Investigation on resistance of the fluorinated epoxy surface layer to corona discharge in SF6

Surface fluorinated epoxy samples together with the unfluorinated (virgin) ones were exposed to the SF 6 corona discharge generated by a multi-needle-to-plate electrode system, to investigate the resistance of the fluorinated layer to the corona discharge. SEM observations and ATR-IR analyses show that thickness of the fluorinated layer was not reduced and no clear evidence for the cleavage of C-F bonds by the corona discharge, although it caused surface morphology change due to attack on some weak points in the fluorinated layer, chain scission, and cross-linking reaction. In contrast with this, the virgin surface layer was degraded by the corona exposure in the form of ablation. Measurements of surface potential and water contact angle indicate that the corona discharge reduced surface conduction of the fluorinated sample and rendered the surface conduction insensitive to humidity. On the contrary, the corona exposure led to an increase in surface conduction of the virgin sample, which is sensitive to humidity.