Studies of the effect of temperature on charge accumulation in PVDF-PMMA double-layered thin films based on depolarization current measurements

Abstract

In this paper, we have reported the interpretation of air gap (Thermally Stimulated Depolarization Current) of surface charges in PVDF-PMMA (Polyvinylidene fluoride (PVDF)–Polymethyl methacrylate (PMMA)) double-layered polymer thin films whose decay could not be observed in metalized electrets with short-circuit TSDC. Since short-circuit TSDC is caused by the relaxations of homo- and hetero-charge flow in one direction and thus makes it difficult to identify, separate, and characterize its components, therefore, an air gap was introduced to the short-circuit TSDC technique to carry out air-gap TSDC. This technique enables one to observe the orientation of dipoles, excess charge decay by ohmic conduction, and decay of surface charge. When a dielectric is charged by an application of an external field, two charges with opposite polarity and different nature can be found. Air-gap TSDC’s of double-layer samples revealed the presence of homo charge; charges trapped at the surface are due to dissipation of space charges thus, the depolarization current is observed to have the same polarity as that of the polarization current. Hetero-charge persists at high temperatures due to the bulk polarization formed because of the electric field created by the homo-charge. Hence, the depolarization current observed in the present study was observed to be of opposite polarity as that of polarization current. The above discussed polymeric layered structure was found to be a source of charge trapping which was identified and confirmed by various calculated parameters.