Study on hydrophobicity transfer of RTV coatings based on a modification of absorption and cohesion theory

Room temperature vulcanized (RTV) silicone rubber coatings are used increasingly on outdoor high voltage (HV) insulators subjected to heavy pollution. An important property of the RTV coatings is the ability to restore the surface hydrophobicity after a pollutant layer has built up on the surface, which can suppress the development of leakage currents, dry band arcing and flashover. The present study analyzes the hydrophobicity and the hydrophobicity transfer of RTV coatings and the factors that affected the hydrophobicity. A modification of absorption and cohesion theory was used to analyze the hydrophobicity transfer mechanisms and the influences of temperature, polydimethylsiloxane (PDMS) molecular weight, degree of cross-linking, extent of soluble and non-soluble components, and the pollutant properties. The hydrophobicity transfer of RTV coatings was also investigated with various conditions of contaminations and various factors, which affect the hydrophobicity transfer, including the composition of RTV coatings and the outside conditions. Results show that the hydrophobicity transfer of RTV coatings is not only dependent on compositions but also on factors of circumstance. The analysis also explains the obvious difference between the hydrophobicity transfer of RTV coatings to kieselguhr and kaolin based on a particle and surface analysis using the Brunauer, Emmett and Teller (BET) method, which explains the relationship between a BET surface area and the hydrophobicity transfer of the RTV coatings. Index Terms--RTV silicone rubber, hydrophobicity, absorption and cohesion.