A conductive flexible pressure sensor based on conjugate oriented electrospinning technology and its preparation method

Abstract

The present invention provides a capacitive flexible pressure sensor and a preparation method thereof. The capacitive flexible pressure sensor comprises upper and lower electrode layers, and an oriented nanofiber membrane located between the upper and lower electrode layers. The upper and lower electrode layers are oriented conductive nanofiber membranes, and the oriented conductive nanofiber membranes are obtained by doping the nanofiber membrane with a conductive substance and a proton acid. The capacitive flexible pressure sensor has a wide detection range and can realize pulse monitoring with weak pressure to limb movement monitoring with greater pressure, and can cover the full range of monitoring of human movement. It also has the advantages of high sensitivity, fast response speed, high elongation and elongation at break, good moisture permeability and the like, and can be applied to wearable flexible pressure sensors. In addition, the capacitive flexible pressure sensor has a simple preparation method, low energy consumption, is comfortable to wear, and has good application prospects.

Description

Technical Field

[0001] The present invention relates to the field of wearable electronic skin prepared by flexible sensors, and specifically to a conductive flexible pressure sensor based on conjugate orientation electrospinning technology and a preparation method thereof, which is applied to real-time monitoring of the full range of human motion. Background Art

[0002] With the development of wearable devices, wearable sensing systems for detecting human motion have attracted widespread attention from academia and industry. Among them, capacitive flexible pressure sensors with low cost, ultra-low power consumption, tolerance to temperature changes, high sensitivity and low hysteresis have become one of the research hotspots.

[0003] Although significant progress has been made in the research of capacitive flexible pressure sensors, several challenges remain for their practical application. For example, in terms of microstructure design, commonly used microstructural construction methods, such as photolithography, etching, 3D printing, and natural mold forming, often suffer from high costs, complex processes, difficulties in industrialization, and poor uniformity and tunability. Furthermore, the sensitivity of flexible capacitive pressure sensors decreases when used under high pressure. Therefore, simultaneously improving the sensor's sensitivity and operating range is a key issue in promoting the application of capacitive flexible pressure sensors in certain fields.

[0004] Furthermore, existing flexible capacitive pressure sensors also face the challenge of poor wearing comfort. Since the base materials used in the sensor fabrication process are often non-breathable, human skin cannot breathe when attached to the body, compromising wearer comfort. Therefore, there is a need to develop a capacitive flexible pressure sensor with high sensitivity, a wide detection range, and breathability.

[0005] Nanofiber membranes not only have the advantages of light weight, large specific surface area, good flexibility and rich microstructure, but also have ultra-high porosity, even exceeding 90%, and therefore have become increasingly popular in research. Summary of the Invention

[0006] Based on the above technical background, the inventors have made great progress and found that: an oriented thermoplastic elastomer polyurethane nanofiber membrane is immersed in a solution obtained by aniline and protonic acid, and then an initiator is added to react to obtain an oriented conductive nanofiber membrane. The oriented conductive nanofiber membrane is placed on the upper and lower layers of the nanofiber membrane to obtain a capacitive flexible pressure sensor. The capacitive flexible pressure sensor has high elongation and breaking strength, excellent mechanical properties, and has the advantages of ultra-high sensitivity, fast response speed, and wide detection range. It can realize pulse monitoring from weak pressure to limb movement monitoring with greater pressure, and can realize full-range monitoring of human body movement. In addition, the capacitive flexible pressure sensor also has the advantages of simple preparation method and low energy consumption, thereby completing the present invention.

[0007] A first aspect of the present invention is to provide a capacitive flexible pressure sensor, the capacitive flexible pressure sensor comprising upper and lower electrode layers, and a dielectric layer located between the upper and lower electrode layers;

[0008] The upper and lower electrode layers are oriented conductive nanofiber membranes, which are made of oriented thermoplastic elastomer polyurethane nanofiber membranes, aniline and protonic acid. The dielectric layer is an oriented thermoplastic elastomer polyurethane nanofiber membrane, which is obtained by conjugated oriented electrospinning of a thermoplastic elastomer polyurethane solution.

[0009] A second aspect of the present invention is to provide a method for preparing the capacitive flexible pressure sensor according to the first aspect of the present invention, the method comprising the following steps:

[0010] Step 1: dissolving thermoplastic elastomer polyurethane in a solvent to obtain a spinning solution;

[0011] Step 2: placing the spinning solution in an electrospinning device for conjugate oriented electrospinning to obtain an oriented thermoplastic elastomer polyurethane nanofiber membrane;

[0012] Step 3: immersing the oriented thermoplastic elastomer polyurethane nanofiber membrane in a mixed solution of aniline and protonic acid, and then reacting in the presence of an initiator to obtain an oriented conductive nanofiber membrane;

[0013] Step 4: Assemble the oriented conductive nanofiber membrane and the oriented thermoplastic elastomer polyurethane nanofiber membrane to obtain a capacitive flexible pressure sensor.

[0014] The third aspect of the present invention is to provide an application of the capacitive flexible pressure sensor according to the first aspect of the present invention or the capacitive flexible pressure sensor prepared by the preparation method described in the second aspect of the present invention, which can be applied to a human body monitoring system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of the conjugate electrospinning device used in the present invention is shown;

[0016] Figure 2 SEM images of the oriented conductive nanofiber membranes prepared in Examples 1 to 3 are shown;

[0017] Figure 3 The stress-strain curves of the conductive nanofiber membrane, nanofiber membrane, and capacitive flexible pressure sensor prepared in Example 2 are shown;

[0018] Figure 4 Showing the sensitivity curves of the flexible pressure sensors prepared in Examples 1 to 3;

[0019] Figure 5 A response time curve of the flexible pressure sensor prepared in Example 2 is shown;

[0020] Figure 6 The permeability bar graph of the oriented nanofiber membrane and the flexible pressure sensor prepared in Example 2 is shown;

[0021] Figure 7 A curve diagram showing recognition of large-scale human body motions by the flexible pressure sensor manufactured in Example 2 is shown;

[0022] Figure 8 A curve chart showing recognition of small-amplitude human body motions by the flexible pressure sensor manufactured in Example 2 is shown.

[0023] Explanation of Figure Numbers

[0024] 1- Roller collector;

[0025] 2-conjugate spinning nozzle;

[0026] 3-Syringe pump;

[0027] 4- positive electrode;

[0028] 5-Negative electrode. DETAILED DESCRIPTION

[0029] The present invention will be described in detail below, and the characteristics and advantages of the present invention will become clearer and more distinct with the following description.

[0030] A first aspect of the present invention is to provide a capacitive flexible pressure sensor, which includes upper and lower electrode layers, and a dielectric layer located between the upper and lower electrode layers.

[0031] The upper and lower electrode layers are oriented conductive nanofiber membranes, which are made of oriented thermoplastic elastomer polyurethane nanofiber membranes, aniline and protonic acid. The dielectric layer is an oriented thermoplastic elastomer polyurethane nanofiber membrane, which is obtained by conjugated oriented electrospinning of a thermoplastic elastomer polyurethane solution.

[0032] The conjugate oriented electrospinning of the present invention refers to the deposition of positively charged oriented fibers obtained by positive electrode spinning and negatively charged oriented fibers obtained by negative electrode spinning on a roller collector to form an oriented fiber film.

[0033] In the oriented conductive nanofiber membrane, the mass ratio of aniline to the thermoplastic elastomer polyurethane nanofiber membrane is 1:1 to 1:4, preferably 1:1 to 1:3, and more preferably 1:1 to 1:2.

[0034] The protonic acid is selected from one or more of sulfosalicylic acid, hydrochloric acid, sulfuric acid, acetic acid, and phytic acid, preferably selected from one or more of sulfosalicylic acid, hydrochloric acid, sulfuric acid, and phytic acid, and more preferably sulfosalicylic acid.

[0035] Experiments have shown that the oriented conductive nanofiber membrane prepared using the above-mentioned proton acid has good conductivity. The flexible pressure sensor obtained using the oriented conductive nanofiber membrane as the upper and lower conductive layers has ultra-high sensitivity, extremely short response time, wide detection range and good stability.

[0036] In the oriented conductive nanofiber membrane, the mass ratio of the protonic acid to the oriented thermoplastic elastomer polyurethane nanofiber membrane is 1:1 to 1:4, preferably 1:1 to 1:2, and more preferably 1:1 to 1:1.5.

[0037] The amount of proton acid added will affect the responsiveness of the pressure sensor. Too much or too little proton acid added will reduce the responsiveness of the pressure sensor. When the mass ratio of proton acid to nanofiber membrane is within the above range, the obtained pressure sensor has high sensitivity, fast response speed and wide detection range.

[0038] The mass concentration of the thermoplastic elastomer polyurethane solution is 5 to 30%, preferably 10 to 25%.

[0039] The positive voltage for electrospinning is 5 to 20 kV, preferably 7 to 15 kV, and more preferably 9 to 12 kV.

[0040] The negative voltage for electrospinning is 5 to 20 kV, preferably 7 to 15 kV, and more preferably 9 to 12 kV.

[0041] The spinning angle of the conjugate spinning nozzle is 15° to 75°, preferably 15° to 60°, and more preferably 20° to 50°. The spinning angle of the conjugate spinning nozzle refers to the angle between the conjugate spinning nozzle and the axial direction of the roller collector 1 facing the positive electrode 4.

[0042] The spinning angle of the conjugate spinning negative nozzle is 15° to 75°, preferably 15° to 60°, and more preferably 20° to 50°.

[0043] The spinning angle of the conjugate spinning negative nozzle refers to the angle between the conjugate spinning negative nozzle and the axial direction of the roller collector 1 facing the negative electrode 5.

[0044] The spinning speed is 0.2 to 5 ml / h, preferably 0.5 to 3 ml / h, and more preferably 0.7 to 2 ml / h.

[0045] The roller rotation speed is 1000 to 5000 rpm, preferably 1500 to 4000 rpm, and more preferably 1700 to 3000 rpm.

[0046] The spinning time is 5 to 60 minutes, preferably 5 to 40 minutes, and more preferably 15 to 40 minutes.

[0047] The thickness of the oriented thermoplastic elastomer polyurethane nanofiber membrane is 50 to 600 μm, preferably 50 to 500 μm, and more preferably 150 to 450 μm.

[0048] The thickness of the oriented conductive nanofiber membrane is 50 to 600 μm, preferably 50 to 400 μm, and more preferably 150 to 300 μm.

[0049] The conductivity of the oriented conductive nanofiber membrane is 1×10 -4 ~9×10 -2 S / cm, preferably 9×10 -4 ~9×10 - 2 S / cm, more preferably 5×10 -3 ~9×10 -2 S / cm.

[0050] The inventors have discovered that when the thickness of the oriented thermoplastic elastomer polyurethane nanofiber membrane and the oriented conductive nanofiber membrane is within the above range, the capacitive flexible pressure sensor has excellent sensitivity and a wide sensing range, and can realize pulse monitoring with weak pressure to limb movement monitoring with greater pressure, and can realize monitoring of various human body movements such as finger bending, wrist bending, and elbow bending.

[0051] The capacitive flexible pressure sensor of the present invention adopts a sandwich structure. Based on the large specific surface area of ​​nanofibers and the excellent performance of the material, when stimulated by external force, the capacitive flexible pressure sensor shows high sensitivity and extremely wide sensing range. The sensitivity of the pressure sensor can reach 1.3kPa. -1 The maximum detection range can reach above 120kPa, and the pressure response time is extremely short, with a response time of 40 to 120ms and a recovery time of 40 to 120ms.

[0052] In addition, the strain of the capacitive flexible pressure sensor can reach 1400% to 1700%, and the water vapor permeability is 500 to 700 (g / m 2 , 24h).

[0053] Among the various methods for preparing nanofiber membranes, electrospinning is considered the most effective due to its controllable process, high production efficiency, and low cost. Therefore, this paper proposes using conjugate electrospinning to prepare flexible nanofiber membranes with controllable microstructure and one-dimensional orientation. Conductive particles are then coated onto the flexible nanofiber membranes via in situ polymerization to produce flexible, oriented, conductive nanofiber membranes. Finally, these membranes are assembled into a capacitive flexible pressure sensor with a sandwich structure. The goal is to create a flexible pressure sensor that is simple to prepare, comfortable to wear, and capable of simultaneously improving sensor sensitivity and operating range.

[0054] A second aspect of the present invention is to provide a method for preparing the capacitive flexible pressure sensor according to the first aspect of the present invention, the method comprising the following steps:

[0055] Step 1: dissolving thermoplastic elastomer polyurethane in a solvent to obtain a spinning solution;

[0056] Step 2: placing the spinning solution in an electrospinning device for conjugate oriented electrospinning to obtain an oriented thermoplastic elastomer polyurethane nanofiber membrane;

[0057] Step 3: immersing the oriented thermoplastic elastomer polyurethane nanofiber membrane in a mixed solution of aniline and protonic acid, and then reacting in the presence of an initiator to obtain an oriented conductive nanofiber membrane;

[0058] Step 4: Assemble the oriented conductive nanofiber membrane and the oriented thermoplastic elastomer polyurethane nanofiber membrane to obtain a capacitive flexible pressure sensor.

[0059] This step is described and explained in detail below.

[0060] Step 1: Thermoplastic elastomer polyurethane is dissolved in a solvent to obtain a spinning solution.

[0061] The solvent is selected from one or more of dimethylformamide, tetrahydrofuran, and dichloromethane, and is preferably selected from one or two of dimethylformamide and tetrahydrofuran.

[0062] The mass ratio of dimethylformamide to tetrahydrofuran is 1:(0.1-2), preferably 1:(0.3-1.5), and more preferably 1:(0.5-1.5). Using a mixed solvent with the above mass ratio can completely dissolve the thermoplastic elastomer polyurethane in the solvent, and the diameter of the fibers after spinning is more uniform.

[0063] In the present invention, the relative molecular mass of the thermoplastic elastomer polyurethane is greater than or equal to 90,000, preferably greater than or equal to 120,000.

[0064] When the polymer molecular weight is too low, there is resistance to the jet stretching flow, and the electrospun nanofibers tend to form a beaded structure. Only when the molecular weight reaches the optimal range will the fibers stabilize and form uniform nanofibers. Electrospinning thermoplastic elastomer polyurethane with this relative molecular weight produces uniform, bead-free fibers with a good morphology.

[0065] The dissolution is preferably carried out under magnetic stirring, the dissolution temperature is room temperature, and the stirring time is 5 to 20 hours, preferably 7 to 17 hours, and more preferably 10 to 15 hours. The spinning solution obtained at the above dissolution temperature is more uniform.

[0066] The mass concentration of the spinning solution is 5 to 30%, preferably 10 to 25%.

[0067] Step 2: placing the spinning solution in an electrospinning device for conjugate oriented electrospinning to obtain an oriented thermoplastic elastomer polyurethane nanofiber membrane.

[0068] The spinning solution is placed in Figure 1 Electrospinning is performed in the electrospinning device shown, which includes a roller collector 1, a conjugate spinning nozzle 2, an injection pump 3, a positive electrode 4, and a negative electrode 5. The conjugate spinning nozzle 2 and the injection pump 3 are respectively located between the roller collector 1 and the positive electrode 4 and the negative electrode 5, and the conjugate spinning nozzle 2 is located between the injection pump 3 and the roller collector 1. The conjugate spinning nozzle 2 includes a conjugate spinning positive nozzle and a conjugate spinning negative nozzle, which are symmetrically distributed on both sides of the roller collector 1 at a certain angle, with the conjugate spinning positive nozzle located on the positive electrode 4 side and the conjugate spinning negative nozzle located on the negative electrode 5 side.

[0069] The distance between the positive electrode 4 and the negative electrode 5 is 5 to 30 cm, preferably 10 to 25 cm, and more preferably 10 to 20 cm.

[0070] The distance between the conjugate spinning nozzle 2 and the roller collector 1 is 5 to 30 cm, preferably 10 to 20 cm, and more preferably 12 to 17 cm.

[0071] The spinning voltage includes a positive electrospinning voltage and a negative electrospinning voltage. The positive electrospinning voltage is 5 to 20 kV, preferably 7 to 15 kV, and more preferably 9 to 12 kV.

[0072] The negative voltage for electrospinning is 5 to 20 kV, preferably 7 to 15 kV, and more preferably 9 to 12 kV.

[0073] Under the action of the electric field, the jets at the tips of the two conjugated spinning spinnerets are stretched to form nanofibers with opposite charges. They attract each other and embrace each other. The solvent in them evaporates and solidifies, and finally deposits on the receiver to obtain an oriented nanofiber membrane.

[0074] The spinning angle of the conjugate spinning nozzle is 15° to 75°, preferably 15° to 60°, and more preferably 20° to 50°. The spinning angle of the conjugate spinning nozzle refers to the angle between the conjugate spinning nozzle and the axial direction of the roller collector 1 facing the positive electrode 4.

[0075] The spinning angle of the conjugate spinning negative nozzle is 15° to 75°, preferably 15° to 60°, and more preferably 20° to 50°. The spinning angle of the conjugate spinning negative nozzle refers to the angle between the conjugate spinning negative nozzle and the axial direction of the roller collector 1 facing the negative electrode 5.

[0076] The spinning speed is 0.2 to 5 ml / h, preferably 0.5 to 3 ml / h, and more preferably 0.7 to 2 ml / h.

[0077] The roller rotation speed is 1000 to 5000 rpm, preferably 1500 to 4000 rpm, and more preferably 1700 to 3000 rpm.

[0078] The roller speed and the spinning speed should be maintained within an appropriate ratio. If the roller speed is too high, it will lead to discontinuous spinning, and if the spinning speed is too high, it will lead to shortcomings such as poor uniformity of nanofiber diameter and fiber membrane thickness. When the roller speed and the spinning speed are within the above range, the obtained nanofiber diameter is uniform and the nanofiber membrane thickness is uniform.

[0079] The spinning time is 5 to 60 minutes, preferably 5 to 40 minutes, and more preferably 15 to 40 minutes.

[0080] The spinning time will affect the morphology of the obtained nanofibers. If the spinning time is too long or too short, the uniformity of the nanofiber diameter will decrease. When the spinning time is within the above range, the diameter of the obtained nanofibers is uniform, which is beneficial to improving the response sensitivity of the sensor.

[0081] Step 3: The oriented thermoplastic elastomer polyurethane nanofiber membrane is immersed in a mixed solution of aniline and protonic acid, and then reacted in the presence of an initiator to obtain an oriented conductive nanofiber membrane.

[0082] The protonic acid is selected from one or more of sulfosalicylic acid, hydrochloric acid, sulfuric acid, acetic acid, and phytic acid, preferably selected from one or more of sulfosalicylic acid, hydrochloric acid, sulfuric acid, and phytic acid, and more preferably sulfosalicylic acid.

[0083] Proton acid plays two roles in the reaction process: providing the acidic environment and proton source required for the polymerization reaction. Polyaniline is a conductive polymer, but its intrinsic state is not conductive. Only after being doped with proton acid can the conductivity be greatly improved. The conductivity of the oriented conductive nanofiber membrane after doping is 1×10 -4 ~9×10 -2 S / cm, preferably 9×10 -4 ~9×10 -2 S / cm, more preferably 5×10 -3 ~9×10 -2 S / cm.

[0084] The mass ratio of aniline to protic acid is 1:1 to 1:4, preferably 1:1 to 1:3, and more preferably 1:1 to 1:1.5.

[0085] Aniline and protonic acid are placed in a solvent to obtain a mixed solution of aniline and protonic acid, and the solvent is preferably water.

[0086] The mass ratio of aniline to the oriented thermoplastic elastomer polyurethane nanofiber membrane is 1:1 to 1:4, preferably 1:1 to 1:3, and more preferably 1:1 to 1:2.

[0087] When the mass ratio of aniline to the oriented thermoplastic elastomer polyurethane nanofiber membrane is within the above range, aniline is loaded more evenly on the surface of the nanofiber membrane, and the obtained nanofiber membrane has good conductivity.

[0088] The soaking time is 5 to 60 minutes, preferably 10 to 50 minutes, and more preferably 10 to 40 minutes.

[0089] After soaking, an initiator is added thereto, wherein the initiator is one or more of ammonium persulfate and potassium persulfate, preferably ammonium persulfate.

[0090] The mass ratio of the initiator to the oriented thermoplastic elastomer polyurethane nanofiber membrane is (1-4):1, preferably (1-3):1, and more preferably (1-2):1.

[0091] The reaction is preferably carried out in an ice-water bath, and the reaction time is 1 to 15 hours, preferably 1 to 12 hours, and more preferably 2 to 10 hours.

[0092] Polyaniline is evenly loaded on the surface of the nanofiber membrane. As the reaction time increases, the polyaniline loaded on the surface of the nanofiber membrane gradually increases and is evenly distributed. In addition, experiments have found that the reaction time also affects the sensitivity of the capacitive flexible pressure sensor. The sensitivity of the pressure sensor first increases and then decreases as the reaction time increases. When the reaction time is within the above range, the pressure sensor has excellent sensitivity.

[0093] Step 4: Assemble the oriented conductive nanofiber membrane and the oriented thermoplastic elastomer polyurethane nanofiber membrane to obtain a capacitive flexible pressure sensor.

[0094] Two oriented conductive nanofiber membranes are respectively placed on the upper surface and the lower surface of the oriented thermoplastic elastomer polyurethane nanofiber membrane, and the oriented thermoplastic elastomer polyurethane nanofiber membrane serves as the middle dielectric layer.

[0095] In the capacitive flexible pressure sensor, the thickness of the oriented thermoplastic elastomer polyurethane nanofiber membrane is 50 to 600 μm, preferably 50 to 500 μm, and more preferably 150 to 450 μm.

[0096] The thickness of the oriented conductive nanofiber membrane is 50 to 600 μm, preferably 50 to 400 μm, and more preferably 150 to 300 μm.

[0097] The thickness of the oriented thermoplastic elastomer polyurethane nanofiber membrane and the oriented conductive nanofiber membrane will affect the sensitivity of the pressure sensor. The thickness of the oriented thermoplastic elastomer polyurethane nanofiber membrane should not be too thick, as too thick a nanofiber membrane will lead to reduced sensitivity.

[0098] The third aspect of the present invention is to provide an application of the capacitive flexible pressure sensor according to the first aspect of the present invention or the capacitive flexible pressure sensor prepared by the preparation method described in the second aspect of the present invention, which can be applied to a human body monitoring system.

[0099] The beneficial effects of the present invention are:

[0100] (1) The present invention utilizes simple conjugated electrospinning technology and in-situ chemical polymerization to prepare a flexible oriented conductive nanofiber membrane, which is finally assembled into a sandwich-structured capacitive flexible pressure sensor. The entire preparation process is simple and easy to operate, with a simple process, and also has the advantages of low cost, low energy consumption, and environmental friendliness.

[0101] (2) Thanks to the unique orientation structure of the oriented conductive nanofiber membrane, the conductive flexible pressure sensor based on conjugated electrospinning prepared by the present invention has a large elongation and high breaking strength, and the mechanical properties are effectively improved;

[0102] (3) The capacitive flexible pressure sensor prepared by the present invention has ultra-high sensitivity, which can reach 1.3kPa -1 The above, at the same time, also has the advantages of fast response speed, wide detection range, comfortable and breathable, good stability, etc. The pressure response time is 30 ~ 120ms, the recovery time is 30 ~ 120ms, and the maximum detection range can reach more than 120kPa;

[0103] (4) The capacitive flexible pressure sensor described in the present invention can be used for real-time human health monitoring and full-range human motion monitoring, and is comfortable to wear. In addition, it also has good anti-interference ability against temperature and humidity.

[0104] Example

[0105] The present invention is further described below through specific examples. These examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0106] Example 1

[0107] 4g of thermoplastic polyurethane particles (M W =130,000) was added into 20 mL of a mixed solvent of dimethylformamide and tetrahydrofuran, wherein the mass ratio of dimethylformamide to tetrahydrofuran was 1:1.3, and magnetic stirring was applied at room temperature for 12 h to obtain a uniform and stable spinning solution.

[0108] A conjugated electrospinning device was built as shown in Figure 1, and the thermoplastic elastomer polyurethane spinning solution obtained above was respectively introduced into the conjugated spinning nozzle 2 through the injection pump 3. The injection pump 3 was respectively connected to the positive electrode 4 and the negative electrode 5. The conjugated spinning nozzle 2 was located between the injection pump 3 and the roller receiver 1. The conjugated spinning nozzle 2 included a conjugated spinning positive nozzle and a conjugated spinning negative nozzle. The conjugated spinning positive nozzle was located on the side of the positive electrode 4, and the conjugated spinning negative nozzle was located on the side of the negative electrode 5. The distance between the positive electrode 4 and the negative electrode 5 was 15 cm, and the distance between the conjugated spinning nozzle 2 and the roller receiver 1 was 15 cm. The electrospinning positive voltage and negative voltage were both set to 10 kV, the spinning angles of the conjugated spinning positive nozzle and the conjugated spinning negative nozzle were both 45°, the spinning push speed was 1.0 ml / h, the roller speed was 2000 rpm, and the spinning time was 30 min to obtain a conjugated electrospun TPU pure film.

[0109] 2.3g of ammonium persulfate powder was added to 50mL of deionized water to prepare Solution A. 1.0g of aniline and 1.2g of sulfosalicylic acid were then dissolved in 50mL of deionized water to prepare Solution B. 1.2g of pure conjugated electrospun TPU (thermoplastic elastomer polyurethane) membrane was immersed in Solution B. After the TPU nanofiber membrane was soaked in Solution B for 30 minutes, Solution A was slowly added to Solution B to ensure thorough mixing. The membrane was then reacted in an ice-water bath for 2 hours. The membrane was then removed from the solution, rinsed several times with deionized water, and dried at room temperature to obtain a flexible, oriented, conductive nanofiber membrane.

[0110] The oriented conductive PANI / TPU nanofiber membranes obtained above were used for the upper and lower electrode layers respectively, and the middle dielectric layer was composed of an oriented TPU nanofiber membrane. The thickness of the upper and lower oriented conductive PANI / TPU nanofiber membranes was 300 μm, and the thickness of the conjugated electrospinning oriented TPU pure membrane was 400 μm. The three layers of materials were assembled by ultrasonic welding to form a capacitive flexible pressure sensor with a sandwich structure.

[0111] Example 2

[0112] The capacitive flexible pressure sensor was prepared in a manner similar to Example 1, except that the reaction was carried out in an ice water bath for 4 h.

[0113] Example 3

[0114] The capacitive flexible pressure sensor was prepared in a manner similar to Example 1, except that the reaction was carried out in an ice-water bath for 6 h.

[0115] Experimental example

[0116] Experimental Example 1 Scanning Electron Microscope Test

[0117] The oriented conductive nanofiber membranes prepared in Examples 1 to 3 were tested by scanning electron microscopy. The morphology test results are as follows: Figure 2 shown.

[0118] from Figure 2 It can be seen that the diameter of the nanofibers in the oriented conductive nanofiber membrane is uniform, with a fiber diameter of 500 to 1500 nm, and the conductive substance polyaniline is evenly loaded on the surface of the nanofiber membrane. At the same time, it can be seen that with the extension of the reaction time, the polyaniline on the surface of the nanofiber membrane gradually increases and is evenly distributed.

[0119] Experimental Example 2 Mechanical Properties Test

[0120] The mechanical properties of the oriented conductive nanofiber membrane and the nanofiber membrane prepared in Example 2 were measured using a film stretching machine. The stress-strain curves are shown in FIG. Figure 3 shown.

[0121] from Figure 3 The mechanical properties of pure TPU (thermoplastic elastomer polyurethane) and oriented conductive nanofiber membranes in the axial and radial directions, respectively, are shown. Mechanical testing along the axial direction significantly outperforms that perpendicular to the axial direction. This is attributed to the excellent orientation and interfiber bonding of the nanofiber membranes prepared by conjugated electrospinning, which significantly enhances the mechanical properties in the axial direction. After conjugated electrospinning, the tensile strain can be increased from approximately 900% to nearly 1600%, and the tensile stress can be increased by 4-5 times.

[0122] Experimental Example 3: Response sensitivity and response time test

[0123] The response sensitivity and response time of the capacitive flexible pressure sensors prepared in Examples 1 to 3 were tested. The specific test process is as follows: first, turn on the precision LCR meter and preheat for 30 minutes; then clamp the prepared sensor device (with oriented TPU nanofiber membrane as the dielectric layer) on the measuring mold, and place a cover glass on the device. After it stabilizes, read the reading, which is recorded as C0 (μF); use tweezers to clamp different standard weights and place them on the slide. After it stabilizes, read the reading, which is recorded as C (μF); the difference between the two is recorded as ΔC; the measured data is plotted with the horizontal axis as pressure P (kPa) and the vertical axis as ΔC / C0. Linear fitting is performed in sections, and the slope is recorded as sensitivity S. The test results are shown as follows: Figure 4 and Figure 5 shown.

[0124] from Figure 4 It can be seen that the sensitivity of the capacitive flexible pressure sensor prepared by the present invention can reach 1.3~1.8kPa -1 , the maximum detection range can reach over 120kPa.

[0125] Figure 5 It can be seen that the capacitive flexible pressure sensor prepared in Example 2 of the present invention has an extremely short response time of 30 to 120 ms and a recovery time of 30 to 120 ms.

[0126] Experimental Example 4 Water Vapor Transmission Rate Test

[0127] The oriented TPU nanofiber pure film and capacitive flexible pressure sensor prepared in Example 2 were tested for their water vapor transmission rate (WVTR) according to the American Society for Testing and Materials E96-98 method. The water vapor transmission rate is the mass of water vapor that passes through a unit area per unit time under certain temperature and humidity conditions. The test results are as follows: Figure 6 shown.

[0128] from Figure 6It can be seen that the water vapor permeability of the capacitive flexible pressure sensor does not change significantly over time, and the water vapor permeability is 500-700 (g / m 2 , 24h). The WVTR of PANI / TPU oriented conductive nanofiber membrane and oriented TPU nanofiber membrane are relatively close, which shows that the addition of PANI has little effect on the permeability of oriented TPU nanofiber membrane. When the flexible pressure sensor is assembled with PANI / TPU oriented conductive nanofiber membrane as the upper and lower electrode layers and oriented TPU nanofiber membrane as the middle dielectric layer, the WVTR is measured to be 554.69 (g / m 2 , 24h), which is 200-500 (g / m2) higher than that of human skin. 2 , 24h), indicating that wearing this sensor does not cause discomfort.

[0129] Experimental Example 5: Real-time response signal test

[0130] The capacitive flexible pressure sensor prepared in Example 2 is fixed on the human body and can realize real-time response signals when the human body moves in a wide range. The test results are as follows: Figure 7 and Figure 8 shown.

[0131] from Figure 7 and Figure 8 It can be seen that the capacitive flexible pressure sensor can monitor various activities in the human body and send out real-time response signals. It can monitor the human body from pulse monitoring to large-scale activities, with a wide monitoring range.

[0132] The present invention has been described in detail above with reference to specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing a capacitive flexible pressure sensor used in a human body monitoring system, characterized in that: The capacitive flexible pressure sensor comprises an upper electrode layer, a lower electrode layer, and a dielectric layer located between the upper electrode layer and the lower electrode layer; The upper and lower electrode layers are oriented conductive nanofiber membranes, which are made of oriented thermoplastic elastomer polyurethane nanofiber membranes, aniline and protonic acid. The dielectric layer is an oriented thermoplastic elastomer polyurethane nanofiber membrane, which is obtained by conjugated oriented electrostatic spinning of a thermoplastic elastomer polyurethane solution. The thickness of the oriented conductive nanofiber membrane is 50~400μm, and the conductivity of the oriented conductive nanofiber membrane is 9×10 -4 ~9×10 -2 S / cm, The mass concentration of the thermoplastic elastomer polyurethane solution is 5-20%. The preparation method comprises the following steps: Step 1, dissolving thermoplastic elastomer polyurethane in a solvent to obtain a spinning solution; Step 2, placing the spinning solution in an electrospinning device for conjugate oriented electrospinning to obtain an oriented thermoplastic elastomer polyurethane nanofiber membrane; Step 3, immersing the oriented thermoplastic elastomer polyurethane nanofiber membrane in a mixed solution of aniline and protonic acid, and then reacting in the presence of an initiator to obtain an oriented conductive nanofiber membrane; Step 4: Assemble the oriented conductive nanofiber membrane and the oriented thermoplastic elastomer polyurethane nanofiber membrane to obtain a capacitive flexible pressure sensor. In step 2, the electrospinning device comprises a roller collector (1), a conjugate spinning nozzle (2), a syringe pump (3), a positive electrode (4) and a negative electrode (5); The conjugate spinning nozzle (2) comprises a conjugate spinning positive nozzle and a conjugate spinning negative nozzle; The conjugate spinning nozzle (2) and the injection pump (3) are respectively located between the roller collector (1) and the positive electrode (4) and the negative electrode (5), and the conjugate spinning nozzle (2) is located between the injection pump (3) and the roller collector (1); The distance between the positive electrode (4) and the negative electrode (5) is 5 to 30 cm, and the distance between the conjugate spinning nozzle (2) and the roller collector (1) is 5 to 30 cm. The positive voltage of electrospinning is 7-15 kV, the negative voltage of electrospinning is 7-15 kV, and the spinning time is 5-60 min; The spinning push speed is 0.5-3 ml / h; the roller speed is 1500-4000rpm; The spinning angle of the conjugate spinning positive nozzle is 15° to 60°, and the spinning angle of the conjugate spinning negative nozzle is 15° to 60°. In step 3, The protonic acid is selected from one or more of sulfosalicylic acid, hydrochloric acid, sulfuric acid, and phytic acid. The mass ratio of aniline to protonic acid is 1:1~1:

4.

2. According to the preparation method of claim 1, the sensitivity of the capacitive flexible pressure sensor can reach 1.3 kPa -1 The maximum detection range is above 120kPa, the pressure response time is 40-120ms, the recovery time is 40-120ms, the strain can reach 1400%-1700%, and the water vapor transmission rate is 500-700 (g / m 2 , 24h).

3. The preparation method according to claim 1, characterized in that: In step 3, The reaction is carried out in an ice water bath for 1 to 15 hours.

Images