APPLICATION OF PHOTOTHERMAL METHODS TO THE MEASUREMENTS OF GLASS-TRANSITION AND VISCOELASTICITY OF POLYMERS

The glass transition temperature T-g can be identified with a sharp in crease of the thermal expansion coefficient chi. We present photoacous tic and constrained photodeformation measurements of the glass transit ion in polystyrene in conditions of weak optical absorption. Since the thermoelastic contribution to the signal prevails in those conditions , we show both theoretically and experimentally that the signal amplit udes exhibit a sharp increase near T-g, allowing its clear identificat ion and the observation of a viscoelastic behavior.