Comparison of the structural and orientational glass-transition dynamics in ethanol

The dynamics of the supercooled-liquid and rotator-phase crystal of the same material, ethanol, are compared from measurements of the complex dielectric susceptibility. The relaxation times for the two phases are Very close and appear to cross at 96 K, the temperature corresponding both to the structural glass transition of the supercooled Liquid and to the orientational glass transition of the rotator phase. Above 96 K, the relaxation time of the supercooled liquid decreases faster than that of the rotator phase, presumably due to the liberation of additional translational degrees of freedom in the former. The dielectric results, coupled with recent specific-heat measurements of the two phases, suggest that the rotational degrees of freedom provide the dominant contribution to structural relaxation near the glass transition, while flow,processes provide a smaller contribution.