Surface potential decay of PMMA and POM in air

Perspex (polymethyl methacrylate (PMMA)) and delrin (polyoxymethylene (POM)) are subjected to high voltages and then the surface potential decay is measured using an electrostatic voltmeter. The surface trapping parameters of PMMA are calculated using isothermal current theory and a plot between trap density and energy level is obtained. It is observed that the maximum electron and the hole traps in the surface layer of PMMA are ~1.5 × 1017 eV−1m3 and 0.8 × 1017 eV−1 m3, respectively, and the energy level of its electron and hole traps are in the range of 0.60–0.90 eV and 0.78–0.9 eV, respectively. The introduction of roughness on POM surface leads to an increase in the energy level from 0.55–0.87 eV to 0.55–0.89 eV. It is also observed that there is an increase, both in peak surface potential and time to decay in PMMA as compared to POM. This holds true for positive as well as negative dc voltages and is caused by the charge retentivity in the material resulting from the length of the polymeric chain.