Effect of low molecular weight fluid on the hydrophobicity of silicone rubber

Silicone rubber (SIR) has good performance when used in outdoor insulators. The hydrophobicity of the surface is maintained in wet conditions as a result of the diffusion of the low molecular weight (LMW) fluid from the bulk to the surface. The amount of LMW fluid on the surface and in the bulk of the material determines the hydrophobicity during the lifetime of SIR used in insulators. The surface free energy of SIR is determined using the harmonic-mean method by measuring the static contact angles of water and methylene iodine. The surface free energy of the cleaned surface of SIR is estimated to be about 26 mJ/m². The removal of LMW fluid from the surface hardly has influence on the static contact angles of water but has influence on that of methylene iodine. It comes from the change in polar non-dispersive force and little change in non-polar dispersive force. It is concluded that the natural surface of SIR is a mixed condition of SIR and LMW fluid molecules. This is due to the compatibility of SIR and LMW fluid molecules.