Surface Potential Decay and DC Conductivity of TiO2-based Polyimide Nanocomposite Films

Polymer nanocomposites have attracted wide interest as a method of enhancing polymer properties and extending their applications. Surface potential decay has been used widely as a tool to monitor charge transport and trapping characteristics of insulating materials. Polyimide (PI) as an engineering material has been paid more attention due to high thermal and chemical stability, good mechanical property and excellent insulating property in a wide range of temperature. There has been a lot of work over last few years on optical, thermal and mechanical properties of polyimide nanocomposites. However, little attention has been given to the effect of nano-fillers on charge transport and trapping in polyimide nanocomposites. In the present paper, pure, 1%, 3%, 5% and 7% polyimide nanocomposites was examined by using surface potential decay in conjunction with dc conductivity measurement and both experiments showed that 3% is the optimal value for electrical insulation

Charge transport mechanisms in corona charged polymeric materials

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

Degraded Broadcast Channel with Side Information, Confidential Messages and Noiseless Feedback

In this paper, first, we investigate the model of degraded broadcast channel with side information and confidential messages. This work is from Steinberg's work on the degraded broadcast channel with causal and noncausal side information, and Csisz$\acute{a}$r-K\"{o}rner's work on broadcast channel with confidential messages. Inner and outer bounds on the capacity-equivocation regions are provided for the noncausal and causal cases. Superposition coding and double-binning technique are used in the corresponding achievability proofs. Then, we investigate the degraded broadcast channel with side information, confidential messages and noiseless feedback. The noiseless feedback is from the non-degraded receiver to the channel encoder. Inner and outer bounds on the capacity-equivocation region are provided for the noncausal case, and the capacity-equivocation region is determined for the causal case. Compared with the model without feedback, we find that the noiseless feedback helps to enlarge the inner bounds for both causal and noncausal cases. In the achievability proof of the feedback model, the noiseless feedback is used as a secret key shared by the non-degraded receiver and the transmitter, and therefore, the code construction for the feedback model is a combination of superposition coding, Gel'fand-Pinsker's binning, block Markov coding and Ahlswede-Cai's secret key on the feedback system.Comment: Part of this paper has been accepted by ISIT2012, and this paper is submitted to IEEE Transactions on Information Theor