Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session L19: Focus Session: Hierarchically and Templated Ordered Systems II |
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Sponsoring Units: DPOLY Chair: Vladimir Tsukruk, Georgia Institute of Technology Room: B118-B119 |
Tuesday, March 16, 2010 2:30PM - 3:06PM |
L19.00001: Dillon Medal Break |
Tuesday, March 16, 2010 3:06PM - 3:18PM |
L19.00002: Self-assembly of ordered mesoporous platinum from nanoparticle-block copolymer mixtures Scott Warren, Frank Disalvo, Ulrich Wiesner Discovery of novel catalyst architectures with enhanced stability and high platinum utilization is essential to progress in fuel cell materials. I present results from the first synthesis and characterization of an ordered, mesoporous metal produced from co-assembly of metal nanoparticles with block copolymers. This process leads to an ordered, inverse hexagonal hybrid mesostructure; pyrolysis converts this to an ordered mesoporous platinum-carbon nanocomposite. Removal of the carbon yields hexagonally ordered, mesoporous platinum. These materials exhibit the highest electrical conductivity yet measured for ordered mesoporous materials fabricated from block copolymer self-assembly. The use of these materials as a fuel cell electrocatalyst is demonstrated. [Preview Abstract] |
Tuesday, March 16, 2010 3:18PM - 3:30PM |
L19.00003: Fluidic Channels Produced by Electro Hydrodynamic Viscous Fingering Kristopher Behler, Eric Wetzel Viscous fingering is a term describing fingerlike extensions of liquid from a column of low viscosity liquid that has been injected into a more viscous liquid. The modification of viscous fingering, known as electro hydrodynamic viscous fingering (EHVF), utilizes large electrical potentials of 10-60 kV. The fingers see a reduction in size and increase in branching behavior due to the potential applied to the system. The resulting finely structured patterns are analogous to biological systems such as blood vessels and the lymphatic system. In this study silicone oils and water were studied in thin channel Hele-Shaw cells. The interfacial tension was optimized by altering the surfactant concentration in the silicone oils. EHVF of liquid filled packed beds consisting of beads and silicone oils showed retardation of the relaxation of the fingers after the voltage was turned off. Decreased relaxation provides a means to solidify patterns into a curable material, such as polydimethylsiloxane (PDMS). After the water is evacuated from the fingers, the cured materials then possess hollow channels that can be refilled and emptied, thus creating an artificial circulatory system. [Preview Abstract] |
Tuesday, March 16, 2010 3:30PM - 3:42PM |
L19.00004: Fabrication of microstructured polymer films using breath-figure-templated assembly Mohan Srinivasarao, Vivek Sharma, Matija Crne Breath figures formed on evaporating polymer solutions exposed to the blast of humid air involve growth and self-assembly of water drops that are non-coalescent. The ordered arrays of nearly monodisperse drops, eventually evaporate away, leaving a microstructured, porous polymer film. We elucidate the mechanism of this breath-figure-templated assembly, by accounting for various transport and thermodynamic processes that control the dynamics of drop nucleation, growth, noncoalescence and self-assembly. The theoretical framework developed in this study allows one to rationalize and predict the structure and size of pores. We provide an exemplary study where we use coat these films with inorganic oxides and mimic the structural color of Papilio palinurus butterfly. [Preview Abstract] |
Tuesday, March 16, 2010 3:42PM - 4:18PM |
L19.00005: Order Through Instability: Patterning with Polymers and Nanoparticles Invited Speaker: Nature provides wonderful inspiration and justification for the development of hierarchical structures in synthetic materials. The balance in structure provides balance in performance and properties, while consuming minimal resources (e.g. energy, materials) during development. A ubiquitous trait in the development or processing of these Natural structures, consistent with the use of minimal resources, is the use of instabilities to guide the shape and building of hierarchical elements. In this paper, an overview is presented of recent efforts in our group to use elastic and fluid instabilities to build hierarchical structures. The physics of developing morphology, or arrangement, for wrinkles and folds in polymer thin films will be discussed, focusing on the impact of geometric constraint, origin of stress, and polymer architecture. Similar strategies, combined with tailored nanoparticle chemistry, are used to develop hierarchical assemblies of quantum dots. The resulting process and structures, in general, always rely upon a unique balance of geometry and materials properties and are designed with an eye toward scaling and application in products ranging from responsive optics to flexible electronics. [Preview Abstract] |
Tuesday, March 16, 2010 4:18PM - 4:30PM |
L19.00006: Templated Organization of Nanoparticles using Self-Assembling Peptides Nikhil Sharma, Joel Schneider, Kristi Kiick, Darrin Pochan Bottom up nanofabrication holds the potential for engineering matter at scales that are limit of current lithographic capability. Herein we describe the template-directed organization of inorganic nanoparticles into linear arrays using two distinct, hierarchically assembled peptide nanostructures. First, a long chain alanine-rich polypeptide was also used to create 1D nanoparticle assemblies. This peptide assembles into fibrils with monodisperse widths and presents charged functional groups in a desired periodic fashion along the length of the fibril. These functional groups bind nanoparticles that results in their spatially modulated linear arrangement. Second, a 20 amino acid peptide, consisting of alternating lysine and valine residues flanking a central diproline turn sequence (VKVKVKVKVPPTKVKVKVKV-NH2) was employed as a template for the organization of 2nm gold particles. This peptide self assembles into a laminated morphology in solution and has a periodic nanostructure. Negatively charged nanoparticles are templated into the positively charged lysine layer and are aligned within the laminated template to form laterally spaced (2D) linear arrays. [Preview Abstract] |
Tuesday, March 16, 2010 4:30PM - 4:42PM |
L19.00007: Peptide -- Silica Hybrid Networks Aysegul Altunbas, Nikhil Sharma, Radhika Nagarkar, Joel Schneider, Darrin Pochan In this study, a bio-inspired route was used to fabricate scaffolds that display hierarchical organization of an inorganic layer around an organic self-assembled peptide fibril template. The 20 amino acid peptide used in this study intramolecular folds into a beta-hairpin conformation on addition of a desired solution stimulus. This intramolecular folding is followed by intermolecular self-assembly of the peptides into a three dimensional network of entangled fibrils rich in beta-sheet with a high density of lysine groups exposed on the fibril-surfaces. The lysine-rich surface chemistry was utilized to create a silica shell around the fibrils. The mineralization process of the fibrils results in a rigid, porous silica network that retains the microscale and nanoscale structure of the peptide fibril network. Structural characterization via Transmission Electron Microscopy, cryogenic-Scanning Electron Microscopy, mechanical characterization via oscillatory rheology, Small Angle X-ray and Neutron Scattering of the silicified hydrogels will be presented. [Preview Abstract] |
Tuesday, March 16, 2010 4:42PM - 4:54PM |
L19.00008: Dimple Patterns in Buckling Surfaces Derek Breid, Alfred Crosby Surface wrinkling has attracted considerable attention in recent years for its ability to generate micro- and nano- scale surface structures via non-lithographic pathways. Although the wrinkle morphology has been considered from an energetic viewpoint for stresses exceeding the critical bifurcation stress, the wrinkle morphology for stress near the critical value is far less understood, in part due to a lack of experimental results in this regime. Recent models for this regime predict the formation of a dimple-phase morphology when the stress is equibiaxial, transitioning to aligned ridges when the stress is anisotropic. Here, we present an experimental investigation into the formation of dimple arrays through the control of the applied stress as well as the geometric parameters of the wrinkling system. We demonstrate the ability to develop dimple arrays over extensive lateral length scales, as well as dimples on the surface of a microscale hemisphere, resulting in a `golf ball' hierarchical structure. These results shed light on the morphology in the near-critical wrinkle regime and provoke many open questions about the underlying materials mechanics in the development of wrinkle surface structures. [Preview Abstract] |
Tuesday, March 16, 2010 4:54PM - 5:06PM |
L19.00009: Flame Suppression of Cotton with Polymer-Clay Thin Film Assemblies Galina Sukhonosova, Yu-Chin Li, Jaime Grunlan Cotton fabric was treated with flame-retardant coatings composed of branched polyethylenimine (PEI) and montmorillonite (MMT), prepared via layer-by-layer (LbL) assembly. Four coatings were created with solutions of BPEI (pH 7 or 10) and MMT (0.2 or 1 wt. {\%}). The thickness and composition of the coatings were studied by ellipsometry and quartz crystal microbalance. PEI at pH 10 produces the thickest films. Each coating recipe was evaluated at 5 and 20 bilayers. Thermogravimetric analysis showed that coated fabrics left 13 {\%} char after heating at 500 \r{ }C, over an order of magnitude more char than from uncoated fabric, with less than 4{\%} coming from the coating itself. Coating reduced afterglow time by 9 seconds in vertical flame tests. Post-burn chars of coated fabrics were examined by scanning electron microscopy, revealing that weave structure and fiber shape in all coated fabrics were preserved through burning. This is the first study of its kind to use layer-by-layer assembly to generate a flame retardant coating on a complex substrate like cotton fabric. [Preview Abstract] |
Tuesday, March 16, 2010 5:06PM - 5:18PM |
L19.00010: Tunable Gas Permeability of Polymer-Clay Nano Brick Wall Thin Film Assemblies Daniel Gamboa, Morgan Priolo, Jaime Grunlan Thin films of anionic natural montmorrilonite (MMT) clay and cationic polyethylenimine (PEI) have been produced by alternately dipping a plastic substrate into dilute aqueous mixtures containing each ingredient. After 40 polymer-clay layers have been deposited, the resulting transparent film exhibits an oxygen transmission rate (OTR) below 0.35 cm$^{3}$/m$^{2} \cdot$ day when the pH of PEI solution is 10. This low permeability is due to a brick wall nanostructure comprised of completely exfoliated clay bricks in polymeric mortar. This brick wall creates an extremely tortuous path at thicknesses below 250 nm and clay concentration above 80 wt{\%}. A 70-bilayer PEI-MMT assembly has an undetectable OTR ($<$ 0.005 cm$^{3}$/m$^{2} \cdot$ day), which equates to a permeability below SiOx when multiplied by its film thickness of 231 nm. With optical transparency greater than 86{\%} and the ability to be microwaved, these thin film composites are good candidates for flexible electronics packaging and foil replacement for food. [Preview Abstract] |
Tuesday, March 16, 2010 5:18PM - 5:30PM |
L19.00011: Super Gas Barrier Thin Films via Layer-by-Layer Assembly of Polyelectrolytes and Clay Morgan Priolo, Daniel Gamboa, Jaime Grunlan Thin composite films of branched polyethylenimine (PEI), polyacrylic acid (PAA) and sodium montmorillonite clay (MMT) platelets were prepared using layer-by-layer assembly. Film thickness, mass deposited per layer, and barrier were shown to increase exponentially with the number of deposition cycles. After 32 layers (i.e., eight PEI/PAA/PEI/MMT quadlayers) are deposited, the resulting transparent film exhibits an oxygen transmission rate below the detection limit of commercial instrumentation ($<$ 0.005 cm$^{3}$/m$^{2} \cdot$ day). This level of oxygen barrier is believed to be due to a nano-brick wall microstructure comprised of exfoliated clay bricks in polymeric mortar, where the enhanced spacing between MMT layers, provided by PEI and PAA, creates channels perpendicular concentration gradient that delay the permeating molecule. These films are good candidates for flexible electronics, food, and pharmaceutical packaging due to their transparency, super gas barrier (that rivals SiOx) and lack of metal. [Preview Abstract] |
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