Phase behavior of the cetyltrimethylammonium tosylate (CTAT)–water system

Abstract

A partial phase diagram of the cetyltrimethylammonium tosylate (CTAT)–water system has been constructed from polarizing optical microscopy and small-angle x-ray scattering studies. This system is found to exhibit a nematic phase over a wide range of CTAT concentration, from about 32 to 45wt.%, which is very unusual for aqueous solutions of pure surfactants. At higher CTAT concentrations a hexagonal phase occurs which is stable up to at least 90°C. Detailed analysis of the diffraction data confirms that the hexagonal phase consists of long cylindrical micelles arranged on a two-dimensional hexagonal lattice.