In the pressent of alcohol, octane and brine, di(2-ethylhexyl) sulfosuccinate (AOT) and cetyltrimethylammonium bromide (CTAB) can form the middle phase microemulsion. Using salinity (or concentration of alcohol) scanning and interfactial tension methods, we investigated the influence of molar ratio of AOT to CTAB, salinity, concentration and kind of alcohol on the formation and characteristic of middle phase microemulsion. This mixed anionic/cationic surfactant system showed very different phenomena with anionic surfactant and mixed and ionic/anionic surfactant system. The results are of partical importance to detergents, cosmetics, and tertiary oil recovery.

Key words: CATIONIC SURTACTANTS, ANIONIC SURFACTANTS, SURFACE TENSION