Interfacial tensions at alkane-aqueous electrolyte interfaces

Abstract

Surface tensions of aqueous electrolytes, and their interfacial tensions against n-dodecane, have been determined at 20°C. The salts studied were LiCl, NaCl, KCl, KBr, NaBr, KI and Na₂SO₄ at concentrations up to about 1 mol kg^–1. For the alkali metal chlorides and Na₂SO₄ the surface and interfacial tension increments are similar for a given electrolyte. The corresponding increments for KBr, NaBr and KI however are found to differ considerably. The results are discussed in terms of both electrostatic theory and dispersion force theory of interfaces. With respect to the latter, it is found that if due allowance is made for the presence of an ion-free layer of water at the interface, an approximate approach in which only a single dominant interaction frequency is considered, gives results in reasonable accord with experiment.