Ethanol-Based Foam Stability As Probed by Foam Lamella Thinning

In this study, we investigate the stability of the bulk-foam and single-foam lamellae using a mixture of two nonionic surfactants in ethanol-based aqueous solutions. The second virial coefficient, which is indicative of the intermicellar interactions in solutions containing both surfactants and ethanol, was measured. We found a good correlation between the foam stability and the second virial coefficient. Surfactant formulations with a more positive virial coefficient lead to a more stable foam. The foam lamella stability was probed by using the capillary force balance. It was observed that the foam lamella thinned in a stepwise manner (stratified). It was found that, at an optimum surfactant formulation, foam stability was at its maximum when the foam lamella was stable and remained at a high equilibrium thickness with a low rate of thickness transition.