Ion pairing and preferential solvation of butylmethylimidazolium chloride ion pair in water-ethanol mixtures by using molecular dynamics simulations

Constrained molecular dynamics simulations are used to compute the potentials of mean force (PMFs) of 1-butyl-3-methylimidazolium chloride (BMIM+ - Cl-) ion pair in water-ethanol mixtures. From the PMFs of BMIM+ - Cl- ion pair, we notice that, as the mole fraction of ethanol increases, the depths of the minima of the contact ion pair (CIP) and solvent assisted ion pair (SAIP) increase. The CIPs and SAIPs are stabilized by entropy in all the mixtures. As the mole fraction of ethanol changes from 1.0 to 0.8, the stabilities of CIPs and SAIPs are reduced significantly due to large enhancement in the local densities of water