Microemulsions of triglyceride-based oils: The effect of co-oil and salinity on phase diagrams

Microemulsification of triglyceride-based oil is challenging due to the formation of undesirable phases such as macroemulsions, liquid crystals, or sponge phases. This research evaluates the formation of artificial sebum microemulsions using linker molecules, with the addition of co-oil to help enhance sebum solubilization. The microemulsion consists of a lipophilic linker (sorbitan monooleate), a hydrophilic linker (hexylglucocide), a main surfactant (sodium dioctyl sulfosuccinate), a co-oil, and artificial sebum. The effect of adding co-oil to the phase behavior and the microstructure of the resulting microemulsion is described. The effect of several types of co-oil is also studied; the co-oils evaluated here are squalene, squalane, isopropyl myristate, and ethyl laurate. The effect of salinity on the microemulsion phase behavior is also presented. Fish diagrams are obtained by plotting total surfactant/linker concentration as a function of sebum fraction in the oil mixture (co-oil + sebum). Different microemulsion types (Winsor Types I, II, III, and IV) are formed, depending on the total surfactant/linker concentration and the fraction of co-oil in the oil mixture. Winsor Type IV (single-phase) microemulsions are observed at high surfactant/linker concentrations. These single-phase, isotropic, and low-viscous fluids are particularly useful for cleansing and delivery of functional ingredients in skin care products. Salt addition shifts the fish diagram towards more hydrophobic oil systems and higher surfactant/linker concentrations.