The primary-relaxation process in a supercooled liquid

Dielectric and ultrasonic measurements have been performed in the temperature and in the frequency domain to investigate the a (or primary) relaxation in the supercooled state of a <<fragile>> molecular liquid. This relaxation is strictly connected with the phenomenon of the glass transition and therefore an understanding of the former is a prerequisite for the explanation of the latter. The dynamic susceptibilities relative to these probes have been analysed with the Cole-Davidson function employing (where required) a Vogel-Fulcher-Tamman law to relate the main relaxation time to temperature. The results obtained are consistent with the dynamic behaviour of liquids of high fragility.