Dynamic surface tension of surfactant systems and its relation to foam formation and liquid film drainage on solid surfaces

Many technological processes for detergency, cosmetics and surface treatment applications often involve surfactant-containing solutions where the surfactant molecules are found in a non-equilibrium state. In this article, we present an analysis of two processes, namely foam formation and drainage of a liquid film from a vertical hard surface, where the dynamics of the surfactant molecules is known to play a major role. We characterize the time behaviour of these non-equilibrium processes by suitable experimental methods over a range of surfactant concentrations and we propose an interpretation of the experimental results based on the Gibbs–Marangoni effect. We also discuss the relation of the present experimental conditions to model calculations of film drainage in the limiting case of an insoluble surfactant. The studied systems contain the non-ionic dodecyl ethoxylate (C12(EO)6) and the anionic dodecyl sulfonate (C12SO3Na) surfactants.