Dielectric Spectroscopy of Aqueous Solutions of KCl and CsCl

Abstract

Results of a dielec. relaxation study of the aq. solns. of KCl and CsCl at 25° are reported using measurements with a vector network analyzer (0.2 ≤ ν/GHz ≤ 20) and with waveguide interferometers (27 ≤ ν/GHz ≤ 89). Similar to previously reported data for NaCl, the spectra of both salts are well fitted by a Cole-Cole equation, although a double-Debye model is competitive at intermediate CsCl concns. The impact of the solute on the water structure, reflected in a decrease in the bulk-water relaxation time with rising electrolyte concn., decreases in the sequence NaCl > KCl > CsCl and appears to be proportional to the surface-charge d. of the cation. The interactions of K+ and Cs+ with their hydration shells are too weak to cause irrotational bonding of H2O mols. It is argued that CsCl exhibits weak ion pairing, although the data are not sufficiently accurate to det. the extent of assocn. and the nature of the ion pair formed.