Dynamic Light Scattering for Studying Mutual Diffusion Coefficients in Electrolyte Systems Comprised Entirely of Ions

This study demonstrates the applicability of heterodyne dynamic light scattering (DLS) for the investigation of molecular diffusive mass transport in electrolyte systems by the determination of mutual diffusion coefficients at macroscopic thermodynamic equilibrium. For four binary model mixtures composed entirely of ions, it could be evidenced that the obtained experimental signals are associated with hydrodynamic modes. In the range from (293 to 353) K, the influence of temperature on the mutual diffusion coefficient and its relation to other thermophysical properties are discussed for the selected systems. These systems are based on three different ionic liquids (ILs) and a salt and always share a common ion in the mixture. A non-ideal behavior is observed for one study on the concentration dependence of the mutual diffusion coefficient for one of the binary IL systems in the mole fraction range between 0.1 and 0.9. For the four systems studied in this work, expanded uncertainties of the mutual diffusion coefficient go down to 3.0% and are 8.0% on average.