43 research outputs found
De Yaoundé à Caen, le bel itinéraire d’une physicienne
No full textDiplômée de l’école de chimie de Clermont-Ferrand (ENSCCF), titulaire d’un DEA de chimie et d’un doctorat portant sur le vieillissement des polymères sous l’action combinée des rayonnements ionisants et de l’eau... Qui aurait parié sur un tel parcours ? Yvette Ngono, qui, à force de persévérance, travaille désormais au Centre de recherche sur les ions, les matériaux et la photonique
Behaviour of ΙΙ-type cοllagen under iοnising radiation : study of model pοlypeptides as substitutes of cοllagen in the condensed phase.
No full textLe collagène, la protéine la plus abondante chez les mammifères, constitue principalement la matrice extracellulaire du cartilage et est essentiel pour ses propriétés mécaniques, grâce à sa structure en triple hélice caractéristique. Dans le contexte de l'hadronthérapie, les effets des rayonnements ionisants sur le collagène de type II ont été examinés en caractérisant les défauts macromoléculaires et les émissions gazeuses radio-induites en utilisant des polymères de substitution, notamment des homopolymères des acides aminés principaux du collagène (polyglycine, poly-DL-alanine et poly-L-proline) ainsi que des peptides modèles à triple hélice. L'irradiation des homopolypeptides, avec ou sans chaînes latérales, a révélé une remarquable stabilité à la radiation, avec environ 20 % des structures altérées, augmentant la prportiond en chaines en random coils et des ruptures de chaînes. En l'absence de chaînes latérales, comme la polyglycine, la rupture de la liaison CO-NH est fréquente, tandis qu'en présence de chaînes latérales, telles que la poly-DL-alanine et la poly-L-proline, la rupture de la liaison CO-CαH semble significative, expliquant la formation d'isocyanates. De plus, dans le cas de la poly-L-proline, les liaisons N-CαH ou N-CH2semblent également être affectées par l'irradiation. Ces résultats diffèrent des observations faites lors de l'irradiation gamma, où la rupture de la liaison Cα-N est considérée comme principale dans les homopolypeptides. Les gaz identifiés étaient H2, CO, CO2 et CH4, et l'effet du transfert d'énergie linéique (TEL) a été observé avec des rendements accrus en H2et CO lorsque le TEL est élevé, ainsi que des bandes IR spécifiques aux irradiations à fort TEL.L'irradiation des peptides modèles de collagène, (PPG)10 et (POG)10, a révélé des nouvelles bandes d'absorption qui ne sont pas spécifiques à la structure en triple hélice, mais plutôt liées aux acides aminés constitutifs du peptide. Les résultats obtenus sur le (POG)10 soulignent l'impact des molécules d'eau et la présence de l'hydroxyproline, avec la formation du radical hydroxyle.Collagen, the most abundant protein in mammals, primarily forms the extracellular matrix of cartilage and is essential for its mechanical properties, owing to its characteristic triple helix structure. In the context of hadron therapy, the effects of ionizing radiation on type II collagen have been examined by characterizing macromolecular defects and radiationinduced gas emissions using substitute polymers, including homopolymers of major collagen amino acids (polyglycine, poly-DL-alanine, and poly-L-proline) as well as triple helix model peptides.Irradiation of homopolypeptides, with or without side chains, revealed remarkable radiation stability, with approximately 20% of altered structures, increasing the proportion of chains in random coils and chain scission. In the absence of side chains, such as polyglycine, CO-NH bond scission is frequent, while in the presence of side chains, such as poly-DL-alanine and poly-L-proline, CO-CαH bond scission seems significant, explaining isocyanate formation. Additionally, in the case of poly-L-proline, N-CαH or N-CH2 bonds also appear affected by irradiation. These results differ from observations during gamma irradiation, where Cα-N bond scission is considered primary in homopolypeptides. Identified gases were H2, CO, CO2, and CH4, and the effect of linear energy transfer (LET) was observed with increased yields of H2 and CO when LET is high, along with IR bands specific to high-LET irradiation.Irradiation of collagen model peptides, (PPG)10 and (POG)10, revealed new absorption bands not specific to the triple helix structure, but rather correlated with constitutive amino acids of the peptide. Results obtained on (POG)10 highlighted the impact of water molecules and the presence of hydroxyproline, with the formation of the hydroxyl radical
Development of a highly Sensitive Polymer for MEMS gamma rays sensors
No full textCe travail de recherche a étudié l'effet des nanoparticules d'or sur le comportement des polymères sous rayonnements ionisants en atmosphère inerte. L'objectif était de développer des matériaux à forte émission gazeuse intégrables dans de nouveaux dosimètres miniatures, passifs, à lecture en temps réel et à longue distance. L’idée était initiale était d’insérer des nanoparticules d’or (AuNPs) dans des matrices polymères afin de tirer avantage des électrons secondaires émis par les AuNPs et d’une potentielle action catalytique pendant la phase chimique de l’irradiation. Au-delà du développement d’un nouveau polymère, cette étude avait également pour objectif d’améliorer la compréhension de l’influence des nanoparticules en phase solide et sous atmosphère inerte. Deux types de polymères ont été étudiés : le PMAA et le PE. Des nanoparticules sphériques d'or de 2 nm de diamètre ont été synthétisées et incorporées dans les polymères. Les nanocomposites ont été irradiés et les défauts macromoléculaires et l'émission gazeuse ont été analysés. Les résultats ont montré que les nanoparticules d'or ont un effet significatif sur le comportement des polymères sous rayonnements ionisants. L'effet observé dépend du type de polymère, de la concentration en nanoparticules et de la distribution des nanoparticules dans la matrice polymère. Dans le PMAA, les nanoparticules d'or accélèrent la scission des chaînes et augmentent le rendement radiochimique de dihydrogène émis dans le polymère. Dans le PE, au-dessus d’un pourcentage molaire de 1%, les nanoparticules d'or radio-protègent le polymère en réduisant la formation de défauts macromoléculaires et l'émission d'hydrogène.In this research work, we studied the effect of gold nanoparticles on the behavior of polymers under ionizing radiation under an inert atmosphere. The initial aim was to develop highly emissive materials for new miniature, passive, real-time, and long-distance read-out dosimeters by inserting gold nanoparticles (AuNPs) in a polymer matrix. The rational behind was to use either the dose enhancement by secondary electrons emitted from AuNPs or their catalytic properties when appropriate. Beyond the development of a new material, one of the objective of this work was to study the influence of nanoparticles in the solid phase and in the absence of oxygen. Two types of polymers were studied: PMAA and PE. Gold nanoparticles with a diameter of 2 nm were synthesized and incorporated into the polymers. The nanocomposites were irradiated under gamma rays or electron beams and both macromolecular defects and gas emission were analyzed. The results showed that gold nanoparticles have a significant effect on the behavior of polymers under ionizing radiation, depending on the polymer polymer, the nanoparticles concentration, and their distribution in the polymer matrix. In PMAA, gold nanoparticles accelerate chain scission and increase the hydrogen emission radiochemical yield. In PE, beyong a molar percentage of 1%, gold nanoparticles radioprotect the polymer by reducing the formation of macromolecular defects and hydrogen emission
Editorial (IRaP 2016 Proceedings)
No full textInternational audienceThis issue of Radiation Physics and Chemistry contains selected papers presented at the 12th Ionizing Radiation and Polymers conference (IRaP 2016) that was held from September 25 to September 30, 2016 at Belambra “Les Criques” in Giens, France.IRaP has the particularity to focus on the effect of ionizing radiations on polymers. This biennial conference was initiated with the three-fold objective to 1) bring together scientists from research centers, universities and industry, 2) provide a forum to exchange knowledge and information in this field and , 3) to promote innovative applications.IRaP 2016 was attended by 125 scientists and 10 accompanying persons from 20 countries. The scientific program consisted of 15 plenary sessions (21 invited and 40 selected lectures), two poster sessions (68 posters), 1 course and 1 keynote. The course, delivered by Emmanuel Balanzat (Caen, France), gave young scientists the opportunity to enlarge their knowledge on the influence of the nature of the projectile on polymer modification, i.e. the specificity of Swift Heavy Ions. The keynote, presented by Pr. Vladimir Feldman (Moscow, Russia), gave a great overview on radiation damage mechanisms at cryogenic temperatures.IRaP2016 in France gave the opportunity to honor the memory of Dr. Natacha Betz, one of the founders of the IRaP conference, for the tenth anniversary of her passing away. In a dedicated tribute, Dr. Serge Bouffard (Caen, France) offered a wealth of insights on her scientific career, testimonials of memorable moments and messages to the polymer irradiation community.IRaP2016 was also the occasion to acknowledge some senior scientists’ contributions. Especially, a special session on gels, devoted to Pr. Janusz Rosiak (Lodz, Poland), was hosted to mark his upcoming retirement. This was an opportunity for his colleagues and friends to congratulate him and to highlight his valuable and remarkable input on the development of hydrogels.Traditional IRaP symposium topics such as fundamental processes, radiation-induced chemical modifications (ageing, degradation, resulting physical properties modification) and their application in the fabrication of advanced materials were addressed. Notably, the nanostructures of polymer thin films through ion-track technology allows the fabrication of interesting advanced polymer-based new materials for sensoring purposes. Radiation-induced grafting technique is still widely developed, using up-to-date polymerization mechanisms (eg. RAFT mechanism), and applied to various industrial fields of interest among which flame retardant materials, energy harvesting or drug delivery systems. It is worth noting that drug delivery devices, combining various radiation-based strategies such as the synthesis of crosslinked nanogels, were widely represented.In addition to synthetic polymers, bio-based and biopolymers were presented as base materials of growing interest. Due to an increasing environmental concern, numerous studies aimed notably at improving the biodegradability of polymers.New sessions (Radiolysis and Lifetime prediction) and new trends (Monte-Carlo calculations for the study of polymer ageing and the association of metal/polymer hybrid nanoparticles for medical applications) have entered the topic list of the 12th IRaP.The present special issue of Radiation Physics and Chemistry gathers the selected articles, peer reviewed by independent referees, among the manuscripts submitted for publication after the conference. The organizing committee gratefully acknowledges all the contributors. We thank the referees for their critical reading of the manuscripts and the associated detailed reviews, ensuring the required standard for RPC. The three guest editors would also like to thank Pr. Laszlo Wojnarovits for his help during the editing process.The success of this 12th edition of the IRaP conference is first assigned to the attendees and the contributors. On behalf of the organizing committee, we would like to thank them for this special issue, the scientific and steering committees for their valuable help in the organization and the local organizing committee (the green team and L. De Baeremaker included) for all the hours of hard work they have pulled to make this conference a great success. We address a special and personal thanks to Dr. Caroline Aymes-Chodur for her precious help all along the conference organization, despite her knowing that she wouldn’t attend the conference. We also thank the staff of the Belambra “Les Criques“ resort, especially Ms. Céline Lacommère for her friendliness and her dedication. All this, added to the gorgeous location and the sunny weather, certainly contributed in the enjoyment of IRaP2016.We would like to acknowledge the institutions, organizations and companies that supported the IRaP 2016: IAEA, IIA (International Irradiation Association), CEA, Andra, CNRS, Université de Caen, Caen la Mer and Ionisos. Thanks to the support of the IAEA and IIA, eight young scientists, selected on the basis of their scientific work, have been granted to attend the IRaP2016 conference.Finally, we would like to address special thanks to the companies who funded an exhibition booth: AERIAL, NIST, Steris and Thermo Scientific
Radio-oxidation mechanisms in polyethylene and spectral signature of final products: a contribution from atomic scale simulations
No full textInternational audienceAgeing of insulating polymers under irradiation is of particular concern for many applications, in particular for cable insulation in nuclear environment. γ-irradiation in oxidative atmosphere (radio-oxidation) leads to the build-up of various carbonyl species in the material, eventually producing modifications of mechanical and functional properties. The kinetics of such process is still not yet fully elucidated, but several studies have monitored the degradation products via infrared spectroscopy or electronic paramagnetic resonance (EPR).The use of atomic scale calculations to screen the viability of elementary reaction mechanisms included in kinetic simulations is proving increasingly valuable, even when based on reactions calculated for a small molecular entity.A further challenge in modelling irradiation effects in polymers is the fact their microstructure involves, in most cases, an intimate mix of nanocrystals and amorphous. In polyethylene, for example, one of the most produced polymers for a variety of application, crystalline lamellae are intermixed with lower density regions.In this paper we first developed an interface model in order to try to grasp the main atomic scale features of crystalline and amorphous regions. Then we show how first principles calculations based on density functional theory (DFT) can be used to check the reliability of some kinetics schemes proposed in the literature and, finally, can be a valuable support for experimental investigation of the accumulated carbonyl concentrations through infrared spectroscopy. The energy barriers associated to several chemical reactions taking part to the degradation process are obtained from DFT and the nudged-elastic-band (NEB) method and discussed in comparison to generally accepted kinetic schemes [1].Furthermore, we calculate frequencies of infrared active modes and their intensity and compare them to the corresponding quantities obtained from experimental analysis of pristine and aged samples of LLDPE (linear low density polyethylene) and XLPE (cross-linked polyethylene). We can for example predict the spread in infrared frequencies for the characteristic peak of each of various carbonyl species, which turns out to be in fair agreement with experiment. We analyse the variations in frequencies and intensities of the peak when the carbonyl is on the surface of a crystalline lamella or in a lower density region, or even inside a crystalline zone. The prevalence of ketone species over esters, carboxylic acids and aldehydes, as in several previous works, is confirmed for our samples and irradiation conditions. [2]References:[1] Y. Ahn, G. Roma, X. Colin, Macromol. 55, 8676 (2022).[2] M. Ferry, Y. Ahn, F. Le Dantec, Y. Ngono, G. Roma, Polymers 15, 1537 (2023)
Radio-oxidation mechanisms in polyethylene and spectral signature of final products: a contribution from atomic scale simulations
No full textInternational audienceAgeing of insulating polymers under irradiation is of particular concern for many applications, in particular for cable insulation in nuclear environment. γ-irradiation in oxidative atmosphere (radio-oxidation) leads to the build-up of various carbonyl species in the material, eventually producing modifications of mechanical and functional properties. The kinetics of such process is still not yet fully elucidated, but several studies have monitored the degradation products via infrared spectroscopy or electronic paramagnetic resonance (EPR).The use of atomic scale calculations to screen the viability of elementary reaction mechanisms included in kinetic simulations is proving increasingly valuable, even when based on reactions calculated for a small molecular entity.A further challenge in modelling irradiation effects in polymers is the fact their microstructure involves, in most cases, an intimate mix of nanocrystals and amorphous. In polyethylene, for example, one of the most produced polymers for a variety of application, crystalline lamellae are intermixed with lower density regions.In this paper we first developed an interface model in order to try to grasp the main atomic scale features of crystalline and amorphous regions. Then we show how first principles calculations based on density functional theory (DFT) can be used to check the reliability of some kinetics schemes proposed in the literature and, finally, can be a valuable support for experimental investigation of the accumulated carbonyl concentrations through infrared spectroscopy. The energy barriers associated to several chemical reactions taking part to the degradation process are obtained from DFT and the nudged-elastic-band (NEB) method and discussed in comparison to generally accepted kinetic schemes [1].Furthermore, we calculate frequencies of infrared active modes and their intensity and compare them to the corresponding quantities obtained from experimental analysis of pristine and aged samples of LLDPE (linear low density polyethylene) and XLPE (cross-linked polyethylene). We can for example predict the spread in infrared frequencies for the characteristic peak of each of various carbonyl species, which turns out to be in fair agreement with experiment. We analyse the variations in frequencies and intensities of the peak when the carbonyl is on the surface of a crystalline lamella or in a lower density region, or even inside a crystalline zone. The prevalence of ketone species over esters, carboxylic acids and aldehydes, as in several previous works, is confirmed for our samples and irradiation conditions. [2]References:[1] Y. Ahn, G. Roma, X. Colin, Macromol. 55, 8676 (2022).[2] M. Ferry, Y. Ahn, F. Le Dantec, Y. Ngono, G. Roma, Polymers 15, 1537 (2023)
Irradiation of Atactic Polystyrene: Linear Energy Transfer Effects
No full textInternational audienceAtactic glassy polystyrene (PS) has been irradiated in anoxic conditions by electron and ion beams. The induced modifications were followed, in situ, by Fourier transform infrared spectroscopy (FTIR). In-film modifications and hydrocarbon gas release were followed. In-situ measurements allowed one to avoid any spurious oxidation of the films after irradiation and also permitted studying in detail the evolution with dose of the FTIR spectra. The data were quantitatively analyzed, and we present a complete analysis of the effects of the Linear Energy Transfer (LET) on the radiation chemical yields of several radiation-induced modifications (alkynes, allenes, alkenes, benzene, and disubstituted benzenes). For a better understanding of the LET effects, the in-film modifications are compared to H2 release data from the literature and to our measurements of hydrocarbon gaseous molecule yields obtained by us. The overall destruction yield becomes very significant at high LET, and the radiation sensitivity of this aromatic polymer merges with typical values of aliphatic polymers: the radiation resistance conferred at low LET to polystyrene by the phenyl side groups is lost at high LET. This loss of radiation resistance equally affects the aromatic and aliphatic moieties. Monosubstituted alkynes are created above a LET threshold, whereas the other radiation-induced modifications are observed in the whole LET range. Several observations indicate that the phenyl ring is broken at high LET. Comparison of the alkyne yield in PS, polyethylene, and polycarbonate as well as the formation of nitrile bonds in poly(vinylpyridine-co-styrene) are consistent with a cleavage of the phenyl ring as the prominent source of alkynes. As the competing damage mechanisms do not have the same LET evolution, the relative importance of a specific modification on the global damage depends on LET. Some (benzene and disubstituted benzenes) dominate at low LET, while others (in-film alkyne and acetylene release) dominate at high LET
