The glass transition beyond the time trap: Opto-acoustic dispersion

High-resolution Brillouin spectroscopy has been used as a crucial experimental technique to investigate the nature of the thermal glass transition in an epoxy. In order to study the coupling between the α-relaxation process and the thermal glass transition around the quasi-static glass transition temperature T g we introduce the opto-acoustic dispersion function as a very sensitive measure of the α-relaxations and show that close to but above T g the related relaxation spectrum still contains components within the microwave frequency region which finally is truncated by the thermal glass transition.