Carbonaceous clusters in irradiated polymers as revealed by small angle X-ray scattering and ESR

Abstract

Carbonaceous clusters are supposed to be carriers of electric conductivity in ion-irradiated polymers. They also influence the optical properties of such materials. Several experimental approaches exist to study those clusters, among which is small angle X-ray scattering, SAXS. Results obtained by this technique are presented here. According to them, the clusters result from electronic, and not from collisional energy transfer processes. Two distinctly different cluster types exist — small spherical clusters around 5–7 nm radius, and large-size fractal objects > 100 nm. It appears that the formation of both these types is closely related to the transferred energy density per track and to the degree of track overlapping: apparently small clusters emerge already within single-ion tracks of energetic heavy ions, whereas light ion irradiation requires ion track overlapping to form large-size fractal objects. The latter ones exhibit slightly ellipsoidal shapes, aligned along the ion track direction. Comparison with recent results gained by UV-Vis spectrometry shows that cluster sizes as obtained by SAXS are considerably larger. Possible reasons for this disagreement are discussed. Finally, new results of recent electron spin resonance measurements on irradiated polymers are presented and discussed in the framework of carbonaceous clusters and polymeric conductivity.