Adsorption of nonionic surfactants onto polystyrene: Kinetics and reversibility

The reversible adsorption and desorption kinetics of nonionic surfactants a t a hydrophobic surface have been studied by reflectometry. This enables th e measurement of the adsorption isotherm with unprecedented accuracy. It is shown that the adsorption mechanism can be split into three processes. The surface is first covered by single monomers that experience a strong hydro phobic interaction. This is followed by a typically cooperative process lea ding to the formation of surface aggregates. At the saturation level, the s urfactant molecules stagger in the interface such that there is a possible overlap of hydrophilic headgroups with hydrophobic tails. All this informat ion comes directly out of the kinetics that can be modeled in terms of a lo cal equilibrium.