COMPARISON OF THE STRUCTURAL AND ORIENTATIONAL GLASS-TRANSITION DYNAMICS IN ETHANOL

The dynamics of the supercooled-liquid and rotator-phase crystal of th e same material, ethanol, are compared from measurements of the comple x dielectric susceptibility. The relaxation times for the two phases a re Very close and appear to cross at 96 K, the temperature correspondi ng both to the structural glass transition of the supercooled Liquid a nd to the orientational glass transition of the rotator phase. Above 9 6 K, the relaxation time of the supercooled liquid decreases faster th an that of the rotator phase, presumably due to the liberation of addi tional translational degrees of freedom in the former. The dielectric results, coupled with recent specific-heat measurements of the two pha ses, suggest that the rotational degrees of freedom provide the domina nt contribution to structural relaxation near the glass transition, wh ile flow,processes provide a smaller contribution.