Comparison of dielectric relaxation and viscoelastic retardation in three viscous liquids

Abstract

The low frequency (10² to 10⁵ Hz) dielectric relaxational behaviour of di-n-butyl phthalate, tri-o-tolyl phosphate and tri-2-chloroethyl phosphate has been studied and one loss process, due to Brownian motions of the molecules, is observed in di-n-butyl phthalate and tri-o-tolyl phosphate. Results for tri-2-chloroethyl phosphate show evidence of bimodal behaviour.

These dielectric loss data are compared with the viscoelastic retardation data at 30 MHz obtained previously by Barlow and Erginsav for the same samples of these materials. For di-n-butyl phthalate and tri-o-tolyl phosphate the Argand diagrams for dielectric relaxation and viscoelastic retardation are very similar for each liquid, suggesting a common mechanism for both processes.

The viscoelastic retardation results are fitted by the empirical Davidson–Cole equation for these two liquids whilst the dielectric relaxation results are fitted better by calculated curves based upon the Williams–Watts empirical relaxation function. It is shown that the defect diffusion stress relaxation functions of Phillips, Barlow and Lamb can be fitted by the Williams–Watts empirical relaxation function with a suitable choice of parameters: these predict, however, a broader dielectric loss curve than is found in practice.