Fluid Phases of Nano-Carbon

Nanoscale carbon?including Single-Walled Carbon Nanotubes (SWNTs) 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 fluid phases of nano-carbon. Biological and environmental applications are likely to require dilute phases of nano-carbon; material processing, e.g., production of coatings and fibers, will require more concentrated phases.

Difficult fluid handling is one of the most important frontiers of applied research in SWNTs and graphene. Nano-carbon fluids are almost considered an oxymoron because dispersing or dissolving SWNTs and graphene into fluid phases is exceedingly difficult.

In this lecture, I will discuss how SWNTs as well as graphene can and should be viewed as hybrids between polymer molecules and colloidal particles. Even at low concentrations (few parts per million), SWNTs form complex fluid phases with intriguing properties. Their interaction can be mediated by polymers and surfactants to produce complex individual architectures. In superacids, SWNTs as well as graphene dissolve spontaneously. At low concentration, these fluids can be used for making transparent, conducting films and coatings. In crowded environments, SWNTs reptate like stiff polymers; their study permits the conclusive determination of the effect of molecular stiffness on the diffusivity of slender filaments. At sufficiently high concentrations, SWNTs form liquid crystals that can be spun into well-aligned, macroscopic fibers. Intriguingly, the self-assembly of SWNTs into liquid crystalline phases can be understood by ?hybridizing? Onsager's theory for colloidal rods with Flory's theory for rod-like polymers.