How ideal are binary mixtures of room-temperature ionic liquids?

Data for the densities, conductivities, viscosities and dielectric properties of binary mixtures of the tetrafluoroborate and the dicyanamide salts of 1-N-ethyl-3-N-methylimidazolium have been measured at 25 °C. The mixtures exhibit practically "ideal" (linear) mixing behaviour with respect to viscosity, molar volume, and the effective dipole moment of the observed relaxation associated with cation reorientation, indicating a smooth change in the structure of the mixtures. On the other hand, the electrical conductivity and dielectric relaxation time deviate considerably from "ideal" mixing behaviour, indicating enhanced translational and rotational dynamics in the mixtures