TOF-SIMS evidence of intercalated molecular gases and diffusion-limited reaction kinetics in an α particle-irradiated PTFE matrix

The chemical evolution of poly(tetrafluoroethylene) (PTFE) that is brought about by increasing levels of irradiation with a particles is accompanied by the emergence and proliferation of functionalized moieties. Families of reaction products specifically identified in the α-irradiated polymer matrix include hydride-, hydroxide-, and oxide-functionalized fluorocarbons. The data also indicate the emergence of hydrogen peroxide (H₂O₂) and hydrazine (N₂H₄), but no distinct evidence suggesting the formation of perfluorinated amines, amides, or cyanogens is found. In this article we substantiate the speciation of emergent species and reveal evidence of intercalated molecular gases with which α particle-generated radicals may react to form the observed products. Furthermore, we present evidence to suggest that the kinetics of α particle-induced reaction is limited by the diffusion of radicals within the polymer matrix. That is to say, chemical additives in the polymer matrix are shown to be scavengers of H·, O·, and F· radicals and limit the rates of reaction that produce functionalized fluorocarbon moieties. Above a threshold dose of α particles, the concentration of radicals exceeds that of the scavenger species, and free radical diffusion commences as evidenced by a sudden increase in the yield of reaction products. Samples of PTFE were irradiated to α doses in the range of 10⁷ to 5 × 10¹⁰ rad with 5.5 MeV ⁴He²⁺ ions from a tandem accelerator. Residual gas analysis (RGA) was utilized to monitor the liberation of molecular gases from PTFE during α particle irradiation of samples in vacuum. Static time-of-flight SIMS (TOF-SIMS), equipped with a 20 keV C₆₀ ⁺ source, was employed to probe chemical changes as a function of a particle irradiation. Chemical images and high-resolution mass spectra were collected in both the positive and negative polarities.