Homogenous mixing of ionic liquids: molecular dynamics simulations.
ABSTRACT Binary mixtures of room temperature ionic liquids (IL) with a common cation were investigated using atomistic molecular dynamics (MD) simulations. Two different binary ILs, viz., [C4mim][PF6]-[C4mim][Cl] and [C4mim][PF6]-[C4mim][BF4], were studied with varying fractions of either anion. The coordination environment of an anion around the cation is altered in the presence of another type of anion. The extent of change is larger for anions with much different radii. Atomistic MD and coarse grain MD simulations do not show any evidence for the clustering of like anions at any concentration. The binary liquids are well mixed at the molecular level.
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ABSTRACT: The effect of replacing bis(trifluoromethylsulphonyl)imide ([NTf2]) by hexafluorophosphate ([PF6]) in room temperature ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide ([BMIm][NTf2]) confined between two gold interfaces is herein reported through molecular dynamics simulations using all-atom non-polarisable force-fields. Five systems were studied ranging from pure [BMIm][NTf2] to pure [BMIm][PF6], with [PF6] molar fractions of 0, 0.125, 0.25, 0.375 and 0.5. Special attention was drawn to investigate the impact of the [PF6] anion on the IL, in particular on the first layers of the liquid in close contact with the solid gold surface.Molecular Simulation 09/2014; 41(5-6):455-462. DOI:10.1080/08927022.2014.986122 · 1.12 Impact Factor
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ABSTRACT: Quantitative prediction of physical properties of room temperature ionic liquids through non-polarizable force field based molecular dynamics simulations is a challenging task. The challenge lies in the fact that mean ion charges in the condensed phase can be less than unity due to polarization and charge transfer effects whose magnitude cannot be fully captured through quantum chemical calculations conducted in gas phase. The present work employed the DDEC/c3 method to calculate site charges of ions using electronic charge densities obtained from periodic density functional theory (DFT) calculations of their crystalline phases. The total ion charges obtained thus range between -0.6e for chloride and -0.8e for PF</sub>6</sub> ion. The mean value of the ion charges obtained from DFT calculations of an ionic liquid closely matches that obtained from the corresponding crystal thus confirming the suitability of using crystal site charges in simulations of liquids. These partial charges were deployed within the well-established CLaP force field, and consequently parameters of its non-bonded and torsional interactions were refined to ensure that they reproduced quantum potential energy scans for ion pairs in gas phase. The refined force field was employed in simulations of seven ionic liquids with six different anions. Nearly quantitative agreement with experimental measurements was obtained for the density, surface tension, enthalpy of vaporization and ion diffusion coefficients.The Journal of Physical Chemistry B 03/2014; 118(12). DOI:10.1021/jp500296x · 3.38 Impact Factor
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ABSTRACT: The dissolution of 1-ethyl-3-methylimidazolium chloride in trihexyltetradecylphosphonium chloride does not only exhibit a large negative entropy. Also, in the resulting mixtures, the phosphonium cation diffuses faster than the much smaller imidazolium cation. Both unexpected features originate from the formation of a large symmetric ion cluster cage in which the imidazolium cation is caught by three chloride anions and four phosphonium cations.Physical Chemistry Chemical Physics 01/2015; 17(6). DOI:10.1039/C4CP05074F · 4.20 Impact Factor