Direct observation of electric double layers at solution surfaces by means of electron spectroscopy

Solutions of fatty acid potassium salts in formamide have been investigated using electron spectroscopy in the angular resolved mode. The variable surface sensitivity thus achieved allows details of the electric double layers formed at the solution surfaces to be investigated. The cation distribution is found to vary as a function of solution concentration. The simple diffuse layer theory based on the Poisson–Boltzmann equations is found inadequate in describing the observed features. The data suggest that structural changes occur at the higher concentrations forming closer bound cation states at the surface. These findings qualitatively confirm recent theoretical model predictions by other workers.