The Influences of Methyl Group at C2 Position in Imidazolium Ring on Tribological Properties

Tribological properties of two kinds of imidazolium ionic liquids (ILs) of 1,2-dimethyl-3-hexylimidazolium bis(trifluoromethylsulfonyl)imide (L-F116) and 1-dimethyl-3-hexylimidazolium bis(trifluoromethylsulfonyl)imide (L-F106) were evaluated as lubricant additives in poly(ethylene glycol) (PEG) for the steel–steel sliding pair by using an Optimol-SRV oscillating friction and wear test at the room temperature. At the same time, their electrochemical corrosion behaviors were measured by Tafel polarization. The morphologies of the worn surfaces were observed using a scanning electron microscope (SEM). The chemical states of several typical elements on the worn surfaces were examined by means of X-ray photoelectron spectroscopy (XPS). The results show that corrosion phenomena of PEG containing ILs on pure copper are negligible compared to PEG at room temperature. The 2-substituted imidazolium IL L-F116 shows excellent tribological performance and is superior to L-F106 in terms of anti-wear performance and load-carrying capacity. The worn surfaces were characterized to have slight abrasion and the XPS results indicated the formation of tribochemical adsorption and chemical reaction films on the worn surfaces.