Effects of AC and DC Corona on the Surface Properties of Silicone Rubber: Characterization by Contact Angle Measurements and XPS High Resolution Scan

This study utilized a multi-needle corona electrode system to investigate the influence of AC and DC coronas on the surface properties of high temperature vulcanized (HTV) silicone rubber. Contact angle measurements and X-ray photoelectron spectroscopy (XPS) analysis were performed to characterize the chemical structure and hydrophobicity changes in state of the silicone rubber surface after corona exposure. The results indicated that the effects of AC corona were greater than that of DC corona, and the effects of negative DC corona were slightly greater than that of positive DC corona. XPS results showed that the C elemental content on the silicone rubber surface decreased, whereas the O elemental content increased. High-resolution scan on Si 2p XPS spectra proved that surface oxidation occurred during corona exposure and caused the high binding energies of Si atoms and silica-like layer. High-resolution C 1s XPS spectra showed that corona exposure destroyed the Si-CH3 groups on the surface. Some C-O and C=O bonds appeared following the corona exposure. High-resolution O 1s XPS spectra confirmed the formation of Si-OH groups and chemically absorbed water, which was ignored in the past research. Chemically absorbed water was detected as one of the essential factors that caused the loss of hydrophobicity of silicone rubber after corona exposure, together with Si-OH groups and silica-like layer.