Distribution of reorientational times of optically anisotropic molecular liquids from depolarized light-scattering studies

Abstract

Several optically anisotropic glass-forming liquids have been studied by depolarized Rayleigh scattering in the region of the a relaxation. These liquids have a fourfold difference in Tg's, a fivefold difference in optical anisotropies γeff2's, and a sevenfold difference in hydrodynamic volumes Vh,'s. The analysis of the distribution of relaxation times has been carried out using both the raw intensity data and the corresponding susceptibility representation of the same data. These results are combined with light scattering and dielectric data obtained at lower frequencies. Notwithstanding the great differences in Tg's, γeff2's, and Vh's, the liquids show that their distributions of relaxation times from light scattering narrow with increasing temperature. In some, though not all, liquids, an unbiased analysis of the data indicates that the distribution tends to narrow towards a single exponential time (Debye) spectrum consistent with the extrapolation of the dielectric relaxation measurements from lower temperatures. The light-scattering results, consistent with dielectric and shear viscosity data, are discussed in their relation to current theoretical interpretations. © 1997 American Institute of Physics.