A flexible graphene conductive composite material and its preparation method

Abstract

A flexible graphene conductive composite material and its preparation method are disclosed. The material comprises a first outer layer and a second outer layer formed from nano-aramid fibers and graphene, and an inner layer located between the first and second outer layers. The graphene concentration in the first and second outer layers is higher than that in the inner layer. A flexible graphene conductive composite material with a non-uniform structure is formed by layering and filtering a graphene / nano-aramid fiber mixture with different graphene concentrations and then hot-pressing it. The thickness of the flexible graphene conductive composite material is 0.04-0.1 mm, and the thickness ratio of the first outer layer, the inner layer, and the second outer layer is (1-3):(2-10):(1-3). This invention prepares a flexible graphene composite film material by decreasing the graphene concentration from the outside to the inside, saving filler usage and imparting good flexibility to the composite material, with a resistivity of 5×10⁻⁶. ‑6 Below Ω·cm, it has enormous application potential in sensors and other fields.

Description

Technical Field

[0001] This invention relates to the field of flexible wearable conductive sensing materials, and in particular to a graphene flexible conductive composite material and its preparation method. Background Technology

[0002] As people's living standards continue to improve, the demand for flexible wearable and portable electronic products (such as flexible foldable displays, e-readers, tablets, and ultra-thin smartphones) is increasing daily. Flexible conductive composite materials occupy a crucial position in fields such as flexible interconnects, printed electronics, and wearable electronics, but they still face many challenges in practical applications. Although the resin matrix in conductive composite materials allows for low-temperature interconnects and is compatible with various difficult-to-wet substrates, it also weakens the conductivity of the composite material.

[0003] In recent years, graphene (RGO), as a unique carbon nanomaterial, has been widely used in flexible electrode materials due to its advantages such as high specific surface area and good conductivity.

[0004] Aramid 1414 is a fully para-polyaramid polymerized by the condensation of p-phenylenediamine and terephthaloyl chloride (PPTA). Due to the rigidity of its molecular chains, it exhibits lyotropic liquid crystal properties and readily forms anisotropic textures in solution under shear forces. Therefore, aramid 1414 can be used to spin high-strength, high-modulus fibers with exceptionally high properties, commercially known as Kevlar fiber, and referred to as aramid 1414 fiber in China. Its thermal decomposition temperature reaches as high as 560℃, exhibiting high heat resistance, as well as high tensile strength and initial elastic modulus fiber strength. Therefore, aramid 1414 fiber shows great potential in composite materials. However, the finished aramid 1414 fibers and yarns are difficult to dissolve and disperse, and their macroscopic morphology limits their application and processing in composite materials.

[0005] Invention CN108752611B discloses a high-mechanical-strength aramid nanofiber hybrid film and its preparation method. The film, by mass, comprises the following components: 100 parts aramid nanofibers and 3-15 parts graphene oxide. This invention utilizes the hydration protonation effect to promote structural reorganization of aramid nanofibers while inducing ordered gelation and self-assembly of the nanofibers, conveniently controlling the thickness of the film material. By filling the one-dimensional nanofiber matrix with a two-dimensional graphene oxide reinforcing phase, the interfacial compatibility advantages between the phase components are effectively utilized, greatly improving the mechanical properties of the aramid fiber composite film material.

[0006] Invention CN103146007A discloses a method for preparing a graphene / aramid 1414 nanofiber composite membrane, comprising: nanofiberizing aramid 1414 yarns through a solution system of dimethyl sulfoxide and potassium hydroxide, then slowly adding a dimethyl sulfoxide solution of graphene oxide, and sequentially forming a membrane by centrifugation, dispersion and filtration to obtain a graphene oxide / aramid 1414 nanofiber composite membrane, and then reducing it with hydroiodic acid, washing and drying to obtain a graphene / aramid 1414 nanofiber composite membrane.

[0007] The aforementioned composite thin film structure has significantly improved mechanical strength compared to the single (oxidized) graphene film and aramid 1414 nanofiber film, but its electrical conductivity and durability are still insufficient, and its overall performance is not enough to support its use in wearable conductive sensing devices for the human body.

[0008] Furthermore, as the aforementioned literature indicates, when macroscopic aramid 1414 fibers are transformed into nanofibers, the composite material of graphene and aramid fibers becomes a reality. Through the composite of aramid fibers and graphene, the composite material can possess both high mechanical strength and thermal stability, as well as excellent electrical conductivity. With macroscopic and microscopic structural design, this novel graphene / aramid 1414 nanofiber composite membrane is expected to demonstrate greater application value in the materials industry and electrochemistry.

[0009] To improve the conductivity of conductive composite materials, methods such as surface treatment, doping with nano-conductive materials, and improving the morphology of conductive fillers can be employed. While these methods can enhance the conductivity of conductive composite materials, they also present technical challenges, including complex synthesis processes, high costs, reduced adhesive strength due to the introduction of solvents, loss of flexibility in flexible conductive composite materials due to nano-sintering, and threats to device reliability due to the introduction of strong acids. Some of these methods sacrifice the mechanical properties of the conductive composite material to improve its conductivity. While altering the microstructure of the conductive composite material can improve its mechanical properties with almost no impact on conductivity, these methods often involve complex processes, difficult processing, and challenges in post-processing for film deposition or printing into flexible devices.

[0010] Therefore, how to provide a flexible graphene conductive composite material that can reduce its resistivity and improve its electrical properties while ensuring its flexibility and mechanical properties so as to meet the requirements of wearable medical devices is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0011] To address the shortcomings of the existing technology, this invention provides a flexible graphene conductive composite material and its preparation method, which, while ensuring its flexibility and mechanical properties, also possesses excellent electrical conductivity.

[0012] In a first aspect, the present invention provides a flexible graphene conductive composite material, comprising a first outer layer and a second outer layer formed of nano-aramid fibers and graphene, and an inner layer located between the first outer layer and the second outer layer; the graphene concentration in the first outer layer and the second outer layer is higher than the graphene concentration in the inner layer; a flexible graphene conductive composite material with a non-uniform structure is formed by stratifying and filtering a graphene / nano-aramid fiber mixture with different graphene concentrations and hot-pressing it. The thickness of the flexible graphene conductive composite material is 0.04-0.1 mm, and the thickness ratio of the first outer layer, the inner layer and the second outer layer is (1-3):(2-10):(1-3). The resistivity of flexible graphene conductive composite materials is 5×10⁻⁶. -6 Below Ω·cm.

[0013] Preferably, the graphene concentration A in the first outer layer, the graphene concentration B in the second outer layer, and the graphene concentration C in the inner layer are such that A:B:C is (1.1-3):(1.1-3):1. The graphene concentration A in the first outer layer and the graphene concentration B in the second outer layer may be the same or different.

[0014] Preferably, the inner layer comprises n unit layers, n≥2, and the graphene concentrations in adjacent unit layers are different.

[0015] Preferably, the graphene concentration increases, decreases, or varies discontinuously among the n unit layers.

[0016] Preferably, (1) when n is odd, ,and ; (2) When n is even, ,and .

[0017] Unlike existing graphene / aramid 1414 nanofiber composite membranes with a single structure and composition, the graphene concentration in the composite membrane material prepared by this invention exhibits non-uniformity, decreasing continuously or discontinuously from the outside to the inside, forming an overall concentration gradient difference. This can save the amount of graphene used, impart good flexibility to the composite material, and basically not reduce the overall electrical properties of the membrane material, thus having promotional application value.

[0018] Secondly, the present invention also provides a method for preparing a flexible graphene conductive composite material, comprising the following steps: Step 1: Prepare a high-concentration graphene / nanoaramid fiber mixture for the first and second outer layers; prepare a low-concentration graphene / nanoaramid fiber mixture for the inner layer. Step 2, Vacuum Filtration: Place the microporous filter membrane on the sand core filter head, and filter the corresponding mixture in the order of the first outer layer, inner layer, and second outer layer to obtain the membrane intermediate; Step 3: Wash the membrane intermediate obtained by vacuum filtration repeatedly with anhydrous ethanol; Step 4: Peel the membrane intermediate from the microporous filter membrane; Step 5: The film intermediate is hot-pressed to obtain a flexible graphene conductive composite material with a non-uniform structure.

[0019] This invention utilizes monolayer graphene highly dispersed within the voids of an isotropic aramid nanofiber gel network structure. Through solvent removal via filtration, the void size is continuously reduced, forming a microstructure with alternating nanofibers and nanosheet graphene. Both nanofibers and nanosheet graphene possess high specific surface areas and are physically bonded together to form a film-like material. The graphene is distributed within the dense spatial network structure of the nanofibers, creating continuous conductive pathways.

[0020] Preferably, the raw materials for the graphene / nanoaramid fiber mixture, by volume, include the following components: 100 parts of nano-aramid fiber gel; 0.5-10 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with the monolayer graphene concentration being 1-10 mg / ml; In the nano-aramid fiber gel, the concentration of aramid fibers is 2-10 mg / ml.

[0021] Preferably, the nano-aramid fiber gel is prepared by the following steps: S1: Dissolve aramid fiber and potassium hydroxide in dimethyl sulfoxide solvent, bathe in water at 40°C or below, and then ultrasonically vibrate for 0.5-1.5 hours. S2: Add deionized water, gradually increase the stirring speed to 1200-1800 rpm at a rate of 100-300 rpm, continue stirring for 20-60 minutes, then increase the stirring speed to over 2000 rpm and stir for 20-30 hours. S3: After stirring, add a large amount of deionized water; gradually increase the stirring speed to 1200-1800 rpm at a rate of 100-300 rpm, continue stirring for 3-10 minutes, then increase the stirring speed to over 2000 rpm and stir for 0.5-2 hours. S4: After stirring, a slightly yellow nano-aramid fiber gel is obtained.

[0022] Preferably, in step one, the first outer layer and the second outer layer are made of a high-concentration graphene / nanoaramid fiber mixture Sw, and the inner layer is made of a low-concentration graphene / nanoaramid fiber mixture S1 to Sn, respectively, where n≥2. In step two, half the volume of the mixture Sw is filtered by vacuum filtration, and mixtures S1 to Sn are filtered sequentially. Finally, the remaining half volume of the mixture Sw is filtered by vacuum filtration.

[0023] Thirdly, based on the aforementioned structure, electrical and mechanical properties of the flexible graphene conductive composite material, the present invention also provides the application of the flexible graphene conductive composite material in flexible sensors or wearable electronic products.

[0024] The present invention provides at least the following beneficial effects: (1) Compared with existing technologies, the flexible composite material preparation process provided by this invention does not involve chemical changes, no chemical bonds are formed between graphene and nanofibers, the good flexibility of the fibers is well maintained, and the conductivity of graphene is not damaged. This composite material preparation method is simple, requires little equipment investment, greatly reduces the preparation cost of flexible composite materials, and has a great promoting effect on the industrial production of graphene flexible conductive composite materials.

[0025] (2) The graphene flexible composite membrane material with multi-layer concentration gradient provided by the present invention can save the amount of filler, give the composite material good flexibility, and maintain the overall electrical properties of the composite membrane material by continuously or discontinuously reducing the graphene concentration from the outside to the inside.

[0026] (3) The composite material provided by the present invention has good electrical conductivity and sensing properties, and its resistivity is within 5×10⁻⁶. -6 Below Ω·cm, it has enormous application potential in flexible sensors or wearable electronic products. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of a graphene conductive composite material according to the present invention; Figure 2 This is a schematic diagram of another graphene conductive composite material according to the present invention; Figure 3 The images shown are SEM morphology images of samples from some embodiments of the present invention, wherein 1 is sample 1 of embodiment 1, 2 is sample 7 of embodiment 7, 3 is sample 8 of embodiment 8, 4 is sample 9 of embodiment 9, and 5 is sample 10 of embodiment 10. Figure 4 This is a high-resolution morphology image of sample 1 from Embodiment 1 of the present invention; Figure 5The graph shows the resistivity test results of samples from some embodiments of the present invention. Figure 6 The figures show the mechanical property test results of samples from some embodiments of the present invention; Figure 7 The graph shows the sensor performance test results of sample 1 in Embodiment 1 of the present invention.

[0028] Reference numerals: 1-First outer layer; 2-Inner layer; 21, 22, 23-Unit layer; 3-Second outer layer. Detailed Implementation

[0029] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] A flexible graphene conductive composite material has a thickness of 0.04-0.1 mm, preferably 0.04-0.08 mm, more preferably 0.045-0.06 mm, and a resistivity of 5 × 10⁻⁶ mm. -6 Below Ω·cm, specifically including the following structures: (1) First outer layer 1: nano-aramid fiber and graphene, with a graphene concentration of A; (2) Second outer layer 3: nano-aramid fiber and graphene, with a graphene concentration of B; wherein A and B may be the same or different; (3) Inner layer 2: Located between the first outer layer 1 and the second outer layer 3, it includes nano-aramid fibers and graphene, with a graphene concentration of C, where C is less than A and C is less than B, and the graphene concentration ratio A:B:C is (1.1-3):(1.1-3), that is, the graphene concentration of the inner layer 2 is lower than that of the two outer layers; preferably, the inner layer 2 contains n unit layers (21,22,23), n≥2, and the graphene concentration increases, decreases or changes discontinuously among the n unit layers; Since the layers after filtration and other treatments are mainly composed of nano-aramid fibers and graphene, the aforementioned graphene concentration can be the ratio of graphene mass to the total mass of the layer, i.e., mass concentration, or the ratio of graphene mass to the total volume of the layer, which can represent the difference in graphene content between the outer and inner layers.

[0031] Specifically, the graphene concentration in inner layer 2 can satisfy the following relationship: (1) When n is odd, ,and ; (2) When n is even, ,and .

[0032] The thickness ratio of the first outer layer 1, the inner layer 2, and the second outer layer 3 is (1-3):(2-10):(1-3). The specific thickness of each layer is mainly reflected by the thickness of the nano-aramid fiber, which can be controlled by the amount of raw materials applied in the preparation method.

[0033] The preparation method of the aforementioned flexible graphene conductive composite material specifically includes the following steps: Step 1: Prepare the first outer layer 1 and the second outer layer 3 using a high-concentration graphene / nanoaramid fiber mixture; prepare the inner layer 2 using a low-concentration graphene / nanoaramid fiber mixture; each step includes: S1. Preparation of nano-aramid fiber gel: 1) Dissolve aramid 1414 fiber and potassium hydroxide in dimethyl sulfoxide solvent, and ultrasonically vibrate for 0.5-1.5 hours in a water bath at a temperature below 40°C. 2) Add deionized water and gradually increase the stirring speed to 1200-1800 rpm at a rate of 100-300 rpm. Continue stirring for 20-60 minutes, then increase the stirring speed to over 2000 rpm and stir for 20-30 hours. 3) After stirring, add a large amount of deionized water; gradually increase the stirring speed to 1200-1800 rpm at a rate of 100-300 rpm, continue stirring for 3-10 minutes, then increase the stirring speed to over 2000 rpm and stir for 0.5-2 hours. 4) After stirring, a slightly yellow nano-aramid fiber gel is obtained; S2. Preparation of graphene / nanoaramid fiber mixture: The raw materials of the graphene / nanoaramid fiber mixture, by volume, include the following components: 100 parts of nano-aramid fiber gel; 0.5-10 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with the monolayer graphene concentration being 1-10 mg / ml; In the nano-aramid fiber gel, the concentration of aramid fibers is 2-10 mg / ml; Based on the difference in graphene concentration between the outer and inner layers, in the outer layer (1, 3), the graphene / nanoaramid fiber mixture S, by volume, w The raw materials include the following components: 100 parts of nano-aramid fiber gel; 3-10 parts of graphene dispersion; In inner layer 2, the raw materials of the graphene / nanoaramid fiber mixture, by volume, include the following components: 100 parts of nano-aramid fiber gel; 0.5-8 parts of graphene dispersion; Preferably, the first outer layer 1 and the second outer layer 3 are made of a high-concentration graphene / nanoaramid fiber mixture S w The inner layer 2 uses a low-concentration graphene / nanoaramid fiber mixture as mixture S1 to Sn, where n≥2, preferably ≥3; Step 2, Vacuum Filtration: Place the microporous membrane on the sand core filter head, and perform layered filtration of the corresponding mixture in the order of first outer layer 1, inner layer 2, and second outer layer 3 to obtain the membrane intermediate; the thickness of each layer is adjusted by controlling the concentration and volume of the mixture; preferably, half the volume of the mixture S is added... w Perform vacuum filtration, filtering mixtures S1 through Sn sequentially, and finally filtering the remaining half-volume mixture S. w Filtration is performed, meaning the graphene concentrations A and B in the first outer layer 1 and the second outer layer 3 are essentially the same, and their thicknesses are also essentially the same; optionally, the total volume of the mixture S1 to Sn is equal to that of the mixture S... w The thickness of each layer is primarily determined by the fiber thickness. If the same concentration of nano-aramid fibers is used in each mixture, the above setup can produce a product where the total thickness of the two outer layers is essentially the same as the total thickness of the inner layer 2. Alternatively, the thickness of each layer and the graphene concentration can be controlled separately by adjusting the material concentration and the volume of the mixture.

[0034] Step 3: Wash the membrane intermediate obtained by vacuum filtration repeatedly with anhydrous ethanol; Step 4: Peel the membrane intermediate from the microporous filter membrane; Step 5: Place the film intermediate peeled off in Step 4 between two flat glass plates and hot press it, keeping the pressure range at 10-20 MPa and the temperature at 50-60℃ for 48 hours. The flexible graphene conductive composite material can then be obtained by opening the mold.

[0035] Example 1 The flexible graphene conductive composite material sample 1 of Example 1 was prepared by the following method: Step 1: Prepare a high-concentration graphene / nanoaramid fiber mixture for the first and second outer layers; prepare a low-concentration graphene / nanoaramid fiber mixture for the inner layer; each step includes: S1. Preparation of nano-aramid fiber gel: 1) Add 100 parts of aramid 1414 fiber and 200 parts of potassium hydroxide to a three-necked flask and dissolve them in dimethyl sulfoxide solvent; 2) After sealing the bottle opening, place it in an ultrasonic vibrator and vibrate for 1 hour. During this period, the water bath temperature for ultrasonic vibration should not exceed 40°C. 3) Measure a certain amount of deionized water and add it to a three-necked flask. The volume ratio of deionized water to the mass of aramid 1414 fiber is approximately 20 ml: 1 g. 4) Place the stirring paddle in the three-necked flask and fix the three-necked flask on the iron stand on which the stirrer is installed; 5) Turn on the mixer and gradually increase the mixing speed from 150 rpm to 1500 rpm. Continue mixing for 30 minutes, then increase the mixing speed to over 2000 rpm and mix for 24 hours. 6) After stirring, measure a large amount of deionized water and add it to the three-necked flask; 7) Turn on the mixer and gradually increase the mixing speed from 200 rpm to 1500 rpm. Continue mixing for 5 minutes, then increase the mixing speed to 2000 rpm and mix for 1 hour. 8) After stirring, aramid nanofiber gel was obtained, which was slightly yellow in color and had an aramid fiber concentration of about 5 mg / ml.

[0036] S2. Preparation of graphene / nanoaramid fiber mixture: (1) The first and second outer layers are made of a high-concentration graphene / nanoaramid fiber mixture S w The raw materials, by volume, include the following components: 100 parts of nano-aramid fiber gel; 3 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0037] (2) The inner layer uses a low-concentration graphene / nanoaramid fiber mixture S1, which, by volume, comprises the following components: 100 parts of nano-aramid fiber gel; One part of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0038] Step 2, Vacuum Filtration: Place the microporous membrane on the sand core filter head and perform layered filtration of the corresponding mixture in the order of the first outer layer, inner layer, and second outer layer to obtain the membrane intermediate: (1) Take a high concentration of graphene / nanoaramid fiber mixture S w The volume of the low-concentration graphene / nanoaramid fiber mixture S1 is 30 ml. (2) Take half the volume of the mixture S w Perform vacuum filtration; (3) Filter the mixture S1 by suction; (4) Finally, take the remaining half volume of the mixture S w Perform vacuum filtration; Step 3: Wash the membrane intermediate obtained by vacuum filtration repeatedly with anhydrous ethanol; Step 4: Peel the membrane intermediate from the microporous filter membrane; Step 5: Place the film intermediate peeled out in Step 4 between two flat glass plates and hot press it, keeping the pressure range at 15±1 MPa and the temperature at 55℃ for 48 hours. After opening the mold, the flexible graphene conductive composite material can be obtained. In Sample 1, the graphene concentrations A and B of the first and second outer layers are basically the same, and the thicknesses are also basically the same, about 0.012 mm. The inner layer thickness is 0.024 mm, and the overall film thickness is about 0.048 mm. The thickness ratio of the first outer layer, inner layer, and second outer layer is about 1:2:1.

[0039] Example 2 The difference between this embodiment and Embodiment 1 lies in the high concentration of graphene / nanoaramid fiber mixture S. w Due to the different volume of the low-concentration graphene / nanoaramid fiber mixture S1, the final composite material has different layer thicknesses.

[0040] (1) Take a high concentration of graphene / nanoaramid fiber mixture S w The volume of the low-concentration graphene / nanoaramid fiber mixture S1 is 35 ml. (2) Take half the volume of the mixture S w Perform vacuum filtration; (3) Filter the mixture S1 by suction; (4) Finally, take the remaining half volume of the mixture S w Perform vacuum filtration.

[0041] The graphene concentrations A and B of the first and second outer layers of sample 2 are basically the same, and their thicknesses are also basically the same, approximately 0.01 mm. The inner layer thickness is 0.028 mm, and the overall film thickness is approximately 0.048 mm. The thickness ratio of the first outer layer, inner layer, and second outer layer is approximately 1:2.8:1.

[0042] Example 3 The difference between this embodiment and Embodiment 1 lies in the high concentration of graphene / nanoaramid fiber mixture S. w Due to the different volume of the low-concentration graphene / nanoaramid fiber mixture S1, the final composite material has different layer thicknesses.

[0043] (1) Take a high concentration of graphene / nanoaramid fiber mixture S w The volume of the low-concentration graphene / nanoaramid fiber mixture S1 is 40 ml, with a volume of 20 ml. (2) Take half the volume of the mixture S w Perform vacuum filtration; (3) Filter the mixture S1 by suction; (4) Finally, take the remaining half volume of the mixture S w Perform vacuum filtration.

[0044] The graphene concentrations A and B of the first and second outer layers of sample 3 are basically the same, and their thicknesses are also basically the same, approximately 0.008 mm. The inner layer thickness is 0.032 mm, and the overall film thickness is approximately 0.048 mm. The thickness ratio of the first outer layer, inner layer, and second outer layer is approximately 1:4:1.

[0045] Example 4 The difference between this embodiment and Embodiment 1 lies in the high concentration of graphene / nanoaramid fiber mixture S. w Due to the different volume of the low-concentration graphene / nanoaramid fiber mixture S1, the final composite material has different layer thicknesses.

[0046] (1) Take a high concentration of graphene / nanoaramid fiber mixture S w The volume of the low-concentration graphene / nanoaramid fiber mixture S1 is 18ml, and the volume of the low-concentration graphene / nanoaramid fiber mixture S1 is 42ml. (2) Take half the volume of the mixture S w Perform vacuum filtration; (3) Filter the mixture S1 by suction; (4) Finally, take the remaining half volume of the mixture S w Perform vacuum filtration.

[0047] The graphene concentrations A and B of the first and second outer layers of sample 4 are basically the same, and their thicknesses are also basically the same, approximately 0.007 mm. The inner layer thickness is 0.034 mm, and the overall film thickness is approximately 0.048 mm. The thickness ratio of the first outer layer, inner layer, and second outer layer is approximately 1:5:1.

[0048] Example 5 The difference between this embodiment and Embodiment 1 lies in the high concentration of graphene / nanoaramid fiber mixture S. w Due to the different volume of the low-concentration graphene / nanoaramid fiber mixture S1, the final composite material has different layer thicknesses.

[0049] (1) Take a high concentration of graphene / nanoaramid fiber mixture S w The volume of the low-concentration graphene / nanoaramid fiber mixture S1 is 45 ml. (2) Take half the volume of the mixture S w Perform vacuum filtration; (3) Filter the mixture S1 by suction; (4) Finally, take the remaining half volume of the mixture S w Perform vacuum filtration.

[0050] The graphene concentrations A and B of the first and second outer layers of sample 5 are basically the same, and their thicknesses are also basically the same, approximately 0.006 mm. The inner layer thickness is 0.036 mm, and the overall film thickness is approximately 0.048 mm. The thickness ratio of the first outer layer, inner layer, and second outer layer is approximately 1:6:1.

[0051] Example 6 The difference between sample 6 in this embodiment and sample 1 in embodiment 1 is that the graphene content in the low-concentration graphene / nanoaramid fiber mixture S1 is different, that is, the content of inner layer graphene is different: The inner layer uses a low-concentration graphene / nanoaramid fiber mixture S1, which, by volume, comprises the following components: 100 parts of nano-aramid fiber gel; 0.5 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0052] Example 7 The difference between sample 7 in this embodiment and sample 1 in Example 1 is that the high-concentration graphene / nanoaramid fiber mixture S w The graphene content varies, meaning the outer graphene content varies: The first and second outer layers are made with a high-concentration graphene / nanoaramid fiber mixture S w The raw materials, by volume, include the following components: 100 parts of nano-aramid fiber gel; 2.5 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0053] Example 8 The difference between this embodiment and Example 1 lies in the different proportions of graphene dispersion in the graphene / aramid nanofiber gel mixture and the different amounts of the mixture S. w The volume of mixture S1 is different: (1) The first and second outer layers are made of a high-concentration graphene / nanoaramid fiber mixture S w The raw materials, by volume, include the following components: 100 parts of nano-aramid fiber gel; 5 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0054] (2) The inner layer uses a low-concentration graphene / nanoaramid fiber mixture S1, which, by volume, comprises the following components: 100 parts of nano-aramid fiber gel; 3 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0055] Step 2, Vacuum Filtration: Place the microporous membrane on the sand core filter head and perform layered filtration of the corresponding mixture in the order of the first outer layer, inner layer, and second outer layer to obtain the membrane intermediate: (1) Take a high concentration of graphene / nanoaramid fiber mixture S w The volume of the low-concentration graphene / nanoaramid fiber mixture S1 is 35 ml. (2) Take half the volume of the mixture S w Perform vacuum filtration; (3) Filter the mixture S1 by suction; (4) Finally, take the remaining half volume of the mixture S w Perform vacuum filtration; Step 3: Wash the membrane intermediate obtained by vacuum filtration repeatedly with anhydrous ethanol; Step 4: Peel the membrane intermediate from the microporous filter membrane; Step 5: Place the film intermediate peeled out in Step 4 between two flat glass plates and hot press it, keeping the pressure range at 15±1 MPa and the temperature at 55℃ for 48 hours. After opening the mold, the flexible graphene conductive composite material can be obtained. Among them, the graphene concentrations A and B of the first and second outer layers of sample 8 are basically the same, and the thicknesses are also basically the same, about 0.01 mm. The inner layer thickness is 0.028 mm, the overall film thickness is about 0.048 mm, and the thickness ratio of the first outer layer, inner layer, and second outer layer is about 1:2.8:1.

[0056] Example 9 The difference between this embodiment and Example 1 lies in the different proportions of graphene dispersion in the graphene / aramid nanofiber gel mixture and the different amounts of the mixture S. w The volume of mixture S1 is different: (1) The first and second outer layers are made of a high-concentration graphene / nanoaramid fiber mixture S w The raw materials, by volume, include the following components: 100 parts of nano-aramid fiber gel; 7 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0057] (2) The inner layer uses a low-concentration graphene / nanoaramid fiber mixture S1, which, by volume, comprises the following components: 100 parts of nano-aramid fiber gel; 5 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0058] Step 2, Vacuum Filtration: Place the microporous membrane on the sand core filter head and perform layered filtration of the corresponding mixture in the order of the first outer layer, inner layer, and second outer layer to obtain the membrane intermediate: (1) Take a high concentration of graphene / nanoaramid fiber mixture S w The volume of the low-concentration graphene / nanoaramid fiber mixture S1 is 40 ml, with a volume of 20 ml. (2) Take half the volume of the mixture S w Perform vacuum filtration; (3) Filter the mixture S1 by suction; (4) Finally, take the remaining half volume of the mixture S w Perform vacuum filtration; Step 3: Wash the membrane intermediate obtained by vacuum filtration repeatedly with anhydrous ethanol; Step 4: Peel the membrane intermediate from the microporous filter membrane; Step 5: Place the film intermediate peeled out in Step 4 between two flat glass plates and hot press it, keeping the pressure range at 15±1 MPa and the temperature at 55℃ for 48 hours. After opening the mold, the flexible graphene conductive composite material can be obtained. Among them, the graphene concentrations A and B of the first and second outer layers of sample 9 are basically the same, and the thicknesses are basically the same, about 0.008 mm. The inner layer thickness is 0.032 mm, the overall film thickness is about 0.048 mm, and the thickness ratio of the first outer layer, inner layer, and second outer layer is about 1:4:1.

[0059] Example 10 The difference between this embodiment and Example 1 lies in the different proportions of graphene dispersion in the graphene / aramid nanofiber gel mixture and the different amounts of the mixture S. w The volume of mixture S1 is different: (1) The first and second outer layers are made of a high-concentration graphene / nanoaramid fiber mixture S w The raw materials, by volume, include the following components: 100 parts of nano-aramid fiber gel; 8 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0060] (2) The inner layer uses a low-concentration graphene / nanoaramid fiber mixture S1, which, by volume, comprises the following components: 100 parts of nano-aramid fiber gel; 6 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0061] Step 2, Vacuum Filtration: Place the microporous membrane on the sand core filter head and perform layered filtration of the corresponding mixture in the order of the first outer layer, inner layer, and second outer layer to obtain the membrane intermediate: (1) Take a high concentration of graphene / nanoaramid fiber mixture S w The volume of the low-concentration graphene / nanoaramid fiber mixture S1 is 18ml, and the volume of the low-concentration graphene / nanoaramid fiber mixture S1 is 42ml. (2) Take half the volume of the mixture S w Perform vacuum filtration; (3) Filter the mixture S1 by suction; (4) Finally, take the remaining half volume of the mixture S w Perform vacuum filtration; Step 3: Wash the membrane intermediate obtained by vacuum filtration repeatedly with anhydrous ethanol; Step 4: Peel the membrane intermediate from the microporous filter membrane; Step 5: Place the film intermediate peeled out in Step 4 between two flat glass plates and hot press it, maintaining the pressure range at 15±1 MPa and the temperature at 55℃ for 48 hours. After opening the mold, the flexible graphene conductive composite material can be obtained. Among them, the graphene concentrations A and B of the first and second outer layers of Sample 10 are basically the same, and the thicknesses are basically the same, about 0.007 mm. The inner layer thickness is 0.034 mm, the overall film thickness is about 0.048 mm, and the thickness ratio of the first outer layer, inner layer, and second outer layer is about 1:5:1.

[0062] Example 11 The difference between this embodiment and Example 1 lies in the different proportions of graphene dispersion in the graphene / aramid nanofiber gel mixture and the different amounts of the mixture S. w The volume of mixture S1 is different: (1) The first and second outer layers are made of a high-concentration graphene / nanoaramid fiber mixture S wThe raw materials, by volume, include the following components: 100 parts of nano-aramid fiber gel; Nine parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0063] (2) The inner layer uses a low-concentration graphene / nanoaramid fiber mixture S1, which, by volume, comprises the following components: 100 parts of nano-aramid fiber gel; 7 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0064] Step 2, Vacuum Filtration: Place the microporous membrane on the sand core filter head and perform layered filtration of the corresponding mixture in the order of the first outer layer, inner layer, and second outer layer to obtain the membrane intermediate: (1) Take a high concentration of graphene / nanoaramid fiber mixture S w The volume of the low-concentration graphene / nanoaramid fiber mixture S1 is 45 ml. (2) Take half the volume of the mixture S w Perform vacuum filtration; (3) Filter the mixture S1 by suction; (4) Finally, take the remaining half volume of the mixture S w Perform vacuum filtration; Step 3: Wash the membrane intermediate obtained by vacuum filtration repeatedly with anhydrous ethanol; Step 4: Peel the membrane intermediate from the microporous filter membrane; Step 5: Place the film intermediate peeled out in Step 4 between two flat glass plates and hot press it, keeping the pressure range at 15±1 MPa and the temperature at 55℃ for 48 hours. After opening the mold, the flexible graphene conductive composite material can be obtained. Among them, the graphene concentrations A and B of the first and second outer layers of sample 11 are basically the same, and the thicknesses are basically the same, about 0.006 mm. The inner layer thickness is 0.036 mm, the overall film thickness is about 0.048 mm, and the thickness ratio of the first outer layer, inner layer, and second outer layer is about 1:6:1.

[0065] Example 12 The difference between this embodiment and Embodiment 1 is that the inner layer uses a low-concentration graphene / nanoaramid fiber mixture, namely mixtures S1, S2, and S3: (1) The first and second outer layers are made of a high-concentration graphene / nanoaramid fiber mixture S wThe raw materials, by volume, include the following components: 100 parts of nano-aramid fiber gel; 3 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0066] (2) In the graphene dispersion, the concentration of monolayer graphene is 3 mg / ml: (2.1) Corresponding to the inner unit layer 21, the low-concentration graphene / nanoaramid fiber mixture S1, by volume, comprises the following components: 100 parts of nano-aramid fiber gel; One part of graphene dispersion; (2.2) Corresponding to the inner unit layer 22, the low-concentration graphene / nanoaramid fiber mixture S2, by volume, comprises the following components: 100 parts of nano-aramid fiber gel; 0.9 parts of graphene dispersion; (2.3) Corresponding to the inner unit layer 23, the low-concentration graphene / nanoaramid fiber mixture S3, by volume, includes the following components: 100 parts of nano-aramid fiber gel; 0.8 parts of graphene dispersion; Step 2, Vacuum Filtration: Place the microporous membrane on the sand core filter head, and perform layered filtration of the corresponding mixtures in the order of first outer layer 1, unit layer 21, unit layer 22, unit layer 23, and second outer layer 3 to obtain the membrane intermediate: (1) Take a high concentration of graphene / nanoaramid fiber mixture S w The volume of the solution is 30ml, and the volumes of the low-concentration graphene / nanoaramid fiber mixtures S1, S2, and S3 are 10ml each. (2) Take half the volume of the mixture S w Perform vacuum filtration; (3) The mixtures S1, S2 and S3 are filtered sequentially; (4) Finally, take the remaining half volume of the mixture S w Perform vacuum filtration; Step 3: Wash the membrane intermediate obtained by vacuum filtration repeatedly with anhydrous ethanol; Step 4: Peel the membrane intermediate from the microporous filter membrane; Step 5: Place the film intermediate peeled out in Step 4 between two flat glass plates and hot press it, keeping the pressure range at 15±1 MPa and the temperature at 55℃ for 48 hours. After opening the mold, the flexible graphene conductive composite material can be obtained. Among them, the graphene concentrations A and B of the first and second outer layers of sample 12 are basically the same, and the thicknesses are also basically the same, about 0.012 mm. The inner layer is divided into three layers, each with a thickness of about 0.008 mm. The overall film thickness is about 0.048 mm. The thickness ratio of the first outer layer 1, unit layer 21, unit layer 22, unit layer 23 and the second outer layer 3 is about 3:2:2:2:3.

[0067] Example 13 The difference between this embodiment and Embodiment 1 is that the inner layer uses a low-concentration graphene / nanoaramid fiber mixture, namely mixtures S1, S2, and S3: (1) The first and second outer layers are made of a high-concentration graphene / nanoaramid fiber mixture S w The raw materials, by volume, include the following components: 100 parts of nano-aramid fiber gel; 3 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0068] (2) In the graphene dispersion, the concentration of monolayer graphene is 3 mg / ml: (2.1) Corresponding to the inner unit layer 21, the low-concentration graphene / nanoaramid fiber mixture S1, by volume, comprises the following components: 100 parts of nano-aramid fiber gel; One part of graphene dispersion; (2.2) Corresponding to the inner unit layer 22, the low-concentration graphene / nanoaramid fiber mixture S2, by volume, comprises the following components: 100 parts of nano-aramid fiber gel; 0.5 parts of graphene dispersion; (2.3) Corresponding to the inner unit layer 23, the low-concentration graphene / nanoaramid fiber mixture S3, by volume, includes the following components: 100 parts of nano-aramid fiber gel; One part of graphene dispersion; Step 2, Vacuum Filtration: Place the microporous membrane on the sand core filter head, and perform layered filtration of the corresponding mixtures in the order of first outer layer 1, unit layer 21, unit layer 22, unit layer 23, and second outer layer 3 to obtain the membrane intermediate: (1) Take a high concentration of graphene / nanoaramid fiber mixture S w The volume of the solution is 30ml, and the volumes of the low-concentration graphene / nanoaramid fiber mixtures S1, S2, and S3 are 10ml each. (2) Take half the volume of the mixture S w Perform vacuum filtration; (3) The mixtures S1, S2 and S3 are filtered sequentially; (4) Finally, take the remaining half volume of the mixture S w Perform vacuum filtration; Step 3: Wash the membrane intermediate obtained by vacuum filtration repeatedly with anhydrous ethanol; Step 4: Peel the membrane intermediate from the microporous filter membrane; Step 5: Place the film intermediate peeled out in Step 4 between two flat glass plates and hot press it, maintaining the pressure range at 15±1 MPa and the temperature at 55℃ for 48 hours. After opening the mold, the flexible graphene conductive composite material can be obtained. Among them, the graphene concentrations A and B of the first and second outer layers of sample 13 are basically the same, and the thicknesses are also basically the same, about 0.012 mm. The inner layer is divided into three layers, each with a thickness of about 0.008 mm. The overall film thickness is about 0.048 mm. The thickness ratio of the first outer layer 1, unit layer 21, unit layer 22, unit layer 23 and the second outer layer 3 is about 3:2:2:2:3.

[0069] Comparative Example 1 The difference between this comparative example and Example 1 is that the thicknesses (or thickness ratios) of the first outer layer, the inner layer, and the second outer layer are different: (1) Take a high concentration of graphene / nanoaramid fiber mixture S w The volume of the low-concentration graphene / nanoaramid fiber mixture S1 is 8 ml, and the volume of the low-concentration graphene / nanoaramid fiber mixture S1 is 52 ml. (2) Take half the volume of the mixture S w Perform vacuum filtration; (3) Filter the mixture S1 by suction; (4) Finally, take the remaining half volume of the mixture S w Perform vacuum filtration; The graphene concentrations A and B of the first and second outer layers of Comparative Sample 1 are basically the same, and their thicknesses are also basically the same, approximately 0.0032 mm. The inner layer thickness is 0.0416 mm, and the overall film thickness is approximately 0.048 mm.

[0070] Comparative Example 2 The difference between this comparative example and Example 1 is that the graphene / nanoaramid fiber mixture S in the first and second outer layers... w Different graphene contents: (1) The first and second outer layers are made of a graphene / nanoaramid fiber mixture S w The raw materials, by volume, include the following components: 100 parts of nano-aramid fiber gel; 11 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0071] (2) The inner layer uses a low-concentration graphene / nanoaramid fiber mixture S1, which, by volume, comprises the following components: 100 parts of nano-aramid fiber gel; One part of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0072] Comparative Example 3 The difference between this comparative example and Example 1 is that the graphene / nanoaramid fiber mixture S in the first and second outer layers... w The graphene content varies, and the graphene concentration is the same in the first outer layer, the inner layer, and the second outer layer, meaning there is essentially no concentration gradient.

[0073] The first outer layer, inner layer, and second outer layer are made of a graphene / nanoaramid fiber mixture S, which, by volume, comprises the following components: 100 parts of nano-aramid fiber gel; One part of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with a monolayer graphene concentration of 3 mg / ml.

[0074] The parameter settings for the above embodiments and comparative examples are shown in Table 1, where A represents the first outer layer, B represents the inner layer, and C represents the second outer layer.

[0075] Table 1:

[0076] Test methods and results: 1. SEM surface morphology observation was performed on the samples of Examples 1 and 7-10, wherein 1 is sample 1 of Example 1, 2 is sample 7 of Example 7, 3 is sample 8 of Example 8, 4 is sample 9 of Example 9, and 5 is sample 10 of Example 10.

[0077] from Figure 3 As can be seen, the graphene particles are encapsulated within aramid nanofibers, and the graphene in each sample is evenly distributed without obvious agglomeration.

[0078] Figure 4 The high-resolution morphology image of Example 1 shows that the conductive composite material forms a continuous hollow network structure, with graphene particles exhibiting a highly dispersed distribution on the surface of the aramid nanofibers, forming a good conductive pathway. Furthermore, the formed network structure also endows the composite material with good flexibility.

[0079] 2. Resistivity test: Test steps and conditions: First, turn on the four-probe resistivity meter and preheat for 30 minutes. Press the "constant current source" button on the control panel, select resistivity / sheet resistance, and select the current between 0.1-100μA. Then place the sample on the plate and gently press the probe on the flat part of the sample for a certain period of time. After the voltage value stabilizes, the corresponding resistivity value can be recorded.

[0080] Resistivity tests were performed on samples from Examples 1, 7-13, and Comparative Examples 1-3. Figure 5 As can be seen, the samples in the examples exhibit excellent conductivity and low resistivity, meeting the application requirements of flexible conductive materials. Specifically, by appropriately reducing the graphene content in the inner layer while maintaining sufficient thickness, graphene content, and concentration in the outer layer, the desired conductivity can be maintained. This also helps improve the flexibility of the composite material, reduce costs, and yield a composite material with excellent overall performance, as seen in Examples 12 and 13. Although the outer layer graphene concentration in Examples 8-11 is higher than in Example 1, the overall resistivity is not significantly improved due to the difficulty in uniformly dispersing graphene. Therefore, in practical applications, samples with lower outer layer graphene content can be appropriately selected for testing. Comparative Example 1, with its insufficient outer layer thickness and total graphene content, and Comparative Example 3, with its excessively low outer layer graphene content, both fail to meet the conductivity requirements of the composite material. Comparative Example 2 has a high outer layer graphene content and concentration, resulting in low resistivity, but its surface morphology and flexibility are significantly reduced, leading to insufficient overall performance for widespread application and high costs.

[0081] 3. Mechanical property testing: Samples from Examples 1, 8-11 were prepared into standard specimen strips with a gauge length of 20 mm and an initial distance of 20 mm between the fixtures. Tensile tests were conducted at a speed of 1 mm / min to test their tensile strain properties. The results are as follows: Figure 6 As shown in the figure, the samples in the embodiments all exhibit significant elongation, demonstrating excellent flexibility and providing a solid mechanical performance foundation for their application in sensors.

[0082] 4. Sensor performance test: A sensor was fabricated using the sample from Example 1, and a pulse signal acquisition system was built. A USB-6363 data acquisition card was used to acquire the signal, which was then transmitted to a LabVIEW program on the host computer for filtering. The USB-6363 data acquisition card was connected to a 15V power supply to ensure its operation. The pulse signal observed on the LabVIEW program was as follows: Figure 7 The pulse waveform diagram is shown. The sensor made from the flexible graphene conductive composite material of Example 1 showed good contact with the pulse during the test. Analysis of the diagram reveals that the sensor obtained from this embodiment of the invention, compared to similar products in the prior art, can more clearly, obviously, and orderly obtain the systolic and diastolic phases of the pulse fluctuation, enabling more accurate monitoring of pulse fluctuations and pathological analysis, and possessing significant potential for product development and market application.

[0083] In summary, this invention has developed a flexible graphene conductive composite material with simple process, low cost and easy industrialization, and its preparation method, and the resulting product has excellent performance.

[0084] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A flexible graphene conductive composite material, characterized in that, The material comprises a first outer layer and a second outer layer formed of nano-aramid fibers and graphene, and an inner layer located between the first outer layer and the second outer layer; the graphene concentration in the first outer layer and the second outer layer is higher than the graphene concentration in the inner layer; a flexible graphene conductive composite material with a non-uniform structure is formed by stratifying and filtering a graphene / nano-aramid fiber mixture with different graphene concentrations and hot-pressing it. The thickness of the flexible graphene conductive composite material is 0.04-0.1 mm, and the thickness ratio of the first outer layer, the inner layer and the second outer layer is (1-3):(2-10):(1-3). The resistivity of flexible graphene conductive composite materials is 5×10⁻⁶. -6 Below Ω·cm.

2. The flexible graphene conductive composite material as described in claim 1, characterized in that, The graphene concentration in the first outer layer is A, the graphene concentration in the second outer layer is B, and the graphene concentration in the inner layer is C, where A:B:C is (1.1-3):(1.1-3):

1.

3. The flexible graphene conductive composite material as described in claim 2, characterized in that, The inner layer comprises n unit layers, where n ≥ 2, and the graphene concentrations in adjacent unit layers are different.

4. The flexible graphene conductive composite material as described in claim 3, characterized in that, The graphene concentration may increase, decrease, or vary discontinuously among the n unit layers.

5. The flexible graphene conductive composite material as described in claim 3, characterized in that, (1) When n is odd, ,and ; (2) When n is even, ,and .

6. A method for preparing a flexible graphene conductive composite material as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Prepare a high-concentration graphene / nanoaramid fiber mixture for the first and second outer layers; prepare a low-concentration graphene / nanoaramid fiber mixture for the inner layer. Step 2, Vacuum Filtration: Place the microporous filter membrane on the sand core filter head, and filter the corresponding mixture in the order of the first outer layer, inner layer, and second outer layer to obtain the membrane intermediate; Step 3: Wash the membrane intermediate obtained by vacuum filtration repeatedly with anhydrous ethanol; Step 4: Peel the membrane intermediate from the microporous filter membrane; Step 5: The film intermediate is hot-pressed to obtain a flexible graphene conductive composite material with a non-uniform structure.

7. The preparation method according to claim 6, characterized in that, The raw materials of the graphene / nanoaramid fiber mixture, by volume, include the following components: 100 parts of nano-aramid fiber gel; 0.5-10 parts of graphene dispersion; The graphene dispersion contains monolayer graphene, sodium dodecyl sulfonate, and deionized water, with the monolayer graphene concentration being 1-10 mg / ml; In the nano-aramid fiber gel, the concentration of aramid fibers is 2-10 mg / ml.

8. The preparation method according to claim 7, characterized in that, Nano-aramid fiber gel is prepared through the following steps: S1: Dissolve aramid fiber and potassium hydroxide in dimethyl sulfoxide solvent, bathe in water at 40°C or below, and then ultrasonically vibrate for 0.5-1.5 hours. S2: Add deionized water, gradually increase the stirring speed to 1200-1800 rpm at a rate of 100-300 rpm, continue stirring for 20-60 minutes, then increase the stirring speed to over 2000 rpm and stir for 20-30 hours. S3: After stirring, add a large amount of deionized water; gradually increase the stirring speed to 1200-1800 rpm at a rate of 100-300 rpm, continue stirring for 3-10 minutes, then increase the stirring speed to over 2000 rpm and stir for 0.5-2 hours. S4: After stirring, a slightly yellow nano-aramid fiber gel is obtained.

9. The preparation method according to any one of claims 6-8, characterized in that, In step one, the first and second outer layers are made with a high-concentration graphene / nanoaramid fiber mixture S w The inner layer uses a low-concentration graphene / nanoaramid fiber mixture, which consists of mixtures S1 to Sn, where n≥2. In step two, half the volume of the mixture S w Perform vacuum filtration, filtering mixtures S1 through Sn sequentially, and finally filtering the remaining half-volume mixture S. w Perform vacuum filtration.

10. The flexible graphene conductive composite material according to any one of claims 1-5 is used in flexible sensors or wearable electronic products.

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