PHASE-DIAGRAM OF WATER-SODIUM PERFLUORODECANOATE-SODIUM DECYLSULFONATE SYSTEM

Phase diagrams of sodium perfluorodecanoate-water and sodium decylsulf onate-water systems were drawn from changes of solubility and critical micelle concentration (CMC) with temperature. The mixed CMC values of the two surfactants of different compositions were determined and two kinds of micelles were found to be formed; one is a fluorocarbon-domi nant micelle and the other is a hydrocarbon-rich micelle with some flu orocarbon surfactants. The precipitate from aqueous solution containin g the two surfactants below the micellization temperature of the mixed surfactants was analyzed by X-ray diffraction and was found to be a m ixture of the two surfactant crystals, Analysis was made of the temper ature dependence of the electrical conductivity of an aqueous solution containing suspended precipitates which were formed at low temperatur e from solution of a certain molar ratio of the two surfactants, and t he phase diagram of the three-component system was constructed. The th ree-dimentional phase diagram was quite different from that of mixed s urfactants which are able to form mixed micelles of any composition. ( C) 1996 Academic Press. inc.