DISTRIBUTION OF REORIENTATIONAL TIMES OF OPTICALLY ANISOTROPIC MOLECULAR LIQUIDS FROM DEPOLARIZED LIGHT-SCATTERING-STUDIES

Several optically anisotropic glass-forming liquids have been studied by depolarized Rayleigh scattering in the region of the alpha relaxati on. These liquids have a fourfold difference in T-g's, a fivefold diff erence in optical anisotropies gamma(eff)(2)'s, and a sevenfold differ ence in hydrodynamic volumes V-h's. The analysis of the distribution o f relaxation times has been carried out using both the raw intensity d ata and the corresponding susceptibility representation of the same da ta. These results are combined with light scattering and dielectric da ta obtained at lower frequencies. Notwithstanding the great difference s in T-g's, gamma(eff)(2)'s, and V-h's, the liquids show that their di stributions of relaxation times from light scattering narrow with incr easing temperature. In some, though not all, liquids, an unbiased anal ysis of the data indicates that the distribution tends to narrow towar ds a single exponential time (Debye) spectrum consistent with the extr apolation of the dielectric relaxation measurements from lower tempera tures. The light-scattering results, consistent with dielectric and sh ear viscosity data, are discussed in their relation to current theoret ical interpretations. (C) 1997 American Institute of Physics.