The transport properties of ionic liquids (ILs) are crucial properties in view of their applications in electrochemical devices. One of the most important advantages of ILs is that their chemical-physical properties and consequently their bulk performances can be well tuned by optimizing the chemical structures of their ions. This will require elucidating the structural features of the ions that fundamentally determine the characteristics of the nanostructures and the viscosities of ILs. Here we showed for the first time that the “rigidity”

the order

and the compactness of the three-dimensional ionic networks generated by the anions and the cation head groups determine the formation and the sizes of the nanostructures in the apolar domains of ILs. We also found that the properties of ionic networks are governed by the conformational flexibility and the symmetry of the anion and/or the cation head group. The thermal stability of the nanostructures of ILswas shownto be controlled by the sensitivity of the conformational equilibrium of the anion to the change of temperature. We showed that the viscosity of ILs is strongly related to the symmetry and the flexibility of the constitute ions rather than to the size of the nanostructures of ILs. Therefore

the characteristics of the nanostructures and the viscosities of ILs

especially the thermal stability of the nanostructures

can be fine-tuned by tailoring the symmetry and the conformational flexibility of the anion.