Stability of Aqueous Foams in the Presence of Oil: On the Importance of Dispersed vs Solubilized Oil

Abstract

Aqueous foams containing oils are encountered in a variety of processing operations. The present study investigates the influence of both the dispersed and solubilized oils, and the surfactant concentration (above the critical micelle concentration) on the stability of an aqueous foaming system. The oil spreading, entering, and bridging coefficients were calculated based on the measurements of the surface and interfacial tensions. The stability of a foam cell, the coalescence time of an oil drop at the air–liquid interface, and the second virial coefficient of solutions containing solubilized oil were monitored to explain the stability of the aqueous foam. Results showed that the spreading, entering, and bridging coefficients are unable to explain the effects of the type of oil (aliphatic or aromatic) added or the effects of the surfactant concentration on the rate of destabilization of foams. However, good correlations were found between the foaming ability (or inability) of the two types of oil, the surfactant concentration used, the stability of the foam cells containing oil drops, and the change in second virial coefficients.