A new molecular thermodynamic model of liquid-liquid interfacial tension

Abstract

• A new molecular thermodynamic model of interfacial tension is derived. • This model yields satisfactory prediction results for interfacial tension. • It doesn't require mutual solubility data for interfacial tension predictions. • This model is simple in implementation and reliable in application. Interfacial tension between water and organic liquids plays an important role in the design and optimization of various processes, such as enhanced oil recovery, the entrapment and migration of non-aqueous phase liquid (NAPL), chemical separation technology (liquid-liquid extraction) relevant to ex-situ hazardous waste remediation and chemical processing. A new molecular thermodynamic approach of monolayer interface model was developed in this work, in which the total interfacial energy includes contributions from the excess interface cohesive energy and excess interface entropy (entropy from partially mixing and entropy from free volume change). The accuracy of this model in the prediction of interfacial tension for water-organic liquid and mercury-nonmetallic liquid systems has been examined with satisfactory results. The investigation results indicates that for water-organic liquid systems, the excess interface entropy term makes considerable contribution (9.5%∼46.6%) to the total interfacial energy, which may result in the interaction parameter of Girifalco and Good model being greater than unity (1.04≤ Φ ≤1.15) for water-alcohols; while for mercury-nonmetallic liquid systems, the contribution to the total interfacial energy from interfacial entropy is negligible (1.2%∼2.7%), the difference in cohesive energy of molecules between the bulk phase and interfacial phase dominates the wetting process. This method doesn't require measured mutual solubility data for interfacial tension predictions, which is simple in implementation and reliable in application.