SYNCHROTRON RADIATION STUDIES OF POLY(TETRAFLUOROETHYLENE) PHOTOCHEMISTRY

Irradiation of poly (tetrafluoroethylene) (PTFE) with monochromatic photons in the energy range 25 eV < hv < 1000 eV protects the surface against alkali etching used to prepare the surface for adhesion. Previous studies have shown that this protection against etching is associated with radiation-induced cross-linking and/or branching. The absence of a true threshold energy behavior (i.e., no energy at which the effect turns on or off) at the C(ls) and F(ls) core levels demonstrates that radiation-induced cross-linking results from low-energy valence excitations. Photon-stimulated desorption (PSD) of neutral fluorocarbon fragments evolved during irradiation have been correlated with the cross-linking kinetics and subsequent etch resistance. Both an increase in the fluorocarbon desorption rate and a decrease in the radiation dose required to achieve a given etch resistance are found for photon energies just above the F(ls) binding energy. These changes result from the increase in the photon absorption coefficient at the core level, suggesting that both experimental observations result from the increased cross-linking in the near-surface region. Simple kinetic models are used to explain both the initial prompt onset and subsequent linear rise in the fluorocarbon PSD profiles. Mechanistic aspects affecting the efficiency of cross-linking and the use of PSD to monitor this near-surface photochemistry are discussed. © 1990, American Chemical Society. All rights reserved.