Anisotropic flexible strain sensor and preparation method and application thereof

Abstract

The application discloses an anisotropic flexible strain sensor and a preparation method and application thereof, and belongs to the technical field of flexible strain sensors.The anisotropic flexible strain sensor comprises orthogonally stacked rectangular conductive fiber films, and the rectangular conductive fiber films are composed of a plurality of fiber film matrices with directional alternating segmented structures.When the anisotropic flexible strain sensor is subjected to in-plane strain in different directions, different changes can be experienced through a conductive network, so that different resistance changes are generated, so that the recognition of the strain direction is realized; in addition, when the sensor is subjected to in-plane strain, strain redistribution on the surface of the fiber can be realized, so that the crack propagation of the conductive material on the surface of part of the fiber film matrix is slowed down, so that the strain range is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of flexible strain sensors, and particularly relates to an anisotropic flexible strain sensor and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of wearable electronic devices, flexible strain sensors capable of converting external loads into visual electrical signals have attracted much attention due to their potential applications in human motion detection, real-time health monitoring, human-computer interaction and intelligent robots. Resistance strain sensors have become the most widely studied type of strain sensors due to their simple structure, simple manufacturing process, high sensitivity and other advantages, and their sensing performance is determined by the flexible polymer matrix, conductive material and structural design. Although remarkable progress has been made in improving the sensing performance of strain sensors, due to the uniform distribution of conductive materials in the polymer matrix or on the surface and the Poisson effect, they exhibit strong coupling response to strain in any direction, i.e. the conductive network undergoes similar deformation and thus exhibits similar resistance changes. Therefore, most reported strain sensors cannot accurately identify the strain direction, which limits their application in detecting complex multi-axial strain. For example, they can only monitor whether the wrist joint is in motion, but cannot identify whether it is moving up and down or left and right. Therefore, it is of great significance to prepare strain sensors that can identify different strain directions.

[0003] In order to expand the application of strain sensors, many studies have been made to manufacture strain sensors with direction recognition capability. One method is to design the structure of the matrix, and researchers have combined soft elastomers with rigid elastomers by soft lithography to prepare a flexible matrix with variable stiffness, which produces different strain distributions in the flexible part when strain is applied in different directions, thereby causing the conductive network on its surface to form different morphological changes to achieve direction recognition. However, due to the small difference in the change of the conductive network of the conductive material in the orthogonal direction during the strain process, the direction recognition is poor. Another method is to design the micro / nano structure of the conductive material. Due to the special decoupling structure, orderly arranged conductive materials have unique advantages in the preparation of anisotropic sensors, such as orderly arranged silver nanowires, carbon nanotubes and vertical graphene sheets, etc. Researchers have prepared parallel arranged vertical graphene (PAVG) by metal-induced and plasma chemical vapor deposition. Due to the parallel arrangement of vertical graphene, PAVG can form different physical contact changes when stretched in different directions, thereby producing different electrical signals to achieve direction recognition. However, this method can achieve good strain direction recognition, but the process is complex and the preparation cost is high. In addition, due to the rapid loss of connection of PAVG during the strain process, the conductive network is quickly destroyed, thus having poor strain range and being unable to monitor complex motion under large strain. SUMMARY

[0004] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide an anisotropic flexible strain sensor and its preparation method and application, so as to solve the technical problem that the existing directional conductive material is completely destroyed under large tensile strain.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] The present application discloses an anisotropic flexible strain sensor, comprising orthogonally stacked rectangular conductive fiber membranes, conductive glue and copper wires; both ends of the rectangular conductive fiber membrane are coated with conductive glue and copper wires are drawn out.

[0007] The rectangular conductive fiber membrane is composed of a plurality of fiber membrane substrates, and the outer surface of the fiber membrane substrate is coated with a conductive material; the fiber membrane substrate has a directional alternating segmented structure.

[0008] Further, the material of the fiber membrane substrate is TPU@PI electrospun membrane, and the material of the conductive material is Ti3C2T x The conductive glue is silver conductive glue; the length of the rectangular conductive fiber membrane is 3 cm, and the width is 1 cm.

[0009] Further, when the external strain direction is parallel to the rectangular conductive fiber membrane, the sensitivity of the anisotropic flexible strain sensor in the range of 0-60% strain is 486.2; when the external strain direction is perpendicular to the rectangular conductive fiber membrane, the sensitivity of the anisotropic flexible strain sensor in the range of 0-60% strain is 2.8; the anisotropic flexible strain sensor has a selectivity of 10.74.

[0010] The present application also discloses a preparation method of the above-mentioned anisotropic flexible strain sensor, S1: preparing a pretreated fiber membrane substrate from polyurethane spinning solution and polyimide spinning solution by coaxial electrospinning process; the pretreated fiber membrane substrate is treated by pre-stretching to obtain a fiber membrane substrate with an alternating segmented structure;

[0011] S2: coating the surface of the fiber membrane substrate with a conductive material, and then cutting a plurality of fiber membrane substrates coated with a conductive material into a rectangle along the directional direction as the long side to obtain a rectangular conductive fiber membrane, stacking two pieces of rectangular conductive fiber membranes by orthogonal stacking, and then coating the two ends of the two pieces of rectangular conductive fiber membranes with conductive glue and drawing out copper wires.

[0012] Further, in S1, the polyurethane spinning solution is prepared by adding polyurethane particles into a mixed solvent of N,N-dimethylformamide and tetrahydrofuran, and magnetically stirring under water bath until completely dissolved to obtain the polyurethane spinning solution; the mass fraction of polyurethane in the polyurethane spinning solution is 18%-24%;

[0013] The polyimide spinning solution is prepared by adding polyimide powder into N-methyl pyrrolidone, and magnetically stirring under water bath until completely dissolved to obtain the polyimide spinning solution; the mass fraction of polyimide in the polyimide spinning solution is 12%-18%; the deformation amount of the pre-stretching treatment is 10%-100%.

[0014] Further, in S1, the coaxial electrospinning process comprises the following steps: the polyurethane spinning solution is sucked into a syringe and connected with an inner needle as a core layer, and the polyimide spinning solution is sucked into a syringe and connected with an outer needle as a shell layer, then the polyurethane spinning solution and the polyimide spinning solution in the syringes are extruded out of the needles by a pump, and a drum is used as a receiver under an electric field to obtain a fiber membrane matrix with an alternating segmented structure.

[0015] Further, the extrusion speed of the polyurethane spinning solution is 1.0 mL / h, the extrusion speed of the polyimide spinning solution is 0.6 mL / h, the loading voltage is 10 kV, and the rotating speed of the drum is 500-2500 r / min.

[0016] Further, in S2, the conductive material is Ti3C2T x At this time, the step of coating the conductive material on the surface of the fiber membrane matrix comprises the following steps: Ti3AlC2 powder is added into a mixed solution of hydrochloric acid and lithium fluoride, and magnetically stirred under water bath until completely etched to obtain a reaction solution, the reaction solution is centrifuged to obtain multi-layer Ti3C2T x ; the multi-layer Ti3C2T x dispersion solution is ultrasonically treated under argon, and then centrifuged and freeze-dried to obtain few-layer Ti3C2T x powder; the few-layer Ti3C2T x powder is prepared into a few-layer Ti3C2T x dispersion solution with a mass concentration of 5-15 mg / mL, and then the few-layer Ti3C2T x dispersion solution is dip-coated on the surface of the fiber membrane matrix, and then vacuum dried.

[0017] Further, the mass ratio of the Ti3AlC2 powder, hydrochloric acid and lithium fluoride is 1:20:1, the water bath temperature is 35-40℃, and the magnetic stirring time is 30-72 h; when the reaction solution is centrifuged, the rotating speed is 3500 r / min, the centrifugation time is 5-10 min, and the centrifugation is stopped until the pH value of the reaction solution is 5.

[0018] The multilayer Ti3C2T x The dispersion liquid is ultrasonically treated under argon for 1-2h, the centrifugal speed is 3500r / min, the centrifugal time is 30-35min, the dipping coating is performed for 3-5 times, and the vacuum drying temperature is 35-40 DEG C.

[0019] The application also discloses application of the anisotropic flexible strain sensor.

[0020] Compared with the prior art, the application has the following beneficial effects:

[0021] The application discloses an anisotropic flexible strain sensor, which comprises orthogonally stacked rectangular conductive fiber membranes, and the rectangular conductive fiber membranes are composed of a plurality of fiber membrane bases with a directional alternating segmented structure.

[0022] The application also discloses a preparation method of the anisotropic flexible strain sensor.

[0023] The application also discloses application of the anisotropic flexible strain sensor. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Fig. 1 is a structural schematic diagram of the anisotropic flexible strain sensor of the application;

[0025] Figure 2 Fig. 4 is a field emission scanning electron microscope diagram of the fiber membrane base of the application;

[0026] Figure 3 Fig. 6 is a surface field emission scanning electron microscope diagram of the rectangular conductive fiber membrane of the application under different strains when stretched in a vertical directional direction;

[0027] Wherein: a - fiber surface morphology under 0% strain; b - fiber surface morphology under 70% strain;

[0028] Figure 4 Surface field emission scanning electron microscope images of the rectangular conductive fiber film of the present application under different strains when stretched in the parallel orientation direction;

[0029] Wherein: a - strain distribution 1 of the fiber surface at 30%; b - strain distribution 2 of the fiber surface at 70%; c-e - fiber surface morphology and its magnified image under 30% strain; f-g: fiber surface morphology under 70% strain;

[0030] Figure 5 Schematic diagram of the preparation method of the anisotropic flexible strain sensor of the present application;

[0031] Figure 6 Resistance change curve of the anisotropic flexible strain sensor of Example 1 of the present application under different strains;

[0032] Figure 7 Cyclic tensile resistance change curve of the anisotropic flexible strain sensor of Example 1 of the present application under different strains;

[0033] Figure 8 Cyclic tensile resistance change curve of the anisotropic flexible strain sensor of Example 1 of the present application under different frequencies;

[0034] Figure 9 Resistance change curve of the anisotropic flexible strain sensor of Example 1 of the present application under 5000 cycles of tensile;

[0035] Figure 10 Resistance change curve of the anisotropic flexible strain sensor of Example 1 of the present application under different tensile strain angles;

[0036] Figure 11 Resistance change curve of the anisotropic flexible strain sensor of Example 1 of the present application for wrist motion signal detection. DETAILED DESCRIPTION

[0037] To enable persons skilled in the art to understand the characteristics and effects of the present application, the following is a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific words used herein have their usual meanings to those skilled in the art of the present application, and in case of conflict, the definition in the specification shall prevail.

[0038] Theories or mechanisms described and disclosed herein, whether correct or not, should not be considered limiting the scope of the present application, i.e., the present application can be practiced without regard to any particular theory or mechanism.

[0039] Herein, all features defined by a numerical range or a percentage range, such as numerical values, amounts, contents and concentrations, are merely for the sake of brevity and convenience. Accordingly, the description of the numerical range or the percentage range should be considered to have encompassed and specifically disclosed all possible sub-ranges and individual numerical values (including integers and fractions) within the range.

[0040] Herein, unless otherwise specifically stated, "comprise", "include", "contain", "have" or similar terms are used inclusively, in the sense of "comprising", "including", "containing", "having" or "consisting of", for example, "A comprises a" encompasses "A comprises a and other" and "A comprises only a".

[0041] Herein, for the sake of brevity, all possible combinations of the various technical features in the various embodiments or examples are not described. Therefore, the various technical features in the various embodiments or examples can be combined in any manner as long as there is no contradiction, and all possible combinations should be considered to be within the scope of the present specification.

[0042] As shown in Figure 1 , the present application discloses an anisotropic flexible strain sensor, comprising two pieces of orthogonally stacked rectangular conductive fiber films, the rectangular conductive fiber film is composed of a plurality of fiber film matrices 1, the fiber film matrix 1 is coated with a conductive material 2, and the two ends of the rectangular conductive fiber film are coated with conductive glue 3 and lead out copper wires 4; wherein the fiber film matrix 1 has a directional alternating segmented structure, as shown in Figure 2 .

[0043] Preferably, the material of the above-mentioned fiber film matrix 1 is an electrospun film, the conductive material 2 is Ti3C2T x , and the conductive glue 3 is silver conductive glue.

[0044] Preferably, the length of the rectangular conductive fiber film is 3 cm, and the width is 1 cm.

[0045] The working principle of the anisotropic flexible strain sensor disclosed by the present application is as follows:

[0046] When the direction of the applied strain is perpendicular to the rectangular conductive fiber film, only the distance between the fibers increases, and Ti3C2T x coated on the surface of the fiber does not produce cracks, thereby causing the resistance to be almost unchanged, as shown in Figure 3 ; when the direction of the applied strain is parallel to the rectangular conductive fiber film, Ti3C2T x coated on the surface of the fiber will produce cracks, thereby causing the resistance to increase; at the same time, due to the redistribution of strain on the surface of the fiber, as shown in Figure 4 a and Figure 4As shown in b, the strain will be concentrated on the surface of the TPU fiber, so it will slow down the Ti3C2T x crack propagation, as shown in Figure 4 c-g, thereby improving the strain range.

[0047] The preparation method of the above anisotropic flexible strain sensor disclosed by the present application, as shown in Figure 5 , comprises the following steps:

[0048] 1) Add polyurethane particles (TPU) to a mixed solvent of N, N-dimethylformamide (DMF) and tetrahydrofuran (THF), and add polyimide powder (PI) to N-methyl pyrrolidone (NMP), and magnetically stir under water bath until completely dissolved, to obtain TPU spinning solution and PI spinning solution;

[0049] 2) Prepare a highly directional arrangement of TPU@PI fiber membrane by coaxial electrospinning of the TPU spinning solution and the PI spinning solution;

[0050] 3) Fix the TPU@PI fiber membrane on a stretching device, and prepare a fiber membrane matrix 1 with an alternating segmented structure (TPU@PI fiber membrane with directional alternating segmented structure) by pre-stretching treatment;

[0051] 4) Add Ti3AlC2 powder to a mixed solution of 9M hydrochloric acid and lithium fluoride, and magnetically stir under water bath until completely etched, centrifuge the reaction solution, and obtain multi-layer Ti3C2T x ;

[0052] 5) Further ultrasonic treatment of the multi-layer Ti3C2T x dispersion under argon, and obtain few-layer Ti3C2T x powder after centrifugation and freeze-drying;

[0053] 6) Repeat the immersion coating of the few-layer Ti3C2T x dispersion on the TPU@PI fiber membrane with directional alternating segmented structure, and obtain a conductive material 2 (Ti3C2T x / TPU@PI conductive fiber membrane) after vacuum drying;

[0054] 7) Cut the obtained Ti3C2T x / TPU@PI conductive fiber membrane into a rectangle along the directional direction as the long side, combine two pieces of rectangular membrane by orthogonal stacking, and connect copper wires at the ends of the fiber membrane respectively using silver conductive glue, to obtain an anisotropic flexible strain sensor.

[0055] The application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application. Furthermore, it should be understood that after reading the content of the application, those skilled in the art can make various modifications or changes to the application, and these equivalent forms also fall within the scope defined by the appended claims.

[0056] The following examples use the conventional apparatus in the art. The experimental method in the following examples, if not specified, is usually carried out according to the conventional conditions, or according to the conditions suggested by the manufacturer. The following examples use various raw materials, unless otherwise specified, and the conventional commercially available products are used, and the specifications are conventional specifications in the art. In the specification of the application and the following examples, unless otherwise specified, "%" means weight percent, "parts" means weight parts, and the ratio means weight ratio.

[0057] Example 1

[0058] A preparation method of an anisotropic flexible strain sensor, comprising the following steps:

[0059] S1: 4.62 g of TPU particles and 10 mL of DMF and 10 mL of THF were poured into a sample port bottle, and magnetically stirred in a water bath at 60°C for 8 h until the TPU was completely dissolved, and the obtained TPU spinning solution was left to stand for 12 h to eliminate bubbles; at the same time, 1.81 g of PI powder and 10 mL of NMP were poured into a sample port bottle, and magnetically stirred in a water bath at 80°C for 24 h until the PI was completely dissolved, and the obtained PI spinning solution was left to stand for 12 h to eliminate bubbles; the prepared TPU spinning solution and PI spinning solution were respectively sucked into a syringe, wherein the TPU spinning solution was connected to the 21# inner needle as the core layer, and the PI spinning solution was connected to the 22# outer needle as the shell layer; then the extrusion speed of the TPU spinning solution was set to 1 mL / h, the extrusion speed of the PI spinning solution was set to 0.6 mL / h, the load voltage was set to 10 kV, the rotating speed of the drum was set to 2500 r / min, the distance from the needle to the receiver was set to 15 cm, and the environmental humidity and temperature were controlled at 45% RH and 25°C, respectively, to prepare a pretreated fiber membrane matrix (TPU@PI fiber membrane with directional structure) by coaxial electrospinning;

[0060] The two ends of the pretreated fiber membrane matrix were fixed on a stretching device, and a fiber membrane matrix 1 with an alternating segmented structure (TPU@PI fiber membrane with a directional alternating segmented structure) was obtained by a pre-stretching deformation of 50%;

[0061] S2: 2g of lithium fluoride and 40mL of 9M hydrochloric acid were magnetically stirred in a PTFE beaker for 30min. Then, 2g of Ti3AlC2 was slowly added to the PTFE beaker. The reaction temperature was adjusted to 35℃, and stirring was continued for 72h to obtain the reaction solution. Finally, the reaction solution was centrifuged (3500r / min, 5min), the supernatant was discarded, and deionized water was added to the precipitate in the centrifuge tube. The mixture was shaken by hand to ensure thorough mixing of the precipitate and deionized water. Centrifugation was continued (3500r / min, 5min) several times until the pH of the liquid discharged after centrifugation was 5, yielding multilayer Ti3C2T. x ; Multilayer Ti3C2T x The Ti3C2T fraction was dispersed in deionized water and sonicated at 200W for 1 hour under argon protection. The dispersion was then centrifuged at 3500 rpm for 30 minutes, and the supernatant was collected and freeze-dried to obtain a few-layer Ti3C2T fraction with high electrical conductivity. x ;

[0062] 200mg of few-layer Ti3C2T x Add 40 mL of deionized water to a sample bottle, and ultrasonically disperse for 3 min to obtain Ti3C2T. x Dispersion; then the fiber membrane substrate 1 with alternating segmented structure is immersed in Ti3C2T x After soaking in the dispersion for 5 minutes, the sample was removed and dried in a vacuum drying oven at 35°C. This process was repeated three times to obtain a surface coated with a conductive material (Ti3C2T). x / TPU@PI conductive fiber membrane); then, several fiber membrane substrates 1 with conductive material 2 on their surfaces are cut into rectangles with a length of 3cm and a width of 1cm along the orientation direction as the long side. The two rectangular membranes are combined by orthogonal stacking, and the two rectangular conductive fiber membranes are stacked by orthogonal stacking. Then, conductive adhesive 3 is coated on both ends of the two rectangular conductive fiber membranes and copper wires 4 are led out to obtain an anisotropic flexible strain sensor.

[0063] Example 2

[0064] The preparation process of Example 2 is the same as that of Example 1, except that the pre-stretching deformation in S1 is 10%. The final result is an anisotropic flexible strain sensor.

[0065] Example 3

[0066] The preparation process of Example 3 is the same as that of Example 1, except that the pre-stretching deformation in S1 is 100%. The final result is an anisotropic flexible strain sensor.

[0067] Example 4

[0068] The preparation process of Example 4 is the same as that of Example 1, except that the rotating speed of the roller in S1 is 500 r / min, and the final isotropic flexible strain sensor is obtained.

[0069] Example 5

[0070] A preparation method of an anisotropic flexible strain sensor, comprising the following steps:

[0071] S1: 4.62 g of TPU particles, 10 mL of DMF and 10 mL of THF were poured into a sample port bottle, and magnetic stirring was performed in a water bath at 60°C for 8 h until the TPU was completely dissolved, and the obtained TPU spinning solution was left standing for 12 h to eliminate bubbles; at the same time, 1.81 g of PI powder and 10 mL of NMP were poured into a sample port bottle, and magnetic stirring was performed in a water bath at 80°C for 24 h until the PI was completely dissolved, and the obtained PI spinning solution was left standing for 12 h to eliminate bubbles; the prepared TPU spinning solution and PI spinning solution were respectively sucked into syringes, wherein the TPU spinning solution was connected to the inner needle of 21# as the core layer, and the PI spinning solution was connected to the outer needle of 22# as the shell layer; then the extrusion speed of the TPU spinning solution was set to 1 mL / h, the extrusion speed of the PI spinning solution was set to 0.6 mL / h, the load voltage was set to 10 kV, the rotating speed of the roller was set to 2500 r / min, the distance from the needle to the receiver was set to 15 cm, and the environmental humidity and temperature were controlled at 45% RH and 25°C respectively, and a pretreated fiber membrane matrix (TPU@PI fiber membrane with directional structure) was prepared by coaxial electrospinning;

[0072] The two ends of the pretreated fiber membrane matrix were fixed on the stretching device, and a fiber membrane matrix 1 with an alternating segmented structure (TPU@PI fiber membrane with a directional alternating segmented structure) was obtained by a pre-stretching deformation of 50%;

[0073] S2: 2 g of lithium fluoride was mixed with 9 M, 40 mL of hydrochloric acid in a polytetrafluoroethane beaker and stirred magnetically for 30 min; then 2 g of Ti3AlC2 was slowly added to the above polytetrafluoroethane beaker, the reaction temperature was adjusted to 35°C, and the stirring was continued for 30 h to obtain a reaction solution; finally, the reaction solution was centrifuged (3500 r / min, 10 min), the supernatant was discarded, and deionized water was added to the precipitate in the centrifuge tube, which was shaken by hand to mix the precipitate and deionized water uniformly, and then centrifuged again (3500 r / min, 10 min), and the process was repeated several times until the pH value of the liquid poured out after centrifugation was 5, and a multi-layer Ti3C2T x ; The multi-layer Ti3C2T xDispersed in deionized water and ultrasonically treated under the protection of argon at a power of 200 W for 2 h; then the dispersion was centrifuged at 3500 r / min for 35 min, the supernatant was collected, and after freeze-drying, a few-layer Ti3C2T x ;

[0074] 300 mg of the few-layer Ti3C2T x was loaded into a sample bottle with 20 mL of deionized water, ultrasonically dispersed for 3 min to obtain a Ti3C2T x dispersion; then the fiber membrane matrix 1 with an alternating segmented structure was immersed in the Ti3C2T x dispersion for 5 min, taken out and dried in a vacuum drying oven at 40℃, repeated 5 times to obtain a conductive material (Ti3C2T x / TPU@PI conductive fiber membrane) coated on the surface; then a plurality of fiber membrane matrix 1 coated with conductive material 2 was cut into a rectangle with a length of 3 cm and a width of 1 cm along the orientation direction as the long side, two pieces of rectangular membranes were combined by orthogonal stacking, two pieces of rectangular conductive fiber membranes were stacked by orthogonal stacking, and then conductive glue 3 was coated on both ends of the two pieces of rectangular conductive fiber membranes and copper wires 4 were led out to obtain an anisotropic flexible strain sensor.

[0075] Figure 6 The resistance change curve of the anisotropic flexible strain sensor of Example 1 of the present application under different strains, Figure 6 It is disclosed that when the strain direction is parallel to the fiber orientation direction, the relative resistance change of the anisotropic flexible strain sensor increases with the increase of the strain, and its sensitivity in the range of 0-60% strain is 486.2; when the strain direction is perpendicular to the fiber orientation direction, the relative resistance change of the anisotropic flexible strain sensor hardly changes with the increase of the strain, and its sensitivity in the range of 0-60% strain is 2.8. It shows that the sensor has a wide strain range and direction recognition ability.

[0076] Figure 7 The cyclic tensile resistance change curve of the anisotropic flexible strain sensor of Example 1 of the present application under different strains is shown, Figure 7 It shows that the sensor has stable resistance change under different strains.

[0077] Figure 8 The cyclic tensile resistance change curve of the anisotropic flexible strain sensor of Example 1 of the present application under different frequencies is shown, Figure 8 It shows that the resistance change of the sensor is not affected by the frequency.

[0078] Figure 9 The resistance change curve of the anisotropic flexible strain sensor of Example 1 of the present application under 5000 cycles of tensile is shown, Figure 9It is shown that the sensor has good repeatability, stability and reliability.

[0079] The anisotropic flexible strain sensor prepared by the application was tested for recognizing different strain directions, and the results are shown in Figure 10 Figure 10 It can be seen that when the stretching direction changes from 0° to 90°, as shown in Figure 10 b-figf, the GF in the x-axis direction gradually decreases, and the GF in the y-axis direction gradually increases. Through the difference of GF, Figure 10 h shows that the sensor has excellent selectivity of 10.74, indicating its ability to recognize different strain directions.

[0080] The anisotropic flexible strain sensor prepared by the application was attached to the wrist to detect the strain in different directions caused by the human body movement such as bending up and down and swinging left and right of the wrist. As shown in Figure 11 a, when the wrist is bent up and down, the resistance in the y-axis direction increases, and the resistance in the x-axis direction hardly changes; as shown in Figure 11 b, when the wrist swings left and right, the resistance in the y-axis direction decreases, and the resistance in the x-axis direction increases; this lays the foundation for correcting the posture of exercise training.

[0081] The preparation conditions and performance test results of examples 2-3 and example 4 are shown in table 1. From example 1-3, it can be seen that the pre-stretching amount of TPU@PI fiber film will affect the strain range and sensitivity of the anisotropic flexible strain sensor prepared by the application. With the increase of the pre-stretching amount, the strain range decreases, and the sensitivity increases. When measuring a small strain, the strain sensor does not need a wide strain range, but needs higher sensitivity, so the strain sensor of example 3 is more suitable for detecting small strain signals such as facial muscle movement; when measuring a larger strain, the strain sensor does not need higher sensitivity, but needs a larger strain detection range, so the strain sensor of example 2 is more suitable for detecting large strain signals such as knee joint. Therefore, by controlling the pre-stretching amount of TPU@PI fiber film, the application can prepare flexible anisotropic strain sensors suitable for different application scenarios.

[0082] In addition, from example 1 and example 4, it can be seen that the rotating speed of the roller will affect the in-plane direction recognition ability of the anisotropic flexible strain sensor prepared by the application. With the increase of the rotating speed of the roller, the orientation degree of TPU@PI fiber is improved, thereby realizing direction recognition.

[0083] Table 1 preparation conditions and performance test results of example 2-3

[0084]

[0085] ​The above merely illustrates the technical idea of the present application, and cannot limit the protection scope of the present application. Any modification made according to the technical idea of the present application on the basis of the technical scheme falls within the protection scope of the present application.

Claims

1. An anisotropic flexible strain sensor, characterized by, It comprises rectangular conductive fiber film, conductive glue (3) and copper wire (4) which are orthogonally stacked; the two ends of the rectangular conductive fiber film are coated with conductive glue (3) and copper wire (4) is led out; The rectangular conductive fiber film is composed of a plurality of fiber film substrates (1), and the outer surface of the fiber film substrate (1) is coated with a conductive material (2); the fiber film substrate (1) has a directional alternating segmented structure; The material of the fiber membrane base (1) is a TPU@PI electrospun membrane, the material of the conductive material (2) is Ti3C2T x ; the conductive adhesive (3) is a silver conductive adhesive; the length of the rectangular conductive fiber membrane is 3 cm, and the width is 1 cm.

2. The anisotropic flexible strain sensor of claim 1, wherein, When the external strain direction is parallel to the rectangular conductive fiber film, the sensitivity of the anisotropic flexible strain sensor in the range of 0-60% strain is 486.2; when the external strain direction is perpendicular to the rectangular conductive fiber film, the sensitivity of the anisotropic flexible strain sensor in the range of 0-60% strain is 2.8; the anisotropic flexible strain sensor has a selectivity of 10.

74.

3. A method of manufacturing an anisotropic flexible strain sensor according to claim 1 or 2, characterized in that, It comprises the following steps: S1: preparing a pretreated fiber film substrate by coaxial electrospinning process of polyurethane spinning solution and polyimide spinning solution; The pretreated fiber film substrate is prepared into a fiber film substrate (1) with an alternating segmented structure by pre-stretching treatment; S2: coating the surface of the fiber film substrate (1) with a conductive material (2), then cutting a plurality of fiber film substrates (1) coated with a conductive material (2) into rectangles along the directional direction as long edges to obtain rectangular conductive fiber films, stacking two rectangular conductive fiber films by orthogonal stacking, then coating the two ends of the two rectangular conductive fiber films with conductive glue (3) and leading out copper wire (4).

4. The method of claim 3, wherein the anisotropic flexible strain sensor is prepared by the steps of: In S1, the preparation method of the polyurethane spinning solution is: adding polyurethane particles into a mixed solvent of N, N-dimethylformamide and tetrahydrofuran, and magnetically stirring under water bath until completely dissolved to obtain the polyurethane spinning solution; the mass fraction of polyurethane in the polyurethane spinning solution is 18%-24%; The preparation method of the polyimide spinning solution is: adding polyimide powder into N-methyl pyrrolidone, and magnetically stirring under water bath until completely dissolved to obtain the polyimide spinning solution; the mass fraction of polyimide in the polyimide spinning solution is 12%-18%; the deformation amount of the pre-stretching treatment is 10%-100%.

5. The method of claim 3, wherein the anisotropic flexible strain sensor is prepared by the steps of: In S1, the steps of the coaxial electrospinning process are: the polyurethane spinning solution is sucked into a syringe and connected with the inner needle as the core layer, at the same time, the polyimide spinning solution is sucked into a syringe and connected with the outer needle as the shell layer, then the polyurethane spinning solution and the polyimide spinning solution in the syringe are extruded out of the needle by a pump, and a drum is used as a receiver under an electric field to obtain a fiber film substrate (1) with an alternating segmented structure.

6. The method of claim 5, wherein the anisotropic flexible strain sensor is prepared by the steps of: The extrusion speed of the polyurethane spinning solution is 1.0 mL / h, the extrusion speed of the polyimide spinning solution is 0.6 mL / h, the loading voltage is 10 kV, and the rotating speed of the drum is 500-2500 r / min.

7. The method of claim 3, wherein the anisotropic flexible strain sensor is prepared by the steps of: S2, the material of the conductive material (2) is Ti3C2T x At this time, the step of coating the conductive material (2) on the surface of the fiber membrane substrate (1) is: adding Ti3AlC2 powder into a mixed solution of hydrochloric acid and lithium fluoride, magnetically stirring under water bath condition until complete etching, obtaining a reaction liquid, centrifuging the reaction liquid to obtain multi-layer Ti3C2T x ; ultrasonic treatment is performed on the dispersion liquid of the multi-layer Ti3C2T x under argon, and after centrifugation, freeze-drying is performed to obtain few-layer Ti3C2T x powder; the Ti3C2T x powder is prepared into a few-layer Ti3C2T x dispersion liquid with a mass concentration of 5-15 mg / mL, then the few-layer Ti3C2T x dispersion liquid is immersed and coated on the surface of the fiber membrane substrate (1), and then vacuum drying treatment is performed.

8. The method of claim 7, wherein the anisotropic flexible strain sensor is prepared by the steps of: The mass ratio of the Ti3AlC2 powder, hydrochloric acid and lithium fluoride is 1:20:1, the water bath temperature is 35-40℃, and the magnetic stirring time is 30-72h; the rotating speed of the centrifugation of the reaction liquid is 3500 r / min, the centrifugation time is 5-10 min, and the centrifugation is stopped until the pH value of the reaction liquid is 5. The multilayer Ti3C2T x The dispersion liquid is ultrasonically treated for 1-2 h under argon, centrifuged at 3500 r / min for 30-35 min; the number of times of dip coating is 3-5 times, and the temperature of vacuum drying is 35-40℃.

9. Use of an anisotropic flexible strain sensor according to claim 1 or 2, characterized in that The anisotropic flexible strain sensor is used to detect multi-directional strain of motion.

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