Dicationic ionic liquids as lubricants

Abstract

Twelve dicationic ionic liquids have been investigated for their potential inlubricants. The dications selected were synthesized from oligoethylene glycols linking two cationic moieties based on either N-methylimidazolium or N-methylpyrrolidinium at the extremities. As anions, chloride, bis(trifluoromethanesulfonyl)imide (Tf2N), methanesulfonate and butansulfonate were chosen. Thermal stability of the IL has been evaluated by thermogravimetric analysis and differential scanning calorimetry showing good properties up to 150 °C for all IL. SRV tribotests of neat IL using steel–steel contacts with ball-on-disc geometry were performed at 50 °C, 100 °C and 150 °C. Friction and wear were significantly influenced by both anion structure and chain length of the oligoethylene glycol moiety where longer chains yielded better tribological behavior. The tribological behavior improved with a mixture of different types of ILcontaining F, O, S in their anions. A large variation of ionic liquids corrosiveness and corrosion inhibition, respectively, was found attributed to structure variation. A general tendencyof improving the corrosion resistance when increasing the chain length of the neat ILshas been found. In addition to the neat dicationic ionic liquids, mixtures of 1% of the mostinteresting IL in polypropylene glycol base oil have been studied at 100 °C resulting in more favorable tribological properties for ionic liquids with Tf2N anion. X-ray photoelectron spectroscopy analysis showed that the structures with Tf2N anion create a tribofilm of inorganic fluorine that greatly improves the performance of the base oil.

Pyridinium based dicationic ionic liquids as base lubricants or lubricant additives

“…On the other hand, anion influence on tribological properties of ionic liquids were already demonstrated by Kronberger et al [21], with similar trends detected for ionic liquids containing RSO À 4 , and NTf À 2 anions, as well as Pagano et al [13], who detected the presence of a tribolayer of inorganic fluoride by XPS, generated from NTf À 2 anion, being responsible for the good performance. Additionally, [C 1 Py(CH 2 OCH 2 ) 3 (10), where noticeable reduction of COF (0.099), even with an addition of 0.25% of IL, was observed.…”

“…Previous works on the use of DILs derived from imidazolium [11,12] and pyrrolidinium [13] for lubrication have shown very promising results. Nevertheless, to our knowledge, no papers were published about using pyridinium DILs as lubricants or lubricant additives.…”

“…¼7.4 Hz, J 2 ¼ 4.9 Hz, J 3 ¼1.0 Hz), 3.62-3.53 (8H, m), 3.47 (4H, t, J¼ 6.5 Hz), 2.82 (4H, t, J ¼ 7.7 Hz), 1.99 (4H, m) 13. C NMR (CDCl 3 ): δ 29.5, 34.8, 70.1, 70.5, 70.6, 121.0, 122.9, 136.3, 149.2, 161.7.…”

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].…”