Nonionic surfactant systems and surface solubilization of oil at the silica-water interface

The present paper deals with the interfacial behaviour of nonionic surfactant systems at silica studied by ellipsometry. The technique is shown to be an excellent tool for the investigation of the adsorption of surfactants, since it allows fast and non destructive in situ measurements of the mean thickness and the refractive index of thin interfacial films. The independent determination of these properties means that it is possible to obtain information on the surface excess as well as the structure of the adsorbed layer. Few other techniques, if any, allow such measurements with the relevant time-resolution, Ellipsometry measurements are shown to reveal a great deal about how adsorbed surfactant layers are built up and disintegrated with time during adsorption and desorption, respectively. We discuss the behaviour observed for monodisperse polyethylene glycol monoalkyl ether (C(n)E(m)) systems. In addition, new results on the adsorption and desorption of mixed surfactant-surfactant and surfactant-oil systems are presented. The findings from these studies are important for the understanding of the adsorption of polydisperse surfactants and copolymers and the phenomenon of surface solubilisation.