Maxwell–Wagner polarization and interfacial charge at the multi-layers of thermoplastic polymers

In this paper, the effect of electrode materials on the formation of the interfacial charge between two dielectrics has been investigated. A sandwich structure constituted by two dielectric films: Low Density Polyethylene (LDPE) and Fluorinated Ethylene Propylene (FEP), was subjected to high DC electric stresses for extended periods of time and space charge measurements were taken using the pulsed electro acoustic (PEA) technique. Aluminum, gold, and carbon black-loaded polyethylene were used as electrodes to investigate the charging behavior of the electrode/dielectric and dielectric/dielectric interfaces. The time dependence of the space charge distribution was subsequently recorded at room temperature under field (polarization) and short circuit conditions (depolarization). Experimental results demonstrated that a charge injected process took place in all cases. However it is shown that the sign and the amount of interfacial charge depend strongly on the nature and the polarity of the electrodes. It is shown that a traditional description of the interfacial charge by Maxwell–Wagner–Sillar effects is not adequate to describe the phenomena of space charge when two non-identical dielectric films constitute the interface. The accumulation of space charge at the dielectric interfaces is controlled by the injection of charge and the processes of generation by dissociation are non-existent.