Thermally stimulated current studies of Perspex magneto-electrets

Previous studies on magnetoelectrets (ME) of Perspex (polymethylmethacrylate) by Qureshi and Bhatnagar^1–2 have shown that ME samples prepared below the softening temperature (120°C) of the polymer have a positive isocharge accompanied by a slight increase in dielectric constant. At forming temperatures above the softening temperature, contribution of positive idio-charge (positive charge on N-pole facing surface and negative on S-pole facing surface) increases, accompanied by a decrease in dielectric constant. As surface charge decays with time, there is a change in the dielectric constant; a decrease in dielectric constant in the former case and an increase in the later case. The increase in dielectric constant was attributed to the orientation of side chains of the polymer along the field direction. At higher temperatures, these side chains are thought to orient the main chain segments in a direction perpendicular to the direction of the field, thereby causing a decrease in dielectric constant of the ME samples. As the surface charge decays, there is a recovery in the dielectric constant due to the reorientation of the polymer chains.