The local excess chemical potentials µ ex i (r) in Eq. ( ) accounts for the ionic finite size effects and the electrostatic correlations . Since in this paper we will only consider solutions of low salt concentrations, under 1M, the steric effects can be ignored -except for the formation of the Stern layer at the surface of a nonoparticle. The electrostatic correlations between ions result in ionic repulsion from a neutral hard wall. This can be understood as follows . In the bulk of suspension, ion electric field is screened by the counterion cloud, resulting in a negative electrostatic solvation free energy. Presence of a wall breaks the spherical symmetry of the ionic cloud, diminishing the screening of electric field produced by the ion and, therefore, the magnitude of the (negative) electrostatic solvation free energy. This results in an effective repulsion of ions from a neutral hard wall. For monovalent ions this effect is small and can be neglected, on the other hand for multi-valent ions it becomes significant. The solvation free-energy can be readily computed using Green function formalism (for details, see Appendix A). Neglecting the curvature effects we obtain: