A simple method to estimate the dynamic surface pressure of surfactant mixtures

The exact description of the adsorption kinetics for surfactant mixtures is possible when the co-adsorbing species follow the same adsorption model. In general cases, the equilibrium state can be understood only by an approximate model so that the simulation of the adsorption kinetics process requires some special assumptions. Based on a diffusional mechanism, we discuss the adsorption of surfactant mixtures and present a procedure which allows a sufficiently accurate determination of the competitive adsorption process of two surfactants via the characteristic parameters of the single components. A correction involved in the simplified model becomes necessary due to differences in the subsurface concentration for each components adsorbing alone or in competition. The results are compared with experimental data for homologous alkyl dimethyl phosphine oxides.