Study of effects of space charge in polyethylene by its direct probing

The laser-induced-pressure-pulse technique studies quantitatively the behavior of space charge in unoxidized and oxidized low-density polyethylene (PE) samples whose thicknesses ranged from 25 μm to 1 mm. The distribution of space charge changes with the applied field, temperature, extent of oxidation, and thickness of the samples. It was found that prominent negative space charge was formed near the cathode in oxidized PE, indicating that oxidation enhanced electron injection from the cathode. The amount of the negative charge increased with applied field, which suggests that the electron injection is enhanced by the applied field. The depth of the charge centroid from the cathode became larger with increasing temperature and applied field. This indicates that the effective mobility increases with temperature. The complicated behavior of the space charge suggests that space-charge formation is determined by electron injection from the cathode, transport, trapping, detrapping, and charge exchange at the anode