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

Complex permittivity measurements on aqueous solutions of CdCl 2 , CuCl 2 , MgSO 4 , CdSO 4 , Na 2 SO 4 , Cd(ClO 4 ) 2 , and MgCl 2 in the frequency range from 0.9 to 90 GHz are reported. The data analysis reveals the superposition of 2 Debye dispersion steps for the solvent thus supporting multi‐step relaxation mechanisms discussed for water in the literature. An additional low frequency process is found for CdCl 2 , CuCl 2 , MgSO 4 , CdSO 4 , and Na 2 SO 4 solutions due to solute relaxation, but not for Cd(ClO 4 ) 2 and MgCl 2 solutions. – The decrease of the static solvent permittivity at increasing electrolyte concentrations is interpreted in terms of irrotational bonding and kinetic depolarization and is used to determine effective solvation numbers. The dependence of the main (low frequency) relaxation time of water on electrolyte concentration 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 approximately concentration independent, whereas the dispersion amplitude of the process increases with electrolyte concentration.