Energy transfer in polymers submitted to ionizing radiation: A review

As a result of the energy deposition of ionizing radiation in organic polymers and in organic compounds in general, excited and ionized species are formed. The latter can readily react with emitted electrons to form excited species that will eventually lead to macromolecular defects and gas emission - their counterpart. Charges from ionized species and excitations can also be transferred, and trapped, far from their creation sites before leading to defects creation. In dense materials submitted to irradiation, excitations, charge transfer or mass transport from one molecule to the other has been proven to happen since the early 1930's in organic molecules mixtures and the 1950's in polymers. Radical stemming from the evolution of the excited molecules, which results either from direct energy deposition by the radiations or from the electron-hole recombination, can also migrate before being trapped or reacting, on a site far from its creation site. Radical, excitation, electron and hole transfers are gathered in the generic term of energy transfer. In this review is presented an overview on the research performed in this field. We evaluate the influence of different parameters that can alter the efficiency of energy transfer: these can be related to the polymer composition (chemical structure of the molecules composing the monomers or the additives inserted in the bulk) or to the irradiation characteristics (radiation type among ionizing radiations, dose and temperature for example). To get rid of the complexity brought by the polymer structure and the existence of different levels of organization, polymers are sometimes modelled by molecules, either pure or as mixtures. To take this into account, some studies on energy transfer in molecule mixtures are also presented.