Polyfluoroalkyl, Polyethylene Glycol, 1,4-Bismethylenebenzene, or 1,4-Bismethylene-2,3,5,6-Tetrafluorobenzene Bridged Functionalized Dicationic Ionic Liquids: Synthesis and Properties as High Temperature Lubricants

Abstract

A new class of geminal dicationic ionic liquids was formed with a bridging moiety, such as a polyalkyl ether, polyfluoroalkyl, 1,4-bismethylenebenzene, or 1,4-bismethylene-2,3,5,6-tetrafluorobenzene link, between alkyl-substituted imidazolium rings. Their properties were modified by varying the linker chains and/or alkyl substituents on the imidazolium ring. The polyfluoroalkyl bridged dicationic ionic liquids exhibit the highest densities and viscosities. Although melting points are directly proportional to the length of the alkyl substituent, the densities decrease concomitantly. With 1,4-bismethylene-2,3,5,6tetrafluorobenzene as the linking chain and with longer alkyl substituents on the imidazolium rings, the nonpolar character of the ionic liquid greatly increases, e.g., the solubilities in toluene of dicationic ionic liquids 36 and 37, where the ring substituents are C 10 H 21 and C 14 H 29 , increase markedly. Some of the salts exhibit higher conductivities than an equimolar tetrabutylammonium iodide solution in acetonitrile/ toluene. These new ionic liquids (except with PF 6 as anion) display outstanding tribological properties in temperature ramp tests by performing very well at 300 °C, thus meeting one criterion for high-temperature lubricants.

New Frontiers in Materials Science Opened by Ionic Liquids

“…Thereto, it has been proposed to synthesize IL-lubricants with high thermal stability up to 400 8C, [49,[67][68][69] based on the fact that geminal dicationic ILs possess extremely high thermal stability. [72] 3.…”

Solution and thermal behaviour of novel dicationic imidazolium ionic liquids

“…1,2 Room temperature ionic liquids with dipositive cations are rare, hence their physical behaviour is not well understood. [3][4][5][6][7][8][9] Tripositive cations are even scarcer. [10][11][12] The interest in dicationic ionic liquids is largely due to their high thermal stability, higher than that normally characterising the corresponding monocationic ionic liquids.…”

Time-Resolved Characterization of Dynamic Tribochemical Processes for Dicationic Imidazolium Ionic Liquid

“…The structures of the dicationic IL (IL2-di) and its monocationic analogue (IL2), which was used as a benchmark in this study, are shown in Figure 1. connecting chain [28][29][30][31] that was associated with better tribological properties, higher stability, lower toxicity and corrosiveness of the dicationic ILs [14,[31][32][33][34][35][36][37][38][39][40][41]. In the literature, there is a consensus of opinions that the good friction-reduction and wearresistant properties of ILs are owed to their ability to form stable adsorbed layers and protective tribofilms [4,27,[42][43][44].…”

“…Another approach relies on bridging two cationic head groups by PEG chain. Molecular dynamics simulation and advanced spectroscopy have revealed significant differences in structural heterogeneity and nano-organization between monocationic and geminal dicationic ILs with a long connecting chain [28][29][30][31] that was associated with better tribological properties, higher stability, lower toxicity and corrosiveness of the dicationic ILs [14,[31][32][33][34][35][36][37][38][39][40][41].…”