Mobility and association of ions in aqueous solutions: the case of imidazolium based ionic liquids

Abstract

The mobility and the mechanism of ion pairing of 1,1 electrolytes in aqueous solutions were investigated systematically on nine imidazolium based ionic liquids (ILs) from 1-methylimidazolium chloride, [MIM][Cl], to 1-dodecyl-3-methylimidazolium chloride, [1,3-DoMIM][Cl], with two isomers 1,2-dimethylimidazolium chloride, [1,2-MMIM][Cl], and 1,3-dimethylimidazolium chloride, [1,3-MMIM][Cl]. Molecular dynamics (MD) simulations, statistical mechanics calculations in the framework of the integral equation theory using one-dimensional (1D-) and three-dimensional (3D-) reference interaction site model (RISM) approaches as well as conductivity measurements were applied. From experiment and MD simulations it was found that the mobility/diffusion coefficients of cations in the limit of infinite dilution decrease with an increasing length of the cation alkyl chain, but not linearly. The aggregation tendency of cations with long alkyl chains at higher IL concentrations impedes their diffusivity. Binding free energies of imidazolium cations with the chloride anion estimated by RISM calculations, MD simulations and experiments reveal that the association of investigated ILs as model 1,1 electrolytes in water solutions is weak but evidently dependent on the molecular structure (alkyl chain length), which also strongly affects the mobility of cations.

Aqueous ionic liquids redistribute local enzyme stability via long-range perturbation pathways

“… [119] or MD simulation studies in ref. [120] , [121] , respectively. Box side lengths of 80 Å for all systems were used to define the system dimensions.…”

Imidazolium-Based Ionic Liquids: Some Research Methods, Applications and Physico-Chemical Properties

“…Furthermore, values of Λ° decrease with increasing alkyl chain length of the imidazolium chloride ILs (from b to j) in water medium. [76] From Table 1. it can be seen that K A values for presented ILs are biggest in DCM, [81] 1-BuOH, [75,83] 1-PrOH, [82,83] and 2-PrOH.…”

“…[85] Weak ion association is present in DMSO, [86] and in W solvent. [76][77][78] These results suggest that the imidazolium cation and anions of ILs are less associated or fully disociated in the solvent, which possesses a high relative permittivity due to the independent solvation od ions. One of the important factors affecting the ionic association is the ion-solvent interaction.…”

Chronopotentiometric Evaluation of Ionization Degree and Dissociation Constant of Imidazolium-Based Ionic Liquid [C6Meim][NTf2] in Polymeric Plasticized Membranes

“…Meanwhile, in [24], it was shown that ionization of the IL leads to the decrease of viscosity of the studied systems. The dissociation constant of IL [C 6 Meim]Cl (0.385 mol/L), as well as the diffusion coefficient of [C 6 Meim] + cation (7.65 × 10 −6 cm 2 /s), were estimated in [25] for infinitely diluted aqueous solutions. A nearly 10-fold lower diffusion coefficient was measured in [26] for pure IL [C 2 Meim][NTf 2 ] with NMR spectroscopy: 3 × 10 −7 cm 2 /s to 9 × 10 −7 cm 2 /s, depending on the temperature and applied electric field.…”