Reversals in Electrical Current and Other Anomalies in Insulating Polymers

The literature on anomalous currents in polymers has been assembled. The effects have been classified into isothermal decay reversals, reversals in thermally stimulated depolarization, abnormal charging curves, oscillations, and other effects. It has not been possible to identify the conditions which lead to unusual behavior, owing to the disparate nature of the available experimental work. The models for these effects include space charge relaxation with detrapping, ionic drift and temperature dependence of the dielectric permittivity. Each model explains a large part of the effects within its range of applicability. However, several of the charge transport models are based on inconsistent assumptions, and invoke blocking effects at electrodes, for which there is little independent confirmation. It is noted that many of the experiments may be vitiated by artefacts such as imperfect conditioning and inadequate time delays for equilibration. It is recommended that careful sample preparation, rigorous tests of conditioning, and monitoring of charge location should be routinely employed.