The boundary tension at water-organic liquid interfaces

Abstract

The reciprocal solubilities of the water-organic liquid systems selected for this study were determined. The aqueous phase was analyzed by means of an interferometer and the organic phase by means of the Karl Fischer reagent. The pendent drop method was used for the determination of the equilibrium values of the surface tensions of organic liquids and of the saturated aqueous phases as also of the interfacial tensions for these systems. The interfacial tensions at water-organic liquid interfaces were found to be a linear function of the log of the "degree of miscibility" of the water with the organic liquids. A close parallelism between the behavior of the interfacial tension in the vicinity of the critical solution temperature and the behavior of the surface tension in the vicinity of the critical temperature was noted. Organic liquids were arbitrarily divided into three groups based upon the lens forming tendency of the liquids. Group I: Organic liquids which form lenses and for which the surface tension of the organic liquid, S2, plus the interfacial tension S23, is greater than the surface tension of water, S3. Group II: Organic liquids which initially spread forming a film over water after which, at equilibrium, a lens having contact angles of appreciable size (for example, angles greater than 10°) is formed. Group III: Organic liquids which form no lenses or at most lenses which have very low angles of contact on water. Antonoff's rule was shown to be valid only when applied to the liquids of Group III.