Effect of AC corona discharge on hydrophobic properties of silicone rubber nanocomposites

In wet conditions, corona discharges may occur on composite insulator surfaces of well-designed power transmission equipment. Corona exposure gradually reduces the surface hydrophobicity and degrades the polymer surface. Recently, much attention has been paid on improvement of corona surface resistance by dispersing nanofillers in the base polymer. This paper presents experimental investigations to understand how silica filler loading can affect hydrophobic properties of RTV silicone rubber nanocomposites under AC corona discharge. Nano precipitated SiO₂ with size of ~20 nm was used as filler. Silicone rubber nanocomposites with different nano SiO₂ loading by weight were fabricated using mechanical stirring and ultrasonic water bath methods. A point-to-plane electrode geometry housed in a glass chamber was used to produce corona discharge at standard atmospheric pressure. The nanocomposite samples were placed between the electrodes, in direct contact with the plane electrode (ground) but separate from the point electrode by a fixed 5 mm air gap. The changes in hydrophobicity of test samples as a function of corona exposure time were determined by measuring the water static contact angle with a goniometer. The surface free energies of nanocomposite samples were calculated by considering the static contact angles of water and diiodomethane in relation to corona exposure duration. The surface morphology of nanocomposite samples was also studied by means of Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM).