Behaviour of amorphous poly(ethylene terephthalate) annealed at T<T
g by thermally stimulated currents |
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Authors: | J Belana M Mudarra J C Canadas P Colomer |
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Affiliation: | (1) Department de Física i Enginyeria Nuclear, Universität Politècnica de Catalunya, C. Colom 11, 08222 Terrassa, Spain;(2) Department de Màquines i Motors Tèrmics/Laboratori de Termodinàmica i Físico-Química, ETS d'Enginyers Industrials de Terrassa, Universität Politècnica de Catalunya, C. Colom 11, 08222 Terrassa, Spain |
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Abstract: | Thermally stimulated current (TSC) discharges in open circuit of amorphous poly(ethylene terephthalate) (PET) corona-charged electrets show a heteropolar relaxation at 87 °C, 1 between and 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 1 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, *, that corresponds to 1 The area of * 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 1 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 1 vanishes and * disappears, whereas and are modified. This suggests that relaxation is related to a Maxwell-Wagner-Sillars effect. |
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