Abstract
Phase transition from a positive to negative-curved self-organized structure was noted to occur in a binary water/polyoxyethylene-type nonionic surfactant system with decrease in the number of ethyleneoxide (EO) units at constant temperature. Effective cross sectional area per each surfactant decreased with reduction in the EO chain length. The mechanism for phase transition is discussed based on the revised packing parameter theory. The effects of oil type on the surfactant layer curvature are explained as due to penetration and/or swelling of oil. Due to the oil effect, surfactant changes from water- to oil-soluble in a narrow range of temperature or EO-chain length in the presence of oil. This is the reason for the appearance of HLB temperature or PIT in water-oil system.
