Solubility, length characterization, and cryo-TEM of pristine and functionalized single-walled carbon nanotubes in surfactant and superacid systems, with application to spinning SWNT fibers
Parra-Vasquez, A. Nicholas G.
Doctor of Philosophy
Single wall carbon nanotubes (SWNTs) have remarkable properties: the thermal conductivity of diamond, the electrical conductivity of copper, and mechanical properties greater than steel at a sixth of the weight. If these properties can be retained at the macroscale, SWNT fibers could be used in many high performance applications. The difficulty lies with dispersing SWNTs at high concentrations. Strong van der Waals attractive forces cause bundle formation, which limits SWNT self-assembly into highly aligned macro-structures. Using additives, SWNTs can be dispersed as individuals at low concentrations. Although spinning fibers is difficult to do with these dispersions, I have exploited their ability to disperse individual SWNT to develop an easy technique to measure the SWNT length distribution through the bulk measurements of viscosity or polarized absorbance in an external magnetic field. Determining length is important for fiber spinning, since longer nanotubes offer promise of stronger, more conductive fibers at the cost of higher viscosities and difficulty in dispersing. To produce neat SWNT fibers, we use superacids, which can disperse SWNTs at high concentrations, forming liquid crystalline phases that are valuable in forming highly-aligned SWNT fibers. I found that functionalization improves SWNT stabilization and solubility at lower concentrations, but at high concentrations, most of functional groups studied prevents the formation of highly aligned phases, which translated into poorly-aligned fibers. I found that chlorosulfonic acid is the most effective solvent, yielding high isotropic solubility and liquid crystallinity at high concentrations. Moreover, cryo-TEM shows that chlorosulfonic acid dissolves as individuals 500mum-long SWNTs and MWNTs.