On the Validity of Stokes–Einstein and Stokes–Einstein–Debye Relations in Ionic Liquids and Ionic‐Liquid Mixtures |
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Authors: | Thorsten Köddermann Ralf Ludwig Prof. Dr. Dietmar Paschek Dr. |
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Affiliation: | 1. Institut für Chemie, Abteilung Physikalische Chemie, Universit?t Rostock, Dr.‐Lorenz‐Weg 1, 18059 Rostock (Germany), Fax: (+49)?381‐498‐6524;2. Leibniz‐Institut für Katalyse, an der Universit?t Rostock, Albert‐Einstein‐Str. 29a, 18059 Rostock (Germany);3. Fakult?t Chemie, Physikalische Chemie III, Technische Universit?t Dortmund, Otto‐Hahn‐Str. 6, 44221 Dortmund (Germany) |
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Abstract: | Stokes–Einstein (SE) and Stokes–Einstein–Debye (SED) relations in the neat ionic liquid (IL) [C2mim][NTf2] and IL/chloroform mixtures are studied by means of molecular dynamics (MD) simulations. For this purpose, we simulate the translational diffusion coefficients of the cations and anions, the rotational correlation times of the C(2)? H bond in the cation C2mim+, and the viscosities of the whole system. We find that the SE and SED relations are not valid for the pure ionic liquid, nor for IL/chloroform mixtures down to the miscibility gap (at 50 wt % IL). The deviations from both relations could be related to dynamical heterogeneities described by the non‐Gaussian parameter α(t). If α(t) is close to zero, at a concentration of 1 wt % IL in chloroform, both relations become valid. Then, the effective radii and volumes calculated from the SE and SED equations can be related to the structures found in the MD simulations, such as aggregates of ion pairs. Overall, similarities are observed between the dynamical properties of supercooled water and those of ionic liquids. |
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Keywords: | computer chemistry ionic liquids molecular dynamics Stokes– Einstein relations Stokes– Einstein– Debye relations |
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