Diffusion Coefficients in Electrolyte MixturesInfluence of the Solute Characteristics

Fick diffusion coefficients D11 of
binary electrolyte mixtures consisting of seven different solutes
dissolved in either acetonitrile (ACN) or diethyl carbonate (DEC)
are presented. The solutes were selected with respect to a systematic
variation of their characteristics such as size, mass, polarity, and
charge delocalization. D11 was determined
by dynamic light scattering (DLS) and molecular dynamics (MD) simulations
at temperatures up to 398 K and at a solute amount fraction of 0.05.
The results contribute to an extension of the existing database for D11 in binary electrolyte mixtures and allow
its investigation as a function of the solute characteristics. With
the help of MD simulations, the coordination or solvation number,
which represents the solvation of solute ions by solvent molecules
present in the first solvation shell, could be accessed and used to
investigate the influence of the fluid structure on D11. Here, for ACN as a solvent, a larger D11 for the solute [Na][NTf2] in comparison
to that for [Li][NTf2] could be attributed to a less defined
and more fragile solvation shell surrounding the larger [Na]+ cation.