MECHANISMS FOR THE INTERACTIONS BETWEEN ACIDIC OILS AND SURFACTANT-ENHANCED ALKALINE-SOLUTIONS

An interfacial activity model has been proposed to predict the equilib rium interfacial tension of acidic oil/surfactant-enhanced alkaline sy stems. The model accounts for a mixed interfacial layer and mixed mice lle formation by the acid, ionized acid, and added surfactant. The mas s action model was adopted for the formation of micelles in conjunctio n with an empirical relationship for the critical micelle concentratio n change. The agreement between model predictions and experiments is s atisfactory and confirms the mechanisms proposed. For the acidic oil/a lkali system, it has been found that the unionized acid adsorbs onto t he interface along with the ionized acid, resulting in lower interfaci al tension, but fails to produce ultralow values because the ionic str ength is not constant as the pH is varied. It has been also found that the acid lowers the interfacial tension of the oil/added surfactant s ystems by simultaneously adsorbing onto the interface and reduces the critical micelle concentration of the added surfactant. (C) 1996 Acade mic Press, Inc.