Polyvinylidene fluoride-based piezoelectric composites, their preparation and use

Abstract

A polyvinylidene fluoride (PVDF) piezoelectric composite material and its preparation and application are disclosed. The method involves preparing a solution of PVDF-TrFE copolymer (PVDF-TrFE) as the matrix material, adding a solution of organic small-molecule phytic acid (PA) as a functional dopant, and mixing thoroughly to obtain a PVDF-TrFE / PA composite solution. The composite solution is then used to form a PVDF-TrFE / PA composite film through solution casting, spin coating, or electrospinning. After polarization treatment, an improved PVDF piezoelectric composite film is prepared. This invention maintains the material's flexibility and processability while also considering high-voltage piezoelectric performance and long-term stability, overcoming the limitations of both organic-inorganic composite systems and all-organic systems.

Description

Technical Field

[0001] This invention relates to a technology in a specific field, specifically a polyvinylidene fluoride piezoelectric composite material and its preparation and application. Background Technology

[0002] Existing PVDF-based piezoelectric materials have limitations in improving performance: the organic-inorganic composite system has discontinuous interface, poor dispersion, and insufficient stability; although the fully organic modified system has flexibility and compatibility, the dopants have low dielectric constants and limited polarization efficiency, making it difficult to balance high-voltage performance and long-term stability. Summary of the Invention

[0003] This invention addresses several problems in existing inorganic filler doping systems, including poor interfacial compatibility, dielectric constant mismatch, and insufficient dispersion, which lead to limited piezoelectric phase induction efficiency and performance degradation during long-term use. It also addresses the issues of low dopant dielectric constants and limited polarization efficiency in existing all-organic modified systems, resulting in limited improvement in piezoelectric performance, and insufficient formation and stability of the piezoelectric phase, making it difficult to simultaneously achieve both high piezoelectric performance and long-term stability. The invention proposes a method for preparing polyvinylidene fluoride piezoelectric composite films that maintains material flexibility and processability while simultaneously ensuring high piezoelectric performance and long-term stability, thus overcoming the limitations of both organic-inorganic composite systems and all-organic systems.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to an improved method for preparing polyvinylidene fluoride piezoelectric composite films. A polymer solution is prepared by dissolving and preparing a polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE) as the matrix material. A phytic acid (PA) solution containing polyhydroxyl and high dielectric groups is added to the polymer solution to ensure thorough mixing at the molecular level, forming a PVDF-TrFE / PA composite solution. The PVDF-TrFE / PA composite film is then formed by solution casting, spin coating, or electrospinning. An external electric field is applied to the composite film for polarization treatment, thereby forming stable intermolecular hydrogen bonds and a locally high dielectric polarization synergistic structure between the PVDF-TrFE segments and PA molecules, thus obtaining the polyvinylidene fluoride piezoelectric composite film.

[0006] The aforementioned configuration refers to dissolving polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) in N,N-dimethylformamide (DMF) or dimethyl sulfoxide (DMSO) solvent.

[0007] The volume ratio of DMF to acetone in the mixed solvent is 6:4, and the concentration of the solute is 0.07-0.15 mg / mL.

[0008] The phytic acid (PA) solution is a 50% PA aqueous solution, and its dosage to the mass ratio of the matrix material is (0.5-10):100, preferably 6:100.

[0009] The polarization treatment refers to placing the composite film under an applied electric field for polarization treatment, so that the hydroxyl groups in the PA molecule and the C–F groups in the PVDF-TrFE chain interact through hydrogen bonding, inducing and stabilizing the formation of the β phase. At the same time, the high dielectric constant of the phosphate groups in the PA molecule helps to enhance the local polarization electric field and improve the polarization efficiency.

[0010] The applied electric field is preferably an AC electric field of 50–100 MV / m.

[0011] This invention relates to an improved polyvinylidene fluoride piezoelectric composite film prepared by the above method, which has a thickness of 20–40 μm, a smooth and dense surface, and a uniform microstructure; the film has a crystallinity of about 75%, a β phase content of about 62%, and stable polarization performance; the dielectric constant is significantly improved compared to pure PVDF-TrFE film (about 22 at 100 Hz); the film has good flexibility and mechanical integrity, and no cracks are generated under repeated bending conditions; in terms of electrical properties, the voltage retention rate exceeds 95% after 8000 cycles of loading, and the output waveform shows no significant attenuation.

[0012] This invention relates to the application of the above-mentioned improved polyvinylidene fluoride piezoelectric composite film, including: for the preparation of flexible wearable piezoelectric sensors or array sensors. Technical effect

[0013] This invention addresses the issue of interfacial discontinuity by constructing a synergistic interfacial structure of polyhydroxyl-containing high-dielectric small molecules (PA) / PVDF-TrFE segments through the uniform dispersion of PA molecules within a polymer matrix. The high-dielectric groups of PA provide a locally enhanced electric field, improving dipole orientation efficiency. Furthermore, the β-phase structure is stabilized through the combined effects of hydrogen bonding and the electric field, ensuring performance retention during long-term cycling. Compared to existing technologies, this invention achieves efficient induction and stabilization of the β-phase in PVDF-TrFE molecular chains through PA molecules rich in hydroxyl and high-dielectric groups, significantly increasing the β-phase content. The resulting composite film exhibits excellent piezoelectric properties, with a piezoelectric charge constant... Up to approximately 87 pC / N, piezoelectric voltage constant Reachable While significantly outperforming unmodified PVDF-TrFE, it maintains stable output under 8000 mechanical cyclic loading conditions, demonstrating good long-term stability and environmental adaptability. Attached Figure Description

[0014] Figure 1 This is a schematic cross-sectional view of the sensing unit of the present invention;

[0015] Figure 2 This is a schematic diagram showing the residual polarization values ​​of pure polyvinylidene fluoride-trifluoroethylene and pure polyvinylidene fluoride-trifluoroethylene films doped with phytic acid under different electric field strengths.

[0016] Figure 3 A schematic diagram showing the piezoelectric coefficients of polyvinylidene fluoride-trifluoroethylene films with different phytic acid contents;

[0017] Figure 4 A schematic diagram illustrating the working stability of a polyvinylidene fluoride-trifluoroethylene / phytate membrane under 8000 cycles of loading.

[0018] Figure 5 Schematic diagram of the pressure response and recovery performance of the polyvinylidene fluoride-trifluoroethylene / phytic acid sensor;

[0019] Figure 6 This is a schematic diagram of pressure signal collection at different bending angles of a joint using a polyvinylidene fluoride-trifluoroethylene / phytic acid sensor.

[0020] Figure 7 This is a schematic diagram of real-time monitoring of pulse wave signals in Example 2;

[0021] Figure 8 This is a schematic diagram of distributed pressure sensing in Example 3;

[0022] Figure 9 This is a schematic diagram illustrating the application of the present invention. Detailed Implementation Example 1

[0023] This embodiment relates to a method for preparing PA-modified PVDF-TrFE piezoelectric composite films, including:

[0024] Step 1: Preparation of raw materials and solutions: Weigh 0.7g of PVDF-TrFE with a molar ratio of 70:30, dissolve it in 10mL of N,N-dimethylformamide (DMF) solvent, and stir magnetically for 3h until completely dissolved to obtain a transparent solution; add phytic acid (PA) solution at a mass fraction of 6wt%, and ultrasonically disperse for 30min to ensure uniform mixing to obtain a PVDF-TrFE / PA composite solution.

[0025] Step 2, Film Formation Process: The composite solution is uniformly spin-coated onto a clean glass substrate at 2000 rpm for 60 s. After spin-coating, it is dried in a vacuum oven at 80℃ for 12 h to remove residual solvent. Then, it is annealed at 150℃ for 1 h to obtain a film with a thickness of approximately 30 μm. Films are formed on temporary substrates (such as polished Si). They can be edge-wetting and peeled off using deionized water / ethanol and transferred to the target flexible substrate (ClearFlex / PDMS / PI). The upper and lower surfaces of the film are then coated with 10–50 μm PDMS or ClearFlex as flexible encapsulation and support layers (spin-coating at 1500 rpm × 60 s, crosslinking at 80℃ × 30 min).

[0026] This embodiment is based on the piezoelectric performance test of the above-mentioned PVDF-TrFE / PA composite film, and is achieved through the following method:

[0027] Step i. Electrode Preparation: Before preparing the electrodes, the surface of the PVDF-TrFE / PA composite film was thoroughly cleaned with anhydrous ethanol and deionized water to remove surface impurities, and then dried in a vacuum oven at 60°C for 1 hour. A gold electrode layer with a thickness of approximately 100 nm was deposited on the upper and lower surfaces of the film using thermal evaporation or magnetron sputtering. The electrode area size was controlled to 1 cm × 1 cm using a metal mask to ensure complete alignment of the upper and lower electrodes and avoid leakage or edge effects. Copper wires were soldered to the surfaces of the upper and lower electrodes using conductive silver paste and cured at room temperature for 12 hours to ensure good electrical contact.

[0028] Step ii. Polarization treatment: The polarized film sample is placed in an oil bath to avoid air discharge. At 90°C, a DC electric field of 80-100 MV / m is applied using a high-voltage power supply for 30 min. During polarization, the voltage is gradually increased (10 MV / m per minute) until the target electric field is reached to prevent sample breakdown. After polarization, the sample is slowly cooled to room temperature while maintaining the electric field for 10 min to fix the dipole orientation. During polarization, the hydroxyl groups in the PA molecule form hydrogen bonds with the C–F groups in the PVDF-TrFE segments, promoting the formation and stabilization of the β phase. Finally, a polarization-stable PVDF-TrFE / PA piezoelectric composite film is obtained.

[0029] Step iii. Performance Testing: Structural Characterization: XRD and FT-IR test results show that the β-phase content in the PVDF-TrFE / PA composite film reaches approximately 67%, which is 25% higher than that of the pure PVDF-TrFE film (approximately 42%). Ferroelectric Properties: P–E curve testing revealed that the residual polarization intensity Pr of the 6wt% PA-doped film is 6.9. The 4.6% concentration of the purer PVDF-TrFE membrane... The performance was improved by approximately 50%; the coercive electric field Ec decreased to 41.1 MV / m, a reduction of approximately 31% compared to the pure film (59.9 MV / m). Piezoelectric properties: measured using compression equilibrium analysis. The value is 87 pC / N, which is approximately 2.9 times that of a pure PVDF-TrFE membrane (30 pC / N). The value is 614 This is also far superior to the level of pure piezoelectric films. Cyclic stability: Under 8000 cycles of 3N force loading, the output voltage showed almost no decay, with only minor fluctuations, indicating excellent long-term stability.

[0030] As demonstrated by the above embodiments, the PA-modified PVDF-TrFE piezoelectric composite film prepared by this invention is significantly superior to existing PVDF-TrFE films in terms of β-phase content, ferroelectric properties, and piezoelectric properties. Its piezoelectric charge constant... Increased by approximately 290%, voltage constant Increased to 600 The above-mentioned properties also demonstrate excellent cycling stability and flexibility. This indicates that the molecular interface hydrogen bond engineering strategy proposed in this invention can effectively improve the performance and durability of PVDF-based piezoelectric composite materials, providing reliable technical support for their application in flexible sensors, electronic skin, and wearable devices.

[0031] like Figure 2 As shown in the figure, all data points were obtained by polarizing pure polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) films and phytate-doped PVDF-TrFE / PA composite films under different electric field intensities (40, 60, 80, 100 MV / m). The data in the figure show that, under the same electric field strength, the remanent polarization value of the phytate-doped composite film is significantly higher than that of the undoped film. Specifically, at 100 MV / m, the remanent polarization value of the PVDF-TrFE / PA film reaches approximately 7.8 μC / cm², while that of the pure PVDF-TrFE film is approximately 4.5 μC / cm². As can be seen from the figure, the introduction of phytate molecules can significantly improve the polarization efficiency and remanent polarization intensity of the material, thereby effectively promoting the induction and stabilization of the piezoelectric β phase.

[0032] like Figure 3 As shown in the figure, all data points were obtained by standardizing the piezoelectric charge constant of PVDF-TrFE / PA composite films with different phytic acid doping contents (0%, 4%, 6%, 8%). The data in the figure shows that as the phytic acid content increases, the composite membrane... (The sentence is incomplete and requires further context to translate accurately.) The piezoelectric value first increases and then decreases, reaching a maximum of approximately 87 pC / N with 6 wt% phytic acid, significantly higher than that of pure PVDF-TrFE films (approximately 30 pC / N). As shown in the figure, an appropriate amount of phytic acid can maximize the piezoelectric performance through hydrogen bond induction and local high dielectric enhancement, while excessive doping will disrupt the chain segment regularity and lead to a decrease in performance. Therefore, 6 wt% is the optimal doping amount.

[0033] like Figure 4 As shown in the figure, all data points were obtained after performing a total of 8000 cycles of testing on the PVDF-TrFE / PA composite film under a 3N force periodic loading condition. The overall curve in the figure represents the voltage response output during the entire cycle. The insets show the voltage response waveforms within 10 cycles at 3312 seconds and 5512 seconds, respectively. The test results show that the signal amplitude and waveform remain basically consistent before and after cycling, with no significant attenuation. As can be seen from the figure, the composite film of this invention has excellent cycle stability and structural durability, and its piezoelectric output remains highly stable under long-term mechanical loading conditions.

[0034] like Figure 5 As shown in the figure, all data points were obtained through a single loading and unloading test on the PVDF-TrFE / PA composite sensor. The gray area represents the electrical response and recovery process after pressure is applied, with a rapid rise within approximately 70 ms and a complete release within approximately 80 ms. The data in the figure indicate that the sensor exhibits a fast and stable voltage response during both pressure application and depressurization, with no significant hysteresis. As can be seen from the figure, the sensor of this invention has fast response characteristics, with a response time of approximately 70–80 ms, which can meet the requirements of dynamic pressure sensing and real-time monitoring.

[0035] like Figure 6 As shown in the figure, all data points were obtained by attaching a PVDF-TrFE / PA composite sensor to the elbow joint and collecting voltage signals generated by bending movements at different bending angles (30°, 60°, 90°, etc.). The data in the figure shows that the peak output voltage of the sensor increases significantly with increasing bending angle, and the signal repeatability is good. The inset in the figure illustrates the actual posture at different bending angles. As can be seen, the sensor of this invention can accurately capture changes in joint bending amplitude, exhibiting excellent motion recognition capabilities and potential for wearable human motion monitoring applications.

[0036] Thanks to the aforementioned structural stability and piezoelectric enhancement mechanism, the composite film prepared in this embodiment can work stably in scenarios such as flexibility, human-computer interaction, wearable electronics and electronic skin, as detailed below. Example 2

[0037] This embodiment relates to the application of the composite film obtained in Example 1, including: cutting the PVDF-TrFE / PA composite film into 1cm×1cm pieces, using a polyimide (PI) film as a flexible substrate, attaching flexible copper electrodes to both sides, and encapsulating with PDMS or polyimide (PI) to form a flexible wearable piezoelectric sensor.

[0038] like Figure 7 As shown, by fixing the sensor to the radial artery of the subject's wrist and connecting it to an oscilloscope for real-time voltage signal acquisition, the characteristic waveforms in the pulse signal, including the P wave, T wave, and D wave, can be clearly distinguished, and the signal frequency is consistent with the heart rate (approximately 80 bpm). By attaching the sensor to the surface of the elbow joint and bending the subject to 30°, 60°, and 90° respectively, the voltages measured are 1.1V, 1.7V, and 2.6V, showing a direct proportionality to the bending angle. By attaching the sensor to the surface of tuning forks of different frequencies, high-frequency vibration signals with a high signal-to-noise ratio (SNR=20) were successfully acquired, verifying its sensitive response capability to high-frequency dynamic signals. Example 3

[0039] This embodiment relates to the fabrication and application of a piezoelectric sensing array sensor, including:

[0040] Step 1: Prepare a flexible substrate using spin coating: Spin coat the Clear flex solution uniformly onto the cleaned glass substrate at 2000 rpm for 60 seconds, and then pre-bake at 80°C for 30 minutes to obtain a flexible substrate film with a thickness of about 20 μm.

[0041] Step 2: Using a microelectronic printer, print a 4×4 array of lower electrodes on the flexible substrate prepared in step 1 using silver paste.

[0042] The printing process used a nozzle diameter of 100μm, a printing speed of 2mm / s, and an electrode thickness of approximately 500nm.

[0043] The spacing between each electrode unit in the lower electrode array is 6 mm.

[0044] Step 3: After the electrode array is completed, the pre-prepared PVDF-TrFE / PA composite solution is uniformly spin-coated (at 1500 rpm for 60 s) or drop-coated onto the electrode surface, and then annealed at 80°C for 2 h to form a uniform and continuous piezoelectric active layer with a thickness of about 50 μm.

[0045] Step 4: Repeat steps 1 and 2. After printing the electrode array on the surface of the active layer obtained in step 3, use laser cutting technology to divide the active layer into circular units with a diameter of 4 mm, forming a 4×4 pixelated array, with each pixel serving as an independent piezoelectric sensing unit.

[0046] The upper electrode array and the lower electrode array are strictly aligned.

[0047] like Figure 8 As shown, the piezoelectric sensing array sensor in this embodiment completes the final encapsulation by attaching the upper electrode array prepared in step 4 onto a flexible support film (such as PDMS). The output signals of different pixels are synchronously acquired through an external acquisition circuit. When a local pressure of 10–50 kPa is applied, the signal is concentrated only at the corresponding pixel, and the positioning error is less than 1 mm, indicating that the array has good distributed pressure sensing and spatial resolution capabilities. Example 4

[0048] This embodiment relates to the fabrication of an arrayed sensor keyboard and its application in intelligent human-computer interaction devices, including:

[0049] Step 1: Preparation of the flexible substrate: After cleaning and drying, a polyethylene terephthalate (PET) film is used as the substrate material. To enhance adhesion, the PET surface is treated with oxygen plasma for 2 minutes, and then an electrode array is printed on the substrate using a microelectronic printer.

[0050] Each lower electrode in the lower electrode array is made of conductive silver paste material with a thickness of about 500nm. The electrode layout is designed as a 4×4 independent key unit, with each key having an area of ​​6×6mm² and a spacing of 2mm between adjacent keys, to simulate the arrangement of a small flexible keyboard.

[0051] After the lower electrode array is fabricated, the flexible substrate is flipped over, and a uniformly distributed array of silver nanowires (AgNWs) is sprayed onto its back side. The sprayed AgNWs layer, approximately 80–150 nm thick, forms a low-impedance nanonetwork structure, which can create charge conduction channels on the back side of the array units. This effectively reduces lateral electric field diffusion between adjacent pixels, suppresses signal crosstalk, and improves the signal independence and recognition accuracy of each piezoelectric unit in the array. The sprayed silver nanowire layer is then thermo-cured at 70 °C for 10 min to enhance adhesion and conductive continuity.

[0052] Step 2: The PVDF-TrFE / PA composite solution (8wt% DMF solution) is uniformly spin-coated onto the surface of the lower electrode array. The spin-coating parameters are 2000 rpm for 60 s and the annealing conditions are 120℃ for 2 h. After obtaining a piezoelectric active layer with a thickness of about 50 μm, the upper electrode array is prepared on its surface again using microelectronic printing technology. The active layer is then divided into corresponding 4×4 independent sensing units by laser cutting process to ensure that the polarization direction of each unit matches the upper and lower electrodes.

[0053] Step 3: The entire structure is flexibly encapsulated with polydimethylsiloxane (PDMS) to obtain the following result. Figure 1 The sensor units shown are approximately 200 μm thick, providing mechanical protection and enhancing flexibility. Each electrode unit is connected to an external signal acquisition circuit via flexible wires, forming a complete array of sensor keyboards.

[0054] Step 4: Connect the array sensor as an input terminal to a Bluetooth wireless module and develop a host computer interface. When the user applies light pressure (<10kPa) to different key positions, the corresponding pixel unit generates a voltage signal. The signal is collected by an analog-to-digital converter and wirelessly transmitted to a computer or mobile phone. Experimental results show that this flexible keyboard can achieve fast and accurate key recognition, with a response time of approximately 70ms and a recognition accuracy rate exceeding 98%. When the array sensor is fixed on a desktop or flexible support board, it can achieve input functions similar to existing keyboards. When attached to gloves or sleeves, users can complete input operations by lightly touching with their fingers, realizing wearable intelligent interaction. In virtual reality (VR) and augmented reality (AR) scenarios, this sensor array can serve as a lightweight flexible input terminal, enhancing the immersive interactive experience.

[0055] Through specific practical experiments, using an Arduino 2560 main control board (12-bit ADC resolution), an HC-05 Bluetooth wireless communication module, a 4×4 PVDF-TrFE / phytic acid piezoelectric sensor array (unit size 6 mm × 6 mm, spacing 2 mm, active layer thickness approximately 50 μm), and a sampling frequency of 200 Hz, the system was tested with finger pressure triggering, array signal acquisition, feature recognition, and wireless transmission. The results were as follows: Figure 9 As shown, the detection method is as follows:

[0056] 1) Key trigger recognition accuracy: Finger press trigger (pressing force about 5-10 kPa) was performed on each of the 16 units of the array. Each unit was tested 20 times, for a total of 320 input events. The number of successful recognitions was 314, and the recognition accuracy rate was 98%.

[0057] 2) Voltage output amplitude and resolution: The peak voltage output by the array unit is in the range of 0.1–0.5 V, and the output difference between each key (mean square error of repeated tests) is kept within 5%, which can support the effective resolution of the array key.

[0058] 3) Response speed and wireless latency: The voltage response time of the composite sensor is approximately 70–80 ms; after wireless transmission via the HC-05 Bluetooth module, the end-to-end input latency displayed on the terminal is measured to be 92–108 ms, which can meet the requirements of real-time interaction.

[0059] 4) Wireless input stability test: Finger touch input was performed according to the preset number sequence (such as "1–5–9–#") for 50 consecutive rounds, with a total of 20 input events. 18 of these were successful, with a success rate of 90%.

[0060] 5) Dialing Function Verification: The array was mapped to a mobile phone dial pad. The phone number "135××××××××" was entered into the dial pad. A total of 20 rounds of testing were conducted, involving 220 keystrokes. 214 keystrokes were successfully recognized, achieving a success rate of 97.27%, with all dialing operations successfully completed. The above experimental results demonstrate that the 4×4 PVDF-TrFE / PA flexible piezoelectric array of this invention exhibits comprehensive performance in human-computer interaction applications, including high sensitivity, high accuracy, fast response, and stable wireless transmission. It can be used in flexible keyboards, wearable input devices, smart terminal control, and real-time interaction applications.

[0061] In summary, compared with existing rigid touch devices, the PVDF-TrFE / PA array sensor of this invention not only has good flexibility and wearability, but also achieves high voltage sensitivity (35mV / kPa) by increasing the β phase content, which is significantly higher than that of traditional flexible piezoelectric films, thus achieving high-precision signal recognition under low pressure. This makes it show broad application prospects in human-computer interaction, wearable electronic input terminals and intelligent control systems. Secondly, through the array unit structure design and signal conditioning circuit optimization, this invention effectively reduces signal crosstalk between keys, making the key recognition accuracy of the 4×4 array reach more than 98%, which is significantly better than the stability of traditional flexible touch films under bending conditions. (4) The preparation process of this invention is simple and the conditions are controllable. The resulting composite material has high voltage performance, flexibility and durability, and is suitable for applications such as flexible sensors, wearable electronic devices and electronic skin.

[0062] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for preparing a polyvinylidene fluoride-based piezoelectric composite material, characterized by, Polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE) is dissolved and prepared as a matrix material to obtain a polymer solution. Phytic acid (PA) solution containing polyhydroxyl groups and high dielectric groups is added to the polymer solution to fully mix it at the molecular level to form a PVDF-TrFE / PA composite solution. The PVDF-TrFE / PA composite film is then formed by solution casting, spin coating or electrospinning. An external electric field is applied to the film to polarize it, thereby forming stable intermolecular hydrogen bonding and local high dielectric polarization synergistic structure between PVDF-TrFE segments and PA molecules to obtain a polyvinylidene fluoride piezoelectric composite film.

2. The method for preparing the polyvinylidene fluoride piezoelectric composite material according to claim 1, characterized in that, The aforementioned configuration refers to dissolving polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) in N,N-dimethylformamide (DMF) or dimethyl sulfoxide (DMSO) solvent.

3. The method for preparing the polyvinylidene fluoride piezoelectric composite material according to claim 1, characterized in that, The volume ratio of DMF to acetone in the mixed solvent is 6:4, and the concentration of the solute is 0.07-0.15 mg / mL.

4. The method for preparing the polyvinylidene fluoride piezoelectric composite material according to claim 1, characterized in that, The phytic acid (PA) solution is a 50% PA aqueous solution, and its mass ratio to the matrix material is (0.5-10):

100.

5. The method for preparing the polyvinylidene fluoride piezoelectric composite material according to claim 1, characterized in that, The polarization treatment refers to placing the composite film under an applied electric field for polarization treatment, so that the hydroxyl groups in the PA molecule and the C–F groups in the PVDF-TrFE chain interact through hydrogen bonding, inducing and stabilizing the formation of the β phase. At the same time, the high dielectric constant of the phosphate groups in the PA molecule helps to enhance the local polarization electric field and improve the polarization efficiency.

6. The method for preparing the polyvinylidene fluoride piezoelectric composite material according to claim 5, characterized in that, The applied electric field is an AC electric field of 50–100 MV / m.

7. An improved polyvinylidene fluoride piezoelectric composite film prepared by the method according to any one of claims 1-6, characterized in that, Its thickness is 20–40 μm, the crystallinity of the film is 75%, the β phase content is 62%, the dielectric constant at 100 Hz is 22, and the voltage retention rate exceeds 95% after 8000 cycles of loading.

8. An application of a polyvinylidene fluoride piezoelectric composite film prepared by any one of claims 1-6 or as described in claim 6, characterized in that, Used to fabricate wearable piezoelectric sensors, piezoelectric sensing array sensors, or arrayed sensing keyboards.

9. The application according to claim 8, characterized in that, The wearable piezoelectric sensor is formed by cutting a PVDF-TrFE / PA composite film into square pieces, using a polyimide (PI) film as a flexible substrate, attaching flexible copper electrodes to both sides, and encapsulating it with PDMS or polyimide (PI).

10. The application according to claim 8, characterized in that, The piezoelectric sensing array sensor or arrayed sensing keyboard is constructed by uniformly spin-coating or drop-coating a PVDF-TrFE / PA composite solution onto the surface of the lower electrode array, annealing to form a uniform and continuous piezoelectric active layer, then further preparing an upper electrode array on the surface of the piezoelectric active layer, and finally cutting out several piezoelectric sensing units and attaching their upper electrode arrays to a flexible support film.

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