A ferroelectric polymer with enhanced intrinsic piezoelectric response and preparation method and application thereof

Abstract

The application belongs to the field of flexible piezoelectric polymer materials, and discloses a ferroelectric polymer for improving intrinsic piezoelectric response, a preparation method and application. The method comprises the following steps: dissolving a ferroelectric ternary copolymer with relaxation characteristics and containing chlorine elements in an organic solvent to obtain a polymer solution; performing a dehydrochlorination reaction under a protective atmosphere, and introducing C=C double bond defects in the polymer molecular chain by adjusting the reaction time to form a quasi-morphotropic phase boundary of coexisting trans-ferroelectric phase / spiral relaxation phase in the material; after the reaction is completed, the reaction solution is precipitated and purified, and then a film is cast to obtain a ferroelectric polymer material with intrinsic piezoelectric response. The application constructs a quasi-morphotropic phase boundary of coexisting trans-ferroelectric phase / spiral relaxation phase in the ferroelectric polymer through intramolecular defect engineering, improves the intrinsic piezoelectric response performance of the ferroelectric polymer material, and is stable and controllable in process, and can be widely applied in the field of flexible devices.

Description

Technical Field

[0001] This invention belongs to the field of ferroelectric polymers and flexible piezoelectric materials, and in particular relates to a ferroelectric polymer that enhances intrinsic piezoelectric response, its preparation method, and its application. Background Technology

[0002] Piezoelectric materials enable the conversion between mechanical and electrical energy, making them core functional components in sensors, actuators, and energy harvesting devices. Compared to brittle piezoelectric ceramics, ferroelectric polymers, represented by polyvinylidene fluoride (PVDF), exhibit enormous application potential in flexible electronics and wearable devices due to their lightweight, mechanical flexibility, biocompatibility, and excellent processability.

[0003] However, the intrinsic piezoelectric coefficient of traditional PVDF-based ferroelectric polymers d 33 Typically low (e.g., PVDF is only -26 pC N). -1 The piezoelectric properties of piezoelectric materials (around 1000 mM) are limited by their high strength (around 1000 mM), which hinders their large-scale application in high-performance electromechanical systems. Existing technologies have explored methods to improve piezoelectric properties by introducing C=C double bonds into ternary polymer molecular chains (e.g., patent publication number CN118772457A). However, the excitation of piezoelectric properties in these technologies relies on an externally applied high-intensity DC bias electric field (typically 40-60 MV m). -1 In practical device applications, this reliance on an external high bias electric field presents several serious challenges: maintaining a high-voltage electric field continuously in flexible wearable devices significantly increases the risk of breakdown and safety hazards; additional bias power supplies increase the complexity of circuit design, device size, and overall power consumption; for sensors that directly utilize the positive piezoelectric effect to generate charge from pressure (such as foot pressure sensors, human pulse monitoring, etc.), the intrigued response mechanism makes it difficult for the device to operate in an environment without electric field assistance.

[0004] In the field of ferroelectric materials, constructing quasi-isomorphic phase boundaries has proven to be a highly effective strategy for enhancing the piezoelectric properties of materials. Recent studies have shown that adjusting the monomer ratio during polymer copolymerization induces the formation of quasi-isomorphic phase boundaries within the polymer, resulting in significantly improved piezoelectric performance. However, the construction of quasi-isomorphic phase boundaries in traditional PVDF-based ferroelectric polymers relies on strict control of the monomer ratio during copolymerization, leading to difficulties in chemical synthesis and batch-to-batch instability. Therefore, the key to achieving high intrinsic piezoelectric response by constructing quasi-isomorphic phase boundaries through simple and controllable intramolecular defect engineering without relying on an external bias electric field is crucial for their practical application in flexible electronics. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a ferroelectric polymer with improved intrinsic piezoelectric response, preparation method and application, aiming to solve the defects of existing modification technology that high performance piezoelectric response is highly dependent on external high voltage DC bias electric field, resulting in poor safety of piezoelectric devices and difficulty in achieving high sensitivity sensing directly in zero field environment.

[0006] To achieve the objective of this invention, according to a first aspect of this invention, a method for preparing a ferroelectric polymer material with enhanced intrinsic piezoelectric response is provided, comprising the following steps: (1) A ferroelectric terpolymer containing chlorine with relaxation properties is dissolved in an organic solvent to obtain a polymer solution; under a protective atmosphere, a dehydrochlorination reaction is carried out, and C=C double bond defects are introduced into the polymer molecular chain by adjusting the reaction time, so as to form a quasi-isomorphic phase boundary in which the anti-ferroelectric phase and the helical relaxation phase coexist in the material; wherein, the content of C=C double bond defects introduced into the polymer molecular chain is 0.5~6.0 mol% (2) After the reaction is completed, the reaction solution in step (1) is precipitated and purified, and then cast into a film to obtain a ferroelectric polymer material with intrinsic piezoelectric response in the absence of an external bias electric field.

[0007] Preferably, the ferroelectric terpolymer containing chlorine and possessing relaxation properties is polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene or polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene. In the polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene, the content of trifluoroethylene is 30~75 mol% and the content of chlorofluoroethylene is 3~10 mol%; in the polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene, the content of trifluoroethylene is 30~75 mol% and the content of chlorofluoroethylene is 3~10 mol%.

[0008] Preferably, the ferroelectric terpolymer with relaxation properties containing chlorine is the polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene, wherein the trifluoroethylene content is 30-40 mol% and the chlorofluoroethylene content is 3-7 mol%.

[0009] Preferably, the content of C=C double bond defects introduced into the polymer molecular chain is 1.0~4.0 mol.

[0010] Preferably, by adjusting the reaction time to 1-40 hours, C=C double bond defects are introduced into the polymer molecular chain of the terpolymer.

[0011] Preferably, the dehydrochlorination reaction is carried out under a protective atmosphere, specifically including: adjusting the pH of the polymer solution to the range of 8-11 using a weakly basic organic reagent under a protective atmosphere, and then carrying out the dehydrochlorination reaction at a reaction temperature of 20-50°C; preferably, the weakly basic organic reagent is one or a mixture of N,N-diethylmethylamine, trimethylamine, or tripropylamine.

[0012] Preferably, the organic solvent is dimethylformamide, dimethyl sulfoxide, methyl ethyl ketone, or cyclohexanone; the concentration of the polymer solution is 200 mg / mL. -1 ~5000 mg mL -1 .

[0013] Preferably, the precipitation purification specifically includes: precipitating the reaction solution from step (1) in a mixture of water and ethanol, collecting the precipitate, redissolving it in an organic solvent, and then precipitating it again in a mixture of water and ethanol. The concentration of the polymer solution is 200 mg / mL. -1 ~5000 mg mL -1 .

[0014] According to another aspect of the present invention, a ferroelectric polymer material prepared as described above is provided.

[0015] According to another aspect of the present invention, an application of the ferroelectric polymer material as described above in a flexible device is provided, which generates an intrinsic piezoelectric response in the absence of an external bias electric field.

[0016] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages: 1. This invention utilizes controllable intramolecular chemical defect engineering (dehydrochlorination reaction) to introduce controllable amounts of C=C double bond defects into the molecular chain by controlling the reaction time. The introduction of double bond defects reduces the interchain steric hindrance caused by the large-volume chlorofluorocarbon units, establishing long-range order in the ternary relaxor ferroelectric polymer. This drives the system to precisely construct a quasi-isomorphic phase boundary where the all-trans ferroelectric phase and the helical relaxor phase coexist, achieving a high intrinsic piezoelectric response without the need for external bias electric field excitation. The reaction conditions are mild, and the process is stable and controllable.

[0017] 2. The ternary ferroelectric copolymer containing chlorine and possessing relaxation characteristics of the present invention is polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene or polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene. Preferably, the chlorine content of the polymer is in the relatively small range of 3-7 mol%. During the dehydrochlorination reaction, on the one hand, the limited number of reactive sites and their relatively isolated distribution on the molecular chain effectively suppress the excessive generation of conjugated double bonds caused by continuous elimination, thereby enabling precise and controllable introduction of C=C double bond defects. On the other hand, since the polymer chain segment conformation in this range is already near the critical region of phase transition, the introduction of a small amount of defects is sufficient to break and reshape the local phase equilibrium. This allows the system to more easily achieve the construction of quasi-isomorphic phase boundaries in the polymer structure under extremely small structural damage, thereby improving piezoelectric performance.

[0018] 3. The ferroelectric polymer material prepared by the method of this invention can be used in flexible piezoelectric devices such as flexible sensors, flexible actuators, and wearable energy harvesting devices. This is achieved by utilizing the intrinsic piezoelectric response generated by the prepared ferroelectric polymer material in an environment without an external bias electric field. This invention eliminates the dependence of existing high-performance ternary relaxor ferroelectric polymers on an external high-voltage DC bias electric field (e.g., 40-60 MV / m), solving the breakdown safety hazards and high system energy consumption problems caused by high bias electric fields, and enabling direct application of devices under zero bias electric field. Attached Figure Description

[0019] Figure 1 This is an example of the crystal form change before and after intramolecular defect modification in Example 1 of the present invention.

[0020] Figure 2 This is a diagram illustrating the changes in molecular conformation before and after intramolecular defect modification, as exemplified in Example 1 of the present invention.

[0021] Figure 3 This is a diagram illustrating the change in hysteresis loop before and after intramolecular defect modification, as exemplified in Example 1 of the present invention.

[0022] Figure 4 This is an example of the strain curves under an electric field before and after intramolecular defect modification in Embodiment 1 of the present invention. The slope corresponds to the inverse compressive effect. d 33 Numerical value.

[0023] Figure 5 Example 1 of this invention illustrates the relationship between intramolecular defect modification and PVDF before and after modification. d 33 |Comparison. Detailed Implementation

[0024] 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.

[0025] In the following embodiments, all instruments and other equipment used, unless otherwise specified, are conventional products that can be purchased through legitimate channels. Unless otherwise specified, all methods described are conventional methods, and all raw materials are available from publicly available commercial sources.

[0026] The intrinsic piezoelectric coefficient of existing PVDF-based ferroelectric polymers d 33 Low (typically below -30 pC N) -1 To address the problems of high-performance piezoelectric response in existing modification technologies, which are highly dependent on external high-voltage DC bias fields, resulting in poor device safety and difficulty in achieving high-sensitivity sensing directly in a zero-field environment, this invention provides a high intrinsic value piezoelectric response technology. d 33 This invention discloses PVDF-based ferroelectric polymer materials and their preparation methods. By constructing quasi-isomorphic phase boundaries in relaxor ferroelectric polymers through intramolecular defect engineering, this invention achieves a high intrinsic piezoelectric response without the need for external bias electric field excitation.

[0027] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a ferroelectric polymer material with enhanced intrinsic piezoelectric response includes the following steps: (1) Dissolve the terpolymer containing chlorine monomers with relaxor ferroelectric properties in an organic solvent and stir to obtain a homogeneous polymer solution; under a protective atmosphere, carry out a controlled dehydrochlorination reaction by adjusting the pH and temperature of the polymer solution, and at the same time, introduce a controlled amount of C=C double bond defects in the polymer molecular chain by adjusting the reaction time, so as to form a quasi-isomorphic phase boundary in which the anti-ferroelectric phase and the helical relaxor phase coexist in the material. (2) After the reaction is completed, the solution after the reaction in step (1) is precipitated and purified, and then cast into a film to obtain a ferroelectric polymer film with a high intrinsic piezoelectric coefficient.

[0028] In the preparation system of this invention, by selecting a ferroelectric ternary copolymer containing chlorine elements with relaxation characteristics, and under a protective atmosphere, a nucleophilic reaction is used to introduce controllable C=C double bond defects into the molecular chain through controlled reaction time. Then, by utilizing controllable intramolecular chemical defect engineering (dehydrochlorination reaction), a quasi-isomorphic phase boundary where the all-trans ferroelectric phase and the helical relaxation phase coexist is precisely constructed, achieving a high intrinsic piezoelectric response without the need for external bias electric field excitation, thus enhancing the membrane material's performance. d 33 The process has been improved to ensure stability and controllability. Furthermore, the ferroelectric terpolymers containing chlorine and possessing relaxation properties are polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene (P(VDF-TrFE-CFE)) and polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene (P(VDF-TrFE-CTFE)). Specifically, in polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene (P(VDF-TrFE-CFE)), the content of trifluoroethylene (TrFE) is 30 mol%~75 mol%, and the content of chlorofluoroethylene (CFE) is 3 mol%~10 mol%; and in polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene (P(VDF-TrFE-CTFE)), the content of trifluoroethylene (TrFE) is 30 mol%~75 mol%, and the content of chlorofluoroethylene (CTFE) is 3 mol%~10 mol%.

[0029] More preferably, the chlorine-containing terpolymer with relaxation properties is polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene (P(VDF-TrFE-CFE)), with a trifluoroethylene (TrFE) content of 30 mol%~40 mol% and a chlorofluoroethylene (CFE) content of 3 mol%~7 mol%.

[0030] Furthermore, the content of C=C double bond defects introduced into the polymer molecular chain is 0.5~6.0 mol%. Combined with the controlled dehydrochlorination reaction, and by adjusting the reaction time, a controlled amount of C=C double bond defects is introduced into the polymer molecular chain to ensure the precise construction of a quasi-isomorphic phase boundary in which all-trans ferroelectric phase / helical relaxor phase coexist in the relaxor ferroelectric polymer.

[0031] Furthermore, by precisely adjusting the reaction time to 1-40 hours, the content of C=C double bonds introduced into the polymer molecular chain is controlled at 0.5 mol%~6.0 mol%, preferably 1.0 mol%~4.0 mol%, more preferably 2.0 mol%.

[0032] Further, the dehydrochlorination reaction is carried out under a protective atmosphere, specifically including: adjusting the pH of the polymer solution to the range of 8.0-11 using a weakly basic organic reagent under the protection of inert nitrogen gas, and then carrying out the dehydrochlorination reaction at a reaction temperature of 20-50°C; preferably, the reaction is carried out at 40°C and a stirring rate of 700 rpm. One or more of the weakly basic organic reagents N,N-diethylmethylamine (DEMA), trimethylamine (TMA), or tripropylamine (TPA) are used, preferably N,N-diethylmethylamine (DEMA).

[0033] Furthermore, the concentration of the polymer solution is 200 mg / mL. -1 ~5000 mg mL -1 .

[0034] Furthermore, the ferroelectric terpolymer containing chlorine with relaxation properties is dissolved in an organic solvent, such as dimethylformamide (DMF), dimethyl sulfoxide (DMSO), methyl ethyl ketone (MEK), or cyclohexanone (CYC).

[0035] Further, the precipitation purification specifically includes: pouring the reaction solution after the reaction in step (1) into a mixture of water and ethanol for precipitation, collecting the precipitate, redissolving it in an organic solvent, and pouring it back into a mixture of water and ethanol for precipitation, and repeating this process at least three times to completely remove residual reagents.

[0036] A ferroelectric polymer material prepared by the above-described method for preparing a ferroelectric polymer material with high intrinsic piezoelectric response is disclosed. The resulting cross-linked polyvinylidene fluoride ferroelectric polymer piezoelectric material possesses a quasi-isomorphic phase boundary with the coexistence of an all-trans ferroelectric phase and a helical relaxation phase, achieving a high intrinsic piezoelectric response without the need for external bias electric field excitation. Preferably, under conditions without a bias electric field, the polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene with relaxation properties, after introducing 2.0 mol% double bond defects, exhibits a higher intrinsic piezoelectric response. d 33 |By 50.8 pC N -1 Upgraded to 129.0 pC N -1 This greatly improves the sensitivity and conversion efficiency of flexible sensors and energy harvesting devices in the absence of an electric field.

[0037] This invention discloses a method for preparing ferroelectric polymer materials with high intrinsic piezoelectric response, enabling the application of such materials in flexible piezoelectric devices such as flexible sensors, flexible actuators, and wearable energy harvesting devices. The application leverages the intrinsic piezoelectric response generated by the prepared ferroelectric polymer material in the absence of an external bias electric field. This invention eliminates the dependence of existing high-performance ternary relaxor ferroelectric polymers on an external high-voltage DC bias electric field (e.g., 40-60 MV / m), solving the breakdown safety hazards and high system energy consumption problems caused by high bias electric fields, and enabling direct application of devices under zero bias electric field conditions.

[0038] The present invention will now be described in further detail with reference to specific embodiments.

[0039] Example 1: 2.4 g of P(VDF-TrFE-CFE) terpolymer powder (59.4 / 35.7 / 4.9 mol%) was weighed and dissolved in 40 mL of DMF. The solution was stirred overnight to ensure complete dissolution. Then, 1 mL of DEMA was added to the solution as a reaction reagent. The reaction vessel was placed in an oil bath under a nitrogen atmosphere, and the dehydrochlorination reaction was carried out at a constant temperature of 40°C with a magnetic stirring speed of 700 rpm. The C=C double bond defects in the final product were adjusted by controlling the reaction time to 12 hours. After the reaction, the reaction solution was poured into 800 mL of a water-ethanol mixture for precipitation to terminate the reaction and remove residual DEMA and chloride byproducts. The precipitated polymer was collected by filtration, redissolved in 4 mL of DMF, and then poured into another 200 mL of a water-ethanol mixture for precipitation. This redissolution-precipitation purification step was repeated three times to ensure complete removal of impurities. The resulting modified polymer was dried in a forced-air drying oven at 40°C for 24 hours. The total amount of C=C double bond defects in the product at this time was calculated to be 2.0 mol using NMR spectroscopy.

[0040] The sample was then redissolved in DMF and stirred overnight at room temperature. The polymer solution was then cast onto a glass substrate. The wet film was first placed in a vacuum oven and dried at 60°C for 12 hours to remove the solvent, followed by vacuum annealing at 120°C for another 12 hours to improve crystallinity. After cooling, it was peeled off from the substrate to obtain a modified polymer film with a thickness of approximately 30 µm. d 33 | 129.0 ± 5.0 pC N -1 .

[0041] Example 2: 2.4 g of P(VDF-TrFE-CFE) terpolymer powder (59.4 / 35.7 / 4.9 mol%) was weighed and dissolved in 40 mL of DMF. The solution was stirred overnight to ensure complete dissolution. Then, 1 mL of DEMA was added to the solution as a reaction reagent. The reaction vessel was placed in an oil bath under a nitrogen atmosphere, and the dehydrochlorination reaction was carried out at a constant temperature of 40°C with a magnetic stirring speed of 700 rpm. The C=C double bond defects in the final product were adjusted by controlling the reaction time to 8 hours. After the reaction, the reaction solution was poured into 800 mL of a water-ethanol mixture for precipitation to terminate the reaction and remove residual DEMA and chloride byproducts. The precipitated polymer was collected by filtration, redissolved in 4 mL of DMF, and then poured into 200 mL of a water-ethanol mixture for precipitation again. This redissolution-precipitation purification step was repeated three times to ensure complete removal of impurities. The resulting modified polymer was dried in a forced-air drying oven at 40°C for 24 hours. The total amount of C=C double bond defects in the product at this time was calculated to be 1.5 mol using NMR spectroscopy.

[0042] The sample was then redissolved in DMF and stirred overnight at room temperature. The polymer solution was then cast onto a glass substrate. The wet film was first placed in a vacuum oven and dried at 60°C for 12 hours to remove the solvent, followed by vacuum annealing at 120°C for another 12 hours to improve crystallinity. After cooling, it was peeled off from the substrate to obtain a modified polymer film with a thickness of approximately 30 µm. d 33 | is 112.0 ± 4.4 pC N -1 .

[0043] Example 3: 2.4 g of P(VDF-TrFE-CFE) terpolymer powder (59.4 / 35.7 / 4.9 mol%) was weighed and dissolved in 40 mL of DMF. The solution was stirred overnight to ensure complete dissolution. Then, 1 mL of DEMA was added to the solution as a reaction reagent. The reaction vessel was placed in an oil bath under a nitrogen atmosphere, and the dehydrochlorination reaction was carried out at a constant temperature of 40°C with a magnetic stirring speed of 700 rpm. The C=C double bond defects in the final product were adjusted by controlling the reaction time to 20 hours. After the reaction, the reaction solution was poured into 800 mL of a water-ethanol mixture for precipitation to terminate the reaction and remove residual DEMA and chloride byproducts. The precipitated polymer was collected by filtration, redissolved in 4 mL of DMF, and then poured into another 200 mL of a water-ethanol mixture for precipitation. This redissolution-precipitation purification step was repeated three times to ensure complete removal of impurities. The resulting modified polymer was dried in a forced-air drying oven at 40°C for 24 hours. The total amount of C=C double bond defects in the product at this time was calculated to be 3.0 mol using NMR spectroscopy.

[0044] The sample was then redissolved in DMF and stirred overnight at room temperature. The polymer solution was then cast onto a glass substrate. The wet film was first placed in a vacuum oven and dried at 60°C for 12 hours to remove the solvent, followed by vacuum annealing at 120°C for another 12 hours to improve crystallinity. After cooling, it was peeled off from the substrate to obtain a modified polymer film with a thickness of approximately 30 µm. d 33 | is 105.0 ± 4.1 pC N -1 .

[0045] Example 4: 2.4 g of P(VDF-TrFE-CFE) terpolymer powder (59.4 / 35.7 / 4.9 mol%) was weighed and dissolved in 40 mL of DMF. The solution was stirred overnight to ensure complete dissolution. Then, 1 mL of DEMA was added to the solution as a reaction reagent. The reaction vessel was placed in an oil bath under a nitrogen atmosphere, and the dehydrochlorination reaction was carried out at a constant temperature of 40°C with a magnetic stirring speed of 700 rpm. The C=C double bond defects in the final product were adjusted by controlling the reaction time to 5 hours. After the reaction, the reaction solution was poured into 800 mL of a water-ethanol mixture for precipitation to terminate the reaction and remove residual DEMA and chloride byproducts. The precipitated polymer was collected by filtration, redissolved in 4 mL of DMF, and then poured into another 200 mL of a water-ethanol mixture for precipitation. This redissolution-precipitation purification step was repeated three times to ensure complete removal of impurities. The resulting modified polymer was dried in a forced-air drying oven at 40°C for 24 hours. The total amount of C=C double bond defects in the product at this time was calculated to be 1.0 mol using NMR spectroscopy.

[0046] The sample was then redissolved in DMF and stirred overnight at room temperature. The polymer solution was then cast onto a glass substrate. The wet film was first placed in a vacuum oven and dried at 60°C for 12 hours to remove the solvent, followed by vacuum annealing at 120°C for another 12 hours to improve crystallinity. After cooling, it was peeled off from the substrate to obtain a modified polymer film with a thickness of approximately 30 µm. d 33 | 102.0 ± 3.0 pC N -1 .

[0047] Example 5: 2.4 g of P(VDF-TrFE-CFE) 61 / 35 / 4 mol% terpolymer powder was weighed and dissolved in 40 mL of DMF. The solution was stirred overnight to ensure complete polymer dissolution. Then, 1 mL of DEMA was added to the solution as a reaction reagent. The reaction vessel was placed in an oil bath under a nitrogen atmosphere, and the dehydrochlorination reaction was carried out at a constant temperature of 40°C with a magnetic stirring speed of 700 rpm. The C=C double bond defects in the final product were adjusted by controlling the reaction time to 9 hours. After the reaction, the reaction solution was poured into 800 mL of a water-ethanol mixture for precipitation to terminate the reaction and remove residual DEMA and chloride byproducts. The precipitated polymer was collected by filtration, redissolved in 4 mL of DMF, and then poured into another 200 mL of a water-ethanol mixture for precipitation. This redissolution-precipitation purification step was repeated three times to ensure complete removal of impurities. The resulting modified polymer was dried in a forced-air drying oven at 40°C for 24 hours. The total amount of C=C double bond defects in the product at this time was calculated to be 1.5 mol using NMR spectroscopy.

[0048] The sample was then redissolved in DMF and stirred overnight at room temperature. The polymer solution was then cast onto a glass substrate. The wet film was first placed in a vacuum oven and dried at 60°C for 12 hours to remove the solvent, followed by vacuum annealing at 120°C for another 12 hours to improve crystallinity. After cooling, it was peeled off from the substrate to obtain a modified polymer film with a thickness of approximately 30 µm. d 33 | 99.7 ± 3.3 pC N -1 .

[0049] Example 6: 2.4 g of P(VDF-TrFE-CTFE) 60 / 35 / 5 mol% terpolymer powder was weighed and dissolved in 40 mL of DMF, stirred overnight to ensure complete polymer dissolution. Then, 1 mL of DEMA was added to the solution as a reaction reagent. The reaction vessel was placed in an oil bath under a nitrogen atmosphere, with the magnetic stirring speed set to 700 rpm, and the dehydrochlorination reaction was carried out at a constant temperature of 40°C. The C=C double bond defects in the final product were adjusted by controlling the reaction time to 8 hours. After the reaction, the reaction solution was poured into 800 mL of a water-ethanol mixture for precipitation to terminate the reaction and remove residual DEMA and chloride byproducts. The precipitated polymer was collected by filtration, redissolved in 4 mL of DMF, and then poured into 200 mL of a water-ethanol mixture again for precipitation. The above redissolution-precipitation purification steps were repeated three times to ensure complete removal of impurities. The final modified polymer was dried in a forced-air drying oven at 40°C for 24 hours. The total amount of C=C double bond defects in the product at this time was calculated to be 1.5 mol using NMR spectroscopy.

[0050] The sample was then redissolved in DMF and stirred overnight at room temperature. The polymer solution was then cast onto a glass substrate. The wet film was first placed in a vacuum oven and dried at 60°C for 12 hours to remove the solvent, followed by vacuum annealing at 120°C for another 12 hours to improve crystallinity. After cooling, it was peeled off from the substrate to obtain a modified polymer film with a thickness of approximately 30 µm. d 33 |75.4±2.9 pC N -1 After structural and piezoelectric property verification, it was found that it also induced the formation of quasi-isomorphic phase boundaries.

[0051] Comparative Example 1: 2.4 g of P(VDF-TrFE-CFE) 75 / 20 / 5 mol% terpolymer powder (a non-relaxing ferroelectric polymer) was weighed and dissolved in 40 mL of DMF, stirred overnight to ensure complete dissolution. Then, 1 mL of DEMA was added to the solution as a reaction reagent. The reaction vessel was placed in an oil bath under a nitrogen atmosphere, with the magnetic stirring speed set to 700 rpm, and the dehydrochlorination reaction was carried out at a constant temperature of 40°C. The C=C double bond defects in the final product were adjusted by controlling the reaction time to 5 hours. After the reaction, the reaction solution was poured into 800 mL of a water-ethanol mixture for precipitation to terminate the reaction and remove residual DEMA and chloride byproducts. The precipitated polymer was collected by filtration, redissolved in 4 mL of DMF, and then poured into another 200 mL of a water-ethanol mixture for precipitation. This redissolution-precipitation purification step was repeated three times to ensure complete removal of impurities. The resulting modified polymer was dried in a forced-air drying oven at 40°C for 24 hours. The total amount of C=C double bond defects in the product at this time was calculated to be 1.0 mol using NMR spectroscopy.

[0052] The sample was then redissolved in DMF and stirred overnight at room temperature. The polymer solution was then cast onto a glass substrate. The wet film was first placed in a vacuum oven and dried at 60°C for 12 hours to remove the solvent, followed by vacuum annealing at 120°C for another 12 hours to improve crystallinity. After cooling, it was peeled off from the substrate to obtain a modified polymer film with a thickness of approximately 30 µm. d 33 | is 55.2 ± 2.7 pC N -1 .

[0053] Comparative Example 2: 2.4 g of P(VDF-TrFE-CFE) 79.5 / 15.6 / 4.9 mol% terpolymer powder (a non-relaxing ferroelectric polymer) was weighed and dissolved in 40 mL of DMF, stirred overnight to ensure complete dissolution. Then, 1 mL of DEMA was added to the solution as a reaction reagent. The reaction vessel was placed in an oil bath under a nitrogen atmosphere, with the magnetic stirring speed set to 700 rpm, and the dehydrochlorination reaction was carried out at a constant temperature of 40°C. The C=C double bond defect in the final product was adjusted by controlling the reaction time to 12 hours. After the reaction, the reaction solution was poured into 800 mL of a water-ethanol mixture for precipitation to terminate the reaction and remove residual DEMA and chloride byproducts. The precipitated polymer was collected by filtration, redissolved in 4 mL of DMF, and then poured into 200 mL of a water-ethanol mixture again for precipitation. The above redissolution-precipitation purification steps were repeated three times to ensure complete removal of impurities. The resulting modified polymer was dried in a forced-air drying oven at 40°C for 24 hours. Nuclear magnetic resonance (NMR) analysis showed that the total amount of C=C double bond defects in the product at this point was 2.0 mol%.

[0054] The sample was then redissolved in DMF and stirred overnight at room temperature. The polymer solution was then cast onto a glass substrate. The wet film was first placed in a vacuum oven and dried at 60°C for 12 hours to remove the solvent, followed by vacuum annealing at 120°C for another 12 hours to improve crystallinity. After cooling, it was peeled off from the substrate to obtain a modified polymer film with a thickness of approximately 30 µm. d 33 | is 29.7 ± 1.3 pC N -1 .

[0055] Comparative Example 3: Weigh 2.4 g of P(VDF-TrFE-CFE) 69 / 28 / 3 mol% terpolymer powder (a non-relaxing ferroelectric polymer) and dissolve it in 40 mL of DMF. Stir overnight to ensure complete dissolution. Then, add 1 mL of DEMA as a reaction reagent. Place the reaction vessel in an oil bath under a nitrogen atmosphere, set the magnetic stirring speed to 700 rpm, and conduct the dehydrochlorination reaction at a constant temperature of 40°C. Adjust the C=C double bond defects in the final product by controlling the reaction time to 18 hours. After the reaction, pour the reaction solution into 800 mL of a water-ethanol mixture for precipitation to terminate the reaction and remove residual DEMA and chloride byproducts. Collect the precipitated polymer by filtration, redissolve it in 4 mL of DMF, and then pour it into 200 mL of a water-ethanol mixture again for precipitation. Repeat the above redissolution-precipitation purification steps three times to ensure complete removal of impurities. The resulting modified polymer was dried in a forced-air drying oven at 40°C for 24 hours. Nuclear magnetic resonance (NMR) analysis showed that the total amount of C=C double bond defects in the product at this point was 2.0 mol%.

[0056] The sample was then redissolved in DMF and stirred overnight at room temperature. The polymer solution was then cast onto a glass substrate. The wet film was first placed in a vacuum oven and dried at 60°C for 12 hours to remove the solvent, followed by vacuum annealing at 120°C for another 12 hours to improve crystallinity. After cooling, it was peeled off from the substrate to obtain a modified polymer film with a thickness of approximately 30 µm. d 33 |36.0±1.0 pC N -1 .

[0057] It should be noted that in this embodiment, the modified polymer was characterized by NMR, and then the integral area of ​​the characteristic peak was calculated to determine the molar ratio of VDF to TrFE in the copolymer, or to quantitatively calculate the C=C double bond content. For modified samples containing C=C double bonds, the characteristic peak area A was used. i The ratio is calculated based on the following formula for double bond content:

[0058] In the formula, Ai is the integral area of ​​the chemical shift peak, corresponding to the chemical shift ranges of 2.2-2.5 ppm, 2.5-3.2 ppm, 4.8-5.8 ppm and 5.8-6.4 ppm, respectively.

[0059] First, the modified polymers obtained in the embodiments of the present invention were characterized by XRD and FTIR: like Figure 1As shown, the crystal structure changes before and after the introduction of C=C double bond modification in Example 1 of this invention, indicating that the pure film (unmodified P(VDF-TrFE-CFE) directly cast into a film) is a typical relaxor ferroelectric polymer, and its internal crystalline region is basically dominated by a disordered helical relaxor phase. Therefore, in 2 θ A single characteristic diffraction peak is observed at approximately 18.3°. In Example 1, the crystal diffraction peak of the double-bonded modified P(VDF-TrFE-CFE) shows significant broadening, with a peak at approximately 18.3°. θ A shoulder peak corresponding to the all-intrans ferroelectric phase appears at approximately 19.2°. ， This indicates that long-range order has been established within the system.

[0060] like Figure 2 The figure shows the conformational changes of the molecule before and after the introduction of the C=C double bond in Example 1 of the present invention. In Example 1, the molecule is located at 1285 cm⁻¹. -1 and 840 cm -1 The intensity of the characteristic absorption peak representing the all-trans conformation increases significantly, located at 508 cm⁻¹. -1 The decrease in the intensity of the characteristic absorption peak representing the helical conformation further reflects the enhanced long-range ferroelectric order within the polymer. The mechanism mainly involves the reduction of steric hindrance after the introduction of double bond defects by the dehydrochlorination reaction, thereby lowering the energy barrier between the helical and all-trans conformations. Therefore, the double bond defects introduced by the dehydrochlorination reaction successfully induced the formation of quasi-isomorphic phase boundaries in the P(VDF-TrFE-CFE) relaxor ferroelectric polymer.

[0061] Furthermore, in Example 6, the polymer material prepared using P(VDF-TrFE-CTFE) as a raw material was structurally verified to have also induced the formation of quasi-isomorphic phase boundaries.

[0062] like Figure 3 As shown, the hysteresis loop changes before and after the introduction of C=C double bond modification in Example 1 of this invention. The pure film exhibits typical relaxor ferroelectric behavior, with its hysteresis loop displaying a narrow "waist" characteristic, indicating that the polarization reversal response within the material is still dominated by short-range ordered polar microregions. In Example 1, the hysteresis loop gradually evolves into a rectangular loop with typical ferroelectric characteristics, further verifying the establishment of long-range order in the double bond modified P(VDF-TrFE-CFE).

[0063] Unlike studies on P(VDF-TrFE) binary non-relaxed ferroelectric copolymers (Nat. Commun., 2025, 16:8758), the NaOH-induced dehydrofluorination reaction mainly occurs on the VDF monomer. The resulting C=C double bond defect disrupts the long-range ferroelectric structural order of the polymer, making the disordered 3 / 1 helical conformation more energy-stable. In contrast, in the chlorine-containing ferroelectric ternary copolymer with relaxant properties proposed in this invention, the bulky chlorine-containing monomer itself acts as a large-size structural defect. Its physical pinning effect effectively increases the interchain spacing and confines the long-range ferroelectric domain size to the nanoscale, thus promoting the formation of the relaxant ferroelectric phase. Therefore, in this study, the dehydrochlorination reaction weakens the steric hindrance effect brought by the chlorine-containing monomer, which is beneficial to the stability of the all-trans conformation (e.g., ...). Figure 1-2 Macroscopically, this manifests as a significant increase in remanent polarization intensity (Pr) and coercive field (Ec) (e.g. Figure 3 ).

[0064] The core structural commonality between the ternary copolymer powders involved in Examples 2-6 and P(VDF-TrFE-CFE) in Example 1 lies in the fact that they are both typical relaxor ferroelectric ternary copolymers. Their molecular chains contain relatively large-volume CFE / CTFE monomers. The introduction of these large-volume groups disrupts the long-range order of the original ferroelectric phase, causing the material to be dominated by a disordered helical relaxor phase in its initial state. Therefore, in the dehydrochlorination reaction, if the content of C=C double bonds introduced into the polymer molecular chain is less than 0.5 mol%, the number of defects is too small to effectively reduce the steric hindrance caused by the bulky chlorine-containing monomers (such as CFE or CTFE), and cannot drive the system from the helical relaxation phase to the all-trans ferroelectric phase. If the content of C=C double bonds introduced into the polymer molecular chain is greater than 6.0 mol%, excessive dehydrochlorination will lead to the formation of continuous conjugated double bond segments in the molecular chain, destroying the ordered crystal structure of the polymer and thus reducing the piezoelectric properties. Therefore, by controlling the reaction time to introduce an appropriate amount of C=C double bond defects, the steric hindrance caused by the bulky CFE groups can be effectively reduced. This reduction in steric hindrance lowers the energy barrier for the transition from the helical to the all-trans conformation in these systems. This also theoretically and experimentally proves that by introducing double bond defects into relaxor ferroelectric polymers, the coexistence of the all-trans ferroelectric phase and the helical relaxation phase can be successfully induced, thereby constructing a quasi-isomorphic phase boundary (MPB).

[0065] Meanwhile, the piezoelectric properties of the modified polymers obtained in the embodiments and comparative examples of the present invention were tested under conditions without an external electric field: like Figure 4The figure shows the strain curves under an electric field before and after the introduction of C=C double bond modification in Example 1. The slope corresponds to the reverse compressive effect. d 33 The value, displayed on the pure membrane, is the measured value. d 33 | 50.8 pm V -1 In Example 1, the C=C double bond modified P(VDF-TrFE-CFE) | d 33 | Reached 128.4 pm V -1 .

[0066] like Figure 5 As shown, this illustrates the relationship between PVDF and C=C double bond modification before and after the introduction of C=C double bonds in Example 1. d 33 In contrast, in direct piezoelectric effect measurements... d 33 Verification was conducted. Specifically, the pure membrane measured... d 33 Approximately 50.8 pC N -1 The double-bond modified P(VDF-TrFE-CFE) film measured in Example 1 d 33 Up to -129.5 pC N -1 Combined with the appendix Figure 4 The result obtained from the inverse piezoelectric effect test | d 33 The results reflect the influence of the construction of the quasi-isomorphic phase boundary induced by double bonds on the intrinsic properties of P(VDF-TrFE-CFE). d 33 The improvement.

[0067] Furthermore, other chlorine-containing ferroelectric ternary copolymers with relaxation properties (such as P(VDF-TrFE-CTFE)) can also achieve stable construction of quasi-isomorphic phase boundaries by introducing C=C double bond defects. Near this phase boundary, the energy barrier for polarization reversal is significantly lowered, resulting in a several-fold enhancement of the piezoelectric response under both the direct and inverse piezoelectric effects (strain curve slope). Therefore, as long as the material system satisfies the structural characteristics of a relaxor ferroelectric ternary copolymer and a chlorine-containing bulk unit, and employs the same double bond defect engineering strategy, the construction of quasi-isomorphic phase boundaries can be reproduced, and intrinsic phase boundaries can be obtained. d 33 |Significant improvement; specific details in different embodiments| d 33 The numerical differences depend only on defect concentration, phase boundary ratio, and test conditions, but the universality of the mechanism ensures the effectiveness of this strategy for similar materials. Therefore, in the same improvement mechanism, the intrinsic properties of Examples 2-6 are essentially the same. d33 Compared to the intrinsic properties of pure membranes d 33 It improved by about 2-3 times, showing a significant improvement effect.

[0068] Furthermore, compared to the significant improvement in piezoelectric performance in the embodiments, the intrinsic properties of Comparative Examples 1-3 are significantly improved. d 33 Compared to pure membrane d 33 Instead, a decrease occurred. This is because the P(VDF-TrFE-CFE) components selected for the comparative examples (such as 75 / 20 / 5, 79.5 / 15.6 / 4.9, or 69 / 28 / 3 mol%) belong to normal ferroelectric polymers with non-relaxation properties. In their unmodified initial state, the system itself is already dominated by a highly long-range ordered all-trans ferroelectric phase. In this normal ferroelectric system, the C=C double bonds introduced by the dehydrochlorination reaction no longer play the role of "lowering the potential barrier and inducing quasi-isomorphic phase boundaries," but instead act as structural impurities and random defects, disrupting the originally perfect long-range ordered ferroelectric crystalline regions and leading to a decrease in the overall crystallinity of the material. Ultimately, this resulted in no significant improvement in the piezoelectric response performance of the modified polymer in the comparative examples.

[0069] In summary, this invention constructs a quasi-isomorphic phase boundary in a ferroelectric polymer containing chlorine elements and possessing relaxation properties through intramolecular defect engineering. This allows for the coexistence of an all-trans ferroelectric phase and a helical relaxant phase, thereby improving the intrinsic piezoelectric response performance of the ferroelectric polymer material. The process is stable and controllable. Furthermore, this invention eliminates the dependence of existing high-performance ternary relaxant ferroelectric polymers on an external high-voltage DC bias field (e.g., 40-60 MV / m), solving the breakdown safety hazards and high system energy consumption problems caused by high bias fields. It enables direct application of devices under zero bias fields.

[0070] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of protection of this invention and its equivalents, this invention also intends to include these modifications and variations.

Claims

1. An application of a ferroelectric polymer material in a flexible piezoelectric device, which generates an intrinsic piezoelectric response in the absence of an external bias electric field; the preparation method of the ferroelectric polymer material includes the following steps: (1) A ferroelectric ternary copolymer containing chlorine with relaxation properties is dissolved in an organic solvent to obtain a polymer solution; under a protective atmosphere, the pH of the polymer solution is adjusted to the range of 8-11 by a weakly alkaline organic reagent, and then a dehydrochlorination reaction is carried out at a reaction temperature of 20-50℃. At the same time, C=C double bond defects are introduced into the polymer molecular chain by adjusting the reaction time to form a quasi-isomorphic phase boundary in which the anti-ferroelectric phase and the helical relaxation phase coexist in the material; wherein, the content of C=C double bond defects introduced into the polymer molecular chain is 0.5-6.0 mol%; the ferroelectric ternary copolymer containing chlorine with relaxation properties is polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene or polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene; in the polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene, the content of trifluoroethylene is 30-75 mol% and the content of chlorofluoroethylene is 3-10 mol%. mol%; in the polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene, the trifluoroethylene content is 30~75 mol%, and the trifluorochloroethylene content is 3~10 mol%; the weakly basic organic reagent is N,N-diethylmethylamine; (2) After the reaction is completed, the reaction solution in step (1) is precipitated and purified, and then cast into a film to obtain a ferroelectric polymer material with intrinsic piezoelectric response in the absence of an external bias electric field.

2. The application of the ferroelectric polymer material according to claim 1 in flexible piezoelectric devices, characterized in that, In the polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene, the content of trifluoroethylene is 30~40 mol% and the content of chlorofluoroethylene is 3~7 mol%.

3. The application of the ferroelectric polymer material according to claim 1 in flexible piezoelectric devices, characterized in that, The content of C=C double bond defects introduced into the polymer molecular chain is 1.0~4.0 mol.

4. The application of the ferroelectric polymer material according to claim 1 in flexible piezoelectric devices, characterized in that, By adjusting the reaction time to 1-40 hours, C=C double bond defects are introduced into the polymer molecular chain of the terpolymer.

5. The application of the ferroelectric polymer material according to claim 1 in flexible piezoelectric devices, characterized in that, The organic solvent is dimethylformamide, dimethyl sulfoxide, methyl ethyl ketone, or cyclohexanone; the concentration of the polymer solution is 200 mg / mL. -1 ~5000 mg mL -1 .

6. The application of the ferroelectric polymer material according to claim 1 in flexible piezoelectric devices, characterized in that, The precipitation purification specifically includes: pouring the reaction solution from step (1) into a mixture of water and ethanol for precipitation, collecting the precipitate, redissolving it in an organic solvent, and then pouring it back into the mixture of water and ethanol for precipitation.

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