Stern potential near gold and chromium surfaces in contact with aqueous and alcoholic ammonium salt solutions

Abstract

The repulsive force between two solid surfaces immersed in electrolyte solution is created by overlapping of the electrical double layers adjacent to the solid surfaces when the separation is large enough so that solvation forces can be neglected. When the repulsive force is known, one can calculate the Sternpotential at the solid surfaces. The repulsive interactions in electrolyte solutions were directly measured between two high-grade polished fused silica plates, one planar, the other spherically curved. The surfaces were covered with thin gold or chromium layers and separated by aqueous and alcoholic solutions of NH₄Cl, NH₄Br and NH₄SCN in concentrations 10⁻⁵–10⁻² M. The absolute value of the negative Stern potential derived from the repulsive forces increased when regarding the anions in the order

$${\text{Cl}}^ -< {\text{Br}}^ -< {\text{SCN}}^ - ,$$

in parallel to the strength of specific adsorption.