Dipolar and conductivity relaxations in LiCl–propylene glycol systems

Abstract

The effect of LiCl on the dielectric properties of propylene glycol has been studied both in their glassy and liquid states over a wide frequency range. The data are analyzed in terms of both the complex permittivity ε* and complex electrical modulus M* formalisms. The dielectric and modulus relaxation rates follow a Vogel–Fulcher–Tamman equation, and the dc conductivity follows a non-Arrhenius relation. The data are expressed in terms of a single relaxation time for ionic or protonic conduction process, and an asymmetric distribution of relaxation times for the dipolar process. The two processes which are separate in pure propylene glycol become merged at high LiCl concentrations with an increase in the distribution of relaxation times, which is attributed to ion-pair formation and/or partial breaking of the H-bonded structure of the solvent. The electrical properties of these solutions are adequately described in terms of a formalism for M* that does not assume a nonexponential decay of electric field due to ionic diffusion, and it is maintained that ionic and/or protonic conduction in viscous liquids is Maxwellian in character.