The Free Energy of the Double Layer of a Colloidal Particle and the Charging Process

Abstract

A detailed analysis is given of the alternative charging processes used by Verwey and Overbeek and the author to determine the free energy associated with the electric double layer of a colloidal particle. A general statistical proof of the equivalence of these methods is obtained. It is shown that the use of the different charging processes is equivalent to assuming an additional, hypothetical, thermodynamic variable to describe the colloidal system; this can be simply interpreted as an arbitrary `chemical' potential of the ions adsorbed on the particle surface. The expression for the free energy derived by Verwey and Overbeek is extended to apply to more general cases, and the treatment by these authors of the so-called chemical energy is clarified.