Modified ferroelectric polymer composite film and preparation method and application thereof

Abstract

This invention provides a modified ferroelectric polymer composite film, its preparation method, and its applications, belonging to the field of piezoelectric composite material technology. The modified ferroelectric polymer composite film includes a ferroelectric polymer base film and a plurality of composite nanoparticles and multi-walled carbon nanotubes dispersed within the ferroelectric polymer base film. The composite nanoparticles have a core-shell structure, comprising a core and an inner shell layer and an outer shell layer sequentially surrounding 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. This invention fully utilizes the synergistic effect of the composite nanoparticles and multi-walled carbon nanotubes on the dielectric and piezoelectric properties of P(VDF-TrFE) materials, thereby preparing a composite material with high dielectric constant, low dielectric loss, and excellent piezoelectric properties to meet the stringent performance requirements of high-performance sensors and other application fields.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric composite materials technology, specifically to a modified ferroelectric polymer composite film, its preparation method, and its application. Background Technology

[0002] P(VDF-TrFE) (poly(vinylidene fluoride-trifluoroethylene)) is an important ferroelectric polymer material with broad application prospects in the sensor field. It possesses excellent piezoelectric, pyroelectric, and ferroelectric properties, enabling it to effectively convert physical quantities such as mechanical energy and thermal energy into electrical signals, thus achieving the detection of various physical quantities. To improve the performance of P(VDF-TrFE) sensors, doping modification is often employed. For example, nanoparticles (such as carbon nanotubes and metal oxide nanoparticles) can be doped into P(VDF-TrFE). Carbon nanotubes have excellent electrical and mechanical properties; doping can improve the material's conductivity and mechanical strength. Metal oxide nanoparticles (such as zinc oxide nanoparticles) can enhance the material's dielectric properties and improve the sensor's signal response characteristics. By introducing nanofillers, such as BaTiO3, ZnO, and SiO2, the polarization degree of the piezoelectric material can be increased, promoting the formation of the β phase in P(VDF-TrFE), thereby improving its piezoelectric constant.

[0003] While modifying P(VDF-TrFE) with nanofillers can improve its performance to some extent, several problems exist. For example, adding certain metal oxide nanofillers, although increasing the dielectric constant, often leads to a significant increase in dielectric loss. This is because the interfacial compatibility between metal oxide nanofillers and the P(VDF-TrFE) matrix is ​​poor, and under an electric field, charge accumulation and scattering easily occur at the interface, thus increasing energy loss. Taking the common titanium dioxide (TiO2) nanofiller as an example, dielectric loss can increase by more than 50% after the addition amount exceeds a certain threshold, which severely limits the application of sensors 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 interactions, carbon nanotubes are prone to agglomeration in polymer matrices. This agglomeration leads to uneven distribution of carbon nanotubes in the material, preventing them from fully utilizing their excellent electrical and mechanical properties. For example, in the preparation of MWCNTs / P(VDF-TrFE) composites, if conventional mechanical blending methods are used, the presence of carbon nanotube aggregates will create stress concentration points within the composite material. This not only reduces the material's mechanical strength but also significantly diminishes its piezoelectric performance enhancement. Studies have shown that the piezoelectric coefficient of severely aggregated MWCNTs / P(VDF-TrFE) composites is only 10%-20% higher than that of P(VDF-TrFE) without added carbon nanotubes, far below the expected performance improvement.

[0004] Therefore, there is an urgent need to develop a modified ferroelectric polymer material to improve the dispersibility of fillers and the interfacial compatibility between fillers and ferroelectric polymer matrix, thereby enhancing 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 electrical performance caused by poor filler dispersion and poor interfacial compatibility between filler and ferroelectric polymer matrix in existing ferroelectric polymer-based materials.

[0006] In a first aspect, the present invention provides a modified ferroelectric polymer composite membrane, comprising a ferroelectric polymer base membrane and a plurality of composite nanoparticles and multi-walled carbon nanotubes dispersed in the ferroelectric polymer base membrane; the composite nanoparticles have a core-shell structure, the core-shell structure comprising a core and an inner shell layer and an outer shell layer sequentially covering the core.

[0007] The core material consists of a composite piezoelectric ceramic material composed of potassium sodium niobate and barium titanate, the inner shell layer consists of polydopamine, and the outer shell layer consists of MnO2.

[0008] Preferably, the mass fraction of composite nanoparticles in the modified ferroelectric polymer composite film is 2.5wt%~7.5wt%.

[0009] 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.

[0010] Preferably, the ferroelectric polymer-based film includes a P(VDF-TrFE)-based film.

[0011] Secondly, embodiments of the present invention provide a method for preparing a modified ferroelectric polymer composite film, comprising the following steps:

[0012] S1. Preparation of composite piezoelectric ceramic material: KNbO3, NaNbO3 and BaTiO3 were mixed and ball-milled, and then washed, dried and sintered to obtain a composite piezoelectric ceramic material composed of potassium sodium niobate and barium titanate.

[0013] S2. Preparation of composite nanoparticles: Dopamine was dispersed in Tri-HCl buffer solution, and then composite piezoelectric ceramic material was added and stirred at room temperature. After centrifugation, washing, and drying, an intermediate was obtained. The intermediate and KMnO4 were dispersed in water and subjected to hydrothermal reaction. After washing and drying, the composite nanoparticles were obtained.

[0014] S3. Preparation of modified ferroelectric polymer composite film: The composite nanoparticles are dispersed in an organic solution of ferroelectric polymer and mixed evenly. Then, multi-walled carbon nanotubes are added and mixed evenly. The mixture is then cast into a film at room temperature and dried to obtain the modified ferroelectric polymer composite film.

[0015] In this embodiment of the invention, in step S2, the intermediate is a polydopamine-coated composite piezoelectric ceramic material, namely KNN-BT@PDA.

[0016] Preferably, in step S1, the ball-to-material ratio in the ball mill is (15~20):1, and the ball milling speed is 50~80 rpm. Ball milling can uniformly mix the raw material powder, refine the particles, increase the reactivity, improve the material uniformity, promote sintering, and reduce defects.

[0017] Preferably, in step S1, the sintering temperature is 1000~1200℃ and the sintering time is 2~5h.

[0018] Preferably, in step S1, the heating rate during sintering is 3~5℃ / min.

[0019] 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.

[0020] Preferably, in step S2, the pH of the Tris-HCl buffer solution is 8-9.

[0021] Preferably, in step S2, the stirring reaction time at room temperature is 12~24h.

[0022] Preferably, in step S2, the hydrothermal reaction temperature is 160~180℃ and the hydrothermal reaction time is 12~24h.

[0023] Preferably, in step S3, the drying temperature is 60~80℃.

[0024] Preferably, in step S3, the thickness of the modified ferroelectric polymer composite film is controlled to be 30~45μm.

[0025] Thirdly, the present invention provides the application of the above-mentioned modified ferroelectric polymer composite film in the preparation of piezoelectric sensors.

[0026] The principle of the technical solution of this invention is as follows:

[0027] Both KNN (potassium sodium niobate) and BT (barium titanate) are lead-free piezoelectric materials, conforming to global environmental protection trends and replacing 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 quasi-isomorphic phase boundary (MPB), which synergistically enhances 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 controlling the composition.

[0028] Dopamine can spontaneously undergo oxidative self-polymerization in a weakly alkaline environment, forming a polydopamine (PDA) layer on the surface of the KNN-BT composite piezoelectric ceramic material. The polydopamine (PDA) has abundant functional groups such as amino and hydroxyl groups. The PDA coating can improve the interfacial compatibility between the inorganic piezoelectric ceramic and the polymer matrix. The PDA layer provides active sites for subsequent MnO2 deposition. The dielectric gradient between PDA (low dielectric) and MnO2 (high dielectric) can homogenize the interfacial electric field distribution, reduce local electric field distortion, and improve the breakdown field strength.

[0029] The high conductivity of MWCNTs forms a three-dimensional conductive pathway in the polymer matrix, enhancing charge collection efficiency. The interfacial polarization effect between MWCNTs and piezoelectric materials can induce an additional dipole moment, amplifying the piezoelectric output.

[0030] The core-double-shell structure of KNN-BT@PDA@MnO2 particles optimizes interface polarization through dielectric constant, while the conductive network of MWCNTs promotes rapid charge transport. The two work together to enhance piezoelectric output. The double-shell layer isolates the piezoelectric particles from direct contact with MWCNTs, avoiding leakage current problems caused by excessive conductive filler, and maintaining a balance between high dielectric constant and low loss.

[0031] In this invention, the unique structure formed by the composite of MnO2 and KNN-BT@PDA is the result of the combined effects of PDA encapsulation, morphology regulation of MnO2, enhanced interfacial bonding, and promotion of electron and ion migration. Specifically, the MnO2 portion encapsulates the KNN-BT@PDA to provide additional support and protection, while some MnO2 connects the surrounding ceramic particles together in a linear structure, enhancing the overall structural stability. Furthermore, the formation of Mn-N bonds between MnO2 and PDA significantly strengthens interfacial bonding, thereby improving the material's structural stability and electrochemical performance.

[0032] In this invention, MWCNTs exhibit multiple interactions with P(VDF-TrFE) and KNN-BT@PDA@MnO2, including physical adsorption and chemical bonding. Physical adsorption: The hydroxyl / amino groups of the PDA layer form weak hydrogen bonds (F···HN or F···HO) with the fluorine atoms (-CF2) of P(VDF-TrFE), enhancing interfacial compatibility; the rough MnO2 surface of the core-shell nanoparticles is "anchored" in the polymer matrix, inhibiting particle aggregation through mechanical interlocking. Chemical bonding: The amino groups (-NH2) of PDA form metal-ligand coordination bonds (Mn-N bonds) with the Mn-O structure on the MnO2 surface, strengthening interfacial bonding.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] This invention provides a modified ferroelectric polymer composite film by embedding KNN-BT@PDA@MnO2 composite nanoparticles and multi-walled carbon nanotubes (MWCNTs) into a ferroelectric polymer base film. This fully leverages the synergistic effect of KNN-BT@PDA@MnO2 composite nanoparticles and MWCNTs on the dielectric and piezoelectric properties of the ferroelectric polymer base film material, thereby preparing a ferroelectric polymer composite film material with high dielectric constant, low dielectric loss, and excellent piezoelectric properties to meet the stringent material performance requirements of applications such as high-performance sensors. Attached Figure Description

[0035] Figure 1 The XRD patterns of KNN-BT@PDA@MnO2 nanoparticles prepared in Example 1 and Comparative Example 7 are shown below.

[0036] Figure 2 This is a SEM image of the KNN-BT@PDA@MnO2 nanoparticles in Example 1 of the present invention. Detailed Implementation

[0037] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0038] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0039] In the embodiments of the present invention, the molar ratio of monomer VDF:TrFE in polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) is 70:30.

[0040] The NaNbO3 and KNbO3 used in the embodiments of this invention are prepared by the following method:

[0041] Preparation of NaNbO3: Weigh 1.33g Nb2O5 and dissolve it in 60mL of NaOH (10mol / L) solution. Stir magnetically until completely mixed and homogeneous. Transfer the mixture to a reaction vessel and place it in an oven for hydrothermal reaction at 200℃ for 12h. After the hydrothermal reaction is complete, wash with deionized water until neutral and dry in a vacuum drying oven at 60℃ for 6h to obtain NaNbO3 nanoparticles.

[0042] Preparation of KNbO3: Weigh 1.33g Nb2O5 and dissolve it in 60mL of KOH (10mol / L) solution. Stir magnetically until completely mixed and homogeneous. Transfer the mixture to a reaction vessel and place it in an oven for hydrothermal reaction at 220℃ for 24h. After the hydrothermal reaction is completed, wash with deionized water until neutral and dry in a vacuum drying oven at 60℃ for 6h to obtain KNbO3 nanoparticles.

[0043] I. Preparation Method

[0044] Example 1

[0045] A method for preparing a KNN-BT@PDA@MnO2-MWCNTs / P(VDF-TrFE) magnetic polymer composite film with a KNN-BT@PDA@MnO2 content of 5wt% and a MWCNTs content of 0.1wt% includes the following steps:

[0046] Preparation of S1 and KNN-BT materials

[0047] KNbO3, NaNbO3, and BaTiO3 were mixed in a stoichiometric ratio (96KNN-4BT) (molar ratio of KNbO3, NaNbO3, and BaTiO3 was 48:48:4), and then ball-milled. Zirconia balls were added, the ball-to-material ratio was 20:1, the rotation speed was 60 rpm, and the ball-milling time was 6 h. The ball-milled material was washed with deionized water and alcohol and dried. It was then placed in a tube furnace for sintering, heated to 1070℃ at a heating rate of 5℃ / min, and sintered at 1070℃ for 2 h. After cooling, it was ground for 30 min to obtain (K,Na)NbO3-BaTiO3 (denoted as KNN-BT) composite piezoelectric ceramic material.

[0048] Preparation of S2, KNN-BT@PDA@MnO2 composite nanoparticles

[0049] 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 ultrasonication. Place the solution at room temperature and stir for 24 hours to allow dopamine to undergo a self-polymerization reaction on the surface of KNN-BT to form a polydopamine (PDA) film that uniformly coats the surface of KNN-BT. After the reaction is completed, centrifuge and wash with deionized water and ethanol. Dry the washed KNN-BT@PDA composite material in a 60℃ oven for 6 hours to obtain the final KNN-BT@PDA composite material.

[0050] Preparation of KNN-BT@PDA@MnO2: 80 mL of deionized water and 0.878 g of KNN-BT@PDA were added to a beaker at a mass ratio of KNN-BT@PDA:KMnO4 = 2:1 and stirred until homogeneous. Then, 0.439 g of KMnO4 was added, and stirring was continued for 15 minutes. The mixture was then poured into a reaction vessel and hydrothermally reacted at 170 °C for 12 hours. The product was washed with deionized water and anhydrous ethanol, and then placed in a vacuum drying oven and dried at 60 °C for 6 hours to obtain KNN-BT@PDA@MnO2 nanoparticles.

[0051] S3, Preparation of modified ferroelectric polymer composite film

[0052] P(VDF-TrFE) was dissolved in DMF organic solvent to obtain a mixed solution of 0.5 g / mL. The prepared KNN-BT@PDA@MnO2 nanoparticles were mixed with the above solution and stirred for 6 h. MWCNTs were then added, and stirring continued for another 6 h. The mixed solution was then cast onto a glass plate at room temperature and dried in a vacuum drying oven to obtain two composite films with a thickness of 30 μm. The amount of KNN-BT@PDA@MnO2 nanoparticles added was 5 wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles, and MWCNTs; the amount of MWCNTs added was 0.1 wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles, and MWCNTs.

[0053] Example 2

[0054] The difference between this embodiment and Embodiment 1 is that in step S3, the amount of KNN-BT@PDA@MnO2 nanoparticles added is 5wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the amount of MWCNTs added is 0.3wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the remaining steps are the same as in Embodiment 1.

[0055] Example 3

[0056] The difference between this embodiment and Embodiment 1 is that in step S3, the amount of KNN-BT@PDA@MnO2 nanoparticles added is 5wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the amount of MWCNTs added is 0.5wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the remaining steps are the same as in Embodiment 1.

[0057] Example 4

[0058] The difference between this embodiment and Embodiment 1 is that in step S3, the amount of KNN-BT@PDA@MnO2 nanoparticles added is 5wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the amount of MWCNTs added is 0.7wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the remaining steps are the same as in Embodiment 1.

[0059] Comparative Example 1

[0060] The difference between this comparative example and Example 1 is that the amount of KNN-BT@PDA@MnO2 nanoparticles added is 0wt%, and the amount of MWCNTs added is 0wt%.

[0061] Comparative Example 2

[0062] The difference between this comparative example and Example 1 is that the amount of KNN-BT@PDA@MnO2 nanoparticles added is 0wt%.

[0063] Comparative Example 3

[0064] The difference between this embodiment and Embodiment 1 is that in step S3, the amount of KNN-BT@PDA@MnO2 nanoparticles added is 2.5wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the amount of MWCNTs added is 0wt%; the remaining steps are the same as in Embodiment 1.

[0065] Comparative Example 4

[0066] The difference between this comparative example and Example 1 is that in step S3, the amount of KNN-BT@PDA@MnO2 nanoparticles added is 5 wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the amount of MWCNTs added is 0 wt%; the remaining steps are the same as in Example 1.

[0067] Comparative Example 5

[0068] The difference between this embodiment and Embodiment 1 is that in step S3, the amount of KNN-BT@PDA@MnO2 nanoparticles added is 7.5wt% of the total mass of P(VDF-TrFE) powder, KNN-BT@PDA@MnO2 nanoparticles and MWCNTs; the amount of MWCNTs added is 0wt%; the remaining steps are the same as in Embodiment 1.

[0069] Comparative Example 6

[0070] 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 obtain a P(VDF-TrFE) composite membrane modified with KNN-BT@PDA and MWCNTs.

[0071] Comparative Example 7

[0072] The difference between this comparative example and Example 1 is that, in step S3, the mass ratio of KNN-BT@PDA to KMnO4 in the preparation of the KNN-BT@PDA@MnO2 composite nanoparticle material is 1:1.

[0073] II. Testing Methods

[0074] 1. Material characterization testing

[0075] The material's structure was tested using an X-ray diffractometer, and its morphology was tested using a scanning electron microscope.

[0076] 2. Dielectric properties of modified ferroelectric polymer composite films

[0077] The dielectric properties of the modified ferroelectric polymer composite films prepared in the examples and comparative examples were tested using a broadband dielectric spectroscopy system (Agilent Technologies 4284A precision impedance LCR meter). The test conditions were: room temperature, and the test frequency range was 10 Hz. 2 ~10 7 The dielectric constants of different modified ferroelectric polymer composite film samples at 100 Hz were statistically analyzed. ɛ r ), dielectric loss test results.

[0078] 3. Piezoelectric properties of modified ferroelectric polymer composite films

[0079] The piezoelectric properties of different modified ferroelectric polymer composite films prepared in the examples and comparative examples were tested using 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 under room temperature conditions were statistically analyzed.

[0080] 4. Test of electrical output performance of piezoelectric nanogenerator

[0081] Fabrication of the piezoelectric nanogenerator: After sputtering Au electrodes onto both sides of the composite film using an ion sputtering apparatus, the film 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 fabricate the composite piezoelectric nanogenerator, copper wires were then connected to the Au electrodes of the nanogenerator. When the piezoelectric nanogenerator is subjected to mechanical energy, it harvests electrical energy. Finally, the entire assembly was encapsulated using polyimide (PI) tape to protect it from environmental factors such as temperature and humidity.

[0082] Test method: Keithley 6514 electrometer: When the piezoelectric nanogenerator generates static charge, these charges will induce corresponding charges on the measuring electrodes of the electrometer. The output voltage, current and charge of the piezoelectric nanogenerator can be indirectly measured by measuring the induced charge.

[0083] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0084] 1. Characterization and test results of composite membrane materials

[0085] The composite systems of KNN-BT@PDA and KMnO4 with different mass ratios were analyzed by X-ray diffraction (XRD). Figure 1 The XRD patterns of the KNN-BT@PDA@MnO2 nanoparticles prepared in Example 1 and Comparative Example 7 are shown below. Figure 1 As 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 the PDA on the outer layer of KNN-BT caused by excess KMnO4, leading to the formation of other products. Furthermore, 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 moderate, and low-valence manganese oxides, such as MnO or MnO2, are successfully formed.

[0086] The microstructure of the KNN-BT@PDA@MnO2 composite material was characterized using scanning electron microscopy (SEM). Figure 2 As shown, the microstructure of MnO2 exhibits a two-dimensional layered structure. These layered structures interweave to form a three-dimensional network with a thickness of only a few nanometers, equivalent to a few atomic layers. In the KNN-BT@PDA@MnO2 composite material, MnO2 exists mainly in linear and layered forms. Some MnO2 encapsulates KNN-BT@PDA to provide additional support and protection, while the other part connects the surrounding ceramic particles together in a linear structure, enhancing the overall structural stability and forming a unique microstructure. Polydopamine (PDA), due to its excellent adhesion and film-forming properties, can form a uniform coating layer on the surface of KNN-BT@PDA. This coating not only enhances the stability of the material but also provides additional electron conduction pathways, thereby improving the electrochemical performance of the composite material. The unique structure formed after the MnO2 and KNN-BT@PDA composite is the result of the combined effects of PDA coating, MnO2 morphology regulation, enhanced interfacial bonding, and promotion of electron and ion migration. This structure not only improves the electrochemical performance of the material but also enhances its overall stability and conductivity. Furthermore, the formation of Mn-N bonds between MnO2 and PDA significantly strengthens interfacial bonding, thereby improving the material's structural stability and electrochemical performance.

[0087] 2. Dielectric properties of modified ferroelectric polymer composite films

[0088] Dielectric constants of different modified ferroelectric polymer composite film samples at 100 Hz ɛ r The results of the dielectric loss test are shown in Table 1 below.

[0089] Table 1

[0090]

[0091] As shown in Table 1, the modified ferroelectric polymer composite film prepared in the embodiments of the present invention has good dielectric properties. The mass fraction of MWCNT has a significant effect on the dielectric constant. When the mass fraction increases from 0 to 0.7 wt%, the dielectric constant in the low-frequency range 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 will destroy the material uniformity. When the mass ratio of multi-walled carbon nanotubes to composite nanoparticles is 1:10, a good synergistic effect is observed.

[0092] Comparative Examples 3-5 show that the mass fraction of KNN-BT@PDA@MnO2 affects both the dielectric constant and dielectric loss of the composite film. Comparative Example 6 and Example 2 indicate that the addition of MnO2 also has a certain impact on the dielectric properties of the composite system. This is because the redox properties of the MnO2 surface can generate additional ionic polarization contributions, leading to an increase in both dielectric constant and loss with increasing content. When the filler mass fraction exceeds a critical threshold, filler clusters cause the gradual formation of a percolation network. The locally high concentration of MnO2 semiconductor phase induces carrier migration paths, significantly increasing leakage current. The resulting Joule heating effect hinders dipole orientation polarization, thus inhibiting the growth of the dielectric constant.

[0093] 3. Piezoelectric properties of modified ferroelectric polymer composite films

[0094] The piezoelectric coefficient test results of different modified ferroelectric polymer composite film samples (diameter 3 mm) under an electric field of 80 MV / m and at room temperature are shown in Table 2 below.

[0095] Table 2

[0096]

[0097] As shown in Table 2, the presence of KNN-BT@PDA@MnO2 can significantly improve the piezoelectric coefficient of P(VDF-TrFE) under low electric field conditions. d 33 As the mass fraction of KNN-BT@PDA@MnO2 increases, the piezoelectric constant of the composite film increases. d 33 The piezoelectric coefficient of the composite film KNN-BT@PDA@MnO2 shows an increasing trend. When the mass fraction of KNN-BT@PDA@MnO2 is 5wt%, the piezoelectric coefficient of the composite film KNN-BT@PDA / P(VDF-TrFE) is... d 33 Optimal; when the multi-walled carbon nanotubes are 0.5 wt%, d 33 Optimal.

[0098] Comparative Example 6 and Example 2 show that the addition of MnO2 effectively enhances the multi-level polarization mechanism and interfacial charge synergistic effect of the composite system. The abundant redox active sites on the MnO2 surface induce additional ionic polarization contributions; the space charge layer formed at the MnO2 / PDA heterointerface suppresses carrier recombination probability through local Schottky barrier modulation, resulting in a more uniform polarization field distribution. This promotes spontaneous polarization of the two-dimensional nanosheets, leading to a higher piezoelectric constant. d 33 Increase.

[0099] 4. Piezoelectric sensor output performance

[0100] Table 3

[0101]

[0102] Table 3 shows that the double coating of PDA and MnO2 improves the interfacial bonding strength between the piezoelectric filler and the polymer matrix P(VDF-TrFE). This coating structure reduces the mechanical property mismatch between the filler and the matrix, and promotes stress transfer through surface modification, thereby inducing the piezoelectric effect more efficiently during mechanical deformation. Furthermore, the PDA and MnO2 coating layers reduce filler aggregation through physical barrier effects, ensuring uniform dispersion of the filler in the polymer matrix. The doping of MWCNTs forms conductive pathways within the composite material, accelerating the separation and transport of piezoelectric charges. This is because the introduction of conductive fillers can improve the dielectric constant and conductivity, but the loading must be controlled to avoid dielectric losses caused by agglomeration. Appropriate doping of MWCNTs may balance conductivity and dielectric strength, thereby improving piezoelectric output performance.

[0103] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A modified ferroelectric polymer composite film, characterized by, The modified ferroelectric polymer composite film comprises a ferroelectric polymer base film and a plurality of composite nanoparticles and multi-walled carbon nanotubes dispersed in the ferroelectric polymer base film; the composite nanoparticles have a core-shell structure comprising a core and an inner shell layer and an outer shell layer successively coated outside the core; The core comprises a composite piezoelectric ceramic material composed of potassium sodium niobate KNN and barium titanate BT, the inner shell layer comprises polydopamine PDA, and the outer shell layer comprises MnO2. The polydopamine PDA-coated composite piezoelectric ceramic material is an intermediate KNN-BT@PDA. MnO2 exists in linear and layered forms, a part of MnO2 wraps the intermediate KNN-BT@PDA to provide additional support and protection, and another part of MnO2 connects the surrounding ceramic particles together in a linear structure to enhance the stability of the overall structure. The mass fraction of the composite nanoparticles in the modified ferroelectric polymer composite film is 2.5wt%-7.5wt%. 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. The ferroelectric polymer base film comprises a P(VDF-TrFE) base film. The preparation method of the composite nanoparticles comprises dispersing the intermediate KNN-BT@PDA and KMnO4 into water for reaction, and the mass ratio of the intermediate KNN-BT@PDA to KMnO4 is (1.5-2):

1.

2. A method for preparing a modified ferroelectric polymer composite film as claimed in claim 1, characterized by, The method comprises the following steps: S1. Preparation of a composite piezoelectric ceramic material: mixing KNbO3, NaNbO3 and BaTiO3, ball milling, washing, drying and sintering to obtain the composite piezoelectric ceramic material; S2. Preparation of composite nanoparticles: dispersing dopamine into a Tris-HCl buffer solution, adding the composite piezoelectric ceramic material for stirring reaction at room temperature, centrifugal separation, washing and drying to obtain an intermediate KNN-BT@PDA; dispersing the intermediate KNN-BT@PDA and KMnO4 into water for hydrothermal reaction, washing and drying to obtain the composite nanoparticles; S3. Preparation of a modified ferroelectric polymer composite film: dispersing the composite nanoparticles into an organic solution of a ferroelectric polymer, mixing, adding multi-walled carbon nanotubes, mixing, casting into a film at room temperature, drying to obtain the modified ferroelectric polymer composite film.

3. The method for preparing the modified ferroelectric polymer composite film according to claim 2, 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.

4. The method for preparing the modified ferroelectric polymer composite film according to claim 2, characterized in that, In the step S1, the sintering temperature is 1000-1200℃, and the sintering time is 2-5h.

5. The method for preparing the modified ferroelectric polymer composite film according to claim 2, characterized in that, In the step S2, the mass ratio of the composite piezoelectric ceramic material to dopamine is 1:(1-3).

6. The method for preparing the modified ferroelectric polymer composite film according to claim 2, 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℃, and the time of the hydrothermal reaction is 12-24h.

7. Use of the modified ferroelectric polymer composite film of claim 1 in the preparation of a piezoelectric sensor.

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