Impact of interface between polyethylene and surface fluorinated polyethylene on space charge accumulation in the layered structures

Polyethylene (PE) plates were surface fluorinated in a laboratory vessel using a F₂/N₂ mixture at 95 °C and 0.1 MPa for 60 minutes. Attenuated total reflection infrared analysis and scanning electron microscopy cross-section observation indicated a substantial change in chemical composition of the plate surface layer by the fluorination and a formation of 0.70 μm thick fluorinated layer. Space charge measurements on the surface fluorinated plate sample and on a layered sample consisting of a PE film and the surface fluorinated plate revealed that the fluorinated layer at the semicon electrode interface can effectively block the charge injection, and the fluorinated layer at the film/surface fluorinated plate interface also has an obvious blocking effect on charge transport from the film into the plate, although not as significantly as the former. As a result, there is only limited space charge accumulation in the surface fluorinated plate of the layered sample, mainly in the vicinity of the dielectric interface, during the 1440 minutes poling at 50 kV/mm dc and 40 °C. In addition, the results also indicated that charges can be injected from the semicon electrode into the PE so long as the electric field at the electrode interface is nonzero. This can explain a significant charge accumulation observed at the film/surface fluorinated plate interface just after the dc field was applied.