Time filter

Source Type

Anouti M.,University of Tours | Jacquemin J.,Queens University of Belfast | Porion P.,CNRS Center for Research on Divided Matter
Journal of Physical Chemistry B | Year: 2012

We present a study on the transport properties through conductivity (σ), viscosity (η), and self-diffusion coefficient (D) measurements of two pure protic ionic liquids-pyrrolidinium hydrogen sulfate, [Pyrr][HSO 4], and pyrrolidinium trifluoroacetate, [Pyrr][CF3COO]-and their mixtures with water over the whole composition range at 298.15 K and atmospheric pressure. Based on these experimental results, transport mobilities of ions have been then investigated in each case through the Stokes-Einstein equation. From this, the proton conduction in these PILs follows a combination of Grotthuss and vehicle-type mechanisms, which depends also on the water composition in solution. In each case, the displacement of the NMR peak attributed to the labile proton on the pyrrolidinium cation with the PILs concentration in aqueous solution indicates that this proton is located between the cation and the anion for a water weight fraction lower than 8%. In other words, for such compositions, it appears that this labile proton is not solvated by water molecules. However, for higher water content, the labile protons are in solution as H3O+. This water weight fraction appears to be the solvation limit of the H+ ions by water molecules in these two PILs solutions. However, [Pyrr][HSO4] and [Pyrr][CF 3COO] PILs present opposed comportment in aqueous solution. In the case of [Pyrr][CF3COO], η, σ, D, and the attractive potential, Epot, between ions indicate clearly that the diffusion of each ion is similar. In other words, these ions are tightly bound together as ion pairs, reflecting in fact the importance of the hydrophobicity of the trifluoroacetate anion, whereas, in the case of the [Pyrr][HSO4], the strong H-bond between the HSO4 - anion and water promotes a drastic change in the viscosity of the aqueous solution, as well as on the conductivity which is up to 187 mS•cm-1 for water weight fraction close to 60% at 298 K. © 2012 American Chemical Society.

Porous materials are known to adsorb fluid and can be characterised by measurement of fluid adsorption isotherms. Many nanoporous materials exhibit linear pores such as MCM-41 and porous silicon or alumina. In such systems, data adsorption analysis is considered to be straightforward within the approximation of independent domains. This article, which reviews previous molecular simulation works, aims at showing that the presence of heterogeneities within the pores actually invalidates this hypothesis, with consequences for porosity characterisation. To enlighten the effects, starting from perfect cylinders, the number of heterogeneities is progressively increased, up to large numbers, for which specific simulation tools are used to take into account the interdependence between the domains. The adsorption/desorption isotherms are calculated and correlated to the appearance of an exponentially large number of metastable states. © 2014 Taylor & Francis.

Puibasset J.,CNRS Center for Research on Divided Matter
Journal of Physics Condensed Matter | Year: 2011

An improved approach is proposed to analyze the density of metastable states within any hysteresis loop, such as those observed in magnetic materials or for adsorption in porous materials. Except for a few analytically tractable models, most calculations have to be performed numerically on finite systems. The main points to be addressed thus concern the average over various material samples (the so-called realizations of the disorder), and the finite size analysis to estimate the thermodynamic limit. As an improvement of previously existing methods, it is proposed to introduce the Fourier transform of the density of metastable states (characteristic function). Its logarithm is shown to be additive and can straightforwardly be averaged over disorder. This procedure leads to a new definition of the complexity in finite size, giving the usual quenched complexity in the thermodynamic limit, while being better suited to performing finite size analysis. The calculations are illustrated on a molecular simulation based model for a simple fluid adsorbed in heterogeneous siliceous tubular pores mimicking mesoporous materials like MCM-41 or porous silicon. This approach is expected to be of general interest for hysteresis phenomena, including magnetic materials. © 2011 IOP Publishing Ltd.

Sinturel C.,CNRS Center for Research on Divided Matter | Vayer M.,CNRS Center for Research on Divided Matter | Morris M.,University College Cork | Hillmyer M.A.,University of Minnesota | Hillmyer M.A.,LE STUDIUM Institute for Advanced Studies
Macromolecules | Year: 2013

This Perspective provides a critical analysis of the current knowledge concerning solvent vapor annealing (SVA) of block polymer thin films. Herein, we identify key challenges that will be important to overcome for future development of SVA as a practical, reliable, and universal technique for the valorization of block polymer thin films in a wide range of technologies. The Perspective includes a brief background on thin film block polymer self-assembly, a historical account of the SVA technique, an overview of the SVA fundamentals that are necessary to develop a more comprehensive picture of the overall process, and summaries of relevant and important contributions from the recent literature. We also offer our outlook on SVA and suggest important future directions. © 2013 American Chemical Society.

Gao Q.,CNRS Center for Research on Divided Matter | Demarconnay L.,CNRS Center for Research on Divided Matter | Raymundo-Pinero E.,CNRS Center for Research on Divided Matter | Beguin F.,CNRS Center for Research on Divided Matter | Beguin F.,Poznan University of Technology
Energy and Environmental Science | Year: 2012

This study investigates the large voltage range of symmetric carbon/carbon capacitors in environmentally friendly aqueous lithium sulfate electrolyte. A high over-potential related to the hydrogen sorption mechanism at the negative electrode contributes usefully to enhance the operating voltage up to 1.9 V with an excellent stability during 10000 charge/discharge cycles. Such a voltage value is two times higher than the values generally demonstrated with symmetric carbon/carbon capacitors in conventional aqueous media, while avoiding the disadvantages of the corrosive properties of acidic and basic electrolytes. Temperature programmed desorption analysis of the electrodes after long-term cycling gives the evidence that the maximum voltage is essentially limited by an irreversible electro-oxidation process at the positive electrode. If the potential of the positive electrode goes beyond a given value during cell operation, a massive electro-oxidation of carbon leads to a further deleterious increase of the maximum potential of the electrode and an increase of electrode resistance resulting in a decrease of capacitance. Inconvenience can be sidestepped by performing a controlled chemical oxidation of the carbon surface using hydrogen peroxide. As a consequence, the maximum potential of the electrode remains stable during operation of the cell at 1.9 V, and the system can be charged/discharged during 10000 cycles with very moderate loss of capacitance or increase of resistance. © 2012 The Royal Society of Chemistry.

Discover hidden collaborations