Linear stimuli-responsive flexible porous composite material and preparation and application thereof

Abstract

This invention belongs to the field of functional composite materials, specifically relating to a linear stimulus-responsive flexible porous composite material and its preparation and application. The invention provides a composite material whose raw materials include polymer 1, polymer 2, filler 1, and filler 2. Polymer 1 is a thermoplastic elastomer polymer, polymer 2 is a water-soluble thermoplastic polymer, filler 1 is a zero-dimensional filler, and filler 2 is a fiber. Polymer 2 is dispersed within polymer 1, and a clear interface exists between them. Filler 1 is distributed at the interface formed by polymer 1 and polymer 2, and filler 2 penetrates through polymer 2, with its end located at the interface between polymer 1 and polymer 2. The composite material obtained by this invention, as a flexible multi-stimulus responsive strain sensing material, exhibits excellent interfacial stability and good, stable, and controllable linear resistive-mechanical strain response characteristics; it can also serve as a stretchable, waterproof, and breathable strain sensing material.

Description

Technical Field

[0001] This invention belongs to the field of functional composite materials, specifically relating to a stretchable, compressible, and bendable breathable multifunctional linear stimulus-response flexible porous composite material and its preparation and application. Background Technology

[0002] With the rapid development of technologies such as flexible electronics, the Internet of Things, and intelligent robots, the importance of flexible stretchable strain sensing materials is becoming increasingly apparent, and users' demands for the performance and functionality of these materials are growing daily. The fundamental requirement is to simply and accurately measure the strain generated by an object in practical applications and provide real-time feedback, similar to the function of human skin. Moreover, the strain range of objects in such applications is typically wide and the changes are relatively complex. Traditional electronic materials, due to their relatively simple sensing functions, usually cannot meet the needs of such applications. Therefore, the development of flexible stretchable electronic materials (electronic skin) with good conformability and fit to the target object, and a linear response of electrical signals to strain, is particularly important. Among these, to meet the performance requirements of elasticity and breathability in practical applications, the development of porous polymer conductive composite materials with a wide range of stretchable, compressible, and bending functions, and a rapid linear response of electrical signals to strain, is of paramount importance. In addition, for flexible pressure sensors, the ability to accurately distinguish between positive and negative pressure is also one of the important performance indicators in practical applications, and it has broad application prospects in the fields of flexible biomimetic underwater robots and intelligent fluid detection pumps.

[0003] Generally, integrating sensors with different functions onto a polymer substrate in a specific manner and using different circuit designs to distinguish signals is the main method for preparing flexible strain sensing materials with multiple strain sensing functions. Although this method is very simple, it cannot achieve the miniaturization, overall flexibility and stability, and low-power integration of materials and devices, thus still facing many difficulties and challenges in practical applications. Furthermore, as a skin-like multifunctional strain sensing material, porous polymer conductive composites have a more significant advantage in multifunctional strain sensor applications due to their excellent comprehensive physical and mechanical properties and air permeability. Currently, the main methods for preparing porous polymer conductive composites include coating conductive materials on the surface of foam, or preparing conductive composite materials (which can be in the form of slurry or powder mixtures) through techniques such as sacrificial template method, freeze drying, 3D printing, and foaming. However, porous conductive materials prepared in this way have compressive properties but struggle to guarantee good stretchability, and their electrical properties are difficult to meet the requirements of varying over a wide range of tensile or compressive strain. Therefore, polymer blending and etching methods are also used to prepare polymer conductive composites, but composites prepared by these methods typically cannot simultaneously achieve stretchability and compressibility over a wide strain range. Furthermore, the robustness of the porous framework is often insufficient, and the interaction between conductive nanomaterials and polymer materials is not strong enough. This leads to nonlinear changes in the electrical signal with strain loading during mechanical deformation, ultimately resulting in complex signal processing and difficulty in finding the zero point in practical applications. Currently, this problem severely restricts the practical application of flexible strain sensing materials and flexible stretchable electronic skin, and methods to solve such problems are very limited. Although using different conductive composite materials to prepare robust conductive networks, or periodically combining resistors with different resistance values, can suppress the rapid destruction of conductive pathways during stretching to a certain extent, it is difficult to simultaneously achieve a wide operating range, high sensitivity, and multiple strain sensing functions. Moreover, the processing methods are complex and cannot be scaled up or customized in structure. In addition, existing flexible pressure sensors cannot accurately distinguish between positive and negative pressure, and this area is essentially unexplored. Summary of the Invention

[0004] To address the shortcomings and limitations of existing technologies, this invention provides a method for constructing an overpass-like electronic network structure within a polymer material. Water-etching removes the water-soluble polymer phase, resulting in a spatially heterogeneous porous polymer conductive composite material. The resulting porous polymer conductive composite material exhibits excellent mechanical properties and stable conductive nanomaterial-polymer interface, demonstrating good, stable, and controllable linear resistivity-mechanical strain response characteristics. It also exhibits good tensile, compressive, and bending strain sensing performance and signal linearity over a wide strain loading range. Furthermore, this pressure sensing material can effectively distinguish between positive and negative pressure.

[0005] The technical solution of the present invention:

[0006] The first technical problem to be solved by the present invention is to provide a composite material, wherein the raw materials of the composite material include polymer 1, polymer 2, filler 1 and filler 2, wherein polymer 1 is a thermoplastic elastomer polymer, polymer 2 is a water-soluble thermoplastic polymer, filler 1 is a zero-dimensional filler (such as a spherical filler), and filler 2 is a fiber; and polymer 2 is dispersed in polymer 1 and there is a clear interface between the two, filler 1 is distributed at the interface formed by polymer 1 and polymer 2, filler 2 penetrates through polymer 2, and the end of filler 2 is located at the interface between polymer 1 and polymer 2.

[0007] Furthermore, the polymer 1 is selected from polyolefin elastomers or thermoplastic elastomers.

[0008] Furthermore, the polymer 1 is selected from: ethylene-octene copolymer (ORC or OBC), ethylene-butene copolymer (SBS or SEBS), thermoplastic polyurethane (TPU), or ethylene-vinyl acetate copolymer (EVA), etc.

[0009] Furthermore, the polymer 2 is selected from polyethylene oxide, polyvinyl alcohol, or polyacrylamide, etc.

[0010] Preferably, polymer 1 is an ethylene-octene copolymer or an ethylene-vinyl acetate copolymer, and polymer 2 is polyethylene oxide.

[0011] Furthermore, the filler 1 is selected from conductive fillers such as carbon black, carbon quantum dots, and metal clusters, or silica, alumina nanospheres, carbon black, carbon dots, or graphene quantum dots.

[0012] Furthermore, the filler 2 is selected from carbon fiber, glass fiber, basalt fiber or heat-resistant polymer fiber, etc.

[0013] Preferably, the filler 1 is carbon black, and the filler 2 is carbon fiber or glass fiber.

[0014] In the composite material of the present invention, polymer 2 is dispersed in polymer 1 at a certain size, and there is a relatively clear interface between the two; wherein, spherical low-dimensional carbon material is dispersed / distributed at the interface of the two polymers as particles or aggregates of a certain size, while fibrous or rod-shaped carbon material is mainly dispersed / distributed in water-soluble polymer 2; and conductive fillers, thermally conductive fillers, etc. can be introduced according to actual needs to obtain a spatial heterogeneous conductive composite material or thermally conductive composite material with an overpass-like three-dimensional spatial network structure.

[0015] The second technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned composite material. The method is as follows: first, polymer 2 is melt-blended with filler 1 and filler 2 to obtain a blend; then, polymer 1 is added to the obtained blend for further melt-blending; finally, polymer 2 is removed by water etching; thus, a spatial heterogeneous composite material with an overpass-like three-dimensional spatial network structure can be obtained.

[0016] Furthermore, in the above preparation method, the mass ratio of polymer 1 to polymer 2 is controlled at 2:3 to 3:2 (preferably 1:1).

[0017] Furthermore, in the above preparation method, the mass ratio of polymer 1 to filler 1 and filler 2 is as follows: polymer 1 is selected as 100 parts by weight, filler 1 is selected as 1 to 10 parts by weight, and filler 2 is selected as 1 to 10 parts by weight.

[0018] Furthermore, in the above preparation method, the melt blending includes torque blending and melt extrusion.

[0019] The third technical problem to be solved by the present invention is to specify the above-mentioned composite material as a flexible conductive material, a flexible strain sensing material, a flexible stretchable electrode, a flexible thermal conductive material, or a thermal interface material.

[0020] Furthermore, when the composite material is used as a flexible strain sensing material, the sensing material is a multi-response material capable of simultaneously detecting tensile, compressive, and bending strain.

[0021] The fourth technical problem to be solved by the present invention is to provide a flexible pressure sensor, the sensor comprising a flexible strain sensing material and electrodes, wherein the conductive material of the flexible strain sensing material comprises polymer 1, polymer 2, filler 1 and filler 2, and fillers 1 and 2 are both conductive fillers; wherein polymer 1 is a thermoplastic elastomer polymer, polymer 2 is a water-soluble thermoplastic polymer, filler 1 is a zero-dimensional filler, and filler 2 is a one-dimensional fibrous filler; furthermore, polymer 2 is dispersed in polymer 1 and there is a clear interface between the two, filler 1 is distributed at the interface formed by polymer 1 and polymer 2, filler 2 penetrates through polymer 2, and the fiber ends of filler 2 are located at the interface between polymer 1 and polymer 2.

[0022] Furthermore, the polymer 1 is selected from polyolefin elastomers or thermoplastic elastomers.

[0023] Furthermore, the polymer 2 is selected from polyethylene oxide, polyvinyl alcohol, or polyacrylamide, etc.

[0024] Preferably, polymer 1 is an ethylene-octene copolymer or an ethylene-vinyl acetate copolymer, and polymer 2 is polyethylene oxide.

[0025] Furthermore, the filler 1 is selected from conductive fillers such as carbon black, carbon quantum dots, and metal clusters, or silica, alumina nanospheres, carbon black, carbon dots, or graphene quantum dots.

[0026] Furthermore, the filler 2 is selected from carbon fiber, glass fiber, basalt fiber or heat-resistant polymer fiber, etc.

[0027] Preferably, the filler 1 is carbon black, and the filler 2 is carbon fiber or glass fiber.

[0028] Furthermore, the flexible pressure sensor can distinguish between positive and negative pressure within the range of -0.09 MPa to 0.4 MPa.

[0029] Furthermore, the flexible pressure sensor can simultaneously detect tensile, compressive, and bending strain.

[0030] The fifth technical problem to be solved by this invention is to provide a method for fabricating the aforementioned flexible pressure sensor, wherein the method involves encapsulating a flexible conductive material and electrodes using an elastomer material. This invention utilizes existing conventional methods to fabricate the pressure sensor.

[0031] Furthermore, the encapsulation elastomer material can be a thermoplastic elastomer film material or a rubber elastomer that is easy to cast, preferably a castable silicone rubber elastomer Ecoflex.

[0032] Furthermore, the electrode can be made of ordinary commercial fine wires or flexible stretchable conductors.

[0033] The beneficial effects of this invention are:

[0034] The spatial heterogeneous flexible conductive composite material with an electronic transmission network mimicking an overpass structure obtained by this invention has the following advantages:

[0035] 1) This invention employs an electronic transmission network with a simulated overpass structure to be constructed inside a porous polymer matrix, thereby achieving the preparation of a spatially heterogeneous flexible composite material. The resulting conductive composite material, as a flexible multi-stimulus responsive strain sensing material, exhibits excellent interfacial stability and good, stable, and controllable linear resistive-mechanical strain response characteristics. It can be used as a stretchable, waterproof, and breathable strain sensing material. Furthermore, it has excellent and stable sensitivity and signal linearity over a wide strain loading range, and can simultaneously linearly sense tensile, bending, and compressive strain.

[0036] 2) The electronic transmission network obtained by this invention has a spatial heterogeneous flexible conductive composite material with a simulated overpass structure. The conductive materials have electrical and modulus heterogeneity, which is of great help in the planning of local strain and in suppressing the rapid increase in resistance caused by the rapid propagation of microcracks during the stretching process. The construction method of this dual heterogeneous porous structure is simple and efficient, and has great advantages in constructing micron-level modulus and electrical heterogeneous structures on the surface of micro-nano porous polymers. It is expected to be extended to the structural design of more heterogeneous strain sensing materials or stretchable electronic materials.

[0037] 3) The electronic transmission network obtained by this invention is a spatial heterogeneous flexible conductive composite material with a simulated overpass structure that can simultaneously measure a wide range of tensile and compressive strains, and has stable and repeatable strain sensing performance.

[0038] 4) The electronic transmission network obtained by this invention has the characteristic that the electrical signal changes linearly with various mechanical strains within a wide strain range; and the diameter and wall thickness of the pores can be controlled by changing the mass ratio and viscosity ratio of the two polymers, thereby achieving effective control of mechanical and electromechanical properties.

[0039] 5) The electronic transmission network obtained by this invention is a spatial heterogeneous flexible conductive composite material with a simulated overpass structure, which can monitor human movement and health across the entire range, monitor the movement of bionic fish, and monitor the switching between positive and negative pressure. Attached Figure Description

[0040] Figure 1 Electron microscopy images of the cross-sectional structure of the P-ORC-4CB / 4MCF composite material obtained in Example 1: (a) Schematic diagram of the structure of the PEO / ORC-CB / CF composite material and the P-ORC-CB / CF composite material with an electron transmission network mimicking an overpass structure; (b) Scanning electron microscopy images of the cross-section of the PEO / ORC-4CB / 4MCF and (c) P-ORC-4CB / 4MCF composite materials, where carbon fibers are marked in green, and the images (b-b'', c-c'') contain photographs of the cross-section of the 17 cm × 17 cm P-ORC-4CB / 4MCF composite material with an electron transmission network mimicking an overpass structure at different magnifications.

[0041] Figure 2 The image shows an electron microscope image of the cross-sectional structure of the P-ORC-4CB / 4MCF composite material obtained in Example 1 at 100% tensile strain. The red area represents the damage to the conductive pathway, while the green area represents the intact conductive pathway.

[0042] Figure 3The following figures illustrate the electrical conductivity, tensile and compressive properties of the examples and comparative examples, as well as the recoverability of Example 1 at 1000% tensile strain and Example 2 at 50% compressive strain: Figure a shows the dependence of electrical resistance on carbon fiber content for Example 2 and Comparative Example 2; Figure b shows the relationship between tensile mechanical properties and carbon fiber content for Example 1 and Comparative Example 1; Figure c shows the relationship between compressive strength and carbon fiber content for Example 2 and Comparative Example 2; Figure d shows photographs of Example 1 before and after being stretched to 1000% strain; Figure e shows photographs of Example 2 before and after being compressed to 50% strain.

[0043] Figure 4 The tensile strain comprehensive sensing performance of Examples 1 and Comparative Example 1 with different lengths of carbon fibers under the same filler ratio is compared as follows: Figure a shows the relationship between the relative resistance change of Examples 1 and Comparative Example 1 and tensile strain loading; Figure b shows the relationship between the strain sensitivity factor and tensile strain loading; Figure c shows the relationship between the relative resistance of the composite materials prepared with the same length of carbon fibers in Examples 1 at different filler ratios and Comparative Example 1 and tensile strain loading; Figure d shows the relationship between the strain sensitivity factor and linear operating range of Examples 1 and Comparative Example 1 with different lengths of carbon fibers; Figure e shows the change of relative resistance of Examples 1 after 8500 cycles at a maximum tensile strain of 50% over time.

[0044] Figure 5 The following is a comparison of the overall pressure sensing performance of Example 2 and Comparative Example 2: Figure a shows the relationship between the relative current change and pressure loading for Example 2 and Comparative Example 2 with different carbon fiber lengths under the same carbon fiber / carbon black ratio; Figure b shows the relationship between the pressure sensitivity and pressure loading for Example 2 and Comparative Example 2 with different carbon fiber / carbon black ratios under the same carbon fiber / carbon black ratio; Figure c shows the relationship between the relative current change and pressure loading for Example 2 and Comparative Example 2 with different carbon fiber / carbon black ratios under the same carbon fiber length; Figure d shows the relationship between the pressure sensitivity and linear operating range for Example 2 and Comparative Example 2 with different carbon fiber / carbon black ratios and different carbon fiber lengths; Figure e shows the pressure sensing response time of Example 2; Figure f shows the relative current change of Example 2 during four cycles at different maximum pressures; Figure g shows the pressure sensing curve of Example 2 after 38,000 cycles at a maximum pressure of 0.5 MPa.

[0045] Figure 6 The following are comparative examples of the relationship between relative resistance change and tensile strain: Figure a shows the curve of relative resistance change as a function of tensile strain in Comparative Example 1; Figure b shows the curve of relative resistance change as a function of tensile strain in Comparative Example 3.

[0046] Figure 7The following is a comparison of the relative current change versus pressure relationship in Example 2: The left graph shows the relative current change as a function of pressure loading from 0 to 1.5 MPa; the right graph is an enlarged view of the relative current change as a function of pressure loading from 0 to 0.6 MPa.

[0047] Figure 8 The graph shows the relative current change versus pressure relationship in Comparative Example 3.

[0048] Figure 9 The flexible pressure sensor fabricated in Example 2 is used for positive and negative pressure detection: Figure a is a schematic diagram of the testing device; Figure b is a positive and negative pressure test diagram; Figure c is a test diagram of 3 cycles under different positive and negative pressures.

[0049] Figure 10 The images shown are electron microscope images of the cross-sectional structure of the P-EVA-3CB / 3MCF composite material obtained in Example 4: the left image is a low-magnification scanning microscope photograph of the cross-sectional morphology of the material; the middle image is a magnified view of the morphology of the area within the red dashed box in the left image; and the right image is a magnified view of the morphology of the light blue area in the middle image.

[0050] Figure 11 Electron micrographs of the cross-sectional structure of the P-ORC-3CB / 8GF composite material obtained in Example 5 are shown below: the left image is a low-power micrograph of the cross-sectional morphology of the material; the middle image is an enlarged view of the morphology of the area within the red dashed box in the left image; and the right image is an enlarged view of the morphology of the area within the light blue dashed box in the middle image. Detailed Implementation

[0051] This invention provides a composite material comprising polymer 1, polymer 2, filler 1, and filler 2. Polymer 1 is a thermoplastic elastomer polymer, polymer 2 is a water-soluble thermoplastic polymer, filler 1 is a zero-dimensional filler (e.g., spherical filler), and filler 2 is a fiber filler. When the introduced filler is a conductive filler, a spatially heterogeneous flexible conductive composite material with an electron transmission network mimicking an overpass structure can be obtained. The spatially heterogeneous electron transmission network structure with an overpass-like structure is characterized by: conductive filler 1 (e.g., carbon black particles) dispersed / distributed on the surface of the polymer 1 (e.g., ethylene-octene copolymer) skeleton; conductive filler 2 (e.g., carbon fiber) with a large aspect ratio penetrating the entire pore, and its ends embedded in the polymer 1 / conductive filler 1 composite material. The modulus of carbon fiber exhibits significant heterogeneity with that of the porous skeleton material, and the modulus of the pore skeleton and the air within the pores also exhibits heterogeneity. Furthermore, the electrical conductivity of carbon fiber differs greatly from that of the ethylene-octene copolymer / carbon black conductive composite material. This invention constructs an overpass-like electronic transmission network within a porous polymer matrix, enabling the preparation of a spatially heterogeneous flexible composite material. The resulting conductive composite material, as a flexible multi-stimulus responsive strain sensing material, possesses excellent interfacial stability and exhibits good, stable, and controllable linear resistivity-mechanical strain response characteristics. It can serve as a stretchable, waterproof, and breathable strain sensing material, and demonstrates excellent and stable sensitivity and signal linearity over a wide strain loading range, while simultaneously linearly sensing tensile, bending, and compressive strain.

[0052] The following embodiments are specific descriptions of the present invention. It should be noted that the following embodiments are only used to further illustrate the present invention and are not intended to limit the present invention in any way. Non-essential improvements and adjustments made by those skilled in the art based on the above-described content of the present invention, such as changing the processing method of the porous polymer, the type and proportion of the polymer matrix, and the type of conductive nanomaterials, are still within the scope of protection of the present invention. Samples prepared by mixing carbon black with different types of carbon fibers in different mass ratios in the present invention are also examples. However, considering the comprehensive strain sensing performance comparison, P-ORC-4CB / 4MCF and P-ORC-2CB / 2SCF are selected as the main examples, specifically described in Examples 1 and 2 below.

[0053] In this embodiment of the invention, the polymer 2 used is selected from Dow's polyethylene oxide, the carbon black is selected from Printex's high-conductivity carbon black, and the carbon fiber (CF, T700, average diameter 7 μm, length specifications are divided into three types: 125 μm, 250 μm and 700 μm) is selected from Toray's high-strength carbon fiber, and the three types of carbon fiber are named SCF (125 μm), MCF (250 μm) and LCF (700 μm) respectively; polymer 1 is selected from Dow's ethylene-octene random copolymer ORC; in the following embodiments, the resulting composite material is abbreviated as P-ORC-xCB / yCF (CF includes SCF / MCF / LCF), where x represents the mass percentage of CB added to ORC, and y represents the mass percentage of CF added to ORC.

[0054] Example 1:

[0055] The fabrication method of the porous flexible strain sensor includes the following steps:

[0056] 1) Preparation of polyethylene oxide / carbon black / carbon fiber blend: 25 g of polyethylene oxide, 1 g of carbon black and 1 g of carbon fiber (250 μm in length) were added to a torque rheometer for melt blending. The blending temperature was 150 ℃, the rotation speed was 60 rpm and the blending time was 5 minutes.

[0057] 2) Preparation of polyethylene oxide / ethylene-octene copolymer / carbon black / carbon fiber conductive composite material: 25 g of ethylene-octene copolymer was added to the blend obtained in step (1), and the mixture was melt-blended using a torque rheometer at a blending temperature of 150 ℃, a speed of 60 rpm, and a blending time of 10 minutes.

[0058] 3) Preparation of conductive composite material samples of polyethylene oxide / ethylene-octene copolymer / carbon black / carbon fiber: The conductive composite material obtained in step (2) was pressed into rectangular block samples of 35 mm × 25 mm × 2 mm using a flat vulcanizing machine at a pressure of 10 MPa and a pressing temperature of 150°C. o C, compression time is 30 min.

[0059] 4) Etching polyethylene oxide: The conductive composite material sample obtained in step (3) was immersed in deionized water, and the deionized water was replaced every 12 hours for a total of 72 hours. Then it was dried in a 35°C oven for 24 hours to obtain a spatially heterogeneous porous polymer conductive composite material (P-ORC-4CB / 4MCF) with an internal overpass-like electronic transmission network.

[0060] The structural image of the P-ORC-4CB / 4MCF porous conductive composite material obtained in Example 1 under an electron microscope is shown below. Figure 1As shown, the carbon black conductive layer and carbon fibers together construct an electron transport network with a simulated overpass structure within the porous ethylene-octene copolymer elastomer. A scanning electron microscope image of the P-ORC-4CB / 4MCF porous conductive composite material obtained in Example 1 under 100% tensile strain is shown below. Figure 2 As shown, under high strain, the overpass-like electron transport channels formed by carbon fibers can effectively connect the undamaged carbon black conductive layer, achieving effective electron transport. The electrical conductivity and mechanical properties of the P-ORC-4CB / 4MCF porous conductive composite material obtained in Example 1 are as follows: Figure 3 As shown, the tensile strain sensing performance is as follows: Figure 4 As shown, it can achieve a linear response over an extremely wide strain range and has excellent stability.

[0061] In addition, the carbon fiber content in step 1 was changed by 0.5 g (corresponding to...) Figure 3 b contains 2% CF (i.e., the CF addition accounts for 2% of the OCR mass) and 2 g (corresponding to Figure 3 (b) The CF content is 8%. In addition, the length of the carbon fiber is changed to 125 μm and 700 μm. The final composite materials are denoted as P-ORC-4CB / SCF (P-ORC-4CB / 4SCF means that the amount of SCF added accounts for 4% of OCR) and P-ORC-4CB / LCF, respectively.

[0062] Example 2:

[0063] The fabrication method of the porous flexible strain sensor includes the following steps:

[0064] 1) Preparation of polyethylene oxide / carbon black / carbon fiber blend: 25 g of polyethylene oxide, 0.5 g of carbon black and 0.5 g of carbon fiber (length 125 μm) were added to a torque rheometer for melt blending. The blending temperature was 150 ℃, the rotation speed was 60 rpm and the blending time was 5 minutes.

[0065] 2) Preparation of polyethylene oxide / ethylene-octene copolymer / carbon black / carbon fiber conductive composite material: 25 g of ethylene-octene copolymer was added to the blend obtained in step (1), and the mixture was melt-blended using a torque rheometer at a blending temperature of 150 ℃, a speed of 60 rpm, and a blending time of 10 minutes.

[0066] 3) Preparation of conductive composite material samples of polyethylene oxide / ethylene-octene copolymer / carbon black / carbon fiber: The conductive composite material obtained in step (2) was pressed into rectangular block samples of 35 mm × 25 mm × 2 mm using a flat vulcanizing machine. The pressure was 10 MPa, the pressing temperature was 150 ℃, and the pressing time was 30 min.

[0067] 4) Etching polyethylene oxide: The conductive composite material sample obtained in step (3) was immersed in deionized water, and the deionized water was replaced every 12 h for a total of 72 h. Then it was dried in a 35 ℃ forced-air oven for 24 h to obtain a spatially heterogeneous porous polymer conductive composite material (P-ORC-2CB / 2SCF).

[0068] The electrical conductivity of the P-ORC-2CB / 2SCF porous conductive composite material obtained in Example 2 is as follows: Figure 3 As shown, the pressure sensing performance is as follows Figure 5 As shown, it can achieve a linear response over a very wide pressure range and has excellent stability.

[0069] In addition, the carbon fiber content in step 1 was changed by 0.25 g (corresponding to...) Figure 3 a contains 1% CF), 1 g (corresponding to) Figure 3 a contains 4% CF) and 2 g (corresponding to Figure 3 (The CF content in c is 8%). In addition, the length of the carbon fiber is changed to 250 μm and 700 μm. The resulting composite materials are denoted as P-ORC-2CB / MCF and P-ORC-2CB / LCF, respectively.

[0070] Example 3

[0071] The method for fabricating a porous flexible strain sensor using ethylene-vinyl acetate copolymer (EVA) instead of ethylene-octene random copolymer (ORC) includes the following steps:

[0072] 1) Preparation of polyethylene oxide / carbon black / carbon fiber blend: 25 g of polyethylene oxide, 0.75 g of carbon black and 0.75 g of carbon fiber (250 μm in length) were simultaneously added to a torque rheometer for melt blending. The blending temperature was 150 ℃, the rotation speed was 60 rpm, and the blending time was 5 minutes.

[0073] 2) Preparation of polyoxyethylene / ethylene-vinyl acetate copolymer / carbon black / carbon fiber conductive composite material: 25 g of ethylene-vinyl acetate copolymer was added to the blend obtained in step (1), and the mixture was melt-blended using a torque rheometer at a temperature of 150 ℃, a speed of 60 rpm, and a blending time of 10 minutes.

[0074] 3) Preparation of conductive composite material samples of polyethylene oxide / ethylene-vinyl acetate copolymer / carbon black / carbon fiber: The conductive composite material obtained in step (2) was pressed into rectangular block samples of 35 mm × 25 mm × 2 mm using a flat vulcanizing machine. The pressure was 10 MPa, the pressing temperature was 150 ℃, and the pressing time was 30 min.

[0075] 4) Etching polyethylene oxide: The conductive composite material sample obtained in step (3) was immersed in deionized water, and the deionized water was replaced every 12 h for a total of 72 h. Then it was dried in a 35 ℃ forced-air oven for 24 h to obtain a porous polymer conductive composite material with spatial heterogeneity (P-EVA-3CB / 3MCF).

[0076] The structural image of the P-EVA-3CB / 3MCF porous conductive composite material obtained in Example 3 is shown under an electron microscope. Figure 10 As shown in the figure, the carbon black conductive layer and carbon fiber together construct an electronic transmission network with a simulated overpass structure inside the porous ethylene-vinyl acetate copolymer elastomer.

[0077] Example 4

[0078] The fabrication method of a porous flexible strain sensor using 3 mm chopped glass fiber instead of carbon fiber includes the following steps:

[0079] 1) Preparation of polyethylene oxide / carbon black / glass fiber blend: 25 g of polyethylene oxide, 0.75 g of carbon black and 2 g of glass fiber were simultaneously added to a torque rheometer for melt blending. The blending temperature was 150 ℃, the rotation speed was 60 rpm and the blending time was 5 minutes.

[0080] 2) Preparation of polyoxyethylene / ethylene-octene copolymer / carbon black / glass fiber conductive composite material: Add 25g of ethylene-octene copolymer to the blend obtained in step (1), and continue to melt blend using a torque rheometer. The blending temperature is 150 ℃, the speed is 60 rpm, and the blending time is 10 minutes.

[0081] 3) Preparation of conductive composite material samples of polyethylene oxide / ethylene-octene copolymer / carbon black / glass fiber: The conductive composite material obtained in step (2) was pressed into rectangular block samples of 35 mm × 25 mm × 2 mm using a flat vulcanizing machine at a pressure of 10 MPa and a pressing temperature of 150°C. o C, compression time is 30 min.

[0082] 4) Etching polyethylene oxide: The conductive composite material sample obtained in step (3) was immersed in deionized water, and the deionized water was replaced every 12 hours for a total of 72 hours. Then it was dried in a 35°C oven for 24 hours to obtain a spatially heterogeneous porous polymer conductive composite material (P-ORC-3CB / 8GF) with an internal overpass-like electronic transmission network.

[0083] The structural image of the P-ORC-3CB / 8GF porous conductive composite material obtained in Example 4 is shown under an electron microscope. Figure 11As shown, the carbon black conductive layer and glass fiber together construct an electronic transmission network with a simulated overpass structure inside the porous ethylene-octene copolymer elastomer.

[0084] Comparative Example 1: No carbon fiber added

[0085] 1) Preparation of polyethylene oxide / carbon black blend: 25 g of polyethylene oxide and 1 g of carbon black were simultaneously added to a torque rheometer for melt blending at a blending temperature of 150°C. o C, the speed is 60 rpm, and the mixing time is 5 minutes.

[0086] 2) Preparation of polyethylene oxide / ethylene-octene copolymer / carbon black conductive composite material: 25 g of ethylene-octene copolymer was added to the blend obtained in step (1), and the mixture was melt-blended using a torque rheometer at a temperature of 150 ℃, a speed of 60 rpm, and a blending time of 10 minutes.

[0087] 3) Preparation of conductive composite material samples of polyethylene oxide / ethylene-octene copolymer / carbon black: The conductive composite material obtained in step (2) was pressed into rectangular block samples of 35 mm × 25 mm × 2 mm using a flat vulcanizing machine. The pressure was 10 MPa, the pressing temperature was 150 ℃, and the pressing time was 30 min.

[0088] 4) Etching polyethylene oxide: The conductive composite material sample obtained in step (3) was immersed in deionized water, with the deionized water replaced every 12 hours for a total of 72 hours. Then, it was etched at 35°C. o The composite material (P-ORC-4CB) with spatial heterogeneity was dried in a forced-air oven for 24 h to obtain a porous polymer conductive composite material with internal spatial heterogeneity.

[0089] The tensile strain sensing properties of the P-ORC-4CB conductive composite material obtained in Comparative Example 1 are as follows: Figure 6 As shown in Figure a, a linear response cannot be achieved due to the single nature of the electron transport pathway.

[0090] Comparative Example 2 did not contain carbon fiber.

[0091] 1) Preparation of polyethylene oxide / carbon black blend: 25 g of polyethylene oxide and 0.5 g of carbon black were simultaneously added to a torque rheometer for melt blending at a blending temperature of 150°C. o C, the speed is 60 rpm, and the mixing time is 5 minutes.

[0092] 2) Preparation of polyethylene oxide / ethylene-octene copolymer / carbon black conductive composite material: 25 g of ethylene-octene copolymer was added to the blend obtained in step (1), and melt blending was continued using a torque rheometer at a blending temperature of 150°C. oC, the speed is 60 rpm, and the mixing time is 10 minutes.

[0093] 3) Preparation of conductive composite material samples of polyethylene oxide / ethylene-octene copolymer / carbon black: The conductive composite material obtained in step (2) was pressed into rectangular block samples of 35 mm × 25 mm × 2 mm using a flat vulcanizing machine. The pressure was 10 MPa, the pressing temperature was 150 ℃, and the pressing time was 30 min.

[0094] 4) Etching polyethylene oxide: The conductive composite material sample obtained in step (3) was immersed in deionized water, with the deionized water replaced every 12 hours for a total of 72 hours. Then, it was etched at 35°C. o The composite material (P-ORC-2CB) with internal spatial heterogeneity was dried in a forced-air oven for 24 h to obtain a porous polymer conductive composite material.

[0095] The pressure sensing performance of the P-ORC-2CB conductive composite material obtained in Comparative Example 2 is as follows: Figure 7 As shown, due to the singularity of the electron transport pathway, a linear response cannot be achieved.

[0096] Comparative Example 3 did not contain carbon black.

[0097] 1) Preparation of polyethylene oxide / carbon fiber blend: 25 g of polyethylene oxide and 12.5 g of carbon fiber (250 μm in length) were simultaneously added to a torque rheometer for melt blending at a blending temperature of 150 °C. o C, the speed is 60 rpm, and the mixing time is 5 minutes.

[0098] 2) Preparation of polyethylene oxide / ethylene-octene copolymer / carbon fiber conductive composite material: 25g of ethylene-octene copolymer was added to the blend obtained in step (1), and melt blending was continued using a torque rheometer at a blending temperature of 150°C. o C, the speed is 60 rpm, and the mixing time is 10 minutes.

[0099] 3) Preparation of polyethylene oxide / ethylene-octene copolymer / carbon fiber conductive composite material samples: The conductive composite material obtained in step (2) was pressed into rectangular block samples of 35 mm × 25 mm × 2 mm using a flat vulcanizing machine at a pressure of 10 MPa and a pressing temperature of 150°C. o C, compression time is 30 min.

[0100] 4) Etching polyethylene oxide: The conductive composite material sample obtained in step (3) was immersed in deionized water, with the deionized water replaced every 12 hours for a total of 72 hours. Then, it was etched at 35°C. oThe composite material (P-ORC-50CF) with spatial heterogeneity and porous polymer conductivity was obtained by drying in a C-type forced-air oven for 24 h.

[0101] The tensile strain sensing properties of the P-ORC-50CF conductive composite material obtained in Comparative Example 3 are as follows: Figure 6 As shown in b, the pressure sensing performance is as follows: Figure 8 As shown, due to the singularity of the electron transport pathway, a linear response cannot be achieved.

[0102] By comparing the electromechanical properties (the ratio between relative resistance change and strain, and the sensitivity factor) of the conductive composite materials obtained in Examples 1 and 2 (P-ORC-4CB / 4MCF, P-ORC-2CB / 2SCF) and Comparative Examples 1, 2, and 3 (P-ORC-4CB, P-ORC-2CB, P-ORC-50CF), the spatially heterogeneous porous polymer conductive composite material with an internal overpass-like electronic transport network described in this invention exhibits good linear response and excellent, stable sensitivity over a very wide strain / pressure loading range. This is because its internal overpass-like electronic transport network can effectively maintain the electron transport channel under large deformation, thereby delaying the rate of change in resistance or reducing the degree of such change. In contrast, the porous polymer conductive composite material with a single conductive path shown in the comparative examples cannot achieve a linear response because the resistance increases rapidly once the conductive structure in the single conductive path is damaged. This method is not limited to polyethylene oxide and ethylene-octene copolymers, as well as carbon black and carbon fiber materials. It can select the type of elastic polymer matrix, soluble auxiliary phase, and composite conductive filler with size differences as needed, providing ideas for preparing conductive composite materials with an extremely wide linear response range.

[0103] As can be seen from the above embodiments, the present invention uses polymer 1 as the matrix phase and polymer 2 as the auxiliary porous phase, introducing conductive material filler 1 (such as carbon black particles) and filler 2 (such as carbon fiber). Since polymer 1 and polymer 2 have poor compatibility, and carbon black particles and carbon fibers have selective distribution characteristics in the polymer 1 / polymer 2 blend, by controlling the blending ratio of polymer 1 and polymer 2, the above materials are blended using a melt blending method. During the blending process, a composite material with a double percolation structure is formed due to phase separation, wherein carbon black is distributed at the phase interface of the two polymers, and carbon fiber is distributed in polymer 2; after selectively etching polymer 2, the remaining... Polymer 1 has a porous structure with continuous pores. Carbon black is semi-embedded on the surface of polymer 1 to form a conductive continuous layered structure. Carbon fibers are distributed in the pores and penetrate the entire pore, with some nodes embedded in the carbon black layer, forming a conductive network structure similar to an overpass. This results in excellent performance: a multifunctional, breathable, and linearly responsive resistive flexible strain sensing material that is stretchable, compression-resistant, and bendable. The obtained resistive flexible strain sensing material uses conductive materials with dimensional differences to construct an overpass-like conductive network inside the porous polymer matrix. Pressure sensors made using this sensing material can distinguish between positive and negative pressure.

[0104] Although the present invention has been described above in conjunction with embodiments, those skilled in the art should understand that various modifications can be made to the above embodiments without departing from the spirit and scope of the claims.

Claims

1. A composite material, characterized by, The raw materials of the composite material are polymer 1, polymer 2, filler 1 and filler 2, wherein the polymer 1 is ethylene-octene copolymer or ethylene-vinyl acetate copolymer, the polymer 2 is polyethylene oxide, the composite material has an electronic network structure similar to a viaduct, the filler 1 is selected from carbon black, carbon quantum dots, carbon dots or graphene quantum dots, and the filler 2 is selected from carbon fibers; the mass ratio of the polymer 1 to the polymer 2 is controlled to be 2:3-1:1; the mass ratio of the polymer 1 to the fillers 1 and 2 is that the polymer 1 is 100 parts by weight, the filler 1 is 1-10 parts by weight, and the filler 2 is 1-10 parts by weight; the preparation method of the composite material is that the polymer 2 is melt-blended with the fillers 1 and 2 to obtain a blend, then the polymer 1 is further melt-blended in the obtained blend, the polymer 2 is dispersed in the polymer 1 and there is a clear interface between the two, the filler 1 is distributed at the interface formed by the polymer 1 and the polymer 2, the filler 2 penetrates into the polymer 2, and the end of the filler 2 is located at the interface of the polymer 1 and the polymer 2, and finally water etching is performed to remove the polymer 2; thus the composite material is obtained.

2. The composite material is used as a flexible conductive material, a flexible strain sensing material, a flexible stretchable electrode, a flexible thermal conductive material, or a thermal interface material, wherein, The composite material is the composite material of claim 1.

3. The composite material according to claim 2 for use as a flexible conductive material, a flexible strain sensing material, a flexible stretchable electrode, a flexible thermal conductive material, or a thermal interface material, characterized in that, The composite material is used as a flexible strain sensing material, the sensing material is a multi-response material, and can simultaneously detect tensile, compressive and bending strain.

4. A flexible pressure sensor, said sensor comprising a flexible strain sensing material and an electrode, characterized in that, The raw materials of the conductive material in the flexible strain sensing material are polymer 1, polymer 2, filler 1 and filler 2, and the fillers 1 and 2 are both conductive fillers; wherein the polymer 1 is ethylene-octene copolymer or ethylene-vinyl acetate copolymer, the polymer 2 is polyethylene oxide, and the conductive material in the flexible strain sensing material has an electronic network structure similar to a viaduct; the filler 1 is selected from carbon black, carbon quantum dots, carbon dots or graphene quantum dots; the filler 2 is selected from carbon fibers; the mass ratio of the polymer 1 to the polymer 2 is controlled to be 2:3-1:1; the mass ratio of the polymer 1 to the fillers 1 and 2 is that the polymer 1 is 100 parts by weight, the filler 1 is 1-10 parts by weight, and the filler 2 is 1-10 parts by weight; the conductive material in the flexible strain sensing material is prepared by the following method: the polymer 2 is melt-blended with the fillers 1 and 2 to obtain a blend, then the polymer 1 is further melt-blended in the obtained blend, the polymer 2 is dispersed in the polymer 1 and there is a clear interface between the two, the filler 1 is distributed at the interface formed by the polymer 1 and the polymer 2, the filler 2 penetrates into the polymer 2, and the end of the filler 2 is located at the interface of the polymer 1 and the polymer 2, and finally water etching is performed to remove the polymer 2; thus the conductive material is obtained; the flexible pressure sensor can distinguish positive pressure and negative pressure within-0.09 MPa-0.4 MPa.

5. The method of claim 4, wherein the flexible pressure sensor is prepared by the steps of: The preparation method is that the flexible conductive material and the electrode are packaged by using an elastomer material.

6. The method of claim 5, wherein the flexible pressure sensor is prepared by the steps of: The elastomer material for packaging is a thermoplastic elastomer film material or a rubber elastomer that is easy to be cast into shape.

7. The method of claim 5, wherein the flexible pressure sensor is prepared by the steps of: The electrode is a common commercial fine wire or a flexible stretchable conductor.

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