ON THE EQUIVALENCE OF FREE (1) ENERGY AND PRESSURE PROFILE METHODS FOR DETERMINING THE MECHANICAL-PROPERTIES OF DOUBLE-LAYERS

The thermodynamics of electrified interfaces (electrode\electrolyte an d colloid systems) are re-examined, leading to a quantitative expressi on for the lowering of interfacial tension (surface pressure) due to t he adsorbed ions in terms of hydrostatic and electrostatic contributio ns. Expressions are derived for the variation of these quantities acro ss the double layer. It is shown that the classical expression for the double layer free energy leads to an incorrect result when applied to a double layer with a mobile layer of surface ions. Explicit results are given for a simplified model for the diffuse ionic layer based on a mean-field approximation (Gouy-Chapman theory).