Ionic liquids as tribological performance improving additive for in-service and used fully-formulated diesel engine lubricants

In recent years, several papers have been published that investigate the potential use of ionic liquids (ILs) as additives in lubricants. However, corrosive attack of ILs on lubricated metal surfaces and low miscibility of ILs in the non-polar oils are major obstacles to maintaining an optimum lubrication performance level. High miscibility and no corrosive behaviour of Trihexyltetradecyl phosphonium bis(2,4,4-tri-methylpentyl) phosphinate and Trihexyltetradecyl phosphonium bis(2-ethylhexyl) phosphate, as lubricating oil additives have recently been described in literature. This article presents work on using these phosphonium based ILs as an additive in the fully formulated diesel engine lubricants. This approach could allow the used lubricants to recover their tribological performance for further use at the end of service life. This extension of service life has the potential to generate significant economic and environmental benefits. Also it will add to the much needed knowledge about the effect of interaction between ILs and existing additives in engine-aged lubricants on the tribological performance of ring-liner tribo-system of diesel engines. Results revealed an improvement in friction and antiwear performance of used lubricant by addition of both ILs. However an increase in wear was noted for new (fresh) and in-service lubricant samples. An interesting interference between existing lubricant additives and added ILs in a boundary film formation process has been observed

Ionic liquids as an additive in fully formulated wind turbine gearbox oils

This work presents the friction and wear behaviour of two fully formulated (polyalphaolefin- and mineral-based) wind turbine gearbox oils separately additivated with two ionic liquids ([Choline][NTf2] and [BMP][NTf2]) at 5wt% concentration. A tribometer using a ball-on-plate reciprocating configuration is adopted for friction and wear experiments. Friction is measured during tests and the worn surface is measured and analysed by confocal microscopy, SEM, EDS and XPS. The friction and wear results show that both ionic liquids used as an additive have a slight friction modifier character but a strong wear reducing performance, with [BMP][NTf2] performing better than [Choline][NTf2]. In addition, EDS and XPS analysis demonstrated the temperature-related chemical interactions and their influence on tribological behaviour

Grafted ionomer complexes and their effect on protein adsorption on silica and polysulfone surfaces

We have studied the formation and the stability of ionomer complexes from grafted copolymers (GICs) in solution and the influence of GIC coatings on the adsorption of the proteins β-lactoglobulin (β-lac), bovine serum albumin (BSA), and lysozyme (Lsz) on silica and polysulfone. The GICs consist of the grafted copolymer PAA28-co-PAPEO22 {poly(acrylic acid)-co-poly[acrylate methoxy poly(ethylene oxide)]} with negatively charged AA and neutral APEO groups, and the positively charged homopolymers: P2MVPI43 [poly(N-methyl 2-vinyl pyridinium iodide)] and PAH∙HCl160 [poly(allylamine hydrochloride)]. In solution, these aggregates are characterized by means of dynamic and static light scattering. They appear to be assemblies with hydrodynamic radii of 8 nm (GIC-PAPEO22/P2MVPI43) and 22 nm (GIC-PAPEO22/PAH∙HCl160), respectively. The GICs partly disintegrate in solution at salt concentrations above 10 mM NaCl. Adsorption of GICs and proteins has been studied with fixed angle optical reflectometry at salt concentrations ranging from 1 to 50 mM NaCl. Adsorption of GICs results in high density PEO side chains on the surface. Higher densities were obtained for GICs consisting of PAH∙HCl160 (1.6 ÷ 1.9 chains/nm2) than of P2MVPI43 (0.6 ÷ 1.5 chains/nm2). Both GIC coatings strongly suppress adsorption of all proteins on silica (>90%); however, reduction of protein adsorption on polysulfone depends on the composition of the coating and the type of protein. We observed a moderate reduction of β-lac and Lsz adsorption (>60%). Adsorption of BSA on the GIC-PAPEO22/P2MVPI43 coating is moderately reduced, but on the GIC-PAPEO22/PAH∙HCl160 coating it is enhanced

Two phosphonium cation-based ionic liquids as lubricant additive to a polyalphaolefin base oil

This paper studies the tribological performance of two phosphonium cation-based ionic liquids: trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl) phosphinate ([P6,6,6,14][(iC8)2PO2]) and trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate ([P6,6,6,14][BEHP]), as lubricant additive at 1 wt% to a polyalphaolefin. A comparison of their tribological behavior was made to that of one type of zinc dialkyldithiophosphate (ZDDP). Stribeck curve tests were made in a Mini Traction Machine (MTM) tribometer at entrainment speeds ranging from 2000 to 10 mm/s, 30 N-load, slide-to-roll ratio (SRR) of 50%, and temperatures of 40, 60, 80 and 100 °C. Tribofilm formation tests were also conducted in the MTM at 100 °C, load of 50 N, entrainment speed of 150 mm/s, SRR of 50%, and duration of 60 min. Additionally, reciprocating 60-min wear tests at 60 N-load, frequency of 15 Hz, stroke length of 4 mm and at room temperature were performed with IL-containing mixtures at 0.5 and 1 wt%. Coefficient of friction was recorded during the tests, and wear on the discs surface was measured using confocal microscopy. SEM-EDS and XPS were also used for studying the lubricant-surface interactions after these tests. Lubricants including [P6,6,6,14][(iC8)2PO2] exhibited better tribological performance than [P6,6,6,14][BEHP] ones and close to the ZDDP results. SEM images of worn surfaces exhibited evidence of plastic deformation and adhesive wear and EDS analysis showed that only active elements (P, S, Zn) were detected for mixtures containing ZDDP. XPS analysis indicated a different lubrication mechanism of the blends with ionic liquids compared with the ZDDP ones

Antifriction and Antiwear Properties of an Ionic Liquid with Fluorine-Containing Anion Used as Lubricant Additive.

Tribological behavior of trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) imide [P66614][NTf2] ionic liquid (IL) used as additive in a diester oil at concentrations of 0.25, 0.5 and 1 wt% was studied in this research. The IL solubility in the base oil was measured using the inductively coupled plasma mass spectrometry (ICP-MS) technique, and corrosion analysis was done at room temperature at relative humidity of 49–77%. Tribological tests were conducted for 30 min at room temperature, 15 Hz frequency, 4 mm of stroke length, a load of 80 N (corresponding to 2 GPa of maximum contact pressure) and relative humidity of 35–53%. Friction coefficient was recorded during tests, and the wear scar was measured by confocal microscopy. Worn surface was also analyzed by SEM, EDS and XPS. Results showed that a saturated solution of [P66614][NTf2] in the base oil contains about 30 wt% of IL and corrosion activity for the highest concentration of IL (1 wt%) was not found after a 20-day test. Although the base oil and the mixtures had similar friction behavior, only the 1 wt% sample exhibited slightly lower wear volume than the base oil. SEM images exhibited similar wear track width (707–796 µm) and wear mechanism (adhesive) for all samples tested. In addition, the EDS spectra only showed the elements present in the steel. Finally, the XPS measurements could not detect differences regarding iron chemical state among the samples, which is consistent with the tribological behavior obtained