Two glass transitions in ethanol: a comparative dielectric relaxation study of the supercooled liquid and the plastic crystal

Ethanol is known to form two different kinds of glassy state, namely a structural glass and a glassy crystal, both showing the same glass transition temperature . The molecular dynamics in the different phases (supercooled liquid/plastic crystal) and during the corresponding phase transition is studied by dielectric spectroscopy in the frequency range (30 K-250 K). Extracting the time constant, width parameter and relaxation strength of the main relaxation (the -process), very similar dielectric loss is found in both phases, including also the high-frequency wing. Comparing the temperature dependence of the time constants , the plastic crystal exhibits a less fragile behaviour. Additionally, a secondary relaxation is detected, again essentially the same in the two glassy states. We conclude that the motional mechanisms probed in the plastic crystal and in the supercooled liquid state are very similar.