MXPA04005761A

MXPA04005761A - Preparation of stable carbon nanotube dispersions in liquids.

Info

Publication number: MXPA04005761A
Application number: MXPA04005761A
Authority: MX
Inventors: Zhang Zhiqiang
Original assignee: Ashland Inc
Priority date: 2001-12-12
Filing date: 2002-12-06
Publication date: 2004-11-01
Also published as: WO2003050332A1; AU2002357065B2; BR0215135B1; CA2470113C; CN1617958A; NZ533941A; CA2470113A1; AU2002357065A1; BR0215135A; EP1495171A4; CN1304657C; EP1495171A1

Abstract

The introduction of nanotubes in a liquid provides a means for changing the physical and/or chemical properties of the liquid. Improvements in heat transfer, electrical properties, viscosity, and lubricity can be realized upon dispersion of nanotubes in liquids; however, nanotubes behave like hydrophobic particles and tend to clump together in liquids. Methods of preparing stable dispersions of nanotubes are described and surfactants/dispersants are identified which can disperse carbon nanotubes in aqueous and petroleum liquid medium. The appropriate dispersant is chosen for the carbon nanotube and the water or oil based medium and the dispersant is dissolved into the liquid medium to form a solution. The carbon nanotube is added to the dispersant containing the solution with agitation, ultrasonication, and/or combinations thereof.

Description

PREPARATION OF STAPLE CARBON NANOTUBE DISPERSIONS IN LIQUIDS BACKGROUND OF THE INVENTION This application claims the priority of the request of States United Non-Provisional Serial No. 10/021, 767 entitled "Preparation of dispersions of stable carbon nanotube in liquids".

Technical Field The methods are described and the surfactants. are identified as those that can disperse carbon nanotubes in liquid petroleum and aqueous media using selected dispersants and mixing methods to form stable carbon nanotube dispersions.

Description of the Prior Art Carbon nanotubes are a new form of the material formed by elemental carbon, which has different properties to the other forms of carbon materials. These have a unique atomic structure, very high aspect ratio, and extraordinary mechanical properties (strength and flexibility), making them ideal reinforcement fibers in composites and other structural materials. Carbon nanotubes are generally characterized as three-dimensional structures of rigid porous carbon comprising carbon nanofibers and having a surface area and porosity, low volume density, low amount of micropores and increased frictional resistance. The present process is applied to nanotubes with or without amorphous carbon. The term "nanotube" refers to elongated structures having a cross section (e.g., angular fibers having edges) or diameter (e.g., rounded) less than 1 micron. The structure can be either hollow or solid. According to the above, the term includes "nanofibrils" and "anti-diffuser tubes". Such structures provide significant surface area when incorporated into a structure due to their size and shape. In addition, such fibers can be processed with high purity and uniformity. Preferably, the nanotube used in the present invention has a diameter of less than 1 micron, preferably less than 0: 5 microns, and more preferably less than 0.1 micron and even more preferably less than 0.05 microns. The term "internal structure" refers to the internal structure of an assembly that includes the relative orientation of the fibers, the diversity of and the total percentage of the orientations of the fiber, the proximity of the fibers to each other, the empty space or pores created by the insterties and spaces between the fibers and size, shape, humerus and orientation of the flow channels or trajectories formed by the connection of the empty spaces and / or pores. The structure can also include features related to the size, space and orientation of aggregate particles that make up the assembly. The term "relative orientation" refers to the orientation of an individual fiber or aggregate with respect to the others (ie, aligned versus non-aligned). The "diversity of" and "total percentage" of fiber or aggregate orientations refers to the range of fiber orientations within the structure (alignment and orientation with respect to the external surface of the structure). Carbon nanotubes can be used to form rigid associations or can be made having diameters in the range of 3.5 to 70 nanometers. The nanotubes, fibrils, anti-diffuser tubes and fringes referred to in this application are distinguished from commercially available continuous carbon fibers as reinforcing materials. In contrast to nanotubes, which have desirable long, but inevitably finite aspect ratios, continuous carbon fibers have aspect ratios (L / D) of at least 104 and occasionally 106 or more. The diameter of the continuous fibers is also much longer than that of the nanotubes, always being > 1 .0 micron and typically 5 to 7 microns. Continuous carbon fibers are made by the pyrolysis of organic precursor fibers, usually rayon, polyacrylonitrile (PAN) and resin. Thus, these may include heteroatoms within their structure. The granite nature of continuous carbon fibers "as done" varies, but these may be subject to a subsequent step of graphitization. Differences in the degree of graphitization, orientation and crystallinity of graphite planes, if present, the potential presence of heteroatoms and even the absolute difference in substrate diameter make experience with poor continuous fiber predictors of nanofiber chemistry.

Carbon nanotubes are typically hollow graphite tubules having a diameter generally of several tens of nanometers. Carbon nanotubes exist in many forms. Nanofibers can be in the form of discrete fibers or aggregated particles of nanofibers. The above results are in a structure that has fairly uniform characteristics. The latest results are in a structure with a two-row architecture comprising a macro total structure encompassing aggregate nanofiber particles bonded together to form the porous mass and a micro structure of interlaced nanofibers within the individual aggregated particles. For example, a form of carbon fibrils is characterized by a substantially constant diameter, length greater than about 5 times the diameter, an ordered external region of catalytically developed, multiple, substantially continuous layers of carbon atoms with an outer diameter between approximately 3.5 and 70 nanometers and a different internal central region. Each of the layers and the center are arranged substantially concentric on the cylindrical axis of the fibril. The fibrils are substantially free of the pyrolytically deposited thermal carbon with the diameter of the fibrils being equal to the outer diameter of the external ordered region. In addition, a convenient carbon nanotube for use with the current process defines a cylindrical carbon fibril characterized by a substantially constant diameter between 3.5 and about 70 nanometers, a length greater than about 5 times the diameter and less than about 5000 times the diameter , an outer region of multiple layers of carbon atoms and a different inner central region, each of the layers and the center are arranged substantially concentric on the cylindrical axis of the fibril. Preferably the whole carbon nanotube is substantially free of a thermal carbon cover. The term "cylindrical" is used in the present in the broad geometrical sense, that is, the surface traced by a straight line moving in parallel to a fixed straight line and intersecting a curve. A circle or an ellipse are two of the many possible curves of a cylinder. The inner central region of the nanotube can be hollow, or it can comprise carbon atoms which are less ordered than the atoms of the outer region. "Ordered carbon atoms", as the phrase is used herein, means granitic domains having their axes c substantially perpendicular to the cylindrical axis of the nanotube. In one embodiment, the length of the nanotube is greater than about 20 times the diameter of the nanotube. In another modality, the diameter of the. nanotube is approximately 7 and about 25 nanometers. In another embodiment, the inner central region has a diameter greater than about 2 nanometers. Dispersing nanotubes in organic and aqueous media has been a serious challenge. Nanotubes tend to aggregate, form agglomerates, and separate from the dispersion. Some industrial applications require a method of preparing a stable dispersion of a selected carbon nanotube in a liquid medium. For example, the U.S. Patent. 5,523,006 from Strumban teaches the user a medium of oil and a surfactant agent; however, the particles are particles of the Cu-Ni-Sn-Zn alloy with the size of 0.01 micron and the suspension is stable for a limited period of time of approximately 30 days. In addition, the tense-active agents do not include dispersants typically used in the industry. of lubricants. The U.S. Patent 5,560,898 to Uchida et al. teaches that a liquid medium is an aqueous medium that contains a surfactant agent; however, the stability of the suspension is of little consequence in that the liquid is centrifuged on the suspension. The U.S. Patent 5,853,877 from Shibuta teaches the dispersion by untangling nanotubes in a polar solvent and forming a coating composition with additives as dispersing agents; however, a method to obtain stable dispersion is not taught. U.S. Patent 6,099,965 to Tennent et al. it uses a kneading instruction by mixing a dispersant with other surfactants in a liquid medium using a high-torque dispersion tool, but sustaining the stability of the dispersion does not appear to be taught or suggested. None of the conventional methods taught provide a process for dispersing and maintaining suspension nanotubes as described and claimed in the present invention below.

BRIEF DISPLACEMENT OF THE INVENTION In this invention, physical and chemical treatments are combined to derive a method for obtaining a stable nanotube dispersion. The present invention provides a method of preparing stable dispersion of a selected carbon nanotube in a liquid medium, such as water or any water-based solution, or oil, with the combined use of surfactants and agitation (eg, ultrasonication) or other means of agitation. The carbon nanotube can be either single-walled or multi-walled, with a typical aspect ratio of 500-5000; however, it is contemplated that nanotubes of other configurations may also be used with the present invention. It is contemplated that a mixture containing carbon nanotubes having a length of 1 micron or more and a diameter of 50 nm or less. The raw material may contain carbon nanotubes having a size outside the ranges mentioned. The surface of the carbon nanotube is not required to be treated by providing a hydrophilic surface for dispersion within an aqueous medium, but optionally it can be treated. The selected surfactant is soluble or dispersible in the liquid medium. The term "surfactant" in the present invention refers to any chemical compound that reduces the surface tension of a liquid when it dissolves therein, reduces the interfacial tension between two liquids, or between a liquid and a solid. This is generally, but not exclusively, a long chain molecule comprised of two halves: a hydrophilic moiety and a lipophilic moiety. The "hydrophilic" and "lipophilic" halves refer to the segment in the molecule with affinity for water, and with affinity for the oil, respectively. It is a broad term that covers all materials that have surface activity, including wetting agents, dispersants, emulsifiers, detergents and foaming agents, etc. The term "dispersant" in the present invention refers to a surfactant agent added to a medium to cause uniform suspension of extremely fine solid particles, occasionally of colloidal size. In the lubricant industry the term "dispersant" is generally accepted to describe the long chain of soluble oil or possible dispersion compounds which function to disperse the "cold sediment" formed in engines. These two terms are especially interchangeable in the present invention; however, in some cases the term "dispersant" is used with the tendency to emphasize, but not restrict, those commonly used in the lubricant industry. The method of making stable dispersions containing particles includes physical agitation in combination with chemical treatments. The physical mixture includes a mixture subjected to a high constant stress, such as with a high speed mixer, homogenizers, microfluidizers, a Kady mill, a colloid mill, etc., high impact mix, such as a friction, mill of balls and bowls, etc., and methods of ultrasonication. The mixing methods are further assisted by electrostatic stabilization by electrolytes, and spherical stabilization by polymeric surfactants (dispersants). The chemical treatment and the use of the demanded surfactant / dipser agents are critical to the long-term stability of the nanotube liquid mixtures. The treatment involves dissolving a selected dispersant within the liquid medium. The chemical treatment includes a two-step procedure: dissolving the dispersant within a liquid medium, and then adding the selected carbon nanotube into the mixture of the liquid dispersant medium with mechanical agitation and / or ultrasonication. These steps may be reversible but may not produce a satisfactory result. The liquid medium can be water or any solution of water, petroleum distillate, petroleum oil, synthetic oil, or vegetable oil. The dispersant for the oily liquid medium is a surfactant with low balance of hydrophilic-lipophilic (HLB) value (HLB <8) or a polymeric dispersant of the type used in the lubricant industry. It is preferably. non-ionic, or a mixture of non-ionic and ionic. A preferred dispersant for aqueous liquid media is high HBL value (HLB> 10), preferably a type of surfactant nonylphenoxypoxy (ethyleneoxy) ethanol. Of course, other alcohols based on glycols having a high HLB value can also be used. The uniform dispersion of the nanotubes is obtained with a designated viscosity in the liquid medium. The dispersion of nanotubes can be obtained in the form of a paste, gel or Vaseline, either a liquid petroleum medium or an aqueous medium. The dispersion may also contain large amounts of one or more chemical compounds, preferably polymers, not for the purpose of dispersing, but to assume the thickening and other desired liquid characteristics. An objective in the present invention is to provide a method of preparing a stable dispersion of the carbon nanotube in a liquid medium with the combined use of dispersants and physical agitation. Another objective in the present invention is to use a carbon nanotube with either a single wall or multiple walls, with a typical aspect ratio of 500-5000. Another objective of the present invention is to use carbon nanotubes which can optionally be treated to be hydrophilic on the surface to facilitate dispersion within an aqueous medium. Another object of the present invention is to use a dispersant which is soluble for a selected liquid medium. Another object of the present invention is to use a method of preparation by dissolving the dispersant within the liquid medium first, and then adding the carbon nanotube into the mixture while stirring or strongly ultrasonically. Another objective of the present invention is to add the carbon nanotube inside the liquid while stirring or ultrasonically, and then adding the surfactant. Another object of the present invention is to use a petroleum distillate or petroleum synthetic oil as the liquid medium. Another object of the present invention is to use a liquid medium of the type used in the lubricant industry, or a surfactant, or a mixture of surfactants with a low HLB (<8), preferably non-ionic or a mixture of agents non-ionic surfactants with ionics. More typically, the dispersant may be the ashless polymer dispersant used in the lubricant industry. Another object of the present invention is to use a typical dispersant-detergent additive (DI) package sold in the lubricant industry as the surfactant / dispersing agent. Another objective of the present invention is to use a liquid medium consisting of water or any other water-based solution. Another object of the present invention is to use a dispersant having a high HLB (> 1 0), preferably a type of surfactant nonylphenoxypoly (ethyl.enooxy) ethanol. Another object of the present invention is to use a uniform dispersion with a designated viscosity having a nanotube in the petroleum liquor medium. Another object of the present invention is to obtain a uniform dispersion in the form of gel or paste containing nanotubes in a liquid petroleum medium or an aqueous medium. Another objective of the present invention is to obtain a uniform dispersion of nanotubes in the form of petrolatum obtained from the dispersion of carbon nanotube in a liquid petroleum medium or an aqueous medium.

Another object of the present invention is to form a uniform and stable dispersion of carbon nanotubes containing non-dispersible dissolved, "other" compounds in the medium based on liquid oil. Still another objective in the present invention is to form a uniform and stable dispersion in a form containing carbon nanotubes with non-dispersible disbuds, "other" compounds in the liquid water medium. The foregoing and other objects and advantages of the invention will be set forth herein or evidently in the following description.

DESCRIPTION OF PREFERRED MODALITY The present invention provides a method of dispersing carbon nanotubes within a liquid medium. As stated above, nanotubes can have a single wall, or have multiple walls with a typical nano-scale diameter of 1 -500 nanometers. More typically the diameter will be around 10-30 nanometers. The length of the tube can be in submicron or micron scale, usually from 500 nanometers to 500 microns. More typically the length will be from 1 micron to 100 microns. The aspect ratio of the tube can be formed by hundreds to thousands, more typically 500 to 5000. The carbon nanotubes, fibers, particles or combination thereof can be used as they are in production. The nano carbon particles comprising carbon nanotubes, carbon fibers, carbon particles or combinations thereof can be used as a substrate in the present invention "as is" as a direct commercial product of a commercial production process. A preferred embodiment in the present invention was obtained using a nanoparticle product having the surface chemically treated to assume a certain level of hydrophilicity by means of an activated carbon treatment. In addition, a certain level of hydrophilicity can be assumed using a steam disposal process using chemicals such as hydrogen sulfide; and / or by means of treatment with a strong acid or base. A preferred embodiment used a carbon nanotube product obtained from Carbolex at the University of Kentucky which contains amorphous carbon particles and which is believed to utilize an activated carbon treatment to increase the level of hydrophilicity. Carbolex carbon nanotubes comprise single-walled nanotubes, multi-walled nanotubes, and combinations thereof. In addition, the combination may include small fractions of the carbonaceous materials made from disordered spherical particles and / or small carbon nanotubes.

Liquid Base of Petroleum Bases The liquid petroleum medium can be any distillate of petroleum or synthetic petroleum oils, vaselines, gels, or oil-soluble polymer composition. More typically, they are used in the mineral base or synthetic base lubricants industry, for example Group I (refined solvent mineral oils), Group II (hydrocracked mineral oils), Group III (severely hydrocracked oils, sometimes described as oils synthetic or semi-synthetic), Group IV (polyalphaolefins), and Group V (esters, nafanos and others). A preferred group includes polyalphaolefins, synthetic esters and polyalkyl glycols. Synthetic lubricating oils include hydrocarbon oils and halo-substituted hydrocarbon oils such as polymerized and interpolymerized defines (eg, polybutylenes, polypropylenes, propylene-isobutylene copolymers, chlorinated polybutylenes, poly (1-octanes), poly (1 -decanes), etc. ., and their mixtures, alkylbenzenes (for example, dodecylbenzenes, tetradecylbenzenes, dinoniLbenzenes, di- (2-ethylhexyl) benzenes, etc.), polyphenyls (for example biphenyls, triphenyls, alkylated polyphenyls, etc.), alkylated diphenyl, ethers and alkylated diphenylsulfides and the derivatives, their analogs and homologs thereof and the like Alkaline oxide polymers and interpolymers and their derivatives where the terminal hydroxyl groups have been modified by esterification, etherification, etc., constitute another class of oils known synthetics Another convenient class of synthetic oils comprises esters of dicarboxylic acids (e.g.; italic acid, succinic acid, succinic acid alkyl and succinic alkenyl acid, maleic acid, azelaic acid, suberic acid, sebasic acid, fumaric acid, adipic acid, malonic alkenyl acids, etc.) with a variety of alcohols (eg, butyl alcohol , hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol diethylene glycol monoether, etc.). Specific examples of these asters include dibutyl adipate, di (2-ethylhexyl) sebacate, dihexyl fumarate, dioctyl sebacate, diisoctyl acelate, diisoctyl acelate, dioctyl phthalate, didecyl phthalate, diciosyl sebacate, linoleic acid dimer 2-ethylene oxide diester, the ester complex formed by reacting one mole of sebasic acid with a mole of tetraethylene glycol and two moles of 2-ethylhexanoic acid, and the like. The asters useful as synthetic oils also include those made from C5 to C12 monocarboxylic acids and polyols and polyol ethers such as neopentyl glycol, trimethylpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, etc. Other synthetic oils include liquid esters of acids. containing phosphorus (for example, tricresyl phosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid, etc.), polymeric tetrahydrofurans and the like. Preferred polyalphaolefins (PAO) include those sold by the Mobil Chemical Company as SHF fluids, and those sold by Ethyl Corporation under the name ETHYLFLO, or ALBERMARLE. PAOs include the ethyl flow series by Ethyl Corporation, "Albermarle Corporation", including ethyl flow 162, 164, 166, 168 and 174, having variant viscosity from about 2 to about 460 centistokes. Mobil SH F-42 from Mobil Chemical Company, Emery 3004 and 3006, and Quantum Chemical Company provide polyalphaolefins for additional solutions. For example, the polyalphaolefin Emery 3004 has a viscosity of 3.86 centistokes at 212 ° F (1 00 ° C) and 16.75 centistokes at 104 ° F (40 ° C). It has a viscosity index of 125 and a pour point of -36.6 ° C and also has a flash point of 222.2 ° C and a fire point of 247.7 ° C. In addition, the polyalphaolefin Emery 3006 has a viscosity of 5.88 centistokes at + 37.7 ° C and 31.22 centistokes at + 40 ° C. It has a viscosity index of 135 and a pour point of -30.5 ° C. It also has a flash point of + 240 ° C and a fire point of + 267.7 ° C. Additional satisfactory polyalphaolefins are those sold by Uniroyal Inc. under the brand Synton PAO-40, which are polyalphaolefins of 40 centistokes. Also useful are polyalphaolefins of the Oronite brand manufactured by Chevron Chemical Company. It is contemplated that the GuífSynfluid 4sCt PAO, commercially available from Gula Oil Chemicals Company, a subsidiary of Chevron corporation, which is similar in many respects to the Emery 3004, may also be used herein. Mobil SHF-41 PAO, commercially available from Mobil Chemical Company, is also similar in many respects to Emery 3004. Preferably the polyalphaolefins will have a viscosity in the range of about 2-40 centistokes at 100 ° C, with a particularly preferred viscosity of 4 to 10 centistokes. The most preferred synthetic oil-based ester additives are the polyols and diesters such as the di-aliphatic diesters of alkyl carboxylic acids such as di-2-ethylexylactal, di-isodecyldipate, and de-tridecyldipate, commercially available under the trade name Emery 2960 from Emery Chemicals, described in United States Patent 4,859,352 to Waynick. Other suitable ppliolésteros are manufactured by Mobil OH. Molecular polyesters Mobil P-43, M-045 containing two alcohols, and Hateo Corp. 2939 are particularly preferred. Diesters and other synthetic oils have been used as re-lubricants of mineral oil in liquid lubricants. Diesters have outstanding properties of extreme low temperature and good residence to oxidative breakdown. The diester oil may include an aliphatic diester of dicarboxylic acidor the diester oil may comprise a dialkyl diester of an alkyl dicarboxylic acid, such as di-2-ethylexyl acetal, di-isodecyl acelate, si-tricedyl acetal, di-isodecyl adipate, di-tricedyl adipate. For example, Di-2-ethylhexyl acelate is commercially available under the trade name Emery 2958 from Emery Chemicals. Also useful are the polyol esters such as Emery 2935, 2936 and 2939 from Emery Group of Hankel Corporation and the polyether esters Hateo 2352, 2962, 2925, 2938, 2939, 2970, 3178 and 4322 of Hateo Corporation, described in the U.S. Pat. 5,344,579 to Ohtani et al. and Mobil P 24 ester from Mobil Chemical Company. Mobil esters made by reacting dicarboxylic acids, glycols, and either monobasic acids or monohydric alcohols such as Emery 2936 from synthetic-lubricant solutions from Quantum Chemical Corporation and Mobil P 24 from Mobil Chemical Company can be used. The polyol esters have good oxidation and hydrolytic stability. The polyol ester for use herein has a pour point of about -100 ° C or less at -40 ° C and a viscosity of about 2-460 centistokes at 100 ° C. Group I II oils are occasionally referred to as hydrogenated oil to be used as the single base oil component of the present invention providing superior performance to conventional engine oils without another synthetic oil base or mineral oil base. A hydrogenated oil is a mineral oil subject to hydrogenation or hydrocracking under special conditions to remove undesirable chemical compositions and impurities resulting in an oil based on mineral oil having components of synthetic oils and properties. Typically hydrogenated oil is defined as petroleum-based solutions in Group II I oil with a sulfur level of less than 0.03, severely hydrotreated and iso-enriched with saturated greater than or equal to 90 and a viscosity index greater than or equal to 120 may optionally be used in amounts up to 90 percent by volume, more preferably 5.0 to 50 percent by volume and more preferably 20 to 40 percent by volume when used in combination with a synthetic or mineral oil. The hydrogenated oil can be used as the single base oil component of the present invention providing superior performance to conventional engine oils without another synthetic oil base or mineral oil base. When used in combination with other conventional synthetic oils such as those containing polyalphaolefins or esters, or when used in combination with mineral oil, the hydrogenated oil may be present in an amount of up to 95 percent by volume, more preferably about 10 percent by volume. at 80 percent by volume, more preferably from 20 to 60 percent by volume and better still from 10 to 30 percent by volume of the oil-base compound. The mineral oil solution of Group I or I I can be incorporated in the present invention as a portion of the concentrate or a solution to which the concentrate can be added. The preferred mineral oil solutions are the ASHLAND 325 Neutral defined as the neutral refined solvent with a viscosity SABOLT UNIVERSAL of 325 SUS @ 37.7 ° C and ASHLAND 100 Neutral defined as a neutral refined solvent with a viscosity SABOLT UNIVERSAL of 325 SUS @ 37.7 ° C, manufactured by Marathon Ashland Petroleum. Other liquid petroleum base acceptable compositions include white mineral, paraffinic and naphthenic MVI oils having a viscosity range of about 20-400 centistokes. Preferred white mineral oils include those available from Witco Corporation, Arco Chemical Company, PSI and Penreco. Preferred paraffinic oils include neutral solvent oils available from Exxon Chemical Company, HVI neutral oils available from Shell Chemical Company, and solvent-treated neutral oils available from Arco Chemical Company. Preferred MIF naphthenic oils include solvent oils extracted from Exxon Chemical Company, MVI oils treated for acid extraction available from Shell Chemical Company, and naphthenic oils come under the names HydroCal by Calumet, and described in U.S. Patent 5,348,668 of Oldiges . Finally, vegetable oils can also be used as a liquid medium in the present invention.

Aqueous Medium The selected aqueous medium is water, or it can be any water-based solution including alcohol and its derivatives, such as glycols and any inorganic salt soluble in water or organic compound.

Tensoactives / Dispersing Dispersants used in the Lubricant Industry Dispersants used in the lubricant industry are typically used to disperse "cold sediments" formed in gasoline and diesel engines, which can be either "ashless dispersants" , or containing metal atoms. These can be used in the present invention since they have been found to be an excellent dispersing agent for soot, amorphous forms of carbon particles generated in the engine crankcase and incorporated with dirt and petrolatum. The ashless dispersants commonly used in the automotive industry contain a group of Mpofilic hydrocarbons and a polar functional hydrophilic group. The polar functional group can be of the carboxylate, ester, amino, amide, imine, metric, hydroxyl, ether, epoxide, phosphorus, carboxyl, anhydride, or nitrile class. The lipophilic group can be oligomeric or polymeric to the natural, usually from 70 to 200 carbon atoms to ensure the solubility of the oil. Hydrocarbon polymers treated with various reagents to introduce polar functions include products prepared by treating polyolefins such as polyisobutane first with maleic anhydride, or sulfur or phosphorus chloride, or by thermal treatment, and then with reagents such as polyamine, amine, ethylene oxide , etc. Of these ashless dispersants which are typically used in the petroleum industry include the succinimides and succinates of polyisobutenyl N-substuides, alkyl methacrylate-vinyl pyrrolidinone copolymers, alkyl methacrylate-dialkylaminoethyl methacrylate copolymers, alkyl methacrylate-polyethylene glycol copolymers, and polyesteamides. Preferred oil-based dispersants that are most important in the present invention include the dispersants of the chemical classes alkyl succinimide, succinate esters, high molecular weight amines, derivatives of Mannich base and phosphoric acid. Some specific examples are poly-isobutenyl cuccinimido-polyethylenepolyamino, succinic ester polyisobutenyl, hydrobenzyl-polyethylenepolyaminopolyisobutenyl, phosphorate bis-hydroxypropyl. The dispersant can be combined with other additives used in the lubricant industry to form a "detergent-dispersant (DI)" additive package, for example, Lubrizol ™ 9802a, and the complete DI package can be used as a dispersing agent for the suspension of nanotube. For example, LUBRIZOL 9802A is described in the technical brochure (SECURITY MATERIAL INFORMATION SHEET No. 1922959- 1232446-3384064) of The Lubrizol Corporation in Wickliffe, OH and is incorporated herein by reference. LUBRIZOL 9802A is described as an engine additive oil, believed to contain a zinc dithiophosphate and / or zinc alkyldithiophosphate as an active ingredient. The LU BRIZOL 4999 is described in this Technical Brochure (SHEET) DE NORMATION OF SAFETY MATERIAL No. 1272553-1 192556-331 0026) of The Lubrizol Corporation in Wickliffe, OH and is incorporated herein by reference. LU BRIZOL 9802A is described as an engine additive oil and contains from 5 to 9.9 percent zinc alkyldithiophosphate as an active ingredient. OLOA 9061 is described in the Technical Booklet "SAFETY MATERIAL INFORMATION SHEET No. 006703" of Chevron Chemical Company and is incorporated herein by reference. OLOA 9061 is described as a compound of zinc alkyldithiophosphate. The IGEPAL CO-630 is described in the Technical Brochure "LEAF OF TRAINING MATERIAL DE SEGU RI DAD "by Roída Inc. and is incorporated herein by reference, IGEPAL CO-630 is described as a branched ethanol compound of oxinonylphenol poly (ethyleneoxy).

Other Types of Dispersants Alternatively a surfactant or a mixture of surfactants with low HLB value (typically less than or equal to 8), preferably non-ionic, or a mixture of non-ionic and ionic, can be used in the present invention. . The dispersant for the dispersion of water-based carbon nanotubes must be of high HLB value (typically less than or equal to 10), ethoxylated polyoxynonphenol (ethyleneoxy) surfactants are preferably used. In both cases of water or oil base, the selected dispersants must be soluble or dispersible in the liquid medium. The dispersant can be in a range of up to 0.001 to 30 percent, more preferably in a range of between 0.5 percent and 20 percent, more preferably in a range of between 1.0 and 8.0 percent, and even more preferably in a range between 2 and 6 percent. The carbon nanotube can be of any desired percentage of weight in a range. from 0.0001 to 50 percent. For a practical application it is usually in a range of between 0.01 percent to 2 percent, and more preferably in a range of 0.05 percent to 0.5 percent. The remainder of the formula is the selected oil or water medium. It is believed that in the present invention the dispersant functions by absorption of the carbon nanotube on the surface. The dispersant contains a hydrophilic segment and a hydrophobic segment which surrounds the carbon particles in such a way as to provide a means of isolation and dispersion for the carbon particles. The selection of a dispersant with a particular HLB value is important to determine the characteristics of the dispersant such as the quotient and the degree of stabilization over time.

Other Chemical Compound Additives This dispersion may also contain a large amount of one or more other chemical compounds, preferably polymers, not for the purpose of dispersion, but to assume the thickening and other desired liquid characteristics. The viscosity promoters used in the lubricant industry can be used in the present invention for the oil medium, which includes copolymers of olefin (OCP), polymethacrylates (PA), hydrogenated diene-styrene (STD), and polymers of Styrene polyester (STPE). Olefin copolymers are rubber-like materials prepared from mixtures of ethylene and propylene through vanadium-based Ziegler-Natta catalysis. The diene-styrene polymers are produced by anionic polymerization of styrene and butadiene or isoprene. The polymethyl acrylates are produced by a free radical polymerization of alkyl methacrylates. The polyester-styrene polymers are prepared first by the co-polymerization of styrene and maleic anhydride and then by esterification of the intermediate using a mixture of alcohols. Other compounds that may be used in the present invention in any of the aqueous or oil media include: acrylic polymers such as polyacrylic acid and sodium poly-acrylate, high molecular weight polymers of ethylene oxide such as Polyox® WSR of Union Carbide, of cellulose such as carboxymethylcellulose, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), xanthan gum and guar gum, polysaccharides, alkanolamides, polyamide amine salts such as the King Industries Disparlon AQ series, modified ethylene oxide urethane hydrophobically (eg Rohmax Acrysol series), silicates, and fillers such as mica, silicones, cellulose, wood flour, clays (including organoclays) and nanoclays, and resin polymers such as polyvinyl butyral resins, polyurethane resins, acrylic resins and epoxies resins. Chemical compounds such as plasticizers can also be used in the present invention and can be selected from the group including phthalate, adipates, sebacate esters, and particularly: glyceryl tri (acetoxy stearate), epoxidized soybean oil, epoxidized linasse oil, N, n-butyl benzene sulfonamide, aliphatic polyurethane, epoxidized soybean oil, polyester glutarate, caprate / Triethylene glycol caprylate, long chain alkyl ether, dialkyl dialkyl glutarate, monomer, polymer, and epoxy plasticizers, polyester based on atypical acid, hydrogenated dimer acid, distilled dimer acid, polymerized trimer fatty acid, ethyl ester of collagen hydrolyzate, isostearic acid and sorbic oleate and hydrolyzed cocoyl keratin, lanolin oil PPG-12 / PPG-65, dialkyl adipate, alkylaryl phosphate, diaryl alkyl phosphate, modified triaryl phosphate, triaryl phosphate, benzyl butyl phthalate, benzyl phthalate octyl, benzyl alkyl phthalate, ethyl dibutoxy ethoxy adipate, 2-ethylhexyldifenium phosphate, ethyl dibutoxy ethoxy formyl, adipate di-isopro pil, di-isopropyl sebacate, isodecyl oleate, neopentyl glycol dicaprate, neopenti glycol diotanoate, idohexyl neopentanoate, ethoxylated lanolins, polyoxyethylene cholesterol, propoxylated lanolin alcohols (2 moles), ethoxylated lanolin alcohols, acetylated polyoxyethylene derived from lanolin, and dimethylpolylsiloxane. Other plasticizers which can be substituted for and / or used with the aforementioned plasticizers including glycerin, polyethylene glycol, dibutyl phthalate, and 2,2,4-trimethyl-1,3-epntanedium monotisobutyrate, and di-isononyl phthalate all being soluble in a solvent carrier.

Physical Agitation The physical mixture includes a mixture subjected to a high constant effort, such as with a high speed mixer, homogenizers, microfluidizers, a Kady mill, a colloid mill, etc., high impact mix, such as a friction, mortar, etc., and ultrasonication methods. Ultrasonication is the preferred physical method in the present invention because it is less destructive to the structure of the carbon nanotube than the other described methods. Ultrasonication can be done either in the bath-type ultrasonicator, or by the extremity-type ultrasonicator. More typically, tip-type ultrasonication is applied for higher energy outputs. Sonication at medium-high instrumental intensity is desirable for up to 30 minutes, and usually a range of 10 to 20 minutes to better assure homogeneity. A useful dismemberment for the preparation of the present invention is a Model 550 Sonic Dismemberment manufactured by Fisher Scientific Company, located in Pittsburg Pennsylvania. Publication No. FS-IM-2 of the instruction manual published in November of 1996 that describes the use of the Fisher Scientific Model 550 Shatter Separator is incorporated herein by reference. The power supply of the generator converts the power line 50/60 HzAC to 20 kHz electric power which is fed to the converter where it is transformed into mechanical vibration. The heart of the converter is a crystal of lead zirconate lead titanate (Piezoelectric) which, when subjected to an alternating voltage, expands and contracts. The converter vibrates in the longitudinal direction and transmits this movement to the tip of the extremity immersed in the liquid solution. Cavitation results, in which microscopic bubbles of vapor form momentarily and implode, making powerful expansive waves to radiate through the sample from the face of the limb. The tips and probes amplify the longitudinal vibration of the converter; greater amplification (or increase) results in more intense cavitation action and more interruption. The greater the length of the extremity of the probe, the greater the volume that can be processed but at less intensity. The converter is tuned to vibrate at a fixed frequency of 20 kHz. All tips and probes are resonant bodies, and they are also tuned to vibrate at 20 kHz. Of course it is contemplated that other models and competent ultrasonic mixing devices may be used in accordance with the present invention. The raw material mixture can be sprayed by any known method of dry or wet spraying. A spraying method includes spraying the raw material mixture in the liquid mixture of the present invention to obtain the concentrate, and the pulverized product can then be further dispersed in a liquid medium with the aid of the dispersants described above.

However, pulverization or grinding reduces the percentage of the aspect ratio of the carbon nanotube. The present method of forming a stable suspension of nanotubes in a solution consists of two primary steps. First, select the appropriate dispersant for the carbon nanotube and the medium, and dissolve the dispersant within the liquid medium to form a solution, and secondly add the carbon nanotube inside the dispersant containing solution while the solution is strongly stirred, grind it with ball or ultrasound. The present invention is described and illustrated more fully in the following examples: EXAMPLES Example 1 Percentage of Components Description weight Untreated surface, Nanotube ratio of 2000 aspect, diameter 25 nm, 0.1 carbon length 50 μ? T? Dispersant Lubrizol ™ 9802A 4.8 Poly (α-olefin) Fluid, 6 cSt 95.1 Sonic Dismembrator 550 Fisher Scientific Sonication, 15 minutes Example 2 Percentage Components Description weight Untreated surface, Nanotube ratio of 2000 aspect, diameter 25 nm, 0.1 carbon length 50 p. Dispersant Lubrizol ™ 4999 4.8 Poii liquid (α-olefin), 6 cSt 95.1 Sonic dismemberment 550 Fisher Scientific Sonication, 15 minutes Example 3 Percentage of Components Description weight Untreated surface, Nanotube ratio of 2000 aspect, diameter 25 nm, 0.1 carbon length 50 pM Dispersant OLOA 9061 4.8 Poly (α-olefin) fluid, 6 cSt 95.1 Sonic dismembler 550 Fisher Scientific Sonication, 15 minutes Example 4 The dispersions in Examples 1-4 are very uniform, and will remain, in a stable dispersion without any sign of separation or aggregation for at least one year. It is contemplated that substitute dispersants may be used in the examples set forth in Examples 1-4 and produce similar results. For example, in Example 1 up to 4.8 weight percent of a zinc dithiophosphate can be substituted by LUBRIZOL 9802A because it is the primary active ingredient of the product. In Example 2, up to 4.8 weight percent of a zinc alkyldithiophosphate can be substituted for the product LUBRIZOL 4999 and expected to produce similar results because zinc alkyldithiophosphate is the active ingredient in the product of LUBRIZOL 4999. In the Example 3, up to 4.8 weight percent a zinc alkyl dithiophosphate compound can be replaced by OLOA 9061 since the alkyl dithiophosphate compound is the active ingredient in the OLOA 9061 product. Finally, in Example 4, up to 5.0 weight percent of an ethanol of oxynoyl phenyl poly (ethyloxy), branched compound may be substituted by the product IGEPAL CO-630 because the ethanol of oxynoyl phenyl poly (ethyloxy), branched compound is the primary active ingredient in the IGEPAL CO-630 product. In addition, the weight percent of the carbon nanotube can be up to 10 weight percent and more preferably up to 1 weight percent and more preferably from 0.01 to 1 weight percent in the formulations depending on the preferred viscosity and the chemical properties and. of the resulting products. According to the above, the weight percent of the liquid medium can be reduced and the weight percent of the dispersant can be increased to 20 weight percent, more preferably from 0.01 to 10 weight percent and more preferably still from 3 to 6 weight percent. The amount of nanotubes, dispersant, and liquid medium can be varied as long as the desirable value of HBL is maintained to produce compounds having a gel, petrolatum or wax-like consistency.

It is intended that the specific compositions, methods, or modalities discussed be solely illustrative of the invention disclosed by this specification. The variation in these compositions, methods, or modalities are readily apparent to a person skilled in the art based on the teachings of this specification and therefore it is intended to be included as part of the disclosed inventions herein. The reference made to the documents in the specification is considered to give rise to such patents or literature cited expressly incorporated herein by reference, including any reference to patents or other literature cited within such documents as if fully established in this specification. The above detailed description is given above all for clarity of understanding and unnecessary limitations should not be understood, because the modification will become obvious to experts in the field of reading this access and can be made from the spirit of the invention and the scope of the appended claims. According to the foregoing, this invention is not intended to be limited by the specific exemplification presented herein above. On the contrary, what is intended to be covered is within the spirit and scope of the appended claims.

CLAIMS 1. A method of preparing stable dispersion of the carbon nanotube in a liquid medium with the combined use of dispersants and physical agitation (eg, ultrasonication). 2. The method of claim 1, characterized in that said carbon nanotube is either single-walled or multi-walled, with an aspect ratio of 500-5000. The method of claim 1, characterized in that said carbon nanotube is not required, but may optionally require the treated surface to be hydrophilic in. the surface for ease of dispersion within the aqueous medium. 4. The method of claim 1, characterized in that said dispersant is soluble in said liquid medium. 5. The method of claim 1 includes the two-step process: first, dissolving said dispersant within said liquid medium, and then adding said carbon nanotube within the above mixture while stirring strongly or ultrasonically. The method of claim 5, characterized in that the carbon nanotube is added into the liquid while it is being stirred or ultrasonicated, and then the surfactant is added. The method of claim 1, characterized in that said liquid medium can be a petroleum distillate or a synthetic petroleum oil. 8. The dispersant for said liquid medium according to claim 6 is of the type used in the lubricant industry, or. is

Claims

a surfactant or a mixture of surfactants with low HLB (< 8), preferably non-ionic or a mixture of non-ionic and ionic surface active agents. More typically, said dispersant may be the ashless polymer dispersant used in industrial lubricants. 9. The dispersant of claim 7 is included in a dispersant-detergent additive (DI) package typically sold in the lubricant industry. The method of claim 1, characterized in that said liquid medium can be water or any water-based solution. 1. The dispersant for said liquid medium of claim 8 is high HLB (> 10), preferably surface active agents of the nonylphenoxypoly- (ethylenoxy) ethanol type. 12. The uniform dispersion with the designated viscosity obtained from the method of claim 1 of the nanotube in liquid petroleum medium. 13. The uniform dispersion in a form such as a gel or paste obtained from the method of claim 1 of the nanotube in liquid petroleum medium or aqueous medium. 14. The uniform dispersion in a form such as petrolatum obtained from the method of claim 1 of the nanotube in liquid petroleum medium or aqueous medium. 15. The uniform and stable dispersion in a form containing "other" non-dispersing compounds dissolved in the liquid medium of claim 6. 16. The uniform and stable dispersion in a form containing "other" non-dispersing compounds dissolved in the liquid medium of claim 8.