Modified ferroelectric polymer composite membrane as well as preparation method and application thereof

Abstract

The invention provides a modified ferroelectric polymer composite film as well as a preparation method and application thereof, and belongs to the technical field of piezoelectric composite materials. The modified ferroelectric polymer composite film comprises a ferroelectric polymer base film, and a plurality of composite nanoparticles and multi-walled carbon nanotubes which are dispersed in the ferroelectric polymer base film, the composite nano-particle has a core-shell structure, and the core-shell structure comprises a core, and an inner shell layer and an outer shell layer which are sequentially coated outside the core; the core comprises a composite piezoelectric ceramic material composed of potassium sodium niobate and barium titanate, the inner shell layer comprises polydopamine, and the outer shell layer comprises MnO2. According to the invention, the synergistic effect of the composite nanoparticles and the multi-walled carbon nanotubes on the dielectric and piezoelectric properties of the P (VDF-TrFE) material is fully exerted, so that the composite material with high dielectric constant, low dielectric loss and excellent piezoelectric property is prepared to meet the strict requirements of application fields such as high-performance sensors and the like on material properties.

Description

Technical Field

[0001] The present invention relates to the technical field of piezoelectric composite materials, and particularly relates to a modified ferroelectric polymer composite film, a preparation method thereof and an application thereof. Background Art

[0002] P(VDF-TrFE) (poly(vinylidene fluoride-trifluoroethylene)) is an important ferroelectric polymer material and has broad application prospects in the field of sensors. It has good piezoelectricity, pyroelectricity, ferroelectricity and other properties, and these properties enable it to effectively convert physical quantities such as mechanical energy and thermal energy into electrical signals, thereby realizing the detection of various physical quantities. In order to improve the performance of P(VDF-TrFE) sensors, doping modification methods are often used. For example, doping nanoparticles (such as carbon nanotubes, metal oxide nanoparticles, etc.) into P(VDF-TrFE). Carbon nanotubes have excellent electrical and mechanical properties, and after doping, the conductivity and mechanical strength of the material can be improved. Metal oxide nanoparticles (such as zinc oxide nanoparticles) can enhance the dielectric properties of the material and improve the signal response characteristics of the sensor. By introducing nano-fillers such as BaTiO3, ZnO, SiO2, etc., the polarization degree of the piezoelectric material can be increased, the formation of the β-phase of P(VDF-TrFE) can be promoted, and thus its piezoelectric constant can be improved.

[0003] When modifying P(VDF-TrFE) with nanofillers, although its properties can be improved to a certain extent, there are still many problems. For example, when adding certain metal oxide nanofillers, although the dielectric constant can be increased, it often leads to a significant increase in the dielectric loss of the material. This is because the interfacial compatibility between the metal oxide nanofillers and the P(VDF-TrFE) matrix is poor. Under the action of an electric field, charge accumulation and scattering are likely to occur at the interface, thus increasing the energy loss. Taking the common titanium dioxide (TiO2) nanofiller as an example, when the addition amount exceeds a certain threshold, the dielectric loss can increase by more than 50%, which severely limits the application of the sensor in high-frequency or high-precision detection scenarios. For the addition of carbon nanotubes to P(VDF-TrFE), their dispersibility is a key limiting factor. Due to their high aspect ratio and strong interaction, carbon nanotubes are prone to agglomeration in the polymer matrix. This agglomeration phenomenon will result in uneven distribution of carbon nanotubes in the material, and their excellent electrical and mechanical properties cannot be fully utilized. For example, when preparing MWCNTs / P(VDF-TrFE) composites, if the conventional mechanical blending method is used, the presence of carbon nanotube agglomerates will form stress concentration points inside the composites, not only reducing the mechanical strength of the material, but also greatly reducing the improvement effect on its piezoelectric properties. According to research, the piezoelectric coefficient of MWCNTs / P(VDF-TrFE) composites with severe agglomeration is only 10%-20% higher than that of P(VDF-TrFE) without adding carbon nanotubes, far lower than the expected performance improvement effect.

[0004] Therefore, it is urgent to develop a modified ferroelectric polymer material to improve the filler dispersibility and the interfacial compatibility between the filler and the ferroelectric polymer matrix, and enhance its electrical and mechanical properties. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present invention provides a modified ferroelectric polymer composite film, its preparation method and application, aiming to solve the technical problems of poor filler dispersibility and poor interfacial compatibility between the filler and the ferroelectric polymer matrix in the existing ferroelectric polymer-based materials, resulting in poor electrical properties.

[0006] In the first aspect, the present invention provides a modified ferroelectric polymer composite film, which includes a ferroelectric polymer-based film and a number of composite nanoparticles and multi-walled carbon nanotubes dispersed in the ferroelectric polymer-based film; the composite nanoparticles have a core-shell structure, and the core-shell structure includes a core and an inner shell layer and an outer shell layer sequentially coated outside the core; Among them, the core includes a composite piezoelectric ceramic material composed of sodium potassium niobate and barium titanate, the inner shell layer includes polydopamine, and the outer shell layer includes MnO2.

[0007] Preferably, the mass fraction of the composite nanoparticles in the modified ferroelectric polymer composite film is 2.5 wt% to 7.5 wt%.

[0008] Preferably, the mass ratio of multi-walled carbon nanotubes to composite nanoparticles in the modified ferroelectric polymer composite film is (0.02 - 0.14):1.

[0009] Preferably, the ferroelectric polymer-based film includes a P(VDF-TrFE)-based film.

[0010] In a second aspect, an embodiment of the present invention provides a method for preparing a modified ferroelectric polymer composite film, including the following steps: S1. Preparation of the composite piezoelectric ceramic material: Mix KNbO3, NaNbO3, and BaTiO3 and then ball-mill them. After washing, drying, and sintering, a composite piezoelectric ceramic material composed of sodium potassium niobate and barium titanate is obtained; S2. Preparation of the composite nanoparticles: Disperse dopamine in a Tri-HCl buffer solution, then add the composite piezoelectric ceramic material and stir and react at room temperature. After centrifugal separation, washing, and drying, an intermediate is obtained; Disperse the intermediate and KMnO4 in water and carry out a hydrothermal reaction. After washing and drying, the composite nanoparticles are obtained; S3. Preparation of the modified ferroelectric polymer composite film: Disperse the composite nanoparticles in an organic solution of the ferroelectric polymer and mix well, then add multi-walled carbon nanotubes and mix well. Cast a film at room temperature and dry it to obtain the modified ferroelectric polymer composite film.

[0011] In the embodiment of the present invention, in step S2, the intermediate is a composite piezoelectric ceramic material coated with polydopamine, that is, KNN-BT@PDA.

[0012] Preferably, in step S1, the ball-to-material ratio of ball-milling is (15 - 20):1, and the rotation speed of ball-milling is 50 - 80 rpm. Ball-milling can make the raw material powders uniformly mixed, refine the particles, increase the reaction activity, improve the material uniformity, promote sintering, and reduce defects.

[0013] Preferably, in step S1, the sintering temperature is 1000 - 1200 °C, and the sintering time is 2 - 5 h.

[0014] Preferably, in step S1, the heating rate during sintering is 3 - 5 °C / min.

[0015] Preferably, in step S2, the mass ratio of the composite piezoelectric ceramic material to dopamine is 1:(1 - 3), and the mass ratio of KNN-BT@PDA to KMnO4 is (1.5 - 2):1 Preferably, in step S2, the pH of the Tris-HCl buffer solution is 8 - 9.

[0016] Preferably, in step S2, the stirring reaction time at room temperature is 12 to 24 h.

[0017] Preferably, in step S2, the hydrothermal reaction temperature is 160 to 180 °C, and the hydrothermal reaction time is 12 to 24 h.

[0018] Preferably, in step S3, the drying temperature is 60 to 80 °C.

[0019] Preferably, in step S3, the film thickness of the modified ferroelectric polymer composite film is controlled to be 30 to 45 μm.

[0020] In a third aspect, the present invention provides an application of the above-mentioned modified ferroelectric polymer composite film in the preparation of a piezoelectric sensor.

[0021] The principle of the technical solution of the present invention is as follows: Both KNN (sodium potassium niobate) and BT (barium titanate) are lead-free piezoelectric materials, which conform to the global environmental protection trend and replace traditional lead-based PZT materials; KNN-based materials have a high piezoelectric coefficient, while BT-based materials have a high Curie temperature and temperature stability. The combination of the two can form a morphotropic phase boundary (MPB) to synergistically enhance the piezoelectric response; the preparation process of KNN-BT is compatible with traditional piezoelectric ceramics, and the phase structure and piezoelectric activity can be optimized by composition regulation.

[0022] Dopamine can spontaneously undergo oxidative self-polymerization in a weakly alkaline environment to form a polydopamine (PDA) layer on the surface of the KNN-BT composite piezoelectric ceramic material. Polydopamine (PDA) has rich functional groups such as amino and hydroxyl groups. The coating of PDA can improve the interfacial compatibility between the inorganic piezoelectric ceramic and the polymer matrix; the PDA layer provides active sites for the subsequent deposition of MnO2; the dielectric gradient of PDA (low dielectric) and MnO2 (higher dielectric) can homogenize the interfacial electric field distribution, reduce local electric field distortion, and enhance the breakdown field strength.

[0023] The high conductivity of MWCNTs forms a three-dimensional conductive path in the polymer matrix, enhancing the charge collection efficiency. The interfacial polarization effect between MWCNTs and the piezoelectric material can induce an additional dipole moment to amplify the piezoelectric output.

[0024] The core-double shell structure of KNN-BT@PDA@MnO2 particles optimizes the interfacial polarization through the dielectric gradient, while the conductive network of MWCNTs promotes the rapid charge transfer. The two work together to enhance the piezoelectric output; the double shell layer isolates the direct contact between the piezoelectric particles and MWCNTs, avoiding the leakage current problem caused by excessive conductive fillers and maintaining the balance between high dielectric constant and low loss.

[0025] In the present invention, the special structure formed after the combination of MnO2 and KNN-BT@PDA is the result of the combined effects of the coating of PDA, the morphology regulation of MnO2, the strengthening of the interfacial bonding, and the promotion of electron and ion migration. Among them, part of MnO2 wraps KNN-BT@PDA to provide additional support and protection. At the same time, part of MnO2 connects the surrounding ceramic particles together in a linear structure, enhancing the stability of the overall structure. In addition, by forming Mn-N bonds between MnO2 and PDA, the interfacial bonding can be greatly enhanced, thereby improving the structural stability and electrochemical performance of the material.

[0026] In the present invention, there are multiple interactions such as physical adsorption and chemical bonding between MWCNTs, P(VDF-TrFE), and KNN-BT@PDA@MnO2. Physical adsorption: The hydroxyl / amino groups of the PDA layer form weak hydrogen bonds (F···H-N or F···H-O) with the fluorine atoms (-CF2) of P(VDF-TrFE), improving the interfacial compatibility; the rough surface of MnO2 in the core-shell nanoparticles is "anchored" in the polymer matrix, suppressing particle agglomeration through mechanical interlocking; the rough surface of MnO2 in the core-shell nanoparticles is "anchored" in the polymer matrix, suppressing particle agglomeration through mechanical interlocking. Chemical bonding: The amino group (-NH2) of PDA forms a metal-ligand coordination bond (Mn-N bond) with the Mn-O structure on the surface of MnO2, strengthening the interfacial bonding.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a modified ferroelectric polymer composite film. KNN-BT@PDA@MnO2 composite nanoparticles and multi-walled carbon nanotubes (MWCNTs) are embedded in the ferroelectric polymer-based film, giving full play to the synergistic effects of KNN-BT@PDA@MnO2 composite nanoparticles and multi-walled carbon nanotubes (MWCNTs) on the dielectric and piezoelectric properties of the ferroelectric polymer-based film material, thereby preparing a ferroelectric polymer composite film material with a high dielectric constant, low dielectric loss, and excellent piezoelectric properties to meet the strict requirements for material properties in application fields such as high-performance sensors. Description of the Drawings

[0028] Figure 1 XRD spectrum of the KNN-BT@PDA@MnO2 nanoparticles prepared in Example 1 and Comparative Example 7; Figure 2 SEM image of the KNN-BT@PDA@MnO2 nanoparticles in Example 1 of the present invention. Detailed Embodiments

[0029] The embodiments of the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, so they are only examples and cannot be used to limit the protection scope of the present invention.

[0030] For those not specifying specific technologies or conditions in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For the reagents or instruments not indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0031] In the polyvinylidene fluoride-trifluoroethylene P(VDF-TrFE) used in the embodiments of the present invention, the molar ratio of the monomers VDF:TrFE is 70:30.

[0032] NaNbO3 and KNbO3 used in the embodiments of the present invention are prepared by the following methods: Preparation of NaNbO3: Weigh 1.33 g of Nb2O5, dissolve it in 60 mL of NaOH (10 mol / L) solution, stir magnetically until completely mixed evenly, transfer it to a reaction kettle, place it in an oven for hydrothermal reaction. The hydrothermal reaction temperature is 200 °C and the time is 12 h. After the hydrothermal reaction is completed, wash it with deionized water until neutral, and dry it in a vacuum drying oven at 60 °C for 6 h to obtain NaNbO3 nanoparticles.

[0033] Preparation of KNbO3: Weigh 1.33 g of Nb2O5, dissolve it in 60 mL of KOH (10 mol / L) solution, stir magnetically until completely mixed evenly, transfer it to a reaction kettle, place it in an oven for hydrothermal reaction. The hydrothermal reaction temperature is 220 °C and the time is 24 h. After the hydrothermal reaction is completed, wash it with deionized water until neutral, and dry it in a vacuum drying oven at 60 °C for 6 h to obtain KNbO3 nanoparticles.

[0034] I. Preparation method Example 1 A preparation method of a KNN-BT@PDA@MnO2-MWCNTs / P(VDF-TrFE) magnetic polymer composite membrane with 5 wt% of KNN-BT@PDA@MnO2 and 0.1 wt% of MWCNTs, comprising the following steps: S1. Preparation of KNN-BT material Mix KNbO3, NaNbO3 and BaTiO3 according to the stoichiometric ratio (96KNN-4BT) (the molar ratio of KNbO3, NaNbO3 and BaTiO3 is 48:48:4), then ball-mill them. Put zirconium balls into the mixture with a ball-to-material ratio of 20:1, rotate at a speed of 60 revolutions per minute for 6 hours. Wash the milled materials with deionized water and alcohol and dry them. Put the dried materials into a tube furnace for sintering. Heat up at a rate of 5 °C / min to 1070 °C and sinter at 1070 °C for 2 hours. After cooling, grind for 30 minutes to obtain (K,Na)NbO3-BaTiO3 (denoted as KNN-BT) composite piezoelectric ceramic materials.

[0035] Preparation of S2, KNN-BT@PDA@MnO2 composite nanoparticle materials Preparation of KNN-BT@PDA: Prepare a 0.1 mol / L Tri-HCl buffer solution and adjust the pH to about 8.5. Add 2 g of dopamine (DA) to 60 mL of the above buffer solution and stir until completely dissolved. Then add 1.2 g of KNN-BT sample and disperse it by ultrasonic wave. Place the solution at room temperature and stir for 24 hours to make dopamine undergo self-polymerization reaction on the surface of KNN-BT to form a polydopamine (PDA) film, which uniformly coats the surface of KNN-BT. After the reaction, centrifuge and separate, wash with deionized water and ethanol, and dry the washed KNN-BT@PDA composite material in an oven at 60 °C for 6 hours to obtain the final KNN-BT@PDA composite material; Preparation of KNN-BT@PDA@MnO2: According to the mass ratio of KNN-BT@PDA:KMnO4 = 2:1, add 80 mL of deionized water and 0.878 g of KNN-BT@PDA to a beaker and stir until uniform. Then add 0.439 g of KMnO4 and continue to stir for 15 minutes. Then pour the mixture into a reaction kettle and carry out hydrothermal reaction at 170 °C for 12 hours. Wash the product with deionized water and absolute ethanol, and put the product into a vacuum drying oven and dry at 60 °C for 6 hours to obtain KNN-BT@PDA@MnO2 nanoparticles.

[0036] Preparation of modified ferroelectric polymer composite film Dissolve P(VDF-TrFE) in the organic solvent DMF to obtain a mixed solution with a concentration of 0.5 g / mL; mix the prepared KNN-BT@PDA@MnO2 nanoparticles with the above solution, stir for 6 h, then add MWCNTs and continue stirring for 6 h; then cast the mixed solution onto a glass plate at room temperature and dry it in a vacuum drying oven to obtain two composite films with a thickness of 30 μm. Among them, the addition amount of KNN-BT@PDA@MnO2 nanoparticles is 5 wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the addition amount of MWCNTs is 0.1 wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs.

[0037] Example 2 The difference between this example and Example 1 is that in step S3, the addition amount of KNN-BT@PDA@MnO2 nanoparticles is 5 wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the addition amount of MWCNTs is 0.3 wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the remaining steps are the same as those in Example 1.

[0038] Example 3 The difference between this example and Example 1 is that in step S3, the addition amount of KNN-BT@PDA@MnO2 nanoparticles is 5 wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the addition amount of MWCNTs is 0.5 wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the remaining steps are the same as those in Example 1.

[0039] Example 4 The difference between this example and Example 1 is that in step S3, the addition amount of KNN-BT@PDA@MnO2 nanoparticles is 5 wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the addition amount of MWCNTs is 0.7 wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the remaining steps are the same as those in Example 1.

[0040] Comparative Example 1 The difference between this comparative example and Example 1 is that the addition amount of KNN-BT@PDA@MnO2 nanoparticles is 0 wt%, and the addition amount of MWCNTs is 0 wt%.

[0041] Comparative Example 2 The difference between this comparative example and Example 1 is that the addition amount of KNN-BT@PDA@MnO2 nanoparticles is 0 wt%.

[0042] Comparative Example 3 The difference between this example and Example 1 is that in step S3, the addition amount of KNN-BT@PDA@MnO2 nanoparticles is 2.5 wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the addition amount of MWCNTs is 0 wt%; the remaining steps are the same as those in Example 1.

[0043] Comparative Example 4 The difference between this comparative example and Example 1 is that in step S3, the addition amount of KNN-BT@PDA@MnO2 nanoparticles is 5 wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the addition amount of MWCNTs is 0 wt%; the remaining steps are the same as those in Example 1.

[0044] Comparative Example 5 The difference between this example and Example 1 is that in step S3, the addition amount of KNN-BT@PDA@MnO2 nanoparticles is 7.5 wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the addition amount of MWCNTs is 0 wt%; the remaining steps are the same as those in Example 1.

[0045] Comparative Example 6 The difference between this comparative example and Example 1 is that in step S3, KNN-BT@PDA@MnO2 is replaced with KNN-BT@PDA to prepare a KNN-BT@PDA and MWCNTs modified P(VDF-TrFE) composite membrane.

[0046] Comparative Example 7 The difference between this comparative example and Example 1 is that in the preparation process of the KNN-BT@PDA@MnO2 composite nanoparticle material in step S3, the mass ratio of KNN-BT@PDA to KMnO4 is 1:1.

[0047] II. Test Methods 1. Characterization Tests of Materials The structure of the materials was tested using an X-ray diffractometer, and the morphology of the materials was tested using a scanning electron microscope.

[0048] 2. Dielectric properties of the modified ferroelectric polymer composite film The dielectric properties of different modified ferroelectric polymer composite films prepared in the examples and comparative examples were tested by broadband dielectric spectroscopy (Agilent 4284A precision impedance LCR tester); the test conditions were: room temperature, test frequency range 10 2 ~10 7 ; the dielectric constants ( ɛ r ) and dielectric loss test results of different modified ferroelectric polymer composite film samples at 100 Hz were counted.

[0049] 3. Piezoelectric properties of the modified ferroelectric polymer composite film The piezoelectric properties of different modified ferroelectric polymer composite films prepared in the examples and comparative examples were tested by a quasi-static piezoelectric constant tester; the test conditions were: room temperature, quasi-static; the piezoelectric coefficients of different modified ferroelectric polymer composite film samples at room temperature were counted.

[0050] 4. Test of the electrical output performance of the piezoelectric nanogenerator Preparation of the piezoelectric nanogenerator: After sputtering Au electrodes on both sides of the composite film by an ion sputtering instrument, it was polarized in an oil bath at 65 °C and a high electric field of 100 MV / m for 30 minutes to obtain piezoelectricity. To prepare the composite piezoelectric nanogenerator, copper wires were then connected to the Au electrodes of the nanogenerator, and electrical energy was collected when the piezoelectric nanogenerator was subjected to mechanical energy. Finally, the entire assembly was encapsulated using polyimide (PI) tape to protect it from environmental problems such as temperature and humidity.

[0051] Test method: Measured by a Keithley 6514 electrometer: When the piezoelectric nanogenerator generates static charges, these charges will induce corresponding charges on the measurement electrodes of the electrometer, so the output voltage, current, and charge of the piezoelectric nanogenerator are indirectly measured by measuring the induced charges.

[0052] III. Analysis of the test results of each example and comparative example 1. Test results of the composite film material characterization The composite system with different mass ratios of KNN-BT@PDA and KMnO4 was analyzed by X-ray diffraction (XRD). Figure 1 XRD patterns of the KNN-BT@PDA@MnO2 nanoparticles prepared in Example 1 and Comparative Example 7 are shown in Figure 1As shown, when the mass ratio of KNN-BT@PDA to KMnO4 is 1:1, impurity phases are observed in the XRD pattern after hydrothermal treatment. Considering the strong oxidizing property of KMnO4, these impurity phases may be due to the oxidation of PDA on the outer layer of KNN-BT by excessive KMnO4, resulting in the formation of other products. Further, when the mass ratio of KNN-BT@PDA to KMnO4 is adjusted to 2:1, no obvious impurity phases are observed. The amount of KMnO4 is appropriate, and low-valent manganese oxides such as MnO or MnO2 are successfully formed.

[0053] The microstructure of the KNN-BT@PDA@MnO2 composite material was characterized by scanning electron microscopy (SEM). As Figure 2 shown, the microscopic morphology of MnO2 presents a two-dimensional layered gauze-like structure. These layered structures are intertwined to form a three-dimensional network, and its thickness is only a few nanometers, equivalent to the scale of several atomic layers. In the KNN-BT@PDA@MnO2 composite material, MnO2 mainly exists in the form of lines and layers. Some MnO2 wraps around KNN-BT@PDA to provide additional support and protection, while the other part connects the surrounding ceramic particles in a linear structure, enhancing the stability of the overall structure and forming a special microstructure. Due to its excellent adhesion and film-forming properties, polydopamine (PDA) can form a uniform coating layer on the surface of KNN-BT@PDA. This coating effect not only enhances the stability of the material but also provides an additional electron conduction path for the material, thereby improving the electrochemical performance of the composite material. The special structure formed after the combination of MnO2 and KNN-BT@PDA is the result of the combined action of the coating effect of PDA, the morphology regulation of MnO2, the strengthening of interface bonding, and the promotion of electron and ion migration. This structure not only improves the electrochemical performance of the material but also enhances the overall stability and conductivity. In addition, by forming Mn-N bonds between MnO2 and PDA, the interface bonding can be greatly enhanced, thereby improving the structural stability and electrochemical performance of the material.

[0054] 2. Dielectric Properties of Modified Ferroelectric Polymer Composite Films The dielectric constant ([[]] ɛ r ) and dielectric loss test results of different modified ferroelectric polymer composite film samples at 100 Hz are shown in Table 1 below.

[0055] Table 1

[0056] As can be seen from the results in Table 1, the modified ferroelectric polymer composite film prepared in the embodiment of the present invention has good dielectric properties. The mass fraction of MWCNT has a significant effect on the dielectric constant. When it increases from 0 to 0.7 wt%, the dielectric constant in the low-frequency band first increases and then decreases. This is attributed to the fact that an appropriate amount of MWCNT increases the polarization centers, while an excessive amount destroys the material uniformity. A better synergistic effect is exhibited when the mass ratio of multi-walled carbon nanotubes to composite nanoparticles is 1:10.

[0057] The data of Comparative Examples 3-5 show that the mass fraction of KNN-BT@PDA@MnO2 has an impact on both the dielectric constant and dielectric loss of the composite film. The results of Comparative Example 6 and Example 2 show that the addition of MnO2 also has a certain impact on the dielectric properties of the composite system. Because the redox characteristics on the surface of MnO2 can produce additional ionic polarization contributions, resulting in both the dielectric constant and loss increasing with the increase in content. When the filler mass fraction exceeds the critical threshold, the filler clusters cause the gradual formation of a percolation network, and the local high-concentration MnO2 semiconductor phase induces the carrier migration path, significantly increasing the leakage conduction current. The Joule heat effect generated by it hinders the dipole orientation polarization, instead suppressing the increase in the dielectric constant.

[0058] 3. Piezoelectric properties of the modified ferroelectric polymer composite film The piezoelectric coefficient test results of different modified ferroelectric polymer composite film samples (diameter 3 mm) under an electric field of 80 MV / m at room temperature are shown in Table 2 below.

[0059] Table 2

[0060] As can be seen from the results in Table 2, the presence of KNN-BT@PDA@MnO2 can significantly improve the piezoelectric coefficient of P(VDF-TrFE) in a low electric field environment. d 33 . As the mass fraction of KNN-BT@PDA@MnO2 increases, the piezoelectric constant of the composite film d 33 shows an increasing trend. When the mass fraction of KNN-BT@PDA@MnO2 is 5 wt%, the piezoelectric coefficient of the composite film KNN-BT@PDA / P(VDF-TrFE) d 33 is optimal; when the multi-walled carbon nanotubes are 0.5 wt%, d 33 is optimal.

[0061] The results of Comparative Example 6 and Example 2 show that the addition of MnO2 effectively enhances the multi-level polarization mechanism and the interfacial charge synergy effect of the composite system. The abundant redox active sites on the surface of MnO2 induce additional ionic polarization contributions; the space charge layer formed at the MnO2 / PDA heterojunction suppresses the carrier recombination probability through local Schottky barrier regulation, making the polarization field strength distribution more uniform. Promote the spontaneous polarization of two-dimensional nanosheets, so that the piezoelectric constant d 33 increases.

[0062] 4. Electrical output performance of piezoelectric sensors Table 3

[0063] The results in Table 3 show that the double-layer coating of PDA and MnO2 improves the interfacial bonding strength between the piezoelectric filler and the polymer matrix P(VDF-TrFE). This coating structure can reduce the mechanical property mismatch between the filler and the matrix, and at the same time promote stress transfer through surface modification, so as to more efficiently induce the piezoelectric effect during mechanical deformation. In addition, the coating layers of PDA and MnO2 reduce the aggregation of fillers through physical barrier effects, ensuring their uniform dispersion in the polymer matrix. The doping of MWCNTs forms a conductive path inside the composite material, accelerating the separation and transmission of piezoelectric charges. This is because the introduction of conductive fillers can increase the dielectric constant and conductivity, but the loading amount needs to be controlled to avoid dielectric loss caused by agglomeration. The appropriate doping of MWCNTs may balance the conductivity and dielectric strength, thereby improving the piezoelectric output performance.

[0064] It should be noted that the present invention is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same constitution and the same function and effect as the technical idea within the technical solution scope of the present invention are all included in the technical scope of the present invention. In addition, within the scope not departing from the gist of the present invention, various modifications that those skilled in the art can think of to the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of the present invention.

Claims

1. A modified ferroelectric polymer composite film, characterized in that, It includes a ferroelectric polymer-based film and a number of composite nanoparticles and multi-walled carbon nanotubes dispersed in the ferroelectric polymer-based film; the composite nanoparticles have a core-shell structure, and the core-shell structure includes a core and an inner shell layer and an outer shell layer sequentially coated outside the core; Among them, the core includes a composite piezoelectric ceramic material composed of sodium potassium niobate and barium titanate, the inner shell layer includes polydopamine, and the outer shell layer includes MnO2.

2. The modified ferroelectric polymer composite film according to claim 1, wherein The mass fraction of the composite nanoparticles in the modified ferroelectric polymer composite film is 2.5wt% - 7.5wt%.

3. The modified ferroelectric polymer composite film according to claim 2, wherein The mass ratio of the multi-walled carbon nanotubes to the composite nanoparticles in the modified ferroelectric polymer composite film is (0.02 - 0.14):

1.

4. A modified ferroelectric polymer composite film according to claim 1, wherein The ferroelectric polymer-based film includes a P(VDF-TrFE)-based film.

5. A method for preparing a modified ferroelectric polymer composite film as described in any one of claims 1 to 4, characterized in that, It includes the following steps: S1. Preparation of the composite piezoelectric ceramic material: Mix KNbO3, NaNbO3, and BaTiO3 and then ball-mill them. After washing, drying, and sintering, the composite piezoelectric ceramic material is obtained; S2. Preparation of the composite nanoparticles: Disperse dopamine in a Tris-HCl buffer solution, and then add the composite piezoelectric ceramic material and stir and react at room temperature. After centrifugal separation, washing, and drying, an intermediate is obtained; Disperse the intermediate and KMnO4 in water, carry out a hydrothermal reaction, and after washing and drying, the composite nanoparticles are obtained; S3. Preparation of the modified ferroelectric polymer composite film: Disperse the composite nanoparticles in an organic solution of the ferroelectric polymer and mix well, then add multi-walled carbon nanotubes and mix well. Cast a film at room temperature and dry it to obtain the modified ferroelectric polymer composite film.

6. The preparation method of the modified ferroelectric polymer composite film according to claim 5, characterized in that, In the step S1, the ball-to-material ratio of the ball-milling is (15 - 20):1, and the rotation speed of the ball-milling is 50 - 80 rpm.

7. The preparation method of the modified ferroelectric polymer composite film according to claim 5, characterized in that, In the step S1, the sintering temperature is 1000 - 1200 °C, and the sintering time is 2 - 5 h.

8. The preparation method of the modified ferroelectric polymer composite film according to claim 5, characterized in that, In the step S2, the mass ratio of the composite piezoelectric ceramic material to dopamine is 1:(1 - 3), and the mass ratio of KNN-BT@PDA to KMnO4 is (1.5 - 2):

1.

9. The preparation method of the modified ferroelectric polymer composite film according to claim 5, characterized in that, In the step S2, the pH of the Tris-HCl buffer solution is 8 - 9, the temperature of the hydrothermal reaction is 160 - 180 °C, and the time of the hydrothermal reaction is 12 - 24 h.

10. Use of the modified ferroelectric polymer composite film according to any one of claims 1 - 4 in the preparation of a piezoelectric sensor.

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