The free volume hole relaxation of polycarbonate (PC) was investigated by using positron annihilation lifetime (PAL) spectroscopy as a function of annealing time at different temperatures (116 �C, 125 �C) below the PC glass transition temperature (Tg ~ 161 �C). A slight decrease of the free volume of ortho-positronium (o-Ps) was observed with increasing aging time, while the o-Ps lifetime remains substantially unchanged, this may be attributed to a decrease in the amount of defects in the process of annealing. Differential scanning calorimetry (DSC) was used to characterize the thermal behavior as a result of aging time, and it is shown that enthalpy of relaxation (DH) has a clear increase with annealing time. The changes in nanostructure caused by annealing below Tg measured by PALS and DSC, seem in general not to be closely related. In conclusion, free volume relaxation appears to occur within minutes at room temperature after annealing even though the bulk thermal history is retained (DH).   is comparison of the fractional free volume (FFV) (top) and enthalpy of relaxation at different temperatures as a function of annealing time.

Experiments to correlate positron annihilation to thermal aging in polycarbonate

248th National Meeting (2014)

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