Mapping Ion-Pair Dissociation Across the Hydration Spectrum of [HMIM][Cl]: A Molecular Dynamics Perspective

Molecular dynamics was utilized to investigate the dissociation process of the 1-hexyl-3-methylimidazolium chloride ionic liquid ([HMIM][Cl] IL). To further study the mechanism at the molecular scale, the local microstructure variation in the mixtures with the increase of water content was analyzed in detail. The simulation results show that there are still 35.89% of free ions in pure ILs. With the increase in water content, water molecules preferentially bind to free ions. When the water content is greater than 0.8, the water molecules gradually insert the anion and cation from the periphery of the cation-anion pair and finally almost replace the anion around the cation. The analysis of spatial distribution function, solvent accessible area, and ion diffusion coefficient further confirmed this conclusion. These quantitative ion pairing and dissociation mechanisms shed light on the rational design of the IL aqueous toward their applications in the chemical-related fields and provide key parameters for the modeling of IL aqueous solution.