HYDROPHOBICITY LOSS AND RECOVERY OF SILICONE HIGH VOLTAGE INSULATION

摘要

Most silicone high voltage insulator materials are based on high-consistency, peroxide/heat-cured PDMS elastomers. It has long been known that their original hydrophobic surface is changed to a hydrophilic surface when exposed to corona discharge and that hydrophobic recovery ensues when the corona treatment is discontinued. A variety of surface characterization studies by ourselves (including the present work) and others, using primarily contact angle and XPS techniques, have established that prolonged exposure to corona results in the formation of a silica-like layer of the order of 10 nm thick. Much the same situation prevails with RF plasma treated PDMS. The extensive cross-linking of the silica-like layer makes it brittle and prone to crack during sample handling and measurement. It also suggests that it cannot readily reorient between hydrophilic and hydrophobic states and we believe that the surface restructuring, chain reorientation mechanism of hydrophobic recovery is unlikely to be important except in cases of light corona oxidation before the silica-like layer develops. In our opinion, diffusion of low molecular weight PDMS components is the key mechanism of hydrophobic recovery. These latest studies of PDMS systems, solvent extracted to be free of diffusible species, also show hydrophobic recovery suggesting that low molecular weight PDMS might be produced in-situ by depolymerization.