Molecular dynamics simulations of the structure and dynamics in mixtures of ionic liquids and alcohols†

Abstract

Molecular dynamics simulations were conducted on mixtures of ionic liquids (ILs) and alcohols, specifically methanol, ethanol, and 1-propanol. Two different ILs, [Mmim][MeSO₄] and [Bmim][MeSO₄], were used with varying alcohol mole fractions to investigate the impact of alkyl chain length of cations, alcohol types, and alcohol concentrations on different structural and dynamic properties. Unique characteristics of the ILs were observed due to the varying polarity of solvents and the creation of diverse local environments surrounding the ILs. The alcohols weaken the hydrogen bond network of the ILs. A better anion–cation packing was observed for [Mmim][MeSO₄]–alcohol than for [Bmim][MeSO₄]–alcohol mixtures. The free volume and clustering of alcohol molecules in [Mmim][MeSO₄]–alcohol mixtures were stronger than those in [Bmim][MeSO₄]–alcohol mixtures; these effects were stronger for mixtures containing longer-chain alcohols. Alcohols accelerate the dynamics of ILs, examined in terms of the anion/cation diffusion coefficients, dynamics of ion-pair formation/rupture, and dynamics of the hydrogen bond formed between the anion and the cation. This effect is more pronounced for mixtures of ILs with shorter-chain alcohols. These findings are consistent with the results obtained for the structural perturbations in ILs in the presence of alcohols, i.e., weakening of the hydrogen bond network in ILs upon addition of (shorter-chain) alcohols to the ILs, and reduced alcohol clustering.