Preparation method of polyvinylidene fluoride-based polymer piezoelectric film

Abstract

The invention discloses a preparation method of a polyvinylidene fluoride-based polymer piezoelectric film, which comprises the following steps: S1, adding a poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer and a poly (vinylidene fluoride-trifluoroethylene) binary copolymer into a solvent, and uniformly mixing to obtain a mixed solution; and S2, drying the mixed solution obtained in the step S1 to obtain a polymer blend membrane, and performing combination and treatment on the blend membrane to obtain a membrane sample. The preparation method comprises the following steps: carrying out solution blending on a poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer and a poly (vinylidene fluoride-trifluoroethylene) biopolymer as raw materials, controlling the mixing ratio of the two polymers, and carrying out post-treatment matching combination to prepare the polyvinylidene fluoride-based polymer piezoelectric film with high piezoelectric property.

Description

Technical Field

[0001] The invention relates to the technical field of ferroelectric polymers, in particular to a method for preparing a polyvinylidene fluoride-based polymer piezoelectric film. Background Art

[0002] Piezoelectric materials are generally divided into two categories: inorganic piezoelectric materials and polymer piezoelectric materials. Compared with inorganic piezoelectric materials, polymer piezoelectric materials, such as the most common polyvinylidene fluoride and poly (vinylidene fluoride-trifluoroethylene), have good flexibility and biocompatibility, and show great application potential in flexible electronic devices and other fields. However, the piezoelectric coefficient (d 33 <30 picoelectric coefficients per newton) is extremely low and cannot meet the actual use requirements. Therefore, how to significantly increase the piezoelectric coefficient of polymer materials has become the focus of extensive research by researchers at home and abroad.

[0003] In the prior art, in order to improve the piezoelectric properties of polyvinylidene fluoride based ferroelectric polymers, researchers are usually committed to increasing the polarization intensity. First, the polarization intensity is composed of stress-induced polarization and permanent residual polarization. Therefore, permanent residual polarization is very important for piezoelectricity, which is why polyvinylidene fluoride based polymers usually need to be macroscopically polarized to obtain a good piezoelectric performance. Secondly, stress-induced polarization is also very important. When the polymer dielectric constant is high, the stress-induced polarization is usually high. Therefore, in order to make the polymer present high piezoelectric properties, it is usually required that the polymer has strong polarity and dielectric constant at the same time. However, the high dielectric constant and residual polarization intensity polarization of polyvinylidene fluoride based polymers are often not available at the same time. For example, the relaxor ferroelectric poly (vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) has an extremely high dielectric constant, but its internal ferroelectric domain size is extremely small, so the residual polarization intensity is low, which makes the piezoelectric performance of the polymer low.

[0004] To this end, this patent proposes a method for preparing a polyvinylidene fluoride-based polymer piezoelectric film to simultaneously take into account a high dielectric constant and a high residual polarization strength, thereby obtaining high piezoelectric performance. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a polyvinylidene fluoride-based polymer piezoelectric film.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a polyvinylidene fluoride based polymer piezoelectric film, comprising the following steps:

[0008] Adding poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer and poly(vinylidene fluoride-trifluoroethylene) binary copolymer into a solvent, and mixing them evenly to obtain a mixed solution;

[0009] The mixed solution is dried to obtain a polymer blend film, and the blend film is combined and post-treated to obtain four groups of different film samples;

[0010] The molar content of vinylidene fluoride in the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer is 62.6-66.6%, and the molar content of trifluoroethylene is 24.2-28.2%. The molar percentage of vinylidene fluoride and trifluoroethylene in the poly(vinylidene fluoride-trifluoroethylene) binary copolymer is 55 / 45%.

[0011] In some possible implementations, the mass ratio of the poly(vinylidene fluoride-trifluoroethylene) binary copolymer to the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) ternary copolymer is 9:1, 8:2, 7:3, 6:4, 5:5, 4:6 and 0:10.

[0012] In some possible implementations, the molar content of trifluoroethylene in the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) copolymer is 64.6%, and the molar content of chlorofluoroethylene is 26.2%.

[0013] In some possible implementations, the weight average relative molecular mass of the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer is 500,000 g / mol. The weight average molecular mass of the poly(vinylidene fluoride-trifluoroethylene) binary copolymer is 450,000 g / mol.

[0014] In some possible implementations, the drying process is air-blast drying, and the temperature of the air-blast drying is 45 to 65° C., and the time is 22 to 30 hours.

[0015] In some possible implementations, the solvent is N,N-dimethylformamide.

[0016] In some possible implementations, the purity of the solvent is greater than 99.9%.

[0017] The present application also provides a polyvinylidene fluoride-based polymer piezoelectric film prepared by the above preparation method.

[0018] The preparation method of the polyvinylidene fluoride based polymer piezoelectric film provided in the present application uses a poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer and a poly(vinylidene fluoride-trifluoroethylene) binary copolymer as raw materials for solution blending, and controls the mixing ratio of the two polymers, and combines post-processing to prepare a polyvinylidene fluoride based polymer piezoelectric film with high piezoelectric properties.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention uses poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer and poly(vinylidene fluoride-trifluoroethylene) binary copolymer as raw materials for solution blending, controls the mixing ratio of the two polymers, and combines post-treatment to prepare a polyvinylidene fluoride-based polymer piezoelectric film with high piezoelectric performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a performance display diagram of the polyvinylidene fluoride-based polymer piezoelectric film in Examples 1-8 and Comparative Example 1. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The present invention provides a method for preparing a polyvinylidene fluoride based polymer piezoelectric film, comprising the following steps:

[0024] Adding poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer and poly(vinylidene fluoride-trifluoroethylene) binary copolymer into a solvent, and mixing them evenly to obtain a mixed solution;

[0025] The mixed solution is dried to obtain a blended film, and the blended film is combined and post-treated to obtain four groups of different film samples;

[0026] The molar content of vinylidene fluoride in the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer is 62.6-66.6%, and the molar content of trifluoroethylene is 24.2-28.2%. The molar percentage of vinylidene fluoride and trifluoroethylene in the poly(vinylidene fluoride-trifluoroethylene) binary copolymer is 55 / 45%.

[0027] The present application starts from a high dielectric and strong polar polyvinylidene fluoride based polymer, and prepares films with different mixing ratios by blending poly(vinylidene fluoride-trifluoroethylene-chloroethylene) and poly(vinylidene fluoride-trifluoroethylene). The addition of the binary copolymer greatly improves the residual polarization strength of the blended film.

[0028] Among them, the blending of high dielectric constant poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer and strong polar poly(vinylidene fluoride-trifluoroethylene) binary copolymer can make the mixture have both high dielectric constant and remanent polarization strength. Increasing the proportion of strong polar poly(vinylidene fluoride-trifluoroethylene) binary copolymer is an effective measure to improve the remanent polarization strength of the blended film. The addition of poly(vinylidene fluoride-trifluoroethylene) can effectively induce dipole flipping, resulting in the transformation of the cis-trans conformation to the all-trans conformation.

[0029] In some embodiments, the mass ratio of the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer to the lithium salt is 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, and 0:10.

[0030] Preferably, the mass ratio of the poly(vinylidene fluoride-trifluoroethylene) binary copolymer to the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) ternary copolymer is 8:2.

[0031] When the mass ratio of poly(vinylidene fluoride-trifluoroethylene) binary copolymer and poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) ternary copolymer is 8:2, the induced oriented amorphous content is 0.5, the polarization residual strength can reach 43 millicoulombs / square meter, and the dielectric constant is 20.3. After the above-mentioned stretching, annealing, and polarization treatment of poly(vinylidene fluoride-trifluoroethylene) binary copolymer and poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) ternary copolymer with a mass ratio of 8:2, the direct piezoelectric coefficient can reach 34 picocoulombs / newton.

[0032] In some embodiments, the molar content of vinylidene fluoride in the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer is 64.6%, and the molar content of trifluoroethylene is 26.2%. The weight average relative molecular mass of the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer is 500,000 g / mol. The weight average molecular weight of the poly(vinylidene fluoride-trifluoroethylene) binary copolymer is 450,000 g / mol.

[0033] The weight-average relative molecular mass of the poly(vinylidene fluoride-trifluoroethylene-fluorochloroethylene) used in the present application is 500,000 g / mol, wherein the molar ratio of vinylidene fluoride: trifluoroethylene: fluorochloroethylene is 64.6:26.2:9.2, and it has suitable polarity and high dielectric constant. Therefore, the mixed film obtained by mixing with the highly polar poly(vinylidene fluoride-trifluoroethylene) and drying has both high dielectric constant and residual polarization strength.

[0034] The drying process includes air blast drying, the temperature of the air blast drying is 45-65° C., and the time is 22-30 hours.

[0035] During the drying process, excess solvent in the mixed solution can be removed by air drying.

[0036] In some embodiments, the solvent is N,N-dimethylformamide (DMF).

[0037] The blended film can be obtained by dissolving poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) and poly(vinylidene fluoride-trifluoroethylene) in a solvent, mixing them evenly, and drying them. This method is simple to operate, low in cost, and suitable for large-scale production.

[0038] The present application also provides a polyvinylidene fluoride-based polymer piezoelectric film prepared by the preparation method.

[0039] The scheme of the present invention will be explained below in conjunction with specific embodiments and comparative examples. It will be understood by those skilled in the art that the following examples are only used to explain the present invention and cannot be understood as limiting the present invention.

[0040] Example 1

[0041] A method for preparing a solid poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) piezoelectric film comprises the following steps:

[0042] (1) Preparation of mixed solution: Poly(vinylidene fluoride-trifluoroethylene) with a vinylidene fluoride molar content of 55% and a trifluoroethylene content of 45% and poly(vinylidene fluoride-trifluoroethylene-fluorochloroethylene) with a vinylidene fluoride molar content of 64.6% and a trifluoroethylene molar content of 26.2% are dissolved in 60 mg / ml N,N-dimethylformamide solvent, stirred at room temperature for 12 hours to form a uniform solution, and mixed in a solute mass ratio of 8:2 to obtain a blended solution. The weight average relative molecular mass of the poly(vinylidene fluoride-trifluoroethylene-fluorochloroethylene) is 500,000 g / mol; the weight average molecular weight of the poly(vinylidene fluoride-trifluoroethylene) binary copolymer is 450,000 g / mol.

[0043] (2) Preparation of blend film: Pour the mixed solution prepared in (1) into a glass culture dish and place it in a forced air oven at 55°C for 24 hours to obtain a blend film. The blend film is stretched, annealed and polarized to obtain poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) / poly(vinylidene fluoride-trifluoroethylene) polymer piezoelectric film (45S-82-SAP150).

[0044] Example 2

[0045] The difference between Example 2 and Example 1 is that the mass ratio of poly(vinylidene fluoride-trifluoroethylene) to poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) in step (1) is 9:1 (45S-91-SAP150).

[0046] Example 3

[0047] The difference between Example 3 and Example 1 is that in step (1), the mass ratio of poly(vinylidene fluoride-trifluoroethylene) to poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) is 7:3 (45S-73-SAP150).

[0048] Example 4

[0049] The difference between Example 4 and Example 1 is that in step (1), the mass ratio of poly(vinylidene fluoride-trifluoroethylene) to poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) is 6:4 (45S-64-SAP150).

[0050] Example 5

[0051] The difference between Example 5 and Example 1 is that the mass ratio of poly(vinylidene fluoride-trifluoroethylene) to poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) in step (1) is 5:5 (45S-55-SAP150).

[0052] Example 6

[0053] The difference between Example 6 and Example 1 is that in step (1), the mass ratio of poly(vinylidene fluoride-trifluoroethylene) to poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) is 4:6 (45S-46-SAP150).

[0054] Comparative Example 1

[0055] The difference between Comparative Example 1 and Example 1 is that in step (1), the mass ratio of poly(vinylidene fluoride-trifluoroethylene) to poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) is 0:10, and the post-treatment method in step (2) is stretching (45S-010-SP150).

[0056] The dielectric constants (ε r '), residual polarization intensity (P r ), direct piezoelectric coefficient (d 33 ) and the test methods are as follows:

[0057] (1) Dielectric constant: Before measurement, a plasma magnetic sputtering coating apparatus was used to sputter gold electrodes with a diameter of 6 mm on the upper and lower surfaces of the polyvinylidene fluoride-based polymer piezoelectric film sample. The dielectric constant was measured using a broadband dielectric spectrometer.

[0058] (2) Remanent polarization intensity: The polarization-electric field loop (DE l oop) test is performed using a ferroelectric tester combined with a high-voltage amplifier. Gold electrodes are sputtered on both sides of the above-mentioned film sample, and the gold-plated film is immersed in silicone oil to avoid corona discharge in the air. A sinusoidal voltage is applied to obtain the DE l oop curve. The remanent polarization intensity is obtained based on the intersection of the curve and the ordinate.

[0059] (3) Direct piezoelectric coefficient measurement: After the film is subjected to unidirectional polarization treatment, the direct piezoelectric coefficient test is performed using an experimental device built independently in the laboratory. The piezoelectric coefficients of several groups of samples obtained after testing are plotted into a data graph for comparison.

[0060] The performance test results of the polyvinylidene fluoride polymer piezoelectric films prepared in Examples 1-6 and Comparative Example 1 are as follows: Figure 1 shown.

[0061] Combination Figure 1 , the performance test results are analyzed as follows:

[0062] (1) As the mixing ratio of poly(vinylidene fluoride-trifluoroethylene) increases, the dielectric constant shows a trend of gradually decreasing, indicating that the dipole moment of the amorphous region of Examples 1-6 after stretching, annealing and polarization treatment at room temperature along the electric field direction is weakened.

[0063] (2) As the proportion of poly(vinylidene fluoride-trifluoroethylene) binary polymer increases, the remnant polarization intensity gradually increases, which is mainly attributed to the ferroelectricity of the binary polymer.

[0064] (3) Combined with the formula provided by the above test method, the direct piezoelectric coefficients of Examples 1-6 and Comparative Example 1 can be obtained. For Comparative Example 1, its piezoelectric coefficient is only 1.5 picoelectric coefficient. With the addition of poly(vinylidene fluoride-trifluoroethylene), the piezoelectric coefficient of the co-film sample after annealing and polarization tends to increase. Compared with Example 1, when the mixing ratio reaches 8:2, the direct piezoelectric coefficient reaches a maximum value of 34 picoelectric coefficients, which is 22 times that of the comparative example. This is because the poly(vinylidene fluoride-trifluoroethylene) binary copolymer brings a greater residual polarization strength. Comparing Example 2 with Example 1, when the proportion of poly(vinylidene fluoride-trifluoroethylene) increases to 9:1, the direct piezoelectric coefficient decreases instead, which may be caused by the reduction of the oriented amorphous content. From the perspective of the change in dielectric constant, the dielectric constant from Example 1 to Example 2 only decreases from 20.1 to 18.3, but the piezoelectric coefficient directly decreases from 34 picoelectric coefficients to 27 picoelectric coefficients, a decrease of 20%. It is speculated that the reason is that compared with Example 2, the oriented amorphous content of Example 1 is increased, so that it obtains a higher direct piezoelectric coefficient.

[0065] In summary, the blending of high dielectric constant poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer and strong polar poly(vinylidene fluoride-trifluoroethylene) binary copolymer can make the mixture have both high dielectric constant and remanent polarization strength. The addition of poly(vinylidene fluoride-trifluoroethylene) can effectively induce dipole flipping, leading to the transformation of cis-trans conformation to all-trans conformation, which is an effective measure to improve the remanent polarization strength of the blended film. The development prospects are broad.

[0066] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0067] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing a polyvinylidene fluoride-based polymer piezoelectric film, characterized in that: The following steps are involved: S1, adding poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer and poly(vinylidene fluoride-trifluoroethylene) binary copolymer to a solvent, and mixing them uniformly to obtain a mixed solution; S2. Drying the mixed solution obtained in step S1 to obtain a polymer blend film, and performing post-combination treatment on the blend film to obtain a film sample.

2. The method for preparing the polyvinylidene fluoride-based polymer piezoelectric film according to claim 1, characterized in that: The molar content of vinylidene fluoride in the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer is 62.6-66.6%, and the molar content of trifluoroethylene is 24.2-28.2%. The molar percentage of vinylidene fluoride and trifluoroethylene in the poly(vinylidene fluoride-trifluoroethylene) binary copolymer is 55 / 45%.

3. The method for preparing the polyvinylidene fluoride-based polymer piezoelectric film according to claim 2, characterized in that: The molar content of vinylidene fluoride in the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer is 64.6%, and the molar content of trifluoroethylene is 26.2%. The molar percentage of vinylidene fluoride and trifluoroethylene in the poly(vinylidene fluoride-trifluoroethylene) binary copolymer is 55 / 45%.

4. The method for preparing the polyvinylidene fluoride-based polymer piezoelectric film according to any one of claims 1 to 3, characterized in that: The weight average relative molecular mass of the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer is 500,000 g / mol; the weight average molecular mass of the poly(vinylidene fluoride-trifluoroethylene) binary copolymer is 450,000 g / mol.

5. The method for preparing the polyvinylidene fluoride-based polymer piezoelectric film according to any one of claims 1 to 3, characterized in that: The mixing mass ratios of the poly(vinylidene fluoride-trifluoroethylene) binary copolymer and the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) ternary copolymer are 9:1, 8:2, 7:3, 6:4, 5:5, 4:6 and 0:

10.

6. The method for preparing the polyvinylidene fluoride-based polymer piezoelectric film according to claim 1, characterized in that: The post-processing processes are respectively: Stretching sample: The blended film cast from the blended solution obtained above is uniaxially stretched to a stretching ratio of about 200% to 500% using a universal electronic testing machine at room temperature; Stretching and polarizing samples: applying a polarizing electric field of 150 to 300 mV / m to the stretched film at room temperature and performing polarization treatment 20 to 60 times; Stretched and annealed samples: The above stretched films were annealed at 130 °C for 24 h; Stretched, annealed and polarized samples: The stretched and annealed samples were subjected to 20 to 60 unidirectional polarization treatments by applying a polarizing electric field of 150 to 300 mV / m at room temperature.

7. The method for preparing the polyvinylidene fluoride-based polymer piezoelectric film according to claim 1, characterized in that: The mixed solution is dried by air blast drying at a temperature of 45 to 65° C. for 22 to 30 hours.

8. The method for preparing the polyvinylidene fluoride-based polymer piezoelectric film according to claim 1, characterized in that: The solvent is N,N-dimethylformamide.

9. The method for preparing the polyvinylidene fluoride-based polymer piezoelectric film according to claim 8, characterized in that: The solvent purity is greater than 99.9%.

10. A polyvinylidene fluoride-based polymer piezoelectric film, characterized in that: The method is prepared according to any one of claims 1 to 8.

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