Modeling hydrophobic recovery of electrically discharged polydimethylsiloxane elastomers.

Theoretical models are proposed to account for the hydrophobic recovery kinetics of electrically discharged silicone elastomers, in which the effects of both the diffusion and adsorption of in situ produced low molecular weight (LMW) species are considered. A homogeneous solid diffusion model or a pore diffusion model well represents the surface restructuring of silicone elastomers exposed to partial electrical discharges. The computed diffusivity of the in situ produced LMW species through an inorganic, silica-like layer to the outermost part of the oxidized polymer is much smaller than that calculated from the absorption experiment of a silicone elastomer. At severe discharge intensity, no significant difference in the hydrophobic recovery is observed for extracted samples and those doped with free dimethylsiloxane fluid, whereas fluorinated siloxane fluid containing samples recover their hydrophobicity faster than the others. Modeling studies indicate that the faster recovery of the later samples may be due to the faster diffusion of the species produced from the fragmentation of the fluorinated siloxane fluid preexisting in the polymer during electrical discharge.