Investigation of the electric charge structure and the dielectric permittivity at surfaces of solutions containing ionic surfactants

We introduce a new method for the elucidation of the electrical properties of surfaces of liquids containing surface-active salts. The approach combines two different techniques. Neutral impact collision ion scattering spectroscopy (NICISS) provides an insight into the ion distribution near the surface on a microscopic scale. On the other hand, the electrical surface potential is measured with a Kelvin probe. The results of both methods are combined to get information about the dielectric properties in the surface layer. The estimated dielectric permittivities are considerably lower than those in the bulk of the solution. The measurements have been carried out in the polar solvent formamide which contains surface-active tetrabutyl-onium salts with different anions. These salts are of interest as phase-transfer catalysts in organic synthesis.