Abstract
We study the solvation and the association properties of ion pairs in aqueous dimethyl sulfoxide (DMSO) solution by atomistic molecular dynamics (MD) simulations. The ion pair is composed of two lithium and a single sulfonated diphenyl sulfone ion whose properties are studied under the influence of different DMSO concentrations. For increasing mole fractions of DMSO, we observe a non-ideal behavior of the solution as indicated by the derivatives of the chemical activity. Our findings are complemented by dielectric spectra, which also verify a complex DMSO-water mixing behavior. In agreement with these results, further simulation outcomes reveal an aqueous homoselective solvation of the ion species which fosters the occurrence of pronounced ion association constants at higher DMSO mole fractions. The consequences of this finding are demonstrated by lower ionic conductivities for increasing concentrations of DMSO.
Highlights
Ion pairing is an ubiquitous effect in concentrated salt solutions[1,2,3] which has some important consequences for complex fluids.[4,5,6,7,8,9,10,11] The formation of ion aggregates significantly influences dynamic properties like ionic conductivities or diffusivities
We study the solvation and the association properties of ion pairs in aqueous dimethyl sulfoxide (DMSO) solution by atomistic molecular dynamics (MD) simulations
We studied the properties of ion pairs in binary solvent mixtures of DMSO and water by molecular dynamics simulations
Summary
Ion pairing is an ubiquitous effect in concentrated salt solutions[1,2,3] which has some important consequences for complex fluids.[4,5,6,7,8,9,10,11] The formation of ion aggregates significantly influences dynamic properties like ionic conductivities or diffusivities. In terms of electrochemical applications, the suppression and modification of ion pair formation is highly desirable.[12] In general, one can distinguish between contact and solvent-separated ion pairs,[1,3,13,14] while the mechanisms leading to the formation of these aggregates are still under debate.[1,14,15] Previous results demonstrated that the solvent itself as well as the solvent chemical activity[1,16,17] strongly influence many effects, e.g. the formation of ion pairs,[1,3] the occurrence of specific ion effects[18,19,20,21] and the ion condensation behavior around macromolecules.[22,23,24,25,26,27,28,29,30] Based on these findings, one can assume that tunable mixtures provide a controllable influence on the ion pairing mechanism.
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