Dielectric Relaxation of Rigid Molecules in Supercooled Decalin

Abstract

The equilibrium dielectric permittivity of pure decalin and the dielectric permittivity and loss of dilute solutions of chlorobenzene, bromobenzene, toluene, tetrahydrofuran, 1-fluoronaphthalene, 1-chloronaphthalene, 1-bromonaphthalene, and 1-methylnaphthalene in decalin have been measured from 50 Hz to 100 kHz at several temperatures between −135 and −155°C. The equilibrium dielectric permittivity of solutions shows no significant short-range order tending to align the dipoles preferentially. All the rigid molecules show a broad dispersion region which does not seem to be describable by any simple distribution function. It is shown that the introduction of the solvent as a viscoelastic medium, with frequency-dependent viscosity, can account for the broad dispersion region. An additional region of dielectric absorption at relatively high frequencies appears to be present in all of these solutions. The Arrhenius plots of the relaxation time are nonlinear, with the activation energy increasing from 25 kcal/mole to 70 kcal/mole with decreasing temperature. The relaxation behavior of all these solutions is remarkably similar to the α relaxation in amorphous organic polymers.