PVDF-based elastic ferroelectric material and preparation method and application thereof

Abstract

The invention provides a PVDF-based elastic ferroelectric material and a preparation method and application thereof, and relates to the technical field of ferroelectric materials. A ferroelectric crystal phase region of the PVDF-based elastic ferroelectric material is protected to the maximum extent, and a uniform three-dimensional elastic network structure formed by firm C-C bonds is constructed in an amorphous region by a PVDF-based ferroelectric polymer and a crosslinking sensitizer through radiation crosslinking; the PVDF-based elastic ferroelectric material has excellent ferroelectricity, great flexibility and elasticity, proper strength and excellent fatigue resistance at the same time. According to the preparation method of the PVDF-based elastic ferroelectric material, the technical bottlenecks of thermal crosslinking and photo-crosslinking are fundamentally overcome through a mild, pure and uniform radiation process, so that controllable preparation of the PVDF-based elastic ferroelectric material with excellent ferroelectricity, great flexibility and elasticity, proper strength and excellent fatigue resistance becomes reality; the preparation method is simple, efficient and high in universality, and is very suitable for large-scale industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ferroelectric materials, in particular to a PVDF-based elastic ferroelectric material, a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of modern science and technology, material science is increasingly widely used in the fields of electronics, energy, medical treatment, etc. Among them, ferroelectric materials have spontaneous polarization characteristics and can undergo polarization reversal under the action of an external electric field. This characteristic makes them have important application value in the fields of memory, sensors, actuators, etc. However, traditional ferroelectric materials usually have high brittleness and lack of elasticity, which limits their application in emerging fields such as flexible electronics and wearable devices. Therefore, developing materials with excellent elasticity and ferroelectric properties has become one of the current research hotspots.

[0003] The research on elastic ferroelectric materials originated from the demand for modification of traditional ferroelectric materials. Traditional ferroelectric materials such as barium titanate (BaTiO3) and lead zirconate titanate (PZT) have excellent ferroelectric properties, but they are highly brittle and difficult to withstand large deformations, which limits their application in flexible electronic devices. In order to solve this problem, researchers began to explore the design idea of combining ferroelectricity with elasticity. By introducing flexible molecular chains or nanostructures and cross-linking to form a network structure, the mechanical properties of the material can be effectively improved, allowing it to maintain ferroelectricity while having certain elasticity.

[0004] Currently, thermal cross-linking and photo-crosslinking are mainly used to cross-link PVDF-based ferroelectric bodies and cross-linking agents to form a three-dimensional network structure, thereby giving the ferroelectric polymer elastic recovery. PVDF-based polymers usually include crystalline regions and amorphous regions, and their ferroelectricity is derived from the regular β phases formed by the molecular chains in the crystalline regions. The Curie temperature of these materials is usually between room temperature and 140 ℃, and the melting point is usually around 150 ℃. Thermal cross-linking requires high temperature (240 ℃) and long time (1 h), which can destroy the directional arrangement of the ferroelectric domains of the PVDF-based ferroelectric body, causing the crystalline regions to transform from polar β phases to non-polar α phases or amorphous state. This directly leads to a decrease in the ferroelectric properties of the material. Although photo-crosslinking can be carried out at room temperature and for a shorter time, the crystalline regions inside the PVDF-based polymer will strongly scatter ultraviolet light, preventing the light from penetrating deep into the material, resulting in high cross-linking degree on the surface of the ferroelectric material and low or even no cross-linking inside. This leads to uneven mechanical properties of the PVDF-based ferroelectric body. In addition, in order to ensure the cross-linking reaction, an excess of photo-initiator is usually added. However, these initiators are difficult to completely consume or remove after the reaction, and will remain in the PVDF-based ferroelectric body, leading to poor ferroelectric properties and mechanical properties of the PVDF-based ferroelectric body.

[0005] Therefore, how to develop a more efficient, simple and suitable for large-scale industrial preparation method of elastic ferroelectric material with excellent flexibility and ferroelectricity and suitable strength and fatigue resistance is a problem to be solved at present. SUMMARY

[0006] In view of the deficiencies in the prior art, the present application provides a PVDF-based elastic ferroelectric material and a preparation method and application thereof. The PVDF-based elastic ferroelectric material has excellent flexibility and ferroelectricity, and also has suitable strength and fatigue resistance. The preparation method of the elastic ferroelectric material has the advantages of simplicity, efficiency and strong universality, and is very suitable for large-scale industrial production.

[0007] The specific technical scheme of the present application is as follows: In a first aspect, the present application provides a PVDF-based elastic ferroelectric material having a three-dimensional network structure formed by a PVDF-based ferroelectric polymer and a cross-linking sensitizer through radiation cross-linking. In the three-dimensional network structure: the crystalline region of the PVDF-based ferroelectric polymer serves as a ferroelectric functional phase for maintaining the stability of ferroelectricity through overall movement during deformation; and the amorphous region of the PVDF-based ferroelectric polymer and the cross-linking sensitizer are connected by forming carbon-carbon covalent bonds through radiation-induced free radicals, for jointly forming an elastic skeleton bearing tensile stress.

[0008] In a possible implementation, the PVDF-based ferroelectric polymer includes one or more of P(VDF-TrFE), P(VDF-CTFE), P(VDF-TrFE-CFE) and P(VDF-TrFE-CTFE).

[0009] In a possible implementation, the cross-linking sensitizer includes polyethylene glycol diacrylate (PEGDA) and / or polyethylene glycol dimethacrylate (PEGDMA), the molecular weight of the polyethylene glycol diacrylate is 200-5000, and the molecular weight of the polyethylene glycol dimethacrylate is 200-5000.

[0010] In a possible implementation, the mass ratio of the cross-linking sensitizer to the PVDF-based ferroelectric polymer is 1:(0.1-100).

[0011] In a second aspect, the present application provides a preparation method of the above-mentioned PVDF-based elastic ferroelectric material, comprising the following steps: S1, blending a PVDF-based ferroelectric polymer and a cross-linking sensitizer in a solvent to form a mixed solution; S2, forming a thin film from the mixed solution of step S1 and drying to form a precursor thin film; S3, irradiating the precursor film of step S2 with an energy beam to make the precursor film absorb energy to generate free radicals, and to initiate a free radical recombination crosslinking reaction between the amorphous region of the PVDF-based ferroelectric polymer and the crosslinking sensitizer to form carbon-carbon covalent bond crosslinking points, so as to obtain an elastic ferroelectric material with a three-dimensional network structure.

[0012] In a possible implementation, in step S1, the solvent includes one or more of cyclohexanone, DMF, acetonitrile, acetone and isofuroleone, the mass / volume ratio of the PVDF-based ferroelectric polymer and the solvent in the mixed solution is 10-300 mg / mL, and the mass / volume ratio of the crosslinking sensitizer and the solvent is 3-150 mg / mL.

[0013] In a possible implementation, in step S1, the blending temperature is 10-50 ℃, the blending time is greater than 5 min, the blending mode is that the PVDF-based ferroelectric polymer solution and the crosslinking sensitizer solution are blended, the configuration process of the PVDF-based ferroelectric polymer solution is that the PVDF-based ferroelectric polymer is dissolved in the solvent, the dissolving temperature is 10-60 ℃, and the dissolving time is greater than 1 min; and the configuration process of the crosslinking sensitizer solution is that the crosslinking sensitizer is dissolved in the solvent, the dissolving temperature is 10-50 ℃, and the dissolving time is greater than 1 min.

[0014] In a possible implementation, in step S2, the film preparation mode is flow casting or spin coating, the spin coating includes first-stage spin coating and second-stage spin coating performed in sequence, the rotation speed of the first-stage spin coating is greater than 10 rpm, and the time is greater than 1 s, the rotation speed of the second-stage spin coating is greater than 200 rpm, and the time is greater than 10 s; and the drying includes fume hood drying and vacuum drying performed in sequence, the fume hood drying temperature is 0-90 ℃, the time is 6-48 h, the vacuum drying temperature is 35-75 ℃, and the time is 2-24 h.

[0015] In a possible implementation, in step S3, the energy beam includes β a ray, gamma a ray, X one or more of a ray, an ion beam, an electron beam and a neutron beam.

[0016] In a third aspect, the present application provides application of the above-mentioned PVDF-based elastic ferroelectric material in a flexible electronic device, a wearable device, a flexible sensor or an energy collection device.

[0017] On the basis of common sense in the art, the above-mentioned embodiments can be combined arbitrarily.

[0018] The reagents and raw materials used in the present application are commercially available.

[0019] The positive progress effect of the present application is that: The present application provides a PVDF-based elastic ferroelectric material, a preparation method and application thereof. The ferroelectric crystal phase region of the PVDF-based elastic ferroelectric material is maximally protected, and a uniform three-dimensional elastic network structure composed of firm C-C bonds is constructed in the amorphous region by radiation crosslinking of a PVDF-based ferroelectric polymer and a crosslinking sensitizer, so that the PVDF-based elastic ferroelectric material simultaneously has excellent ferroelectricity, large flexibility, suitable strength and excellent fatigue resistance. The preparation method of the PVDF-based elastic ferroelectric material fundamentally overcomes the technical bottlenecks of thermal crosslinking and photo-crosslinking through a mild, pure and uniform radiation process, so that the controllable preparation of the PVDF-based elastic ferroelectric material which simultaneously has excellent ferroelectricity, large flexibility, suitable strength and excellent fatigue resistance becomes a reality. The preparation method is simple, efficient and has strong universality, and is very suitable for large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Stress-strain curve of the PVDF-based elastic ferroelectric material prepared for Examples 1-4.

[0021] Figure 2 Stress-strain curve of the PVDF-based elastic ferroelectric material prepared for Examples 5 and 6.

[0022] Figure 3 Stress-strain curve of the PVDF-based elastic ferroelectric material prepared for Examples 2, 7 and 8.

[0023] Figure 4 Stress-strain curve of the PVDF-based elastic ferroelectric material prepared for Examples 9-13.

[0024] Figure 5 Stress-strain curve of the PVDF-based ferroelectric material prepared for Comparative Examples 1-3.

[0025] Figure 6 Cyclic stress-strain curve of the PVDF-based ferroelectric material prepared for Comparative Example 1.

[0026] Figure 7 Cyclic stress-strain curve of the PVDF-based ferroelectric material prepared for Example 1.

[0027] Figure 8 DSC graph of the PVDF-based ferroelectric material prepared for Example 1.

[0028] Figure 9 Electric hysteresis loop graph of the PVDF-based ferroelectric material prepared for Example 1.

[0029] Figure 10 Figure 6 is a graph of the hysteresis loop of the PVDF-based ferroelectric material prepared in Example 10. DETAILED DESCRIPTION

[0030] In order to make the above objectives, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation method and typical parameters of the present application, and are not used to limit the parameter range described in the present application, and the reasonable changes derived therefrom are still within the protection scope of the present application.

[0031] It should be noted that the endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and the values stated are approximate values. Ranges between the endpoints are included in the present application. The endpoints of the ranges and the values stated are approximate values. The endpoints of the ranges and the values stated are approximate values. Between the individual point values or the endpoints of the ranges, new ranges can be derived that are either entirely within the context of the present application or encompassing both limits of the context of the present application. These derived ranges are to be considered as disclosed herein.

[0032] Unless otherwise defined, all terms, symbols and other scientific terminology used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. In some cases, terms with commonly understood meanings are defined herein for clarity and / or for ready reference, and the inclusion of such definitions herein should not necessarily be construed to mean that the terms are in any way being redefined in such a manner as to depart from their normal or customary meanings as understood by those skilled in the art. The technical methods described or referenced herein are generally well known to those skilled in the art and are employed by conventional methods. Unless otherwise stated, the use of commercially available kits and reagents, instruments are carried out according to the protocols and parameters given by the manufacturer.

[0033] Terminology: Energy beam: In the context of the present application, energy beam refers to a stream of particles or electromagnetic waves generated by artificial or natural radiation sources, with high energy and capable of generating free radicals in the molecules of matter through ionization or excitation. It can be a stream of high-speed particles or high-frequency electromagnetic waves, which have the common characteristic of high enough energy to directly break the chemical bonds in the polymer molecular chain or crosslinking agent molecules, thereby generating active free radicals for forming crosslinking points. Unlike low-energy photons such as ultraviolet light or visible light, these energy beams have strong penetration ability and can penetrate deep into the material to achieve uniform crosslinking in the bulk phase, rather than only acting on the surface of the material.

[0034] Radiation crosslinking: In the context of the present application, radiation crosslinking refers to the chemical process of forming covalent bonds between polymer chains through energy beam irradiation, thereby constructing a three-dimensional network structure.

[0035] The specific technical solutions of the present application are: In a first aspect, the present application provides a PVDF-based elastic ferroelectric material having a three-dimensional network structure formed by cross-linking a PVDF-based ferroelectric polymer and a cross-linking sensitizer by irradiation, wherein: crystalline regions of the PVDF-based ferroelectric polymer serve as a ferroelectric functional phase for maintaining stability of ferroelectricity by bulk movement during deformation; and amorphous regions of the PVDF-based ferroelectric polymer and the cross-linking sensitizer are connected by carbon-carbon covalent bonds formed by irradiation-induced free radicals, for jointly forming an elastic skeleton that bears tensile stress.

[0036] In the PVDF-based elastic ferroelectric material provided by the present application, the PVDF-based ferroelectric polymer and the cross-linking sensitizer form a three-dimensional network structure by cross-linking through irradiation, overcoming the defects of high-temperature damage to material structure in thermal cross-linking and uneven cross-linking and residual initiators in photo-cross-linking. The cross-linking through irradiation can be performed at room temperature or near room temperature, avoiding the high-temperature environment of 240℃ required by thermal cross-linking. The process of cross-linking through irradiation at room temperature perfectly preserves the integrity of the crystalline regions as the “ferroelectric functional phase”, thereby ensuring that the PVDF-based elastic ferroelectric material has excellent and stable ferroelectricity. The cross-linking through irradiation directly generates free radicals by ionization or excitation of the PVDF-based ferroelectric polymer molecules through high-energy particle bombardment, without the need for any small-molecule photo-initiator. Since there is no introduction and residual of external initiators, the three-dimensional network structure formed is very pure. This solves the problem of degradation of electrical properties such as high dielectric loss, poor insulation, and low breakdown field strength caused by residual initiators in photo-cross-linking, providing a “clean” matrix for the excellent ferroelectricity of the material. The high-energy rays (such as electron beams and gamma rays) used in cross-linking through irradiation have strong penetrating ability and can easily penetrate the semi-crystalline structure of PVDF to reach every corner of the material. This uniform irradiation in the bulk phase ensures uniform generation of free radicals in the amorphous regions of the entire PVDF, and further forms a three-dimensional network with uniform cross-linking density. This uniform network is the “elastic skeleton that bears tensile stress”. It avoids the gradient structure of “hard outside and soft inside” caused by insufficient penetration in photo-cross-linking, thereby making the material exhibit uniform flexibility, high elastic recovery rate, and excellent fatigue resistance on a macroscopic level, and not easily damaged by stress concentration under repeated deformation. The carbon-carbon covalent bonds formed by cross-linking through irradiation have high bond energy and high stability, and the cross-linking points are uniformly distributed, ensuring the stability of the cross-linking points; at the same time, the uniformly distributed cross-linking points can effectively transmit stress, avoid molecular chain slipping, and enable the material to maintain a certain mechanical strength under large deformation.

[0037] In one possible implementation, the PVDF-based ferroelectric polymer includes one or more of P(VDF-TrFE), P(VDF-CTFE), P(VDF-TrFE-CFE), and P(VDF-TrFE-CTFE). The above PVDF-based ferroelectric polymers are all PVDF-based semi-crystalline polymers, and the amorphous regions thereof can be cross-linked with a cross-linking sensitizer to form an elastic network, and the crystalline regions thereof provide ferroelectricity. Non-PVDF monomer units (such as TrFE, CTFE, and CFE) in the copolymer can destroy the regular crystallization of PVDF, increase the proportion of amorphous regions, provide more reaction sites for radiation cross-linking, facilitate the formation of a uniform three-dimensional network, and improve the elastic recovery rate.

[0038] P(VDF-TrFE), which is a binary copolymer, has a high crystallinity and a high spontaneous polarization strength, and is suitable for scenarios with high requirements for ferroelectric properties, such as non-volatile memories and high-precision ferroelectric sensors. P(VDF-CTFE), which is a binary copolymer, contains CTFE units, can reduce the crystallinity of the material, increase the dielectric constant, and maintain a certain ferroelectricity, and is suitable for scenarios with dielectric-ferroelectric synergy, such as energy storage capacitors and dielectric elastomer actuators. P(VDF-TrFE-CFE), which is a ternary copolymer, presents a relaxor ferroelectric characteristic after the introduction of CFE units, has a wide temperature range of ferroelectric response and low dielectric loss, and is suitable for sensors and flexible piezoelectric energy harvesters in a wide temperature range. P(VDF-TrFE-CTFE), which is a ternary copolymer, combines the high polarization of TrFE and the dielectric regulation of CTFE, can precisely customize ferroelectric, dielectric, and mechanical properties by adjusting the monomer ratio, and is suitable for complex scenarios with multiple performance synergies.

[0039] In one possible implementation, the cross-linking sensitizer includes polyethylene glycol diacrylate (PEGDA) and / or polyethylene glycol dimethacrylate (PEGDMA), the molecular weight of the polyethylene glycol diacrylate being 200-5000, and the molecular weight of the polyethylene glycol dimethacrylate being 200-5000. The acrylate / methacrylate groups at the ends of the PEGDA and PEGDMA molecules contain unsaturated C=C double bonds. These double bonds are extremely easy to be activated to generate free radicals under the action of radiation, thereby serving as efficient "cross-linking bridges" to quickly combine with the free radicals generated in the amorphous regions of the PVDF-based polymer to form firm carbon-carbon covalent bonds. Moreover, the polyethylene glycol (PEG) segments in the PEGDA / PEGDMA molecules are long-chain and flexible ether bond (-C-O-C-) structures. When they are integrated into a three-dimensional network as bridging units between cross-linking points, the flexibility and mobility of the molecular chains are greatly increased, which can significantly reduce the modulus of the PVDF-based elastic ferroelectric material, increase the elongation at break, and improve the elastic recovery rate. The molecular weight of the polyethylene glycol diacrylate and the polyethylene glycol dimethacrylate is limited to 200-5000, which provides an interval for regulating the performance of the PVDF-based elastic ferroelectric material. When the molecular weight of the polyethylene glycol diacrylate and the polyethylene glycol dimethacrylate is 200-700, the segments are shorter, the bridges between the cross-linking points are shorter, and the network formed is more compact. A material with higher strength and relatively larger modulus can be prepared, which is suitable for flexible devices that require certain support. When the molecular weight of the polyethylene glycol diacrylate and the polyethylene glycol dimethacrylate is 1000-5000, the PEG flexible segments are longer, providing longer and highly stretchable "springs" between two cross-linking points, which can greatly improve the elongation at break and the elasticity of the material. A rubber-like elastomer that is extremely soft and can withstand huge deformation is prepared, which is very suitable for wearable devices that require large stretching.

[0040] In a possible implementation, the mass ratio of the cross-linking sensitizer to the PVDF-based ferroelectric polymer is 1:(0.1-100). The mass ratio of the cross-linking sensitizer to the PVDF-based ferroelectric polymer is 1:(0.1-100), so that the application can prepare a series of materials with different properties. When the mass ratio of the cross-linking sensitizer to the PVDF-based ferroelectric polymer is 1:(50-100), a small amount of cross-linking sensitizer is introduced to form a sparse "micro-crosslinking" network, which plays a role in strengthening, toughening and anti-creep; it can moderately improve the mechanical strength and dimensional stability of the PVDF-based polymer while maintaining the original high crystallinity and excellent ferroelectricity of the PVDF-based polymer to the maximum extent. This is applicable to application scenarios that are extremely demanding on ferroelectric performance but need to improve the brittleness or plasticity of the PVDF-based ferroelectric polymer. When the mass ratio of the cross-linking sensitizer to the PVDF-based ferroelectric polymer is 1:(1-50), the cross-linking network has the least interference with the crystalline region, can maximize the crystallinity of PVDF and the integrity of the ferroelectric domain while obtaining good resilience, and thus obtain the highest residual polarization strength and other ferroelectric parameters. When the mass ratio of the cross-linking sensitizer to the PVDF-based ferroelectric polymer is 1:(0.1-1), a large amount of cross-linking sensitizer is added to form a dense three-dimensional cross-linking network, so that the PVDF-based ferroelectric material exhibits low elongation at break, high modulus and poor resilience.

[0041] Preferably, the mass ratio of the cross-linking sensitizer to the PVDF-based ferroelectric polymer is 1:(0.5-20). When the mass ratio of the cross-linking sensitizer to the PVDF-based ferroelectric polymer is 1:(0.5-20), the best balance between the ferroelectricity and the elasticity of the PVDF-based elastic ferroelectric material can be established: near the ratio of 1:20, the sparse cross-linking network maximizes the integrity of the PVDF crystalline region while imparting significant elasticity to the material, thereby maintaining excellent ferroelectric performance; and near the ratio of 1:0.5, the higher cross-linking density builds a more dense elastic skeleton, so that the material exhibits high resilience and fatigue resistance like rubber, while ensuring the ferroelectric function.

[0042] In a possible implementation, the elastic strain of the elastic ferroelectric material is 2%-800%, and the elastic recovery rate is ≥50%.

[0043] In a second aspect, the application provides a preparation method of the PVDF-based elastic ferroelectric material. S1, blending the PVDF-based ferroelectric polymer and the cross-linking sensitizer in a solvent to form a mixed solution; In step S1, the PVDF-based ferroelectric polymer and the cross-linking sensitizer are blended in a solvent to ensure that they are uniformly mixed at the molecular level in the solution system, laying a foundation for the subsequent formation of a uniform and defect-free three-dimensional cross-linking network; S2, forming a film of the mixed solution of step S1 and drying to form a precursor film; In step S2, the mixed solution is formed into a film and dried to form a precursor film with a dense structure and no solvent residue, thereby avoiding side reactions or defects such as bubbles that may be caused by the solvent in subsequent irradiation, and facilitating the integrity of the structure and electrical reliability of the PVDF-based elastic ferroelectric material in subsequent PVDF-based elastic ferroelectric material. S3, irradiating the precursor film of step S2 with an energy beam to cause the precursor film to absorb energy and generate free radicals, thereby causing a free radical complex crosslinking reaction between the amorphous region of the PVDF-based ferroelectric polymer and the crosslinking sensitizer to form carbon-carbon covalent bond crosslinking points, and obtaining an elastic ferroelectric material with a three-dimensional network structure.

[0044] In step S3, the irradiation is performed at room temperature using an energy beam, thereby avoiding the destruction of the ferroelectric structure of the crystalline region of the PVDF-based ferroelectric polymer caused by the high temperature required for thermal crosslinking. The crystalline region of the PVDF-based ferroelectric polymer is preserved as a "ferroelectric functional phase", thereby ensuring the stability of the ferroelectricity of the PVDF-based elastic ferroelectric material under deformation. The high-energy particles in the energy beam directly excite the polymer and the sensitizer molecules to generate free radicals, without the need for any chemical initiator, thereby overcoming the problem of "excessive residual photoinitiator" in photo-crosslinking. The strong penetration ability of the high-energy rays in the energy beam overcomes the problem of uneven crosslinking caused by the scattering of ultraviolet light due to the semi-crystalline nature of PVDF in photo-crosslinking. The energy beam irradiation uniformly generates free radicals and forms crosslinking points throughout the thickness of the film, thereby constructing a uniform three-dimensional network. This uniform network is the microstructure basis for the material to exhibit high elastic recovery rate (≥50%), large elastic strain (2%-800%) and excellent fatigue resistance (hundreds of millions of cycles).

[0045] The preparation method of the PVDF-based elastic ferroelectric material provided by the present application uses a mild, pure and uniform irradiation process to construct a uniform three-dimensional elastic network structure composed of firm C-C bonds in the amorphous region while protecting the ferroelectric crystal phase of the PVDF-based polymer to the greatest extent. This method not only fundamentally overcomes the technical bottlenecks of thermal crosslinking and photo-crosslinking, but also enables the controllable preparation of PVDF-based elastic ferroelectric materials with excellent ferroelectricity, large flexibility, appropriate strength and excellent fatigue resistance. It is a simple, efficient and highly versatile preparation method that is very suitable for large-scale industrial production.

[0046] In one possible implementation, the solvent of step S1 includes one or more of cyclohexanone, DMF, acetonitrile, acetone and isofuroleone. The above-mentioned solvents have good solubility for the PVDF-based ferroelectric polymer and the crosslinking sensitizer, and can form a uniform, stable and phase-separated initial mixed solution.

[0047] In a possible implementation, in step S1, the mass / volume ratio of the PVDF-based ferroelectric polymer and the solvent in the mixed solution is 10-300 mg / mL, and the mass / volume ratio of the crosslinking sensitizer and the solvent is 3-150 mg / mL.

[0048] The solution concentration of the PVDF-based ferroelectric polymer is a core parameter affecting the film thickness. When the mass / volume ratio of the PVDF-based ferroelectric polymer and the solvent is 10-50 mg / mL, it is suitable for preparing an ultrathin and uniform film with a thickness of submicron to several microns. When the mass / volume ratio of the PVDF-based ferroelectric polymer and the solvent is 150-300 mg / mL, it is suitable for preparing a self-supporting thick film with a thickness of tens to hundreds of microns. The mass / volume ratio of the crosslinking sensitizer and the solvent is 3-150 mg / mL, which ensures that the crosslinking sensitizer can be completely dissolved and uniformly dispersed in the solution system.

[0049] In a possible implementation, the temperature of the blending in step S1 is 10-50 ℃, and the blending time is greater than 5 min. Blending at a temperature in the range of 10-50 ℃ for 5 min can effectively accelerate the relaxation and stretching of the molecular chain of the PVDF-based polymer, so that the PVDF-based polymer is fully dissolved, and it can also ensure that the crosslinking sensitizer is completely dispersed to form a uniform and stable mixed solution.

[0050] In a possible implementation, the blending manner in step S1 is to blend the PVDF-based ferroelectric polymer solution and the crosslinking sensitizer solution. The configuration process of the PVDF-based ferroelectric polymer solution is to dissolve the PVDF-based ferroelectric polymer in the solvent, the dissolving temperature is 10-60 ℃, and the dissolving time is greater than 3 min. The configuration process of the crosslinking sensitizer solution is to dissolve the crosslinking sensitizer in the solvent, the dissolving temperature is 10-50 ℃, and the dissolving time is greater than 1 min. In view of the distinct physical and chemical properties of the PVDF-based ferroelectric polymer and the crosslinking sensitizer, the strategy of separately dissolving in the solvent is adopted. The PVDF-based ferroelectric polymer generally needs a slightly higher temperature and a longer stirring time to be completely dissolved and the chain segment to be stretched. The crosslinking sensitizer is relatively sensitive to heat and shear force. Separately preparing the solution can provide sufficient and undisturbed dissolving conditions for the PVDF-based ferroelectric polymer, and can also minimize the risk of premature polymerization or degradation of the active double bond of the crosslinking sensitizer in the preparation stage, so as to ensure that the reaction activity is fully used in the key radiation crosslinking step.

[0051] In one possible implementation, the thin film preparation method in step S2 is either casting or spin coating. The spin coating includes a first-stage spin coating and a second-stage spin coating performed sequentially. The first-stage spin coating has a rotation speed greater than 10 rpm and a time greater than 1 s, while the second-stage spin coating has a rotation speed greater than 200 rpm and a time greater than 10 s. Spin coating is suitable for preparing small-area, ultra-thin, and highly uniform thin films on flat, rigid substrates, meeting the needs of microelectronic devices and high-end sensors. Casting is suitable for preparing large-area, thicker, and self-supporting thin films, making it easier to scale up production and meeting the requirements of applications such as flexible actuators and wearable devices that require both area and mechanical strength. The phased spin coating process helps to achieve the best balance between film thickness and quality: the first phase uses low-speed rotation to allow the solution enough time to flow under centrifugal force and completely cover the entire substrate, which helps to eliminate large air bubbles entrained in the mixed solution and form a preliminary uniform liquid film, providing an ideal starting point for the next phase of high-speed spin coating; the second phase uses the strong centrifugal force and surface tension generated by high-speed rotation to effectively eliminate any thickness fluctuations that may remain in the first phase and obtain a film with an extremely smooth surface and nanometer-scale uniform thickness.

[0052] In one possible implementation, the drying in step S2 includes sequential fume drying and vacuum drying, wherein the fume drying is performed at a temperature of 0-90 °C for 6-48 h, and the vacuum drying is performed at a temperature of 35-75 °C for 2-24 h. Step S2 employs a two-stage combination of fume hood drying and vacuum drying to achieve safe, thorough, and efficient solvent removal: the fume hood drying stage uses a drying temperature of 0-90 ℃ and a time of 6-48 h. The slow evaporation rate allows sufficient time for the solvent inside the solution to migrate to the surface and evaporate. The gentle drying process enables the PVDF-based ferroelectric polymer and crosslinking sensitizer molecules to arrange and stack in an orderly manner, forming a dense and uniformly composed gel film. The vacuum drying stage uses a drying temperature of 35-75 ℃ and a time of 2-24 h. Under vacuum conditions, the boiling point of the solvent is significantly reduced, allowing solvents that are difficult to volatilize under normal pressure, those with high boiling points, or residual solvents encapsulated within the polymer chains to be deeply and effectively removed. This ensures that the precursor film before final crosslinking is a pure polymer matrix.

[0053] In one possible implementation, the energy beam in step S3 includes β ray, gamma ray, X One or more of the following energy beams: X-rays, ion beams, electron beams, and neutron beams. All of the above energy beams can initiate crosslinking of PVDF-based ferroelectric polymers and crosslinking sensitizers at room temperature or low temperature, and can easily penetrate the semi-crystalline structure of PVDF to achieve uniform crosslinking in the bulk phase.

[0054] In a possible implementation, the absorbed dose of the irradiation in step S3 is 0.1-500 kGy. The absorbed dose directly determines the number of generated free radicals, and in turn determines the final crosslinking density. When the absorbed dose is 0.1-10 kGy, on the one hand, enough free radicals can be generated to form a minimum continuous network, thereby endowing the material with the most basic elastic recovery characteristics, and on the other hand, mild crosslinking (micro-crosslinking) can be achieved. This can moderately improve the mechanical integrity and creep resistance of the material without substantially impairing the crystallinity and ferroelectric properties of PVDF, and is suitable for scenarios where the ferroelectric properties are extremely high. When the absorbed dose is 10-100 kGy, the PVDF-based elastic ferroelectric material prepared can have excellent ferroelectric properties and high elasticity, and the mechanical properties and electrical properties thereof are in the best balanced state. When the absorbed dose is 100-500 kGy, sufficient and dense crosslinking can be achieved, so that the PVDF-based elastic ferroelectric material has high elasticity, and also takes into account the mechanical strength and toughness.

[0055] In a third aspect, the present application provides application of the above-mentioned PVDF-based elastic ferroelectric material in a flexible electronic device, a wearable device, a flexible sensor or an energy harvesting device.

[0056] On the basis of common general knowledge in the art, the above-mentioned embodiments can be combined arbitrarily.

[0057] In the following, the technical solutions of the present application are further illustrated by specific examples. All reagents used in the examples are commercially available or synthesized according to conventional methods, and can be used directly without further treatment. The instruments used in the examples are commercially available.

[0058] Example 1 This example provides a PVDF-based elastic ferroelectric material having a three-dimensional network structure formed by radiation crosslinking of a PVDF-based ferroelectric polymer and a crosslinking sensitizer. The PVDF-based ferroelectric polymer is P(VDF-TrFE), and the crosslinking sensitizer is polyethylene glycol diacrylate (PEGDA). In the three-dimensional network structure: the crystalline region of the PVDF-based ferroelectric polymer serves as a ferroelectric functional phase for maintaining the stability of ferroelectricity by overall movement during deformation; and the amorphous region of the PVDF-based ferroelectric polymer and the crosslinking sensitizer are connected by radiation-induced free radicals to form carbon-carbon covalent bonds, for jointly forming an elastic skeleton that bears tensile stress. The PVDF-based elastic ferroelectric material is prepared by the following steps: S0, select P(VDF-TrFE) with VDF:TrFE ratio of 50:50, dissolve 0.5 g of P(VDF-TrFE) in 1 mL of cyclohexanone, shake and dissolve at room temperature for 1 h to obtain a ferroelectric polymer solution; dissolve 0.075 g of PEGDA with a molecular weight of 600 in 0.5 mL of cyclohexanone, shake and dissolve at room temperature for 15 min to obtain a crosslinking sensitizer solution; S1, blend the ferroelectric polymer solution and the crosslinking sensitizer solution obtained in step S0 at room temperature for 40 min to obtain a mixed solution; S2, pour the blended solution obtained in step S1 on a clean glass slide at room temperature to make it flow automatically, and dry it in a fume hood for 36 h to obtain a blended film with a mass ratio of crosslinking sensitizer to ferroelectric polymer of 0.15:1; place the blended film in a vacuum oven and dry it at 25 ℃ for 3 h and then at 50 ℃ for 6 h to obtain a precursor film; S3, irradiate the precursor film obtained in step S2 in an electron accelerator with an acceleration voltage of 2 MeV, and an absorbed dose of 15 kGy to make the precursor film absorb energy to generate free radicals, and initiate a free radical complex crosslinking reaction between the amorphous region of P(VDF-TrFE) and PEGDA to form carbon-carbon covalent bond crosslinking points, thereby obtaining a PVDF-based elastic ferroelectric material with a three-dimensional network structure.

[0059] Example 2 The difference between this example and Example 1 is that the mass ratio of crosslinking sensitizer to ferroelectric polymer is 0.25:1, and the others are the same as those in Example 1.

[0060] Example 3 The difference between this example and Example 1 is that the mass ratio of crosslinking sensitizer to ferroelectric polymer is 0.35:1, and the others are the same as those in Example 1.

[0061] Example 4 The difference between this example and Example 1 is that the mass ratio of crosslinking sensitizer to ferroelectric polymer is 0.5:1, and the others are the same as those in Example 1.

[0062] Example 5 The difference between this example and Example 1 is that the absorbed dose is 50 kGy, and the others are the same as those in Example 1.

[0063] Example 6 The difference between this example and Example 1 is that the absorbed dose is 100 kGy, and the others are the same as those in Example 1.

[0064] Example 7 This example differs from Example 2 in that the absorbed dose is 50 kGy, and otherwise is the same as Example 2.

[0065] Example 8 This example differs from Example 2 in that the absorbed dose is 100 kGy, and otherwise is the same as Example 2.

[0066] Example 9 This example differs from Example 1 in that the PVDF-based ferroelectric polymer is P(VDF-CTFE) with a VDF:CTFE ratio of 90:10, the solvent is DMF, and otherwise is the same as Example 1.

[0067] Example 10 This example differs from Example 1 in that the PVDF-based ferroelectric polymer is P(VDF-TrFE-CFE) with a VDF:TrFE:CFE ratio of 63:29:8, the solvent is acetonitrile, and otherwise is the same as Example 1.

[0068] Example 11 This example differs from Example 1 in that the PVDF-based ferroelectric polymer is P(VDF-TrFE-CTFE) with a VDF:TrFE:CTFE ratio of 60:30:10, the solvent is acetone, and otherwise is the same as Example 1.

[0069] Example 12 This example differs from Example 1 in that the crosslinking sensitizer is PEGDMA with a molecular weight of 2000, the solvent is isofuron, and otherwise is the same as Example 1.

[0070] Example 13 This example differs from Example 1 in that the PVDF-based ferroelectric polymer is P(VDF-TrFE-CFE) with a VDF:TrFE:CFE ratio of 62:27:6, the crosslinking sensitizer is PEGDMA with a molecular weight of 3000, and otherwise is the same as Example 1.

[0071] Example 14 This example provides a PVDF-based elastic ferroelectric material having a three-dimensional network structure formed by crosslinking a PVDF-based ferroelectric polymer and a crosslinking sensitizer through radiation, in which the three-dimensional network structure: the crystalline region of the PVDF-based ferroelectric polymer serves as a ferroelectric functional phase for maintaining the stability of ferroelectricity through bulk movement during deformation; and the amorphous region of the PVDF-based ferroelectric polymer and the crosslinking sensitizer are connected through carbon-carbon covalent bonds formed by radiation-induced free radicals, for jointly constituting an elastic skeleton that bears tensile stress, and is prepared by the following method: S0, P(VDF-TrFE) with VDF:TrFE ratio of 50:50 was selected, 50 mg of P(VDF-TrFE) was dissolved in 0.5 mL of cyclohexanone, and the solution was shaken for 1 h at room temperature to obtain a ferroelectric polymer solution; 7.5 mg of polyethylene glycol diacrylate (PEGDA) with a molecular weight of 600 was dissolved in 0.4 mL of cyclohexanone, and the solution was shaken for 15 min at room temperature to obtain a crosslinking sensitizer solution; S1, the ferroelectric polymer solution and the crosslinking sensitizer solution obtained in step S0 were blended at room temperature for 40 min to obtain a mixed solution; S2, the gold-plated silicon wafer was placed on the suction disc of the spin coater, and the blended solution obtained in step S1 was dropped onto the gold-plated silicon wafer using a dropper. The spin coater was started, and the wafer was first spun at a speed of 400 rpm for 8 s and then at a speed of 1500 rpm for 40 s to obtain a blended film with a mass ratio of crosslinking sensitizer to ferroelectric polymer of 0.15:1. The blended film was placed in a vacuum oven and dried at 25 ℃ for 3 h and then at 50 ℃ for 6 h to obtain a precursor film; S3, the precursor film obtained in step S2 was irradiated in an electron accelerator with an acceleration voltage of 2 MeV, and the absorbed dose was 15 kGy. The precursor film absorbed energy to generate free radicals, which induced a free radical complex crosslinking reaction between the amorphous region of P(VDF-TrFE) and PEGDA to form carbon-carbon covalent bond crosslinking points, thereby obtaining a PVDF-based elastic ferroelectric material with a three-dimensional network structure.

[0072] Example 15 The difference between this example and Example 14 is that P(VDF-TrFE-CFE) with a VDF:TrFE:CFE ratio of 64.1:31:4.9 was selected, and the other steps were the same as those of Example 14.

[0073] Comparative Example 1 This comparative example provides a PVDF-based ferroelectric material without irradiation and without adding a crosslinking sensitizer, which was prepared by the following steps: S0, P(VDF-TrFE) with a VDF:TrFE ratio of 50:50 was selected, and 0.5 g of P(VDF-TrFE) was dissolved in 1 mL of cyclohexanone and shaken for 1 h at room temperature to obtain a ferroelectric polymer solution; S1, the ferroelectric polymer solution obtained in step S0 was poured onto a clean glass slide and allowed to flow flat naturally, and the glass slide was placed in a fume hood and dried for 36 h to obtain a ferroelectric polymer film; S2, the ferroelectric polymer film obtained in step S1 was placed in a vacuum oven and dried at 25 ℃ for 3 h and then at 50 ℃ for 6 h to obtain a PVDF-based ferroelectric material without irradiation and without adding a crosslinking sensitizer.

[0074] Comparative Example 2 The present comparative example provides a PVDF-based ferroelectric material which has been irradiated but without adding a crosslinking sensitizer, which is prepared by the following steps: S0, P(VDF-TrFE) with VDF:TrFE ratio of 50:50 is selected, 0.5 g of P(VDF-TrFE) is dissolved in 1 mL of cyclohexanone, and shaken and dissolved at room temperature for 1 h to obtain a ferroelectric polymer solution; S1, the ferroelectric polymer solution obtained in step S0 is poured on a clean glass slide at room temperature to automatically flow flat, and is placed in a fume hood to dry for 36 h to obtain a ferroelectric polymer film; the ferroelectric polymer film is placed in a vacuum oven to dry at 25 ℃ for 3 h and then at 50 ℃ for 6 h to obtain a precursor film; S2, the precursor film obtained in step S1 is irradiated in an electron accelerator with an absorption dose of 20 kGy to obtain a PVDF-based ferroelectric material which has been irradiated but without adding a crosslinking sensitizer.

[0075] Comparative Example 3 The present comparative example provides a PVDF-based elastic ferroelectric material which has not been irradiated but with adding a crosslinking sensitizer, which is prepared by the following steps: S0, P(VDF-TrFE) with VDF:TrFE ratio of 50:50 is selected, 0.5 g of P(VDF-TrFE) is dissolved in 1 mL of cyclohexanone, and shaken and dissolved at room temperature for 1 h to obtain a ferroelectric polymer solution; 0.015 g of PEGDA with molecular weight of 600 is dissolved in 0.5 mL of cyclohexanone, and shaken and dissolved at room temperature for 15 min to obtain a crosslinking sensitizer solution; S1, the ferroelectric polymer solution and the crosslinking sensitizer solution obtained in step S0 are blended at room temperature for 40 min to obtain a mixed solution; S2, the blended solution obtained in step S1 is poured on a clean glass slide at room temperature to automatically flow flat, and is placed in a fume hood to dry for 36 h to obtain a blended film with mass ratio of crosslinking sensitizer to ferroelectric polymer of 0.06:1; the blended film is placed in a vacuum oven to dry at 25 ℃ for 3 h and then at 50 ℃ for 6 h to obtain a PVDF-based elastic ferroelectric material which has not been irradiated but with adding a crosslinking sensitizer.

[0076] The PVDF-based elastic ferroelectric materials prepared in Comparative Examples 1-13 and the PVDF-based ferroelectric materials prepared in Comparative Examples 1-3 are subjected to the following performance tests.

[0077] Mechanical performance test: The mechanical properties of elastic ferroelectric network structures and inelastic structures were tested using a universal testing machine, with the testing rate / speed set to 0.5 mm / mm / min. During the experiment, the samples were cut into standard specimens.

[0078] Figure 1 The figures show the stress-strain curves of the PVDF-based elastic ferroelectric materials prepared in Examples 1-4. (The text abruptly ends here, likely due to an incomplete sentence or missing information.) Figure 1 Analysis shows that the strain of the PVDF-based elastic ferroelectric material prepared in Example 1 can reach over 800%, and the stress continuously increases with strain, exhibiting extremely strong large deformation elasticity. This indicates that it can still stably bear stress under high strain and has excellent elastic recovery performance, making it suitable for applications requiring high large deformation elasticity, such as flexible electronic devices. The strain of the PVDF-based elastic ferroelectric material prepared in Example 2 is about 600%, and the stress growth trend is relatively robust. The strain of the PVDF-based elastic ferroelectric materials prepared in Examples 3 and 4 is around 200%. As the proportion of crosslinking sensitizer gradually increases, the elastic deformation range of the PVDF-based elastic ferroelectric material shows a decreasing trend, while the initial rate of stress growth increases, but the final stress peak decreases. This is because the crosslinking sensitizer, as a soft segment, participates in the construction of the network. The higher the proportion, the more flexible segments in the network, and the more sensitive the initial stress response. However, too many soft segments will restrict the overall movement space of the crystalline region, leading to a decrease in the elastic bearing capacity under large deformation. The reason may be that the low crosslinking sensitizer ratio in Example 1 allows the network to retain more "rigid support" of the ferroelectric polymer crystallization region, thus enabling it to continuously bear stress under large deformation of more than 800%, making it suitable for scenarios with high requirements for ultra-large elastic deformation; while the high crosslinking sensitizer ratio in Example 4 sacrifices some elasticity under large deformation, but the initial stress increases rapidly, making it suitable for scenarios with high sensitivity requirements for small deformation stress, such as micro-strain sensors.

[0079] Figure 2 The images show the stress-strain curves of the PVDF-based elastic ferroelectric materials prepared in Examples 5 and 6. Through analysis of... Figure 2Analysis shows that, as the absorbed dose increases from 50 kGy to 100 kGy, the elastic deformation range of the material decreases (the strain is approximately 400% in Example 5 and approximately 300% in Example 6), and the overall slope of stress increase increases (i.e., the modulus increases). This is because a higher absorbed dose results in more radiation-induced free radicals, a higher crosslinking density, shorter polymer chain segment lengths between adjacent crosslinking points, and reduced chain segment flexibility, leading to a compression of the elastic space of the material during deformation, but with an increase in mechanical strength (stress). Specifically, the PVDF-based elastic ferroelectric material prepared in Example 5 has a moderate crosslinking density and can still maintain good elastic load-bearing capacity within approximately 400% strain, making it suitable for scenarios with high requirements for the balance between deformation and strength. The high crosslinking density of the PVDF-based elastic ferroelectric material prepared in Example 6 results in higher mechanical strength, but a narrower elastic deformation range, making it suitable for applications where strength requirements are prioritized and deformation requirements are secondary, such as elastic actuators with low deformation and high stress.

[0080] Figure 3 The figures show the stress-strain curves of the PVDF-based elastic ferroelectric materials prepared in Examples 2, 7, and 8. (The text abruptly ends here, likely due to an incomplete sentence or missing information.) Figure 3 Analysis shows that the elastic deformation range of the PVDF-based elastic ferroelectric material prepared in Example 2 can reach over 600%, and the stress steadily increases with strain throughout the deformation process without a significant yield point. This is because at low absorbed doses, the number of radiation-induced free radicals is small, the crosslinking density is low, the polymer chain length between adjacent crosslinking points is long, the chain segment flexibility is high, and it can be fully stretched to adapt to large deformations. Furthermore, the elastic skeleton formed by the amorphous region and the crosslinking sensitizer can effectively disperse stress. In Example 7, the elastic deformation range of the PVDF-based elastic ferroelectric material prepared narrows to 130%. A medium absorbed dose increases the crosslinking density, shortens the network chain length, and limits the chain segment stretching space. In Example 8, the elastic deformation range of the PVDF-based elastic ferroelectric material prepared further narrows to 110%. At high absorbed doses, the crosslinking density increases sharply, the network chain length further shortens, and the chain segment flexibility decreases significantly.

[0081] Figure 4 The figures show the stress-strain curves of the PVDF-based elastic ferroelectric materials prepared in Examples 9-13. (The text abruptly ends here, likely due to an incomplete sentence or missing information.) Figure 6From the analysis, it can be seen that in Examples 9, 10 and 11, the PVDF-based ferroelectric materials of different PVDF matrices are dissolved in different solvents, but after introducing an appropriate amount of crosslinking sensitizer and irradiating an appropriate absorption dose, there is no obvious yield phenomenon, indicating that the preparation of elastic ferroelectric materials using the radiation crosslinking method has certain universality. Through the analysis of the stress-strain curves of Examples 12 and 13, it can be seen that the difference in molecular weight of the crosslinking sensitizer also affects the mechanical properties of the elastic ferroelectric material. Under the same mass ratio, the introduction of a crosslinking sensitizer with a higher molecular weight reduces the crosslinking sites provided by the crosslinking sensitizer, reduces the crosslinking density, and increases the elastic strain range (about 300% for Example 12 and about 600% for Example 13).

[0082] Figure 5 The stress-strain curve of the PVDF-based ferroelectric material prepared in Comparative Example 1 is shown in the figure. As can be seen from the figure, the PVDF-based ferroelectric material prepared in Comparative Example 1 without irradiation and without adding a crosslinking sensitizer, the PVDF-based ferroelectric material prepared in Comparative Example 2 without adding a crosslinking sensitizer after irradiation, and the PVDF-based elastic ferroelectric material prepared in Comparative Example 3 without irradiation but with the addition of a crosslinking sensitizer all have obvious yield phenomena, indicating that P(VDF-TrFE) itself is a plastic material, and simple irradiation cannot construct an elastic ferroelectric network structure, and a crosslinking sensitizer needs to be added. However, if the content of the crosslinking sensitizer is too low, the material will also exhibit plasticity, so it is necessary to balance the ratio of the crosslinking sensitizer and the ferroelectric polymer to achieve appropriate mechanical properties. Through the overall analysis of the stress-strain curves of Examples 1-13 and Comparative Examples 1-3, it can be seen that Comparative Examples 1-3 have a stress drop within the first 30% of the strain range, which is a clear yield behavior and is a typical plastic material. In contrast, Examples 1-13 have a steady increase in stress with strain within the 30% strain range, without a yield point in the traditional sense, indicating that PVDF-based elastic ferroelectric materials can be prepared by this method of radiation crosslinking.

[0083] Figure 6 The cyclic stress-strain curve of the PVDF-based ferroelectric material prepared in Comparative Example 1 is shown in the figure. As can be seen from the figure, under the condition of 25%-85% strain, there is a large strain hysteresis. The "hysteresis loop area" of the cyclic stress-strain curve represents the energy loss, and the larger the area, the greater the loss, and the worse the elastic recovery and cycle stability. Therefore, the existence of large strain hysteresis and yield phenomenon indicates that the ferroelectric material prepared in Comparative Example 1 does not have elasticity.

[0084] Figure 7The cycle stress-strain curve of the PVDF-based elastic ferroelectric material prepared in Example 1 is shown in the figure. As can be seen from the figure, the curve at all strains presents a closed shape of "stress rising during stretching and stress falling to close to the initial value during unloading", indicating that the material can maintain good elastic recovery ability in the strain range of 20%-160%, without obvious plastic residue. With the increase of the cycle strain from 20% to 160%, the "hysteresis loop area" of the curve slightly increases, but the overall is still in a small range, indicating that the material has low energy loss under large strain cycles and excellent fatigue resistance. The PVDF-based elastic ferroelectric material has excellent elastic recovery rate and cycle stability in a wide strain range, and can adapt to different deformation requirements in the wearable field.

[0085] Thermodynamic performance test: The thermodynamic performance of the elastic ferroelectric network structure was tested using a DSC performance tester, with a temperature range of -50 to 180 ℃ and a temperature rising and falling rate of 10 ℃ / min.

[0086] Figure 8 The DSC graph of the PVDF-based elastic ferroelectric material prepared in Example 1 is shown, including the processes of first heating (1st heating), first cooling (1st cooling) and second heating (2nd heating). In the first heating curve, an obvious endothermic peak appears at 140.27 ℃, corresponding to the melting process of the material, i.e. the melting of the crystalline region of the ferroelectric polymer; at the same time, the baseline change of the curve can reflect the glass transition, corresponding to the chain segment movement of the amorphous region of the ferroelectric polymer, indicating that the material retains the crystallization characteristics of the PVDF-based ferroelectric polymer; in the first cooling curve, an exothermic peak appears in the temperature range of 125-150 ℃, corresponding to the recrystallization process of the crystalline region, indicating that the material can still recrystallize after heating and melting, indicating that the PVDF-based elastic ferroelectric material has thermal stability; the endothermic peak of the second heating is consistent with the first heating, indicating that after the "heating-cooling" cycle, the crystallization behavior of the material does not change significantly, further verifying that the PVDF-based elastic ferroelectric material formed by radiation crosslinking in the present application, through the cooperation of the crystalline region and the crosslinked network in the thermal cycle process, not only retains the thermal phase transition characteristics of the ferroelectric material, but also avoids the irreversible destruction of the crystalline region through the crosslinked network, ensuring the thermal stability of the ferroelectric performance. (Please confirm whether the above content is accurately expressed) As can be seen from the DSC curve, the glass transition temperature of the PVDF-based elastic ferroelectric material prepared in Example 1 is -21.32 ℃, the Curie transition temperature is 60 ℃, and the melting point is 140.27 ℃, and the crystallinity can be calculated to be 37%, indicating that the thermodynamic performance of the elastic ferroelectric network structure is similar to that of the P(VDF-TrFE) raw material.

[0087] The calculation method of the crystallinity is: The enthalpy change of 100% crystalline PVDF is 103.4 J / g, and assuming only VDF participates in crystallization, P(VDF-TrFE) is selected as the base material, and the calculation formula of crystallinity is: Crystallinity = (△ H c + △ H m ) / (a*w(VDF)*△ H 0 ) Wherein, a: the mass ratio of P(VDF-TrFE) in the crosslinked film; w(VDF): the mass ratio in P(VDF-TrFE); △ H 0 : the enthalpy value of 100% crystalline PVDF; △ H c : the Curie transition enthalpy value; △ H m : the melting enthalpy value.

[0088] Figure 9 The hysteresis loop diagram of the PVDF-based elastic ferroelectric material prepared in Example 1 is shown in the figure. As can be seen from the figure, the hysteresis loop of the PVDF-based elastic ferroelectric material prepared in Example 1 is a typical loop, indicating that the material has spontaneous polarization characteristics and the ferroelectric domain can be reversed, and is a typical ferroelectric material. When the electric field increases, the polarization intensity first rises rapidly to saturation, and when the electric field decreases to zero, there is a "residual polarization". Under the action of the reverse electric field, the polarization can be reversed. When the reverse electric field increases to a certain value, the polarization intensity is exactly zero. At this time, the value of the electric field intensity is called the coercive field. It fully meets the core performance requirements of ferroelectric sensing, storage and other applications. The shapes of multiple loops in multiple electric field cycles are highly coincident, and there is no obvious polarization intensity decay or loop distortion. It shows that the material has stable ferroelectric properties and excellent electric field fatigue resistance during the electric field cycling process. The saturation polarization intensity and the residual polarization intensity of the loop are in a reasonable range, and the coercive field is moderate, indicating that the elastic ferroelectric network constructed by radiation crosslinking in the application guarantees the elasticity while not sacrificing the core performance of the PVDF-based ferroelectric material.

[0089] Figure 10 The hysteresis loop diagram of the PVDF-based elastic ferroelectric material prepared in Example 10 is shown in the figure. The difference between this hysteresis loop and the hysteresis loop of the PVDF-based elastic ferroelectric material prepared in Example 1 is that the coercive field and the residual polarization intensity of the former are much smaller than those of the latter, and the hysteresis loop presents an elongated feature, which is a relaxor-type ferroelectric. It shows that the elastic ferroelectric network constructed by radiation crosslinking in the application guarantees the elasticity while not sacrificing the ferroelectricity of the PVDF-based elastic ferroelectric material, fully meeting the requirements of actuation, energy storage and other applications.

[0090] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A PVDF-based elastic ferroelectric material, characterized in that, It has a three-dimensional network structure formed by radiation crosslinking of PVDF-based ferroelectric polymer and crosslinking sensitizer. In the three-dimensional network structure: the crystalline region of the PVDF-based ferroelectric polymer serves as a ferroelectric functional phase, which maintains ferroelectric stability through overall movement during deformation; the amorphous region of the PVDF-based ferroelectric polymer and the crosslinking sensitizer are connected by carbon-carbon covalent bonds formed by radiation-initiated free radicals, which together form an elastic skeleton that bears tensile stress.

2. The PVDF-based elastic ferroelectric material according to claim 1, characterized in that, The PVDF-based ferroelectric polymer includes one or more of P(VDF-TrFE), P(VDF-CTFE), P(VDF-TrFE-CFE), and P(VDF-TrFE-CTFE).

3. The PVDF-based elastic ferroelectric material according to claim 1, characterized in that, The crosslinking sensitizer includes polyethylene glycol diacrylate (PEGDA) and / or polyethylene glycol dimethacrylate (PEGDMA), wherein the molecular weight of the polyethylene glycol diacrylate is 200-5000 and the molecular weight of the polyethylene glycol dimethacrylate is 200-5000.

4. The PVDF-based elastic ferroelectric material according to claim 1, characterized in that, The mass ratio of the crosslinking sensitizer to the PVDF-based ferroelectric polymer is 1:(0.1-100).

5. A method for preparing a PVDF-based elastic ferroelectric material as described in any one of claims 1-4, characterized in that, Includes the following steps: S1, PVDF-based ferroelectric polymer and crosslinking sensitizer are blended in a solvent to form a mixed solution; S2. The mixed solution described in step S1 is made into a thin film and dried to form a precursor film; S3. Irradiate the precursor film described in step S2 with an energy beam to cause the precursor film to absorb energy and generate free radicals, which trigger a free radical composite crosslinking reaction between the amorphous region of the PVDF-based ferroelectric polymer and the crosslinking sensitizer to form carbon-carbon covalent crosslinking points, thereby obtaining an elastic ferroelectric material with a three-dimensional network structure.

6. The method for preparing the PVDF-based elastic ferroelectric material according to claim 5, characterized in that, In step S1, the solvent includes one or more of cyclohexanone, DMF, acetonitrile, acetone and isoflurane, the mass-volume ratio of the PVDF-based ferroelectric polymer to the solvent in the mixed solution is 10-300 mg / mL, and the mass-volume ratio of the crosslinking sensitizer to the solvent is 3-150 mg / mL.

7. The method for preparing the PVDF-based elastic ferroelectric material according to claim 5, characterized in that, In step S1, the blending temperature is 10-50 ℃, the blending time is greater than 5 min, and the blending method is to blend a PVDF-based ferroelectric polymer solution and a crosslinking sensitizer solution. The preparation process of the PVDF-based ferroelectric polymer solution is to dissolve the PVDF-based ferroelectric polymer in the solvent, the dissolution temperature is 10-60 ℃, and the dissolution time is greater than 1 min; the preparation process of the crosslinking sensitizer solution is to dissolve the crosslinking sensitizer in the solvent, the dissolution temperature is 10-50 ℃, and the dissolution time is greater than 1 min.

8. The method for preparing the PVDF-based elastic ferroelectric material according to claim 5, characterized in that, The thin film preparation method in step S2 is casting or spin coating. The spin coating includes a first stage spin coating and a second stage spin coating performed sequentially. The first stage spin coating has a rotation speed greater than 10 rpm and a time greater than 1 s, and the second stage spin coating has a rotation speed greater than 200 rpm and a time greater than 10 s. The drying includes fume hood drying and vacuum drying performed sequentially. The fume hood drying temperature is 0-90 ℃ and the time is 6-48 h, and the vacuum drying temperature is 35-75 ℃ and the time is 2-24 h.

9. The method for preparing the PVDF-based elastic ferroelectric material according to claim 5, characterized in that, The energy beam mentioned in step S3 includes β ray, γ ray, X One or more of the following: X-rays, ion beams, electron beams, and neutron beams.

10. The application of the PVDF-based elastic ferroelectric material as described in any one of claims 1-4 in flexible electronic devices, wearable devices, flexible sensors, or energy harvesting devices.

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