Positron annihilation lifetime spectroscopy to study the structural relaxation of PC far below the glass transition temperature

摘要

We report the dynamics of the physical aging of polycarbonate (PC) far below T-g by means of positron annihilation lifetime spectroscopy (PALS). This technique is able to detect the isothermal relaxation of the free volume after rejuvenation above T-g. The isothermal relaxation was done at different temperatures far below T-g and for different aging times. The free volume relaxation results were modeled according to a phenomenological model presented by Struik, so as to obtain the equilibrium relaxation times of the aging process at each aging temperature. The results suggest two possible scenarios for aging far below T-g: a) the relaxation process of PC is dominated by the beta process, although the fast modes of the a process remain present even at the lowest investigated temperature; b) an Arrhenius type process, resulting from cooperative dynamics of several beta processes, determines the aging far below T-g.