Nanoporous beta-PVDF membranes with selectively functionalized pores

International audiencePoly (vinylidene fluoride) ( -PVDF) nanoporous membranes are obtained by heavy ion irradiation and track etching leading to cylindrical pores. Pores diameter measured by Scanning Electron Microscopy and Small Angle Neutron Scattering lies in the 20-50nm range. Electron Paramagnetic Resonance study gives evidence that radicals still remains in PVDF membrane after track-etching. These radicals allows acrylic acid polymerization to be initiated onto membrane. So radiografted and functionalized membranes are characterized using Infrared Spectroscopy, weighing measurements and Energy Dispersive Spectroscopy. Finally, radiografted poly(acrylic-acid) (PAA) has been selectively labeled by fluorophores and imaged by Confocal Laser Scanning Microscopy. Images show the localisation of PAA specifically inside nanopores

Modifications structurales et défauts ponctuels paramagnétiques induits par irradiation électronique externe de la hollandite Ba1.16Al2.32Ti5.68O16

Des matrices BaxCsy (M,Ti)8O16 (x+y<2, M cation trivalent) de type hollandite, sont envisagées pour confiner spécifiquement le césium radioactif. Afin de simuler l'effet des rayonnements b, les modifications structurales et les défauts ponctuels paramagnétiques produits par irradiation électronique externe à température proche de l'ambiante d'une hollandite de composition simplifiée sans césium Ba1,16Al2,32Ti5,68O16 ont été étudiés par RPE et RMN. Des modifications ont été observées au niveau de l'environnement des cations Al3+ et Ti4+, résultant de la formation de lacunes d'oxygène et d'une augmentation du désordre dans les tunnels associée à des déplacements d'ions baryum. Des centres à électrons (Ti3+) et à trous électroniques (O2-) ont été observés. Ceux-ci sont relativement stables à température ambiante mais des recuits (traitements isochrones entre 50 et 800°C, traitements isothermes à 300°C) engendrent la formation d'autres défauts issus des défauts précédents correspondant à des ions Ti3+ de surface de type titanyl et des agrégats d'oxygène

Photoconductivity and Photoemission of Diamond Under Femtosecond Vuv Irradiation

In order to gain some insight on the electronic relaxation mechanisms occuring in diamond under high intensity laser excitation and/or VUV excitation, we studied experimentally the pulsed conductivity induced by femtosecond VUV pulses, as well as the energy spectra of the photoelectrons released by the same irradiation. The source of irradiation consists in highly coherent VUV pulses obtained through high order harmonic generation of a high intensity femtosecond pulse at a 1.55 eV photon energy (titanium-doped sapphire laser). Harmonics H9 to H17 have been used for photoconductivity (PC) and harmonics H13 to H27 for photoemission experiments (PES). As the photon energy is increased, it is expected that the high energy photoelectrons will generate secondary e-h pairs, thus increasing the excitation density and consequently the PC signal. This is not what we observe : the PC signal first increases for H9 to H13, but then saturates and even decreases. Production of low energy secondary e-h pairs should also be observed in the PES spectrum. In fact we observe very few low energy electrons in the PES spectrum obtained with H13 and H15, despite the sufficient energy of the generated free carriers. At the other end (H21 and above), a very intense low energy secondary electron peak is observed. As a help to interprete such data, we realized the first ab initio calculations of the electronic lifetime of quasiparticles, in the GW approximation in a number of dielectrics including diamond. We find that the results are quite close to a simple "Fermi-liquid" estimation using the electronic density of diamond. We propose that a quite efficient mechanism could be the excitation of plasmons by high energy electrons, followed by the relaxation of plasmons into individual e-h pairs

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

Efficient hydrogen production from irradiated aluminum hydroxides

International audienceRadiation-catalysis is a well-known process leading to H2 production through radiolysis of adsorbed water on oxides. In this article, we show that common, easily accessible, hydroxides can be as much efficient for H2 production as the more efficient oxide identified until now. H2 radiolytic yields were determined from the same nanostructured hydrated samples that differ by their particle size (AlOOH L and AlOOH S for large and small particle size, respectively). The measured yields are of the order of 10−8 mol J−1. It means that such an irradiated material produces more efficiently H2 than an equivalent mass of water. H radicals, trapped electrons (F centers), and related O− centers were identified by electron paramagnetic resonance (EPR), at room and low temperature. Adsorbed water seems to play a role in the secondary processes of radical recombination, allowing a very efficient H2 production in these systems. This raises interesting questions about the energy transfer mechanism underlying this efficient hydrogen production and provide design lines for the design of efficient radiation-catalytic materials for H2 production

Radiation effects on a linear model compound for polyethers

No commentInternational audienceRadiation effects on a model polyether - poly(tetramethylene) glycol (PTMG) induced by high energy radiation were investigated. To understand the degradation mechanism, electron paramagnetic resonance (EPR), Fourier transform infra-red spectroscopy (FTIR), electrospray and gas mass spectrometry (ESI-MS and gas-MS), were carried out to identify radicals and chemical modifications. Size exclusion chromatography (SEC) was used to follow the evolution of the distribution of molecular weight. On the basis of the results, a mechanism of degradation for PTMG is proposed. © 2011 Elsevier Ltd. All rights reserved

of diazonium with SWNT to enhance CNTFETs performances

Tuning of metallic vs semiconducting selectivity in the reactio

Understanding the redox-induced polymer grafting process: a dual surface-solution analysis

International audienc

VUV grafting process: An efficient tool for 3D bulk patterning of polymer sheets

International audienceNumerous fields such as electronics, biotechnology, optics, energy, etc. require polymer films with 2D or increasingly 3D structuration and with a combination of different physicochemical properties. For this purpose, methods usually used are based on: (i) phase separation of block copolymers which leads to polymer blend films with an isotropic structure or (ii) radiation-induced graft polymerization to obtain isotropic architecture by an electron beam or g-ray radiation or an anisotropic structure by swift heavy ion irradiation or by X-rays or Extreme UltraViolet (EUV) light radiation. However, these processes present some limitations such as block copolymer and film synthesis, drastic safety procedures or the high cost of ionising sources. To overcome these drawbacks, we propose here an innovative process, based on VUV irradiation, which proves efficient not only for surface modification, but also for the bulk modification of industrially relevant polymers such as b-polyvinylidene fluoride (b-PVDF), polyethylene (PE) or fluorinated ethylene propylene (FEP). Contrary to common expectations, we assume that VUV irradiation of a PVDF film can induce radical active species at depths up to 50 micrometers, as demonstrated by ESR. Those active species are able to initiate the radical polymerization of a vinylic or acrylate monomer as acrylic acid through the polymer film, as confirmed by the EDX profile of the film thickness. Similar results are obtained on PE and FEP films, while aromatic polymers such as PET strongly absorb VUV energy and dissipate it along other pathways. By mixing this process and photolithographic masks, 3D structuration of commercial polymer films is obtaine