Nanoscale carbon – including Single-Walled Carbon Nanotubes (SWNTs), fullerenes, and 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.
The quest for a true solvent is key for the development of materials based on SWNTs and graphene. In Fact, fluid handling is one of the most important frontiers of applied research in SWNTs and graphene.
In this lecture, I will discuss how SWNTs, graphene, and fullerenes all dissolve spontaneously in strong sulfonic acids such as sulfuric and chlorosulfonic acids. Dissolution is due to reversible protonation of the carbon surfaces by the acid; highly curved structures such as fullerenes and thin SWNTs are more easily dissolved than lower-curvature ones, such as large diameter carbon nanotubes and graphene.
Even at low concentrations (few parts per million), SWNTs and graphene in acids form complex fluid phases. At low concentration, these fluids can be used for making transparent, conducting films and coatings by a variety of methods such as dip coating and filtration. At sufficiently high concentrations, both SWNTs and graphene in acids form liquid crystals with complex polydomain structure. 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. These liquid crystals of SWNTs and graphene can be spun into well-aligned, macroscopic fibers whose properties combine promising strength and electrical conductivity.