More data about dielectric and electret properties of poly(methyl methacrylate)

Abstract

We have used the probe technique together with the thermally stimulated discharge (TSD) method in order to determine the potential distribution V(x) in poly(methyl methacrylate) (PMMA) thermoelectrets polarized at temperatures below the glass transition temperature . We have obtained current - voltage (j - V) characteristics for PMMA at temperatures on the basis of the V(x) distribution and some theoretical considerations. This characteristic is of sub-ohmic shape, namely , where n<1 and g= constant. On the basis of the above relation, a two-layer condensor (PMMA with one-sided metallized and an air gap) was considered as a model for the formation of PMMA thermoelectrets. It follows from this model that the interfacial charge density changes nonlinearly with the applied polarizing voltage . The theoretical results have been compared with experimental data of PMMA thermoelectrets. The problems of the mean real charge depth and the charge decay in these electrets have also been considered. In particular we can state that the isothermal absorption current, current - voltage characteristic and, moreover, charge decay after poling of PMMA and of the composite are interrelated.