New Coarse-Grained Models of Imidazolium Ionic Liquids for Bulk and Interfacial Molecular Simulations

We introduce new coarse-grained models for two imidazolium-based ionic liquids, namely, 1-butyl-3-methyl-imidazolium tetrafluoroborate [BMI][BF4] and 1-ethyl-3-methylimidazolium tetrafluoroborate [EMI][BF4], derived from the original force field of Roy and Maroncelli (J. Phys. Chem. B2010, 114, 12629–12631) representing the 1-butyl-3-methylimidazolium hexafluorophosphate [BMI][PF6] ionic liquid. We evaluate static and dynamic properties between 298 and 500 K and show that they agree with previous experimental and all-atom simulation studies. The models are used to conduct simulations of the liquid–vapor interface and accurately predict surface tensions at 400 K. Capacitive properties are also examined by doing molecular dynamics simulations of the ionic liquids in contact with graphite electrodes. The obtained structures and capacitances are consistent with all-atom simulation results reported on these systems.