Transport Properties of the Ionic Liquid 1-Ethyl-3-Methylimidazolium Chloride from Equilibrium Molecular Dynamics Simulation. The Effect of Temperature

Abstract

We present here equilibrium molecular dynamics simulation results for self-diffusion coefficients, shear viscosity, and electrical conductivity in a model ionic liquid (1-ethyl-3-methylimidazolium chloride) at different temperatures. The Green-Kubo relations were employed to evaluate the transport coefficients. When compared with available experimental data, the model underestimates the conductivity and self-diffusion, whereas the viscosity is overpredicted, showing only a semiquantitative agreement with experimental data. These discrepancies are explained on the basis of the rigidity and lack of polarizability of the model. Despite this, the experimental trends with temperature are remarkably well reproduced, with a good agreement on the activation energies when available. No significant deviations from the Nernst-Einstein relation can be assessed on the basis of the statistical uncertainty of the simulations, although the comparison between the electric current and the velocity autocorrelation functions suggests some degree of cross-correlation among ions in a short time scale. The simulations reproduce remarkably well the slope of the Walden plots obtained from experimental data of 1-ethyl-3-methylimidazolium chloride, confirming that temperature does not alter appreciably the extent of ion pairing.

Partial financial support for this work has been provided by the Spanish government under project no. CTQ2005-00296/PPQ and by the Generalitat de Catalunya (SGR2005-00288). C. Rey-Castro acknowledges an I3P (CSIC) postdoctoral research contract from the Spanish Government (Ministerio de Educación y Ciencia) cofunded by the European Social Fund, EU. This research has been carried out partially using computational resources from CESCA (Catalunya, Spain).