Charge transport mechanisms in corona charged polymeric materials

Abstract

Polymeric materials have been widely used as an insulator due to their excellent electrical properties, light weight and low cost. Surface potential measurement is one of the simplest and low cost tools to gauge electrical properties of materials. Once charged, the surface charges or surface potential tend to decay over a period of time, and the exact pattern of the decay represents the characteristic of the material. For corona charged sample, it has been observed that the potential of sample with an initial high surface potential decays faster than that with an initial lower surface potential, known as the cross-over phenomenon. Various theories and models have been proposed to explain the phenomenon. The common feature of these models is that they are all based on single charge carrier injection from corona charged surface. With the recent experimental results on comparing different types of ground of corona charged low density polyethylene sample, bipolar charge injection from both electrodes has been verified. Based on this fact, a new model based on bipolar charge injection has been proposed. In this thesis, the detail of the new model was tested both experimentally and numerically. The new simulation results show that several features experimentally observed can be readily revealed using the bipolar charge injection model. More importantly, the modelling can illustrate charge dynamics across the sample and allows one to extract parameters that are associated with material properties. The effect on different charging polarities and charging times were also discussed in the thesis. Additionally, experiments have been done to nano polyimide materials and the results clearly show that adding different amounts of nano-particles can change the material's electrical property.

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