A ferroelectric polymer thin film with high piezoelectric coefficient and a preparation method thereof

Abstract

The application belongs to the technical field of flexible piezoelectric materials, and discloses a grafted ferroelectric polymer thin film with a high piezoelectric coefficient and a preparation method thereof, wherein the preparation method comprises the following steps: obtaining a polymer solution by selecting a polyvinylidene fluoride-based ferroelectric polymer; adding a grafting agent reagent to the polymer solution and uniformly mixing to obtain a mixed solution; uniformly casting the mixed solution on the surface of a glass substrate, heating in an oven to volatilize the solvent, then increasing the temperature of the oven to perform a grafting reaction to obtain a grafted thin film; after the oven is naturally cooled to room temperature, the grafted thin film is peeled off from the glass substrate, and a polarization process is adopted to obtain the grafted ferroelectric polymer thin film with a high piezoelectric coefficient. The polyvinylidene fluoride-based ferroelectric polymer is modified by grafting side chains, the relative stability of different molecular conformation energies in the ferroelectric polymer is regulated by grafting side chains in the polymer, the ferroelectric phase and the relaxor phase in the ferroelectric polymer are induced to compete with each other, and the piezoelectric coefficient of the material is significantly improved.

Description

Technical Field

[0001] This invention belongs to the technical field of flexible piezoelectric materials, and more specifically, relates to a thin film grafted with a high piezoelectric coefficient and its preparation method. Background Technology

[0002] With the rapid development of flexible wearable electronics, healthcare, smart homes, and industrial inspection, piezoelectric materials, capable of efficiently converting mechanical energy into electrical energy, have become core materials supporting the development of high-performance devices in these fields. Among them, polyvinylidene fluoride ferroelectric polymers (PVDF) exhibit unique advantages that traditional inorganic piezoelectric materials cannot match, thanks to their superior flexibility, lightweight, solution-processable nature, stable ferroelectric properties, and good biocompatibility. These advantages are difficult to overcome in applications such as flexible wearable physiological signal sensors and piezoelectric actuators in minimally invasive medical devices. However, the piezoelectric coefficient of traditional PVDF ferroelectric polymer materials... d 33 The piezoelectric coefficient of piezoelectric materials is a core indicator for measuring a material's mechanical and electrical energy conversion capabilities. d 33 The low efficiency directly limits the material's energy conversion efficiency, sensing sensitivity, and other properties, seriously hindering the wider application of ferroelectric polymers.

[0003] Therefore, there is an urgent need for a new method that can efficiently improve the piezoelectric properties of polyvinylidene fluoride ferroelectric polymers to meet the pressing demand for high-performance piezoelectric materials in various fields. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a grafted ferroelectric polymer film with a high piezoelectric coefficient and its preparation method, which solves the problem that the traditional polyvinylidene fluoride ferroelectric polymer material has a low piezoelectric coefficient, which hinders the wider application of ferroelectric polymers.

[0005] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a thin film grafted with a high voltage coefficient of ferroelectric polymer is provided, comprising:

[0006] S1, a polymer solution is obtained by dissolving polyvinylidene fluoride ferroelectric polymer in an organic solvent;

[0007] S2, add grafting agent to the polymer solution and mix evenly to obtain a mixed solution;

[0008] S3, the mixed solution is uniformly cast onto the surface of a glass substrate, heated in an oven to evaporate the solvent, and then the oven temperature is increased to carry out a grafting reaction to obtain a grafted film.

[0009] S4. After the oven has cooled naturally to room temperature, the grafted film is peeled off from the glass substrate and processed using a polarization process to obtain a high voltage coefficient grafted ferroelectric polymer film.

[0010] According to the method for preparing a high-voltage grafted ferroelectric polymer film provided by the present invention, the polyvinylidene fluoride ferroelectric polymer in S1 is:

[0011] Polyvinylidene fluoride-trifluoroethylene, wherein the trifluoroethylene content is 35 mol%~45 mol%;

[0012] Alternatively, it may be polyvinylidene fluoride-tetrafluoroethylene, wherein the tetrafluoroethylene content is 5 mol%~10 mol%;

[0013] Alternatively, it may be polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene, wherein the content of trifluoroethylene is 30 mol%~40 mol% and the content of chlorofluoroethylene is 5 mol%~7 mol%.

[0014] Alternatively, it can be polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene, with a trifluoroethylene content of 30 mol%~40 mol% and a trifluorochloroethylene content of 5 mol%~7 mol%.

[0015] In the method for preparing a grafted ferroelectric polymer film with a high voltage coefficient provided by the present invention, the organic solvent in S1 is selected from one of cyclohexanone, N,N-dimethylamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0016] According to the preparation method of the high voltage coefficient grafted ferroelectric polymer film provided by the present invention, the concentration of polyvinylidene fluoride ferroelectric polymer in the polymer solution prepared in S1 is 40~100 mg / ml.

[0017] According to the preparation method of grafted ferroelectric polymer thin film with high voltage coefficient provided by the present invention, the grafting agent in S2 is a monoamine small molecule grafting agent.

[0018] According to the method for preparing a grafted ferroelectric polymer film with a high voltage coefficient provided by the present invention, the grafting agent is one or more combinations of n-propylamine, n-butylamine, n-hexylamine, n-decylamine, cyclopentylamine, cyclohexylamine, and aniline.

[0019] According to the preparation method of the grafted ferroelectric polymer film with high voltage coefficient provided by the present invention, the molar ratio of grafting agent to polyvinylidene fluoride ferroelectric polymer in the mixed solution prepared in S2 is 0.6~4.5:100.

[0020] According to the preparation method of the grafted ferroelectric polymer film with high voltage coefficient provided by the present invention, the reaction conditions of the grafting reaction in S3 are as follows: the oven temperature is raised to 200~220°C in an air or inert gas atmosphere, and the reaction time is 2~4 h.

[0021] According to the preparation method of the grafted ferroelectric polymer thin film with high voltage coefficient provided by the present invention, the polarization process in S4 includes contact polarization process or corona polarization process.

[0022] The polarization parameters for the contact polarization process are a DC electric field of 100~150 MV / m and a polarization time of 10~30 min; the polarization parameters for the corona polarization process are a voltage of 10~16 kV, a needle tip-film distance of 3~6 cm, and a polarization time of 10 min~60 min.

[0023] According to another aspect of the present invention, a high-voltage grafted ferroelectric polymer film is provided, which is prepared by the preparation method of the high-voltage grafted ferroelectric polymer film described in any of the above claims.

[0024] In summary, compared with the prior art, the technical solutions conceived in this invention provide a high-voltage grafted ferroelectric polymer thin film and its preparation method:

[0025] 1. This invention incorporates the grafting modification step into the membrane preparation step. Under heating conditions, the polyvinylidene fluoride ferroelectric polymer is modified by grafting side chains. Small molecule side chains are grafted onto the traditional polyvinylidene fluoride ferroelectric polymer through a nucleophilic reaction. This can regulate the relative stability of the energy of different molecular conformations in the ferroelectric polymer, thereby inducing the ferroelectric phase and relaxation phase to compete with each other in the ferroelectric polymer, and achieving a significant improvement in the piezoelectric coefficient of the material.

[0026] 2. This invention is based on solution casting technology, which is simple in procedure, has a short production cycle, and has the potential for large-scale manufacturing;

[0027] 3. The grafted modified ferroelectric polymer film prepared by this invention has uniform thickness and smooth surface, and its elongation at break is significantly improved compared with that before modification, making it more suitable for the human body fit requirements of wearable devices.

[0028] 4. This invention significantly enhances the piezoelectric response of polyvinylidene fluoride polymers, with a maximum... d 33 It reaches approximately -90 pC / N, meeting the requirements for high-sensitivity sensing and efficient energy harvesting. Attached Figure Description

[0029] Figure 1 This is a schematic flowchart of the preparation method of the high voltage coefficient grafted ferroelectric polymer thin film provided by the present invention.

[0030] Figure 2 This is a schematic diagram of the grafting reaction mechanism provided by the present invention.

[0031] Figure 3 This is a schematic diagram of the X-ray diffraction and infrared spectra of the samples obtained in Examples 1-4 of the present invention and the original polymer (P(VDF-TrFE) 55 / 45mol%).

[0032] Figure 4 This is a comparison chart of the fracture growth rate of the samples obtained in Examples 1-4 of the present invention and the original polymer (P(VDF-TrFE) 55 / 45mol%).

[0033] Figure 5 This is a physical image of the sample obtained in Example 3 of the present invention and a schematic diagram of the thickness uniformity in different regions.

[0034] Figure 6 The samples obtained in Examples 1-4 of this invention and the original polymer (P(VDF-TrFE) 55 / 45mol%) are from... d 33 Tester measured d 33 Comparison chart. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0036] Please see Figure 1 This embodiment provides a method for preparing a thin film grafted with a high voltage coefficient ferroelectric polymer, the method comprising:

[0037] S1, a polymer solution is obtained by dissolving polyvinylidene fluoride ferroelectric polymer in an organic solvent;

[0038] S2, add grafting agent to the polymer solution and mix evenly to obtain a mixed solution;

[0039] S3, the mixed solution is uniformly cast onto the surface of a glass substrate, heated in an oven to evaporate the solvent, and then the oven temperature is increased to carry out a grafting reaction to obtain a grafted film.

[0040] S4. After the oven has cooled naturally to room temperature, the grafted film is peeled off from the glass substrate and processed using a polarization process to obtain a high voltage coefficient grafted ferroelectric polymer film.

[0041] Traditional grafting modification strategies generally focus on inducing polar conformations, but their effect on improving piezoelectric coefficients is very limited when applied to ferroelectric polymers. This embodiment proposes combining grafting modification with the membrane preparation process, integrating the grafting modification step into the membrane preparation process. Specifically, a grafting agent is added to a polyvinylidene fluoride (PVDF) ferroelectric polymer solution. After thorough mixing, the mixture is cast onto a glass substrate. The solvent is first evaporated by heating, and then the grafting reaction between the polymer and the grafting agent is directly carried out by raising the temperature. This embodiment utilizes a special grafting process design, using the grafting agent to directly graft PVDF ferroelectric polymers at a set temperature. During the grafting reaction, small molecule side chains are grafted onto the polymer via nucleophilic reactions, forming a branched polymer structure. The presence of short branches increases the interchain distance, enhances conformational disorder, helps break long-range ferroelectric interactions, and forms a stable relaxor phase. The competition between the two phases promotes the improvement of the material's piezoelectric coefficient. d 33 Significant improvement.

[0042] refer to Figure 2 In this embodiment, the specific reaction mechanism of the grafting reaction is as follows: under alkaline catalysis, the polyvinylidene fluoride ferroelectric polymer first undergoes dehydrofluorination to form carbon-carbon double bonds. Then, an amine grafting agent undergoes a Michael addition reaction with the carbon-carbon double bonds, attaching side chains to the polymer. Finally, under heating conditions, further dehydrofluorination is carried out to form more stable carbon-nitrogen double bonds. Thus, small molecule side chains are grafted onto the polymer, improving the conformational disorder and helping to break long-range ferroelectric interactions, forming a stable relaxor phase. The competition between the two phases promotes a significant increase in the piezoelectric coefficient of the material.

[0043] In this embodiment, the polyvinylidene fluoride ferroelectric polymer in S1 is in powder form; the grafting agent in S2 is in liquid form. After adding the grafting agent to the polymer solution in a certain proportion, the mixture can be stirred at 200-400 rpm / min for 1-2 hours to obtain a uniform mixed solution; in S3, the mixed solution can be uniformly cast onto a smooth glass substrate surface and heated in an oven at 60 °C for 8 hours to evaporate the solvent.

[0044] In some embodiments, the polyvinylidene fluoride ferroelectric polymer in S1 is:

[0045] Polyvinylidene fluoride-trifluoroethylene, wherein the trifluoroethylene content is 35 mol%~45 mol%;

[0046] Alternatively, it may be polyvinylidene fluoride-tetrafluoroethylene, wherein the tetrafluoroethylene content is 5 mol%~10 mol%;

[0047] Alternatively, it may be polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene, wherein the content of trifluoroethylene is 30 mol%~40 mol% and the content of chlorofluoroethylene is 5 mol%~7 mol%.

[0048] Alternatively, it can be polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene, with a trifluoroethylene content of 30 mol%~40 mol% and a trifluorochloroethylene content of 5 mol%~7 mol%.

[0049] In some embodiments, the organic solvent in S1 is selected from one of cyclohexanone, N,N-dimethylamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0050] Optionally, the concentration of polyvinylidene fluoride ferroelectric polymer in the polymer solution prepared in S1 is 40~100 mg / ml.

[0051] Furthermore, the grafting agent mentioned in S2 is a monoamine-based small molecule grafting agent. The grafting agent can be a pure grafting agent or a grafting agent solution, as long as the required ratio of grafting agent to polymer is met; no specific limitation is made. This embodiment proposes using a monoamine-based small molecule grafting agent for polymer grafting modification, which enables the grafting of small molecule side chains onto the polymer, thereby better improving the piezoelectric coefficient of the membrane material.

[0052] In some embodiments, the grafting agent is one or more combinations of n-propylamine, n-butylamine, n-hexylamine, n-decylamine, cyclopentylamine, cyclohexylamine, and aniline.

[0053] Optionally, the molar ratio of grafting agent to polyvinylidene fluoride ferroelectric polymer in the mixed solution prepared in S2 is 0.6~4.5:100.

[0054] In some embodiments, the grafting reaction conditions in S3 are as follows: the oven temperature is raised to 200~220°C in an air or inert gas atmosphere, and the reaction time is 2~4 h.

[0055] In some embodiments, the polarization process in S4 includes a contact polarization process or a corona polarization process.

[0056] The polarization parameters for the contact polarization process are a DC electric field of 100~150 MV / m and a polarization time of 10~30 min; the polarization parameters for the corona polarization process are a voltage of 10~16 kV, a needle tip-film distance of 3~6 cm, and a polarization time of 10 min~60 min.

[0057] In other embodiments, a high-voltage grafted ferroelectric polymer film is also provided, which is prepared by any of the above-described methods for preparing a high-voltage grafted ferroelectric polymer film.

[0058] The following specific examples illustrate the preparation process and effects of grafted ferroelectric polymer films with high voltage coefficients.

[0059] Example 1: 300 mg of P(VDF-TrFE) 55 / 45 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Then, n-butylamine was added to the homogenized polymer solution at a molar ratio of 100:0.6. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0060] Example 2: 300 mg of P(VDF-TrFE) 55 / 45 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Then, n-butylamine was added to the homogenized polymer solution at a molar ratio of 100:1.2. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0061] Example 3: 300 mg of P(VDF-TrFE) 55 / 45 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Then, n-butylamine was added to the homogenized polymer solution at a molar ratio of 100:2.25. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0062] Example 4: 300 mg of P(VDF-TrFE) 55 / 45 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Then, n-butylamine was added to the homogenized polymer solution at a molar ratio of 100:4.5. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0063] Example 5: 300 mg of P(VDF-TrFE) 55 / 45 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Then, n-hexylamine was added to the homogenized polymer solution at a molar ratio of 100:0.6. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0064] Example 6: 300 mg of P(VDF-TrFE) 55 / 45 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Then, n-hexylamine was added to the homogenized polymer solution at a molar ratio of 100:1.2. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0065] Example 7: 300 mg of P(VDF-TrFE) 55 / 45 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Then, n-hexylamine was added to the homogenized polymer solution at a molar ratio of 100:2.25. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0066] Example 8: 300 mg of P(VDF-TrFE) 55 / 45 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Then, n-hexylamine was added to the homogenized polymer solution at a molar ratio of 100:4.5. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0067] Example 9: 300 mg of P(VDF-TrFE) 55 / 45 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Then, n-decylamine was added to the homogenized polymer solution at a molar ratio of 100:2.25. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0068] Example 10: 300 mg of P(VDF-TrFE) 55 / 45 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Cyclopentanylamine was added to the homogenized polymer solution at a molar ratio of 100:2.25. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0069] Example 11: 300 mg of P(VDF-TrFE) 55 / 45 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Cyclohexylamine was added to the homogenized polymer solution at a molar ratio of 100:2.25. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0070] Example 12: 300 mg of P(VDF-TrFE) 55 / 45 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Then, n-propylamine was added to the homogenized polymer solution at a molar ratio of 100:2.25. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0071] Example 13: 300 mg of P(VDF-TrFE) 55 / 45 mol% was added to 5 ml of N,N-dimethylamide solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C and 400 rpm / min for 12 h. Then, n-butylamine was added to the homogenized polymer solution at a molar ratio of 100:0.6. The solution was stirred at 40 °C and 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0072] Example 14: 300 mg of P(VDF-TFE) 95 / 5 mol% was added to 5 ml of N,N-dimethylamide solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Then, n-butylamine was added to the homogenized polymer solution at a molar ratio of 100:0.6. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0073] Comparative Example 1: 300 mg of P(VDF-TrFE) 55 / 45 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Aniline was added to the homogenized polymer solution at a molar ratio of 100:2.25. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0074] Comparative Example 2: 300 mg of P(VDF-TrFE) 55 / 45 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Then, n-decylamine was added to the homogenized polymer solution at a molar ratio of 100:4.5. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate, and the solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate and contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0075] Comparative Example 3: 300 mg of P(VDF-TrFE) 80 / 20 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Then, n-butylamine was added to the homogenized polymer solution at a molar ratio of 100:2.25. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0076] Comparative Example 4: 300 mg of P(VDF-TrFE) 80 / 20 mol% was added to 5 ml of cyclohexanone solvent to prepare a polymer solution with a concentration of 60 mg / ml. The solution was stirred at 40 °C at a rate of 400 rpm / min for 12 h. Then, n-butylamine was added to the homogenized polymer solution at a molar ratio of 100:4.5. The solution was stirred at 40 °C at a rate of 400 rpm / min for 1 h. The polymer solution was then cast onto a glass substrate. The solvent was dried at 60 °C. The temperature was then raised to 220 °C and held for 3 h to carry out the grafting reaction. After the temperature slowly dropped to room temperature, the grafting was peeled off from the substrate. Contact polarization was performed using a DC electric field of 120 MV / m for 15 min.

[0077] The piezoelectric coefficients of the films prepared in the above specific embodiments and comparative examples are detailed in Table 1 below:

[0078] Table 1. Examples and Comparative Examples and Original Polymers d 33 Tester measured d 33 contrast

[0079]

[0080] As can be seen from Examples 1-13 and Comparative Examples 1-2 above, when the polymer uses P(VDF-TrFE) 55 / 45 mol%, the type of grafting agent, the range of molar ratio of grafting agent to polymer, and the type of organic solvent in the polymer solution provided by the present invention all improve the piezoelectric coefficient of the film material prepared by the original P(VDF-TrFE) 55 / 45 mol%. The improvement in piezoelectric coefficient is particularly significant when the molar ratio of grafting agent to polymer is in the range of 1.2-2.25:100. The preferred grafting agent is any one of n-propylamine, n-butylamine, n-hexylamine, n-decylamine, cyclopentylamine, and cyclohexylamine. The comparison between Example 14 and the original P(VDF-TFE) 95 / 5 mol%, and the comparison between Comparative Examples 3-4 and the original P(VDF-TrFE) 80 / 20 mol%, demonstrates that the grafting modification process provided by this invention can also improve the piezoelectric coefficient of the prepared membrane material when the polymer concentration ratio provided by this invention is not the preferred polymer concentration ratio provided by this invention. This demonstrates the effectiveness of the grafting modification process provided by this invention.

[0081] Appendix Figure 3 X-ray diffraction and infrared spectra of the samples obtained in Examples 1-4 and the original b polymer (P(VDF-TrFE) 55 / 45 mol%); wherein Figure 3 In the figure, a represents X-ray diffraction and b represents the infrared spectrum at the corresponding wavenumber of the all-trans conformation. As the grafting concentration increases, the content of the all-trans conformation in the material gradually decreases, while the content of the relaxor phase gradually increases.

[0082] Appendix Figure 4 The graph shows a comparison of the fracture growth rate of the samples obtained in Examples 1-4 and the original polymer (P(VDF-TrFE) 55 / 45 mol%). As the grafting concentration increases, the elongation at break of the material also increases significantly.

[0083] Appendix Figure 5 The images shown are physical pictures of the sample obtained in Example 3 and schematic diagrams illustrating the thickness uniformity in different regions. Figure 5 In the diagram, 'a' is a physical image and 'b' is a schematic diagram of the thickness uniformity in different regions. The film thickness variation in different regions is within 10%, indicating good uniformity.

[0084] Appendix Figure 6 The samples obtained in Examples 1-4 of this invention and the original polymer (P(VDF-TrFE) 55 / 45 mol%) were derived from... d 33 Tester measured d 33Comparison chart.

[0085] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a thin film of a ferroelectric polymer grafted with a high piezoelectric coefficient, characterized in that, The preparation method comprises the following steps: S1, selecting polyvinyl fluoride-based ferroelectric polymer to be dissolved in an organic solvent to obtain a polymer solution; S2, adding a grafting agent to the polymer solution and uniformly mixing to obtain a mixed solution; S3, uniformly casting the mixed solution on the surface of a glass substrate, heating in an oven to volatilize the solvent, then increasing the temperature of the oven to perform a grafting reaction to obtain a grafted film; S4, after the oven is naturally cooled to room temperature, the grafted film is peeled off from the glass substrate, and a polarization process is performed to obtain a grafted ferroelectric polymer film with a high piezoelectric coefficient; the grafting agent is one or a combination of the following: n-propylamine, n-butylamine, n-hexylamine, n-decylamine, cyclopentylamine, cyclohexylamine, and aniline; the molar ratio of the grafting agent to the polyvinyl fluoride-based ferroelectric polymer in the mixed solution prepared in S2 is 0.6-4.5:

100.

2. The method for preparing a high-voltage grafted ferroelectric polymer thin film as described in claim 1, characterized in that, the polyvinyl fluoride-based ferroelectric polymer in S1 is: polyvinyl fluoride-trifluoroethylene, wherein the content of trifluoroethylene is 35 mol%-45 mol%; or polyvinyl fluoride-tetrafluoroethylene, wherein the content of tetrafluoroethylene is 5 mol%-10 mol%; or polyvinyl fluoride-trifluoroethylene-chlorofluoroethylene, wherein the content of trifluoroethylene is 30 mol%-40 mol% and the content of chlorofluoroethylene is 5 mol%-7 mol%; or polyvinyl fluoride-trifluoroethylene-trifluorochloroethylene, wherein the content of trifluoroethylene is 30 mol%-40 mol% and the content of trifluorochloroethylene is 5 mol%-7 mol%.

3. The method for preparing a high-voltage grafted ferroelectric polymer thin film as described in claim 1, characterized in that, the organic solvent in S1 is selected from one of the following: cyclohexanone, N,N-dimethylformamide, dimethyl sulfoxide, and N-methyl pyrrolidone.

4. The method for preparing a high-voltage grafted ferroelectric polymer thin film as described in claim 1, characterized in that, the concentration of the polyvinyl fluoride-based ferroelectric polymer in the polymer solution prepared in S1 is 40-100 mg / ml.

5. The method of claim 1-4, wherein the method of preparing a thin film of a ferroelectric polymer with a high piezoelectric coefficient is characterized by, the reaction conditions of the grafting reaction in S3 are as follows: increasing the temperature of the oven to 200-220°C under an air or inert gas atmosphere, and the reaction time is 2-4 h.

6. The method for preparing a high-voltage grafted ferroelectric polymer thin film according to any one of claims 1-4, characterized in that, the polarization process in S4 comprises a contact polarization process or a corona polarization process; wherein the polarization parameters of the contact polarization process are a direct current electric field of 100-150 MV / m and a polarization time of 10-30 min; the polarization parameters of the corona polarization process are a voltage of 10-16 kV, a needle-film distance of 3-6 cm, and a polarization time of 10 min-60 min.

7. A thin film of a ferroelectric polymer grafted with a high piezoelectric coefficient, characterized in that, obtained by the preparation method of the grafted ferroelectric polymer film with a high piezoelectric coefficient according to any one of the preceding claims.

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