Liquid crystal behavior of single-walled carbon nanotubes dispersed in biological hyaluronic acid solutions.

We report the spontaneous liquid crystal phase separation of nanotubes (single-walled carbon nanotubes, SWNTs) stabilized in aqueous biological (hyaluronic acid, HA) solutions. Sonication of SWNTs in solutions of HA produced well-dispersed single-phase isotropic dispersions which, over time, phase separated into dispersions containing birefringent nematic domains in equilibrium with an isotropic phase. The time required for phase separation to occur was shown to depend on the concentration of SWNT and HA, with the attractive interactions between the SWNT and HA shifting the onset of the phase separation toward lower concentration. This phase separation is accompanied by an increase in the dispersion viscosity with this increase qualitatively matching the degree of phase separation. The formation of ordered phases in biological media can offer wide opportunities for processing conducting biomaterials with aligned and oriented domains.