The solvation shell in ionic solutions:: variational mean spherical scaling approximation

The non-specific solvent effects in neutral dipolar (or better yet, effective dipolar) solvents were discussed in the literature with success, However the situation is not so clear when the solvent is an electrolyte, where the reaction field approach is no longer valid. In the present communication we present a theory based on the Mean Spherical Scaling Approximation in which the system is encapsulated in a ionic cloud that is represented by an equivalent capacitor of shape determined by precise prescriptions derived from exact relations and sum rules. The construction of the equivalent capacitor depends on the geometry of the system, on the nature of the solvent and on the nature and concentration of the ions. The treatment proposed here satisfies exact relations like the Stillinger-Lovett sum rules, the perfect screening sum rules, and the high and low coupling conditions and constitutes an interpolation scheme between exact high density and low density limits in it simplest form. The calculation is illustrated with an example of an ellipsoidal cavity. (C) 1999 Elsevier Science B.V. All rights reserved.