Transfer and State Changes of Fluorine at Polytetrafluoroethylene/Titania Boundaries by Mechanical Stressing and Thermal Annealing
Fluorine in polytetrafluoroethylene (PTFE) changes its states and transfers to titania by comilling and annealing of a titania-PTFE mixture. XPS, F-19 MAS NMR, FT-IR. Raman spectra, TEM and EDX analyses consistently indicated the oxidative decomposition of PTFE, inducing partial fluorination of titania. Incorporation of fluorine into titania was unambiguously confirmed by the appearance of a new XPS F1s peak at similar to 685 eV, similar to those observed from TiOF2. The intensity of the new F1s peak increased with comilling time and became a sole peak after milling for 3 h. At the same time, F-19 MAS NMR lines specific to PTFE disappeared. From these observations, we concluded that extensive decomposition of PTFE with simultaneous change in the chemical states of fluorine took place with the aid of titania. Upon annealing the comilled mixture in air, the amount of fluorine in the mixture decreased with increasing temperature, while the remaining fluorine migrated into the titania lattice, as confirmed by the decrease in the chemical shift of the F-19 MAS NMR lines and the decrease in the rutile (211) and (220) interplanar distances. These findings allow us to devise how to control the amount, states, and spatial distribution of the fluorine incorporated into titania.