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Issue 7, 2011
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Molecular dynamics simulations of ionic liquid–vapour interfaces: effect of cation symmetry on structure at the interface

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Abstract

The influence of alkyl chain symmetry of the imidazolium cation on the structure and properties of the ionic liquid–vapour interface has been addressed through molecular dynamics simulations.

The anion chosen is bis(trifluoromethylsulfonyl)imide (NTf2). Profiles of number densities, orientation of cations, charge density, electrostatic potential, and surface tension have been obtained. At the interface, both cations and anions were present, and the alkyl chains of the former preferred to orient out into the vapour phase. A large fraction of cations preferred to be oriented with their ring-normal parallel to the surface and alkyl chains perpendicular to it. These orientational preferences are reduced in ionic liquids with symmetric cations. Although the charge densities at the interface were largely negative, an additional small positive charge density has been observed for systems with longer alkyl chains. The electrostatic potential difference developed between the liquid and the vapour phases were positive and decreased with increasing length of the alkyl group. The calculated surface tension of the liquids also decreased with increasing alkyl chain length, in agreement with experiment. The surface tension of an ionic liquid with symmetric cation was marginally higher than that of one with an asymmetric, isomeric cation.

Graphical abstract: Molecular dynamics simulations of ionic liquid–vapour interfaces: effect of cation symmetry on structure at the interface

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Publication details

The article was received on 22 Jul 2010, accepted on 26 Oct 2010 and first published on 13 Dec 2010


Article type: Paper
DOI: 10.1039/C0CP01272F
Citation: Phys. Chem. Chem. Phys., 2011,13, 2714-2722
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    Molecular dynamics simulations of ionic liquid–vapour interfaces: effect of cation symmetry on structure at the interface

    S. S. Sarangi, S. G. Raju and S. Balasubramanian, Phys. Chem. Chem. Phys., 2011, 13, 2714
    DOI: 10.1039/C0CP01272F

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