M Yao

Imidazolium Ionic Liquids As Antiwear and Antioxidant Additive in Poly(ethylene glycol) for Steel/Steel Contacts

Three imidazolium-based ionic liquids containing sterically hindered phenol groups were synthesized. The cation was 1-(3,5-ditert-butyl-4-hydroxybenzyl)-3-methyl-imidazolium, and the anions were tetrafluoroborates, hexafluorophosphates, and bis(trifluoromethylsulfonyl)imide. The physical properties of the synthetic products and of poly(ethylene glycol) (PEG) with the additive were evaluated. The oxidative stability of 0.5 wt % 1-(3,5-di-tert-butyl-4-hydroxybenzyl)-3-methyl-imidazolium hexafluorophosphates in PEG were assessed via rotating bomb oxidation test (RBOT), thermal analysis, and copper strip test. The tribological behaviors of the additives for PEG application in steel/steel contacts were evaluated on an Optimol SRV-IV oscillating reciprocating friction and wear tester as well as on MRS-1J four-ball testers. The worn steel surface was analyzed by a JSM-5600LV scanning electron microscope and a PHI-5702 multifunctional X-ray photoelectron spectrometer. RBOT test, thermal analysis, and copper strip test results revealed that synthesized ionic liquids possessed excellent antioxidant properties. Tribological application results revealed that these could effectively reduce friction and wear of sliding pairs compared with the PEG films used without the additives. Specifically, (BHT-1)MIMPF(6) exhibited better antiwear properties at an optimum concentration of 1 wt %. At this level, its antiwear property significantly improved by 100 times with respect to using just the PEG base oil. Boundary lubrication films composed of metal fluorides, organic fluorines, organic phosphines, and nitride compounds were formed on the worn surface, which resulted in excellent friction reduction and antiwear performance.

Bisimidazolium ionic liquids as the high-performance antiwear additives in poly(ethylene glycol) for steel-steel contacts.

Bisimidazolium ionic liquids [C(10)(m(2)im)(2)(NTf(2))(2), C(10)(m(2)im)(2)(PF(6))(2), and C(10)(m(2)im)(2)(BF(4))(2)] with different anions were evaluated as the antiwear additives in poly(ethylene glycol) at room temperature. Results showed that they could effectively reduce the friction and wear of sliding pairs compared with the cases without these additives. Especially, C(10)(m(2)im)(2)(NTf(2))(2) showed better antiwear properties with an optimum concentration of 3 wt %, by which a significant improvement of its antiwear property by dozens of times with respect to the base oil was achieved. The excellent tribological properties are attributed to the formation of high-quality physical adsorption films and tribochemical product during friction and the good miscibility of ionic liquids with base oil.

Synthesis, Characterization, Thermal Analyses, and Spectroscopic Properties of Novel Naphthyl-Functionalized Imidazolium Ionic Liquids

A series of novel ionic liquids based on naphthyl-functionalized imidazolium cation have been prepared. Their structure was characterized by NMR. The thermal stabilities of the prepared liquids were studied by thermal gravimetric analysis. The new ionic liquids containing NTf-2 anion display significantly higher thermal stabilities (>400°C). Anion exchange to PF-6, BF-4, and Br– decreases the thermal stabilities of such ionic liquids. Fluorescence and UV–Vis absorption spectroscopy were used to study the spectroscopic properties of the ionic liquids. Compared with common ionic liquids, the described ionic liquids provide robust fluorescence properties and remarkably increased UV–Vis absorption. This research may enrich the field of functionalized ionic liquids and provide a platform for extension of ionic liquid applications.