The Interaction between an Anionic Surfactant and Oily Material at Oil/Water Interface

Abstract

The interaction in an oil-water system between an anionic surfactant and oily materials has been studied by the observation with a polarizing microscope and by the measurement of the interfacial tension at oil/water interface. When dodecane, a non-polar oily material, was gently in contact with SDS solution, no change occurred at the interface. On the other hand, in the case of 1-dodecanol, a polar oily material, spontaneous emulsification occurred in the water phase or liquid crystal formed at the oil/water interface. These were affected by the concentration of SDS in water. In the case of oleic acid, a polar oily material, spontaneous emulsification occurred in the water and/or oil phases, and the liquid crystal formed only at high concentration of SDS in water. The interfacial tension was 3.3 dyn/cm when the liquid crystal formed at the 1-dodecanol/water interface, and that in case of oleic acid was 1.1 dyn/cm. Further, in the case of 1-dodecanol, the composition of the liquid crystal formed at the interface was the same as that of the liquid crystal region in a phase diagram of the ternary system.