Hierarchical Structure and Dynamics in Ionic Liquids

Abstract

In the past decade, ionic liquids (ILs) have gained increasing attention in many fields, since they possess several unique properties, such as negligible vapor pressure, high ionic conductivity, and wide range of solubility. One of the most interesting features in imidazolium-based ILs is a higher order structure reflecting the nanoscale segregation of polar and nonpolar domains. The structure and dynamics of the ILs were investigated by means of neutron diffraction and quasielastic scattering techniques. It was found that the nanostructure drastically grows upon cooling. Furthermore, we have successfully observed the relaxation of nanostructure, ionic diffusion, imidazolium relaxation, and alkyl reorientation separately. From the anion/cation dependence of the relaxation processes, it is concluded that the hierarchical dynamics in the ILs is predominantly governed by the Coulombic interaction between the polar parts of cations and anions.