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Stevanovic S.,French National Center for Scientific Research | Costa Gomes M.F.,Institute of Chemistry of Clermont-Ferrand
Journal of Chemical Thermodynamics

The density and viscosity of the ionic liquids 1-butyl-1- methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate [C 1C4Pyrro][eFAP] and trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate [P66614][eFAP] were measured as a function of temperature and pressure and as a function of temperature, respectively. These two ionic liquids are more viscous than those based in the same anion associated to imidazolium cations. The effect of the addition of water on the density and viscosity of [P66614][eFAP] was studied at pressures close to atmospheric and as a function of the temperature. This ionic liquid is only partially miscible with water, its solubility being of around XH2O=0.2 in the range of (303 to 315) K. Experimental values of the solubility of carbon dioxide, nitrous oxide, ethane, and nitrogen were obtained as a function of temperature and at pressures close to atmospheric. Carbon dioxide and nitrous oxide are the more soluble gases with mole fraction solubilities up to 7 · 10-2. Ethane is four times and 1.3 times less soluble than carbon dioxide in [C1C4Pyrro] [eFAP] and [P66614][eFAP], respectively. Nitrogen is one order of magnitude less soluble than the others gases in the two ionic liquids studied. In order to understand behavior of the different gases with these ionic liquids, the thermodynamic functions of solvation such as enthalpy and entropy were calculated from the variation of the Henry's law constant with temperature. It is shown that the more favorable interactions of the gases with the ionic liquid explain the larger solubility of carbon dioxide and nitrous oxide in [C 1C4Pyrro][eFAP]. In the case of [P66614][eFAP], it is the less favorable entropic contribution that explains the lower solubility of ethane in this ionic liquid. © 2012 Elsevier Ltd. All rights reserved. Source

Ghoufi A.,Rennes Institute of Physics | Malfreyt P.,Institute of Chemistry of Clermont-Ferrand
Molecular Simulation

For a half century, the calculation of local pressure components and surface tension along the normal to the surface have been carried out using mechanical definitions. This has led to three principal definitions: Irving and Kirkwood, Harasima and Kirkwood-Buff. Recently, thermodynamic definitions based on the energy calculation have been introduced to compute the local properties. We propose here to compare both definitions for Lennard-Jones particles interacting through a truncated and shifted potential. For this, two locations of the pairwise interaction involved in the calculation of the local pressure components and surface tension within the thermodynamic routes are investigated. For the first time, we show that the thermodynamic definition suffers, to one least degree with respect to the mechanical definition, from the same ambiguity. From a numerical standpoint, thermodynamic definition is more simple and less computationally expensive. Therefore, with the complicated potential, the thermodynamic approach appears to be most interesting to compute macroscopic and local pressure and surface tension. © 2013 Taylor and Francis Group, LLC. Source

The relative longevity of the research in the field of the molecular simulations of the liquid-vapour interfaces of Lennard-Jones (LJ) particles can be explained by the dependence of the surface tension on many methodological factors. After a few illustrations on the parameters that can impact the results of surface tension on the LJ interfaces, we establish the ability of the current methodologies to quantitatively predict the surface tension of various liquid-vapour interfaces of pure components at different temperatures. We also show that the methods perform very well for the reproduction of the interfacial tension of binary mixtures in a wide range of pressures. © 2014 © 2013 Taylor & Francis. Source

Boutinaud P.,Institute of Chemistry of Clermont-Ferrand
Journal of Physics Condensed Matter

Zircon and fergusonite-type vanadates either undoped or doped with Eu3+or Pr3+are synthesized in the system (Y,Bi)2O3-V2O5by solid state and coprecipitation procedures. Their optical properties are investigated at 300 and 77 K and the luminescence mechanisms are discussed on the basis of energy level schemes that combine the host and the dopant states. Fergusonite BiVO4is shown to glow in the deep red region at 77 K upon excitation at 450 nm and shorter wavelengths. Host sensitization is demonstrated in Eu3+-doped fergusonite BiVO4and zircon BiVO4at 77 K, but lost as temperature is raised to 300 K. The origin of this effect is addressed by considering the nature of the host-band edge states and self-quenching processes. The near-UV excited luminescence in the system (Y, Bi)VO4:Pr3+(zircon) consists of the yellow bandlike emission of the zircon host and of the characteristic red 1D2→3H4emission lines of Pr3+in vanadates. The relative contribution of these features can be fine-tuned at room temperature by adjusting the composition of the materials or the excitation wavelength. © 2014 IOP Publishing Ltd. Source

Kirchner B.,University of Bonn | Holloczki O.,University of Bonn | Canongia Lopes J.N.,University of Lisbon | Canongia Lopes J.N.,New University of Lisbon | Padua A.A.H.,Institute of Chemistry of Clermont-Ferrand
Wiley Interdisciplinary Reviews: Computational Molecular Science

Ionic liquids-which are special solvents composed entirely of ions-are difficult albeit interesting to study for several reasons. Owing to the many possible cation and anion combinations that form ionic liquids, common properties are hard to classify for them, which makes the theoretical investigation crucial for ionic liquids. The system size, the amount of possible isomers including cation-anion orientation and coordination, as well as the rotation of the side chain(s) prevent the use of high-level electronic structure methods, and density functional theory is the method of choice. Dispersion forces-although they are small compared to electrostatics-play a major role in ionic liquids; therefore, methods that describe such kind of interplay are preferred. Between the cation and the anion, there is a sizable charge transfer, which has important consequences for molecular dynamics simulations and force field development. Already based on the first generation of force fields important discoveries were made, namely that ionic liquids are nanostructured. Moreover, it was possible to predict that their distillation is possible. Throughout the construction of these force fields, transferability was taken into account which allowed them to describe homologous series. For studying reactions in ionic liquid (IL) media, continuum models were found to improve the results. Ab initio molecular dynamics (AIMD) and quantum mechanics (QM)/molecular mechanics (MM) approaches are well suited for spontaneous events. In case of very large systems, such as cellulose in ionic liquids, coarse-grained methods are providing insight and are applied more frequently. This makes ionic liquids real multiscalar systems. © 2014 John Wiley & Sons, Ltd. Source

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