Effect of static charge on hydrophobicity of corona treated glass and silicone rubber surfaces

This paper presents the results obtained from an experiment which was carried out in order to identify a possible correlation between the presence of static charge and the loss of hydrophobicity on partially and highly hydrophobic surfaces (glass and RTV silicone rubber coating, respectively). Glass and RTV silicone rubber coating samples were initially exposed to corona impingement, and subsequent measurements of charge decay and hydrophobicity recovery (contact angle) were taken. Data obtained from such measurements clearly show that as surface charge decay takes place, hydrophobicity is correspondingly recovered. This observation is valid not only for RTV silicone rubber samples, but also for glass samples. In the silicone rubber compound, recovery could be attributed to a mechanism of migration of silicone oil from the bulk of the polymer to the surface, but in glass samples that mechanism can be totally excluded as the likely responsible agent for hydrophobicity recovery. Therefore, a mechanism different from that of silicone oil migration should be determining the trends observed. When a comparison between both calculated and real surface charge decay times was made, a fairly strong agreement was found. As an additional proof for supporting the hypothesis here presented, when the surface and volume resistance characteristics of the original RTV silicone rubber compound were modified and after exposure to corona impingement, its hydrophobic properties remained unaltered.