Corona aging and hydrophobicity of surface fluorinated silicone rubbers

We have reported that hydrophobicity of silicone rubber (SIR) can be significantly enhanced by direct fluorination. In this work, surface fluorinated SIR samples, together with the unfluorinated (virgin) ones were corona treated using a multi-needle-to-plate electrode system, to further evaluate corona resistance of the fluorinated SIR layer. ATR-IR analyses suggest that there may be oxidation of the partially fluorinated methyl groups and cleavage of Si-C bonds during the corona treatment, but the cleavage led to formation of Si-F bonds rather than Si-OH bonds. SEM surface and cross section images show that the corona treatment did not change the fluorinated layer thickness, although surface morphology was changed to some degree. In contrast with this, the virgin surface layer was severely degraded or ablated, forming a degraded layer on which aggregates of silica particles and/or degradation products of the SIR matrix material were left. Measurements of water contact angle and surface potential decay further confirm good resistance of the fluorinated layer to corona discharge.

I. Introduction

Silicone rubber (SIR) has many desirable properties and is widely used in industrial and technical fields. For instance, in electrical industry, especially due to its good hydrophobicity and unique hydrophobicity recovery, high temperature vulcanized SIR is the preferred housing material for composite insulators, and room temperature vulcanized one is used as coatings of ceramic and glass insulators to prevent pollution flashover. However, SIR will be aged or degraded by electrical, thermal, environmental, and mechanical stresses, and its hydrophobicity will be decreased. In addition, its recovery ability of the hydrophobicity will be also reduced with the decrease of silicone oil in the bulk by natural washing, constant wetting and discharge activity etc., so that the pollution flashover may occur, especially in the case of heavy pollution and high humidity.