Phase transitions in cationic and anionic surfactant mixtures

The phase behavior of cationic and anionic surfactant mixtures strongly depends on the molar ratio and actual concentration of surfactants. The phase diagram contains large areas of coexisting solid crystalline catanionic surfactant and liquid crystalline phases. Intermediate phases from pure solid crystalline catanionic surfactant to mixed micelles were examined by light microscopy under crossed polarizers and potentiometric and electrophoretic measurements. The mixed liquid crystalline phase is composed of both cationic and anionic surfactants. Its appearance as lamellar droplets may be explained by the increase in electrostatic repulsion at the bilayer surface.