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

Magnetic nanoconstrictions made from nickel electrodeposition in polymeric bi-conical tracks: Magneto-transport behavior

International audienceSingle nanoconstriction per magnetic wire is obtained by bi-conical track etching and electrodeposition. Magnetoresistance measurements at various angles result in irreversible jumps. Resulting jumps of magnetization have been attributed to the pinning and depinning of a constrained magnetic domain wall. a b s t r a c t In a cylindrical magnetic nanowire, a magnetic domain wall (DW) can move along the wire when an applied magnetic field or a spin-polarized current is applied. We show that in a magnetic device composed of two conical nanowires connected by a nanosized constriction, a DW can be trapped and detrapped. The magnetoreistance and the relaxation processes of the DW exhibit a specific behavior. Such a device has been fabricating by Ni electrodeposition in bi-conical tracks polymer membrane made of Swift Heavy Ions bombarded poly(VDF-co-TrFE) copolymer and poly(ethylene terephtalate) PET thin films. The latter method allows to monitor the conicity of the bi-conical wires and to give access to a panel of very well-defined structures.

Trapped and transient radicals observed in ethylene–propylene–diene terpolymers

International audienceRadicals formed by irradiation by high energy electron in ethylene–propylene–hexadiene terpolymer (EP–HD) have been studied using electron spin resonance (ESR). Two methods were used to analyse the different radicals formed by irradiation: firstly, classical low temperature irradiations were carried out, secondly, rapid quenching in liquid nitrogen of the material after high dose rate irradiation. The feasibility and the efficiency of the latter method to observe short-lived radicals have been demonstrated. This type of experiment provides unique information concerning the rate of production and the rate of reaction of radical

Matériaux organiques irradiés à très basse température et à différents pouvoirs d'arrêt (cas du polyéthylène et des molécules de cyclohexane isolées en matrice)

CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Comportement des verres cyclohexane/benzène et des copolymères éthylène/styrène sous rayonnements ionisants (transferts d'énergie et d'espèces entre les groupements alipathiques et aromatiques)

L objectif général de ce travail est de comprendre la façon dont les groupements aliphatiques et aromatiques interagissent sous rayonnements ionisants. Trois axes de recherche ont été explorés : la détermination de la contribution relative des transferts d énergie et de radicaux, la détermination de la contribution relative des transferts intra-chaîne et intermoléculaires, ainsi que l influence de la répartition des unités aliphatiques et aromatiques dans la chaîne de polymère. Trois systèmes composés d aliphatiques et d aromatiques ont été étudiés : les verres organiques cyclohexane/benzène (réactions intermoléculaires), les copolymères aléatoires éthylène/styrène (réactions intra-chaîne et inter-chaînes) et diblocs éthylène/styrène (l influence de la répartition des deux types de groupements dans le matériau). Au vu des résultats que nous avons obtenu, nous concluons que les transferts d énergie sont prépondérants dans l effet de radioprotection de la composante aliphatique par les cycles aromatiques, bien que les transferts de radicaux y participent de façon minoritaire. Les transferts intermoléculaires sont très efficaces en phase solide et leur efficacité semble comparable à celle des transferts intra-chaîne. Grâce à l utilisation de la spectroscopie infrarouge, nous avons montré un effet important de radiosensibilisation de la composante aromatique, quels que soient la température d irradiation et le système étudié : les transferts d énergie vers la phase aromatique s effectuent au détriment de sa stabilité. Enfin, la répartition des deux groupements le long de la chaîne de polymère n est pas un facteur important dans les effets induits par les transferts d énergie.The aim of this study is to understand how aliphatic and aromatic groups interact under ionizing radiations. Three research orientations were explored: the determination of the relative contribution of energy and radical transfers, the determination of the intermolecular and intra-chain relative contribution, and the influence of the repartition of the aliphatic and aromatic units inside the polymer chain. Three systems composed of aromatic and aliphatic units were studied: the cyclohexane/benzene organic glasses (intermolecular reactions), the ethylene/styrene random copolymers (inter-chain and intra-chain reactions) and ethylene/styrene diblocs copolymers (influence of the repartition of the aliphatic and aromatic units in the material).Considering the results obtained, we have concluded that energy transfers are the most important transfers in the radiation protection effect of the aliphatic moiety by the aromatic one, although radical transfers are also contributing. Intermolecular transfers are efficient in the solid state and their efficiency seems equivalent to that of the intra-chain ones. Thanks to the use of infrared spectroscopy, we have shown an important effect of radiation sensitization of the aromatic moiety, whatever the irradiation temperature and the system studied: energy transfers to the aromatic moiety are carried out at the detriment of its stability. Finally, the repartition of the aliphatic and aromatic units in the polymer chain is not an important factor in the effects induced by the energy transfers.CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Radio-oxydation d'un élastomère de type EPDM lors d'irradiations faiblement ou fortement ionisantes (mesure et modélisation de la consommation de dioxygène)

CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

ETUDE DE L'OXYDATION ET DE LA TENUE D'ELASTOMERES IRRADIES (CONSEQUENCES SUR L'INTEGRITE DES CABLES ELECTRIQUES LORS D'UNE SITUATION ACCIDENTELLE D'UN REACTEUR A EAU PRESSURISE)

CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

L'EMISSION GAZEUSE DES POLYMERES ALIPHATIQUES SOUS IRRADIATION (EFFET DU POUVOIR D'ARRET ELECTRONIQUE)

CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Effect of oxygen on gas emitted from polymer irradiated using Swift Heavy Ion beams

International audienceAt the end of their life, polymers used in the nuclear industry are placed in Intermediate Level – Long Lived Waste packages. For safety purposes, the amount of gas emitted by these organic materials has to be estimated. γ ir-radiations are commonly used to simulate β and γ-emitters; α-emitters simulation are more problematic because of experimental difficulties. It is proposed in France to use particle accelerators with ions providing stopping power values in polymers equivalent to the one of α-emitters. This approach has been validated under inert atmosphere; the question now arises of the effect of the presence of oxygen. We showed that the hydrogen release is slightly affected by atmosphere of irradiation and increases with LET. The evolution with LET of CO2 release is dependent on the polymer: it increases for polymers with low G(CO2) at low LET and decreases for polymers presenting relatively high G(CO2) at low LE

Investigation of initial stage of chemical etching of ion tracks in polycarbonate

International audienceChemical track etching and the growth of nanochannels in ion-irradiated polycarbonate foils were investigated by loss of weight measurements and IR-spectroscopy. The data provided by both methods are in good agreement and allow us to shed light on the early stage of pore formation including times where the breakthrough of the pores has not yet occurred. Clear evidence is shown that the pore growth as a function of etching time depends on the irradiation fluence. For fixed etching parameters, foils containing 7 X 109 tracks/cm2 exhibit much smaller pores than samples with 2 X 108 tracks/cm2. This effect is independent of the etching temperature and appears for irradiations with Pb ions as well as for Ca–ion tracks sensitized by UV exposure. Model calculations for different etching times and fluences show that the data for low track densities can be fitted quite well by describing the radial etching rate by the track etch rate changing into the bulk etch rate with a Gaussian-shaped transition