Flexible self-repairing piezoresistive pressure sensor and preparation method and application thereof

Abstract

The invention discloses a flexible self-repairing pressure sensor and a preparation method and application thereof.A conductive hydrogel part of the sensor uses a polyvinyl alcohol and gelatin dual-network as a flexible base material, a borate dynamic covalent bond as a self-repairing bridge, and a helical carbon nanotube with silver chemically deposited on the surface as a conductive filler; and packaging with a copper electrode and an insulating tape to obtain the self-repairable flexible piezoresistive pressure sensor. The conductive network of the hydrogel is deformed by applying an external force, so that a resistance change signal of the hydrogel is formed, a physiological signal of a human body is monitored, and the hydrogel becomes one of elements of the flexible wearable electronic equipment.

Description

Technical Field

[0001] The present invention relates to the field of piezoresistive flexible pressure sensors, and in particular to a flexible self-repairing piezoresistive pressure sensor and a preparation method and application thereof. Background Art

[0002] With the advancement of digital smart medical and manufacturing industries, the flexibility and deformability of flexible wearable devices are better adapted to the current needs for monitoring human movement and health signals. In flexible wearable devices, a key component is the flexible pressure sensor used for pressure detection.

[0003] Pressure sensors are devices that sense pressure signals and convert force signals into electrical signals for output. Traditional pressure sensors are usually made of rigid materials such as metals or semiconductors, can only withstand small strains, have small pressure detection ranges and sensing ranges, and are bulky and inflexible, limiting their application in actual health testing. Flexible pressure sensors are usually made of supporting materials and active materials. They have great adaptability to various substrates and can accurately monitor human physiological and motion signals in real time. Common pressure sensors include capacitive, piezoelectric, and piezoresistive types, each with different sensing mechanisms and characteristics. Piezoresistive sensors have the characteristics of high sensitivity and good dynamic stability.

[0004] Pressure sensors made of flexible substrates have greater mechanical flexibility and can adapt to different working environments to a certain extent, meeting the human body's deformation requirements for equipment. The Chinese invention patent with publication number CN 115901031 A and titled "A method for preparing a flexible pressure sensor and its application" uses TPU as a flexible substrate material and carbon black as a conductive filler to prepare a flexible pressure sensor, and performs an array design to achieve recognition of different walking states such as walking, running, and standing upright. Summary of the invention

[0005] The main purpose of the present invention is to provide a flexible self-repairing pressure sensor, which, under the premise of meeting the deformation requirements of the human body for the equipment, achieves the improvement of conductivity and sensing performance by depositing nanosilver particles on the conductive filler, and has good anti-oxidation performance; through the self-repairing ability of the material, the reliability and durability of the flexible pressure sensor are increased, and the expansion of tiny cracks during use, which may cause device breakage and damage, is avoided.

[0006] To achieve the above-mentioned purpose of the invention, the technical solution of the present invention is as follows:

[0007] The first object of the present invention is to provide a method for preparing a flexible self-healing piezoresistive pressure sensor, comprising the following steps:

[0008] Step 1, synthesizing a spiral carbon nanotube with chemically deposited silver on the surface;

[0009] Step 2, preparing a self-healing polyvinyl alcohol and gelatin conductive hydrogel loaded with the above-mentioned spiral carbon nanotubes;

[0010] Step 3, cutting the conductive hydrogel and placing it on a conductive copper electrode, and connecting the copper wire to the electrode and leading it out;

[0011] Step 4: Use insulating tape to encapsulate the above device to obtain a flexible self-repairable piezoresistive pressure sensor.

[0012] As a preferred embodiment, in the method for preparing the flexible self-healing piezoresistive pressure sensor, in step 1, the synthesis step of the spiral carbon nanotubes with chemically deposited silver on the surface is:

[0013] 273 mg of helical carbon nanotubes were dispersed in 200 mL of a sodium citrate solution with a concentration of 0.039 mol / L and ultrasonically treated for 15 min. The mixed solution was transferred to 300 mL of water, heated to boiling under stirring, and then 25 mL of a silver nitrate solution with a concentration of 0.03 mol / L was added and kept boiling for 5 min. The suspension was filtered, washed, and dried to obtain helical carbon nanotubes with chemically deposited silver on the surface.

[0014] As a preferred embodiment, in the method for preparing the flexible self-healing piezoresistive pressure sensor, in step 1, in the synthesis of the spiral carbon nanotubes with chemically deposited silver on the surface, the volume ratio of sodium citrate to silver nitrate is 8:1.

[0015] As a preferred embodiment, in the method for preparing the flexible self-healing piezoresistive pressure sensor, in step 2, the synthesis steps of the self-healing polyvinyl alcohol and gelatin conductive hydrogel are:

[0016] A 30 mL polyvinyl alcohol solution with a concentration of 230 g / L and a 13 mL gelatin solution with a concentration of 354 g / L are mixed and stirred at 55° C. for 30 min, 0.273 g to 0.546 g of the spiral carbon nanotubes with surface chemically deposited silver prepared in step 1 are added, stirred, and then 0.04 mol / L sodium tetraborate solution is added dropwise until a gel-like substance is formed, thereby obtaining a polyvinyl alcohol and gelatin conductive hydrogel.

[0017] As a preferred embodiment, in the method for preparing the flexible self-healing piezoresistive pressure sensor, in step 2, the content of the spiral carbon nanotubes in the polyvinyl alcohol and gelatin conductive hydrogel is 0.5wt%-1wt%.

[0018] As a preferred embodiment, in the method for preparing the flexible self-healing piezoresistive pressure sensor, in step 3, the conductive hydrogel is cut into 20 mm×20 mm and placed on a conductive copper electrode, and the copper wire is connected to the electrode and led out.

[0019] The second object of the present invention is to provide a flexible self-healing piezoresistive pressure sensor obtained by the preparation method, comprising two layers of insulating tape, a layer of conductive hydrogel between the two layers of insulating tape and a layer of conductive copper electrode, the conductive copper electrode is attached to one side of the conductive hydrogel, two copper wires are connected to the copper electrode and led out to connect to an external device to collect signals; the conductive hydrogel is a self-healing polyvinyl alcohol and gelatin conductive hydrogel loaded with spiral carbon nanotubes, and silver is chemically deposited on the surface of the spiral carbon nanotubes.

[0020] The third object of the present invention is to provide an application of a flexible self-healing piezoresistive pressure sensor in monitoring human physiological signals: the packaged flexible self-healing piezoresistive pressure sensor is attached to different parts of the human body, and the electrode copper wire in the sensor is led out to an external electrical signal acquisition device to detect the change in the relative resistance of the sensor when different parts move.

[0021] The conductive hydrogel part of the sensor uses a double network of polyvinyl alcohol and gelatin as a flexible matrix material, a borate dynamic covalent bond as a self-healing "bridge", and a spiral carbon nanotube with chemically deposited silver on the surface as a conductive filler. After being packaged with copper electrodes and insulating tape, a self-healing flexible piezoresistive pressure sensor is obtained. The conductive network of the hydrogel is deformed by applying external force, thereby forming a resistance change signal of the gel, and then monitoring human physiological signals, becoming one of the components of flexible wearable electronic devices.

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

[0023] A flexible self-healing piezoresistive pressure sensor of the present invention adopts polyvinyl alcohol and gelatin as matrix materials, a borax solution as a cross-linking agent, and spiral carbon nanotubes with chemically deposited silver on the surface as conductive fillers. Each preparation method is simple, the raw materials are easily available, and the reaction time is short. Silver particles are deposited on the spiral carbon nanotubes to increase the conductivity of the material. The composite hydrogel has excellent mechanical properties, short response time and reliable signal output, and can monitor physiological signals of various parts of the human body. The dynamic borate bonds between polyvinyl alcohol and borax hydrolyzate, and the chain entanglement and hydrogen bonds between gelatin and the polyvinyl alcohol matrix provide short-time self-healing performance, thereby increasing the durability and reliability of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a scanning electron microscope image of the surface chemically deposited silver helical carbon nanotubes of the present invention;

[0025] Figure 2A schematic diagram of the sensor package of the present invention;

[0026] Figure 3 The stress-strain diagram of the hydrogel before and after self-healing of the present invention is a tensile comparison;

[0027] Figure 4 It is the sensitivity diagram of the sensor of the present invention;

[0028] Figure 5 It is the static stability diagram of the sensor of the present invention;

[0029] Figure 6 This is a resistance-time variation diagram of the sensor of the present invention when the finger is bent;

[0030] Figure 7 This is a time diagram of the response of the sensor of the present invention to a force signal. DETAILED DESCRIPTION

[0031] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0032] The embodiment provides a method for preparing a flexible self-healing piezoresistive pressure sensor, comprising the following steps:

[0033] Step 1, synthesizing a spiral carbon nanotube with chemically deposited silver on the surface;

[0034] Step 2, preparing a self-healing polyvinyl alcohol and gelatin conductive hydrogel loaded with the above-mentioned spiral carbon nanotubes;

[0035] Step 3, cutting the conductive hydrogel and placing it on a conductive copper electrode, and connecting the copper wire to the electrode and leading it out;

[0036] Step 4: Use insulating tape to encapsulate the above device to obtain a flexible self-repairable piezoresistive pressure sensor.

[0037] In some embodiments: In step 1, the synthesis steps of the spiral carbon nanotubes with chemically deposited silver on the surface are:

[0038] 273 mg of helical carbon nanotubes were dispersed in 200 mL of a sodium citrate solution with a concentration of 0.039 mol / L and ultrasonically treated for 15 min. The mixed solution was transferred to 300 mL of water, heated to boiling under stirring, and then 25 mL of a silver nitrate solution with a concentration of 0.03 mol / L was added and kept boiling for 5 min. The suspension was filtered, washed, and dried to obtain helical carbon nanotubes with chemically deposited silver on the surface.

[0039] In some embodiments: In step 1, in the synthesis of the spiral carbon nanotubes with chemically deposited silver on the surface, the volume ratio of sodium citrate to silver nitrate is 8:1.

[0040] In some embodiments: In step 2, the synthesis steps of the self-healable polyvinyl alcohol and gelatin conductive hydrogel are:

[0041] A 30 mL polyvinyl alcohol solution with a concentration of 230 g / L and a 13 mL gelatin solution with a concentration of 354 g / L are mixed and stirred at 55° C. for 30 min, 0.273 g to 0.546 g of the spiral carbon nanotubes with surface chemically deposited silver prepared in step 1 are added, stirred, and then 0.04 mol / L sodium tetraborate solution is added dropwise until a gel-like substance is formed, thereby obtaining a polyvinyl alcohol and gelatin conductive hydrogel.

[0042] In some embodiments: in step 2, the content of the spiral carbon nanotubes in the polyvinyl alcohol and gelatin conductive hydrogel is 0.5wt%-1wt%.

[0043] In some embodiments: in step 3, the conductive hydrogel is cut into pieces of 20 mm×20 mm and placed on a conductive copper electrode, and a copper wire is connected to the electrode and led out.

[0044] Some embodiments provide a flexible self-healing piezoresistive pressure sensor obtained by the preparation method, comprising two layers of insulating tape, a layer of conductive hydrogel between the two layers of insulating tape, and a layer of conductive copper electrode, the conductive copper electrode is attached to one side of the conductive hydrogel, two copper wires are connected to the copper electrode and led out to connect to an external device to collect signals; the conductive hydrogel is a self-healing polyvinyl alcohol and gelatin conductive hydrogel loaded with spiral carbon nanotubes, and silver is chemically deposited on the surface of the spiral carbon nanotubes.

[0045] Some embodiments provide the application of flexible self-healing piezoresistive pressure sensors in monitoring human physiological signals: a packaged flexible self-healing piezoresistive pressure sensor is attached to different parts of the human body, and part of the electrode copper wire in the sensor is led out to an external electrical signal acquisition device to detect changes in the relative resistance of the sensor when different parts move.

[0046] Example 1

[0047] 1) Preparation of surface chemically deposited silver helical carbon nanotubes:

[0048] Prepare 1 wt% sodium citrate solution: completely dissolve 2 g of trisodium citrate dihydrate in 198 mL of deionized water. Prepare 1 wt% silver nitrate solution: completely dissolve 0.25 g of silver nitrate in 24.75 mL of deionized water for later use.

[0049] Take 273 mg of spiral carbon nanotubes and disperse them in 200 mL of sodium citrate solution and ultrasonicate for 15 minutes. Add 300 mL of deionized water to make the system volume 500 mL. Wrap the beaker with tin foil and place it on a hot plate to heat it to boiling. Add 25 mL of silver nitrate solution to the solution and keep boiling for 5 minutes. After cooling to room temperature, the mixed solution is filtered, washed, and dried to obtain 273 mg of spiral carbon nanotubes with chemically deposited silver on the surface. Its microscopic morphology is as follows: Figure 1 shown.

[0050] 2) Preparation of conductive hydrogel:

[0051] 7g of polyvinyl alcohol particles were dissolved in 30mL of water by stirring at 95℃ for 2h, and then 273mg of spiral carbon nanotubes with chemically deposited silver on the surface were added and stirred until the material was evenly dispersed; 4.6g of gelatin particles were dissolved in 13mL of water by stirring at 55℃ for 30min; the two solutions were mixed and stirred until the two solutions were evenly mixed. 0.04mol / L sodium tetraborate solution was slowly added to the mixture under continuous stirring until a uniform gel material was completely formed.

[0052] 3) Packaging of flexible pressure sensor:

[0053] Cut the conductive hydrogel into 20mm×20mm pieces and place them on the conductive electrodes. Connect copper wires to both ends of the electrodes and lead out the copper wires. Use insulating tape to encapsulate the above device. The schematic diagram is shown in the figure. Figure 2 As shown, a flexible and self-repairable piezoresistive pressure sensor is obtained.

[0054] The hydrogel prepared by the above method was subjected to a stretching test:

[0055] The hydrogel was placed in a national standard type 2 dumbbell-shaped mold for hot pressing, and the dumbbell-shaped hydrogel was used to test the tensile properties of the universal testing machine to obtain the tensile stress-strain curve before self-healing; the fracture of the stretched sample was placed in contact for 2 hours and then the tensile properties were measured again to obtain the tensile stress-strain curve after self-healing, as shown in FIG. Figure 3 As shown in the figure, the sample after 2h of self-healing has a much higher tensile property than that before self-healing because the polymer content of the system increases after water loss.

[0056] The flexible pressure sensor prepared by the above method was tested:

[0057] The sensor is pasted on the fixed panel, and the sensor electrode is connected to a digital multimeter using copper wire to measure the resistance change. The sensitivity and linear range are obtained by pasting the weighing sensor on the front end of the servo electric cylinder and hitting the sensor active layer with different pressures to obtain different resistance change rates under different pressures, such as Figure 4As shown. The horizontal axis of the curve is pressure, the vertical axis is the relative resistance change rate, and the slope is the sensitivity of the sensor. After linear fitting, the sensitivity in a certain pressure range can be obtained. The sensitivity of the sensor is 0.00181kPa after linear fitting of the curve in the pressure range of 0-25kPa. -1 , the linearity is 0.92.

[0058] To test its static stability, place the sensor still, connect the wire to a digital multimeter to measure its resistance change, and obtain a resistance-time curve, such as Figure 5 As shown in the figure, the sensor has good static stability. To test its feedback on human physiological signals, the sensor is placed on the back of the hand, and the five fingers are repeatedly stretched and bent. The resistance change of the sensor is monitored as follows: Figure 6 Amplify one of the peaks of the dynamic resistance change to see the sensor's response time to the force signal, as shown in Figure 7 As shown, it can be seen that the response time of the sensor is 42ms.

[0059] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing a flexible self-repairing piezoresistive pressure sensor, characterized in that: The following steps are involved: Step 1, synthesizing a spiral carbon nanotube with chemically deposited silver on the surface; Step 2, preparing a self-healing polyvinyl alcohol and gelatin conductive hydrogel loaded with the above-mentioned spiral carbon nanotubes; Step 3, cutting the conductive hydrogel and placing it on a conductive copper electrode, and connecting the copper wire to the electrode and leading it out; Step 4: Use insulating tape to encapsulate the above device to obtain a flexible self-repairable piezoresistive pressure sensor.

2. The method for preparing the flexible self-repairing piezoresistive pressure sensor according to claim 1, characterized in that: In step 1, the synthesis steps of the spiral carbon nanotubes with chemically deposited silver on the surface are: 273 mg of helical carbon nanotubes were dispersed in 200 mL of a sodium citrate solution with a concentration of 0.039 mol / L and ultrasonically treated for 15 min. The mixed solution was transferred to 300 mL of water, heated to boiling under stirring, and then 25 mL of a silver nitrate solution with a concentration of 0.03 mol / L was added and kept boiling for 5 min. The suspension was filtered, washed, and dried to obtain helical carbon nanotubes with chemically deposited silver on the surface.

3. The method for preparing the flexible self-healing piezoresistive pressure sensor according to claim 2, characterized in that: In step 1, in the synthesis of the spiral carbon nanotubes with chemically deposited silver on the surface, the volume ratio of sodium citrate to silver nitrate is 8:

1.

4. The method for preparing the flexible self-repairing piezoresistive pressure sensor according to claim 1, characterized in that: In step 2, the synthesis steps of the self-healing polyvinyl alcohol and gelatin conductive hydrogel are: A 30 mL polyvinyl alcohol solution with a concentration of 230 g / L and a 13 mL gelatin solution with a concentration of 354 g / L are mixed and stirred at 55° C. for 30 min, 0.273 g to 0.546 g of the spiral carbon nanotubes with surface chemically deposited silver prepared in step 1 are added, stirred, and then 0.04 mol / L sodium tetraborate solution is added dropwise until a gel-like substance is formed, thereby obtaining a polyvinyl alcohol and gelatin conductive hydrogel.

5. The method for preparing the flexible self-repairing piezoresistive pressure sensor according to claim 1, characterized in that: In step 2, the content of the spiral carbon nanotubes in the polyvinyl alcohol and gelatin conductive hydrogel is 0.5wt%-1wt%.

6. The method for preparing the flexible self-repairing piezoresistive pressure sensor according to claim 1, characterized in that: In step 3, the conductive hydrogel is cut into pieces of 20 mm×20 mm and placed on a conductive copper electrode. The copper wire is connected to the electrode and led out.

7. The flexible self-healing piezoresistive pressure sensor obtained by the preparation method according to any one of claims 1 to 6, characterized in that: The invention comprises two layers of insulating tape, a layer of conductive hydrogel between the two layers of insulating tape and a layer of conductive copper electrode, wherein the conductive copper electrode is attached to one side of the conductive hydrogel, and two copper wires are connected to the copper electrode and led out to connect to an external device for collecting signals; the conductive hydrogel is a self-repairable polyvinyl alcohol and gelatin conductive hydrogel loaded with spiral carbon nanotubes, and silver is chemically deposited on the surface of the spiral carbon nanotubes.

8. Application of the flexible self-healing piezoresistive pressure sensor according to claim 7 in monitoring human physiological signals, characterized in that: The packaged flexible self-healing piezoresistive pressure sensor is attached to different parts of the human body. The electrode copper wire in the sensor is connected to an external electrical signal acquisition device to detect the change in the relative resistance of the sensor when different parts move.

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