Dielectric relaxation of aqueous electrolyte solutions. I. Solvent relaxation of 1:2, 2:1, and 2:2 electrolyte solutions

Abstract

Complex permittivity measurements on aq. solns. of CdCl2, CuCl2, MgSO4, CdSO4, Na2SO4, Cd(ClO4)2, and MgCl2 in the frequency range from 0.9 to 90 GHz are reported. The data anal. reveals the superposition of 2 Debye dispersion steps for the solvent thus supporting multi-step relaxation mechanisms discussed for water in the literature. An addnl. low frequency process is found for CdCl2, CuCl2, MgSO4, CdSO4, and Na2SO4 solns. due to solute relaxation, but not for Cd(ClO4)2 and MgCl2 solns. The decrease of the static solvent permittivity at increasing electrolyte concns. is interpreted in terms of irrotational bonding and kinetic depolarization and is used to det. effective solvation nos. The dependence of the main (low frequency) relaxation time of water on electrolyte concn. is explained with the help of the reorientation and residence times of water in the hydration spheres of ions and in the bulk. The high frequency relaxation time is approx. concn. independent, whereas the dispersion amplitude of the process increases with electrolyte concn.