Effective ionic charges, permittivity and screening length: dressed ion theory applied to 1:2 electrolyte solutions

Abstract

The concept of effective charges of charged particles in electrolyte solutions is discussed and defined in a general and exact way for cases with ‘exponential’ screening. The effective charges thus obtained are equivalent to those used in dressed ion theory (DIT) (Kjellander, R., and Mitchell, D. J., 1992, Chem. Phys. Lett., 200, 76; 1994, J. chem. Phys., 101, 603), which is an exact reformulation of the statistical mechanics of electrolytes, DIT is particularly suited for use in analyses of screening phenomena in electrolytes, and the reasons why it has this property are discussed in some detail. The DIT formalism is applied to obtain effective ionic charges q*, effective permittivity E, and screening length 1/K, of 1:2 aqueous electrolyte solutions in the hypernetted chain approximation. In the limit of infinite dilution q* → the actual charge, E → the permittivity of the solvent and 1/K ˜ the Debye length. The values of these quantities deviate much more from these limiting values compared with similar 1:1 and 2:2 electrolytes, and this is the case even at quite low concentrations.