A method for preparing a flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure

Abstract

This invention provides a method for preparing a flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure, comprising the following steps: S1, electrochemically anodizing a titanium foil in an organic electrolyte to generate a TiO2 layer in situ on the surface; S2, immersing the titanium foil treated in step S1 in a barium-containing solution for a hydrothermal reaction to generate a BaTiO3 layer in situ on the surface; S3, coating the BaTiO3 layer surface with a P(VDF-TrFE) solution and annealing it to form a flexible P(VDF-TrFE) / BaTiO3 composite film; S4, subjecting the flexible P(VDF-TrFE) / BaTiO3 composite film to polarization treatment to obtain the final product. This invention prepares a piezoelectric composite film with a layer-by-layer interlocking structure, which possesses both excellent piezoelectric properties and deformability, and can be used in energy harvesting, piezoelectric sensors, and piezoelectric catalysis.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric thin film preparation technology, specifically to a method for preparing a flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite thin film with a layer-by-layer interlocking structure. Background Technology

[0002] Piezoelectric materials, as a traditional functional material, can convert mechanical energy into electrical energy due to the unique non-centrosymmetry of their crystal structure, and have wide applications in fields such as electronics, energy industry, and catalysis and medicine. Among them, piezoelectric thin films, with their advantages of small size, light weight, high frequency response, and wide bandwidth, are widely used in smart applications such as energy harvesting, sensors, and flexible electronics. However, the brittleness of common piezoelectric ceramics such as lead zirconate titanate, lead magnesium niobate, and barium titanate severely limits the application scenarios of thin films; piezoelectric polymers with good deformability, such as polytetrafluoroethylene and its copolymers, have limited use in energy conversion and sensing due to their low piezoelectric coefficients. Therefore, a thin film material that combines flexibility and excellent piezoelectric properties has become an urgent need. Piezoelectric composite thin films are materials that combine piezoelectric ceramics and polymers to leverage the advantages of both. Filling the polymer matrix with a piezoelectric ceramic reinforcing phase can improve the piezoelectric properties of the material to a certain extent while retaining the flexibility of the polymer system. However, with the expansion of its application scope, piezoelectric thin films still face some challenges in practical applications. First, piezoelectric composite films lack a support structure for coordinated deformation, resulting in low durability. Second, although the piezoelectric properties of piezoelectric composite films are improved compared to pure piezoelectric polymer materials, they still fall short of the performance of bulk piezoelectric materials, failing to meet the demands for energy harvesting, sensing, and other applications.

[0003] Patent CN110690342A discloses a flexible piezoelectric energy conversion device based on carbon-coated barium titanate / PVDF. By uniformly mixing polyvinylidene fluoride with carbon-coated barium titanate nanoparticles, it can convert low-frequency mechanical energy into electrical energy to power wearable electronic devices. However, its piezoelectric performance is poor, and the piezoelectric film has defects. Patent CN104734563A discloses a method for fabricating a flexible lead-free barium titanate piezoelectric generator, providing a portable, self-powered flexible lead-free barium titanate piezoelectric generator and its fabrication method. However, the selected substrate reduces the overall flexibility of the piezoelectric generator.

[0004] Existing methods for preparing barium titanate piezoelectric coatings often employ micro-arc oxidation, which uses an aqueous solvent system as the electrolyte. This method results in a low barium titanate content in the prepared micro-arc oxidation coating, with the barium titanate dispersed throughout the coating. The overall macroscopic piezoelectric properties of the coating are not apparent; only microscopic piezoelectric effects are observed in localized micro-regions containing barium titanate crystals. To improve the piezoelectric properties of piezoelectric composite films, the structural design of the composite material has received widespread attention. The dispersion form and degree of the piezoelectric filler phase in the matrix material affect the piezoelectric properties of the material. However, the dispersion of the material system disrupts the continuity of piezoelectric particles, causing discontinuous changes in performance. Maintaining the continuity of piezoelectric phase properties has become an important consideration for improving the piezoelectric performance of materials. However, simply increasing interfacial bonding through horizontal interfaces or geometric structures often fails to optimize the performance of each piezoelectric phase. Therefore, there is an urgent need for a piezoelectric composite film with excellent piezoelectric particle continuity. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure. This invention utilizes a flexible titanium foil substrate to generate a BaTiO3 piezoelectric layer in situ. The piezoelectric properties of the BaTiO3 film are improved by impregnation with a P(VDF-TrFE) solution. Employing a naturally transforming three-dimensional particle network structure with interlocking between the two piezoelectric structures, a high-performance P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure is obtained while fully utilizing the piezoelectric polarization transition. This piezoelectric composite film possesses both excellent piezoelectric properties and deformability. Its inherent layer-by-layer interlocking structure overcomes the traditional requirement for uniform dispersion of the matrix and filler in the preparation of piezoelectric composite materials, making it suitable for applications in energy harvesting, piezoelectric sensors, and piezoelectric catalysis.

[0006] The objective of this invention can be achieved through the following methods:

[0007] In a first aspect, the present invention provides a method for preparing a flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure, comprising the following steps:

[0008] S1. In an organic electrolyte, titanium foil is subjected to electrochemical anodic oxidation to generate a TiO2 layer on the surface in situ; wherein the anode is titanium foil and the cathode is an inert conductive electrode.

[0009] S2. The titanium foil treated in step S1 is placed in a barium-containing solution for hydrothermal reaction, and a BaTiO3 layer is generated in situ on the surface.

[0010] S3. Coat the surface of the BaTiO3 layer with P(VDF-TrFE) solution and anneal it to form a flexible P(VDF-TrFE) / BaTiO3 composite film.

[0011] S4. The flexible P(VDF-TrFE) / BaTiO3 composite film is subjected to polarization treatment to obtain the flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film.

[0012] As one technical solution of the present invention, in step S1, the titanium foil is a foil of pure titanium or titanium alloy, with a thickness of 20-100 μm. Preferably, the thickness of the titanium foil is 20-50 μm.

[0013] As a technical solution of the present invention, in step S1, the titanium foil is a titanium foil that has been pretreated and cleaned; the pretreatment step includes: sealing the titanium foil on one side with (PET) tape, ultrasonically cleaning the sealed titanium foil in acetone, ethanol and pure water for 5-10 minutes in sequence, and drying it with cold air.

[0014] In this invention, the electrochemical anodizing is performed using a dual-electrode system; after anodizing, the titanium foil is rinsed with deionized water and dried.

[0015] As one technical solution of the present invention, in step S1, the organic electrolyte comprises 0.01–0.3 mol / L ammonium fluoride and 0.1–3 mol / L ethylene glycol. Preferably, the organic electrolyte comprises 0.05–0.08 mol / L ammonium fluoride and 0.5–0.8 mol / L ethylene glycol.

[0016] As one technical solution of the present invention, in step S1, the parameters for the electrochemical anodizing are set as follows: water bath temperature is 20–30°C, stirring speed is 5–25 rpm, DC power supply is in constant voltage mode with a voltage of 40–80V, and processing time is 30–90 min. Preferably, the parameters for the electrochemical anodizing are set as follows: water bath temperature is 20–26°C, stirring speed is 5–10 rpm, DC power supply is in constant voltage mode with a voltage of 55–70V, and processing time is 40–60 min.

[0017] As one technical solution of the present invention, in step S1, the inert conductive electrode includes any one of a graphite electrode, a platinum electrode, and a pure titanium electrode. Preferably, the inert conductive electrode is a graphite electrode.

[0018] As one technical solution of the present invention, in step S2, the barium-containing solution comprises an aqueous solution of barium hydroxide with a concentration of 1-2 mol / L. Preferably, the concentration of the barium-containing solution is 1.5-2 mol / L. In some embodiments, the barium hydroxide aqueous solution is prepared by dissolving Ba(OH)₂·8H₂O powder in deionized water that has been boiled for 10-30 minutes.

[0019] As one technical solution of the present invention, in step S2, the temperature of the hydrothermal reaction is 180-220°C, and the reaction time is 1-5 days. Too low a hydrothermal reaction temperature will affect the conversion rate and degree of conversion; too high a hydrothermal reaction temperature will cause the hydrothermal reactor to be unable to withstand the pressure. Preferably, the reaction time of the hydrothermal reaction is 2-5 days.

[0020] In some embodiments, after the BaTiO3 layer is formed, the titanium foil is removed and rinsed with a 5-20% (by volume) dilute acetic acid solution and deionized water for 5-10 minutes, and then dried. Preferably, the dilute acetic acid solution has a volume content of 5-10%.

[0021] As a technical solution of the present invention, in step S3, the concentration of the P(VDF-TrFE) solution is 0.5–3 g / L. Preferably, the concentration of the P(VDF-TrFE) solution is 0.5–1.0 g / L. In some embodiments, the P(VDF-TrFE) solution is obtained by dissolving polyvinylidene fluoride (PVDF) powder, and the solvent used includes any one of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetone, and N-methylpyrrolidone (NMP).

[0022] As a technical solution of the present invention, in step S3, the annealing treatment is divided into two stages: the first stage is vacuum holding at 60-80℃ for 1-4 hours, and the second stage is holding at 120-140℃ for 6-12 hours. The first stage allows the organic solvent to fully evaporate, and the second stage allows P(VDF-TrFE) to fully crystallize.

[0023] As a technical solution of the present invention, in step S4, the parameters for the polarization treatment are set as follows: the distance between the needle tip and the sample surface is controlled between 5 and 20 mm, the voltage displayed by the high-voltage DC power supply is adjusted to 5 to 20 kV, and the polarization time is 30 to 90 min. Preferably, the parameters for the polarization treatment are set as follows: the distance between the needle tip and the sample surface is controlled between 5 and 10 mm, the voltage displayed by the high-voltage DC power supply is adjusted to 10 to 20 kV, and the polarization time is 30 to 60 min. The polarization treatment of the present invention uses non-contact corona polarization treatment to excite the piezoelectric properties of the thin film.

[0024] Secondly, the present invention provides a flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure obtained by the preparation method described above.

[0025] Compared to existing micro-arc oxidation methods for preparing barium titanate layers, which use aqueous electrolytes and produce rough, porous ceramic oxide layers with irregular pore structures and micrometer-scale pore sizes, this method results in a barium titanate coating (i.e., a titanium dioxide layer) containing both crystalline and amorphous phases. After hydrothermal treatment, the relative content of barium titanate crystals is low, and there is no transition region between the structure and composition of the barium titanate. Furthermore, this barium titanate layer cannot form a layer-by-layer interlocking structure with PVDF. In contrast, this invention employs anodic oxidation with organic solvents as the electrolyte. The resulting anodic amorphous titanium dioxide layer has a nanopillar array structure with non-interconnected and uniformly distributed nanopores. After hydrothermal treatment, a coating with a gradual transition in structure and composition is formed, enabling it to form a layer-by-layer interlocking structure with PVDF and significantly improving the piezoelectric coefficient.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] (1) This invention generates a flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure on the surface of titanium foil in situ through anodic oxidation and in-situ hydrothermal synthesis, thereby realizing the superior piezoelectric performance output of the flexible composite film.

[0028] (2) This invention optimizes the hydrothermal reaction process to control the phase content and crystallinity of BaTiO3 inside the film, providing a theoretical and technical basis for the design and preparation of high voltage composite films.

[0029] (3) The method of this invention proposes the concept of two-phase composite piezoelectric materials with a layer-by-layer interlocking structure, which fully coordinates the piezoelectric response between different piezoelectric materials and provides a novel approach for the preparation of piezoelectric composite materials.

[0030] (4) The method of the present invention is a new strategy for preparing piezoelectric composite films, which solves the problem of the incompatibility between the piezoelectric properties and flexibility of piezoelectric films, and the preparation process is simple, efficient and low cost. Attached Figure Description

[0031] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0032] Figure 1 The cross-sectional SEM microstructure of the P(VDF-TrFE) / BaTiO3 film prepared in the examples is shown below.

[0033] Figure 2The piezoelectric coefficient d of the piezoelectric thin films prepared in Examples 1-5 and Comparative Examples 1-3 33 ;

[0034] Figure 3 The hysteresis loop of the P(VDF-TrFE) / BaTiO3 thin film sample;

[0035] Figure 4 A schematic diagram of the assembled device and the piezoelectric output curve of the P(VDF-TrFE) / BaTiO3 thin film sample;

[0036] Figure 5 The images show typical surface morphology and cross-sectional micromorphology of the anodic oxide coating in Example 1; the left image shows the surface micromorphology of the anodic oxide coating, and the right image shows the cross-sectional micromorphology of the anodic oxide coating.

[0037] Figure 6 The figures show typical surface and cross-sectional micromorphology of the micro-arc oxidation coating in Comparative Example 3; the left figure shows the surface micromorphology of the micro-arc oxidation coating, and the right figure shows the cross-sectional micromorphology of the micro-arc oxidation coating. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following examples are implemented under the premise of the technical solution of the present invention, providing detailed implementation methods and specific operating procedures, which will help those skilled in the art to further understand the present invention. It should be noted that the scope of protection of the present invention is not limited to the following embodiments; any adjustments and improvements made under the concept of the present invention are all within the scope of protection of the present invention.

[0039] Example 1

[0040] This embodiment provides a method for in-situ generating a flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure on the surface of titanium foil, the steps of which are as follows:

[0041] (1) Cut TA1 titanium foil with a thickness of 50μm into square samples of 50mm×50mm, seal one side with PET tape, and then ultrasonically clean them in acetone, ethanol and pure water for 10min respectively. After drying, the pretreated titanium foil samples are obtained.

[0042] (2) The titanium foil sample after step (1) was immersed in an electrolyte containing 0.05 mol / L ammonium fluoride and 0.5 mol / L ethylene glycol. The graphite electrode was used as the cathode and the titanium foil sample was used as the anode. The constant voltage DC power supply was used to output 60V constant voltage. The anodic oxidation treatment was carried out at 25℃ and 10 rpm solution stirring speed for 45 min. The titanium dioxide layer was grown in situ on the surface of the titanium foil. After the titanium foil was taken out, the surface was thoroughly cleaned with deionized water and dried.

[0043] (3) Dissolve Ba(OH)2·8H2O powder in deionized water boiled for 10 min to prepare a 2 mol / L barium hydroxide aqueous solution. Pour the solution into the polytetrafluoroethylene liner of the hydrothermal reactor. Place the anodic titanium foil from step (2) into the polytetrafluoroethylene liner. After sealing the reactor, place it in an oven and keep it at 200℃ for 4 days to generate a barium titanate layer on the surface of the titanium foil. After taking out the sample, rinse the sample surface with 10% acetic acid and deionized water and dry it.

[0044] (4) Dissolve polyvinylidene fluoride (PVDF) powder in N,N-dimethylformamide (DMF) to prepare a 1 g / L PVDF casting solution. Use a syringe to pour the casting solution onto the surface of the single-sided barium titanate titanium foil obtained in step (3). First, place the sample in a vacuum drying oven and keep it at 70°C for 2 h. Then, transfer it to an oven and keep it at 130°C for 10 h. The PVDF solution evaporates the solvent and crystallizes fully.

[0045] (5) The P(VDF-TrFE) / BaTiO3 sample was polarized using a corona polarization device. The P(VDF-TrFE) / BaTiO3 sample obtained in step (4) was tightly attached to the sample stage surface. The distance between the needle tip and the sample surface was 5 mm. The high voltage DC power supply voltage was set to 10 kV. There was obvious corona discharge at the needle tip. After 30 min of polarization treatment, a P(VDF-TrFE) / BaTiO3 sample with residual polarization could be obtained.

[0046] Through the steps of the above embodiments, a flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layered interlocking structure can be prepared in situ on the surface of TA1 titanium foil. The microstructure of the sample cross-section under a scanning electron microscope shows that the P(VDF-TrFE) / BaTiO3 piezoelectric composite film has a clear layered interlocking structure. The lower layer is a relatively dense barium titanate layer, the middle layer is a transition layer where barium titanate particles and PVDF are interlocked, and the upper layer is a simple PVDF layer. Figure 1 ).

[0047] Figure 2 It adopts the quasi-static piezoelectric coefficient d 33 The piezoelectric coefficients of the thin films were measured by the measuring instrument. Among them, the sample of Example 1, which underwent hydrothermal treatment for 4 days, had the highest piezoelectric coefficient d. 33 The value was -271 pC / N, indicating that the flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure exhibits excellent piezoelectric properties.

[0048] Figure 3The ferroelectric loops obtained by testing the P(VDF-TrFE) / BaTiO3 piezoelectric composite film using a ferroelectric tester show that the film sample has high spontaneous polarization characteristics, exhibits low coercive electric field and high remanent polarization, indicating that the prepared sample can maintain good piezoelectric performance.

[0049] A schematic diagram of the P(VDF-TrFE) / BaTiO3 device assembled in Example 1 is shown below. Figure 4 The left figure shows a top encapsulation PI layer 1, a top conductive silver paste electrode 2, a P(VDF-TrFE) / BaTiO3 piezoelectric thin film layer 3, a bottom titanium substrate electrode 4, and a bottom encapsulation PI layer 5.

[0050] Figure 4 The right figure is a schematic diagram of the device composed of P(VDF-TrFE) / BaTiO3 piezoelectric composite film and the piezoelectric open-circuit voltage output curve obtained by bending deformation. This result shows that the film sample has good piezoelectric output performance.

[0051] Example 2

[0052] This embodiment provides a method for generating a flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure in situ on the surface of titanium foil. The steps are basically the same as those in Example 1, except that in this example, the hydrothermal reaction time of the anodized titanium foil in step (3) is adjusted to 5 days.

[0053] The P(VDF-TrFE) / BaTiO3 piezoelectric thin film prepared in this embodiment was measured by a quasi-static piezoelectric coefficient measuring instrument. 33 The value is -274 pC / N (d obtained in Example 1). 33 The value was -271 pC / N. Compared with Example 1, extending the hydrothermal time did not significantly improve the piezoelectric coefficient.

[0054] Example 3

[0055] This embodiment provides a method for generating a flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure in situ on the surface of titanium foil. The steps are basically the same as those in Example 1, except that in this experimental example, the hydrothermal reaction time of the anodized titanium foil in step (3) is adjusted to 3 days.

[0056] The P(VDF-TrFE) / BaTiO3 piezoelectric composite film prepared in this embodiment was measured by a quasi-static piezoelectric coefficient measuring instrument. 33 The value is -204 pC / N (d obtained in Example 1) 33With a value of -271 pC / N, compared to Example 1, the hydrothermal time was shortened, the barium titanate content and crystallinity decreased, and the piezoelectric properties of the thin film weakened.

[0057] Example 4

[0058] This embodiment provides a method for generating a flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure in situ on the surface of titanium foil. The steps are basically the same as those in Embodiment 1, except that in this embodiment, the hydrothermal reaction time of the anodized titanium foil in step (3) is adjusted to 2 days.

[0059] The P(VDF-TrFE) / BaTiO3 piezoelectric composite film prepared in this embodiment was measured by a quasi-static piezoelectric coefficient measuring instrument. 33 The value is -131pC / N (d obtained in Example 1) 33 With a value of -271 pC / N, compared to Example 1, the barium titanate content and crystallinity decreased, and the piezoelectric properties of the thin film weakened.

[0060] Example 5

[0061] This embodiment provides a method for generating a flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure in situ on the surface of titanium foil. The steps are basically the same as those in Example 1, except that in this example, the hydrothermal reaction time of the anodized titanium foil in step (3) is adjusted to 1 day.

[0062] The P(VDF-TrFE) / BaTiO3 piezoelectric thin film prepared in this embodiment was measured by a quasi-static piezoelectric coefficient measuring instrument. 33 The value is -45 pC / N (d obtained in Example 1) 33 With a value of -271 pC / N, compared to Example 1, the hydrothermal reaction is insufficient, resulting in a lower content of the crystalline barium titanate phase that can provide a higher piezoelectric response, and a weakening of the thin film piezoelectric properties.

[0063] Comparative Example 1

[0064] The preparation method of this comparative example is basically the same as that of Example 1. The same PVDF film formation process as step (4) in Example 1 is used to obtain a single P(VDF-TrFE) piezoelectric film. The same corona polarization device and polarization parameters as in step (5) of Example 1 are used to polarize the P(VDF-TrFE) piezoelectric film. The only difference is that steps (2)-(3) are omitted.

[0065] The P(VDF-TrFE) piezoelectric thin film prepared in this comparative example was tested using a quasi-static piezoelectric coefficient measuring instrument. 33The value is -27 pC / N (d obtained in Example 1) 33 With a value of -271 pC / N, compared to Example 1, the single P(VDF-TrFE) piezoelectric film without a barium titanate layer has a lower piezoelectric coefficient. Therefore, by using anodic oxidation and hydrothermal treatment to generate a barium titanate piezoelectric layer in situ on the surface of titanium foil, and then using solution casting process to prepare a P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure, the piezoelectric properties of the piezoelectric film can be significantly improved.

[0066] Comparative Example 2

[0067] This comparative example only prepared a barium titanate piezoelectric film on the surface of titanium foil by anodic oxidation hydrothermal conversion. The same anodic oxidation process as in steps (1) and (2) of Example 1 and the same hydrothermal process as in step (3) were used to obtain the barium titanate piezoelectric film on the surface of titanium foil. The same corona polarization device and polarization parameters as in step (5) of Example 1 were used to polarize it.

[0068] The barium titanate piezoelectric thin film prepared in this comparative example was obtained by measuring the d-value using a quasi-static piezoelectric coefficient measuring instrument. 33 The value is -56pC / N (d obtained in Example 1). 33 With a value of -271 pC / N, compared to Example 1, the barium titanate film without a surface solution-cast P(VDF-TrFE) coating lacks a layer-by-layer interlocking structure, and its piezoelectric coefficient is lower than that of the layer-by-layer interlocking P(VDF-TrFE) / BaTiO3 piezoelectric composite film. Therefore, preparing a P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure can significantly improve its piezoelectric properties.

[0069] Comparative Example 3

[0070] The preparation method of this comparative example is basically the same as that of Example 1. The only difference is that the electrolyte in step (2) is replaced with an aqueous solvent system electrolyte to perform micro-arc oxidation on TA1 titanium foil. The electrolyte is prepared by mixing 0.014 mol / L sodium silicate nonahydrate and 0.017 mol / L sodium hexametaphosphate.

[0071] Figure 5 The typical surface and cross-sectional morphology of the anodic oxide layer in Example 1 are shown. Example 1 involves anodic oxidation of TA1 titanium foil in an ethylene glycol organic solvent electrolyte system. The anodic oxide amorphous titanium dioxide layer has a nanopillar array structure, with non-interconnected nanopores of uniform size distribution. After hydrothermal treatment, a coating with gradually transitioning structure and composition is formed (see...). Figure 1Comparative Example 3 used an aqueous solvent electrolyte system to perform micro-arc oxidation on TA1 titanium foil. The prepared micro-arc oxidation coating was a rough and porous ceramic oxide layer with an irregular pore structure and micron-sized pores. The coating phase structure mainly consisted of amorphous phases containing Si and P and crystalline titanium dioxide phases. The amorphous structure also contained amorphous titanium dioxide forms (such as...). Figure 6 As shown, the relative content of barium titanate crystals after hydrothermal treatment is low, and barium titanate has no transition region in structure and composition, which is significantly different from the microstructure and phase composition of Example 1.

[0072] The barium titanate prepared in Comparative Example 3 had a low content and no component transition in the coating. After being coated with PVDF, the composite coating showed a high dg. 33 The value is only the piezoelectric coefficient d of PVDF 33 Approximately -26 pC / N (see Figure 2 The barium titanate in the coating has no effect on improving the macroscopic piezoelectric properties of the coating. The barium titanate prepared in Example 1 transitions from dense to porous layers, and after hydrothermal treatment, the coating surface is entirely composed of barium titanate, with its d... 33 With a value as high as -271 pC / N, the differences in barium titanate content and structure resulted in significant differences in piezoelectric properties between Comparative Example 3 and Example 1.

[0073] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure, characterized in that, Includes the following steps: S1. In an organic electrolyte, titanium foil is subjected to electrochemical anodic oxidation to generate a TiO2 layer on the surface in situ; wherein the anode is titanium foil and the cathode is an inert conductive electrode. S2. The titanium foil treated in step S1 is placed in a barium-containing solution for hydrothermal reaction, and a BaTiO3 layer is generated in situ on the surface. S3. Coat the surface of the BaTiO3 layer with P(VDF-TrFE) solution and anneal it to form a flexible P(VDF-TrFE) / BaTiO3 composite film. S4. The flexible P(VDF-TrFE) / BaTiO3 composite film is subjected to polarization treatment to obtain the flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film.

2. The preparation method according to claim 1, characterized in that, In step S1, the titanium foil is a foil of pure titanium or titanium alloy with a thickness of 20 to 100 μm.

3. The preparation method according to claim 1, characterized in that, In step S1, the organic electrolyte includes 0.01–0.3 mol / L ammonium fluoride and 0.1–3 mol / L ethylene glycol.

4. The preparation method according to claim 1, characterized in that, In step S1, the parameters for the electrochemical anodizing are set as follows: water bath temperature is 20-30℃, stirring speed is 5-25 rpm, DC power supply adopts constant voltage mode with voltage of 40-80V, and processing time is 30-90 min; the inert conductive electrode includes any one of graphite electrode, platinum electrode, and pure titanium electrode.

5. The preparation method according to claim 1, characterized in that, In step S2, the barium-containing solution includes an aqueous solution of barium hydroxide with a concentration of 1 to 2 mol / L.

6. The preparation method according to claim 1, characterized in that, In step S2, the temperature of the hydrothermal reaction is 180–220°C, and the reaction time is 1–5 days.

7. The preparation method according to claim 1, characterized in that, In step S3, the concentration of the P(VDF-TrFE) solution is 0.5–3 g / L.

8. The preparation method according to claim 1, characterized in that, In step S3, the annealing process consists of two stages: the first stage is vacuum holding at 60-80℃ for 1-4 hours, and the second stage is holding at 120-140℃ for 6-12 hours.

9. The preparation method according to claim 1, characterized in that, In step S4, the parameters for the polarization treatment are set as follows: the distance between the needle tip and the sample surface is controlled between 5 and 20 mm, the voltage of the high-voltage DC power supply is adjusted to 5 to 20 kV, and the polarization time is 30 to 90 min.

10. A flexible P(VDF-TrFE) / BaTiO3 piezoelectric composite film with a layer-by-layer interlocking structure obtained by the preparation method according to any one of claims 1-9.

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