EFFECT OF THE ELECTROLYTE ANION ON THE SALINITY CONTRIBUTION TO OPTIMUM FORMULATION OF ANIONIC SURFACTANT MICROEMULSIONS

The anionic surfactant-oil-water-alcohol systems exhibit a microemulsion-excess oil-excess water three-phase behavior when a so-called correlation for optimum formulation is fulfilled by the physicochemical variables. Up to now the contribution of the aqueous phase salinity to this correlation has been limited mostly to the sodium chloride effect. The correlation is extended to most sodium salts from monovalent to tetravalent and to their mixtures. A generalized equivalent salinity is proposed as SNe = 2 SN (1 + Z), where SN is the sodium normality and Z the anion valence. The equivalent salinity is found to be independent of the sodium salt used. The term 2 (1 + Z) is referred to as the "valence activity factor" (VAF); the VAF of a mixture is found to obey a linear mixing rule based on the mole fractions of the salts. © 1990.