The origin of the β transition and its influence on physical ageing

Volume dilatometry was used to explore the origin of the β transition ( T β ) and its influence on physical ageing. The results show that volume recovery does occur even at temperatures below T β , a phenomenon indicating the existence of molecular rearrangements and cooperative motions below this point. Lowering the ageing temperatures through T β progressively retards short-term molecular rearrangements and cooperative motions. Nonetheless, the T β quench does not incur any excess free-volume trapping, and its associated change in specific volume follows a linear relationship with respect to temperature. The existence of T β is time-dependent, which leads to the conclusion that the formation of T β has a kinetic origin.