Method for preparing carbon nanotube continuous network film

Abstract

The application provides a preparation method of a continuous network film of carbon nanotubes. The method comprises the following steps: obtaining a preset amount of carbon nanotube powder, placing the carbon nanotube powder in a preset dispersion medium to obtain a carbon nanotube dispersion; placing the carbon nanotube dispersion on a substrate surface to obtain an original carbon nanotube film in which the carbon nanotubes are mutually separated and loosely overlapped; placing the original carbon nanotube film and the substrate in a heating furnace cavity; setting a heating program to make the original carbon nanotube film and the substrate interact with each other, so that the carbon nanotubes in the original carbon nanotube film are assembled to obtain an assembled continuous network film of carbon nanotubes. The method can improve the transparency, conductivity, mechanical properties and other properties of the assembled continuous network film of carbon nanotubes, realize large-area, flexible and self-supporting, and the substrate area is not limited during preparation. The length and width of the assembled continuous network film of carbon nanotubes are not limited, so that large-area preparation is realized.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a method for preparing a continuous network of carbon nanotube films. Background Technology

[0002] Flexible transparent conductive film (FTCF) is widely used in modern electronic devices, including displays in various electronic terminals, dimming windows in smart buildings, defrosters for automotive and aircraft windows in the transportation sector, and solar cells in the energy industry. For FTCF, transparency, conductivity, and mechanical properties (such as flexibility and tensile strength) are crucial parameters, depending on the coverage, density / thickness, and structure of the conductive network. Indium tin oxide (ITO) possesses excellent electrical and optical properties and is currently the most widely used transparent conductive material. However, indium's limited reserves, being a non-renewable resource, hinder the low-cost, sustainable production of ITO. Furthermore, ITO's brittleness and high areal density make it difficult to use in cutting-edge fields requiring flexibility and lightweight design, such as flexible displays, wearable devices, and aerospace.

[0003] Over the past few decades, various conductive nanomaterials, such as conductive polymers, MXene, graphene, metal nanoparticles, carbon nanotubes (CNTs), and metal nanowires, have been used to manufacture FTCFs due to their excellent conductivity and solution processability. Among them, CNTs are considered the most competitive and ideal material because of their excellent electrical and optical properties, flexibility, outstanding stability, and lightweight, radiation resistance, and ultra-fatigue resistance properties urgently needed for future military and aerospace applications. On the other hand, the prerequisite for the widespread application of FTCFs is not only that they possess excellent physical properties, but also that they can be prepared on a large scale, even on a large scale. CNTs themselves can be mass-produced, and various dispersions already exist, demonstrating the potential for large-scale production.

[0004] CNT FTCFs are generally prepared through two conventional methods: direct growth, such as by arc discharge, laser ablation, and chemical vapor deposition (CVD); and post-processing powder film deposition, with solution / slurry deposition (SBD) being the most common of the various physicochemical methods, where CNT dispersants are used to coat the film. However, due to their respective limitations, neither CVD nor SBD methods can currently achieve large-area, large-scale production of CNT FTCFs with excellent transparent conductivity that meet industrial production requirements. Direct growth methods can produce CNT FTCFs with good physical properties, but their scale is limited and costs are high. SBD, based on a wide range of dispersants and low cost, shows potential for large-area, large-scale production, but its methods for improving the physical properties and controlling the structure of CNT FTCFs are very limited, especially in addressing the weak interactions and disordered, loose bonding between CNTs dispersed in the SBD method. The ever-evolving field of device manufacturing, especially the development of next-generation flexible electronics / devices, flexible optoelectronics / devices, and wearable devices / systems, places increasingly higher demands on the physical properties and application scalability of FTCFs. TCFs are required to not only possess excellent transparent conductivity but also flexibility, high strength, and even self-supporting transfer capabilities, while also being able to be fabricated on a large scale and over large areas. This would provide an effective solution to the key technical challenge of large-area TCFs. Therefore, developing a method to connect loosely X-shaped, relatively discrete CNTs into a continuous network structure, thereby improving their transparent conductivity and mechanical properties, while enabling large-scale production of CNT FTCFs without area limitations, is of great significance and application value. Summary of the Invention

[0005] In view of the above problems, the present invention proposes a method for preparing a continuous network thin film of carbon nanotubes that overcomes or at least partially solves the above problems.

[0006] One objective of this invention is to achieve large-area fabrication of continuous carbon nanotube network films.

[0007] A further objective of this invention is to prepare assembled carbon nanotube continuous network films with good performance based on carbon nanotube powder.

[0008] Specifically, the present invention provides a method for preparing a continuous network of carbon nanotube films, comprising:

[0009] A predetermined amount of carbon nanotube powder is placed in a predetermined dispersion medium to obtain a carbon nanotube dispersion.

[0010] A carbon nanotube dispersion was placed on the substrate surface to obtain a raw carbon nanotube film in which the carbon nanotubes were separated and loosely connected.

[0011] The original carbon nanotube film and the substrate were placed in the heating furnace cavity;

[0012] A heating program is set up to allow the original carbon nanotube film to interact with the substrate, thereby assembling the carbon nanotubes in the original carbon nanotube film to obtain an assembled carbon nanotube continuous network film.

[0013] Optionally, after the step of placing the carbon nanotube dispersion on the substrate surface, the method further includes:

[0014] A volatile organic solvent was added dropwise to the original carbon nanotube film to wet the original carbon nanotube film, thereby increasing the contact between the loose carbon nanotubes and the substrate surface.

[0015] After the organic solvent has evaporated, the original carbon nanotube film and the substrate are placed in the heating furnace cavity.

[0016] Optionally, the carbon nanotubes in the carbon nanotube powder include at least one or a mixture of any of the following: single-walled carbon nanotubes, double-walled carbon nanotubes, few-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0017] The density of the carbon nanotube dispersion is greater than a preset density so that the sheet resistance of the carbon nanotube dispersion after being placed on the substrate surface is less than 10000 Ω / □.

[0018] Pre-defined dispersions include atmospheric dispersion, liquid dispersion, and carbon nanotube powder spreading;

[0019] The methods for placing carbon nanotube dispersions on the substrate surface include any one or a combination of multiple methods such as fluidized bed vapor deposition, powder coating deposition, powder vapor spraying, coating, blade coating, spraying, drop coating, centrifugal film formation, and powder pick-up.

[0020] Organic solvents include any one or more solvents selected from ethanol, propanol, butanol, ethylene glycol, isopropanol, acetone, n-hexane, cyclohexane, anisole, and chlorobenzene;

[0021] The substrate material includes any one of the following metals: copper, platinum, gold, nickel, titanium, iron, lead, palladium, silver, tungsten, aluminum, zinc, chromium, gold, or an alloy of any combination of these metals.

[0022] Optionally, the steps of causing the virgin carbon nanotube film to interact with the substrate include:

[0023] The substrate and the gas in the heating furnace cavity undergo surface reconstruction, which is accompanied by the transport of facet atoms that constitute the facets, forming facets. The facets appear as regular steps on the substrate surface at the mesoscale.

[0024] The facets interact with the original carbon nanotube film to remove impurities. At least some of the carbon nanotubes in the original carbon nanotube film move under the drive of the facets, and adjacent carbon nanotubes or bundles tend to come closer together, so that the carbon nanotubes in the original carbon nanotube film are assembled to obtain an assembled carbon nanotube continuous network film.

[0025] Optionally, the gas is a gas in the heating furnace cavity that can undergo surface reconstruction with the substrate, including a mixture of one or more of the same type of oxidizing or reducing gas;

[0026] The sources of gas include: any one or more of the following forms: gas, liquid, and solid.

[0027] Optionally, the step of surface reconstruction of the substrate with the gas in the heating furnace cavity to form facets includes:

[0028] The heating furnace cavity is purged to control the partial pressure of the gas in the heating furnace cavity that undergoes surface reconstruction with the substrate within a set range;

[0029] The furnace cavity is heated to control the surface reconstruction of the substrate with the gas, thereby forming facets.

[0030] Optionally, the steps of causing the facets to interact with the original carbon nanotube film include:

[0031] Continue heating to gradually grow the facets on the substrate, thereby controlling at least some of the carbon nanotubes in the original carbon nanotube film to gradually adhere to the facets, and the impurities in the original carbon nanotube film to gradually dissolve.

[0032] As the facets grow, the carbon nanotubes in the original carbon nanotube film move and approach each other, thus assembling the carbon nanotubes into a long common segment Y-shaped interconnected network, resulting in a continuous network film of assembled carbon nanotubes.

[0033] Optionally, the temperature range for forming the facets is configured to be greater than or equal to 400°C;

[0034] The temperature range at which the carbon nanotube network gradually adheres to the facet is configured to be greater than or equal to 600°C.

[0035] The temperature range for the gradual dissolution of impurities is set to be greater than or equal to 500℃.

[0036] The steps to make the facets interact with the original carbon nanotube film also include: continuing to heat the film to gradually eliminate the morphological features of the facets, wherein the temperature range at which the morphological features of the facets gradually disappear is configured to be greater than or equal to 800°C.

[0037] The gases used in the gas washing process include any one or a combination of nitrogen, argon, and hydrogen.

[0038] Optionally, the step of causing the facets to interact with the original carbon nanotube film further includes:

[0039] The assembled continuous network of carbon nanotube films was cooled at a preset cooling rate.

[0040] The cooled assembled continuous network of carbon nanotubes was etched away from the substrate in a substrate etchant, floated on the surface of the substrate etchant, and then rinsed with a rinsing solution.

[0041] Optionally, before placing the carbon nanotube dispersion on the substrate surface, the method further includes: pre-treating the substrate to make the substrate surface flat;

[0042] Pretreatment methods include any one of mechanical polishing, electrochemical polishing, high-temperature annealing, or any combination of these methods;

[0043] The shape of the substrate includes foil substrates.

[0044] The method for preparing a continuous carbon nanotube network film of the present invention firstly obtains a predetermined amount of carbon nanotube powder and places it in a predetermined dispersion medium to obtain a carbon nanotube dispersion; the carbon nanotube dispersion is placed on the surface of a substrate to obtain a raw carbon nanotube film in which the carbon nanotubes are separated and loosely overlapped; the raw carbon nanotube film and the substrate are placed in a heating furnace cavity; a heating program is set to cause the raw carbon nanotube film and the substrate to interact, thereby assembling the carbon nanotubes in the raw carbon nanotube film to obtain an assembled continuous carbon nanotube network film. The assembled carbon nanotube continuous network film obtained by this method, as a flexible transparent conductive carbon nanotube film (i.e., CNT FTCF), can assemble the originally loosely X-shaped overlapping carbon nanotubes into a long common segment Y-shaped interconnected continuous network under faceting drive, thereby optimizing the network structure at the microscopic level and synergistically improving various properties of CNT FTCF such as transparency, conductivity, and mechanical properties. Furthermore, this method uses a method based on placing carbon nanotube powder on a substrate to obtain the initial loosely X-shaped overlapping structure of CNTs and CNT bundles. The substrate area is not limited, and it has scalability, which can produce assembled CNT FTCF with no limit on length and width. Therefore, it can realize large-scale, batch, large-area preparation.

[0045] Furthermore, the method for preparing the continuous carbon nanotube network film of the present invention involves setting a heating program in a heating furnace cavity to cause surface reconstruction between the substrate and the gas in the furnace cavity. This, along with the transport of facet atoms constituting the facets, forms facets, which, at the mesoscopic scale, appear as regular steps on the substrate surface. Subsequently, the facets interact with the original carbon nanotube film, thereby removing impurities from the original film. At least some of the carbon nanotubes in the original film shift position under the drive of the facets, and adjacent carbon nanotubes or bundles tend to move closer together, assembling the carbon nanotubes in the original film to obtain an assembled continuous carbon nanotube network film. The assembled continuous carbon nanotube network film obtained by this method, as a transparent conductive film, forms a more efficient conductive network internally compared to the original carbon nanotube film, improving the performance of the transparent conductive film and also achieving self-support.

[0046] The above and other objects, advantages and features of the present invention will become more apparent to those skilled in the art from the following detailed description of specific embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0047] The following sections will describe some specific embodiments of the invention in a detailed manner by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or portions. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0048] Figure 1 This is a schematic flowchart of a method for preparing a continuous network thin film of carbon nanotubes according to an embodiment of the present invention;

[0049] Figure 2 This is a schematic flowchart of a method for preparing a continuous network thin film of carbon nanotubes according to another embodiment of the present invention;

[0050] Figure 3A A copper-faceted SEM image with a scale bar of 2 μm is shown, illustrating a method for preparing a continuous network thin film of carbon nanotubes according to an embodiment of the present invention.

[0051] Figure 3B A copper-faceted SEM image with a scale bar of 500 nm is shown, illustrating a method for preparing a continuous network thin film of carbon nanotubes according to an embodiment of the present invention.

[0052] Figure 4A This is a schematic diagram illustrating the facet-growth process of a method for preparing a continuous carbon nanotube network thin film according to an embodiment of the present invention.

[0053] Figure 4BThis is a schematic diagram showing the gradual growth of facets in a method for preparing a continuous carbon nanotube network film according to an embodiment of the present invention.

[0054] Figure 4C This is a schematic diagram of the interaction between the facets and carbon nanotubes in a method for preparing a continuous network thin film of carbon nanotubes according to an embodiment of the present invention.

[0055] Figure 4D This is a schematic diagram showing the disappearance of facet morphology features in a method for preparing a continuous network thin film of carbon nanotubes according to an embodiment of the present invention.

[0056] Figure 5A The image shows a 500 nm scale SEM image of the original carbon nanotube film on a copper foil surface, illustrating a method for preparing a continuous network of carbon nanotube films according to an embodiment of the present invention.

[0057] Figure 5B The image shows an SEM image of an assembled carbon nanotube continuous network film on a faceted copper foil surface, with a scale bar of 500 nm, illustrating a method for preparing a carbon nanotube continuous network film according to an embodiment of the present invention.

[0058] Figure 6A An optical photograph with a scale bar of 2 cm shows a method for preparing a continuous carbon nanotube network film according to an embodiment of the present invention, in which the assembled continuous carbon nanotube network film based on direct coating is self-supporting and floats on the water surface.

[0059] Figure 6B An optical photograph with a scale bar of 2 cm shows the transfer of an assembled carbon nanotube continuous network film based on direct coating onto a quartz substrate, illustrating a method for preparing a carbon nanotube continuous network film according to an embodiment of the present invention.

[0060] Figure 7 Optical photographs with a scale bar of 2 cm showing the preparation method of a continuous carbon nanotube network film according to an embodiment of the present invention, showing the transfer of assembled continuous carbon nanotube network films with different transmittances based on direct coating to a quartz substrate.

[0061] Figure 8 These are test images of the transparency and conductivity of assembled carbon nanotube continuous network films with different transmittances based on direct coating, prepared by a method for preparing carbon nanotube continuous network films according to an embodiment of the present invention.

[0062] Figure 9A The image shows SEM images of the original loosely X-shaped overlapped CNTs and CNT bundles, all with a scale bar of 1 μm, illustrating a method for preparing a continuous carbon nanotube network film according to an embodiment of the present invention.

[0063] Figure 9BThe image shows SEM images of assembled carbon nanotube continuous network films with a scale bar of 1 μm, illustrating a method for preparing a carbon nanotube continuous network film according to an embodiment of the present invention.

[0064] Figure 10 The image shows SEM images of unassembled, loosely X-shaped CNTs and CNT bundles at a scale bar of 2 μm, illustrating a method for preparing a continuous carbon nanotube network film according to another embodiment of the present invention.

[0065] Figure 11 This is a transparent conductivity test image of a sample without carbon nanotube network assembly, prepared by a method for preparing a continuous carbon nanotube network thin film according to another embodiment of the present invention.

[0066] Figure 12 The image shows a 500 nm scale SEM image of a spray-assembled continuous carbon nanotube network film prepared by a method for preparing a continuous carbon nanotube network film according to another embodiment of the present invention.

[0067] Figure 13A The optical image shown is a self-supporting carbon nanotube continuous network film in ammonium persulfate, with a scale bar of 2 cm, illustrating a method for preparing a carbon nanotube continuous network film according to another embodiment of the present invention.

[0068] Figure 13B The image shows an optical image of the assembled carbon nanotube continuous network film, with a scale bar of 2 cm, on the surface of deionized water, illustrating a method for preparing a carbon nanotube continuous network film according to another embodiment of the present invention.

[0069] Figure 14 The image shows an optical image of the assembled carbon nanotube continuous network film in deionized water with a scale bar of 5 cm, illustrating a method for preparing a carbon nanotube continuous network film according to another embodiment of the present invention.

[0070] Figure 15A This invention illustrates a method for preparing a continuous carbon nanotube network film according to another embodiment of the present invention. The image shows a scale bar of 2 cm and an optical image of the assembled continuous carbon nanotube network-graphene film self-supporting in deionized water.

[0071] Figure 15B The image shows a 1 μm scale SEM image of an assembled carbon nanotube continuous network-graphene film, illustrating a method for preparing a carbon nanotube continuous network film according to another embodiment of the present invention. Detailed Implementation

[0072] Those skilled in the art should understand that the embodiments described below are merely a part of the embodiments of the present invention, and not all of the embodiments of the present invention. These partial embodiments are intended to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Based on the embodiments provided by the present invention, all other embodiments obtained by those skilled in the art without creative effort should still fall within the scope of protection of the present invention.

[0073] CNT FTCFs are generally prepared through two conventional methods: direct growth, such as arc discharge, laser ablation, and chemical vapor deposition (CVD); and post-processing powder deposition, with solution / slurry deposition (SBD) being the most common physicochemical method, where CNTs are coated to form a film. However, most current research on CVD-based carbon nanotube thin films remains in the small-area experimental stage, with only a few studies proposing large-area preparation methods. While the length of single-walled carbon nanotube flexible transparent conductive films (SWCNT–FTCF) is unlimited in continuous fabrication, its width is limited by the growth principle. Although the area of ​​self-supporting multi-walled carbon nanotube flexible transparent conductive films (MWCNT–FTCF) prepared by super-aligned array spinning can be expanded, their transparency and conductivity are limited. Therefore, the production of large-area CNTFTCFs based on CVD remains difficult to apply.

[0074] The SBD method deposits a dispersion of carbon nanomaterials onto a substrate to form a film. Compared to the CVD method, this method can be easily scaled up to large areas, achieving large-scale preparation and greatly reducing costs. However, the SBD method also has many limitations in the production of FTCF: (1) Most SBD film formation methods are directly deposited on polymer substrates, making it difficult to achieve transfer, post-processing, and other steps, which limits its transparency, conductivity, and application scenarios. (2) The loose X-shaped overlap and weak interaction between CNTs can achieve unassisted transfer on substrates such as quartz and silicon wafers, but require a high thickness. When the thickness is less than 200 nm, most of these SBD methods cannot achieve self-support, resulting in damage. A few filtration methods can achieve self-support on the water surface with a thickness of less than 200 nm by introducing capillary force, but the area is limited due to the filter membrane and filtration device. Moreover, the pore size of the filter material and the permeability of the dispersion must be precisely designed, making the process very complex and limiting the application scenarios. In some studies, polymer additives or binders are often added or combined with polymers to facilitate peeling or transfer, which greatly increases the sheet resistance and limits the application range. Therefore, CNT FTCF often requires auxiliary transfer, which can cause pollution, damage and other problems. At present, the large-area production of high-quality TCF below 200nm based on SBD method is still the main challenge of SBD method; (3) Since the TCF produced by SBD method has a high thickness, its transparency is often limited to 70% to 80%. Some studies have used SBD method to directly dry the dispersion on a transparent substrate to form a film, avoiding the transfer process, and can obtain a thinner thickness and up to 90% transmittance. However, CNT FTCF produced in this way also faces the problem of CNTs loosely intersecting and weakly interacting with each other, resulting in a large resistance. In addition, CNTs in CNTFTCF produced by SBD method are often separated and loosely stacked, making it difficult to form an efficient conductive path. Therefore, the overall sheet resistance is higher, often exceeding 1000Ω / □, or even tens of thousands. To solve this problem, it is often necessary to improve conductivity through post-treatment methods such as chemical doping (HNO3, AuCl3, TFSA, etc.). However, these methods not only introduce other elements into CNT FTCF, but also face problems such as poor stability, high price, and complex process. Most of the dopants also lead to a decrease in transmittance and an increase in areal density. (4) In order to improve the physical properties of CNT films, the post-treatment methods of CNT FTCF produced by the SBD method focus on improving the properties of CNTs themselves, and there is a serious lack of means to improve the structure. It is difficult to form an effective connection between loosely X-shaped CNTs, leaving CNTs in a relatively discrete state. Some works use welding methods, such as laser welding, to achieve the connection between CNTs to form a continuous network, but the cost is very high.

[0075] To this end, the present invention proposes a method for preparing a continuous network film of carbon nanotubes, which can connect and assemble loosely X-shaped overlapping and relatively discrete CNT powders to form a continuous network structure, thereby improving its transparent conductivity and mechanical properties, achieving self-support, and enabling the large-scale production of assembled continuous network films of carbon nanotubes with no area limitation.

[0076] Figure 1 This is a schematic flowchart of a method for preparing a continuous network thin film of carbon nanotubes according to an embodiment of the present invention. In this embodiment, the process generally includes:

[0077] Step S101: A predetermined amount of carbon nanotube powder is placed in a predetermined dispersion medium to obtain a carbon nanotube dispersion. In some optional embodiments, the carbon nanotube powder is a powdery substance composed of a large number of carbon nanotubes, possessing a series of excellent physical, chemical, and mechanical properties. The carbon nanotubes in the carbon nanotube powder generally include at least one or a mixture of multiple types of carbon nanotubes, such as single-walled carbon nanotubes, double-walled carbon nanotubes, few-walled carbon nanotubes, and multi-walled carbon nanotubes. When the transparency of the target product is greater than or equal to 80%, a preferred option for the specific material of the carbon nanotube powder is to select single-walled carbon nanotubes, double-walled carbon nanotubes, or a mixture of single-walled and double-walled carbon nanotubes. If the transparency of the target product is less than 80%, any one type of carbon nanotube or a mixture of multiple types of carbon nanotubes mentioned above can be selected.

[0078] The pre-defined dispersion can generally include dispersion in an atmosphere, dispersion in a liquid, and carbon nanotube powder spreading. A preferred embodiment, for example, involves selecting liquid dispersion as the pre-defined dispersion. The step of obtaining a pre-defined amount of carbon nanotube powder and placing it in the pre-defined dispersion generally includes: placing the pre-defined amount of carbon nanotube powder in a carbon nanotube dispersion liquid, adding a surfactant, and using a pre-defined dispersion method to ensure that the carbon nanotube powder is uniformly dispersed in the carbon nanotube dispersion liquid. Optionally, the dispersant used in the carbon nanotube dispersion liquid generally includes any one of water, ethanol, N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), butyl acetate, isopropanol, poly(Methyl Acrylate) (PMA), and N,N-dimethylacetamide (DMAC), and the pre-defined dispersion method generally includes any one of shaking, stirring, and ultrasonic dispersion.

[0079] During the preparation of carbon nanotube dispersions, the density (number or mass per unit area) of the carbon nanotube dispersions should be sufficient to meet the consumption of CNTs during the subsequent formation of a continuous Y-shaped interconnect network on the facets. Furthermore, the facets must drive the formation of complete pores and a continuous network of CNTs, avoiding the formation of discontinuous networks or incomplete pores. Optionally, the density of the carbon nanotube dispersion is greater than a preset density, so that the sheet resistivity of the carbon nanotube dispersion after being placed on the substrate surface is less than 10000 Ω / □. In some preferred embodiments, the sheet resistivity of the carbon nanotube dispersion after being placed on the substrate surface can be less than 5000 Ω / □.

[0080] It should be noted that the various optional items listed in the above embodiments of the present invention are all preferred solutions. Those skilled in the art can choose other items besides the above examples to obtain carbon nanotube dispersions according to actual conditions.

[0081] Step S102: The carbon nanotube dispersion is placed on the substrate surface to obtain a raw carbon nanotube film in which the carbon nanotubes are discrete and loosely overlapped. In some optional embodiments, the raw carbon nanotube film is formed by loosely X-shaped overlap of discrete CNTs and CNT bundles, and the overlap method between CNTs and CNT bundles is generally X-shaped, that is, multiple CNTs and CNT bundles are loosely overlapped together in a cross manner to form the raw carbon nanotube film.

[0082] Optionally, the substrate material can generally include, but is not limited to, metals, semiconductors, and other compounds. Metals generally include: copper, platinum, gold, nickel, titanium, iron, lead, palladium, silver, tungsten, aluminum, zinc, chromium gold, and alloys of several metals. Semiconductors generally include: silicon, germanium, gallium arsenide, gallium nitride, indium phosphide, titanium oxide, aluminum oxide, iron sulfide, nickel sulfide, cadmium selenide, etc. Other compounds generally include vanadium oxide, manganese oxide, silicon oxide, etc. Preferably, the substrate material can be any one of copper, platinum, gold, nickel, titanium, iron, lead, palladium, silver, tungsten, aluminum, zinc, chromium gold, or an alloy of any combination of these metals. Those skilled in the art can select a suitable substrate material according to actual production needs.

[0083] Optionally, the carbon nanotube dispersion can be placed on the substrate surface by methods including, but not limited to, simple placement, powder dipping, or further treatment with organic solvents, as well as any one or a combination of multiple methods such as fluidized bed vapor deposition, powder coating deposition, powder vapor spraying, coating, blade coating, spraying, drop coating, and centrifugal film formation. Preferably, after placing the carbon nanotube dispersion on the substrate surface, a pre-defined film formation method can be used, such as natural drying, forced air drying, thermal evaporation, or vacuum drying, to better form the carbon nanotube dispersion.

[0084] It should be noted that the above are only some optional examples, and it is not only possible to select the corresponding placement method or film formation method from the above examples. Those skilled in the art can select the appropriate placement method and the corresponding preset film formation method according to the actual situation.

[0085] In some optional embodiments, the step of placing the carbon nanotube dispersion on the substrate surface may further include: pre-treating the substrate to make the substrate surface flat; the pre-treatment method includes any one of mechanical polishing, electrochemical polishing, high-temperature annealing, or any combination of the above methods. Those skilled in the art can determine the substrate pre-treatment method according to the actual situation.

[0086] Step S103: Place the original carbon nanotube film and the substrate in the heating furnace cavity.

[0087] Step S104: Set a heating program to allow the original carbon nanotube film to interact with the substrate, thereby assembling the carbon nanotubes in the original carbon nanotube film to obtain an assembled carbon nanotube continuous network film.

[0088] In some optional embodiments, the step of causing the original carbon nanotube film to interact with the substrate generally includes: causing the substrate to undergo surface reconstruction with the gas in the heating furnace cavity, accompanied by the transport of facet atoms constituting the facets, forming facets, which appear as regular steps on the substrate surface at the mesoscale; causing the facets to interact with the original carbon nanotube film, thereby removing impurities from the original carbon nanotube film, at least some of the carbon nanotubes in the original carbon nanotube film undergo positional movement driven by the facets, and adjacent carbon nanotubes or bundles tend to come closer together, thereby assembling the carbon nanotubes in the original carbon nanotube film to obtain an assembled carbon nanotube continuous network film. In this process, driven by faceting, at least some of the short, discrete carbon nanotubes in the original carbon nanotube film aggregate at the steps. Adjacent short carbon nanotubes or bundles tend to be close together, forming larger bundles bound by van der Waals forces. When the carbon nanotube density is appropriate, the larger bundles at the steps approach each other, forming longer bundles that surround the faceted steps. These longer bundles aggregate to form pores. The facets are close together, causing the pores to be adjacent to each other, resulting in Y-shaped connections between the contacting longer bundles, thus forming a continuous Y-shaped interconnected network with uniform pores. This allows the carbon nanotubes in the original carbon nanotube film to be assembled into a continuous network film of assembled carbon nanotubes. It should be noted that the substrate material is not limited in the method of this invention. Depending on the substrate material, a corresponding reactive gas can be selected to reconstruct the substrate surface, thereby forming facets.

[0089] Optionally, the gas is a gas within the heating furnace cavity capable of surface reconstruction with the substrate. It generally includes a mixture of one or more gases of the same class, either oxidizing or reducing. These "same class" gases refer to gases with similar chemical properties; for example, multiple oxidizing gases of the same class, such as oxygen, chlorine, and bromine, can be selected. The gas source generally includes any one or more of the following forms: gas, liquid, or solid. Those skilled in the art can select the appropriate gas and its source capable of surface reconstruction with the substrate based on the actual material and structure of the substrate.

[0090] The step of surface reconstruction between the substrate and the gas in the heating furnace cavity to form facets generally includes: purging the heating furnace cavity to control the partial pressure of the gas undergoing surface reconstruction with the substrate within a set range; and heating the heating furnace cavity to control surface reconstruction on the substrate surface, thus forming facets. In some optional embodiments of the present invention, purging is a process of removing impurity gases from the mixed gas. The gas used in the purging process generally includes any one or a mixture of nitrogen, argon, and hydrogen. Those skilled in the art can determine the specific gas type used for purging according to the actual situation. When the substrate material is selected as a metal or alloy, an oxidizing gas is generally selected as the gas undergoing surface reconstruction with the substrate. Preferably, when the substrate material is selected as copper, an example of an oxidizing gas preferred in the heating furnace cavity of the present invention is oxygen. In this case, the partial pressure of the gas in the heating furnace cavity can be called the oxygen partial pressure. The oxygen partial pressure refers to the partial pressure value of oxygen in a gas mixture and is an indicator of oxygen concentration. It reflects the pressure of oxygen in the gas mixture, usually expressed in millimeters of mercury (mmHg) or kilopascals (kPa). Different substrate materials require different oxygen partial pressures to react with oxygen to form facets. Optionally, the oxygen partial pressure range for different substrates can generally be ≤1 Torr, 1-10 Torr, or ≥10 Torr. Those skilled in the art can select a substrate that forms facets under certain conditions and interacts with the reactants, based on the specific target product, and determine the set range of the gas partial pressure corresponding to this substrate. Meanwhile, the thickness of the substrate is not limited in principle, nor are its rigidity and flexibility. However, considering that the substrate usually needs to be flexible in the limited growth space of the growth zone in the heated furnace cavity, a preferred substrate example is a foil substrate.

[0091] Once the substrate is determined and the oxygen partial pressure in the furnace cavity is controlled within a set range, the furnace cavity needs to be heated to control the oxygen adsorbed on the substrate surface to undergo surface reconstruction, forming facets. The specific temperature value will vary depending on the substrate material. Optionally, for most substrates, the temperature range for facet formation is configured to be greater than or equal to 400°C.

[0092] Optionally, the steps for causing the facets to interact with the original carbon nanotube film generally include: continuing heating to allow the facets on the substrate to gradually grow, thereby controlling at least some of the carbon nanotubes in the original carbon nanotube film to gradually adhere to the facets, and the impurities in the original carbon nanotube film to gradually dissolve; the carbon nanotubes in the original carbon nanotube film move and approach each other as the facets grow, thereby assembling the carbon nanotubes into a long common segment Y-type interconnected network, resulting in an assembled carbon nanotube continuous network film. During the movement, the initially loosely connected X-shaped carbon nanotubes aggregate at the steps under the drive of the facets. Adjacent short carbon nanotubes or bundles tend to move closer to each other, forming larger bundles bound by van der Waals forces. When the carbon nanotube density is appropriate, the larger bundles at the steps move closer to each other, forming long bundles that surround the facet steps. The longer bundles aggregate to form pores. The facets are close together, causing the pores to be adjacent to each other. This allows the contacting longer bundles to form Y-shaped connections, thereby forming a continuous long shared segment Y-shaped interconnected network. This allows the carbon nanotubes in the original carbon nanotube film to be assembled into an assembled continuous network film of carbon nanotubes. Optionally, the temperature range for controlling the gradual contact of the carbon nanotube network with the facet can generally be configured to be greater than or equal to 600℃; the temperature range for the gradual dissolution of impurities can generally be configured to be greater than or equal to 500℃. During the process of carbon nanotubes moving and approaching each other as the facet grows, defective carbon nanotubes and bundles in the original carbon nanotubes and bundles are removed, all of which cause changes in the pore diameter (also called pore size) of the assembled network. Except for a few pores that do not change significantly, most pore sizes slightly increase or decrease. The assembled network is also constrained by the facet size; generally, the pores of the assembled carbon nanotubes are arranged along the edges of the facet steps. Therefore, under the dual effects of removing impurities, defective carbon nanotubes and bundles, and the facet constraints, the network structure of the assembled continuous carbon nanotube network film is optimized, and the pore diameter becomes more uniform.

[0093] Preferably, the step of allowing the facets to interact with the original carbon nanotube film may further include: continuing heating to gradually eliminate the morphological features of the facets, wherein the temperature range for the gradual elimination of the facet morphological features is configured to be greater than or equal to 800°C. When the heating temperature reaches the temperature range where the facet morphological features gradually disappear, the carbon nanotube assembly process is essentially complete. It should be noted that the specific values ​​of the above-mentioned multiple temperature ranges are specific examples of substrates of certain materials under general conditions. Those skilled in the art can determine the specific temperature range corresponding to different operations based on the actual substrate material.

[0094] An alternative example of substrate faceting in this process is shown in Figure 3. Figure 3A A copper-faceted SEM image with a scale bar of 2 μm is shown, illustrating a method for preparing a continuous network thin film of carbon nanotubes according to an embodiment of the present invention. Figure 3B The image shown is a copper-faceted SEM image with a scale bar of 500 nm, illustrating a method for preparing a continuous network of carbon nanotube films according to an embodiment of the present invention. Here, SEM image refers to an image generated by a scanning electron microscope (SEM). Figure 3A and Figure 3B All of them showed in 10 -2 SEM image of copper facets obtained by rapidly cooling copper at 10 °C / min under Torr oxygen partial pressure.

[0095] Optionally, the schematic diagram of the faceted pushing process for assembling the original carbon nanotube film is shown in Figure 4: Figure 4A This is a schematic diagram illustrating the facet-growth process of a method for preparing a continuous carbon nanotube network thin film according to an embodiment of the present invention. Figure 4B This is a schematic diagram showing the gradual growth of facets in a method for preparing a continuous carbon nanotube network film according to an embodiment of the present invention. Figure 4C This is a schematic diagram of the interaction between the facets and carbon nanotubes in a method for preparing a continuous network thin film of carbon nanotubes according to an embodiment of the present invention. Figure 4D This is a schematic diagram illustrating the disappearance of facet morphology features in a method for preparing a continuous carbon nanotube network thin film according to an embodiment of the present invention. When the heating temperature reaches T1, facets begin to grow on the substrate 410. At this time, carbon nanotubes 420 and 421, oxygen 430, and impurities 440 are all located on the surface of the substrate 410, such as... Figure 4A As shown. When the heating temperature reaches T2℃, obvious facets appear on the substrate surface, and some impurities begin to dissolve; as the temperature continues to rise, the facets gradually grow larger, as shown... Figure 4BAs shown, when the heating temperature reaches T3, the step width of the facet continues to grow by nearly 100 nm, and the interaction between the CNTs and the substrate becomes significant. The CNTs adhere tightly to the substrate surface, and with the growth of the facets, the CNTs move noticeably, as shown... Figure 4C As shown; when the temperature approaches the melting point of the substrate, the facets gradually disappear, at which point impurity 440 has disappeared, as... Figure 4D As shown.

[0096] Figure 5 shows a structural comparison between the original carbon nanotube film and the assembled continuous carbon nanotube network film. Figure 5A The image shows a 500 nm scale SEM image of the original carbon nanotube film on a copper foil surface, illustrating a method for preparing a continuous network of carbon nanotube films according to an embodiment of the present invention. The dashed circle indicates the loose X-shaped overlap of the original carbon nanotubes. Figure 5B The image shows an SEM image of an assembled carbon nanotube continuous network film on a faceted copper foil surface, with a scale bar of 500 nm, illustrating a method for preparing a carbon nanotube continuous network film according to an embodiment of the present invention. Figure 5B The image shown is in 10 -2 SEM image of an assembled continuous network of carbon nanotube films / copper foil obtained by rapid cooling after heating to 900℃ under Torr oxygen partial pressure, scale bar 500 nm. Overall, the total amount of visible impurities (particulate matter) is reduced. Figure 5A and Figure 5B The comparison shows that the loose X-shaped overlaps of the original carbon nanotubes were assembled into a continuous network after being processed by this method. The dashed and solid lines indicate the CNTs or CNT bundles that tend to form Y-shaped long common segment interconnection networks under the faceting drive, and the boxes indicate the intersections of CNTs or CNT bundles when they form Y-shaped long common segment interconnection networks under the faceting drive.

[0097] The assembled carbon nanotube continuous network film obtained by this method serves as a flexible transparent conductive carbon nanotube film (CNT FTCF). This allows the loosely X-shaped overlapped carbon nanotubes to assemble into a continuous network under faceting-driven conditions, optimizing the network structure at the microscopic level. This synergistically enhances various properties of the CNT FTCF, including transparency, conductivity, and mechanical properties. Furthermore, this method uses carbon nanotube powder placed on a substrate to obtain a preliminary, loosely X-shaped overlapped disordered structure of CNTs and CNT bundles. The substrate area is unrestricted, exhibiting scalability, and allowing for the fabrication of assembled CNT FTCFs with unlimited length and width. Therefore, it enables large-scale, batch-produced large-area fabrication.

[0098] Optionally, after placing the carbon nanotube dispersion on the substrate surface, the method may further include: dropping a volatile organic solvent onto the original carbon nanotube film to wet the original carbon nanotube film, thereby increasing the contact between the loose carbon nanotubes and the substrate surface; and after the organic solvent has evaporated, placing the original carbon nanotube film and the substrate in a heating furnace cavity. This method is not limited to the type of organic solvent; a preferred example is that the organic solvent may include any one of ethanol, propanol, butanol, ethylene glycol, isopropanol, acetone, n-hexane, cyclohexane, anisole, and chlorobenzene. Those skilled in the art can select the appropriate organic solvent according to the actual situation.

[0099] Optionally, after the step of allowing the facets to interact with the original carbon nanotube film, the process may further include: cooling the assembled continuous carbon nanotube network film at a preset cooling rate; etching away the substrate in a substrate etchant, allowing the cooled assembled continuous carbon nanotube network film to float on the surface of the substrate etchant, and rinsing it with a rinsing solution. The substrate etchant can be determined based on the substrate material and structure; in some embodiments of the present invention, the substrate etchant may generally include any one of the following: ammonium persulfate solution, ferric chloride solution, hydrochloric acid solution, or a mixture of hydrochloric acid and hydrogen peroxide. Those skilled in the art can select the substrate etchant according to the actual situation. Some optional examples of the preset cooling rate are: <10℃ / min, 10-100℃ / min, >100℃ / min, with a preferred embodiment being 100℃ / min. In some optional embodiments, the rinsing solution depends on the substrate etchant. Preferably, deionized water is used as the rinsing solution. Those skilled in the art can select the rinsing solution according to the actual situation. Optionally, the rinsing step may generally include: rinsing with preferred deionized water. After rinsing with deionized water, a large-area, self-supporting, continuously assembled carbon nanotube network film can be obtained on a water surface without polymer-assisted transfer. A large-area, self-supporting, continuously assembled carbon nanotube network film in air can also be obtained. This self-supporting, continuously assembled carbon nanotube network film can be transferred non-destructively to any substrate.

[0100] Figure 2 This is a schematic flowchart illustrating a method for preparing a continuous network of carbon nanotube films according to another embodiment of the present invention. In some optional embodiments, the process generally includes:

[0101] Step S201: Obtain a preset amount of carbon nanotube powder and place it in a preset dispersion medium to obtain a carbon nanotube dispersion.

[0102] Step S202: Pre-treat the substrate to make the substrate surface flat.

[0103] Step S203: Place the carbon nanotube dispersion on the substrate surface to obtain a raw carbon nanotube film in which the carbon nanotubes are separated and loosely connected.

[0104] Step S204: A volatile organic solvent is dropped onto the original carbon nanotube film to wet the original carbon nanotube film.

[0105] In step S205, after the organic solvent has evaporated, the original carbon nanotube film and the substrate are placed in the heating furnace cavity.

[0106] Step S206: The heating furnace cavity is purged to control the partial pressure of the gas in the heating furnace cavity that undergoes surface reconstruction with the substrate within a set range.

[0107] Step S207: The furnace cavity is heated to control the surface reconstruction of the substrate surface with the gas, thereby forming a facet.

[0108] In step S208, heating continues, causing the facets on the substrate to gradually grow, thereby controlling at least some of the carbon nanotubes in the original carbon nanotube film to gradually adhere to the facets, and the impurities in the original carbon nanotube film to gradually dissolve.

[0109] In step S209, the carbon nanotubes in the original carbon nanotube film move and approach each other as the facets grow, thereby assembling the carbon nanotubes into a long common segment Y-shaped interconnected network, resulting in an assembled carbon nanotube continuous network film.

[0110] Step S210: Continue heating to gradually eliminate the morphological features of the facets.

[0111] Step S211: The assembled carbon nanotube continuous network film is cooled at a preset cooling rate.

[0112] In step S212, the cooled assembled carbon nanotube continuous network film is etched away from the substrate in a substrate etchant and floats on the surface of the substrate etchant.

[0113] Step S213: Rinse with rinsing solution.

[0114] The assembled carbon nanotube continuous network film obtained by this method serves as a flexible transparent conductive carbon nanotube film (also referred to as assembled CNT FTCF in this specification). This allows the originally loosely overlapping X-shaped carbon nanotubes to assemble into a continuous network under faceting-driven conditions, optimizing the network structure at the microscopic level. This synergistically enhances various properties of the CNT FTCF, including transparency, conductivity, and mechanical properties. Furthermore, this method uses a substrate-based approach to obtain a preliminary loosely overlapping X-shaped structure of CNTs and CNT bundles. The substrate area is unrestricted, exhibiting scalability, and allowing for the fabrication of assembled CNT FTCFs with unlimited length and width. Therefore, it enables large-scale, batch-produced large-area fabrication.

[0115] The beneficial effects of the assembled carbon nanotube continuous network film prepared by this method are described in detail below.

[0116] 1. Effectively assembles loosely X-shaped overlapping CNT powders into a Y-shaped tightly interconnected continuous CNT network, thereby obtaining assembled CNT TCFT with a continuous network.

[0117] While CNT powder film formation has the potential for large-scale, large-area production, the CNTs in the film dispersion often rely solely on physical contact and, in some cases, on the weak capillary forces generated during solvent evaporation using SBD-based methods, resulting in a loosely structured, X-shaped bond with poor mechanical properties and difficulty in transfer. Although unassisted transfer can be achieved on substrates such as quartz and silicon wafers, high thicknesses are required. For thicknesses below 200 nm, most SBD methods fail to achieve self-supporting transfer, leading to breakage. For thicknesses above 200 nm, transparency is significantly reduced, typically below 50%, limiting its applications. A few filtration methods can achieve self-supporting on water surfaces with thicknesses below 200 nm by introducing capillary forces; however, the area is limited by the filter membrane and filtration device, and the pore size of the filter material and the permeability of the dispersion must be precisely designed, making the process very complex. These methods also result in small areas, high time costs, and limited scalability, further restricting their applications. In some applications, polymer additives or binders are often added or combined with polymers to facilitate peeling or transfer, which greatly increases the surface resistivity and limits the application range. The above methods can only loosely X-shaped overlap in specific CNT dispersions, enhancing the simple contact between CNTs to a certain extent, but cannot assemble loose CNT powder into a high-quality continuous network.

[0118] In this invention, CNTs undergo positional shifts under the influence of facets. The originally discrete, loosely X-shaped CNTs and CNT bundles are thus constrained by the facets, forming a continuous network. Driven by the facets, the initially short CNTs aggregate at the steps, and adjacent short CNTs or CNT bundles tend to approach each other, forming larger diameter bundles constrained by van der Waals forces. When the CNT density is appropriate, the larger diameter bundles at the steps approach each other, forming longer bundles. Around the facet steps, these longer bundles aggregate to form pores. The facets are close together, causing the pores to be adjacent, resulting in contacting longer bundles forming Y-shaped connections, thus forming a continuous, long, shared-segment Y-shaped interconnect network. Therefore, the CNTs and CNT bundles transform from a discrete, loosely disordered, and weakly interacting state into a compact, strongly interacting continuous network structure, significantly improving mechanical properties. Self-supporting transfer can be achieved at thicknesses below 200 nm, with no area limitations, and without the need for additional additives or complex processes. It should be noted that the "discrete" state described in this invention includes the film-forming methods mentioned above and the pre-film-forming methods involved in this method, where CNTs and CNT bundles are in direct physical contact with each other (including but not limited to simple stacking, overlapping, or adjacent states without van der Waals force constraints or bonding), as well as the discrete state without physical contact but meeting the preset conditions for the dispersion in this patent. The biggest difference between this method and other methods is that it can assemble loosely X-shaped overlapping CNT powders (discrete CNTs) into a continuous CNT network through faceted drive, obtaining a CNT FTCF with a strongly interacting Y-shaped tightly continuous network.

[0119] 2. CNT powder is faceted and driven to become a network, which synergistically improves multiple properties (transparency, conductivity, mechanical properties).

[0120] This faceted-drive process of CNTs assembling into a dense network enables the formation of a more efficient conductive network, resulting in a significant synergistic improvement in the sheet resistance and transmittance of the CNT FTCF. The prepared assembled carbon nanotube continuous network film, without doping or post-treatment, exhibits a sheet resistance below 1000 Ω / □ at ~90% transmittance. Using higher-quality CNT dispersions (e.g., longer single-walled CNTs, dispersants with better dispersibility) can effectively reduce the sheet resistance of the initial CNT film. Alternatively, appropriate substrate treatments (e.g., annealing, single crystallization) can further modulate the faceted structure, significantly enhancing the transparency and conductivity of the final assembled carbon nanotube continuous network film. This allows for the acquisition of large-area, self-supporting assembled CNT FTCFs with transmittance exceeding 90% and sheet resistance below 100 Ω / □, as well as transparent conductive films based on them.

[0121] However, CNTs and CNT bundles obtained by CNT powder deposition methods (mostly the SBD method) are often discrete, loosely connected, and lack X-shaped overlap, which often fail to form an effective conductive network due to percolation effects, requiring extremely high sheet resistance (>10000Ω / □) to achieve high transmittance. This invention assembles a CNT FTCF network structure through a faceted driving mechanism, overcoming the limitation of the mutual constraint between transmittance and conductivity in FTCF. This synergistic enhancement of transparent conductivity and flexibility in the assembled continuous carbon nanotube network film has significant application value in the fields of flexible electronics and optoelectronic device manufacturing.

[0122] Traditional CNT powder-based film deposition methods often improve the conductivity of the film through doping and post-processing, but these methods may lead to a decrease in the film's transparency, failing to achieve a synergistic improvement in transparency and conductivity. Compared to post-processing methods such as chemical doping and metal deposition, the CNT network assembled in this method has many advantages: (1) It does not introduce any other elements, thus not increasing the areal density of the CNT FTCF, nor limiting its application scenarios. (2) It does not change the conductivity type (semiconductor / metallic) of the CNT FTCF, maintaining its most intrinsic properties. (3) It avoids problems such as dopant failure (decomposition, volatilization, hydrolysis) and metal corrosion, ensuring the long-term stability of the CNT FTCF. (4) It avoids problems such as the high cost of some dopants and metals and the complexity of the deposition process, making it a simple and economical method.

[0123] In this invention, the assembled continuous network of carbon nanotube films, including films with a transmittance higher than 80%, can be self-supported and transferred to other substrates. In contrast, loose powder with the same transmittance cannot be self-supported; it either disintegrates, agglomerates, or disperses directly on the liquid surface, or breaks or fragments during substrate etching or transfer. In this invention, the assembled continuous network of carbon nanotube films forms a tight connection through faceted assembly. The originally loosely overlapping and discrete X-shaped CNTs form a more compact bundle and a Y-shaped network structure with longer common segments. This continuous network structure is a more robust mechanical structure, thus possessing greater mechanical strength. It not only exhibits good flexibility but also achieves self-support on the liquid surface and even in air.

[0124] Therefore, the present invention can drive CNT powder into a continuous network through faceting, thereby synergistically improving multiple properties.

[0125] 3. To provide a processing and post-processing platform for CNT FTCF produced by the CNT powder film formation method, thereby expanding its application scenarios.

[0126] Most CNT powder-based film deposition methods (such as the SBD method) for CNT FTCF involve directly placing CNTs onto a polymer substrate. The interaction between the CNTs and the substrate is often stronger than the interaction between CNTs themselves, making transfer difficult. Furthermore, polymer substrates are not heat-resistant and cannot withstand common heat treatments for CNTs, nor chemical treatments that could damage the substrate. This significantly limits the conditions and types of post-processing steps. CNT FTCF obtained through CNT powder deposition methods often contains various impurities due to different dispersions, including catalysts, dispersant particles, and amorphous carbon. This not only leads to increased light absorption, but the impurity particles, acting as scattering centers, also affect the conductivity of the film. Moreover, additional metal elements can limit the application of the film in certain special environments (such as non-magnetic environments).

[0127] In this invention, since a high-melting-point substrate (e.g., copper up to 1083°C) can be selected, various CNT heat treatment methods can be used in an oxygen-free atmosphere. During the assembly of CNTs and CNT bundles onto the substrate to form a continuous network, the CNTs and CNT bundles adhere tightly to the substrate surface. This allows impurities such as catalyst particles, amorphous carbon contaminants, and dispersants in the original CNT film to directly contact the substrate surface and dissolve during heat treatment, thereby removing impurities from the CNT FTCF and significantly improving the cleanliness of the assembled CNT FTCF. Because catalyst particles are often composed of transition metals, especially magnetic iron particles, CNT FTCF prepared from unpurified CNT dispersions is difficult to apply in some special scenarios. For example, the presence of magnetic iron particles in a precision electron microscope chamber can cause equipment damage. The application scenarios of assembled carbon nanotube continuous network films with catalyst particles and other impurities removed are much broader.

[0128] 4. Provide a better growth platform for various functional composite FTCFs, and realize the preparation of higher quality functional composite membranes.

[0129] This method utilizes the pushing action of substrate facets to prepare assembled CNT FTCFs. Various other thin film materials can be grown on different substrates. Based on the tightly continuous, high-quality CNT network achieved in this invention, large-area composite films of CNTs and other materials can be developed, including but not limited to carbon materials, metals, semiconductors, and ceramics. For example, copper and nickel substrates are suitable for graphene growth, allowing for the preparation of large-area assembled CNT continuous network-graphene composite films. These composite films, due to the graphene filling the pores of the CNTs, achieve higher carrier efficiency, thus improving conductivity. After substrate removal, the mechanical strength provided by the assembled CNT continuous network is sufficient for self-support and transfer at the liquid surface. Therefore, the composite film can be transferred to various reagents for chemical treatment to functionalize it, further broadening its application range.

[0130] 5. It is compatible with dispersions of various CNT powders, applicable to various film-forming methods, and can be prepared on a large scale and in an environmentally friendly manner.

[0131] The development of any new method for producing FTCF needs to enable large-area or even large-scale fabrication to be of significant importance in industrial production. This is because only large-area FTCF can meet the needs of practical applications in devices and equipment, and large-scale production is essential for industry to meet market demands, improve product quality, and reduce costs. However, currently, there are very few new methods for producing FTCF capable of large-area or even large-scale fabrication.

[0132] The method for preparing assembled carbon nanotube continuous network thin films provided by this invention can achieve large-area and even large-scale scaling. Since a loose X-shaped overlapping structure of CNTs and CNT bundles is initially obtained by coating a CNT dispersion onto the substrate surface, this process is low-cost, the substrate size is not spatially limited, and the length and width can be expanded, easily producing self-supporting large-area CNT FTCFs larger than 1cm × 1cm. Furthermore, this method is compatible with various CNT types, including single-walled, few-walled, multi-walled, and various mixtures of CNTs, as well as various CNT dispersions, including gas-phase, liquid-phase (aqueous and organic) dispersions, and powder spreading. It is also compatible with various film formation processes, including but not limited to various gas-flow deposition of CNT powders, coating, blade coating, and spray coating of CNT dispersions. It is important to emphasize that pre-forming a film on the substrate in this invention is only a preferred method, not a necessary step. Any CNT powder and its dispersion are suitable for this method. For example, CNT powder can be directly coated onto the substrate, simply impregnated with an organic solvent until it evaporates, and then adhered to the substrate surface. A continuous CNT network can also be formed by assembling the powder through substrate facets. The impurity purification process during the assembly of CNTs and CNT bundles into a network greatly increases the range of selectable CNT dispersion qualities, allowing for a certain amount of impurities and contamination, and saving costs associated with purification, cleaning, and acid soaking. The successful preparation of large-area CNT FTCF samples demonstrates that this technology can be scaled up to large areas and even large-scale applications.

[0133] Furthermore, the method of this invention does not involve any toxic or harmful substances, which is beneficial to environmental protection in large-scale production. Our preparation process does not involve any toxic or harmful substances throughout, making it an environmentally friendly production method, which is especially important for future industrial production.

[0134] 6. Optimize the network structure to provide new ideas for the design of FTCF.

[0135] The mechanism for faceted CNTs and CNT bundles assembling into a network provided by this invention optimizes the network structure of CNT FTCF. Due to the formation and growth of facets on the substrate surface, the original short CNTs aggregate at the steps under the drive of the facets. Adjacent short CNTs or CNT bundles tend to move closer together, forming larger diameter bundles constrained by van der Waals forces. When the CNT density is appropriate, the larger diameter bundles at the steps move closer together to form longer bundles. These longer bundles aggregate around the facet steps to form pores. The facets are close together, causing the pores to be adjacent to each other, resulting in Y-shaped connections between the contacting longer bundles, thus forming a continuous, long, shared-segment Y-shaped interconnect network. This is a more efficient conductive network and a more robust mechanical structure. Simultaneously, the removal of CNTs and CNT bundles with more defects slightly increases the pore size of the assembled CNT network, but under the constraint of the facets, it does not exceed the size of the facet steps, thus improving the uniformity of the pore size. The optimized network structure enables a synergistic improvement in various properties of CNT FTCF (transmittance, conductivity, mechanical strength, cleanliness, etc.).

[0136] Previous studies have involved heating CNT films / substrates under a reducing environment. However, the presence of oxygen is not allowed in a reducing environment, thus preventing the formation of facets. Consequently, the CNTs and their bundles do not undergo significant positional migration, and the films do not show obvious carbon consumption. The network structure of the CNT FTCF remains essentially unchanged before and after this treatment, making it impossible to optimize the film's network structure.

[0137] The optimization of this CNT network structure can not only provide a new perspective for the structural design and performance optimization of FTCF, but also provide new ideas for research on other applications of thin films (such as high-strength thin films, ultra-flat thin films, etc.) and the removal of impurities from thin films.

[0138] The following detailed description of a method for preparing large-area assembled carbon nanotube continuous network films based on carbon nanotube powder is provided below.

[0139] Example 1: Preparation method of assembled continuous network thin film of carbon nanotubes based on direct coating

[0140] (1) Prepare a CNT (single-walled, 5-30 micrometers long, tube diameter <2nm) dispersion with a concentration of 0.2mg / mL. The surfactant is SDS (1wt%) and the dispersant is an equal ratio of ethanol and water. After thorough mixing, ultrasonically disperse for 4 hours.

[0141] (2) Electrochemical polishing of copper foil to make its surface smooth.

[0142] (3) Lay the copper foil flat and evenly scrape the CNT dispersion onto the surface of the copper foil. The height of the scraped liquid surface is 80, 100, 120, 160 and 200 micrometers respectively, and they are marked as samples 1, 2, 3, 4 and 5 respectively.

[0143] (4) Allow to stand and air dry to obtain CNT film / copper foil, the surface resistivity of which is less than 5000Ω / □. Preferably, a few drops of ethanol are added to wet the CNT film / copper foil to improve the contact between the two.

[0144] (5) After the organic solvent has evaporated, place the CNT film / copper foil into the heating furnace. Use argon gas to purge the furnace until the oxygen partial pressure inside the chamber is below 10. -2 Torr. A heating program was set up to heat the CNT film / copper foil in a non-reducing environment. When the heating temperature exceeded 700℃, obvious facets appeared on the copper foil surface, and some impurities began to dissolve; as the temperature continued to rise, the facets gradually grew. When the heating temperature reached 900℃, the step width of the facets was nearly 100nm, and the interaction between the CNTs and the copper foil became significant. The CNTs adhered tightly to the copper surface, and as the facets grew, the CNTs moved, initiating the assembly process to form a continuous network; the temperature was held at 900℃ for 30 minutes to allow sufficient time for the facet growth process and the CNT assembly process.

[0145] As the temperature rises, the facets continue to grow, and the CNTs on them move and move closer to each other more significantly. The loose X-shaped overlap between the original CNTs forms a tight connection under the push of the facets: the original short CNTs gather at the steps, and adjacent short CNTs or CNT bundles tend to move closer to each other, forming larger diameter bundles constrained by van der Waals forces. When the CNT density is appropriate, the larger diameter bundles at the steps move closer to each other, forming long bundles. Around the facet steps, the longer bundles gather to form pores. The facets are close to each other, causing the pores to be adjacent to each other, so that the contacting longer bundles form Y-shaped connections, and thus form a continuous long common segment Y-shaped interconnection network. At the same time, the CNTs and tube bundles with more defects are removed, and the pore size of the assembled CNT network is slightly increased under the constraint of the facets.

[0146] (6) After the heating process is over, quickly cool the assembled CNT continuous network film / copper foil to room temperature and then take it out.

[0147] (7) The assembled CNT continuous network film / copper foil was floated in an ammonium persulfate solution and the copper foil was etched away to obtain an assembled carbon nanotube continuous network film floating on the surface of the ammonium persulfate solution. Finally, it was rinsed with deionized water to obtain a self-supporting assembled carbon nanotube continuous network film. The self-supporting CNT FTCF was transferred to a quartz substrate for performance testing.

[0148] Figure 6A An optical photograph with a scale bar of 2 cm shows a method for preparing a continuous carbon nanotube network film according to an embodiment of the present invention, in which the assembled continuous carbon nanotube network film based on direct coating is self-supporting and floats on the water surface. Figure 6B An optical photograph with a scale bar of 2 cm shows the transfer of an assembled continuous carbon nanotube network film, based on direct coating, onto a quartz substrate, illustrating a method for preparing a continuous carbon nanotube network film according to an embodiment of the present invention. Figure 6A and Figure 6B As shown, the two thinnest and most transparent samples (samples 1 and 2) exhibited very good transparency and uniformity, and could be transferred to the quartz substrate without damage while self-supporting on the water surface. Figure 7 Optical photographs of the transfer of assembled carbon nanotube continuous network films with different transmittances onto a quartz substrate based on direct coating, illustrating a method for preparing a continuous carbon nanotube network film according to an embodiment of the present invention. Figure 7 As shown, sample 710 is sample 1, which can be transferred non-destructively to obtain sample 711, which achieves a transmittance of ~90% at a scale bar of 550 nm and a surface resistivity of less than 1000 Ω / □ without any treatment; sample 720 is sample 2, which can be transferred non-destructively to obtain sample 721, which achieves a transmittance of ~85% at a scale bar of 550 nm; sample 730 is sample 3, which can be transferred non-destructively to obtain sample 731, which achieves a transmittance of ~78% at a scale bar of 550 nm; sample 740 is sample 4, which can be transferred non-destructively to obtain sample 741, which achieves a transmittance of ~70% at a scale bar of 550 nm; and sample 750 is sample 5, which can be transferred non-destructively to obtain sample 751, which achieves a transmittance of ~55% at a scale bar of 550 nm. Figure 8 These are transparency and conductivity test images of assembled carbon nanotube continuous network films with different transmittances based on direct coating, according to a method for preparing a carbon nanotube continuous network film according to an embodiment of the present invention. Figure 8 As can be seen, the surface resistance of samples 1-5 is less than 1000Ω / □ without any treatment.

[0149] Figure 9A The image shows SEM images of the original loosely X-shaped overlapped CNTs and CNT bundles, all with a scale bar of 1 μm, illustrating a method for preparing a continuous carbon nanotube network film according to an embodiment of the present invention. Figure 9B This image shows SEM images of an assembled continuous carbon nanotube network film, with a scale bar of 1 μm, illustrating a method for preparing a continuous carbon nanotube network film according to an embodiment of the present invention. Figure 9A and Figure 9BThe comparison reveals that the original, discrete, loosely connected CNTs and CNT bundles have pore sizes ranging from tens to hundreds of nanometers. The connections between CNTs and bundles are relatively loose, and there are some impurities on the network. In contrast, the pore sizes of assembled CNT networks are mostly in the hundreds of nanometers. The larger pores improve dimensional uniformity. The loose X-shaped connections between the original CNTs are transformed into a continuous, long, shared Y-shaped interconnect network by faceting, and there are fewer visible impurities on the network.

[0150] Using higher quality CNT dispersions (e.g., longer single-walled CNTs, dispersants with better dispersibility) can effectively reduce the sheet resistance of the CNT film in step (4), or by performing appropriate treatments on the copper foil (e.g., annealing, single crystallization) to further control the faceted structure, the transparent conductivity of the final assembled carbon nanotube continuous network film will be greatly improved. Assembled CNT FTCFs with a transmittance of over 90% and a sheet resistance of less than 100 Ω / □, and transparent conductive films based thereon, can be obtained.

[0151] To clearly demonstrate the advantages of the assembled carbon nanotube continuous network film prepared by the present invention, a comparative example 2 is presented:

[0152] (1) Prepare a CNT (single-walled, 5-30 micrometers long, tube diameter <2nm) dispersion with a concentration of 0.2mg / mL. The surfactant is SDS (1wt%) and the dispersant is an equal ratio of ethanol and water. After thorough mixing, ultrasonically disperse for 4 hours.

[0153] (2) Perform oxygen plasma treatment on the quartz glass slide, with a power of 60W and a time of 30 seconds.

[0154] (3) The CNT dispersion was uniformly coated on the surface of a quartz glass slide. The height of the coated liquid surface was 80 micrometers and 40 micrometers, and was denoted as sample A1 and sample A2.

[0155] (4) Electrochemically polish the copper foil to make its surface smooth.

[0156] (5) Lay the copper foil flat and uniformly scrape the CNT dispersion onto the surface of the copper foil. The height of the scraped liquid surface is 80 micrometers, and this is recorded as sample B.

[0157] (6) Allow to stand and air dry to obtain CNT film / quartz (A1, A2) and CNT film / copper foil (B), respectively. Preferably, add a few drops of ethanol to wet samples A and B to improve their contact.

[0158] (7) After the organic solvent has evaporated, sample B is placed in the heating furnace. Hydrogen gas is introduced at a rate of 40 sccm throughout the process, and the heating program in Example 1 is set to heat sample B. When the heating temperature exceeds 700°C, no facets appear on the copper foil surface. When the heating temperature reaches 900°C and is held constant for 30 minutes, facets still do not appear. The CNTs and CNT bundles are loosely X-shaped and overlapped on the copper surface, and impurities in the network cannot adhere tightly to the copper surface. The CNTs show almost no movement. With increasing temperature, facets still do not appear, and there are no significant changes in the CNTs and CNT bundles.

[0159] (8) After the heating process is over, quickly cool sample B to room temperature and then take it out.

[0160] (9) Sample B was floated in an ammonium persulfate solution to etch away the copper foil, resulting in a CNT film floating on the surface of the ammonium persulfate solution. The film broke during the rinsing process in deionized water and could not be self-supported for transfer to the quartz substrate. Only the fragments were characterized in morphology.

[0161] (10) Test the transparent conductivity of sample A.

[0162] SEM image of sample B as follows Figure 10 As shown, Figure 10 This illustration shows SEM images of raw CNTs and CNT bundles without carbon nanotube assembly, at a scale bar of 2 μm, illustrating a method for preparing a continuous carbon nanotube network film according to another embodiment of the present invention. Figure 10 As can be seen, the CNTs are only loosely connected in an X-shape, without forming a tight and effective interconnection network, and a large number of fragments and disconnections are generated during the transfer process.

[0163] The transparent conductivity of samples A1 and A2 is as follows: Figure 11 As shown, Figure 11 This is a transparency conductivity test image of a sample without carbon nanotube assembly, obtained using a method for preparing a continuous carbon nanotube network thin film according to another embodiment of the present invention. From... Figure 11 As can be seen, sample A1 has a transmittance of 78% and a sheet resistance of 931 Ω / □, which is more than twice as high as sample A3 in Example 1 at the same transmittance. Compared with sample A1 in Example 1, its transmittance is 12% lower at the same sheet resistance. Sample A2 has a transmittance of 89% and a sheet resistance of 2132 Ω / □, which is more than twice as high as sample A1 in Example 1 at similar transmittance. These comparative examples demonstrate that using the method of the present invention to assemble CNT networks through faceting significantly improves the transparency, conductivity, and mechanical properties of CNT FTCF.

[0164] Example 3: Preparation method of assembled continuous network thin film of carbon nanotubes based on powder vapor phase spraying

[0165] (1) Weigh 0.3g of CNT (single-walled and multi-walled mixed, 3-10 micrometers long) and place it in the cavity of the vapor phase spraying device. Then, introduce 1L of nitrogen to form a circulation and mix thoroughly.

[0166] (2) Electrochemical polishing of copper foil to make its surface smooth.

[0167] (3) Lay the copper foil flat and use a vapor phase spraying device to uniformly spray the gas mixed with CNTs onto the surface of the copper foil, which has been heated to 60 degrees Celsius and moistened with ethanol. The spraying amount is approximately 0.015 mg / cm². 2 .

[0168] (4) Let stand and dry, then cool the copper foil to room temperature to obtain CNT film / copper foil. The surface resistance of the CNT film is less than 5000Ω / □.

[0169] (5) Place the CNT film / copper foil into the heating furnace. Purge the furnace with argon gas to reduce the oxygen partial pressure inside the chamber to below 10. - 1 Torr. A heating program was set up to heat the CNT film / copper foil in a non-reducing environment. When the heating temperature exceeded 700℃, obvious facets appeared on the copper foil surface, and some impurities began to dissolve; with continued heating, the facets gradually grew. When the heating temperature reached 900℃, the step width of the facets was nearly 100nm, and the interaction between the CNTs and the copper foil became significant. CNTs and CNT bundles adhered tightly to the copper surface. As the facets grew, the CNTs moved, initiating the assembly process to form a continuous network. The temperature was held at 900℃ for 30-90 minutes to allow sufficient time for the facet growth process and the CNT assembly process. Subsequently, when the temperature was further increased to 1030℃, due to proximity to the melting point of copper, the pre-melting of the copper surface became more pronounced, the morphological features of the facets essentially disappeared, and the assembly process was completed.

[0170] As the temperature rises, the facets continue to grow, and the CNTs and CNT bundles on them move and move closer to each other more significantly. The loose X-shaped overlap between the original CNTs forms a tight connection under the push of the facets: the original short CNTs gather at the steps, and adjacent short CNTs or CNT bundles tend to move closer to each other, forming larger diameter bundles constrained by van der Waals forces. When the CNT density is appropriate, the larger diameter bundles at the steps move closer to each other, forming long bundles. Around the facet steps, the longer bundles gather to form pores. The facets are close to each other, causing the pores to be adjacent to each other, so that the contacting longer bundles form Y-shaped connections, and then assemble to form a continuous long common segment Y-shaped interconnection network. At the same time, some of the CNTs and tube bundles with more defects are removed, so that the pore size of the assembled CNT network is slightly increased under the constraint of the facets. Figure 12This image shows a 500 nm scale SEM image of a spray-assembled continuous carbon nanotube network film, illustrating a method for preparing a continuous carbon nanotube network film according to another embodiment of the present invention. Figure 12 As shown: Because the assembled CNT network forms a tight connection, the aperture edges and tube bundles will hinder the diffusion and transport of copper, causing the facets to become islands. The morphology of the assembled CNT network (the network distributed along the edge of the island) can be clearly observed in the flat area around the island. The tightly connected CNT network forms a long common segment Y-shaped network with uniform apertures.

[0171] (6) After the heating process is over, quickly cool the assembled CNT continuous network film / copper foil to room temperature and then take it out.

[0172] (7) The assembled CNT continuous network film / copper foil was floated in an ammonium persulfate solution and the copper foil was etched away to obtain an assembled carbon nanotube continuous network film floating on the surface of the ammonium persulfate solution. Finally, it was rinsed with deionized water to obtain a self-supporting assembled carbon nanotube continuous network film, as shown in Figure 13. Figure 13A The optical image shown is a self-supporting carbon nanotube continuous network film in ammonium persulfate, with a scale bar of 2 cm, illustrating a method for preparing a carbon nanotube continuous network film according to another embodiment of the present invention. Figure 13B This image shows a self-supporting optical image of an assembled continuous carbon nanotube network film on a deionized water surface, with a scale bar of 2 cm, illustrating a method for preparing a continuous carbon nanotube network film according to another embodiment of the present invention. Figure 13A and Figure 13B As can be seen, the sample can be self-supported and transferred into deionized water, exhibiting very good transparency and uniformity.

[0173] Example 4: A method for preparing large-area assembled continuous network thin films of carbon nanotubes based on direct coating

[0174] (1) Prepare a CNT (single-walled, 5-30 micrometers long, tube diameter <2nm) dispersion with a concentration of 0.2mg / mL. The surfactant is SDS (1wt%) and the dispersant is an equal ratio of ethanol and water. After thorough mixing, ultrasonically disperse for 4 hours.

[0175] (2) Electrochemical polishing of copper foil to make its surface smooth.

[0176] (3) Lay out a large area of ​​copper foil, and uniformly scrape the CNT dispersion onto the surface of the copper foil. The height of the scraped liquid surface is 80 micrometers.

[0177] (4) Allow to stand and air dry to obtain CNT film / copper foil, with a CNT film surface resistivity of less than 5000 Ω / □. Preferably, add a few drops of ethanol to wet the CNT film / copper foil to improve contact between the two.

[0178] (5) Step (5) in this embodiment is the same as step (5) in embodiment 1, and will not be repeated here.

[0179] As the temperature rises, the facets continue to grow, and the CNTs on them move more significantly and move closer to each other. The loose X-shaped overlap between the original CNTs forms a tight connection under the push of the facets, and then assembles into a continuous long common segment Y-shaped interconnection network. At the same time, some of the CNTs and tube bundles with more defects are removed, and the pore size of the assembled CNT network is slightly increased under the constraint of the facets.

[0180] (6) After the heating process is over, quickly cool the assembled CNT continuous network film / copper foil to room temperature and then take it out.

[0181] (7) A large-area assembled CNT continuous network film / copper foil was floated in an ammonium persulfate solution and the copper foil was etched away to obtain a large-area (>10cm×10cm) assembled carbon nanotube continuous network film floating on the surface of the ammonium persulfate solution. Finally, it was rinsed with deionized water to obtain a flexible, self-supporting large-area (>100cm) film. 2 Assemble continuous network films of carbon nanotubes, such as Figure 14 As shown, Figure 14 The image shows a large-area assembled carbon nanotube continuous network film in deionized water, with a scale bar of 5 cm, illustrating a method for preparing a carbon nanotube continuous network film according to another embodiment of the present invention.

[0182] Example 5: A method for preparing large-area assembled continuous network thin films of carbon nanotubes based on powder vapor phase spraying

[0183] (1) Weigh 3g of CNT (single-walled, 3-10 micrometers long) and place it in the cavity of the vapor phase spraying device. Then, introduce 10L of nitrogen to form a circulation and mix thoroughly.

[0184] (2) Electrochemical polishing of copper foil to make its surface smooth.

[0185] (3) After laying a large area of ​​copper foil flat, place it on a roller and rotate it slowly under the drive of a motor. Use a vapor phase spraying device to uniformly spray the gas mixed with CNTs onto the surface of the copper foil, which has been heated to 60 degrees Celsius and moistened with ethanol. The spraying amount is approximately 0.02 mg / cm². 2 After the sprayed area dries and cools to room temperature, it is rolled up by rollers.

[0186] (4) After the entire area is sprayed and rolled up, the CNT film / copper foil is unrolled. The surface resistance of the CNT film is less than 5000Ω / □. After covering with graphite paper, it is rolled up again. The graphite paper separates the back of the rolled-up copper foil from the CNT film.

[0187] (5) is the same as step (5) in Example 1, and will not be repeated here.

[0188] As the temperature rises, the facets continue to grow, and the CNTs and CNT bundles on them move and move closer together more significantly. The loose X-shaped overlaps between the original CNTs are pushed together by the facets to form tight connections, thus assembling into a continuous, long, shared-segment Y-shaped interconnect network. At the same time, some CNTs and tube bundles with more defects are removed, causing the aperture size of the assembled CNT network to increase slightly under the constraint of the facets. Because the assembled CNT network forms a tight connection, the aperture edges and tube bundles hinder the diffusion and transport of copper, turning the facets into islands. The morphology of the assembled CNT network (the network distributed along the edges of the islands) can be clearly observed in the flat areas around the islands, showing the tightly connected assembled CNT network forming a long, shared-segment Y-shaped network.

[0189] (6) After the heating process is over, quickly cool the large-area assembled CNT continuous network film / copper foil to room temperature and then take it out.

[0190] (7) The large-area assembled CNT continuous network film / copper foil was unfolded and floated in an ammonium persulfate solution to etch away the copper foil, thereby obtaining a large-area assembled carbon nanotube continuous network film floating on the surface of the ammonium persulfate solution. Finally, it was rinsed with deionized water to obtain a self-supporting, flexible large-area assembled carbon nanotube continuous network film.

[0191] Example 6: Preparation method of assembled carbon nanotube continuous network-graphene composite FTCF based on assembled CNT continuous network

[0192] (1) Prepare a CNT (single-walled, 5-30 micrometers long, tube diameter <2nm) dispersion with a concentration of 0.2mg / mL. The surfactant is SDS (1wt%) and the dispersant is an equal ratio of ethanol and water. After thorough mixing, ultrasonically disperse for 4 hours.

[0193] (2) Electrochemical polishing of copper foil to make its surface smooth.

[0194] (3) Lay the copper foil flat and uniformly scrape the CNT dispersion onto the surface of the copper foil. The height of the scraped liquid surface is 80 micrometers.

[0195] (4) Allow to stand and air dry to obtain CNT film / copper foil, with a CNT film surface resistivity of less than 5000 Ω / □. Preferably, add a few drops of ethanol to wet the CNT film / copper foil to improve contact between the two.

[0196] (5) is the same as step (5) in Example 3, and will not be repeated here.

[0197] As the temperature rises, the facets continue to grow, and the CNTs on them move more significantly and move closer to each other. The loose X-shaped overlap between the original CNTs forms a tight connection under the push of the facets, and then assembles into a continuous long common segment Y-shaped interconnection network. At the same time, some of the CNTs and tube bundles with more defects are removed, and the pore size of the assembled CNT network is slightly increased under the constraint of the facets.

[0198] (6) Continue to keep warm at 1030℃ for 10 min, while simultaneously introducing 2 sccm of methane and 40 sccm of hydrogen to grow graphene.

[0199] (7) After the heating process is over, the assembled CNT continuous network-graphene film / copper foil based on the assembled CNT network is rapidly cooled to room temperature and then removed.

[0200] (8) The assembled CNT continuous network-graphene film / copper foil was floated in an ammonium persulfate solution and the copper foil was etched away to obtain the assembled CNT continuous network-graphene composite FTCF floating on the surface of the ammonium persulfate solution. Finally, it was rinsed with deionized water to obtain a self-supporting assembled CNT continuous network-graphene FTCF based on the assembled CNT network, as shown in Figure 15. Figure 15A The image shows an optical image of an assembled carbon nanotube continuous network-graphene film in deionized water, with a scale bar of 2 cm, illustrating a method for preparing a carbon nanotube continuous network film according to another embodiment of the present invention. Figure 15B The image shows a 1 μm scale SEM image of an assembled carbon nanotube continuous network-graphene film, illustrating a method for preparing a carbon nanotube continuous network film according to another embodiment of the present invention.

[0201] Example 7: Preparation method of assembled continuous network thin film of carbon nanotubes based on carrier gas purging nickel foil

[0202] (1) Carbon nanotubes were grown using the gas phase pyrolysis method.

[0203] (2) Electrochemically polish the nickel foil to make its surface smooth.

[0204] (3) Use a carrier gas containing carbon nanotubes to uniformly purge the nickel foil, placing it on the surface of the nickel foil. The purging rate is approximately 0.02 mg / cm³. 2 This yields the initial CNT film. Preferably, a few drops of acetone are added to wet the carbon CNT film / nickel foil to improve contact between the two.

[0205] (4) After the organic solvent has evaporated, place the CNT film / nickel foil into the heating furnace. Purge the gas to ensure the oxygen partial pressure inside the chamber is below 1 Torr. Set the heating program to heat the carbon nanotube film / nickel foil in a non-reducing environment. When the heating temperature exceeds 800℃, obvious facets appear on the nickel foil surface, and some impurities begin to dissolve; as the temperature continues to rise, the facets gradually grow. When the heating temperature reaches 1000℃, the step width of the facets is nearly 100nm, and the interaction between the CNTs and the facets becomes significant, adhering tightly to the nickel surface. As the facets grow, the CNTs move and begin the assembly process to form a continuous network; maintain the temperature at 1000℃ for 30 minutes to allow sufficient time for the facet growth process and the CNT assembly process.

[0206] As the temperature rises, the facets continue to grow, and the CNTs on them move and move closer to each other more significantly. The loose X-shaped overlap between the original CNTs forms a tight connection under the push of the facets: the original short CNTs gather at the steps, and adjacent short CNTs or CNT bundles tend to move closer to each other, forming larger diameter bundles constrained by van der Waals forces. When the CNT density is appropriate, the larger diameter bundles at the steps move closer to each other, forming long bundles. Around the facet steps, the longer bundles gather to form pores. The facets are close to each other, causing the pores to be adjacent to each other, so that the contacting longer bundles form Y-shaped connections, and thus form a continuous long common segment Y-shaped interconnection network. At the same time, the CNTs and tube bundles with more defects are removed, and the pore size of the assembled CNT network is slightly increased under the constraint of the facets.

[0207] (6) After the heating process is over, quickly cool the assembled CNT continuous network film / nickel foil to room temperature and then take it out.

[0208] (7) The assembled CNT continuous network film / nickel foil was floated in an ammonium persulfate solution and the nickel foil was etched away to obtain an assembled carbon nanotube continuous network film floating on the surface of the ammonium persulfate solution. Finally, it was rinsed with deionized water to obtain a self-supporting assembled carbon nanotube continuous network film.

[0209] Example 8: Preparation method of assembled continuous network thin film of carbon nanotubes based on carrier gas purging platinum foil

[0210] (1) Carbon nanotubes were grown using the gas phase pyrolysis method.

[0211] (2) Electrochemically polish the platinum foil to make its surface smooth.

[0212] (3) Use a carrier gas containing carbon nanotubes to uniformly purge the platinum foil, placing it on the surface of the platinum foil. The purging rate is approximately 0.03 mg / cm³. 2 This yields the initial CNT film. Preferably, a few drops of acetone are added to wet the CNT film / platinum foil to improve contact between the two.

[0213] (4) After the organic solvent has evaporated, place the CNT film / platinum foil into the heating furnace. Purge the gas to ensure the oxygen partial pressure inside the chamber is below 1 Torr. Set the heating program to heat the carbon nanotube film / platinum foil in a non-reducing environment. When the heating temperature exceeds 1000℃, obvious facets appear on the surface of the platinum foil, and some impurities begin to dissolve; as the temperature continues to rise, the facets gradually grow. When the heating temperature reaches 1300℃, the step width of the facets is nearly 100nm, and the interaction between the CNTs and the platinum foil becomes significant, adhering tightly to the platinum surface. As the facets grow, the CNTs move and begin the assembly process to form a continuous network; maintain the temperature at 1300℃ for 30min to allow sufficient time for the facet growth process and the CNT assembly process.

[0214] As the temperature rises, the facets continue to grow, and the CNTs on them move and move closer to each other more significantly. The loose X-shaped overlap between the original CNTs forms a tight connection under the push of the facets: the original short CNTs gather at the steps, and adjacent short CNTs or CNT bundles tend to move closer to each other, forming larger diameter bundles constrained by van der Waals forces. When the CNT density is appropriate, the larger diameter bundles at the steps move closer to each other, forming long bundles. Around the facet steps, the longer bundles gather to form pores. The facets are close to each other, causing the pores to be adjacent to each other, so that the contacting longer bundles form Y-shaped connections, and thus form a continuous long common segment Y-shaped interconnection network. At the same time, the CNTs and tube bundles with more defects are removed, and the pore size of the assembled CNT network is slightly increased under the constraint of the facets.

[0215] (6) After the heating process is over, quickly cool the assembled CNT continuous network film / platinum foil to room temperature and then remove it.

[0216] (7) The assembled CNT continuous network film / platinum foil was floated in an ammonium persulfate solution and the platinum foil was etched away to obtain an assembled carbon nanotube continuous network film floating on the surface of the ammonium persulfate solution. Finally, it was rinsed with deionized water to obtain a self-supporting assembled carbon nanotube continuous network film.

[0217] Therefore, those skilled in the art should recognize that although numerous exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Thus, the scope of the present invention should be understood and construed as covering all such other variations or modifications.

Claims

1. A method for preparing a continuous carbon nanotube network film, comprising: A predetermined amount of carbon nanotube powder is placed in a predetermined dispersion medium to obtain a carbon nanotube dispersion. The carbon nanotube dispersion is placed on the substrate surface to obtain a raw carbon nanotube film in which the carbon nanotubes are separated and loosely overlapped. The original carbon nanotube film and the substrate were placed in a heating furnace cavity; A heating program is set up to cause the original carbon nanotube film to interact with the substrate, thereby assembling the carbon nanotubes in the original carbon nanotube film to obtain an assembled carbon nanotube continuous network film. The step of causing the original carbon nanotube film to interact with the substrate includes: causing the substrate to undergo surface reconstruction with the gas in the heating furnace cavity to form facets, and causing the facets to interact with the original carbon nanotube film.

2. The method for preparing a continuous network of carbon nanotube films according to claim 1, wherein, The step of placing the carbon nanotube dispersion on the substrate surface further includes: A volatile organic solvent is dropped onto the original carbon nanotube film to wet the original carbon nanotube film, thereby increasing the contact between the loose carbon nanotubes and the substrate surface. After the organic solvent has evaporated completely, the step of placing the original carbon nanotube film and the substrate in the heating furnace cavity is performed.

3. The method for preparing a continuous network thin film of carbon nanotubes according to claim 2, wherein, The carbon nanotubes in the carbon nanotube powder include at least one or more of single-walled carbon nanotubes, double-walled carbon nanotubes, few-walled carbon nanotubes, and multi-walled carbon nanotubes, or a mixture of any combination of multiple types of carbon nanotubes. The density of the carbon nanotube dispersion is greater than a preset density, so that the sheet resistance of the carbon nanotube dispersion after being placed on the substrate surface is less than 10000 Ω / □. The dispersion methods of the carbon nanotube dispersions include dispersion in an atmosphere, dispersion in a liquid, and carbon nanotube powder spreading. The method of placing the carbon nanotube dispersion on the substrate surface includes any one or a combination of multiple methods selected from fluidized bed vapor deposition, powder coating deposition, powder vapor spraying, coating, blade coating, spraying, drop coating, centrifugal film formation, and powder dipping. The organic solvent includes any one or a mixture of solvents selected from ethanol, propanol, butanol, ethylene glycol, isopropanol, acetone, n-hexane, cyclohexane, anisole, and chlorobenzene. The substrate is made of any one of the following metals: copper, platinum, gold, nickel, titanium, iron, lead, palladium, silver, tungsten, aluminum, zinc, chromium, gold, or an alloy of any combination of these metals.

4. The method for preparing a continuous network thin film of carbon nanotubes according to claim 1, wherein, The step of causing the original carbon nanotube film to interact with the substrate includes: The substrate and the gas in the heating furnace cavity undergo surface reconstruction, accompanied by the transport of facet atoms that constitute the facets, forming the facets. The facets appear as regular steps on the surface of the substrate at the mesoscale. The facets interact with the original carbon nanotube film to remove impurities from the original carbon nanotube film. At least some of the carbon nanotubes in the original carbon nanotube film move under the drive of the facets, and adjacent carbon nanotubes or bundles tend to come closer together, so that the carbon nanotubes in the original carbon nanotube film are assembled to obtain an assembled carbon nanotube continuous network film.

5. The method for preparing a continuous network of carbon nanotube films according to claim 4, wherein, The gas is a gas in the heating furnace cavity that can undergo surface reconstruction with the substrate, including a mixture of one or more gases of the same type, either oxidizing or reducing; The source of the gas includes: any one or more of the following forms: gas, liquid, and solid.

6. The method for preparing a continuous network thin film of carbon nanotubes according to claim 5, wherein, The step of forming facets by surface reconstruction of the substrate with the gas in the heating furnace cavity includes: The heating furnace cavity is purged to control the partial pressure of the gas in the heating furnace cavity that undergoes surface reconstruction with the substrate within a set range; The furnace cavity is heated to control the surface reconstruction of the substrate surface with the gas, thereby forming the facet.

7. The method for preparing a continuous network of carbon nanotube films according to claim 6, wherein, The step of causing the facets to interact with the original carbon nanotube film includes: Heating continues, causing the facets on the substrate to gradually grow, thereby controlling at least some of the carbon nanotubes in the original carbon nanotube film to gradually adhere to the facets, and the impurities in the original carbon nanotube film to gradually dissolve. The carbon nanotubes in the original carbon nanotube film move and approach each other as the facets grow, thereby assembling the carbon nanotubes into a long common segment Y-shaped interconnected network, resulting in the assembled carbon nanotube continuous network film.

8. The method for preparing a continuous network of carbon nanotube films according to claim 7, wherein, The temperature range for forming the facets is configured to be greater than or equal to 400 °C; The temperature range for controlling the carbon nanotube network to gradually adhere to the facet is configured to be greater than or equal to 600 °C; The temperature range at which the impurities gradually dissolve is configured to be greater than or equal to 500 °C; The step of causing the facets to interact with the original carbon nanotube film further includes: continuing to heat the surface to gradually eliminate the morphological features of the facets, wherein the temperature range at which the morphological features of the facets gradually disappear is configured to be greater than or equal to 800 °C. The gases used in the gas washing process include any one or a combination of nitrogen, argon, and hydrogen.

9. The method for preparing a continuous network of carbon nanotube films according to claim 4, wherein, The step of causing the facets to interact with the original carbon nanotube film further includes: The assembled carbon nanotube continuous network film is cooled at a preset cooling rate. The cooled assembled carbon nanotube continuous network film is etched away from the substrate in a substrate etchant, floats on the surface of the substrate etchant, and is then rinsed with a rinsing solution.

10. The method for preparing a continuous network thin film of carbon nanotubes according to claim 1, wherein, The step of placing the carbon nanotube dispersion on the substrate surface further includes: pre-treating the substrate to make the substrate surface flat; The pretreatment method includes any one of mechanical polishing, electrochemical polishing, and high-temperature annealing, or any combination of these methods. The shape of the substrate includes a foil substrate.

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