Study of space charge relaxation in PMMA at high temperatures by dynamic electrical analysis

Dynamic electrical analysis shows that at high temperatures (above the glass transition temperature), the electrical properties of polymethyl methacrylate are strongly influenced by space charge. In this paper we present an study of space charge in this material and its conductive properties by dynamic electrical analysis, using the electric modulus formalism. The complex part of the electric modulus was fitted to Coelho's model, which considers ohmic conductivity and diffusion as the prevailing mechanisms of charge transport. The complex part of the electric modulus exhibits a peak in the low frequency range that can be associated with space charge and a good agreement between experimental and calculated data is observed after the fitting process to the Coelho's model. The data obtained indicate that the electrode is partially blocked. The conductivity determined is thermally activated and it increases with the temperature due to an increasing mobility, that is also thermally activated. (C) 2000 Elsevier Science Ltd. All rights reserved.