Thermodynamic Investigation of Cationic Surfactants Effect on Oil-Water Interfacial Tension

Multi-phase fluid flow through porous media is strongly dependent on interfacial tension of immiscible fluids. Fluid mechanics will be affected by changing the interfacial tension. This paper describes a new approach to predict the interfacial tension at the oil-water system in the presence of an ionic surfactant. This study equation is based on Butler equation, often used for obtaining surface tension equations at different interfaces. The Debye–Hückel theory is used to determine activity coefficients of surfactant in the bulk phase. Cationic surfactants, including decyl trimethylammonium bromide (C10TAB) and dodecyl trimethylammonium bromide (C12TAB), are used to validate the equation. The new final equation can properly describe the alkane-water interfacial tension in the presence of single surfactant solutions. In this study, alkanes, including hexane, heptane, octane, decane, dodecane, and tetradecane are considered as the oil phase. The following parameters are obtained by curve-fitting: 1- molar surface area, and 2- bulk-surface distribution coefficient of surfactant. The alteration of equation parameters at different alkane-water systems is discussed. The newly developed equation is in a good agreement with the literature experimental data. This approach can be particularly important in the practical use of surfactants for the reduction of oil-water interfacial tension when experimental data are rare.