Equation of Organic Phase-Water Interfacial Tension in the Presence of Sodium Dodecyl Sulfate (SDS) Surfactant

This study presents a new thermodynamic equation for interfacial tension at the organic phase/water interface in the presence of anionic surfactant. The anionic Sodium Dodecyl Sulfate (SDS) is selected to check the validity of the derived equation. The temperature and pressure from the reference are considered as 25°C and 1atm, respectively. It is shown that the newly derived equation can properly describe the organic phase/water interfacial tension in the presence of a single surfactant. In this study, hydrocarbons including n-heptadecane, n-decane, n-nonane, n-octane, n-hexane, 1-octane, 1-hexene, n-cyclohexane, n-cyclohexene, n-butylbenzene, and benzene are considered as the organic phase. By curve-fitting of the experimental data, the following two parameters are obtained: 1) molar surface area, and 2) bulk-surface distribution coefficient of surfactant. In all cases investigated, errors for the proposed equation of this study are less than one of the latest previous works in the literature. The Mean Squared Error (MSE) ranges for the proposed equation and the previous work are 0.5-5.1 (mN/m)2 and 1.8-23.9 (mN/m)2, respectively. The results show a good agreement with the experimental data in the concentration region below and near the Critical Micelle Concentration (CMC).