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

The effects of intermolecular H bonds on the equilibrium permittivity, es , the relaxation rate, f m , 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, es , decreases, the distribution characteristics of the processes changes, and the rate of relaxation, f m , of processes I and III remains constant within analytical errors, while that of process II is reduced. The temperature dependencies of f m ,I and f m ,II are non-Arrhenius while that of f m ,III is Arrhenius. The temperature dependence of the dc conductivity, s0 is also non-Arrhenius, but the parameters of the fit differ from those of f m ,I and are closer to those of f m ,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 f m ,I and f m ,III remain constant on the addition of LiClO4 , and f m ,II decreases slightly, an expected decrease in viscosity would seem to be unrelated to the relaxation rates of these processes. In that case, s0 is decoupled from these dipolar relaxation modes. © 2002 American Institute of Physics. @DOI: 10.1063/1.1448289#