Effective modulation of surface conductivity of epoxy resin insulators by direct fluorination

Epoxy resin samples were surface fluorinated using a F₂/N₂ mixture at different temperatures for the same time. ATR-IR analyses indicate substantial changes in surface chemical composition and structure by the fluorinations. SEM observations show an increase of thickness of the fluorinated layer and a change of its surface morphology with fluorination temperature. Conductivity measurements reveal a large increase in surface conductivity and surface potential measurements consistently show a low initial surface potential and rapid potential decay after corona charging, strongly depending on fluorination temperature and environmental humidity. The initial surface potential was found to decrease dramatically above a critical surface conductivity and almost to zero when surface conductivity increased to 10^-12 S. Surface polarity of the epoxy sample was found to dramatically increase with fluorination temperature. An increase in degree of chain scission with fluorination temperature is considered to be the main cause for the increases of surface conductivity and surface polarity.