Interfacial tensions and phase behavior of alcohol-hydrocarbon-water-sodium chloride systems

The phase behavior and interfacial tensions of mixtures of alcohol, alkane, water, and sodium chloride that split into two or three liquid phases at 25�C are reported as a function of type of alcohol and alkane and sodium chloride concentration. The patterns of phase and tension behavior are similar to those observed with surfactant-based microemulsion systems but in a higher tension regime. The qualitative patterns of phase and tension behavior in the alcohol systems appear to be characteristic of all amphiphile-oil-brine systems, although the magnitudes of the interfacial tensions of microemulsion against oil-rich or water-rich phases can be some hundredfold smaller than the corresponding tensions of the alcohol-rich phase against oil-rich or water-rich phases. This difference appears to be a distinguishing feature of microemulsions and presumably arises from the relatively large scale of microemulsion microstructure. Microemulsions in multiphase equilibria incorporate tenfold or more water or oil than do corresponding alcohol solutions, and this argues for the topology and persistence of that microstructure. � 1987 American Chemical Society