A method for preparing a high-density parallel array of carbon nanotubes

Abstract

The application provides a preparation method of a high-density carbon nanotube parallel array. The method inserts a substrate into a carbon nanotube dispersion liquid, moves the substrate away from the liquid surface of the carbon nanotube dispersion liquid, and forms a high-density carbon nanotube parallel array on the substrate. The preparation method is simple, the preparation condition is loose, and the method is easy to realize. The obtained high-density carbon nanotube parallel array can be continuously and uniformly deposited on the substrate, and meets the use requirement of the carbon nanotube parallel array.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of carbon nanotube material preparation, and particularly relates to a preparation method of high-density carbon nanotube parallel array. BACKGROUND

[0002] Carbon nanotubes have ideal one-dimensional structure and excellent physical and chemical properties, and have attracted extensive attention since the 1990s. They have broad application prospects in the fields of mechanics, optoelectronics, sensing, nanoelectronics, etc. High-density carbon nanotube parallel array can exhibit more excellent performance, including high electrical conductivity, high current carrying capacity, high mechanical strength and polarization absorption of light, etc. For example, the high electron and hole mobility, adjustable band gap, quasi-ballistic carrier transport properties and inhibition of short channel effect of semiconductor single-walled carbon nanotubes make them an ideal choice for field effect transistor channel materials. To manufacture competitive high-performance integrated circuits, single-walled carbon nanotubes must be assembled into highly ordered high-density single-layer parallel arrays with a density of 100-200 per micron. However, this goal has not been fully achieved. The preparation of carbon nanotube parallel array has become a key technical bottleneck restricting the application of carbon nanotubes.

[0003] In the past three decades, with the development of carbon nanotube growth, dispersion and sorting technologies, various matching deposition and assembly methods have been proposed and put into practice. Through substrate induction and air flow assistance, nearly perfect parallel carbon nanotube arrays can be directly grown. The highest density so far is 160 per micron. However, the higher the density, the lower the semiconductor purity that can be achieved, which cannot meet the requirements of high-purity and high-density for high-performance applications. Therefore, the main process route of array preparation at present is to first obtain a high-purity carbon nanotube dispersion liquid through solution purification and sorting steps, and then perform solution assembly to obtain a parallel array, so as to meet the requirements of purity and density at the same time. In this route, many solution assembly methods relying on external fields, interfaces and contact lines, or patterned substrates for orientation have also been successful, but only a few of them have reached the density target of 100-200 per micron, and there are still limitations such as complex system and operation, slow assembly speed and only suitable for specific dispersion liquid, etc.

[0004] Controllable aggregation of carbon nanotubes is a prerequisite for high-density solution assembly. In the methods of dimensional confinement self-assembly and binary liquid interface limited self-assembly, hydrogen bonding between solvent and carbon nanotube dispersant drives carbon nanotubes to aggregate at the liquid-liquid interface, and assemble into a single-layer parallel array of 120 carbon nanotubes per micron. The Langmuir-Schaefer method compresses the water surface area by moving the slide barrier, so that the carbon nanotubes on the surface aggregate and assemble into a double-layer parallel array of 500 carbon nanotubes per micron. In contrast, the evaporation-induced self-assembly method relies on capillary compensation flow generated when the solvent evaporates to make carbon nanotubes aggregate near the contact line between the dispersion and the substrate. The device is simple and has wide applicability. However, the capillary compensation flow is weak, and the aggregation of carbon nanotubes is not sufficient, so the density of the carbon nanotube parallel array prepared is only 10-20 carbon nanotubes per micron. In addition, the capillary compensation flow depends on the pinning of the contact line, which can cause the array to be unable to be continuously deposited, and finally form separated strips.

[0005] Therefore, the present application provides a method for forming a high-density parallel array of carbon nanotubes on a substrate by using Marangoni flow to improve the density of the parallel array of carbon nanotubes and meet the needs of users. SUMMARY

[0006] To solve the above problems, the present application provides a method for preparing a high-density parallel array of carbon nanotubes. The method inserts a substrate into a carbon nanotube dispersion, and uses the difference in vapor pressure and surface tension between the solvent components dispersing the carbon nanotubes to form a strong Marangoni flow at the contact line between the substrate and the carbon nanotube dispersion. During the relative separation and movement of the substrate and the carbon nanotube dispersion interface, a high-density parallel array of carbon nanotubes is obtained on the substrate. The carbon nanotube parallel array has a high linear density and a dense film, and has good application prospects. Thus, the present application is completed.

[0007] The present application aims to provide a method for preparing a high-density parallel array of carbon nanotubes. In the method, a substrate is inserted into a carbon nanotube dispersion, and the substrate is moved away from the liquid surface of the carbon nanotube dispersion to form a high-density parallel array of carbon nanotubes on the substrate.

[0008] The carbon nanotube parallel array is a single-layer carbon nanotube parallel array, a near-single-layer carbon nanotube parallel array, or a carbon nanotube film with a carbon nanotube parallel array on the top layer.

[0009] The carbon nanotube dispersion is a dispersion obtained by dispersing carbon nanotubes in a mixed solvent. The mixed solvent is a homogeneous mixture of two or more solvents. In the mixed solvent, the product of the difference between the vapor pressure of each component and the weighted average vapor pressure and the difference between the surface tension and the weighted average surface tension is volume fraction weighted average, which is negative and has an absolute value greater than or equal to 2 kPa·mN / m.

[0010] The application also aims to provide the high-density carbon nanotube parallel array prepared by the preparation method of the high-density carbon nanotube parallel array. The high-density carbon nanotube parallel array is a single-layer carbon nanotube parallel array, a near single-layer carbon nanotube parallel array or a carbon nanotube film with a carbon nanotube parallel array on the top layer. The carbon nanotube parallel array is uniformly arranged on the substrate.

[0011] The density of the high-density carbon nanotube parallel array is greater than or equal to 100 per micron.

[0012] The preparation method of the high-density carbon nanotube parallel array provided by the application has the following beneficial effects:

[0013] (1) The preparation method of the high-density carbon nanotube parallel array provided by the application promotes the occurrence of the Marangoni flow near the contact line of the carbon nanotube dispersion liquid, the substrate and the air, and makes the carbon nanotubes deposited on the substrate during the movement of the substrate. The preparation method is simple, the preparation condition is loose, and is easy to realize.

[0014] (2) The preparation method of the high-density carbon nanotube parallel array provided by the application is more universal, can be carried out by using various solvent systems, can effectively improve the preparation speed, and the obtained carbon nanotube parallel array can be continuously and uniformly deposited on the substrate.

[0015] (3) The preparation method of the high-density carbon nanotube parallel array provided by the application can prepare a single-layer carbon nanotube parallel array, a near single-layer carbon nanotube parallel array or a carbon nanotube film with a carbon nanotube parallel array on the top layer. The density of the carbon nanotube parallel array is high, and can reach 100 per micron. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The experimental device schematic diagram for preparing the high-density carbon nanotube parallel array in Example 1 of the application is shown;

[0017] Figure 2 The direction diagram of the Marangoni flow and the migration of the carbon nanotubes near the contact line of the carbon nanotube dispersion liquid and the substrate is shown;

[0018] Figure 3 a shows the atomic force microscope (AFM) characterization image of the carbon nanotubes deposited on the substrate by the carbon nanotube dispersion liquid prepared by using toluene as the solvent in Comparative Example 1 of the application;

[0019] Figure 3 b shows the AFM characterization image of the carbon nanotubes deposited on the substrate by the carbon nanotube dispersion liquid prepared by using toluene and decane as the solvents in Comparative Example 2 of the application;

[0020] Figure 3c shows AFM characterization image of carbon nanotubes deposited on substrate from carbon nanotube dispersion prepared in Comparative Example 3 of the present application using toluene and o-xylene as solvents;

[0021] Figure 3 d shows AFM characterization image of parallel array of carbon nanotubes deposited on substrate from carbon nanotube dispersion prepared in Example 1 of the present application using toluene and o-dichlorobenzene as solvents;

[0022] Figure 4 shows AFM characterization images of parallel array of carbon nanotubes prepared in Example 2 of the present application using silicon wafer, glass sheet and quartz sheet as substrates, respectively;

[0023] Figure 5 shows AFM characterization image of initial site of parallel array of carbon nanotubes prepared in Example 2 of the present application using silicon wafer as substrate;

[0024] Figure 6 shows AFM characterization images of parallel array of carbon nanotubes prepared in Example 3 using pulling speeds of 10, 20 and 50 μm / s, respectively;

[0025] Figure 7 a shows AFM characterization image of parallel array of carbon nanotubes prepared in Example 4 using carbon nanotube dispersion prepared from ternary solvent;

[0026] Figure 7 b shows AFM characterization image of parallel array of carbon nanotubes prepared in Example 5 using carbon nanotube dispersion prepared from quaternary solvent;

[0027] Figure 8 shows AFM characterization image of parallel array of carbon nanotubes prepared in Example 6 using carbon nanotube dispersion prepared from water and acetonitrile;

[0028] Figure 9 shows scanning electron microscope (SEM) characterization image of strip-shaped parallel array of carbon nanotubes prepared in Comparative Example 4;

[0029] Figure 10 shows SEM characterization image of parallel array of carbon nanotubes prepared in Comparative Example 5;

[0030] Figure 11 shows SEM characterization image of parallel array of carbon nanotubes prepared in Comparative Example 6;

[0031] Figure 12 shows optical photograph and SEM characterization image of parallel array of carbon nanotubes prepared in Comparative Example 7;

[0032] Figure 13 shows SEM characterization image of parallel array of carbon nanotubes prepared in Comparative Example 8;

[0033] Figure 14 AFM characterization images of the carbon nanotube parallel array prepared in Comparative Example 9 are shown. DETAILED DESCRIPTION

[0034] The present application will be described in detail below with specific embodiments, and the features and advantages of the present application will become more apparent with these descriptions.

[0035] The present application provides a method for preparing a high-density carbon nanotube parallel array. In the method, a substrate is inserted into a carbon nanotube dispersion liquid, the substrate is moved away from the liquid surface of the carbon nanotube dispersion liquid, and a high-density carbon nanotube parallel array is formed on the substrate.

[0036] The carbon nanotube parallel array is a single-layer carbon nanotube parallel array, a near-single-layer carbon nanotube parallel array, or a carbon nanotube film with a top layer being a carbon nanotube parallel array. The near-single-layer carbon nanotube parallel array is a carbon nanotube parallel array in which the area proportion of the single-layer carbon nanotube parallel array is greater than 50%.

[0037] The carbon nanotube is one or more of a single-walled carbon nanotube, a double-walled carbon nanotube, and a multi-walled carbon nanotube, and is preferably a single-walled carbon nanotube. Preferably, the carbon nanotube has an impurity content of less than 40 wt%, preferably less than 20 wt%, and more preferably less than 10 wt%. Preferably, the relative intensity ratio of the G peak and the D peak of the Raman spectrum of the carbon nanotube is ≥1, preferably ≥5, and more preferably ≥20.

[0038] The carbon nanotube dispersion liquid is a dispersion liquid obtained by dispersing carbon nanotubes in a mixed solvent. The mixed solvent is a homogeneous mixed solvent of two or more solvents. In the mixed solvent, the volume fraction weighted average of the product of the difference between the vapor pressure of each component and the weighted average vapor pressure and the difference between the surface tension of each component and the weighted average surface tension is negative, and the absolute value is greater than or equal to 2 kPa·mN / m. The process of volume fraction weighted average of the product of the difference between the vapor pressure of each component and the weighted average vapor pressure and the difference between the surface tension of each component and the weighted average surface tension is specifically shown in formula (1):

[0039]

[0040] wherein,

[0041]

[0042] i is the 1st, 2nd, 3rd, …, n solvent component, V i , p i , S i are the volume fraction, vapor pressure, and surface tension of solvent component i, respectively.

[0043] When the high-boiling component (whose vapor pressure is lower than the weighted average vapor pressure) has a higher surface tension (the surface tension is higher than the weighted average surface tension), the result is negative; when the high-boiling component (whose vapor pressure is lower than the weighted average vapor pressure) has a lower surface tension (the surface tension is higher than the weighted average surface tension), the result is positive; the greater the difference between the boiling point (vapor pressure) and the surface tension, the greater the absolute value of the result.

[0044] The boiling point of the mixed solvent is 50-280℃, preferably 60-250℃, more preferably 70-220℃, and the surface tension of the mixed solvent is 10-80 mN / m, preferably 15-75 mN / m, more preferably 20-75 mN / m.

[0045] In the present application, the boiling points and vapor pressures of the solvent components in the mixed solvent dispersion obtained by reasonably selecting and preparing the solvent components are different, resulting in different evaporation rates and regional distribution of solvent concentration. Because different solvents have different surface tensions, the regional distribution of solvent concentration is accompanied by the regional distribution of surface tension, resulting in a surface tension gradient in the solution, thereby triggering the Marangoni flow. Subsequently, when depositing and preparing high-density carbon nanotube parallel arrays on the substrate, the Marangoni flow can drive the migration and aggregation of carbon nanotubes, and the carbon nanotubes are squeezed and aligned in a specific direction, finally forming a high-density parallel array. The difference between the boiling points (vapor pressures) and the surface tensions of the solvent components increases, which can trigger stronger Marangoni flow, which is conducive to the preparation of carbon nanotube parallel arrays. However, if the boiling point of the solvent is too high, higher than 280℃, the deposition process of the carbon nanotubes will be too slow; if the boiling point of the solvent is too low, lower than 50℃, the evaporation speed will be too fast, and the flow will be difficult to stabilize. Too high or too low surface tension of the solvent will lead to difficulty in matching the appropriate wettability of the substrate.

[0046] The solvent components in the mixed solvent are selected from two or more of water and organic solvents with carbon number less than 14, preferably selected from two or more of water, methanol, ethanol, isopropanol, tert-butanol, ethylene glycol, 1,2-propanediol, glycerol, acetonitrile, acetone, diethyl ether, dipropyl ether, petroleum ether, dioxane, acetic acid, trifluoroacetic acid, ethyl acetate, triethylamine, tetrahydrofuran, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, trichloroethylene, pentane, hexane, heptane, octane, nonane, decane, cyclohexane, gasoline, dichloromethane, trichloromethane, carbon tetrachloride, dichloroethane, trichloroethane, pyridine, benzene, toluene, o-xylene, m-xylene, p-xylene, mesitylene, styrene, chlorobenzene, o-chlorotoluene, m-chlorotoluene, p-chlorotoluene, o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, bromobenzene, o-bromotoluene, m-bromotoluene, p-bromotoluene, o-dibromobenzene, m-dibromobenzene, p-dibromobenzene, aniline, diphenyl ether, anisole, benzaldehyde, benzyl alcohol, and nitrobenzene, more preferably two or more of benzene, toluene, o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, o-chlorotoluene, m-chlorotoluene, p-chlorotoluene, and nitrobenzene, or two or more of water, methanol, acetonitrile, and acetone.

[0047] The concentration of the carbon nanotubes in the carbon nanotube dispersion is 1 μg / mL to 1 mg / mL, preferably 5 μg / mL to 400 μg / mL, and more preferably 10 μg / mL to 200 μg / mL. If the concentration is too low, below 1 μg / mL, the carbon nanotubes cannot be effectively aggregated and extruded, and the density and parallel degree of the carbon nanotube parallel array prepared are low. If the concentration is too high, above 1 mg / mL, the carbon nanotubes are difficult to be well dispersed individually, and the entanglement between the carbon nanotubes affects the quality of the carbon nanotube parallel array.

[0048] The method for preparing the carbon nanotube dispersion is not specifically limited in the present application, and any method capable of obtaining a uniform carbon nanotube dispersion can be used. Preferably, the carbon nanotubes are dispersed in one solvent, and then other solvent components are added.

[0049] The dispersing agent for dispersing the carbon nanotubes in the solvent is selected from one or more of surfactants, water-soluble biomolecules, conjugated polymers, and aryl-containing compounds, preferably one or more of conjugated polymers and nucleic acids, and more preferably single-stranded DNA or a conjugated polymer containing carbazolyl and fluorenyl groups.

[0050] After the dispersing agent is added, it is coated on the surface of the carbon nanotubes, and under the action of ultrasonic waves, the carbon nanotubes are no longer aggregated to form bundles, but are dispersed in the solvent in the form of single tubes. Preferably, when the solvent contains a water component, the dispersing agent is a water-soluble biomolecule, such as single-stranded DNA; when the solvent is an organic solvent, the dispersing agent is a conjugated polymer, such as poly[9-(1-octylnonyl)-9H-carbazole].

[0051] The mass ratio of the carbon nanotubes to the dispersant is 1:(0.15-6), preferably 1:(0.25-4), and more preferably 1:(0.5-2.5). Too high or too low amount of the dispersant will reduce the utilization of the carbon nanotubes or the dispersant.

[0052] In the present application, the dispersant disperses the carbon nanotubes at a low free concentration. Preferably, the carbon nanotube dispersion is subjected to one or more of dialysis, centrifugal sedimentation followed by redispersion, and filtration followed by redispersion to remove excess dispersant, so as to avoid the co-deposition of the excess dispersant with the carbon nanotubes and affect the quality of the parallel array of carbon nanotubes. In the filtration, the pore size of the filter membrane is less than 0.5 μm, and preferably less than 0.2 μm, so as to reduce the loss of the carbon nanotubes.

[0053] In the present application, the substrate material is not particularly limited and can be selected from one of gold, copper, aluminum, silicon, germanium, graphene, highly oriented pyrolytic graphite, glass, ceramic, mica, fluorine crystal mica, silicon dioxide, aluminum oxide, hafnium dioxide, and organic polymer, and is preferably one of silicon, quartz, and glass, and more preferably a silicon wafer (with or without a surface oxide layer). The root mean square roughness of the substrate surface is less than 10 nm, preferably less than 2 nm, and more preferably less than 0.5 nm. It has been found through experiments that the method for preparing the parallel array of carbon nanotubes of the present application does not depend on the type of the substrate, but a lower surface roughness is preferred to reduce the pinning effect of the contact line.

[0054] In the present application, the lower part of the substrate is inserted into the carbon nanotube dispersion, a contact line is formed at the three-phase contact of the substrate, the carbon nanotube dispersion, and air, and a high-density parallel array of carbon nanotubes is formed at the contact line as the substrate is pulled upward.

[0055] The contact angle of the carbon nanotube dispersion on the substrate is 5°-75°, preferably 10°-70°, and more preferably 15°-60°. A contact angle of 5°-75° can ensure that a contact meniscus of an appropriate thickness is formed at the contact line of the carbon nanotube dispersion and the substrate. If the contact angle is too small, the meniscus is too thin, the compensating flow of the Marangoni flow is difficult to develop, the stability of the Marangoni flow is reduced, and the uniformity of the prepared parallel array of carbon nanotubes is reduced. If the contact angle is too large, the meniscus is too thick, and too much solution is present, which will result in a small change in the concentration caused by the difference in the evaporation of the mixed solvents, a weak Marangoni flow, and a reduction in the density and the orientation degree of the parallel array of carbon nanotubes.

[0056] Preferably, the substrate is subjected to a surface modification treatment to ensure the wettability of the carbon nanotube dispersion to the substrate, so that the contact angle is in the range of 5° to 75°. The surface modification treatment is selected from one or more of annealing, acid or base soaking, piranha solution heating soaking, plasma surface cleaning, silane, siloxane or silazane solution soaking / rinsing. Preferably, the surface modification treatment is piranha solution heating soaking followed by rinsing. The heating temperature is 80 to 100°C, and the soaking time is 20 to 40 minutes. The piranha solution is prepared by mixing concentrated sulfuric acid with 30wt% hydrogen peroxide solution in a volume ratio of (2 to 3.5):1.

[0057] The surface modification treatment can remove impurities on the substrate surface and properly adjust the contact angle of the carbon nanotube dispersion to the substrate, so as to improve the quality of the prepared carbon nanotube parallel array. The surface modification treatment can also be used to regulate the interaction properties and strength between the substrate and the carbon nanotube, so as to selectively prepare a single layer / near single layer carbon nanotube parallel array, or a carbon nanotube film with a carbon nanotube parallel array on the top layer.

[0058] The angle between the substrate and the vertical direction is 0° to 75°, preferably 0° to 10°, and more preferably 0°, i.e. the substrate is vertically immersed in the mixed solvent dispersion of the carbon nanotube. The direction of the substrate also affects the meniscus shape, and the device and operation for vertically immersing and pulling the substrate are the simplest.

[0059] Preferably, after the substrate is immersed in the carbon nanotube dispersion, the substrate is allowed to be stationary in the carbon nanotube dispersion for a period of time, so as to calm the disturbance to the liquid caused by the immersion process, and to make the evaporation of the mixed solvent and the regional distribution of the component concentrations near the contact line reach a steady state, thereby improving the uniformity of the preparation of the carbon nanotube parallel array. The stationary time is 1 to 30 minutes, and preferably 10 to 20 minutes.

[0060] The moving speed of the substrate away from the liquid surface of the carbon nanotube dispersion is 0.1 μm / s to 1 mm / s, preferably 0.2 μm / s to 200 μm / s, and more preferably 0.5 μm / s to 50 μm / s. The upward movement of the substrate is at a constant speed or a variable speed, and preferably at a constant speed. It has been found through experiments that if the moving speed is too fast, the induced viscous flow will interfere with the Marangoni flow in the dispersion, and at the same time, the aggregation time of the carbon nanotube will be reduced, resulting in a decrease in the order degree and density of the prepared carbon nanotube parallel array; and if the moving speed is too slow, the preparation process will be time-consuming, and the dispersion will change significantly in concentration due to evaporation, resulting in a decrease in the uniformity of the prepared carbon nanotube parallel array. The movement can be achieved by pulling the substrate, or by changing the position of the dispersion container.

[0061] When the substrate is moved upward from the carbon nanotube dispersion liquid surface, the temperature of the carbon nanotube dispersion liquid is between the freezing point and the boiling point of the carbon nanotube dispersion liquid, preferably 10-30°C higher than the freezing point of the high freezing point solvent component in the carbon nanotube dispersion liquid. In the above temperature range, the rotational diffusion movement of the carbon nanotubes can be inhibited, which is beneficial to the formation of the array and improves the parallel degree of the array, but too low temperature will result in too slow deposition process of the carbon nanotubes; and too high temperature will result in too fast volatilization speed and unstable flow.

[0062] The Marangoni flow near the contact line of the carbon nanotube dispersion liquid and the substrate and the direction of the carbon nanotube migration are shown as Figure 2 The solvent mass transfer between the carbon nanotube dispersion liquid phase near the contact line and the environment is more sufficient than that between the body phase dispersion liquid and the environment, and the solvent volatilization rate is faster. At the same time, the volatilization rate of the low boiling point (high vapor pressure) component in the mixed solvent of the carbon nanotube dispersion liquid is faster, resulting in that the concentration of the high boiling point (low vapor pressure) component in the carbon nanotube dispersion liquid phase near the contact line is higher than that in the body phase carbon nanotube dispersion liquid. When the deposition is carried out using the carbon nanotube dispersion liquid reasonably prepared, the surface tension of the high boiling point (low vapor pressure) component is higher, so the Marangoni flow on the meniscus will point to the vicinity of the contact line with the substrate from the outside of the dispersion liquid surface, and the convection will gradually develop inside the dispersion liquid. The carbon nanotubes in the carbon nanotube dispersion liquid migrate and gather toward the contact line under the push of the flow, are squeezed with each other and are arranged along the direction of the contact line, and finally a high-density parallel array of carbon nanotubes is deposited on the substrate.

[0063] It is found through experiments that, by the method of the present application, the combination of the carbon nanotube dispersion liquid formed by selecting different mixed solvents and the substrate can obtain a carbon nanotube parallel array with a thickness of a single layer or close to a single layer, and can also obtain a multi-layer carbon nanotube film, in which the top layer is a carbon nanotube parallel array and the other layers are randomly oriented carbon nanotube networks.

[0064] When the interaction force between the carbon nanotubes in the dispersion liquid and the substrate is mainly attractive force, the carbon nanotubes will be randomly adsorbed to the surface of the substrate immersed in the dispersion liquid, and then the carbon nanotube parallel array assembled at the gas-liquid-solid three-phase contact line during the pulling will be deposited on the adsorption layer, and finally the multi-layer carbon nanotube film is formed; wherein, the position where the dispersion liquid is first pulled out has a shorter adsorption time, and the randomly oriented carbon nanotube network attached to the substrate will be relatively sparse, and even a carbon nanotube parallel array close to a single layer can be deposited. When the interaction force between the carbon nanotubes in the dispersion liquid and the substrate is mainly repulsive force, the random adsorption of the carbon nanotubes is difficult to occur, and finally a carbon nanotube parallel array with a thickness of a single layer or close to a single layer is prepared.

[0065] Preferably, all the dispersion liquid prepared with organic solvent, such as carbon nanotube dispersion liquid prepared with toluene and o-dichlorobenzene mixed solvent, toluene and nitrobenzene mixed solvent, toluene, benzene and nitrobenzene mixed solvent, toluene, benzene, chlorobenzene and nitrobenzene mixed solvent, can prepare carbon nanotube film with carbon nanotube parallel array as top layer on silicon, quartz and glass substrate surface.

[0066] Carbon nanotube dispersion liquid prepared with aqueous solvent, such as water and acetonitrile mixed solvent, can prepare near single layer carbon nanotube parallel array on silicon, quartz and glass substrate surface.

[0067] The present application also provides high density carbon nanotube parallel array prepared by the method.

[0068] The high density carbon nanotube parallel array is single layer carbon nanotube parallel array, near single layer carbon nanotube parallel array or carbon nanotube film with carbon nanotube parallel array as top layer. The carbon nanotube parallel array is continuous and uniform on the substrate.

[0069] The density of the high density carbon nanotube parallel array is greater than or equal to 100 per micron.

[0070] Examples

[0071] Example 1

[0072] The high density carbon nanotube parallel array is prepared by using the device as shown in Figure 1 The commercially available single-walled carbon nanotubes (Carbon Solutions, AP-SWNT, carbon purity 60-70%, relative intensity ratio of Raman G peak and D peak > 30) and poly[9-(1-octylnonyl)-9H-carbazole] are mixed in a mass ratio of 1:1 and added to toluene. The single-walled carbon nanotubes are well dispersed in the toluene in a probe-type ultrasonic instrument. After centrifugation at 21 kG for 20 minutes, the supernatant is taken and filtered through a hydrophilic polytetrafluoroethylene microporous filter with a pore size of 0.1 μm. The filtered single-walled carbon nanotubes are re-dispersed in toluene, and the ultrasonic dispersion and centrifugation steps are repeated. The supernatant is taken and diluted to a concentration of about 30 μg / mL to obtain a toluene dispersion of single-walled carbon nanotubes.

[0073] The o-dichlorobenzene is added to the above toluene dispersion to obtain a carbon nanotube dispersion liquid with a volume fraction of o-dichlorobenzene of 20%.

[0074] Toluene has a boiling point of 110.6 °C, a vapor pressure of 2.93 kPa, and a surface tension of 28.5 mN / m. O-Dichlorobenzene has a boiling point of 180.5 °C, a vapor pressure of 0.13 kPa, and a surface tension of 37.2 mN / m. The result of formula (1) for the toluene + o-dichlorobenzene mixed solvent is -3.9 kPa-mN / m, which meets the requirement. Therefore, the toluene + o-dichlorobenzene mixed solvent dispersion is reasonably prepared, and the Marangoni flow induced thereby is strong enough and is directed towards the contact line.

[0075] The silicon wafer substrate was put into piranha solution (concentrated sulfuric acid and 30 wt% hydrogen peroxide aqueous solution were mixed in a volume ratio of 7:3), heated at 90 °C for 30 minutes, and then cleaned with water and ethanol, and the surface root mean square roughness was 0.2-0.5 nm. The cleaned silicon wafer was fixed on a pulling machine and vertically immersed in the above carbon nanotube dispersion, respectively, at 20-25 °C, and was static for 15 minutes. Then the silicon wafer was pulled at a speed of 2 μm / s until it was completely pulled out of the dispersion, and a high-density carbon nanotube parallel array was obtained. The AFM test result is shown in Fig. 2d, and it can be seen that the top layer is a carbon nanotube parallel array, and the lower layer is a randomly oriented carbon nanotube network, which indicates that the carbon nanotube dispersion prepared with toluene and o-dichlorobenzene as mixed solvents can prepare a carbon nanotube film with a carbon nanotube parallel array as the top layer. Figure 3

[0076] Example 2

[0077] A high-density carbon nanotube parallel array was obtained by the method of Example 1, and the difference was that when the mixed solvent dispersion of carbon nanotubes was prepared, nitrobenzene (20% by volume) was added to the toluene dispersion of carbon nanotubes; and in the subsequent pulling step, the substrates used were silicon wafers, glass wafers, and quartz wafers, and the surface root mean square roughness of the silicon wafer was 0.2-0.5 nm, and the pulling speed was 5 μm / s.

[0078] Toluene has a boiling point of 110.6 °C, a vapor pressure of 2.93 kPa, and a surface tension of 28.5 mN / m. Nitrobenzene has a boiling point of 210.9 °C, a vapor pressure of 0.026 kPa, and a surface tension of 44.0 mN / m. The result of formula (1) for the toluene + nitrobenzene mixed solvent is -7.2 kPa-mN / m, which meets the requirement. Therefore, the toluene + nitrobenzene mixed solvent dispersion is reasonably prepared, and the Marangoni flow induced thereby is strong enough and is directed towards the contact line.

[0079] The AFM test result is shown in Fig. 4d. It can be seen that the top layer is a carbon nanotube parallel array, and the lower layer is a randomly oriented carbon nanotube network, which indicates that the carbon nanotube dispersion prepared with toluene and nitrobenzene as mixed solvents can prepare a carbon nanotube film with a carbon nanotube parallel array as the top layer. Figure 4 Figure 4 ​​It can be seen that no matter the substrate is silicon wafer, glass wafer or quartz wafer, the multi-layer carbon nanotube film can be obtained by using the carbon nanotube dispersion liquid prepared by using the mixed solvent of toluene and nitrobenzene, wherein the top layer is the parallel array of carbon nanotubes and the lower layer is the network of randomly oriented carbon nanotubes. This shows that the preparation method described in the application is not dependent on a specific substrate and has universality.

[0080] The product prepared by pulling out the position of the carbon nanotube dispersion liquid on the surface of the silicon wafer substrate first is tested by AFM, and the test result is shown in Figure 5 .

[0081] It can be seen from Figure 5 that due to the short adsorption time, the substrate at this position has almost no network of randomly oriented carbon nanotubes attached thereto, thereby facilitating the characterization of the density of the top layer parallel array. The linear density in the direction perpendicular to the array is higher than 100 per micron, and the positions of the carbon nanotubes are shown by red arrows. Since part of the carbon nanotubes are adhered by the polymer dispersant and cannot be accurately identified, the actual array density should be higher.

[0082] Example 3

[0083] The high-density carbon nanotube parallel array is prepared according to the method of Example 2, and the difference is that the substrate used is a silicon wafer, and the pulling speed is 10 μm / s, 20 μm / s and 50 μm / s, respectively.

[0084] The product prepared in Example 3 is tested by AFM, and the test result is shown in Figure 6 .

[0085] It can be seen from Figure 6 that when the pulling speed is 10 μm / s, 20 μm / s and 50 μm / s, the multi-layer carbon nanotube film is obtained, wherein the top layer is the parallel array of carbon nanotubes and the lower layer is the network of randomly oriented carbon nanotubes. Examples 1-3 collectively show that the preparation method described in the application shows good applicability to various pulling speeds.

[0086] Example 4

[0087] The high-density carbon nanotube parallel array is prepared according to the method of Example 1, and the difference is that when the mixed solvent dispersion liquid of carbon nanotubes is prepared, benzene and nitrobenzene (volume fractions are 10% and 20%, respectively) are added to the toluene dispersion liquid of carbon nanotubes to form a ternary solvent carbon nanotube dispersion liquid; in the subsequent pulling step, the pulling speed is 5 μm / s.

[0088] Toluene has a boiling point of 110.6 °C, a vapor pressure of 2.93 kPa, and a surface tension of 28.5 mN / m. Benzene has a boiling point of 80.1 °C, a vapor pressure of 10.01 kPa, and a surface tension of 28.9 mN / m. Nitrobenzene has a boiling point of 210.9 °C, a vapor pressure of 0.026 kPa, and a surface tension of 44.0 mN / m. The result of equation (1) for the ternary mixture is -9.1 kPa-mN / m, which meets the requirement. Therefore, the ternary solvent dispersion is properly formulated, and the Marangoni flow induced is strong enough and directed toward the contact line.

[0089] The product of Example 4 was tested by AFM, and the test results are shown in Figure 7 a. As can be seen from Figure 7 a, the carbon nanotube dispersion prepared using the ternary solvent of toluene, benzene, and nitrobenzene produces a multi-layer carbon nanotube film, in which the top layer is a parallel array of carbon nanotubes, and the lower layer is a network of randomly oriented carbon nanotubes.

[0090] Example 5

[0091] High-density parallel arrays of carbon nanotubes were prepared according to the method of Example 4, except that benzene, chlorobenzene, and nitrobenzene were added to the toluene dispersion of carbon nanotubes to form a carbon nanotube dispersion of a quaternary solvent, with volume fractions of 10%, 10%, and 20%, respectively.

[0092] Toluene has a boiling point of 110.6 °C, a vapor pressure of 2.93 kPa, and a surface tension of 28.5 mN / m. Benzene has a boiling point of 80.1 °C, a vapor pressure of 10.01 kPa, and a surface tension of 28.9 mN / m. Nitrobenzene has a boiling point of 210.9 °C, a vapor pressure of 0.026 kPa, and a surface tension of 44.0 mN / m. The result of equation (1) for the ternary mixture is -9.1 kPa-mN / m, which meets the requirement. Therefore, the ternary solvent dispersion is properly formulated, and the Marangoni flow induced is strong enough and directed toward the contact line.

[0093] The product of Example 5 was tested by AFM, and the test results are shown in Figure 7 b. The product of Example 5 was tested by AFM, and the test results are shown in Figure 7 b. As can be seen from Figure 7 b, the carbon nanotube dispersion prepared using the quaternary solvent of toluene, benzene, chlorobenzene, and nitrobenzene also produces a multi-layer carbon nanotube film, in which the top layer is a parallel array of carbon nanotubes, and the lower layer is a network of randomly oriented carbon nanotubes.

[0094] Example 6

[0095] High density carbon nanotube parallel arrays were prepared according to the method of Example 1, with the only difference that when preparing the carbon nanotube dispersion, commercially available single-walled carbon nanotubes and single-stranded DNA were mixed in a mass ratio of 1:2.5 and added to water; when preparing the carbon nanotube dispersion, acetonitrile was added to the water dispersion of the carbon nanotubes diluted to 100 μg / mL (the final volume fraction was 15%); and in the subsequent pulling step, the pulling speed was 1 μm / s.

[0096] The boiling point of water is 100°C, the vapor pressure is 2.34 kPa, and the surface tension is 72.9 mN / m. The boiling point of acetonitrile is 82°C, the vapor pressure is 9.33 kPa, and the surface tension is 29.3 mN / m. The calculation result of the water + acetonitrile mixed solvent according to formula (1) is -38.9 kPa·mN / m, which meets the requirement. Therefore, the water + acetonitrile mixed solvent dispersion is reasonably prepared, and the induced Marangoni flow is strong enough and directed towards the contact line.

[0097] AFM test was performed on the product prepared in Example 6, and the test result is shown in Figure 8 .

[0098] As can be seen from Figure 8 , the near-single-layer carbon nanotube parallel array can be prepared using the carbon nanotube dispersion of the water + acetonitrile mixed solvent which is reasonably prepared, and more than 50% of the entire carbon nanotube parallel array area is single-layer according to statistical analysis. As can be seen from Figure 8 , there are no or few randomly oriented carbon nanotubes under the near-single-layer array. This is because the single-walled carbon nanotubes dispersed by the single-stranded DNA in the water phase dispersion and the silicon wafer substrate surface modified by the piranha solution are both negatively charged, and the interaction force between them is mainly electrostatic repulsion, which prevents the random adsorption of carbon nanotubes.

[0099] According to the statistical analysis, the linear density of the carbon nanotubes is higher than 100 per micron. The results of Examples 1-6 collectively show that the preparation method described in the present application is not dependent on a specific dispersant and solvent combination and has universality.

[0100] Comparative Example

[0101] Comparative Example 1

[0102] High density carbon nanotube parallel arrays were prepared according to the method of Example 1, with the only difference that the o-dichlorobenzene was replaced with an equal volume of toluene.

[0103] AFM test was performed on the product after deposition, and the test graph is shown in Figure 3 a. It can be seen that no ordered carbon nanotube parallel array is obtained.

[0104] Comparative Example 2

[0105] The high-density carbon nanotube parallel array was prepared according to the method of Example 1, except that the o-dichlorobenzene was replaced by an equal volume of decane.

[0106] The boiling point of toluene is 110.6°C, the vapor pressure is 2.93 kPa, and the surface tension is 28.5 mN / m. The boiling point of decane is 174.1°C, the vapor pressure is 0.095 kPa, and the surface tension is 23.8 mN / m. The calculation result of formula (1) of the toluene+decane mixed solvent is 2.1 kPa·mN / m, which is positive, and does not meet the requirements. Compared with toluene, decane has a higher boiling point (lower vapor pressure) and a lower surface tension, and therefore, the toluene+decane mixed solvent dispersion is incorrectly prepared, the Marangoni flow induced thereby is far away from the contact line, and the carbon nanotube parallel array cannot be obtained.

[0107] The product after deposition was tested by AFM, and the test image is as shown in Figure 3 b. It can be seen that no ordered carbon nanotube parallel array is obtained.

[0108] Comparative Example 3

[0109] The high-density carbon nanotube parallel array was prepared according to the method of Example 1, except that the o-dichlorobenzene was replaced by an equal volume of o-xylene.

[0110] The boiling point of toluene is 110.6°C, the vapor pressure is 2.93 kPa, and the surface tension is 28.5 mN / m. The boiling point of o-xylene is 144°C, the vapor pressure is 0.65 kPa, and the surface tension is 30.3 mN / m. The calculation result of formula (1) of the toluene+o-xylene mixed solvent is -0.7 kPa·mN / m, and the absolute value is less than 2 kPa·mN / m, which does not meet the requirements. The surface tension of o-xylene is relatively close to that of toluene, and therefore, the toluene+o-xylene mixed solvent dispersion cannot induce a strong enough Marangoni flow, and the carbon nanotube parallel array cannot be obtained.

[0111] The product after deposition was tested by AFM, and the test image is as shown in Figure 3 c. It can be seen that no ordered carbon nanotube parallel array is obtained.

[0112] Comparative Example 4

[0113] The strip-shaped carbon nanotube parallel array was prepared according to the method of Michael Engel et al. ACS Nano, 2008, 2, 2445-2452.

[0114] A silicon wafer substrate was vertically immersed into a water-based dispersion of single-walled carbon nanotubes, with water as the solvent and 1% sodium dodecyl sulfate as the dispersant. As the dispersion volatilized, the parallel array of ribbon-like carbon nanotubes separated by blank areas gradually deposited onto the substrate along the air-liquid-solid three-phase contact line at a linear density of 10-20 nanotubes per micrometer, as shown in the SEM image of FIG. 1. Figure 9

[0115] Unlike the present invention, the above process relies on the capillary compensation flow generated by the volatilization of a single solvent to push the carbon nanotubes to aggregate and assemble into parallel arrays at the contact line. The capillary compensation flow is weak due to the lack of surface tension gradient caused by the differential volatilization of mixed solvents, and thus the aggregation of carbon nanotubes is insufficient and the array density is low. To avoid interference with the weak capillary compensation flow by processes such as pulling, the contact line is allowed to descend by the natural volatilization of the dispersion, resulting in very slow deposition. In addition, the capillary compensation flow relies on the pinning of the contact line position, which can lead to discontinuous deposition of the array and eventually result in separated ribbons with jumps in the contact line position.

[0116] Comparative Example 5

[0117] A parallel array of carbon nanotubes was prepared using the method in the literature Lijun Liu et al. Science, 2020, 368, 850-856.

[0118] A silicon wafer substrate was vertically immersed into a 1,1,2-trichloroethane dispersion of single-walled carbon nanotubes, with poly[9-(1-octylnonyl)-9H-carbazole] as the dispersant and the excess free dispersant being removed in advance. Then a liquid-liquid interface was formed by adding a small amount of 2-butyne-1,4-diol, which is immiscible with the dispersion, above the liquid surface. As the substrate was pulled upwards at a speed of 2 pm / s, a continuous parallel array of carbon nanotubes gradually deposited onto the substrate along the liquid-liquid-solid three-phase contact line at a linear density of more than 100 nanotubes per micrometer, as shown in the SEM image of FIG. 4. Figure 10

[0119] Unlike the present invention, the above process relies on the interaction between the dispersant of carbon nanotubes and the polyol 2-butyne-1,4-diol to promote the aggregation of carbon nanotubes at the liquid-liquid interface, resulting in pre-assembly, and finally deposition as a parallel array of carbon nanotubes during the pulling process. Hydrogen bonding is believed to be the key to this interaction, which relies on a specific dispersant and solvent system and thus limits the universality of this method, which cannot assemble a parallel array of carbon nanotubes with an aqueous dispersion. Due to the small proportion of nitrogen atoms in the molecular structure of the dispersant that can form hydrogen bonds, the strength of hydrogen bonding is limited, which makes the aggregation of carbon nanotubes at the liquid-liquid interface slow, and accordingly limits the pulling speed of the substrate. In addition, the multi-phase system containing the liquid-liquid interface is more unstable than the single-phase dispersion and is easily disturbed, which also limits the pulling speed of the substrate.​​

[0120] Comparative Example 6

[0121] A carbon nanotube parallel array was prepared by the method in the literature Huiwen Shi et al. Nature Electronics, 2021, 4, 405-415.

[0122] A silicon wafer was vertically immersed in ethylene glycol, and then an organic phase dispersion of single-walled carbon nanotubes immiscible with ethylene glycol was injected above the liquid surface to form a liquid-liquid interface, the organic phase solvent of which was m-chlorotoluene, and the dispersant was poly[2-methyl-7-(6'-methyl-[2,2'-bipyridine]-6-yl)-9-(2-octylacyl)-9H-carbazole], and the free excess dispersant was removed in advance. As the substrate was pulled up at a speed of 10 μm / s, a continuous carbon nanotube parallel array gradually deposited onto the substrate along the liquid-liquid-solid three-phase contact line, with a linear density of more than 100 per micron, as shown in the SEM image of Figure 11 .

[0123] Unlike the present application, the above process relies on similar principles to Comparative Example 5 to achieve the preparation of the array, and therefore also has the problems of poor universality, slow preparation speed, and the interface being easily disturbed. Although it replaces the dispersant of carbon nanotubes and polyhydric alcohol with a kind that has more hydrogen-bonding atoms, the pulling speed of the substrate is still limited to within 10 μm / s.

[0124] Comparative Example 7

[0125] A strip-shaped carbon nanotube parallel array separated by random network regions was prepared by the method in the literature Katherine R. Jinkins et al. Langmuir, 2017, 33, 13407-13414.

[0126] A silicon wafer substrate after surface modification treatment was vertically immersed in pure water, and then an organic phase dispersion of single-walled carbon nanotubes immiscible with water was injected drop by drop by a syringe pump at a rate of 2.5 μL per drop, 50 drops per minute, to form a liquid-liquid interface above the water surface, the organic phase solvent of which was chloroform, and the dispersant was poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(6,6'-{2,2'-bipyridine})], and the free excess dispersant was removed in advance. During the dropwise addition process, the substrate was pulled up at a speed of 9 mm / min, and a carbon nanotube parallel array separated by random network regions gradually deposited onto the substrate along the liquid-liquid-solid three-phase contact line, with a linear density of about 50 per micron, as shown in the photo and SEM image of Figure 12 .

[0127] Unlike the present invention, the above process relies on tangential flow generated by the spreading of the dispersion on the water surface and the liquid crystalline aggregation of carbon nanotubes at the liquid-liquid interface to achieve assembly. Although this process is accompanied by the evaporation of the dispersion, the evaporation is not the driving force for the assembly of the array. When the array deposited at the liquid-liquid-solid three-phase contact line rises to the gas-liquid-solid three-phase contact line, the position of the latter on the substrate is pinned by the array, resulting in the jumps of both contact line positions during the pulling process, making the array unable to be continuously deposited, and finally forming strips separated by random network regions. The aggregation of carbon nanotubes at the liquid-liquid interface relies on the existence of the phase interface and specific intermolecular interactions, and thus limits the universality of this method, for example, it is difficult to assemble the aqueous dispersion of carbon nanotubes. The multi-phase system containing the liquid-liquid interface is also more unstable than the single-phase dispersion and is easily disturbed. In addition, the aggregation of carbon nanotubes is limited, and the array density is low.

[0128] Comparative Example 8

[0129] The carbon nanotube parallel array was prepared by the method in the literature Katherine R. Jinkins et al. Science Advances, 2021, 7, eabh0640.

[0130] The surface-modified silicon wafer substrate and the barrier layer were placed in parallel with a 3 mm interval and inclined at an angle of 45 degrees and immersed in pure water. Then, the water-immiscible organic phase dispersion of single-walled carbon nanotubes was injected into the water surface between the substrate and the barrier layer at a rate of 4 mL / min to form a liquid-liquid interface, the solvent was chloroform, and the dispersant was poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(6,6'-{2,2'-bipyridine})], and the free excess dispersant was removed in advance. During the injection process, the substrate and the barrier layer were pulled at a speed of 160 mm / min, and the continuous carbon nanotube parallel array was gradually deposited on the substrate along the liquid-liquid-solid three-phase contact line, and the linear density was about 50 per micron, as shown in the SEM image of Figure 13 .

[0131] Unlike the present invention, the above process relies on tangential flow generated by the spreading of the dispersion on the water surface and the liquid crystalline aggregation of carbon nanotubes at the liquid-liquid interface to achieve assembly. Although this process is accompanied by the evaporation of the dispersion, the evaporation is not the driving force for the assembly of the array. When the array deposited at the liquid-liquid-solid three-phase contact line rises to the gas-liquid-solid three-phase contact line, the position of the latter on the substrate is pinned by the array, resulting in the jumps of both contact line positions during the pulling process, making the array unable to be continuously deposited, and finally forming strips separated by random network regions. The aggregation of carbon nanotubes at the liquid-liquid interface relies on the existence of the phase interface and specific intermolecular interactions, and thus limits the universality of this method, for example, it is difficult to assemble the aqueous dispersion of carbon nanotubes. The multi-phase system containing the liquid-liquid interface is also more unstable than the single-phase dispersion and is easily disturbed. In addition, the aggregation of carbon nanotubes is limited, and the array density is low.

[0132] Comparative Example 9

[0133] Carbon nanotube parallel arrays were prepared by the method described in Xiaolin Li et al. Journal of the American Chemical Society, 2007, 129, 4890-4891.

[0134] A substrate such as a silicon wafer was vertically immersed in pure water, and then an organic phase dispersion of water-immiscible single-walled carbon nanotubes was injected onto the water surface. The solvent was 1,2-dichloroethane, and the dispersant was poly[(m-phenylvinylene)-co-(2,5-dioctyloxy-p-phenylvinylene)]. The free excess dispersant was removed in advance. After the solvent was completely evaporated, the carbon nanotubes were dispersed on the water surface to form an insoluble monolayer. The monolayer was densified by compressing the water surface area with a barrier in multiple isothermal cycles until a parallel array was formed. Then the substrate was slowly pulled upwards, and the surface pressure was kept stable by moving the barrier. The carbon nanotube parallel array gradually deposited onto the substrate along the air-liquid-solid three-phase contact line, and the linear density was about 50 nanotubes per micron, as shown in the AFM image of Figure 14 .

[0135] Unlike the present application, the above process relies on compressing the water surface area to cause the carbon nanotubes to aggregate and press against each other, thereby finally forming a parallel array. Since the carbon nanotubes need to form an insoluble monolayer on the water surface, this method is difficult to assemble a water phase dispersion of carbon nanotubes. Forming a dense Langmuir-Blodgett film requires multiple isothermal cycles of barrier compression and release, and the surface pressure needs to be kept stable when pulling the substrate, so the preparation speed is slow and is easily disturbed. In addition, the aggregation degree of the carbon nanotubes is limited, and the array density is low.

[0136] The above detailed description of the application in conjunction with the specific embodiments and / or exemplary examples and the accompanying drawings should not be construed as limiting the application. Those skilled in the art understand that various equivalent substitutions, modifications or improvements can be made to the technical solutions and embodiments of the application without departing from the spirit and scope of the application, and these all fall within the scope of the application. The scope of protection of the application is subject to the appended claims.

Claims

1. A method for preparing a high-density carbon nanotube parallel array, wherein a substrate is inserted into a carbon nanotube dispersion, and the substrate is moved away from the surface of the carbon nanotube dispersion to form a high-density carbon nanotube parallel array on the substrate. The carbon nanotube dispersion is obtained by dispersing carbon nanotubes in a mixed solvent, wherein the mixed solvent is a homogeneous mixed solvent of two or more solvents. In the mixed solvent, the volume fraction-weighted average of the product of the difference between the vapor pressure of each component and the weighted average vapor pressure and the difference between the surface tension and the weighted average surface tension is negative, and the absolute value thereof is greater than or equal to 2 kPa·mN / m, The surface tension of the mixed solvent is 10 to 80 mN / m, The contact angle of the carbon nanotube dispersion on the substrate is 5° to 75°.

2. The method according to claim 1, characterized in that The carbon nanotubes are one or more of single-walled carbon nanotubes, double-walled carbon nanotubes and multi-walled carbon nanotubes.

3. The method according to claim 1, characterized in that The carbon nanotubes are single-walled carbon nanotubes.

4. The method according to claim 1, wherein The boiling point of the mixed solvent is 50-280° C., and the surface tension of the mixed solvent is 15-75 mN / m.

5. The method according to claim 1, wherein The boiling point of the mixed solvent is 60-250° C., and the surface tension of the mixed solvent is 20-75 mN / m.

6. The method according to claim 1, characterized in that The boiling point of the mixed solvent is 70-220°C.

7. The method according to claim 1, characterized in that In the mixed solvent, the solvent components are selected from two or more of water and an organic solvent having a carbon number less than 14.

8. The method according to claim 1, characterized in that In the mixed solvent, the solvent component is selected from water, methanol, ethanol, isopropanol, tert-butanol, ethylene glycol, 1,2-propylene glycol, glycerol, acetonitrile, acetone, ether, propyl ether, petroleum ether, dioxane, acetic acid, trifluoroacetic acid, ethyl acetate, triethylamine, tetrahydrofuran, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, trichloroethylene, pentane, hexane, heptane, octane, nonane, decane, cyclohexane, gasoline, dichloromethane , chloroform, carbon tetrachloride, dichloroethane, trichloroethane, pyridine, benzene, toluene, o-xylene, m-xylene, p-xylene, mesitylene, styrene, chlorobenzene, o-chlorotoluene, m-chlorotoluene, p-chlorotoluene, o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, bromobenzene, o-bromotoluene, m-bromotoluene, p-bromotoluene, o-dibromobenzene, m-dibromobenzene, p-dibromobenzene, aniline, diphenyl ether, anisole, benzaldehyde, benzyl alcohol and nitrobenzene.

9. The method according to claim 1, characterized in that In the carbon nanotube dispersion, the concentration of carbon nanotubes is 1 μg / mL to 1 mg / mL.

10. The method according to claim 1, characterized in that In the carbon nanotube dispersion, the concentration of the carbon nanotubes is 5 μg / mL to 400 μg / mL.

11. The method according to claim 1, wherein In the carbon nanotube dispersion, the concentration of carbon nanotubes is 10 to 200 μg / mL.

12. The method according to claim 1, characterized in that The dispersant for dispersing the carbon nanotubes in the solvent is selected from one or more of surfactants, water-soluble biomolecules, conjugated polymers and aromatic compounds.

13. The method according to claim 1, wherein The dispersant for dispersing the carbon nanotubes in the solvent is selected from one or more of conjugated polymers and nucleic acid molecules.

14. The method according to claim 1, wherein The dispersant for dispersing the carbon nanotubes in the solvent is selected from single-stranded DNA or a conjugated polymer of carbazole and fluorene.

15. The method according to claim 1, wherein When preparing the carbon nanotube dispersion, the mass ratio of the carbon nanotubes to the dispersant is 1:(0.15-6), and the carbon nanotube dispersion is subjected to one or more processes of dialysis, centrifugal sedimentation followed by redispersion, and filtration followed by redispersion to remove excess dispersant.

16. The method according to claim 15, characterized in that When preparing the carbon nanotube dispersion, the mass ratio of the carbon nanotube to the dispersant is 1:(0.25-4).

17. The method according to claim 15, characterized in that When preparing the carbon nanotube dispersion, the mass ratio of the carbon nanotube to the dispersant is 1:(0.5-2.5).

18. The method according to claim 1, wherein The contact angle of the carbon nanotube dispersion on the substrate is 10° to 70°, and the speed at which the substrate moves away from the surface of the carbon nanotube dispersion is 0.1 μm / s to 1 mm / s.

19. The method according to claim 1, wherein The contact angle of the carbon nanotube dispersion on the substrate is 15° to 60°. The speed at which the substrate moves away from the surface of the carbon nanotube dispersion liquid is 0.2 μm / s to 200 μm / s.

20. The method according to claim 1, wherein The speed at which the substrate moves away from the surface of the carbon nanotube dispersion liquid is 0.5 μm / s to 50 μm / s.

21. A high-density carbon nanotube parallel array prepared according to the method for preparing a high-density carbon nanotube parallel array according to any one of claims 1 to 20, characterized in that: The high-density carbon nanotube parallel array is a single-layer carbon nanotube parallel array, a nearly single-layer carbon nanotube parallel array, or a carbon nanotube film with a top layer of a carbon nanotube parallel array. The high-density carbon nanotube parallel array is continuously and uniformly deposited on a substrate. The density of the high-density carbon nanotube parallel array is greater than or equal to 100 per micron.

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