Stability and thinning behaviour of aqueous foam films containing fluorocarbon and hydrocarbon surfactant mixtures

Abstract

The stability and thinning behaviour of the liquid foam film containing fluorocarbon and hydrocarbon surfactant mixtures were investigated quantitatively by using the optical interferometry technique. Multiscale characterization methods were employed to study the relationships between foam stability, film thinning behaviour, and bulk and interfacial properties. The results show that the liquid film from the SDS solution is unstable with rapid marginal regeneration. Adding fluorocarbon surfactant FC1157 can significantly enhance film stability and slow down liquid drainage rates of the liquid film. For the SDS film with mobile surfaces, the film thinning process follows a power-law behaviour and the thinning exponent becomes less negative by increasing FC1157 concentrations. At very high FC1157 concentrations, the film surface becomes relatively immobile and the thicknesses profile is close to the theoretical prediction of a rigid film. It should be emphasized that the bulk aggregation and surface adsorption behaviours of surfactants affect the thinning rate and stability of the liquid film. Large aggregates assembled from FC1157 molecules produce a viscous solution that offers high resistance to liquid motion. Due to low compression velocities at the film border, the film containing SDS/FC1157 mixtures with relatively immobile surfaces has larger marginal regeneration wavelengths than that of the mobile film stabilized by SDS alone. In addition, foam stability results indicate that there is a qualitative relationship between the macroscale foam and microscale single film in terms of their lifetime.