Order-disorder transition induced by surfactant micelles in single-walled carbon nanotubes dispersions

The observation of spontaneously formed microns-long islands of orientationally ordered SWNT in isotropic dispersions of spherical surfactant micelles is reported. The micelles co-exist with surfactant-coated individual SWNT of like charge. Inter-tube distances of 25 to 16 nanometres and an unexpected first order transition into a random phase induced by an increased ionic strength cannot be explained by classical depletion interactions or electrostatic repulsion. We suggest that coupling between the nanostructures and the assembled molecules modifies the effective interactions in an unexpected way. As the nanometrically thin SWNT share common features with rigid polymers, rod-like particle suspensions, and biological polymers such as microtubules and actin in crowded cellular environments, the observed phenomenon is believed to be general and expected in other systems.