WO2008000163A1 - Aerogel carbon nanotube, and methods for preparing the same, membrane and composite material containing the same - Google Patents

Aerogel carbon nanotube, and methods for preparing the same, membrane and composite material containing the same Download PDF

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Publication number
WO2008000163A1
WO2008000163A1 PCT/CN2007/001957 CN2007001957W WO2008000163A1 WO 2008000163 A1 WO2008000163 A1 WO 2008000163A1 CN 2007001957 W CN2007001957 W CN 2007001957W WO 2008000163 A1 WO2008000163 A1 WO 2008000163A1
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Prior art keywords
carbon nanotubes
aerogel
membrane
bundles
arrays
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PCT/CN2007/001957
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French (fr)
Inventor
Fei Wei
Qiang Zhang
Weiping Zhou
Guanghui Xu
Zhou Yang
Weizhong Qian
Guohua Luo
Yao Wang
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Tsinghua University
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/021—Carbon
    • B01D71/0212—Carbon nanotubes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0039—Inorganic membrane manufacture
    • B01D67/0046—Inorganic membrane manufacture by slurry techniques, e.g. die or slip-casting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0039—Inorganic membrane manufacture
    • B01D67/0072—Inorganic membrane manufacture by deposition from the gaseous phase, e.g. sputtering, CVD, PVD
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/021—Carbon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
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    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/158—Carbon nanotubes
    • C01B32/168—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
    • C04B35/111—Fine ceramics
    • C04B35/117—Composites
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    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/64—Burning or sintering processes
    • C04B35/645—Pressure sintering
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    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/71—Ceramic products containing macroscopic reinforcing agents
    • C04B35/78—Ceramic products containing macroscopic reinforcing agents containing non-metallic materials
    • C04B35/80—Fibres, filaments, whiskers, platelets, or the like
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/04—Carbon
    • C08K3/041—Carbon nanotubes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/24—Mechanical properties, e.g. strength
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/26—Electrical properties
    • C—CHEMISTRY; METALLURGY
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2202/00—Structure or properties of carbon nanotubes
    • C01B2202/02—Single-walled nanotubes
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    • C01B2202/00—Structure or properties of carbon nanotubes
    • C01B2202/04—Nanotubes with a specific amount of walls
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    • C01B2202/00—Structure or properties of carbon nanotubes
    • C01B2202/06—Multi-walled nanotubes
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/50—Constituents or additives of the starting mixture chosen for their shape or used because of their shape or their physical appearance
    • C04B2235/52—Constituents or additives characterised by their shapes
    • C04B2235/5284—Hollow fibers, e.g. nanotubes
    • C04B2235/5288—Carbon nanotubes
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
    • C04B2235/74—Physical characteristics
    • C04B2235/77—Density
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
    • C04B2235/96—Properties of ceramic products, e.g. mechanical properties such as strength, toughness, wear resistance

Definitions

  • Carbon nanotubes have many unique properties stemming from the small size, cylindrical structure, and high aspect ratio of length to diameter.
  • Single- walled carbon nanotubes consist of a single graphite sheet wrapped around to form a cylindrical rube.
  • Multi-walled carbon nanotubes comprise an array of such nanotubes that are concentrically nested like the rings of a tree trunk.
  • CNTs have extremely high tensile strength ( ⁇ 150 GPa) 5 high modulus ( ⁇ 1 TPa), large aspect ratio, low density, good chemical and environmental stability, and high thermal and electrical conductivity.
  • Carbon nanotubes have found various applications, including the preparation of conductive, electromagnetic and microwave absorbing and high-strength composites, fibers, sensors, field emission displays, inks, energy storage and energy conversion devices, radiation sources and nanometer-sized semiconductor devices, probes, and interconnect.
  • the present invention is directed to methods for the facile preparation of solvent free and well-dispersed aerogel carbon nanotubes that are useful in the preparation of nanotube membranes and nanocomposite materials.
  • the present invention allows the synthesis of aerogel carbon nanotubes having predetermined and/or controlled density, aspect ratio and diameters with ease.
  • the present invention provides a method for preparing aerogel carbon nanotubes.
  • the method includes contacting a plurality of carbon nanotube aggregates with a shearing means under conditions sufficient to form a plurality of carbon nanotube agglomerates having a density from about 0.1 to about 100 g/L.
  • the method further includes dispersing the plurality of carbon nanotube agglomerates in a gas, and descending the plurality of carbon nanotubes agglomerates to form aerogel carbon nanotubes having a predetermined density.
  • the aggregates are bundles, arrays or a combination of bundles and arrays.
  • the present invention provides aerogel carbon nanotubes.
  • the aerogel carbon nanotubes include a plurality of dispersed carbon nanotube aggregates, wherein said aggregates include bundles, arrays or a combination thereof and wherein said aggregates have a diameter from about 1 nm to about 100 ⁇ m, an aspect ratio from about 10 to about 10 6 , and a density from about 0.1 to about 100g/L.
  • the present invention provides a method for preparing a carbon nanotube membrane.
  • the method includes depositing aerogel carbon nanotubes on a planar solid support under condition sufficient to form a carbon nanotubes membrane.
  • the present invention provides a method for preparing a polymer composite material.
  • the method includes admixing a polymer with aerogel carbon nanotubes under conditions sufficient to form a polymer composite material.
  • the method further includes thermal-pressing the composite to form a membrane.
  • the present invention provides a method for preparing an inorganic composite material.
  • the method includes admixing an inorganic compound with the aerogel carbon nanotubes to form a mixture, heating the mixture, and hot-pressing the mixture under conditions sufficient to form an inorganic composite material.
  • Fig. 1 illustrates a schematic diagram for the preparation of aerogel carbon nanotubes according to an embodiment of the present invention.
  • Figs.2a-d show a scanning electron microphotography (SEM) image of the carbon nanotubes arrays before crushing and/or shearing;
  • Fig. 2b shows an SEM image of the dispersed carbon nanotubes arrays after mechanical crushing and/or shearing;
  • Fig. 2c shows an SEM image of the aerogel carbon nanotubes arrays collected after mechanical crushing and/or shearing, dispersing in gas phase, and descending for 30s;
  • Fig. 2d shows an SEM image of the aerogel carbon nanotubes arrays collected after mechanical crushing and/or shearing, dispersing in gas phase, and descending for 4 minutes.
  • Fig. 3 shows an SEM image of the aerogel carbon nanotubes arrays collected after high gas velocity shearing, dispersing in gas phase, and descending for 1 minute.
  • Fig. 4a-b shows an SEM image of the aerogel carbon nanotubes bundles collected after mechanical crushing and /or shearing, dispersing in gas phase, and descending for 30s;
  • Fig. 4b shows an SEM image of the areogel carbon nanotubes bundles collected after mechanical crushing, dispersing in gas phase, and descending for 3 minutes.
  • Fig. 5 shows an SEM image of the areogel carbon nanotubes arrays collected after mechanical crushing and/or shearing, dispersing in gas phase, and descending for 15 minutes.
  • Fig. 6 shows an SEM image of a carbon nanotube membrane or paper prepared from aerogel carbon nanotubes according to an embodiment of the present invention.
  • Fig. 7 shows an SEM image of a transparent conductive film prepared from aerogel carbon nanotubes according to an embodiment of the present invention.
  • the present invention relates to the methods for the synthesis of well-dispersed aerogel carbon nanotubes having predetermined or controlled physical characteristics and properties; methods for the synthesis of nanotube membranes having unique physical properties; and methods for the synthesis of nanocomposite materials having enhanced and/or improved physical properties.
  • the present invention provides aerogel carbon nanotubes.
  • the aerogel carbon nanotubes are composed of a plurality of well-dispersed carbon nanotubes aggregates.
  • the aggregates are in the form of bundles, arrays or a combination of arrays and bundles.
  • the carbon nanotubes bundles or arrays have a diameter from about 1 nm to about 100 ⁇ m, an aspect ratio from about 10 to about 10 6 , and a density from about 0.1 to about 100g/L.
  • the aerogel carbon nanotubes form a plurality of carbon nanotubes agglomerates.
  • the aerogel carbon nanotubes bundles, arrays or agglomerates can have a diameter ranging from about 0.4-0.6 nm, 0.5-1 nm, 5-6 nm, 1-10 nm, 1-20 nm, 1-30 nm, 1-40 nm, 10-50 nm, 40-100 nm, 1-200 nm, 1-500 nm, 100-700 nm, 100-900 nm, 800 nm -10 ⁇ m, l ⁇ m- 30 urn, 10 ⁇ m-50 ⁇ m, 10 ⁇ m-80 ⁇ m or 10 ⁇ m-100 ⁇ m.
  • the carbon nanotubes bundles, arrays or agglomerates have a diameter ranging from about 1 nm -500 nm, 1 nm -200 nm, 10 nm - 350 nm, 0.5 ⁇ m- 40 ⁇ m or 5 ⁇ m-50 ⁇ m. More preferably, the carbon nanotubes bundles, arrays or agglomerates have a diameter ranging from about 1 ⁇ m-25 ⁇ m, 15 ⁇ m-30 ⁇ m, 50 nm-250 nm, or 10 nm-100 nm.
  • the aerogel carbon nanotubes bundles, arrays or agglomerates have an aspect ratio ranging from about 10-100, 100-500, 10-1000, 100-1000, 100-10000, 1000-10000, 1000-50000, 1000-100000, 10000-100000, 10000-500000, 100000-10 6 .
  • the aerogel carbon nanotubes bundles can have various lengths ranging from about 0.3 ⁇ m to about 5000 ⁇ m, preferably, from about 0.8 ⁇ m- 1600 ⁇ m, more preferably, from about 1 ⁇ m-1500 ⁇ m, even more preferably, from about 100 ⁇ m-1400 ⁇ m, 10 ⁇ m-100 ⁇ m, 1 ⁇ m-10 ⁇ m, 10 ⁇ m-500 ⁇ m or 200 ⁇ m-3000 ⁇ m.
  • the aerogel carbon nanotubes can have various densities.
  • the aerogel carbon nanotubes have a density from about 0.01 to 150 g/L.
  • the aerogel carbon nanotubes have a density from about 0.01-0.05, 0.05-0.1, 0.1-0.5, 0.5-1, 1-1.5, 1.5-2.5, 2.5-10, 10-30, 30-50 or 50-100 g/L.
  • the aerogel carbon nanotubes have a density selected from the group consisting of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.24.5, 5.0, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 50, 60, 70, 80, 90 and 100 g/L.
  • the aerogel carbon nanotubes have a density selected from the group consisting of 0.1, 0.2, 0.5, 1.3, 1.4, 2, 2.2 and 42 g/L.
  • aerogel carbon nanotubes can be multi-walled carbon nanotube bundles, few-walled carbon nanotube bundles, single-walled carbon nanotube bundles, a multi-walled carbon nanotube arrays, few-walled carbon nanotube arrays, single-walled carbon nanotube arrays, or combinations thereof.
  • single-walled carbon nanotubes have a diameter ranging from less than 1 nm to a few nanometers.
  • Double-walled carbon nanotubes have a diameter of several nanometers.
  • Few- walled carbon nanotubes have a diameter ranging from a few nanometers to several tenths of nanometers.
  • Multi- walled carbon nanotubes have a diameter ranging from a few nanometers to 100 nm, such as from about 1 nm-100 nm.
  • the present invention provides a method for the preparation of aerogel carbon nanotubes.
  • the method includes contacting a plurality of carbon nanotube aggregates with a shearing means under conditions sufficient to form a plurality of carbon nanotube agglomerates having a density from about 0.1 to about 100 g/L.
  • the aggregates can be bundles, arrays or a combination of bundles and arrays.
  • the method further includes dispersing the plurality of carbon nanotube agglomerates in a gas; and descending said plurality of carbon nanotube agglomerates to form aerogel carbon nanotubes having a controlled or predetermined density.
  • Conventional device and methods can be used for crushing carbon nanotubes bundles and/or arrays or a mixture of bundles and arrays to form areogel carbon nanotubes.
  • the crushing or shearing can usually be conducted at an ambient temperature, such as at a temperature from about 10-40 0 C.
  • Shearing or crushing of the material can also be conducted at an elevated temperature, such as 50-200 0 C or a temperature less than 5 0 C, such as at a temperature from -197 - 0 0 C.
  • the shearing is conducted at room temperature from about 10-30 0 C. In general, longer crushing or shearing time results in aerogel carbon nanotubes bundles or arrays having smaller diameters.
  • a gaseous or fluidic cooling media can be applied to the shearing means.
  • Exemplary cooling media include, but are not limited to, water, organic solvents or lubricants.
  • a crushing or shearing time from about Is to about 0.5 hour can be used to obtain aerogel carbon nanotubes bundles or arrays having desirable diameters.
  • a shearing time of about 1-5 minutes is preferred.
  • the crushing or shearing means includes, but are not limited to mechanical shearing, high-velocity gas shearing, skives and explosion.
  • a mechanical shearing device contains a cutting means for shearing the carbon nanotubes bundles or arrays.
  • the cutting means can be made of a metal, such as steel; or ceramic, such as silicon carbide, tungsten carbide and the like, hi certain instances, the cutting means is capable of rotating at a certain speed from about 1000 rad/min to about 50000 rad/min, preferably from about 10000-30000 rad/min. In some embodiments, higher rotating speed is desirable since it results in carbon nanotube bundles or arrays having smaller diameters.
  • High velocity gas shearing can also be used for the preparing of aerogel carbon nanotubes bundles or arrays.
  • an inert gas such as nitrogen, air or a noble gas is used.
  • the line velocity of the gas is from about 1-50 m/s.
  • the line velocity is from about 1-20 m/s, more preferably, from about 1-10 m/s.
  • a gas having a line velocity of about 5m/s is used for shearing.
  • the aerogel carbon nanotubes having various densities can be prepared by dispersing the carbon nanotubes agglomerates in a gas, followed by descending and collecting the carbon nanotube agglomerates at various time intervals.
  • the carbon nanotubes agglomerates are dispersed into a housing using a gas.
  • the housing can have various shapes and sizes.
  • the housing can optionally be further connected to a container.
  • a tubular housing connected to a spherical container can be used for the dispersion process.
  • a gas is selected from air, nitrogen, oxygen, noble gas, carbon dioxide, carbon monoxide, C 1-S hydrocarbon gases or mixtures thereof. Cj.
  • hydrocarbon gases include methane, ethane, ethane, propane, propylene, butane, butene, pentane, pentene, hexane, hexene, heptane, heptene, octane, octane, benzene, mixtures and isomers thereof.
  • the dispersion process is typically conducted at a temperature above the boiling point of the gas used. The process can be performed at a temperature from about -100 to 200 0 C, preferably from 0-100 0 C, more preferably at a temperature from about 0-40 0 C.
  • the descending of carbon nanotubes agglomerates in the gas phase and grading the carbon nanotubes agglomerates with different densities can be conducted for about 1 s to about 10 hours.
  • the descending and collecting processes are carried out for about 0.1 min to about 20 minutes, more preferably from about 0.5 min to about 15 min.
  • the process of shearing, dispersing and grading is repeatable until aerogel carbon nanotubes of having desired parameters are obtained. For example, if the product has not reached the desired density, then the CNT can be crushed or sheared again until aerogel nanotubes having a desired density, aspect ratio and diameter are obtained.
  • the present invention provides aerogel carbon nanotubes that can be used as heat conductive, electrical conductive materials itself, or in combination with other materials, such as polymers, ceramic, metals to form structural composite, electrical conductive composite, electromagnetic interference shielding, transparent conductive materials, thermal conductive, mechanical strength enhanced materials, thermal insulating materials or catalyst carriers.
  • the present invention provides a method for the preparation of an aerogel carbon nanotube membrane.
  • the method includes depositing aerogel carbon nanotubes on a planar solid support under conditions sufficient to form a carbon nanotubes membrane.
  • a binder is added to the carbon nanotube membrane together with the carbon nanotubes layer to form a paper like material that exhibits enhanced and/or improved mechanical properties.
  • the membrane is formed by depositing a gas dispersed aerogel carbon nanotubes onto to a solid support.
  • the carbon nanotube membrane is formed by spin coating of a solution of aerogel carbon nanotubes.
  • the solvent can be water or organic solvents, which include pentane, hexanes, petroleum ether, benzene, chlorinated solvent, such as dichloromethane, chloroform and dichloroethylene; ether, tetrahydrofuran (THF), ethanol, methanol and the like.
  • concentration of the aerogel carbon nanotubes can be from about 1 ppm to 100 ppm, for example, 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80 or 90 ppm.
  • the thickness of the membrane can be from 1 nm to about 10 nm.
  • the membrane prepared can be transparent, semi transparent or opaque.
  • the membrane has high thermal and electrical conductivity. For instance, the membrane has a volume resistance less than 10 "2 ⁇ cm, a surface electrical resistance less than 1000 ⁇ /D; and a thermal conductivity greater than 1000W/mK.
  • the membrane also exhibits better mechanical properties than conventional paper. For example, the membrane prepared has a tensile strength greater than 20.2 Mpa and a Young modulation greater than 436 MPa higher than ordinary paper.
  • the solid support used in the present invention can be silica gels, derivatized plastic films, metal film, metal mesh, glass beads, cotton, plastic beads, alumina gels, polymer resins, a zeolite, a carbon, ceramic, an inorganic oxide, an inorganic hydroxide, a mixed inorganic hydroxides or mixed inorganic oxides.
  • Plastic films include polymer films derived from polyalkenes, such as polyethylene and polypropylenes.
  • the metals are typically groups 10-14 metals.
  • Non-limiting examples of polymer resins includes polystyrene resin and epoxy resin.
  • the binders used in the present invention include polymers, ceramic, oxide, glass, metals or semiconductors.
  • Non-limiting exemplary polymers include, but are not limited to, poly(vinylidene fluoride), poly(dicyclopentadiene), poly(tetrafluoroethylene), poly(ether-ether ketone), poly(ether sulfone),' silicones, dimethylsiloxane polymers, poly(pyrrole) 5j epoxy resins, polyacrylates, adhesives and polyaniline.
  • Non-limiting ceramic/oxide or glass includes SiO2, A12O3, MgO and cordierite.
  • Non-limiting metals or semiconductors include, but are not limited to, Ag, Au, Cu, Al, Ni, Fe, Zn, graphite, Ga/As and silicon.
  • the present invention provides a method for the preparation of polymer composite materials.
  • the method includes admixing a polymer composite material with aerogel carbon nanotubes under conditions sufficient to form a polymer composite.
  • Various polymers are suitable for preparing the composite materials.
  • the polymers can be synthetic polymers, such as plastics, rubbers and fibers; or naturally occurring macromolecules, such as proteins, polypeptides, poly(amino acids) and polysaccharides.
  • the synthetic polymers include • those prepared by both addition polymerization and condensation polymerization processes.
  • Exemplary synthetic polymers include, but are not limited to, polyalkenes, such as poly(Cl-8alkylenes) and poly(substituted Cl-8alkylenes); polyethers; polyesters; polyamides; polyacrylates; polynitriles; polysulfones and polyketones.
  • the substituents can attach either to the sp2 or sp3 carbon of the alkylene.
  • Suitable substituents for Cl-8alkylene include, but are not limited to, -F, -Cl 5 -Br, I, aryl, arylalkyl, alkyl aryl, -ORa, -OSi(Ra)3, -OC(O)O-Ra, -OC(O)Ra, -OC(O)NHRa, -OC(O)N(Ra)2, -SH 5 -SRa, -S(O)Ra 5 -S(O)2Ra, -SO2NH2, -S(O)2NHRa,
  • the polymers used in the present invention can be linear, branched or cross-linked.
  • the cross-linked polymers can be polymer resins.
  • aerogel carbon nanotubes are added to a polymer solution.
  • mechanical blending techniques known to a person skilled in the art are used.
  • the aerogel carbon nanotubes can be admixed to the polymers in a ratio from about 0.001 wt% to about 99 wt %.
  • the aerogel carbon nanotubes have a concentration from about 0.003 to about 10%, more preferable from about 0.003 to about 5%.
  • the polymer composite, wherein the aerogel carbon nanotubes can have a weight percentage of about 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.
  • the method further includes pressing the polymer composite to form a membrane.
  • the polymer composite can be mechanically and/or thermally pressed using the device known in the art.
  • thermal pressing is conducted at a temperature above the Tg of the polymer.
  • Composite films having a thickness from about 0.001 mm to about 1 mm can be obtained.
  • the film has a thickness of 0.1 mm.
  • the polymer composite films have a much higher tensile strength compared to the polymers. For example, a polyvinyl alcohol composite film has a tensile strength of at least 27 MPa and a Young modulation of at least about 1956 MPa.
  • the polymer composite materials are electrically and thermally conductive and have a low volume resistance.
  • the polymer composite has a conductivity of at least 10-3S/m, a thermal conductivity of at least 1000W/mK 5 and a volume resistance of l ⁇ cm or less.
  • the present invention provides a method for the preparation of inorganic composite materials.
  • the method includes admixing an inorganic compound or material with aerogel carbon nanotubes to form a mixture, heating the mixture, and hot-pressing the mixture under conditions sufficient to form inorganic composite.
  • the admixing includes, for example, mixing an inorganic compound, such as a metal oxide resin with aerogel carbon nanotubes to obtain a mixture.
  • the mixture can be heated or baked for a desirable amount of time, from about 1 minute to 5 hours.
  • the mixture can be heated at a temperature from about 80 0 C to about 500 0 C for about 2-72 hours.
  • the mixture is heated at about 100-200 0 C for about 24-48 hours.
  • the mixture is heated at 110 °C for about 24 hours.
  • Hot-pressing can be conducted at a temperature from about 700 0 C to about 2000 0 C and a pressure from about 10-60 MPa, preferably, a temperature from 1000-2000 0 C and a pressure from 15-30 MPa.
  • an AI 2 O 3 powder resin is hot pressed at about 1500 0 C, 20 MPa for about 60 minutes.
  • Suitable inorganic materials include, but are not limited to, metal oxides, metal sulfides, metal carbides, metal powders, alloys, semiconductors and combinations of the mixtures.
  • the metals can be either main group metals or transition metals.
  • Non-limiting semiconductors include silicon and gallium arsenide.
  • This example illustrates effect of mechanic shearing on carbon nanotube arrays and the effects of dispersing and descending on aerogel carbon nanotubes.
  • the length of the CNT array was 1.4mm, and the nanotubes have a surface area about several tenths square millimeters.
  • the rotation rate was about 10000 rad/min. After 2min shearing, the CNT array has been destroyed and dispersed well. Due to the week connection on the axis direction, when shearing happened, the CNT array has been tore into small bundles. Due to the flexible of CNT, it can be kept as the primitive length.
  • the SEM image of after crushing CNTs was shown in Fig 2b.
  • the CNT agglomerate has been into the CNT bundles with diameter of l-25 ⁇ m and a length of 100 ⁇ 1400 ⁇ m.
  • the density of CNT bundles were about 2g/L. It can be seen that the CNT array has been into aerogel CNT in big cluster from.
  • the length of the CNT array was 1.Omm, and the nanotubes have a surface area about several tenths square millimeters.
  • the density of aerogel CNTs were about 4g/L.
  • the above aerogel was put into a silica tube with a diameter of 75mm, the inlet air with a flow rate of 0.2m/s on the cross-section of the tube.
  • the CNT volume can be increased and dispersed in air.
  • the CNT aerogel can descend. Collect the sample after lmin.
  • the density of aerogel CNTs were about 1.4g/L.
  • the aerogel CNT product after 5min collection was with a density of 0.2g/L.
  • the length of the CNT bundles was about a few hundreds micrometers. Take 100mg CNT array in the mechanical shearing, and control the rotation rate at 10000 rad/min. After 2min shearing, the CNT array has been destroyed and dispersed well. Take the product out and the SEM image of after crushing CNTs was shown in Fig 4a. It can be seen that the CNT agglomerate has been into the CNT bundles with diameter of 50-250 nm and a length of 100 ⁇ 100 ⁇ m. The density of aerogel CNTs were about 42g/L.
  • the above aerogel was put into a silica tube with a diameter of 75mm, the inlet air with a flow rate of 0.2m/s on the cross-section of the tube.
  • the CNT volume can be increased and dispersed in air.
  • the CNT aerogel can descend. Collect the sample after 3min as shown in Fig. 4b.
  • the density of aerogel CNTs were about 2.2g/L.
  • This example illustrates the effect of mechanical shearing and descending on the dispersion of carbon nanotubes bundles in gas.
  • the length of the CNT bundles was about a few hundreds micrometers. Take 500mg CNT array in the mechanical shearing, and control the rotation rate at 30000 rad/min. After 20 min shearing, the CNT array has been destroyed and dispersed well. Take the product out and the SEM image of after crushing CNTs was shown in Fig 5.
  • the above aerogel was put into a silica tube with a diameter of 75mm, the inlet air with a flow rate of 0.05m/s on the cross-section of the tube. The CNT volume can be increased and dispersed in air. When the inlet air stopped, the CNT aerogel can descend. Collect the sample after 15min. It can be seen that the CNT agglomerate has been into the CNT bundles with diameter of 10-100 nm and a length of 10 ⁇ 500 ⁇ m as shown in Fig.5. The density of aerogel CNTs were about 0.1g/L.
  • This example illustrates the preparation of a carbon nanotube paper from aerogel carbon nanotubes.
  • Example 6 This example illustrates the preparation of polymer-carbon nanotubes composite.
  • Example 7 This Example illustrates the preparation of a carbon nanotube film.
  • This example illustrates the preparation of an electrically conductive polymer carbon-nanotube composite.
  • This example illustrates the preparation of an inorganic carbon-nanotube composite.
  • the aerogel CNT from embodiment 2 with Al 2 O 3 powder resin and mix them well. Bake the mixture at 110 0 C for 24 hr. Then the mixture hot-pressed at 1500 0 C, 20 MPa for 60min to get the Al 2 O 3 /CNT composite.
  • the Al 2 O 3 powder was a density of 3.80 g/cm 3 , tensile strength of 362 MPa; After 1% aerogel CNT adding, the density was 3.76 g/cm 3 , while tensile strength is 420MPa. Therefore, the aerogel CNT enhanced the ceramic powder with better performance.

Abstract

Aerogel carbon nanotube, and method for preparing the same, are provided. The said aerogel carbon nanotube comprises a plurality of dispersed carbon nanotube aggregrates with a diameter from about 1 nm to about 100 microns, and has a density from about 0.1 to about 100 g/L. The method for preparing the same comprises contacting a plurality of carbon nanotube aggregates with a shearing means under conditions sufficient to form a plurality of carbon nanotube agglomerates having a density from about 0.1 to about 100 g/L. The methods 'or preparing membrane, polymer composite material and inorganic composite material, using the said aerogel carbon nanotube as a raw material, are also provided.

Description

AEROGEL CARBON NANOTUBES
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims priority to Chinese Patent Application No. 200610089385.9 filed June 23, 2006, which application is incorporated herein by reference in its entirety and for all .purposes.
BACKGROUND OF THE INVENTION
[0002] Carbon nanotubes (CNT) have many unique properties stemming from the small size, cylindrical structure, and high aspect ratio of length to diameter. Single- walled carbon nanotubes (SWCNTs) consist of a single graphite sheet wrapped around to form a cylindrical rube. Multi-walled carbon nanotubes (MWCNTs) comprise an array of such nanotubes that are concentrically nested like the rings of a tree trunk. CNTs have extremely high tensile strength (~ 150 GPa)5 high modulus (~ 1 TPa), large aspect ratio, low density, good chemical and environmental stability, and high thermal and electrical conductivity. Carbon nanotubes have found various applications, including the preparation of conductive, electromagnetic and microwave absorbing and high-strength composites, fibers, sensors, field emission displays, inks, energy storage and energy conversion devices, radiation sources and nanometer-sized semiconductor devices, probes, and interconnect.
[0003] Various carbon nanotubes agglomerates have been prepared. A continuous mass production of carbon nanotubes agglomerates can be achieved using a fluidized bed, mixed gases of hydrogen, nitrogen and hydrocarbon at a low space velocity (WO 02/094713; US Pat. Pub. No. 2004/0151654). Single-walled carbon nanotubes have also been prepared at a high space velocity and in the absence of nitrogen (WO 01/94260). The carbon-nanotube arrays can be obtained in large scale by floating catalyst methods on a particle surface (Chinese Patent Pub. No. 1724343 A). To use carbon nanotubes as additives for other materials, the carbon nanotubes must be well-dispersed.
[0004] Current technologies allow carbon nanotubes to be dispersed in liquid. The carbon nanotube agglomerates are dispersed well in water (ZL02117419.9). However, to use carbon nanotubes in various technological important areas, such as the production of composite materials, the carbon nanotubes have to be mixed with matrix materials, which require that the carbon nanotubes be separated from solvent. Thus, it is desirable to have solvent free aerogel carbon nanotubes. [0005] Therefore, there is a need to develop methods for the facile preparation of wellτdispersed aerogel carbon nanotubes that are useful in the preparation of a variety of nanocomposite materials. The present invention meets this and other needs.
BRIEF SUMMARY OF THE INVENTION
[0006] The present invention is directed to methods for the facile preparation of solvent free and well-dispersed aerogel carbon nanotubes that are useful in the preparation of nanotube membranes and nanocomposite materials. Advantageously, the present invention allows the synthesis of aerogel carbon nanotubes having predetermined and/or controlled density, aspect ratio and diameters with ease.
[0007] In one aspect, the present invention provides a method for preparing aerogel carbon nanotubes. The method includes contacting a plurality of carbon nanotube aggregates with a shearing means under conditions sufficient to form a plurality of carbon nanotube agglomerates having a density from about 0.1 to about 100 g/L. In one embodiment, the method further includes dispersing the plurality of carbon nanotube agglomerates in a gas, and descending the plurality of carbon nanotubes agglomerates to form aerogel carbon nanotubes having a predetermined density. In another embodiment, the aggregates are bundles, arrays or a combination of bundles and arrays.
[0008] In another aspect, the present invention provides aerogel carbon nanotubes. The aerogel carbon nanotubes include a plurality of dispersed carbon nanotube aggregates, wherein said aggregates include bundles, arrays or a combination thereof and wherein said aggregates have a diameter from about 1 nm to about 100 μm, an aspect ratio from about 10 to about 106, and a density from about 0.1 to about 100g/L.
[0009] In yet another aspect, the present invention provides a method for preparing a carbon nanotube membrane. The method includes depositing aerogel carbon nanotubes on a planar solid support under condition sufficient to form a carbon nanotubes membrane.
[0010] In still another aspect, the present invention provides a method for preparing a polymer composite material. The method includes admixing a polymer with aerogel carbon nanotubes under conditions sufficient to form a polymer composite material. In one embodiment, the method further includes thermal-pressing the composite to form a membrane.
[0011] In a further embodiment, the present invention provides a method for preparing an inorganic composite material. The method includes admixing an inorganic compound with the aerogel carbon nanotubes to form a mixture, heating the mixture, and hot-pressing the mixture under conditions sufficient to form an inorganic composite material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Fig. 1 illustrates a schematic diagram for the preparation of aerogel carbon nanotubes according to an embodiment of the present invention.
[0013] Figs.2a-d: Fig. 2a shows a scanning electron microphotography (SEM) image of the carbon nanotubes arrays before crushing and/or shearing; Fig. 2b shows an SEM image of the dispersed carbon nanotubes arrays after mechanical crushing and/or shearing; Fig. 2c shows an SEM image of the aerogel carbon nanotubes arrays collected after mechanical crushing and/or shearing, dispersing in gas phase, and descending for 30s; Fig. 2d shows an SEM image of the aerogel carbon nanotubes arrays collected after mechanical crushing and/or shearing, dispersing in gas phase, and descending for 4 minutes.
[0014] Fig. 3 shows an SEM image of the aerogel carbon nanotubes arrays collected after high gas velocity shearing, dispersing in gas phase, and descending for 1 minute.
[0015] Fig. 4a-b: Fig. 4a shows an SEM image of the aerogel carbon nanotubes bundles collected after mechanical crushing and /or shearing, dispersing in gas phase, and descending for 30s; Fig. 4b shows an SEM image of the areogel carbon nanotubes bundles collected after mechanical crushing, dispersing in gas phase, and descending for 3 minutes.
[0016] Fig. 5 shows an SEM image of the areogel carbon nanotubes arrays collected after mechanical crushing and/or shearing, dispersing in gas phase, and descending for 15 minutes.
[0017] Fig. 6 shows an SEM image of a carbon nanotube membrane or paper prepared from aerogel carbon nanotubes according to an embodiment of the present invention.
[0018] Fig. 7 shows an SEM image of a transparent conductive film prepared from aerogel carbon nanotubes according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The present invention relates to the methods for the synthesis of well-dispersed aerogel carbon nanotubes having predetermined or controlled physical characteristics and properties; methods for the synthesis of nanotube membranes having unique physical properties; and methods for the synthesis of nanocomposite materials having enhanced and/or improved physical properties. [0020] In one aspect, the present invention provides aerogel carbon nanotubes. The aerogel carbon nanotubes are composed of a plurality of well-dispersed carbon nanotubes aggregates. In some embodiments, the aggregates are in the form of bundles, arrays or a combination of arrays and bundles. In a preferred embodiment, the carbon nanotubes bundles or arrays have a diameter from about 1 nm to about 100 μm, an aspect ratio from about 10 to about 106, and a density from about 0.1 to about 100g/L. In some embodiments, the aerogel carbon nanotubes form a plurality of carbon nanotubes agglomerates.
[0021] In one embodiment, the aerogel carbon nanotubes bundles, arrays or agglomerates can have a diameter ranging from about 0.4-0.6 nm, 0.5-1 nm, 5-6 nm, 1-10 nm, 1-20 nm, 1-30 nm, 1-40 nm, 10-50 nm, 40-100 nm, 1-200 nm, 1-500 nm, 100-700 nm, 100-900 nm, 800 nm -10 μm, lμm- 30 urn, 10 μm-50 μm, 10 μm-80 μm or 10 μm-100 μm. Preferably, the carbon nanotubes bundles, arrays or agglomerates have a diameter ranging from about 1 nm -500 nm, 1 nm -200 nm, 10 nm - 350 nm, 0.5 μm- 40 μm or 5 μm-50μm. More preferably, the carbon nanotubes bundles, arrays or agglomerates have a diameter ranging from about 1 μm-25 μm, 15 μm-30 μm, 50 nm-250 nm, or 10 nm-100 nm.
[0022] -In another embodiment, the aerogel carbon nanotubes bundles, arrays or agglomerates have an aspect ratio ranging from about 10-100, 100-500, 10-1000, 100-1000, 100-10000, 1000-10000, 1000-50000, 1000-100000, 10000-100000, 10000-500000, 100000-106. The aerogel carbon nanotubes bundles can have various lengths ranging from about 0.3 μm to about 5000 μm, preferably, from about 0.8 μm- 1600 μm, more preferably, from about 1 μm-1500 μm, even more preferably, from about 100 μm-1400 μm, 10 μm-100 μm, 1 μm-10 μm, 10 μm-500 μm or 200 μm-3000 μm.
[0023] The aerogel carbon nanotubes can have various densities. In one embodiment, the aerogel carbon nanotubes have a density from about 0.01 to 150 g/L. In another embodiment, the aerogel carbon nanotubes have a density from about 0.01-0.05, 0.05-0.1, 0.1-0.5, 0.5-1, 1-1.5, 1.5-2.5, 2.5-10, 10-30, 30-50 or 50-100 g/L. In a yet another embodiment, the aerogel carbon nanotubes have a density selected from the group consisting of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.24.5, 5.0, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 50, 60, 70, 80, 90 and 100 g/L. For example, the aerogel carbon nanotubes have a density selected from the group consisting of 0.1, 0.2, 0.5, 1.3, 1.4, 2, 2.2 and 42 g/L.
[0024] Various carbon nanotubes bundles, arrays, or a combination of bundles and arrays can be used in the present invention. For example, aerogel carbon nanotubes can be multi-walled carbon nanotube bundles, few-walled carbon nanotube bundles, single-walled carbon nanotube bundles, a multi-walled carbon nanotube arrays, few-walled carbon nanotube arrays, single-walled carbon nanotube arrays, or combinations thereof. Typically, single-walled carbon nanotubes have a diameter ranging from less than 1 nm to a few nanometers. Double-walled carbon nanotubes have a diameter of several nanometers. Few- walled carbon nanotubes have a diameter ranging from a few nanometers to several tenths of nanometers. Multi- walled carbon nanotubes have a diameter ranging from a few nanometers to 100 nm, such as from about 1 nm-100 nm.
[0025] In another aspect, the present invention provides a method for the preparation of aerogel carbon nanotubes. The method includes contacting a plurality of carbon nanotube aggregates with a shearing means under conditions sufficient to form a plurality of carbon nanotube agglomerates having a density from about 0.1 to about 100 g/L. The aggregates can be bundles, arrays or a combination of bundles and arrays. In one embodiment, the method further includes dispersing the plurality of carbon nanotube agglomerates in a gas; and descending said plurality of carbon nanotube agglomerates to form aerogel carbon nanotubes having a controlled or predetermined density. [0026] Conventional device and methods can be used for crushing carbon nanotubes bundles and/or arrays or a mixture of bundles and arrays to form areogel carbon nanotubes. The crushing or shearing can usually be conducted at an ambient temperature, such as at a temperature from about 10-40 0C. Shearing or crushing of the material can also be conducted at an elevated temperature, such as 50-2000C or a temperature less than 5 0C, such as at a temperature from -197 - 0 0C. Preferably, the shearing is conducted at room temperature from about 10-30 0C. In general, longer crushing or shearing time results in aerogel carbon nanotubes bundles or arrays having smaller diameters. A gaseous or fluidic cooling media can be applied to the shearing means. Exemplary cooling media include, but are not limited to, water, organic solvents or lubricants. A crushing or shearing time from about Is to about 0.5 hour can be used to obtain aerogel carbon nanotubes bundles or arrays having desirable diameters. A shearing time of about 1-5 minutes is preferred.
[0027] The crushing or shearing means includes, but are not limited to mechanical shearing, high-velocity gas shearing, skives and explosion. In one embodiment, a mechanical shearing device contains a cutting means for shearing the carbon nanotubes bundles or arrays. The cutting means can be made of a metal, such as steel; or ceramic, such as silicon carbide, tungsten carbide and the like, hi certain instances, the cutting means is capable of rotating at a certain speed from about 1000 rad/min to about 50000 rad/min, preferably from about 10000-30000 rad/min. In some embodiments, higher rotating speed is desirable since it results in carbon nanotube bundles or arrays having smaller diameters. High velocity gas shearing can also be used for the preparing of aerogel carbon nanotubes bundles or arrays. Preferably, an inert gas, such as nitrogen, air or a noble gas is used. The line velocity of the gas is from about 1-50 m/s. Preferably, the line velocity is from about 1-20 m/s, more preferably, from about 1-10 m/s. In one embodiment, a gas having a line velocity of about 5m/s is used for shearing. [0028] The aerogel carbon nanotubes having various densities can be prepared by dispersing the carbon nanotubes agglomerates in a gas, followed by descending and collecting the carbon nanotube agglomerates at various time intervals. Typically, the carbon nanotubes agglomerates are dispersed into a housing using a gas. The housing can have various shapes and sizes. The housing can optionally be further connected to a container. For example, a tubular housing connected to a spherical container can be used for the dispersion process. A gas is selected from air, nitrogen, oxygen, noble gas, carbon dioxide, carbon monoxide, C1-S hydrocarbon gases or mixtures thereof. Cj.8 hydrocarbon gases include methane, ethane, ethane, propane, propylene, butane, butene, pentane, pentene, hexane, hexene, heptane, heptene, octane, octane, benzene, mixtures and isomers thereof. The dispersion process is typically conducted at a temperature above the boiling point of the gas used. The process can be performed at a temperature from about -100 to 2000C, preferably from 0-100 0C, more preferably at a temperature from about 0-400C. The descending of carbon nanotubes agglomerates in the gas phase and grading the carbon nanotubes agglomerates with different densities can be conducted for about 1 s to about 10 hours. Preferably, the descending and collecting processes are carried out for about 0.1 min to about 20 minutes, more preferably from about 0.5 min to about 15 min. As shown in Figure 1 , the process of shearing, dispersing and grading is repeatable until aerogel carbon nanotubes of having desired parameters are obtained. For example, if the product has not reached the desired density, then the CNT can be crushed or sheared again until aerogel nanotubes having a desired density, aspect ratio and diameter are obtained.
[0029] In yet another aspect, the present invention provides aerogel carbon nanotubes that can be used as heat conductive, electrical conductive materials itself, or in combination with other materials, such as polymers, ceramic, metals to form structural composite, electrical conductive composite, electromagnetic interference shielding, transparent conductive materials, thermal conductive, mechanical strength enhanced materials, thermal insulating materials or catalyst carriers.
[0030] In one embodiment, the present invention provides a method for the preparation of an aerogel carbon nanotube membrane. The method includes depositing aerogel carbon nanotubes on a planar solid support under conditions sufficient to form a carbon nanotubes membrane. In certain instances, a binder is added to the carbon nanotube membrane together with the carbon nanotubes layer to form a paper like material that exhibits enhanced and/or improved mechanical properties. In one embodiment, the membrane is formed by depositing a gas dispersed aerogel carbon nanotubes onto to a solid support. In another embodiment, the carbon nanotube membrane is formed by spin coating of a solution of aerogel carbon nanotubes. The solvent can be water or organic solvents, which include pentane, hexanes, petroleum ether, benzene, chlorinated solvent, such as dichloromethane, chloroform and dichloroethylene; ether, tetrahydrofuran (THF), ethanol, methanol and the like. For spin coating, the concentration of the aerogel carbon nanotubes can be from about 1 ppm to 100 ppm, for example, 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80 or 90 ppm.
[0031] The thickness of the membrane can be from 1 nm to about 10 nm. The membrane prepared can be transparent, semi transparent or opaque. The membrane has high thermal and electrical conductivity. For instance, the membrane has a volume resistance less than 10"2Ωcm, a surface electrical resistance less than 1000 Ω/D; and a thermal conductivity greater than 1000W/mK. The membrane also exhibits better mechanical properties than conventional paper. For example, the membrane prepared has a tensile strength greater than 20.2 Mpa and a Young modulation greater than 436 MPa higher than ordinary paper.
[0032] The solid support used in the present invention can be silica gels, derivatized plastic films, metal film, metal mesh, glass beads, cotton, plastic beads, alumina gels, polymer resins, a zeolite, a carbon, ceramic, an inorganic oxide, an inorganic hydroxide, a mixed inorganic hydroxides or mixed inorganic oxides. Plastic films include polymer films derived from polyalkenes, such as polyethylene and polypropylenes. The metals are typically groups 10-14 metals. Non-limiting examples of polymer resins includes polystyrene resin and epoxy resin.
[0033] The binders used in the present invention include polymers, ceramic, oxide, glass, metals or semiconductors. Non-limiting exemplary polymers include, but are not limited to, poly(vinylidene fluoride), poly(dicyclopentadiene), poly(tetrafluoroethylene), poly(ether-ether ketone), poly(ether sulfone),' silicones, dimethylsiloxane polymers, poly(pyrrole)5j epoxy resins, polyacrylates, adhesives and polyaniline. Non-limiting ceramic/oxide or glass includes SiO2, A12O3, MgO and cordierite. Non-limiting metals or semiconductors include, but are not limited to, Ag, Au, Cu, Al, Ni, Fe, Zn, graphite, Ga/As and silicon.
[0034] In another embodiment, the present invention provides a method for the preparation of polymer composite materials. The method includes admixing a polymer composite material with aerogel carbon nanotubes under conditions sufficient to form a polymer composite. Various polymers are suitable for preparing the composite materials. The polymers can be synthetic polymers, such as plastics, rubbers and fibers; or naturally occurring macromolecules, such as proteins, polypeptides, poly(amino acids) and polysaccharides. The synthetic polymers include • those prepared by both addition polymerization and condensation polymerization processes. Exemplary synthetic polymers include, but are not limited to, polyalkenes, such as poly(Cl-8alkylenes) and poly(substituted Cl-8alkylenes); polyethers; polyesters; polyamides; polyacrylates; polynitriles; polysulfones and polyketones. The substituents can attach either to the sp2 or sp3 carbon of the alkylene. Suitable substituents for Cl-8alkylene include, but are not limited to, -F, -Cl5 -Br, I, aryl, arylalkyl, alkyl aryl, -ORa, -OSi(Ra)3, -OC(O)O-Ra, -OC(O)Ra, -OC(O)NHRa, -OC(O)N(Ra)2, -SH5 -SRa, -S(O)Ra5 -S(O)2Ra, -SO2NH2, -S(O)2NHRa,
-C(O)NH25 -C(O)NHRa, -C(O)N(Ra)2, -C(O)Ra, -C(O)H,
-C(=S)Ra, -NHC(O)Ra, -NRaC(O)Ra5 -NHC(O)NH25 -NRaC(0)NH2, -NRaC(O)NHRa, -NHC(O)N HRa, -NRaC(O)N(Ra)2, -NHC(O)N(Ra)2, -CO2H, -CO2Ra, -NHCO2Ra, -NRaCO2Ra, -CN5 -NO2, -NH2, -NHRa5 -N(Ra)2, -NH-OH5 -NRa-OH, -NRa-ORa, -N=C=O, -N=C=S. -Si(Ra)3, -NH-NHRa, -NHC(0)NHNH2 and -S-CN, wherein each Ra is independently -H, C 1 -8alkyl or aryl. The polymers used in the present invention can be linear, branched or cross-linked. The cross-linked polymers can be polymer resins. For soluble polymers, aerogel carbon nanotubes are added to a polymer solution. For insoluble polymers, mechanical blending techniques known to a person skilled in the art are used.
[0035] The aerogel carbon nanotubes can be admixed to the polymers in a ratio from about 0.001 wt% to about 99 wt %. Preferably, the aerogel carbon nanotubes have a concentration from about 0.003 to about 10%, more preferable from about 0.003 to about 5%. For instance, the polymer composite, wherein the aerogel carbon nanotubes can have a weight percentage of about 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.
[0036] In certain instances, the method further includes pressing the polymer composite to form a membrane. The polymer composite can be mechanically and/or thermally pressed using the device known in the art. In one embodiment, thermal pressing is conducted at a temperature above the Tg of the polymer. Composite films having a thickness from about 0.001 mm to about 1 mm can be obtained. In one embodiment, the film has a thickness of 0.1 mm. The polymer composite films have a much higher tensile strength compared to the polymers. For example, a polyvinyl alcohol composite film has a tensile strength of at least 27 MPa and a Young modulation of at least about 1956 MPa.
[0037] The polymer composite materials are electrically and thermally conductive and have a low volume resistance. In one embodiment, the polymer composite has a conductivity of at least 10-3S/m, a thermal conductivity of at least 1000W/mK5 and a volume resistance of lΩcm or less.
[0038] In yet another embodiment, the present invention provides a method for the preparation of inorganic composite materials. The method includes admixing an inorganic compound or material with aerogel carbon nanotubes to form a mixture, heating the mixture, and hot-pressing the mixture under conditions sufficient to form inorganic composite.
[0039] In certain instances, the admixing includes, for example, mixing an inorganic compound, such as a metal oxide resin with aerogel carbon nanotubes to obtain a mixture. The mixture can be heated or baked for a desirable amount of time, from about 1 minute to 5 hours. For instance, the mixture can be heated at a temperature from about 80 0C to about 500 0C for about 2-72 hours. Preferably, the mixture is heated at about 100-200 0C for about 24-48 hours. In a preferred embodiment, the mixture is heated at 110 °C for about 24 hours. Hot-pressing can be conducted at a temperature from about 700 0C to about 2000 0C and a pressure from about 10-60 MPa, preferably, a temperature from 1000-2000 0C and a pressure from 15-30 MPa. In a preferred embodiment, an AI2O3 powder resin is hot pressed at about 1500 0C, 20 MPa for about 60 minutes.
[0040] Various inorganic compounds and/or inorganic materials can be used for the preparation of composites. Suitable inorganic materials include, but are not limited to, metal oxides, metal sulfides, metal carbides, metal powders, alloys, semiconductors and combinations of the mixtures. The metals can be either main group metals or transition metals. Non-limiting semiconductors include silicon and gallium arsenide.
Examples
Example 1
[0041] This example illustrates effect of mechanic shearing on carbon nanotube arrays and the effects of dispersing and descending on aerogel carbon nanotubes.
[0042] Taken the CNT arrays product by floating catalyst methods, the length of the CNT array was 1.4mm, and the nanotubes have a surface area about several tenths square millimeters. Take lOOmg CNT array in the mechanical shearing, and the rotation rate was about 10000 rad/min. After 2min shearing, the CNT array has been destroyed and dispersed well. Due to the week connection on the axis direction, when shearing happened, the CNT array has been tore into small bundles. Due to the flexible of CNT, it can be kept as the primitive length. The SEM image of after crushing CNTs was shown in Fig 2b. It can be seen that the CNT agglomerate has been into the CNT bundles with diameter of l-25μm and a length of 100~1400μm. The density of CNT bundles were about 2g/L. It can be seen that the CNT array has been into aerogel CNT in big cluster from.
[0043] The above aerogel was put into a silica tube with a diameter of 75mm, the inlet air with a flow rate of 0.2m/s on the cross-section of the tube. The CNT volume can be increased and dispersed in air. When the inlet air stopped, the CNT aerogel can descend. Collect the sample after 0.5min, the typical SEM images were shown in Fig. 2c. The CNT has been with a diameter of l-25μm and a length of 1100~ 1400μm. The cluster size has been minimized into a few hundreds micrometers. The density of aerogel CNTs were about 1.3g/L. [0044] After 4min descend, the typical SEM images were shown in Fig. 2d. The CNT has been with a diameter of l-25μm and a length of 1100~1400μm. The cluster size has been minimized into a few hundreds micrometers. The density of aerogel CNTs were about 0.5g/L.
Example 2
[0045] This example illustrates the effect of gas shearing on the dispersion of carbon nanotube arrays.
[0046] Taken the CNT arrays product by floating catalyst methods, the length of the CNT array was 1.Omm, and the nanotubes have a surface area about several tenths square millimeters. Take 1.0 g CNT array in the gas shearing, and control the line- velocity at 5m/s. After 2min shearing, the CNT array has been destroyed and dispersed well. Take the product out and the SEM image of after crushing CNTs was shown in Fig 3. It can be seen that the CNT agglomerate has been into the CNT bundles with diameter of 15-30μm and a length of 100~ 1 OOOμm. The density of aerogel CNTs were about 4g/L. The above aerogel was put into a silica tube with a diameter of 75mm, the inlet air with a flow rate of 0.2m/s on the cross-section of the tube. The CNT volume can be increased and dispersed in air. When the inlet air stopped, the CNT aerogel can descend. Collect the sample after lmin. The density of aerogel CNTs were about 1.4g/L. The aerogel CNT product after 5min collection was with a density of 0.2g/L.
Example 3
[0047] This example illustrates the effect of mechanical shearing on the dispersion of carbon nanotube bundles.
[0048] Taken the CNT bundles product by chemical vapor deposition, the length of the CNT bundles was about a few hundreds micrometers. Take 100mg CNT array in the mechanical shearing, and control the rotation rate at 10000 rad/min. After 2min shearing, the CNT array has been destroyed and dispersed well. Take the product out and the SEM image of after crushing CNTs was shown in Fig 4a. It can be seen that the CNT agglomerate has been into the CNT bundles with diameter of 50-250 nm and a length of 100~100μm. The density of aerogel CNTs were about 42g/L. The above aerogel was put into a silica tube with a diameter of 75mm, the inlet air with a flow rate of 0.2m/s on the cross-section of the tube. The CNT volume can be increased and dispersed in air. When the inlet air stopped, the CNT aerogel can descend. Collect the sample after 3min as shown in Fig. 4b. The density of aerogel CNTs were about 2.2g/L. Example 4
[0049] This example illustrates the effect of mechanical shearing and descending on the dispersion of carbon nanotubes bundles in gas.
[0050] Taken the CNT bundles product by chemical vapor deposition, the length of the CNT bundles was about a few hundreds micrometers. Take 500mg CNT array in the mechanical shearing, and control the rotation rate at 30000 rad/min. After 20 min shearing, the CNT array has been destroyed and dispersed well. Take the product out and the SEM image of after crushing CNTs was shown in Fig 5. The above aerogel was put into a silica tube with a diameter of 75mm, the inlet air with a flow rate of 0.05m/s on the cross-section of the tube. The CNT volume can be increased and dispersed in air. When the inlet air stopped, the CNT aerogel can descend. Collect the sample after 15min. It can be seen that the CNT agglomerate has been into the CNT bundles with diameter of 10-100 nm and a length of 10~500μm as shown in Fig.5. The density of aerogel CNTs were about 0.1g/L.
Example 5
[0051] This example illustrates the preparation of a carbon nanotube paper from aerogel carbon nanotubes.
[0052] Take the aerogel CNTs and disperse them in air. Then collect them aerogel CNT to a copper net with pressure difference. Then thin paper can be obtained on the copper film; with the help of resin, the paper has been solidified with a thickness of 0.1mm. The microstructure of the paper can be seen in Fig.6. It was with a low volume resistance 10~2Ωcm and thermal conductivity of 1000W/mK. The tensile strength was about 20.2 MPa, with Yong modulation of 436.3MPa.
Example 6 [0053] This example illustrates the preparation of polymer-carbon nanotubes composite.
[0054] Fixed the paper in the filtration equipment and let the 1% PVA solution passed them. Then CNT/PVA film can be obtained. After thermal press, the thickness was about 0. lmm, with a low volume resistance lΩcm and thermal conductivity of 300W/mK. The tensile strength was about 27.42 MPa, with Yong modulation of 1956.3MPa5 which was much higher than PVA film. So the composite was with good performance which can be used as structural composite, electrical conductive composite, and thermal conductive composite.
Example 7 [0055] This Example illustrates the preparation of a carbon nanotube film.
[0056] Put the aerogel CNT from Example 2 in water with a concentration of lOppm. With rotation coating, transparent conductive film with 80% transparence and surface electrical resistance of 1000 Ω/cm2 was obtained.
Example 8
[0057] This example illustrates the preparation of an electrically conductive polymer carbon-nanotube composite.
[0058] Put the aerogel CNT from embodiment 2 with resin and get composite with electrical percolation threshold of <0.003 wt%, the S was lower than 10~3S/m. It is indicated that aerogel CNT was good additive for electrical conductive materials.
Example 9
[0059] This example illustrates the preparation of an inorganic carbon-nanotube composite.
[0060] Put the aerogel CNT from embodiment 2 with Al2O3 powder resin and mix them well. Bake the mixture at 110 0C for 24 hr. Then the mixture hot-pressed at 1500 0C, 20 MPa for 60min to get the Al2O3 /CNT composite. The Al2O3 powder was a density of 3.80 g/cm3, tensile strength of 362 MPa; After 1% aerogel CNT adding, the density was 3.76 g/cm3, while tensile strength is 420MPa. Therefore, the aerogel CNT enhanced the ceramic powder with better performance.
[0061] It is understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims. All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety for all purposes.

Claims

WHAT IS CLAIMED IS;
1. A method for preparing aerogel carbon nanotubes, said method comprising: contacting a plurality of carbon nanotube aggregates with a shearing means under conditions sufficient to form a plurality of carbon nanotube agglomerates having a density from about 0.1 to about 100 g/L.
2. The method of claim 1, further comprising: dispersing said plurality of carbon nanotube agglomerates in a gas; and descending said plurality of carbon nanotubes agglomerates to form aerogel carbon nanotubes having a predetermined density.
3. The method of claim 1, wherein said shearing means is selected from the group consisting of mechanical shear, gas shear, skive and explosion.
4. The method of claim 1, wherein said aggregates are selected from the group consisting of bundles, arrays or a combination thereof.
5 . The method of claim 4, wherein said plurality of carbon nanotubes aggregates is selected from a plurality of multi- walled carbon nanotubes bundles, a plurality of few- walled carbon nanotubes bundles, a plurality of single- walled carbon nanotubes bundles, a plurality of multi- walled carbon nanotubes arrays, a plurality of few- walled carbon nanotubes arrays, a plurality of single- walled carbon nanotubes arrays, or combinations thereof.
6 . The method of claim 2, wherein said gas is selected from the group consisting of air, nitrogen, oxygen, noble gas, carbon dioxide, carbon monoxide, C1-8 hydrocarbon gases and mixtures thereof.
7. The method of claim 2, wherein said dispersing is performed at a temperature from about -100 0C to about 150 0C.
8. Aerogel carbon nanotubes comprising: a plurality of dispersed carbon nanotube aggregates, wherein said aggregates comprise bundles, arrays or a combination thereof and wherein said aggregates have a diameter from about 1 nm to about 100 μm, an aspect ratio from about 10 to about 106, and a density from about 0.1 to about 100g/L.
9. The aerogel carbon nanotubes of claim 8, wherein said plurality of carbon nanotube aggregates is selected from a plurality of multi- walled carbon nanotubes bundles, a plurality of few-walled carbon nanotubes bundles, a plurality of single-walled carbon nanotubes bundles, a plurality of multi- walled carbon nanotubes arrays, a plurality of few- walled carbon nanotubes arrays, a plurality of single- walled carbon nanotubes arrays, or combinations thereof.
10. Aerogel carbon nanotubes prepared according to the method of claim 1 or 2.
11. A method for preparing a carbon nanotube membrane, said method comprising: depositing aerogel carbon nanotubes on a planar solid support under condition sufficient to form a carbon nanotubes membrane.
12. The method of claim 11, wherein said depositing comprises administering a binder to said membrane.
13. The method of claim 12, wherein the binder is epoxy resin.
14. The method of claim 11, wherein said solid support is selected from the group consisting of silica gel, a plastic film, a metal film, a metal mesh, glass beads, cotton, plastic beads, alumina gels, a polymer resin, a zeolite, a carbon and ceramic.
15. The method of claim 11, wherein the membrane has a thickness from about 1 μm to about 10 mm.
16. The method of claim 11, wherein said aerogel carbon nanotubes are dispersed in gas phase.
17 . The method of claim 11, wherein said depositing comprising spin-coating a solution of aerogel carbon nanotubes.
18. The method of claim 11 , wherein the membrane has a volume resistance less than 10'2Ωcm.
19. The method of claim 11, wherein said membrane has a surface electrical resistance less than 1000 Ω/D.
20. The method of claim 11, wherein said membrane has a thermal conductivity of at least 1000W/mK.
21. The method of claim 11, wherein said membrane has a tensile strength of at least 20.2 MPa.
22. The method of claim 11, wherein said membrane has a Young modulation of at least 436 MPa.
23. A method for preparing a polymer composite material, said method comprising: admixing a polymer with aerogel carbon nanotubes under conditions sufficient to form a polymer composite material.
24. The method of claim 23, further comprising: thermal-pressing said composite to form a membrane.
25. The method of claim 23, wherein said polymer is selected from the group consisting of synthetic plastics, fibers, rubbers, polypeptides and polysaccharides.
26. The method of claim 23, wherein said aerogel carbon nanotubes have a weight concentration from about 0.001% to about 99%.
27. The method of claim 26, wherein said aerogel carbon nanotubes have a weight concentration of about 0.003%.
28. The method of claim 27, wherein said composite has a conductivity of about 10"3S/m.
29. The method of claim 23 or 24, wherein said composite is electrically conductive.
30. The method of claim 24, wherein said membrane has a volume resistance less than lΩcm.
31. The method of claim 24, wherein said membrane is thermally conductive.
32. The method of claim 31, wherein said membrane has a thermal conductivity of about 300W/mK.
33. A method for preparing an inorganic composite material, said method comprising: admixing an inorganic compound with a plurality of aerogel carbon nanotubes to form a mixture; heating said mixture; and hot-pressing said mixture under conditions sufficient to form an inorganic composite material.
34. The method of claim 33, wherein said aerogel carbon nanotubes have a weight concentration of about 1%.
35. The method of claim 33, wherein said mixture is heated at a temperature from about 800C to about 5000C for about 0.5 to about 72 hours.
36. The method of claim 35, wherein said mixture is heated at 110 0C for about 24 hours.
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