Supramolecular Ionic-Liquid Gels with High Ionic Conductivity

Abstract

Supramolecular ionogels were prepared by the gelation of room-temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF 4 ]) with (S,S)-bis(leucinol)oxalamide. Remarkably, the ionic conductivity of solutions and ionogels with low gelator concentrations is higher than that of neat [BMIm][BF 4 ]. On the basis of molecular dynamics simulations and quantum mechanical calculations, the origin of this phenomenon is attributed to the higher affinity of gelator molecules towards [BF 4 ] - ions, which reduces the electrostatic attraction between [BMIm] + and [BF 4 ] - and thus increases their mobility. With increasing gelator concentration, the ionic conductivity decreases due to the formation of a denser gelator matrix, which hinders the pathways for ionic transport. However, even for very dense ionogels, this decrease is less than one order of magnitude relative to neat [BMIm][BF 4 ], and thus they can be classified as highly conductive materials with strong potential for application as functional electrolytes.