Effects of ions on the dielectric permittivity and relaxation rate and the decoupling of ionic diffusion from dielectric relaxation in supercooled liquid and glassy 1-propanol

Abstract

The effects of intermolecular H bonds on the equilibrium permittivity, ?s, the relaxation rate, fm, and changes in the dielectric relaxation spectra of 1-propanol were studied by adding a strongly dissociating electrolyte LiClO4. The spectra of both 1 mol?% LiClO4 containing 1-propanol (1 molecule of LiClO4 per 99 molecules of 1-propanol), and of pure 1-propanol were measured over a temperature range from ~90?160 K in the frequency range 1 mHz?1 MHz. An analysis of the spectra showed that the three relaxation processes (I, II, and III in ascending rapidity), that occur in the pure alcohol persist in the presence of ions, the equilibrium permittivity, ?s, decreases, the distribution characteristics of the processes changes, and the rate of relaxation, fm, of processes I and III remains constant within analytical errors, while that of process II is reduced. The temperature dependencies of fm,I and fm,II are non-Arrhenius while that of fm,III is Arrhenius. The temperature dependence of the dc conductivity, ?0 is also non-Arrhenius, but the parameters of the fit differ from those of fm,I and are closer to those of fm,II. Its 1000-fold increase on adding 1 mol?% LiClO4 is due to the increase in ion concentration and a decrease in the viscosity as a result of the breaking of H bonds. However, as fm,I and fm,III remain constant on the addition of LiClO4, and fm,II decreases slightly, an expected decrease in viscosity would seem to be unrelated to the relaxation rates of these processes. In that case, ?0 is decoupled from these dipolar relaxation modes.