Friction costs a significant amount of undesirable energy and fuel consumption, decreases component lifetime, and contributes to environmentally harmful emissions. In 2009, passenger cars worldwide consumed ˜56 billion gallons of fuel (diesel and gasoline) to overcome friction in their engines, transmissions, tires, and brakes. Friction in the boundary lubrication (BL) regime is generally the most severe, and thus critically impacts fuel efficiency and lifetime of the powertrain components in motor vehicles.
Both organic and inorganic friction modifiers (FMs) have been widely used in engine oils to reduce BL regime friction. Organic FMs are generally long, slim molecules with a straight hydrocarbon chain and a polar group at one end. The effectiveness of these additives is, in a large part, determined by the ability to form an adsorbed molecular layer on a surface. This functionality can be achieved through a polar head which can undergo chemical interactions with the metal surface via physisorption or chemisorption. Enhancing the polarity of such an end group could strengthen surface adsorption of FM molecules and improve anti-friction functionality in the BL regime.
In light of the foregoing, it can be an object of the present invention to provide various friction modifier compositions, related composites and/or methods of using such compositions to reduce boundary lubrication friction, thereby overcoming various deficiencies and shortcomings of the prior art, including those outlined above. It will be understood by those skilled in the art that one or more aspects of this invention can meet certain objectives, while one or more other aspects can meet certain other objectives. Each objective may not apply equally, in all its respects, to every aspect of this invention. As such, the following objects can be viewed in the alternative with respect to any one aspect of this invention.
It can be an object of the present invention to provide a molecular scaffold affording structural variation and corresponding anti-friction and anti-wear functionality.
It can also be an object of the present invention to provide a range of cyclen friction modifier compounds to reduce boundary lubrication regime friction.
It can also be an object of the present invention, alone or in conjunction with one or more of the proceeding objectives, to provide one or more cyclen compounds for incorporation into a range of oil compositions, including without limitation motor oil compositions of the sort useful in the lubrication of crank train, valve train, piston liner and various other components of a gasoline engine.
Other objects, features, benefits and advantages of the present invention will be apparent from this summary and its descriptions of certain embodiments, and will be readily apparent to those skilled in the art having knowledge of oil compositions and their use to reduce boundary lubrication friction. Such objects, features, benefits and advantages will be apparent from the above as taken into conjunction with the accompanying examples, data, figures and all reasonable inferences to be drawn therefrom.
In part, the present invention can be directed to a composition comprising an oil component and a component comprising at least one cylen compound of a formula
wherein each of R1, nR2, R3 and R4 (R1-R4) can be a moiety independently selected from about C5-about C24 linear, substituted linear, branched and substituted branched alkyl moieties, where such substituents can be selected from mono- and multi-valent substituents including but not limited to oxa (—O—), aza (—NH— or —N—), aryl, carbonyl, alkylcarbonyl, arylcarbonyl, oxycarbonyl (—OC(O)—), alkoxycarbonyl, amido (—NHC(O)—), alkylcarboxamido, arylcarboxamido, hydroxy, alkoxy, aryloxy, amino, alkylamino, arylamino, heteroaryl, heteroarylalkyl, heteroaryloxy and combinations of such substituents; and n can be an integer selected from 0- about 10 or greater. Each of nR2 can be the same moiety, or different from at least one of another and independently selected from such moieties to provide a mixture thereof. Accordingly, each of R1-R4 can, without limitation, be independently selected from a wide range of alkyl, ether, alcohol, ester, amine, amide, ketone and aldehyde moieties.
In certain embodiments, each of R1-R4 can be independently selected from any of said C10-C20 moieties. In certain such embodiments, at least R1 can be a linear C11 alkyl moiety. Without limitation, each of R1-R4 can be a C11-C18 alkyl moiety. More specifically, without limitation, each of R1-R4 can be a C11 linear, unsubstituted alkyl moiety. As a separate consideration, without limitation as to any R1-R4 moieties, a composition of this invention can comprise a plurality of such cyclen compounds. Regardless, such an oil component can be selected from base oils and formulated commercially-available motor oils. As used in conjunction therewith, one or more such cyclen compounds can be up to about 0.1 wt. %, to about 0.2 wt. % . . . to about 0.5 wt. % . . . or to about 1.0 wt. % or more of such a composition.
In part, the present invention can also be directed to a composition comprising an oil component and a component comprising at least one cyclen compound of a formula
wherein each of R1, nR2, R3 and R4 (R1-R4) can be a moiety independently selected from about C5- about C24 linear and branched alkyl moieties; and n can be an integer selected from 0- about 10. Such alkyl moieties can be as discussed above or illustrated elsewhere herein. In certain embodiments, such an oil component can be selected from base oils and formulated commercially-available motor oils. In certain such embodiments, such a cyclen component can be about 0.1 wt. % to about 1.0 wt. % of such a composition. Regardless, such a cyclen component can comprise a plurality of cyclen compounds.
In part, the present invention can also be directed to a composite comprising a metal substrate and a composition of the sort described above or illustrated elsewhere herein, such a composition coupled to such a substrate. Without limitation, each of the N-heteroatoms of such a cyclen compound can be adsorbed to the surface of such a substrate, as can be observed or determined at temperatures up to and greater than about 200° C. Regardless, an oil component of such a composition can be a formulated, commercially-available motor oil. Without limitation as to the identity of any particular oil component, a cyclen component used in conjunction therewith can be as discussed above or illustrated elsewhere herein. As can be indicative thereof, such a resulting composite can provide a water contact angle greater than about 90 degrees.
In part, the present invention can also be directed to a method of using a cyclen compound to reduce boundary lubrication friction. Such a method can comprise providing opposed first and second metal substrates; applying an oil-cyclen composition of this invention to at least one such metal substrate; and contacting such opposed metal substrates, such contact inducing boundary lubrication friction therebetween, such a composition in an amount sufficient to reduce boundary lubrication friction between such substrates as compared to boundary lubrication friction induced by substrate contact with application of a composition absent such a cyclen compound. Without limitation, an oil component and one or more cyclen compounds of such a composition can be as discussed above or illustrated elsewhere herein. Regardless, such first and second metal substrates can be selected from the crank train, valve train and piston liner components of a gasoline engine. Such contact can be over a temperature range of about 20° C. to about 260° C., and friction reduction can be realized over such a temperature range.
Illustrating various embodiments of this invention, stable nitrogen (N)-heterocycles can be used as organic BL additives. The nitrogen atoms employed, as discussed herein, have high Lewis basicity which promotes absorption to metal surfaces via hydrogen bonding or acid-base interactions. This invention teaches that the surface absorption of BL additives can be increased by increasing the number of basic nitrogen atoms in the polar head group. Incorporation of a nitrogen-containing heterocyclic molecular structure is a way to achieve this in a single molecule. The American Society for Testing and Materials (ASTM) sequence IIIG specifies a “moderately high” temperature for automotive engine oil as 150° C., which is equivalent to a truck operating under heavy loads on a hot summer day. (International, A. West Conshohocken, Pa., 2012; Vol. ASTM D7320-14.) N-heterocycles can be synthesized with high thermal stability and good oxidation-resistance.
Two nitrogen heterocycles, a tri- dodecyl hexahydro-1,3,5-triazine (TC12T) and a tetradodecyl-1,4,7,10-cyclen (C12Cyc) were synthesized and evaluated as heterocyclic BL additives (inset of
The effectiveness of TC12T and C12Cyclen at reducing BL friction was analyzed by a pin-on-disk tribometry. Film thickness calculation shows that pin-on-disk tests at 1.5 and 15 mm/s are within the BL regime (
BL friction reduction of C12Cyc is also compared to Pennzoil®, a commercial fully-formulated motor oil. Pennzoil® has a lower CoF than the neat Group III oil over the tested temperature range. However, Pennzoil® is outperformed by inclusion of 1 wt % C12Cyc in Group III at every temperature point at 1.5 mm/s, and most at 15 mm/s. At high temperatures, the CoFs for C12Cyc are more than 40% lower than those for Pennzoil®. Employing C12Cyc in commercial motor oils could yield beneficial BL regime friction reduction.
A thermostable heterocyclic molecule with multiple polar centers reinforces the adsorbed lubricant film and promote an effective asperity separation. Nanoscratch tests on steel substrates dip-coated in additive solutions demonstrate the enhanced surface adsorption for C12Cyc (
Contact angle goniometry with water is used to determine the hydrophobicity of the dip-coated surface. The non-polar hydrocarbon chains on the additive will repel polar water molecules and allow a relative comparison of their concentration. In
Molecular dynamics (MD) simulations are used to complement the experimental results and confirm that increasing the number of hydrogen bond acceptors, nitrogen atoms, in the central ring will increase the ability of the additive to form an adsorbed layer on the metal surface. As the center of mass of additives approaches the substrate, the energy of interaction increases (
Analyses of the wear scars from the pin-on-disk tests were carried out by white light interferometry. TC12T, which has much poorer thermal stability, also has much poorer anti-wear functionality. C12Cyc is able to substantially reduce the wear coefficient at 1.5 mm/s on the steel substrate (
As discussed above, among the heterocyclic additives studied, cyclen derivatives demonstrate great potential for motor oil applications. Development continues to address two on-going concerns: Instable friction process at relatively high speeds and oil solubility of cyclens with long side chains (e.g., C18Cyc). Initial BL tests at 15 mm/s showed that C12Cyc did not perform as well as C18Cyc at temperatures below 125° C., but the former outperformed the latter at temperatures above 125° C. Moreover, at the relatively low speed (i.e. 1.5 mm/s), both cyclens demonstrated similar performance. However, C18Cyc exhibited a long- term solubility issue, particularly at low temperatures. In particular, C18Cyc fell out of solution below 50° C., creating a waxy coating on the mechanical surface.
To improve the lubrication stability and solubility of cyclens, hybrid cyclen derivatives with a mixture of side chains were designed and synthesized. It was thought that breaking the symmetry of the molecule would help reduce the likelihood of molecules crystalizing and falling out of solution. This objective was achieved by introduction of a mixture of alkyl side chains during synthesis. For instance, this approach affords 4-5 types of cyclen molecules in the product mixture, ranging from no C18 chains with only C12 chains to only C18 chains with no C12 chains. By varying the ratio of C12:C18, the hybrid products can be varied to an extent, as shown by Electron Spray Ionization-Mass Spectrometry (ESI-MS) in
During the high temperature experiments, simple mixtures with the same side chain ratios were also studied as references. Three C12:C18 ratios were tested for the simple mixtures and hybrids of cyclens: 1:3, 1:1, and 3:1. Both mixtures and hybrids can improve oil solubility of long-chain cyclens. For the high temperature BL tests carried out, the C12:C18 ratios of 1:1 and 1:3 were found to be the best combinations for simple mixtures and hybrids, respectively. The results are shown in
Lubrication breakdown and oil aeration normally occur during start/stop operations for engines and transmissions. Asperity friction is especially severe at cold starts. To assess such issues, a temperature ramping study was adopted in the pin-on-disk tests. During the tests, temperature increased from 25° C. to 210° C. in 40 minutes. All tests results are compared with the commercial FMs, and representative results are shown
The following non-limiting examples and data illustrate various aspects and features relating to the compositions, composites and/or methods of the present invention, including cyclen compounds comprising a variety of pendent alkyl moieties, as are available through the synthetic methods described herein. In comparison with the prior art, the present compositions, composites and methods provide results and data which are surprising, unexpected and contrary thereto. While the utility of this invention is illustrated through the use of several compositions, cyclen components and moieties and/or substituents which can be incorporated therein, it will be understood by those skilled in the art that comparable results are obtainable with various other compositions and cyclen components/moieties/substituents, as are commensurate with the scope of this invention.
Materials. 1-Dodecylamine, 37% formaldehyde solution in methanol, 1-bromododecane and 2.5M n-butyllithium in hexanes were commercially obtained from Sigma Aldrich and used as received. 1,4,7,10-Tetraazacyclododecane (cyclen) was commercially obtained from Matrix Scientific and used as received. All manipulations of air-sensitive materials were carried out with rigorous exclusion of oxygen and moisture in flame- or oven-dried Schlenk-type glassware on a dual-manifold Schlenk line. Tetrahydrofuran (THF) was purified by distillation from Na/benzophenone ketyl. The deuterated solvents chloroform-d (CDCl3) and cyclohexane-d12 (C6D12) were obtained from Cambridge Isotope Laboratories (>99 atom % D) and dried over 3 Å molecular sieves. A commercial Group III oil from Ashland Inc. was used as the base oil without further treatment, which is a typical base oil for automotive applications. A commercial fully formulated oil (Pennzoil® motor oil) was used as a reference in tribo-tests. E52100 steel disks from McMaster-Carr were used in tribo-tests, and their hardness was measured to be ˜545.19 HV (5.347 GPa). Its typical chemical composition is as the following: sulfur, ˜0.025 wt. %; silicon, ˜0.15-0.35 wt. %; phosphorus, ˜0.025 wt. %; manganese, ˜0.25-0.45 wt. %; chromium, ˜1.30-1.60 wt. %; carbon, ˜0.95-1.1 wt. %; and balance iron.
Characterizations and tribological investigations. Nuclear magnetic resonance (NMR) spectra were recorded on Varian UNITY Inova™ 500 (FT, 500 MHz, 1H; 125 MHz, 13C) or Agilent F500 (DDR2, FT, 500 MHz, 1H; 125 MHz, 13C) instruments. Chemical shifts for 1H and 13C spectra were referenced using internal solvent resonances. Elemental analyses were performed by Galbraith Laboratories, Inc. (Knoxville, TN).
In order to investigate stability while in a solvated state, NMR samples of the additives were heated at 90° C. for two days in cyclohexane-d12. Chloroform-d1 was used for 1H- and 13C-NMR to verify structure and purity because peaks were better resolved and the chloroform solvent peak (δ 7.26 ppm) did not overlap with compound peaks; however, cyclohexane-d12 was chosen for thermal stability 1H-NMR tests because it would better mimic the nonpolar aprotic environment of base oil, even though the cyclohexane solvent peak (δ 1.41 ppm) overlaps with some of the alkyl proton peaks. After these two days, 0.1 mL of deionized H2O was added to the NMR samples, mixed and heated for two more days to mimic atmospheric moisture dissolved in the base oil. NMR spectra were taken once each day during the test.
With reference to
With reference to
Water contact angles were measured using an AmScope MU300 Microscope Digital Camera. Nanoscratch tests were carried out in a nanoindentation-tribotesting system (NanoTest 600, Micro Materials Ltd, UK) by varying the loads from 2 mN to 50 mN. BL additives were coated on 52100 steel substrates before the nanoscratch experiments. Samples for water contact angle goniometry and for nanoscratch tests were prepared by dip-coating a 52100 polished steel substrate (1 cm×1 cm) in a 5 wt. % solution of the additive in PAO4 oil at 120° C. for 12 hours, and then washing with toluene until there was no streaking on the surface.
Pin-on-disk tests were carried out using a CETR UMT-2 tribometer. As shown in
In order to confirm that pin-on-disk tests are carried out in the BL regime, film thicknesses are calculated first for the Group III oil by numerically solving the following Reynolds equation:
where, x and y are the bearing width and length coordinates; P is fluid film pressure; u is the relative rolling speed; h is fluid film thickness; ρ is fluid density; and η is treated as the averaged viscosity across the film. Kinematic viscosity used for the calculations were measured using a capillary viscometer (CANNON® Instrument Company) in a constant-temperature bath. The kinematic viscosity of Group III oil are 33.7 cst and 4.23 cst at 25° C. and 100° C., respectively. An exponential viscosity-pressure model and Dowson-Higginson density-pressure relationship were used. A discrete convolution-fast Fourier transform (DC-FFT) method was utilized to calculate elastic deformation.
In the base oil, lubricating film thickness is calculated to range from several nanometers to about one micrometer (
Wear tracks were examined using a 3D Optical Surface Profiler (Zygo® NewView™ 7300). Wear coefficient is calculated using the below Archard equation:
Synthesis of 1,3,5-Tri(dodecyl) hexahydro-1,3,5-triazine (TC12T). A single-neck 250 mL round bottom flask with a stir bar, was charged with 1-dodecylamine (12 mL, 54 mmol) and 50 mL of MeOH. Formaldehyde (37 wt. % in H2O, 6.2 mL, 75mmol) was added gradually with magnetic stirring. The reaction was allowed to mix for 5 hours, then the product was extracted with hexanes, washed three times with deionized (DI) water, dried with MgSO4 for 5 hours, filtered to remove particulate and concentrated to dryness with rotary evaporation to yield a clear, viscous liquid (60.9% yield of major product). 1H NMR of major product (CDCl3): δ 3.25 (s, 6H, —NCH2N—), 2.39 (t, 6H, —NCH2CH2—), 1.44 (qu, 6H, —NCH2CH2CH2—), 1.25 (m, 54H, hydrocarbon chain), 0.88 (t, 9H, —CH2CH3). 13C NMR (CDCl3): 86.83, 74.88, 55.07, 53.04, 49.88, 31.74, 29.84, 29.80, 29.73, 29.67, 29.52, 28.91, 27.81, 27.70, 27.37, 22.85, 14.27. Elemen. Anal. Calc'd for C56H116N4: C, 79.11; H, 13.79; N, 7.10. Found: C, 75.05; H, 18.79; N, 6.16.
Synthesis of 1,4,7,10-Tetra(dodecyl)-1,4,7,10-tetraazacyclododecane (C12Cyc). Synthesis adapted from Xiong, X.-Q. et al. (Xiong, X.-Q.; Liang, F.; Yang, L.; Wang, X.-L.; Zhou, X.; Zheng, C. -Y.; Cao, X.-P. Chem. Biodivers. 2007, 4, 2791.) Charged a 250 mL oven-dried Schlenk flask and stir bar with 1,4,7,10-tetraazacyclododecane (1 g, 5.8 mmol), cap with a rubber septum and evacuated on Schlenk line for 15 minutes. Placed Schlenk flask under positive nitrogen pressure and added 75 mL of THF by syringe. Cooled reaction flask to −78° C. in a dry ice-acetone bath with magnetic stirring. Added n-BuLi solution (2.5 M in hexanes, 10.2 mL, 25.5 mmol) gradually by syringe and let mix for 1 hour at −78° C., then transferred to an ice-water bath and let stir for 1 hour at 0° C. Added 1-bromododecane (5.6 mL, 23.2 mmol) by syringe and let stir for 2 hours at 0° C. Quenched reaction with 5 mL of ethanol. Removed solvent with rotary evaporation, dissolved remaining residue in dichloromethane, filtered out insoluble particles and concentrated to dryness. Purified by recrystallization from methanol and then recrystallization from hexanes to yield a fluffy, white solid (31% yield). 1H NMR (CDCl3): δ 2.61 (s, 16H, —NCH2CH2N—), 2.36 (t, 8H, —NCH2CH2—), 1.43 (qu, 8H, —NCH2CH2CH2—), 1.26 (m, 72H, hydrocarbon chain), 0.88 (t, 12H, —CH2CH3). 13C NMR (CDCl3): 56.23, 52.19, 31.95, 29.74, 29.71, 29.70, 29.68, 29.39, 27.75, 27.35, 22.71, 14.14. Exact Mass (ESI-MS) 845.13 m/z. Elem. Anal. Calc'd for C56H116N4: C, 79.55; H, 13.83; N, 6.63. Found: C, 79.59; H, 14.37; N, 6.64.
While the synthesis of C12Cyc (n=1) is described in the preceding example, it will be understood by those skilled in the art and made aware of this invention that various other such N-heterocyclic compounds can be prepared and utilized as described herein, in accordance with other embodiments of this invention—such preparation using synthetic techniques of the sort described above or straight-forward variations thereof, as would also be understood by those skilled in the art and made aware of this invention, such N-heterocyclic compounds limited only by the commercial or synthetic availability of corresponding azacycloalkane, bromoalkane and substituted (i.e., alkyl substituents including but not limited to those discussed above) bromoalkane starting materials.
Molecular dynamic (MD) simulation of the surface adsorption. An all atom MD simulation was used to explain the adsorption process of the additive molecules on a hydrated silica surface. Base oil [polyalphaolefin (PAO)] molecules, TC12T molecules, and C12Cyc molecules were simulated in LAMMPS. For the silica substrate, two hydroxyl was artificially grafted on each silicon atom on its (100) surface. (Lopes, P. E. M.; Murashov, V.; Tazi, M.; Demchuk, E.; MacKerell, A. D. J. Phys. Chem. B 2006, 110, 2782.) By doing so a hydroxyl coverage was about 8 molecules/nm2. This coverage was the partial charge of all the atoms in the simulation cell were calculated and assigned by the Charge Equilibration (QEq) method in the Material studio. (Rappe, A. K.; Goddard, W. A. J. Phys. Chem. 1991, 95, 3358.)
The forcefield used for the silicon substrate was a widely used Tersoff forcefield. (Tersoff, J. phys. Rev. B 1988, 37, 6991.) The forcefield used for the BL additive molecules was Consistent Valence Forcefield (CVFF). (Dauber-Osguthorpe, P.; Roberts, V. A.; Osguthorpe, D. J.; Wolff, J.; Genest, M.; Hagler, A. T. Proteins: Struct., Funct., Bioinf. 2004, 4, 31; Maple, J. R.; Dinur, U.; Hagler, A. T. Proc. Natl. Acad. Sci. U.S.A. 1988, 85, 5350.)
The simulation configuration is shown in
A variety of cyclen compounds, were synthesized, then structurally and tribologically characterized. As compared to the prior art, the cyclen compounds had much greater thermal stability, as evidenced by NMR studies and TGA, as well as greater surface adsorption and BL enhancement, shown experimentally by pin-on-disk tests, nanoscratch measurements, and contact angle goniometry. MD simulations support the experimental observations and conclusions about surface adsorption, showing that, for instance, the C12Cyc energy of interaction is preserved at elevated temperature (200° C. ). Such performance can be attributed to having four or more hydrogen bond acceptors in a central ring, which improves surface adsorption, and multiple hydrocarbon chains in the same molecule, which improves interaction with base oil and asperity separation. Anti-wear functionality is a beneficial side effect of cyclen anti-friction capability.
This application claims priority to and the benefit of application Ser. No. 62/179,564 filed on May 11, 2015, the entirety of which is incorporated herein by reference. This invention was made with government support under DE-EE0006449 awarded by the Department of Energy. The government has certain rights in the invention.
Number | Date | Country | |
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62179564 | May 2015 | US |