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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 | Year: 2015

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.


Stevanovic S.,French National Center for Scientific Research | Costa Gomes M.F.,Institute of Chemistry of Clermont-Ferrand
Journal of Chemical Thermodynamics | Year: 2013

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.


Ghoufi A.,Rennes Institute of Physics | Malfreyt P.,Institute of Chemistry of Clermont-Ferrand | Tildesley D.J.,Ecole Polytechnique Federale de Lausanne
Chemical Society Reviews | Year: 2016

This review presents the state of the art in molecular simulations of interfacial systems and of the calculation of the surface tension from the underlying intermolecular potential. We provide a short account of different methodological factors (size-effects, truncation procedures, long-range corrections and potential models) that can affect the results of the simulations. Accurate calculations are presented for the calculation of the surface tension as a function of the temperature, pressure and composition by considering the planar gas-liquid interface of a range of molecular fluids. In particular, we consider the challenging problems of reproducing the interfacial tension of salt solutions as a function of the salt molality; the simulations of spherical interfaces including the calculation of the sign and size of the Tolman length for a spherical droplet; the use of coarse-grained models in the calculation of the interfacial tension of liquid-liquid surfaces and the mesoscopic simulations of oil-water-surfactant interfacial systems. © The Royal Society of Chemistry 2016.


Ghoufi A.,Rennes Institute of Physics | Malfreyt P.,Institute of Chemistry of Clermont-Ferrand
Molecular Simulation | Year: 2013

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.


Mendonca A.C.F.,Institute of Chemistry of Clermont-Ferrand | Padua A.A.H.,Institute of Chemistry of Clermont-Ferrand | Malfreyt P.,Institute of Chemistry of Clermont-Ferrand
Journal of Chemical Theory and Computation | Year: 2013

We report nonequilibrium molecular dynamics of ionic liquids interacting with metallic surfaces. A specific set of interaction parameters for ionic liquids composed of alkylammonium cations and alkylsulfonate anions with an iron surface, which has been previously developed (J. Chem. Theory Comput.2012, 8, 3348) is used here. We develop a procedure for a quantitative prediction of the friction coefficient at different loads and shear rates. The simulated friction coefficient agrees very well with the available experimental ones. The dependence of friction on the load, shear velocity, surface topology, and length of alkyl side chains in the ionic liquid is also investigated. The changes in the frictional forces are explained in terms of the specific arrangements and orientations of groups forming the ionic liquid at the vicinity of the surface. © 2013 American Chemical Society.


Cisnetti F.,Institute of Chemistry of Clermont-Ferrand | Gautier A.,Institute of Chemistry of Clermont-Ferrand
Angewandte Chemie - International Edition | Year: 2013

Subtle differences: Two recent crystal structures have provided the first insight into nitrate/nitrite exchangers (example shown with bound nitrite), which are crucial to bacterial metabolism. A direct comparison of the structures reveals how the proteins can distinguish between their highly similar substrates and translate this into a conformational change to translocate ions across the membrane. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Andanson J.-M.,Institute of Chemistry of Clermont-Ferrand | Traikia M.,Institute of Chemistry of Clermont-Ferrand | Husson P.,Institute of Chemistry of Clermont-Ferrand
Journal of Chemical Thermodynamics | Year: 2014

Several experimental techniques were used to study ionic association and interactions in aqueous [C1C2Im][MeSO4], 1-ethyl-3-methylimidazolium methylsulfate, and [C1C 4Im][MeSO4], 1-butyl-3-methylimidazolium methylsulfate. Two transport properties, viscosity and electrical conductivity, were determined for these two binary mixtures. For a better assessment of the ionic association and the perturbation of water into the molecular structure of the ionic liquid, diffusion coefficients of ions and water molecules were obtained by NMR spectroscopy while molecular interactions were probed by IR spectroscopy. The comparison of the two ionic liquids shows that for the shorter alkyl chain the viscosity was lower and the electrical conductivity was higher. While the viscosity of the mixture drops already with small additions of water, the electrical conductivity of the solution is only significantly increased for high water concentrations. A maximum is observed for compositions around x water = (0.90 to 0.95). The SO3 asymmetric stretching band of the IR spectrum can be used as a probe to observe the evolution of the structure around the anion which was mainly occurring for high concentrations of water. Several experimental techniques show than the main change in the ionic association was only observed for high water contents (water mole fraction > 0.8). © 2014 Elsevier Ltd. All rights reserved.


Malfreyt P.,Institute of Chemistry of Clermont-Ferrand
Molecular Simulation | Year: 2014

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.


Mendonca A.C.F.,Institute of Chemistry of Clermont-Ferrand | Malfreyt P.,Institute of Chemistry of Clermont-Ferrand | Padua A.A.H.,Institute of Chemistry of Clermont-Ferrand
Journal of Chemical Theory and Computation | Year: 2012

An atomistic force field for ionic liquids interacting with a metal surface is built on the basis of quantum methods. Density functional calculations of alkylammonium cations and alkylsulfonate anions interacting with a cluster of iron atoms were performed, at a series of distances and orientations, using the M06 functional that represents noncovalent interactions. A site-site potential function was then adjusted to the BSSE-corrected DFT interaction energies. Finally, the polarization of the metal by the ions was taken into account using induced dipoles to reproduce the interaction energy between charges and a conductor surface. When combined with a molecular force field for the ionic liquid and a suitable potential for metals, our model allows the computer simulation of heterogeneous systems containing metal surfaces or nanoparticles in the presence of ionic liquids. Our aim is to study tribological systems with ionic lubricants. We report molecular dynamics results on the structure of the interfacial layer of several alkylammonium alkylsulfonate ionic liquids at a flat iron surface, including analyses of the positional and orientational ordering of the ions near the surface, and charge density profiles. Both anions and cations are found in the first ordered layer of ions near the surface, with the oxygen atoms of the sulfonyl groups interacting more strongly with the metal. The interfacial layer is essentially one ion thick, except for very short chain ionic liquids in which a second layer is observed. The effects of different lengths of the nonpolar alkyl side chains on the cation and the anion are different: whereas butyl chains on the sulfonate anions tend to be directed away from the surface, those on ammonium cations lie more parallel to the surface. © 2012 American Chemical Society.


Boutinaud P.,Institute of Chemistry of Clermont-Ferrand
Journal of Physics Condensed Matter | Year: 2014

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.

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