A resilient ferroelectric body, a method for producing the same, and use thereof

Abstract

The application relates to the technical field of ferroelectric materials, and discloses a resilient ferroelectric body as well as a preparation method and application thereof. The resilient ferroelectric body comprises a ferroelectric material and a crosslinking agent; the mass ratio of the ferroelectric body to the crosslinking agent is 3-50:1; and the crosslinking density of the resilient ferroelectric body is 0.01-20%. The preparation method comprises the following steps: dissolving and mixing the ferroelectric material and the crosslinking agent, and then performing covalent crosslinking to obtain the resilient ferroelectric body. In the application, a trace amount of crosslinking agent is mixed with the ferroelectric material to obtain a ferroelectric body with a network structure and reversible inversion of ferroelectric domains; finally, the obtained ferroelectric body has excellent resilience and flexibility, higher residual polarization strength, higher thermal stability, shorter switching time, and excellent comprehensive performance.

Description

Technical Field

[0001] This invention relates to the field of ferroelectric materials technology, specifically to a resilient ferroelectric material, its preparation method, and its application. Background Technology

[0002] Ferroelectrics are widely used due to their spontaneous polarization reversal and excellent electromechanical coupling properties. With the development of wearable and flexible electronics technologies, ferroelectrics need to possess elasticity in addition to flexibility to better meet the operational requirements of devices.

[0003] Traditional ferroelectric materials include oxide ferroelectrics and polyvinylidene fluoride (PVDF) polymer ferroelectrics. Among them, oxide ferroelectrics are prone to brittle fracture and failure when subjected to external strain. PVDF polymer ferroelectrics have greater plasticity and can withstand strains exceeding 500%. However, due to intermolecular slippage, their deformation cannot be recovered after the stress is removed, making them unable to meet the working requirements.

[0004] Commonly used structural engineering or material blending methods for elasticizing materials can produce many side effects. In structural engineering, rigid device units are connected by elastic structures that can withstand strain, such as islands, folds, or serpentine structures, to achieve overall elasticity of the device. However, this can lead to problems such as modulus mismatch between the elastic structure and the device unit, difficulty in miniaturization, and complex fabrication processes. Blending refers to obtaining the ability to withstand strain by physically blending rigid materials with elastomers. In addition to the problem of different material interfaces, physical blending of ferroelectrics and elastomers can also cause polarization problems. Since the ferroelectric domains of the ferroelectric are randomly oriented after blending, they need to be polarized to achieve a consistent orientation in order to obtain better ferroelectricity.

[0005] The resistivity of elastomers is much higher than that of ferroelectrics. According to the principle of voltage division in series circuits, the electric field is mainly distributed on the elastomer, resulting in a relatively low effective electric field for the ferroelectric. To effectively polarize the ferroelectric particles in the composite material, the electric field strength needs to be further increased, but the increased electric field is still mostly distributed on the elastomer. On the other hand, the breakdown field strength of the elastomer is not more than three orders of magnitude higher than the polarization field strength of the ferroelectric, causing the elastomer to break down before the ferroelectric particles are effectively polarized. Furthermore, during polarization, the ferroelectric particles with accumulated charge attract or repel each other. Since the modulus of inorganic ferroelectrics is three to five orders of magnitude higher than that of elastomers, the ferroelectric particles compress the elastomer, causing electromechanical breakdown.

[0006] Chemical crosslinking of linear molecules can effectively prevent slippage between molecular chains. However, while the high crosslinking density of typical chemical crosslinking increases the modulus, tensile strength, and electrical breakdown strength of the resulting polymer / composite material, it also significantly reduces the material's tensile properties and elastic recovery. Therefore, materials obtained from linear ferroelectrics through ordinary crosslinking are difficult to use in wearable electronic devices due to their poor tensile properties, high modulus, and lack of elastic recovery. Thus, developing a low-modulus, flexible ferroelectric material with high elastic recovery is crucial for the wearable device field.

[0007] CN105622871A discloses a cross-linked fluoropolymer-based dielectric elastomer composite material and its preparation method. The method uses 60-90 parts of fluoropolymer matrix, 8-40 parts of functional cross-linking agent and 1-3 parts of catalyst to obtain an all-organic dielectric elastomer composite material with low driving voltage and large electroinduced deformation. The material has large deformation under low electric field, but it does not have ferroelectric properties. Summary of the Invention

[0008] This invention addresses the problems of insufficient resilience, irreversible deformation, and inability to rebound in ferroelectric materials by providing a resilient ferroelectric material that maintains excellent ferroelectricity while exhibiting high resilience, resulting in superior overall performance.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A resilient ferroelectric material, comprising a ferroelectric material and a crosslinking agent; wherein the mass ratio of the ferroelectric material to the crosslinking agent is 3-50:1.

[0011] The crosslinking density of the resilient ferroelectric is 0.01-20%, and its structure includes a resilient micro-crosslinked network structure and ferroelectric domains, which are connected to the network structure by covalent bonds.

[0012] In some embodiments, according to the reaction formula, the crosslinking density (ρ) is defined as the proportion of the number of crosslinking points (v) to the total number of repeating units (N0) in the polymer ferroelectric material before crosslinking, i.e., ρ = v / N0. For example, in the structure of the crosslinked 1,1-difluoroethylene-trifluoroethylene copolymer P(VDF-TrFE), ρ = v / N0 = (x+y) / (m+n).

[0013]

[0014] Where m and n are the proportions of repeating VDF and TrFE units in the P(VDF-TrFE) structure, and x and y are the proportions of repeating units in the crosslinking portion of the crosslinking agent. Since the crosslinking density is relatively low, it is determined by the amount of polymer ferroelectric and crosslinking agent before crosslinking. In this application, the crosslinking density is calculated based on the assumption that the crosslinking agent has completely undergone the crosslinking reaction.

[0015] In some embodiments, the crosslinking density is expressed according to the amount of raw materials input. Specifically, when the ferroelectric material is P(VDF-TrFE) and the crosslinking agent is an amino compound containing a diamine structure, the crosslinking density ρ = 100% × 2(a / M1) / (b / M2). Wherein, M1 is the average molecular weight of a single repeating unit in P(VDF-TrFE), M2 is the molecular weight of the crosslinking agent, and a:b is the mass ratio of the crosslinking agent to P(VDF-TrFE).

[0016] This invention utilizes linear polymer ferroelectric materials and crosslinking agents to form a ferroelectric material possessing both a network structure and reversibly inverted ferroelectric domains. The linear polymer ferroelectric material imparts high ferroelectricity to the elastic ferroelectric material, while the network structure formed by micro-crosslinking with a crosslinking density of 0.1%-20% is stable, soft, and elastic, thus endowing the ferroelectric material with elasticity while retaining its ferroelectricity. The network structure is formed by the linear polymer ferroelectric material itself, allowing for the designability of its chemical structure and avoiding performance mismatch issues caused by dissimilar material interfaces. Furthermore, it can meet the requirements for miniaturized device dimensions. The reversibly inverted ferroelectric domains originate from the polar phase in the crystalline region of the ferroelectric polymer material, resulting in a ferroelectric material with excellent resilience and flexibility, as well as higher remanent polarization, thermal stability, and shorter switching time.

[0017] The ferroelectric material includes polyvinylidene fluoride (PVDF) ferroelectric materials and / or nylon ferroelectric materials. Preferably, the ferroelectric material is a PVDF ferroelectric material.

[0018] In some embodiments, the polyvinylidene fluoride-based ferroelectric material comprises a copolymer formed from any one or more monomers selected from 1,1-difluoroethylene, vinyl fluoride, polyvinyl methyl ether, trifluorochloroethylene, trifluoroethylene, hexafluoropropylene, tetrafluoroethylene, and chlorofluoroethylene.

[0019] In some embodiments, the polyvinylidene fluoride-based ferroelectric material includes a self-polymer of 1,1-difluoroethylene, i.e., polyvinylidene fluoride; or, it includes a binary, ternary, or quaternary copolymer formed from 1,1-difluoroethylene and any one of vinyl fluoride, polyvinyl methyl ether, trifluorochloroethylene, trifluoroethylene, hexafluoropropylene, tetrafluoroethylene, or chlorofluoroethylene.

[0020] More preferably, the ferroelectric material is a copolymer of 1,1-difluoroethylene-trifluoroethylene (P(VDF-TrFE)).

[0021] The crosslinking agent includes one or more of amino compounds, polyphenolic compounds, peroxides, and polythiophenolic compounds.

[0022] The amino compounds include, but are not limited to, one or more of polyoxyethylene diamine, bis(aminopropyl)-terminated polydimethylsiloxane, and α-ω diamines with 6-30 intermediate carbon atoms.

[0023] The polyphenolic compounds include, but are not limited to, any one or more of hydroquinone, bisphenol A, bisphenol AF, bisphenol-terminated polyethylene glycol, and bisphenol-terminated polydimethylsiloxane.

[0024] The peroxides include, but are not limited to, benzoyl peroxide, bis(tert-butyl peroxide), dicumyl peroxide, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylhexane, 2,5-bis(butylperoxy)-2,5-dimethylhexane, and 1,4-bis(tert-butylperoxyisopropylbenzene).

[0025] In some embodiments, the crosslinking agent is one or more of polyoxyethylene diamine, bis(3-aminopropyl)-terminated poly(dimethylsiloxane), 1,4-bis-tert-butylperoxyisopropylbenzene, and 1,2-poly(butadiene) oligomers.

[0026] Preferably, in some embodiments, the polyoxyethylene diamine has a molecular weight of 500-5000; the bis(3-aminopropyl)-terminated poly(dimethylsiloxane) has a molecular weight of 1000-5000. These macromolecules can act as crosslinking agents and plasticizers, thereby reducing the modulus and increasing resilience, thus meeting the requirements of wearable devices for soft and elastic materials.

[0027] More preferably, in some embodiments, the polyoxyethylene diamine has a molecular weight of 1000; and the bis(3-aminopropyl)-terminated poly(dimethylsiloxane) has a molecular weight of 2500.

[0028] Furthermore, polyoxyethylene diamine with a molecular weight of 1000 is preferred. The resilient ferroelectric material prepared by this crosslinking agent and polyvinylidene fluoride has better overall ferroelectric and resilient properties.

[0029] In some embodiments, the crosslinking density of the resilient ferroelectric is 0.1-20%, where crosslinking density refers to the proportion of crosslinking points to the linear polymer repeating units. Excessive crosslinking density will affect the material's resilience. The inventors discovered that achieving micro-crosslinking within the system is necessary to balance the material's resilience and ferroelectricity.

[0030] Preferably, in some embodiments, the crosslinking density of the resilient ferroelectric is 0.2-10%, such as 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or any value between them.

[0031] More preferably, the crosslinking density of the resilient ferroelectric is 0.3-5%.

[0032] More preferably, the crosslinking density of the resilient ferroelectric is 0.43-2.16%.

[0033] In some embodiments, the mass ratio of the ferroelectric material to the crosslinking agent is 3-50:1; preferably 8-20:1. For example, the mass ratio can be 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, or any value between them.

[0034] Preferably, the mass ratio of the ferroelectric material to the crosslinking agent is 5-35:1, more preferably 8-35:1.

[0035] In this invention, a low dose of crosslinking agent is mixed with ferroelectric materials to achieve micro-crosslinking inside the ferroelectric materials while maintaining ferroelectricity. However, excessive crosslinking leads to a decrease in the elasticity of the finished product and a reduction in crystallinity, resulting in a decrease in residual polarization or even the disappearance of ferroelectricity.

[0036] Preferably, in a system using polyethylene oxide diamine as a crosslinking agent, the crosslinking density is 0.1-5%. If it exceeds 5%, the elasticity of the material will decrease, and even the ferroelectricity will decrease.

[0037] The elastic recovery rate of the resilient ferroelectric is 10-400%, the resilience is above 60%, and the remanent polarization is 3 μC / cm. 2 above.

[0038] The elastic recovery rate is defined as the ratio of the length recovered by the sample after the tensile stress is removed to the original length, i.e., elastic recovery rate = 100% × (L1 - L2) / (L1 - L0), where L... o L1 is the original straight length of the sample without external force; L2 is the length of the sample after external force is applied; L3 is the straight length of the sample after a certain period of time after the external force is removed.

[0039] The present invention also provides a method for preparing the resilient ferroelectric material, comprising the steps of: mixing ferroelectric material and crosslinking agent and then performing covalent crosslinking to obtain the resilient ferroelectric material; or, mixing ferroelectric material, crosslinking agent and inorganic ferroelectric material and then performing covalent crosslinking to obtain the resilient ferroelectric material.

[0040] The mixing includes any one of the following methods: solution mixing, melt blending, extrusion, injection molding, etc.

[0041] In some embodiments, the solvents used in the dissolution and mixing process include one or more of N,N-dimethylformamide, cyclohexane, trifluoroacetic acid, cyclohexanone, diethyl carbonate, isoflavone, etc. After dissolution and mixing, the solvent is removed by evaporation or drying.

[0042] In some embodiments, specifically, after dissolving and mixing, the solution is cast into a film, and after most of the solvent evaporates at room temperature, it is placed in a vacuum oven at 60-80°C for 4-24 hours to dry.

[0043] The covalent crosslinking includes chemical crosslinking and / or irradiation crosslinking.

[0044] The chemical crosslinking includes the steps of: thermally crosslinking the mixture at 100-350°C for more than 1 minute; in some embodiments, the mixture is thermally crosslinked at 200-350°C for more than 30 minutes, such as at 220°C, 240°C, 260°C, 280°C, 300°C, 320°C, and 340°C, with thermal crosslinking times of more than 40 minutes, more than 1 hour, more than 1.5 hours, more than 2 hours, and more than 2.5 hours, respectively.

[0045] The radiation crosslinking includes the step of placing the mixture in any one of the following environments: ultraviolet light, visible light, near-infrared light, electrons, seeds, alpha particles, beta particles, X-rays, or gamma rays for electromagnetic radiation crosslinking.

[0046] In some embodiments, the preparation method further includes mixing with a co-crosslinking agent.

[0047] In some embodiments, the co-crosslinking agent includes one or more of 1,2-poly(butadiene) oligomers, bis(meth)acrylate-terminated polyethylene glycol, glyceryl acrylate, pentaerythritol acrylate, triphosphate acrylate, isocyanate acrylate, and acryloxytriazine.

[0048] This invention also provides the application of the aforementioned resilient ferroelectric material in wearable devices. This material exhibits excellent softness and high resilience, making it suitable for manufacturing wearable devices requiring high flexibility and elasticity.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] (1) The present invention mixes a small amount of crosslinking agent with ferroelectric material to obtain a ferroelectric material that has both a resilient network structure and reversible ferroelectric domains. The resulting ferroelectric material has excellent resilience and flexibility, as well as higher residual polarization intensity, thermal stability, and shorter switching time, resulting in excellent overall performance.

[0051] (2) The ferroelectric material of the present invention has excellent resilience, flexibility and ferroelectric properties, and can be used in the preparation of wearable devices. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the network structure of the resilient ferroelectric material obtained in Embodiment 1 of the present invention.

[0053] Figure 2 The X-ray near-edge absorption spectra of the resilient ferroelectrics prepared in Examples 1-2 are shown. A represents Example 1, and B represents Example 2.

[0054] Figure 3 The X-ray photoelectron spectrum of the resilient ferroelectric material prepared in Example 1 is shown in Figure A, which is the full spectrum. Figure B is the fine spectrum of nitrogen.

[0055] Figure 4 Stress-strain curves of the resilient ferroelectric material prepared in Example 1 and pure P (VDF-TrFE).

[0056] Figure 5 The inset shows the cyclic stress-strain curve of the resilient ferroelectric material prepared in Example 1, with the inset showing the cyclic stress-strain curve of the pure P(VDF-TrFE) sample.

[0057] Figure 6 The fatigue test results are for the resilient ferroelectric material prepared in Example 1 and the commercial fluororubber.

[0058] Figure 7 The results are from the ferroelectric fatigue test of the resilient ferroelectric material prepared in Example 1.

[0059] Figure 8 Dielectric constant-temperature curves of the resilient ferroelectric material prepared in Example 1 and pure P(VDF-TrFE).

[0060] Figure 9 The DSC curve of the resilient ferroelectric material prepared in Example 1.

[0061] Figure 10 Stress-strain curves of resilient ferroelectrics with different crosslinking densities prepared in Examples 1-2.

[0062] Figure 11 The crystallinity of the resilient ferroelectrics with different crosslinking densities prepared in Examples 1-2.

[0063] Figure 12 The stress-strain curve of the resilient ferroelectric material prepared in Example 3.

[0064] Figure 13 The cyclic stress-strain curve of the resilient ferroelectric material prepared in Example 3 under 120% tension.

[0065] Figure 14 Hysteresis curve of PE under 100% tensile strain for the resilient ferroelectric material prepared in Example 3.

[0066] Figure 15 The cyclic stress-strain curve of the resilient ferroelectric material prepared in Example 4 under 100% tensile strain.

[0067] Figure 16 Hysteresis curve of PE at 80% tensile strain for the resilient ferroelectric material prepared in Example 4.

[0068] Figure 17 The cyclic stress-strain curve of the resilient ferroelectric material prepared in Example 5 under 190% tensile strain.

[0069] Figure 18 Hysteresis curve of PE at 150% tensile strain for the resilient ferroelectric material prepared in Example 5.

[0070] Figure 19 The cyclic stress-strain curve of the resilient ferroelectric material prepared in Example 6 under 150% tensile strain.

[0071] Figure 20 Hysteresis curve of PE at 120% tensile strain for the resilient ferroelectric material prepared in Example 6.

[0072] Figure 21 This is a schematic diagram of the fabrication process of the fully elastic device in Application Example 1.

[0073] Figure 22 The results of tensile fatigue tests on the fully elastic device in Application Example 1 under 70% cyclic strain are shown.

[0074] Figure 23 The PE hysteresis curves of the fully elastic device in Example 1 under different electric field intensities when the strain is 0.

[0075] Figure 24 The PE hysteresis curves of the fully elastic device in Example 1 at different frequencies are shown.

[0076] Figure 25 The PE hysteresis curve, saturation polarization intensity curve, residual polarization intensity curve and coercive field curve of the fully elastic device in Example 1 under different tensile strains are shown. Detailed Implementation

[0077] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0078] All raw materials used in the following specific embodiments were purchased commercially, and the copolymer P(VDF-TrFE) of 1,1-difluoroethylene-trifluoroethylene was purchased from Arkema Piezotech. FC45, in which the molar ratio of VDF to TrFE is 55 / 45 mol%. The crosslinking density is calculated as follows:

[0079] The average molecular weight of a single repeating unit in P(VDF-TrFE) is M1, and the molecular weight of the crosslinking agent is M2. The mass ratio of the crosslinking agent to P(VDF-TrFE) is a:b. In the crosslinking system, the crosslinking density ρ = 100% × 2(a / M1) / (b / M2).

[0080] The mechanical properties of the material were tested in accordance with GB / T 528-2009.

[0081] Example 1

[0082] 0.2 g of P(VDF-TrFE) and 0.02 g of polyoxyethylene diamine (PEG-diamine) with a molecular weight of 1000 Da were dissolved in 1 mL of N,N-dimethylformamide, and then the dissolved solution was cast in a mold to prepare a mixed film.

[0083] After evaporating most of the solvent from the mixed membrane at room temperature, it was placed in a vacuum oven and dried overnight at room temperature. Then, it was dried at 60°C for 6 hours, followed by crosslinking at 250°C for 0.5 hours. Finally, it was cooled to room temperature to obtain an elastic ferroelectric material with a thickness of 60 μm, hereinafter referred to as crosslinked P(VDF-TrFE). The mass ratio of ferroelectric material to crosslinking agent was 10:1, corresponding to a crosslinking density of 1.44%. The reaction formula of the crosslinking system is shown below:

[0084]

[0085] In this crosslinked P(VDF-TrFE), it is assumed that all amino groups are completely crosslinked into imine bonds, and the crosslinking point is twice that of the raw material PEG. The VDF to TrFE ratio (n / m) in P(VDF-TrFE) is 55 / 45 mol%, and the average molecular weight of the repeating unit is M1 = 0.55 × 64.034 + 0.45 × 82.024 = 72.1295 (the molecular weight of VDF is 64.034, and the molecular weight of TrFE is 82.024).

[0086] Therefore, in a crosslinking system where the mass ratio of the crosslinking agent raw material PEG diamine (molecular weight M1 = 1000) to P(VDF-TrFE) is a:b (1:10 in this example), the crosslinking density ρ = 100% × 2(a / M2 / (b / M1) = 100% × 2 × (1 / 1000) / (10 / 72.1295) = 1.44%.

[0087] A schematic diagram of the prepared resilient ferroelectric network structure is shown below. Figure 1 As shown, 1 represents a ferroelectric domain and 2 represents a crosslinking point. This material exhibits excellent resilience, can shrink back after stretching, and has stable performance.

[0088] The cross-linked P(VDF-TrFE) and PEG-diamine raw materials prepared in Example 1 were subjected to X-ray near-edge absorption spectroscopy (XANES) testing, and the results are as follows: Figure 2 In section A, no peak of PEG-diamine was observed in the crosslinked P(VDF-TrFE), indicating that the crosslinking agent PEG-diamine had basically completely reacted. X-ray photoelectron spectroscopy (XPS) was performed on both samples, and the results... Figure 3 As shown, Figure A is the full spectrum and Figure B is the fine spectrum of nitrogen elements, which also proves that the peak of the raw material diamine has completely disappeared, indicating that the crosslinking is complete.

[0089] Figure 4 The stress-strain curves of cross-linked P(VDF-TrFE)a with a cross-linking density of 1.44% and pure P(VDF-TrFE)b are presented. It can be seen that the elongation at break and modulus of cross-linked P(VDF-TrFE) are significantly lower than those of pure P(VDF-TrFE), the necking phenomenon disappears, and the stress-strain curve of cross-linked P(VDF-TrFE) exhibits the mechanical properties of an elastomer.

[0090] Figure 5Cyclic stress-strain curves of crosslinked P(VDF-TrFE) with a crosslinking density of 1.44% are presented. The inset shows the cyclic stress-strain curve of the pure P(VDF-TrFE) sample. It can be clearly seen that the resilient ferroelectric material obtained in this embodiment is an elastic material with obvious resilience. Compared with the cyclic stress-strain curve of P(VDF-TrFE), after ten cycles of stretching and unloading, when the maximum strain is 125%, the elastic recovery rate can still reach more than 90%, showing better elastic properties.

[0091] The resilient ferroelectric material prepared in Example 1 was compared with commercially available fluororubber (Daikin, Japan, brand name: DAI-EL). TM G-801, whose main component is P(VDF-HFP) elastomer, underwent fatigue testing for comparison, and the results are as follows: Figure 6 As shown, the resilience of crosslinked P(VDF-TrFE) in Example 1 is essentially comparable to that of commercially available elastomers. The test results show that the elastic recovery rate of both the crosslinked P(VDF-TrFE) film and the commercial fluoroelastomer film decreases with increasing cycle number, but stabilizes after 200 cycles. Compared to the elastic recovery rate of fluororubber after 200 cycles (>80%), the elastic recovery rate of crosslinked P(VDF-TrFE) is slightly lower (>70%), indicating a slight difference in elastic recovery performance.

[0092] Figure 7 The ferroelectric fatigue test results of the resilient ferroelectric material prepared in Example 1 show that the polarization direction of the ferroelectric domains in the resilient ferroelectric material can be flipped more than 5 million times without a significant decrease in the residual polarization intensity.

[0093] Figure 8 The results of the temperature-dependent dielectric constant test of cross-linked P(VDF-TrFE) and pure P(VDF-TrFE) are shown. It can be seen that both exhibit a sudden change in dielectric constant at 63℃, meaning that the cross-linked P(VDF-TrFE) film still has the same Curie transition as pure P(VDF-TrFE) and remains a ferroelectric material.

[0094] Figure 9 The DSC curve of the prepared crosslinked P(VDF-TrFE) shows obvious glass transition (-20℃), Curie transition (63℃) and crystallization melting peak (153℃), proving that the crosslinked film still has similar thermal properties to pure P(VDF-TrFE) and its ferroelectric properties will remain good.

[0095] Example 2

[0096] According to the preparation process parameters of Example 1, the amounts of P(VDF-TrFE) and polyoxyethylene diamine with a molecular weight of 1000 Da were changed to ratios of 100:3, 100:5, 100:8, 100:12, and 100:15, respectively, resulting in crosslink densities of 0.43%, 0.72%, 1.15%, 1.73%, and 2.16%, respectively. The calculation method for crosslink density was the same as in Example 1.

[0097] Figure 2 In section B, X-ray near-edge absorption spectra (XANES) of cross-linked P (VDF-TrFE) and PEG-diamine raw materials with different cross-linking densities are given. It can also be seen that in the resilient ferroelectric materials with different cross-linking densities, the cross-linking agent raw materials are basically completely reacted and the cross-linking is complete.

[0098] Figure 10 Stress-strain curves of resilient ferroelectrics with different crosslinking densities P(VDF-TrFE) are presented. It can be seen that as the crosslinking density increases, the material modulus continuously decreases. The decrease in modulus is conducive to the realization of elasticity, the yield point disappears, and the material gradually transitions from plastic deformation to elastic deformation.

[0099] Figure 11 The crystallinity of resilient ferroelectrics with different crosslinking densities P(VDF-TrFE) obtained by DSC testing is presented. It can be seen that the crystallinity of the crosslinked film decreases with increasing crosslinking density. The crystallinity of the ferroelectric film greatly determines its polarization intensity. Increasing the crosslinking density strengthens the effect of the crosslinking network on crystal refinement and disrupts the ordered arrangement of molecular chains, thus reducing crystallinity. Therefore, a suitable crosslinking density is required to balance elasticity and ferroelectricity.

[0100] Example 3

[0101] 1 g of P(VDF-TrFE) and 0.3 g of bis(3-aminopropyl)-terminated poly(dimethylsiloxane) with a molecular weight of 2500 Da were dissolved in 3 mL of cyclohexane. The mass ratio of ferroelectric material to crosslinking agent was 10:3, and the corresponding crosslinking density was 3%. The dissolved solution was then spin-coated onto a conductive substrate to prepare a hybrid film.

[0102] After evaporating most of the solvent from the mixed membrane at room temperature, it was placed in a vacuum oven and dried at room temperature overnight. Then it was dried at 60°C for 6 hours, and then heated to 250°C for 0.5 hours for crosslinking. Finally, it was cooled to room temperature to obtain an elastic ferroelectric material with a thickness of 1 μm.

[0103] Figure 12-14 The test curve of the resilient ferroelectric material obtained in Example 3 is shown. Figure 12 The stress-strain curve; Figure 13 The cyclic stress-strain curve under 120% tension is shown. Figure 14The hysteresis curve of PE under 100% tensile strain shows that the elastic ferroelectric material still has good ferroelectric properties under large strain.

[0104] Example 4

[0105] 15g of 1,1-difluoroethylene-trifluoroethylene copolymer and 0.3g of 1,4-di-tert-butylperoxyisopropylbenzene were mixed and added to an injection extruder, and then the mixture was obtained in block form through different molds and fixtures.

[0106] The mixture was placed in a vacuum oven and crosslinked at 320°C for 1 hour, then cooled to room temperature. The mass ratio of ferroelectric material to crosslinking agent was 50:1, resulting in an elastic ferroelectric with a crosslinking density of 2%.

[0107] Figure 15-16 The test curves for the resilient ferroelectric material obtained in Example 4 are shown. Figure 15 Cyclic stress-strain curves of a resilient ferroelectric material under 100% tensile strain; Figure 16 The hysteresis curve of PE under 80% tensile strain shows that the elastic ferroelectric material still has good ferroelectric properties under large strain.

[0108] Example 5

[0109] 2g of a copolymer of 1,1-difluoroethylene-trifluoroethylene-trifluorochloroethylene and 0.3g of 1,4-di-tert-butylperoxyisopropylbenzene were dissolved in 4mL of cyclohexanone, and then the dissolved solution was cast in a mold to prepare a mixed film.

[0110] After evaporating most of the solvent from the mixed membrane at room temperature, it was placed in a vacuum oven and dried at room temperature overnight. Then it was dried at 60°C for 6 hours, and then heated to 250°C for 0.5 hours for crosslinking. After that, it was cooled to room temperature. The mass ratio of ferroelectric material to crosslinking agent was 20:3, and an elastic ferroelectric material with a crosslinking density of 10% and a thickness of 32 μm was obtained.

[0111] Figure 17-18 The test curve of the resilient ferroelectric material obtained in Example 5 is shown. Figure 17 The cyclic stress-strain curve is shown at 190% tensile strain. Figure 18 The hysteresis curve of PE under 150% tensile strain shows that the elastic ferroelectric material still has good ferroelectric properties under large strain, and is a relaxor ferroelectric material.

[0112] Example 6

[0113] 3g of nylon-5 copolymer and 0.3g of 1,4-di-tert-butylperoxyisopropylbenzene were dissolved in 6mL of a mixed solvent of trifluoroacetic acid and acetone (molar ratio 6:4), and then the dissolved solution was cast in a mold to prepare a mixed film.

[0114] After evaporating most of the solvent from the mixed membrane at room temperature, it was placed in a vacuum oven and dried overnight at room temperature. Then it was dried at 60°C for 6 hours, and then heated to 220°C for 0.5 hours for crosslinking. After that, it was cooled to room temperature. The mass ratio of ferroelectric material to crosslinking agent was 7.5:1, resulting in an elastic ferroelectric material with a crosslinking density of 3% and a thickness of 80 μm.

[0115] Figures 19-20 The test curves for the resilient ferroelectric material obtained in Example 6 are shown. Figure 19 The cyclic stress-strain curve is shown at 150% tensile strain. Figure 20 The hysteresis curve of PE under 120% tensile strain shows that the elastic ferroelectric material obtained from cross-linked nylon also exhibits good ferroelectric properties under large strain. Comparative Example 1: No cross-linking agent added, no cross-linking step performed.

[0116] 0.2 g of polyvinylidene fluoride was dissolved in 1 mL of N,N-dimethylformamide, and then the dissolved solution was cast in a mold to prepare an organic film.

[0117] After evaporating most of the solvent from the organic membrane at room temperature, it was placed in a vacuum oven and dried at room temperature overnight. Then it was dried at 60°C for 6 hours and then cooled to room temperature to obtain a ferroelectric material with a thickness of 60 μm.

[0118] Comparative Example 2

[0119] 0.2 g of 1,1-difluoroethylene-trifluoroethylene and 0.003 g of polyoxyethylene diamine with a molecular weight of 1000 Da were dissolved in 1 mL of N,N-dimethylformamide, and then the dissolved solution was cast in a mold to prepare a mixed film.

[0120] After evaporating most of the solvent from the mixed film at room temperature, it was placed in a vacuum oven and dried overnight at room temperature. Then, it was dried at 60°C for 6 hours, and then heated to 250°C for 0.5 hours for crosslinking. After cooling to room temperature, the mass ratio of ferroelectric material to crosslinking agent was 66.7:1, resulting in an elastic ferroelectric with a crosslinking density of 0.1% and a thickness of 60 μm. Its stress-strain curve still showed a yield point, indicating that it still exhibited soft plastic deformation rather than elastic deformation due to the low crosslinking density.

[0121] Comparative Example 3

[0122] 0.2 g of polyvinylidene fluoride and 0.4 g of polyoxyethylene diamine with a molecular weight of 1000 Da were dissolved in 1 mL of N,N-dimethylformamide, and then the dissolved solution was cast in a mold to prepare a mixed film.

[0123] After evaporating most of the solvent from the mixed film at room temperature, it was placed in a vacuum oven and dried overnight at room temperature. Then it was dried at 60°C for 6 hours, and then heated to 250°C for 0.5 hours for crosslinking. After that, it was cooled to room temperature. The mass ratio of ferroelectric material to crosslinking agent was 0.5:1, resulting in an elastic ferroelectric with a crosslinking density of 40% and a thickness of 60 μm. Its stress modulus increased to 300 MPa and its yield strain was 3%, exhibiting typical hard plastic deformation characteristics.

[0124] The ferroelectric materials prepared in Examples 1, 3-6, and Comparative Examples 1-3 were cut into rectangular strips and subjected to mechanical property tests. The test results are shown in Table 1. Tensile strain: The ferroelectric thin films were tested according to GBT528-2009, cut to standard dimensions, and then tested on a universal material sample testing machine. Saturation polarization, remanent polarization, and coercive electric field data were obtained using a Premiere II instrument (manufacturer: Radiant, USA). Test conditions: at room temperature, applied in increments of 20 and 40 MV / m to the polymer film, with a test frequency range of 0.05–10 kHz.

[0125] Table 1 Performance data of Examples 1, 3-6 and Comparative Examples 1-3

[0126]

[0127] Application examples

[0128] Hysteresis loop: Electrodes are deposited on both sides of a ferroelectric thin film, and then the hysteresis loop is tested using a Sawyer-Tower circuit. For example... Figure 21 As shown, the fabrication process of the fully elastic device specifically includes: spin-coating a 5% dextran solution onto a silicon wafer; after the solvent evaporates, spin-coating a mixture of a copolymer of 1,1-difluoroethylene-trifluoroethylene (number-average molecular weight of 240,000, purchased from Piezotech, France) and a polyoxyethylene diamine with a molecular weight of 1,000 (mass ratio of 10:1) onto the dextran; after the solvent has completely evaporated in a vacuum, crosslinking is performed at 240°C for 1 hour under vacuum to obtain a crosslinked polymer layer; a layer of liquid gallium is brushed onto the crosslinked polymer layer using a mask; then a layer of polydimethylsiloxane is cured on the liquid gallium; the dextran is then dissolved and removed with water; finally, another layer of liquid gallium is brushed onto the other side of the crosslinked polymer layer in a direction perpendicular to the upper layer of liquid gallium to obtain the fully elastic device.

[0129] Tensile fatigue testing was performed on the fully elastic device under 70% cyclic strain, such as... Figure 22 As shown, the fully elastic device can still recover more than 70% after more than eight million tensile cycles.

[0130] Figure 23The PE hysteresis curves of the fully elastic device with zero strain under different electric field intensities are shown. Among them, s is the PE hysteresis curve with an electric field intensity of 40MV / m, t is the PE hysteresis curve with an electric field intensity of 80MV / m, u is the PE hysteresis curve with an electric field intensity of 119MV / m, v is the PE hysteresis curve with an electric field intensity of 160MV / m, w is the PE hysteresis curve with an electric field intensity of 178MV / m, x is the PE hysteresis curve with an electric field intensity of 198MV / m, y is the PE hysteresis curve with an electric field intensity of 218MV / m, and z is the PE hysteresis curve with an electric field intensity of 240MV / m.

[0131] Figure 24 The PE hysteresis curves of the fully elastic device at different frequencies are given, where j is the PE hysteresis curve at 100Hz, k is the PE hysteresis curve at 200Hz, m is the PE hysteresis curve at 500Hz, n is the PE hysteresis curve at 1000Hz, p is the PE hysteresis curve at 2000Hz, q is the PE hysteresis curve at 5000Hz, and r is the PE hysteresis curve at 10000Hz.

[0132] Figure 25 The curves show the PE hysteresis, saturation polarization, remanent polarization, and coercive field of a fully elastic device under different tensile strains. Specifically, A represents the PE hysteresis curve at 0% tensile strain, B at 5% tensile strain, C at 10% tensile strain, D at 20% tensile strain, E at 30% tensile strain, F at 40% tensile strain, G at 50% tensile strain, H at 60% tensile strain, J at 70% tensile strain, K represents the coercive field as a function of strain, L represents the saturation polarization as a function of strain, and M represents the remanent polarization as a function of strain.

[0133] As can be seen from the above, the fully elastic device obtained in this test example can still maintain good elasticity at 125% cyclic tensile strain. As the frequency increases, the saturation polarization intensity and remanent polarization intensity of the fully elastic device decrease.

[0134] In summary, the network-structured elastic ferroelectric material prepared by this invention exhibits high elasticity while maintaining good ferroelectric properties. Specifically, increasing the amount of crosslinking agent leads to an increase in crosslinking density, gradually transforming the deformation from plastic to elastic, while slightly reducing ferroelectricity. In Comparative Example 1, since no crosslinking agent was added, the product had no crosslinking points and remained in plastic deformation with a noticeable yield point. In Comparative Example 2, the crosslinking density was still relatively low, resulting in plastic deformation. In Comparative Example 3, the crosslinking density was too high, leading to a significant increase in modulus and strength, a noticeable yield point, and a decrease in elongation at break. Simultaneously, the low crystallinity resulted in a drastic decrease in ferroelectricity.

Claims

1. A resilient ferroelectric body, characterized by, The resilient ferroelectric body comprises a ferroelectric material and a crosslinking agent, and has a micro-crosslinked network structure with resilience. The mass ratio of the ferroelectric material to the crosslinking agent is 3-50:1; the crosslinking density of the resilient ferroelectric body is 0.4-5%; the elastic strain of the resilient ferroelectric body is 5-400%, and the number of tensile strain cycles is 10 6 above; The ferroelectric material comprises a polyvinylidene fluoride-based ferroelectric material and / or a nylon-based ferroelectric material. The crosslinking agent is any one or more of polyoxyethylene diamine, bis(3-aminopropyl) terminated poly(dimethylsiloxane), 1,4-bis-tert-butyl peroxyisopropyl benzene. The crosslinking density ρ = 100% × 2(a / M1) / (b / M2), the mass ratio of the crosslinking agent to the ferroelectric material is a:b, M1 is the average molecular weight of a single repeating unit of the ferroelectric material, and M2 is the molecular weight of the crosslinking agent. The preparation of the resilient ferroelectric body comprises the steps of: dissolving and mixing the ferroelectric material and the crosslinking agent, and then performing chemical crosslinking to obtain the resilient ferroelectric body; and the chemical crosslinking comprises the steps of: heat-crosslinking the mixture at 100-350°C for 30 min or more.

2. The resilient ferroelectric body of claim 1, wherein, The polyvinylidene fluoride-based ferroelectric material comprises a copolymer formed by any one or more of 1,1-difluoroethylene, fluoroethylene, polyvinyl methyl ether, chlorotrifluoroethylene, trifluoroethylene, hexafluoropropylene, tetrafluoroethylene, and chlorofluoroethylene.

3. The method of claim 1 or 2, wherein the ferroelectric material is a relaxor ferroelectric material. The preparation of the resilient ferroelectric body comprises the steps of: dissolving and mixing the ferroelectric material and the crosslinking agent, and then performing chemical crosslinking to obtain the resilient ferroelectric body; and the chemical crosslinking comprises the steps of: heat-crosslinking the mixture at 100-350°C for 30 min or more.

4. The method of claim 3, wherein the ferroelectric material is a relaxor ferroelectric material. The preparation further comprises mixing a co-crosslinking agent.

5. The method of claim 4, wherein the ferroelectric material is a relaxor ferroelectric material. The co-crosslinking agent comprises any one or more of 1,2-poly(butadiene) oligomer, bis(meth)acrylate-terminated polyethylene glycol, glyceryl acrylate, pentaerythritol acrylate, phosphoric acid triacrylate, isocyanate acrylate, acryloxytriazine, polyamino compound, polyphenol compound, and polythiol compound.

6. Use of the resilient ferroelectric body according to claim 1 or 2 in a wearable device.

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