Corona ageing of the epoxy nanocomposites surface exhibits a high influence on contact angle of the material. A reduction in corona inception voltage due to water droplet, upon corona ageing, is less with epoxy composites, which has Wollastonite as filler followed with nano-micro silica filler added epoxy composites. Charge accumulation studies indicate that charge retention time drastically reduces with corona aged epoxy composite specimen. Epoxy composites with Wollastonite as filler have shown higher mean charge lifetime. Adoption of laser induced breakdown spectroscopy (LIBS) technique for characterisation of samples is unique. Measure of threshold fluence and plasma temperatures through LIBS studies enables to classify the ageing condition of the composite material. Plasma temperature and threshold fluence are clear indicators to classify different materials. Plasma temperature is also an indicator of the hardness of the material. Epoxy composite with Wollastonite as filler is not affected by laser abrasion, which is in accordance with its superior performance with corona ageing, proving as discharge resistant material.

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Epoxy nanocomposites being used in the high-energy radiation zones as an insulant may undergo changes in their dielectric properties during service. In the present study, the performance of base epoxy resin (S1) is compared with epoxy resin with ion trapping particle (Sample S2) and epoxy resin with nanotitania (Sample S3) particle. The influence of gamma irradiation on nanocomposites was analysed. Corona inception voltage due to water droplet initiated discharge and contact angle reduces post-gamma-ray irradiation. Surface potential decay time constant reduced drastically for gamma-ray-irradiated specimens. Trap distribution characterisation indicated that charge mobility increases after irradiation. The surface roughness of the sample increases with the irradiation dosage. Dielectric relaxation spectroscopy shows that permittivity reduces and loss tangent increases with the gamma-irradiated specimens. Water diffusion rate increases for the gammaray-irradiated specimen. No change in elemental composition, measured using laser-induced breakdown spectroscopy, of test specimens was observed. The hardness of the material and plasma temperature formed during laser shine decreases with gamma-ray irradiation intensity for Sample S1, whereas samples S2 and S3 showed only marginal variation. The performance of Sample S2 is found to be better than Samples S1 and S3.

Corona inception voltage (CIV) due to water droplet on gamma‐irradiated silicone rubber indicates that its value reduces with increase of conductivity and with number of droplet in the electrode gap along the axis of the electrode. Increase in dosage of gamma irradiation to silicone rubber reduces the CIV. The UHF signal generated during corona inception due to water droplet has frequency bandwidth in the range of 0.3–1.2 GHz. The discharges occur in the phase range of 30°–130° in the positive half cycle and about 210°–270° in the negative half cycle. The water droplet shape gets altered on application of voltage. Surface charge accumulation studies indicate characteristic change with gamma irradiated specimen. In the presence of water droplet, the charge decay occurs rapidly with a single droplet and with three droplets. Thermal analysis of gamma radiation dosed samples reveals the destabilization of silicone material and the formation of higher order cyclic siloxane oligomers and oxygenated organics, which are expected to act as potential charge trapping sites. POLYM. ENG. SCI., 59:182–191, 2019. © 2018 Society of Plastics Engineers

In the present study moisture absorption behavior of titania (TiO 2 ) and silica (SiO 2 ) doped room temperature vulcanized (RTV) silicone rubber (SR) nanocomposites immersed in deionized water, aqueous sodium chloride (NaCl) and nitric acid (HNO 3 ) solution was investigated. It is realized that the diffusion coefficient of the material is high with nanocomposites compared to virgin RTV SR material. To understand the surface condition of the material and characteristic variation in material properties water droplet-initiated corona inception voltage measurements, atomic force microscopy study, surface potential variation studies, Fourier transform infrared spectroscopy and thermogravimetric analysis was carried out with the virgin and aqueous solution aged specimens. The discharge resistance of the material was analyzed using corona discharge studies. The level of hydrophobicity variations was analyzed through contact angle measurements. The experimental results confirmed that the performance of TiO 2 doped RTV SR nanocomposites is superior to the SiO 2 doped and virgin RTV SR material.