The solvation shell in ionic solutions: variational mean spherical scalingapproximation

The non-specific solvent effects in neutral dipolar (or better yet, effecti ve dipolar) solvents were discussed in the literature with success, However the situation is not so clear when the solvent is an electrolyte, where th e reaction field approach is no longer valid. In the present communication we present a theory based on the Mean Spherical Scaling Approximation in wh ich the system is encapsulated in a ionic cloud that is represented by an e quivalent capacitor of shape determined by precise prescriptions derived fr om exact relations and sum rules. The construction of the equivalent capaci tor 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 s atisfies exact relations like the Stillinger-Lovett sum rules, the perfect screening sum rules, and the high and low coupling conditions and constitut es an interpolation scheme between exact high density and low density limit s in it simplest form. The calculation is illustrated with an example of an ellipsoidal cavity. (C) 1999 Elsevier Science B.V. All rights reserved.