Frumkin’s adsorption model – a successful approach for understanding surfactant adsorption layers

Abstract There are various thermodynamic models to quantitatively describe the adsorption of surfactant molecules at the surface of their aqueous solutions. The Frumkin adsorption model is one of the most successful ones as it provides essential parameters, such as the surface activity of the studied surfactant, the minimal required molecular area at the interface, and the intermolecular interaction in the adsorption layer. Since it was published 100 years ago, the model has served as the starting point for various refinements, such as for molecular reorientations or two-dimensional aggregations at fluid interfaces or as generalized model for the adsorption of surfactant mixtures. Also, the recently developed approach for understanding the cooperativity in the formation of surfactant adsorption layers at water/oil interfaces is based on Frumkin’s model. Due to its clear physical idea, it was successfully applied to quantitatively describe various types of surfactant systems. The values of the three model parameters allow for a categorization of surfactants with respect to their efficient application in numerous technological fields.