Pressure‐viscosity behaviour and film thickness in elastohydrodynamic regime of lubrication of ionic liquids and other base oils

Abstract

Viscosities at high pressures for 16 base oils (six polyolesters, three polyglycols, six ionic liquids and squalane) were used to analyze the influence of their chemical structure on the pressure‐viscosity coefficient, α. Comparisons with literature α values for vegetable bases (canola, soybean and jojoba oils) are also performed. For the molecular lubricants, we found trends that are coherent with the literature, whereas for ionic liquids (ILs), new trends were found. ILs based on tris(pentafluoroethyl)trifluorophosphate anion [FAP]−are those which present higher α values. The role of the lubricants in the central thickness in the isothermal elastohydrodynamic regime of lubrication was evaluated through the product η00.69 α0.56, η0 being the viscosity at 0.1 MPa. One of the [FAP]− ILs provides film thicknesses close to the polyglycols with similar viscosity. Bis(trifluoromethylsulfonyl)imide ILs and the shorter polypropyleneglycoldimethyl ethers are the lubricants that better avoid the changes on the film thicknesses with the temperature owing to a high viscosity index. Copyright © 2013 John Wiley & Sons, Ltd.

Volumetric behaviour of six ionic liquids from T = (278 to 398) K and up to 120 MPa

“…In general, the compressibility of ILs is much lower than that of standard hydraulic mineral oils and even lower than that of water [3] in several cases under broad temperature and pressure conditions. Besides, in previous papers [16][17][18][19] we have found that most of the ILs analysed have low pressure-viscosity coefficients in comparison with most of the conventional lubricants. According to Mia and Ohno [20], high bulk modulus fluids having low pressure-viscosity coefficient, indicate an efficient hydraulic fluid.…”

Antiwear performance of ionic liquid+graphene dispersions with anomalous viscosity-temperature behavior

“…The dispersion of graphene in ILs has been shown to achieve enhanced tribological performance [6,15,[18][19][20][21]. The rheological study of ionic liquids, nanofluids and dispersions is an important aspect for their practical applications, particularly as thermal fluids and lubricants or lubricant additives [22].…”

Nanolubrication by ionic liquids: molecular dynamics simulations reveal an anomalous effective rheology

“…5 ILs feature several favorable characteristics that can prevent those undesired situations, including high thermal stability, non-flammability, negligible volatility, and appropriate pressure-viscosity and temperatureviscosity dependence. 3,[5][6][7] ILs were also suggested as lubricants in spatial applications owing to their low vapor pressure and high radiation resistance properties. 8 They were as well considered in lubricated systems for their use as additives 3 or with additives 5 and can exhibit in both cases better responses than usual lubricants.…”