TOF-SIMS Evidence of Intercalated Molecular Gases and Diffusion-Limited Reaction Kinetics in an α Particle-Irradiated PTFE Matrix

Abstract

The chemical evolution of poly(tetrafluoroethylene) (PTFE) that is brought about by increasing levels of irradiation with alpha particles is accompanied by the emergence and proliferation of functionalized moieties. Families of reaction products specifically identified in the alpha-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 alpha particle-generated radicals may react to form the observed products. Furthermore, we present evidence to suggest that the kinetics of alpha 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 alpha 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 alpha doses in the range of 10(7) to 5 x 10(10) 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 alpha 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 alpha particle irradiation. Chemical images and high-resolution mass spectra were collected in both the positive and negative polarities.

Surface Analysis of Supercapacitor Electrodes After Long-Lasting Constant Current Tests in Organic Electrolyte

“…In the negatively charged ion spectrum, the characteristic peaks of PTFE include C 2 F 5 − (119 m/z). 18,19 In addition to the contaminants generated by electrochemically induced oxidation/reduction processes, common contaminants such as Na + (23m/z), K + (39 m/z), Ca + (40 m/z) and adventitious hydrocarbons in the positive ion spectra and Cl − (from synthesis of (C 2 H 5 ) 3 CH 3 NBF 4 salt) were observed. The positively and negatively charged ion-specific images, are given in Fig.…”

Time-of-flight MeV-SIMS with beam induced secondary electron trigger

“…The signature peaks for positive ion SIMS spectra of PTFE [22] can be seen in both spectra; the expected combinations of C and F ion masses were identified and used for calibration of both spectra separately. Differences in relative peak heights arise from the differing resolution but also from the fact that the two spectra were not taken at the same time and from the same spot of the sample surface.…”

Surface structural changes, surface energy and antiwear properties of polytetrafluoroethylene induced by proton irradiation

“…So far, many techniques have been developed to target specific parts of the modified PTFE, such as incorporation of various fillers into the polymer material [6][7][8][9][10][11][12] and surface modification using charged particle irradiation [13][14][15][16]. Judging from current experimental results, the combination of fillers and polymer material could affect the main body properties of the polymer [11,12].…”