PHYSICOCHEMICAL MODIFICATIONS INDUCED IN POLYMERS BY SWIFT HEAVY-IONS

We have studied the effects of dense electronic excitations on the physico-chemical modifications of polymers by performing heavy ion irradiations in the energy range of some MeV amu-1. The effects induced by swift heavy ion irradiations were compared to those induced by MeV electron irradiations performed in similar experimental conditions in polyethylene and poly(vinylidene difluoride) films. The irradiated samples were analysed ex situ by means of Fourier transform infrared spectroscopy in the transmission mode High electronic stopping power, (dE/dx)e, irradiations are characterised by a significant increase of the yield of chain scission. Vinyl terminal unsaturations are recorded with radiochemical yields increasing markedly as (dE/dx)e increases. Moreover, characteristic bands of alkyne terminal groups were observed only above a threshold of (dE/dx)e. The overall set of results is analysed taking into account the radial dose deposition predicted by numerical calculations and the defect creation measured after electron irradiations. This allows us to elucidate the kind of chemical modifications influenced by the local dose rate; i.e. for which a specific effect due to a dense electronic excitation appears.