Abstract: A series of microemulsions with various ester contents and emulsifier ratios were prepared by lauric acid polyoxyethylene esters and polyethylene oleic acid diester as emulsifiers and oleic acid ester as an oil phase, and the effect of emulsion concentration on the electrical conductivity and viscosity of the resulting microemulsions was investigated. The results indicated that these microemulsions exhibited a phaseinversion process from oil in water to water in oil with an increase of emulsion concentration. There is a correlation between the electrical conductivity and viscosity as follows: the increase of conductivity up to a stable stage corresponds to the slowly rising stage of viscosity, which results in an oil-in-water (O/W) microemulsion; the drastic decrease in conductivity corresponds to the mutation stage of viscosity, which caused the coexistence of O/W and water-in-oil (W/O) microemulsions; the gradual decrease in conductivity from a low value corresponds to the slow decline stage of viscosity, which leads to a W/O microemulsion. In addition, the viscosity of microemulsions was significantly reduced by polyether-type surfactants in the phase inversion process, and the isomeric polyether alcohol exhibited an optimum reducing effectiveness for viscosity.

Key words: microemulsion, phase transition, electrical conductivity, viscosity