Preparation method and application of pressure and humidity integrated flexible sensor based on MXene

Abstract

The invention discloses a preparation method and application of a pressure and humidity integrated flexible sensor based on MXene, and relates to the field of pressure sensors and humidity sensors. The preparation method comprises the following steps: firstly, preparing MXene dispersion liquid; then preparing a template through a laser etching method and using PDMS reverse mold to obtain a PDMS thin film with a micro-bulge structure, then spraying an MXene dispersion liquid on the PDMS thin film, and obtaining a pressure sensing sensitive layer (MXene-PDMS) after airing; thirdly, three interdigital electrodes are prepared in a magnetron sputtering mode, and the middle electrode and MXene-PDMS are assembled to obtain a pressure sensor; and dispensing MXene dispersion liquid on the other two electrodes, and airing to obtain the humidity sensor. The pressure and humidity integrated flexible sensor has the advantages of being capable of responding to pressure and humidity signals at the same time and high in sensitivity, and the detection accuracy of the sensor is greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of pressure sensors and humidity sensors, and specifically to a preparation method and application of a MXene-based integrated pressure and humidity flexible sensor. Background Art

[0002] With the development of flexible electronic devices, flexible sensors are increasingly used in fields such as health monitoring, motion detection, electronic skin, and flexible robots. Traditional flexible sensors usually have problems such as low integration, complex preparation process, and single detection signal, which makes it difficult to meet the growing market demand. In recent years, in order to broaden the practical application scenarios of flexible sensors, researchers have selected various sensitive materials and used various preparation methods (such as 3D printing, template method, electrospinning, etc.) to develop flexible sensors that can detect multiple signals. However, although these flexible sensors have improved the integration of sensors to a certain extent, they use a variety of sensitive materials and technologies, which makes the preparation process of flexible sensors more complicated and the cost is greatly increased. Therefore, how to use a single sensitive material to prepare a multifunctional flexible sensor is an important issue facing sensors. Summary of the invention

[0003] In order to solve the problem of how to prepare a multifunctional flexible sensor using a single sensitive material, the present invention provides a preparation method and application of a MXene-based pressure and humidity integrated flexible sensor.

[0004] The present invention is achieved through the following technical solution: a method for preparing a MXene-based pressure and humidity integrated flexible sensor, comprising the following steps: 1) Preparation of MXene dispersion: ① In a polytetrafluoroethylene beaker, slowly add 1-2 g of lithium fluoride to 20-25 mL of hydrochloric acid and stir for 30 minutes after the addition is complete; ② Slowly add 2 g MAX-Ti3AlC2 into the liquid product beaker of step ①, adjust the reaction temperature to 35~40℃, and continue stirring for 24~36 h; ③ Centrifuge the reaction liquid obtained in step ② at a speed of 3000-4000 rpm for 8-12 min, pour out the supernatant after centrifugation, continue to add deionized water to the precipitates in multiple centrifuge tubes respectively, mix the precipitates and deionized water evenly, then put the centrifuge tubes into a high-power ultrasonic machine for 10-15 min, take out and continue centrifugation at a speed of 8000-12000 rpm for 8-12 min, repeat several times until the pH value of the supernatant poured out after centrifugation reaches 5-6; ④ Pour out the remaining upper liquid as much as possible, dry the lower sediment in a vacuum oven, add 20-40 mL of ethanol to the centrifuge tube, sonicate for 1 h, centrifuge at 8000-12000 rpm for 8-12 min, and collect the lower sediment; ⑤ Add 20-25 mL of deionized water to the precipitate product centrifuged in step ④, shake well, perform ultrasound for 20-30 min, and then centrifuge at 3000-4000 rpm for 3-5 min to collect the dark brown upper layer as the MXene dispersion; ⑥ Repeat step ⑤ to collect multiple MXene dispersions; ⑦ Take about 8-10 mL of MXene dispersion for suction filtration, vacuum drying, and weighing to obtain the concentration value of MXene dispersion; the concentration value of the prepared MXene dispersion is 4 mg / mL.

[0005] 2) Preparation of electrodes: Using polyimide film as the substrate material, a substrate sheet of the required size is obtained by laser cutting; a mask is covered on the surface of the polyimide substrate, and a thin layer of gold is deposited by magnetron sputtering technology to form the required three interdigital electrodes; the middle interdigital electrode is used as the electrode of the pressure sensor, and the interdigital electrodes on both sides are used as the electrodes of the humidity sensor; 3) Preparation of pressure sensor: ① Fabrication of template and microstructure film: Si wafer was directly patterned by UV laser marking to obtain template, and the adjacent distance of microstructure was 110 µm; then, the produced silicon mold was first surface treated with a release agent; then, PDMS was spin-coated on the silicon mold and cured at 80°C for 1 hour to form a PDMS film, and the PDMS film with micro-protrusion structure was obtained after peeling off the PDMS film; ② Fabrication of the pressure sensing unit: First, the PDMS film with a micro-convex structure is treated with oxygen plasma for 1-2 min to improve its hydrophilicity; then the previously prepared MXene dispersion is sprayed on the PDMS film with a spray gun; after drying, the MXene-PDMS film is cut into squares and assembled with the interdigital electrodes in the middle to obtain a pressure sensing unit; 4) Preparation of humidity sensing unit: First, the interdigital electrodes on both sides of the polyimide substrate were treated with oxygen plasma to improve their hydrophilicity; then the pre-prepared MXene dispersion droplets were coated on the interdigital electrodes on both sides, and then the sample was dried at 60°C for 1 hour to form a humidity sensing unit; 5) Packaging of the integrated pressure and humidity flexible sensor: A thin film with a thickness of about 0.4-0.5 mm is obtained by spin coating PDMS, and then cut into a fixed shape by laser and integrated with the pressure sensing unit prepared in step 3) and the humidity sensing unit prepared in step 4) to obtain an integrated pressure and humidity flexible sensor.

[0006] The present invention provides a method for preparing a MXene-based integrated pressure and humidity flexible sensor, which comprises the following steps: first preparing a MXene dispersion; then preparing a template by laser etching and using PDMS to mold a PDMS film with a micro-convex structure; then spraying the MXene dispersion on the PDMS film, and obtaining a pressure sensing layer (MXene-PDMS) after drying; then preparing three interdigitated electrodes by magnetron sputtering, assembling the middle electrode with MXene-PDMS to obtain a pressure sensor; and then dripping the MXene dispersion on the other two electrodes and drying to obtain a humidity sensor. The pressure and humidity integrated flexible sensor has the characteristics of being able to respond to pressure and humidity signals simultaneously and being highly sensitive.

[0007] Preferably, in step ① of step 3), the thickness of the Si wafer is 500 μm, the release agent is octyltrichlorosilane; and the mass ratio of the main agent and the curing agent of PDMS is 10:1.

[0008] Preferably, in step ② of step 3), the PDMS film with the micro-protrusion structure is treated with oxygen plasma for 1 to 2 min, and the MXene-PDMS film is cut into squares with a side length of 5 to 6 mm.

[0009] The application of the MXene-based pressure and humidity integrated flexible sensor prepared by the above method in the detection of pressure signals and humidity signals can be applied to the detection of the motion state and physiological state of human joints, as well as to electronic skin and flexible robots. Human joints include wrists, elbows, knees, shoulders and elbows, and physiological states include elbow bending and sweat, wrist bending and sweat, carotid artery and neck sweat; when the human body is in motion, the joint movement is accompanied by the evaporation of water vapor on the surface of the human body. The pressure sensing unit and humidity sensing unit in the sensor can detect pressure and humidity signals respectively, which can reflect the motion state and physiological state of the human body.

[0010] In the above application, the principle of pressure sensing is: when the sensing unit is subjected to pressure, the micro-protrusion structure on the MXene-PDMS film is squeezed, and the contact area with the bottom interdigital electrode increases, resulting in an increase in the number of conductive paths, a decrease in resistance, and an increase in current; the change in the current of the pressure sensor can reflect the magnitude of the pressure on the device; the prepared MXene-based integrated pressure and humidity flexible sensor has a pressure detection sensitivity of 1911.75 kPa -1 , the detection range is 0~120 kPa. The principle of humidity sensing is: the oxygen-containing groups on the MXene material interact with water molecules. When the humidity increases, the water molecules will enter between the MXene layers, thereby expanding the interlayer spacing of the MXene, increasing its resistance. Different relative humidity will cause different resistance changes.

[0011] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing a MXene-based integrated pressure and humidity flexible sensor and its application: (1) By giving full play to the excellent conductivity and good hydrophilicity of MXene, a sensitive material and an extremely simple structural system are used to realize the integration of pressure sensor and humidity sensor, thereby improving the portability of the sensor and reducing the cost; (2) The prepared pressure sensing unit and humidity sensing unit have different sensing mechanisms, so there is no need to consider the problem of signal decoupling during detection, which greatly improves the accuracy of sensor detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The figure is a schematic diagram of the preparation process of the pressure and humidity integrated flexible sensor of the present invention.

[0013] Figure 2 This is a SEM photograph of the PDMS microstructure of the present invention, with a micro-protrusion height of 100 μm and a spacing of 110 μm.

[0014] Figure 3 It is a schematic diagram of PDMS cutting for packaging according to the present invention.

[0015] Figure 4 This is a physical picture of the pressure and humidity integrated flexible sensor of the present invention.

[0016] Figure 5 Schematic diagram of pressure sensing principle.

[0017] Figure 6 This is a diagram showing the pressure and humidity signal results of different parts of the human body under different motion states detected by the integrated sensor prepared by the present invention. DETAILED DESCRIPTION

[0018] The present invention is further described below in conjunction with specific embodiments.

[0019] A method for preparing a MXene-based integrated pressure and humidity flexible sensor, the process is as follows Figure 1 As shown, the following steps are included: 1) Preparation of MXene dispersion: ① In a polytetrafluoroethylene beaker, slowly add 1-2 g of lithium fluoride to 20-25 mL of hydrochloric acid and stir for 30 minutes after the addition is complete; ② Slowly add 2 g MAX-Ti3AlC2 into the liquid product beaker of step ①, adjust the reaction temperature to 35~40℃, and continue stirring for 24~36 h; ③ Centrifuge the reaction liquid obtained in step ② at a speed of 3000-4000 rpm for 8-12 min, pour out the supernatant after centrifugation, continue to add deionized water to the precipitates in multiple centrifuge tubes respectively, mix the precipitates and deionized water evenly, then put the centrifuge tubes into a high-power ultrasonic machine for 10-15 min, take out and continue centrifugation at a speed of 8000-12000 rpm for 8-12 min, repeat several times until the pH value of the supernatant poured out after centrifugation reaches 5-6; ④ Pour out the remaining upper liquid as much as possible, dry the lower sediment in a vacuum oven, add 20-40 mL of ethanol to the centrifuge tube, sonicate for 1 h, centrifuge at 8000-12000 rpm for 8-12 min, and collect the lower sediment; ⑤ Add 20-25 mL of deionized water to the precipitate product centrifuged in step ④, shake well, perform ultrasound for 20-30 min, and then centrifuge at 3000-4000 rpm for 3-5 min to collect the dark brown upper layer as the MXene dispersion; ⑥ Repeat step ⑤ to collect multiple MXene dispersions; ⑦ Take about 8-10 mL of MXene dispersion for suction filtration, vacuum drying, and weighing to obtain the concentration value of MXene dispersion; the concentration value of the prepared MXene dispersion is 4 mg / mL.

[0020] 2) Preparation of electrodes: Using polyimide film as the substrate material, a substrate sheet of the required size is obtained by laser cutting; a mask is covered on the surface of the polyimide substrate, and a thin layer of gold is deposited by magnetron sputtering technology to form the required three interdigital electrodes; the middle interdigital electrode is used as the electrode of the pressure sensor, and the interdigital electrodes on both sides are used as the electrodes of the humidity sensor; 3) Preparation of pressure sensor: ① Fabrication of template and microstructure film: Si wafer (500 µm thick) was directly patterned by UV laser marking to obtain a template, and the adjacent distance of the microstructure was 110 µm; then, the resulting silicon mold was first surface treated with a release agent (octyl trichlorosilane); then, PDMS (main agent: curing agent mass ratio of 5:1) was spin-coated on the silicon mold and cured at 80°C for 1 hour to form a PDMS film. After peeling off the PDMS film, a PDMS film with a micro-protrusion structure was obtained, and the cross-sectional scanning electron microscope image is shown in the figure. Figure 2 As shown; ② Fabrication of the pressure sensing unit: First, the PDMS film with a micro-convex structure is treated with oxygen plasma for 1-2 min to improve its hydrophilicity; then the previously prepared MXene dispersion is sprayed on the PDMS film with a spray gun; after drying, the MXene-PDMS film is cut into squares (with a side length of 5-6 mm) and assembled with the interdigital electrodes in the middle to obtain a pressure sensing unit. Figure 3 Schematic diagram of PDMS cutting for packaging; 4) Preparation of humidity sensing unit: First, the interdigital electrodes on both sides of the polyimide substrate were treated with oxygen plasma to improve their hydrophilicity; then the pre-prepared MXene dispersion droplets were coated on the interdigital electrodes on both sides, and then the sample was dried at 60°C for 1 hour to form a humidity sensing unit; 5) Packaging of pressure and humidity integrated flexible sensor: A thin film with a thickness of about 0.4-0.5 mm is obtained by spin coating PDMS, and then cut into a fixed shape by laser and integrated with the pressure sensing unit obtained in step 3) and the humidity sensing unit obtained in step 4) to obtain a pressure and humidity integrated flexible sensor. The obtained sensor structure is as follows: Figure 4 shown.

[0021] The application of the MXene-based integrated pressure and humidity flexible sensor prepared in this embodiment in the detection of pressure signals and humidity signals can be applied to the detection of the motion state and physiological state of human joints, as well as to electronic skin and flexible robots. Human joints include wrists, elbows, knees, shoulders and elbows, and physiological states include elbow bending and sweat, wrist bending and sweat, carotid artery and neck sweat; when the human body is in motion, the joint movement is accompanied by the evaporation of water vapor from the human body surface, and the pressure sensing unit and humidity sensing unit in the sensor can detect pressure and humidity signals respectively, which can reflect the motion state and physiological state of the human body.

[0022] In the above applications, the principle of pressure sensing is as follows Figure 5As shown in the figure, when the sensing unit is subjected to pressure, the micro-protrusion structure on the MXene-PDMS film is squeezed, and the contact area with the bottom interdigital electrode increases, resulting in an increase in the number of conductive paths, a decrease in resistance, and an increase in current; when the pressure is removed, the micro-protrusion structure returns to its initial state, and the resistance and current values ​​also return to their initial values. The change in the current of the pressure sensor can reflect the magnitude of the pressure on the device; the sensitivity of the pressure detection of the prepared MXene-based pressure and humidity integrated flexible sensor is 1911.75 kPa -1 , the detection range is 0~120 kPa. The principle of humidity sensing is: the oxygen-containing groups on the MXene material interact with water molecules. When the humidity increases, the water molecules will enter between the MXene layers, thereby expanding the interlayer spacing of the MXene, increasing its resistance. Different relative humidity will cause different resistance changes.

[0023] like Figure 6 As shown, the integrated pressure and humidity flexible sensors are attached to the elbow, wrist and carotid artery of the human body respectively to detect real-time information about the body's activity status: (a) the pressure signal generated at the elbow (walking state); (b) the humidity signal generated at the elbow (static state, walking state and running state respectively); (c) the pressure signal detected when the wrist is bent to different states; (d) the humidity signal generated at the wrist (static state, walking state and running state respectively); (e) the pressure signal generated at the carotid artery (static state, walking state and running state respectively); (f) the humidity signal generated at the carotid artery (static state, walking state and running state respectively).

[0024] The scope of protection claimed by the present invention is not limited to the above specific embodiments. For those skilled in the art, the present invention may have various deformations and changes. Any modifications, improvements and equivalent substitutions made within the concept and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a MXene-based integrated pressure and humidity flexible sensor, characterized in that: The steps include: 1) Preparation of MXene dispersion: ① In a polytetrafluoroethylene beaker, add 1-2 g lithium fluoride to 20-25 mL hydrochloric acid and stir for 30 minutes after the addition is complete; ② Add 2 g MAX-Ti3AlC2 into the liquid product beaker of step ①, adjust the reaction temperature to 35~40 ℃, and continue stirring for 24~36 h; ③ Centrifuge the reaction liquid obtained in step ② at a speed of 3000-4000 rpm for 8-12 min, pour out the supernatant after centrifugation, continue to add deionized water to the precipitates in multiple centrifuge tubes respectively, mix the precipitates and deionized water evenly, then put the centrifuge tubes into a high-power ultrasonic machine for 10-15 min, take out and continue centrifugation at a speed of 8000-12000 rpm for 8-12 min, repeat several times until the pH value of the supernatant poured out after centrifugation reaches 5-6; ④ Pour out the remaining upper liquid, dry the lower sediment in a vacuum oven, add 20-40 mL of ethanol to the centrifuge tube, sonicate for 1 h, centrifuge at 8000-12000 rpm for 8-12 min, and collect the lower sediment; ⑤ Add 20-25 mL of deionized water to the precipitate product centrifuged in step ④, shake well, perform ultrasound for 20-30 min, and then centrifuge at 3000-4000 rpm for 3-5 min to collect the dark brown upper layer as the MXene dispersion; ⑥ Repeat step ⑤ to collect multiple MXene dispersions; ⑦ Take about 8-10 mL of MXene dispersion for suction filtration, vacuum drying, and weighing to obtain the concentration of MXene dispersion; 2) Preparation of electrodes: Using polyimide film as the substrate material, a substrate sheet of the required size is obtained by laser cutting; a mask is covered on the surface of the polyimide substrate, and a thin layer of gold is deposited by magnetron sputtering technology to form the required three interdigital electrodes; the middle interdigital electrode is used as the electrode of the pressure sensor, and the interdigital electrodes on both sides are used as the electrodes of the humidity sensor; 3) Preparation of pressure sensor: ① Fabrication of template and microstructure film: Si wafer was directly patterned by UV laser marking to obtain template, and the adjacent distance of microstructure was 110 µm; then, the produced silicon mold was first surface treated with a release agent; then, PDMS was spin-coated on the silicon mold and cured at 80°C for 1 hour to form a PDMS film, and the PDMS film with micro-protrusion structure was obtained after peeling off the PDMS film; ② Fabrication of the pressure sensing unit: First, the PDMS film with a micro-convex structure is treated with oxygen plasma to improve its hydrophilicity; then the previously prepared MXene dispersion is sprayed on the PDMS film with a spray gun; after drying, the MXene-PDMS film is cut into squares and assembled with the interdigital electrodes in the middle to obtain a pressure sensing unit; 4) Preparation of humidity sensing unit: First, the interdigital electrodes on both sides of the polyimide substrate were treated with oxygen plasma to improve their hydrophilicity; then the pre-prepared MXene dispersion droplets were coated on the interdigital electrodes on both sides, and then the sample was dried at 60°C for 1 hour to form a humidity sensing unit; 5) Packaging of the integrated pressure and humidity flexible sensor: A thin film with a thickness of about 0.4-0.5 mm is obtained by spin coating PDMS, and then cut into a fixed shape by laser and integrated with the pressure sensing unit prepared in step 3) and the humidity sensing unit prepared in step 4) to obtain an integrated pressure and humidity flexible sensor.

2. The method for preparing a MXene-based integrated pressure and humidity flexible sensor according to claim 1, characterized in that: The concentration of the MXene dispersion prepared in step 1) is 4 mg / mL.

3. The method for preparing a MXene-based integrated pressure and humidity flexible sensor according to claim 1, characterized in that: In step ① of step 3), the thickness of the Si wafer is 500 µm, the release agent is octyltrichlorosilane; and the mass ratio of the main agent and the curing agent of PDMS is 10:

1.

4. The method for preparing a MXene-based integrated pressure and humidity flexible sensor according to claim 1, characterized in that: In step ② of step 3), the PDMS film with the micro-convex structure is treated with oxygen plasma for 1 to 2 minutes, and the MXene-PDMS film is cut into squares with a side length of 5 to 6 mm.

5. The application of the MXene-based integrated pressure and humidity flexible sensor prepared in claims 1 to 4 in the detection of pressure signals and humidity signals can be applied to the detection of the motion state and physiological state of human joints, as well as to electronic skin and flexible robots.

6. The use according to claim 5, characterized in that: The principle of pressure sensing is: when the sensing unit is subjected to pressure, the micro-protrusion structure on the MXene-PDMS film is squeezed, and the contact area with the bottom interdigital electrode increases, resulting in an increase in the number of conductive paths, a decrease in resistance, and an increase in current; the change in the current of the pressure sensor can reflect the magnitude of the pressure on the device; the prepared MXene-based integrated pressure and humidity flexible sensor has a pressure detection sensitivity of 1911.75 kPa -1 , the detection range is 0~120 kPa.

7. The use according to claim 5, characterized in that: The principle of humidity sensing is: the oxygen-containing groups on the MXene material enable it to interact with water molecules. When the humidity increases, the water molecules will enter between the MXene layers, thereby expanding the interlayer spacing of the MXene, increasing its resistance. Different relative humidity will cause different resistance changes.

8. The use according to claim 5, characterized in that: When applied to the detection of the motion state and physiological state of human joints, the human joints include wrists, elbows, knees, shoulders and elbows; the physiological states include elbow bending and sweat, wrist bending and sweat, carotid artery and neck sweat; when the human body is in motion, the joint movement is accompanied by the evaporation of water vapor from the human body surface, and the pressure sensing unit and humidity sensing unit in the sensor can detect the pressure and humidity signals respectively, which can reflect the motion state and physiological state of the human body.

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