Abstract
Emulsion type is highly related to the phase behavior of surfactant in water and oil. When surfactant forms an aqueous micelle, O/W emulsion is formed. In case that surfactant forms a reverse micelle, W/O emulsion is produced. The O/W emulsion changes to W/O emulsion at HLB temperature or PIT in a water/polyoxyethylene nonionic surfactant/oil system at which the surfactant-layer curvature is zero and a bicontinuous microemulsion coexists with excess water and oil. The effect of type of added oil on the HLB temperature is highly related to the oil influence on the surfactant-layer curvature. We discuss about the penetration or swelling effect of oil or perfume on the surfactant-layer curvature when oil is solubilized in the surfactant aggregates. The correlation between the HLB temperature and the oil effect on the surfactant-layer curvature is also described. When hydrocarbon oil, especially, high-molecular-weight oil is used, the surfactant-layer curvature changes to be more positive. Hence, in the presence of the oil, a discontinuous micellar cubic phase is produced. When excess oil is dispersed in the cubic phase, a highly viscous and gel-like cubic-phase-based emulsion is produced.
