Image analysis of hydrophobicity of silicone rubber insulator

Hydrophobicity of a silicone rubber insulator surface was studied by using image data analysis. Effect of water absorption during aging in water and its recovery in air on the hydrophobicity of silicone rubber was measured. Both of the contact angle of distilled water on the sample surface and the hydrophobic surface image of water droplets on the surface were measured. The former was measured parallel (horizontal) to the surface and the latter was measured from vertical direction to the surface. Using CCD camera we digitized the hydrophobic images of the sample surface. The droplets on the surface were made not only distilled water, which had typical surface free energy of 72.8 mN/m, but also colored water and solutions that had lower surface free energies compared to the distilled water. Using these hydrophobic images hydrophobicity class (STRI's HC level) was determined by the observer and then by the image indexes. The latter was such as size distribution and shape factor of the droplets that were measured by image data analysis