High frequency permittivity and its use in the investigation of solution properties

Abstract

Recent results from permittivity measurements at microwave to far-infrared frequencies are reported for various liquid electrolyte and non-electrolyte systems. They enlarge our knowledge on processes which produce (by their complex interplay of orientational, intramolecular, kinetic, H-bonding, diffusional and migrational modes) the properties of pure solvents, solvent mixtures and solutions. Protic solvents show three relaxational processes: re-establishment of the perturbed solvent structure, “intramolecular” rotation of solvent molecules as monomers and in H-bonded chains or networks, and very short relaxation times of about 1 ps due to H-bond dynamics. Aprotic solvents display a more or less continuous relaxation time distribution. Solvent mixtures show a particular behaviour related to the properties of their constituents. The addition of salt affects the relaxation times of the solvents, but no new modes are generated by free ions. In contrast, ion pairs and other solute complexes act as dipoles and display specific relaxation processes. Information from high frequency permittivity measurements is used to explanation and calculation of solution properties required by fundamental and applied research. © 1991, IUPAC