Polar phase polyvinylidene fluoride film as well as preparation method and application thereof

Abstract

The invention discloses a polar phase polyvinylidene fluoride film as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) mixing polyvinylidene fluoride powder and a polar solvent to form a 10-30wt% polyvinylidene fluoride solution; (2) carrying out tape casting on the polyvinylidene fluoride solution to obtain a polar phase polyvinylidene fluoride initial film; wherein more than two different temperature sections are arranged on a traction road section; the drafting rate is 1-4 m / min; and (3) carrying out annealing treatment on the polar phase polyvinylidene fluoride initial film at 50-160 DEG C to obtain the polar phase polyvinylidene fluoride film. According to the preparation method disclosed by the invention, the polyvinylidene fluoride film which is basically in a pure polar phase can be obtained, and the polyvinylidene fluoride film has relatively good electrical property.

Description

Technical Field

[0001] This invention relates to a polar phase polyvinylidene fluoride thin film, its preparation method, and its application. Background Technology

[0002] Polyvinylidene fluoride (PVDF) can be used as a piezoelectric material. Piezoelectric PVDF materials show promising applications in medicine, sensing, and energy. The significant difference in electronegativity between carbon (C) and fire (F) atoms creates an electric dipole moment. PVDF has various crystal forms, including α, β, and γ. In the α phase, the dipole moments cancel each other out, making it a nonpolar phase and not exhibiting electrical activity. In contrast, the β and γ phases are typical polar phases, exhibiting electrical activity and piezoelectric properties.

[0003] For PVDF to be applied, the preparation method of polyvinylidene fluoride film is also crucial. For example, spin coating cannot achieve continuous production and forms an α phase that does not have piezoelectricity; electrospinning is too expensive and not suitable for industrial applications; casting can achieve continuous preparation and has a lower cost, but how to control the formation of polar phase is still a technical problem that needs to be solved by those skilled in the art.

[0004] CN113248762A discloses a method for rapidly preparing γ-phase polyvinylidene fluoride (PVDF) films. A 3-8% (w / w) PVDF solution is prepared using N,N-dimethylformamide (DMF) as a solvent. A solution-casting method is used to prepare the PVDF cured film. At a temperature of 140-160°C, PVDF rapidly nucleates into α-phase nuclei, and after holding at 165-170°C for 4-9 days, the phase transforms into γ-phase nuclei, improving the γ-phase nucleation ability of PVDF, with the γ-phase content reaching 80%. However, this patent requires a long holding time for the γ-phase transformation, which is not conducive to industrial production, and the γ-phase content remains relatively low.

[0005] CN117624672A discloses a method for preparing and applying a polyimide-doped polyvinylidene fluoride (PVDF) composite film. The method includes using N,N-dimethylformamide as a solvent to prepare a mixed solution of PVDF and polyimide as the solute, and curing the mixed solution into a cured film. The cured film is then crystallized after melting to eliminate its thermal history, yielding the polyimide-doped PVDF composite film. The addition of polyimide induces nucleation of PVDF crystals, increasing the γ-phase nucleation rate. However, this patent requires doping, and the resulting film is still a composite film with both α and γ phases.

[0006] CN109082050A discloses a method for preparing CQDs@PVP / PVDF composite dielectric films. This method first prepares carbon quantum dots (CQDs) through electrolysis using graphite rod electrodes. Then, the CQDs are coated with PVP in a solution to improve their dispersibility and interfacial compatibility. Finally, the CQDs are mixed with a PVDF solution, cast into a film, and hot-pressed to obtain the composite film. The patent document shows that the intensity and area of ​​the α-crystalline peak in the composite film are smaller than the area of ​​the β-crystalline peak.

[0007] CN117070039A discloses a high-energy-storage binary ferroelectric blend dielectric film and its preparation method. The dielectric film is prepared by blending, casting, and drying polyvinylidene fluoride-chlorofluoroethylene copolymer and polyvinylidene fluoride-hexafluoropropylene copolymer. The dielectric film exhibits increased content of β-phase and γ-phase, meaning it remains a multiphase film. Summary of the Invention

[0008] In view of the above, one object of the present invention is to provide a wet continuous preparation method for a polar phase polyvinylidene fluoride (PVDF) film. This preparation method can obtain a PVDF film with a substantially pure polar phase. The obtained polar phase PVDF film has good piezoelectric properties. Another object of the present invention is to provide a polar phase PVDF film prepared according to the preparation method described above. A further object of the present invention is to provide an application of the polar phase PVDF film in the preparation of electroactive materials. The present invention achieves the above objects using the following technical solutions.

[0009] This invention provides a method for preparing a polar phase polyvinylidene fluoride thin film, comprising the following steps:

[0010] (1) Polyvinylidene fluoride powder is mixed with a polar solvent to form a 10-30 wt% polyvinylidene fluoride solution;

[0011] (2) Polyvinylidene fluoride solution is cast to obtain polar phase polyvinylidene fluoride initial film; wherein, two or more different temperature sections are set sequentially in the traction section; the stretching rate is 1 to 4 m / min.

[0012] (3) The polar polyvinylidene fluoride initial film is annealed at 50-160°C to obtain a polar polyvinylidene fluoride film.

[0013] According to the preparation method of the present invention, preferably, in step (1), the polar solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethyl sulfoxide, acetylacetone, methyl ethyl ketone and acetone.

[0014] According to the preparation method of the present invention, preferably, in step (1), polyvinylidene fluoride powder is mixed with a polar solvent and heated to dissolve at 50-90°C to form a 10-30 wt% polyvinylidene fluoride solution.

[0015] According to the preparation method of the present invention, preferably, before casting, residual air bubbles in the polyvinylidene fluoride solution are removed.

[0016] According to the preparation method of the present invention, preferably, the formed polyvinylidene fluoride solution is placed in a vacuum environment and allowed to stand for more than 1 hour to remove residual bubbles in the polyvinylidene fluoride solution.

[0017] According to the preparation method of the present invention, preferably, in step (2), three or more different temperature sections are sequentially set in the traction section; the temperature range of the temperature sections is between 75 and 120°C.

[0018] According to the preparation method of the present invention, preferably, in step (2), four different temperature segments are set sequentially in the traction section, including a first temperature segment, a second temperature segment, a third temperature segment and a fourth temperature segment. The temperature range of the first temperature segment is 75-80℃; the temperature range of the second temperature segment is 85-90℃; the temperature range of the third temperature segment is 100-110℃; and the temperature range of the fourth temperature segment is 115-120℃.

[0019] According to the preparation method of the present invention, preferably, the stretching rate is 1.5 to 2.5 m / min; and the annealing temperature is 100 to 160 °C.

[0020] On the other hand, the present invention also provides a polar phase polyvinylidene fluoride film prepared according to the preparation method described above, which is almost 100% γ-crystalline polyvinylidene fluoride film with a thickness of 10-100 μm; and its polar phase polyvinylidene fluoride film with a thickness of 10-100 μm. -1 833cm -1 1234cm -1 It exhibits infrared characteristic absorption peaks of the γ phase.

[0021] In another aspect, the present invention also provides the application of the polar phase polyvinylidene fluoride film as described above in the preparation of electroactive materials.

[0022] The preparation method of this invention can obtain polyvinylidene fluoride (PVDF) films with a essentially pure polar phase. This preparation method uses only a polar solvent and does not add other blends, such as polyimide or ionic liquids. The resulting polar phase PVDF films exhibit good piezoelectric properties. The preparation method of this invention is relatively simple to operate, can be implemented in a continuous wet process, is beneficial for industrialization, and can produce high-performance piezoelectric polar phase PVDF films of varying thicknesses in large quantities. Attached Figure Description

[0023] Figure 1 Infrared spectra of the initial polyvinylidene fluoride (PVDF) film and the PVDF film.

[0024] Figure 2 The graph shows the DSC test results of the initial polyvinylidene fluoride (PVDF) film and PVDF films at different annealing temperatures.

[0025] Figure 3 The figure shows the piezoelectric properties of the initial polyvinylidene fluoride (PVDF) film and PVDF films at different annealing temperatures.

[0026] Figure 4 The graph shows the ferroelectric properties of the initial polyvinylidene fluoride (PVDF) film and PVDF films at different annealing temperatures.

[0027] Figure 5 This is a partial structural diagram of the casting machine used in this invention.

[0028] Explanation of reference numerals in the attached figures:

[0029] 1-Base belt, 2-Roller, 3-Slurry hopper, 4-Scraper, 5-Drying oven, 6-Collection roller, 71-Upper drive roller, 72-Lower drive roller; A-Supply to be cast, M-Polyvinylidene fluoride film. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0031] This invention can obtain polyvinylidene fluoride films with essentially pure polar phases, which have good piezoelectric properties.

[0032] <Preparation Method>

[0033] This invention provides a method for preparing a polar phase polyvinylidene fluoride (PVDF) film, comprising: a PVDF solution preparation step; a casting step; and an annealing step. The method is described in detail below.

[0034] Polyvinylidene fluoride solution preparation steps

[0035] Polyvinylidene fluoride powder is mixed with a polar solvent to form a 10-30 wt% polyvinylidene fluoride solution.

[0036] In this invention, the polyvinylidene fluoride powder is polyvinylidene fluoride powder. Commercially available powders can be used.

[0037] In this invention, the polar solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethyl sulfoxide, acetylacetone, methyl ethyl ketone, and acetone. Preferably, the polar solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and N,N-dimethyl sulfoxide. More preferably, the polar solvent is N,N-dimethylacetamide. This is beneficial for the next step of casting a polyvinylidene fluoride film with a pure polar phase.

[0038] When forming the solution, heating can be used to dissolve it, thereby improving efficiency. In some embodiments, polyvinylidene fluoride powder is mixed with a polar solvent and heated to dissolve at 50–90°C to form a 10–30 wt% polyvinylidene fluoride solution. The heating and dissolving temperature is preferably 60–80°C, more preferably 70–75°C. The heating and dissolving time can be 2–10 h, preferably 3–9 h, more preferably 4–8 h.

[0039] The concentration of the polyvinylidene fluoride solution can be 10–30 wt%, preferably 15–25 wt%, even more preferably 18–23 wt%, and more preferably 20–21 wt%. This is beneficial for forming a polyvinylidene fluoride film with a pure polar phase.

[0040] In this invention, residual air bubbles in the polyvinylidene fluoride solution also need to be removed. According to one embodiment of the invention, the polyvinylidene fluoride solution obtained by heating and dissolving is placed in a vacuum environment and allowed to stand for more than 1 hour to remove residual air bubbles. This facilitates the casting of a polar phase polyvinylidene fluoride film of uniform thickness.

[0041] Casting steps

[0042] A polyvinylidene fluoride (PVDF) solution is cast to obtain a polar phase PVDF initial film. In this invention, two or more different temperature zones are sequentially set in the traction section. Preferably, three or more different temperature zones are sequentially set in the traction section, and the temperature range of the temperature zones is between 75 and 120°C. More preferably, four different temperature zones are sequentially set in the traction section, including a first temperature zone, a second temperature zone, a third temperature zone, and a fourth temperature zone, wherein the temperature range of the first temperature zone is 75–80°C; the temperature range of the second temperature zone is 85–90°C; the temperature range of the third temperature zone is 100–110°C; and the temperature range of the fourth temperature zone is 115–120°C.

[0043] The preferred temperature range for the first temperature range is 75–77°C. The preferred temperature range for the second temperature range is 85–86°C. The preferred temperature range for the third temperature range is 105–110°C; and the preferred temperature range for the fourth temperature range is 117–120°C.

[0044] According to a specific embodiment of the present invention, four different temperature sections are sequentially set in the traction section, including a first temperature section, a second temperature section, a third temperature section and a fourth temperature section. The temperature of the first temperature section is 75°C; the temperature of the second temperature section is 85°C; the temperature of the third temperature section is 110°C; and the temperature of the fourth temperature section is 120°C.

[0045] The drawing rate in the traction section can be 1–4 m / min, preferably 1.5–2.5 m / min, more preferably 1.8–2.3 m / min, and even more preferably 1.8–2.2 m / min. In some specific embodiments, the drawing rate is 2.0–2.1 m / min. This is beneficial for obtaining a polyvinylidene fluoride film with a pure polar phase. Through extensive research and experimentation, this invention has found that the preparation method of this invention can directly obtain a pure polar phase polyvinylidene fluoride initial film.

[0046] This invention employs a casting machine for casting. The casting machine can be any type known in the art. The casting machine may include a base belt, rollers, a slurry hopper, a doctor blade, a drying oven, drive rollers (including an upper drive roller and a lower drive roller arranged parallel to each other), and a collecting roller. The base belt moves under the drive of the rollers, drawing the polyvinylidene fluoride (PVDF) solution from the slurry hopper onto the base belt. The solution is then evenly spread by the doctor blade. The evenly spread solution layer passes through the drying oven, which contains three or more different temperature zones sequentially (i.e., three or more different temperature zones are sequentially set in the traction section). After passing through the drying oven, a polar phase PVDF film is formed. The polar phase PVDF film moves forward under the drive of the drive rollers and is collected into a roll by the collecting roller.

[0047] Annealing steps

[0048] The initial polyvinylidene fluoride (PVDF) film was annealed at 50–160 °C to obtain a polar PVDF film. This resulted in a highly crystalline polar PVDF film, which exhibited superior piezoelectric properties.

[0049] The annealing temperature can be 50–160℃, preferably 100–160℃, even more preferably 100–150℃, and more preferably 110–150℃. The annealing time can be 8–30 h, preferably 12–30 h, even more preferably 18–26 h, and more preferably 18–24 h. This invention has found that the initial polyvinylidene fluoride film obtained by casting has low crystallinity and poor piezoelectric properties. After annealing, the crystallinity is significantly improved, and the piezoelectric properties are significantly improved. The piezoelectric properties of the polar phase polyvinylidene fluoride film obtained by this invention first increase and then decrease with increasing annealing temperature.

[0050] <Polar phase polyvinylidene fluoride film>

[0051] The present invention also provides a polar phase polyvinylidene fluoride film prepared according to the preparation method described above. The thickness of this polar phase polyvinylidene fluoride film is 10–100 μm, preferably 20–50 μm, more preferably 20–30 μm, and even more preferably 25–28 μm. This polar phase polyvinylidene fluoride film has a thickness of 811 cm⁻¹. -1 833cm -1 1234cm -1 The polar polyvinylidene fluoride film exhibits infrared characteristic absorption peaks of the γ phase (strong γ phase infrared characteristic absorption peaks), and is almost 100% γ crystal polyvinylidene fluoride film, which may contain trace amounts of β crystals.

[0052] piezoelectric strain constant d 33 It can be above 40 pC / N, preferably above 45 pC / N, and can even reach above 60 pC / N.

[0053] <Application>

[0054] This invention also provides an application of the polar polyvinylidene fluoride (PVDF) film described above in the preparation of electroactive materials. In this invention, before using the polar PVDF film to prepare electroactive materials, the polar PVDF film can be contact-polarized. The polarization steps include: (1) attaching a copper sheet to the polar PVDF film to increase the contact polarization area; (2) heating an oil bath (the heating temperature can be 40-120°C), immersing the polar PVDF film in silicone oil, and allowing it to stand to stabilize the temperature; (3) after the temperature stabilizes, applying an electric field to polarize the polar PVDF film, wherein the polarization electric field can be 50-130 MV / m, and the polarization time can be 10-60 min; (4) maintaining the polarization electric field, removing the polar PVDF film from the oil bath, cooling it to room temperature, turning off the electric field, and ending the polarization.

[0055] The heating temperature is preferably 60–70℃, more preferably 60–65℃. The polarization electric field is preferably 65–100 MV / m, even more preferably 70–80 MV / m, and more preferably 70–75 MV / m. The polarization time can be 10–60 min, preferably 25–35 min, and more preferably 30–35 min.

[0056] The electroactive materials include piezoelectric materials.

[0057] The following describes the testing methods used in the examples:

[0058] Fourier transform infrared spectroscopy test: The test was performed using an infrared instrument of model Spectrum 100FTIR spectrometer (manufacturer: Perkin-Elmer).

[0059] DSC testing: The test was conducted using a DSC model Q-2000 (manufacturer: TA Instrument).

[0060] Piezoelectric testing: A positive piezoelectric testing instrument was assembled using a LinMot E1100 linear motor and a Keithley 6517A electrometer.

[0061] Ferroelectric testing: Premiere II ferroelectric tester (Radiant Technologies) and Trek 10 / 10B-HS high voltage amplifier (0-10kV AC) were used.

[0062] The following describes the raw materials and equipment used in the example:

[0063] Polyvinylidene fluoride powder: purchased from Sinochem Lantian, grade 2320-HP; N,N-dimethylacetamide (DMAC): purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0064] Casting machine: purchased from Shenzhen Shanying Automation Co., Ltd., model GTB800C.

[0065] Example 1

[0066] (1) Mix polyvinylidene fluoride powder with N,N-dimethylacetamide (DMAC) at a mass ratio of 1:4 and heat at 75°C for 8 hours to form a 20wt% polyvinylidene fluoride solution; place the polyvinylidene fluoride solution in a vacuum environment and let it stand for 1 hour to remove residual bubbles in the solution.

[0067] (2) The polyvinylidene fluoride solution (i.e., the casting solution A) after removing residual bubbles is cast using a casting machine to obtain a uniform polar polyvinylidene fluoride initial film with a thickness of 25 μm; wherein, the casting conditions specifically include: four different temperature sections of 75℃, 85℃, 110℃ and 120℃ are set sequentially in the traction section (i.e., four different temperature sections are set sequentially in the drying oven 5); the stretching rate is 2 m / min;

[0068] (3) The polar polyvinylidene fluoride initial film was annealed at 100°C for 24 hours to obtain a polar polyvinylidene fluoride film with a thickness of 25 μm.

[0069] A partial structural diagram of the casting machine is shown below. Figure 5As shown. The base belt 1 moves under the drive of the roller 2, drawing the casting solution A from the slurry hopper 3 onto the base belt 1. It is then evenly spread by the scraper 4. The evenly spread solution layer passes through the drying oven 5, which contains four different temperature zones. The upper drive roller 71 and the lower drive roller 72 move the polar phase polyvinylidene fluoride film M, and the collecting roller 6 collects the obtained polar phase polyvinylidene fluoride film M into a roll.

[0070] Examples 2-10

[0071] The only difference from Example 1 is the annealing temperature. In Examples 2 to 10, the annealing temperatures were 75°C, 90°C, 110°C, 125°C, 130°C, 135°C, 140°C, 150°C, and 160°C, respectively.

[0072] Experiment Example 1 - Infrared Testing

[0073] The polar phase polyvinylidene fluoride initial film obtained in Example 1 was subjected to infrared spectroscopy to determine the polar phase of the crystal form.

[0074] The annealed polar polyvinylidene fluoride (PVDF) films obtained in Examples 1 to 10 were subjected to infrared spectroscopy to determine whether the crystal structure of the PVDF films (i.e., polyvinylidene fluoride films) changed after annealing.

[0075] See results Figure 1 As shown. Infrared spectrum of the initial polar polyvinylidene fluoride film (denoted as ori). Figure 1 It can be seen that the infrared spectrum (IR) shows that before annealing, at 811 cm⁻¹ -1 833cm -1 1234cm -1 The infrared characteristic peaks at the specified locations correspond to the γ phase, yielding a PVDF film that is almost entirely composed of γ crystals (containing trace amounts of β crystals). After annealing at different temperatures for 24 hours, the positions of the characteristic peaks in the infrared spectra of the obtained samples remained consistent with those before annealing, indicating that annealing has no effect on the crystal structure of the PVDF film. The crystal structure after annealing still exists as a polar phase.

[0076] Experiment Example 2 - DSC Test

[0077] To determine the change in crystallinity of polyvinylidene fluoride (PVDF) films after annealing, DSC tests were performed on PVDF films annealed at different temperatures. Details are as follows:

[0078] The initial polar polyvinylidene fluoride film obtained in Example 1 was subjected to DSC testing; and polar polyvinylidene fluoride films annealed at 75°C, 100°C, 110°C, 125°C, 130°C, 135°C, 140°C, 150°C, and 160°C (i.e., the products of Examples 1 to 10, respectively) were also subjected to DSC testing. The results are shown below. Figure 2 .

[0079] Depend on Figure 2 It can be seen that annealing significantly improves the crystallinity of PVDF films, and the crystallinity first increases and then decreases with increasing annealing temperature. The crystallinity reaches its maximum value at 125℃.

[0080] Experimental Example 3 - Testing of Piezoelectric and Ferroelectric Properties

[0081] (I) Contact polarization treatment is required before testing the positive piezoelectric properties. The polarization procedure for the sample to be tested (i.e., the polyvinylidene fluoride film to be tested) before positive piezoelectric testing is as follows: ①: Use a copper sheet to attach to the sample to increase the contact polarization area; ②: Heat the oil bath to 60°C and immerse the sample to be tested in silicone oil; let the sample to be tested stand in the silicone oil for 10 minutes to stabilize the temperature; ③: After the temperature stabilizes, apply an electric field of 70MV / m to the sample to be tested for 30 minutes to polarize it; ④: Maintain the 70MV / m polarization electric field and remove the sample to be tested from the oil bath to cool for 20 minutes; cool the sample to room temperature, turn off the electric field, and end the polarization.

[0082] The results of the positive piezoelectric performance test are shown below Figure 3 .Depend on Figure 3 It can be seen that the polar polyvinylidene fluoride film obtained by this invention exhibits good piezoelectric properties. The piezoelectric properties of the polyvinylidene fluoride film are significantly improved after annealing at 100–160 °C, and first increase and then decrease with increasing annealing temperature (piezoelectric strain constant d). 33 The piezoelectric strain constant is generally between 40 pC / N and 60 pC / N, with a maximum value exceeding 60 pC / N. This may be because the initial PVDF film obtained through casting has low crystallinity, resulting in poor piezoelectric properties. After annealing, the piezoelectric properties are improved. However, after annealing at 75℃ and 90℃, the piezoelectric strain constant did not increase but instead decreased.

[0083] (II) The residual polarization value (Pr) of the polar polyvinylidene fluoride film obtained in this invention first decreases and then increases with increasing annealing temperature, exhibiting a trend opposite to that of the piezoelectric properties. See the results below. Figure 4 .

[0084] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for preparing a polar phase polyvinylidene fluoride thin film, characterized in that, Includes the following steps: (1) Polyvinylidene fluoride powder is mixed with a polar solvent to form a 10-30 wt% polyvinylidene fluoride solution; (2) Polyvinylidene fluoride solution is cast to obtain polar phase polyvinylidene fluoride initial film; wherein, two or more different temperature sections are set sequentially in the traction section; the stretching rate is 1 to 4 m / min. (3) The polar polyvinylidene fluoride initial film is annealed at 50-160°C to obtain a polar polyvinylidene fluoride film.

2. The preparation method according to claim 1, characterized in that, In step (1), the polar solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethyl sulfoxide, acetylacetone, methyl ethyl ketone and acetone.

3. The preparation method according to claim 1, characterized in that, In step (1), polyvinylidene fluoride powder is mixed with a polar solvent and heated to dissolve at 50-90°C to form a 10-30 wt% polyvinylidene fluoride solution.

4. The preparation method according to claim 1, characterized in that, Before casting, residual air bubbles in the polyvinylidene fluoride solution are removed.

5. The preparation method according to claim 4, characterized in that, The formed polyvinylidene fluoride solution was placed in a vacuum environment and allowed to stand for more than 1 hour to remove residual bubbles from the polyvinylidene fluoride solution.

6. The preparation method according to claim 1, characterized in that, In step (2), three or more different temperature sections are set sequentially on the traction section; the temperature range of the temperature sections is between 75 and 120°C.

7. The preparation method according to claim 1, characterized in that, In step (2), four different temperature sections are set sequentially on the traction section, including the first temperature section, the second temperature section, the third temperature section and the fourth temperature section. The temperature range of the first temperature section is 75-80℃; the temperature range of the second temperature section is 85-90℃; the temperature range of the third temperature section is 100-110℃; and the temperature range of the fourth temperature section is 115-120℃.

8. The preparation method according to claim 1, characterized in that, The drawing rate is 1.5–2.5 m / min; the annealing temperature is 100–160 °C.

9. A polar polyvinylidene fluoride film prepared by the preparation method according to any one of claims 1 to 8, characterized in that, It is a polyvinylidene fluoride film that is almost 100% γ-crystalline, with a thickness of 10-100 μm; It is 811cm -1 833cm -1 1234cm -1 It exhibits infrared characteristic absorption peaks of the γ phase.

10. The application of the polar phase polyvinylidene fluoride thin film according to claim 9 in the preparation of electroactive materials.

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