MXene-based sr@ms sponge, preparation method and application thereof in flexible wearable pressure sensor

Abstract

The present application belongs to the technical field of pressure sensing, and particularly relates to a SR (silicone rubber)@MS (melamine sponge) sponge based on MXene, a preparation method and application thereof in a flexible wearable pressure sensor. The present application prepares a MXene / CB (MXene / carbon black) composite solution by adsorbing carbon black nanoparticles on MXene through an in-situ polymerization method, and prepares a SR@MS sponge through PDA (polydopamine) modification and a layer-by-layer self-assembly method. The electrode is encapsulated on the upper and lower sides of the sponge to complete the preparation of the MXene / CB-SR@MS sponge pressure sensor by impregnating the MXene / CB composite solution and low-temperature drying. The flexible pressure sensor not only can realize short-time rapid response / recovery, but also exhibits good pressure response, and can detect the application effect of joint activities of each part of the human body, and has good application potential in the fields of human motion health monitoring and wearable devices.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of pressure sensing, and particularly relates to an SR@MS sponge based on MXene and a preparation method thereof and application thereof in a flexible wearable pressure sensor. BACKGROUND

[0002] The flexible wearable pressure sensor can be pasted to key parts of the body to monitor various types of activities of the human body. Scholars have constructed flexible pressure sensors with higher sensitivity and better stability by regulating sensitive materials and designing microstructures. However, poor flexibility, slow response / recovery speed, and narrow measurement range still limit the practical application of flexible wearable pressure sensors. In addition, the complex preparation process also hinders the large-scale production of flexible pressure sensors, further affecting their application in the fields of wearable devices and human-computer interaction.

[0003] The flexible materials commonly used in flexible piezoresistive pressure sensors include ultraviolet adhesives, hydrogels, and silicone elastomers. Among them, the ultraviolet adhesives can significantly improve the manufacturing speed due to their fast curing characteristics, but the strain range of the prepared sensors is small, and the application range is limited. Hydrogels have high tensile properties and self-repairing ability, but are easily disturbed by moisture and temperature. Silicone rubber (SR) has excellent mechanical properties, good resilience, and excellent mechanical repeatability. Moreover, SR is not affected by temperature and has good biocompatibility, making it a common material for wearable devices. However, the chemical activity of SR is poor, and the polarity difference between SR and common conductive sensitive materials is large, resulting in weak interaction. Therefore, it is difficult for conductive sensitive materials to tightly combine with SR. Therefore, how to solve the problem of weak interaction between SR and common conductive sensitive materials has become one of the key problems in the industry. SUMMARY

[0004] Therefore, the application discloses an SR@MS sponge based on MXene, a preparation method thereof, and application thereof in a flexible wearable pressure sensor.

[0005] To achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0006] A first technical purpose of the application is to provide an SR@MS sponge based on MXene, which is an MXene / CB-SR@MS sponge prepared by coating an MXene / CB composite material on an SR@MS sponge skeleton through a solution immersion and low-temperature drying method.

[0007] The MXene / CB composite material is CB nanoparticles deposited on MXene nanosheets by electrostatic adsorption, and the MXene nanosheets are obtained by selective etching of Ti3AlC2 through a hydrochloric acid / lithium fluoride etching solution.

[0008] A second technical object of the present application is to provide a preparation method of the MXene-based SR@MS sponge as described above, which specifically comprises the following steps:

[0009] 1) MXene nanosheets are obtained by selective etching of Ti3AlC2 through a hydrochloric acid / lithium fluoride etching solution, and then a dispersed MXene solution is obtained through ultrasonic and centrifugal treatment;

[0010] 2) CB nanoparticles are stirred in deionized water, then the MXene solution prepared in step 1) is added and mixed thoroughly, and a MXene / CB composite solution is obtained after heating and stirring, which is ready for use;

[0011] 3) Tris(hydroxymethyl)aminomethane is dissolved in distilled water, and dopamine (DA) is added and stirred to dissolve; MS is placed in the solution, and under the action of tris(hydroxymethyl)aminomethane, DA is self-polymerized on the surface of the MS skeleton and forms polydopamine PDA, thereby obtaining PDA-modified MS;

[0012] 4) The SR@MS porous sponge prepared in step 3) is immersed in the MXene / CB composite solution obtained in step 2), and then soaked in an SR / ligroin solution, dried and repeated the above operation, so as to coat the MXene / CB composite material and SR on the SR@MS sponge skeleton through a layer-by-layer self-assembly method, thereby obtaining a MXene / CB-SR@MS sponge, i.e., the MXene-based SR@MS sponge.

[0013] It should be noted that the SR (silicone rubber) elastic polymer is often structurally designed to further improve the mechanical properties of the device due to its flexibility and high plasticity, and MXene exhibits good mechanical strength and excellent metal conductivity. However, oxygen in the air can attack Ti atoms in MXene to cause oxidation of MXene, thereby affecting the conductivity. Therefore, the key to improving the stability and sensing ability of MXene lies in blocking the contact between oxygen and Ti atoms. Conductive nanomaterials are widely used in sensing, energy storage, electromagnetic shielding and metal corrosion due to their excellent performance, and have become an exciting research material. Common conductive nanomaterials include carbon black (CB), polypyrrole, nano-gold, polyaniline, etc. Among them, carbon black as a particulate material has very good conductivity. However, it will appear agglomeration in organic solvents and is difficult to dissolve, making it difficult to prepare subsequent sensors. Through the in-situ polymerization method of the composite material, CB can form a continuous coating or film on various types of materials, thereby solving the problem of CB agglomeration in solution and making it difficult to adhere to the sensor. In-situ growth of CB in MXene solution can uniformly deposit CB nanoparticles on MXene nanosheets, and CB nanoparticles can exhibit a protective coating effect on Ti atoms. At the same time, the combination of two-dimensional MXene nanosheets and zero-dimensional CB nanoparticles increases the conductive path in the sensing layer and improves the conductivity of the sensor.

[0014] The present application prepares a MXene / CB-SR@MS sponge flexible wearable pressure sensor by using a simple method, wherein the SR@MS sponge is prepared by PDA modification and layer-by-layer self-assembly method, and CB is adsorbed on the MXene solution by in-situ polymerization method to prepare a MXene / CB composite solution. This flexible wearable pressure sensor not only realizes short-time rapid response / recovery of 150 / 180 ms, but also exhibits good pressure response, with a sensitivity of 7.44 kPa -1 , and a measurement range of 0-240 kPa. In addition, the application also studies the application effect of the MXene / CB-SR@MS sponge sensor in detecting joint activities of various parts of the human body, and the results show that the MXene / CB-SR@MS sponge sensor has good application potential in the field of human motion health monitoring.

[0015] Further, in step 1), the Ti3AlC2 is selectively etched by using a hydrochloric acid / lithium fluoride etching solution, and the operation is as follows:

[0016] Ti3AlC2 is added to the pre-cooled LiF / HCl solution in batches and stirred to react, and then washed, centrifuged until the pH value of the supernatant is stable at 6, the obtained precipitate is dispersed in deionized water, and ultrasonic is performed under argon protection, and the upper clear liquid is obtained by centrifugation, separation and collection, to obtain a high-purity MXene nanosheet solution.

[0017] Further, in the LiF / HCl solution, the mass ratio of lithium fluoride to hydrochloric acid is 1:(4.8-5.2); the mass ratio of the LiF / HCl solution to Ti3AlC2 is (5.2-5.5):1, the temperature of the whole reaction mixture is maintained at 40-50 DEG C, and continuous stirring is ensured within the temperature range for 24 hours.

[0018] Further, in step 2), the mass ratio of the CB and MXene solution is (0.1-0.5):5; the concentration of the MXene solution is 10 mg / mL, and the mass ratio of CB to MXene nanosheet is 2:1; the MXene / CB mixed solution is mechanically stirred for 30 min and then ultrasonically treated for 15 min.

[0019] Further, tris(hydroxymethyl)aminomethane is dissolved in distilled water to maintain the pH value at 8-9; the MS is immersed in the solution at room temperature for 2 h, and under the action of tris(hydroxymethyl)aminomethane, the DA is self-polymerized on the surface of the MS skeleton and forms a polydopamine (PDA) adhesion layer.

[0020] Further, in step 4), in the SR / stone oil solution, the mass ratio of silicone rubber to stone oil is 1:1; the immersion time is 1 h, the drying temperature is 60-80 DEG C, and the drying time is 6 h.

[0021] A third technical purpose of the present application is to provide an application of the MXene-based SR@MS sponge prepared by the above-mentioned method in a flexible wearable pressure sensor, which can be used not only in a flexible wearable pressure sensor for detecting human physiological signals, but also in a wearable sensor for detecting joint activities of various parts of the human body.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] The present application absorbs CB on the MXene solution by in-situ polymerization to prepare a MXene / CB composite solution, and prepares an SR@MS sponge by layer-by-layer self-assembly, and through immersion of the MXene / CB composite solution and low-temperature drying, an electrode is encapsulated on the upper and lower sides of the sponge to complete the preparation of the MXene / CB-SR@MS sponge pressure sensor. This flexible pressure sensor not only can realize short-time rapid response / recovery, but also shows good pressure response, and can detect the application effect of joint activities of various parts of the human body, and has good application potential in the field of human motion health monitoring. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, the accompanying drawings in the following description only only the embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of the provided drawings.

[0025] Figure 1 The preparation flowchart of MXene / CB-SR@MS is shown.

[0026] Figure 2 (a, b) scanning electron microscope images of MXene / CB-SR@MS pressure sensor; (c) image of conductive sponge supported on the leaf; (d) X-ray diffraction patterns of CB, MXene and MXene / CB composite.

[0027] Figure 3 The sensing mechanism analysis of MXene / CB-SR@MS pressure sensor is shown.

[0028] Figure 4 (a, b) pressure-strain curves of MS and MXene / CB-SR@MS sensor; (c) loading-unloading cycle of MXene / CB-SR@MS sensor at 80% strain; (d) pressure-strain curve of MXene / CB-SR@MS at 40% strain for 60 cycles.

[0029] Figure 5 (a) relationship between relative resistance change and pressure of MXene / CB-SR@MS sensor; (b) I-V curves of MXene / CB-SR@MS sensor under different pressures.

[0030] Figure 6 (a) response / recovery time of MXene / CB-SR@MS sensor; (b) current response of MXene / CB-SR@MS sensor under continuous same pressure; (c) change curve of resistance value after releasing pressure; (d) repeated loading-unloading response curve.

[0031] Figure 7 (a) wrist pulse detection current signal; (b, c) finger bending detection signal; (d) elbow bending detection signal; (e) human respiration detection signal.

[0032] Figure 8 The schematic diagram and physical diagram of plantar gait detection sensing array based on MXene / CB-SR@MS sensor are shown.

[0033] Figure 9The resistance response of the plantar gait detection sensor array based on the MXene / CB-SR@MS sensor in the walking phase. The five phases are: I initial landing period, II support reaction period, III midpoint support period, IV post-support period, and V pre-swing period.

[0034] Figure 10 The resistance response of the plantar gait detection sensor array based on the MXene / CB-SR@MS sensor when running.

[0035] Figure 11 The resistance response of the plantar gait detection sensor array based on the MXene / CB-SR@MS sensor when climbing stairs. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0037] Here, the special term "embodiment" as "exemplary" of any embodiment does not necessarily mean that it is superior or better than other embodiments. In the performance index test of the embodiments of the present application, unless otherwise specified, the conventional test method in the art is adopted. It should be understood that the terms described in the present application are only for describing the specific embodiments, and are not used to limit the disclosure of the present application.

[0038] Unless otherwise specified, the technical and scientific terms used herein have the same meaning as generally understood by those of ordinary skill in the art to which the present application belongs; as the experimental methods and technical means not specially noted in the present application are all experimental methods and technical means generally used by those of ordinary skill in the art.

[0039] In the description of the present application, it should be understood that the terms "middle", "upper", "lower", "rise", "fall", "vertical", "face", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0040] For a better understanding of the present application, numerous specific details are given in the following detailed description. One skilled in the art will understand that the application can be practiced without certain specific details, which are set forth in the following detailed description. In the examples, some methods, means, instruments, apparatuses, etc. known to those of ordinary skill in the art are not described in detail in order to avoid obscuring the subject matter of the present application.

[0041] The technical features disclosed in the embodiments of the present application can be combined arbitrarily without conflict, and the resulting technical solutions belong to the disclosure of the present application.

[0042] The application discloses an MXene-based SR@MS sponge, a preparation method and application in a flexible wearable pressure sensor.

[0043] Embodiment 1

[0044] A preparation method of an MXene-based SR@MS sponge (MXene / CS-SR@MS sponge) is as follows:

[0045] 1) Materials

[0046] The chemical raw materials used are silicone rubber, carbon black, tris(hydroxymethyl) aminomethane, hydrochloric acid (analytical pure), naphtha, lithium fluoride (≥98%), titanium aluminum carbide powder and dopamine hydrochloride, all of which are used without further purification, and the water used is deionized water.

[0047] 2) Preparation of MXene / CB composite solution

[0048] ①LiF / HCl solution is used to chemically etch Ti3AlC2, and the purpose is to synthesize MXene nanosheets with uniform structure. The detailed preparation process is as follows:

[0049] In the initial stage, 2 grams of LiF was mixed with 20 mL of hydrochloric acid with a concentration of 9 M and stirred for 5 minutes under magnetic stirring to ensure thorough mixing. In order to precisely control the temperature of the reaction system and avoid excessive temperature due to exothermic reaction, an ice-water bath was used to cool the etching solution. Then, 2 grams of Ti3AlC2 was added in small batches to the pre-cooled mixed solution, and the temperature of the overall reaction mixture was maintained at 35°C, which was to alleviate the temperature fluctuations that might be caused by the exothermic reaction. In addition, continuous stirring was ensured at a temperature range of 40 to 50°C for 24 hours, while maintaining proper ventilation of the container to exhaust the gas that might be generated. After the reaction was completed, the reaction mixture was washed several times with deionized water and centrifuged at a speed of 3500 rpm for 5 minutes, and this step was repeated until the pH value of the supernatant stabilized at 6. Thereafter, the obtained precipitate was collected and re-dispersed in deionized water, and under the condition of argon protection, ultrasonic treatment was carried out for 1 hour, while using an ice-water bath to prevent possible heat accumulation during the ultrasonic process from causing irreversible damage to the sample. The last step was to separate and collect the supernatant by centrifuging at 3500 rpm for 1 hour, thereby obtaining the desired high-purity MXene nanosheet solution.

[0050] ②Adsorption of CB nanoparticles to MXene nanosheet solution

[0051] The mass ratio of CB, deionized water and MXene solution was 0.1:10:5; the concentration of MXene solution was 10 mg / mL, CB and MXene were mechanically stirred in a ratio of 2:1 for 30 min and then ultrasonically treated for 15 min to obtain a well-dispersed MXene / CB composite solution.

[0052] 3) Preparation of PDA-MS porous sponge

[0053] The MS cubic block was washed with ethanol and water respectively and dried in an oven at 50°C for 1 h. Tris(hydroxymethyl)aminomethane was dissolved in distilled water to maintain a pH value of 8-9, and dopamine (DA) was added and dissolved. The cleaned MS was immersed in the above solution at room temperature for 2 h. Under the action of tris(hydroxymethyl)aminomethane, DA self-polymerizes on the surface of the MS skeleton and forms a polydopamine (PDA) adhesion layer, obtaining a PDA-MS sponge.

[0054] 4) Preparation of MXene / CS-SR@MS sponge

[0055] After drying PDA-MS in a drying oven at 50℃ for 2h, it was thoroughly immersed in MXene / CB composite solution and dried at 50℃. The PDA on the surface of the sponge had a strong mutual bonding effect with the MXene / CB composite material. Next, MS was immersed in SR / naphtha solution for 15s and hung in the air to drain the excess solution to form a uniform coating layer on the surface of the sponge skeleton. Then, MS was thoroughly immersed in MXene / CB composite solution and SR / naphtha solution and cured at 80℃ for 6h. In this process, the cured SR layer acts as a connecting skeleton between MXene / CB. The above steps were repeated to achieve the purpose of layer-by-layer self-assembly, and MXene / CS-SR@MS sponge was obtained.

[0056] 5) Sensor structure analysis and characterization

[0057] The morphology of the sample was characterized by scanning electron microscopy. As shown in Figure 2 -a and Figure 2 -b, the MXene / CS-SR@MS sponge is a typical porous grid structure inside, with a skeleton diameter of about 5-10μm. The good coating of SR provides good protection for the sensing material. As shown in Figure 2 -c, the MXene / CB-SR@MS pressure sensor has a prominent weight advantage, even a single leaf can support the sensor without any deformation. The phase composition of the sensing material (CB, MXene and MXene / CB) was characterized by X-ray diffraction technology, as shown in Figure 2 -d. The characteristic peak of MXene / CB composite material at 6.36° is mainly attributed to MXene, and the characteristic peaks near 25° and 40° belong to the (002) and (100) planes of CB, respectively, indicating the existence of CB, MXene and the successful preparation of MXene / CB composite material.

[0058] Example 2

[0059] A method for preparing a MXene-based SR@MS sponge (MXene / CB-SR@MS sponge) is the same as that in Example 1 above, except that the drying temperature is 60℃, and the remaining steps are the same.

[0060] Example 3

[0061] A method for preparing a MXene-based SR@MS sponge (MXene / CB-SR@MS sponge) is the same as that in Example 1 above, except that the drying temperature is 70℃, and the remaining steps are the same.

[0062] I. Sensing mechanism and performance test of MXene / CB-SR@MS flexible wearable pressure sensor

[0063] 1) Sensor sensing mechanism

[0064] MXene / CB-SR@MS pressure sensor was prepared by PDA modification and layer-by-layer self-assembly method to dip MXene / CB composite solution and SR / naphtha solution and dryness. The electrode was packaged on the upper and lower sides of the sponge to complete the preparation of the device. Figure 3 The sensing mechanism of MXene / CB-SR@MS pressure sensor is disclosed. In the initial state, the sponge inside shows a 3D grid connection structure similar to a honeycomb. The conductive sensitive material on the skeleton only contacts each other at the connection points of different skeletons, and the number of conductive paths inside the sensor is limited in this state. When pressure starts to be applied to the sensor, that is, the first working area, at this time the MS deforms slightly, the connection between part of the skeleton is broken, causing part of the originally contacted conductive sensitive material to break, so the conductive path decreases to a certain extent, and the resistance value of MXene / CB-SR@MS sensor increases. When the external pressure gradually increases, the sponge deformation also continues to increase, and the air in the sponge pores is squeezed out, at this time the sensor works in the second area, the sponge skeleton starts to collapse, the gap also starts to gradually decrease, many sponge skeletons contact each other, and the conductive sensitive material attached to the sponge skeleton starts to contact, generating a large number of conductive contact sites, and then forming more conductive paths, increasing the overall conductivity of the sensor, and reducing the resistance value of MXene / CB-SR@MS sensor.

[0065] 2) Sensor performance test

[0066] (1) Mechanical performance test

[0067] It is essential to evaluate the mechanical performance of flexible pressure sensors, as they need to maintain good flexibility and excellent mechanical performance. Figure 4 -a is the pressure-strain curve of MS without attached sensitive material, which can be divided into three stages. The first stage is when the strain is less than 20%, the increase in pressure is mainly due to the resistance between the sponge skeletons. The second stage is when the strain is between 20% and 60%, the increase in pressure is significantly slower than the first stage, which is because the increase in pressure in this stage is mainly due to the compression of the sponge internal porous skeleton. The third stage is when the strain is greater than 60%, the pressure increases rapidly, because the air in the sponge pores is basically discharged.

[0068] Figure 4 -b is the pressure-strain curve of MXene / CB-SR@MS sensor. At the same strain, the pressure of MXene / CB-SR@MS sensor is significantly greater than that of pure MS. Figure 4 -c, the pressure hysteresis of the sensor is 21.7%.Figure 4 -d is the continuous 60 times loading-unloading test of MXene / CB-SR@MS pressure sensor at 40% strain. It can be seen that the pressure curve of sponge loading decreases slightly, which is because of the relaxation characteristics of sponge as a porous block structure, but the pressure curve of unloading is basically coincided and the pressure value at 40% strain is almost the same, which benefits from the enhancement of the mechanical properties of the sensor by the modified sponge and SR buffer layer.

[0069] (2) Sensing performance test

[0070] Figure 5 -a reflects that the response of the sensor electrical signal can be divided into four parts. When the pressure is less than 2 kPa, due to the slight deformation of MS, the connection between part of the skeleton is disconnected, which causes the conductive sensitive material originally in contact to be disconnected, reducing the conductive contact points, making the sensor resistance slightly increase. When the pressure is 2-20 kPa, the collapse of the sponge skeleton leads to the rapid shrinkage of the internal pores, and the conductive material on the internal pore wall contacts each other, resulting in more conductive paths, which leads to a significant decrease in resistance. Because of the existence of pores, the sensor can show obvious resistance signal response without applying a large force, so the sensitivity reaches a peak (7.44 kPa -1 ) at this stage. When the pressure is 20-80 kPa, the contact between different sponge skeletons is relatively sufficient. With the increase of pressure, the skeleton body is also compressed, at this time the increase of conductive sites in the sponge comes only from the contact of sensitive materials between different skeletons, the number of increased conductive paths decreases, and the sensitivity decreases rapidly. When the pressure is greater than 80 kPa, the sponge skeleton is almost completely contacted. Figure 5 -b is the current signal diagram of MXen / CBe-SR@MS pressure sensor when applying -1V to 1V voltage signal under different pressures. The slope of the curve increases with the increase of pressure. When the pressure is small, the slope of the I-V curve changes slowly. When the pressure is constant, the slope of the curve basically remains unchanged, indicating that the sensor has good linearity and reliability.

[0071] Figure 6 -a reflects that the response time and recovery time of the sensor are 150 ms and 180 ms respectively, and when the pressure is released, the current quickly reaches the initial value and remains stable. This shows that the sponge sensor can quickly release the internal potential energy after the pressure is released, and there is little pressure relaxation.

[0072] From Figure 6 -b it can be seen that the initial value of the current recovered after repeated compression of the sensor is also relatively stable. In order to determine whether the sensor has creep, the pressure is applied to the sensor and kept for a certain time Figure 6-c), it can be found that the resistance of the sensor has changed, and according to the definition of creep (AR / time), the sensor has a creep of 0.31.

[0073] 3700 loading-unloading tests were carried out at 10 kPa Figure 6 -d) After a long time of loading, the resistance response of the sensor remains stable, indicating that the sensor has excellent stability and broad application prospects. Compared with other sponge pressure sensors, the MXene / CB-SR@MS sensor has the advantages of large measurement range and high sensitivity.

[0074] II. Application research of MXene / CB-SR@MS flexible wearable pressure sensor

[0075] 1) Human physiological signal detection

[0076] The MXene / CB-SR@MS sensor has the performance advantages of wide measurement range and high sensitivity, and can be used to detect various human motion signals. In this type of test, the sensor is packaged with PI tape on the skin contact surface and the side of the sensor to ensure that the tester's skin does not come into contact with the sensitive material. As shown in Figure 7 -a, the sensor is fixed on the radial artery of the adult male's wrist with insulating tape, and a relatively stable current response waveform can be received. Analysis and calculation of the waveform show that the tester's pulse signal frequency is 78 times / min, which is within the normal range in a calm state. The three characteristic peaks of the pulse in the enlarged waveform, namely the impact wave (P), the tidal wave (T) and the diastolic wave (D), can be used to evaluate the human cardiovascular health status. The sensor's response to finger bending was also investigated.

[0077] Figure 7 -b and Figure 7 -c reflects that as the degree of finger bending increases, the resistance response of the sensor increases. Therefore, by judging the size of the response signal, it is easy to determine the bending of the finger. In addition, the MXene / CB-SR@MS sensor also has good repeatability at the same finger bending angle. In addition, the sensor can also detect the pressure signal when the elbow is bent Figure 7 -d).

[0078] Small strain motion monitoring based on micro-pressure signals is also particularly important in human physiological signal detection. Figure 7 -e is the monitoring of human deep and shallow breathing behavior by a sponge sensor fixed on a mask. The action of breathing will cause a small deformation of the mask, which in turn will exert pressure on the sensor. According to the frequency of the response signal, it can be judged whether the tester is performing deep or shallow breathing and the specific frequency indicators of breathing. The above results reflect the potential value of the sensor in the application of human physiological motion detection systems.

[0079] 2) Human gait signal detection

[0080] Six MXene / CB-SR@MS sensors were distributed on the heel, midfoot, and forefoot, respectively defined as S1-S6. Due to the less pressure exertion on the midfoot and heel during gait, one sensor was placed on each. In the forefoot, four sensors were placed to improve the resolution of foot pressure measurement at the initial and final stages of walking, which played a key role in analyzing gait. Figure 8 In addition, the super low density of the sponge did not bring extra burden to the tester's foot, causing gait changes.

[0081] During walking, a gait cycle consists of five phases, namely initial ground contact, support reaction, midfoot support, post-support, and swing. Figure 9 The dynamic response of the sensor array for plantar gait detection based on MXene / CB-SR@MS sensors (swing leg is the dark leg in the figure). The response time of the sensor during walking is about 0.1-0.2 s.

[0082] Running is a kind of movement similar to walking, but the movement speed is faster. The step frequency is smaller, and the foot will be subjected to greater pressure, showing greater resistance response. Compared with walking, the impact of the heel in the running state is more instantaneous. Figure 10 It reflects that the time spent from the beginning to the end of the movement is shorter, which indicates that the foot is on the ground for a very short time.

[0083] Figure 11 is the detection situation of the state of climbing stairs. First, the full foot is shown to be in contact with the ground, but the resistance response of the sensors at different parts of the forefoot is different. In other stages, the pressure on the forefoot is similar to that in the walking state, and the forefoot bears more pressure than the midfoot and heel, so the resistance response of the sensor is also higher than that in the walking state. Compared with other walking states, the bending of the human foot in the state of climbing stairs will be significantly reduced, which is reflected in the output of the sensor as a more obvious step-shaped resistance response.

[0084] In summary, the MXene / CB-SR@MS flexible pressure sensor has great application potential in smart wearable devices and human motion detection.

[0085] The stability and reliability of the MXene / CB-SR@MS flexible pressure sensor bring the possibility for human physiological detection and motion monitoring. In summary, the MXene / CB-SR@MS sponge flexible pressure sensor has great application potential in smart wearable devices and human motion detection.

[0086] The above description of disclosed embodiments enables one of ordinary skill in the art to make or use the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An MXene-based SR@MS sponge, characterized in that, The MXene-based SR@MS sponge is a MXene / CB-SR@MS sponge, which is prepared by coating MXene / CB composite material on the SR@MS sponge framework through solution immersion and low-temperature drying method. The MXene / CB composite material is that CB nanoparticles are deposited on MXene nanosheets by electrostatic adsorption, and the MXene nanosheets are obtained by selectively etching Ti3AlC2 with hydrochloric acid / lithium fluoride etching solution.

2. A method of preparing a MXene-based SR@MS sponge according to claim 1, characterized in that, The method specifically comprises the following steps: 1) First, MXene nanosheets are obtained by selectively etching Ti3AlC2 with hydrochloric acid / lithium fluoride etching solution, and then dispersed MXene solution is obtained by ultrasonic and centrifugal treatment; 2) CB nanoparticles are stirred in deionized water, then the MXene solution prepared in step 1) is added and mixed, and a MXene / CB composite solution is obtained after heating and stirring, which is ready for use; 3) Tris(hydroxymethyl)aminomethane is dissolved in distilled water, and dopamine (DA) is added and stirred to dissolve; MS is placed in the solution, and under the action of tris(hydroxymethyl)aminomethane, DA is self-polymerized on the surface of the MS framework and forms polydopamine PDA, thereby obtaining PDA-modified MS; 4) The SR@MS porous sponge prepared in step 3) is immersed in the MXene / CB composite solution obtained in step 2), and then soaked in an SR / ligroin solution, dried and repeated the above operation, so that the MXene / CB composite material and SR are coated on the SR@MS sponge framework by layer-by-layer self-assembly method, and finally the MXene / CB-SR@MS sponge, i.e. the MXene-based SR@MS sponge, is obtained.

3. The method of claim 2, wherein the MXene-based SR@MS sponge is prepared by the steps of: In step 1), the operation of selectively etching Ti3AlC2 to obtain MXene nanosheets with hydrochloric acid / lithium fluoride etching solution is as follows: Ti3AlC2 is added to the pre-cooled LiF / HCl solution in batches and stirred to react, then washed and centrifuged until the pH value of the supernatant is stable at 5-7, the obtained precipitate is dispersed in deionized water, and ultrasonic treatment is carried out under argon protection, then centrifuged, separated, and the upper clear liquid is collected to obtain a high-purity MXene nanosheet solution.

4. The method of claim 3, wherein the MXene-based SR@MS sponge is prepared by the steps of: In the LiF / HCl solution, the mass ratio of lithium fluoride to hydrochloric acid is 1:(4.8-5.2); the mass ratio of the LiF / HCl solution to Ti3AlC2 is (5.2-5.5):1, the temperature of the whole reaction mixture is maintained at 40-50℃, and continuous stirring is ensured for 24 hours within this temperature range.

5. The method of claim 2, wherein the MXene-based SR@MS sponge is prepared by the steps of: In step 2), the mass ratio of CB to MXene solution is (0.1-0.5):5; the concentration of the MXene solution is 10 mg / mL, and the mass ratio of CB to MXene nanosheet is (2-10):1; the MXene / CB mixed solution is mechanically stirred for 30-60 min, and then ultrasonic treatment is carried out for 15-30 min.

6. The method of claim 2, wherein the MXene-based SR@MS sponge is prepared by the steps of: Tris(hydroxymethyl)aminomethane is dissolved in distilled water to keep the pH value at 8-9; the MS is immersed in the solution at room temperature for 1-3 h; under the action of tris(hydroxymethyl)aminomethane, DA on the surface of the MS skeleton is self-polymerized to form a polydopamine (PDA) adhesion layer.

7. The method of claim 2, wherein the MXene-based SR@MS sponge is prepared by the steps of: In step 4), the mass ratio of the silicone rubber to the naphtha in the SR / naphtha solution is (1-3):1; the immersion time is 0.5-2 h, the drying temperature is 60-80℃, and the drying time is 4-8 h.

8. Use of the MXene-based SR@MS sponge according to claim 1 or the MXene-based SR@MS sponge prepared by the method according to claim 2 in a flexible wearable pressure sensor.

9. Use according to claim 8, characterized in that, The MXene-based SR@MS sponge can be used in a flexible wearable pressure sensor for human physiological signal detection.

10. Use according to claim 8, characterized in that, The MXene-based SR@MS sponge can be used in a wearable sensor for detecting joint activities of various parts of the human body. The MXene-based SR@MS sponge can be used in a wearable sensor for detecting joint activities of various parts of the human body.

Images