A method for surface modification of carbon nanotube / silk fibroin composite film

Abstract

The application discloses a method for surface modification of carbon nanotube / silk fibroin composite film, which comprises the following steps: carbon nanotube film is immersed in chlorosulfonic acid, after being taken out, constant external force is applied to the carbon nanotube film to stretch it, and after heat pressing treatment, a pretreated carbon nanotube film is obtained; the pretreated carbon nanotube film is subjected to surface modification treatment, the modified carbon nanotube film is immersed in a silk fibroin solution, after being taken out, heat pressing treatment is conducted, and a surface-modified carbon nanotube / silk fibroin composite film is obtained. The application adopts three different surface modification treatment processes of oxygen plasma surface modification treatment, nitric acid surface oxidation modification treatment and polydopamine surface modification treatment to improve the interface performance of the CNT film, and further improves the interaction force between SF-CNT and SF-SF and the load transfer efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon nanotube composite film, and particularly to a method for surface modification of carbon nanotube / silk fibroin composite film. BACKGROUND

[0002] In recent years, carbon nanotube composite film has attracted extensive interest and great attention due to its unique mechanical, electromagnetic, optical, chemical and thermal conductivity properties. Based on its unique physical and chemical properties, carbon nanotube composite film has good potential application prospects in nanoelectronic devices, flat panel displays, electrochemical detection, sensors, pollutant separation and even tissue engineering materials.

[0003] Carbon nanotubes (CNT) have a highly crystalline surface and chemical inertness. In the process of preparing carbon nanotube / silk fibroin (SF) composite film, it is found that the combination between silk fibroin macromolecular segments and carbon nanotubes is more dependent on physical adhesion and the wrapping and adhesion of silk fibroin itself. When subjected to external force, part of the silk fibroin macromolecular segments are prone to fall off from the carbon nanotube bundle, resulting in that the mechanical properties of the composite film cannot reach the expected level. Therefore, it is urgent to develop a method for surface modification of carbon nanotube / silk fibroin composite film to enhance the mechanical properties of the carbon nanotube / silk fibroin composite film. SUMMARY

[0004] To solve the above technical problems, the purpose of the present application is to provide a method for surface modification of carbon nanotube / silk fibroin composite film, which has low cost and strong operability.

[0005] The present application is realized by the following technical solutions:

[0006] The present application provides a method for surface modification of carbon nanotube / silk fibroin composite film, comprising the following steps:

[0007] (1) dipping the carbon nanotube film in chlorosulfonic acid (CSA), taking it out, applying a constant external force to stretch the carbon nanotube film, then removing the excess chlorosulfonic acid, and performing heat pressing treatment to obtain a pretreated carbon nanotube film;

[0008] (2) performing surface modification treatment on the pretreated carbon nanotube film obtained in step (1) to obtain a modified carbon nanotube film; the surface modification treatment is oxygen plasma surface modification treatment, nitric acid surface oxidation modification treatment or polydopamine surface modification treatment;

[0009] (3) dissolving the silk fibroin freeze-dried powder in a solvent to obtain a silk fibroin solution; the solvent is formic acid, lithium bromide aqueous solution, hexafluoroisopropanol, dimethyl sulfoxide, trifluoroacetic acid or calcium chloride-ethanol-water ternary system solution; dipping the modified carbon nanotube film obtained in step (2) in the silk fibroin solution, taking out the dipped carbon nanotube film and performing hot pressing treatment to obtain a surface-modified carbon nanotube / silk fibroin composite film.

[0010] The surface modification and surface modification process is a good post-treatment process for the CNT film, which can effectively improve the interface performance of the CNT film, so that the interaction force between the silk fibroin macromolecular chain segment and the carbon nanotube bundle is improved, and the two are more effectively and firmly combined together, so as to achieve the effect of improving the mechanical performance of the CNT composite film.

[0011] The purpose of the application is to enhance the interaction between carbon nanotubes and silk fibroin, form a composite material with more compact structure and more excellent performance, and improve the interface performance of the CNT film by using three different surface modification processes of oxygen plasma surface modification treatment, nitric acid surface oxidation modification treatment and polydopamine surface modification treatment, to further improve the interaction force between SF-CNT and SF-SF and the load transfer efficiency.

[0012] Further, in step (1), the organic solvent is selected from one or more of acetone, ethanol and benzene.

[0013] Further, in step (1), the dipping time is 20-40s.

[0014] Further, in step (1), after taking out, a constant external force is applied to the carbon nanotube film within 20-40s to stretch it to 30-50% deformation.

[0015] Further, in step (1), the stretched carbon nanotube film is placed in an acetone solution to wash away the chlorosulfonic acid.

[0016] Further, in step (1), the hot pressing treatment conditions are: hot pressing temperature is 140-160℃, pressure is 0.5-1.5MPa, and time is 1-3h.

[0017] Further, in step (2), the method of oxygen plasma surface modification treatment is: placing the pretreated carbon nanotube film obtained in step (1) in a plasma treatment machine, treating it in an oxygen atmosphere at a power of 40-60W for 150-200s to obtain a modified carbon nanotube film.

[0018] Further, in step (2), the method of nitric acid surface oxidation modification treatment is: immersing the pretreated carbon nanotube film obtained in step (1) in nitric acid, removing the excess nitric acid, and obtaining the modified carbon nanotube film.

[0019] Further, the immersion time is 1-3 h.

[0020] Further, after removing the excess nitric acid, a drying step is further included.

[0021] Further, in step (2), the method of polydopamine surface modification treatment is: immersing the pretreated carbon nanotube film obtained in step (1) in a polydopamine aqueous solution, removing the excess polydopamine, and obtaining the modified carbon nanotube film.

[0022] Further, the polydopamine aqueous solution is prepared by the following method: dissolving dopamine hydrochloride in water, adding a pH adjuster to adjust the pH value to 8-9, and reacting to obtain a polydopamine aqueous solution.

[0023] Further, the pH adjuster is an alkaline compound, such as Tris, sodium hydroxide, etc.

[0024] Further, the immersion time is 20-24 h.

[0025] Further, the concentration of polydopamine in the polydopamine aqueous solution is 1-5 g / L.

[0026] Further, after removing the excess polydopamine, a drying step is further included.

[0027] Further, in step (3), the silk fibroin lyophilized powder is prepared by the following method:

[0028] S1. Placing raw silk in a urea solution, performing two heat treatments, and after washing and drying, obtaining silk fibroin fibers after urea degumming;

[0029] S2. Dissolving the silk fibroin fibers after urea degumming in a lithium bromide aqueous solution to obtain a silk fibroin / lithium bromide mixed solution;

[0030] S3. Using a dialysis bag with a molecular weight cut-off of 8000-14000 Da to dialyze the silk fibroin / lithium bromide mixed solution, and after centrifugation, obtaining a silk fibroin suspension;

[0031] S4. Freeze-drying the silk fibroin suspension to obtain the silk fibroin lyophilized powder.

[0032] Further, in step (3), the concentration of silk fibroin in the silk fibroin solution is 1-7 wt%, preferably 3-7 wt%.

[0033] Further, in step (3), the time of the impregnation is 5-15 min, preferably 5-10 min.

[0034] Further, in step (3), the heat pressing treatment is performed under the conditions of a temperature of 40-60℃, a pressure of 3-5 MPa, and a time of 20-40 min.

[0035] Further, in step (3), after the heat pressing treatment, a step of standing at room temperature for 10-12 h is further included.

[0036] The application also protects a surface-modified carbon nanotube / silk fibroin composite film prepared by the above method.

[0037] The application has the following beneficial effects:

[0038] The application adopts three different surface modification treatment processes, i.e., oxygen plasma surface modification treatment, nitric acid surface oxidation modification treatment, and polydopamine surface modification treatment, to improve the interface performance of the CNT film, further improve the interaction force between SF-CNT and SF-SF and the load transfer efficiency, and thus improve the mechanical performance of the carbon nanotube composite film. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 are the water contact angle test results of the carbon nanotube films prepared by different surface modification treatment methods; wherein (a) is a CSA-CNT film, (b) is an O-Plasma-CNT film, (c) is a Nitric acid-CNT film, and (d) is a PDA-CNT film.

[0040] Figure 2 are the surface SEM images of the carbon nanotube films prepared by different surface modification treatment methods; wherein (a) and (b) are O-Plasma-CNT films, (c) and (d) are Nitric acid-CNT films, and (e) and (f) are PDA-CNT films.

[0041] Figure 3 are the surface SEM images of the carbon nanotube / silk fibroin composite films prepared by different surface modification treatment methods; wherein (a) and (b) are CSA-CNT / SF composite films, (c) and (d) are O-Plasma-CNT / SF composite films, (e) and (f) are Nitric acid-CNT / SF composite films, and (g) and (h) are PDA-CNT / SF composite films.

[0042] Figure 4 is the stress-strain curve of the CSA-CNT / SF composite film under a strain rate of 1900 s -1Figure 1 is a diagram of the dynamic mechanical property test results of the carbon nanotube / silk fibroin composite films prepared by different surface modification treatment methods under quasi-static conditions.

[0043] Figure 5 Figure 1 is a diagram of the dynamic mechanical property test results of the carbon nanotube / silk fibroin composite films prepared by different surface modification treatment methods under quasi-static conditions.

[0044] Figure 6 Figure 1 is a diagram of the dynamic mechanical property test results of the carbon nanotube / silk fibroin composite films prepared by different surface modification treatment methods under quasi-static conditions. -1 Figure 2 is a diagram of the tensile fracture morphology of the carbon nanotube / silk fibroin composite films prepared by different surface modification treatment methods; wherein (a), (b) and (c) are CSA-CNT / SF composite films, (d), (e) and (f) are O-Plasma-CNT / SF composite films, (g), (h) and (i) are Nitric acid-CNT / SF composite films, (j), (k) and (l) are PDA-CNT / SF composite films. DETAILED DESCRIPTION

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0046] The present application provides a preparation method of a carbon nanotube / silk fibroin composite film, comprising the following steps:

[0047] (1) dipping a carbon nanotube film in chlorosulfonic acid, taking out the carbon nanotube film, applying a constant external force to stretch the carbon nanotube film, then removing excess chlorosulfonic acid, and performing heat pressing treatment to obtain a pretreated carbon nanotube film;

[0048] (2) performing surface modification treatment on the pretreated carbon nanotube film obtained in step (1) to obtain a modified carbon nanotube film; the surface modification treatment is oxygen plasma surface modification treatment, nitric acid surface oxidation modification treatment or polydopamine surface modification treatment;

[0049] (3) dissolving silk fibroin freeze-dried powder in formic acid to obtain a silk fibroin solution; dipping the modified carbon nanotube film obtained in step (2) in the silk fibroin solution, taking out the dipped carbon nanotube film and performing heat pressing treatment to obtain a surface-modified carbon nanotube / silk fibroin composite film.

[0050] The silk fibroin freeze-dried powder is prepared by the following method:

[0051] S1. The raw silk is placed in a urea solution, and is subjected to two heat treatments, and after washing and drying, the silk fibroin fibers after urea degumming are obtained;

[0052] S2. The silk fibroin fibers after urea degumming are dissolved in a lithium bromide aqueous solution to obtain a silk fibroin / lithium bromide mixed solution;

[0053] S3. The silk fibroin / lithium bromide mixed solution is subjected to dialysis using a dialysis bag with a molecular weight cut-off of 8000-14000 Da, and after centrifugation, a silk fibroin suspension is obtained;

[0054] S4. The silk fibroin suspension is subjected to freeze-drying treatment to obtain the silk fibroin freeze-dried powder.

[0055] In the following examples, the silk fibroin freeze-dried powder is prepared by the following method:

[0056] S1. 20 g of raw silk is placed in 600 mL of a urea solution with a concentration of 8.0 mol / L, and is subjected to treatment at a water bath temperature of 90℃ for 2 h, and is subjected to treatment again under the same conditions using the above-mentioned urea solution with the same concentration for 1 h, and is washed thoroughly with warm water, and is dried in an oven at 60℃ to obtain silk fibroin fibers after urea degumming;

[0057] S2. 10 g of silk fibroin fibers after urea degumming are dissolved in 200 mL of a lithium bromide aqueous solution with a concentration of 9.3 mol / L, and are continuously stirred at 60℃ for 60 min until they are completely dissolved to obtain a silk fibroin / lithium bromide mixed solution;

[0058] S3. After the silk fibroin / lithium bromide mixed solution is cooled to room temperature, it is loaded into a dialysis bag with a molecular weight cut-off of 8000-14000 Da, and is then placed in deionized water at 4℃ for dialysis for 72 h, and the water is changed every 8 h, and after centrifugation at a speed of 8000 r / min for 10 min, a silk fibroin suspension is obtained;

[0059] S4. The silk fibroin suspension is placed in a freeze-drying machine, and after freeze-drying for 48 h, a silk fibroin freeze-dried powder is obtained.

[0060] The application will be further described in conjunction with the drawings and specific examples, so that those skilled in the art can better understand the application and implement it, but the examples are not limiting to the application.

[0061] In the following examples, the experimental methods used are conventional methods, and the materials, reagents, etc. used are commercially available unless otherwise specified.

[0062] Example 1

[0063] A method for surface modification of carbon nanotube / silk fibroin composite film by oxygen plasma, comprising the following steps:

[0064] (1) The carbon nanotube film is immersed in chlorosulfonic acid for 30 s, and after being taken out, a constant external force is applied to the carbon nanotube film within 30 s to stretch it to 40% deformation, and then it is placed in an acetone solution to wash away the chlorosulfonic acid. After hot pressing on a hot press at a temperature of 150°C and a pressure of 1 MPa for 2 h, a pretreated carbon nanotube (CSA-CNT) film is obtained.

[0065] (2) The pretreated carbon nanotube film obtained in step (1) is placed in a plasma treatment machine and treated in an oxygen atmosphere at a power of 50 W for 180 s to obtain an oxygen plasma surface modified carbon nanotube (O-Plasma-CNT) film.

[0066] (3) Silk fibroin freeze-dried powder is dissolved in formic acid to obtain a silk fibroin solution with a concentration of 5 wt%; the oxygen plasma surface modified carbon nanotube film obtained in step (2) is immersed in the silk fibroin solution with a concentration of 5 wt% for 10 min, and the immersed carbon nanotube film is taken out and hot pressed on a hot press at a temperature of 50°C and a pressure of 4 MPa for 30 min, followed by normal temperature placement for 12 h to obtain an oxygen plasma surface modified carbon nanotube / silk fibroin (O-Plasma-CNT / SF) composite film.

[0067] Example 2

[0068] A method for surface modification of carbon nanotube / silk fibroin composite film by nitric acid oxidation, comprising the following steps:

[0069] (1) The carbon nanotube film is immersed in chlorosulfonic acid for 30 s, and after being taken out, a constant external force is applied to the carbon nanotube film within 30 s to stretch it to 40% deformation, and then it is placed in an acetone solution to wash away the chlorosulfonic acid. After hot pressing on a hot press at a temperature of 150°C and a pressure of 1 MPa for 2 h, a pretreated carbon nanotube film is obtained.

[0070] (2) The pretreated carbon nanotube film obtained in step (1) is immersed in nitric acid for 2 h, and repeatedly washed with deionized water to remove excess nitric acid to obtain a nitric acid surface oxidized carbon nanotube (Nitric acid-CNT) film.

[0071] (3) Dissolve the silk fibroin lyophilized powder in formic acid to obtain a silk fibroin solution with a concentration of 5wt%; immerse the nitric acid surface-oxidized modified carbon nanotube film obtained in step (2) in the silk fibroin solution with a concentration of 5wt% for 10min, take out the immersed carbon nanotube film, and hot-press the carbon nanotube film on a hot press at a temperature of 50°C and a pressure of 4MPa for 30min, and then place the carbon nanotube film at room temperature for 12h to obtain a nitric acid surface-oxidized modified carbon nanotube / silk fibroin (Nitric acid-CNT / SF) composite film.

[0072] Example 3

[0073] A method for preparing a polydopamine surface-modified carbon nanotube / silk fibroin composite film, comprising the following steps:

[0074] (1) immerse the carbon nanotube film in chlorosulfonic acid for 30s, apply a constant external force to the carbon nanotube film within 30s to stretch the carbon nanotube film to a deformation of 40%, then wash the carbon nanotube film in an acetone solution to remove the chlorosulfonic acid, and hot-press the carbon nanotube film on a hot press at a temperature of 150°C and a pressure of 1MPa for 2h to obtain a pretreated carbon nanotube film.

[0075] (2) immerse the pretreated carbon nanotube film obtained in step (1) in a polydopamine aqueous solution for 24h, repeatedly rinse the carbon nanotube film with deionized water to remove excess polydopamine, and dry the carbon nanotube film in a vacuum oven at 60°C overnight to obtain a polydopamine surface-modified carbon nanotube (PDA-CNT) film; the polydopamine aqueous solution is prepared by the following method: uniformly dissolve 1g of dopamine hydrochloride particles in 500mL of deionized water, add 0.6g of Tris particles to adjust the pH value of the solution to 8.5, and prepare a polydopamine solution with a concentration of 2g / L.

[0076] (3) dissolve the silk fibroin lyophilized powder in formic acid to obtain a silk fibroin solution with a concentration of 5wt%; immerse the polydopamine surface-modified carbon nanotube film obtained in step (2) in the silk fibroin solution with a concentration of 5wt% for 10min, take out the immersed carbon nanotube film, and hot-press the carbon nanotube film on a hot press at a temperature of 50°C and a pressure of 4MPa for 30min, and then place the carbon nanotube film at room temperature for 12h to obtain a polydopamine surface-modified carbon nanotube / silk fibroin (PDA-CNT / SF) composite film.

[0077] Comparative Example 1

[0078] A method for preparing a carbon nanotube / silk fibroin composite film, comprising the following steps:

[0079] (1) carbon nanotube film is immersed in chlorosulfonic acid for 30s, after taking out, the carbon nanotube film is stretched to 40% deformation by applying constant external force within 30s, then it is washed with acetone solution to remove chlorosulfonic acid, after hot pressing on a hot press at a temperature of 150℃ and a pressure of 1MPa for 2h, the pretreated carbon nanotube (CSA-CNT) film is obtained;

[0080] (2) silk fibroin lyophilized powder is dissolved in formic acid to obtain a silk fibroin solution with a concentration of 5wt%; the pretreated carbon nanotube film obtained in step (1) is immersed in the silk fibroin solution with a concentration of 5wt% for 10min, the immersed carbon nanotube film is taken out, and hot pressed on a hot press at a temperature of 50℃ and a pressure of 4MPa for 30min, then it is placed at room temperature for 12h to obtain a carbon nanotube / silk fibroin (CSA-CNT / SF) composite film.

[0081] The element content of the carbon nanotube films prepared by different surface modification treatment methods is tested by X-ray photoelectron spectroscopy (XPS), and the test results are shown in Table 1:

[0082] Table 1

[0083] Atomic content / % C 1s N 1s O 1s CSA-CNT film 88.49 2.14 9.37 O-Plasma-CNT film 77.61 2.11 20.28 Nitric acid-CNT film 82.79 5.35 11.86 PDA-CNT film 82.87 3.52 13.61

[0084] As can be seen from Table 1, after surface modification treatment, the intensity of N1s and O1s peaks increases, and the intensity of C1s peak decreases significantly. After oxygen plasma surface modification treatment, the intensity of O1s peak increases significantly, and after nitric acid surface oxidation modification treatment, the intensity of N1s peak increases significantly, which indicates that the bombardment of oxygen plasma and electron high-energy active particles on the surface of CNT film is very effective, so that a small amount of oxygen-containing particles are still left in the nano-scale micro-pits, and a large amount of oxygen-containing functional groups are adhered on the CNT bundle by nitric acid. The intensity of N1s and O1s peaks of the sample treated by polydopamine surface modification is higher, which indicates that polydopamine particles are uniformly distributed in the CNT film.

[0085] The water contact angle of the carbon nanotube films prepared by different surface modification treatment methods is tested, and the test results are shown in Table 2: Figure 1As shown, the carbon nanotube itself has hydrophobicity, and the contact angle of the CSA-CNT film can be seen at about 104°; after the surface modification treatment by oxygen plasma, the surface of the CNT film is etched under the bombardment of high-energy active particles in the oxygen plasma, a large number of nanoscale pits are generated, the interface performance of the surface of the CNT bundle is significantly improved, the contact angle of the O-Plasma-CNT film is only 5.6°, and the CNT film has super hydrophilic property; after the surface modification treatment by nitric acid oxidation, a small amount of oxygen-containing functional groups are generated on the surface of the CNT bundle under the long-time immersion treatment of the CNT bundle in nitric acid, the interface performance of the CNT film is improved, the contact angle of the CNT film reaches 89°, and the wettability is enhanced; after the surface modification treatment by polydopamine, a layer of nanoscale polydopamine particles is uniformly coated on the CNT bundle, the outer surface of the CNT bundle becomes rough, the interface performance of the CNT film is improved, the water contact angle of the CNT film reaches 88°, the wettability is enhanced, and the CNT film shows hydrophilic property.

[0086] The carbon nanotube films prepared by different surface modification treatment methods were characterized by scanning electron microscopy (SEM), and the characterization results are shown in Figure 2 As shown, the surface of the CNT bundle in the CNT film after the surface modification treatment by oxygen plasma is very rough, which is due to the fact that the surface modification treatment by oxygen plasma will cause the damage of the CNT bundle and form rough surface morphology, and the CNT dropped after the damage of part of the CNT bundle will be aggregated with part of the impurities and adhered to the surface of the bundle; the surface of the CNT film after the surface modification treatment by nitric acid oxidation does not change obviously, and only the reduction of the impurities can be observed; the CNT bundle of the CNT film after the surface modification treatment by polydopamine is uniformly covered with a layer of polydopamine, the combination between the polydopamine and the CNT bundle is very close, and part of the remaining polydopamine forms an aggregate between the bundles.

[0087] The carbon nanotube / silk fibroin composite films prepared by different surface modification treatment methods were characterized by scanning electron microscopy (SEM), and the characterization results are shown in Figure 3As shown, the CNT film after oxygen plasma surface modification treatment is not well combined with silk fibroin, and the silk fibroin is not uniformly distributed on the CNT bundle. The rough morphology of the CNT surface after oxygen plasma surface modification treatment is not completely repaired under the action of silk fibroin, and a small amount of impurities form agglomerates with silk fibroin and adhere to the surface of the bundle. Due to the obstruction of the impurity agglomerates, silk fibroin cannot fully enter the inside of the CNT film, and its distribution in the inside of the CNT film is not uniform, resulting in poor filling effect of the gap between the CNT bundles. In the carbon nanotube / silk fibroin film prepared after nitric acid surface oxidation modification treatment, the silk fibroin is well combined with the CNT bundle, and the film surface is relatively flat and smooth. However, due to the adhesion of many oxygen-containing functional groups to the CNT bundle under the action of nitric acid, and the possible shedding of these oxygen-containing functional groups into the silk fibroin solution, the interaction force between the CNT bundle and the silk fibroin and between the silk fibroin and the silk fibroin is increased, and the silk fibroin forms a relatively thick accumulation layer on the CNT bundle, and irregular cracks appear on the surface after drying. The carbon nanotube / silk fibroin film prepared after polydopamine surface modification treatment has a better flatness and smoothness of the film surface, and the silk fibroin is well combined with the CNT bundle under the adhesion of polydopamine and is very uniformly and densely coated on the CNT bundle. Moreover, due to the good adhesion effect of polydopamine on the CNT bundle, polydopamine will not fall off, and silk fibroin will not form an accumulation on the CNT bundle. At the same time, polydopamine is a nano-sized particle and will not hinder the silk fibroin from entering the inside of the CNT film, and the gap between the CNT bundles is also well filled.

[0088] The dynamic mechanical properties of the carbon nanotube / silk fibroin composite films prepared by different surface modification treatment methods (Examples 1-3) were tested under a strain rate of 1900s -1 The dynamic mechanical properties of the carbon nanotube / silk fibroin composite films prepared by different surface modification treatment methods (Examples 1-3) were tested under a strain rate of 1900s Figure 4 The dynamic mechanical properties of the carbon nanotube / silk fibroin composite films prepared by different surface modification treatment methods (Examples 1-3) were tested under a strain rate of 1900s Figure 5 The dynamic fracture strength and specific energy absorption value of the carbon nanotube / silk fibroin composite film prepared by polydopamine surface treatment of carbon nanotubes were 2138.74 MPa and 104.01 MJ / m 3Compared to the untreated composite film in Comparative Example 1, the performance was improved by 150.14% and 128.26%, respectively, which is superior to the carbon nanotube / silk fibroin composite films prepared by oxygen plasma surface modification and nitric acid surface oxidation modification. This demonstrates that polydopamine has good adhesion properties, enhancing the interaction force between silk fibroin and carbon nanotubes, allowing silk fibroin to adhere more firmly and tightly to the carbon nanotube bundles, and better utilizing the uniform shear deformation and molecular stick-slip deformation of silk fibroin, making the load transfer between adjacent CNTs more efficient. Although nitric acid surface treatment can enhance the dynamic mechanical properties of the carbon nanotube / silk fibroin composite film, the thicker stacked layer of silk fibroin reduces the load transfer efficiency between the outer silk fibroin layer and the inner carbon nanotube layer. Under external force, relative sliding easily occurs between the outer silk fibroin layer and the inner carbon nanotube layer, thus preventing the mechanical properties of the carbon nanotube / silk fibroin composite film from reaching the expected level. The carbon nanotube / silk fibroin composite film prepared by oxygen plasma surface modification treatment exhibits low dynamic mechanical properties because oxygen plasma treatment causes damage to the surface of carbon nanotube bundles and some bundles break.

[0089] At a strain rate of 1900 s -1 Tensile fracture morphology images of carbon nanotube / silk fibroin composite films prepared by different surface modification methods are shown below. Figure 6 Atomic content / % C 1s N 1s O 1s CSA-CNT film O-Plasma-CNT film Nitric acid-CNT film PDA-CNT film Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Atomic content / % C 1s N As shown, the fracture surfaces of carbon nanotube / silk fibroin composite films prepared by nitric acid surface oxidation modification and polydopamine surface modification are relatively smoother. The CNT bundles extracted from the fracture surface of the carbon nanotube / silk fibroin composite film prepared by oxygen plasma surface modification are longer but fewer in number. Although SF is relatively uniformly covered on the CNT bundles, the large amount of SF causes the CNT bundles to aggregate together to form thicker CNT bundles, and a thick layer of SF accumulates on the film surface, which to some extent affects the tensile properties of the composite film. On the other hand, the CNT bundles extracted from the fracture surface of the carbon nanotube / silk fibroin composite film prepared by polydopamine surface modification are not only thinner but also very dense, indicating that SF is evenly distributed on the CNT bundles, thus exhibiting better dynamic tensile properties, which is consistent with the tensile test data.

[0090] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for surface-modified carbon nanotube / silk fibroin composite films, characterized in that, Includes the following steps: (1) Immerse the carbon nanotube film in chlorosulfonic acid for 20-40 s, take it out and apply a constant external force to the carbon nanotube film within 20-40 s to stretch it to 30-50% deformation, then remove the excess chlorosulfonic acid and perform hot pressing to obtain the pretreated carbon nanotube film. (2) The pretreated carbon nanotube film obtained in step (1) is subjected to surface modification treatment to obtain a modified carbon nanotube film; the surface modification treatment is oxygen plasma surface modification treatment, nitric acid surface oxidation modification treatment or polydopamine surface modification treatment. The oxygen plasma surface modification treatment method is as follows: the pretreated carbon nanotube film obtained in step (1) is placed in a plasma treatment machine and treated with a power of 40~60 W for 150~200 s in an oxygen atmosphere to obtain the modified carbon nanotube film. The method of surface oxidation modification treatment with nitric acid is as follows: the pretreated carbon nanotube film obtained in step (1) is immersed in nitric acid for 1-3 h to remove excess nitric acid and obtain the modified carbon nanotube film. The method for surface modification of polydopamine is as follows: the pretreated carbon nanotube film obtained in step (1) is immersed in a polydopamine aqueous solution for 20-24 h to remove excess polydopamine and obtain the modified carbon nanotube film; the concentration of polydopamine in the polydopamine aqueous solution is 1-5 g / L. (3) Dissolve the lyophilized silk fibroin powder in a solvent to obtain a silk fibroin solution; the solvent is formic acid, lithium bromide aqueous solution, hexafluoroisopropanol, dimethyl sulfoxide, trifluoroacetic acid or calcium chloride-ethanol-water ternary system solution; immerse the modified carbon nanotube film obtained in step (2) in the silk fibroin solution, take out the immersed carbon nanotube film and perform hot pressing treatment to obtain a surface-modified carbon nanotube / silk fibroin composite film.

2. The method according to claim 1, characterized in that, The polydopamine aqueous solution is prepared by the following method: dissolving dopamine hydrochloride in water, adding a pH adjuster to adjust the pH value to 8-9, and reacting to obtain the polydopamine aqueous solution.

3. The method according to claim 2, characterized in that, The pH adjuster is an alkaline compound.

4. A surface-modified carbon nanotube / silk fibroin composite film prepared by the method according to any one of claims 1 to 3.

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