Flexible sensor based on silver nanowire material and preparation method and application thereof

Abstract

The invention discloses a flexible sensor based on a silver nanowire material and a preparation method and application thereof.The flexible sensor comprises a polyurethane electrostatic spinning film, a polyvinylidene fluoride piezoelectric film and a silver nanowire three-dimensional network material, by optimizing the silver nanowire synthesis technology, the average length-diameter ratio of the flexible sensor is 1500, the low initial resistance of the flexible sensor is 26.7 ohm, and the flexible sensor can be used as a flexible sensor. The surface of a polyvinylidene fluoride piezoelectric film is dispensed with the nano-particles to serve as an electrode and a sensing layer, then a polyurethane electrostatic spinning film is attached to serve as a substrate, the flexibility and stability of the sensor are improved, the prepared flexible sensor can measure piezoelectric signals and piezoresistive signals at the same time, more comprehensive mechanical sensing is achieved, and the application range is wide. And the sensor has the technical characteristics of high sensitivity, wide strain range, quick response, excellent cycling stability and the like, and can be widely applied to various scenes.

Description

TECHNICAL FIELD

[0001] The present application relates to a sensor and a preparation method and application thereof, more particularly to a flexible sensor based on silver nanowire material and a preparation method and application thereof, and belongs to the field of multi-disciplinary intersection of sensor technology, flexible electronics and material science. BACKGROUND

[0002] Compared with traditional rigid sensors, flexible sensors have the characteristics of high toughness, good tensile performance, bendability, good ductility, wearability, easy portability, lightness and high sensitivity, and are widely used in various fields. According to the existing research results at home and abroad in recent decades, the development of flexible sensors has made great progress, especially in the environment of continuous development of new materials and nanotechnology, flexible sensors have great development potential in the fields of intelligent wearable devices, electronic skin, smart home and robot touch.

[0003] The Chinese patent document with the patent number CN201911328978.X discloses a preparation method of a capacitive sensor. The sensor is composed of upper and lower electrode layers made of flexible conductive silicone rubber and a middle functional layer made of pure silicone rubber. By introducing surface microstructures with different roughnesses to the electrode layers and the functional layer, the sensor has different sensitivities. However, the design of the microstructures can only maintain high sensitivity response under a small pressure, and the strain range is small, which limits the application range.

[0004] The Chinese patent document with the patent number CN2019111300990.X discloses a multifunctional flexible sensor and a preparation method and application thereof. The functional flexible sensor is composed of a bottom flexible substrate, a lower surface electrode, a middle functional layer, a conductive electrode, an upper surface electrode and a top flexible substrate from bottom to top. A microstructure protrusion is designed on the surface of the flexible functional layer, and a lead wire is connected to one end of the upper surface electrode to realize temperature, distance and stress measurement. However, the metal electrode reduces the flexibility to some extent.

[0005] The Chinese patent document with the patent number CN202510022111.0 discloses a flexible conductive film with high base adhesion and a preparation method and application thereof. The functional flexible sensor utilizes the characteristics that the conductive material and the substrate can be integrated when heated and solidified, eliminating the mechanical mismatch between the conductive material and the substrate due to delamination, improving the interface stability and the interfacial adhesion between the conductive material and the substrate. However, the preparation method requires high requirements for spraying process and preparation temperature, which is difficult to be put into mass production and large-scale use.

[0006] Therefore, the flexible sensor prepared by the prior art has the following disadvantages: 1) the resistance cycle stability of the flexible sensor is insufficient, and the repeatability of the sensor is low; 2) the stability of the flexible sensor under different strain conditions is insufficient and fluctuates greatly; 3) the adaptability and durability of the flexible sensor under extreme conditions are insufficient; 4) the process for preparing the flexible sensor inevitably reduces the flexibility of the sensor; and 5) the preparation process of the flexible sensor is complex and difficult to mass reproduce. SUMMARY

[0007] One of the purposes of the present application is to provide a flexible sensor based on silver nanowire material, which has the technical features of being able to improve the flexibility, stability, reliability and resistance cycle stability of the sensor, simultaneously measuring piezoelectric signals and piezoresistive signals, and being able to realize more comprehensive mechanical perception.

[0008] One of the purposes of the present application is to provide a preparation method of a flexible sensor based on silver nanowire material, which has the technical features of being simple in method, strong in operability, good in stability and high in capacitance of the obtained multifunctional composite sensor, and providing a new idea for the production and development of flexible sensors.

[0009] One of the purposes of the present application is to provide an application of a flexible sensor based on silver nanowire material.

[0010] In order to achieve the above-mentioned purposes, the present application is realized by the following technical solutions:

[0011] The flexible sensor based on silver nanowire material comprises a substrate, a functional layer, an electrode and a sensing layer, the functional layer is provided with the electrode and the sensing layer on both sides, and the substrate is provided outside the electrode and the sensing layer to combine into a flexible thin film sensor.

[0012] The silver nanowire three-dimensional network material with a length-diameter ratio of 1500-1921 (i.e. the length-diameter ratio of the silver nanowire is 1500:1-1921:1) is used as the electrode and the sensing layer, the polyvinylidene fluoride (PVDF) piezoelectric film is used as the functional layer, and the thermoplastic polyurethane nanofiber film is used as the substrate.

[0013] Further, the polyurethane nanofiber film (also known as: polyurethane electrospun membrane / electrospun membrane) is obtained by reacting the following raw materials by weight:

[0014] Thermoplastic polyurethane 17-19 parts

[0015] N,N-dimethylacetamide 81-83 parts.

[0016] Further, the polyurethane nanofiber film is prepared by the following method:

[0017] The polyurethane and dimethylacetamide are formulated into a 18wt% solution, and heated and stirred in a 70℃ water bath for 9h until the solution is transparent and uniform, then placed in a 70℃ oven overnight; a portion of the solution is loaded into a syringe, fixed on the electrospinning device, the spinning voltage is set to 14kV, the distance between the needle and the collection roller is 15cm, the collection roller rotation speed is 250rpm, the injection pump flow rate is 0.8mL / h, the spinning temperature is kept at 25±2℃, and the polyurethane nanofiber membrane is obtained by spinning for 6h.

[0018] Further, the polyvinylidene fluoride PVDF piezoelectric film is obtained by reacting the following raw materials by weight:

[0019] Polyvinylidene fluoride PVDF 14-16 parts

[0020] Dimethyl sulfoxide 84-86 parts.

[0021] Further, the polyvinylidene fluoride PVDF piezoelectric film is prepared by the following method:

[0022] The polyvinylidene fluoride PVDF is placed in a beaker containing dimethyl sulfoxide, the concentration of the polyvinylidene fluoride PVDF is 15wt%, the mixture is stirred uniformly by a stirrer, the mixed liquid is placed in a 60℃ oven for 12h to remove the gas bubbles in the solution, and then the prepared solution is placed on a polytetrafluoroethylene plate coated with silicone oil, a doctor blade coater is used to scrape a 70μm thin film, vacuum heating is performed to volatilize the dimethyl sulfoxide in the solution, and the polyvinylidene fluoride PVDF film is obtained, which is taken out and air-dried to room temperature; the film is uniaxially stretched, the stretched film is placed in a vacuum oven for annealing, and then taken out and air-dried to room temperature; the annealed polytetrafluoroethylene film is pressed between two electrode plates and immersed in silicone oil, a high-voltage power supply is connected to the two electrode plates, the polarization voltage is set to 90MV / m, and the polarization time is 30min, after polarization, the film is taken out and cooled to room temperature in air.

[0023] Further, the silver nanowire three-dimensional network material is obtained by reacting the following raw materials by weight:

[0024]

[0025] Further, the silver nanowire three-dimensional network material is prepared by the following method:

[0026] Silver nitrate is used as raw material, polyvinylpyrrolidone is used as inducer, and copper chloride is used as inhibitor, after stirring and dissolving in a polyol solvent system, different batches of silver nanowire solution are prepared by reacting at 130-150℃ for 6-8h, centrifugation, washing, and dispersion to obtain non-agglomerated silver nanowires.

[0027] Further, different molecular weight polyvinylpyrrolidone is weighed and dissolved in ethylene glycol, stirred until the solution is uniform and stable, then poured into a three-necked flask, then dropwise added with anhydrous copper chloride dissolved in ethylene glycol, a magnetic stirrer is put in, the flask is sealed, and stirring is carried out at 200 rpm in an oil bath at 150℃ for 1h; in a completely dark environment, silver nitrate is weighed and dissolved in ethylene glycol in a measuring cylinder wrapped with tin paper, after stirring uniformly, the three-necked flask is dropwise added with the solution at a speed of 75 rpm by using a peristaltic pump, the temperature is kept at 150℃, and reaction is carried out for 6-8h; after the reaction is completed, the solution is cooled to room temperature at a ventilation opening, and then is divided into centrifuge tubes, ethanol is added, centrifugation is carried out at 8000 rpm for 20 minutes, the supernatant is discarded, and washing is repeated for 4 times to obtain purified silver nanowires, which are dispersed in anhydrous ethanol for use; different molecular weight polyvinylpyrrolidone includes M W :5.8x10 4 and 1.3x10 6 .

[0028] The application discloses a preparation method of a flexible sensor based on silver nanowire materials, and the method comprises the following steps:

[0029] Step S1: a 3.5*3.5cm polyvinylidene fluoride (PVDF) piezoelectric film is placed in a culture dish, four edges are adhered with adhesive tape, a non-metalized edge and a surplus of electrode leads are reserved, and a functional layer is obtained;

[0030] Step S2: dispersed silver nanowires with a concentration of 3mg / mL are dropwise coated on both sides of the polyvinylidene fluoride (PVDF) piezoelectric film of the functional layer for multiple times, the ethanol in the system is volatilized, a reticular conductive layer is formed, and the adhesive tape is removed;

[0031] Step S3: conductive silver glue is applied on both sides, and copper sheets are attached, so that electrodes and sensing layers are arranged on both sides of the functional layer;

[0032] Step S4: a part of a polyurethane nanofiber film with a non-edge interval of 3.5*3.5cm is taken as a substrate and placed in a culture dish;

[0033] Step S5: a layer of the polyurethane nanofiber film with a non-edge interval of 3.5*3.5cm is attached to the electrodes and the sensing layers respectively, and a pressure roller is used to press tightly, so that a target flexible sensor is formed.

[0034] The application discloses an application of the flexible sensor based on silver nanowire materials in the fields of motion monitoring, human health monitoring and human-computer interaction. The piezoresistive signal (resistance change) and the piezoelectric signal (capacitance change) of the flexible sensor are used to realize monitoring and identification.

[0035] The flexible sensor has low initial resistance of 26.7Ω; a strain range of 0%-150%, different sensitivities in different strain intervals, and a response time of 112ms; and a resistance change rate of 0%-2% after 3000 stretching cycles under a tensile strain of 0%-10%. That is, the flexible sensor based on the silver nanowire material has a sensitivity of up to 21.04, a response time of 112ms, and a resistance change rate of ≤2% after 3000 cycles under a tensile strain of 0%-10%. The flexible sensor has good cycle stability, and the bending angle is monitored by a piezoelectric signal (capacitance change), and the tensile strain is monitored by a piezoresistive signal (resistance change), so that more comprehensive mechanical sensing can be realized.

[0036] Compared with the prior art, the present application has the beneficial technical effects that: the polyurethane film is prepared by electrospinning, the polyvinylidene fluoride (PVDF) piezoelectric film is prepared by a casting method, a flexible film material with a composite component is formed, the flexibility, stability, reliability and cycle stability of the resistance of the sensor are improved, the silver nanowire is prepared into a three-dimensional network layer as an electrode and a sensing layer by a drop coating method. The drop coating method replaces the high-temperature sputtering method in the prior art, reduces the damage to the film material, and improves the sensitivity of the sensor; the method is simple and has strong operability, the obtained sensor has good stability and high capacitance, and provides a new idea and method for the production and development of flexible sensors; the present application belongs to a multifunctional composite sensor, and can realize simultaneous measurement of piezoelectric signals and piezoresistive signals, and realize more comprehensive mechanical sensing. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 Figure 1 is a SEM image of the silver nanowire of the present application.

[0038] Figure 2 Figure 2 is a network structure diagram of the silver nanowire of the present application.

[0039] Figure 3 Figure 3 is an XRD diagram of the silver nanowire of the present application.

[0040] Figure 4 Figure 4 is a disassembly diagram of the flexible film sensor of the silver nanowire material of the present application.

[0041] Figure 5 Figure 5 is a SEM image of the surface of the sensor of the present application.

[0042] Figure 6 Figure 6 is a resistance curve diagram of the flexible film sensor of the silver nanowire material of the present application under different stresses.

[0043] Figure 7 Figure 7 is a V-I curve relationship diagram of the flexible film of the silver nanowire material of the present application under different strains.

[0044] Figure 8 Figure 8 is a schematic diagram of the stretching and bending structure of the present application.

[0045] Figure 9 It is a cyclic resistance curve diagram of the sensor under 0%-10% tensile strain of the present invention.

[0046] Figure 10 This is a graph showing the bending angle and relative capacitance output of the present invention.

[0047] Figure 11 It is a tensile mechanical performance diagram of the present invention.

[0048] Figure 12 It is a schematic diagram of the structure of the flexible thin film sensor made of silver nanowire material of the present invention. DETAILED DESCRIPTION

[0049] The following is a combination of the embodiments of the present invention Figures 1-12 The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0050] Technical solution / principle of the present invention: A polyurethane film is prepared by electrospinning, and silver nanowires with an aspect ratio of up to 1921 are prepared by alcohol reduction. Electrodes and sensing layers are prepared by drop coating. The prepared polyvinylidene fluoride (PVDF) piezoelectric film is used as the functional layer. The resulting sensor has low initial resistance (26.7Ω), a high strain range (0%-150%), high sensitivity and fast response time (112ms) and excellent durable cycle performance (3000 times). The sensor prepared by this invention has more sensitive conduction and achieves more comprehensive mechanical perception at a lower cost.

[0051] A method for preparing a flexible thin film sensor based on silver nanowire material includes an electrospun polyurethane substrate and silver nanowires (AgNWs) drop-coated on the substrate; the thermoplastic polyurethane nanofiber membrane (abbreviated as polyurethane, TPU) is composed of the following components in parts by weight:

[0052] 18 parts of thermoplastic polyurethane

[0053] 82 parts of N,N-dimethylacetamide.

[0054] By comparing the SEM images of polyurethane films prepared by different preparation methods, it is found that compared with casting method and immersion phase separation method, the polyurethane nanofiber film prepared by electrospinning has better uniformity, more excellent stability, and has a suitable pore size of the pore, which can improve the conductivity, air permeability and anti-permeability of the film, the structure can provide stable support and dispersion environment for silver nanowires, prevent the agglomeration of silver nanowires, and fully exert the excellent performance of silver nanowires. In order to improve the conductivity, air permeability, anti-permeability and strength of the film, electrospinning method is used to prepare polyurethane film.

[0055] A specific way: the polyurethane nanofiber film is prepared by the following method:

[0056] Step S01: weigh 1.8g of polyurethane and put it into a 60℃ oven to reduce the moisture absorption of polyurethane in the air.

[0057] Step S02: quickly put the polyurethane obtained in S01 into a sample bottle containing 8.2g of dimethylacetamide, seal it and perform magnetic stirring at 70℃, 5-6h, until the solution is transparent and uniform.

[0058] Step S03: take 4-5mL of the solution in S02 and place it in a syringe, and fix it on an electrospinning device, set the spinning voltage to 14kV, the receiving roller distance from the needle tip is 15cm, the receiving roller rotating speed is 250rpm, the injection pump injection speed is 0.8mL / h, and the spinning temperature is kept at 25±2℃, after 6-7h, the polyurethane nanofiber film is prepared.

[0059] The silver nanowire has an aspect ratio of 1500:1 to 1921:1, and the silver nanowire with a higher aspect ratio will have better conductivity, higher transparency and lower contact resistance.

[0060] The application provides a method for preparing silver nanowires with a higher aspect ratio. The silver nanowires are obtained by reacting raw materials in the following proportions: silver nitrate 0.5 parts, polyvinylpyrrolidone 1.86-1.87 parts, copper chloride 0.3-0.4 parts, and polyhydric alcohol 125-200 parts. The silver nanowires are prepared by the following method: using silver nitrate as the precursor, dropping at different speeds, using polyvinylpyrrolidone as the inducer, using copper chloride as the inhibitor, stirring and dissolving in the polyhydric alcohol solvent system, and then reacting at 130-150℃ for 6-8h (8h is the best reaction time), to obtain different batches of silver nanowire solution, centrifugation, washing, and dispersion to obtain non-agglomerated silver nanowires. Preferably, the application uses a dropping speed of 1.5mL / min to add silver nitrate into the polyvinylpyrrolidone, copper chloride and polyhydric alcohol system.

[0061] A specific method for preparing silver nanowires, comprising the following steps:

[0062] Step S001: Take 0.69g of polyvinylpyrrolidone (M W : 5.8*10 4 ) and 1.17g of polyvinylpyrrolidone (M W : 1.3*10 6 ), use 50mL of ethylene glycol to dissolve the above polyvinylpyrrolidone powder with magnetic stirring until the solution is uniform and stable, then use ethylene glycol to rinse the three-necked flask and slowly pour the prepared solution into the three-necked flask.

[0063] Step S002: Take 1mL of 3mmol / L CuCl2 (solvent is ethylene glycol) and drop it into the three-necked flask, put a magnet, seal the three-necked flask with a glass plug and fix it in an oil bath pot at 150℃, stir at a speed of 200rpm for 1-2h.

[0064] Step S003: Weigh 0.5g of silver nitrate and 25mL of ethylene glycol as solvent in a completely dark environment, put them all into a measuring cylinder wrapped with tin paper, and stir magnetically at room temperature until the solution is uniform. The peristaltic pump is used to drop the solution into the three-necked flask at a speed of 1.5mL / min, and the heating is continued at 150℃.

[0065] Step S004: Prepare silver nanowires with a reaction time of 8h, marked as A82.

[0066] Step S005: Open the three-necked flask in the fume hood and cool it to room temperature, then divide it into centrifuge tubes. Add 1mL of silver nanowire mixed solution and 2mL of ethanol to each centrifuge tube, centrifuge at a speed of 8000rpm for 20min, and pour out the supernatant. Add 6mL of anhydrous ethanol and repeat 4 times to prepare pure silver nanowires. Disperse the obtained pure silver nanowires in anhydrous ethanol to prevent agglomeration.

[0067] The vinylidene fluoride is obtained by reacting raw materials in the following proportions by weight: 15 parts of polyvinylidene fluoride (PVDF) and 85 parts of dimethyl sulfoxide. The polyvinylidene fluoride (PVDF) piezoelectric film is prepared by the following method: polyvinylidene fluoride (PVDF) is placed in a beaker containing dimethyl sulfoxide, wherein the concentration of the polyvinylidene fluoride (PVDF) is 15%, and the mixture is stirred uniformly by a stirrer. The mixed liquid is placed in an oven at 60°C for 12 hours to remove the bubbles in the solution. The prepared solution is then placed on a polytetrafluoroethylene plate coated with silicone oil, and a doctor blade coater is used to scrape a 70μm thin film. Vacuum heating is performed to volatilize the dimethyl sulfoxide in the solution, and a polyvinylidene fluoride (PVDF) film is obtained. The film is taken out and air-dried to room temperature. The stretched film is placed in a vacuum oven for annealing, and then taken out and air-dried to room temperature. The annealed polytetrafluoroethylene film is pressed between two electrode plates and immersed in silicone oil. A high-voltage power supply is connected to the two electrode plates, and the voltage and time are set for polarization. After polarization is completed, the film is taken out and cooled to room temperature in air.

[0068] The above-mentioned method for preparing a flexible film sensor based on a silver nanowire material is prepared by the following steps:

[0069] Step S1: A 3.5*3.5cm polyvinylidene fluoride (PVDF) piezoelectric film is placed in a culture dish, and the four edges are taped with adhesive tape, leaving a non-metalized edge and a margin for electrode leads.

[0070] Step S2: A concentration of 3mg / mL of dispersed silver nanowires is repeatedly and uniformly dropped on both sides of the polyvinylidene fluoride (PVDF) piezoelectric film. After the ethanol in the system is volatilized, a network conductive layer is formed, and the adhesive tape is removed.

[0071] Step S3: Conductive silver paste is applied to both sides, and copper sheets are attached to realize that both sides of the functional layer are paved with electrodes and sensing layers.

[0072] Step S4: A 3.5*3.5cm portion of the non-edge region of the polyurethane nanofiber membrane is taken as the substrate and placed in a culture dish.

[0073] Step S5: A layer of 3.5cm*3.5cm polyurethane nanofiber membrane in the non-edge region is attached to the electrode and sensing layer respectively, and is pressed tightly with a press roller to form the target flexible sensor.

[0074] In the present application, the method for preparing the polyurethane substrate can be any one of the casting method, the immersion phase separation method, and the electrospinning method. Further, the polyurethane prepared by electrospinning is selected as the substrate, and the culture dish is selected as the platform for preparing the sensor. The planar substrate is cleaned with alcohol before use and is dried in an oven. Ethanol is selected as the dispersant for silver nanowires, and the sensor is kept in a sealed space at room temperature before testing.

[0075] Example 1:

[0076] 1.8 g of polyurethane was weighed into 8.2 g of N,N-dimethylacetamide to make a solution with a concentration of 18 wt%, and was stirred magnetically in a water bath at 70 °C for 5 h to make a uniform, transparent spinning solution for use in the subsequent electrospinning process. Subsequently, 5 mL of the spinning solution was taken into a syringe and fixed on an electrospinning device, and the spinning speed was set to 0.8 mL / h, the voltage was set to 14.07 kV, the distance between the needle and the receiving roller covered with aluminum foil was set to 15 cm, the speed of the receiving roller was set to 220 r / min, and the spinning temperature was maintained at 25 ± 2 °C. After the electrospinning was completed, the polyurethane nanofiber membrane was obtained by peeling it off from the aluminum foil.

[0077] 0.69 g of polyvinylpyrrolidone (58,000 (Da)) and 1.17 g of polyvinylpyrrolidone (1,300,000 (Da)) were weighed, and 50 mL of ethylene glycol was measured, and the polyvinylpyrrolidone was slowly added under stirring to prevent it from coagulating into a lump, and stirring was performed with a magnetic stirrer until the crystal was completely dissolved. 50 mL of the ethylene glycol solution was used to rinse the beaker, and the mixed solution was all poured into a three-necked flask. The three-necked flask was placed in an oil bath, and 1 mL of a 3 mmol / L copper chloride solution was added dropwise to the polyvinylpyrrolidone and ethylene glycol mixed solution. A magnet was placed, and stirring was performed with a magnetic stirrer at a speed of 200 r / min for 1 h, and the oil bath temperature of the stirrer was 150 °C.

[0078] In complete darkness, 0.5 g of silver nitrate crystals was weighed into a beaker covered with tin foil, and 25 mL of ethylene glycol solution was added, and after stirring with a magnetic stirrer to make a uniform solution, the silver nitrate solution was added dropwise into a three-necked flask at a rate of 1.5 mL / min using a peristaltic pump at a speed of 75 rpm, and silver nanowires were generated by heating at 150 °C for 6 h. The three-necked flask was opened in a ventilated place and left to stand, and after the temperature was reduced to room temperature, the liquid was divided into centrifuge tubes, 1 mL of the silver nanowire mixed solution was added to the centrifuge tubes, 2 mL of ethanol was added, and centrifugal separation was performed at a speed of 8000 r / min for 20 min, and then the upper liquid was discarded and 6 mL of anhydrous ethanol was added, and centrifugal separation was performed again. This was repeated 4 times to obtain pure silver nanowires, and the obtained silver nanowires were dispersed in anhydrous ethanol to prevent agglomeration.

[0079] Polyvinylidene fluoride (PVDF) was placed in a beaker containing dimethyl sulfoxide, wherein the concentration of the polyvinylidene fluoride (PVDF) was 15%, and stirred by a blender for 2 h. The mixed liquid was placed in an oven at 60°C for 12 h to remove the bubbles in the solution. The prepared solution was placed on a polytetrafluoroethylene plate coated with silicone oil, and a 70 μm thin film was scraped out by a doctor blade coater. The solution was placed in a vacuum box at 80°C and 10 MPa atmospheric pressure for 2 h to volatilize dimethyl sulfoxide in the solution, and polyvinylidene fluoride (PVDF) film was obtained. The film was taken out and air-dried to room temperature, and then uniaxially stretched at 90°C with a stretching ratio of 5 times and a speed of 100 mm / min. The stretched film was placed in a vacuum oven at 135°C and annealed for 2 h. The annealed polytetrafluoroethylene film was pressed between two electrode plates and immersed in silicone oil at 80°C. A high-voltage power supply of 90 MV / m was connected to the two electrode plates, and polarization was performed for 30 min. After polarization, the film was taken out and cooled to room temperature in air.

[0080] A 3.5*3.5 cm polyvinylidene fluoride (PVDF) piezoelectric film was placed in a culture dish, and the four edges were taped with adhesive tape, leaving a non-metallized edge and a margin for electrode leads. A concentration of 3 mg / mL of dispersed silver nanowires was repeatedly and uniformly dropped on both sides of the polyvinylidene fluoride (PVDF) piezoelectric film, and placed in a completely light-proof place for ventilation for 40 min. After the ethanol in the system was volatilized, a network conductive layer was formed. The adhesive tape was removed, and acetone and alcohol were used as etchants to perform non-metallization treatment on the edges of the film. Conductive silver paste was applied to both ends, and copper sheets (thickness: 0.02 mm, length: 2 cm, width: 0.5 cm) were attached. A 3.5*3.5 cm portion of the non-edge region of the polyurethane electrospun film was taken as a substrate and placed in a culture dish. The sandwich structure of silver nanowire-polyvinylidene fluoride (PVDF)-silver nanowire was attached to the polyurethane film, and then a layer of electrospun film with a non-edge region of 3.5 cm*3.5 cm was overlaid on the upper layer, and a press roller was used to press tightly, to prepare the present application.

[0081] Example 2

[0082] 1.8 g of polyurethane was weighed into 8.2 g of N,N-dimethylacetamide to prepare a solution with a concentration of 18 wt%, and the solution was stirred magnetically under a water bath at 70°C for 5 h to become a uniform and transparent spinning solution for subsequent electrospinning process. Then, 5 mL of the spinning solution was taken and placed in a syringe, and fixed on an electrospinning device. The spinning speed was set to 0.8 mL / h, the voltage was 14.07 kV, the distance between the needle and the aluminum foil-covered receiving roller was 15 cm, the speed of the receiving roller was 220 r / min, and the spinning temperature was maintained at 25±2°C. After the electrospinning was completed, the polyurethane nanofiber membrane was obtained by peeling off from the aluminum foil.

[0083] Weigh 0.69 g of polyvinylpyrrolidone (58,000 (Da)) and 1.17 g of polyvinylpyrrolidone (1,300,000 (Da)), and 50 mL of ethylene glycol, and slowly add the polyvinylpyrrolidone under stirring to prevent it from coagulating into a lump, and stir with a magnetic stirrer until the crystal is completely dissolved. Rinse the beaker with 50 mL of the ethylene glycol solution, and pour the entire mixed solution into a three-necked flask. Place the three-necked flask in an oil bath, and drop 1 mL of a 3 mmol / L copper chloride solution into the polyvinylpyrrolidone and ethylene glycol mixed solution. Place a magnet, and stir for 1 h at 200 r / min using a magnetic stirrer, and set the oil bath temperature of the stirrer to 150°C.

[0084] Under complete light shielding, weigh 0.5 g of silver nitrate crystals, and place them in a beaker wrapped with tin paper, and add 25 mL of an ethylene glycol solution, and stir to make a uniform solution using a magnetic stirrer, and then use a peristaltic pump to drop the silver nitrate solution into a three-necked flask at a rate of 1.5 mL / min, and heat at 150°C for 7 h to produce silver nanowires. Open the three-necked flask at a ventilated place, and let it stand until the temperature decreases to room temperature, and then divide the liquid into centrifuge tubes, and add 1 mL of the silver nanowire mixed solution, 2 mL of ethanol, and centrifuge at a rate of 8000 r / min for 20 min, and then pour off the upper liquid and add 6 mL of anhydrous ethanol, and centrifuge again. Repeat this process four times to obtain pure silver nanowires, and disperse the obtained silver nanowires in anhydrous ethanol to prevent agglomeration.

[0085] Place polyvinylidene fluoride (PVDF) in a beaker containing dimethyl sulfoxide, wherein the concentration of the polyvinylidene fluoride (PVDF) is 15%, and stir for 2 h using a stirrer, and place the mixed liquid in an oven at 60°C for 12 h to remove the gas bubbles in the solution, and then place the prepared solution on a polytetrafluoroethylene plate coated with silicone oil, and use a doctor blade coater to scrape a 70 μm thin film, and place the thin film in a vacuum tank at 80°C and 10 MPa of atmospheric pressure for 2 h to volatilize the dimethyl sulfoxide in the solution, and obtain a polyvinylidene fluoride (PVDF) thin film, and take it out to air dry to room temperature, and perform uniaxial stretching at 90°C, with a stretching ratio of 5 times and a speed of 100 mm / min, and place the stretched thin film in a vacuum oven at 135°C for annealing for 2 h, and then take it out to air dry to room temperature, and press the annealed polytetrafluoroethylene thin film between two electrode plates, and immerse it in silicone oil at 80°C, and connect a high-voltage power supply of 90 MV / m to the two electrode plates, and perform polarization for 30 min, and after polarization is completed, take out the thin film and place it in air to cool to room temperature.

[0086] Take 3.5*3.5cm polyvinylidene fluoride (PVDF) piezoelectric film, place it in a culture dish, and stick the four edges with tape, leaving the non-metallized edge and the excess electrode lead. Then, multiple times, evenly drop the dispersed silver nanowire solution with a concentration of 3mg / mL on both sides of the polyvinylidene fluoride (PVDF) piezoelectric film, and place it in a completely light-proof place for ventilation for 40min. After the ethanol in the system is volatilized, a reticular conductive layer is formed, the tape is removed, and acetone and alcohol are used as etchants to perform non-metallization on the edge of the film. Apply conductive silver paste to both ends and attach copper pieces (thickness: 0.02mm, length: 2cm, width: 0.5cm). Take a 3.5*3.5cm section of the polyurethane electrospun film from the non-edge area and place it in a culture dish. Attach the silver nanowire-polyvinylidene fluoride (PVDF)-silver nanowire sandwich structure to the polyurethane film, then cover it with another 3.5cm*3.5cm electrospun film from the non-edge area, and press it tightly with a roller to prepare the present application.

[0087] Example 3

[0088] Weigh 1.8g of polyurethane into 8.2g of N,N-dimethylacetamide to prepare a solution with a concentration of 18wt%, and stir it in a 70℃ water bath for 5h to make it a uniform and transparent spinning solution for subsequent electrospinning process. Then, take 5mL of the spinning solution and place it in a syringe, and fix it on the electrospinning device. Set the spinning speed to 0.8mL / h, the voltage to 14.07kV, the distance between the needle and the aluminum foil-covered receiving roller to 15cm, and the receiving roller speed to 220r / min, and keep the spinning temperature at 25±2℃. After electrospinning, the polyurethane nanofiber membrane is obtained by peeling it off from the aluminum foil.

[0089] Weigh 0.69g of polyvinylpyrrolidone (58,000(Da)) and 1.17g of polyvinylpyrrolidone (1,300,000(Da)), and then weigh 50mL of ethylene glycol. Slowly add the polyvinylpyrrolidone under stirring to prevent it from clumping, and stir it with a magnetic stirrer until the crystals are completely dissolved. Rinse the beaker with 50mL of ethylene glycol solution, and pour the mixed solution into a three-necked flask. Place the three-necked flask in an oil bath, and add 1mL of 3mmol / L copper chloride solution to the polyvinylpyrrolidone and ethylene glycol mixed solution. Place the magnet, and stir it with a magnetic stirrer at a speed of 200r / min for 1h, and the oil bath temperature of the stirrer is 150℃.

[0090] In the case of complete light shielding, 0.5 g of silver nitrate crystals is weighed into a beaker coated with tin foil, 25 mL of ethylene glycol solution is added, and the solution is stirred into a uniform solution with a magnetic stirrer. The silver nitrate solution is then dropped into a three-necked flask at a rate of 1.5 mL / min using a peristaltic pump at a rotation speed of 75 rpm, and silver nanowires are generated by heating at 150°C for 8 h. The three-necked flask is opened to the air and left to stand, and after the temperature has decreased to room temperature, the liquid is divided into centrifuge tubes. 1 mL of the silver nanowire mixed solution and 2 mL of ethanol are added to the centrifuge tubes, and the mixture is centrifuged at a rotation speed of 8000 rpm for 20 min. The upper liquid is then discarded, 6 mL of anhydrous ethanol is added, and the mixture is centrifuged again. This process is repeated four times to obtain pure silver nanowires, which are dispersed in anhydrous ethanol to prevent agglomeration.

[0091] Polyvinylidene fluoride (PVDF) is dissolved in a beaker containing dimethyl sulfoxide, wherein the concentration of the polyvinylidene fluoride (PVDF) is 15%, and the mixture is stirred for 2 h. The liquid is then placed in an oven at 60°C for 12 h to remove the bubbles in the solution. The prepared solution is then placed on a polytetrafluoroethylene plate coated with silicone oil, and a 70 μm thin film is scraped out using a doctor blade coater. The solution is then placed in a vacuum box at 80°C and 10 MPa of atmospheric pressure for 2 h to volatilize the dimethyl sulfoxide in the solution, and a polyvinylidene fluoride (PVDF) thin film is obtained. The film is then taken out and left to cool to room temperature, and is subjected to uniaxial stretching at 90°C at a stretching ratio of 5 times and a speed of 100 mm / min. The stretched film is then placed in a vacuum oven at 135°C and annealed for 2 h. The annealed polytetrafluoroethylene thin film is then compressed between two electrode plates, immersed in silicone oil at 80°C, and subjected to polarization using a high-voltage power supply of 90 MV / m connected to the two electrode plates for 30 min. After polarization, the film is taken out and left to cool to room temperature in the air.

[0092] Take 3.5*3.5cm polyvinylidene fluoride (PVDF) piezoelectric film, place it in a culture dish, stick four edges with tape, reserve non-metallized edge and excess amount of electrode lead-out. Then multiple times, evenly drop the dispersed silver nanowire with a concentration of 3mg / mL on both sides of the polyvinylidene fluoride (PVDF) piezoelectric film, place it in a completely light-avoiding place and ventilate for 40min, after the ethanol in the system is volatilized, form a reticular conductive layer, remove the tape, use acetone and alcohol as etchant, and do non-metallization treatment on the edge of the film. Smear conductive silver glue on both ends, and attach copper sheets (thickness: 0.02mm, length: 2cm, width: 0.5cm). Take a 3.5*3.5cm part of the polyurethane electrospun film non-edge area as the substrate, place it in a culture dish. Attach the silver nanowire-polyvinylidene fluoride (PVDF)-silver nanowire sandwich structure to the polyurethane film, then cover another layer of electrospun film with a non-edge area of 3.5cm*3.5cm on the upper layer, and press it tightly with a roller to prepare the present application.

[0093] Comparative Example 1

[0094] Compared with Example 1, the dropping speed of silver nitrate solution is 0.5mL / min, and other steps remain unchanged.

[0095] Comparative Example 2

[0096] Compared with Example 1, the dropping speed of silver nitrate solution is 2.0mL / min, and other steps remain unchanged.

[0097] Comparative Example 3

[0098] Compared with Example 2, the dropping speed of silver nitrate solution is 0.5mL / min, and other steps remain unchanged.

[0099] Comparative Example 4

[0100] Compared with Example 2, the dropping speed of silver nitrate solution is 2.0mL / min, and other steps remain unchanged.

[0101] Comparative Example 5

[0102] Compared with Example 3, the dropping speed of silver nitrate solution is 0.5mL / min, and other steps remain unchanged.

[0103] Comparative Example 6

[0104] Compared with Example 3, the dropping speed of silver nitrate solution is 2.0mL / min, and other steps remain unchanged.

[0105] Compare the flexible sensors in Examples 1-3 with the sensors in Comparative Examples 1-5, see Table 1 for details:

[0106]

[0107] As shown in Table 1, the experiment is carried out at 150 DEG C, the silver nitrate solution is added to the reaction system at a speed of 1.5 mL / min, and stirring is continued for 8h, at which time the silver nanowires obtained reach the best state in terms of morphology and aspect ratio.

[0108] As shown in Table 1, the sensor resistance prepared in Example 3 is the lowest. As shown in Table 1, because the present application is a multifunctional composite sensor, piezoelectricity and piezoresistance can be monitored simultaneously. When the external stress is too large, the polyvinylidene fluoride (PVDF) functional layer breaks, and the silver nanowires, which simultaneously act as electrodes and strain sensitive elements, will take on the role of sensing, and the polyurethane electrospun film has high elasticity and can enable the sensor to operate normally in a high strain range.

[0109] As described above, the present application is a flexible thin film sensor with high aspect ratio (average aspect ratio 1500 or more) silver nanowires as flexible sensor electrodes and sensing layers, polyvinylidene fluoride (PVDF) piezoelectric film as functional layer, and polyurethane electrospun film as flexible substrate. The flexible sensor composed of the flexible sensor can simultaneously measure piezoelectric signals and piezoresistance signals, realize more comprehensive mechanical sensing, has high sensitivity (up to 21.04), wide strain range (0%-150%), fast response (112ms) and excellent cycle stability (resistance basically unchanged after 3000 cycles), the tensile strain and sensitivity show a positive correlation trend, R 2 up to 0.99, the bending angle of the sensor and the capacitance output show a linear positive correlation trend, R2 can reach 0.996, and the slope is significantly different from zero. The present application uses high aspect ratio (average length 1500, up to 1921) silver nanowires as electrodes and sensing layers, polyvinylidene fluoride (PVDF) as a functional layer, and electrospun film as a flexible substrate, and is a multifunctional composite sensor. The preparation method is simple, the equipment requirement is low, the cost is low, the service life of the sensor is long, and the present application provides a new method for improving the flexible thin film sensor.

[0110] Finally, it should be noted that the present application is not limited to the above examples, but can have many variations. All variations that can be directly derived or inferred from the disclosure of the present application by those of ordinary skill in the art should be considered within the scope of the present application.

Claims

1. A flexible sensor based on silver nanowire material, characterized by: The flexible thin film sensor comprises a substrate, a functional layer, an electrode and a sensing layer, wherein the electrodes and the sensing layer are laid on both sides of the functional layer, and the substrate is laid outside the electrodes and the sensing layer to form a flexible thin film sensor; Silver nanowire three-dimensional network material with an aspect ratio of 1500 to 1921 is used as the electrode and sensing layer, polyvinylidene fluoride (PVDF) piezoelectric film is used as the functional layer, and thermoplastic polyurethane nanofiber membrane is used as the substrate.

2. The flexible sensor based on silver nanowire material according to claim 1, characterized in that: The polyurethane nanofiber membrane is obtained by reacting the following raw materials in parts by weight: 18 parts thermoplastic polyurethane 82 parts of N,N-dimethylacetamide.

3. The flexible sensor based on silver nanowire material according to claim 2, characterized in that: The polyurethane nanofiber membrane was prepared by the following method: Polyurethane and dimethylacetamide were prepared into an 18 wt% solution, and heated and stirred in a 70 ° C water bath for 9 hours until the solution was transparent and uniform, and then allowed to stand in a 70 ° C oven overnight; part of the solution was loaded into a syringe, fixed on an electrospinning device, and the spinning voltage was set to 14 kV, the distance between the needle and the collecting roller was 15 cm, the collecting roller speed was 250 rpm, the injection pump flow rate was 0.8 mL / h, the spinning temperature was maintained at 25 ± 2 ° C, and the polyurethane nanofiber membrane was obtained by spinning for 6 hours.

4. The flexible sensor based on silver nanowire material according to claim 1, characterized in that: The polyvinylidene fluoride (PVDF) piezoelectric film is obtained by reacting the following raw materials in parts by weight: 15 parts of polyvinylidene fluoride (PVDF) 85 parts of dimethyl sulfoxide.

5. The flexible sensor based on silver nanowire material according to claim 4, characterized in that: The polyvinylidene fluoride (PVDF) piezoelectric film is prepared by the following method: The method comprises the following steps: placing polyvinylidene fluoride (PVDF) in a beaker containing dimethyl sulfoxide to dissolve the polyvinylidene fluoride (PVDF), wherein the concentration of the polyvinylidene fluoride (PVDF) is 15 wt %, stirring the mixture evenly in a blender, placing the mixed liquid in an oven at 60° C. and keeping the mixture warm for 12 hours to remove bubbles in the solution, placing the prepared solution on a polytetrafluoroethylene plate coated with silicone oil, scraping out a 70 μm film with a doctor blade applicator, vacuum heating to volatilize the dimethyl sulfoxide in the solution to obtain a polyvinylidene fluoride (PVDF) film, taking the film out and airing it to room temperature; performing uniaxial stretching on the film, placing the stretched film in a vacuum oven, annealing the film, and then taking the film out and airing it to room temperature; pressing the annealed polytetrafluoroethylene film between two electrode plates and immersing the film in silicone oil, connecting a high-voltage power supply to the electrode plates at both ends, setting the polarization voltage to 90 MV / m, and the polarization time to 30 minutes. After polarization is completed, the film is taken out and placed in air to cool to room temperature.

6. The flexible sensor based on silver nanowire material according to claim 1, characterized in that: The silver nanowire three-dimensional network material is obtained by reacting the following raw materials in parts by weight:

7. The flexible sensor based on silver nanowire material according to claim 6, characterized in that: The silver nanowire three-dimensional network material is prepared by the following method: Silver nitrate is used as raw material, polyvinyl pyrrolidone is used as an inducer, and copper chloride is used as an inhibitor. After stirring and dissolving in a polyol solvent system, the solution is reacted at 130-150°C for 6-8 hours to prepare different batches of silver nanowire solutions. The silver nanowires are then centrifuged, washed, and dispersed to obtain non-agglomerated silver nanowires.

8. The flexible sensor based on silver nanowire material according to claim 7, characterized in that: Weigh polyvinyl pyrrolidone of different molecular weights and dissolve it in ethylene glycol. Stir until the solution is uniform and stable, then pour it into a three-necked flask, then drop anhydrous copper chloride dissolved in ethylene glycol, add a magnetic stirrer, seal the flask and stir it at 200 rpm in a 150°C oil bath for 1 hour; in a completely dark environment, weigh silver nitrate and dissolve it in ethylene glycol in a tin foil-wrapped measuring cylinder, stir evenly and then drop it into the three-necked flask at a speed of 75 rpm using a peristaltic pump, maintain the temperature at 150°C, and react for 6-8 hours; after the reaction, cool the solution to room temperature at the vent, divide it into centrifuge tubes, add ethanol and centrifuge at 8000 rpm for 20 minutes, discard the supernatant, repeat washing 4 times to obtain purified silver nanowires, which are dispersed in anhydrous ethanol for later use; polyvinyl pyrrolidone of different molecular weights including M W :5.8×10 4 and 1.3×10 6 .

9. The method for preparing a flexible sensor based on silver nanowire material according to any one of claims 1 to 8, characterized in that The method comprises the following steps: Step S1: Take a 3.5*3.5 cm polyvinylidene fluoride (PVDF) piezoelectric film, place it in a culture dish, and tape the four edges together, leaving room for non-metallized edges and electrode leads, to obtain a functional layer. Step S2: Dispersed silver nanowires with a concentration of 3 mg / mL are drop-coated multiple times and evenly on both sides of the polyvinylidene fluoride (PVDF) piezoelectric film of the functional layer. After the ethanol in the system evaporates, a mesh-like conductive layer is formed, and the tape is removed; Step S3: Apply conductive silver glue on both sides and attach copper sheets to ensure that electrodes and sensing layers are laid on both sides of the functional layer; Step S4: taking a 3.5*3.5 cm portion of the non-edge area of ​​the polyurethane nanofiber membrane as a substrate and placing it in a culture dish; Step S5: A layer of 3.5 cm*3.5 cm polyurethane nanofiber membrane in the non-edge area is attached to the electrode and the sensing layer respectively, and pressed with a pressing roller to form a target flexible sensor.

10. Application of the flexible sensor based on silver nanowire material according to claims 1 to 9 in the fields of motion monitoring, human health monitoring, and human-computer interaction.

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