Microscopic Structural and Dynamic Features in Triphilic Room Temperature Ionic Liquids.

Fabrizio Lo Celso,Alessandro Triolo,Uwe Keiderling,Olga Russina,Lorenzo Gontrani,Edward W Castner,Man Zhao,Elisabetta Simonetti,Giovanni B Appetecchi

doi:10.3389/fchem.2019.00285

Abstract

Here we report a thorough investigation of the microscopic and mesoscopic structural organization in a series of triphilic fluorinated room temperature ionic liquids, namely [1-alkyl,3-methylimidazolium][(trifluoromethanesulfonyl)(nonafluorobutylsulfonyl)imide], with alkyl = ethyl, butyl, octyl ([Cnmim][IM14], n = 2, 4, 8), based on the synergic exploitation of X-ray and Neutron Scattering and Molecular Dynamics simulations. This study reveals the strong complementarity between X-ray/neutron scattering in detecting the complex segregated morphology in these systems at mesoscopic spatial scales. The use of MD simulations delivering a very good agreement with experimental data allows us to gain a robust understanding of the segregated morphology. The structural scenario is completed with determination of dynamic properties accessing the diffusive behavior and a relaxation map is provided for [C2mim][IM14] and [C8mim][IM14], highlighting their natures as fragile glass formers.

Highlights

Ionic liquids (ILs) constitute an interesting class of compounds, composed solely of ionic species and with a melting point below 100◦C
We report on the structural properties of a series of 1-alkyl-3-methyimidazolium ([Cnmim], where n indicates the number of carbon atoms along the side alkyl chain, with n = 2, 4, and 8)(nonafluorobutylsulfonyl) imide ([IM14], 1 and 4 represent the number of carbon atoms on the two sides of the imide anion) [see e.g., (Johansson et al, 2010; Montanino et al, 2012; Jeremias et al, 2013; Russina et al, 2013, 2017a; Castiglione et al, 2014; Paolone et al, 2018)], at ambient conditions
As recently reported in a series of papers (Shen et al, 2012; Russina et al, 2013; Hettige et al, 2014; Hollóczki et al, 2015; Lo Celso et al, 2017, 2018a,b), neutron scattering succeed in detecting the occurrence of fluorous tails clusters embedded into the charged matrix: the results presented in Figures 1, 2 confirm this observation, indicating that the perfluorobutyl chains in the [IM14] anions tend to associate into small fluorous domains and in the rest of the manuscript we will further explore this structural feature in the probed Fluorinated Ionic Liquids (FILs)