DISTRIBUTION OF IONS IN SUBSURFACE LAYERS OF LIQUID SOLUTIONS STUDIED BY ARXPS

A numerical method for generating depth concentration profiles on the basis of angular resolved XPS data has been applied to the study of a classical physico-chemical phenomenon, i.e. the formation of electric double layers in fatty acid salts solutions in polar liquids. Results from investigations of solutions of potassium octanoate in formamide and ethylene glycol are presented. The characteristic features of a double layer structure are confirmed from the calculations, with a strongly segregated anion overlayer and an underlying mainly diffuse cation distribution in the subsurface layers. At higher bulk concentrations evidence is found for the formation of contact pairing in the uppermost surface layer.