A method for preparing a graphene fabric conductive composite material

Abstract

The application relates to a preparation method of a graphene fabric conductive composite material, belonging to the field of conductive composite materials. The material is composed of a self-supporting graphene fabric and PDMS with different curing agent / primary agent ratios, and the graphene fabric filled with the PDMS with different curing agent / primary agent ratios exhibits different strain sensing performances. The preparation includes two steps: preparation of a self-supporting graphene conductive fabric and filling of the PDMS with different curing agent / primary agent ratios. The composite material realizes good self-supporting performance of the graphene conductive fabric and different tensile strain-resistance change rates; when the PDMS curing agent / primary agent ratio is 0.8:10, the graphene / PDMS conductive composite material has a sensitivity of up to 214 under a strain of 20%, the graphene fabric composite material filled with the PDMS with different curing agent / primary agent ratios exhibits different sensitivities under the same strain, and the sensitivity presents a trend of first increasing and then decreasing with the change of the curing agent ratio. The application provides a new idea for preparing and researching the graphene conductive composite material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of flexible conductive composite material devices, mainly to the preparation method of graphene fabric / PDMS composite material, and researches on flexible strain sensors. BACKGROUND

[0002] In recent years, with the increasing attention to flexible intelligent robots, human body intelligent health monitoring and other directions, many practical application products have entered people's daily life, and therefore how to improve a key device, i.e. flexible strain sensor, has become the focus of many researchers. Compared with traditional conductive materials such as metal nanoparticles / lines, graphite and the like, emerging ion gels, flexible carbon materials, biomass conductive materials and the like are paid more and more attention due to their good flexibility; among carbon materials, carbon black, carbon nanotubes, carbon nanofibers, graphene and the like are most studied as representative carbon-based conductive materials, and through compounding these carbon materials with flexible polymer substrates, flexible conductive composite materials can be prepared, which have excellent tensile / compressive mechanical properties and good conductive, thermal and electromagnetic shielding properties. However, the small strain range of pure carbon materials to some extent limits their application in the field of flexible strain sensors.

[0003] Since 2004, graphene materials have been widely concerned due to their excellent conductive / thermal properties, chemical inertness and excellent mechanical properties. Through constructing graphene-based multi-dimensional structures, graphene doped with metal ions or graphene doped with other structural carbon nanomaterials and the like, the research and application of graphene materials in various fields are greatly enriched; especially in the field of flexible strain sensors, through constructing different structures of graphene materials, the problem of small strain range of pure carbon materials as flexible strain sensors can be greatly improved. Among them, the method of growing graphene on the surface of metal mesh or metal foam by chemical vapor deposition and then removing the metal to obtain pure graphene fabric is one of the commonly used and efficient methods for preparing graphene conductive composite materials. However, through the method of compounding graphene fabric with high polymer substrates to graphene conductive composite materials, the overall sensitivity is low, the internal wire paste position is covered by the high polymer substrate, which leads to the increase of overall resistance, and the strain mode of the composite material is limited by the thickness of the high polymer substrate, and the like, which to some extent affects the in-depth research and application of graphene fabric conductive composite materials. SUMMARY

[0004] The purpose of the present application is to overcome the defects of small strain range and low sensitivity of existing graphene conductive network composite materials, and to provide a preparation method of graphene / PDMS (polydimethylsiloxane) conductive composite material and its application.

[0005] The application is realized by the following technical scheme: a preparation method of a graphene fabric / PDMS conductive composite material, characterized by filling PDMS prepared by different curing agent / primary agent ratios into the self-supporting graphene conductive network to realize different strain sensing performances of the conductive network structure of the same material and apply the same to a flexible conductive composite material, and the preparation steps are as follows:

[0006] (1) The nickel mesh is sequentially cleaned by ultrasonic cleaning with acetone, ethanol and deionized water, and then dried at 80°C for standby.

[0007] (2) A graphene film is grown on the surface of the nickel mesh by a chemical vapor deposition method to obtain a nickel-graphene fabric.

[0008] (3) The obtained nickel-graphene fabric is wrapped with polymethyl methacrylate (PMMA), and the internal nickel skeleton is removed to obtain a hollow PMMA / graphene fabric composite material.

[0009] (4) The obtained hollow PMMA / graphene fabric composite material is placed in a polytetrafluoroethylene mold and the sample is completely immersed in PDMS, and then placed under vacuum for 2 hours and dried by blowing for 3 hours to obtain a PMMA / graphene / PDMS composite material filled with PDMS inside.

[0010] In the experiment, the PDMS is prepared by curing the polymer and the cross-linking agent in different proportions, the polymer is commonly called the primary agent, and the main component is polydimethylsiloxane; the cross-linking agent is commonly called the curing agent, and the main component is an organosilicon compound containing active silane groups, such as methyl triethoxysilane and methyl tripropoxysilane, and the commonly used preparation ratio of the two is 10:1 by weight ratio of primary agent to curing agent; in the present application, the PDMS is prepared by adjusting the ratio of the curing agent while keeping the ratio of the primary agent unchanged, and the subsequent description is different curing agent ratio PDMS.

[0011] (5) The obtained PMMA / graphene / PDMS composite material is immersed in acetone to remove the surface PMMA to obtain a self-supporting graphene / PDMS composite material.

[0012] The experimental process is as follows: first, after growing graphene on the surface of the nickel mesh by the CVD method, the graphene can form a stable graphene fabric because of the support of the internal nickel skeleton; removing the internal nickel skeleton will cause the completely hollow graphene fabric structure to collapse or be damaged, thereby affecting its performance. Therefore, before the nickel removal experiment, a layer of PMMA is coated on the surface of the nickel-graphene fabric to protect the graphene structure; similarly, when the PMMA coated on the surface is removed, the PDMS filled inside plays the same supporting role as the nickel skeleton.

[0013] Secondly, if not coated with PMMA directly after removing nickel and filling PDMS or coated with PMMA and directly removing PMMA after removing nickel, then filling PDMS into the hollow graphene fabric is also a feasible method, but compared with the previous method, doing so will make the graphene fabric after removing nickel or PMMA have problems such as structural instability, inability to ensure that PDMS is only filled into the fabric when filling pure hollow graphene fabric with PDMS, and inconsistency of the structure of the graphene fabric before and after filling. Finally, the main functions of filling PDMS inside are two: 1. serving as an internal skeleton when removing PMMA to ensure the structural integrity of the graphene fabric; 2. providing a large strain range for the graphene fabric strain sensor to improve the problems of small strain range of pure graphene fabric and uneven and unstable structural changes when stretching.

[0014] Further, in step (1), the mesh number of the nickel used is 200 mesh, and a higher or lower mesh number can also be used instead in the comparative experiment.

[0015] Further, in step (2), the carbon source in the chemical vapor deposition experiment is methane gas, the flow rate is 25-31 sccm, and the volume fraction of methane gas in the total gas is 3.8%-4.2% and 9.8%-10.2%, respectively.

[0016] Further, in step (2), the graphene growth temperature in the chemical vapor deposition experiment is 980-1020℃, and the growth time is 18-22 minutes.

[0017] Further, in step (3), the obtained PMMA / nickel-graphene composite material is placed in a 3M-HCl / 0.5M-FeCl3 aqueous solution and soaked at 80℃ until the metal nickel is completely removed. Further, in step (4), the ratio of the PDMS curing agent to the main agent used is in the range of 0.5:10-2:10.

[0018] Further, in step (5), the obtained PMMA / graphene / PDMS composite material is placed in acetone at 30℃ and soaked for 10 minutes, then washed and repeated steps 4-5 times until the surface-coated PMMA is completely removed to obtain a self-supporting graphene / PDMS composite material.

[0019] Further, the tensile modulus of the three kinds of PDMS with a curing agent to main agent ratio of 0.5:10, 1:10 and 2:10 at a strain of 50% is 0.3MPa, 1.2MPa and 2.4MPa, respectively; and the mechanical properties of the three kinds of samples with different curing agent ratios can be stably maintained at a strain of 25%.

[0020] Further, the graphene / PDMS composite material has a sensitivity as high as 214 when the filling ratio of the PDMS curing agent to the main agent is 0.8:10, has a very high resistance change rate under low strain, and when the filling ratio of the PDMS curing agent to the main agent is 0.5:10, realizes a strain range greater than 30% and a sensitivity of 27.2.

[0021] wherein the sensitivity is a strain sensitivity factor, equal to (the change value of the resistance / the initial resistance value) / strain, i.e. wherein ΔR represents the resistance change value, R0 represents the initial resistance, ΔL represents the sensor change length, and L0 represents the initial length of the sensor.

[0022] Note that the resistance change rate and the resistance change sensitivity are two concepts, the resistance change rate is equal to the resistance change value divided by the initial resistance, i.e. (wherein R1 represents the instantaneous resistance, and R0 represents the initial resistance), and the resistance change sensitivity is equal to the resistance change rate divided by the strain. The resistance change sensitivity is one of the most important indicators for evaluating the performance of a sensor, and under the same strain range, we usually default that the higher the resistance change sensitivity value, the better the performance of the sensor.

[0023] The present application firstly prepares a graphene fabric conductive composite material by filling PDMS with different curing agent ratios into a self-supporting graphene fabric, studies the influence of PDMS with different moduli on the tensile strain resistance change rate of the graphene fabric after filling, and finally obtains a perfect self-supporting graphene fabric / PDMS composite material by coating the graphene fabric prepared by a CVD method with PMMA, removing the metal nickel, filling PDMS with different curing agent ratios into the graphene fabric through a vacuum filling method, and then removing the PMMA. The structure of the graphene wrapped PDMS guarantees a high sensitivity of the conductive composite material, and the wire bonding part is basically not affected, while the PDMS with different moduli fundamentally improves the strain range and sensitivity of the graphene composite material. In summary, the method for preparing a flexible conductive composite material by filling graphene fabric with PDMS with different curing agent ratios can effectively improve the research of graphene materials in the field of strain sensors and provide a new idea for other researches.

[0024] The present application has the following advantages:

[0025] (1) In the present application, the graphene composite material is prepared by filling the polymer into the self-supporting graphene fabric, and the structure can improve the strain sensing performance of the graphene conductive composite material. In addition, the self-supporting graphene fabric filled with PDMS with different curing agent / main agent ratios is prepared and studied as a conductive composite material for the first time in the present application, and different strain sensing performances are realized after the same graphene fabric conductive network is filled with PDMS with different moduli, and different resistance change rates are realized under different strains. (2) The graphene flexible fabric has excellent conductive performance, and at the same time, the flexibility of the self-supporting graphene fabric is further improved after being compounded with the polymer, so it is an excellent conductive composite material. Compared with the traditional coated graphene composite material, the graphene fabric filled with PDMS has better bending or stretching mode, and can easily realize special stretching modes such as spiral bending. (3) All the experimental reagents involved in the present application are non-toxic and harmless, and meet the human body fitting use standard. The performance regulation and control of the present application are simple and low in cost, and it is expected to provide a new idea for the application research of carbon-based materials, especially graphene-based conductive composite materials in the field of flexible elastomer conductive materials. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The schematic diagram of 50 times of tensile strain cycles of pure PDMS prepared for the curing agent:main agent ratio of 0.5:10 (a), 1:10 (b) and 2:10 (c) under 50% strain, Figure 1 The data show that with the increase of the curing agent ratio, the modulus of the PDMS sample is gradually increased.

[0027] Figure 2 The scanning electron microscope diagram of the nickel-graphene fabric prepared for 4% methane concentration. Figure 2 a is a low magnification diagram, and it can be seen from the diagram that the fiber diameter of the graphene fabric is about 50 microns, and the fabric is composed in a weaving manner; Figure 2 b is a local enlarged view of 2a, and it can be seen from the diagram that the fiber surface is smooth, and the graphene sheet layer is tightly attached to the surface of the nickel mesh.

[0028] Figure 3 Figure 2 The scanning electron microscope diagram of the self-supporting graphene / PDMS after filling PDMS in the nickel sample. Figure 3 a is a low magnification diagram, and it can be seen from the diagram that the fiber diameter is basically unchanged after filling, and the overall structure of the graphene fabric is not changed; Figure 3 b is Figure 3 a local enlarged view, and it can be found from the diagram that obvious cracks are generated on the fiber surface, the sheet structure of graphene appears, and the fiber surface is relatively rough.

[0029] Figure 4 Figure 3 ​​The schematic diagram of 3D structure of graphene fabric. Mainly illustrates the filling mode of PDMS inside the graphene fabric / PDMS composite material.

[0030] Figure 5 The strain resistance change diagram of graphene fabric filled with PDMS with different curing agent proportions for 4% methane concentration growth, Figure 5 a is the tensile strain resistance change diagram, Figure 5 b is the tensile strain sensitivity diagram of PDMS filled with different curing agent proportions. From Figure 5 a can be seen that when the curing agent: main agent ratio is 0.8:10, the graphene / PDMS conductive composite material has the highest resistance change rate under the same strain range, and when the curing agent: main agent ratio is 0.5:10, the resistance change rate of the graphene / PDMS conductive composite material is the lowest, but the strain range is the largest; from Figure 5 b can be seen that when the strain is 20%, the graphene / PDMS composite material with a curing agent: main agent ratio of 0.8:10 has a strain sensitivity of up to 214, and at this time the sensitivity of the graphene / PDMS composite material filled with PDMS with other curing agent proportions is: 0.5:10 is 27.2, 0.67:10 is 105, 1:10 is 67, 1.5:10 is 47, and 2:10 is 38.

[0031] Figure 6 The strain resistance change diagram of graphene fabric filled with PDMS with different curing agent proportions for 10% methane concentration growth, Figure 6 a is the tensile strain resistance change diagram, Figure 6 b is the tensile strain sensitivity diagram of PDMS filled with different curing agent proportions. From Figure 6 a can be seen that when the curing agent: main agent ratio is 0.8:10, the graphene / PDMS conductive composite material has the highest resistance change rate under the same strain, and when the curing agent: main agent ratio is 0.5:10, the resistance change rate of the graphene / PDMS conductive composite material is the lowest, but the strain range is the largest; in the strain is 25%, from Figure 6 b can be seen that the graphene / PDMS composite material with a curing agent: main agent ratio of 0.8:10 has a strain sensitivity of up to 159, and at this time the sensitivity of the graphene / PDMS composite material with other curing agent: main agent ratios is: 0.5:10 is 39, 0.67:10 is 124, 1:10 is 97.6, 1.5:10 is 73.2, and 2:10 is 53. DETAILED DESCRIPTION

[0032] Example 1:

[0033] (1) 200 mesh nickel mesh was sequentially cleaned with acetone, ethanol, and deionized water under ultrasonic wave and then dried for standby use.

[0034] (2) Using chemical vapor deposition method, carbon source is methane gas, flow rate is 25-31 sccm, keeping the volume fraction of methane gas in total gas at 3.8%-4.2%, temperature is 1000℃, growing for 20 minutes, obtaining nickel-graphene fabric;

[0035] (3) After the obtained nickel-graphene fabric is wrapped with polymethyl methacrylate (PMMA), it is placed in 3M-HCl / 0.5M-FeCl3 aqueous solution, and soaked at 80℃ until the internal nickel skeleton is completely removed, obtaining hollow PMMA / graphene composite material;

[0036] (4) The obtained hollow PMMA / graphene composite material is placed in a polytetrafluoroethylene mold, and the sample is completely immersed in PDMS with a curing agent:main agent ratio of 0.5:10, and then placed under vacuum for 2h, and dried to obtain PMMA / graphene / PDMS composite material;

[0037] (5) The obtained PMMA / graphene / PDMS composite material is soaked in 30℃ acetone for 10min, then washed, and the steps 4-5 are repeated for 5 times, and after removing the surface PMMA, a self-supporting graphene / PDMS composite material is obtained.

[0038] (6) The obtained graphene / PDMS composite material is fixed in a tensile clamp, and a tensile testing machine-digital source meter combination is used to measure the resistance change rate of the material under uniaxial tensile strain. It is found that the resistance of the composite material changes sharply Figure 5 a) with the gradual increase of strain, the resistance change rate shows a uniform increasing trend, from Figure 5 b) it can be concluded that the resistance change sensitivity of the material is 27.2 at 20% strain.

[0039] Example 2:

[0040] (1) A 200-mesh nickel mesh is sequentially cleaned with acetone, ethanol, and deionized water, and then dried for standby use.

[0041] (2) Using chemical vapor deposition method, carbon source is methane gas, flow rate is 25-31 sccm, keeping the volume fraction of methane gas in total gas at 3.8%-4.2%, temperature is 1000℃, growing for 20 minutes, obtaining nickel-graphene fabric;

[0042] (3) After the obtained nickel-graphene fabric is wrapped with polymethyl methacrylate (PMMA), it is placed in 3M-HCl / 0.5M-FeCl3 aqueous solution, and soaked at 80℃ until the internal nickel skeleton is completely removed, obtaining hollow PMMA / graphene composite material;

[0043] (4) The hollow PMMA / graphene composite material obtained above is placed in a polytetrafluoroethylene mold, and the sample is completely immersed in PDMS prepared by mixing a curing agent and a main agent at a ratio of 0.67:10, and then placed under vacuum for 2 h. After drying, a PMMA / graphene / PDMS composite material is obtained;

[0044] (5) The PMMA / graphene / PDMS composite material obtained above is immersed in acetone at 30°C for 10 min, washed, and repeated step 4-5 times. After removing the surface PMMA, a self-supporting graphene / PDMS composite material is obtained.

[0045] (6) The graphene / PDMS composite material obtained above is fixed in a tensile clamp, and a tensile testing machine-digital source meter combination is used to measure the resistance change rate of the material under uniaxial tensile strain. It is found that the resistance of the composite material changes sharply during uniaxial tension, and the resistance change rate is Figure 5 As can be seen from b, the resistance change sensitivity of the material is 105 under a strain of 20%, and the resistance change rate increases uniformly with the gradual increase of the strain Figure 5 a).

[0046] Example 3:

[0047] (1) A 200-mesh nickel mesh is sequentially cleaned with acetone, ethanol, and deionized water under ultrasonic waves, and then dried for standby use.

[0048] (2) A nickel-graphene fabric is grown by chemical vapor deposition using methane gas as the carbon source at a flow rate of 25-31 sccm, maintaining a methane gas volume fraction of 3.8%-4.2% in the total gas, and a temperature of 1000°C for 20 minutes;

[0049] (3) The nickel-graphene fabric obtained is wrapped with polymethyl methacrylate (PMMA) and then placed in a 3M-HCl / 0.5M-FeCl3 aqueous solution at 80°C for immersion until the internal nickel skeleton is completely removed, obtaining a hollow PMMA / graphene composite material;

[0050] (4) The hollow PMMA / graphene composite material obtained above is placed in a polytetrafluoroethylene mold, and the sample is completely immersed in PDMS prepared by mixing a curing agent and a main agent at a ratio of 0.67:10, and then placed under vacuum for 2 h. After drying, a PMMA / graphene / PDMS composite material is obtained;

[0051] (5) The PMMA / graphene / PDMS composite material obtained above is immersed in acetone at 30°C for 10 min, washed, and repeated step 4-5 times. After removing the surface PMMA, a self-supporting graphene / PDMS composite material is obtained.

[0052] (6) The graphene / PDMS composite material obtained above was fixed in a stretching clamp, and a tension machine-digital source table combination was used to measure the resistance change rate of the material under uniaxial tensile strain. It was found that the resistance of the composite material changed sharply during uniaxial stretching, and the resistance change rate of the composite material was 214 at a strain of 20%, Figure 5 as can be seen from b, the resistance change sensitivity of the material is 214 at a strain of 20%, and the resistance change rate presents a uniform increasing trend as the strain gradually increases. Figure 5 a).

[0053] Example 4:

[0054] (1) A 200-mesh nickel mesh was sequentially cleaned with acetone, ethanol and deionized water under ultrasonic wave and then dried for standby use.

[0055] (2) A nickel-graphene fabric was obtained by chemical vapor deposition method using methane gas as carbon source, a flow rate of 25-31 sccm, maintaining the volume fraction of methane gas in the total gas at 3.8%-4.2%, and growing at a temperature of 1000°C for 20 minutes;

[0056] (3) The obtained nickel-graphene fabric was wrapped with polymethyl methacrylate (PMMA) and then immersed in a 3M-HCl / 0.5M-FeCl3 aqueous solution at 80°C until the internal nickel skeleton was completely removed, to obtain a hollow PMMA / graphene composite material;

[0057] (4) The obtained hollow PMMA / graphene composite material was placed in a polytetrafluoroethylene mold, and the sample was completely immersed in PDMS prepared by mixing a curing agent with a main agent at a ratio of 1:10, and then placed under vacuum for 2h, to obtain a PMMA / graphene / PDMS composite material after drying;

[0058] (5) The obtained PMMA / graphene / PDMS composite material was immersed in acetone at 30°C for 10 minutes, washed, and the steps 4-5 were repeated for 5 times, to obtain a self-supporting graphene / PDMS composite material after removing the surface PMMA.

[0059] (6) The graphene / PDMS composite material obtained above was fixed in a stretching clamp, and a tension machine-digital source table combination was used to measure the resistance change rate of the material under uniaxial tensile strain. It was found that the resistance of the composite material changed sharply during uniaxial stretching, and the resistance change rate of the composite material was 214 at a strain of 20%, Figure 5 as can be seen from b, the resistance change sensitivity of the material is 214 at a strain of 20%, and the resistance change rate presents a uniform increasing trend as the strain gradually increases. Figure 5 a).

[0060] Example 5:

[0061] (1) 200 mesh nickel mesh was sequentially cleaned with acetone, ethanol, and deionized water by ultrasonic cleaning, and then dried for standby use.

[0062] (2) Using chemical vapor deposition method, carbon source is methane gas, flow rate is 25-31 sccm, keeping the volume fraction of methane gas in total gas is 3.8%-4.2%, temperature is 1000℃, growing for 20 minutes, obtaining nickel-graphene fabric;

[0063] (3) The obtained nickel-graphene fabric is wrapped with polymethyl methacrylate (PMMA) and then placed in 3M-HCl / 0.5M-FeCl3 aqueous solution at 80℃, until the internal nickel skeleton is completely removed, obtaining hollow PMMA / graphene composite material;

[0064] (4) The above obtained hollow PMMA / graphene composite material is placed in a polytetrafluoroethylene mold, and the sample is completely immersed in PDMS prepared by mixing curing agent and main agent at a ratio of 1.5:10, and then placed under vacuum for 2h, and then dried to obtain PMMA / graphene / PDMS composite material;

[0065] (5) The above obtained PMMA / graphene / PDMS composite material is soaked in 30℃ acetone for 10min, then cleaned, and steps 4-5 are repeated for 5 times, and after removing the surface PMMA, a self-supporting graphene / PDMS composite material is obtained.

[0066] (6) The above obtained graphene / PDMS composite material is fixed in a tensile clamp, and a tensile machine-digital source meter combination is used to measure the resistance change rate of the material under uniaxial tensile strain. It is found that the resistance of the above composite material changes sharply during uniaxial stretching, and the resistance change rate is Figure 5 As can be seen from b, the resistance change sensitivity of the material is 73.2 at a strain of 20%, and the resistance change rate increases uniformly with the gradual increase of the strain Figure 5 a).

[0067] Example 6:

[0068] (1) 200 mesh nickel mesh was sequentially cleaned with acetone, ethanol, and deionized water by ultrasonic cleaning, and then dried for standby use.

[0069] (2) Using chemical vapor deposition method, carbon source is methane gas, flow rate is 25-31 sccm, keeping the volume fraction of methane gas in total gas is 3.8%-4.2%, temperature is 1000℃, growing for 20 minutes, obtaining nickel-graphene fabric;

[0070] (3) The obtained nickel-graphene fabric is wrapped with polymethyl methacrylate (PMMA) and then placed in a 3M-HCl / 0.5M-FeCl3 aqueous solution at 80°C until the internal nickel skeleton is completely removed, to obtain a hollow PMMA / graphene composite material;

[0071] (4) The obtained hollow PMMA / graphene composite material is placed in a polytetrafluoroethylene mold, and the sample is completely immersed in PDMS prepared by mixing a curing agent and a main agent at a ratio of 2:10, and then placed under vacuum for 2h, to obtain a PMMA / graphene / PDMS composite material after drying;

[0072] (5) The obtained PMMA / graphene / PDMS composite material is immersed in acetone at 30°C for 10min, washed, and the step 4-5 is repeated for 5 times, to obtain a self-supporting graphene / PDMS composite material after removing the surface PMMA.

[0073] (6) The obtained graphene / PDMS composite material is fixed in a tensile clamp, and a tensile testing machine-digital source meter combination is used to measure the resistance change rate of the material under uniaxial tensile strain. It is found that the resistance of the composite material changes sharply during uniaxial tension, and the resistance change rate is Figure 5 As can be seen from b, the resistance change sensitivity of the material is 53 at a strain of 20%, and the resistance change rate shows a stable increasing trend as the strain gradually increases Figure 6 a).

[0074] Example 7:

[0075] (1) A 200-mesh nickel mesh is sequentially cleaned with acetone, ethanol, and deionized water under ultrasonic wave, and then dried for standby use.

[0076] (2) A nickel-graphene fabric is obtained by chemical vapor deposition method, using methane gas as the carbon source, at a flow rate of 25-31sccm, maintaining the volume fraction of methane gas in the total gas at 9.8%-10.2%, and at a temperature of 1000°C for 20min;

[0077] (3) The obtained nickel-graphene fabric is wrapped with polymethyl methacrylate (PMMA) and then placed in a 3M-HCl / 0.5M-FeCl3 aqueous solution at 80°C until the internal nickel skeleton is completely removed, to obtain a hollow PMMA / graphene composite material;

[0078] (4) The hollow PMMA / graphene composite obtained above was placed in a polytetrafluoroethylene mold, and the PDMS curing agent: base agent ratio used was 0.5:10, 0.67:10, 0.8:10, 1:10, 1.5:10 and 2:10. The sample was completely immersed in PDMS and then placed under vacuum for 2 h. After drying, a PMMA / graphene / PDMS composite material was obtained;

[0079] (5) The PMMA / graphene / PDMS composite material obtained above was immersed in acetone at 30°C for 10 min, washed and repeated step 4-5 times. After removing the surface PMMA, a self-supporting graphene / PDMS composite material was obtained.

[0080] (6) The graphene / PDMS composite material obtained above was fixed in a tensile clamp, and a tensile testing machine-digital source meter combination was used to measure the resistance change rate of the material under uniaxial tensile strain. It was found that during the uniaxial tensile process, the resistance of the composite material changed sharply, and the resistance change rate of the graphene / PDMS composite material prepared by filling PDMS with a curing agent: base agent ratio of 0.5:10 was 39, 0.67:10 was 124, 0.8:10 was 159, 1:10 was 97.6, 1.5:10 was 73.2 and 2:10 was 53 at a strain of 25%. Figure 5 As can be seen from b, the sensitivities of the graphene / PDMS composite materials prepared by filling PDMS with different curing agent: base agent ratios were 39, 124, 159, 97.6, 73.2 and 53 at a strain of 25%, respectively. After filling the graphene fabric with PDMS with different curing agent ratios, the resistance change rate of the graphene fabric filled with PDMS with different curing agent ratios still showed a uniform increasing trend with the gradual increase of the strain, and the tensile resistance change law of the graphene composite material filled with PDMS with different curing agent ratios was consistent with that of the graphene fabric prepared at a methane concentration of 4%, which fully demonstrated the repeatability of the experiment.

[0081] Comparative Example

[0082] Comparative Example 1

[0083] (1) Nickel meshes with different mesh numbers (300 mesh, 400 mesh, 500 mesh, etc.) were sequentially cleaned with acetone, ethanol and deionized water under ultrasonic waves and then dried for standby use.

[0084] (2) A nickel-graphene fabric was obtained by chemical vapor deposition using methane gas as the carbon source at a flow rate of 25-31 sccm, maintaining the volume fraction of methane gas in the total gas at 3.8%-4.2% and a temperature of 1000°C for 20 min.

[0085] (3) The nickel-graphene fabric obtained was wrapped with polymethyl methacrylate (PMMA) and then placed in a 3M-HCl / 0.5M-FeCl3 aqueous solution and immersed at 80°C until the internal nickel skeleton was completely removed, thereby obtaining a hollow PMMA / graphene composite material.

[0086] (4) The hollow PMMA / graphene composite material obtained above was placed in a polytetrafluoroethylene mold, and the sample was completely immersed in PDMS with a curing agent: base ratio of 0.5:10, 0.8:10, 1:10, 1.5:10, and 2:10, and then placed under vacuum for 2 h. After drying, a PMMA / graphene / PDMS composite material was obtained;

[0087] (5) The PMMA / graphene / PDMS composite material obtained above was immersed in acetone at 30°C for 10 min, washed, and repeated step 4-5 times. After removing the surface PMMA, a self-supporting graphene / PDMS composite material was obtained.

[0088] (6) The graphene / PDMS composite material obtained above was fixed in a tensile clamp, and a tensile testing machine-digital source meter combination was used to measure the resistance change rate of the material under uniaxial tensile strain. Graphene fabrics prepared using nickel meshes of different mesh sizes have different graphene fiber diameters and graphene network surface densities, which can be used as comparative experiments for exploration.

[0089] Comparative Example 2:

[0090] (1) A 200-mesh nickel mesh was sequentially cleaned with acetone, ethanol, and deionized water under ultrasonic waves, and then dried for standby use.

[0091] (2) A nickel-graphene fabric was obtained by chemical vapor deposition using methane gas as the carbon source, a flow rate of 25-31 sccm, maintaining a methane gas volume fraction of 3.8%-4.2% in the total gas, and a temperature of 1000°C for 20 min;

[0092] (3) The obtained nickel-graphene fabric was wrapped with polymethyl methacrylate (PMMA) and then placed in a 3M-HCl / 0.5M-FeCl3 aqueous solution and immersed at 80°C until the internal nickel skeleton was completely removed, obtaining a hollow PMMA / graphene composite material;

[0093] (4) The hollow PMMA / graphene composite material obtained above was placed in a polytetrafluoroethylene mold, and the sample was completely immersed in PDMS with a curing agent: base ratio of 2.5:10, and then placed under vacuum for 2 h. After drying, a PMMA / graphene / PDMS composite material was obtained;

[0094] (5) The PMMA / graphene / PDMS composite material obtained above was immersed in acetone at 30°C for 10 min, washed, and repeated step 4-5 times. After removing the surface PMMA, a self-supporting graphene / PDMS composite material was obtained.

[0095] (6) The graphene / PDMS composite material obtained above is fixed in a tensile clamp, and a tensile machine-digital source table combination is used to measure the resistance change rate of the material under uniaxial tensile strain. It is found that the resistance of the composite material changes sharply during uniaxial stretching, and the resistance strain sensitivity of the material is less than 50 at a strain of 20% according to the data analysis. With the gradual increase of the strain, the resistance change rate also shows a uniform increasing trend.

[0096] With the filling of PDMS with different curing agent: main agent ratios, the graphene / PDMS composite material shows different strain-resistance change rates. It is found that when the curing agent: main agent ratio is 0.8:10, the resistance change rate is the largest under the same strain, and from Figure 6 a and Figure 5 Both figures a and 6a show that after filling with PDMS with a curing agent: main agent ratio of 0.5:10, although the resistance strain sensitivity is low under the same strain, the maximum strain range is higher than that of the graphene composite material filled with PDMS with other ratios. Finally, if sensors made of different materials or different structures are compared, it is meaningful to compare the sensitivity under the same strain, because for a nonlinear strain sensor, the strain amount changes, and the sensor sensitivity value must change. However, to adjust the sensitivity, the resistance change rate of the sensor under the same strain should be improved, and the corresponding sensor sensitivity will be higher. ​ a and 6a, after filling with PDMS with a curing agent: main agent ratio of 0.5:10, although the resistance strain sensitivity is low under the same strain, the maximum strain range is higher than that of the graphene composite material filled with PDMS with other ratios. Finally, if sensors made of different materials or different structures are compared, it is meaningful to compare the sensitivity under the same strain, because for a nonlinear strain sensor, the strain amount changes, and the sensor sensitivity value must change. However, to adjust the sensitivity, the resistance change rate of the sensor under the same strain should be improved, and the corresponding sensor sensitivity will be higher.

[0097] According to the analysis of the previous experimental results, with the further increase of the curing agent ratio in PDMS, the crosslinking degree of PDMS will further increase, and the strain-resistance change rate will further decrease, so the sensitivity under the same strain will decrease, that is, with the increase of the curing agent ratio, the effective strain range of the sensor and the sensitivity under the same strain will decrease, but this decrease will not decrease indefinitely, and with the gradual increase of the curing agent ratio, the sensitivity will gradually tend to a stable value.

[0098] If PMMA is not used for wrapping in preparation, and PDMS is filled directly after removing nickel, the surface morphology of graphene fabric will collapse, and PDMS can be filled into the graphene fabric surface or between graphene layers, which will cause the initial resistance of graphene fabric / PDMS sensor to increase, the resistance change in tensile strain to be unstable, although the strain sensitivity of the sensor can be improved to some extent, but the strain range is greatly reduced.

[0099] Under the premise that other preparation parameters remain unchanged, the concentration of methane gas decreases, and the graphene layer on the nickel mesh decreases; the concentration of methane increases, and the thickness of graphene grown on the nickel mesh increases; in short, the concentration of methane affects the growth thickness of graphene, and too high or too low concentration of methane is not conducive to the stability of the structure and performance of graphene fabric. Secondly, in the CVD experiment, high temperature provides energy to crack the C-H bond in the methane gas and produces various C-Hx functional groups, and finally catalyzes the dehydrogenation of C-C bond on the surface of nickel metal, so high temperature is one of the most basic elements of this reduction reaction; if the temperature is too low, it will lead to insufficient cracking, resulting in low utilization rate of methane with the same concentration, discontinuous graphene layer structure and other problems. It should be noted that in the CVD preparation of graphene experiment, temperature is a key factor, and the temperature will affect the layer structure of graphene, and different graphene materials will be prepared. Many researchers at home and abroad are exploring the relationship between temperature parameters and graphene growth structure, and the optimal growth temperature parameters for different graphene application research. The experiment in this invention is based on the previous research of the research group to select 1000 DEG C, which can only represent that this temperature is suitable for this experimental study, but it cannot represent that 1000 DEG C is the optimal temperature for CVD method to prepare graphene.

[0100] The proportion of crosslinking agent added is controlled, and the crosslinking degree of PDMS high polymer is mainly changed, thereby affecting the modulus and the interfacial bonding force with graphene, and finally making the graphene / PDMS composite material produce different structural changes under the same tensile strain, and show different resistance change rates. In addition, this study does not change the temperature for exploration, and the temperature range written during preparation is a range value. Because the heat preservation performance of the equipment and the environmental temperature and other factors during the specific experimental preparation cannot completely guarantee that the temperature remains at 1000 DEG C at all times, and 1000 DEG C is used in the subsequent specific examples.

[0101] The focus of the present application is the influence of the graphene sensor strain sensing performance after filling the graphene fabric with PDMS of different curing agent:main agent ratios.

Claims

1. A method of preparing a graphene fabric conductive composite material, characterized by By filling PDMS with different curing agent / primary agent ratio into the self-supporting graphene fabric, the different strain sensing performance of the same network structure conductive material is realized and applied to prepare flexible conductive composite material, and the preparation steps are as follows: (1) The nickel mesh is sequentially cleaned by ultrasonic cleaning with acetone, ethanol and deionized water, and then dried for standby; (2) A graphene film is grown on the surface of the nickel mesh by chemical vapor deposition to obtain a nickel-graphene fabric; (3) The obtained nickel-graphene fabric is wrapped with polymethyl methacrylate (PMMA), and then the internal nickel skeleton is removed to obtain a hollow PMMA / graphene fabric; (4) The hollow PMMA / graphene fabric obtained in step (3) is placed in a polytetrafluoroethylene mold, and then filled with PDMS by vacuumizing to fill the PDMS into the graphene fabric, and then dried to obtain a PMMA / graphene / PDMS composite material with graphene wrapped PDMS structure; if PMMA is not used during preparation, and PDMS is filled directly after removing nickel, the surface morphology of the graphene fabric will collapse, and the PDMS may be filled into the surface or the graphene layer, which will cause the initial resistance of the graphene fabric / PDMS sensor to increase, the resistance change in the tensile strain to be unstable, although the strain sensitivity of the sensor can be improved to a certain extent, but the strain range is greatly reduced; (5) The PMMA / graphene / PDMS composite material obtained in step (4) is soaked in acetone to remove the surface PMMA to obtain a self-supporting graphene / PDMS composite material.

2. The method for preparing the graphene fabric conductive composite material as described in claim 1, characterized in that, In the step (1), the mesh number of the nickel mesh used is 200 meshes; in the step (1), after cleaning, it is dried at 80 DEG C.

3. The method for preparing the graphene fabric conductive composite material as described in claim 1, characterized in that, In the step (2), in the chemical vapor deposition experiment, the carbon source is methane gas, the flow rate is 25-31 sccm, and the volume fraction of methane gas in the total gas is maintained at 3.8%-4.2%.

4. The method for preparing the graphene fabric conductive composite material as described in claim 1, characterized in that, In the step (2), in the chemical vapor deposition experiment, the graphene growth temperature is 980-1020 DEG C, and the growth time is 18-22 minutes.

5. The method for preparing the graphene fabric conductive composite material as described in claim 1, characterized in that, In the step (3), the obtained PMMA / graphene fabric is placed in a 3M-HCl / 0.5M-FeCl3 aqueous solution and soaked at 80 DEG C until the metal nickel is completely removed.

6. The method for preparing the graphene fabric conductive composite material as described in claim 1, characterized in that, In the step (4), the ratio of the curing agent to the primary agent used is 0.5:10-2:

10.

7. The method for preparing the graphene fabric conductive composite material as described in claim 1, characterized in that, In the step (5), the obtained PMMA / graphene / PDMS composite material is placed in 30 DEG C acetone for 10 minutes, cleaned and repeated for 4-5 times, until the surface coated PMMA is completely removed to obtain a self-supporting graphene fabric / PDMS composite material.

8. The method for preparing the graphene fabric conductive composite material as described in claim 1, characterized in that, The tensile modulus of the three kinds of PDMS with curing agent:primary agent ratio of 0.5:10, 1:10 and 2:10 at 50% strain is 0.3 MPa, 1.2 MPa and 2.4 MPa respectively, and the three kinds of curing agent ratio samples can maintain stable mechanical properties at 25% strain.

9. The method for preparing the graphene fabric conductive composite material as described in claim 1, characterized in that, The graphene / PDMS composite has a sensitivity of 214 when the filling ratio of the PDMS curing agent to the main agent is 0.8:10, has a very high resistance change rate under low strain; when the filling ratio of the PDMS curing agent to the main agent is 0.5:10, a strain range greater than 30% is achieved and the sensitivity is 27.2.

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