E. Balanzat

Chemical modifications of PET induced by swift heavy ions

Abstract Ion induced chemical modifications of polyethylene terephthalate (PET) were studied by Fourier-transform infrared spectroscopy. The irradiations with Kr (8.6 MeV/u) and with Mo (5.6 MeV/u) ions were performed under vacuum and in oxygen atmosphere, respectively. The overall degradation of the polymer was investigated as a function of the ion fluence in the range from 1 × 1011to 6 × 1012 ions/cm2. A significant loss of crystallinity is related to scission processes of the main chains at the ethylene glycol residue. The benzene ring structures show only small changes under irradiation and do not seem to participate in the degradation process significantly. While various degradation processes known from photochemical degradation take place, the creation of alkynes near the track core is found to be a unique process induced by heavy ions. The presence of oxygen during irradiation enhances the overall degradation of PET and leads to enhanced formation of alkynes and CO2.

Swift heavy ion modification of polymers

Abstract We have studied the effects of dense electronic excitations on vinyl linear polymers, by performing swift heavy ion, SHI, irradiations. We used different ion beams, from C to Pb, provided by the GANIL accelerator at energies of a few MeV/u. We mainly studied the physico-chemical modifications induced in polyethylene (PE), but the role of chemical substitutions has also been investigated by studying the swift heavy ion induced damage in polyvinylidene fluoride (PVDF) and polystyrene (PS). The irradiated samples were analysed ex-situ by means of Fourier transform infrared spectroscopy in the transmission mode. Any contact with air was avoided: oxidation does not occur. Swift heavy ion irradiations are characterised by a significant increase of the yield of chain scission associated with unsaturated end groups. Moreover, we have evidences for specific modifications, i.e. modifications which are never observed when using low ionising particles as electrons or gamma-rays; namely the creation of alkyne and allene end groups. These specific modifications are little sensitive to chemical substitutions. For instance, alkyne formation is observed in PE, PVDF and PS. A simultaneous ionisation of the different atoms of a constituting monomer is likely needed for triggering the formation of the specific swift heavy ion induced modifications. On the other hand, if we pay attention to the physico-chemical modifications which are easily induced by low ionising particles, it is observed that increasing the electronic stopping power does not significantly modify the creation yield of, for instance in PE, trans-vinylene or trans-trans diene groups.

PYROLYTIC EFFECTS INDUCED BY ENERGETIC IONS IN POLYMERS

Abstract Degradation processes in various polymers (polycarbonate, poly(ethyleneterephthalate), polyimide, and polysulfone) induced by krypton and molybdenum ions of several hundred MeV were studied by infrared and mass spectroscopy. A wide spectrum of degradation products well known from low ionizing radiation were found, which are strongly enhanced if the irradiation takes place in oxygen atmosphere. Most notables are the formation of triple bonded species such as alkynes, cyanates and acetylene. They are created within a radius of about 3–4 nm around the ion trajectory. The complementing observation of degradation products in the bulk polymer and as volatile fragments allows a detailed description of the underlying decomposition mechanisms. The observation of degradation products in close analogy to pyrolysis and the thermal stability of acetylene, strongly suggest that transient temperatures above 1500 K are involved in the track formation process.

High-Energy Heavy-Ion Irradiations of Fe85B15 Amorphous Alloy: Evidence for Electronic Energy Loss Effect

Amorphous metallic Fe85B15 alloy has been irradiated at low temperature with Ar, Kr and Xe ions of initial energies of 1.8, 2.7 and 3.0 GeV, respectively. Electrical resistance was measured in situ on samples piled up along the beam direction. It is shown that above a given electronic stopping power threshold the electronic losses play a crucial role in radiation-induced damage.

Physico-chemical modifications induced in polymers by swift heavy ions☆

Abstract 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, (d E /d x ) 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 (d E /d x ) e increases. Moreover, characteristic bands of alkyne terminal groups were observed only above a threshold of (d E /d x ) 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.

Atomic displacements and atomic motion induced by electronic excitation in heavy-ion-irradiated amorphous metallic alloys

In amorphous metallic alloys irradiated with swift heavy ions, electronic excitation induces atomic displacements at the beginning of the irradiation and anisotropic growth above an incubation fluence. The authors provide here an extensive review of their data on amorphous Fe85B15 (including work that is already published), as well as a general description of the topic. Samples were irradiated at various temperatures (20 K, 90 K, 223 K) with a large variety of high-energy (GeV) heavy ions (Ar to U). The atomic rearrangements occurring during irradiation were studied by in situ electrical resistance experiments. The influence of the irradiation geometry as well as of a uniaxial stress applied to the sample was investigated. The whole set of data is accounted for with a two-hit phenomenological model allowing one to extract physical parameters. A description of the ion-target interaction on the basis of the Coulomb explosion mechanism is also provided.

Swift heavy ions on polymers: Hydrocarbon gas release ☆

Abstract In order to understand how bond cleavages occur during ion–polymer interaction, we have made quantitative measurements of the gases evolved under irradiation from the polymers polyethylene, polypropylene and polybutene. The ions used for irradiation were 10.2 MeV amu−1 13C, 2.6 MeV amu−1 14N and 6 MeV amu−1 58Ni. We conceived a new set-up using a Fourier Transform Infrared analysis of the gas mixture released from the polymer film. Observation of the recorded spectra clearly shows that molecular emission is extremely sensitive to the electronic stopping power (dE/dx)e. At low (dE/dx)e, gas yields are strongly polymer dependent and we mainly observe the scission of the tertiary bond: Polypropylene (PP) releases methane and Polybutene (PB) ethane. At high (dE/dx)e, we observe principally acetylene emission, other unsaturated molecules are also greatly favoured. Gas yields are therefore less specific of a given polymer. We show in this work, that the chemical identification of the molecules outgassing the polymer film explains how a polymer chain reacts towards clustered ionisation induced by swift heavy ions.

Swift heavy ion irradiation of polystyrene

Abstract We have studied by Fourier transform infrared spectroscopy the chemical modifications induced by swift heavy ions in polystyrene. The overall destruction yield becomes very significant at high electronic stopping power ( d E d x ) e and the radiation sensitivity of this aromatic polymer merges typical values of equivalent aliphatic polymers as polyethylene. So, the radiation resistance conferred, at low ( d E d x ) e , to polystyrene by the phenyl side group is lost at high ( d E d x ) e . The creation of different unsaturated groups is also observed. They correspond to the vibration frequencies of alkyne, allene, vinylidene, vinyl and trans-vinylene groups. Moreover, the emergence of a wide band without any structure around 1600 cm−1 reveals the presence of double bonds with different degrees of conjugation. By comparison with the modifications induced in polyethylene, we discuss the role played by the phenyl side group and we consider the multiple ionisation of the aromatic ring as one possible way to induce the observed modifications.

Radiation Damage Induced by Electronic-Energy Loss in Amorphous Metallic Alloys

The electrical resistance of amorphous metallic Fe85B15 ribbons irradiated with 3 GeV Xe ions at different tilting angles with respect to the incident ion beam has been measured in situ at 77 K. The results show that irradiation induces large sample growth due to electronic-energy loss effects. The existence of a new mechanism leading to damage creation in metallic alloys by electronic excitation alone is also demonstrated.

The nature of the atom species involved in the reversible relaxation of metallic glasses

Abstract We have studied the reversible relaxation which appears in a number of metallic glasses, when cycled thermally. More precisely, we have analysed the variations of their electrical resistance, measured at 4.2 K, after sequential isochronal treatments conducted between ambiant and crystallisation temperatures. Among the 15 alloys studied, it occurs that all the alloys with several metallic elements exhibit a distinct reversible effect. In the alloys made of a single metal and one or several metalloids, a reversible component exists only for certain compositions. The kinetics and structural aspects of these results are discussed in terms of compositional short range ordering.