Luminescence and color of radiation-modified polytetrafluoroethylene in blocks

Abstract

Spectral-luminescent analysis has shown that γ-irradiation of bulky PTFE samples (blocks) in the range 330–340°C initiates generation of the same optical centers as in thin films. The irradiated samples become fluorescent and acquire a color ranging from light yellow to yellow. The spectral composition of fluorescence and the color of the samples depend on the absorbed dose and the irradiation temperature. The spectrum of fluorescence excited at a wavelength of 313 nm lies within 350–600 nm, and it is determined by various optical emitting centers. The fluorescence and color centers are distributed over the bulk of the samples in different ways. The concentration of optical centers in the near-surface layers of the samples (to a depth of 0.3–1.0 mm, depending on the sample) is higher than that in layers remote from the surface. In the latter layers, the spectral composition of fluorescence is primarily determined by shorter wavelength fluorescence centers. Almost no fluorescence is emitted from the central zone of the sample, and this zone is colorless. It is inferred that the nonuniform distribution of optical centers is related to the concentration gradient of molecular oxygen in the bulk of the samples appearing in the course of their radiation treatment (the inner layers are depleted of oxygen, while the surface layers are enriched in oxygen). New evidence is derived that polyene structures responsible for the fluorescent behavior and color of the modified PTFE are formed in main chains. The structure of these moieties is described by the structural formula ...CF₂-(CF=CF)n-CF₂, where ...n = 4–7.