Interfacial properties of the ionic liquid [bmim][triflate] over a wide range of temperatures
Por:
Rivera, Jose L., Molina-Rodriguez, Luis, Ramos-Estrada, Mariana, Navarro-Santos, Pedro, Lima, Enrique
Publicada:
1 ene 2018
Resumen:
We carried out molecular dynamics simulations of the liquid/vacuum equilibrium of the ionic liquid [bmim][triflate] in a wide range of temperatures (323.15 to 573.15 K). The results showed liquid phases with high densities even at temperatures close to the decomposition temperature of the liquid. The density and surface tension behaviors are linear across this wide range of temperatures, which is an extension of the behaviors of these systems at low temperatures, where these properties have been experimentally measured. The interfacial region shows peaks of adsorption of the ions; they are ordered, with the alkyl chains of the [bmim] cations pointing out of the liquid, and the tailing angle of the chains becomes 90° at higher temperatures. The alkyl chains are part of the outermost interfacial region, where intra- and intermolecular tangential forces are in equilibrium; thus, they do not contribute to the total surface tension. Unlike simpler organic liquids, the surface tension is composed of positive normal contributions of intermolecular interactions; these are almost in equilibrium with the negative normal contributions of intramolecular interactions, which are mainly vibrations of the distance and the angle of valence. The pressure profiles show that the molecules are in 'crushed' conformations internally in the bulk liquid and even more so in the normal direction at the interface. The total pressure profiles show values with physical meaning, where the tangential peaks show higher values than normal pressures and give rise to the surface tension. Short cutoff radii for the calculation of intermolecular forces (less than 16.5 Å) produce a system that is not mechanically stable in the region of the bulk liquid (confirmed by radial distribution function calculations); this produces a difference between the normal pressure and the average of the tangential pressures, which affects the calculation of the surface tension due to overestimation by up to 20% when using the global expression, which is extensively used for the calculation of surface tension. The use of a sufficiently long cutoff radius avoids these mechanical balance problems. © 2018 The Royal Society of Chemistry.
Filiaciones:
Rivera, Jose L.:
Graduate School of Physics Engineering, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Michoacan, Mexico
Faculty of Chemical Engineering, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Mexico
Univ Michoacana, Grad Sch Phys Engn, Morelia 58000, Michoacan, Mexico
Univ Michoacana, Fac Chem Engn, Morelia 58000, Michoacan, Mexico
Molina-Rodriguez, Luis:
Faculty of Chemical Engineering, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Mexico
Univ Michoacana, Fac Chem Engn, Morelia 58000, Michoacan, Mexico
Ramos-Estrada, Mariana:
Faculty of Chemical Engineering, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Mexico
Univ Michoacana, Fac Chem Engn, Morelia 58000, Michoacan, Mexico
Navarro-Santos, Pedro:
Institute of Chemical Biology Sciences, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Mexico
Univ Michoacana, Inst Chem Biol Sci, Morelia 58000, Michoacan, Mexico
Lima, Enrique:
Laboratorio de Fisicoquímica y Reactividad de Superficies (LaFReS), Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito Exterior S/N, CU, Del. Coyoacán, Ciudad de México, Mexico
Univ Nacl Autonoma Mexico, Inst Invest Mat, Lab Fisicoquim & Reactividad Superfis LaFReS, Circuito Exterior S-N, Mexico City, DF, Mexico
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