Characteristics and electrical properties of epoxy resin surface layers fluorinated at different temperatures

Epoxy resin sheets were surface fluorinated in a laboratory vessel using a F2/N2 mixture with 12.5% F2 by volume at the different temperatures of 25, 55, 75, and 95 °C for the same time of 30 min, to investigate the effect of fluorination temperature on surface electrical properties. ATR-IR analyses indicate that fluorination led to substantial changes in surface chemical composition and structure, depending on fluorination temperature, and SEM surface and cross section images show an evolution of surface morphology and an increase of thickness of the fluorinated layer with fluorination temperature. Conductivity measurements reveal that the surface fluorinated samples have higher surface conductivities than the unfluorinated sample, and surface conductivity significantly increases with fluorination temperature. Surface potential measurements, performed about 10 s after corona charging, indicate lower initial surface potentials for the surface fluorinated samples than the unfluorinated sample, and a decrease of the initial surface potential with surface conductivity. The initial surface potential was found to decrease dramatically above a critical surface conductivity (3.0×10^-14 S), and almost to zero when surface conductivity increased to 10^-12 S. Contact angle measurements and surface energy calculations show a much higher surface polarity of the surface fluorinated samples compared to the unfluorinated sample and a dramatic increase of the surface polarity with fluorination temperature. An increase in degree of chain scission is considered to be the main cause for the increases of surface conductivity and surface polarity with fluorination temperature.