Properties of Apolar Solutes in Alkyl Imidazolium-Based Ionic Liquids: The Importance of Local Interactions

The solvation and the dynamic properties of apolar model solutes in alkyl imidazolium-based ionic liquids (IL) are studied by using all-atom molecular dynamics simulations. In regards to specific IL effects, we focused on the often used 1-ethyl-3-methyl imidazolium cation in combination with the anions tetrafluoroborate, acetate, and bis(trifluoromethanesulfonyl)imide. Our findings reveal that the size of the anion crucially influences the accumulation behavior of the cations, which results in modified IL solvation properties. Deviations between the different alkyl imidazolium-based IL combinations can be also observed with regard to the results for the radial distribution functions, the number of surrounding molecules, and the molecular orientation. The analysis of the van Hove function further shows pronounced differences in the dynamic behavior of the solutes. The simulations verify that the solute mobilities are mainly influenced by the composition of the local solvent shell and the properties of the underlying Lennard-Jones interactions. Additional simulations with regard to modified short-range dispersion energies for alkyl imidazolium-based ILs validate our conclusions.