assembly of Plasmonic Nanomaterials Invited Speaker: Andrea Tao A critical need in nanotechnology is the development of new tools and methods to organize, connect, and integrate solid-state nanocomponents. Self-assembly -- where components spontaneously organize themselves -- can be carried out on a massively parallel scale to construct large-scale architectures using solid-state nanocrystal building blocks. I will present our recent work on the synthesis and self-assembly of nanocrystals for plasmonics, where light is propagated, manipulated, and confined by solid-state components that are smaller than the wavelength of light itself. We show the organization of polymer-grafted metal nanocrystals into hierarchical nanojunction arrays that possess intense ``hot spots'' due to electromagnetic field localization. We also show that doped semiconductor nanocrystals can serve as a new class of plasmonic building blocks, where shape and carrier density can be actively tuned to engineer plasmon resonances. These examples demonstrate that nanocrystals possess unique electromagnetic properties that rival top-down structures, and the potential of self-assembly for fabricating designer plasmonic materials. [Preview Abstract] |
Monday, March 18, 2013 8:36AM - 9:12AM |
A11.00002: Polymer Functionalized Nanoparticles in Polymer Nanocomposites Invited Speaker: Arthi Jayaraman Significant interest has grown around the ability to control spatial arrangement of nanoparticles in a polymer nanocomposite to engineer materials with target properties. Past work has shown that one could achieve controlled assembly of nanoparticles in the polymer matrix by functionalizing nanoparticle surfaces with homopolymers. This talk will focus on our recent work using Polymer Reference Interaction Site Model (PRISM) theory and Monte Carlo simulations and GPU-based molecular dynamics simulations to specifically understand how heterogeneity in the polymer functionalization in the form of a) copolymers with varying monomer chemistry and ~monomer sequence, and b) polydispersity in homopolymer grafts can tune effective interactions between functionalized nanoparticles, and the assembly of functionalized nanoparticles. [Preview Abstract] |
Monday, March 18, 2013 9:12AM - 9:48AM |
A11.00003: Gels from soft hairy nanoparticles in polymeric matrices Invited Speaker: Dimitris Vlassopoulos Hairy particles represent a huge class of soft colloids with tunable interactions and properties. Advances in synthetic chemistry have enabled obtaining well-characterized such systems for specific needs. In this talk we present two model hairy soft particles with diameters of the order of tens of nanometers, star polymers and polymerically grafted spherical particles. In particular, we discuss design strategies for dispersing them in polymeric matrices and eventually creating and breaking gels. Control parameters are the matrix molar mass, the grafting density (or functionality) and the size of the grafts (or arms). The linear viscoelastic properties and slow time evolution of the gels are examined in view of the existing knowledge from colloidal gels consisting of micron-sized particles, and compared. In the case of stars we start from a concentrated glassy suspension in molecular solvent and add homopolymer at increasing concentration, and as a result of the induced osmotic pressure the stars shrink and a depletion gel is formed. For the grafted colloidal particles, they are added at low concentration to a polymer matrix, and it has been shown that under certain conditions the anisotropy of interactions gives rise to network formation. We then focus on the nonlinear rheological response and in particular the effect of shear flow in inducing a solid to liquid transition. Our studies show that the yielding process is gradual and shares many common features with that of flocculated colloidal suspensions, irrespectively of the shape of the building block of the gel. Whereas shear can melt such a gel, it cannot break it into its constituent blocks and hence fully disperse the hairy nanoparticles. On the other hand, the hairy particles are intrinsically hybrid. We show how this important feature is reflected on the heating of the gels. In that case, the mismatch of thermal expansion coefficients of core and shell appears to play a role on the particle response as it imposes and internal strain on the particle, which in turn changes the shell conformation and under some conditions can lead to thermal melting of the gel. These alternative avenues for manipulating the gel-to-liquid transition have potential implications in directing the properties of hairy nanoparticles and their assemblies in viscoelastic matrices. Parts of this work reflect collaboration with D. Truzzolillo (FORTH), J. F. Moll and S. K.Kumar (Columbia). R. H. Colby (Penn State), M. Gauthier (Waterloo) and B. C. Benicewicz (Univ. South Carolina). [Preview Abstract] |
Monday, March 18, 2013 9:48AM - 10:24AM |
A11.00004: Canopy Dynamics in Nanoscale Ionic Materials Probed by NMR Invited Speaker: Peter Mirau Nanoscale ionic materials (NIMs) are hybrids prepared from ionically functionalized nanoparticles (NP) neutralized by oligomeric polymer counter-ions. NIMs are designed to behave as liquids under ambient conditions in the absence of solvent and have no volatile organic content, making them useful for a number of applications. We have used NMR relaxation and pulse-field gradient NMR to probe local and collective canopy dynamics in NIMs based on silica nanoparticles (NP), fullerols and proteins in order to understand the relationship between the core and canopy structure and the bulk properties. The NMR studies show that the canopy dynamics depend on the degree of neutralization, the canopy radius of gyration and molecular crowding at the ionically modified NP surface. The viscosity in NIMs can be directly controlled with the addition of ions that enhance the exchange rate for polymers at the NP surface. These results show that NIMs for many applications can be prepared by controlling the dynamics of the NP interface. [Preview Abstract] |
Monday, March 18, 2013 10:24AM - 11:00AM |
A11.00005: Colloidal Crystallization in Confinement: Icosahedral Symmetry {\&} Plastic-Crystal Transitions Invited Speaker: Alfons van Blaaderen The crystallization of spherical nanoparticles in liquid droplets results under certain conditions in crystals with an icosahedral shape. Experiments with larger spherical colloids and computers simulations of hard particles demonstrate that such crystal shapes do not rely on energetic arguments, but already result from confinement and entropy alone. Experiments on rod shaped fluorescent colloidal particles that are monodisperse enough to form nematic and smectic liquid crystal phases under conditions where the double layer thickness is small compared to the diameter of the rods show that if the double layer thickness is significantly larger than the rod length plastic crystals with a body centered crystal structure are formed. In such crystals there is three dimensional positional order, but no orientational order of the rods. These plastic crystals under strong planar confinement show intriguing phase behavior where plastic crystal and full crystal phases alternate as a function of the separation between the confining plates. [Preview Abstract] |
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