In situ study of simultaneous adsorption of surfactant at model solid-liquid and liquid-liquid interfaces using the two-liquid contact angle method

A direct method of in situ investigation of adsorption mechanisms at related solid/liquid and liquid/liquid interfaces is presented, based on the two-liquid-phase contact angle measurement. Using a model system represented by a self-assembled monolayer (SAM) surface/hydrocarbon drop/aqueous surfactant solution, it is shown that the method constitutes a simple way to characterize both the dynamic behavior and equilibrium quantities of adsorption. In addition to the consistency of these results with the usual diffusion controlled models, some interesting phenomena such as structural transitions in the adsorbed layer are clearly evidenced from adsorption kinetics.