DYNAMICS OF EXCESS FREE-VOLUME IN SEMICRYSTALLINE PEEK STUDIED BY POSITRON-ANNIHILATION

The dynamical behavior of the free-volume creation and its relaxation in the amorphous regions of two-phase PEEK were monitored during isothermal crystallization as a function of annealing time up to 60 min at 160-degrees-C (T(g) = 145-degrees-C) by positron annihilation lifetime measurements. The kinetics of the isothermal crystallization was analyzed by the Avrami equation. The development of the relative crystallinity, mean free-volume hole size, and relative free-volume fraction as a function of annealing time were obtained from the observed o-Ps lifetime and intensity using analytical equations derived from a quantum mechanical model. The maximum values of the mean free-volume hole size and the fraction as a function of annealing were observed and were explained in terms of two competing processes, i.e., the creation of the excess free volume at the boundary of the growing crystal spherulite and the relaxation of the excess free volume diffusing into the amorphous region.