Dielectric and dynamic Kerr-effect studies in liquid systems

Studies have been made of the dielectric relaxation and dynamic Kerr-effect of supercooled fluorenone +o-terphenyl and tri-n-butyl ammonium picrate +o-terphenyl solutions in the frequency range 104 to 10–2 Hz and over a range of temperature. One process, the α process, was observed, and is primarily due to the reorientational motions of the dipolar solute molecules. The dielectric relaxation times τD, and the Kerr-effect decay (relaxation) times τK,d were found to be the same for the fluorenone +o-terphenyl system, being consistent with a “fluctuation-relaxation” model for reorientation, and inconsistent with the small-angle rotational-diffusion model. The same result applies to the ion-pair +o-terphenyl system at the lower temperatures, but as the temperature is raised τD and τK,d become different, with at higher temperature τD∽ 3τK,d being indicative of a small-angle rotational diffusion situation. These data are discussed in terms of models for cooperative reorientation in viscous liquids.