Films at oil-water interfaces. I

Abstract

A number of methods of measuring interfacial tensions between two liquids are compared, and it is concluded that the “sessile bubble” is most convenient and trustworthy. For systems where the interface does not age appreciably the drop-volume method gives results in agreement to within ±0.2 dyne/cm. with the sessile bubble method. The interfacial tension of benzene solutions of a number of alcohols and acids against conductivity water at 23°C. have been determined, together with the freezing points of the solutions. The Traube rule does not apply at the benzene-water interface, from which it is concluded that the molecules in an expanded film are not oriented parallel to the interface. From calculations of the adsorption at the interface, force-area curves are deduced for the adsorbed film. The fatty acids give curves with a transition point similar to those obtained with myristic acid on water at 25°C. and, at the highest pressure used, occupy an area of about 40 Å 2. The alcohols appear to be more condensed in the surface film than the corresponding acids, and close pack to an area of about 20 Å 2.