Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session J3: Invited Session: Colloidal Carbon Nanotubes |
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Sponsoring Units: DCMP GSNP Chair: Erik K. Hobbie, North Dakota State University Room: Ballroom III |
Tuesday, March 19, 2013 2:30PM - 3:06PM |
J3.00001: Soft Materials Approaches to Carbon Nanotubes: from Gels to Composites Invited Speaker: Mohammad Islam Carbon nanotubes combine low density with exceptional mechanical, electrical and optical properties. Unfortunately, these nanoscale properties have not been retained in bulk structures. I will describe surface modification assisted self-assembly of single wall carbon nanotube into macroscopic nanotube networks - hydrogels and aerogels. The nanotube networks are ultra-lightweight, electrically conducting and thermally insulating. The shapes and sizes of these nanotube networks are readily tunable and is a tremendous strength of our fabrication method. The interesting properties and structure of these nanotube networks make them suitable for diverse applications. For example, we have used these networks as scaffolds to enhance elastic modulus of polymers by 36,000{\%}. The porous nanotube networks also show high capacitance, and can be impregnated with catalysts nanoparticles at high loading, which can then be simultaneously used as electrodes and catalysts supports in electrochemical cells. A weakness of the nanotube networks is their fragility -- but we have recently developed a method to transform these inelastic networks into superelastic materials by coating them with between one and five layers of graphene nanoplates. [Preview Abstract] |
Tuesday, March 19, 2013 3:06PM - 3:42PM |
J3.00002: Connectedness percolation of carbon nanotube dispersions: impact of interactions, polydispersity and external fields Invited Speaker: Paul van der Schoot There is considerable industrial interest in novel flexible, transparent electrodes for electro-optical applications, in part because of dwindling natural reserves of indium, a component of transparent electrodes used, e.g., in LCD display technology. For this purpose, frantic research is currently being conducted worldwide into polymeric composites containing electrically conducting inorganic and metallic nanowires, carbon nanotubes, grafite flakes, graphene and so on. One of the objectives is to get as high as possible a conduction for as low as possible a nanoparticle loading but progress is slow. Unclear is why, e.g., carbon nanotubes dispersed in plastic matrix materials can have such widely diverging electrical percolation thresholds, even when their mean physical dimensions and other characteristics seem very similar. In an effort to shed light on this, we apply continuous space connectedness percolation theory to collections of anisometric particles with arbitrary polydispersity in length, width and levels of conduction between them. We find that the percolation threshold is extremely sensitive to even quite modest degrees of polydispersity and of alignment induced in the processing of the fluid composites before they set and become the final solid product. We find that the way polydispersity influences the percolation threshold depends on whether or not the length and width distributions are coupled or not. Finally, we provide an explanation why composites with graphene filler seems to have a larger percolation threshold than those with carbon nanotubes. [Preview Abstract] |
Tuesday, March 19, 2013 3:42PM - 4:18PM |
J3.00003: Fluid Phases of Carbon Nanotubes and Graphene Invited Speaker: Matteo Pasquali Nanoscale carbon---including Carbon Nanotubes (CNTs) as well as graphene, i.e., graphite in its single layered form---has remarkable electrical, thermal, and mechanical properties, more so than previously known polymer molecules or colloidal particles. Realizing these properties in applications requires understanding and controlling the behavior of fluid phases of CNTs and graphene. Biological and environmental applications are likely to require dilute phases of CNTs and graphene; material processing, e.g., production of coatings and fibers, will require more concentrated phases. Fluid processing is one of the most important frontiers of applied research in CNTs and graphene. Nano-carbon fluids are almost considered an oxymoron because dispersing or dissolving CNTs and graphene into fluid phases is exceedingly difficult. This talk reviews advances in understanding and controlling fluid phases of CNTs and graphene, with specific focus on single-object properties and true solutions. The dynamics of individual CNTs can be studied by fluorescence microscopy, revealing that their translational and rotational motion and bending stiffness can be described well by the semiflexible chain model. Even at low concentrations (few parts per million), CNTs form complex fluid phases with intriguing properties. In strong acids, CNTs as well as graphene dissolve spontaneously. At low concentration, these fluids can be used for making transparent, conducting films and coatings. In crowded environments, CNTs reptate like stiff polymers. At sufficiently high concentrations, CNTs and graphene form liquid crystals that can be spun into well-aligned, macroscopic fibers. Like in polymeric systems, the properties of macroscopic CNT materials depend on the length (molecular weight) of the constituent CNT macromolecules. [Preview Abstract] |
Tuesday, March 19, 2013 4:18PM - 4:54PM |
J3.00004: Field-assisted assembly and orientational order of colloidal ellipsoids Invited Speaker: Michael Solomon Colloidal particles with anisotropy in shape and interactions can potentially be assembled into colloidal crystals with unusual structure and symmetry. Field-assisted assembly is likewise a means to produce structures that are otherwise difficult to achieve by equilibrium self-assembly. Here we show, by means of confocal microscopy direct visualization, how controlled application of electric fields can improve general prospects for assembly of any anisotropic colloid. By studying the model case of ellipsoidal colloidal rods, we find that applied fields can be designed which produce liquid crystal phases of colloids in a simple, versatile manner. By directly visualizing the assembled particles in three dimensions we learn that the quality of orientational order achieved is comparable to that of materials such as liquid crystalline polymers. We understand the results in terms of the underlying electrokinetics of the system as well as connect the observed field-induced orientational order to the equilibrium isotropic-nematic transition predicted for rods with prolate spheroidal shape. Specifically, the applied field generates a force that is balanced by a gradient in osmotic pressure generated by the density dependence of the rod suspension. If the field strength is sufficiently large, the resultant osmotic pressure produces a phase transition. We discuss how the required field conditions for assembly can be tailored based on the shape and size of the anisotropic building block. [Preview Abstract] |
Tuesday, March 19, 2013 4:54PM - 5:30PM |
J3.00005: DNA-wrapped Carbon nanotubes as a model rod-like colloid system Invited Speaker: Ming Zheng Single-wall carbon nanotubes (SWCNTs) exhibit many fascinating physical behavior as the result of their quasi one-dimensional crystalline structures. SWCNTs can be dispersed into rod-like colloid particles by a few small molecules and polymers, among which the most effect one is single-stranded DNA (\textbf{\textit{Nature Materials}} 2, 338, 2003). The structure of a DNA-SWCNT hybrid is controlled by both the sequence of the wrapping DNA, and the atomic configuration, or chirality, of the SWCNT (\textbf{\textit{Science}} 302, 1545, 2003). This has been exploited by us to purify single-chirality SWCNTs from synthetic mixtures via liquid chromatography (\textbf{\textit{Nature}} 460, 250, 2009; \textbf{\textit{JACS}} 133, 12998, 2011). DNA-SWCNTs have well-defined surface structures, tunable aspect-ratios, and ultra-small diameters. These attributes provide unique advantages to the DNA-SWCNT colloid system in probing inter-particle interactions in crowded and high salt environment (\textbf{\textit{ACS Nano}} 5, 8258, 2011). In this talk, I will present some recent observations we made on DNA-SWCNT clustering that shed new light on the Hofmeister effect. [Preview Abstract] |
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