A flexible piezoresistive sensor and a method of manufacturing the same

Abstract

The application provides a flexible piezoresistive sensor and a preparation method thereof, and relates to the technical field of flexible pressure sensor preparation. The preparation of the flexible piezoresistive sensor comprises the following steps: S1, preparing an AgNWs dispersion liquid, a PVDF encapsulating solution, and pretreating a PVDF substrate; S2, coating a conductive silver paste on the surface of the pretreated PVDF substrate, adding the AgNWs dispersion liquid drop by drop after solidification, and preparing an AgNWs / PVDF composite film; and S3, adding the PVDF encapsulating solution drop by drop on the surface of the AgNWs / PVDF composite film, and preparing the flexible piezoresistive sensor after solidification, hot water immersion, and vacuum drying. The flexible piezoresistive sensor has a porosity of up to 78% and a pore diameter of 410 nm, has excellent air permeability and moisture permeability, and is suitable for high-performance intelligent wearable devices.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible pressure sensor preparation, in particular to a flexible piezoresistive sensor and a preparation method thereof. BACKGROUND

[0002] As a special kind of flexible pressure sensor, the flexible piezoresistive sensor has outstanding mechanical flexibility, high sensitivity, wide pressure detection range and simple preparation process, and thus has significant application potential and unique advantages in the fields of medical health monitoring (such as pulse waveform analysis and respiratory pattern recognition) and intelligent wearable devices. However, to realize the long-term physiological monitoring application of the flexible piezoresistive sensor on the surface of human skin, two key technical bottlenecks, i.e. wearing comfort and device stability, still need to be broken through.

[0003] At present, most researchers are committed to solving the problems of wearing comfort and device stability by optimizing the flexible substrate and the internal microstructure of the device. In view of the problem of wearing comfort, researchers usually use electrospinning technology to prepare a porous substrate to improve the air permeability and moisture permeability, although this method improves the comfort of the wearer, but the sensor made by this method often lacks sufficient stability. On the contrary, in order to enhance the stability and durability of the sensor, researchers try to use a polymer film as an encapsulation material to encapsulate the sensor, so as to improve the mechanical properties and durability of the sensor, however, the dense polymer film material also sacrifices the air permeability and moisture permeability, which may cause skin inflammation or allergy and other adverse consequences after long-term wearing.

[0004] In view of the fact that the existing solutions can only meet the requirements of wearing comfort or device stability, it is urgent to develop a flexible piezoresistive sensor which can guarantee air permeability and moisture permeability and provide sufficient stability to meet the needs of practical applications. SUMMARY

[0005] Therefore, the present application provides a flexible piezoresistive sensor and a preparation method thereof, which aims to realize excellent wearing comfort and device stability at the same time to meet the needs of long-term intelligent wearing.

[0006] In a first aspect, the present application provides a preparation method of a flexible piezoresistive sensor, comprising the following steps:

[0007] S1, preparing an AgNWs dispersion liquid, a PVDF encapsulation solution and pretreating a PVDF substrate;

[0008] S2, coating a conductive silver paste on the surface of the pretreated PVDF substrate, and after curing, dropping the AgNWs dispersion liquid to prepare an AgNWs / PVDF composite film;

[0009] S3, dropping a PVDF encapsulating solution on the surface of the AgNWs / PVDF composite film, and then performing hot water immersion and vacuum drying to obtain a flexible piezoresistive sensor.

[0010] In one or some possible embodiments, in step S1, the AgNWs dispersion liquid is prepared by dispersing AgNWs in anhydrous ethanol; and the concentration of the AgNWs dispersion liquid is 1.3 mg / L to 8.24 mg / L.

[0011] Further, the mass-volume ratio of the AgNWs to the anhydrous ethanol is (2.02-8.24) mg:(1-1.5) L.

[0012] In one or some possible embodiments, in step S1, the PVDF encapsulating solution is prepared by dissolving PVDF powder and PVP powder (polyvinylpyrrolidone) in an organic solvent; and the concentration of the PVDF encapsulating solution is 9.6-10.6 wt%.

[0013] Further, the organic solvent is selected from one of DMF (dimethylformamide), DMSO (dimethyl sulfoxide) or NMP (N-methyl-2-pyrrolidone); and the mass ratio of the PVDF powder, the PVP powder and the organic solvent is (4.8-5.3):(0.24-0.26):(44.55-45).

[0014] In one or some possible embodiments, in step S1, the diameter of the PVDF substrate can be selected according to actual needs, and in the present application, the diameter of the substrate is preferably 40-50 mm based on the principle of easy carrying and wearing.

[0015] In one or some possible embodiments, in step S2, the amount of the conductive silver paste varies with the diameter of the PVDF substrate.

[0016] In one or some possible embodiments, in step S2, the areal density of the AgNWs on the AgNWs / PVDF composite film is 0.0272-0.2261 mg / cm 2 .

[0017] In one or some possible embodiments, in step S2, the areal density of the AgNWs on the AgNWs / PVDF composite film is 0.0452-0.1804 mg / cm 2 .

[0018] Further, the AgNWs dispersion liquid is used in an amount of 2-10 mL. Specifically, the AgNWs dispersion liquid can be used in an amount of 2 mL, 4 mL, 6 mL, 8 mL or 10 mL and any value between the adjacent two numbers. Preferably, the AgNWs dispersion liquid is used in an amount of 2 mL, 4 mL, 6 mL, 8 mL or 10 mL, and the corresponding areal densities are 0.0272 mg / cm 2 , 0.0452 mg / cm 2 , 0.0904 mg / cm 2 , 0.1804 mg / cm 2 , 0.2261 mg / cm 2 .

[0019] Further preferably, the amount of the conductive silver paste is inversely proportional to the areal density. That is, in the present application, when the areal density is 0.0272 mg / cm 2 -0.2261 mg / cm 2 , the amount of the conductive silver paste is 10-2 mg. That is, in the present application, when the areal density is 0.0272 mg / cm 2 , the amount of the conductive silver paste is 10 mg; when the areal density is 0.0452 mg / cm 2 , the amount of the conductive silver paste is 8 mg; when the areal density is 0.2261 mg / cm 2 , the amount of the conductive silver paste is 2 mg, and so on.

[0020] In one or some possible embodiments, in step S3, the amount of the PVDF encapsulation solution is proportional to the size of the PVDF substrate. That is, in the present application, when the size of the PVDF substrate is 30 mm, the amount of the PVDF encapsulation solution is 3 mL; when the size of the PVDF substrate is 40 mm, the amount of the PVDF encapsulation solution is 4 mL; when the size of the PVDF substrate is 50 mm, the amount of the PVDF encapsulation solution is 5 mL, and so on.

[0021] In one or some possible embodiments, in step S3, the soaking temperature is 50-65℃ and the soaking time is 10-20 min.

[0022] By using the above technical solution, if the soaking time is too long, the stability and service life of the device will be affected; if the time is too short, the pore size is not large enough to ensure good air and moisture permeability, thereby affecting the comfort during wearing and the performance during long-term wearing.

[0023] In one or some possible embodiments, in step S3, the drying temperature is 50-65℃ and the drying time is 12-14 h.

[0024] In a second aspect, the present application relates to a flexible piezoresistive sensor prepared by the above preparation method. The sensor realizes the wearing comfort and stability of the device by optimizing the packaging process and the areal density of AgNWs (silver nanowires). Specifically, the present application uses an organic solution of PVDF-PVP as the packaging layer material. After the solution is solidified on the surface of the electrode layer, it is treated by water immersion to form a porous structure. In this process, the PVP and a small amount of organic solvent in the solidified solution are dissolved in water, thereby generating the required porous packaging layer. This packaging process, combined with the electrospun PVDF substrate, forms a permeable structure that is conducive to air and moisture permeability.

[0025] The flexible piezoresistive sensor and its preparation method provided by the present application have the following beneficial effects compared with the prior art:

[0026] (1) The preparation method of the flexible piezoresistive sensor of the present application precisely controls the pore size and porosity by optimizing the immersion time and the areal density of AgNWs, achieving a porosity of up to 78% and a pore size of 410 nm.

[0027] (2) The preparation method of the flexible piezoresistive sensor of the present application optimizes the packaging process, not only reducing the impact of long-term use of the sensor on the conductive material, but also firmly packaging the conductive material inside the sensor to prevent it from falling off, thereby providing higher stability than existing devices with air and moisture permeability technology, and increasing the cycle life by 6 times (MIYAMOTO A, LEE S, COORAY N F, et al. Inflammation-free, gas-permeable, lightweight, stretchable on-skin electronics with nanomeshes [J]. Nat Nanotechnol, 2017, 12(9): 907-13.). In addition, the preparation method also makes the packaging layer of the sensor form a porous structure. This structure not only ensures the stability of the device, but also endows the sensor with excellent air and moisture permeability, allowing it to be worn continuously for 12 hours without causing skin inflammation, effectively solving the problem of lack of air and moisture permeability in the stable device structure in the prior art, and successfully preparing a high-performance, comfortable wearable device.

[0028] (3)The flexible piezoresistive sensor prepared by the application ensures that no skin inflammation is caused after long-term wearing of 12 hours.At the same time, the sensor is enhanced in stability of the device due to the firm encapsulation layer, so that the sensor has a durability of up to 3000 cycles, and in the actual wearing test, the sensor shows a significant resistance change rate, indicating that the sensor can effectively respond to external pressure changes while maintaining high stability, embodying the potential application value of the sensor in the field of smart wearable devices. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0030] Figure 1 XRD test chart of the flexible piezoresistive sensor prepared for the embodiments 1-6 of the application;

[0031] Figure 2 Scanning electron microscope chart of the flexible piezoresistive sensor prepared for the embodiments 2-3 and the comparative examples 13-15 of the application;

[0032] Figure 3 Scanning electron microscope chart of the flexible piezoresistive sensor prepared for the embodiments 1, 2, 4 and the comparative examples 3, 4, 18 of the application;

[0033] Figure 4 Wearable time change chart of the flexible piezoresistive sensor prepared by the application under different AgNWs surface densities;

[0034] Figure 5 Wearable time change chart of the flexible piezoresistive sensor prepared by the application under different soaking times;

[0035] Figure 6 Chart of resistance change over time of the flexible piezoresistive sensor prepared by the application during wearing test;

[0036] Figure 7 Chart of resistance change rate change over time of the flexible piezoresistive sensor prepared by the application during wearing test;

[0037] Figure 8 Chart of resistance change rate change over cycle time of the flexible piezoresistive sensor prepared by the embodiment 5 of the application during cycle test. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0039] The present application will be further described in conjunction with specific examples. The protection scope of the present application is not limited by the following examples. The materials mainly involved in the examples are commercially available if no special source is indicated.

[0040] In the following examples, the preparation of silver nanowires (AgNWs) adopts the following steps:

[0041] Preheat 30 mL EG (ethylene glycol) solution in an oil bath at 65℃, and dissolve 0.24 g PVP powder in the EG solution under stirring. After the above solution is cooled to room temperature, 0.5 g of AgNO3 is added, and the stirring is continued until it is dissolved. Then, 7 mL of FeCL3 / EG solution (0.6 mM) is slowly dropped into the completely dissolved AgNO3 / EG solution. After the above mixed solution is stirred at room temperature for 3 min, it is condensed and refluxed at 130℃ for 5 h until the mixed solution has a metallic luster and appears silver gray. After standing and cooling to room temperature, it is centrifuged at 7500 r / min for 5 min. The AgNWs at the bottom are washed with acetone and EtOH (absolute ethanol) solution for multiple times to remove unreacted EG, and silver nanowires (AgNWs) are prepared.

[0042] Example 1

[0043] The present embodiment provides a preparation method of a flexible piezoresistive sensor, which comprises the following steps:

[0044] S1, 2.975 mg of AgNWs is added into 1 L of EtOH, and stirred for 1 h to prepare an AgNWs dispersion solution for standby use;

[0045] An EtOH is used to clean a PVDF filter membrane with a size of 50 mm (purchased from Longjin Membrane Industry Co., Ltd.) for standby use.

[0046] 5 g of PVDF powder and 0.25 g of PVP powder are dissolved in 44.75 g of N,N-dimethylformamide (DMF) to prepare a PVDF packaging solution for standby use.

[0047] S2, 6 mg of conductive silver paste is coated on the surface of the PVDF filter membrane, and stands for 6 h. After curing, 6 mL of the AgNWs dispersion solution is added dropwise on the surface of the PVDF filter membrane, and cured to prepare an AgNWs / PVDF composite membrane.

[0048] S3, 5 mL of the PVDF encapsulation solution was dropped on the surface of the AgNWs / PVDF composite film, after curing, the whole was immersed in hot water at 60℃ for 10 min, and then vacuum dried at 60℃ for 12 h to obtain the flexible piezoresistive sensor.

[0049] Example 2

[0050] The embodiment provides a preparation method of a flexible piezoresistive sensor, comprising the following steps:

[0051] S1, 2.975 mg of AgNWs was added into 1 L of EtOH, and stirred for 1 h to obtain an AgNWs dispersion solution for standby;

[0052] A PVDF filter membrane with a size of 50 mm (purchased from Longjin Membrane Industry Co., Ltd.) was cleaned with EtOH for standby;

[0053] 5 g of PVDF powder and 0.25 g of PVP powder were dissolved in 44.75 g of N,N-dimethylformamide (DMF) to obtain a PVDF encapsulation solution for standby.

[0054] S2, 6 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, and stood for 6 h, after curing, 6 mL of the AgNWs dispersion solution was dropped on the surface of the PVDF filter membrane, and cured to obtain an AgNWs / PVDF composite film.

[0055] S3, 5 mL of the PVDF encapsulation solution was dropped on the surface of the AgNWs / PVDF composite film, after curing, the whole was immersed in hot water at 60℃ for 15 min, and then vacuum dried at 60℃ for 12 h to obtain the flexible piezoresistive sensor.

[0056] Example 3

[0057] The embodiment provides a preparation method of a flexible piezoresistive sensor, comprising the following steps:

[0058] S1, 4.453 mg of AgNWs was added into 1 L of EtOH, and stirred for 1 h to obtain an AgNWs dispersion solution for standby;

[0059] A PVDF filter membrane with a size of 50 mm (purchased from Longjin Membrane Industry Co., Ltd.) was cleaned with EtOH for standby;

[0060] 5 g of PVDF powder and 0.25 g of PVP powder were dissolved in 44.75 g of N,N-dimethylformamide (DMF) to obtain a PVDF encapsulation solution for standby.

[0061] S2, 4 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, and was left to stand for 6 h. After curing, 8 mL of the AgNWs dispersion was added dropwise on the surface of the PVDF filter membrane, and was cured to obtain an AgNWs / PVDF composite membrane.

[0062] S3, 5 mL of the PVDF encapsulation solution was added dropwise on the surface of the AgNWs / PVDF composite membrane, and was left to stand for 6 h. After curing, the whole was immersed in hot water at 60℃ for 15 min, and was vacuum dried at 60℃ for 12 h to obtain a flexible piezoresistive sensor.

[0063] Example 4

[0064] The embodiment provides a preparation method of a flexible piezoresistive sensor, comprising the following steps:

[0065] S1, 2.231 mg of AgNWs was added into 1 L of EtOH, and was stirred for 1 h to obtain an AgNWs dispersion, which was prepared for use;

[0066] A PVDF filter membrane with a size of 50 mm (purchased from Longjin Membrane Industry Co., Ltd.) was cleaned with EtOH, and was prepared for use;

[0067] 5 g of PVDF powder and 0.25 g of PVP powder were dissolved in 44.75 g of N,N-dimethylformamide (DMF) to obtain a PVDF encapsulation solution, which was prepared for use.

[0068] S2, 8 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, and was left to stand for 6 h. After curing, 4 mL of the AgNWs dispersion was added dropwise on the surface of the PVDF filter membrane, and was cured to obtain an AgNWs / PVDF composite membrane.

[0069] S3, 5 mL of the PVDF encapsulation solution was added dropwise on the surface of the AgNWs / PVDF composite membrane, and was left to stand for 6 h. After curing, the whole was immersed in hot water at 60℃ for 20 min, and was vacuum dried at 60℃ for 12 h to obtain a flexible piezoresistive sensor.

[0070] Example 5

[0071] The embodiment provides a preparation method of a flexible piezoresistive sensor, comprising the following steps:

[0072] S1, 2.975 mg of AgNWs was added into 1 L of EtOH, and was stirred for 1 h to obtain an AgNWs dispersion, which was prepared for use;

[0073] A PVDF filter membrane with a size of 50 mm (purchased from Longjin Membrane Industry Co., Ltd.) was cleaned with EtOH, and was prepared for use;

[0074] A PVDF encapsulation solution was prepared by dissolving 5 g of PVDF powder and 0.25 g of PVP powder in 44.75 g of N,N-dimethylformamide (DMF), and was ready for use.

[0075] S2, 6 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, and was left to stand for 6 h. After curing, 6 mL of the AgNWs dispersion was added dropwise on the surface of the PVDF filter membrane, and was cured to obtain an AgNWs / PVDF composite film.

[0076] S3, 5 mL of the PVDF encapsulation solution was added dropwise on the surface of the AgNWs / PVDF composite film, and was left to stand for 10 min. After curing, the whole was immersed in hot water at 60°C for 20 min, and was vacuum dried at 60°C for 12 h to obtain a flexible piezoresistive sensor.

[0077] Example 6

[0078] The present example provides a method for preparing a flexible piezoresistive sensor, comprising the following steps:

[0079] S1, 4.453 mg of AgNWs was added into 1 L of EtOH, and was stirred for 1 h to obtain an AgNWs dispersion, which was ready for use.

[0080] A PVDF filter membrane with a size of 50 mm (purchased from Longjin Membrane Industry Co., Ltd.) was cleaned with EtOH, and was ready for use.

[0081] A PVDF encapsulation solution was prepared by dissolving 5 g of PVDF powder and 0.25 g of PVP powder in 44.75 g of N,N-dimethylformamide (DMF), and was ready for use.

[0082] S2, 4 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, and was left to stand for 6 h. After curing, 8 mL of the AgNWs dispersion was added dropwise on the surface of the PVDF filter membrane, and was cured to obtain an AgNWs / PVDF composite film.

[0083] S3, 5 mL of the PVDF encapsulation solution was added dropwise on the surface of the AgNWs / PVDF composite film, and was left to stand for 10 min. After curing, the whole was immersed in hot water at 60°C for 20 min, and was vacuum dried at 60°C for 12 h to obtain a flexible piezoresistive sensor.

[0084] Example 7

[0085] The present example provides a method for preparing a flexible piezoresistive sensor, comprising the following steps:

[0086] S1, 2.02 mg of AgNWs was added into 1 L of EtOH, and was stirred for 1 h to obtain an AgNWs dispersion, which was ready for use.

[0087] PVDF filter membrane (purchased from Longjin Membrane Industry Co., Ltd.) with a size of 40 mm was cleaned with EtOH and reserved for later use;

[0088] 4.8 g of PVDF powder and 0.24 g of PVP powder were dissolved in 44.55 g of N,N-dimethylformamide (DMF) to prepare a PVDF packaging solution, which was reserved for later use.

[0089] S2, 8 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, and was left to stand for 6 h. After curing, 2.82 mL of the AgNWs dispersion was added dropwise on the surface of the PVDF filter membrane, and was cured to prepare an AgNWs / PVDF composite film.

[0090] S3, 4 mL of the PVDF packaging solution was added dropwise on the surface of the AgNWs / PVDF composite film, and was left to stand for curing. After curing, the whole was immersed in hot water at 50℃ for 20 min, and was vacuum dried at 50℃ for 14 h to prepare a flexible piezoresistive sensor.

[0091] Example 8

[0092] The present example provides a preparation method of a flexible piezoresistive sensor, which comprises the following steps:

[0093] S1, 8.24 mg of AgNWs was added into 1.5 L of EtOH, and was stirred for 1 h to prepare an AgNWs dispersion, which was reserved for later use.

[0094] PVDF filter membrane (purchased from Longjin Membrane Industry Co., Ltd.) with a size of 40 mm was cleaned with EtOH and reserved for later use;

[0095] 5.3 g of PVDF powder and 0.26 g of PVP powder were dissolved in 45 g of N,N-dimethylformamide (DMF) to prepare a PVDF packaging solution, which was reserved for later use.

[0096] S2, 6 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, and was left to stand for 6 h. After curing, 4.15 mL of the AgNWs dispersion was added dropwise on the surface of the PVDF filter membrane, and was cured to prepare an AgNWs / PVDF composite film.

[0097] S3, 4 mL of the PVDF packaging solution was added dropwise on the surface of the AgNWs / PVDF composite film, and was left to stand for curing. After curing, the whole was immersed in hot water at 65℃ for 15 min, and was vacuum dried at 65℃ for 12 h to prepare a flexible piezoresistive sensor.

[0098] Comparative Example 1

[0099] The present example provides a preparation method of a flexible piezoresistive sensor, which comprises the following steps:

[0100] S1, 2.231 mg of AgNWs were taken into 1 L of EtOH, stirred for 1 h, to prepare an AgNWs dispersion solution, ready for use;

[0101] PVDF filter membranes with a size of 50 mm (purchased from Longjin Membrane Industry Co., Ltd.) were cleaned with EtOH, ready for use;

[0102] 5 g of PVDF powder and 0.25 g of PVP powder were dissolved in 44.75 g of N,N-dimethylformamide (DMF) to prepare a PVDF encapsulation solution, ready for use.

[0103] S2, 8 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, and after standing for 6 h, 4 mL of the AgNWs dispersion solution was added dropwise on the surface of the PVDF filter membrane, and after curing, an AgNWs / PVDF composite film was prepared.

[0104] S3, 5 mL of the PVDF encapsulation solution was added dropwise on the surface of the AgNWs / PVDF composite film, and after curing, the whole was immersed in hot water at 60°C for 4 min, and then vacuum dried at 60°C to prepare a flexible piezoresistive sensor.

[0105] Comparative Example 2

[0106] The preparation method of the flexible piezoresistive sensor provided by the comparative example comprises the following steps:

[0107] S1, 2.975 mg of AgNWs were taken into 1 L of EtOH, stirred for 1 h, to prepare an AgNWs dispersion solution, ready for use;

[0108] PVDF filter membranes with a size of 50 mm (purchased from Longjin Membrane Industry Co., Ltd.) were cleaned with EtOH, ready for use;

[0109] 5 g of PVDF powder and 0.25 g of PVP powder were dissolved in 44.75 g of N,N-dimethylformamide (DMF) to prepare a PVDF encapsulation solution, ready for use.

[0110] S2, 6 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, and after standing for 6 h, 6 mL of the AgNWs dispersion solution was added dropwise on the surface of the PVDF filter membrane, and after curing, an AgNWs / PVDF composite film was prepared.

[0111] S3, 5 mL of the PVDF encapsulation solution was added dropwise on the surface of the AgNWs / PVDF composite film, and after curing, the whole was immersed in hot water at 60°C for 4 min, and then vacuum dried at 60°C to prepare a flexible piezoresistive sensor.

[0112] Comparative Example 3

[0113] The preparation method of the flexible piezoresistive sensor provided by the comparative example comprises the following steps:

[0114] S1, 4.453 mg of AgNWs were taken into 1 L of EtOH, stirred for 1 h, to prepare an AgNWs dispersion solution, ready for use;

[0115] PVDF filter membranes with a size of 50 mm (purchased from Longjin Membrane Industry Co., Ltd.) were cleaned with EtOH and ready for use;

[0116] 5 g of PVDF powder and 0.25 g of PVP powder were dissolved in 44.75 g of N, N-dimethylformamide (DMF) to prepare a PVDF encapsulation solution, ready for use.

[0117] S2, 4 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, and stood for 6 h. After curing, 8 mL of AgNWs dispersion solution was added on the surface, and cured to prepare an AgNWs / PVDF composite film.

[0118] S3, 5 mL of PVDF encapsulation solution was added on the surface of the AgNWs / PVDF composite film, and after curing, the whole was immersed in hot water at 60°C for 4 min, and then vacuum dried at 60°C to prepare a flexible piezoresistive sensor.

[0119] Comparative Example 4

[0120] The preparation method of the flexible piezoresistive sensor provided by the comparative example comprises the following steps:

[0121] S1, 2.686 mg of AgNWs were taken into 1 L of EtOH, stirred for 1 h, to prepare an AgNWs dispersion solution, ready for use;

[0122] PVDF filter membranes with a size of 50 mm (purchased from Longjin Membrane Industry Co., Ltd.) were cleaned with EtOH and ready for use;

[0123] 5 g of PVDF powder and 0.25 g of PVP powder were dissolved in 44.75 g of N, N-dimethylformamide (DMF) to prepare a PVDF encapsulation solution, ready for use.

[0124] S2, 10 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, and stood for 6 h. After curing, 2 mL of AgNWs dispersion solution was added on the surface, and cured to prepare an AgNWs / PVDF composite film.

[0125] S3, 5 mL of PVDF encapsulation solution was added on the surface of the AgNWs / PVDF composite film, and after curing, the whole was immersed in hot water at 60°C for 5 min, and then vacuum dried at 60°C to prepare a flexible piezoresistive sensor.

[0126] Comparative Example 5

[0127] The preparation method of the flexible piezoresistive sensor provided by the comparative example comprises the following steps:

[0128] S1, 2.231 mg of AgNWs was added into 1 L of EtOH, stirred for 1 h, and an AgNWs dispersion was prepared for standby;

[0129] A PVDF filter membrane with a size of 50 mm (purchased from Longjin Membrane Industry Co., Ltd.) was cleaned with EtOH for standby;

[0130] 5 g of PVDF powder and 0.25 g of PVP powder were dissolved in 44.75 g of N,N-dimethylformamide (DMF) to prepare a PVDF encapsulation solution for standby.

[0131] S2, 8 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, and after standing for 6 h, 4 mL of the AgNWs dispersion was added dropwise on the surface of the PVDF filter membrane, and after curing, an AgNWs / PVDF composite film was prepared.

[0132] S3, 5 mL of the PVDF encapsulation solution was added dropwise on the surface of the AgNWs / PVDF composite film, and after curing, the whole was immersed in hot water at 60°C for 5 min, and then vacuum dried at 60°C to prepare a flexible piezoresistive sensor.

[0133] Comparative Example 6

[0134] The preparation method of the flexible piezoresistive sensor provided by the comparative example comprises the following steps:

[0135] S1, 2.975 mg of AgNWs was added into 1 L of EtOH, stirred for 1 h, and an AgNWs dispersion was prepared for standby;

[0136] A PVDF filter membrane with a size of 50 mm (purchased from Longjin Membrane Industry Co., Ltd.) was cleaned with EtOH for standby;

[0137] 5 g of PVDF powder and 0.25 g of PVP powder were dissolved in 44.75 g of N,N-dimethylformamide (DMF) to prepare a PVDF encapsulation solution for standby.

[0138] S2, 6 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, and after standing for 6 h, 6 mL of the AgNWs dispersion was added dropwise on the surface of the PVDF filter membrane, and after curing, an AgNWs / PVDF composite film was prepared.

[0139] S3, 5 mL of the PVDF encapsulation solution was added dropwise on the surface of the AgNWs / PVDF composite film, and after curing, the whole was immersed in hot water at 60°C for 5 min, and then vacuum dried at 60°C to prepare a flexible piezoresistive sensor.

[0140] Comparative Example 7

[0141] The preparation method of the flexible piezoresistive sensor provided by the comparative example comprises the following steps:

[0142] S1, 4.453 mg of AgNWs was added to 1 L of EtOH and stirred for 1 h to prepare an AgNWs dispersion solution for standby;

[0143] A PVDF filter membrane with a size of 50 mm (purchased from Longjin Membrane Industry Co., Ltd.) was cleaned with EtOH for standby;

[0144] 5 g of PVDF powder and 0.25 g of PVP powder were dissolved in 44.75 g of N,N-dimethylformamide (DMF) to prepare a PVDF packaging solution for standby.

[0145] S2, 4 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, and after standing for 6 h, 8 mL of the AgNWs dispersion solution was added dropwise on the surface of the PVDF filter membrane, and after curing, an AgNWs / PVDF composite film was prepared.

[0146] S3, 5 mL of the PVDF packaging solution was added dropwise on the surface of the AgNWs / PVDF composite film, and after curing, the whole was immersed in hot water at 60°C for 5 min, and then vacuum dried at 60°C to prepare a flexible piezoresistive sensor.

[0147] Comparative Example 8

[0148] The preparation method of the flexible piezoresistive sensor provided by the comparative example comprises the following steps:

[0149] S1, 4.453 mg of AgNWs was added to 1 L of EtOH and stirred for 1 h to prepare an AgNWs dispersion solution for standby;

[0150] A PVDF filter membrane with a size of 50 mm (purchased from Longjin Membrane Industry Co., Ltd.) was cleaned with EtOH for standby;

[0151] 5 g of PVDF powder and 0.25 g of PVP powder were dissolved in 44.75 g of N,N-dimethylformamide (DMF) to prepare a PVDF packaging solution for standby.

[0152] S2, 4 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, and after standing for 6 h, 8 mL of the AgNWs dispersion solution was added dropwise on the surface of the PVDF filter membrane, and after curing, an AgNWs / PVDF composite film was prepared.

[0153] S3, 5 mL of the PVDF packaging solution was added dropwise on the surface of the AgNWs / PVDF composite film, and after curing, the whole was immersed in hot water at 60°C for 5 min, and then vacuum dried at 60°C to prepare a flexible piezoresistive sensor.

[0154] Comparative Example 9

[0155] The difference from Example 1 is that in step S2, 10 mg of conductive silver paste is coated on the surface of the PVDF filter membrane, and after standing for 6 h, 2 mL of AgNWs dispersion is added dropwise on the surface after curing, and the AgNWs / PVDF composite film is prepared. The remaining steps remain unchanged.

[0156] Comparative Example 10

[0157] The difference from Example 1 is that in step S2, 8 mg of conductive silver paste is coated on the surface of the PVDF filter membrane, and after standing for 6 h, 4 mL of AgNWs dispersion is added dropwise on the surface after curing, and the AgNWs / PVDF composite film is prepared. The remaining steps remain unchanged.

[0158] Comparative Example 11

[0159] The difference from Example 1 is that in step S2, 4 mg of conductive silver paste is coated on the surface of the PVDF filter membrane, and after standing for 6 h, 8 mL of AgNWs dispersion is added dropwise on the surface after curing, and the AgNWs / PVDF composite film is prepared. The remaining steps remain unchanged.

[0160] Comparative Example 12

[0161] The difference from Example 1 is that in step S2, 2 mg of conductive silver paste is coated on the surface of the PVDF filter membrane, and after standing for 6 h, 10 mL of AgNWs dispersion is added dropwise on the surface after curing, and the AgNWs / PVDF composite film is prepared. The remaining steps remain unchanged.

[0162] Comparative Example 13

[0163] The difference from Example 2 is that in step S2, 10 mg of conductive silver paste is coated on the surface of the PVDF filter membrane, and after standing for 6 h, 2 mL of AgNWs dispersion is added dropwise on the surface after curing, and the AgNWs / PVDF composite film is prepared. The remaining steps remain unchanged.

[0164] Comparative Example 14

[0165] The difference from Example 2 is that in step S2, 8 mg of conductive silver paste is coated on the surface of the PVDF filter membrane, and after standing for 6 h, 4 mL of AgNWs dispersion is added dropwise on the surface after curing, and the AgNWs / PVDF composite film is prepared. The remaining steps remain unchanged.

[0166] Comparative Example 15

[0167] The difference from Example 2 is that: in step S2, 2 mg of conductive silver paste is coated on the surface of the PVDF filter membrane, and after standing for 6 h, 10 mL of AgNWs dispersion is added dropwise on the surface of the cured PVDF filter membrane, and the AgNWs / PVDF composite film is prepared. The remaining steps remain unchanged.

[0168] Comparative Example 16

[0169] The difference from Example 4 is that: in step S2, 10 mg of conductive silver paste is coated on the surface of the PVDF filter membrane, and after standing for 6 h, 2 mL of AgNWs dispersion is added dropwise on the surface of the cured PVDF filter membrane, and the AgNWs / PVDF composite film is prepared. The remaining steps remain unchanged.

[0170] Comparative Example 17

[0171] The difference from Example 4 is that: in step S2, 2 mg of conductive silver paste is coated on the surface of the PVDF filter membrane, and after standing for 6 h, 10 mL of AgNWs dispersion is added dropwise on the surface of the cured PVDF filter membrane, and the AgNWs / PVDF composite film is prepared. The remaining steps remain unchanged.

[0172] Comparative Example 18

[0173] The preparation method of the flexible piezoresistive sensor provided by the comparative example comprises the following steps:

[0174] S1, 7.18 mg of AgNWs is added into 1 L of EtOH, and stirred for 1 h to prepare an AgNWs dispersion, which is prepared for use;

[0175] A PVDF filter membrane with a size of 50 mm (purchased from Longjin Membrane Industry Co., Ltd.) is cleaned with EtOH and prepared for use.

[0176] 5 g of PVDF powder and 0.25 g of PVP powder are dissolved in 44.75 g of N,N-dimethylformamide (DMF) to prepare a PVDF encapsulation solution, which is prepared for use.

[0177] S2, 8 mg of conductive silver paste is coated on the surface of the PVDF filter membrane, and after standing for 6 h, 4 mL of AgNWs dispersion is added dropwise on the surface of the cured PVDF filter membrane, and the AgNWs / PVDF composite film is prepared.

[0178] S3, 5 mL of PVDF encapsulation solution is added dropwise on the surface of the AgNWs / PVDF composite film, and after curing, the whole is immersed in hot water at 60°C for 25 min, and then vacuum dried at 60°C to prepare a flexible piezoresistive sensor.

[0179] Comparative Example 19

[0180] The difference from Comparative Example 18 is as follows: S2, 6 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, allowed to stand for 6 hours to cure, and then 6 mL of AgNWs dispersion was dropped onto its surface and cured to obtain the AgNWs / PVDF composite membrane. The remaining steps remained unchanged.

[0181] Comparative Example 20

[0182] The difference from Comparative Example 18 is as follows: S2, 4 mg of conductive silver paste was coated on the surface of the PVDF filter membrane, allowed to stand for 6 hours to cure, and then 8 mL of AgNWs dispersion was dropped onto its surface and cured to obtain the AgNWs / PVDF composite membrane. The remaining steps remained unchanged.

[0183] The inventors performed XRD tests on the flexible piezoresistive sensors prepared in Examples 1-6, and the results are as follows: Figure 1 As shown.

[0184] Depend on Figure 1 It can be seen that the silver nanowires were successfully spread on the PVDF substrate.

[0185] The inventors performed scanning electron microscopy tests on the flexible piezoresistive sensors prepared in Examples 2-3 and Comparative Examples 13-15, and the results are as follows: Figure 2 As shown.

[0186] Depend on Figure 2 It is known that excessively high or low areal density will affect the conductive network and pore size inside the device, thereby affecting the sensor's air and moisture permeability and electrical signal changes.

[0187] The inventors performed scanning electron microscopy tests on the flexible piezoresistive sensors prepared in Comparative Examples 3-4, Examples 1, 2, 4, and Comparative Example 18. The results are as follows: Figure 3 As shown.

[0188] Depend on Figure 3 It can be seen that the pore size inside the device increases with the increase of immersion time. Although a larger pore size results in better air permeability and better force transmission, the stability of the device will gradually decrease.

[0189] Taking Examples 1-6 and Comparative Examples 1-20 as examples, the flexible piezoresistive sensors prepared therein were subjected to wear comfort tests. The test method was as follows: Since most people's swallowing habits are usually concentrated within 12 hours a day, this invention uses whether an inflammatory reaction occurs on the skin surface after wearing for 12 hours as the standard for assessing whether it is suitable for long-term wear. The specific judgment criteria are: if the wearing time reaches or exceeds 12 hours and no skin inflammation is caused, it is judged as "√"; if the wearing time is less than 12 hours or skin inflammation occurs, it is judged as "×". The test results are shown in Table 1.

[0190] Table 1 Wearable Time Description

[0191]

[0192]

[0193] The inventors further analyzed the flexible piezoresistive sensors prepared in the above examples and comparative examples, and the results are shown in Figure 4 、 5 .

[0194] As can be seen from Table 1 and Figure 4 , when the soaking time in step S3 is constant, the wearable time gradually decreases as the AgNWs surface density increases. It can be explained that when the influence of soaking time on the pore size is fixed, the increase in the number of silver nanowires will gradually cover the porous structure of the sensor, resulting in poor air and moisture permeability of the device, and thus affecting the wearable time.

[0195] As can be seen from Table 1 and Figure 5 , when the AgNWs surface density in step S2 is constant, the wearable time gradually increases as the soaking time increases. It can be explained that in terms of air and moisture permeability, when the influence of AgNWs surface density on the pore size is fixed, the longer the soaking time, the larger the pore size, the greater the porosity, and thus the better the air and moisture permeability.

[0196] To balance the influence of AgNWs surface density and soaking time on wearable devices, the inventors conducted wearable physiological information monitoring tests on the examples 1-6, comparative examples 4-5, comparative examples 9-10, comparative examples 13-14, comparative example 16, and comparative examples 18-20.

[0197] The electrical signal acquisition device (DMM7510 digital multimeter) was connected to the interdigital electrode of the prepared flexible piezoresistive sensor by wire, and the flexible piezoresistive sensor was pasted on the volunteer's Adam's apple for physiological information monitoring. In combination with the signal acquisition software (Kick Start 2), the resistance change rate (△R / R0) was obtained by recording the signal of the change of resistance with time during the swallowing process. The size of the obtained resistance change rate was used to determine whether the subsequent cycle stability test was needed. If the resistance change rate did not exceed 1% or the signal offset, the cycle test was not considered.

[0198] The inventors first selected samples with AgNWs surface densities of 0.0272 mg / cm 2 and 0.0452 mg / cm 2 , and soaking times from 5 min to 20 min, including comparative example 4, comparative example 9, comparative example 13, comparative example 16, comparative example 5, comparative example 10, comparative example 14, and example 4. The test results are shown in Figure 6 .

[0199] Depend on Figure 6 It can be seen that in Comparative Examples 4 to 16, due to the low content of silver nanowires, no significant change in electrical signal occurred during the pressure process. However, in Comparative Examples 5 to Example 4, as the soaking time increased, a weak electrical signal appeared after 20 minutes of soaking, indicating that low areal density requires long-term soaking to create large pores in order to improve force conduction and thus generate an electrical signal.

[0200] The inventors then performed the above tests on Examples 1-3, Examples 5-6, and Comparative Examples 18-20, and obtained the following results: Figure 7 The test results are shown.

[0201] Combining Examples 1, 2, and 5 and Figure 7 It can be seen that, with a constant areal density, the rate of change of resistivity increases with increasing immersion time. This indicates that, under a superior internal conductive network, a longer immersion time results in a larger pore size, which is more conducive to force conduction, thereby improving the change in electrical signal.

[0202] Combining Examples 2-3 and Examples 5-6 and Figure 7 It can be seen that, with a constant soaking time, the rate of change of resistivity gradually decreases. This indicates that the surface density is 0.1804 mg / cm³. 2 The internal conductive network is too dense, causing the internal contact point changes to not occur under pressure (0.0904 mg / cm). 2 There are more changes.

[0203] Combining comparative examples 18–20 and Figure 7 It can be seen that within a reasonable range of AgNWs areal density, excessive soaking time will cause the pore size to be too large, resulting in structural instability and thus signal drift.

[0204] The resistance change rate records of Examples 1 to 6 during wearable testing are compiled in Table 2 below.

[0205] Table 2 Wearable Test Results

[0206] Rate of resistance change / % Example 1 3.5％ Example 2 5％ Example 3 4％ Example 4 1％ Example 5 6％ Example 6 4.5％

[0207] The inventors used the flexible piezoresistive sensors prepared in Examples 1-6 as examples to conduct cyclic stability tests. The test method was as follows: after connecting the prepared sensor and the electrical signal acquisition device, it was placed in a pressure testing device (INSTRON 5967 universal testing machine) and subjected to dynamic cyclic testing, performing continuous loading-unloading cyclic tests at 10 kPa. The test results are shown in Table 3 and... Figure 8 As shown.

[0208] Table 3 Results of Cyclic Test

[0209] Rate of resistance change / % Cycle time Example 1 5％ 3000s Example 2 10％ 2000s Example 3 11％ 2000s Example 4 1％ 1000s Example 5 9.5％ 1000s Example 6 10.5％ 1000s

[0210] Combine Tables 1-3 and Figure 8 It can be known that:

[0211] (1) From the resistivity change rate of Examples 1 and 2, the surface density is 0.0904 mg / cm³. 2 To achieve a higher electrical signal, the immersion time needs to be extended.

[0212] (2) It can be seen from the resistance change rate of Examples 2 and 3 that the resistance change rate gradually increases under the same soaking time.

[0213] (3) As can be seen from Examples 1-2 and Examples 4-6, the cycle stability decreases as the soaking time increases.

[0214] (4) In Example 4, the resistivity change rate was small due to the low surface density during long soaking time.

[0215] (5) Examples 4-6 show that as the surface density gradually increases, the rate of change of resistivity also increases. When it exceeds 0.0904 mg / cm³, the rate of change of resistivity also increases. 2 It began to show a downward trend at that time.

[0216] This demonstrates that, in achieving long-term wearability, both areal density and immersion time affect the rate of change in electrical resistance. Specifically, when areal density is constant, longer immersion time can increase the rate of change in electrical resistance, but excessively long immersion times will lead to a decrease in cycle life. When immersion time is constant, increasing areal density can increase the rate of change in electrical resistance, but continuously increasing areal density will not lead to a sustained increase in the rate of change in electrical resistance; instead, it will increase production costs.

[0217] Therefore, to further balance the relationship between areal density and immersion time, and to fabricate a flexible piezoresistive sensor that combines wearability and device stability, the inventors further optimized the areal density of AgNWs to be 0.0452–0.1804 mg / cm³. 2 Soaking time is 10-20 minutes.

[0218] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating a flexible piezoresistive sensor, characterized in that, Includes the following steps: S1. Prepare AgNWs dispersion and PVDF encapsulation solution and pretreat the PVDF substrate; S2. A conductive silver paste is coated on the surface of the pretreated PVDF substrate, and after curing, AgNWs dispersion is added dropwise to obtain an AgNWs / PVDF composite film. S3. A PVDF encapsulation solution was dropped onto the surface of the AgNWs / PVDF composite film. After curing, the film was soaked in hot water and then vacuum dried to obtain a flexible piezoresistive sensor. In step S1, the PVDF encapsulation solution is prepared by dissolving PVDF powder and PVP powder in an organic solvent; the concentration of the PVDF encapsulation solution is 9.6~10.6 wt%.

2. The method for fabricating a flexible piezoresistive sensor as described in claim 1, characterized in that, In step S1, the AgNWs dispersion is prepared by dispersing AgNWs in anhydrous ethanol; the concentration of the AgNWs dispersion is 1.3 mg / L to 8.24 mg / L.

3. The method for fabricating the flexible piezoresistive sensor as described in claim 2, characterized in that, The mass-to-volume ratio of the AgNWs to the anhydrous ethanol is (2.02~8.24) mg: (1~1.5) L.

4. The method for fabricating the flexible piezoresistive sensor as described in claim 1, characterized in that, The organic solvent is selected from DMF, DMSO or NMP; The mass ratio of the PVDF powder, the PVP powder, and the organic solvent is (4.8~5.3):(0.24~0.26):(44.55~45).

5. The method for fabricating a flexible piezoresistive sensor as described in claim 1, characterized in that, In step S2, the areal density of the AgNWs on the AgNWs / PVDF composite film is 0.0272~0.2261 mg / cm³. 2 .

6. The method for fabricating a flexible piezoresistive sensor as described in claim 5, characterized in that, In step S2, the areal density of the AgNWs on the AgNWs / PVDF composite film is 0.0452~0.1804 mg / cm³. 2 .

7. The method for fabricating a flexible piezoresistive sensor as described in claim 1, characterized in that, In step S3, the soaking temperature is 50~65℃ and the soaking time is 10~20min.

8. The method for fabricating a flexible piezoresistive sensor as described in claim 7, characterized in that, In step S3, the temperature is 50~65℃ and the drying time is 12~14h.

9. A flexible piezoresistive sensor, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

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