Novel nanotubes from a cationic surfactant and an anionic stiff aromatic counter-ion

A novel class of nanotubes (NT) is reported which consists of two components, a cationic surfactant cetyltrimethylammoniumbromide (CTAB) and an anionic UV absorber, 2-phenylbenzimidazole-5-sulfonic acid (PBSA). When aqueous solutions of the components are mixed, a turbid low-viscosity solution is formed immediately. This solution is stable for several days. Then, within 1 day, the turbid samples are transformed into transparent, isotropic soft gels that contain thin single-walled tubuli (SWNT). The SWNT have been characterized by cryo-TEM micrographs. The NT have an extremely narrow size distribution of the outer (o.d.) and inner (i.d.) diameters. The tubes have an o.d. of 13 +/- 0.5 nm and an i.d. of about 6 nm. Despite their small diameter, the NT are extremely stiff with a persistence length l(p) greater than several micrometers. It is assumed that the tubuli consist of bilayers of the cationic and anionic compounds with a one-to-one ratio. In solution, the tubuli seem to be stabilized by the adsorption of one of the excess amphiphilic compounds.