Flexible composite film based on multi-walled carbon nanotube dopamine graphene and preparation method thereof

Abstract

The invention discloses a flexible composite thin film based on multi-walled carbon nanotube dopamine graphene and a preparation method of the flexible composite thin film, and belongs to the technical field of composite thin films. Graphene is modified by dopamine hydrochloride, the dispersity of graphene in a solution is improved, and the flexibility of the flexible composite thin film is improved; a compact conductive network can be built through the one-dimensional carbon nanotubes and the two-dimensional flaky material dopamine graphene, the conductivity of the composite film is improved, the polyvinylidene fluoride-hexafluoropropylene copolymer is used, one-dimensional conductive filler and two-dimensional conductive filler are fused, and the mechanical performance of the composite film is improved. The flexible composite film is simple in preparation process, short in period and excellent in film performance, can reach a steady-state temperature in a short time, and has excellent heat-conducting property and excellent electromagnetic shielding property.

Description

Technical Field

[0001] The present invention relates to the technical field of multifunctional flexible composite conductive films, and particularly relates to a flexible composite film based on dopamine-functionalized graphene with multi-walled carbon nanotubes and a preparation method thereof. Background Art

[0002] With the rapid development of the communication era and continuous development of science and technology, the intelligent technology of electronic products has made great progress in fields such as aerospace, biomedicine, and artificial intelligence. High-performance electronic devices have brought great convenience to people's lives. However, long-term operation of electronic devices will cause unexpected electromagnetic radiation and inevitable heat conduction problems, which will not only damage the service life of the devices, but also cause environmental pollution and even endanger human health. Therefore, how to quickly and effectively solve the problems of electromagnetic radiation and heat conduction has become a key issue for current advanced electronic devices.

[0003] Therefore, it is urgent to explore and develop new flexible multifunctional composite materials with both high thermal conductivity and electromagnetic shielding performance to meet the requirements of high-end electronic devices and new applications.

[0004] In recent years, conductive fillers including metal nanowires, graphene, carbon nanotubes, transition metal nitrides, carbides or carbonitrides (MXene), etc. have attracted extensive attention due to their easy processing, low density and corrosion resistance. Among them, graphene, due to its extremely high electrical conductivity, chemical stability, excellent mechanical strength and low cost, has become a potential nano filler. However, due to its chemical inertness, it is extremely difficult to disperse in a polymer matrix, mainly occurring in common solution and melt mixing processes, which usually leads to the aggregation of graphene, resulting in the formation of discontinuous conductive paths in the matrix. Therefore, it is very necessary to modify graphene to improve its dispersibility and make the conductivity of the film more uniform. In addition, in order to further improve other properties of the film, carbon nanotubes are also selected as conductive fillers in this study. Carbon nanotubes have been widely used in thermal management materials due to their excellent electrical, thermal and other properties. Combining the two together to form a dense conductive network. However, the mechanical properties of the composite film are poor and cannot meet the use requirements of some structural materials. Therefore, in order to obtain a flexible film with high mechanical properties, a common strategy is to compound polymers with conductive fillers, such as cellulose nanofibers, polyvinyl alcohol, polyurethane, etc. These polymers, as adhesives, can effectively improve the mechanical properties and flexibility of the conductive film, but their inherent properties, such as poor moisture resistance and poor durability, affect their application in heat conduction. Therefore, polyvinylidene fluoride-hexafluoropropylene copolymer is selected. Polyvinylidene fluoride-hexafluoropropylene copolymer has become one of the most promising matrix materials for compounding with conductive fillers due to its excellent corrosion resistance and excellent mechanical properties. Summary of the Invention

[0005] To this end, the present invention provides a flexible composite film based on multi-walled carbon nanotube dopamine graphene and a preparation method thereof, which can be applied to the fields of electric heating and electromagnetic shielding. The prepared composite film has excellent thermal conductivity, outstanding superhydrophobicity and good electromagnetic shielding effectiveness, and can show great potential in the fields of flexible electronics, electromagnetic shielding and thermal management.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] According to a first aspect of the present invention, there is provided a method for preparing a flexible composite film, comprising the following steps:

[0008] 1) heating and stirring dopamine hydrochloride and graphene to prepare dopamine-based graphene, followed by freeze-drying and grinding into powder;

[0009] 2) dispersing the amino-modified multi-walled carbon nanotubes into N,N-dimethylformamide solution until they are completely dissolved for later use;

[0010] 3) dispersing the dopamine-modified graphene in the N,N-dimethylformamide solution simultaneously and ultrasonically dispersing the dopamine-modified graphene together with the aminated multi-walled carbon nanotubes;

[0011] 4) Add polyvinylidene fluoride-hexafluoropropylene copolymer, stir to blend, and dry to form a film.

[0012] Preferably, dopamine hydrochloride and graphene are heated and stirred to prepare dopamineized graphene, followed by freeze drying and grinding into powder, comprising:

[0013] Pretreatment with Tris solution: weigh Tris particles and pour into deionized water for thorough stirring. After the Tris particles are dissolved, neutralize the solution with 1 mmol / mL HCl, and finally prepare a Tris solution with a pH of 8.5.

[0014] Preparation of dopamine-treated graphene: Pour the weighed graphene powder into the pre-prepared Tris solution and stir for 30 minutes. Then, disperse the weighed dopamine hydrochloride in the mixed solution. The mass ratio of graphene powder to dopamine hydrochloride is 1:1. Then stir for another 30 minutes and perform ultrasonic dispersion for 1 hour. Then, stir in an oil bath at 40°C for 24 hours, freeze-dry, and grind to obtain dopamine-treated graphene powder.

[0015] Preferably, the aminated multi-walled carbon nanotubes are dispersed in an N,N-dimethylformamide solution until they are completely dissolved for standby use, comprising:

[0016] Pour the weighed amino-functionalized multi-walled carbon nanotubes into N,N-dimethylformamide solution at a mass-to-volume ratio of (1-2) g: 200 mL, and stir magnetically for 1 h until the amino-functionalized multi-walled carbon nanotubes are completely dissolved to obtain a mixed solution.

[0017] Preferably, the dopamine-functionalized graphene is simultaneously dispersed in the N,N-dimethylformamide solution and ultrasonically dispersed together with the amino-functionalized multi-walled carbon nanotubes, including:

[0018] Subsequently, the weighed dopamine-functionalized graphene and amino-functionalized multi-walled carbon nanotubes are added and dispersed in the mixed solution at a mass ratio of 1:1, and ultrasonic treatment is carried out for 30 min.

[0019] Preferably, polyvinylidene fluoride-hexafluoropropylene copolymer is added, stirred and fused, and dried into a film, including:

[0020] The weighed polyvinylidene fluoride-hexafluoropropylene copolymer particles are added to the mixed solution, and then magnetically stirred for 3.5-4 h. Finally, a quantitative mixed solution is transferred to a polytetrafluoroethylene mold with a pipette and placed in an oven for curing and drying at 60 °C to obtain a composite film.

[0021] Preferably, the mass ratio of the polyvinylidene fluoride-hexafluoropropylene copolymer to the dopamine-functionalized graphene is 1:1.

[0022] According to the second aspect of the present invention, a flexible composite film based on multi-walled carbon nanotube dopamine-functionalized graphene prepared by the above method is provided.

[0023] Preferably, the flexible composite film reaches a temperature of 172 °C at a working voltage of 5 V and has an electromagnetic shielding of 32.54 dB in the range of 8.2-12.4 GHz (X-band).

[0024] Preferably, the water contact angle of the flexible composite film is 170°.

[0025] The present invention has the following advantages:

[0026] Dopamine hydrochloride is used to modify graphene to improve the dispersibility of graphene in solution. A dense conductive network can be built through one-dimensional carbon nanotubes and two-dimensional flaky materials (dopamine-functionalized graphene), improving the conductivity of the composite film. By using polyvinylidene fluoride-hexafluoropropylene copolymer, not only can the one-dimensional and two-dimensional conductive fillers be integrated, but also the mechanical properties of the composite film can be improved, effectively enhancing the comprehensive performance of the conductive composite film. The preparation process of this flexible composite film is simple and has a short cycle. The film has excellent properties and can reach a steady-state temperature in a short time. Under the condition of a safe voltage, the highest steady-state temperature can reach about 172 °C. And it has an electromagnetic shielding of 32.54 dB in the range of 8.2 - 12.4 GHz (X-band), indicating that this composite film has excellent thermal conductivity and outstanding electromagnetic shielding performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, without creative efforts, other implementation drawings can also be obtained based on the provided drawings.

[0028] The structures, ratios, sizes, etc. shown in this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limited conditions for the implementation of the present invention. Therefore, they do not have a substantial technical meaning. Any modification of the structure, change in the ratio relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present invention.

[0029] Figure 1 It is the TEM image of the dopamine-functionalized graphene of the present invention;

[0030] Figure 2 It is the SEM image of the composite film of the present invention;

[0031] Figure 3 It is the water contact angle image of the composite film of the present invention;

[0032] Figure 4 It is the electric heating image of the composite film of the present invention;

[0033] Figure 5 It is the electromagnetic shielding image of the composite film of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0035] This application provides a method for preparing a flexible composite film, which includes the following steps:

[0036] 1) Heat and stir hydrochloric acid dopamine and graphene to prepare dopamine-functionalized graphene, then freeze-dry and grind it into powder;

[0037] 2) Disperse amino-functionalized multi-walled carbon nanotubes into N,N-dimethylformamide solution until completely dissolved for standby;

[0038] 3) Disperse dopamine-functionalized graphene in N,N-dimethylformamide solution at the same time, and perform ultrasonic dispersion together with amino-functionalized multi-walled carbon nanotubes;

[0039] 4) Then add polyvinylidene fluoride-hexafluoropropylene copolymer, stir and fuse, and dry to form a film.

[0040] Preferably, the step of heating and stirring hydrochloric acid dopamine and graphene to prepare dopamine-functionalized graphene, then freeze-drying and grinding it into powder includes:

[0041] Perform pretreatment with tris(hydroxymethyl)aminomethane solution: Weigh tris(hydroxymethyl)aminomethane particles and pour them into deionized water for full stirring. After the tris(hydroxymethyl)aminomethane particles dissolve and disappear, neutralize the solution with 1 mmol / mL HCl, and finally prepare a Tris solution with a pH of 8.5;

[0042] Preparation of dopamine-functionalized graphene: Pour the weighed graphene powder into the pre-prepared Tris solution and stir for 30 min. Then, disperse the weighed hydrochloric acid dopamine in the mixed solution. The mass ratio of graphene powder to hydrochloric acid dopamine is 1:1. Then stir for another 30 min and perform ultrasonic dispersion for 1 h. Then stir in an oil bath at 40 °C for 24 h, perform freeze-drying and grinding to obtain dopamine-functionalized graphene powder.

[0043] Preferably, the step of dispersing amino-functionalized multi-walled carbon nanotubes into N,N-dimethylformamide solution until completely dissolved for standby includes:

[0044] Pour the weighed amino-functionalized multi-walled carbon nanotubes into N,N-dimethylformamide solution according to the mass-volume ratio of (1-2) g: 200 mL, and magnetically stir for 1 h until the amino-functionalized multi-walled carbon nanotubes are completely dissolved to obtain a mixed solution.

[0045] Preferably, the dopamine-functionalized graphene is dispersed in N,N-dimethylformamide solution and ultrasonically dispersed together with the amino-functionalized multi-walled carbon nanotubes, including:

[0046] Subsequently, the weighed dopamine-functionalized graphene and amino-functionalized multi-walled carbon nanotubes are added and dispersed in the mixed solution according to a mass ratio of 1:1, and ultrasonic treatment is carried out for 30 min.

[0047] Preferably, polyvinylidene fluoride-hexafluoropropylene copolymer is added, stirred and fused, and dried into a film, including:

[0048] The weighed polyvinylidene fluoride-hexafluoropropylene copolymer particles are added to the mixed solution, and then magnetic stirring is carried out for 3.5 - 4 h. Finally, a quantitative mixed solution is transferred to a polytetrafluoroethylene mold with a pipette and placed in an oven for curing and drying at 60 °C to obtain a composite film.

[0049] Preferably, the mass ratio of polyvinylidene fluoride-hexafluoropropylene copolymer to dopamine-functionalized graphene is 1:1.

[0050] The reagents and materials used in the present invention are as follows:

[0051] Graphene, N,N-dimethylformamide (DMF), amino-functionalized multi-walled carbon nanotubes (MWCNT-NH 2 2), dopamine hydrochloride, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), tris(hydroxymethyl)aminomethane (Tris), deionized water, etc., are all obtained commercially.

[0052] The experimental equipment used in the present invention is as follows:

[0053] In the present invention, the surface morphology of graphene was observed by transmission electron microscopy (TEM, Hitachi H7650), the surface morphology of the composite film was observed by field emission scanning electron microscopy (FE-SEM, Regulus 8100), the water droplet contact angle of the film surface was measured by an automatic contact angle measuring instrument (DSA30S, Krüss, Germany), the electrothermal performance of the composite film was measured by using a DC power supply (DC, MS-605D) with a thermocouple connected to both ends of the film, and the electromagnetic interference shielding performance of the composite film was measured by using a vector network analyzer (Agilent E5071C) in the frequency range of 8.2 to 12.4 (X-band).

[0054] The present invention will be described in detail below with specific examples.

[0055] Example 1

[0056] 1. Pretreat the Tris solution. Weigh 0.1 g of Tris granules and pour them into 500 mL of deionized water, and stir well. After the Tris granules disappear, neutralize the solution with 1 mmol / mL HCl, and finally prepare a Tris solution with a pH of 8.5.

[0057] 2. Subsequently, pour 0.5 g of graphene powder into the pre-prepared Tris solution and stir for 30 min. Then, disperse 0.5 g of dopamine hydrochloride in the mixed solution, stir for 30 min, and perform ultrasonic dispersion for 1 h. Subsequently, stir in an oil bath at 40 °C for 24 h, perform freeze-drying and grinding to obtain dopamine-functionalized graphene powder (P@GNs). See Figure 1 , for the modified graphene, wrinkles will be found on the surface, indicating successful modification.

[0058] 3. Pour 0.1 g of MWCNT-NH 2 into DMF and stir magnetically for 1 h until MWCNT-NH 2 is completely dissolved. Subsequently, disperse 0.2 g of P@GNs in the mixed solution and perform ultrasonic treatment for 30 min. Then add 1 g of PVDF-HFP particles and stir magnetically for 3.5 - 4 h. Finally, use a pipette to transfer a quantitative amount of the mixed solution to a polytetrafluoroethylene mold and place it in an oven to cure and dry at 60 °C to obtain a composite film. See Figure 2 , in which MWCNT-NH 2 and P@GNs are uniformly distributed in the PVDF-HFP matrix. The resistance of this composite film is about 50 Ω, and the maximum temperature can reach 170 °C under a voltage of 10 V.

[0059] Example 2

[0060] On the basis of the above Example 1, optimize the ratio of each additive component as follows:

[0061] 1. Pretreat the Tris solution. Weigh 0.1 g of Tris granules and pour them into 500 mL of deionized water, and stir well. After the Tris granules disappear, neutralize the solution with 1 mmol / mL HCl, and finally prepare a Tris solution with a pH of 8.5.

[0062] 2. Subsequently, pour 0.5 g of graphene powder into the pre-prepared Tris solution and stir for 30 min. Then, disperse 0.5 g of dopamine hydrochloride in the mixed solution, stir for 30 min, and perform ultrasonic dispersion for 1 h. Subsequently, stir in an oil bath at 40 °C for 24 h, perform freeze-drying and grinding to obtain dopamine-functionalized graphene powder (P@GNs).

[0063] 3. Pour 0.2 g of MWCNT-NH 2 into DMF and stir magnetically for 1 h until MWCNT-NH 2 is completely dissolved. Subsequently, disperse 0.2 g of P@GNs in the mixed solution and perform ultrasonic treatment for 30 min. Then add 1 g of PVDF-HFP particles and stir magnetically for 3.5 - 4 h. Finally, use a pipette to transfer a quantitative amount of the mixed solution into a polytetrafluoroethylene mold and place it in an oven for curing and drying at 60 °C. The resistance of the obtained composite film (named MPP) is about 5 Ω. Refer to Figure 4 , at a voltage of 5 V, the temperature can reach 172 °C, indicating that the film has excellent electrothermal performance. At the same time, refer to Figure 3 , based on the water contact angle of the flexible composite film being 170 °, it indicates that the film has good hydrophobic properties; refer to Figure 5 , within the range of 8.2 - 12.4 GHz (X-band), the film has an EMI SE of 32.54 dB in the X-band, indicating that the composite film is excellent in electromagnetic shielding performance.

[0064] Comparative Example 1

[0065] On the basis of the above Example 2, without adding MWCNT-NH 2 and P@GNs, only add PVDF-HFP particles to the Tris solution (other experimental conditions are the same, omitted), then stir magnetically for 3.5 - 4 h. Finally, use a pipette to transfer a quantitative amount of the mixed solution into a polytetrafluoroethylene mold and place it in an oven for curing and drying at 60 °C to obtain a composite film (named PVDF-HFP).

[0066] Comparative Example 2

[0067] On the basis of the above Example 2, only add MWCNT-NH 2 and P@GNs, without adding PVDF-HFP particles (other experimental conditions are the same, omitted), stir magnetically for 3.5 - 4 h. Finally, use a pipette to transfer a quantitative amount of the mixed solution into a polytetrafluoroethylene mold and place it in an oven for curing and drying at 60 °C to obtain a composite film (named MP).

[0068] Refer to Figure 3 , for the films prepared in Comparative Example 1 and Comparative Example 2, their contact angles are 85 ° and 102 ° respectively, and the water contact angle of the flexible composite film MPP in Example 2 is 170 °, indicating that the film has good hydrophobic properties. Through the optimal ratio of each component, a good hydrophobic effect is achieved. Refer to Figure 5, for the flexible composite film MP prepared in Comparative Example 2, within the range of 8.2 - 12.4 GHz, the film has 9.5 dB EMI SE in the X-band, while Example 2 has 32.54 dB EMI SE, indicating that the composite film of Example 2 is more excellent in terms of electromagnetic shielding performance (Comparative Example 1 does not have electromagnetic shielding performance and there is no experimental data).

[0069] Although the present invention has been described in detail with general descriptions and specific embodiments above, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A method for preparing a flexible composite film, characterized in that: The steps include: 1) heating and stirring dopamine hydrochloride and graphene to prepare dopamine-based graphene, followed by freeze-drying and grinding into powder; 2) dispersing the amino-modified multi-walled carbon nanotubes into N,N-dimethylformamide solution until they are completely dissolved for later use; 3) dispersing the dopamine-modified graphene in the N,N-dimethylformamide solution simultaneously and ultrasonically dispersing the dopamine-modified graphene together with the aminated multi-walled carbon nanotubes; 4) Add polyvinylidene fluoride-hexafluoropropylene copolymer, stir to blend, and dry to form a film.

2. The method for preparing a flexible composite film according to claim 1, characterized in that: in, The dopamine hydrochloride and graphene are heated and stirred to prepare dopamine-based graphene, which is then freeze-dried and ground into powder, including: Pretreatment with Tris solution: weigh Tris particles and pour into deionized water for thorough stirring. After the Tris particles are dissolved, neutralize the solution with 1 mmol / mL HCl, and finally prepare a Tris solution with a pH of 8.

5. Preparation of dopamine-treated graphene: Pour the weighed graphene powder into the pre-prepared Tris solution and stir for 30 minutes. Then, disperse the weighed dopamine hydrochloride in the mixed solution. The mass ratio of graphene powder to dopamine hydrochloride is 1:

1. Then stir for another 30 minutes and perform ultrasonic dispersion for 1 hour. Then, stir in an oil bath at 40°C for 24 hours, freeze-dry, and grind to obtain dopamine-treated graphene powder.

3. The method for preparing a flexible composite film according to claim 1, characterized in that: in, Dispersing the amino-modified multi-walled carbon nanotubes into N,N-dimethylformamide solution until they are completely dissolved for later use, including: The weighed aminated multi-walled carbon nanotubes were poured into the N,N-dimethylformamide solution at a mass volume ratio of (1-2) g: 200 mL, and magnetically stirred for 1 h until the aminated multi-walled carbon nanotubes were completely dissolved to obtain a mixed solution.

4. The method for preparing a flexible composite film according to claim 3, characterized in that: in, The dopamine-modified graphene is dispersed in the N,N-dimethylformamide solution and ultrasonically dispersed together with the aminated multi-walled carbon nanotubes, comprising: Then, the weighed dopamine-treated graphene and amino-treated multi-walled carbon nanotubes were added and dispersed in the mixed solution in a mass ratio of 1:1, and ultrasonically treated for 30 minutes.

5. The method for preparing a flexible composite film according to claim 4, characterized in that: in, Then add polyvinylidene fluoride-hexafluoropropylene copolymer, stir and blend, and dry to form a film, including: The weighed polyvinylidene fluoride-hexafluoropropylene copolymer particles were added to the mixed solution, and then magnetic stirring was performed for 3.5-4 hours. Finally, a certain amount of the mixed solution was transferred to a polytetrafluoroethylene mold using a pipette, and placed in an oven for curing and drying at 60° C. to obtain a composite film.

6. The method for preparing a flexible composite film according to claim 5, characterized in that: The mass ratio of the polyvinylidene fluoride-hexafluoropropylene copolymer to the dopamine-treated graphene is 1:

1.

7. A flexible composite film based on multi-walled carbon nanotube dopamine graphene prepared by the method according to any one of claims 1 to 6.

8. The flexible composite film according to claim 7, characterized in that: The temperature of the flexible composite film reaches 172° C. at an operating voltage of 5V and has an electromagnetic shielding capability of 32.54 dB within 8.2-12.4 GHz (X band).

9. The flexible composite film according to claim 7, characterized in that: The water contact angle of the flexible composite film is 170°.

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