TITLE OF THE INVENTION

NANOSPACER LUBRICATION FIELD OF THE INVENTION

[0001] This invention is concerned on the basic problems of tribology, namely the nature of friction and methods to reduce the friction, or lubrication, occurring between moving solid parts of machines. As virtually every movement of matters on earth and in space induces frictions, and movements are controlled by lubrication, the invention is related with virtually all aspects of dynamic industrial operations.

BACKGROUND OF THE INVENTION

[0002] It is well-recognized in recent years that lubrication oil, the long-time background hero in all branches of industry involving solid parts in relative shearing motion, has a few serious defects that pertain to rapid destruction of environments on global scale. A well visible manifestation of the problem will be the disposal of waste lubrication oil, which cannot be burnt because large amounts of metallic particles would be released in air as oxides in the form of small particles together with the large amounts of carbon dioxide. The amount of waste lubrication oil is estimated to reach lOMt annually in the world (Non-Patent Literature 1).

[0003] The disposal problem originates from an inherent defect of oil, which is the mechanical weakness of thin film of oil under boundary conditions in lubrication (NPL2). According to the fusion theory of friction by Bowden (NPL3), friction starts when the moving solids directly touch each other at their microscopic asperities, thereupon the frictional process quickly replicates through contact-fusion-bonding steps. It is therefore imperative that an ideal lubrication system has a reliable mechanism to avoid the direct contacts between the surfaces in relative motion at the asperities, hopefully in its incipient stage. However, the thin oil film is totally powerless to prevent the microscopic contact to take place, because it breaks up readily when the asperities on the surfaces approach too close under boundary condition. In this regard it was a mistake to use oil for lubrication from the beginning.

[0004] Oil-less solid lubrication, spacer lubrication and many other improvements have been conceived and tested, and some of them adopted for particular purposes with considerable success (NPL4), but none of them could compete with lubrication oil in terms of low cost, general applicability, easy handling and secured safety. For this reason recent trends in the lubrication technology has been to implement more and more new additives into lubrication oil. The use of additives often leads to increase in friction coefficients of lubrication oil, which have always been in the mediocre ranges of 0.2-0.3.

[0005] A new problem arose as the energy consumption increased rapidly in industrially developing countries leading to higher and higher prices of petroleum. At the moment there is no immediate prospect of recovering the past price levels. It is therefore highly desirable that lubrication systems appear with much smaller friction coefficient than the present level.

[0006] Under such circumstances, it is clear that we need to find a new fluid lubrication system which never allows disastrous direct touch between the moving solid parts, has high environmental compatibility and achieves very low friction coefficient. Conventional lubrication oil is regarded as one of the last necessary evils like fluorescent lamps and petrol fuels.

SUMMARY OF THE INVENTION

Technical aspects of problems

[0007] We believe that the only viable method of absolutely forbidding the incipient contacts between asperity tips in the moving solid surface is to use spacers. Ball bearing embedded in grease may look formally the oldest forerunner of spacer lubrication. However, the steel or ceramic balls make direct contacts with the moving surfaces to produce wear and scars, and the balls must be kept in special closed containers to keep them at the contact points. Hence such systems are out of question for our present needs. The advantage of ball bearing system is the fact that the friction consist predominantly of rolling friction, which is usually less than 1%.

[0008] An interesting development was seen by the introduction of so-called magnetic fluid (NPL5), which actually consists of single-nano magnetic and spherical particles, and applied as spacers for the ferromagnetic surfaces. Magnetic spacers always completely cover the metal surfaces, hence they are available anytime whenever boundary condition appears. This is an excellent extension of the ball-bearing lubrication, but can be applied only to ferromagnetic metals and costly. Also questionable are the durability and stability of magnetic nanoparticles under high load or under conditions that erode the magnetic fluids.

[0009] Clearly the above two examples of spacer lubrication do not meet our three major purposes mentioned above. Let us itemize the requirements that a spacer should meet in order to achieve our goal of inventing a new lubrication system:

(1) Ubiquity. We need to deliver enough number of spacers to the site of incipient true contact under boundary condition. Highly concentrated dispersion of spacers or fluid of spacer is needed.

(2) Sphericity. This is an essential asset for a spacer lubrication to achieve low friction coefficient. If the sphericity of the spacer is high enough, then the friction consists of rolling friction alone.

(3) Dispersity. A very close idea has been put forward by many people when C ₆ o was discovered. However, there was no effect when C ₆ o particles were added to, for example engine oils. The reason is that the C ₆₀ is highly associative through their active surfaces, and forms extremely tight and large aggregates in fluids. Therefore, important conditions of our spacers are that they must form stable dispersion in fluids, and that they should not aggregate during the spacer action.

(4) Hardness and Strength. Since the entire load is concentrated at the few tips of asperities in the incipient contact, the spacer must have the highest hardness and strength, but still should not damage the lubricating surfaces and soluble in fluid medium. For the latter purpose, the best remedy would be to cover the surface of spacer with soft layer(s).

(5) Availability. The two components of spacer lubrication, spacers and dispersing medium, must be readily available anywhere at a cost at least comparable to or more desirably lower than lubrication oils.

(6) Health risk. In view of strong doubts in the health risk of nanocarbon particles like fullerenes and nanotubes, health risk of spacer particles would be a great social concern when we think of general applications. Solution to the problems

[0010] We disclose here that dilute colloidal solutions of single-nano diamond particles in some liquid media display surprisingly low friction coefficients (FIG. 1). The results are interpreted in terms of high number density of single-nano particles in its colloidal solution (NPL6,7), which allows for them to act as ubiquitous spacers whenever boundary condition appears. Single-nano diamond crystals have all the other requirements for this purpose (NPL8). It is likely that we will finally be able to get rid of oil which persisted too long as the only lubrication fluid.

[0011] The most unusual and seemingly unlikely feature of nanospacer lubrication will be ubiquitous availability of spacers at the incipient true contact points under boundary condition. As this feature comprises a central issue of the present invention, let us first rationalize the background, which originates from an overlooked principle of nanotechnology (NPL6,7).

[0012] The spacer particles that we use in the present invention are the primary particles of detonation nanodiamond (FIG. 2), which we recently re-discovered (NPL9). Throughout this description we call it by a factual name of 5-nm bucky diamond (5nBD, NPL10). A 5nBD particle measures only 4.7 nm in size: so small and so light that only a nominal weight of 5nBD contains astronomical number of particles (FIG. 2). For example, Ιμΐ of its 1% aqueous colloid solution contains 10 ¹³ (100 billion) particles of 5nBD\ In addition, 5nBD is endowed with all other properties required for spacers: the hardest material on earth, quasi-spherical in shape (vide infra), giving stable colloid (FIG. 2), simple preparation (NPL7), and others (see below).

[0013] Let us explain how the Number Effect (NPL6,7) works in actual situation. Suppose a couple of metal plates are in relative motion in 1% 5nBD aqueous colloidal solution, and are approaching towards each other too close (FIG. 3(1)). When the linear distance between the closest asperities decreased to the limiting distance of 7 nm, the effective diameter of hydrated 5nBD (FIG. 2), the spacers start to feel the plates (FIG. 3(2)). If we assume that both asperities have a circular tip of Ιμπι in diameter, then we may expect 316 5nBD particles forming a single-particle layer in the micro-space S*h (FIG. 3(2)'), according to simple calculations. The assumed diameter of asperity tips is considered to correspond to an early stage of friction in view of the fact that the smallest reported true contact point is 26μηι (NPL3). We believe that this picture of 300 nanospacers trapped between the asperity tips is reasonable, and this many spacers will be enough to stop further approach of plates.

[0014] Thereupon the pinched 300 5nBD spacers will start to roll themselves (FIG. 3(2)' ). Thus, a pair of asperities that were closing in until a moment before are moved apart (FIG. 3(2)→(3)). In this way, every incipient true contact point between plates will be repeatedly rejected at its early stage by the rolling actions of ubiquitous nanospacers and no real friction process will ever start, as long as the spacers remain dispersed and keep quasi-spherical shape under the load.

[0015] It may seem that the story was told too well, so did we. Hence we were genuinely surprised when 1% 5nBD aqueous colloid showed superlubricity ( fJ. =0.005-0.01) when tested against sapphire-ball (2 mmD )/Si wafer system (Example 3). Pure water displayed a /J value of 0.086 under identical conditions (FIG. 1). Clearly, such low friction coefficients indicate that conventional fusion mechanism of friction (NPL3) disappeared and the major source of friction changed to that of rolling nanospacers.

[0016] This explanation implies that our 5nBD spacers should be shaped spherical or at least quasi-spherical. Actually we have long been perplexed by the TEM images of 5nBD which hardly looked like octahedral or its truncated shapes expected for diamond (NPL8,9, 11 ), but now we realize that the images actually represent edge-worn

quasi-spherical shapes (FIG. 4) as the result of beads-milling (NPL12). Independently we recently revealed surface geometrical transformation pathways from octahedral to many faceted quasi-spherical shapes taking place in natural diamonds during the ascent process from deep underground to earth's surface (NPL13). It is likely that similar surface morphological changes occurred during beads-milling to produce 5nBD particles in quasi-spherical shapes. Recognition of the abraded surface morphologies in 5nBD played a crucial role in interpreting superlubricity of nanospacer lubrication, although more accurate pictures on the shape of 5nBD particles still remain to be found.

[0017] The following features of 5nBD appear to have contributed to the remarkably low friction of its aqueous solutions obtained in the course of our validation of nanospacer lubrication scheme. First, a few layers of defective fullerenic patches are believed to have been formed by phase transition of the surface diamond layers on the { 111 } facets of nanodiamond crystals, based on SCC DFTB calculations (NPL14), intense G bands in Raman resonance (NPL9), and relative X-ray diffraction intensities (NPL15, FIG. 2). These graphene-like patches should have served as solid lubricants for both Si and sapphire surfaces.

[0018] Second, abnormally tight hydration on the surface of nanodiamond crystal has been interpreted as the results of strong H-bond formation between solvent water molecules and highly negative electrostatic charges on the { 111 } facets (NPL16) and also based on the observation on a differential scanning calorimeter of a non-freezing water in 5nBD hydrogel (NPL17, 18, FIG. 2). Soft hydration shell should have reduced the shearing stress involving the spacer, thus reducing rolling friction as well.

[0019] We wish to know the lowest possible concentration or the minimum number of spacers necessary to achieve acceptable μ, e.g., 0.02 or less. While reducing the 5nBD concentration in aqueous lubricant, we observed rather fast increase in μ up to 0.015 occurring at 0.3% concentration of 5nBD (FIG. 1). The increase in μ should be due to accelerated escape of spacers from the contact area at lower concentrations. The loss of spacers at the last moment may be prevented by increasing the viscosity of dispersing medium. However, too high viscosities increase viscosity resistance in the movements of fluid lubricants which increases μ. Hence too viscous media are to be avoided.

[0020] For these reasons, we chose ethylene glycol (EG) as the next medium to be tested for our nanospacer lubrication. EG has considerably good affinity towards 5nBD and gives highly stable colloidal solutions up to 3.5% by direct solvent-substitution method (Example 1). [0021] As expected 5nBD/EG colloid displayed quite satisfactory friction coefficient of 0.01 even at 0.1% concentration (FIG. 1). EG fluid is sixteen times more viscous than water but showed a comparable friction coefficient as water; hence EG itself has some lubrication effect even in the absence of spacer. In view of low cost, absence of any acute toxicity, easy handling, transparency, no coloration, and free miscibility with water, EG is a strong candidate for the general-purpose fluid medium.

[0022] The importance of viscosity is clearly demonstrated by using dimethyl sulfoxide (DMSO) as the fluid medium. DMSO has about the same viscosity as water and showed a friction coefficient of 0.095 in the absence of 5nBD. Hence its lubrication property can be judged as comparable to water. When 0.1% of 5nBD was dissolved in DMSO, the resulting colloid showed an acceptable friction coefficient of 0.023 was obtained (FIG. 1), but this value was twice inferior to EG, probably reflecting some escape of spacers at the moment of pinching between Si wafer and sapphire ball. It should be noted that DMSO is recognized as the best known solvent (actually dispersant) for 5nBD (NPLl l), quickly dissolving 5nBD up to more than 10%, and miscible with water and virtually all other known solvents. Hence DMSO will be a convenient medium when extremely high number density of 5nBD becomes necessary. Mixed solvents with EG and other media would also be interesting.

[0023] Colloidal solutions of 5nBD in other organic solvents are interesting, but so far only a few solvents showed practicable affinity to 5nBD. Polyhydric alcohols including poly(vinyl alcohol), polyoxyethylene like diethylene glycol and triethylene glycol, glycerin and their esters or ethers, polyalkylene glycols like propylene glycols and 1,4-butanediol, generally gives stable colloids of 5nBD up to a few%. Polyhydric alcohols cover a wide range from viscous fluids to high melting solids, hence it seems straightforward to expand and apply the principle of nanospacer lubrication to greases and waxes.

[0024] In the course of words that culminated in this invention, we found a convenient synthesis of well-dispersed 5nBD colloid in polyhydric alcohols and other high-boiling solvents by direct solvent exchange reaction (DSER) from its aqueous colloid, rather than dissolving dried aggregates of 5nBD into the solvents as generally practiced in this field. The success of DSER is primarily due to two factors. One factor is the high thermal stability of colloidal solution. The other factor is the fact that both water and polyhydric alcohols are good solvents for 5nBD, which means that there will be fast exchange of solvents in the solvation shell on the surface of 5nBD.

[0025] In concluding the summary section, let us once again review how 5nBD satisfies the six requirements proposed for a spacer in our new lubrication system, the goal of which is to replace notorious lubrication oil.

[0026] (1) Ubiquity. This requirement looked at first formidable but was solved quickly by the Number Effect inherent to the nanoparticles (NPL6,7). As a matter of fact, our scheme of spacer lubrication works only with nanoparticles because of the Number Effect. Perhaps there will be many other phenomena in which the Number Effect plays an essential role.

[0027] How small should the nanospacers be in order for them to work efficiently? The upper limit of spacer size depends on the smoothness of surface σ _α in relative movements: if the diameter D of a nanospacer is larger than σ _α of the surface, then the nanospacer will also be pinched between the hollow areas, thus damaging the surface. If D is smaller than σ _α , nanospacers will remain hidden under asperities and do no harm. Hence nanospacer lubrication with 5nBD will not work for highly polished surfaces having σ _α smaller than 5 nm.

[0028] (2) Sphericity . The situation with this requirement resembles the first one; we never thought that 5nBD would satisfy it at first. Almost independently from the work of nanospacer lubrication, we found quite a few almost spherical but many-faceted surface morphology in small natural diamond crystals and inferred that quasi-sphericity is the best strategy to survive under harsh conditions like the ascent from 150-300km underground to earth's surface. We assume that the disintegration of agglutinated detonation nanodiamond crystals by beads-milling likewise impose harsh conditions upon nanodiamonds (NPL13).

[0029] (3) Dispersity. Once again this requirement was fulfilled in unexpected manner. When we first succeeded in disintegrating agglutinates of detonation nanodiamond by beads-milling in water, we obtained black but homogeneous solution without any precipitation. We were much surprised and wondered how diamond could be dissolved in water. This problem was solved when we noticed non-freezing peak in DSC of 5nBD gel (NPL17,18). Later we learned that 5nBD particles are spontaneously polarized due to its unique geometrical and electronic structure to produce high electrostatic fields over the facets. Hydrogen-bonding solvents like water, alcohols and a few of dipolar aprotic solvents strongly interact with the negative electrostatic charges on the surface of 5nBD (NPL12, 13,14). Rigorously speaking what we have is not a true solution but a colloid, but as we cannot see dispersed 5-nm particles the colloid looks like a real solution. Good 'solubility' of 5nBD in some solvents is one of the great advantages that make up this invention.

[0030] (4) Hardness and Strength. These typical characteristics of diamond are well-expected to work when 5nBD was chosen as the spacer. However, diamond is noted for its ready cleavage along the directions of { 111 } plane. As these cleaving facets are supposed to have been covered with graphitic patches, cleavage will happen only after repeated application of force along the plane and there are very large excess of 5nBD particles in our nanospacer lubrication system, we think that cleavage will not occur so often as to affect the spacer action.

[0031] (5) Availability. Raw material of 5nBD is the expired military explosive called Composition B, which is the most popular and overproduced military explosive. Even if piece prevails and all the countries in the world stop armament race, we believe that other method should be found, such as laser abrasion of graphite. At least for half a century from now, we will have ample supply from the military countries.

[0032] (6) Health risk. Diamond has no chemical reactivity, hence there is no toxicity. The total absence of cytotoxicity has been well studied and confirmed (NPL19-21).

[0033] In conclusion, we think nanotechnology made it possible to use 5nBD particles as an ideal material for nanospacer lubrication. Without the knowledge of nanotechnology, the idea of nanospacer lubrication would have never been borne out. As the result, we have here a new concept of clean, practicable and highly efficient lubrication, believed to have capability of replacing lubrication oil in the near future.

Advantageous effects

[0034] As shown in FIG. 1, the low friction coefficients in nanospacer lubrication of 5nBD are quite remarkable, generally giving superlubricity with μ<0.01. An immediate effect of superlubricity would be disappearance or virtually no exothermicity in the lubrication system. As the result of strict exclusion of contacts among the moving surfaces in nanospacer lubrication, no metal particles will be produced. Lubrication system will run uncontaminated for long time. This means that the closed lubrication system may become feasible and low-boiling fluids like water can be used as lubrication fluids.

[0035] The most beneficial effect of superlubricity is naturally the increase in the energy efficiency. In the case of automobile, for example, superlubricity in shearing contacts of metallic parts leads to reduced consumption of fuel, and decrease in the production of CO2 emission in the exhaust gas. General effect of nanospacer lubrication upon both economy and environment will be great.

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0036] The summary, as well as the following detailed description, is further understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings exemplary embodiments of the invention; however, the invention is not limited to the specific methods, compositions, and devices disclosed. In addition, the drawings are not necessarily drawn to scale. In the drawings:

[0037] FIG. 1 depicts a Table illustrating the effects of dispersing small amounts of 5nBD, primary particles of detonation nanodiamond, in lubrication fluid upon frictional coefficient of sapphire/Si wafer.

[0038] FIG. 2 depicts a Table illustrating selected properties of 5nBD relevant to nanospacer lubrication. Complex surface structures are further illustrated below the Table in cross sections and also in 3D models. On the left are spherical seamless models and on the right truncated octahedral holey bucky models.

[0039] FIG. 3 illustrates cross sectional perspective snapshots of the incipient direct contact between a pair of asperities from the surfaces in relative shearing motion under boundary condition (1), wherein the thin film of lubrication fluid still maintains two surfaces untouched. As the interfacial distance decreases to a critical distance of 7 nm (2), the nanospacers that happen to be pinched between the asperities begin to feel the tips of asperities. In cases when the concentration of 5nBD is in the range 0.1 to 1%, the number of 5nBD pinched in the microscopic space particles are 30-300. These particles will stay in this space if the dispersing fluid has appropriate viscosity, and starts rotating due to the sphericity of spacers. Then, as shown in (3), the head-on clash to asperity tips will be avoided and a good distance will be recovered between the surfaces. If the spacers are smaller than the roughness of surface, which is usually the case, true contacts followed by deformation and fusion of asperities will never occur.

[0040] FIG. 4 depicts TEM image of 5nBD particles. Note the scale bar to recognize the size of 5nBD particles. These do not seem like sharp-edged polyhedra but more like quasi-spherical multi-faceted worn-out diamond crystal particles.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0041] The present invention may be understood more readily by reference to the following detailed description taken in connection with the accompanying Figures and examples, which form a part of this disclosure. It is to be understood that this invention is not limited to the specific devices, methods, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the claimed invention. Also, as used in the specification including the appended claims, the singular forms "a", "an," and "the" include the plurl, and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. When a range of values is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value form another embodiment. The term "plurality" means two or more of something. All ranges are inclusive and combinable.

[0042] It is to be appreciated that certain features of the invention which are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any sub-combination. Further, references to values stated in ranges include each and every value within that range.

[0043] Preparation of 5nBD colloidal solutions. The first disintegration of agglutinates of detonation nanodiamond into primary particles (5nBD) by wet beads-milling in water took place in the laboratory of NanoCarbon Research Institute, Japan, in 2002 and marked one of the memorable breakthroughs in nanotechnology (PLl). Nanocarbon colloid was first prepared by dissolving C ₆₀ in various organic solvents in the early 1990 ^th after Kratschmer's successful isolation of C ₆ o- By all accounts, Οβο behaved very much like large organic molecules. However, the colloidal solutions of 5nBD particles behaved differently: 5nBD dissolved in water up to 8% to give smooth and stable sol in deep black color! Clearly we obtained the first typical nanocolloid. These and subsequent strange behaviors of 5nBD colloid have perplexed us but with time many behaviors are understood.

[0044] The almost exclusive, popular, and convenient form of 5nBD product is aqueous colloid. Details of the first-generation beads-milling procedure to produce aqueous 5nBD colloid have been published elsewhere, and we will soon disclose the

second-generation procedure. As the present invention is concerned with 5nBD colloidal solutions in viscous organic solvents, we disclose here their convenient preparation by direct solvent exchange reactions (DSER) on aqueous colloid. In this reaction, aqueous colloid of 5nBD is placed in a Kjeldahl evaporation flask and attached to a conventional rotary evaporator. After starting evaporation of water under mild condition, a solvent like EG is slowly and continuously introduced into the evaporation flask through a thin PP pipe and a valve without breaking vacuum. Evaporated water was collected into a graduated receiving flask until calculated amount of water is distilled out. As EG has a boiling point of 197.3°C, this short-path distillation quickly works out the solvent exchange and gives clean colloid of 5nBD in polyhydric alcoholic solvents containing less than 0.5% of water. Concentration, particle-size distribution, viscosity, pH and ζ-potential are measured by using the known methods. Examples are given below.

[0042] Remarks on Particle-Size Determination of 5nBD in Dilute Solutions. We recently noticed that 5nBD aggregates upon dilution of its colloidal solution. The cause of dilution aggregation is not completely understood, but we know that the aggregation extends to involve a few particles in aqueous colloid. The aggregates could not be re-dispersed by immersing in supersonic washing bath for a few hours. Re-dispersion took place only after irradiating with powerful supersonic processor.

[0043] Properties of 5nBD colloidal solutions. Colloidal solutions for nanospacer lubrication are dilute; usually less than 0.1%, hence the appearance and characteristics of lubricants are almost those of pure solvent: stable, non-flammable, clear, clean, pure, almost colorless, light, smooth, transparent, freely miscible with water, and non-toxic. There will be virtually no emission of heat from friction, hence no thermal degradation of solvent will occur. As the result, lubricants will stay clean for long time, and 5nBD particles will stay well-dispersed and never precipitate. The handling of nanospacer lubricants is easy and comfortable compared to lubrication oil. Spilled drops can be quickly washed out with running water. There is no inflammability because of relatively high viscosity.

[0044] Determination of friction coefficient in nanospacer lubrication.

Dynamic friction coefficients were measured on a linear reciprocal friction microtester (manufactured by KOYO Precision Instruments, Mitaka, Tokyo, Type KH-851) using hemi-spherical sapphire with 1-2 mm in diameter as slider and l x l cm pieces of silicon wafer as substrate under 10-40 raN of load, 10Hz of frequency and 1.5 mm of amplitude. Friction force was monitored with a high-sensitive transducer. The Si plate was held on a vibrator and covered with the colloidal solution.

EXAMPLES AND OTHER ILLUSTRATIVE EMBODIMENTS

[0045] Materials. 5nBD particles are prepared at NanoCarbon Research Institute, Ueda, Japan, by disintegrating crude agglutinates of detonation nanodiamond, which was purchased from Guangzhou Panyu Guangda Electromechanical Co., Guangzhou, China. Procedure, characteristics, geometrical as well as electronic structures and properties are published elsewhere (NPL6-8). Average size of the primary single-crystals of cubic diamond is 4.7±0.7 nm. Diamond carbon constitute 92wt% of the current product as determined by X-ray diffraction intensity measurements calibrated by internal standard (NaF). Guaranteed grade of EG and other chemicals were used as purchased. Water content of EG was 0.12±0.03% as determined by Karl Fischer method (see below).

[0046] Methods. Water contents of 5nBD colloid in organic solvents, mainly polyhydric alcohols, were determined by Karl Fischer method using 787 KF Titrino, 806 Exchange Unit and 703 Titration Stand interfaced to Metrodata VESUV Software, all from Metrohm Ltd., Switzerland.

Example 1

[0047] Preparation of 3.5% EG colloid of 5nBD. In a 300ml Kjeldahl flask was placed 100ml of 5.27% aqueous colloid of 5nBD and 50ml of EG slowly added through a dropping funnel in 30 min under magnetic stirring and nitrogen flow. No precipitation took place. The flask was attached to a Yamato rotary evaporator type RE440 and water was distilled at 60°C under 40 hPa in the course of three hours. During this period a total of 100 ml of EG was added in two portions through a valve-controlled inlet without breaking vacuum. A total of 107ml of distillate was collected. Karl Fischer titration of a portion of the residual black colloid revealed water content of 0.49±0.02%. DLS analysis revealed an average particle distribution of 4.8±0.5 nm (100.00 vol %). The starting aqueous colloid showed a distribution of 4.8±0.5 nm (100.00 vol %), hence the EG colloid maintained perfect dispersion during the solvent exchange. The EG colloid thus prepared was deep and clear black in color, and never precipitated anything visible at least for three months. It should be noted that when dried 5nBD particles (aggregates) were re-dissolved in EG, it took three days of intense sonication and frequent agitating operations by magnetic stirrer and by hands, but the product was somewhat turbid and the maximum concentration that could be achieved was about 2%.

Example 2

[0048] Preparation of 5% DMSO colloid of 5nBD. In a 2L Kjeldahl flask was first placed 800ml of 5.80% aqueous colloid of 5nBD and the flask attached to the rotary evaporator and 480 ml water was distilled out at 60°C under 50 hPa in one hour. Thereupon 300ml of the same mother aqueous colloid and 200ml of fresh DMSO were introduced into the evaporation flask through a valve-controlled inlet without breaking vacuum, and evaporation of water continued. During the following one hour a total of 1L of DMSO was similarly introduced into the evaporation flask under constant evaporation of water. After the DMSO addition is complete, water removal was continued for three more hours while gradually increasing the bath temperature and decreasing the pressure, eventually up to 70°C under 35 hPa. At the end of this period, a total of 1060ml of water was collected. Thus, recovery of water reached 96%. According to DLS analysis the aliquots of DMSO colloid left in the evaporation flask, the particle size of 5nBD turned out to be 5.8±0.7 nm (100.00 vol%), which was significantly larger than the starting aqueous colloid (see Example 1). Hence the crude DMSO colloid was irradiated with powerful supersonic waves using Ultrasonic Processor UP-400S (400W, 24kHz) equipped with Sonotrode H22 (tip diameter 22mm, acoustic power density 85 W/cm ² , both manufactured by Dr. Hielscher GmbH, Teltow, Germany) while circulating the colloidal solution by means of a peristaltic pump at a speed of ca 300 ml/min for one hour. Thereupon the particle size decreased to an acceptable range of 4.4±0.3 nm (100.00 vol %). Concentration of 5nBD was determined to be 6.71 w/v% by simple drying method. The resulting colloid looked similar as that of Example 1, and never produced any precipitates at least for three months of storage at room temperature under stray light.

Example 3

[0049] Determination of friction coefficients μ in water. Concentrations of aqueous 5nBD colloid were adjusted to 5.0 to 0.1%, and the colloid was injected along the reciprocating path between the sapphire slider and silicon plate in the friction measurement setup and dynamic μ was recorded under vibration. Compared to pure water medium which showed a μ value of about 0.086, water containing 1% of 5nBD showed surprisingly smaller μ values of about 0.005 to 0.01. This superlubricity was maintained at least for 500 min, indicating that sufficient number of spacers is available. Then we thought increasing the concentration would lead to better lubrication. However, 5% colloid did not outperform 1%, meaning that 1% already contains more than enough number of particles, which is reasonable in view of the Number Effect. Upon dilution, μ value stayed in super-lubrication level for some concentration range but began increasing from 0.3% and below. This increase was interpreted as due to too low viscosity of water (see above).

Example 4

[0050] Determination of frication coefficients in EG. Our choice for other solvents was limited because there were only a few solvents for 5nBD. Among them EG and its analogues (polyoxyethylene) seemed most promising. As expected, EG colloid of 5nBD showed superlubricity at 0.1% level.

Example 5

[0051] Determination of frication coefficients in DMSO. DMSO is by far the best solvent for 5nBD, somewhat better than water in terms of the saturation concentration, which has never been determined accurately but probably exceeds 10%. Presumably because of this high salvation power, DMSO maintained very low μ value even with 0.1 % concentration in 5nBD. However, DMSO suffers from low viscosity.

[0052]Citation List

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LIST OF SYMBOLS AND ABBREVIATIONS

[0053]

5nBD 5-nm bucky diamond

D diameter

DLS dynamic light scattering

DMSO dimethyl sulfoxide

DSC differential scanning calorimetry

DSER direct solvent exchange reaction

EG ethylene glycol

PP Polypropylene

SCC DFTB Self-consistent charge density functional tight binding

a surface roughness in terms of vertical difference between the highest and lowest points