Molecular dynamics simulations of imidazolium-based ionic liquid/water mixtures: Alkyl side chain length and anion effects

This paper describes molecular dynamics (MD) simulations of three ionic liquid (IL)/water mixtures at various water mole fractions: 1-butyl-3-methylimidazolium (BMIM+)/BF4−, 1-octyl-3-methylimidazolium (OMIM+)/BF4−, and OMIM+/Cl−. The goal is to elucidate the effect of alkyl side chain length and anion on the structure and dynamics of the mixtures. Replacing the BMIM+ cation with OMIM+ results in stronger aggregation of the cations and slower diffusion of the anions. Replacing the BF4− anion with Cl− alters the water distribution at low water mole fractions and slows diffusion in the mixtures. Potential experimental manifestations of the behavior in both cases are given.