Polymetalates based organic-inorganic nanocomposites

New nanocomposites materials have been synthesized. They present electrochemical and photochromic properties. They are based on a hybrid organic-inorganic network, in which tungsten heteropolyoxometalates (PW12O40(3-), SiW12O40(4-), W10O32(4-), polymeric tungstate) are entrapped. High tungsten ratios could be reached and films or bulk materials have been obtained. The structure of these materials is described on the basis of multi-spectroscopic investigations (IR, EPR, NMR). Electrochemical redox reactions have been observed in thin films. Dark blue reversible coloration of the materials is obtained under UV irradiation. The photochromic mechanism has been investigated and shows the reversible formation of carbonyl group

Photochromic organic-inorganic nanocomposites as holograpahic storage media

This paper describes the properties of some new organic-inorganic photochromic layers. They are based on a hybrid organic-inorganic matrix in which tungsten heteropolyoxometallates (SiW12O404-, PW12O403-) are entrapped in a network obtained from the reaction of 3-glycidoxy-propyltrimethoxysilane. The high homogeneity of these materials on the nanoscale leads to transparent monoliths and layers of controlled thicknesses up to 40 µm. The optical properties of the blend are emphasised and the construction of amplitude gratings in the materials by two-wave-mixing experiments is described. The results of the optical experiments and the comparison with the theoretical background are used as a model for photochromic holographic storage processes

Dynamics of the sol-gel transition in organic-inorganic nanocomposites

Two different techniques have been used to follow the gelation of photochromic organic-inorganic nanocomposites. The variations of molecular and macromolecular motions in these complex systems have been analyzed. Photo-correlation spectroscopy probes the formation of the gel network. Forced Rayleigh scattering experiences the microstructure of the mixtures via the measurement of the translational diffusion coefficient of entrapped photoreactive targets. In the different mixtures, a drop of the network mobility could be observed around the sol to gel conversion, while the entrapped molecules do not experience the macroscopic transition

Competing coexisting phases in 2D water

International audienceThe properties of bulk water come from a delicate balance of interactions on length scales encompassing several orders of magnitudes: i) the Hydrogen Bond (HBond) at the molecular scale and ii) the extension of this HBond network up to the macroscopic level. Here, we address the physics of water when the three dimensional extension of the HBond network is frustrated, so that the water molecules are forced to organize in only two dimensions. We account for the large scale fluctuating HBond network by an analytical mean-field percolation model. This approach provides a coherent interpretation of the different events experimentally (calorimetry, neutron, NMR, near and far infra-red spectroscopies) detected in interfacial water at 160, 220 and 250 K. Starting from an amorphous state of water at low temperature, these transitions are respectively interpreted as the onset of creation of transient low density patches of 4-HBonded molecules at 160 K, the percolation of these domains at 220 K and finally the total invasion of the surface by them at 250 K. The source of this surprising behaviour in 2D is the frustration of the natural bulk tetrahedral local geometry and the underlying very significant increase in entropy of the interfacial water molecules

Elaboration et proprietes electrochromes des gels d'oxyde de tungstene

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Multiscale NMR investigation of mesogenic ionic-liquid electrolytes with strong anisotropic orientational and diffusional behaviour

International audienceA new class of mesogenic ionic-liquid electrolytes made of long-chain imidazolium cations mixed with lithium salts is described. Fast, homogeneous and uniform orientational alignment of these systems can be obtained by cooling the mixture from the isotropic melt under magnetic constraint (magnetic fields of 9.4 and 14.1 T). The local orientational behaviour of the different species inside the electrolyte and the ionic diffusional properties in oriented phases of these new materials are investigated by NMR of 2H, 7Li and 11B quadrupolar nuclei and PFG-NMR measurements, respectively. Interestingly, the local orientation of C–H internuclear directions along the alkyl chains of the imidazolium cations is examined using natural abundance deuterium (NAD) 2D-NMR spectroscopy, thus avoiding any isotopic enrichment of material. The large anisotropy of self-diffusion coefficients measured from mobile ions (Li+ and BF4−) evidences the long-range alignment of ionic slabs of these materials

Ion transport in CLIP: Investigation through conductivity and NMR measurements

International audienceThe study deals with the electrochemical and physico-chemical characterizations of new proton-conducting ionic liquids. Through the use of several amines and perfluorinated acids, it attempts to define the most appropriate ionic liquids for use in high temperature PEMFCs. In addition to the usual characterizations based on Pulsed Field Gradient NMR and conductivity measurements, NMR correlation techniques NOESY, HOESY and COSY experiments are used to characterize the interactions and spatial proximities of ionic liquid species

Corrélations structure/propriétés de conduction ionique dans des matériaux hybrides siloxane-poly(oxydepropylène) dopés par des sels de sodium et de potassium

Les matériaux hybrides siloxane-poly(oxyéthylène) (PEO) ou siloxane-poly(oxypropylène) (PPO) obtenus par le procédé sol-gel présentent un grand intérêt scientifique et technologique du fait de l'interpénétration des réseaux inorganique et organique à l'échelle nanométrique. Lorsque ces matériaux hybrides sont dopés avec des sels alcalins, ils présentent une conductivité ionique élevée, similaire aux polymères conducteurs ioniques (10-4 S/cm), tout en présentant des propriétés mécaniques et optiques bien meilleures. Une des limitations de tous ces matériaux est le manque de connaissance sur la nature des espèces mobiles (ions libres ou solvatés, paires ou agrégats d'ions) responsables de la conduction. Afin d'améliorer encore les propriétés ioniques, la connaissance de la nature et de la structure locale autour des ions mobiles est donc fondamentale. En d'autres mots, l'objectif de ce travail est d'établir des corrélations entre la structure locale des porteurs de charge (coordinence, sphère de solvatation) et les aspects électriques macroscopiques (conduction ionique). Notre approche consiste donc à analyser l'ordre local autour des sels dissous par les spectroscopies d'absorption de rayons X (XANES, EXAFS), de Raman et de RMN afin de corréler ces mesures aux paramètres de conduction ionique. L'établissement de telles relations structure/propriétés aux différentes échelles spatiales est évidemment un des points clé pour optimiser de tels matériaux.Siloxane-poly(oxi propylene) (PPO) or Siloxane-poly(oxi propylene) hybrid materials prepared by the sol-gel route show increasing scientific and technological interest due to its particular structure in which the polymer chains are grafted to the inorganic nanoparticules. When doped within alkaline salts these hybrids present ionic conductivity similar to that of ionic conductive polymers (10-4 S/cm), and both their mechanical and optical properties are improved. However, the nature of the mobile species, are responsible for there conductivity (free ions, ion-pairs, aggregates) is not well established. So that the knowledge of the nature and the local structure around the mobile ions is the challenger to improve the ionic properties. The but of this work was to establish the correlations between the local structure around the charge carriers (coordination shell, solvation sphere) and the macroscopic conductivity. To reach this objective the local structure was probed by X ray absorption (XANES and EXAFS), Raman and NMR spectroscopy and the results related to that obtained from conductivity measurements.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Investigation of ion-conducting ormolytes : structure-property relationships

Hybrid organic-inorganic composites with ionic properties, so called ormolytes (organically modified electrolytes) have been prepared by the sol-gel process from mixtures of tetraethoxysilane, tetraethylene glycol, and lithium salt. They show ionic conductivity up to 5 x 10-5 Ω-1 cm-1, with activation energies around 0.6 eV. Their properties have been related to their structure using a multitechnique approach (IR, DSC, NMR, SAXS). These materials can be described as diphasic systems with silica clusters providing the mechanical properties and the organic phase allowing the dissolution of large quantities of salts. Optical transparency and mechanical stability can be explained by the interpenetration of these two phases at a molecular level