A flexible strain sensor with high linearity and low hysteresis, a preparation method and applications thereof

Abstract

The application discloses a flexible strain sensor with high linearity and low hysteresis, a preparation method and application thereof, and belongs to the technical field of sensors. The composite sensitive material prepared by using an electric spray gun has high linearity and low hysteresis performance. The physical contact between silver nanowires and two-dimensional MXene nanosheets makes the sensor have high sensitivity in a tensile state. Meanwhile, the liquid metal particles as a structural framework have inherent room-temperature low-melting-point characteristics, so that the liquid metal particles are in a liquid state at room temperature, and the gap between the MXene nanosheets and the silver nanowires is reduced. The coordination bond formed between the MXene nanosheets and the liquid metal enhances the interface interaction between the MXene nanosheets and the liquid metal, and reduces energy dissipation. The uniform composite sensing network layer obtained based on a spray mixing technology has a uniform distance between the sensitive materials in the composite sensitive layer with the gradual increase of external stress; and the existence of the buckling structure strengthens the interaction between the sensitive materials. Therefore, the resistance has a linear relationship with the change of the stretching amount, that is, high linearity; and the flexible strain sensor has high sensitivity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sensors, and particularly relates to a flexible strain sensor with high linearity and low hysteresis, a preparation method and applications thereof. BACKGROUND

[0002] The growing interest in sports detection and healthcare has made flexible wearable strain sensors show great potential in sports detection, healthcare, human-computer interaction and other fields. Compared with other strain sensors, resistance strain sensors have attracted extensive attention of researchers due to their advantages such as easy fabrication, simple structure, adjustable electrical properties and the like. High-performance strain sensors have high sensitivity (high gauge factor), wide strain range, high linearity, fast response relaxation and low hysteresis and the like. By permeation of a new type of conductive filler (silver nanowire, carbon nanotube, graphene, MXene and the like) in a polymer, the contact area of the conductive filler changes under strain, so that the sensor has excellent sensitivity. However, the strain sensor based only on the percolation of the conductive filler has poor linearity and high hysteresis rate. The linearity of a sensor is an important indicator for measuring the linear relationship between the output signal of the sensor and the measured physical quantity. The high linearity of the sensor can provide high-precision measurement of the physical quantity and ensure the reliability of the measurement data. Therefore, by depositing a conductive coating on a pre-stretched substrate and then performing stress relief, a buckling structure can be created. The buckling structure can improve the problem of poor linearity of the strain sensor. The introduction of the buckling structure can improve the linearity and stability of the sensor. However, the hysteresis problem caused by the interface difference between the constituent materials has not been solved in the process of cyclic stretching-release. SUMMARY

[0003] In response to the shortcomings of the prior art, the present invention provides a flexible strain sensor with high linearity and low hysteresis, a preparation method, and its application. The preparation method of the present invention is to use an electric spray gun to sequentially atomize liquid metal ink and MXene / silver nanowires, and obtain a uniform composite sensing network layer through spray mixing technology; then, the pre-stretching is released to obtain a flexible strain sensor with high linearity and low hysteresis. The main reasons for the high linearity and low hysteresis performance of the flexible strain sensor of the present invention are: first, the silver nanowires and two-dimensional MXene nanosheets form physical contact. Under tension, the two-dimensional MXene nanosheets tend to separate from the stacked state, thereby producing a large resistance change under low stress and having high sensitivity characteristics; second, because the interaction force between the silver nanowires and the MXene nanosheets is very weak, the sensor does not return to its initial state during the recovery process, resulting in significant hysteresis in the silver nanowire / MXene strain sensor. The polymerized liquid metal particles (LMP) serve as the structural framework. Their inherent low melting point at room temperature makes them liquid at room temperature. This property effectively reduces the gap between MXene nanosheets and silver nanowires. The Ti-O→Ga bond formed between MXene nanosheets and liquid metal 3+ The coordination bond enhances the interfacial interaction between the MXene nanosheets and the liquid metal, reducing energy dissipation. Finally, the uniform composite sensing network layer obtained based on the spray mixing technology has a uniform increase in the distance between the sensitive materials in the composite sensitive layer as the external stress gradually increases; and the existence of the buckling structure further strengthens the interaction between the sensitive materials; the change in resistance with the amount of stretching has a good linear relationship, that is, high linearity. Therefore, the flexible strain sensor has high sensitivity and good linearity (R 2 =0.98224) and low hysteresis (0.452%) performance.

[0004] The present invention is achieved through the following technical solutions:

[0005] A method for preparing a flexible strain sensor with high linearity and low hysteresis, comprising the following steps:

[0006] (1) Preparation of liquid metal ink;

[0007] Liquid metal alloy is added to a certain amount of ethanol solution and liquid metal ink is prepared by ultrasonic homogenizer;

[0008] (2) Preparation of MXene / silver nanowire mixed solution;

[0009] First, a certain amount of MXene dispersion and silver nanowire dispersion were mixed and mixed by a magnetic stirrer to obtain a MXene / silver nanowire mixed solution;

[0010] (3) Preparation of liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer;

[0011] Pre-stretch the VHB tape at a certain stretch rate, use an electric spray gun to atomize the liquid metal ink and the MXene / silver nanowire mixed solution in sequence, and under the action of the electric spray gun, the liquid becomes smaller and more uniformly distributed droplets, then the two atomized solutions are sprayed onto the pre-stretched VHB tape at the same time for multiple times, and after the pre-stretching is released, a liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer with a buckling structure is obtained.

[0012] (4) Preparation of a flexible strain sensor with high linearity and low hysteresis;

[0013] The silver wire is fixed at both ends of the liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer using a conductive adhesive material, thereby obtaining a flexible strain sensor with high linearity and low hysteresis.

[0014] Further, step (1) specifically comprises the following steps:

[0015] 1-3g of gallium-indium alloy with a mass ratio of gallium to indium of 1:4-4:1 and a mass ratio of gallium-indium alloy to ethanol of 1:1-1:10 is placed in a beaker containing ethanol, and an ultrasonic cell crusher is used for ultrasonic treatment to obtain a liquid metal particle ink, with an ultrasonic time of 10-40min, a power of 200-600W, an ultrasonic on time of 1-3s, and an ultrasonic off time of 1-3s. Ultrasonic treatment makes the particle size of the liquid metal particles in the liquid metal ink more uniform.

[0016] Further, step (2) specifically comprises the following steps:

[0017] 3-5ml of MXene dispersion liquid with a concentration of 1-5mg / ml and 3-5ml of silver nanowire dispersion liquid with a concentration of 1-3mg / ml are taken and placed in a beaker in sequence, then a stirrer is placed, and the mixture is fully stirred at 500-1500rpm for 20-40min to obtain a MXene / silver nanowire mixed solution.

[0018] Further, the specific synthesis steps of the MXene dispersion liquid in step (2) are as follows:

[0019] Under the action of magnetic stirring, 1-5 g of LiF powder is added into 20-60 ml of 2-10 M HCl; then it is stirred at room temperature for 1-50 min, 1-5 g of Ti3AlC2 powder is added into the above solution within 5-15 min, and it is stirred at 25-40℃ for 12-36 h, and then it is washed with deionized water until the pH value of the solution is 5-6; after drying the solution in a vacuum oven, deionized water is added and ultrasonic treatment is performed for 10-40 min; finally, centrifugation is performed at 2000-4000 rpm for 2-8 min, and the supernatant is the MXene dispersion liquid.

[0020] Further, the specific synthesis steps of the silver nanowire dispersion liquid in step (2) are as follows:

[0021] First, 2-8 g of polyvinylpyrrolidone is added into 200-800 ml of ethylene glycol and completely dissolved in a magnetic stirrer; then 2-8 g of silver nitrate is added and continuously stirred until it is completely dissolved; 5-20 g of iron trichloride dissolved in ethylene glycol is added, and the mixture is stirred at 100-200 degrees for 2-7 hours; finally, the mixture is centrifuged 1-5 times with ethanol and acetone, and stirred at 2000-5000 rpm for 3-7 min to obtain the silver nanowire dispersion liquid.

[0022] Further, step (3) specifically includes the following steps:

[0023] The VHB tape is pre-stretched at a stretching rate of 50-200%; the prepared liquid metal ink and the MXene / silver nanowire mixed solution are respectively placed into an electric spray gun, and under the action of the electric spray gun, the liquid is changed into smaller and more uniformly distributed droplets, and the two solutions are sprayed onto the pre-stretched VHB tape for multiple times to obtain a uniformly distributed liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer; wherein the size distribution range of the liquid metal particles is 500 nm-1 μm; after releasing the pre-stretching, a liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer with a buckling structure is obtained.

[0024] Further, step (4) specifically includes the following steps:

[0025] A metal wire with a diameter of 0.05-0.15 mm is fixed at both ends of the liquid metal nanoparticle (LMP) / MXene / silver nanowire composite sensitive material using a conductive adhesive material, and the conductive adhesive material is dried after 1-10 min, thereby preparing a flexible strain sensor with high linearity and low hysteresis.

[0026] The second aspect of the present application provides a flexible strain sensor with high linearity and low hysteresis, which is prepared by the method of the first aspect, wherein the change rate of resistance and the size of strain in the strain sensor based on the liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer are in a linear relationship; and the flexible strain sensor has low hysteresis, and the hysteresis degree can be as low as 0.452%.

[0027] The third aspect of the present application also provides an application of the flexible strain sensor with high linearity and low hysteresis in finger bending detection. Specifically, the flexible strain sensor is attached to the joint of the index finger (attached when the finger is straight) using 3M tape or other fixing devices, and then the two ends of the flexible strain sensor are connected to a GURLEY 2600 resistance tester. The bending angle at the joint of the index finger is calibrated using a protractor. When the joint of the index finger is bent by 45°, the relative change of the resistance of the flexible strain sensor (△R / R0) is in the range of 0-0.5. When the flexible strain sensor is bent on the finger, the bending causes the distance between the composite sensitive materials composed of liquid metal nanoparticles (LMP) / MXene / silver nanowires to increase. In addition, the bending further causes the contact area between the liquid metal nanoparticles (LMP) / MXene / silver nanowires to decrease. The combined effects of the two make the flexible strain sensor capable of accurately detecting the bending of the finger.

[0028] The present application also provides an application of the flexible strain sensor with high linearity and low hysteresis in breathing detection. Specifically, the flexible strain sensor is attached to the outside of a commercial mask using 3M tape or other fixing devices, and then the two ends of the flexible strain sensor are connected to a GURLEY 2600 resistance tester. When the tester wears the mask with the flexible strain sensor and performs normal inhalation and exhalation, the change value of the resistance of the flexible strain sensor (△R / R0) is in the range of 0.10-0.25. When the tester exhales, the airflow blown by the tester causes the distance between the composite sensitive materials composed of liquid metal nanoparticles (LMP) / MXene / silver nanowires in the flexible strain sensor to increase. In the subsequent inhalation process, the liquid metal nanoparticles / MXene / silver nanowires in the flexible strain sensor tend to return to the original state. Thus, the flexible strain sensor can achieve good monitoring of breathing.

[0029] Compared with the prior art, the present application has the following advantages:

[0030] (1), the liquid metal nanoparticles (LMP) / MXene / silver nanowire composite sensitive material prepared by the electric spray gun has excellent performance of high linearity and low hysteresis. The silver nanowire and the two-dimensional MXene nanosheet form physical contact, so that the sensor has high sensitivity in the stretched state. The polymerized liquid metal particles act as a structural framework, and the inherent room temperature low melting point characteristic makes it liquid at room temperature, which effectively reduces the gap between the MXene nanosheet and the silver nanowire. In addition, the Ti-O→Ga 3+ Coordination bond between MXene nanosheet and liquid metal enhances the interface interaction between MXene nanosheet and liquid metal, reduces energy dissipation. In addition, the uniform composite sensing network layer obtained based on the spray mixing technology, with the gradual increase of external stress, the distance between the sensitive materials in the composite sensitive layer is uniform. And the existence of the buckling structure further enhances the interaction between the sensitive materials. Therefore, the change of resistance with the change of stretching amount has a good linear relationship, that is, high linearity. Therefore, the flexible strain sensor has high sensitivity, good linearity (R 2 =0.98224) and low hysteresis (0.452%).

[0031] (2), using VHB tape, MXene solution, silver nanowire solution and liquid metal as raw materials, has the advantages of easy to obtain, low cost, good biological compatibility and the like;

[0032] (3), the buckling structure formed by the method of releasing after pre-stretching the substrate can effectively reduce energy dissipation, and the prepared flexible strain sensor shows high linearity performance;

[0033] (4), the flexible strain sensor of liquid metal nanoparticles (LMP) / MXene / silver nanowire composite sensitive material can realize super-sensitive detection of finger bending and breathing. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the specific embodiments or prior art description will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, each element or part is not necessarily drawn according to the actual scale.

[0035] Figure 1 is a preparation process schematic diagram of a flexible strain sensor based on liquid metal nanoparticles (LMP) / MXene / silver nanowire composite sensitive material of the present application;

[0036] Figure 2A schematic diagram of changes of three materials in a tensile process of a flexible strain sensor based on a liquid metal nanoparticle (LMP) / MXene / silver nanowire composite sensitive material according to the present application;

[0037] Figure 3 A scanning electron microscope image of the composite sensitive material in a flexible strain sensor based on a liquid metal nanoparticle (LMP) / MXene / silver nanowire composite sensitive material according to the present application;

[0038] Figure 4 A comparison chart of linearity with and without buckling structure in a flexible strain sensor based on a liquid metal nanoparticle (LMP) / MXene / silver nanowire composite sensitive material according to the present application;

[0039] Figure 5 A comparison chart of hysteresis of a flexible strain sensor based on a liquid metal nanoparticle (LMP) / MXene / silver nanowire composite sensitive material according to the present application and silver nanowire sensors, graphene sensors, MXene sensors and liquid metal sensors;

[0040] Figure 6 A chart of the relative change in resistance of a flexible strain sensor based on a liquid metal nanoparticle (LMP) / MXene / silver nanowire composite sensitive material according to the present application with changes in finger bending;

[0041] Figure 7 A chart of the relative change in resistance of a flexible strain sensor based on a liquid metal nanoparticle (LMP) / MXene / silver nanowire composite sensitive material according to the present application with changes in the respiration of a test subject. DETAILED DESCRIPTION

[0042] To clearly and completely describe the technical solutions of the present application and the specific working process thereof, the specific embodiments of the present application are as follows in combination with the accompanying drawings of the specification:

[0043] Embodiment 1

[0044] As shown in Figure 1 , the present embodiment provides a preparation method of a flexible strain sensor with high linearity and low hysteresis, and the specific steps are as follows:

[0045] (1) Preparation of liquid metal ink;

[0046] A 2g gallium-indium alloy formed by mixing gallium and indium with a mass ratio of 3:1 was taken with a rubber bulb dropper and placed in a beaker with a capacity of 25ml containing ethanol, and the mass ratio of gallium-indium alloy to ethanol was 1:5. The outside of the beaker was sleeved with a culture dish with ice blocks to dissipate the heat generated during subsequent ultrasonic treatment. An ultrasonic cell crusher was used for ultrasonic treatment, the ultrasonic power was 300W, the total ultrasonic time was 30min, the ultrasonic on time was 2s, and the ultrasonic off time was 2s, thereby preparing a liquid metal ink.

[0047] (2) Preparation of MXene / silver nanowire mixed solution;

[0048] A 3ml MXene dispersion solution with a concentration of 2mg / ml and a 3ml silver nanowire dispersion solution with a concentration of 2mg / ml were taken with a rubber bulb dropper and placed in a 25ml beaker in turn. Then a magnetic stirrer was placed in it and stirred at 1000rpm for 30min to obtain a MXene / silver nanowire mixed solution.

[0049] The specific synthesis steps of the MXene dispersion solution used are as follows:

[0050] Under the action of magnetic stirring, 2g of LiF powder was slowly added to HCl (9M, 40ml). Then it was stirred at room temperature for 30min, and then 2g of Ti3AlC2 powder was slowly added to the above solution within 10min, and stirred at 35℃ for 24h, and washed with deionized water until the solution pH value was 5.5. After drying the solution in a vacuum oven, deionized water was added and ultrasonicated for 30min. Finally, centrifuged at 3500rpm for 5min, and the supernatant was the MXene solution.

[0051] The specific synthesis steps of the silver nanowire solution used are as follows:

[0052] First, 4g of polyvinylpyrrolidone was added to 500ml of ethylene glycol and completely dissolved in a magnetic stirrer. Then 55g of silver nitrate was added and stirred until it was completely dissolved. 10g of iron trichloride dissolved in ethylene glycol was added. The mixture was stirred at 160 degrees for 5 hours. Finally, the silver nanowire solution was obtained by centrifugation with ethanol and acetone 3 times (4000rpm, 5min) respectively.

[0053] (3) Preparation of liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer;

[0054] The VHB tape is pre-stretched at a stretching rate of 125%. The prepared liquid metal ink and MXene / silver nanowire mixed solution are respectively placed into an electric spray gun. Under the action of the electric spray gun, the liquid is converted into smaller and more uniform small liquid. At the same time, the two solutions are sprayed on the pre-stretched VHB tape for ten times to obtain a uniform distribution of the liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer. After releasing the pre-stretching, the liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer with a buckling structure is obtained.

[0055] (4) Preparation of a flexible strain sensor with high linearity and low hysteresis;

[0056] The silver wire with a diameter of 0.1 mm is fixed at both ends of the liquid metal nanoparticle (LMP) / MXene / silver nanowire composite sensitive material using conductive silver glue, and the conductive silver glue is dried after 5 minutes, thereby successfully preparing a flexible strain sensor with high linearity and low hysteresis.

[0057] Figure 1 The device preparation process of the embodiment is shown in the figure, and it can be seen from the figure that the operation process is simple and complex and tedious processing technology is avoided.

[0058] Figure 2 The changes of the three materials in the stretching process of the liquid metal nanoparticle (LMP) / MXene / silver nanowire composite sensitive material flexible strain sensor are shown in the figure, which can verify the excellent high linearity and low hysteresis performance of the sensor.

[0059] Figure 3 The microscope photos of the surface morphology and relative position of the materials in the liquid metal nanoparticle (LMP) / MXene / silver nanowire composite sensitive material are shown in the figure, and it can be seen from the figure that the silver nanowire and the two-dimensional MXene nanosheet form physical contact, thereby generating a large resistance change under the action of stretching and having high sensitivity characteristics. The uniformly distributed liquid metal nanoparticles act as a skeleton, effectively reducing the gap between the MXene nanosheet and the silver nanowire, so that the device has low hysteresis in the stretching and recovery process.

[0060] Figure 5 The hysteresis of the flexible strain sensor of the embodiment and the silver nanowire sensor, the graphene sensor, the MXene sensor and the liquid metal sensor is compared in the figure, and it can be seen from the figure that the strain sensor based on the liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer prepared in the embodiment has good linearity and low hysteresis characteristics, and the hysteresis is as low as 0.452%. The calculation formula of the hysteresis is:

[0061]

[0062] wherein, As is the area of the stretching curve region, AR is the area of the area of the recovery curve region. The change rate of resistance in the strain sensor based on the liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer and the strain size are linearly related, that is, linear fitting is performed, and the obtained index is R 2 = 0.98224. At the same time, it has low hysteresis characteristics, and the hysteresis degree can be as low as 0.452%.

[0063] Embodiment 2

[0064] The embodiment provides an application of a flexible strain sensor with high linearity and low hysteresis in finger bending detection, and the specific steps are as follows:

[0065] First, the flexible strain sensor is attached to the finger joint using 3M tape (attached when the finger is straightened), and then the leads at both ends of the flexible strain sensor are connected to the Keithley 2600 resistance tester. An angle protractor is used to calibrate the bending angle of the finger joint. When the finger joint is bent by 45°, the relative change (△R / R0) of the resistance of the flexible strain sensor is 0.32. When the flexible strain sensor is bent on the finger, the bending will cause the distance between the composite sensitive material composed of liquid metal nanoparticles (LMP) / MXene / silver nanowires to increase. In addition, the bending will further cause the contact area between the liquid metal nanoparticles (LMP) / MXene / silver nanowires to decrease. The combined effect of the two makes the flexible strain sensor can realize accurate detection of finger bending;

[0066] Figure 6 When the flexible strain sensor with high linearity and low hysteresis prepared from liquid metal nanoparticle (LMP) / MXene / silver nanowire composite sensitive material is attached to the finger joint, the relationship between the relative resistance change of the sensor and the change of the finger bending;

[0067] Embodiment 3

[0068] The embodiment provides an application of a flexible strain sensor with high linearity and low hysteresis in breathing detection, and the specific steps are as follows:

[0069] First, the flexible strain sensor is attached to the outside of the commercial mask using 3M tape, and then the leads at both ends of the flexible strain sensor are connected to the Keithley 2600 resistance tester. When the tester wears the mask with the flexible strain sensor, the change value (△R / R0) of the resistance of the flexible strain sensor is 0.13 when the tester inhales and exhales normally. When the tester exhales, the airflow blown by the tester makes the distance between the composite sensitive material composed of liquid metal nanoparticles (LMP) / MXene / silver nanowires in the flexible strain sensor larger. In the subsequent inhalation process, the liquid metal nanoparticles / MXene / silver nanowires in the flexible strain sensor tend to return to the original state. Therefore, the flexible strain sensor can achieve good monitoring of breathing.

[0070] Figure 7 When the flexible strain sensor prepared from the liquid metal nanoparticle (LMP) / MXene / silver nanowire composite sensitive material with high linearity and low hysteresis is attached to the outside of the commercial mask, the relationship between the relative resistance change of the sensor and breathing when the tester breathes evenly.

[0071] The preferred embodiments of the present application are described in detail above in combination with the drawings, but the present application is not limited to the specific details in the above-described embodiments. Within the technical concept range of the present application, the technical solutions of the present application can be subjected to various simple modifications, and these simple modifications all belong to the protection range of the present application.

[0072] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present application will not further describe various possible combinations.

[0073] In addition, various different embodiments of the present application can also be combined in any manner, as long as they do not deviate from the idea of the present application, and they should also be considered as disclosed by the present application.

Claims

1. A method for preparing a flexible strain sensor with high linearity and low hysteresis, characterized in that: The specific steps are as follows: (1) Preparation of liquid metal ink; Liquid metal alloy is added to a certain amount of ethanol solution and liquid metal ink is prepared by ultrasonic homogenizer; (2) Preparation of MXene / silver nanowire mixed solution; First, a certain amount of MXene dispersion and silver nanowire dispersion were mixed and mixed by a magnetic stirrer to obtain a MXene / silver nanowire mixed solution; (3) Preparation of liquid metal nanoparticles / MXene / silver nanowire composite sensitive material layer; The VHB tape is pre-stretched at a certain stretching rate. The liquid metal ink and MXene / silver nanowire mixed solution are then atomized sequentially using an electric spray gun. The electric spray gun converts the liquid into smaller and more evenly distributed droplets. The two atomized solutions are then sprayed onto the pre-stretched VHB tape multiple times simultaneously. After the pre-stretching is released, a liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer with a buckled structure is obtained. (4) Preparation of flexible strain sensors with high linearity and low hysteresis; Conductive adhesive materials are used to fix the silver wire at both ends of the liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer to obtain a flexible strain sensor with high linearity and low hysteresis.

2. The method for preparing a flexible strain sensor with high linearity and low hysteresis according to claim 1, wherein: Step (1) specifically includes the following steps: 1-3 g of gallium-indium alloy is placed in a beaker filled with ethanol, the mass ratio of gallium to indium in the gallium-indium alloy is 1:4-4:1, and the mass ratio of the gallium-indium alloy to ethanol is 1:1-1:10; an ultrasonic cell crusher is used for ultrasonic treatment to obtain liquid metal particle ink, the ultrasonic time is 10-40 minutes, the power is 200-600W, the ultrasonic on time is 1-3 seconds, and the ultrasonic off time is 1-3 seconds; the ultrasonic effect makes the particle size of the liquid metal particles in the liquid metal ink more uniform.

3. The method for preparing a flexible strain sensor with high linearity and low hysteresis according to claim 1, wherein: Step (2) specifically includes the following steps: Take 3-5 ml of MXene dispersion with a concentration of 1-5 mg / ml and 3-5 ml of silver nanowire dispersion with a concentration of 1-3 mg / ml, put them into a beaker in sequence, then add a stirring bar, and stir thoroughly at 500-1500 rpm for 20-40 minutes to obtain a MXene / silver nanowire mixed solution.

4. The method for preparing a flexible strain sensor with high linearity and low hysteresis according to claim 2, wherein: The specific synthesis steps of the MXene dispersion in step (2) are as follows: Under magnetic stirring, 1-5g of LiF powder was added to 20-60ml of 2-10M HCl; then stirred at room temperature for 1-50min, 1-5g of Ti3AlC2 powder was added to the above solution within 5-15min, stirred at 25-40℃ for 12-36h, and washed with deionized water until the solution pH was 5-6; after drying the solution in a vacuum oven, deionized water was added and ultrasonicated for 10-40min; finally, centrifuged at 2000-4000 rpm for 2-8min, and the supernatant was the MXene dispersion.

5. The method for preparing a flexible strain sensor with high linearity and low hysteresis according to claim 2, wherein: The specific synthesis steps of the silver nanowire dispersion in step (2) are as follows: First, add 2-8g of polyvinyl pyrrolidone to 200-800ml of ethylene glycol and completely dissolve it in a magnetic stirrer. Then, add 2-8g of silver nitrate and stir continuously to completely dissolve it. Add 5-20g of ferric chloride dissolved in ethylene glycol and stir the mixture at 100-200 degrees for 2-7 hours. Finally, centrifuge it with ethanol and acetone 1-5 times respectively and stir it at 2000-5000 rpm for 3-7 minutes to obtain a silver nanowire dispersion.

6. The method for preparing a flexible strain sensor with high linearity and low hysteresis according to claim 1, wherein: Step (3) specifically includes the following steps: The VHB tape is pre-stretched at a stretching rate of 50-200%. The prepared liquid metal ink and MXene / silver nanowire mixed solution are respectively placed in an electric spray gun. Under the action of the electric spray gun, the liquid is transformed into smaller and more evenly distributed droplets. The two solutions are sprayed onto the pre-stretched VHB tape multiple times to obtain a uniformly distributed liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer; wherein the size distribution range of the liquid metal particles is 500nm-1μm; after releasing the pre-stretching, a liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer with a buckled structure is obtained.

7. The method for preparing a flexible strain sensor with high linearity and low hysteresis according to claim 1, wherein: Step (4) specifically includes the following steps: Conductive adhesive material is used to fix metal wires with a diameter of 0.05-0.15 mm at both ends of the liquid metal nanoparticle (LMP) / MXene / silver nanowire composite sensitive material. After 1-10 minutes, the conductive adhesive material dries to prepare a flexible strain sensor with high linearity and low hysteresis.

8. A flexible strain sensor with high linearity and low hysteresis, characterized in that: Prepared by the method according to any one of claims 1 to 7, wherein the rate of change of resistance in the strain sensor based on the liquid metal nanoparticle / MXene / silver nanowire composite sensitive material layer is linearly related to the strain magnitude; and at the same time, it has a low hysteresis characteristic, with the hysteresis being as low as 0.452%.

9. Application of the flexible strain sensor with high linearity and low hysteresis as claimed in claim 8 in detecting finger bending.

10. Application of the flexible strain sensor with high linearity and low hysteresis as claimed in claim 8 in breathing detection.

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