Influence of corona discharge on hydrophobicity of silicone rubber used for outdoor insulation

Abstract

High temperature vulcanized (HTV) silicone rubber (SR) specimens with a clean surface or a surface covered by a contamination layer were exposed to the corona discharge generated by a needle-plate electrode system. Hydrophobicity loss and recovery processes were investigated during and after corona exposure. In addition, physicochemical analyses on the specimens were carried out using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and gas chromatography/mass spectrometry (GC/MS). It was demonstrated that the continuous particle impact from corona discharge can result in physical and chemical damage to the clean SR surface. The side chains and the silicone backbones were destroyed by the simultaneous energy inputs, and the substitution of the hydrophilic hydroxide group by the polar hydrophobic methyl group was considered to be the mechanism responsible for the decay in hydrophobicity of corona-aged SR. After corona exposure, the hydrophobicity of SR returned nearly to its initial level due to the migration of low molecular weight (LMW) polydimethylsiloxane (PDMS) fluid from the bulk material to the aged surface. Meanwhile, the SR surfaces covered by a contamination layer had an inhibiting effect on the hydrophobic loss process. Simultaneously, the loose structure of the contamination layer provided more channels for the migration of LMW PDMS and promoted the hydrophobic recovery process.