Aging resistant TiO2/silicone rubber composites

We have recently shown [1,2] that one component room temperature vulcanized (RTV-1) silicone rubbers (SIR) based on polydimethylsiloxane (PDMS) can be rapidly degraded by low voltage (LV) energized aqueous salt solutions by previously unreported aging mechanisms related to the formation of hypochlorous acid in high voltage (HV) transmission line applications. In this study, we are showing how to improve the resistance of the rubbers to extreme environmental aging by embedding TiO2 micro-particles. Molecular dynamics (MD) simulations were conducted to determine the combined effect of TiO2 and different concentrations of hydrophobic PDMS methyl groups on surface hydrophobicity of a TiO2/PDMS composite. In addition, the effects of both TiO2 and silica on the diffusivities of LV aqueous salt components in the PDMS were predicted and related to unique interfacial interactions between the particles and the methyl groups of the PDMS. Rutile TiO2 reoriented methyl groups away from the particles reducing the diffusivities of water and hypochlorous acid. This effect shielded the PDMS network against environmental chain scissions. On the other hand, silica attracted the groups accelerating acid and water migrations and thus enhancing damage to the network. In the experimental part, TiO2/RTV was subjected independently to hypochlorous acid and electrolyzed LV aqueous salt. As expected, TiO2 greatly increased the contact angle, reduced the surface energy and improved the hydrophobicity of the composite, mitigating the negative effect of the reduced concentrations of methyl groups. As a result, aging damage to the rubber was dramatically reduced by about 50% in highly oxidative environments.