BEHAVIOR OF AMORPHOUS POLY(ETHYLENE-TEREPHTHALATE) ANNEALED AT T-LESS-THAN-TG BY THERMALLY STIMULATED CURRENTS

Thermally stimulated current (TSC) discharges in open circuit of amorphous poly(ethylene terephthalate) (PET) corona-charged electrets show a heteropolar relaxation at 87-degrees-C, rho1, between alpha and rho peaks. This relaxation tends to become homopolar when the sample is annealed at temperatures below the glass transition temperature. This is due to the formation of a trapped charge density on the surface of the material that originates, during the TSC discharge, a current that counteracts the one that results in rho1. This trapping effect, which initially is null, increases with annealing due to the rise in resistivity. On the other hand, TSC discharges in short-circuited annealed samples result in a heteropolar peak, rho*, that corresponds to rho1. The area of rho* increases with the annealing time in a bounded way. This peak is related to the formation of thermal nuclei (embryos) in the bulk of the material that act as heterogeneities. This suggests that rho1 is associated with a barrier-type polarization. If the annealed sample is heated to temperatures above the glass transition temperature, the tendency to the inversion of rho1 vanishes and rho* disappears, whereas alpha and rho are modified. This suggests that rho relaxation is related to a Maxwell-Wagner-Sillars effect.