Patent Publication Number: US-11040468-B2

Title: Method for making carbon nanotube composite structure

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 15/844,509, filed on Dec. 15, 2017, entitled, “METHOD FOR CARBON NANOTUBE COMPOSITE STRUCTURE”, which claims all benefits accruing under 35 U.S.C. § 119 from China Patent Application No. 201710365100.8, filed on May 22, 2017, in the China National Intellectual Property Administration, the disclosure of which is incorporated herein by reference. 
    
    
     FIELD 
     The present application relates to a method for making a carbon nanotube composite structure. 
     BACKGROUND 
     Carbon nanotubes are a novel carbonaceous material having extremely small size and extremely large specific surface area. Carbon nanotubes have interesting and potentially useful electrical and mechanical properties, and have been widely used in various fields such as emitters, gas storage and separation, chemical sensors, and high strength composites. 
     The composite of carbon nanotubes and polymer can be formed by two methods. One method includes dispersing the carbon nanotubes into an organic solvent to form a carbon nanotube dispersion, mixing the carbon nanotube dispersion and a monomer solution, and polymerizing the monomer. However, the carbon nanotubes have poor dispersion in the organic solvent, which affects the uniformity of the carbon nanotubes in the carbon nanotube composite structure. Another method includes completely melting the polymer, and mixing the melted polymer and the carbon nanotubes. However, the carbon nanotubes have poor dispersion in the melted polymer because the melted polymer has greater viscosity. Thus, the uniformity of the carbon nanotubes in the carbon nanotube composite structure is still poor. 
     What is needed, therefore, is to provide a method for making a carbon nanotube composite structure that can overcome the above-described shortcomings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementations of the present technology will now be described, by way of example only, with reference to the attached figures, wherein: 
         FIG. 1  is a schematic process flow of one embodiment of a method for making a carbon nanotube composite structure. 
         FIG. 2  is a scanning electron microscope (SEM) image of a drawn carbon nanotube film. 
         FIG. 3  is an SEM image of a flocculated carbon nanotube film. 
         FIG. 4  is an SEM image of a pressed carbon nanotube film including a plurality of carbon nanotubes arranged along a same direction. 
         FIG. 5  is an SEM image of a pressed carbon nanotube film including a plurality of carbon nanotubes which is arranged along different directions. 
         FIG. 6  is an SEM image of a forth surface of a CNT/PI composite structure. 
         FIG. 7  is an SEM image of the forth surface of the CNT/PI composite structure coated with a gold film. 
         FIG. 8  is an atomic force microscope (AFM) image of the forth surface of the CNT/PI composite structure. 
         FIG. 9  is an AFM image of the forth surface of the CNT/PI composite structure coated with a gold film. 
         FIG. 10  is a schematic process flow of another embodiment of a method for making a carbon nanotube composite structure. 
         FIG. 11  is a schematic process flow of yet another embodiment of a method for making a carbon nanotube composite structure. 
         FIG. 12  is a schematic process flow of yet another embodiment of a method for making a carbon nanotube composite structure. 
     
    
    
     DETAILED DESCRIPTION 
     It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. The drawings are not necessarily to scale, and the proportions of certain parts may be exaggerated to illustrate details and features better. The description is not to be considered as limiting the scope of the embodiments described herein. 
     Several definitions that apply throughout this disclosure will now be presented. 
     The term “substantially” is defined to be essentially conforming to the particular dimension, shape or other word that substantially modifies, such that the component need not be exact. For example, substantially cylindrical means that the object resembles a cylinder, but can have one or more deviations from a true cylinder. The term “comprising” means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in a so-described combination, group, series and the like. 
     The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
     Referring to  FIG. 1 , a method for making a carbon nanotube composite structure  130  of one embodiment includes the following steps: 
     S 1 , placing a carbon nanotube structure  110  on a first surface  102  of a substrate  100 , wherein the carbon nanotube structure  110  has a second surface  112  and a third surface  114  opposite to the second surface  112 , and the third surface  114  is in direct contact with the first surface  102 ; 
     S 2 , coating a monomer solution  140  on the carbon nanotube structure  110 , wherein the monomer solution  140  is formed by dispersing a certain amount of monomers into an organic solvent; 
     S 3 , polymerizing the monomer; and 
     S 4 , removing the substrate  100 . 
     In the step S 1 , the carbon nanotube structure  110  includes a plurality of carbon nanotubes  118  uniformly distributed therein. A gap  116  is defined between adjacent carbon nanotubes  118 . The plurality of carbon nanotubes  118  is parallel to the second surface  112  and the third surface  114 . The plurality of carbon nanotubes  118  is parallel to the first surface  102 . The plurality of carbon nanotubes  118  can be combined by van der Waals attractive force. The carbon nanotube structure  110  can be a substantially pure structure of the carbon nanotubes  118 , with few impurities. The plurality of carbon nanotubes  118  may be single-walled, double-walled, multi-walled carbon nanotubes, or their combinations. The carbon nanotubes  118  which are single-walled have a diameter of about 0.5 nanometers (nm) to about 50 nm. The carbon nanotubes  118  which are double-walled have a diameter of about 1.0 nm to about 50 nm. The carbon nanotubes  118  which are multi-walled have a diameter of about 1.5 nm to about 50 nm. 
     The plurality of carbon nanotubes  118  in the carbon nanotube structure  110  can be orderly or disorderly arranged. The term ‘disordered carbon nanotube  118 ’ refers to the carbon nanotube structure  110  where the carbon nanotubes  118  are arranged along many different directions, and the aligning directions of the carbon nanotubes  118  are random. The number of the carbon nanotubes  118  arranged along each different direction can be almost the same (e.g. uniformly disordered). The carbon nanotubes  118  can be entangled with each other. The term ‘ordered carbon nanotube  118 ’ refers to the carbon nanotube structure  110  where the carbon nanotubes  118  are arranged in a consistently systematic manner, e.g., the carbon nanotubes  118  are arranged approximately along a same direction and/or have two or more sections within each of which the carbon nanotubes  118  are arranged approximately along a same direction (different sections can have different directions). The carbon nanotube structure  110  can be a carbon nanotube layer structure including a plurality of drawn carbon nanotube films, a plurality of flocculated carbon nanotube films, or a plurality of pressed carbon nanotube films. 
     Referring to  FIG. 2 , the drawn carbon nanotube film includes a plurality of successive and oriented carbon nanotubes  118  joined end-to-end by van der Waals attractive force therebetween. The carbon nanotubes  118  in the drawn carbon nanotube film extend along the same direction. The carbon nanotubes are parallel to a surface of the drawn carbon nanotube film. The drawn carbon nanotube film is a free-standing film. The drawn carbon nanotube film can bend to desired shapes without breaking. A film can be drawn from a carbon nanotube array to form the drawn carbon nanotube film. 
     If the carbon nanotube structure  110  includes at least two stacked drawn carbon nanotube films, adjacent drawn carbon nanotube films can be combined by only the van der Waals attractive force therebetween. Additionally, when the carbon nanotubes  118  in the drawn carbon nanotube film are aligned along one preferred orientation, an angle can exist between the orientations of carbon nanotubes  118  in adjacent drawn carbon nanotube films, whether stacked or adjacent. An angle between the aligned directions of the carbon nanotubes  118  in two adjacent drawn carbon nanotube films can be in a range from about 0 degree to about 90 degrees. Stacking the drawn carbon nanotube films will improve the mechanical strength of the carbon nanotube structure  110 , further improving the mechanical strength of the carbon nanotube composite structure  130 . In one embodiment, the carbon nanotube structure  110  includes two layers of the drawn carbon nanotube films, and the angle between the aligned directions of the carbon nanotubes  118  in two adjacent drawn carbon nanotube films is about 90 degrees. 
     Referring to  FIG. 3 , the flocculated carbon nanotube film includes a plurality of long, curved, disordered carbon nanotubes  118  entangled with each other. The flocculated carbon nanotube film can be isotropic. The carbon nanotubes  118  can be substantially uniformly dispersed in the flocculated carbon nanotube film. Adjacent carbon nanotubes  118  are acted upon by van der Waals attractive force to obtain an entangled structure. Due to the carbon nanotubes  118  in the flocculated carbon nanotube film being entangled with each other, the flocculated carbon nanotube film has excellent durability, and can be fashioned into desired shapes with a low risk to the integrity of the flocculated carbon nanotube film. Further, the flocculated carbon nanotube film is a free-standing film. 
     Referring to  FIGS. 4 and 5 , the pressed carbon nanotube film includes a plurality of carbon nanotubes  118 . The carbon nanotubes  118  in the pressed carbon nanotube film can be arranged along a same direction, as shown in  FIG. 4 . The carbon nanotubes  118  in the pressed carbon nanotube film can be arranged along different directions, as shown in  FIG. 5 . The carbon nanotubes  118  in the pressed carbon nanotube film can rest upon each other. An angle between a primary alignment direction of the carbon nanotubes  118  and a surface of the pressed carbon nanotube film is about 0 degree to approximately 15 degrees. The greater the pressure applied, the smaller the angle obtained. If the carbon nanotubes  118  in the pressed carbon nanotube film are arranged along different directions, the pressed carbon nanotube film can have properties that are identical in all directions substantially parallel to the surface of the pressed carbon nanotube film. Adjacent carbon nanotubes  118  are attracted to each other and are joined by van der Waals attractive force. Therefore, the pressed carbon nanotube film is easy to bend to desired shapes without breaking. Further, the pressed carbon nanotube film is a free-standing film. 
     The term “free-standing” includes, but not limited to, the drawn carbon nanotube film, the flocculated carbon nanotube film, or the pressed carbon nanotube film that does not have to be supported by a substrate. For example, the free-standing the drawn carbon nanotube film, the flocculated carbon nanotube film, or the pressed carbon nanotube film can sustain the weight of itself when it is hoisted by a portion thereof without any significant damage to its structural integrity. So, if the free-standing the drawn carbon nanotube film, the flocculated carbon nanotube film, or the pressed carbon nanotube film is placed between two separate supporters, a portion of the free-standing the drawn carbon nanotube film, the flocculated carbon nanotube film, or the pressed carbon nanotube film, not in contact with the two supporters, would be suspended between the two supporters and yet maintain film structural integrity. 
     The first surface  102  of the substrate  100  is very smooth. The height difference between the highest position of the first surface  102  and the lowest position of the first surface  102  is nanoscale. The height difference between the highest position of the substrate surface  102  and the lowest position of the substrate surface  102  can be defines as a smoothness of the substrate surface  102 . The smoothness can also be greater than or equal to 0 nanometers and less than or equal to 30 nanometers. The smoothness can be greater than or equal to 0 nanometers and less than or equal to 20 nanometers. The smoothness can be greater than or equal to 0 nanometers and less than or equal to 10 nanometers. The material of the substrate  100  should be sapphire, monocrystalline quartz, gallium nitride, gallium arsenide, silicon, graphene, or polymer. The melting point of the substrate  100  needs to be greater than the temperature of polymerizing the monomer. The length, width, and thickness of the substrate  100  are not limited. In one embodiment, the substrate  100  is a silicon wafer. 
     Some organic solvent can be dripped on the second surface  112  of the carbon nanotube structure  110 . When the organic solvent is volatilized, the air between the carbon nanotube structure  110  and the first surface  102  can be removed under the surface tension of the organic solvent. Thus, the carbon nanotube structure  110  can be tightly bonded to the first surface  102  of the substrate  100 . The organic solvent can be ethanol, methanol, acetone, dichloroethane, or chloroform. 
     In the step S 2 , the monomer can be any monomer that can be polymerized to form a polymer  120 . The polymer  120  includes a phenolic resin (PF), an epoxy resin (EP), a polyurethane (PU), a polystyrene (PS), a polymethylmethacrylate (PMMA), a polycarbonate (PC), polyethylene terephthalate (PET), phenylcyclobutene (BCB), polycycloolefin or polyimide (PI), polyvinylidene fluoride (PVDF), and the like. In one embodiment, the monomer is an imide, and the polymer  120  is a polyimide. The organic solvent includes ethanol, methanol, acetone, dichloroethane or chloroform. 
     The monomer solution  140  has a small viscosity and good fluidity. When the monomer solution  140  is coated on the second surface  112  of the substrate  100 , the monomer solution  140  can pass through the gaps  116  and contact with a part of the first surface  102 . The first part of the substrate  102  is in direct contact with and coated by the monomer solution  140 , the second part of the substrate surface  102  is in direct contact with the carbon nanotubes  118 . The method for coating the monomer solution  140  is not limited and can be spin coating, injection coating, or the like. In one embodiment, the monomer solution  140  is coated on the carbon nanotube structure  110  by spin coating. 
     In the step S 3 , the method for polymerizing the monomer is not limited, such as high temperature treatment. In one embodiment, the substrate  100  and the carbon nanotube structure  110  coated with the monomer solution  140  are placed in a reaction furnace. The reaction furnace is heated to the temperature of polymerizing the monomer, and the monomer is polymerized to form the polymer  120 . The part surface of the carbon nanotube  118 , that is directly contacted with the first surface  102  of the substrate  100 , is defined as a contact surface  117 . Because the carbon nanotubes  118  are tubular, the third surface  114  of the carbon nanotube structure  110  is in fact a ups and downs surface. The contact surface  117  is parts of the third surface  114 . Except for the contact surface  117 , the rest of third surface  114  is in direct contact with the monomer solution  140 . The gaps  116  are filled with the monomer solution  140 . When the monomer is polymerized to form the solid polymer  120 , the polymer  120  is combined with the carbon nanotube structure  110  to form the carbon nanotube composite structure  130 . 
     In the step S 4 , the method for removing the carbon nanotube composite structure  130  from the first surface  102  of the substrate  100  is not limited. The carbon nanotube composite structure  130  can be peeled off from the first surface  102  of the substrate  100  by water immersion, blade, tape, or other tools. 
     The smoothness of the substrate surface  102  is nanoscale, thus the contact surface  117  can be in direct contact with the substrate surface  102  during coating the monomer solution  140  and polymerizing the monomer. Thus, there is no monomer solution  140  between the contact surface  117  and the first surface  102  during coating the monomer solution  140  and polymerizing the monomer. Thus, when the carbon nanotube composite structure  130  is peeled from the first surface  102 , the contact surface  117  is exposed and is not coated by the polymer  120 . A part of outer wall of the carbon nanotube  118  directly contacting with the first surface  102  is exposed and is not covered by the polymer  120 . Except for the contact surface  117 , the rest of the outer walls of carbon nanotubes  118  are coated by and in direct contact with the polymer  120 . 
     The carbon nanotube composite structure  130  includes the plurality of carbon nanotubes  118  and the polymer  120 . The plurality of carbon nanotubes  118  are uniformly dispersed in the polymer  120 . The plurality of carbon nanotubes  118  can be joined end-to-end and extend along the same direction. The plurality of carbon nanotubes  118  can also extend along different directions, or entangled with each other to form a network-like structure. The carbon nanotube composite structure  130  has a forth surface  132 . The forth surface  132  is in direct contact with the first surface  102  before peeling the carbon nanotube composite structure  130  off from the substrate  100 . The length direction of the plurality of carbon nanotubes  118  is parallel to the forth surface  132 . The surface of the polymer  120  near the substrate  100  is defined as a lower surface  122 . The contact surface  117  and the lower surface  122  together form the forth surface  132 . Thus, the contact surface  117  is a part of the forth surface  132  and exposed from the polymer  120 . The contact surface  117  is an exposed surface and can protrude out of the lower surface  122  of the polymer  120 . The height difference between the exposed surface and the lower surface  122  of the polymer  120  is nanoscale. Since the smoothness of the first surface  102  is at nanoscale level, the forth surface  132  is also smooth at nanoscale level. The height difference between the contact surface  117  and the lower surface  122  can be greater than or equal to 0 nanometers and less than or equal to 30 nanometers. The height difference between the contact surface  117  and the lower surface  122  can be greater than or equal to 0 nanometers and less than or equal to 20 nanometers. The height difference between the contact surface  117  and the lower surface  122  can also be greater than or equal to 0 nanometers and less than or equal to 10 nanometers. 
     In one embodiment, the polymer  120  is polyimide, the carbon nanotube structure  110  is two stacked drawn carbon nanotube films, and the angle between the aligned directions of the carbon nanotubes  118  in two adjacent drawn carbon nanotube films is about 90 degrees. 
     In one embodiment, to synthesize poly(amic acid) (PAA) solution, 2.0024 g of ODA(10 mmol) was placed in a three-neck flask containing 30.68 mL of anhydrous DMAc under nitrogen purge at room temperature. After ODA is completed dissolved in DMAc, 2.1812 g of PMDA(10 mmol) is added in one portion. Thus, the solid content of the solution is about 12%. The mixture is stirred at room temperature under nitrogen purge for 12 h to produce a PAA solution. The two stacked drawn carbon nanotube films are located on a silicon wafer, wherein the angle between the aligned directions of the carbon nanotubes  118  in two adjacent drawn carbon nanotube films is about 90 degrees. Then the PAA solution is coated on the two stacked drawn carbon nanotube films, and the PAA solution will gradually penetrate into the two stacked drawn carbon nanotube films to form a preform. The preform is thermal imidized in muffle furnace at 80° C., 120° C., 180° C., 300° C., and 350° C. for 1 h respectively to form a CNT/PI composite structure. Finally, the CNT/PI composite structure is peeled off from the silicon wafer. 
       FIG. 6  is an SEM image of the first composite structure surface of a CNT/PI composite structure. As shown in  FIG. 6 , the carbon nanotubes  118  are uniformly dispersed in the CNT/PI composite structure. 
       FIG. 7  is an SEM image of the first composite structure surface of the CNT/PI composite structure coated with a gold film, and the thickness of the gold film is about 1 nm. As shown in  FIG. 7 , the forth surface  132  is a smooth surface with no ups and downs from the naked eye. The height difference between the highest position of the forth surface  132  and the lowest position of the forth surface  132  is nanoscale.  FIG. 8  is an atomic force microscope (AFM) image of the first composite structure surface of the CNT/PI composite structure.  FIG. 9  is an AFM image of the first composite structure surface of the CNT/PI composite structure coated with a gold film, and the thickness of the gold film is about 3 nm. As shown in  FIG. 8  and  FIG. 9 , it is also find that the forth surface  132  is a smooth surface. 
     Referring to  FIG. 10 , a method for making a carbon nanotube composite structure  160  of another embodiment includes the following steps: 
     S 21 , placing the carbon nanotube structure  110  on the first surface  102  of the substrate  100 , wherein the carbon nanotube structure  110  has the second surface  112  and the third surface  114  opposite to the second surface  112 , and the third surface  114  is in direct contact with the first surface  102 ; 
     S 22 , locating a graphene layer  150  on the second surface  112 ; 
     S 23 , coating a monomer solution  140  on the graphene layer  150  and the carbon nanotube structure  110 , wherein the monomer solution  140  is formed by dispersing the monomer into the organic solvent; 
     S 24 , polymerizing the monomer; and 
     S 25 , removing the substrate  100 . 
     In this embodiment, the method for making the carbon nanotube composite structure  160  is similar to the method for making the carbon nanotube composite structure  130  above except that the graphene layer  150  is located on the second surface  112  before coating the monomer solution  140 . 
     The graphene layer  150  is a two dimensional film structure. If the graphene layer  150  includes a plurality of graphene films, the plurality of graphene films can overlap each other to form a large area. The graphene film is a one-atom thick planar sheet composed of a plurality of sp 2 -bonded carbon atoms. The graphene layer  150  can be a free-standing structure. The term “free-standing structure” means that the graphene layer  150  can sustain the weight of itself when it is hoisted by a portion thereof without any significant damage to its structural integrity. So, if the graphene layer  150  is placed between two separate supports, a portion of the graphene layer  150  not in contact with the two supports, would be suspended between the two supports and yet maintain structural integrity. When the plurality of graphene films overlap each other, a gap is formed between adjacent two graphene films. During coating the monomer solution  140 , the monomer solution  140  can pass through the graphene layer  150  and the carbon nanotube structure  110  to arrive at the first surface  102 , because both the graphene layer  150  and the carbon nanotube structure  110  have gaps  106 . 
     Referring to  FIG. 11 , a method for making a carbon nanotube composite structure  170  of yet another embodiment includes the following steps: 
     S 31 , placing the carbon nanotube structure  110  on the first surface  102  of the substrate  100  to form a preform structure  172 , wherein the carbon nanotube structure  110  has the second surface  112  and the third surface  114  opposite to the second surface  112 , and the third surface  114  is in direct contact with the first surface  102 ; 
     S 32 , locating two preform structures  172  on a base  174 , wherein the two preform structures  172  are spaced from each other, the substrates  100  of the two preform structures  172  and the base  174  form a mold  176  having an opening, and the carbon nanotube structures  110  of the two preform structures  172  are opposite to each other and inside of the mold  176 ; 
     S 33 , injecting the monomer solution  140  into the inside of the mold  176  from the opening of the mold  176 , wherein the monomer solution  140  is formed by dispersing the monomer into the organic solvent; 
     S 34 , polymerizing the monomer; and 
     S 35 , removing the substrates  100  and the base  174 . 
     In this embodiment, the method for making the carbon nanotube composite structure  170  is similar to the method for making the carbon nanotube composite structure  130  above except the steps S 32  and S 33 . 
     In the step S 32 , the method for making the mold  176  is not limited. For example, the two preforms structures  172  and the base  174  are fixed together by sticking or mechanically fastening to form the mold  176 . In one embodiment, the two preforms structures  172  and the base  174  are fixed by a sealant, and the sealant is  706 B vulcanized silicon rubber. The opening is on the top of the mold  176 . The carbon nanotube structure  110  of each of the two preforms structures  172  is located inside of the mold  176 . The substrate  100  of each of the two preforms structures  172  forms the sidewall of the mold  176 . The material of the base  174  is not limited, such as glass, silica, metal or metal oxide. In one embodiment, the material of the substrate  174  is glass. The carbon nanotube structure  110  in the mold  176  would not fall off from the substrate  100  because the carbon nanotube structure  110  itself has viscosity. The organic solvent can be dripped so that the carbon nanotube structure  110  is firmly adhered to the substrate  100 . 
     Furthermore, the length or width of the carbon nanotube structure  110  can be greater than the length or width of the first surface  102 . When the carbon nanotube structure  110  is disposed on the first surface  102 , the excess carbon nanotube structure  110  can be folded into the back surface of the substrate  100 , and an adhesive can be applied to the back surface of the substrate  100 . Thus, the carbon nanotube structure  110  in the mold  176  is firmly adhered to the substrate  100  and would not fall off from the substrate  100 . The back surface is opposite to the first surface  102 , and the first surface  102  can be considered the front surface. The melting point of the adhesive needs to be greater than the temperature of polymerizing the monomer. 
     In the step S 33 , the monomer solution  140  is slowly injected into the inside of the mold  176  along the inner wall of the mold  176 . The monomer solution  140  completely submerges the carbon nanotube structure  110 . The monomer solution  140  would not break the integrity of the carbon nanotube structure  110  during injecting the monomer solution  140  because the carbon nanotube structure  110  is supported by the substrate  100 . 
     Referring to  FIG. 12 , a method for making a carbon nanotube composite structure  180  of yet another embodiment includes the following steps: 
     S 41 , placing the carbon nanotube structure  110  on the first surface  102  of the substrate  100 , wherein the carbon nanotube structure  110  has the second surface  112  and the third surface  114  opposite to the second surface  112 , and the third surface  114  is in direct contact with the first surface  102 ; 
     S 42 , placing the carbon nanotube structure  110  and the substrate  100  into a container  182 , wherein the container  182  has an opening; 
     S 43 , injecting the monomer solution  140  into the container  182  from the opening of the container  182 , wherein the monomer solution  140  is formed by dispersing the monomer into the organic solvent; 
     S 44 , polymerizing the monomer; and 
     S 45 , removing the substrates  100  and the container  182 . 
     In this embodiment, the method for making the carbon nanotube composite structure  180  is similar to the method for making the carbon nanotube composite structure  130  above except the steps S 42  and S 43 . 
     In the step S 42 , the container  182  has a bottom. When the carbon nanotube structure  110  and the substrate  100  are located in the container  182 , the substrate  100  is located on and in direct contact with the bottom of the container  182 . The carbon nanotube structure  110  is spaced from the bottom by the substrate  100 . The material of the container  182  is not limited, such as silica, metal, glass, or metal oxide. In one embodiment, the material of the container  182  is glass. 
     In the step S 43 , the monomer solution  140  does not break the integrity of the carbon nanotube structure  110  during injecting the monomer solution  140  because the carbon nanotube structure  110  is supported by the substrate  100 . The amount of the monomer solution  140  can be adjusted so that the monomer solution  140  submerges the entire carbon nanotube structure  110 , or submerges only a part of the carbon nanotube structure  110 . When the monomer solution  140  submerges only a part of the carbon nanotube structure  110 , the thickness of the polymer  120  is less than the thickness of the carbon nanotube structure  110 . Thus, in the carbon nanotube composite structure  180 , some carbon nanotubes  118  are located in and completely coated by the polymer  120 , and some carbon nanotubes  118  are exposed from and extend out of the polymer  120 . In one embodiment, the carbon nanotube structure  110  includes three stacked drawn carbon nanotube films, and the monomer solution  140  submerges only a part of the carbon nanotube structure  110 . In the carbon nanotube composite structure  180 , the first drawn carbon nanotube film, the second drawn carbon nanotube film and the third drawn carbon nanotube film are stacked. The second drawn carbon nanotube film is between the first drawn carbon nanotube film and the third drawn carbon nanotube film. The entire outer walls of the carbon nanotubes  118  in the second drawn carbon nanotube film are coated by the polymer  120 . Partial outer wall of the carbon nanotubes  118  in the first drawn carbon nanotube film are exposed. The contact surfaces  117  of the carbon nanotubes  118  in the third drawn carbon nanotube film are exposed. 
     The monomer solution  140  has a smaller viscosity than the molten polymer, thus after coating the monomer solution  140  and polymerizing the monomer, the carbon nanotubes  118  can uniformly dispersed in the polymer  120 . In above methods, the substrate  100  has a nanoscale smooth first surface  102 , thus some carbon nanotubes of the carbon nanotube composites  130 ,  160 ,  170 , and  180  are exposed from the polymer  120 , improving the conductivity of the carbon nanotube composites  130 ,  160 ,  170 , and  180 . 
     The embodiments shown and described above are only examples. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the detail, including in matters of shape, size and arrangement of the parts within the principles of the present disclosure up to, and including, the full extent established by the broad general meaning of the terms used in the claims. 
     Additionally, it is also to be understood that the above description and the claims drawn to a method may comprise some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps.