The behaviour of mixed hydrocarbon-fluorocarbon surface active agents at the air-water interface

Abstract

The behaviour of binary mixtures of ammonium perfluorooctanoate with ammonium octanoate, ammonium decanoate and ammonium dodecanoate at the air-water interface has been investigated in detail by surface tension measurements. These were carried out both below and above the critical micelle concentration for mixtures containing mole fractions of the alkanoate ranging from zero to unity. It was found that the lowest surface tensions (∼ 15 mN m⁻¹) were obtained in the mixture with ammonium octanoate. The variation of the critical micelle concentrations of the mixtures with mole fraction was found to be non-ideal and in the case of ammonium perfluorooctanoate — ammonium dodecanoate was strongly indicative of independent micellisation.