Relationships between the nature of traps and dielectric properties of polymers obtained from mirror measurements

In the field of space charge physics, the nature of traps and their role on charge effect and breakdown properties have not been well-established. In this paper, the contribution of “physical” and “chemical” defects on the trapping and detrapping properties of perfectly defined polymers is reported. First, the effects of “physical” traps, i.e. crystallinity ratio changes have been studied. Second, the effects of “chemical” traps, i.e. oxidised sites have been investigated. These latter defects have been created by UV irradiation resulting in a partial oxidation of polyethylene chain without morphological changes. The concentration of oxidised species has been evaluated using FTIR spectroscopy. The trapping ability and the traps depth of sample were studied using the Mirror-Image method. This technique allows us to study the trapping and detrapping properties of dielectric materials. Indeed, charging conditions can be perfectly controlled and modulated without using electrodes. This study demonstrates that the charging capacity of polymers is correlated to the crystallinity ratio. Secondly, it appears that oxidation strongly affects traps characteristics as seen by Mirror-Image method. Therefore, this study provides a better understanding of traps in polymers and their effects on space charge behaviour