Influence of Contamination on the Hydrophobic Properties of APPJ-treated Silicone Rubber*

Abstract

Hydrophobicity is the key factor for silicone rubber insulators under polluted and wet conditions. The influence of contamination on the hydrophobic properties of atmospheric pressure plasma jet (APPJ) treated silicone rubber was investigated in this paper. The hydrophobicity properties of silicone rubber were determined by the static contact angles between the droplet of distilled water and the horizontal surface of the silicone rubber. Atmospheric pressure plasma jet was applied to treat silicone rubber with three surface conditions: clean surface, artificially contaminated surface and polluted surface with APPJ pretreatment before contamination. The results showed that clean SR lost its hydrophobicity rapidly under APPJ treatment while subsequent hydrophobicity recovery was comparatively slower. In contrast, polluted SR surface changed from hydrophobic state to hydrophilic state with contact angle of 120° after several seconds APPJ treatment. The hydrophilic property did not deteriorate for a long term. The silicone rubber under the third condition also became hydrophobic after APPJ treatment but the process was slower compared to polluted surface without pretreatment. The surface was examined under scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. SEM and XPS showed clean SR surface became rough while organic surface was destroyed gradually and inorganic layer appeared after long time APPJ treatment. FTIR showed that organic groups appeared on the polluted SR surface, making it hydrophobic.