Influence of the Molecular Characteristics of the Solvent and the Solute Cation on Diffusive Mass Transport in Binary Electrolyte Mixtures by Dynamic Light Scattering and Molecular Dynamics Simulations

Fick diffusion coefficients D 11 of binary electrolyte systems consisting of the solutes lithium or 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Li][NTf 2 ] or [EMIm][NTf 2 ]) dissolved in molecular and ionic liquid-based solvents are presented. D 11 was determined by dynamic light scattering (DLS) experiments and molecular dynamics (MD) simulations at temperatures up to 398 K and at a solute mole fraction of 0.05. The results contribute to an extension of the database for D 11 and allow investigation of the influence of the molecular characteristics on D 11 . Through variation of the molecular solvents, the dissociation of solutes in the mixture into ions was identified as a main influencing factor on the diffusive mass transport. Here, the dielectric constant ε r of the solvent was shown to be a good predictor for the ability of a solvent to dissociate the solute, which is quantified by calculating the solvation or coordination number. It could be shown that solvents with a large ε r fully dissociate solutes by forming a solvent shell around the cations, which leads to large D 11 . In solvents with a small ε r , the weaker interactions between solvent molecules and solute ions lead to a formation of ion pairs and clusters as well as to small D 11 .