Abstract:

The effects of co-surfactants （CoS）, i.e. alcohols, on the formation of microemulsions were investigated by the pseudo-ternary phase diagram, the oil/water interfacial tension, the physicochemical properties of microemulsions and the analysis of composition and structure of oils. The gel based on a CoS-free olive oil microemulsion was applied for the research and development of the lip gel. The results showed that CoS could improve the interfacial fluidity of microemulsions of different structural oils to avoid gelation and liquid crystallization. For the oils without -OH, the proper proportion of CoS could expand the region of microemulsion. For the oils containing -OH, the oil/water interface might be easy to form intermolecular hydrogen bonds, which reduced interfacial tension and improved the stability of the interface, but the CoS added would compete with the oil/water hydrogen bonding, which was not conducive to the formation of the microemulsion. Taking advantage of the tendency of alcohol-free microemulsions to form gels, a bicontinuous microemulsion of olive oil-vitamin E succinate with a mass ratio of oil phase to surfactant of 4∶6 and a water content of 50% was selected as the carrier. The lip gel obtained, which was stable and safe, had the mean particle size of （28.31±0.45） nm, the viscosity of （27.4±0.632） Pa·s, the pH of 5.70±0.036, and the appearance of pink transparent gel. It was light, hydrated, and easily absorbed.

Key words: microemulsion, co-surfactant, hydroxyl-containing oil, olive oil, lip gel