Glassy Dynamics Under Superhigh Pressure

TL;DR

This study reveals the emergence of Johari-Goldstein beta-relaxation in glycerol under superhigh pressure, showing pressure-induced changes in glass transition temperature and fragility, advancing understanding of glass dynamics.

Contribution

The paper demonstrates the appearance of a Johari-Goldstein beta-relaxation in glycerol at pressures above 3 GPa using dielectric spectroscopy, a phenomenon not observed at lower pressures.

Findings

Beta-relaxation appears at P > 3 GPa in glycerol.

Glass transition temperature increases with pressure.

Fragility of glycerol increases under high pressure.

Abstract

Nearly all glass-forming liquids feature, along with the structural alpha-relaxation process, a faster secondary process (beta-relaxation), whose nature belongs to the great mysteries of glass physics. However, for some of these liquids, no well-pronounced secondary relaxation is observed. A prominent example is the archetypical glass-forming liquid glycerol. In the present work, by performing dielectric spectroscopy under superhigh pressures up to 6 GPa, we show that in glycerol a significant secondary relaxation peak appears in the dielectric loss at P > 3 GPa. We identify this beta-relaxation to be of Johari-Goldstein type and discuss its relation to the excess wing. We provide evidence for a smooth but significant increase of glass-transition temperature and fragility on increasing pressure.