Flexible conductive composite material and preparation method and application thereof

Abstract

The invention relates to the technical field of conductive materials, and discloses a flexible conductive composite material and a preparation method and application thereof. The flexible conductive composite material comprises the following preparation raw materials: a thermoplastic elastomer, a conductive filler, cellulose nanocrystals, an inorganic salt, an organic solvent and water. According to the flexible conductive composite material provided by the invention, the Pickering emulsion is co-stabilized by the cellulose nanocrystal auxiliary conductive filler, the cellulose nanocrystal raw material is easy to obtain, biodegradable, environment-friendly and pollution-free, the Pickering emulsion is good in stability, the conductive filler is directionally enriched on an emulsion interface to form a continuous path, the bottleneck of filler dispersion is broken through, a conductive network structure is complete, and the stability of the Pickering emulsion is improved. The strain sensing response is sensitive, reversible circulation is achieved, the conductive interval is wide, the conductive seepage threshold value is about 1 wt%-2 wt%, when the addition amount of the conductive filler is 10 wt%, the conductivity is about 25 S / cm, and the conductivity is improved in a breakthrough mode.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of conductive materials, in particular to a flexible conductive composite material and a preparation method and application thereof. BACKGROUND

[0002] In recent years, emerging fields such as foldable displays and artificial manufactured sensor receptors have put forward the performance requirements of stretchable conductive materials. Rigid conductive materials have good conductivity, but are relatively rigid and cannot be deformed, which cannot meet the new performance requirements, so it is urgent to develop a material that has both high conductivity and high elasticity. Among them, polymer-based conductive composites refer to conductive materials prepared by physically or chemically combining conductive fillers and polymer matrices. Because of the characteristics of light weight, easy processing and corrosion resistance, and the advantages of stretchability, deformability and high elasticity, polymer-based conductive composites have attracted much attention.

[0003] Traditional polymer-based conductive composites have poor conductivity at low filler content, and high filler content is prone to agglomeration, resulting in a significant decrease in mechanical properties (such as stretchability). For example, CN 109215833 A discloses a carbon nanotube and PDMS conductive composite and a preparation method thereof. The scheme prepares a carbon nanotube dispersion liquid by mixing carbon nanotube powder and a volatile solvent, prepares a PDMS monomer dispersion liquid by mixing polydimethylsiloxane monomer (PDMS) and a volatile solvent, mixes the carbon nanotube dispersion liquid and the PDMS monomer dispersion liquid, evaporates to remove the volatile solvent, and then adds a curing agent for curing to prepare a carbon nanotube and PDMS conductive composite. This method can improve the dispersibility of carbon nanotubes, improve the conductive network in the carbon nanotube and PDMS conductive composite, and improve the conductivity of the conductive composite. However, in the process of evaporating and removing the solvent and curing, the conductive fillers are prone to agglomeration. When the amount of conductive fillers exceeds 7wt%, serious agglomeration occurs, which significantly reduces the mechanical properties of the material and affects its conductivity and durability.

[0004] The percolation threshold of the existing polymer-based conductive composite is generally high, which limits the conductive performance at low filler content, and the preparation process is complex and the process cost is high. For example, CN 119410149 A discloses a flexible conductive composite material and a preparation method and application thereof. The scheme mixes graphene, carbon nanotubes and a polar organic solvent to obtain a nano-carbon material dispersion liquid, and then adds silicone raw rubber and a silane coupling agent to the nano-carbon material dispersion liquid to perform surface modification treatment to obtain a nano-carbon modified raw rubber mixture liquid. Then, the nano-carbon modified raw rubber mixture liquid is mixed with a crosslinking agent to perform crosslinking reaction to obtain a flexible conductive composite material. The method changes the surface properties of the nano-carbon material by physical adsorption, chemical adsorption and chemical reaction between the silane coupling agent and the silicone raw rubber and the nano-carbon material, and improves the agglomeration of the nano-carbon material in the silicone raw rubber. However, the conductive percolation threshold of the obtained material is relatively high (3.1wt%-4.5wt%), and in the preparation process, multiple layers need to be prepared to strengthen the mechanical properties of the material, which has high process cost and long production cycle, and is not suitable for large-scale industrial production. SUMMARY

[0005] The present application aims to at least solve one of the above-mentioned technical problems in the prior art. To this end, one of the objects of the present application is to provide a flexible conductive composite material.

[0006] A second object of the present application is to provide a preparation method of the flexible conductive composite material.

[0007] A third object of the present application is to provide an application of the flexible conductive composite material.

[0008] A fourth object of the present application is to provide a flexible resistance pressure sensor.

[0009] To achieve the above-mentioned objects, the technical solution adopted by the present application is as follows:

[0010] The first aspect of the present application provides a flexible conductive composite material, which comprises the following raw materials: a thermoplastic elastomer, a conductive filler, cellulose nanocrystals, an inorganic salt, an organic solvent and water.

[0011] In some embodiments of the present application, the mass ratio of the thermoplastic elastomer, the conductive filler, the cellulose nanocrystals and the inorganic salt is (20-50):(1-2.5):(0.8-1.2):1.

[0012] In some preferred embodiments of the present application, the mass ratio of the thermoplastic elastomer, the conductive filler, the cellulose nanocrystals and the inorganic salt is (30-40):(1-2):(0.9-1.1):1.

[0013] In some embodiments of the present application, the mass ratio of the thermoplastic elastomer to the organic solvent is 1: (3-20).

[0014] In some preferred embodiments of the present application, the mass ratio of the thermoplastic elastomer to the organic solvent is 1: (3-10).

[0015] In some embodiments of the present application, the mass ratio of the inorganic salt to water is 1: (400-600).

[0016] In some preferred embodiments of the present application, the mass ratio of the inorganic salt to water is 1: (450-550).

[0017] In some embodiments of the present application, the added amount of the conductive filler in the flexible conductive composite material is 1wt%-10wt% (the added amount of the conductive filler is the ratio of the mass of the conductive filler to the total mass of the thermoplastic elastomer, the conductive filler, the cellulose nanocrystal and the inorganic salt).

[0018] In some preferred embodiments of the present application, the added amount of the conductive filler in the flexible conductive composite material is 2wt%-5wt%.

[0019] In some embodiments of the present application, the conductive filler comprises MXene.

[0020] In some embodiments of the present application, the MXene comprises being prepared by etching MAX, and the specific steps are as follows:

[0021] Concentrated hydrochloric acid (36wt%-38wt%) is mixed with lithium fluoride, and MAX is added in small amounts and multiple times, the temperature is raised to 35-45℃, and the reaction is carried out for 45-50h; deionized water is added to dilute it by one time, the lower layer precipitate is taken by centrifugation, and multiple repeated centrifugation and measurement of the pH of the upper clear liquid are carried out until the pH=5-7; the bottle is filled with nitrogen and ultrasonic treatment is carried out for 1-3h to separate the MXene from the unetched MAX, and the upper clear liquid is taken after 1-1.5h of centrifugation again to obtain single-layer MXene.

[0022] In some embodiments of the present application, the inorganic salt is selected from at least one of sodium chloride, sodium acetate, potassium chloride, and calcium chloride.

[0023] In some embodiments of the present application, the thermoplastic elastomer is selected from at least one of styrene-butadiene-styrene block copolymer (SBS), thermoplastic polyurethane elastomer (TPU), and polydimethylsiloxane (PDMS).

[0024] In some embodiments of the present application, the organic solvent is selected from at least one of cyclohexane, n-hexane, and dichloromethane.

[0025] The second aspect of the present application provides a method for preparing the flexible conductive composite material according to the first aspect of the present application, comprising the following steps:

[0026] S1, mixing a thermoplastic elastomer with an organic solvent to obtain an oil phase;

[0027] S2, mixing a conductive filler, a cellulose nanocrystal and an inorganic salt with water to obtain an aqueous phase;

[0028] S3, mixing the oil phase with the aqueous phase to emulsify to obtain a Pickering emulsion;

[0029] S4, sequentially performing pressure reduction heating and suction filtration on the Pickering emulsion to obtain a pre-film embryo, and hot pressing to obtain the flexible conductive composite material.

[0030] In some embodiments of the present application, the thermoplastic elastomer is mixed with the organic solvent for 1-10h.

[0031] In some preferred embodiments of the present application, the thermoplastic elastomer is mixed with the organic solvent for 2-5h.

[0032] In some embodiments of the present application, the specific operation of mixing the conductive filler, the cellulose nanocrystal and the inorganic salt with water is to first mix the conductive filler and the cellulose nanocrystal with water, ultrasonic dispersion for 5-20min, then add the inorganic salt and oscillate to dissolve.

[0033] In some embodiments of the present application, the emulsification time is 15-30min.

[0034] In some preferred embodiments of the present application, the emulsification time is 20-25min.

[0035] In some embodiments of the present application, the emulsification process is assisted by ultrasonic.

[0036] In some embodiments of the present application, the pressure reduction heating is performed under a protective atmosphere; the protective atmosphere comprises nitrogen.

[0037] In some preferred embodiments of the present application, the pressure reduction heating is performed under a protective atmosphere; the protective atmosphere comprises nitrogen.

[0038] In some embodiments of the present application, the pressure reduction heating is performed under a protective atmosphere; the protective atmosphere comprises nitrogen.

[0039] In some embodiments of the present application, the suction filtration time is 2-12h.

[0040] In some preferred embodiments of the present application, the suction filtration time is 4-8h.

[0041] In some embodiments of the present application, the temperature of the hot pressing is 60-120°C, the pressure is 2-15 MPa, and the time is 5-20 min.

[0042] In some preferred embodiments of the present application, the temperature of the hot pressing is 80-90°C, the pressure is 3-5 MPa, and the time is 10-15 min.

[0043] The basic principle of the present application is as follows:

[0044] A Pickering emulsion is an emulsion system stabilized by solid nanoparticles (rather than traditional surfactants), and its core principle is to use the irreversible adsorption of solid particles at the oil-water interface to form a physical barrier to prevent droplet coalescence. The present application realizes the interfacial directional assembly of conductive fillers by a Pickering emulsion template method, and synchronously optimizes the electrical conductivity, mechanical properties and photothermal function by combining a heat densification process. Specifically:

[0045] 1) A thermoplastic elastomer is used as a polymer matrix and is dissolved in an organic solvent to form an oil phase. The thermoplastic elastomer has a unique structure, with soft segments (such as polybutadiene) providing elastic deformation capability, and hard segments (such as polystyrene) forming physical crosslinking points, so that the material has both high elasticity of rubber and can be shaped like plastic. When preparing a conductive composite material, cyclic processing can be realized, and the modulus is close to the modulus of the human body, which is suitable for preparing flexible wearable devices. The thermoplastic elastomer melts and flows to wrap the conductive fillers during hot pressing, giving the material flexibility and stretchability.

[0046] 2) The conductive fillers are dispersed in water as the water phase. The conductive fillers are used to build conductive paths, wherein MXene has high electrical conductivity and excellent photothermal conversion performance, but the MXene layers are prone to stacking, and the conductive network is incomplete when directly mixed with polymers, and the interface stability is poor when used alone as a Pickering emulsifier. Cellulose nanocrystals (CNC) are a kind of naturally derived material, and the raw material is renewable and biodegradable. It has a high surface charge (mainly from sulfate groups), and can stabilize the emulsion through electrostatic repulsion, steric hindrance and interfacial energy. Therefore, the present application adopts a process path of CNC-assisted MXene co-stabilized Pickering emulsion, so that the abundant hydroxyl groups on the surface of CNC form a strong entangled and disordered interface structure with MXene through hydrogen bonding bridging, and sliding instead of breaking under external force, solving the problem of easy interface rupture when using single MXene emulsion. Inorganic salts are added to adjust the ionic strength of the water phase, compress the CNC / MXene double electric layer, and enhance the interfacial adsorption energy of the particles to improve the stability of the emulsion.

[0047] 3) mixing the above water phase and oil phase to form an O / W type Pickering emulsion, CNC and MXene are co-adsorbed on the oil-water interface, and the MXene sheet layer is inserted into the gap between the CNC nanorods (hydrogen bond bridging) to form a "wrinkled armor layer"; through pressure reduction and heating, the organic solvent is volatilized at low temperature, the droplets shrink, the CNC-MXene interface layer is tightly packed, and a porous conductive preform is formed; through suction filtration to remove residual moisture, preliminary densification is realized, and an operable film embryo is formed; then through hot pressing, the elastomer melts and flows, fills the pores, fully wraps the filler, suppresses stress concentration, pressure drives the MXene sheet layer to slide and contact, forms a continuous path, and the hydrogen bond is thermally strengthened, fixing the CNC-MXene network, realizing the synergistic improvement of the conductive and mechanical properties of the composite material.

[0048] The third aspect of the present application provides the application of the flexible conductive composite material of the first aspect of the present application in the field of flexible electronics.

[0049] The fourth aspect of the present application provides a flexible resistive pressure sensor comprising the flexible conductive composite material of the first aspect of the present application.

[0050] Compared with the prior art, the present application has the following beneficial effects:

[0051] 1) The flexible conductive composite material provided by the present application uses cellulose nanocrystals to assist in stabilizing Pickering emulsion of conductive fillers (such as MXene), the cellulose nanocrystals are easy to obtain, biodegradable, environmentally friendly and pollution-free, the Pickering emulsion has good stability, the conductive fillers are directionally enriched on the emulsion interface to form a continuous path, breaking through the bottleneck of filler dispersion, the conductive network is complete, the strain sensing response is sensitive, the cycle is reversible, the conductive interval is wide, the conductive percolation threshold is about 1wt%-2wt%, and when the conductive filler addition amount is 10wt%, the conductivity is about 25S / cm, and the conductive performance is breakthroughly improved;

[0052] 2) The flexible conductive composite material provided by the present application does not need to be modified, and when MXene is used as the conductive filler, the composite material has photo-thermal conversion performance, and compared with traditional flexible conductive composite materials, it does not need to be powered to generate Joule heat, which is conducive to reducing energy consumption;

[0053] 3) The preparation method of the flexible conductive composite material provided by the present application is simple in steps and mild in process conditions, the conductive and mechanical properties of the composite material can be changed by changing the addition amount of the conductive filler, the process cost is low, and the method is suitable for industrialized production;

[0054] 4) The flexible conductive composite material provided by the application contains a thermoplastic material, has good flexibility such as deformation and bending, can be used for human body surface wearing or flexible resistance type pressure sensor, has good conductivity, high sensitivity, long cycle life, can be used for human body mechanical movement and physiological signal detection, including finger, arm bending and weak pulse beating, and enriches the application scenarios of the product. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 It is a schematic diagram of the preparation process of the flexible conductive composite material in the embodiment.

[0056] Figure 2 It is the SEM diagram (a) of MAX in the embodiment, and the SEM diagram (b) and TEM diagram (c) of Mxene.

[0057] Figure 3 It is the SEM diagram of the Pickering emulsion droplet stabilized by CNC and Mxene in Example 1.

[0058] Figure 4 It is the SEM diagram of the preformed film embryo in Example 2.

[0059] Figure 5 It is the SEM diagram of the surface (a) and cross section (b) of the flexible conductive composite material in Example 2.

[0060] Figure 6 It is the relationship curve between the content of the conductive filler in the flexible conductive composite material and the electrical conductivity.

[0061] Figure 7 It is the verification diagram of the conductive performance of the flexible conductive composite material in Example 2.

[0062] Figure 8 It is the photo-thermal conversion diagram of the flexible conductive composite material in Example 2.

[0063] Figure 9 It is the photo of the flexible conductive composite material before (a) and after (b) stretching with the conductive filler addition amount of 2.5wt%.

[0064] Figure 10 It is the tensile strain curve of the flexible conductive composite material with different conductive filler addition amounts.

[0065] Figure 11 It is the tensile strain-resistance change rate test result of the flexible conductive composite material in Example 1.

[0066] Figure 12 It is the cycle tensile strain-resistance change rate test result of the flexible conductive composite material in Example 1. DETAILED DESCRIPTION

[0067] The present application will be further described in details by specific examples. The raw materials, reagents or devices used in the examples, unless otherwise specified, can be obtained from conventional commercial channels or can be obtained by prior art methods. Unless otherwise specified, the test or test method is the conventional method in the art.

[0068] Figure 1 To illustrate the preparation process of the flexible conductive composite material in the examples, the following will be combined with Figure 1 The preparation process of the flexible conductive composite material in the examples is described.

[0069] The conductive filler used in the examples is prepared by etching MAX, specifically: mix concentrated hydrochloric acid (36wt%-38wt%) with lithium fluoride, react for 30min, add MAX in small amounts and multiple times, heat to 40℃, react for 48h; dilute with deionized water to one time, centrifuge to take the lower layer precipitate, repeat centrifugation multiple times and measure the pH of the upper clear liquid until pH=5-7; bottle and introduce nitrogen and ultrasonic for 2h to separate MXene from unetched MAX, take out and centrifuge again for 1h, take the upper clear liquid to obtain single-layer MXene.

[0070] Figure 2 To illustrate the SEM image of MAX (a) in the examples, as well as the SEM image (b) and TEM image (c) of Mxene; from Figure 2 It can be seen that MAX has a dense layered structure, and Mxene after etching has a single sheet structure, complete morphology, and no obvious multi-layer stacking, indicating that Mxene is successfully prepared.

[0071] Example 1

[0072] This example prepares a flexible conductive composite material, the steps are as follows:

[0073] S11, mix 0.75g SBS with 3.75g cyclohexane, stir at 700rpm at room temperature until SBS is fully dissolved without obvious blocky residue, to obtain an oil phase;

[0074] S21, add 0.021g CNC and 0.0203g Mxene to 10.4377g water, use a cell disrupter to ultrasonic for 15min, then add 0.021g sodium chloride to obtain an aqueous phase;

[0075] S31, add the oil phase to the aqueous phase, use a cell disrupter to ultrasonic emulsify for 24min to obtain a Pickering emulsion stabilized by CNC and Mxene;

[0076] S41, put the Pickering emulsion into an oven, reduce the pressure to 50 kPa, heat to 50℃, and keep for 6h to remove the solvent; the obtained product is suction filtered for 6h to obtain a preformed membrane embryo; the preformed membrane embryo is hot pressed at 80℃ and 3MPa for 10min to obtain a flexible conductive composite material.

[0077] The amount of the conductive filler Mxene added is 2.5wt%.

[0078] Figure 3 The SEM image of the Pickering emulsion droplet co-stabilized by CNC and Mxene in Example 1 is shown in FIG. 2. Figure 3 It can be seen that the Pickering emulsion droplet co-stabilized by CNC and Mxene is uniform in shape, and has obvious Mxene coating wrinkles on the surface, indicating that CNC and MXene in the emulsion co-adsorb on the oil-water interface, and the MXene layers are inserted into the gap between the CNC nanorods to form a "wrinkle armor layer" through hydrogen bonding.

[0079] Example 2

[0080] A flexible conductive composite material is prepared in this example, and the steps are as follows:

[0081] S11, mix 0.75g of SBS with 3.75g of cyclohexane, and stir at room temperature at a speed of 700rpm until the SBS is fully dissolved without obvious blocky residue to obtain an oil phase;

[0082] S21, add 0.021g of CNC and 0.0416g of Mxene to 10.3938g of water, and use a cell disruptor to ultrasonicate for 15min, then add 0.021g of sodium chloride to obtain an aqueous phase;

[0083] S31, add the oil phase to the aqueous phase, and use a cell disruptor to ultrasonicate for 24min to obtain a Pickering emulsion co-stabilized by CNC and Mxene;

[0084] S41, put the Pickering emulsion into an oven, reduce the pressure to 50 kPa, heat to 50℃, and keep for 6h to remove the solvent; the obtained product is suction filtered for 6h to obtain a preformed membrane embryo; the preformed membrane embryo is hot pressed at 80℃ and 3MPa for 10min to obtain a flexible conductive composite material.

[0085] The amount of the conductive filler Mxene added is 5wt%.

[0086] Figure 4 The SEM image of the preformed membrane embryo in Example 2 is shown in FIG. 4. Figure 4 It can be seen that after the Pickering emulsion is subjected to pressure reduction and heating and the solvent is removed by suction filtration, a spherical and closely arranged structure is formed, the surface wrinkles of Mxene are in contact to form a porous conductive network structure, realizing preliminary densification, and providing a structural basis for hot pressing densification.

[0087] Figure 5 The SEM images of the surface (a) and cross-section (b) of the flexible conductive composite material in Example 2 are shown in FIG. 2. Figure 5 It can be seen that the hot pressing makes the elastomer melt and flow, fills the pores, and fully wraps the Mxene. The surface and the interior of the flexible conductive composite material have obvious conductive wrinkle lines, which provide a path for electron movement.

[0088] Example 3

[0089] In this example, a flexible conductive composite material is prepared, and the steps are as follows:

[0090] S11, 0.75g TPU is mixed with 3.75g dichloromethane, stirred at a speed of 700rpm at room temperature until the TPU is fully dissolved without obvious block residues, to obtain an oil phase;

[0091] S21, 0.021g CNC and 0.0416g Mxene are added to 10.4164g water, and a cell disruptor is used for ultrasonic treatment for 15min, and then 0.021g sodium chloride is added to obtain an aqueous phase;

[0092] S31, the oil phase is added to the aqueous phase, and a cell disruptor is used for ultrasonic emulsification for 24min to obtain a Pickering emulsion stabilized by CNC and Mxene;

[0093] S41, the Pickering emulsion is placed in an oven, the pressure is reduced to 50kPa, the temperature is raised to 50℃, and the temperature is kept for 6h to remove the solvent; the obtained product is suction filtered for 6h to obtain a pre-film embryo; the pre-film embryo is hot pressed at 80℃ and 3MPa for 10min to obtain a flexible conductive composite material.

[0094] The addition amount of the conductive filler Mxene is 5wt%.

[0095] Example 4

[0096] In this example, a flexible conductive composite material is prepared, and the steps are as follows:

[0097] S11, 0.75g SBS is mixed with 3.75g cyclohexane, stirred at a speed of 700rpm at room temperature until the SBS is fully dissolved without obvious block residues, to obtain an oil phase;

[0098] S21, 0.021g CNC and 0.0416g Mxene are added to 10.4164g water, and a cell disruptor is used for ultrasonic treatment for 15min, and then 0.021g sodium chloride is added to obtain an aqueous phase;

[0099] S31, the oil phase is added into the water phase, and ultrasonic emulsification is performed using a cell disruptor for 24 min to obtain a Pickering emulsion stabilized by CNC and Mxene;

[0100] S41, nitrogen is introduced into the Pickering emulsion, and the solvent is removed under the nitrogen flow at 70°C for 5 h; the obtained product is suction filtered for 6 h to obtain a preformed membrane embryo; the preformed membrane embryo is hot-pressed at 80°C and 3 MPa for 10 min to obtain a flexible conductive composite material.

[0101] The conductive filler Mxene is added in an amount of 5 wt%.

[0102] Performance test

[0103] 1. The flexible conductive composite materials with conductive filler Mxene added in amounts of 0, 1 wt%, 2.5 wt%, 5 wt%, 7.5 wt% and 10 wt% are prepared according to the method in Example 1, and their conductivities are tested:

[0104] Figure 6 The relationship curve between the content of the conductive filler in the flexible conductive composite material and the conductivity is shown in Figure 6 It can be seen that as the content of Mxene increases, the conductivity of the flexible conductive composite material gradually increases, and the percolation threshold of conductivity is close to 1 wt%. When the content of Mxene is 10 wt%, the conductivity of the flexible conductive composite material is close to 25 S / cm, indicating that the Pickering emulsion is stable, the conductive filler is not easy to agglomerate in a large proportion, and the flexible conductive composite material has excellent conductive performance.

[0105] 2. The flexible conductive composite material in Example 2 is used to replace part of the conductive wires in the circuit to verify its conductive performance:

[0106] Figure 7 The conductive performance verification diagram of the flexible conductive composite material in Example 2 is shown in Figure 7 It can be seen that when the flexible conductive composite material in Example 2 is used to replace part of the conductive wires in the circuit, the small bulb is successfully lit, indicating that the material has good conductive performance.

[0107] 3. The flexible conductive composite material in Example 2 is fixed at a position 40 cm away from the near-infrared light source, and the temperature data of the material surface under different intensity of near-infrared light irradiation are recorded by an infrared thermal imager to verify its photo-thermal conversion performance:

[0108] Figure 8 The photo-thermal conversion diagram of the flexible conductive composite material in Example 2 is shown in Figure 8 It can be seen that the temperature of the surface of the flexible conductive composite material increases with the increase of the intensity of the near-infrared light, and the temperature of the surface of the flexible conductive composite material under the irradiation of the near-infrared light with an intensity of 0.3 W / cm 2Under the near-infrared light intensity, the temperature can be as high as 140 DEG C, indicating that the material has excellent light-heat conversion capacity, and the conventional flexible conductive composite material performs poorly in heating and needs to be powered to generate Joule heat, which cannot achieve good light-heat conversion, while the flexible conductive composite material provided by the application has non-powered heat activation capacity, which is conducive to reducing energy consumption.

[0109] 4. The flexible conductive composite material with the conductive filler Mxene addition amount of 0, 1wt%, 2.5wt%, 5wt% and 7.5wt% was prepared by referring to the method in Example 1, and the tensile strain curve was tested:

[0110] Figure 9 the photos of the flexible conductive composite material with the conductive filler addition amount of 2.5wt% before (a) and after (b) stretching, Figure 10 the tensile strain curve of the flexible conductive composite material with different conductive filler addition amounts, Figure 10 It can be seen that when the addition amount of the conductive filler is 1wt%, the deformation amount of the flexible conductive composite material is as high as 800%, and when the addition amount of the conductive filler is 7.5wt%, the deformation amount can still reach 260%, indicating that the flexible conductive composite material provided by the application has excellent deformation and elastic properties.

[0111] 5. The flexible conductive composite material prepared in Example 1 was adhered to the finger joint, and the resistance change during the bending and stretching process at different angles was recorded, and the flexible conductive composite material prepared in Example 1 was adhered to the elbow, and the resistance change of the material during the 90° bending and stretching cycle of the elbow was recorded:

[0112] Figure 11 the tensile strain-resistance change rate test results of the flexible conductive composite material in Example 1, Figure 11 It can be seen that when the flexible conductive composite material prepared in Example 1 is adhered to the finger joint, the resistance change rate gradually increases as the bending and stretching angle of the finger increases. Figure 12 the cyclic tensile strain-resistance change rate test results of the flexible conductive composite material in Example 1, Figure 12 It can be seen that the resistance change rate of the flexible conductive composite material remains stable after 80 times of 90° bending and stretching cycle of the elbow, indicating that the flexible conductive composite material provided by the application is suitable for flexible wearable devices.

Claims

1. A flexible conductive composite material, characterized in that, The raw materials include: thermoplastic elastomer, conductive filler, cellulose nanocrystals, inorganic salt, organic solvent and water.

2. The flexible conductive composite material according to claim 1, characterized in that, The mass ratio of the thermoplastic elastomer, conductive filler, cellulose nanocrystals, and inorganic salt is (20-50): (1-2.5): (0.8-1.2):

1.

3. The flexible conductive composite material according to claim 2, characterized in that, The mass ratio of the thermoplastic elastomer to the organic solvent is 1:(3-20); And / or, the mass ratio of the inorganic salt to water is 1:(400-600).

4. The flexible conductive composite material according to claim 2, characterized in that, The conductive filler includes MXene; And / or, the inorganic salt is selected from at least one of sodium chloride, sodium acetate, potassium chloride, and calcium chloride.

5. The flexible conductive composite material according to claim 3, characterized in that, The thermoplastic elastomer is selected from at least one of styrene-butadiene-styrene block copolymer, thermoplastic polyurethane elastomer, and polydimethylsiloxane; And / or, the organic solvent is selected from at least one of cyclohexane, n-hexane, and dichloromethane.

6. The method for preparing the flexible conductive composite material according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Mix the thermoplastic elastomer with an organic solvent to obtain the oil phase; S2. The conductive filler, cellulose nanocrystals, inorganic salts and water are mixed to obtain an aqueous phase; S3. Mix the oil phase with the water phase and emulsify to obtain Pickering emulsion; S4. The Pickering emulsion is subjected to depressurization heating and vacuum filtration in sequence to obtain a preform film, which is then hot-pressed to obtain the flexible conductive composite material.

7. The preparation method according to claim 6, characterized in that, The pressure of the pressure reduction heating is 0.1-70 kPa, and the temperature is 30-90℃.

8. The preparation method according to claim 6, characterized in that, The hot pressing temperature is 60-120℃, the pressure is 2-15MPa, and the time is 5-20min.

9. The application of the flexible conductive composite material according to any one of claims 1-5 in the field of flexible electronics.

10. A flexible resistive pressure sensor, characterized in that, Including the flexible conductive composite material according to any one of claims 1-5.

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