Protic ionic liquids with fluorous anions: physicochemical properties and self-assembly nanostructure

Abstract

A series of 11 new protic ionic liquids with fluorous anions (FPILs) have been identified and their self-assembled nanostructure, thermal phase transitions and physicochemical properties were investigated. To the best of our knowledge this is the first time that fluorocarbon domains have been reported in PILs. The FPILs were prepared from a range of hydrocarbon alkyl and heterocyclic amine cations in combination with the perfluorinated anions heptafluorobutyrate and pentadecafluorooctanoate. The nanostructure of the FPILs was established by using small- and wide-angle X-ray scattering (SAXS and WAXS). In the liquid state many of the FPILs showed an intermediate range order, or self-assembled nanostructure, resulting from segregation of the polar and nonpolar hydrocarbon and fluorocarbon domains of the ionic liquid. In addition, the physicochemical properties of the FPILs were determined including the melting point (T(m)), glass transition (T(g)), devitrification temperature (T(c)), thermal stability and the density ρ, viscosity η, air/liquid surface tension γ(LV), refractive index n(D), and ionic conductivity κ. The FPILs were mostly solids at room temperature, however two examples 2-pyrrolidinonium heptafluorobutyrate (PyrroBF) and pyrrolidinium heptafluorobutyrate (PyrrBF) were liquids at room temperature and all of the FPILs melted below 80 °C. Four of the FPILs exhibited a glass transition. The two liquids at room temperature, PyrroBF and PyrrBF, had a similar density, surface tension and refractive index but their viscosity and ionic conductivity were very different due to dissimilar self-assembled nanostructure.

Protic Ionic Liquids: Evolving Structure–Property Relationships and Expanding Applications

“…For example, the melting point of the fluorinated PILs is higher than that of their analoguous hydrocarbon counterparts, and the fluorinated PILs have higher thermal stability. 104 The presence of three domains has also been reported for aprotic ionic liquids, although it appears to be a much weaker fluorinated domain. 122 The interaction of the fluorinated PILs resulting from the hydrocarbon amines with the perfluorinated carboxylic acids with various solvents has been reported.…”

Thermophysical Characterization of Ionic Liquids Based on the Perfluorobutanesulfonate Anion: Experimental and Soft‐SAFT Modeling Results

“…[6,7] Recently,aneoteric family of ILs, the so-called fluorinated ionic liquids (FILs), has become appealing because it can combine the best properties of ILs, (negligible vapor pressure, ease of recovering and recycling, and tuneablet oxicity) with the best ones of somep erfluorocarbons (PFCs, chemically inert compounds with an extremelyl ow surface tension and ah igh capacityt od issolve gases). [8][9][10][11][12] These properties, supplemented by the different possible arrangementso ft he three nanodomains( polar,h ydrogenated nonpolar,a nd fluorinated nonpolar)p resented by FILs, [13] enable the design of the best FIL for ad esired application. In this work, FILs are considered as ionic liquids with fluorinated alkyl chains with at least four carbon atoms in the cation and/or the anion.…”

Triphilic Ionic‐Liquid Mixtures: Fluorinated and Non‐fluorinated Aprotic Ionic‐Liquid Mixtures

“…[36] Recently, MD simulations of fluorinated protic ionic liquids[38] indicated the existence of high structural heterogeneities. [39]…”