Anisotropic carbon nanotube / polyimide composite film material and preparation method thereof

Abstract

The invention discloses an anisotropic carbon nanotube / polyimide composite film material and a preparation method thereof. The preparation method comprises the following steps: preparing a polyamide acid solution, preparing a carbon nanotube / polyamide acid solution and preparing an anisotropic carbon nanotube / polyimide composite film. The piezoelectric spraying technology adopted in the invention can effectively prevent the filler from agglomerating in the polymer, significantly improve the uniformity of the film, and endow the composite film with unique mechanical properties and conductive characteristics in different directions. The technology has the advantages of simple operation, high material utilization rate, easy realization of large-area preparation and the like. The preparation process of the anisotropic film can be simplified, and the production cost is remarkably reduced. And anisotropic composite films with different materials and functions can be designed and prepared according to the adjustment of piezoelectric spraying parameters, so that the application performance of the films in sensors, flexible electronic devices and intelligent materials is improved.

Description

Technical Field

[0001] The present invention relates to the field of material technology, and in particular to an anisotropic carbon nanotube / polyimide composite film material and a preparation method thereof. Background Art

[0002] Anisotropic films are a class of thin-film materials that exhibit varying physical properties in different directions. They are widely used in electronics, optics, magnetism, energy storage, and other fields. Unlike traditional isotropic films, anisotropic films exhibit varying mechanical, electrical, and thermal conductivity properties in different directions. This unique property makes anisotropic films an important research area and application material in many high-tech fields.

[0003] At present, the preparation of anisotropic films usually adopts technologies such as hot pressing, electrochemical deposition and self-assembly to make the films exhibit different physical properties in different directions. However, these methods require more complicated processes during implementation, and the prepared films still have certain challenges in terms of thickness controllability and uniformity. As reported in the document Polymer, 2024, 290: 126491, the technical requirements for the use of electric field-induced filler directional arrangement are relatively high. The film prepared by traditional spraying method in the document Materials Today Communications, 2020, 25: 101432 still has the problem of insufficient precision in controlling thickness and uniformity. Summary of the Invention

[0004] The purpose of the present invention is to provide an anisotropic carbon nanotube / polyimide composite film material and a preparation method thereof. The composite film obtained by the preparation method provided by the present invention has obvious anisotropic conductivity and mechanical properties in different directions, which significantly improves the controllability and uniformity of the film in thickness.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] A method for preparing an anisotropic carbon nanotube / polyimide composite film material comprises the following steps:

[0007] Step 1: preparing a polyamic acid solution using 1,4-bis(4-aminophenoxy) and pyromellitic dianhydride benzene, wherein the solid content of the polyamic acid solution is 15% and the molar ratio of the two monomers is 1:1;

[0008] Step 2: Add the carbon nanotube dispersion to the PAA solution, and dilute and mix the solution with DMF to obtain a CNTs / PAA solution; the mass fraction of the CNTs dispersion is 1% to 3%; the viscosity of the diluted solution is 10 to 15 mPa·s;

[0009] Step 3: The CNTs / PAA solution is piezoelectrically sprayed on a substrate at a constant operating temperature of 60-80° C., and then heat-treated.

[0010] Optionally, the piezoelectric spraying in step three includes: an amplitude of 65 to 95; a liquid feeding speed of 0.1 to 1.0 mL / min; and a guide gas of nitrogen with a pressure of 0.01 to 0.02 MPa.

[0011] Optionally, the distance between the piezoelectric spraying nozzle and the substrate in step three is 20 to 30 mm; and the number of spraying times is 1 to 8 times.

[0012] Optionally, the heat treatment procedure in step three is: heating from room temperature to 70°C for 30 minutes, keeping warm for 1 hour; heating from 70°C to 150°C, keeping warm for 2 hours; heating from 150°C to 200°C, keeping warm for 1 hour; heating from 200°C to 250°C, keeping warm for 1 hour, and cooling to room temperature.

[0013] Optionally, the preparation of the polyamic acid solution includes:

[0014] Continuously introduce argon and use DMF to completely dissolve 1,4-bis(4-aminophenoxy)benzene; add pyromellitic dianhydride and DMF three times with an interval of 10 to 15 minutes between each addition, and continue stirring to promote the amidation reaction to obtain a polyamic acid solution.

[0015] Optionally, stirring is continued for 30 to 60 minutes during the process of completely dissolving 1,4-bis(4-aminophenoxy)benzene in DMF.

[0016] Optionally, the continuous stirring time is 2 to 3 hours.

[0017] Optionally, the amount of the CNTs dispersion is 2-5 g, the amount of the PAA solution is 10-20 g, and the amount of DMF used to dilute the solution is 4-6 g;

[0018] The diluting and mixing of the solution is ultrasonic stirring and mixing, the ultrasonic time is 10 to 20 minutes, and the stirring time is 10 to 20 minutes.

[0019] Optionally, the substrate is a silicon wafer, and the pretreatment method of the silicon wafer is ultraviolet ozone treatment, the ultraviolet wavelength is 185nm or 254nm, and the time is 3 to 5 minutes;

[0020] Alternatively, plasma treatment may be performed with a power of 40 to 100 W and a time of 1 to 2 minutes.

[0021] An anisotropic carbon nanotube / polyimide composite film material is prepared by using any of the preparation methods of the anisotropic carbon nanotube / polyimide composite film materials described in the present invention.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) This invention utilizes piezoelectric spraying technology to design and invent an anisotropic carbon nanotube / polyimide composite film material and its preparation method. This method applies an alternating voltage within a piezoelectric nozzle to induce highly ordered alignment of fillers within the polymer. This effectively prevents filler aggregation within the polymer and imparts unique mechanical and conductive properties to the composite film in different directions.

[0024] (2) Piezoelectric spraying technology has the advantages of simple operation, high material utilization, and easy large-area preparation. It can not only simplify the preparation process of anisotropic films and significantly reduce production costs, but also can design and prepare anisotropic composite films of different materials and functions by adjusting the piezoelectric spraying parameters. At the same time, this method significantly improves the uniformity of the film, providing flexibility to meet diverse application needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following detailed description, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

[0026] Figure 1 Flow chart for preparing the anisotropic CNTs / PI composite film provided by the present invention;

[0027] Figure 2 is a cross-sectional SEM image of the CNTs / PI film in Example 1;

[0028] Figure 3 The stress-strain curves of the CNTs / PI film in Example 1 in the parallel direction (spraying direction), perpendicular direction, and oblique direction;

[0029] Figure 4 This is a photo of the silver paste electrode of the CNTs / PI film in Example 1;

[0030] Figure 5 The resistance diagram of the CNTs / PI film in different directions in Example 1;

[0031] Figure 6 This is the cross-sectional SEM image of the CNTs / PI film in Example 2. DETAILED DESCRIPTION

[0032] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples, and the advantages of the present invention are demonstrated through analysis of comparative examples. However, these figures should not be construed as limiting the scope of protection of the present invention.

[0033] Preparation method of anisotropic carbon nanotube / polyimide composite film material of the present invention:

[0034] Step 1: Prepare the polyamic acid solution. Prepare the polyamic acid (PAA) solution in a three-necked flask equipped with a mechanical stirrer. Continuously flow argon gas throughout the preparation process. Add TPE-Q and DMF and stir for 30-60 minutes to completely dissolve. Add PMDA and DMF three times, with 10-15 minutes between additions. Continue stirring for 2-3 hours to promote the amidation reaction and obtain the PAA solution.

[0035] Step 2: Preparation of carbon nanotube / polyamic acid solution: Add the CNTs dispersion to the PAA solution, dilute the solution with DMF, and mix thoroughly under ultrasonic stirring to obtain a CNTs / PAA solution.

[0036] Step 3: Preparation of anisotropic carbon nanotube / polyimide composite film. Load the CNTs / PAA solution into a piezoelectric spray syringe. Pretreat the silicon wafer substrate and place it on the piezoelectric spraying workbench. Piezoelectric spraying is performed at a constant operating temperature. Start the piezoelectric spraying equipment and set the spraying parameters. After spraying is complete, hold the film at this temperature for a period of time before transferring it to an oven for heat treatment. Once the warm treatment is complete, an anisotropic CNTs / PI composite film is obtained on the silicon wafer surface.

[0037] The solid content of the polyamic acid solution is 15%, and the molar ratio of the two monomers is 1:1.

[0038] The mass fraction of the CNTs dispersion is 1% to 3%, the amount of the dispersion is 2 to 5g, the amount of PAA is 10 to 20g, and the amount of DMF is 4 to 6g. The viscosity of the diluted solution is 10 to 15mPa·s. Preferably, the mass fraction of the CNTs dispersion is 2%, the amount of the dispersion is 3g, the amount of PAA is 15g, the amount of DMF is 4g, and the solution viscosity is 15mPa·s.

[0039] The ultrasonic time is 10 to 20 minutes, and the stirring time is 10 to 20 minutes. The ultrasonic time is 20 minutes, and the stirring time is 20 minutes.

[0040] The substrate pretreatment method is ultraviolet ozone treatment (ultraviolet wavelength of 185nm or 254nm, time of 3-5min) or plasma treatment (power of 40-100W, time of 1-2min). Preferably, the ultraviolet ozone treatment wavelength is 185nm, the treatment time is 5min, and the plasma treatment power is 100W, and the treatment time is 2min.

[0041] The working temperature of the piezoelectric spraying workbench is 60-80° C. The preferred treatment time is 3 minutes.

[0042] The spraying parameters include an amplitude of 65-95°, a liquid feed rate of 0.1-1.0 mL / min, nitrogen as the flow gas at a pressure of 0.01-0.02 MPa, a distance between the nozzle and the silicon wafer of 20-30 mm, and 1-8 sprays. Preferably, the amplitude is 75°, the liquid feed rate is 0.4 mL / min, the pressure is 0.02 MPa, the distance between the nozzle and the silicon wafer is 25 mm, and the number of sprays is 6.

[0043] The workbench heat preservation time is 10 to 30 minutes, preferably 30 minutes.

[0044] The heat treatment procedure is as follows: heating from room temperature to 70°C in 30 minutes, keeping warm for 1 hour; heating from 70°C to 150°C, keeping warm for 2 hours; heating from 150°C to 200°C, keeping warm for 1 hour; heating from 200°C to 250°C, keeping warm for 1 hour, and cooling to room temperature.

[0045] Figure 1 The following is a preparation process for anisotropic carbon nanotube / polyimide composite films. Argon gas is continuously introduced into a three-necked flask equipped with a mechanical stirrer, and TPE-Q and DMF are added and stirred to completely dissolve. PMDA and DMF are added in three batches, and continuous stirring is performed to promote the amidation reaction to obtain a PAA solution. The CNTs dispersion is added to the PAA solution, and the solution is diluted with DMF. Ultrasonic stirring is performed to ensure uniform mixing to obtain a CNTs / PAA solution. The above CNTs / PAA solution is loaded into a piezoelectric spraying syringe. The silicon wafer substrate is pretreated, and the treated substrate is placed on the piezoelectric spraying workbench. Piezoelectric spraying is performed at a constant operating temperature. The piezoelectric spraying equipment is turned on and the spraying parameters are set. After spraying is completed, the temperature is kept for a period of time, and then the film is transferred to an oven for heat treatment. After the heat treatment is completed, an anisotropic CNTs / PI composite film can be obtained on the silicon wafer surface.

[0046] The piezoelectric spraying technology employed in this invention effectively prevents filler aggregation in polymers, significantly improving film uniformity and imparting unique mechanical and conductive properties to composite films in different directions. This technology offers advantages such as ease of operation, high material utilization, and ease of large-scale fabrication. It not only simplifies the preparation process for anisotropic films, significantly reducing production costs, but also enables the design and fabrication of anisotropic composite films with diverse materials and functions by adjusting the piezoelectric spraying parameters, thereby enhancing the performance of these films in applications such as sensors, flexible electronic devices, and smart materials.

[0047] The solution of the present invention is described in detail below with reference to specific embodiments.

[0048] Example 1:

[0049] Argon was continuously bubbled into a three-necked flask. 30 ml of DMF and 5.84 g of TPE-Q were added and stirred for 60 minutes to completely dissolve. Under argon and stirring, 1.454 g of PMDA and 10 ml of DMF were added in three batches, with 10 minutes between additions. Stirring was continued for 3 hours to obtain a PAA solution. 3 g of a 2% CNTs dispersion was weighed and added to 15 g of the PAA solution. 4 g of DMF was added for dilution. Ultrasonication was performed for 20 minutes, followed by stirring for 20 minutes to obtain a CNTs / PAA solution. The CNTs / PAA solution was loaded into a piezoelectric spray syringe. A silicon wafer was treated with UV-ozone at a wavelength of 185 nm for 3 minutes. The treated wafer was then placed on a workbench at 70°C. The piezoelectric sprayer was activated, with the amplitude set to 75, the liquid feed rate to 0.4 mL / min, the flow pressure to 0.02 MPa, the nozzle distance to the wafer to 25 mm, and the number of sprays to 6. According to the computer preset program, the CNTs / PAA solution was sprayed onto the silicon wafer and kept warm on a 70°C workbench for 30 minutes. The silicon wafer and film were transferred to an oven for heat treatment. The heat treatment program was to heat from room temperature to 70°C in 30 minutes and keep warm for 1 hour; from 70°C to 150°C and keep warm for 2 hours; from 150°C to 200°C and keep warm for 1 hour; from 200°C to 250°C and keep warm for 1 hour, and then cooled to room temperature to obtain anisotropic carbon nanotube / polyimide composite film.

[0050] The film obtained in this example was characterized by using a universal tensile testing machine, a scanning electron microscope, and a conductivity test to show that it has anisotropy.

[0051] Figure 2This is a cross-sectional SEM image of a CNTs / PI film produced by piezoelectric spraying. Because carbon nanotubes are conductive materials and the alternating voltage within the piezoelectric nozzle is applied, they experience a directional force in the electric field, causing the carbon nanotubes to align along the electric field lines. The image shows that the CNTs in the piezoelectric sprayed CNTs / PI film are well-aligned and aligned within the PI.

[0052] In CNTs / PI composite films, an appropriate amount of CNT filler not only significantly enhances the mechanical properties of the PI, but also significantly improves the film's conductivity and facilitates current conduction by effectively dispersing stress and providing additional support. The AC voltage applied to the piezoelectric nozzle causes the CNTs to align along the spraying direction, resulting in a continuous and high-content CNT distribution in the spraying direction, while the CNTs perpendicular to the spraying direction are unevenly distributed and have a low content. This uneven CNT distribution leads to significant differences in the film's mechanical properties and conductivity in different directions.

[0053] Figure 3 The stress-strain curves for the composite film in the parallel (spraying direction), perpendicular (or diagonal) and oblique directions are shown. The figure shows that the addition of CNTs enhances the strength and toughness of the PI film compared to pure PI. Furthermore, the tensile strength and elongation at break of the composite film along the spraying direction and the direction of CNT alignment reach maximum values ​​of 96 MPa and 21.7%, respectively. In contrast, the tensile strength and elongation at break of the composite film in the perpendicular direction are only 61 MPa and 10.5%.

[0054] Figure 4 A photo of the silver paste electrodes on the CNTs / PI film. Resistance measurements were performed by applying silver paste at 10° intervals and measuring the resistance between two points along the film's diameter using a source meter to evaluate the composite film's conductive properties. Figure 5 The following plots the resistance of the CNTs / PI film at different orientations. 0° and 180° are parallel to the spraying direction, while 90° is perpendicular to the spraying direction. The plot shows significant anisotropy in the resistance across all directions as the measurement angle changes. The lowest resistance along the spraying direction is 59.92 kΩ, indicating a relatively continuous distribution and high abundance of CNTs. The highest resistance along the perpendicular direction is 89.07 kΩ, indicating a discontinuous distribution and low abundance of CNTs.

[0055] Example 2 (comparative example):

[0056] A three-necked flask was continuously bubbled with argon. 30 ml of DMF and 5.84 g of TPE-Q were added and stirred for 60 minutes to completely dissolve. Under argon and stirring, 1.454 g of PMDA and 10 ml of DMF were added in three batches, with 10 minutes between additions. Stirring was continued for 3 hours to obtain a PAA solution. 3 g of a 2% CNT dispersion was weighed and added to 15 g of the PAA solution. The mixture was sonicated for 20 minutes and then stirred for 20 minutes to obtain a CNTs / PAA solution. The silicon wafer was treated with ultraviolet ozone at an ultraviolet wavelength of 185nm for 3 minutes. The liquid was dropped onto the surface of the silicon wafer using a pipette and spread naturally. The silicon wafer and the film were transferred to an oven for heat treatment. The heat treatment procedure was as follows: heating from room temperature to 70°C for 30 minutes, keeping warm for 1 hour, heating from 70°C to 150°C, keeping warm for 2 hours; heating from 150°C to 200°C, keeping warm for 1 hour; heating from 200°C to 250°C, keeping warm for 1 hour, and cooling to room temperature to obtain a carbon nanotube / polyimide composite film.

[0057] Figure 6 This is a cross-sectional SEM image of a CNTs / PI film prepared by the drop-coating method. The image shows that due to the lack of directional forces, the CNTs in the PI matrix agglomerated and disordered, resulting in the film failing to exhibit anisotropic properties.

[0058] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings. However, the present disclosure is not limited to the specific details of the above embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the scope of protection of the present disclosure.

[0059] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0060] In addition, the various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A method for preparing anisotropic carbon nanotube / polyimide composite film material, characterized in that: The following steps are involved: Step 1: preparing a polyamic acid solution using 1,4-bis(4-aminophenoxy) and pyromellitic dianhydride benzene, wherein the solid content of the polyamic acid solution is 15% and the molar ratio of the two monomers is 1:1; Step 2: Add the carbon nanotube dispersion to the PAA solution, and dilute and mix the solution with DMF to obtain a CNTs / PAA solution; the mass fraction of the CNTs dispersion is 1% to 3%; the viscosity of the diluted solution is 10 to 15 mPa·s; Step 3: The CNTs / PAA solution is piezoelectrically sprayed on a substrate at a constant operating temperature of 60-80° C., and then heat-treated.

2. The method for preparing anisotropic carbon nanotube / polyimide composite film material according to claim 1, characterized in that: The piezoelectric spraying in step 3 includes: The amplitude is 65~95; the liquid inlet speed is 0.1~1.0mL / min; the guide gas is nitrogen, and the gas pressure is 0.01~0.02MPa.

3. The method for preparing anisotropic carbon nanotube / polyimide composite film material according to claim 1 or 2, characterized in that: The distance between the piezoelectric spraying nozzle and the substrate in step 3 is 20 to 30 mm; the number of spraying times is 1 to 8 times.

4. The method for preparing anisotropic carbon nanotube / polyimide composite film material according to claim 1 or 2, characterized in that: The heat treatment procedure in step 3 is as follows: heating from room temperature to 70°C for 30 minutes, keeping warm for 1 hour; heating from 70°C to 150°C, keeping warm for 2 hours; heating from 150°C to 200°C, keeping warm for 1 hour; heating from 200°C to 250°C, keeping warm for 1 hour, and cooling to room temperature.

5. The method for preparing anisotropic carbon nanotube / polyimide composite film material according to claim 1 or 2, characterized in that: The preparation of the polyamic acid solution comprises: Continuously introduce argon and use DMF to completely dissolve 1,4-bis(4-aminophenoxy)benzene; add pyromellitic dianhydride and DMF three times with an interval of 10 to 15 minutes between each addition, and continue stirring to promote the amidation reaction to obtain a polyamic acid solution.

6. The method for preparing anisotropic carbon nanotube / polyimide composite film material according to claim 5, characterized in that: The stirring was continued for 30 to 60 minutes while 1,4-bis(4-aminophenoxy)benzene was completely dissolved in DMF.

7. The method for preparing anisotropic carbon nanotube / polyimide composite film material according to claim 5, characterized in that: The continuous stirring time is 2 to 3 hours.

8. The method for preparing anisotropic carbon nanotube / polyimide composite film material according to claim 1 or 2, characterized in that: The amount of the CNTs dispersion is 2-5 g, the amount of the PAA solution is 10-20 g, and the amount of DMF used to dilute the solution is 4-6 g; The diluting and mixing of the solution is ultrasonic stirring and mixing, the ultrasonic time is 10 to 20 minutes, and the stirring time is 10 to 20 minutes.

9. The method for preparing anisotropic carbon nanotube / polyimide composite film material according to claim 1, characterized in that: The substrate is a silicon wafer, and the pretreatment method of the silicon wafer is ultraviolet ozone treatment, the ultraviolet wavelength is 185nm or 254nm, and the time is 3 to 5 minutes; Alternatively, plasma treatment may be performed with a power of 40 to 100 W and a time of 1 to 2 minutes.

10. An anisotropic carbon nanotube / polyimide composite film material, characterized in that: The anisotropic carbon nanotube / polyimide composite film material is prepared using the preparation method of any one of claims 1-9.

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