MORE DATA ABOUT DIELECTRIC AND ELECTRET PROPERTIES OF POLY(METHYL METHACRYLATE)

We have used the probe technique together with the thermally stimulate d discharge (TSD) method in order to determine the potential distribut ion V(x) in poly(methyl methacrylate) (PMMA) thermoelectrets polarized at temperatures T-p below the glass transition temperature T-g. We ha ve obtained current-voltage (j-V) characteristics for PMMA at temperat ures T-p < T-g On the basis of the V(x) distribution and some theoreti cal considerations. This characteristic is of sub-ohmic shape, namely j = gV(n), where n < 1 and g = constant. On the basis of the above rel ation, a two-layer condenser (PMMA with one-sided metallized and an ai r gap) was considered as a model for the formation of PMMA thermoelect rets. It follows from this model that the interfacial charge density c hanges nonlinearly with the applied polarizing voltage (V-p) The theor etical results have been compared with experimental data of PMMA therm oelectrets. The problems of the mean real charge depth and the charge decay in these electrets have also been considered. in particular we c an state that the isothermal absorption current, current-voltage chara cteristic and, moreover, charge decay after poling of PMMA and of the PMMA/BaTiO3 composite are interrelated.