Nanoparticle containing lubricants

Abstract

A method of preparing a nanoparticle composition, wherein the method comprises: providing a nanoparticle precursor that has a laminar structure; providing an ester-containing compound of Formula I; and milling the nanoparticle precursor in the presence of the ester-containing compound.

Description

[0001] NANOPARTICLE CONTAINING LUBRICANTS

[0002] Field of the Invention

[0003] The present invention relates to additives for lubricants, such as greases, and to methods of preparing the additives. The additives comprise nanoparticles and an a,P-unsaturated ester-containing compounds. The present invention also relates to lubricant compositions containing the additives, and to articles comprising the additives and / or the lubricant compositions.

[0004] Background of the Invention

[0005] For example, lubricants used in ball bearings (e.g. pitch bearings) for application such as wind turbines experience particularly high loads. Despite these high loads, lubricants must be able to provide sufficient cushioning between the moving surfaces. A particular challenge for wind turbine pitch bearing lubrication is the reciprocating / oscillating motion. Similar challenges exist in transport-related applications, such as trains (especially high-speed trains) and electric vehicles (e.g. automobiles), robotics and metalworking fluids.

[0006] Lubricants for space applications can experience extreme environments, for example ultrahigh vacuums, wide temperature ranges, wide speed ranges and / or atomic oxygen irradiation.

[0007] Environmental concerns in the backdrop of evolving efficiency and emission standards have motivated efforts to replace traditional lubricant additives such as molybdenum dithiocarbamate (MoDTC) and zinc dialkyldithiophosphate (ZDDP), and other additives in wind turbine grease containing sulfated ash, phosphorous and sulphur (SAPS) with more environmentally benign alternatives.

[0008] Typically lubricants include a base oil and additives. Common base oils include petroleum fractions (mineral oil), vegetable oil, hydrogenated polyolefins, esters, silicones and / or fluorocarbons. Additives are included to, for example, reduce friction and wear, increase viscosity, and / or improve viscosity index, resistance to corrosion and oxidation, aging and / or contamination. Lithium greases are common multi-purpose greases. Approximately 70 percent of the grease sold worldwide is based on a thickener that is a lithium soap and / or a lithium adducts.

[0009] Lithium soaps are typically formed from stearic acid and lithium hydroxide. The main components of lithium greases are: base oil (75-98wt%); thickener system (2-20wt%) and performance additives (0-10wt%). Greases based on a lithium complex typically have higher dropping point, mechanical stability, water resistance and oil separation resistance than conventional lithium greases.

[0010] Alternative lubricants are required to meet the requirements of particular applications. For example, alternative lubricants are required to protect components in high force applications, such as in the pitch bearings of wind turbines. Alternative lubricants that are water soluble are also required. Alternative lubricants that are suitable for application in space are also required.

[0011] The present invention has been devised with the foregoing in mind.

[0012] Summary of the Invention

[0013] According to a first aspect the present invention provides a method of preparing a nanoparticle composition, wherein the method comprises: providing a nanoparticle precursor that has a laminar structure; providing an ester-containing compound of Formula I; and milling (e.g. ball milling) the nanoparticle precursor in the presence of the ester-containing compound. Formula I is defined as:

[0014] Formula I.

[0015] In the ester-containing compound of Formula I, R1is a hydrocarbon group that is optionally substituted; and R2, R3and R4are each independently H or a Cl-10 hydrocarbon group that is optionally substituted. Milling (e.g. ball milling) is relatively straightforward to perform and readily upscalable.

[0016] It has surprisingly been found that milling (especially ball milling) is very effective for intercalating and exfoliating nanoparticle precursors.

[0017] Surprisingly, residual ester-containing compound of Formula I from the ball milling process can be beneficial for reducing friction and wear. The residual ester-containing compound of Formula I does not need to be removed before the nanoparticle composition can be used as a lubricant. The method of the invention is more facile and environmentally benign.

[0018] In particular, the present method may be termed a “one-pot” method as there is no requirement for post-milling purification of the nanoparticles. Additives can readily be incorporated into the nanoparticle composition to generate mixtures.

[0019] Silica (Mater. Horiz., 2019, 6, 1416 — 1424) and various inorganic salts (Small 2020, 16, 1906734; Nano Lett. 2017, 17, 7767-7772; J. Mater. Chem. A, 2018, 6, 15010- 15026) have previously been used in ball milling to prepare nanoparticulate transition metal dichalcogenides (TMDCs) and carbon dots. However, these processes are complicated by the requirement to remove silica and / or salt after ball-milling.

[0020] Unlike conventional methods for preparing nanoparticles, the ability to avoid using silica and salt means that these do not need to be separated from the nanoparticles after use.

[0021] Furthermore, the method of the invention is able to provide nanoparticles that are small enough to form an effective lubricant, with much smaller nanoparticles than conventional ball milling techniques such as those using dextran or cellulose.

[0022] Dextran (ACS Appl. Nano Mater. 2023, 6, 6662-6669) and cellulose (Cellulose, 2014, 21 :2469-2478) have been used in ball milling to prepare M0S2 nanosheets. However, the size of the obtained nanosheets is too large to be used as a lubricant. While disclosures in the prior art use surfactants in order to increase the stability of dispersions of nanoparticles, the present invention does not need to use surfactants.

[0023] WO 97 / 03151 Al discloses a compressible graphite lubricant and anaerobic pipe sealant composition that functions as a liquid lubricant when exposed to air and in the absence of air cures to form a compressible sealant with memory. The composition includes a mixture of a polymerizable acrylic ester monomer and a peroxy polymerization initiator, and compressible expanded graphite particles. This document describes that the expanded graphite is “formed of graphite flakes which have been subjected to an oxidizing environment at elevated temperature to expand the graphite”, rather than being nanoparticles. The expanded flakes are large in comparison to the nanoparticles of the present invention, ranging in size from about 940pm (0.037 inches) to about 1.4mm (0.055 inches). Furthermore, there is no mention of milling in this document. The composition in this document is formed by simply mixing the different components together, rather than performing any processing (such as milling) on a mixture of the components. In addition, the exfoliated graphite described by WO 97 / 03151 Al is not a “nanoparticle precursor” as required by claim 1, but in fact is a nanoparticle itself. In essence, WO 97 / 03151 Al would provide samples akin to those shown in Vials 2 and 5 of Figure 4 of the present application. This document does not disclose a nanoparticle precursor that is a transition metal dichalcogenide (e.g. M0S2 and WS2), or boron nitride; or an acrylate where R1is a PEG group; or a carrier being included with the composition; or an ionic liquid (e.g. LiTFSI) being included.

[0024] US 11180712 B2 describes lubricant compositions that include particles sized greater than lOOnm in diameter and one or more polymer compounds. The polymers include a variety of acrylates, such as methyl and butyl methacrylates. The examples describe the ultrasonication of hexagonal boron nitride (hBN) with a polymer comprising a “macromonomer” formed of methyl methacrylate, and butyl methacrylate (among other components) to provide particles with a d50 value of 267nm. Milling is described as an alternative way to mix the composition. In contrast to the claimed invention, milling is not used for reducing primary particle size. Furthermore, there is no mention of PEGMA being used as a monomer. This document describes the polymerisation of methacrylate compounds before subjecting them to milling to mix the composition. Furthermore, the particles produced by the invention have diameters up to about lOnm, whereas this document discloses particles larger than 200nm in diameter. Performing ball milling after polymerisation of the methacrylate does not meet the requirements of the claimed invention or allow the same particles to be produced. Having an acrylate present during ball milling and size reduction to prepare the nanoparticles provides the nanoparticles with protection from oxidation. In essence, US 11180712 B2 would provide samples akin to those shown in Vials 1, 2, 4 and 5 of Figure 4 of the present application. Furthermore, the claimed invention primarily relates to transition metal dichalcogenides (e.g. M0S2 and WS2) and graphite rather than hBN. In particular, the preparation of surface-modified transition metal dichalcogenides has been a difficult challenge in the art. In addition, this document relates to additives for lubricant oils and makes no reference to water-based and grease additives (e.g. for application in wind turbines). This document does not disclose nanoparticle precursors of transition metal dichalcogenides (e.g. M0S2), or graphite; or particles with an average particle size of lOOnm or less; or an acrylate where R1is a PEG group; or an ionic liquid (e.g. LiTFSI) being included.

[0025] Nanoparticle precursors include laminar materials. Preferably the nanoparticle precursor is graphite or a transition metal dichalcogenide (e.g. M0S2). Milling (e.g. ball milling) the nanoparticle precursor may provide a dispersion comprising nanoparticulate monolayers of the nanoparticle precursor.

[0026] The method provides nanoparticle compositions that are surprisingly useful in or as lubricants.

[0027] According to a second aspect the present invention provides a nanoparticle composition comprising nanoparticles and an ester-containing compound of Formula I. Typically, preparation is achieved by milling (e.g. ball milling) the composition to form the nanoparticles in the presence of the ester-containing compound of Formula I. Thus, the nanoparticle composition may be obtainable (e.g. obtained) by the method of the first aspect.

[0028] The composition is believed to form a boundary lubrication film (tribofilm) between surfaces. These films may be in excess of 10 nm in thickness. The thickness of the boundary lubrication film can be measured by Focused Ion beam - Transmission Electron Microscopy (FIB-TEM) and / or Scanning Electron Microscopy (SEM). Surprisingly, the nanoparticles produced by milling(e.g. ball milling) have been found to exhibit excellent dispersibility in water (over 1 month) compared to other similar compositions not prepared by milling (e.g. ball milling).

[0029] The presence of the ester-containing compound has also been found to limit or prevent the oxidation of nanoparticles, such as transition metal dichalcogenides.

[0030] It is postulated that the alkene group shown in Formula I is particularly important for the lubrication effects of the nanoparticle composition. The presence of this alkene group (i.e. double bond) may increase the minimum separation between surfaces, even when exposed to extreme forces normal to the surfaces, compared to comparable ester- containing compounds without the double bond. It is postulated that the double bond allows the nanoparticle composition to form relatively thick and robust films on surfaces. This can prevent abrasion between surfaces.

[0031] The presence of the alkene group may decrease the coefficient of friction between surfaces, even when exposed to extreme forces normal to the surfaces, compared to comparable ester-containing compounds without the double bond. This may further reduce abrasion between surfaces.

[0032] The compositions of the claimed invention do not have the steric hindrance of quaternary ammonium and phosphonium cations present in some conventional ionic liquids. These species hinder adsorption as a lubricant additive onto negatively charged substrates, reducing their effectiveness as a lubricant on surfaces such as mica.

[0033] US 10100266 B2 discloses spherical M0S2 particles having a particle size of less than 30nm, produced by both dry ball milling and wet ball milling (specifically in the presence of canola oil or other vegetable oils, which are fatty acid-based oils). However, significant benefits are provided by specifically ball milling in the presence of a compound of Formula I, owing to the alkene group present in this compound. The dispersions produced by US 10100266 B2 are described as not being uniform after a few weeks, unlike the compositions of the invention. Furthermore, the range of particle sizes disclosed in US 10100266 B2 is significantly larger than those typically used by the present invention. In addition, unlike the present invention, the disclosure of US 10100266 B2 provides no option for enhancing aqueous solubility of the compositions. The nanoparticle composition can show exceptional performance in terms of the reduction of friction and the reduction of wear when in carriers such as glycerol. Glycerol is particularly beneficial due to its low environmental impact, making this a “green” chemical, and inherent lubrication properties.

[0034] According to a third aspect, the claimed invention provides a lubricant composition comprising the nanoparticle composition of the second aspect and a carrier. The carrier may comprise water and / or glycerol, and / or a deep eutectic solvent, and / or a grease (e.g. a lithium grease). Deep eutectic solvents may be selected from glyceline (formed from choline chloride and glycerol) and reline (formed from urea and choline chloride).

[0035] Moreover, the inclusion of an ionic liquid (IL) and the nanoparticle composition in a grease has been shown to significantly reduce friction and protect steel surface from wear when compared with the nanoparticle composition alone in the base grease and / or the IL alone in the base grease. It is postulated that the combination of ILs and nanoparticle compositions provide synergistic effects. The IL is preferably a lithium salt (e.g. LiTFSI) adduct of an ester-containing compound of Formula I.

[0036] The compositions of the claimed invention can readily be tuned for different applications, especially by modifying the R1group of the compound of Formula I. For example, where R1is a polyether group, the composition is water soluble. Where R1is an aliphatic (e.g. alkyl and / or alkenyl) and / or aromatic hydrocarbon group, the composition is oil soluble. Where R1is a polyfluorinated hydrocarbon group, the composition is more resistant to radiation, thus making it more suitable for space-related applications.

[0037] According to a fourth aspect the claimed invention provides an article comprising a nanoparticle composition of the second aspect and / or a lubricant composition of the third aspect. The article may contain the nanoparticle composition as a coating of the article, and / or as a coating of a component of the article. The nanoparticle composition may be present on a surface of the article that is mica, a polymer (e.g. polyether ether ketone, PEEK) or a metal (e.g. a steel). It is postulated that the lubrication properties of the lubricant composition are activated by exposing the lubricant composition to tribological stresses, for example friction between two surfaces. This is thought to be one way to cause the alkene groups in the ester-containing compound of Formula I to polymerise, forming a tribofilm that can be a very effectively lubricant.

[0038] According to a fifth aspect the claimed invention provides a method of providing an activated lubricant composition, wherein the method comprises providing a nanoparticle composition according to the second aspect and / or a lubricant composition of the third aspect, and polymerising the ester-containing compound of Formula I. The polymerisation may be effected by subjecting the nanoparticle composition and / or the lubricant composition to tribological stress, for example by exposing these to friction (e.g. a shear force) between surfaces. Polymerisation may be initiated by other means, such as photopolymerisation (e.g. by exposing the ester-containing compound of Formula I to visible and / or ultraviolet radiation), or a chemical polymerisation initiator.

[0039] According to a sixth aspect the claimed invention provides an activated lubricant composition comprising nanoparticles and an ester-containing compound of Formula II. Formula II is defined as:

[0040] Formula II.

[0041] In the ester-containing compound of Formula II, R1is a hydrocarbon group that is optionally substituted; and R2, R3and R4are each independently H or a C l-10 hydrocarbon group that is optionally substituted, n may be 3 or more, such as 10 or more, or 50 or more, for example 100 or more, n may be 10,000 or less (e.g. from 3 to 10,000), such as 1000 or less (e.g. from 3 to 1000). The R groups of Formula II correspond to the R groups of Formula I, and optional features disclosed in relation to Formula I may apply equally to Formula II unless otherwise incompatible.

[0042] The activated lubricant composition may contain a film comprising the ester-containing compound of Formula II and the nanoparticles. The film may have a thickness of lOnm or more, such as 15nm or more, for example from 10 to 500nm, or from 15 to lOOnm. The thickness of the film may be determined by Focused Ion beam - Transmission Electron Microscopy (FIB-TEM) and / or Scanning Electron Microscopy (SEM).

[0043] The activated lubricant composition of the sixth aspect may be obtainable (e.g. obtained) by the method of the fifth aspect.

[0044] Detailed Description of the Invention

[0045] It will be understood that the formulae used to define the present invention cover all tautomers and geometric isomers of the species shown, unless otherwise stated.

[0046] Method of preparing a nanoparticle composition

[0047] The method of preparing a nanoparticle composition comprises providing a nanoparticle precursor that has a laminar structure; providing an ester-containing compound of Formula I; and milling (e.g. ball milling) the nanoparticle precursor in the presence of the ester-containing compound. This provides the nanoparticle composition.

[0048] Ball milling is performed in a ball mill, where grinding media (milling balls) used to reduce the particle size of the nanoparticle precursor. The ball mill may be a planetary- type ball mill. The grinding media and / or the chamber of the ball mill may be steel (e.g. chrome steel), stainless steel, ceramic (e.g. quartz / agate), or rubber. Other specific milling methods include hammer milling, cutting milling and jet milling.

[0049] The method may comprise charging the ester-containing compound to the mill (e.g. ball mill). The method may comprise charging the nanoparticle precursor to the mill. The method may comprise removing the nanoparticle composition from the mill. The method may comprise separating the nanoparticle composition from milling balls, for example by sieving.

[0050] Milling (e.g. ball milling) is preferably performed in an inert atmosphere (e.g. nitrogen and / or argon). The chamber of the mill (e.g. ball mill) may be sealed during milling to maintain the inert atmosphere.

[0051] Milling (e.g. ball milling) may be performed for a period of time of 1 hour or more, such as 6 hours or more, or 12 hours or more, for example 18 hours or more, or 24 hours or more. The period of time may be 2 weeks or less, such as 1 week or less, or 5 days or less, such as 100 hours or less, or 80 hours or less, or 60 hours or less. The period of time may be from 1 hour to 2 weeks, such as from 12 hours to 100 hours, or from 24 hours to 60 hours.

[0052] The rotational speed of the mill (e.g. ball mill) during the milling may be 60rpm or more, such as lOOrpm or more, or 150rpm or more, or 200 rpm or more, for example 250rpm or more, or 300rpm or more. The rotational speed may be 2000rpm or less, or lOOOrpm or less, such as 800rpm or less, or 600rpm or less, for example 500rpm or less. The rotational speed may be from 60rpm to 2000rpm, such as from 200 to 800rpm, or from 300 to 500rpm.

[0053] The method may comprise isolating and / or purifying the nanoparticle composition. The method may comprise dissolving the material obtained after milling in a volatile organic solvent, such as ethanol.

[0054] The method may comprise subjecting the material obtained after milling (e.g. in the volatile organic solvent) to centrifugation, for example to separate smaller particles (that remain dispersed in the solvent) from larger particles (that sediment). Centrifugation may be performed at a rotational speed of 500rpm or more, such as lOOOrpm or more, or 1500rpm or more, for example 1800rpm or more, or 2000rpm or more. The rotational speed may be 10,000rpm or less, such as 6000rpm or less, or 5000rpm or less, for example 4000rpm or less. The rotational speed may be from 500 to 10,000rpm, such as from 1000 to 6000rpm, or from 2000 to 4000rpm. Centrifugation may be performed for a period of time of 30 seconds or more, such as 1 minute or more, or 2 minutes or more, such as 4 minutes or more, or 5 minutes or more. The period of time may be 24 hours or less, such as 12 hours or less, or 6 hours or less, preferably 2 hours or less, or 1 hour or less, such as 30 minutes or less. The period of time may be from 30 seconds to 24 hours, such as from 2 minutes to 6 hours, or from 5 minutes to 30 minutes.

[0055] The method may comprise separating the material obtained after milling (optionally in the volatile organic solvent) from the milling balls by separating the supernatant liquor, by filtration and / or by sieving. After the nanoparticle composition has been isolated and / or purified (e.g. from larger particle sizes and / or the milling balls), the method may comprise removing any volatile organic solvent, for example in vacuo.

[0056] Nanoparticles

[0057] Nanoparticle precursors are preferably laminar materials. Nanoparticle precursors may be selected from the list consisting of graphite, graphyne, borophene, germanene, silicene, stanine, plumbene, phosphorene, antimonene, bismuthine, one or two atom thick platinum film, one or two atom thick rhodium film, (hexagonal) boron nitride, titanate nanosheet, borocarbonitrides, MXenes (i.e. transition metal carbides, nitrides, or carbonitride), two-dimensional silica, niobium bromide (NbsBrg), niobium chloride (NbsCh), transition metal dichalcogenides (e.g. M0S2, MoSe2, MoTe2, WS2, WSe2, HfS2), graphene, germanane, and SiN.

[0058] Preferably the nanoparticle precursor is graphite, a transition metal dichalcogenide (especially M0S2), or (hexagonal) boron nitride.

[0059] The nanoparticle precursor may have an average (e.g. number average) particle diameter of 50nm or more, such as lOOnm or more, or 150nm or more, for example 200nm or more. The average diameter of the nanoparticle precursor may be 5mm or less, such as 1mm or less, or 0.1mm or less, such as 10pm or less, or 1pm or less. The average diameter of the nanoparticle precursor may be from 50nm to 5mm, such as from lOOnm to 5mm, or from lOOnm to 1pm. The average diameter of the particles of the nanoparticle precursor may be determined by dynamic light scattering (e.g. using a Zetasizer ZS90, Malvern Instruments, UK). Milling (e.g. ball milling) may be used to convert the nanoparticle precursor into nanoparticles. The nanoparticles may be nanoparticulate monolayers of the nanoparticle precursor. The nanoparticles of the nanoparticle composition are obtainable (e.g. obtained) by milling (e.g. ball milling).

[0060] The nanoparticles may be monolayers of the nanoparticle precursors, such as graphene or monolayers of graphyne, borophene, germanene, silicene, stanine, plumbene, phosphorene, antimonene, bismuthine, one or two atom thick platinum film, one or two atom thick rhodium film, (hexagonal) boron nitride, titanate nanosheet, borocarbonitrides, MXenes (i.e. transition metal carbides, nitrides, or carbonitride), two-dimensional silica, niobium bromide (NbsBrg), niobium chloride (NbsCU), transition metal dichalcogenides (e.g. M0S2, MoSe2, MoTe2, WS2, WSe2, HfS2), graphene, germanane, or SiN. The nanoparticles are preferably graphite, a transition metal dichalcogenide (especially M0S2), or (hexagonal) boron nitride.

[0061] The nanoparticles may have an average (e.g. number average) particle diameter of lOOnm or less, such as 50nm or less, or 20nm or less, preferably 15nm or less, or lOnm or less, such as 9nm or less, or 8nm or less, such as 7nm or less, or 6mn or less, or 5nm or less, or 4nm or less. The average diameter may be 0.5nm or more, preferably Inm or more, or 2nm or more, such as 3nm or more. The average diameter may be from 0.5nm to lOOnm, such as from Inm to 15nm, or from 2nm to lOnm. The average diameter of the particles may be determined by dynamic light scattering (e.g. using a Zetasizer ZS90, Malvern Instruments, UK).

[0062] R!

[0063] R1is a hydrocarbon group that is optionally substituted, e.g. an alkyl, alkenyl, alkynyl and / or aryl group that is optionally substituted.

[0064] Preferably R1represents a hydrocarbon group that contains 5 or more carbon atoms, such as 6 or more, or 8 or more, or 10 or more, or 20 or more carbon atoms. R1may represent a C5-30 hydrocarbon group. R1may represent a C5-28, C5-26, C5-24, C5-22, or C5-20 hydrocarbon group. It will be understood that these groups can each optionally be substituted. The solubility and / or applications of the nanoparticle composition is highly tuneable by modifying the R1group. For example, where R1is a polyether group, the composition can be made water soluble. Where R1is an aliphatic (e.g. alkyl and / or alkenyl) and / or aromatic hydrocarbon group, the composition can be made oil soluble. Where R1is polyfluorinated hydrocarbon group the composition can be more resistant to radiation, thus making it more suitable for space-related applications.

[0065] One type of substituted hydrocarbon group suitable to represent R1is a polyether. Common polyether groups include polyethylene glycol (PEG) groups and polypropylene glycol groups. Polyether groups may be represented by the formula:

[0066] Wherein R5may be a C 1-10 hydrocarbon group, such as a C 1-8 hydrocarbon group or a Cl -6 hydrocarbon group. R5may be a C2-10 hydrocarbon group, such as a C2-8 hydrocarbon group or a C2-6 hydrocarbon group. Preferably R5is a C2-5 hydrocarbon group, or a C2-4 hydrocarbon group, or a C2 or C3 hydrocarbon group, especially a C2 hydrocarbon group. Preferably the hydrocarbon group is an alkyl or an alkenyl group. More preferably the hydrocarbon group is an alkyl group. More preferably R5is a Cl- 10 alkyl or alkenyl group, such as a Cl -8 alkyl or alkenyl group or a Cl -6 alkyl or alkenyl group, more preferably a C2-5 alkyl or alkenyl group, or a C2-4 alkyl or alkenyl group, or a C2 or C3 alkyl or alkenyl group, especially a C2 or C3 alkyl group. Preferably R5is a C2 alkyl (i.e. ethyl) group, such that the polyether is a polyethylene glycol group. n may be an average of 3 or more, or 5 or more, such as 10 or more, or 15 or more, such as 18 or more, n may be an average of 100 or less, such as 80 or less, or 60 or less, such as 50 or less, or 40 or less, for example 30 or less, or 25 or less, such as 22 or less, n may be an average of from 3 to 100, such as from 5 to 50, or from 10 to 30. The average may be a number average. The average value of n may be determined by NMR, for example by the integration of relevant peaks using NMR. Alternatively, the average value of n may be calculated using mass spectrometry.

[0067] Where the compound of Formula I is PEGMA, the number average molecular weight of the PEGMA may be 250g / mol or more, or 300 g / mol or more, such as 350 g / mol or more, or 450 g / mol or more, such as 750 g / mol or more, or 1000 g / mol or more, or 1200 g / mol or more, such as 1750 g / mol or more, or 3000 g / mol or more, such as 3500 g / mol or more. The number average molecular weight may be 8000 g / mol or less, or 5000 g / mol or less, such as 4500 g / mol or less, or 4200 g / mol or less, or 4000 g / mol or less such as 2500 g / mol or less, or 1750 g / mol or less, or 1250 g / mol or less, such as 750 g / mol or less, or 400 g / mol or less. The number average molecular weight may be from 250 to 8000 g / mol, such as from 250 to 5000 g / mol, or from 250 to 4200 g / mol, such as 300 g / mol, 480 g / mol, 500 g / mol, 950 g / mol, 1500 g / mol, 2000 g / mol or 4000 g / mol.

[0068] The hydrocarbon group may be branched or linear. Preferably the hydrocarbon group is linear.

[0069] In one embodiment the hydrocarbon group is not substituted. R1may be an unsubstituted C l-30 hydrocarbon group, such as an unsubstituted C2-30, C4-30, C5-30, or C6-30 hydrocarbon group. Preferably R1is an unsubstituted C8-30, C 10-30, C 12-30 or C 14- 30 hydrocarbon group, for example an unsubstituted C l 6-30 hydrocarbon group. R1may be an unsubstituted C l -28, C l -26, C l -24, C l -22, or C l -20 hydrocarbon group, or an unsubstituted C4-28, C4-24, or C4-20 hydrocarbon group, or an unsubstituted C8-28, C8-24 or C8-20 hydrocarbon group, for example an unsubstituted C IO-24, C 12-24, C 14- 24 or C l 6-24 hydrocarbon group. The hydrocarbon group may be an aliphatic and / or aromatic hydrocarbon group. Preferably the hydrocarbon group is an alkyl, alkenyl or aryl group, more preferably an alkyl or alkenyl group, most preferably an alkyl group. For instance, R1may be an unsubstituted C l-30, or a C8-30, or a C 12-24 alkyl, alkenyl or aryl group; preferably an unsubstituted C l-30, or a C8-30, or a C 12-24 alkyl or alkenyl group; more preferably an unsubstituted C l-30, or a C8-30, or a C 12-24 alkyl group.

[0070] The hydrocarbon group of R1may be fluorinated (i.e. include one or more fluorine atoms) or polyfluorinated (i.e. include two or three or more fluorine atoms). R1may be a fluorinated or polyfluorinated C l-30 hydrocarbon group, such as a fluorinated or polyfluorinated C2-30, C4-30, or C6-30 hydrocarbon group. R1may be a fluorinated or polyfluorinated C l -28, C l -26, C l -24, C l -22, or C l -20 hydrocarbon group, or a fluorinated or polyfluorinated C4-28, C4-24, or C4-20 hydrocarbon group, or a fluorinated or polyfluorinated C8-28, C8-24 or C8-20 hydrocarbon group. Preferably R1is a fluorinated or polyfluorinated C l-16, C4-16 or C8-16 hydrocarbon group, such as a fluorinated or polyfluorinated C l-12, C4-12 or C8-12 hydrocarbon group. Preferably the fluorinated or polyfluorinated hydrocarbon group is an alkyl, alkenyl or aryl group, more preferably an alkyl or alkenyl group, most preferably an alkyl group. For instance, R1may be a fluorinated or polyfluorinated Cl -30, C4-24, or C4-16 alkyl, alkenyl or aryl group; preferably a fluorinated or polyfluorinated Cl-30, C4-24, or C4-16 alkyl or alkenyl group; more preferably a fluorinated or polyfluorinated Cl-30, C4-24, or C4-16 alkyl group.

[0071] In one embodiment the hydrocarbon group is not substituted except for with one or more fluoride groups. For instance, the ratio of F atoms to H atoms in the hydrocarbon group may be 1 :2 or more, such as 1 : 1 or more, or 2: 1 or more, for instance 3: 1 or more, such as 4: 1 or more. In one embodiment the hydrocarbon group includes no hydrogen atoms. In one embodiment the hydrocarbon group consists of, or consists essentially of, carbon atom(s) and fluorine atom(s).

[0072] R2

[0073] R2is H or a Cl-10 hydrocarbon group that is optionally substituted. Preferably R2is not substituted.

[0074] R2may be H or a Cl -8 hydrocarbon group, for example H or a C 1-6 hydrocarbon group, or H or a C 1-4 hydrocarbon group, such as H or a Cl or C2 or C3 hydrocarbon group. Preferably the hydrocarbon group is an alkyl or an alkenyl group. More preferably the hydrocarbon group is an alkyl group. Yet more preferably R2is H or a Cl -6 alkyl or alkenyl group, or H or a C 1-4 alkyl or alkenyl group, such as H or a C 1-2 alkyl or alkenyl group. More preferably R2is H or a methyl group, most preferably a methyl group.

[0075] R3and R4

[0076] R3and R4are each independently H or a Cl-10 hydrocarbon group that is optionally substituted. Preferably R3and R4are not substituted.

[0077] R3and R4may each independently be H or a C 1-8 hydrocarbon group, for example H or a Cl -6 hydrocarbon group, or H or a C 1-5 hydrocarbon group, or H or a C 1-4 hydrocarbon group, such as H or a Cl or C2 or C3 hydrocarbon group. These groups of R3and R4are optionally substituted, but are preferably unsubstituted.

[0078] Preferably R4is H or a Cl -5 hydrocarbon group (e.g. H or a C 1-4 hydrocarbon group, such as H or a Cl or C2 or C3 hydrocarbon group) and R3is H or a C 1-10 hydrocarbon group. These groups of R3and R4are optionally substituted, but are preferably unsubstituted.

[0079] Preferably any hydrocarbon group is an alkyl or an alkenyl group (i.e. H or a Cl-10 alkyl group or a Cl-10 alkenyl group). More preferably any hydrocarbon group is an alkyl group. Yet more preferably R3and R4are each independently H or a C 1-6 alkyl or alkenyl group, or H or a C 1-4 alkyl or alkenyl group, such as H or a C 1-2 alkyl or alkenyl group. These alkyl / alkenyl groups of R3and R4are optionally substituted, but are preferably unsubstituted. Preferably R3and R4are both the same group. Most preferably R3and R4are both H.

[0080] Substituents

[0081] Each R1, R2, R3and R4group is, independently, optionally substituted. Preferable substitutions of R1are discussed above.

[0082] Each R1, R2, R3and R4group may independently be substituted with one or more internal substituent and / or one or more external substituent. The term “internal substituent” refers to substituents provided between two carbon atoms, i.e. within a hydrocarbon group. The term “external substituent” refers to substituents provided in the replacement of a hydrogen atom of a C-H bond, i.e., on the edge of a hydrocarbon group. Preferably any substituents on the X and / or R1groups are external substituents.

[0083] Internal substituents can include where one or more (e.g., two or more) of the carbon atoms in the hydrocarbon chain are replaced with heteroatoms. The heteroatom(s) may, for example, be selected from O, N, S, SO, SO2, P, B, Si, and combinations thereof. For example, the heteroatom(s) may be selected from O, N, S, and combinations thereof. Preferably the heteroatom for internal substituents is O. In one embodiment from 1 to 5 carbon atoms in the group are replaced with heteroatom(s), e.g., 1, 2 or 3 carbon atoms in the group might be replaced with heteroatom(s). When more than one carbon atom in the group is replaced, the heteroatoms used may be the same or may be different.

[0084] The or each substituent may independently be selected from the list consisting of: - P=CH-, -N=CH-, -O-, -O2-, -OS-, -S-, -SO2-, -S(O)-, -S2-, -N=N-, -ONH-, -NH-, -P=N- , -P(O)HNH-, -POOHNH-, -OPOOHNH-, -P(O)HO-, -POOHO-, -OPOOHO-, -P=P- , -OPH-, -PH-, -C(O)-, -C(O)O-, -C(O)NH-, -N(C(O)-)2, -NHC(O)NH-, -NHC(O)O-, and -NHS(O)2-. These represent internal substituents.

[0085] Therefore, for example, the R1, R2, R3and R4group may independently include an ether, amine, imine, thioether, sulfoxide, sulfone, and / or sulfonamide group. Ether, ester and amide groups are particularly preferred, especially ethers. The number of carbon atoms in the group may be reduced where one or more of the carbon atoms in the group are replaced with heteroatoms. However, the skilled person would readily be able to see how many carbon atoms would have been in the group had one or more of these not been replaced with heteroatoms.

[0086] In each of the R1, R2, R3and R4groups, independently, one or more (e.g. two or more) of the hydrogen atoms of the group may be replaced with substituent groups. In one embodiment from 1 to 10 hydrogen atoms in the group are substituted, such as from 1 to 4 of the hydrogen atoms in the group might be replaced with substituent groups. When more than one hydrogen atom in the R1, R2, R3and / or R4group is replaced, the substituent groups used may be the same or may be different. For example, the R1, R2, R3and / or R4group may be substituted with one or more substituent groups independently selected from ether, ester and amide groups. The group may be substituted with one or more substituent groups independently selected from ether, ester and amide groups, particularly one or more ether groups.

[0087] Each of the R1, R2, R3and R4groups may, independently, optionally be substituted by one or more group independently selected from the list consisting of: cyano, halogen (e g. F, Cl, Br and I), N3, -C(O)RZ, -C(O)ORZ, -OC(O)RZ, -C(O)NHRZ, -NHC(O)RZ, - NHC(O)NHRZ, -NHC(O)ORZ, -OC(O)NHRZ, -OP(O)2ORZ, -S(O)2NHRZ, -NHS(O)2RZ, -NRZ2, -NHRZand -ORZ. These represent external substituents. Each of the R1, R2, R3and R4groups may be substituted with one or more Y groups. The Y groups may be selected from the list consisting of: cyano, halogen (e.g. F, Cl, Br and I), N3, -C(O)RZ, -C(O)ORZ, -OC(O)RZ, -C(O)NHRZ, -NHC(O)RZ, -NRZ2, -NHRZand -ORZ. The Y groups may be selected from the list consisting of: halogen (e.g. F and Cl), -C(O)ORZ, -OC(O)RZ, -C(O)NHRZ, -NHC(O)RZand -ORZ.

[0088] Any Rzgroup independently represents H, Cl -8 alkyl, C2-8 alkenyl, C6-8 aryl, or C4- 8 heterocyclyl. Each Rzmay independently represent H, Cl -6 alkyl, C2-6 alkenyl, C6 aryl, or C4-6 heterocyclyl. For example, each Rzmay independently represent H, Cl-4 alkyl, or C2-4 alkenyl.

[0089] Each of the R1, R2, R3and R4groups may be substituted with 5 or fewer Y groups, such as 3 or fewer, or 2 or fewer Y groups. Preferably each of the R1, R2, R3and R4groups are independently not substituted with any Y groups.

[0090] As discussed above, R1may represent a polyether, such as polyethylene glycol. R1may be fluorinated, for example polyfluorinated.

[0091] Any substituents chosen may be designed to facilitate the solubility of the composition in a particular base oil and / or to match the composition to its intended end use.

[0092] Preferred Ester-Containing Compounds

[0093] In various embodiments:

[0094] R1is a polyether or a Cl-30 hydrocarbon group; and R2, R3and R4and are each independently H or a C 1-8 hydrocarbon group; wherein R1, R2, R3and R4are each optionally substituted.

[0095] R1is a polyether or a Cl-30 hydrocarbon group; and R2, R3and R4and are each independently H or a Cl-4 hydrocarbon group; wherein R1, R2, R3and R4are each optionally substituted.

[0096] R1is a polyether or a Cl-30 hydrocarbon group that is optionally substituted; R2is H or a Cl-4 alkyl or alkenyl group; and R3and R4and are each independently H or a C 1-2 alkyl or alkenyl group.

[0097] R1is a polyether or a Cl-30 hydrocarbon group that is optionally substituted; R2is H or a Cl-4 alkyl or alkenyl group; and R3and R4and are both H. R1is a PEG group or an unsubstituted C l-30 hydrocarbon group or a fluorinated C l-30 hydrocarbon group; and R2, R3and R4and are each independently H or a C l -4 hydrocarbon group.

[0098] R1is a PEG group or an unsubstituted C8-30 alkyl group or a fluorinated C4-20 alkyl group; and R2, R3and R4and are each independently H or a Cl-4 hydrocarbon group.

[0099] R1is a PEG group or an unsubstituted C 12-24 alkyl group or a fluorinated C4- 16 alkyl group; and R2, R3and R4and are each independently H or a C l-4 hydrocarbon group.

[0100] R1is a PEG group or an unsubstituted C 12-24 alkyl group or a fluorinated C4- 16 alkyl group; R2is H or a C l-4 alkyl or alkenyl group; and R3and R4and are each independently H or a C l-2 alkyl or alkenyl group.

[0101] R1is a PEG group or an unsubstituted C 12-24 alkyl group or a fluorinated C4- 16 alkyl group; R2is methyl; R3is H; and R4is H.

[0102] Preferably R2is methyl or H, R3is H, and R4is H, such that the ester-containing compound is an acrylate or a methacrylate ester-containing compound. Thus, the ester- containing compound may be represented by Formula III or Formula IV:

[0103] Formula III Formula IV

[0104] Preferably the ester-containing compound is a methacrylate ester-containing compound, as represented by Formula III.

[0105] The ester-containing compound of Formula I is preferably represented by the following formulae: poly(ethylene glycol) methacrylate, or

[0106] \ H. l / / .2 / / .2 / / -pcrfluorodccyl methacrylate, or dodecyl methacrylate.

[0107] Nanoparticle composition

[0108] The nanoparticle composition comprises nanoparticles and an ester-containing compound of Formula I. The nanoparticles and the compound of Formula I may be as defined in the sections above.

[0109] The nanoparticle composition may comprise and / or the method of preparing the nanoparticle composition may comprise adding the nanoparticles in a proportion of 1 wt% or more, such as 5 wt% or more, or 10 wt% or more, such as 20 wt% or more, or 30 wt% or more, relative to the total weight of the nanoparticle composition (or relative to the other components added before milling). The proportion of the nanoparticles relative to the total weight of the nanoparticle composition may be 99 wt% or less, or 95 wt% or less, or 90 wt% or less, such as 80 wt% or less, or 70 wt% or less, or 60 wt% or less, preferably 50 wt% or less, such as 40 wt% or less, or 35 wt% or less. The proportion of the nanoparticles relative to the total weight of the nanoparticle composition may be from 1 to 99 wt%, such as from 10 to 80 wt%, or from 10 to 50 wt%, for example from 20 to 40 wt%.

[0110] The nanoparticle composition may comprise and / or the method of preparing the nanoparticle composition may comprise adding the compound of Formula I in a proportion of 1 wt% or more, such as 5 wt% or more, or 10 wt% or more, such as 20 wt% or more, or 40 wt% or more, for example 50 wt% or more, or 60 wt% or more, or 65 wt% or more, relative to the total weight of the nanoparticle composition (or relative to the other components added before milling). The nanoparticle composition may comprise the compound of Formula I in a proportion of 99 wt% or less, such as 90 wt% or less, or 80 wt% or less, such as 75 wt% or less, or 70 wt% or less. The nanoparticle composition may comprise the compound of Formula I in a proportion of from 1 to 99 wt%, such as from 20 to 90 wt%, or from 50 to 80 wt%.

[0111] The nanoparticle composition may comprise and / or the method of preparing the nanoparticle composition may comprise adding the nanoparticles in an amount of 1 wt% or more (such as 10 wt% or more, for example from 10 to 50 wt%) and the compound of Formula I in an amount of 1 wt% or more (such as 20 wt% or more, for example from 50 wt% to 90 wt%), relative to the total weight of the nanoparticle composition (or relative to the other components added before milling).

[0112] The nanoparticle composition may contain the compound of Formula I in a proportion, relative to the weight of the nanoparticles, of 10 wt% or more, such as 50 wt% or more, preferably 100 wt% or more, or 120 wt% or more, such as 150 wt% or more, or 180 wt% or more, for example 200 wt% or more. The nanoparticle composition may contain the compound of Formula I in a proportion, relative to the weight of the nanoparticles, of 2000 wt% or less, or 1000 wt% or less, such as 600 wt% or less, or 400 wt% or less, for example 300 wt% or less, or 250 wt% or less, or 220 wt% or less, such as 200 wt% or less. The nanoparticle composition may contain the compound of Formula I in a proportion, relative to the weight of the nanoparticles, of from 10 to 2000 wt%, such as from 100 to 600 wt%, or from 150 to 250 wt%.

[0113] Lubricant composition

[0114] The lubricant composition comprises the nanoparticle composition and a carrier. The carrier should be a liquid.

[0115] The carrier may comprise water, an oil (e.g. hydrocarbon oil), a lithium grease, glycerol. These components may be present in an amount of 20 wt% or more, such as 50 wt% or more, preferably 75 wt% or more of the total weight of the lubricant composition. These components may be present in an amount of 99.5 wt% or less, or 99 wt% or less, preferably 98wt% or less, such as 95 wt% or less, or 90 wt% or less, for example 80 wt% or less. These components may be present in an amount of from 20 to 98 wt%, such as from 50 to 98 wt%, or from 75 to 98 wt%. The lubricant composition may comprise a thickener system in an amount of 0.1 wt% or more, or 1 wt% or more, or 2 wt% or more. The lubricant composition may comprise the thickener system in an amount of 50 wt% or less (e.g. 0.1 to 50 wt%), such as 30 wt% or less, or 20 wt% or less (e.g. from 2 to 20 wt%).

[0116] The lubricant composition may comprise performance additives in an amount of 20 wt% or less, such as 15 wt% or less, or 10 wt% or less. The performance additives may be present in an amount of 0.1 wt% or more (e.g. 0.1 to 20 wt%), such as 1 wt% or more (e.g. 1 to 10 wt%).

[0117] Due to the ability to tailor the solubility of the composition by changing the R1group, the lubricant composition may be polar (e.g. hydrophilic and / or aqueous) or non-polar (e.g. hydrophobic, oil-based) in nature, or a combination of both (i.e. amphiphilic).

[0118] The lubricant composition may comprise water and / or glycerol the nanoparticle composition of the second aspect. This is particularly the case where R1is a hydrophilic group, such as a polyether (e.g. PEG). The lubricant composition may contain water / or glycerol in an amount of 50 wt% or more, such as 60 wt% or more, or 70 wt% or more, such as 75 wt% or more. The amount of water may be 99.99 wt% or less, or 99.95 wt% or less, such as or 99.5 wt% or less, such as 99 wt% or less, or 98.5 wt% or less, such as 98 wt% or less. The amount of water may be from 50 wt% to 99.99 wt%, such as from 60 wt% to 99.5 wt%, or from 70 wt% to 99 wt%, or from 75 wt% to 98 wt%.

[0119] The lubricant composition may be a lithium grease.

[0120] The ester-containing compound may be hydrophobic where R1is Cl-30 a hydrocarbon group that is unsubstituted or that is fluorinated. The lubricant composition may comprise a base oil and the nanoparticle composition of the second aspect. The lubricant composition may comprise other additives (e.g. performance additives).

[0121] The lubricant composition may contain the base oil in an amount of 50 wt% or more, such as 60 wt% or more, or 70 wt% or more, such as 75 wt% or more. The amount of base oil may be 99.99 wt% or less, or 99.95 wt% or less, such as or 99.5 wt% or less, such as 99 wt% or less, or 98.5 wt% or less, such as 98 wt% or less. The amount of base oil may be from 50 wt% to 99.99 wt%, such as from 60 wt% to 99.5 wt%, or from 70 wt% to 99 wt%, or from 75 wt% to 98 wt%.

[0122] The base oil is preferably hydrocarbon based. The base oil may comprise one or two or more component oils. The base oil may be a petroleum fraction, e.g. mineral oil. Base oil(s) are typically highly paraffinic (>90% saturates). The base oil(s) may contain monocycloparaffins, multicycloparaffins and / or non-cyclic isoparaffins. Preferably the base oil(s) have a very low sulfur and / or nitrogen content, such as containing less than 10 ppm of each of sulfur or nitrogen, such as 5 ppm or less of each of these elements. The base oil(s) may be selected from API Group I, Group II, Group III, Group IV, and / or Group V oils, and mixtures thereof. Group III to Group V base oils are preferred due to their exceptional volatility, stability, viscometric and cleanliness features.

[0123] The lubricant composition may contain the nanoparticle composition in an amount of 0.01 wt% or more, preferably 0.05 wt% or more, or 0.1 wt% or more, such as 0.2 wt% or more, or 0.5 wt% or more, such as 0.8 wt% or more, or 1 wt% or more, for example 1.5 wt% or more, or 2 wt% or more. The amount of the nanoparticle composition may be 50 wt% or less, such as 40 wt% or less, or 30 wt% or less, preferably 20 wt% or less, such as 10 wt% or less, or 5 wt% or less, or 4 wt% or less, for example 3 wt% or less. The amount of the nanoparticle composition may be from 0.01 wt% to 50 wt%, such as from 0.05 wt% to 20 wt%, or from 0.05 wt% to 10 wt%, for example from 0.05 wt% to 5 wt%, or from 0.1 wt% to 10 wt%, for example from 0.1 wt% to 5 wt%.

[0124] The skilled person will be aware of various other additives that can be employed in lubricant compositions. For instance, the composition may include additives selected from the list consisting of antioxidants, antiwear agents, dispersants, detergents, corrosion inhibitors, rust inhibitors, metal deactivators, extreme pressure additives, anti-seizure agents, wax modifiers, viscosity index improvers, viscosity modifiers, fluid-loss additives, seal compatibility agents, organic metallic friction modifiers, lubricity agents, anti-staining agents, chromophoric agents, anti-foam agents, demulsifiers, emulsifiers, densifiers, wetting agents, gelling agents, tackiness agents, and colorants. The other additives may be included in the composition in an amount of 20 wt% or less, such as 15 wt% or less, or 10 wt% or less, for example from 0.1 wt% to 20 wt%, or from 1 wt% to 20 wt%, or from 1 wt% to 10 wt%.

[0125] The lubricant composition may include a base oil or water and / or glycerol in an amount of 50 wt% or more, the nanoparticle composition in an amount of 0.01 wt% or more, and optional other additives. For example, the lubricant composition may include a base oil or water and / or glycerol in an amount of from 50 wt% to 99.99 wt%, the nanoparticle composition in an amount of from 0.01 wt% to 50 wt%, and optional other additives in an amount of 20 wt% or less. Preferably the lubricant composition includes a base oil or water and / or glycerol in an amount of from 70 wt% to 99.5 wt%, the nanoparticle composition in an amount of from 0.05 wt% to 20 wt%, and optional other additives in an amount of from 0.1 wt% to 10 wt%.

[0126] In one embodiment the lubricant composition does not include polyacrylates.

[0127] Combination with ionic liquid

[0128] The lubricant composition may comprise an ionic liquid.

[0129] The inclusion of an ionic liquid (IL) and the nanoparticle composition in a lubricant composition has been shown to significantly reduce friction and protect steel surface from wear when compared with the nanoparticle composition alone in the base grease and / or the IL alone in the base grease. It is postulated that the combination of ILs and nanoparticle compositions provide synergistic effects.

[0130] The IL may be oil miscible and / or formed in situ. The IL is preferably a lithium salt adduct of an ester-containing compound of Formula I.

[0131] Preferably the anion of the lithium salt is inorganic, for example wherein the negative charge is not located on a carbon atom (e.g. not a hydrocarbon anion, such as a methyl anion). The lithium salt may be any anionic (e.g. monoanionic or dianionic) salt of lithium. The salt may be a halide (e.g. fluoride, chloride, bromide and / or iodide), hydroxide, a borate, a phosphate or an imide. Preferable examples include a borate, a phosphate and an imide, such as BF4, PFe and TFSI (bis(trifluoromethanesulfonyl)imide, N SC CFs^). More preferably, the lithium salt is a LiBF4, LiPFe or LiTFSI. LiTFSI is particularly preferred due to its lower polarity compared to UBF4 or LiPFe. The adduct may be an ionic adduct, wherein the anion is not covalently bonded to the ester-containing compound.

[0132] Preferably the anion includes elements selected from the list consisting of F, S, P and B, especially F, S and P. Anions containing such elements are preferable because they are very effective at forming boundary lubrication film in tribochemical reactions at elevated temperature. These elements are particularly able to react with iron present in metals such as steel to generate boundary lubrication film.

[0133] For the IL, the compound of Formula I may be dodecyl methacrylate, stearyl methacrylate and / or octadecyl acrylate. The IL may be an adduct of LiTFSI and dodecyl methacrylate, stearyl methacrylate and / or octadecyl acrylate.

[0134] The IL may be trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate ([P6,6,6, 14][BEHP]), trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl) phosphate ([P6,6,6,14] [BTPP]), trihexyltetradecylphosphonium dibutyl phosphate ([P6,6,6,14][BTDP]), or trihexyltetradecylphosphonium bis (2,4,4-trimethylpentyl) dithiophosphinate ([P6,6,6, 14][BTPD]).

[0135] The mixture of (especially oil soluble) ILs with nanoparticles (e.g. of M0S2) is particularly suitable for grease formulations to be applied in wind turbine lubrication to replace traditional friction-reducing and anti-wear additives, such as zinc dialkyldithiophosphate (ZDDP) and molybdenum dithiocarbamates (MoDTC).

[0136] The lithium salt adducts can be prepared by contacting (and optionally mixing, e.g. stirring, and / or heating) the lithium salt with a desired ester-containing compound. Heating may be performed at a temperature of 30 °C or more, such as 40°C or more, and / or 100°C or less, such as 70°C or less, or 60°C or less, e.g. from 30°C to 100°C or from 40°C to 60°C.

[0137] The process may be represented by the following reaction scheme:

[0138] The lithium salt adduct can be represented by the following formula:

[0139] The skilled person will understand that the ratio of lithium salt to ester-containing compound is not particularly limited. Any sensible ratio of the ester-containing compound to the lithium salt will produce the adduct. However, the molar ratio of ester- containing compound to lithium salt may be 100: 1 or less, such as 50: 1 or less, or 20: 1 or less, such as 10: 1 or less, or 7: 1 or less. The molar ratio may be 1 :50 or more, such as 1 :20 or more, or 1 : 10 or more, for example 5: 1 or more, or 1 : 1 or more, such as 2: 1 or more, or 4: 1 or more. The molar ratio may be from 100: 1 to 1 : 100, or from 50: 1 to 1 : 10, or from 50: 1 to 1 : 1, such as from 20: 1 to 1 : 10, or from 20: 1 to 1 : 1, such as from 10: 1 to 2: 1. The resulting lithium salt adduct may contain such an amount of these constituents.

[0140] The molar ratio of ester-containing compound to lithium salt is preferably 1.2: 1 or more, such as 1.3: 1 or more, or 1.5: 1 or more, or 2: 1 or more. For example, the molar ratio of ester-containing compound to lithium salt may be from 100: 1 to 1.2: 1, or from 20: 1 to 1.2: 1, such as from 20: 1 to 1.5: 1, or from 20: 1 to 2: 1.

[0141] The lithium salt adduct should be stable at a temperature of -20°C or more, such as 0°C or more, or 20°C or more, such as stable at least from -20°C to 50°C.

[0142] The formation of the lithium salt adduct may be determined by comparison to the compound that has not been mixed with the lithium salt. For example: • While the lithium salt and / or the compound are typically solids, when isolated from one another, the adduct is typically a transparent liquid.

[0143] • Under thermogravimetric analysis (TGA), the step change in TGA of the adduct is typically higher than that for the compound by itself.

[0144] • The polarity of the lithium adduct is typically higher than the compound itself. For example, the adduct may not be soluble (i.e. may have a solubility of lower than less than 0.1 g per 100 mb) in toluene at 20°C.

[0145] • There is a change in chemical shift of protons and carbon nuclei, as determined by and13C NMR respectively, associated with the carboxylate group in the compound when in the adduct form.

[0146] Articles

[0147] The fourth aspect defines an article comprising a nanoparticle composition of the second aspect and / or a lubricant composition of the third aspect. The article may contain the nanoparticle composition as a coating of the article, and / or as a coating of a component of the article. The nanoparticle composition may be present on a surface of the article that is mica, a polymer (e.g. polyether ether ketone, PEEK) or a metal (e.g. a steel).

[0148] For example, the article may be an engine, rocket engine, gearbox, coupling, bearing, ballscrew, leadscrew, gimbal or gyroscope.

[0149] Examples

[0150] Preparation of nanoparticle compositions

[0151] Nanoparticle compositions were fabricated by ball-milling of pristine M0S2 or graphite in the presence of PEGMA in a planetary -type ball mill (4 X 100 mL) under a nitrogen atmosphere. Pristine M0S2 or graphite (1 g) and polyethylene glycol methacrylate (PEGMA, 2 g) were placed into an agate tank containing agate balls (o5 mm) under nitrogen protection conditions. After covering and sealing the tank, the tank was mounted in a ball-mill machine, and the milling process was performed for 24-60 h at a speed of 300-500 rpm. The obtained product was dissolved in ethanol and centrifugated at 2000-4000 rpm for 5-30 min. The supernatant was collected, and the ethanol was removed by a rotary evaporator. The residue was dried under vacuum at 250C overnight to obtain the nanoparticle composition.

[0152] Particle analysis of nanoparticle compositions

[0153] Figure 1 of the accompanying drawings shows two transmission electron micrograph (TEM) images of particles of pristine M0S2. Figure 1 also shows a graph illustrating the particle size distribution of pristine M0S2, with the peak diameter at 250-300nm, a diameter range of 200-400 nm, and a spherical structure. The particle size distributions were determined by analysis of TEM images using Fiji software (Schindelin, J. et al., Nature Methods volume 9, pages 676-682 (2012))

[0154] Figure 2 of the accompanying drawings shows two TEM images of a nanoparticle composition formed by ball milling M0S2 in the presence of PEGMA (Mn=950g mol"1). Figure 2 also shows a graph illustrating the particle size distribution of the M0S2 / PEGMA nanoparticle composition, with the peak diameter at 3-4nm. The M0S2 nanoparticles had a size of 2-9 nm

[0155] Pristine graphite was not characterised by TEM as its particle diameter is very large (50-800 pm).

[0156] Figure 3 of the accompanying drawings shows two TEM images of a nanoparticle composition formed by ball milling graphite in the presence of PEGMA. Figure 3 also shows a graph illustrating the particle size distribution of the graphite / PEGMA nanoparticle composition, with the peak diameter at 3.0-3.5nm. The carbon nanoparticles ranged in size from 2 to 7 nm in diameter.

[0157] Dispersion stability studies

[0158] The stability of aqueous dispersions of M0S2 nanoparticles or graphite nanoparticles in the presence or absence of PEGMA following sonication for 30 minutes was studied over the course of 1 month. Specifically, photographs of the dispersions were taken at 2 minutes, 4 hours, 48 hours, 7 days, and 1 month after sonication.

[0159] Figure 4 of the accompanying drawings shows the results of this study, where: Vial 1 contained an aqueous dispersion of lwt% M0S2, produced by ball milling pristine M0S2 ground in the absence of PEGMA (comparative),

[0160] Vial 2 contained an aqueous dispersion of M0S2 (0.5wt%) and PEGMA (0.5wt%), which has been prepared by mixing, not by ball milling (comparative), Vial 3 contained an aqueous dispersion of a nanoparticle composition (1 wt%) comprising M0S2 nanoparticles and PEGMA, prepared by ball milling the nanoparticles in the presence of PEGMA, in a ratio of 1 :2 by weight (invention), Vial 4 contained an aqueous dispersion of graphite (lwt%), produced by ball milling pristine graphite in the absence of PEGMA (comparative),

[0161] Vial 5 contained an aqueous dispersion of the mixture of graphite (0.5wt%) and PEGMA (0.5wt%), which has been prepared by mixing, not by ball milling (comparative), and

[0162] Vial 6 contained an aqueous dispersion of a nanoparticle composition (lwt%) comprising graphite nanoparticles and PEGMA, prepared by ball milling the nanoparticles in the presence of PEGMA, in a ratio of 1 :2 by weight (invention).

[0163] The dispersions in Vials 1, 2, 4 and 5 (M0S2, mixture of M0S2 and PEGMA, graphite, and mixture of graphite and PEGMA) were each found to initially disperse well in water, forming homogenous suspensions in the minutes following sonication. However, each of the dispersions in Vials 1, 2, 4 and 5 showed agglomeration and sedimentation of the particles after 4 hours. After 2 days, the M0S2 and the graphite were fully sedimented, even in the presence of PEGMA.

[0164] However, the aqueous dispersions of M0S2 or graphite nanoparticle compositions were stable for more than 30 days, with no significant amounts of sedimentation seen.

[0165] Therefore, compositions formed of the nanoparticle compositions of the invention can have significantly increased dispersion stability compared to other similar dispersions.

[0166] It was also noted that the colour of the aqueous dispersion of Vial 1 (M0S2) changed from light grey (initially) to blue (after 7 days), which is indicative of the presence of dissolved MoOs. This suggests that M0S2 nanoparticles generated during ball milling had oxidised. However, the colour of the solution in Vials 2 and 3 (mixture of M0S2 and PEGMA, and M0S2 nanoparticle composition of the invention) did not change, demonstrating that PEGMA prevented the oxidation of M0S2.

[0167] Therefore, nanoparticle compositions of the invention are more resistant to oxidation than conventional nanoparticle dispersions.

[0168] Tribological performance of nanoparticle compositions

[0169] The tribological performance of compositions comprising nanoparticle compositions of the invention in glycerol was studied and compared to a 50 vol% aqueous glycerol solution.

[0170] Specifically, the tribological performance of the test samples either M0S2 nanoparticle compositions (0.1wt%, 0.5wt%, or lwt%) or graphite nanoparticle compositions (0.1wt%, 0.5wt%, or lwt%) in 50 vol% aqueous glycerol, and a 50 vol% aqueous glycerol solution itself.

[0171] The friction coefficient was characterized by a UMT-TriboLab oscillating reciprocating friction and wear test with a ball-on-disk configuration, under the following conditions: load 100 N (2.15GPa); temperature 25 °C; frequency 25 Hz; stroke 1 mm. The upper ball was a 0 9.5 mm 440C stainless steel ball, and the lower stationary disc was a 43.18 x 30.48 x 5.08 mm (length x width x thickness ) 440C stainless steel disc. The wear volumes of the lower disc were measured by a Profilm 3D optical profilometer.

[0172] Figure 5 of the accompanying drawings shows the friction coefficients of the nanoparticle composition test samples over time. Compared to the glycerol solution, 0.1wt%, 0.5wt%, and lwt% M0S2 nanoparticle compositions (“M0S2 dots”, top graph) reduced the friction coefficient of the water-based solution by around 20%, 30%, and 50%, respectively. Compared to the glycerol solution, 0.1wt%, 0.5wt%, and lwt% graphite nanoparticle compositions (“carbon dots”, bottom graph) reduced the friction coefficient of the water-based solution by around 5%, 7%, and 15%, respectively. The reduction of the friction coefficient was proportional to the amount of the nanoparticle compositions. Figure 6 of the accompanying drawings shows bar graphs indicating the wear volumes of a steel disc lubricated by the test samples. Compared to the glycerol solution, 0.1wt%, 0.5wt%, and lwt% M0S2 nanoparticle compositions (top graph) reduced the wear volumes by about 40%, 60%, and 80%, respectively, indicating excellent friction reducing and anti-wear performance. Compared to the glycerol solution, 0.1wt%, 0.5wt%, and lwt% graphite nanoparticle compositions (bottom graph) reduced the wear volumes by about 10%, 20%, and 22%, respectively. The reduction in wear volume was proportional to the amount of the nanoparticle compositions.

[0173] It was found that both the graphite nanoparticle composition and the M0S2 nanoparticle compositions can reduce friction and protect surface from wear. The friction reduction and anti-wear performance of the M0S2 nanoparticle compositions was particularly good under this experiment.

[0174] Thus, even low concentrations of the nanoparticle compositions can significantly reduce the friction between adjacent components and reduce the wear of components.

[0175] Tribological performance of nanoparticle compositions combined with ionic liquids

[0176] The tribological performance over time was determined for the test samples: lithium grease, and lithium grease with either 3 wt% LiTFSI with dodecyl methacrylate (Ionic Liquid, “IL”), 3 wt% M0S2 nanoparticle composition, 3 wt% pristine M0S2, 3 wt% IL and 3 wt% M0S2 nanoparticle composition, or 3 wt% IL and 3 wt% pristine M0S2. Similar apparatus and conditions were used as described above, except the load was increased to 150N (2.5GPa).

[0177] It was found that the mixture of IL and the M0S2 nanoparticle composition reduced the friction coefficient of the base lithium grease by about 20%.

[0178] Figure 7 of the accompanying drawings shows the wear volume in the presence of the test samples. The wear volume was always reduced by addition of the M0S2 nanoparticle composition compared to pristine M0S2. The wear volume for IL and the M0S2 nanoparticle composition was significantly lower than for IL alone, for the M0S2 nanoparticle composition alone, for the pristine M0S2 or for the IL and pristine M0S2 in the lithium grease. The mixture of IL and the M0S2 nanoparticle composition reduced the wear volume of the base lithium grease by about 65%.

[0179] Further dispersion stability studies

[0180] Further dispersion stability studies were performed to compare the compositions of the invention, prepared with PEGMA, with comparative compositions.

[0181] A first set of experiments compared compositions of the invention with compositions prepared using PMMA. Following the protocol described above, aqueous dispersions of (a) lwt% PMMA-M0S2 (the product of pristine M0S2 ground by ball mill with PMMA; comparative) and (b) 1% PEGMA-M0S2 (invention) were prepared by sonication for 30 min. Photographs were taken at around 2 minutes and 4 hours after sonication.

[0182] Figure 8A of the accompanying drawings shows the photograph taken at 2 minutes after sonication. The nanoparticles are well distributed in both vials.

[0183] Figure 8B of the accompanying drawings shows the photograph taken at 4 hours after sonication. The sample with PMMA had separated but the sample of the invention remained homogenous.

[0184] A second set of experiments were performed with boron nitride. The following aqueous dispersions were prepared by sonication for 30 minutes, and then allowed to stand for 24 hours: (I) boron nitride, ball milled without additives (comparative); (II) boron nitride and PEGMA, not milled (comparative); and (III) boron nitride and PEGMA, ball milled (invention). Photographs were taken of the samples after 2 minutes and 24 hours following sonication.

[0185] Figure 9A of the accompanying drawings shows the photograph taken at 2 minutes after sonication. The samples were well distributed in all three vials.

[0186] Figure 9B of the accompanying drawings shows the photograph taken at 24 hours after sonication. After 24 hours the comparative samples (I) and (II) had separated with the boron nitride settling to the bottom of the vial. Sample (III), of the invention, with boron nitride ball milled with PEGMA, did not separate and remained homogenous. These investigations further show that compositions of the invention have enhanced stability compared to comparative compositions. Prevention of oxidation

[0187] A sample of M0S2 in PEGMA was ball milled and then exposed to air for a period of time. A comparative sample of MoS2 was ball milled and then exposed to air for the same duration. The samples were analysed by XPS.

[0188] Figure 10 of the accompanying drawings shows the XPS spectra of the samples. The sample containing ball milled M0S2 powder (without PEGMA) led to serial oxidation of M0S2, while the sample containing PEGMA during ball milling prevented the oxidation of M0S2.

[0189] This shows that compositions of the invention can prevent the degradation and oxidation of nanoparticles, and therefore be more durable.

Claims

CLAIMS1. A method of preparing a nanoparticle composition, wherein the method comprises: providing a nanoparticle precursor that has a laminar structure; providing an ester-containing compound of Formula I; and milling the nanoparticle precursor in the presence of the ester-containing compound, wherein Formula I is defined as:Formula I, and wherein:R1is a hydrocarbon group that is optionally substituted; andR2, R3and R4are each independently H or a C l- 10 hydrocarbon group that is optionally substituted.

2. The method of claim 1, wherein the nanoparticle precursor is selected from the list consisting of graphite, a transition metal dichalcogenide, and boron nitride.

3. The method of claim 1 or claim 2, wherein milling is ball milling.

4. A nanoparticle composition comprising nanoparticles and an ester-containing compound of Formula I.

5. The nanoparticle composition of claim 4, wherein the nanoparticle composition is obtainable by the method of any one of claims 1 to 3.

6. The nanoparticle composition of claim 4 or claim 5, wherein the nanoparticles are selected from the list consisting of graphene and monolayers of graphyne, borophene, germanene, silicene, stanine, plumbene, phosphorene, antimonene, bismuthine, one or two atom thick platinum film, one or two atom thick rhodium film, boron nitride, titanate nanosheet, borocarbonitrides, MXenes, two-dimensional silica,niobium bromide, niobium chloride, transition metal dichalcogenides, graphene, germanane, and SiN.

7. The nanoparticle composition of claim 6, wherein the nanoparticles are selected from the list consisting of graphite, a transition metal dichalcogenide, and boron nitride.

8. The nanoparticle composition of any one of claims 4 to 7, wherein the nanoparticles have an average particle diameter of lOOnm or less.

9. The method or the nanoparticle composition of any preceding claim, wherein:- R1is a polyethylene glycol (PEG) group;- R2is H or a C 1-6 alkyl or alkenyl group; and / or- R3and R4are each independently H or a C 1-5 hydrocarbon group.

10. The method or the nanoparticle composition of claim 9, wherein:R1is a PEG group;R2is H or a C l -4 alkyl or alkenyl group; andR3and R4and are each independently H or a Cl -2 alkyl or alkenyl group.1 1. The method or the nanoparticle composition of claim 9 or claim 10, wherein the ester-containing compound is represented by Formula III or Formula IV:Formula III Formula IV.

12. The nanoparticle composition of any one of claims 4 to 1 1, wherein the nanoparticle composition comprises the compound of Formula I in a proportion of 10 wt% or more relative to the weight of the nanoparticles.

13. The nanoparticle composition of any one of claims 4 to 12, wherein nanoparticle composition comprises the nanoparticles in a proportion of 1 wt% or more relative to the total weight of the nanoparticle composition.

14. The nanoparticle composition of any one of claims 4 to 13, wherein nanoparticle composition comprises the compound of Formula I in a proportion of 1 wt% or more relative to the total weight of the nanoparticle composition.

15. A lubricant composition comprising the nanoparticle composition of any one of claims 4 to 14 and a carrier.

16. The lubricant composition of claim 15, wherein the lubricant composition contains the nanoparticle composition in an amount of 0.05 wt% or more.

17. The lubricant composition of claim 15 or claim 16, wherein the carrier comprises: a) water and / or glycerol, b) a deep eutectic solvent, and / or c) a grease.

18. The lubricant composition of any one of claims 15 to 17, wherein the lubricant composition further comprises an ionic liquid.

19. The lubricant composition of claim 18, wherein the ionic liquid is selected from the list consisting of: a lithium salt adduct of an ester-containing compound of Formula I, trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate, trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl) phosphate, trihexyltetradecylphosphonium dibutyl phosphate, and trihexyltetradecylphosphonium bis (2,4,4-trimethylpentyl) dithiophosphinate.

20. An article comprising a nanoparticle composition of any one of claims 4 to 14 and / or a lubricant composition of any one of claims 15 to 19.

21. The article of claim 20, wherein the article comprises the nanoparticle composition as a coating of the article, and / or as a coating of a component of the article.

22. The article of claim 20 or claim 21, wherein the nanoparticle composition is present on a surface of the article that is mica, a polymer or a metal.

23. The article of any one of claims 20 to 22, wherein the article is an engine, rocket engine, gearbox, coupling, bearing, ballscrew, leadscrew, gimbal or gyroscope.

24. A method of providing an activated lubricant composition, wherein the method comprises:- providing a nanoparticle composition of any one of claims 4 to 14 and / or a lubricant composition of any one of claims 15 to 19, and- polymerising the ester-containing compound of Formula I.

25. The method of claim 24, wherein polymerisation is effected by subjecting the nanoparticle composition and / or the lubricant composition to tribological stress.

26. An activated lubricant composition comprising nanoparticles and an ester- containing compound of Formula II:wherein:R1is a hydrocarbon group that is optionally substituted;R2, R3and R4are each independently H or a C l-10 hydrocarbon group that is optionally substituted; and n is 3 or more.

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