Dielectric study on mixtures of ionic liquids

Ionic liquidsare promising candidates for electrolytes in energy-storage systems. We demonstrate that mixing two ionic liquidsallows to precisely tune their physical properties, like the dc conductivity. Moreover, these mixtures enable the gradual modification of the fragility parameter, which is believed to be a measure of the complexity of the energy landscapein supercooled liquids. The physical origin of this index is still under debate; therefore, mixing ionic liquidscan provide further insights. From the chemical point of view, tuning ionic liquidsvia mixing is an easy and thus an economic way. For this study, we performed detailed investigations by broadband dielectric spectroscopyand differential scanning calorimetry on two mixing series of ionic liquids. One series combines an imidazole based with a pyridine based ionic liquidand the other two different anions in an imidazole based ionic liquid. The analysis of the glass-transition temperatures and the thorough evaluations of the measured dielectric permittivity and conductivity spectra reveal that the dynamics in mixtures of ionic liquidsare well defined by the fractions of their parent compounds.