Foaming and adsorption behavior of oppositely charged surfactant mixtures

Although the application of liquid foams is widespread, too little is yet understood about stability control. One promising way to tune their properties is the application of oppositely charged surfactant mixtures. These catanionic surfactant mixtures show a strong synergism. This makes them eco-friendly since it allows reducing the required amount of surfactant. Due to the formation of surface active complexes and aggregates the adsorption at liquid-air interfaces is strongly increased [1]. Previous work shows strong impact on thickness and stability of free standing foam films [2]. In general electrostatic interactions between oppositely charged ionic head groups lead to the formation of nonionic surfactant complexes and hence increase adsorption. Surface tension measurements show a strong decrease in critical micelle concentration and lower equilibrium surface tension of such systems which indicates stronger adsorption and a decrease in the minimum molar area of surfactant molecules at the air-water interface. Furthermore, it seems that largest synergism arises for surfactant mixtures similar in chain length.