ABSTRACT
Microemulsions are dispersions of oil and water made with surfactant molecules. In order to explain the spontaneous emulsification of oil and water, they first proposed that the interfacial tensions became negative, thus allowing the free energy to decrease when the oil-water interfacial area is increasing. The process was efficient when the interfacial tensions between the microemulsions and both the oil and the water were very low, below 10-2 dyn/cm. Schulman and co-workers observed that before microemulsion formation the oil-water interfacial tension was below measurable values. A deep minimum of interfacial tension was found for a well-defined number of carbon atoms of the oil. The existence of the minimum in the interfacial tension can be qualitatively understood: it has been shown to be associated with a partition coefficient of the surfactant between oil and water equal to one. Interfacial tension measurements were in good agreement with critical phenomena theory in the whole three-phase region.
