Differences in fundamental reaction mechanisms between high and low-LET in recent advancements and applications of ionizing radiation

International audienceRecent applications of high-LET radiation include boron neutron capture therapy. UV treatment of electron-irradiated UHMWPE impedes degradation caused by allyl radicals. Radiation synthesis of PVP nanogels above 55 1C leads to intra-molecular crosslinking. PCBs in contaminated sediments can be dechlorinated by reactions with hydrated electrons. a b s t r a c t Differences among the mechanisms of energy deposition by high-linear energy transfer (LET) radiation, consisting of neutrons, protons, alpha particles, and heavy ions on one hand, and low-LET radiation, exemplified by electron beam and gamma radiation on the other, are utilized in the selection of types of radiation used for specific applications. Thus, high-LET radiation is used for modification of carbon nanotubes, ion track grafting, and the synthesis of membranes and nanowires, as well as for characterization of materials by means of neutron scattering. Recent applications of low-LET irradiation include minimization of radiolytic degradation upon sterilization of ultra-high molecular weight polyethylene (UHMWPE), radiolytic synthesis of nanogels for drug delivery systems, grafting of polymers in the synthesis of adsorbents for uranium from seawater, and reductive remediation of PCBs

Poly(4-vinyl pyridine) radiografted PVDF track etched membranes as sensors for monitoring trace mercury in water

International audiencePoly-4-vinyl pyridine chains were radiografted inside the etched-tracks of PVDF nanoporous membrane. P4VP grafting was found to be localized on the solid PVDF surface. Coating of these PVDF-g-P4VP membranes with a very thin layer of gold results in an ASV electrochemical sensor. Functionalized ion track-etched PVDF-g-P4VP sensors were found very selective and highly sensitive for mercury LOD 5 ng/L. a b s t r a c t By a radiation-induced grafting technique, we have functionalized track-etched nanoporous polymer membranes with mercury sensitive poly-4-vinyl pyridine (P4VP). Coating of these membranes with a very thin layer of gold results in an electrochemical sensor that is very selective and highly sensitive for mercury LOD 5 ng/L – well below the norms for water (0.015 mg/L potable water and 0.5 mg/L residual waters-French water norms of 27 October 2011). E-beam irradiation permitted optimization of the radiografting synthesis on PVDF thin films prior to ion-track grafting. Synthesis and characterization by EPR, FESEM and FTIR are described in detail. A comparison between FTIR in ATR and transmission modes enabled us to localize the grafting on the surface of the e-beam irradiated PVDF films allowing us to extrapolate what happens on the etched tracks. Using Square Wave Anodic Stripping Voltammetry (SW-ASV), mercury concentrations of 1 mg/L are detected in 2 h and low ng/L concentrations are detected after 24 h of adsorption. The adsorption is passive so sensors do not require instrumentation and the analysis takes only 3–4 min. Also, the P4VP functionalized sensor appears insensitive to pH variations (pHs 3–9), high salt concentrations (up to 1 g/ L) and the presence of other heavy metals in the same solution.

Ion track grafting: A way of producing low-cost and highly proton conductive membranes for fuel cell applications

International audienceKeywords: Ion track grafting Radiografting Swift heavy ions Proton conductivity Polymer electrolyte membrane Proton exchange membrane fuel cell a b s t r a c t Proton conductive individual channels through a poly(vinyl di-fluoride) PVDF matrix have been designed using the ion track grafting technique. The styrene molecules were radiografted and further sulfonated leading to sulfonated polystyrene (PSSA) domains within PVDF. The grafting process all along the cylindrical ion tracks creates after functionalisation privileged paths perpendicular to the membrane plane for proton conduction from the anode to the cathode when used in fuel cells. Such ion track grafted PVDF-g-PSSA membranes have low gas permeation properties against H 2 and O 2. A degree of grafting (Y w) of 140% was chosen to ensure a perfect coverage of PSSA onto PVDF-g-PSSA surface minimizing interfacial ohmic losses with the active layers of the Membrane Electrolyte Assembly (MEA). A three-day fuel cell test has been performed feeding the cell with pure H 2 and O 2 , at the anode and cathode side respectively. Temperature has been progressively increased from 50 to 80 • C. Polarisation curves and Elec-trochemical Impedance Spectroscopy (EIS) at different current densities were used to evaluate the MEA performance. From these last measurements, it has been possible to determine the resistance of the MEA during the fuel cell tests and, thus the membrane conductivity. The proton conductivities of such membranes estimated during fuel cell tests range from 50 mS cm −1 to 80 mS cm −1 depending on the operating conditions. These values are close to that of perfluorosulfonated membrane such as Nafion ® in similar conditions

Des polymérisations classiques en solution aux polymérisations radio-induites contrôlées en milieu confiné

The manuscript of Mrs Marie-Claude Dubois-Clochard reports on the main results obtained in synthesis and structuration of functional polymers at the nanoscale. If the synthesis of functional polymers is the basic of the presented studies, the chronological order of her research activities from 1995 to 2013 shows an evolution from classical polymerisations in solution towards radio-induced polymerisations in confined space controlled by RAFT mechanism. The innovation is about the development of new objects made of polymers and organic/inorganic composites designed at the nanoscale to bring original physical and physico-chemical properties. Three applied fields stand out: Energy-Environment (Engines, Fuel cells, Sensors for water quality), Health (Nanovector for tumour therapies and imaging, Ion and molecules tranlocation through a single nanopore in a polymer membrane) and Nanotechnologies (Magnetoresistance of a single magnetic nanowire). Noteworthy results are: - the setting up of bi-langmuirian adsorption isotherm equations at solid/hydrocarbon interface for macromolecules at low concentrations, and, at high concentration, particular behaviour of reorganisation of these identical macromlecules, not in alternative layers but in reverse hemi-micelles formation. - the synthesis of a novel pH-dégradable polymer allowing an hydrolytic degradation from pH 7.4 (Sang) to pH 5.5 (Intracellular lysosome) to deliver drugs into tumor cells (Santé). - the radiation-induced grafting-through process in solid polymers showed by a cooperative effect of solvent/growing polymer chains into fluoropolymers. - the synthesis of bi-functional nanoporous polymer track-etched membranes having a functionality in the pores and another on the surface. This membrane, after changing in electrode by simple metallisation, has been the subject of valorisation projects to a start-up creation and/or a technological transfer for the development of a sensor able to detect heavy metals ions traces in treated water (Environment). In the same framework, the direct functionalisation of tracks created by Swift Heavy Ions irradiation at GANIL in polymer films has been used to develop new proton exchange membranes for fuel cell (Energy). - Non-described observation of a cooperative effect on ion mobility in a confined space made of a single cylindrical nanopore in a thin polymer membrane. Boost or slow down effect on ions mobility in this single nanopore of charged walls depends only on the chemical nature of the ions and their concentration. - Observation of jumps in the resistance of a biconical magnetic nanowire under a magnetic field (constriction size of 10 nm) beyond the magnetoresistance effect. These jumps depend both on the geometry of the system and the intensity of the injected current. Relaxation effects before and after a jump show an energy-activated system. - Nanopore size tuning of a polymer membrane by radio-induced polymerisation controlled by RAFT mechanism.Le manuscrit HDR de Mme Marie-Claude Dubois-Clochard relate les principaux résultats acquis en synthèse et structuration à l'échelle nanométrique de polymères fonctionnels. Si la synthèse de polymères fonctionnels est à la base des études abordées, l'ordre chronologique des activités de Recherche de 1995 à 2013 montre une évolution des polymérisations classiques en solution vers des polymérisations radio-induites contrôlées par mécanisme RAFT en milieu confiné. L'innovation porte sur le développement de nouveaux objets polymères et composites organique/inorganique façonnés à l'échelle nanométrique aux propriétés physiques et physico-chimiques originales. Trois domaines d'application se détachent : l'Energie-Environnement (Moteurs, Piles à combustible, Capteurs pour la qualité de l'Eau), la Santé (Nanovecteurs pour Thérapie cancéreuse et imagerie, translocation d'ions ou de molécules à travers un nanopore unique dans une membrane polymère) et les Nanotechnologies (Magnétorésistance d'un nanofil magnétique unique de forme cylindrique ou biconique). Les résultats marquants ont été : - l'établissement d'isothermes d'adsorption de type bi-langmuir à l'interface solide/liquide organique pour des macromolécules tensioactives à faible concentration, et, à forte concentration, un comportement particulier de réorganisation de ces mêmes macromolécules, non pas en couches alternées, mais sous forme d'hémicelles inverses. - la synthèse d'un polymère pH-dégradable innovant permettant une dégradation hydrolytique en passant de pH 7.4 (Sang) à pH 5.5 (Lysosome intracellulaire) en vue de délivrer des toxines dans les cellules tumorales (Santé). - la démonstration de l'effet coopératif solvant/polymère en croissance pour la pénétration du greffage induit par irradiation dans des films fluoropolymères. - la synthèse de membranes polymères nanoporeuses à traces attaquées bi-fonctionnelles ayant une fonctionnalité dans les pores et une autre en surface. Cette membrane, après transformation en électrode par simple métallisation aura fait l'objet de projets de valorisation en vue d'une création de start-up et/ou de transfert de technologie pour le développement d'un détecteur de traces métaux lourds dans l'eau traitée (Environnement). Dans la même thématique, la fonctionnalisation directe des traces dans les films de polymères irradiés aux ions lourds rapides du GANIL a permis de développer de nouvelles membranes conductrices de protons pour les piles à combustible (Energie) - l'observation non-décrite d'effets coopératifs sur la mobilité des ions dans un milieu confiné créé par un nanopore cylindrique unique dans une membrane fine de fluoropolymère. L'effet accélérateur ou décélérateur de la mobilité des ions confinés dans le pore aux parois chargées semble dépendre uniquement de la nature chimique des ions et de leur concentration. - L'observation de sauts de résistance bien au-delà de la magnétorésistance d'un nanofil magnétique biconique (constriction de l'ordre de la dizaine de nanomètre) sous champ magnétique ayant une dépendance à la fois en angle et en intensité de courant injecté. Effets de relaxations avant et après saut montrant un système énergétiquement activé. - Le contrôle de taille des nanopores d'une membrane polymère par polymérisation radio-induite contrôlée par mécanisme RAFT

La pile à combustible, une solution vers des véhicules propres

National audienc

Ion Tracks in Polymers

International audienceElectronic excitations produced by ions in polymers results in the formation of free radicals making them highly sensitive to chemical agents. Besides the widely developed application to the etching of membranes with controlled pore sizes and densities, the grafting of molecules selected for their chemical properties inside the tracks of swift heavy ions offers interesting potentialities such as the fabrication of intelligent membranes, detectors and captors. Carbon, silicon or metal clusters which are formed in the heavily damaged core of tracks, especially within partially inorganic polymers, are also of high interest for their optical or magnetic properties

Drapeaux piezolélectriques de nouveaux générateurs à la frontière entre physqiue et mécanique

International audienc

Synthesis of soluble polymers designed to degrade by intramolecular acid catalysis

International audienc

Development of the aconityl degradable element for biomedical polymers

International audienc

Synthesis of soluble polymers for medicine that degrade by intramolecular acid catalysis

International audienc