MICROEMULSIONS IN 3-COMPONENT AND 4-COMPONENT SYSTEMS WITH A CATANIONIC SURFACTANT - OCTYLAMMONIUM OCTANOATE

The ternary surfactant system octylammonium octanoate-octane-water forms a reverse micellar solution phase (microemulsion) in addition to the lamellar liquid crystalline phase. Addition of the ionic surfactant sodium octanoate to the ternary system extends the stability of the solution region toward the water axis. The structure of the solution phase is investigated from the components' self-diffusion coefficients measured by the pulsed-gradient spin-echo FT-NMR method. In the ternary system without the ionic surfactant the measured oil diffusion is rapid and that of water and surfactant is very low; the system consists of water-in-oil type microemulsions. The water and oil diffusion coefficients in the microemulsions containing ionic surfactant are strongly dependent on sample composition, but that of the surfactant is low over the whole solution region. At low water content stable water droplets are present, but at high water concentration, relative self-diffusion coefficients of both water and oil are high and close to each other, indicating the presence of a bicontinuous type microemulsion. The solvation of oil molecules into the micelle is discussed in the light of the two-site and cell diffusion models. © 1991.