Molecular design of advanced lubricant base fluids: hydrocarbon-mimicking ionic liquids

Abstract

This paper describes the molecular design and tribological evaluation of novel room-temperature ionic liquid (RTIL) lubricants, abbreviated as P-SiSOs. The RTILs are designed to mimic hydrocarbons, in order to ensure their compatibility with existing tribosystems as well as enable use of conventional additives.Steel-on-steel ball-on-flat reciprocating tribotests performed under atmospheric conditions show that the neat P-SiSOs exhibit favorable performances, resulting in friction and wear significantly lower than those in the case of the perfluoropolyether lubricants used as references. Tribotests performed at elevated loads and temperatures indicate the formation of friction-reducing boundary films of the neat P-SiSOs. The tribological performance of the P-SiSO is improved further by the incorporation of additives conventionally used in hydrocarbon oils. When used in a concentration of 5 wt%, the additives glycerol monooleate, dibenzyl disulfide, and oleylamine improve the tribological characteristics of P-SiSO. These results indicate that molecular-designed hydrocarbon-mimicking RTIL lubricants can exhibit suitable performances in the neat form and that their performances can be improved further by using conventional additives, as in the case of hydrocarbon base oil-additive systems.

Formation of Boundary Film from Ionic Liquids Enhanced by Additives

“…The inset figures (also found in SI) display the wear scars of the balls lubricated with neat P-SiSO, reference PFPE, and P-SiSO + PNA + OPP, which was the additive combination that produced the lowest coefficient of friction. By comparing the wear scars, it was also clear that all P-SiSO samples performed significantly better than the reference PFPE fluid in terms of wear, which was in line with our previous results using similar RTILs [24]. Although the additives appear to influence the wear scar morphology (as seen from the change in wear scar light reflection in Figure 7c), it was difficult to quantify the change in tribological performance in terms of wear with high accuracy.…”

“…These tests used varying loads and temperatures in a manner similar to experiments in Reference [24], but with a focus on surface analysis as well as friction response. In the first test, V{100-300 N/25 • C/120 min}, the lubricant was evaluated by increasing the load in increments from 100 N to 300 N (corresponding to maximum Hertzian pressures of 2.1-3.0 GPa), at constant temperature, for a total test duration of 120 min.…”

Tribochemistry and thermo-oxidative stability of halogen-free ionic liquids

“…Overall, the friction results show that an increase in the P concentration for the AE (1 : 1) mixture was benecial in providing a sufficient load-carrying capacity to separate the rubbing parts while facilitating the reaction of the phosphonium phosphate IL with the metal surface. 54 As previously reported, when a metal surface is lubricated by IL, a layer structured lm is formed initially by physical adsorption. 55 The anions react rst with the positively charged metal surface to form a layer composed of iron phosphates.…”

“…Due to the presence of two hydroxyl groups at the terminal of its molecule, the friction modier could be adsorbed onto the metal surface thereby providing an extra wear protection. 54 The different frictional and wear behaviours of the evaluated mixtures could be related to the chemical composition of the formed tribolms which will be discussed within the next section.…”

Elastohydrodynamic Performance of a Bio-Based, Non-Corrosive Ionic Liquid

“…Some of these features make them interesting as lubricants and ILs have begun to gain attention for their tribological properties since 2001 [4]. Several researchers have shown that ILs demonstrate low wear and friction in steel-steel contacts [4][5][6][7][8][9], aluminium-steel contacts [4,10,11], nickel-steel contacts [12], copper-steel contacts [4] and ceramic-steel contacts [4,13]. Aside from potential problems with corrosion and additive compatibility most ILs are significantly more expensive to manufacture compared to more common lubricants.…”