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.