OXYGEN AND VUV IRRADIATION OF POLYMERS: ATOMIC FORCE MICROSCOPY (AFM) AND COMPLEMENTARY STUDIES

摘要

Materials in low earth orbit (LEO) are exposed to the various constituents of the space environment, including atomic oxygen (ATOX) and solar UV radiation. Although the individual interactions of the different irradiations with a variety of materials are relatively understood, the synergistic interactions of several irradiations acting simultaneously are much less so. The present study investigates the effects of oxygen and vacuum UV (VUV) irradiations on polymers commonly used in space applications (Teflon FEP, Tefzel, Tedlar and polyethylene) having different C/F ratio. The VUV source employed was a deuterium lamp with a magnesium fluoride window that provided radiation between 115 and 300 nm. The 50-100 eV oxygen was generated using a Kaufman ion source. Atomic Force Microscopy (AFM) was found to be very powerful in detecting the surface degradation from the very early stages. Very low oxygen or VUV fluxes effects which would have been very difficult to detect using any other surface sensitive technique were observed by AFM. Complementary analytical techniques employed included precise mass loss measurements and XPS (changes in surface composition). Teflon FEP was found to be eroded by both individual oxygen and VUV exposure, while all other polymers were eroded only by oxygen. The synergistic effect of VUV added to oxygen (with respect to the oxygen erosion only) was found negative for PE, null for Tedlar and positive for Tefzal and Teflon. The different mechanisms responsible for the individual and synergistic effects of VUV and oxygen exposure of these polymers were resolved.