Double Layer Forces over Large Potential Ranges as Measured in an Electrochemical Surface Forces Apparatus

Electrodes specifically designed for use in the surface forces apparatus (SFA) were employed to study forces between mica and polycrystalline gold under potential control. This control was achieved by soldering a wire to the gold surface and modifying the chamber of the SFA into a three-electrode cell configuration. The interactions measured were a strong function of the applied electrode potential, being more repulsive as the gold potential was moved toward more negative potentials. Independent force measurements between mica surfaces were done to determine the mica surface potential. The experimental results were compared to Derjaguin−Landau−Verwey−Overbeek (DLVO) predictions of the forces between dissimilar charged surfaces. The long range forces correspond well to DLVO predictions, including evidence of saturation in forces at high applied potentials; forces deviate from theory at short range.