Effect of low molecular weight fluid on the surface free energy of an alloy of EPDM/SIR

Ethylene propylene diene rubber (EPDM), silicone rubber (SIR) and their alloys have good performance when used as outdoor insulators. The hydrophobicity of the surface is maintained in wet conditions as a result of diffusion of 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 the alloy of EPDM/SIR used as insulators. The surface free energy of the alloy of EPDM/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 the alloy is estimated to be about 30 mJ/m². The removal of LMW fluid from the surface and migration of the LMW fluid to the surface have influence on the static contact angles of water and methylene iodine, but have a small effect on the surface free energy. It comes from the change in the ratio of two components of the surface free energy due to non-polar dispersive force and polar non-dispersive force.