This dissertation describes the characterization of SWNT phase diagram. The protonation of SWNTs in superacids enables their dispersion at concentration up to 18%wt.; this concentration is an order of magnitude higher than the one achieved for pristine SWNTs in any other solvent. The dispersed SWNTs behave as rigid rods; with increasing concentration the dispersions pass from a isotropic phase (in which rods rotation is inhibited), to a biphasic regime (where an isotropic phase coexists with a liquid crystalline phase), and finally to a single phase liquid crystal. This phase behavior was determined using a combination of rheology, optical microscopy, and UVspectroscopy.
For SWNTs in superacids, the phase transition between isotropic and biphasic region is affected by the SWNT protonation. This has significant effects on the concentration at which the system becomes biphasic. In contrast, SWNT protonation has little effect on the concentration at which the system becomes a single liquid crystalline phase; this is shown from the comparison between the results found in literature for sulfuric acid and the experimental results obtained in this work.
The ability to form lyotropic nematic SWNT liquid crystal directly impacts the development of applications requiring macroscopic assemblies of highly aligned SWNTs.The direct impact of liquid crystalline phase behavior and liquid crystal morphology on fiber microstructure was demonstrated by producing fibers from SWNTs dispersed in 102% H2SO4 and ClSO3H. The results of this research provide a key example of how liquid crystalline phase behavior can be used to facilitate the development of macroscopic structures.