ON THE NATURE OF THE SURFACE AGGREGATION IN SURFACTANT ADSORPTION ONTO POLAR SURFACES

At a certain surfactant concentration called "critical" or "hemimicelle" concentration a spontaneous aggregation takes place of surfactant molecules adsorbed onto polar surfaces. In spite of many works which have been published, the nature of that surface aggregation is still not understood well. The aim of this paper is to explore to which extent the concept of 2D condensation can explain the observed features of that surface aggregation. To that purpose the recent theoretical approach by Koopal is generalized to take the surface heterogeneity into account. This is because the surface heterogeneity is believed to be an important factor affecting the surface aggregation. Some striking similarities between the observed features of surface aggregation and the theoretical predictions based on the concept of 2D condensation are found. That concept, however, cannot at the present stage of the theory explain yet the finite tangent of the linear sections in the experimental isotherms corresponding to the surface aggregation.