A 3-DIMENSIONAL LATTICE MODEL OF WATER-MOLECULES WITH AND WITHOUT SOLUTE MOLECULES AGAINST A CHARGED WALL

A three-dimensional lattice model of water molecules against a charged wall is presented, both in the absence and in the presence of nonpolar monomeric solute molecules. To account for water-water interactions, the water molecules are represented as spheres embodying three partial charges. The statistical-mechanical treatment of this model, which does not embody adjustable parameters, is carried out on the basis of Barker's self-consistent field theory [J. A. Barker, J. Chem. Phys. 44, 4212, (1966)]. In the absence of solute molecules, the model provides the interfacial potential difference, the differential capacity, and the entropy surface excess as a function of the charge density sigma- on the wall; the qualitative behavior of these quantities compares favorably with that of the experimental, Gouy-Chapman corrected quantities at the interface between sp metals and aqueous solutions of nonspecifically adsorbed 1-1 valent electrolytes. Generalizing the model so as to include the presence of nonpolar monomeric solute molecules, yields calculated adsorption isotherms, both at constant charge and at constant potential, which compare favorably with the experimental adsorption behavior of simple, monofunctional aliphatic compounds on mercury from aqueous solutions.