The effect of ions on the permittivity and dielectric relaxation of an uncrystallizableheptanol

Abstract

Solvation of ions in a liquid tends to reduce the extent of intermolecular hydrogenbonding. This changes the effective dipolar orientation correlation factor,g, in most alcohols and in water, and hence the equilibrium permittivityεs, but not therelaxation time, τ. An increase in temperature has a similar effect onεs, butthe relaxation time also decreases. Here we study the dielectric relaxation spectra of two concentrationsof LiClO4 solutions in 5-methyl-2-hexanol, and compare the findings against those for thepure liquid. We also compare the effect of the ions against that observed ina similar study of 1-propanol (Power et al 2002 J. Chem. Phys. 116 4192).εs decreases by∼7% on adding1 mol% LiClO4 at 173 Kbut increases by ∼12% at 223 K, and there is similar change in the strength of the Debye relaxation process. This mayoccur partly as a result of the changing ion–ion pair equilibrium with temperature. Initial additionof LiClO4 (0.5 mol% solution) increases the dc conductivity,σdc, far more than further addition. The addition of electrolyte also causes the slowest relaxation todepart from the Debye process, but its characteristic relaxation rate does not change. Variation inσdc with τ does not follow the Debye–Stokes–Einstein relation for either the pure liquid or theLiClO4 solutions, which indicates that diffusion of ions does not follow the Brownian diffusion ofmolecules.