Preparation method of wearable piezoelectric sensor, piezoelectric test experimental device and application

Abstract

The application belongs to the technical field of nanocomposite fiber synthesis and piezoelectric sensor and energy storage device preparation, and discloses a preparation method of a wearable piezoelectric sensor, a piezoelectric test experimental device and application. The preparation method comprises the following steps: synthesizing and preparing metal conductive ion-doped semiconductor nanocrystal particles by using a chemical hydrothermal method; mixing with a solution containing a piezoelectric organic polymer, and preparing a flexible nanocomposite fiber felt as a piezoelectric layer by using an electrostatic spinning process; sputtering conductive powder slurry as electrodes on the upper and lower surfaces of the flexible nanocomposite fiber felt, and then performing packaging. The application dopes a certain amount of semiconductor nanocrystals and metal nanoparticles in a PVDF polymer, greatly improves the piezoelectric effect of the composite material and the controllability of the output electric performance, and combines a sensor device preparation process method to achieve the application requirements of a flexible wearable device with high sensitivity and durability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanocomposite fiber synthesis and piezoelectric sensor and energy storage device preparation, and particularly relates to a preparation method of a wearable piezoelectric sensor based on a flexible nanocomposite fiber felt, a wearable piezoelectric sensor, a piezoelectric nanogenerator, a pressure sensor and a piezoelectric test experimental device. BACKGROUND

[0002] With the advent of the concept of smart wearable and the development of mechanical energy capture and collection, flexible piezoelectric sensors have received extensive attention in various fields. Small size, light weight, recyclable, fast response, and good feedback to various mechanical energy signals make the development of flexible piezoelectric sensors (FPES) a research hotspot. With the increasing severity of social population aging, people's concern for their own health has increased, and the demand for home self-testing equipment, especially small wearable devices, has increased dramatically. When piezoelectric materials are subjected to pressure, they can convert mechanical energy into electrical energy, making them a choice for new energy storage materials. By using the properties of piezoelectric materials, they can be made into various sensor elements, micro-nano energy devices, etc. The kinetic energy of daily activities can be converted into electrical energy and stored in the device. The stored electrical energy can be used to read and control the sensor signal, providing accurate detection data. Flexible piezoelectric sensors are based on the piezoelectric effect caused by the dielectric polarization of polymers. Under the action of mechanical force, the polarized molecules cause changes in surface charge density due to asymmetry, thereby exhibiting the characteristics of converting mechanical energy into electrical energy. Representative flexible organic polymer matrix materials include one or two of polyvinylidene fluoride (PVDF), polyvinylidene-trifluoroethylene (P(VDFTrFE)), and polyvinylidene fluoride-trifluoroethylene-hexafluoropropylene (P(VDF-TrFE-HFP)). The β phase in the PVDF crystal has the largest piezoelectric, ferroelectric, pyroelectric, and dielectric properties. Researchers in the technical field have tried various methods such as electrospinning, high electric field, stretching PVDF film, and polarity induction of nanofillers to increase the content of polar β crystals in PVDF, with different results. For example, Li et al. published an article in 2020 in the Advanced Materials journal, volume 33, number 2006093, titled "High-Performance Poly(vinylidene difluoride) / Dopamine Core / Shell Piezoelectric Nanofiber and Its Application for Biomedical Sensors", which records the increase in performance by doping fillers. The synthesis of nanofillers and the proportion of co-doping will have different effects on the performance of FPES. Common nanofillers are inorganic piezoelectric materials such as lead zirconate titanate PZT, barium titanate BTO, barium strontium titanate BST, or silver nanofibers, multi-walled carbon nanotubes, etc. are compounded with polymers to form oriented sleeve structure fibers.

[0003] For flexible piezoelectric sensor FPES, the classic structure is always a sandwich composite layer structure, the upper and lower surfaces of the piezoelectric film are pasted with metal foil as electrodes, then lead out the wires, and finally encapsulated with PI and other organic films. However, the existing FPES structure and materials will generate triboelectric signals at the same time of generating piezoelectric signals. Although many papers report the preparation of piezoelectric sensors with sandwich structure, however, the generation of triboelectric signals for this sandwich structure device is inevitable. Long-term mechanical force makes the metal foil electrode and piezoelectric film and the metal foil electrode and organic encapsulation layer produce larger gaps, which will lead to obvious friction, resulting in device heating and failure. For example, Li et al. published an article in 2021 in the journal Chemical Engineering Journal, volume 426, number 130345, titled Boosting piezoelectric and triboelectric effects of PVDF nanofiber through carbon-coated piezoelectric nanoparticles for highly sensitive wearable sensors. The flexible piezoelectric device prepared in the paper can also generate triboelectric signals. Chen et al. published an article in 2022 in the journal Nature Communications, volume 13, number 1391, titled A method for quantitatively separating the piezoelectric component from the as-received“Piezoelectric”signal. The paper proposes a method for distinguishing signals with both triboelectric and piezoelectric characteristics, but does not point out the specific method for preparing FPES with single piezoelectric signal.

[0004] Therefore, it is of practical significance to synthesize suitable nanofillers to increase the piezoelectric properties of PVDF. Moreover, separating triboelectricity from piezoelectricity and preparing FPES with single piezoelectric signal still faces great challenges, and there is no report in this regard. Therefore, the work of the present application is of great significance.

[0005] Electrospinning technology is currently recognized as a simple and low-cost method for preparing micron and nanometer fiber materials. Compared with the commonly used solid thin film, the PVDF composite fiber mat prepared by electrospinning technology has the advantages of good flexibility, high piezoelectric phase content (more than 80%), low density, good air permeability, and the polarization step of traditional piezoelectric PVDF film preparation is omitted, and the simplified preparation process is more conducive to industrial production. At present, the main problem of PVDF material based on piezoelectric performance is that the electric performance output is relatively low, which cannot meet the use demand of piezoelectric sensor.

[0006] Through the above analysis, the problems and defects of the prior art are:

[0007] (1) The preparation process of the prior art is complicated, the manufacturing cost is high, and the piezoelectric device prepared has poor sensitivity and durability.

[0008] (2) In the prior art, the device prepared has different response signals corresponding to different mechanical force excitations, and the signal resolution is poor.

[0009] (3) The flexible piezoelectric sensor prepared in the prior art does not have self-powered characteristics. SUMMARY

[0010] In order to overcome the problems in the related art, the present application provides a preparation method of a wearable piezoelectric sensor based on a flexible nanocomposite fiber mat, a wearable piezoelectric sensor, a piezoelectric nanogenerator, a pressure sensor, and a piezoelectric test experimental device, which specifically relates to an electrospinning method for preparing a nanofiber mat and a piezoelectric sensor device, and a preparation method and energy storage and sensing application, i.e. a preparation method and application of a wearable piezoelectric sensor based on a flexible nanocomposite fiber mat. The present application adopts a certain amount of semiconductor nanocrystals and metal nanoparticles doped in a PVDF polymer, which greatly improves the piezoelectric effect of the composite material and the controllability of the output electric performance, and combines the preparation process of the sensor device to meet the application requirements of a flexible wearable device with high sensitivity and durability.

[0011] The technical solution is as follows: a preparation method of a wearable piezoelectric sensor based on a flexible nanocomposite fiber mat includes:

[0012] Step one, metal conductive ion doped semiconductor nanocrystal particles are synthesized and prepared by a chemical hydrothermal method;

[0013] Step two, a flexible nanocomposite fiber mat is prepared as a piezoelectric layer by mixing a solution containing a piezoelectric organic polymer through an electrospinning process;

[0014] Step three, sputtering conductive slurry on the upper and lower surfaces of the flexible nanocomposite fiber felt as electrodes, and leading out the positive and negative electrode lines; then using double-sided tape to sandwich the prepared nanofiber felt with the upper and lower electrode layers and the electrode line combination into a flexible plastic film for packaging, to obtain the piezoelectric sensor based on the flexible nanocomposite fiber felt.

[0015] In an embodiment, the chemical hydrothermal method for synthesizing metal ion doped semiconductor nanoparticles comprises the following steps: in the first step, a zinc-containing compound, a solvent and deionized water are uniformly mixed, heated in a container, and incubated for a certain time to complete the conversion of the zinc compound into zinc oxide nanocrystals;

[0016] In the second step, ZnO@Ag particles are prepared.

[0017] In an embodiment, in the first step, the zinc-containing compound includes zinc acetate dihydrate, zinc acetylacetonate, or zinc nitrate;

[0018] The solvent includes triethanolamine, oleylamine, and polyether polyol.

[0019] The obtained reaction product is centrifuged and washed with deionized water and ethanol, and dried in a vacuum oven to obtain zinc oxide nanocrystal particles.

[0020] A capping agent is added to the mixture of the zinc-containing compound, the solvent and the deionized water, and the capping agent includes polyethylene glycol and triphenyl phosphate.

[0021] The molar ratio of the zinc compound to the solvent is 1:10-1:100.

[0022] The heating temperature is 100-205℃, and the reaction time is 30-120 minutes.

[0023] In the second step, the preparation of ZnO@Ag particles comprises the following steps:

[0024] Polyvinylpyrrolidone is dissolved in an aqueous silver ion solution, and stirred uniformly in the dark; the concentration of the aqueous silver ion solution is 0.05 mol / L; the content of polyvinylpyrrolidone is 2.5-3.5 g, which is dissolved in 20 ml of the above aqueous silver ion solution; the silver-containing solution is added to the mixture of the zinc oxide nanocrystals in the first step, and the mixture is heated to obtain a dispersion of silver-doped zinc oxide nanoparticles; the obtained product is centrifuged and washed with deionized water and ethanol, and dried in a vacuum oven to obtain silver-doped zinc oxide ZnO@Ag NPs particles.

[0025] In an embodiment, in the second step, the nano-zinc oxide crystal particle powder prepared in the first step is dissolved in deionized water and ultrasonically pulverized, then a silver-containing solution is added and uniformly mixed, heated and kept warm in an oil bath, and cooled to obtain a silver-doped nano-zinc oxide particle solution.

[0026] In an embodiment, in the second step, the piezoelectric organic polymer includes one or two of polyvinylidene fluoride (PVDF), polyvinylidene-trifluoroethylene (P(VDF-TrFE)), and polyvinylidene fluoride-trifluoroethylene-hexafluoropropylene (P(VDF-TrFE-HFP));

[0027] The preparation of a mixed solution containing a piezoelectric organic polymer, and the preparation of a flexible nanocomposite fiber mat as a piezoelectric layer by an electrospinning process specifically includes the following steps:

[0028] (1) Dissolve polyvinylidene fluoride powder in a mixed solution of N,N-dimethylformamide (DMF) and acetone (ACE); the concentration of PVDF is 10-20% by mass ratio, and the solution is magnetically stirred at a temperature of 60°C for 4 hours to obtain a transparent solution;

[0029] (2) Add the prepared ZnO@Ag NPs powder to the obtained polyvinylidene fluoride transparent solution, and ultrasonically oscillate at room temperature for 30 minutes, then continue to magnetically stir for 2 hours to obtain a uniform solution; the solution is ZnO@Ag NPs / PVDF-x%, where x% is the mass content of ZnO@Ag NPs powder;

[0030] (3) Use an electrospinning device to prepare the ZnO@Ag NPs / PVDF nanocomposite fiber mat at a room temperature of 25°C.

[0031] In an embodiment, in the step (1), the volume ratio of DMF to ACE in the mixed solution of N,N-dimethylformamide (DMF) and acetone (ACE) is 3:2, and the concentration of PVDF is 10-20% by mass ratio;

[0032] In the step (2), the mass content of ZnO@Ag NPs powder in the prepared polyvinylidene fluoride solution is 3-7% by mass ratio;

[0033] In the step (3), the electrospinning system is composed of a 5ml syringe with a flow rate of 2ml / h and a 22G flat steel needle spinneret, a positive voltage of 16kV is applied to the spinneret, and a luer connector and a liquid guide are connected between the 5ml syringe and the spinneret; a roller collector with a rotation speed of 1000rpm is placed 15cm away from the spinneret to collect nanofibers.

[0034] Another object of the present invention is to provide a wearable piezoelectric sensor prepared using the preparation method, wherein the wearable piezoelectric sensor comprises: an upper PI packaging layer and a lower PI packaging layer located on the upper and lower surfaces;

[0035] The inner walls of the upper PI packaging layer and the lower PI packaging layer respectively encapsulate the upper copper paste electrode layer and the lower copper paste electrode layer; and a piezoelectric fiber layer is filled between the upper copper paste electrode layer and the lower copper paste electrode layer.

[0036] Another object of the present invention is to provide a piezoelectric nanogenerator prepared using the wearable piezoelectric sensor.

[0037] Another object of the present invention is to provide a pressure sensor prepared using the wearable piezoelectric sensor.

[0038] Another object of the present invention is to provide a piezoelectric testing experimental device equipped with the wearable piezoelectric sensor, comprising a wearable piezoelectric sensor;

[0039] The wearable piezoelectric sensor is connected to a voice coil motor, a signal conversion and acquisition system, and a control system through lines.

[0040] Combining all the above technical solutions, the advantages and positive effects of the present invention are as follows:

[0041] First, in view of the technical problems existing in the above-mentioned prior art and the difficulty of solving these problems, this paper closely combines the technical solutions to be protected by the present invention and the results and data during the research and development process, and analyzes in detail and in depth how the technical solutions of the present invention solve the technical problems and some creative technical effects brought about by solving the problems. The specific description is as follows:

[0042] The present application aims at the shortcomings and limitations of the pure PVDF polymer used in the prior art in piezoelectric performance, and provides a preparation method of a high-performance piezoelectric composite flexible nanofiber mat and a wearable sensor device thereof, wherein a certain amount of semiconductor nanocrystals and metal nanoparticles are doped in the flexible piezoelectric polymer PVDF, so as to greatly improve the piezoelectric effect of the composite material and the controllability of the output electric performance, the metal conductive particles strengthen the surface charge density, and at the same time improve the energy level transition of the surface of the semiconductor particles and strengthen the energy storage characteristics, and experiments show that the addition of the nanoparticles of the present application also improves the content of the beta phase in the PVDF to 20%, thereby further improving the piezoelectric performance of the device. The present application uses the conductive powder slurry of Cu or Ag sputtered or sprayed on the surface of the electrospun fiber mat as two electrodes, which increases the flexibility of the electrodes themselves, avoids the problem of heat generated by friction, and the conductive powder slurry is also used to bond the copper wire to lead out the positive and negative electrodes, and then the device is packaged in the middle of two pieces of flexible plastic film, the preparation process of the present application is simple, the manufacturing cost is low, and the piezoelectric device prepared has high sensitivity of the electric signal output and good durability. The energy storage characteristics of the piezoelectric device are proved by using LED lamp beads, and the output electric signal characteristics of the piezoelectric device and the durability of the device under actual application conditions are verified by using different motion signals. The present application selects environmentally friendly materials, and the piezoelectric sensor after failure or damage can be recycled, the nanofiber mat is dissolved with a solvent to prepare a new spinning solution, and the nanofiber mat is prepared again by electrospinning, and the piezoelectric sensor is made again according to the related design scheme, and the performance is unchanged.

[0043] Secondly, from the perspective of the product as a whole, the technical effects and advantages of the technical solution to be protected by the present application are described as follows:

[0044] The application proposes a new method for enhancing the output performance of a flexible piezoelectric sensor by doping a metal conductive ionic filler with synthetic semiconductor nanoparticles, prepares a piezoelectric sensor based on a flexible ZnO@Ag NPs / PVDF composite fiber felt, and studies the optimal doping proportion of ZnO@Ag NPs powder. The ZnO@Ag NPs in the flexible piezoelectric sensor (FPES) prepared by the application can produce a synergistic effect. First, the conductivity of ZnO@Ag NPs can increase the volume charge density in the electrospinning process, which can enhance the polarization of the dipole in the PVDF molecule. Second, the increased charge density can improve the electric field force, thereby improving the stretching effect of the electric field force on PVDF and synergistically improving the content of the piezoelectric phase of the nanofiber. Meanwhile, ZnO itself is a piezoelectric material, and when the FPES is stressed, ZnO is also stressed to produce a piezoelectric voltage. Ag is a good conductor and has good charge transfer and storage capacity, so that the FPES can generate a larger voltage in a short time. When the optimal doping proportion of the ZnO@Ag NPs powder is 5wt%, the output voltage of the FPES is 13.6V (the contact area is 20mmx10mm), and the current is maintained at 2.605muA. After 5000 cycles, the nanofiber felt still maintains good repeatability, and the fiber morphology of the nanofiber felt after the cycle is found to be the same as that of the original nanofiber felt, and the piezoelectric performance remains unchanged. The PVDF nanofiber felt added with the ZnO@Ag NPs powder has superhydrophobicity on the surface, has waterproof protection in use, and enhances the durability of the device. The application produces different response signals under different mechanical force excitations, has good signal resolution, and has good sensing sensitivity. The method of the application can effectively separate the triboelectricity and output a single piezoelectric signal, effectively improve the piezoelectric output performance of the FPES, and provide a new strategy for the development of flexible piezoelectric sensors. The application also shows that the flexible piezoelectric sensor has self-powered characteristics (without external power supply) when used in wearable electronic devices, and has good application value in the collection of various mechanical energy and signal sensing.

[0045] Third, as the creative auxiliary evidence of the claims of the application, it is also embodied in the following important aspects:

[0046] (1) The application field of the technical scheme of the application after transformation includes intelligent wear of human body, intelligent robots, intelligent mechanical equipment, intelligent observation and control of home, etc., and has high commercial value and expected income.

[0047] (2) The application adds inorganic nanomaterials in the field occupied by flexible organic materials, effectively solves the technical problems of brittleness of inorganic materials and durability of organic materials, and fills the gap in the field of flexible piezoelectric wearable sensors at home and abroad.

[0048] (3) The main problems of the prior art for intelligent wearable devices include: the need to carry a hard power supply, inability to self-power, and the device cannot withstand normal washing. The flexible wearable device of the present application solves the problem of self-powering, and because all flexible deformable materials are used, the prepared sensor can be embedded in clothing or attached to the skin surface, enhancing comfort, having air permeability, and being washable.

[0049] (4) The present application uses human daily movement as an energy source, which has the advantages of not being limited by external factors and being chargeable at any time compared to devices that need to be charged by solar energy. At the same time, the present application selects environmentally friendly materials, and the piezoelectric sensor after failure or damage can be recycled for the preparation of nanofiber mats and piezoelectric sensors, and reused, avoiding resource waste and environmental pollution. BRIEF DESCRIPTION OF DRAWINGS

[0050] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the disclosure.

[0051] Figure 1 is a preparation method flowchart of the wearable piezoelectric sensor based on the flexible nanocomposite fiber mat provided by the embodiment of the present application.

[0052] Figure 2 is a scanning electron microscope photograph of the ZnO particles (Figure 2(a)) and silver-doped ZnO@Ag NPs particles (Figure 2(b)) synthesized by the present application provided by the embodiment of the present application. The scale in the figure is 200 nm. The size of the silver-doped zinc oxide particles is smaller than that of the zinc oxide crystal particles.

[0053] Figure 3 is a surface SEM, XRD and FTIR diagram of the ZnO@Ag NPs / PVDF nanofiber mat prepared by electrospinning provided by the embodiment of the present application; wherein Figure 3(a) is a low-magnification SEM diagram of ZnO@Ag NPs / PVDF-5wt% (the scale is 20 μm); Figure 3(b) is a high-magnification SEM diagram of ZnO@Ag NPs / PVDF-5wt% (the scale is 5 μm); Figure 3(c) is an FTIR diagram of the fibers of ZnO@Ag NPs / PVDF-5wt% and pure PVDF; Figure 3(d) is an XRD diagram of the fibers of ZnO@Ag NPs / PVDF-5wt% and pure PVDF.

[0054] Figure 4 is a schematic diagram of the piezoelectric sensor prepared by the embodiment of the present application (Figure 4(a) is a schematic diagram of the internal structure of the FPES; Figure 4(b) is a physical image of the FPES and a physical image of the ZnO@Ag NPs / PVDF-5wt% fiber mat, which has a size of 30 mm x 10 mm).

[0055] Figure 5This is a diagram of the single piezoelectric signal generation mechanism of the piezoelectric sensor FPES prepared in an embodiment of the present invention.

[0056] Figure 6(a) is a schematic diagram of the power generation principle of the piezoelectric nanogenerator prepared in an embodiment of the present invention. Figure 6(b) shows that its output power instantly drives seven 2.3V LED lamp beads to light up. Figure 6(c) is a schematic diagram of the charging voltage increasing from 0 to 2.41V after 500 cycles of pressurization within 2 minutes.

[0057] Figure 7 shows the open-circuit voltage measurement results generated by different mechanical excitations during the testing of the pressure sensor prepared in accordance with an embodiment of the present invention. Figure 7(a) shows the motion signal of a cantilever beam cyclically bending and extending a person's arm, Figure 7(b) shows the motion signal of cyclic mechanical pressure loading and unloading, and Figure 7(c) shows the motion signal of a person cyclically walking.

[0058] Figure 8 The output voltage Vpp and output current Ipp of the pressure sensor FPES containing 5 wt% ZnO@Ag NPs according to an embodiment of the present invention are compared with the FPES without ZnO@AgNPs.

[0059] FIG9( a ) is a picture of the piezoelectric sensor prepared according to an embodiment of the present invention measuring plantar motion; FIG9( b ) is a diagram of its output electrical signal.

[0060] Figure 10(a) is a CCD digital image of the contact angle of ZnO@Ag NPs / PVDF-5wt% fiber felt to water according to an embodiment of the present invention; Figure 10(b) is a CCD digital image of the contact angle of ZnO@Ag NPs / PVDF-5wt% fiber felt to milk according to an embodiment of the present invention; Figure 10(c) is a CCD digital image of the contact angle of ZnO@Ag NPs / PVDF-5wt% fiber felt to tea according to an embodiment of the present invention; Figure 10(d) is the water contact angle of the pressure sensor FPES containing 5wt% ZnO@Ag NPs and the FPES without ZnO@Ag NPs; Figure 10(e) is the contact angle values ​​of ZnO@Ag NPs / PVDF-5wt% fiber felt to water, milk and tea, respectively;

[0061] Figure 11 This is the sensitivity test curve of the piezoelectric sensor prepared by the present invention. As the pressure increases continuously from 3N to 22N, the output voltage increases from 1.5V to 14V. This curve can be divided into three sections. Its sensitivity is better in the middle section (pressure of 8N to 17N), which is 0.96V / N.

[0062] In the figure: 1. Upper PI packaging layer; 2. Lower PI packaging layer; 3. Upper copper paste electrode layer; 4. Lower copper paste electrode layer; 5. Piezoelectric fiber layer. DETAILED DESCRIPTION

[0063] In order to make the above objectives, characteristics and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below with reference to the drawings. In the following description, a large number of specific details are set forth in order to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the concept of the present application, so the present application is not limited to the specific implementation disclosed below.

[0064] I. Explanation of the embodiments

[0065] The embodiment of the present application provides a preparation method of a wearable piezoelectric sensor based on a flexible nanocomposite fiber felt and application thereof. Metal conductive ion-doped nanometer semiconductor crystal particles (for example, ZnO@Ag NPs) are synthesized and prepared by a chemical hydrothermal method, mixed with a solution containing a piezoelectric polymer (for example, polyvinylidene fluoride (PVDF) and similar polymers), and a flexible nanocomposite (for example, ZnO@Ag NPs / PVDF) nanofiber felt is prepared as a piezoelectric layer by an electrospinning process. Cu or Ag conductive powder slurry is sputtered or sprayed on the upper and lower surfaces of the nanofiber felt as two electrodes, and copper wires are bonded to lead out the positive and negative electrodes. Then, the flexible wearable piezoelectric sensor is obtained by packaging the nanofiber felt in two pieces of flexible plastic film. The flexible wearable piezoelectric sensor has energy storage and sensing dual functions. Due to the material synthesis, structure design, device preparation, coupling piezoelectric effect, synergistic effect and other factors of the flexible wearable piezoelectric sensor, the sensitivity and output efficiency of the flexible piezoelectric sensor are improved, and a new method is provided for the manufacture of self-powered flexible piezoelectric devices and nanogenerators. The flexible wearable piezoelectric sensor of the present application can light up 7 LED lamp beads driven by 2.3V as a nanogenerator, and the energy storage characteristic can charge a capacitor to 2.41V through 500 vibration cycles in 2 minutes. Other applications of the wearable piezoelectric sensor of the present application include human arm bending, foot movement and piezoelectric performance under different mechanical excitations, which have been verified. The higher the frequency of the applied pressure, the higher the output voltage across the film, and the larger the current through the film. The wearable piezoelectric sensor of the present application has excellent durability without performance degradation after 5000 cycles. The advantages of the preparation method include: simple and easy to implement, higher output efficiency at lower cost, high cost performance and good durability.

[0066] Embodiment 1

[0067] The preparation method of the wearable piezoelectric sensor based on the flexible nanocomposite fiber felt provided by the embodiment of the present application includes the following steps:

[0068] The metal conductive ion-doped semiconductor nanocrystal particles (for example, ZnO@Ag NPs) are prepared by a chemical hydrothermal synthesis method, mixed with a solution containing one or two of the piezoelectric organic polymers (for example, polyvinylidene fluoride (PVDF), polyvinylidene-trifluoroethylene (P(VDF-TrFE)), and polyvinylidene-trifluoroethylene-hexafluoropropylene (P(VDF-TrFE-HFP)), and a flexible composite nanofiber felt is prepared by an electrospinning process as a piezoelectric layer. Cu or Ag conductive paste is sputtered or sprayed on the upper and lower surfaces of the nanofiber felt as two electrodes, and copper wires are bonded to the electrodes to lead out the positive and negative electrodes. Then, the nanofiber felt and the electrodes are encapsulated between two flexible plastic films to obtain a flexible wearable piezoelectric sensor with energy storage and sensing functions.

[0069] Embodiment 2

[0070] Based on the preparation method of the wearable piezoelectric sensor based on the flexible nanocomposite fiber felt provided in Embodiment 1 of the present application, as shown in Figure 1 The preparation method of the piezoelectric sensor based on the flexible nanocomposite fiber felt further includes the following steps:

[0071] In step S101, metal conductive ion-doped semiconductor nanocrystal particles (for example, ZnO@Ag NPs) are prepared by a chemical hydrothermal synthesis method. By adjusting the composition and process, the size of the nanoparticles is controlled in the range of 100 nm-600 nm, and the metal ions are attached to the surface of the semiconductor crystal nanoparticles.

[0072] In step S102, a flexible nanocomposite fiber felt is prepared by an electrospinning method. By adjusting the composition and process parameters, high sensitivity and high output electric signal piezoelectric performance are achieved.

[0073] In step S103, Cu or Ag conductive paste is sputtered or sprayed on the upper and lower surfaces of the flexible composite nanofiber felt as two electrodes. The high adhesion between the electrodes and the fiber felt is provided, the thickness of the conductive layer is controlled and the flexibility is maintained, the copper wires are bonded with the conductive paste and fixed with the conductive tape to lead out the positive and negative electrodes. Then, the prepared nanofiber felt and the combination of the upper and lower electrode layers and the electrode wires are encapsulated between two flexible plastic films by double-sided tape to obtain the piezoelectric sensor based on the flexible composite nanofiber felt (FPES).

[0074] In the embodiment of the present application, the step S101 includes the following steps:

[0075] The chemical hydrothermal method for synthesizing metal ion doped semiconductor nanoparticles (e.g., ZnO@Ag NPs) involves mixing a zinc-containing compound, a suitable solvent, and deionized water uniformly, heating the mixture to an appropriate temperature in a container, and maintaining the temperature for a certain period of time to complete the conversion of the zinc compound into zinc oxide nanocrystals. The zinc-containing compound can be zinc acetate dihydrate, zinc acetylacetonate, or zinc nitrate. The solvent can be triethanolamine, oleylamine, polyether polyol, or the like. The reaction product is washed with deionized water and ethanol by centrifugation, and dried in a vacuum oven to obtain zinc oxide nanocrystal particles. To obtain uniformly sized nanoparticles, a capping agent such as polyethylene glycol (PEG), triphenyl phosphate (TPP), or the like can be added. By controlling the heating temperature, the concentration of the zinc compound in the solvent, and the reaction time, zinc oxide nanocrystal particles of different sizes can be obtained. The molar ratio of the zinc compound to the solvent is between 1:10 and 1:100. The heating temperature is between 100°C and 205°C, and the reaction time is between 30 minutes and 2 hours. The size of the obtained ZnO nanocrystal particles is between 200 nm and 600 nm.

[0076] The chemical capping agent polyvinylpyrrolidone (PVP) is dissolved in an aqueous solution containing silver ions (e.g. AgNO3) and stirred uniformly in the dark. The concentration of the aqueous solution containing silver ions is 0.05 mol / L, and the PVP content is between 2.5 and 3.5 g of powder, which is slowly dissolved in 20 ml of the above-mentioned aqueous solution containing silver ions. The silver-containing solution is added to the mixture of the zinc compound, the solvent and deionized water, and the mixture is heated to obtain a dispersion of silver-doped ZnO nanoparticles. After centrifugal washing with deionized water and ethanol, vacuum oven drying is performed to obtain silver-doped nano-zinc oxide ZnO@Ag NPs particles. Alternatively, an appropriate amount of the above-mentioned nano-zinc oxide crystal particle powder is dissolved in deionized water and ultrasonically pulverized, and then a small amount of the above-mentioned silver-containing solution is added and uniformly mixed. The mixture is heated in an oil bath and kept warm until the color turns to gray brown. After cooling to room temperature in air, a silver-doped nano-zinc oxide particle solution is obtained. After centrifugal washing with deionized water and ethanol, vacuum oven drying is performed to obtain silver-doped nano-zinc oxide ZnO@Ag NPs particles. When the molar ratio of the zinc compound to the solvent changes from 1:100 to 1:10, the average particle size of the silver-doped ZnO particles changes from 20-30 nm to 80-100 nm. When other parameters are constant, when the reaction temperature is 140℃, ZnO@Ag particles with a particle size of 30-40 nm are obtained, and when the reaction temperature is 205℃, ZnO@Ag particles with a particle size of about 100 nm are obtained. Figure 2 shows scanning electron microscope images of the ZnO crystal particles (Figure 2(a)) and the silver-doped zinc oxide crystal particles (Figure 2(b)) synthesized in the present application. Comparison shows that when silver ions are heated together with zinc compounds, the size of the synthesized particles is smaller. Analysis of the surface of the nanoparticles shows that silver particles can be firmly attached to the surface of zinc oxide particles, and the molar ratio of silver ions to ZnO is 1:10 or 1:11.

[0077] In the embodiment of the present application, the ratio of zinc acetate dihydrate solid powder, deionized water and triethanolamine is 0.44 g:100 ml:10 ml, the concentration of the aqueous solution containing silver ions (AgNO3) is 0.05 mol / L, and the ratio of the polymer (PVP) to the aqueous solution containing silver ions (AgNO3) is 3.5 g / 20 ml. The silver-containing solution is mixed with the solution containing nano-zinc oxide crystal particles to prepare silver-doped nano-zinc oxide particles, and the molar ratio of silver to zinc oxide is 1:11-1:10.

[0078] In the embodiment of the present application, the step S102 comprises the following steps:

[0079] (1) Dissolve the PVDF powder in a mixed solution of N,N-dimethylformamide (DMF) and acetone (ACE); the concentration of PVDF is 10-20% by mass, and the solution is magnetically stirred at a temperature of 60℃ for 4 hours to obtain a transparent solution;

[0080] (2) In the obtained PVDF transparent solution, the ZnO@Ag NPs powder prepared in step (S101) is added, and ultrasonic oscillation treatment is carried out at room temperature for 30 minutes, followed by continued magnetic stirring for 2 hours, to obtain a grayish brown uniform solution; the solution is marked as ZnO@Ag NPs / PVDF-x%, wherein x% is the mass content of the ZnO@Ag NPs powder;

[0081] (3) The ZnO@Ag NPs / PVDF composite nanofiber felt is prepared using an electrostatic spinning device at room temperature of 25°C.

[0082] In the step (1) in the embodiment of the present application, the volume ratio of DMF to ACE in the mixed solution of N,N-dimethylformamide (DMF) and acetone (ACE) is 3:2, and the concentration of PVDF is 10-20% by mass, preferably 16% by mass.

[0083] In the step (2), the mass content of the ZnO@Ag NPs powder in the PVDF solution prepared in step (2) is 3-7% by mass, preferably 5% by mass.

[0084] In the step (3), the electrostatic spinning system is composed of a 5ml syringe with a flow rate of 2ml / h and a 22G flat steel needle spinneret, a positive voltage direct current power source of 16kV is applied to the spinneret, and a luer connector and a liquid guide are connected between the 5ml syringe and the spinneret; a drum collector with a rotation speed of 1000rpm is placed at a distance of 15cm from the spinneret to collect the nanofiber. The longer the spraying time, the thicker the thickness of the obtained fiber felt.

[0085] Example 3

[0086] Based on the preparation method of the wearable piezoelectric sensor based on the flexible nanocomposite fiber felt provided in the embodiment 1 or the embodiment 2 of the present application, the embodiment of the present application provides a flexible wearable piezoelectric sensor device. According to the application needs of the required device, the ZnO@Ag NPs / PVDF flexible composite fiber felt prepared above is cut into appropriate size, for example, 20mm×10mm, and the thickness is about 50 microns, and Cu or Ag conductive powder slurry is sputtered or sprayed on the upper and lower surfaces as two electrodes, and at the same time, copper wires are bonded to lead out the positive and negative electrodes, and after natural drying, the assembly is clamped between two pieces of flexible plastic film to exclude air bubbles, and packaged with double-sided adhesive tape to obtain a flexible wearable piezoelectric sensor device. The plastic film can be any flexible film material, such as polyimide, polyethylene terephthalate, polycarbonate, silicone elastomer, siloxane elastomer, etc.

[0087] Example 4

[0088] The embodiment of the present application provides a kind of silver-doped nano zinc oxide particles (ZnO@AgNPs) prepared by chemical hydrothermal synthesis, and the specific steps include:

[0089] The zinc-containing compound, the appropriate solvent and the deionized water are mixed uniformly, heated to the appropriate temperature in the container, and incubated for a certain time to complete the conversion of zinc compound into zinc oxide nanocrystals. The optional zinc-containing compound includes zinc acetate dihydrate, zinc acetylacetonate or zinc nitrate. The optional solvent includes triethanolamine, oleylamine, polyether polyol, etc. The obtained reaction product is centrifuged with deionized water and ethanol, vacuum oven dried, and nano zinc oxide crystal particles are obtained. In order to obtain uniform size nanoparticles, a capping agent such as polyethylene glycol (PEG), triphenyl phosphate (TPP) can be added. By controlling the heating temperature, the concentration of zinc compound in the solvent and the chemical reaction time, zinc oxide crystal particles of different particle sizes are obtained. When the molar ratio of zinc compound to solvent is 1:10, the heating temperature is 205°C, and the reaction time is between 30 minutes and 2 hours, the uniform ZnO crystal particle size is between 100 nm and 200 nm.

[0090] The chemical capping agent polyvinylpyrrolidone (PVP) is dissolved in an aqueous solution containing silver ions (such as AgNO3), and stirred uniformly in the dark. The concentration of the silver ion-containing aqueous solution is 0.05 mol / L, and the PVP content is between 2.5 and 3.5 g of powder, which is slowly dissolved in 20 ml of the above-mentioned silver ion-containing aqueous solution. The silver-containing solution is added to the mixture of zinc compound, solvent and deionized water, and the silver-doped ZnO nanoparticles are obtained by heating and reacting together. After centrifugation with deionized water and ethanol, vacuum oven dried, silver-doped nano zinc oxide ZnO@Ag NPs particles are obtained. Or select the appropriate amount of the above-mentioned nano zinc oxide crystal particle powder, dissolve in deionized water and ultrasonic crushing, then add a small amount of the above-mentioned silver-containing solution and mix uniformly, heat in an oil bath and incubate until the color turns to gray brown, and cool to room temperature with air. Silver-doped nano zinc oxide particle solution is obtained. After centrifugation with deionized water and ethanol, vacuum oven dried, silver-doped nano zinc oxide ZnO@Ag NPs particles are obtained. When the molar ratio of zinc compound to solvent changes from 1:100 to 1:10, the average particle size of silver-doped ZnO particles changes from 20-30 nm to 80-100 nm. When other parameters are constant, the reaction temperature is 140°C, and the particle size of ZnO@Ag is 30-40 nm. When the reaction temperature is 205°C, the particle size of ZnO@Ag is about 100 nm. As shown in Figure 2. Comparison shows that when silver ions are heated and reacted with zinc compound, the particle size of the synthesized particles is smaller. Analysis of the surface of the nanoparticles shows that silver particles can firmly adhere to the surface of zinc oxide particles, and the molar ratio of silver ions to ZnO is 1:10 or 1:11.

[0091] Example 5

[0092] Based on the chemical hydrothermal method provided in Example 4 of the present application, silver-doped nano zinc oxide particles (ZnO@Ag NPs) are prepared, and further, a PVDF mixed solution containing PVDF polymer and ZnO@Ag nanoparticles is prepared. The specific steps include:

[0093] The PVDF (or similar polymer matrix) powder is dissolved in the corresponding solvent, and the present application selects a mixed solution of N,N-dimethylformamide (DMF) and acetone (ACE); the proportion can be adjusted according to the needs, for example, the volume ratio of DMF to ACE is 3:2, the concentration of PVDF is 10-20% by mass, preferably 16-18% by mass. The solution is magnetically stirred at 60°C for 4 hours to obtain a transparent solution.

[0094] An appropriate amount of gray-colored nano ZnO@Ag NPs powder is added to the mixed solution of acetone and N,N-dimethylformamide, and the mixing ratio can be adjusted according to the needs, and ultrasonic oscillation is dispersed. The solution containing ZnO@Ag NPs is mixed with the transparent solution containing PVDF, and is uniformly stirred in a sealed state in a water bath. The obtained ZnO@Ag NPs / PVDF composite solution is placed at room temperature, at which time the pressure in the bottle is reduced, the temperature is reduced to room temperature, and the gas bubbles generated in the solution are completely removed. The solute ratio of the PVDF / ZnO@Ag NPs mixed solution is PVDF-16-18wt%, preferably PVDF-16wt%, ZnO@Ag NPs 3-7wt%, preferably ZnO@Ag NPs 5wt%, and the volume ratio of DMF to ACE is 3:2. The obtained solution is packed in a brown glass bottle for standby.

[0095] Example 6

[0096] Based on the chemical hydrothermal method provided in Example 4 of the present application, silver-doped nano zinc oxide particles (ZnO@Ag NPs) are prepared, and further, a PVDF mixed solution containing PVDF polymer and ZnO@Ag nanoparticles is prepared. The specific steps include:

[0097] The electrospinning is performed at room temperature of about 25°C, a needle syringe with a volume of 5ml is selected and loaded with the mixed solution containing PVDF and ZnO@Ag nanoparticles into a needle syringe of the electrospinning equipment, and sprayed to a roller of a receiving end under the action of an electrostatic field, a positive voltage direct current power applied to a spinneret is 16kV, a steel needle with an inner diameter of 0.41mm and an outer diameter of 0.71mm is selected as a needle head of the syringe, a solution injection speed is 2ml / h, a distance between the needle head and the axis of the roller is 15cm, and a roller rotating speed is 1000r / min. Different spraying times are controlled to obtain fiber mats with different thicknesses. According to the application needs of the required device, the fiber mat is cut into any appropriate size, for example, 20mm*10mm, and the thickness is about 50 microns. FIG. 3 shows the appearance structure of the nanofiber mat, and the morphology of the protruding nanoparticles can be observed on the surface of the fiber containing ZnO (FIG. 3(a)), and the morphology of the smoother surface with protruding points is observed on the surface of the fiber containing ZnO@Ag NPs (FIG. 3(b)), and the protruding contacts are beneficial to enhance the sensitivity of the sensor. It is confirmed by the FTIR diagram that the basic structure of PVDF does not change after adding the nanoparticles, and the existence of the β phase in PVDF and the XRD peak values of ZnO and Ag are detected and determined in the XRD test curve.

[0098] Example 7

[0099] Based on the chemical hydrothermal method for synthesizing and preparing silver-doped zinc oxide nanoparticles (ZnO@Ag NPs) provided in the embodiment 4 of the present application, further, the present application provides a preparation and assembly of a flexible wearable piezoelectric sensor device:

[0100] The Cu or Ag conductive slurry is sputtered or sprayed on the upper and lower surfaces of the prepared ZnO@Ag NPs / PVDF flexible composite fiber mat as two electrodes, and the copper wires are bonded to the positive and negative electrodes, and after natural drying, the assembly is clamped between two pieces of flexible plastic film to exclude air bubbles, and packaged with double-sided adhesive tape to obtain a flexible wearable piezoelectric sensor device. The plastic film can be any flexible film material, such as polyimide, polyethylene terephthalate, polycarbonate, silicone elastomer, siloxane elastomer, etc. FIG. 4 shows the internal structure of the piezoelectric sensor designed by the present application (FIG. 4(a)) and the appearance sample photo of the prepared sensor (FIG. 4(b)). Figure 5 The principle diagram of the piezoelectric performance is explained.

[0101] In the embodiment of the present application, the piezoelectric sensor based on the flexible ZnO@Ag NPs / PVDF nanocomposite fiber mat includes:

[0102] The upper PI packaging layer 1 and the lower PI packaging layer 2 located on the upper and lower surfaces;

[0103] The inner walls of the upper PI encapsulation layer 1 and the lower PI encapsulation layer 2 encapsulate the upper copper paste electrode layer 3 and the lower copper paste electrode layer 4, respectively; and the piezoelectric fiber layer 5 is filled between the upper copper paste electrode layer 3 and the lower copper paste electrode layer 4.

[0104] The structure of the piezoelectric sensor is shown in FIG. 4(a), and the preparation method thereof includes the following steps:

[0105] 1) ZnO@Ag NPs powder was prepared by hydrothermal synthesis method, and the powder was gray-brown:

[0106] 0.22 g of zinc acetate dihydrate powder was dissolved in 50 ml of deionized (DI) water, 5 ml of triethanolamine was added dropwise, and then the mixture was stirred at room temperature for 30 minutes. The mixed solution was added to a 100 ml autoclave and sealed, and heated at 100°C for 2 hours. After the reaction was completed, the white precipitate obtained was washed with deionized water and ethanol by centrifugation, and the collected solid part was dried in a vacuum oven at 60°C to obtain white ZnO NPs powder. To prepare a solution containing Ag + , 3.5 g of white PVP powder was slowly dissolved in 20 ml of 0.05 mol / L AgNO3 aqueous solution under dark conditions. 0.89 g of prepared ZnO NPs powder was dispersed in 10 ml of deionized water by ultrasonic oscillation, then the solution containing Ag + ions was added and stirred thoroughly, and the mixed solution was stirred in a water bath at 80°C until the color changed to gray at 10 minutes and further to gray-brown at 30 minutes. The obtained solution was washed with water and ethanol by centrifugation for 5 times, and finally dried in a vacuum oven at 60°C to obtain ZnO@Ag NPs sample, in which the molar ratio of Ag:ZnO was 1:11.

[0107] 2) Preparation of solution for electrospinning fiber mat:

[0108] The polymer PVDF powder was dissolved in a DMF / ACE mixed solution, stirred in a water bath at 60°C for 5 hours until a homogeneous transparent polymer mixture was formed. Among them, the PVDF (Mw=300000) powder content was optimized to 16wt%, and the volume ratio of DMF to ACE was 3:2. Higher concentration of PVDF solution will result in large fiber diameter after spinning and insufficient polarity, while lower than 16wt% of PVDF concentration will result in slow solvent evaporation during electrospinning process and easy to produce melt accumulation. In order to prepare PVDF spinning solution with ZnO@Ag NPs, the ratio of nanoparticles to solution is 5wt%. First, a proper amount of nanoparticles was dispersed into the mixture of ACE / DMF (volume ratio 2:3), then this mixed solution was mixed with the solution added with PVDF until completely dissolved.

[0109] 3) ZnO@Ag NPs / PVDF composite nanofiber mat was prepared by electrospinning method;

[0110] The ZnO@Ag NPs / PVDF composite nanofiber mat was prepared by using the PVDF solution with a concentration of 16wt% obtained in step 2) and the ZnO@Ag NPs-x%, wherein x% is the content of ZnO@Ag NPs particles, by using an electrospinning device at room temperature of 25°C. The ZnO@Ag NPs / PVDF mixed solution was loaded into a needle syringe on the electrospinning device, a needle syringe with a volume of 5ml was selected, and was sprayed onto the drum at the receiving end under the action of an electrostatic field. The positive voltage DC power applied to the spinneret was 16kV, the steel needle with an inner diameter of 0.41mm and an outer diameter of 0.71mm was selected as the needle head, the solution injection speed was 2ml / h, the distance between the needle head and the drum axis was 15cm, and the drum rotation speed was 1000r / min. Different spraying times were controlled to obtain fiber mats with different thicknesses. The fiber mat prepared in this embodiment has a thickness of about 50μm.

[0111] 4) Preparation of ZnO@Ag NPs / PVDF composite nanofiber mat containing piezoelectric sensor device

[0112] The flexible fiber mat prepared in step 3) was cut into a sheet-shaped sample with an outer size of 20mm×10mm, and the thickness thereof was about 50μm. The thickness of the fiber mat was determined by the process parameters and spinning time of electrospinning. Cu or Ag conductive powder slurry was sputtered or sprayed on the upper and lower surfaces thereof as two electrodes, respectively. At the same time, copper wires were bonded with the conductive powder slurry, and the positive and negative electrode wires were fixed by using conductive adhesive tape. Then, a polyimide (PI) film was bonded on the upper and lower surfaces of the nanofiber mat with electrode lead-out wires by using double-sided adhesive tape for packaging, so as to obtain the flexible piezoelectric sensor (FPES).

[0113] Example 8

[0114] Based on the silver-doped nanometer zinc oxide particles (ZnO@Ag NPs) prepared by the chemical hydrothermal method provided in Example 4 of the present application, further, the energy storage characteristics of the flexible wearable piezoelectric sensor prepared by the present application were measured and verified:

[0115] When the optimal doping ratio of ZnO@Ag NPs particles in the electrospinning spraying solution is 5wt%, the piezoelectric nanogenerator is excited by an external mechanical force to produce deformation, and the flexible piezoelectric fiber felt realizes the periodic cycle of compression and loosening under the action of external force. The instantaneous output voltage of the piezoelectric nanogenerator of the flexible ZnO@Ag NPs / PVDF fiber felt prepared by the present application is 13.6V (the contact area is 20mm*10mm), the current is maintained at 2.605μA, and 7 2.3V LED lamp beads can be lit. The piezoelectric nanogenerator prepared by the present application can charge the capacitor to 2.41V through 500 vibration cycles in 2 minutes. Figure 6 shows the power generation principle of the nanogenerator prepared by the present application, Figure 6(a), 7 2.3V LED lamp beads are lit, Figure 6(b), and the capacitor is instantaneously charged to 2.41V by the nanogenerator, Figure 6(c).

[0116] Example 9

[0117] Based on the chemical hydrothermal synthesis method provided in Example 4 of the present application, silver-doped nano-zinc oxide particles (ZnO@Ag NPs) are prepared, and further, the piezoelectric performance of the prepared flexible wearable piezoelectric sensor is measured and verified.

[0118] The flexible wearable piezoelectric sensor prepared by the present application can be used as a pressure sensor, converting human motion and various mechanical motions into electrical signals, and recording the amplitude, frequency, intermittence, pause, etc. of the motion. Due to the enhanced piezoelectric effect, synergistic effect and other factors, the flexible piezoelectric sensor has good output sensitivity. The output open-circuit voltage of the sensor is measured by using the bending-straightening motion of the human arm (cantilever beam state reciprocating vibration), periodic cyclic mechanical pressure loading-unloading motion, and periodic foot walking signal excitation, respectively, and the voltage output curves with amplitudes of 1.5V, 15V and 7.5V are obtained, as shown in Figure 7. It is also found that the actual output power of the flexible wearable piezoelectric sensor prepared by the present application is proportional to the frequency of the external pressure. With the increase of the pressure frequency, the voltage across the film increases, and the current through the film also increases. Figure 8 The output voltage and current of the piezoelectric sensor prepared by the ZnO@Ag NPs / PVDF fiber felt and the pure PVDF fiber felt are shown. The output open-circuit voltages of the two are 13.6V and 4V (increased by 3.4 times) respectively, and the output currents are 2.6μA and 0.5μA (increased by 5 times) respectively.

[0119] Example 10

[0120] Based on the chemical hydrothermal synthesis method provided in Example 4 of the present application, silver-doped nano-zinc oxide particles (ZnO@Ag NPs) are prepared, and further, the piezoelectric performance of the prepared flexible wearable piezoelectric sensor is measured and verified.

[0121] For the energy storage characteristics of the nanogenerator, the output voltage of the piezoelectric nanogenerator can still maintain good repeatability after 5000 cycles. The fiber morphology of the nanofiber mat after cycling is not different from that of the fiber without any testing. The piezoelectric performance remains unchanged. It proves the durability of the piezoelectric sensor device. Figure 9 shows the photos of the piezoelectric sensor prepared by the present application measuring the foot movement and its output electrical signal. Among them, Figure 9(a) is a picture of the piezoelectric sensor prepared by the embodiment of the present application measuring the foot movement; Figure 9(b) is the output electrical signal diagram thereof.

[0122] The surface of the ZnO@Ag NPs / PVDF flexible composite fiber mat prepared by the present application has superhydrophobicity, and the measured water contact angle is greater than 150 degrees, the contact angle with milk is greater than 140 degrees, and the contact angle with tea is 137 degrees. This feature makes the piezoelectric sensor device have waterproof and antifouling protection function, thereby prolonging the durability of the device. As shown in Figure 10. Figure 10(a) is a CCD digital image of the water contact angle of the ZnO@Ag NPs / PVDF-5wt% fiber mat of the embodiment of the present application; Figure 10(b) is a CCD digital image of the milk contact angle of the ZnO@Ag NPs / PVDF-5wt% fiber mat of the embodiment of the present application; Figure 10(c) is a CCD digital image of the tea contact angle of the ZnO@Ag NPs / PVDF-5wt% fiber mat of the embodiment of the present application; Figure 10(d) is the water contact angle of the pressure sensor FPES containing 5wt% of ZnO@Ag NPs and the FPES without ZnO@Ag NPs; Figure 10(e) is the contact angle value of the ZnO@Ag NPs / PVDF-5wt% fiber mat to water, milk and tea, respectively.

[0123] Example 11

[0124] The used piezoelectric sensor FPES is recycled, the nanofiber mat therein is redissolved with DMF and ACE solvents (the volume ratio of DMF to ACE is 3:2) to prepare a new spinning solution. The nanofiber mat is prepared again by electrospinning, and the newly prepared fiber mat is made into a new FPES according to the relevant design scheme.

[0125] The recycled fiber mat is weighed and placed in a brown bottle, the solvent is added in proportion, the bottle cap is covered and sealed, and a new spinning solution is obtained after water bath stirring and heating for 4h. A new nanofiber mat is obtained by electrospinning, and a new piezoelectric sensor is prepared according to the method described above. The piezoelectric voltage output test of the reobtained FPES shows that there is no big difference in piezoelectric output performance between the reobtained FPES and the initially prepared FPES, and the reobtained FPES has good stability.

[0126] The secondary recycling method can greatly utilize the fiber material, recycle and reuse the fiber material, and avoid resource waste and environmental pollution.

[0127] In the above embodiments, the description of each embodiment has its own focus, and the parts not described or recorded in a certain embodiment can be referred to the related description of other embodiments.

[0128] II. Application Examples

[0129] Application Example 1

[0130] Based on the above embodiments, the flexible wearable piezoelectric sensor provided by the embodiments of the present application can convert various pressure motions into electrical energy, and the stored electrical energy can be used as a direct current power source to control the operation of electronic devices, for example, to drive LED lamp beads to emit light. The instantaneous output voltage of the piezoelectric nanogenerator is 13.6V (the contact area is 20mmx10mm), the current is maintained at 2.605μA, and 7 LED lamp beads of 2.3V can be lit. The energy storage characteristics can charge the capacitor to 2.41V through 500 vibration cycles in 2 minutes. After 5000 cycles of use, the output voltage of the piezoelectric nanogenerator can still maintain good repeatability, and the fiber morphology observation of the nanofiber mat after the cycle test is the same as that of the fiber without any test. The piezoelectric performance remains unchanged.

[0131] Application Example 2

[0132] Based on the above embodiments, the flexible wearable piezoelectric sensor provided by the embodiments of the present application can be used as a pressure sensor to convert human motion and various mechanical motions into electrical signals and record the amplitude, frequency, intermittence, pause, etc. of the motion. Due to the enhanced piezoelectric effect, synergistic effect, superhydrophobicity and other factors, the flexible wearable piezoelectric sensor has good output sensitivity (0.71-0.96V / N), energy conversion efficiency and use durability.

[0133] III. Evidence of the effects of the embodiments

[0134] Test Example 1

[0135] In order to prove the beneficial effects of the piezoelectric sensor based on the flexible ZnO@Ag NPs / PVDF fiber mat and the preparation method thereof, the present application briefly describes the specific working process of the piezoelectric sensor in actual use in the test example:

[0136] The different deformations generated by different external forces make the piezoelectric sensor realize the periodic cycle of extrusion and recovery state together with the external force. By measuring the open circuit voltage of the piezoelectric sensor, the output results shown in FIG. 7(a), FIG. 7(b), FIG. 7(c) are obtained. Among them, FIG. 7(a) is the open circuit voltage measurement result of the piezoelectric sensor based on the flexible ZnO@Ag NPs / PVDF fiber felt under the reciprocating motion of the cantilever beam state (bending-straightening of the human arm); FIG. 7(b) is the open circuit voltage test result of the piezoelectric sensor based on the flexible ZnO@Ag NPs / PVDF fiber felt under the periodic cyclic mechanical pressure; FIG. 7(c) is the open circuit voltage test result of the piezoelectric sensor based on the flexible ZnO@Ag NPs / PVDF fiber felt under the motion of walking on the sole.

[0137] From the experimental results, it can be seen that the output open circuit voltage of the piezoelectric sensor based on the flexible ZnO@Ag NPs / PVDF fiber felt is 1.5V, 15V, 7.5V respectively. It should be noted that only three basic mechanical motions are selected as test examples in the test process. The application range of the present application is not limited in any way.

[0138] In addition, it is also found in the research process of the present application that the frequency of the external pressure has a great influence on the actual output power of the piezoelectric sensor based on the flexible ZnO@Ag NPs / PVDF fiber felt of the embodiment of the present application in actual application. With the increase of the pressure frequency, the voltage at both ends of the film increases, and the current passing through the film also increases. Under the driving of 5Hz frequency, the loaded pressure gradually increases from 3N to 22N, and the output voltage increases from 1.5V to 13.6V Figure 11 ), the sensitivity of the piezoelectric sensor prepared by the present application is 0.96V / N in the middle section of the pressure (the pressure is between 8 to 17N).

[0139] Test Example 2

[0140] In order to prove the beneficial effects of the piezoelectric nanogenerator based on the flexible ZnO@Ag NPs / PVDF fiber felt and the preparation method thereof, the present application briefly describes the specific working process of the flexible generator prepared by the present application in actual use in test example 2:

[0141] By applying mechanical force to the piezoelectric nanogenerator based on the flexible ZnO@Ag NPs / PVDF fiber mat in this embodiment, the generator is deformed. The piezoelectric fiber mat realizes a periodic cycle of compression and recovery along with the external force, and the generated output power is connected to the capacitor to charge the capacitor. The DC power supply is then connected to the LED lamp bead. The measurement results are shown in Figures 6(a), 6(b), and 6(c). Among them, Figure 6(a) is the energy collection circuit diagram of the piezoelectric nanogenerator based on the flexible ZnO@Ag NPs / PVDF fiber mat, Figure 6(b) is the instantaneous voltage of the piezoelectric nanogenerator based on the flexible ZnO@Ag NPs / PVDF fiber mat to light up 7 2.3V driven LED lamp beads, and Figure 6(c) is the capacitor charging voltage of the piezoelectric nanogenerator based on the flexible ZnO@Ag NPs / PVDF fiber mat after 500 cycles of cyclic excitation. From the experimental results, it can be seen that the piezoelectric nanogenerator based on flexible ZnO@Ag NPs / PVDF fiber felt can charge the capacitor voltage to 2.41V through 500 vibration cycles within 2 minutes.

[0142] Test Example 3

[0143] To test the durability of the flexible ZnO@Ag NPs / PVDF fiber mat-based piezoelectric sensor (FPES) prepared by the present invention, a high-frequency cyclic pressure shock test was performed on the FPES using a self-developed testing platform. The test device consists of a voice coil motor, a signal conversion and acquisition system, and a control system. More than 5,000 continuous piezoelectric tests were performed at an impact frequency of 5 Hz and an impact force of 50 N. The results showed that the output open-circuit voltage and short-circuit current amplitude remained unchanged, demonstrating the good durability of the flexible piezoelectric sensor prepared by the present invention.

[0144] By measuring and comparing the wetting angles of different liquids on the flexible ZnO@Ag NPs / PVDF fiber felt in this example, as shown in Figure 10, it was found to be superhydrophobic, with a water contact angle greater than 150 degrees. For milk and tea, the contact angles were 149 degrees and 137 degrees, respectively. This shows that the fiber felt prepared by the present invention with the addition of ZnO@Ag nanoparticles has a better self-cleaning and anti-fouling effect than the pure PVDF fiber felt (water contact angle of 135 degrees). Therefore, the durability of the piezoelectric sensor is also improved.

[0145] In summary, the piezoelectric sensor based on the flexible ZnO@Ag NPs / PVDF fiber felt and the preparation method thereof provided by the embodiment of the present application utilize the electrospinning method to add semiconductor crystals and metal ion doped nanoparticles to modify the PVDF fiber in the fiber of PVDF, so as to improve the piezoelectric performance and sensitivity of the final flexible ZnO@Ag NPs / PVDF fiber felt, and the method is novel and simple, and has low manufacturing cost, and is conducive to popularization and application. Meanwhile, the piezoelectric sensor based on the flexible ZnO@Ag NPs / PVDF fiber felt and the preparation method thereof provided by the embodiment of the present application not only have simple preparation process, low cost and easy realization of large-area preparation, but also have good energy storage characteristics and excellent piezoelectric performance, so that the piezoelectric sensor is more suitable for light flexible wearable devices, has self-powered and piezoelectric sensing dual functions, has important popularization and application value and wide application prospect.

[0146] The above merely describes the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any modification, equivalent replacement and improvement made by any person skilled in the art within the technical range disclosed by the present application, as long as it is within the spirit and principle of the present application, should be covered within the protection scope of the present application.

Claims

1. A method for preparing a wearable piezoelectric sensor based on a flexible nanocomposite fiber mat, characterized by, The preparation method of the wearable piezoelectric sensor based on the flexible nanocomposite fiber felt comprises the following steps: Step one, metal conductive ion-doped semiconductor nanocrystalline particles are prepared by a chemical hydrothermal method; Step two, a solution containing a piezoelectric organic polymer is mixed, and a flexible nanocomposite fiber felt is prepared as a piezoelectric layer by an electrospinning process; Step three, conductive powder paste is sputtered on the upper and lower surfaces of the flexible nanocomposite fiber felt as electrodes, and positive and negative electrode lines are led out; the prepared nanofiber felt and the combination of the upper and lower electrode layers and the electrode lines are sandwiched in a flexible plastic film by double-sided tape for packaging to obtain a piezoelectric sensor based on the flexible nanocomposite fiber felt; The chemical hydrothermal method for preparing metal conductive ion-doped semiconductor nanocrystalline particles comprises the following steps: In the first step, the zinc compound, the solvent and the deionized water are mixed uniformly, heated in a container, the heating temperature is 100-205℃, and the reaction time is 30-120 minutes, so that the zinc compound is converted into zinc oxide nanocrystals; In the second step, the polyvinylpyrrolidone is dissolved in the silver ion-containing aqueous solution, and stirred uniformly in the dark; the concentration of the silver ion-containing aqueous solution is 0.05 mol / L; the content of the polyvinylpyrrolidone is 2.5-3.5 g, which is dissolved in 20 ml of the silver ion-containing aqueous solution; the silver ion-containing aqueous solution is added to the mixed solution of the zinc oxide nanocrystals in the first step, and the temperature is raised for reaction to obtain a dispersion solution of silver-doped zinc oxide nanoparticles; the deionized water and ethanol are used for centrifugal cleaning respectively, and the vacuum oven is used for drying to obtain silver-doped nanometer zinc oxide ZnO@Ag NPs particles.

2. The method for preparing a wearable piezoelectric sensor based on a flexible nanocomposite fiber mat according to claim 1, characterized in that: In the first step, the zinc compound is one or more of zinc acetate dihydrate, zinc acetylacetonate or zinc nitrate; the solvent is one or more of triethanolamine, oleylamine or polyether polyol; The reaction product is cleaned by centrifugation with deionized water and ethanol respectively, and dried in a vacuum oven to obtain nanometer zinc oxide crystal particles; In the mixed solution of the zinc compound, the solvent and the deionized water, a capping agent is added simultaneously, and the capping agent is one or more of polyethylene glycol or triphenyl phosphate; The molar ratio of the zinc compound to the solvent is 1:10-1:

100.

3. The method for preparing a wearable piezoelectric sensor based on a flexible nanocomposite fiber mat according to claim 1, characterized in that: In the second step, the nanometer zinc oxide crystal particle powder prepared in the first step is dissolved in deionized water and ultrasonically pulverized, then a silver-containing solution is added and mixed uniformly, heated in an oil bath and kept warm, cooled and then silver-doped nanometer zinc oxide particles solution is obtained.

4. The method for preparing a wearable piezoelectric sensor based on a flexible nanocomposite fiber mat according to claim 1, wherein: In step two, the piezoelectric organic polymer includes one or two of the following materials: polyvinylidene fluoride, polyvinylidene-trifluoroethylene, polyvinylidene fluoride-trifluoroethylene-hexafluoropropylene; In step two, the mixed solution containing the piezoelectric organic polymer is prepared, and the flexible nanocomposite fiber felt is prepared as a piezoelectric layer by an electrospinning process, which comprises the following steps: Step one, the polyvinylidene fluoride powder is dissolved in a mixed solution of N,N-dimethylformamide and acetone; the concentration of the polyvinylidene fluoride is 10-20% by mass, and the solution is magnetically stirred at a temperature of 60℃ for 4 hours to obtain a transparent solution; Step two, in the obtained polyvinylidene fluoride transparent solution, the prepared ZnO@Ag NPs powder is added, ultrasonic oscillation treatment is carried out at room temperature for 30 minutes, then magnetic stirring is continued for 2 hours, and a uniform solution is obtained; the solution is ZnO@Ag NPs / PVDF-x%, wherein x% is the mass content of the ZnO@Ag NPs powder; Step three, the ZnO@Ag NPs / PVDF nanocomposite fiber felt is prepared by using an electrostatic spinning device at room temperature of 25°C.

5. The method for preparing a wearable piezoelectric sensor based on a flexible nanocomposite fiber mat according to claim 4, characterized in that: In the step one, the volume ratio of N,N-dimethylformamide to acetone in the mixed solution of N,N-dimethylformamide and acetone is 3:2, and the concentration of polyvinylidene fluoride is 10%-20% by mass; In the step two, the mass content of the ZnO@Ag NPs powder in the prepared polyvinylidene fluoride solution is 3%-7% by mass; In the step three, the electrostatic spinning system is composed of a 5ml syringe with a flow rate of 2ml / h and a 22G flat steel needle spinneret, a positive voltage direct current power source of 16kV is applied to the spinneret, and a luer connector and a liquid guide tube are connected between the 5ml syringe and the spinneret; a drum collector with a rotating speed of 1000rpm is placed at a distance of 15cm from the spinneret to collect nanofibers.

6. The wearable piezoelectric sensor prepared by the method of claim 1-5. The wearable piezoelectric sensor comprises upper and lower PI packaging layers (1) and (2) on the upper and lower surfaces; The inner walls of the upper and lower PI packaging layers (1) and (2) respectively encapsulate upper and lower copper paste electrode layers (3) and (4); and the upper and lower copper paste electrode layers (3) and (4) are filled with a piezoelectric fiber layer (5).

7. A piezoelectric nanogenerator prepared by using the wearable piezoelectric sensor of claim 6.

8. A pressure sensor prepared by using the wearable piezoelectric sensor of claim 6.

9. A piezoelectric test rig incorporating the wearable piezoelectric sensor of claim 6, wherein, The piezoelectric test experimental device comprises a wearable piezoelectric sensor; the wearable piezoelectric sensor is connected to a voice coil motor, a signal conversion and acquisition system, and a control system through a circuit.

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