A bismuth titanate powder filled polyvinylidene fluoride composite piezoelectric film and a preparation method thereof

Abstract

The application belongs to the technical field of functional composite materials and piezoelectric materials, and specifically discloses a bismuth titanate powder filled polyvinyl fluoride composite piezoelectric film and a preparation method thereof. The preparation method comprises the steps of raw material preparation, preparation of a PVDF composite solvent system, addition and uniform dispersion of fillers, blade coating, low-temperature vacuum drying and stripping. The application realizes the uniform dispersion of bismuth titanate powder or manganese and niobium co-doped bismuth titanate powder in a PVDF matrix by optimizing the ratio of a DMF and acetone composite solvent system, adopting a combined ultrasonic dispersion mode, and introducing a blade coating film forming process and a low-temperature rapid vacuum drying process. Meanwhile, the mass ratio of raw materials is precisely controlled. On the basis of simplifying the preparation process and shortening the film forming period, the piezoelectric performance and structural compactness of the composite film are improved, and the defects of the existing preparation method, such as uneven filler dispersion, insufficient flexibility, low film forming efficiency, and limited improvement of the piezoelectric performance of the film, are solved.

Description

Technical Field

[0001] This invention belongs to the field of functional composite materials and piezoelectric materials technology, specifically relating to a bismuth titanate powder-filled polyvinylidene fluoride composite piezoelectric film and its preparation method. Background Technology

[0002] Polymer-based piezoelectric composite films possess excellent flexibility, high breakdown field strength, high reliability, and cost-effectiveness, making them promising for applications in electronic power systems, energy storage devices, and piezoelectric sensing. Polyvinylidene fluoride (PVDF), a typical ferroelectric polymer, benefits from the high electronegativity of its fluorine atoms, which imparts a high piezoelectric coefficient (dp). 33 With a pC / N ratio of approximately 9~12 and excellent piezoelectric response properties, it has become an ideal matrix material for preparing polymer-based piezoelectric composite films.

[0003] To further improve the piezoelectric properties of PVDF-based composite films, existing technologies generally employ a strategy of introducing highly active piezoelectric ceramic fillers into the PVDF matrix. Commonly used ceramic fillers include silver niobate, barium titanate, and bismuth titanate. Among these, bismuth titanate (Bi4Ti3O) is particularly valuable. 12 As a lead-free ferroelectric ceramic, bismuth titanate (BTi) possesses advantages such as high voltage coefficient, excellent ferroelectric and piezoelectric properties, and environmental friendliness, making it a preferred filler to replace lead-based ceramics. Currently, the preparation of BTi doped PVDF composite films mostly employs a direct mixing method, where BTi powder is blended with a PVDF matrix and then film is formed through methods such as casting and hot pressing. Some studies have attempted to improve the interfacial compatibility between BTi powder and the PVDF matrix by surface modification, but several technical bottlenecks remain, as follows:

[0004] 1. Uneven packing material dispersion: Bismuth titanate, as an inorganic ceramic phase, has poor interfacial compatibility with the organic PVDF matrix. Direct doping can easily lead to packing material agglomeration, which in turn causes defects such as internal pores and microcracks in the film, weakening its mechanical properties and structural compactness.

[0005] 2. High filler content leads to performance degradation: To significantly improve the piezoelectric properties of composite films, existing technologies typically require the addition of high weight fractions (>5 wt.%) of bismuth titanate powder. However, high filler content not only exacerbates filler agglomeration but also significantly reduces the flexibility of the PVDF matrix, affecting the processability and service reliability of the device.

[0006] 3. Limited improvement in piezoelectric performance: The interfacial bonding between unmodified bismuth titanate powder and the PVDF matrix is ​​weak, making it difficult to fully utilize the high piezoelectric properties of bismuth titanate. This results in limited improvement in key properties of the composite film, such as piezoelectric coefficient and energy storage density.

[0007] 4. Insufficient process control: The existing preparation process has relatively crude control over the heat treatment and quenching process after film formation, making it difficult to effectively regulate the crystal transformation of PVDF, which in turn affects the optimization of the ferroelectric and piezoelectric properties of the composite film; moreover, the film formation cycle is long and the efficiency is low. Summary of the Invention

[0008] This invention aims to address the technical shortcomings in the preparation of existing bismuth titanate-based PVDF composite piezoelectric films, such as uneven filler dispersion, insufficient flexibility, low film formation efficiency, and limited improvement in film piezoelectric performance. It provides a simple, convenient, and rapid method for preparing bismuth titanate powder-modified PVDF composite piezoelectric films.

[0009] This invention achieves the production of bismuth titanate (Bi4Ti3O4) by optimizing the ratio of DMF and acetone composite solvents, employing ultrasonic dispersion, and introducing a blade coating method and a low-temperature rapid vacuum drying process. 12 The uniform dispersion of bismuth titanate (BTO) or Mn and Nb co-doped bismuth titanate (denoted as BTO-xMN; x=5%-25%, where x is the sum of the total mass percentages of Mn and Nb in bismuth titanate; Mn and Nb are in equal mass ratios) powder in PVDF matrix, while precisely controlling the mass ratio of raw materials, effectively improves the piezoelectric properties and structural compactness of composite films while simplifying the preparation process and shortening the film formation cycle.

[0010] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows:

[0011] In a first aspect, the present invention provides a method for preparing a bismuth titanate powder-filled polyvinylidene fluoride composite piezoelectric film, comprising the following steps:

[0012] (1) Raw material preparation: Prepare polyvinylidene fluoride (PVDF) powder, filler powder, N,N-dimethylformamide (DMF), and acetone; wherein, the filler powder is bismuth titanate powder or manganese niobium co-doped bismuth titanate, and the manganese niobium co-doped bismuth titanate powder is prepared by hydrothermal method;

[0013] (2) Preparation of PVDF composite solvent system: At room temperature, 0.4-0.6g of PVDF powder was added to a mixed solvent of DMF and acetone, with a mixed solvent volume of 6-8mL, to form a polyvinylidene fluoride mixed solution;

[0014] (3) Addition and uniform dispersion of filler: Add 0.05-0.15g of the filler powder described in step (1) to the above polyvinylidene fluoride mixed solution, and sonicate for 4-6min to obtain a uniformly dispersed composite film-forming liquid.

[0015] (4) Film formation by scraping: The composite film-forming liquid is coated onto the mold by scraping to obtain an initial wet film;

[0016] (5) Low-temperature vacuum drying and peeling: Place the mold with the initial wet film into a vacuum oven and vacuum dry at 75-85℃ for 25-35 minutes. After drying, peel off the bismuth titanate-filled polyvinylidene fluoride composite piezoelectric film.

[0017] Preferably, in step (1), the manganese-niobium co-doped bismuth titanate (BTO-xMN) powder is bismuth titanate powder with a manganese and niobium doping mass ratio of 5-25%, and the mass ratio of manganese to niobium is 1:1. The manganese and niobium doping mass ratio is further preferably 10-25%, at which point the PVDF / BTO-xMN composite film obtained has better piezoelectric properties than the PVDF / BTO composite film obtained using bismuth titanate powder.

[0018] Preferably, in step (2), the volume ratio of N,N-dimethylformamide to acetone in the mixed solvent is 3:4; and the mass ratio of the filler powder in step (3) to the polyvinylidene fluoride powder in step (2) is 1:5.

[0019] More preferably, the amount of N,N-dimethylformamide added is 3 mL, the amount of acetone added is 4 mL, the mass of filler powder is 0.1 g, and the mass of polyvinylidene fluoride powder is 0.5 g.

[0020] Preferably, in step (3), the ultrasonic treatment time is 5 minutes.

[0021] Preferably, in step (5), the vacuum drying temperature is 80°C and the time is 30 min.

[0022] Secondly, the present invention provides a bismuth titanate powder-filled polyvinylidene fluoride composite piezoelectric film prepared by the above-described preparation method. This composite film is formed by low-temperature rapid drying, resulting in uniformly dispersed filler without agglomeration. The film has a dense structure, excellent flexibility, and significantly superior piezoelectric properties compared to pure PVDF films.

[0023] The preparation method of this invention is based on precise raw material ratios, an optimized solvent system, and an efficient film-forming and drying process. Compared with existing technologies, it has significant technical advantages and practical value, with the following specific beneficial effects:

[0024] 1. Simple and efficient process with short film formation cycle: The entire process of this invention is carried out at room temperature and a low temperature of about 80°C. There is no need for high-temperature melting, long-term heat preservation and rapid cooling. The preparation can be completed through the process of "room temperature dissolution - about 5 minutes of ultrasonication - coating film - about 30 minutes of drying", which greatly shortens the film formation cycle of composite film. The operation steps are simple and no complicated equipment is required, making it suitable for rapid preparation in the laboratory and large-scale production.

[0025] 2. Uniformly dispersed filler and dense film structure: Ultrasonic dispersion, combined with the compatibility of DMF and acetone composite solvent, effectively solves the problem of agglomeration of inorganic ceramic filler in organic matrix, achieving uniform dispersion of filler; vacuum drying process avoids bubbles and pinhole defects, ensuring the dense structure of film.

[0026] 3. Precise raw material ratio significantly improves piezoelectric properties: By precisely controlling the mass ratio of filler to PVDF (1:5) and the solvent ratio (DMF:acetone = 3:4), the piezoelectric properties of BTO / BTO-xMN filler and the ferroelectric properties of the PVDF matrix are fully utilized. Experiments show that the piezoelectric coefficient d of the PVDF / BTO composite film is significantly improved. 33 Increased to 18~20 pC / N, d of PVDF / BTO-25%MN composite film 33 It further reaches 43~45 pC / N, which is significantly better than pure PVDF film (13~15 pC / N).

[0027] 4. Low-temperature drying preserves the excellent flexibility of the film: The low-temperature vacuum drying process avoids the damage to the PVDF polymer chain structure caused by high temperature, so that the prepared composite film retains the excellent flexibility of the PVDF matrix, which can be bent and folded, making it suitable for the preparation of flexible piezoelectronic devices and expanding the application scenarios of the devices.

[0028] 5. Low solvent consumption and high raw material utilization: The solvent system of this invention uses only a small amount of DMF and acetone (less than 10 mL) to achieve full dissolution of PVDF powder and uniform dispersion of filler. The low solvent consumption reduces the preparation cost, and vacuum drying can quickly recover some of the solvent, improving the utilization rate of raw materials and solvents, thus combining economy and environmental protection.

[0029] 6. Wide compatibility and flexible adjustment of fillers: This method is applicable to both bismuth titanate (BTO) powder and manganese-niobium co-doped bismuth titanate (BTO-xMN (x=5%-25%, Mn and Nb in equal proportions)) powder as piezoelectric fillers. Composite piezoelectric films with different properties can be prepared by simply changing the filler. It has wide compatibility and can be flexibly adjusted according to the piezoelectric performance requirements of the device, making it highly practical. Attached Figure Description

[0030] Figure 1 The diagram shown is a flowchart of a method for preparing a polyvinylidene fluoride composite film doped with manganese niobium co-doped bismuth titanate BTO-xMN (x=5%-25%, Mn and Nb in equal proportions) powder provided in an embodiment of this application.

[0031] Figure 2 The image shown is a surface morphology diagram of the PVDF film provided in Embodiment 1 of this application under a scanning electron microscope;

[0032] Figure 3 The image shown is a surface morphology image of the PVDF / BTO-25%MN composite film provided in Example 2 of this application under a scanning electron microscope.

[0033] Figure 4 The X-ray diffraction patterns of PVDF film, PVDF / BTO composite film and PVDF / BTO-xMN (x=5%-25%) composite film are shown.

[0034] Figure 5 The infrared spectra of PVDF film, PVDF / BTO composite film and PVDF / BTO-xMN (x=5%-25%) composite film are shown.

[0035] Figure 6 The diagram shows the piezoelectric coefficient of the PVDF / BTO-xMN (x=5%-25%) composite film.

[0036] Figure 7 The figure shows the PE hysteresis loop of PVDF film and PVDF / BTO-25%MN composite film. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0038] Example 1: Preparation of PVDF / BTO composite piezoelectric thin film

[0039] (1) Raw material preparation: Prepare 0.5g PVDF powder, 0.1g bismuth titanate, 3mL DMF and 4mL acetone for later use.

[0040] (2) PVDF composite solvent dissolution: At room temperature, add 0.5g of PVDF powder to a mixed solvent of 3mL DMF and 4mL acetone, stir to wet and fully dissolve the PVDF powder to form a PVDF mixed solution.

[0041] (3) Filler dispersion: Add 0.1g of BTO to the PVDF mixed solution to make the mass ratio of BTO to PVDF 1:5. Sonicate the mixed system for 5 minutes to obtain a uniformly dispersed composite film-forming solution.

[0042] (4) Film formation by scraping: The PVDF / BTO composite film-forming liquid is uniformly coated onto the polytetrafluoroethylene mold by scraping, and the thickness of the scraping is controlled to be consistent to obtain the initial wet film.

[0043] (5) Drying and peeling: Place the mold with the initial wet film into a vacuum oven and dry it at 80°C for 30 minutes. After the film is completely formed and dried, peel it off from the mold to obtain the PVDF / BTO composite piezoelectric film.

[0044] Example 2: Preparation of PVDF / BTO-xMN composite piezoelectric thin film

[0045] This embodiment is basically the same as Embodiment 1, except that the bismuth titanate (BTO) powder is replaced with manganese-niobium co-doped bismuth titanate (BTO-xMN (x=5%-25%)) powder. All other raw material ratios and process parameters remain unchanged. The final result is a PVDF / BTO-xMN (x=5%-25%) composite piezoelectric film, prepared as follows: Figure 1 As shown.

[0046] The manganese-niobium co-doped bismuth titanate was prepared by a hydrothermal method, with the following specific steps: 4 mmol of bismuth nitrate pentahydrate (0.54–2.7 mmol manganese nitrate, 0.36–1.8 mmol niobium chloride) was weighed and dissolved in 60 mL of 3 mol / L sodium hydroxide solution. The mixture was stirred for 30 minutes and then ultrasonically dispersed for 10 minutes. Next, 3 mmol of tetrabutyl titanate was slowly added to the solution while continuously stirring for 30 minutes, followed by ultrasonic dispersion for another 10 minutes. The solution was transferred to a 100 mL reaction vessel and heated to 180°C in an oven. The temperature was maintained for 24 hours before removing it from the oven. Impurities in the product were washed alternately with ethanol and deionized water, and then dried at 80°C for 8 hours to obtain manganese-niobium co-doped bismuth titanate powder.

[0047] More specifically, in this embodiment, bismuth titanate powders co-doped with manganese and niobium with different amounts of Mn and Nb (5%, 10%, 15%, 20%, 25%; mass ratio of Mn to Nb is 1:1) were used to prepare PVDF / BTO-xMN (x=5%-25%) composite piezoelectric films.

[0048] The piezoelectric properties and structural characterization of pure PVDF films, PVDF / BTO composite films prepared in Example 1, and PVDF / BTO-xMN (x=5%-25%) composite films prepared in Example 2 were tested, and the results are as follows:

[0049] 1. Dispersibility: In both composite films prepared in Examples 1-2, the BTO / BTO-25%MN powder was uniformly dispersed in the PVDF matrix without obvious agglomeration. The film surface was smooth, the structure was dense, and there were no bubbles or pinhole defects. Example comparison figures are shown below. Figure 2-3 As shown, BTO is embedded in PVDF, and the filler powder is evenly dispersed.

[0050] 2. Crystal structure analysis: Figure 4X-ray diffraction patterns of pure PVDF films, PVDF / BTO composite films, and PVDF / BTO-xMN composite films with different Mn and Nb doping ratios (5%, 10%, 15%, 20%, 25%) are shown. Figure 4 It can be seen that the composite film contains both characteristic diffraction peaks of PVDF and bismuth titanate. Furthermore, the crystal structure of the composite film remains stable with the change of Mn and Nb doping ratio, indicating that a good composite structure is formed between the filler and the matrix.

[0051] 3. Molecular structure analysis: Figure 5 Infrared spectra of pure PVDF film, PVDF / BTO composite film, and PVDF / BTO-xMN composite film with different Mn and Nb doping ratios (5%, 10%, 15%, 20%, 25%) are shown, and the characteristic peak positions of the α, β, and γ phases are marked. Figure 5 It is evident that the composite film exhibits absorption peaks at characteristic positions of the β phase, indicating that the low-temperature rapid drying process of this invention is beneficial for the formation of the PVDF piezoelectric active phase.

[0052] 4. Piezoelectric coefficient: The piezoelectric coefficient d of pure PVDF film 33 The piezoelectric coefficient of the PVDF / BTO composite film is approximately 13~15 pC / N. 33 Increased to 18~20 pC / N; Figure 6 The piezoelectric coefficient d of PVDF / BTO-xMN composite films with different Mn and Nb doping ratios (5%MN, 10%MN, 15%MN, 20%MN, 25%MN, with equal proportions of Mn and Nb) is shown. 33 The test values ​​show that the piezoelectric coefficient increases with increasing Mn and Nb doping concentrations. The piezoelectric coefficient d of the PVDF / BTO-25%MN composite film is... 33 The piezoelectric performance was improved to 43~45 pC / N, which is significantly better than that of pure PVDF film and PVDF / BTO composite film. Mn and Nb doping further optimized the piezoelectric properties.

[0053] 5. Ferroelectric properties: Figure 7 The figure shows the PE hysteresis loops of pure PVDF thin films and PVDF / BTO-25%MN composite films, with a comparison of the polarization-electric field curves between the two films. Figure 7 It can be seen that the PVDF / BTO-25%MN composite film exhibits significantly enhanced ferroelectric properties and has typical ferroelectric hysteresis characteristics. Its remanent polarization and saturation polarization are much higher than those of the pure PVDF film, indicating that the preparation method of the present invention effectively enhances the energy storage capacity of the composite film.

[0054] 6. Flexibility and formability: Both PVDF / BTO and PVDF / BTO-xMN composite films maintain excellent flexibility, and can be bent up to 180° without cracking or peeling; the film formed by the blade coating method is dried at low temperature for 30 minutes, and the film has good formability, does not stick to the mold, and has neat edges without damage after peeling.

[0055] The above results fully demonstrate that the preparation method of the present invention, through precise raw material ratio, efficient dispersion process and rapid film-forming and drying process, can successfully prepare high-performance PVDF / BTO and PVDF / BTO-xMN composite piezoelectric films. The process is simple, the performance is excellent, and it has good practical application value.

[0056] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. Any changes made by those skilled in the art after reading the specification of the present invention, as long as they are within the scope of the claims of the present invention, will be protected by patent law.

Claims

1. A method for preparing a bismuth titanate powder-filled polyvinylidene fluoride composite piezoelectric film, characterized in that, Includes the following steps: (1) Raw material preparation: Prepare polyvinylidene fluoride powder, filler powder, N,N-dimethylformamide, and acetone; wherein, the filler powder is bismuth titanate powder or manganese niobium co-doped bismuth titanate, and the manganese niobium co-doped bismuth titanate powder is prepared by hydrothermal method; (2) Preparation of PVDF composite solvent system: At room temperature, 0.4-0.6g of polyvinylidene fluoride powder was added to a mixed solvent of N,N-dimethylformamide and acetone, with a mixed solvent volume of 6-8mL, to form a polyvinylidene fluoride mixed solution. (3) Addition and uniform dispersion of filler: Add 0.05-0.15g of the filler powder described in step (1) to the above polyvinylidene fluoride mixed solution, and sonicate for 4-6 minutes to obtain a uniformly dispersed composite film-forming liquid. (4) Film formation by scraping: The composite film-forming liquid is coated onto the mold by scraping to obtain an initial wet film; (5) Low-temperature vacuum drying and peeling: Place the mold with the initial wet film into a vacuum oven and vacuum dry at 75-85℃ for 25-35 minutes. After drying, peel off the bismuth titanate-filled polyvinylidene fluoride composite piezoelectric film.

2. The preparation method according to claim 1, characterized in that, In step (1), the manganese-niobium co-doped bismuth titanate powder is bismuth titanate powder with a total mass ratio of manganese and niobium of 5-25%, and the mass ratio of manganese to niobium is 1:

1.

3. The preparation method according to claim 2, characterized in that, The total mass percentage of manganese and niobium doping is 10-25%.

4. The preparation method according to claim 1, characterized in that, In step (2), the volume ratio of N,N-dimethylformamide to acetone in the mixed solvent is 3:

4.

5. The preparation method according to claim 3, characterized in that, The mass ratio of the filler powder in step (3) to the polyvinylidene fluoride powder in step (2) is 1:

5.

6. The preparation method according to claim 4, characterized in that, The amount of N,N-dimethylformamide added is 3 mL, the amount of acetone added is 4 mL, the mass of filler powder is 0.1 g, and the mass of polyvinylidene fluoride powder is 0.5 g.

7. The preparation method according to claim 1, characterized in that, In step (3), the ultrasonic treatment time is 5 minutes.

8. The preparation method according to claim 1, characterized in that, In step (5), the vacuum drying temperature is 80℃ and the time is 30min.

9. The bismuth titanate powder-filled polyvinylidene fluoride composite piezoelectric film prepared by the preparation method according to any one of claims 1-8.

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