Mesoscopic structural organization in fluorinated room temperature ionic liquids

The presence of fluorous tails in room-temperature ionic liquids imparts new properties to their already rich spectrum of appealing features. The interest towards this class of compounds that are of ionic nature with melting point less than 25 degrees C is accordingly growing; in particular, compounds bearing relatively long fluorous tails have begun to be considered. In this invited presentation, we show recent results arising from the systematic study of structural properties of a series of fluorinated room temperature ionic liquids, with growing fluorous chain length. At odd with the current understanding of this class of compounds, we show experimentally that they are characterized by the presence of segregated fluorous domains whose size depends on the fluorous chain length. This experimental finding, based on the synergic use of X-ray and neutron scattering, provides a structural scenario at the mesoscopic spatial scale that is in agreement with the recent state of the art molecular dynamic simulations. We speculate on the potential role of this significant compartmentalization of the bulk liquid phase into different nanoscale domains, as relevant in a series of applications including separation, solubility, catalysis, and so forth. (C) 2018 Published by Elsevier Masson SAS on behalf of Academie des sciences.