Aliphatic/Aromatic Systems under Irradiation: Influence of the Irradiation Temperature and of the Molecular Organization

Abstract

With the aim of understanding the electronic excitation, charge or reactive species transfers occurring during irradiation, we studied the role of the aromatic content on ethylene/styrene random copolymers (PES) and on cyclohexane/benzene glasses (amorphous organic solids). Radiation-induced modifications were monitored in situ, at the molecular level, using Fourier transform infrared spectroscopy (FTIR). Irradiations were performed under a vacuum, and thanks to in situ measurements, oxidation was avoided. We followed both the C═C bond creation in the aliphatic moiety and the destruction of the aromatic moiety. The influence of the irradiation temperature was investigated by irradiating samples at room temperature and at 11 K. At such a low temperature, long-range migration hardly occurs and its influence is considerably reduced or could even vanish. Therefore, low temperature irradiation gives insight on the relative influence of reactive species transport and electronic excitation and charge transport. We found that the effect of lowering the PES irradiation temperature from room temperature to 11 K is small, indicating a minor role for the reactive species transport. Moreover, the two chosen systems allow the examination of the relative magnitude of intra- and intermolecular transfers. We demonstrate that, under conditions where reactive species are almost frozen, intermolecular transfers are very efficient.

Electronic irradiation ageing in the vicinity of glass transition temperature for PEEK space applications

“…In the literature, several studies report the influence of temperature on radiative ageing [6][7][8].…”

Radio-Oxidation Ageing of XLPE Containing Different Additives and Filler: Effect on the Gases Emission and Consumption

“…This result was attempted because the formation of hydrogen is faster than the formation of peroxide radicals and, thus, of hydroperoxydes, on which antioxidants act. Nonetheless, Irganox 1076 contains an aromatic ring, an efficient energy sink [ 36 , 37 , 38 , 39 ], and no effect was observed. This implied that the Irganox 1076 concentration was not sufficient to give an efficient radiation protection effect in regards to the energy transfer and primary mechanisms.…”

Energy migration effect on the formation mechanism of different unsaturations in ethylene/styrene random copolymers

“…This article is a complement to a previous paper [8]. The objective is now to evaluate on unsaturated groups other than trans-vinylenes, the effect of the presence of aromatic rings in the polymer.…”

“…At the end of the 70's, first reviews devoted to these energy transfers were published, describing more precisely the phenomena embedded in the mechanisms, as for instance those of Forster and Dexter [7]. More recently, we have initiated a systematic study of the impact of excitons and/or radical migration [8][9][10][11] on the radiation behavior of polymers and solid hydrocarbons. The term energy transfers used in this work is wide and includes the mass or reactive species transport (including radicals and ions), lone charge transfers (electrons and holes), and electronic excitation transfers.…”

“…The lower the concentration, the higher the effect per protection unit and the faster their degradation. We have already shown in a previous article [8], by irradiating ethylene/styrene copolymers at different temperatures, that the presence of styrene protects the ethylene moiety, at room temperature (RT) but also at 11 K. At 11 K, it has been supposed that almost all radicals are frozen and cannot migrate. By evaluating, on trans-vinylene formation, the effect of the irradiation temperature and of the styrene content, we showed that radiation protection phenomena are due to both types of transfers at least in the case of the formation of this chemical group.…”