Effects of proton exposure on aluminized Teflon FEP film degradation

Aluminized Teflon FEP films have been widely used on the exterior surfaces of spacecrafts. Under the radiation exposure of charged particles in the Earth radiation belt, Teflon FEP film could be deteriorated. In order to reveal the deterioration mechanism, effects of proton radiation on optical properties and microstructure of the Teflon FEP film were investigated. The energy of protons was chosen as 50 keV, and the flux was ϕ = 5 × 1011 cm−2 s−1. The spectral reflectance ρλ of specimens before and after radiation exposure was measured in-situ in the wavelength region of 200-2500 nm. Experimental results showed that the proton exposure resulted in forming an absorption band in the wavelength region of 280-600 nm. XPS analysis demonstrated that the proton bombard went expelled fluorine atoms from the main-chains and activated the macromolecules in the surface layer of the Teflon FEP films, leading to formation of various active radicals and free carbon atoms. Some functional groups were also generated due to the implantation effect of the protons. The in-situ analysis of mass spectroscopy revealed that during the proton irradiation, a large amount of CF3 free radicals were preferentially formed and readily outgassed from the film surface.