Fractal phenomena. Dependence of hydrophobicity on surface appearance and structural features of SIR insulators

This paper reports the study of the dependence of hydrophobicity on the surface appearances and inherent chemical structure of the high-temperature vulcanized silicone rubber (HTVSR) insulator based on the fractal geometric principle. The fractal phenomena link the surface roughness with the hydrophobicity characteristics of silicone rubber (SIR) insulators. The rough surfaces of the insulators, no matter whether due to salt-fog aging or roughening by sandpaper, show the property of a fractal surface. According to the amount of hydrophobic material on the surface, surface roughness exerts different effects on the hydrophobicity of SIR insulators. Due to the behavior of fractal surfaces, the hydrophobicity of the appropriately roughened insulator can be enhanced, but depressed if dipped in hexane. Outdoor polymer insulating materials could be aged by environmental stresses and contaminants so that their surfaces become rough. The permanent change of surface roughness could be an indicator of aging state of the insulation material. The hydrophobicity of SIR insulators aged in salt fog in a fog chamber are investigated. During this aging, the inorganic filler and the hydrophobic groups in SIR are worn away so that the insulator surface becomes rough. The surface of the aged insulator becomes hydrophilic. After a subsequent rest, the hydrophobic polymer liquid in bulk diffuses and migrates to the insulator surface, which becomes more hydrophobic. Such a unique dependency of hydrophobicity on the surface appearance and chemical structure of SIR material is available for SIR insulator to maintain good contamination performances in outdoor applications.