Vacancy spectroscopy of radiation cross-linked and degraded polytetrafluoroethylenes

Polytetrafluoroethylene samples having different morphology were prepared by radiation induced cross-linking and degradation, and positron annihilation lifetimes were measured to extract information about the vacancy structure from the ortho-positronium (o-Ps) component. The o-Ps intensity I-3 was inversely correlated with the crystallinity confirming that this component is associated with the amorphous part. The o-Ps lifetime tau(3) was distinctly different depending on the phase of the polymer. Below the gamma relaxation temperature, the vacancies produced by degradation could be seen from an increase in the tau(3) value, but at temperatures between the gamma and beta relaxations such vacancies became invisible due to the activated segment motion. And above the beta relaxation temperature vacancies in the interface between crystalline and amorphous parts appear to affect tau(3). The o-Ps intensity did not show stable reproducible results. Accumulation of positive charge can be responsible for it. The results, not only unveiling the not yet well understood behavior of the o-Ps component, demonstrate the uniqueness of the vacancy spectroscopy using o-Ps as a probe. Copyright (C) 1996 Elsevier Science Ltd