Relaxation of Polystyrene near the Glass Transition Temperature Studied by Acoustic Measurements

Two kinds of acoustic experiments have been carried out for polystyrene. An ultrasonic experiment was performed to determine the velocity and attenuation of sound from room temperature up to and slightly above the glass transition temperature T g . Megahertz-frequency longitudinal and transverse sound waves and the pulse echo method were used in the experiment. An anomaly of the sound wave velocity is observed near T g ; the sound attenuation increases very rapidly. A Brillouin scattering experiment in the right-angle geometry was performed in the same temperature range. The longitudinal acoustic mode of the scattered line was mainly observed. The Brillouin line shift shows an anomaly near T g ; the width of the scattered line and the inverse of the line intensity increase very rapidly near and above T g . These rapid increases were considered to be due to a thermal-activation-type relaxation, and the experimental results were explained by considering the mechanism of viscosity relaxation based on the Max...