Role of antioxidants in swift heavy ion tracks in polypropylene

Using synchrotron-based small angle X-ray scattering, ion tracks created in polypropylene foils with different antioxidant contents were investigated. Tracks were created by irradiation with 197Au, 209Bi, and 132Xe ions of energies 2.2 GeV, 710 MeV, and 160 MeV, respectively. The influence of antioxidant concentration in the polymer foils and aging of the samples on the structure of the ion tracks was explored. Polypropylene foils with high antioxidant content show a cylindrical track structure with a highly damaged core with significant mass loss and a gradual transition to the undamaged material. The size of the ion track can directly be correlated to the energy loss. On the other hand, ion tracks in low antioxidant content polypropylene foils exposed to Au/Bi ions reveal a cylindrical core shell structure with an over-dense shell area and a core region that is less dense than the pristine polymer. Oxygen uptake in the foils by the free radicals produced in the shell during the ion irradiation process was attributed to this structure due to prolonged exposure to ambient atmosphere. An overall mass increase was observed for these samples, consistent with the SAXS measurements and additional oxidation in a damaged halo produced by tracks.