Polymer film with high dielectric property and preparation method thereof

Abstract

The invention discloses a polymer film with high dielectric property and a preparation method thereof, and the preparation method of the polymer film comprises the following steps: (1) preparing a polymer solution by using polymer powder as a solute and an organic liquid as a solvent; (2) coating the macromolecular solution on a substrate by utilizing a shear flow regulation and control method; and (3) carrying out evaporation deposition on the coating product on the substrate until the film is shaped, so as to obtain the polymer film with high dielectric property. The polymer film is prepared on the basis of a flow shear regulation and control method, the energy density of the obtained polymer film can be remarkably improved, the dielectric loss of the polymer film is reduced, and the polymer film shows good dielectric properties; the preparation method is simple in process, high in raw material utilization rate, low in cost and easy for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of polymer material processing and functional materials engineering. Specifically, this invention relates to a polymer thin film with high dielectric properties and its preparation method. Background Technology

[0002] With the rapid development of modern technology and the trend towards miniaturization of devices, especially in wearable mobile devices and flexible sensors, enhancing the performance of dielectric polymer materials faces severe challenges. Power density and energy density are important dielectric properties of dielectrics. The aforementioned devices rely on dielectric capacitors made from polymer films as energy storage devices, possessing high power density. However, dielectric capacitors have low energy density, requiring frequent charging and discharging, which leads to reduced device lifespan, rapid performance degradation over long-term use, and even malfunctions.

[0003] In academic research, common methods for enhancing the performance of high-dielectric materials, such as intrinsic modification of polymers based on grafting and cross-linking, incorporation of high-dielectric particles, and thin film structure design, are difficult to promote to actual production due to complex pretreatment and unstable finished product output. Therefore, developing high-dielectric material preparation processes with the potential for large-scale industrial production is crucial. Casting, spin coating, and electrospinning are currently the main polymer thin film preparation processes, all based on the principle of pretreating the solution in different ways before evaporation and deposition to form a thin film. These processes have been widely used due to their rapid preparation and ability to prepare nanofiber structures. However, in order to further enhance the quality and performance of the finished product, researchers have adopted different control methods to effectively improve important dielectric properties such as energy density and dielectric loss by changing the microstructure of the thin film, such as crystal size, crystallinity, phase state, and defects. The introduction of control methods has, to some extent, compensated for the performance defects of polymer dielectric capacitors and further expanded the application scenarios of dielectric polymer materials in high-power and high-energy storage environments. However, current polymer thin film performance control methods are not perfect, limiting the practical application of this material.

[0004] Under current processes, polymer film preparation can only adjust pre-input variables such as solution concentration, evaporation temperature, solvent type, and gas pressure before the preparation process begins. It is difficult to intervene and control the film preparation process in real time and with precision during the evaporation and deposition. For example, casting is a method where a uniform polymer solution is placed into a mold, and then evaporated and deposited to form a film product. It is simple to operate, easy to form, and diverse, making it suitable for large-scale production. However, this method can only adjust the aforementioned variables before deposition, making real-time intervention in the deposition process difficult. Furthermore, due to limitations in casting mold technology, its preparation and control precision is low; under the same macroscopic variables, the film surface is relatively rough, the internal microstructure is highly disordered, and the dielectric properties of the product fluctuate significantly. Spin coating is a method where a solution is placed on a rotating homogenizing stage, and centrifugal force is used to uniformly distribute the solution thickness before deposition to form a film. This method is low-cost, can prepare high-quality small films, and can cover a wide thickness range from nanometers to micrometers. However, the homogenization process is difficult to control directly due to the dynamic evaporation of the liquid during continuous shedding; furthermore, this method is only suitable for small-scale film preparation using high-concentration solutions and cannot be used for large-scale production. Electrospinning uses electrostatic force to spray the solution into fine filaments from micropores, which are then received by a receiving plate in a fibrous structure and deposited as a film. This method can produce nano- or micro-scale polymer fibers, suitable for the preparation of nanoscale fiber materials such as medical nonwoven fabrics. However, intervention in the fiber forming process can damage the micro / nano structure of the spun fibers, reducing the performance of the finished product. Therefore, it is also difficult to control in real time, and the cost is high, hindering large-scale promotion.

[0005] In summary, existing main processes for preparing high-dielectric polymer materials are all difficult to control precisely in real time during the thin film deposition process, and each suffers from drawbacks such as inability to scale up production and high cost. Therefore, there is an urgent need to develop a preparation process that can be finely controlled, has the potential for large-scale production, is low in cost, and can effectively enhance the dielectric properties of polymer materials. Summary of the Invention

[0006] The present invention aims to at least partially solve one of the technical problems in the related art.

[0007] Therefore, one embodiment of the present invention proposes a method for preparing a polymer film with high dielectric properties, which prepares the polymer film by shear flow control method to enhance the dielectric properties of the polymer film.

[0008] Another aspect of the embodiments of the present invention provides a polymer thin film with high dielectric properties.

[0009] The method for preparing a high-dielectric-performance polymer thin film according to an embodiment of the present invention includes the following steps: (1) Prepare a polymer solution using polymer powder as the solute and organic liquid as the solvent; (2) The polymer solution is coated onto the substrate using a shear flow control method; (3) Evaporate and deposit the coating product on the substrate until the film is fixed to obtain the high dielectric polymer film.

[0010] In some embodiments, the preparation method further includes annealing the film obtained after evaporation deposition in step (3). The annealing process is as follows: after the deposited film is cooled to room temperature, it is annealed and then cooled to room temperature.

[0011] In some embodiments, the annealing temperature is 60-150°C and the annealing time is 2-4 hours.

[0012] In some embodiments, in step (1), the polymer powder includes at least one of polyvinylidene fluoride powder, polyvinylidene difluoride-trifluoroethylene powder, polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene powder, and polyvinylidene fluoride-hexafluoropropylene powder. And / or, the organic liquid includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, triethyl phosphate, and acetone; And / or, the mass-volume fraction of the polymer solution is 10-20%.

[0013] In some embodiments, the preparation process of the polymer solution in step (1) includes the following steps: a. First, add a small amount of the organic liquid to the centrifuge tube, then add the polymer powder, and then use the organic liquid to make up the volume. b. Tighten the test tube cap and perform shaking and centrifugation in sequence; c. Open the test tube cap and stir using an ultrasonic stirrer; d. Use the organic liquid to make up the volume difference and replenish the dissolved volume. e. Repeat steps bd until the viscosity of the upper and lower layers of the mixed solution in the centrifuge tube is uniformly distributed when the centrifuge tube is inverted, thus obtaining the polymer solution.

[0014] Furthermore, in step b, the centrifugation speed is 3000-5000 rpm and the centrifugation time is 5-10 min; And / or, in step c, the stirring time is 2-5 minutes.

[0015] In some embodiments, step (2), coating the polymer solution onto the substrate using a shear flow control method, includes the following steps: S1: Fix the substrate onto the preheated heating plate; S2: Place the coating scraper in acetone for ultrasonic cleaning, and then fix the cleaned coating scraper on the scraper holder; S3: Use a pipette to drop the polymer solution onto the substrate directly below the blade head of the coating doctor blade, then lower the blade until it slightly contacts the polymer droplet; then slowly lower the blade again until the blade head contacts the substrate; repeat the slight up-and-down movement of the blade to continuously squeeze the polymer droplet until it is evenly spread under the blade. S4: Move the blade head up to disengage from the substrate and begin coating until the coating blade reaches the end of the motor stroke.

[0016] Further, in step S1, the substrate is a silicon wafer or a quartz glass plate, and the preheating temperature of the heating plate is 50-90°C; And / or, in step S2, the coating blade is rectangular with a width of 1 cm, and has a 200 μm wide groove distributed longitudinally in the middle parallel to the coating direction; the coating blade on the blade holder forms a 10° angle with the coating plane; the long side of the coating blade is parallel to the side of the substrate and is placed in the center, and the blade tip is parallel to the plane of the substrate. And / or, in step S4, during the coating process, the moving speed of the coating blade is 150-8000 μm / s.

[0017] In some embodiments, in step (3), the temperature of the evaporation deposition is 50-90°C.

[0018] The high dielectric polymer film of this invention is prepared by the above-described method.

[0019] The advantages and beneficial effects of the embodiments of the present invention are as follows: (1) The present invention prepares polymer films based on the flow shear control method, which can significantly improve the energy density of the obtained polymer films, reduce the dielectric loss of the polymer films, and make the polymer films exhibit good dielectric properties.

[0020] (2) The preparation method of polymer film in the embodiments of the present invention has low process cost, less material waste, and high raw material utilization rate, which to a certain extent overcomes the problems of expensive spinning method and wasteful spin coating method.

[0021] (3) The preparation method of polymer film in the embodiments of the present invention is simple and easy to scale up; and it provides control ideas and guidance for the preparation of film materials from the perspective of flow affecting crystallization, which is easy to promote to large-scale roll-to-roll production. Attached Figure Description

[0022] Figure 1This is a process flow diagram of the method for preparing high dielectric polymer films according to an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the coating equipment used in the shear flow coating process according to an embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of the parameters of the doctor blade solution interface during shear flow coating according to an embodiment of the present invention.

[0025] Figure 4 This is a schematic diagram illustrating the mechanism by which shear flow affects polymer crystallization.

[0026] Figure 5 The Fourier transform infrared spectra of the polymer films prepared in Examples 1-8 and Comparative Examples 1-8 of this invention are shown.

[0027] Figure 6 This is a diagram showing the orientation state ratio of the polymer films prepared in Examples 1-8 and Comparative Examples 1-8 of the present invention.

[0028] Figure 7 This is a phase distribution diagram of the polymer solution in Example 5 of the present invention.

[0029] Figure 8 The crystal size diagrams are for polymer films with different solutes and different coating speeds in Examples 2, 4, 6, and 8 of the present invention.

[0030] Figure 9 The diagram shows the energy density of polymer films in Examples 6 and 8 and Comparative Examples 5 and 7 of the present invention at different coating speeds.

[0031] Figure 10 The dielectric loss diagrams are for the PVDF-TrFE-CFE films prepared in Example 8 and Comparative Example 7 of this invention.

[0032] Figure 11 The phase distribution diagrams are shown for the PVDF-HFP films prepared in different solvent systems in Examples 9-11 of this invention.

[0033] Figure 12 The diagrams show the phase distribution of PVDF-HFP / DMF films prepared at different annealing temperatures in Examples 13-16 and Comparative Examples 9-12, as well as the energy density diagrams of PVDF-HFP films prepared in different solvent systems in Examples 17-20 and Comparative Examples 13-16. Detailed Implementation

[0034] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0035] In this document, when values ​​are described as ranges, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as the specific numerical values ​​falling within that range, regardless of whether the specific numerical value or specific subrange is explicitly specified.

[0036] In this article, the words “contain” and “include” and their various variations mean that other elements or wholes may be included but not specifically described.

[0037] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three kinds of relationships. For example, A and / or B can represent three cases: A exists alone, A and B exist simultaneously, and B exists alone.

[0038] The following is in conjunction with the appendix Figure 1 The present invention describes in detail the preparation method of a high dielectric polymer film according to embodiments of the present invention.

[0039] The method for preparing a high-dielectric-performance polymer thin film according to an embodiment of the present invention includes the following steps: (1) Prepare a polymer solution using polymer powder as the solute and organic liquid as the solvent; (2) The polymer solution is coated onto the substrate using a shear flow control method; (3) Evaporate and deposit the coating product on the substrate until the film is fixed to obtain the high dielectric polymer film.

[0040] In some embodiments, the preparation method further includes annealing the film obtained after evaporation deposition in step (3). The annealing process is as follows: after the deposited film is cooled to room temperature, it is annealed and then cooled to room temperature.

[0041] In some embodiments, the annealing temperature is 60-150°C and the annealing time is 2-4 hours.

[0042] In some embodiments, in step (1), the polymer powder includes at least one of polyvinylidene fluoride (PVDF) powder, polyvinylidene fluoride-trifluoroethylene (PVDF-TrfE) powder, polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene (PVDF-TrfE-CTFE) powder, and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) powder. And / or, the organic liquid includes at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), triethyl phosphate (TEP), and acetone (ACE); And / or, the mass-volume fraction of the polymer solution is 10-20%.

[0043] It should be noted that the polymer powder in the embodiments of the present invention was accurately weighed using an analytical balance. The analytical balance was model MT103 with an accuracy of 0.0001g and was purchased from Mettler Toledo.

[0044] In some embodiments, the preparation process of the polymer solution in step (1) includes the following steps: a. First, add a small amount of the organic liquid to the centrifuge tube, then add the polymer powder, and then use the organic liquid to make up the volume. b. Tighten the test tube cap and perform shaking and centrifugation in sequence; c. Open the test tube cap and stir using an ultrasonic stirrer; d. Use the organic liquid to make up the volume difference and replenish the dissolved volume. e. Repeat steps bd until the viscosity of the upper and lower layers of the mixed solution in the centrifuge tube is uniformly distributed when the centrifuge tube is inverted, thus obtaining the polymer solution.

[0045] Furthermore, in step b, the centrifugation speed is 3000-5000 rpm and the centrifugation time is 5-10 min; And / or, in step c, the stirring time is 2-5 minutes.

[0046] In some embodiments, step (2), coating the polymer solution onto the substrate using a shear flow control method, includes the following steps: S1: Fix the substrate onto the preheated heating plate; S2: Place the coating scraper in acetone for ultrasonic cleaning, and then fix the cleaned coating scraper on the scraper holder; S3: Use a pipette to drop the polymer solution onto the substrate directly below the blade head of the coating doctor blade, then lower the blade until it slightly contacts the polymer droplet; then slowly lower the blade again until the blade head contacts the substrate; repeat the slight up-and-down movement of the blade to continuously squeeze the polymer droplet until it is evenly spread under the blade. S4: Move the blade head up to disengage from the substrate and begin coating until the coating blade reaches the end of the motor stroke.

[0047] Further, in step S1, the substrate is a silicon wafer or a quartz glass plate, and the preheating temperature of the heating plate is 50-90°C; And / or, in step S2, the coating blade is rectangular with a width of 1 cm, and has a 200 μm wide groove distributed longitudinally in the middle parallel to the coating direction; the coating blade on the blade holder forms a 10° angle with the coating plane; the long side of the coating blade is parallel to the side of the substrate and is placed in the center, and the blade tip is parallel to the plane of the substrate. And / or, in step S4, during the coating process, the moving speed of the coating blade is 150-8000 μm / s.

[0048] In some embodiments, the specific process of evaporating and depositing the coating product on the substrate in step (3) is as follows: after coating is completed, slowly lift the coating squeegee, remove the coating substrate, keep the polymer film horizontal, and quickly transfer it to the preheated heating plate for evaporation and deposition until the film is shaped and a stable polymer film is formed.

[0049] Furthermore, the temperature of the evaporation deposition is 50-90°C.

[0050] The structural schematic diagram of the coating equipment used in the embodiments of the present invention is shown below. Figure 2 As shown, observations reveal a complex flow field beneath the meniscus during the coating process. The pressure difference and boundary-driven flow oriented to the right of the scraper groove and the moving guide approximate a two-dimensional Poisson's velocity profile. Stable evaporative mass transfer occurs at the meniscus, while the concentration and temperature gradients below the surface induce a tension gradient, leading to disrupted Marangoni-Bernard convection. Additionally, various other flows, including capillary flow, are present. The intense evaporation in the flow area drives the nucleation of polymer chain clusters, resulting in a phase transition, which is then stably evaporated and condensed into crystals after being swept by the scraper.

[0051] The interface between the doctor blade and the solution during coating is as follows Figure 3 As shown. By strictly controlling different temperatures and coating speeds, the stability and repeatability of the coating process are ensured.

[0052] This invention employs a shear flow control method to prepare polymer films with high dielectric properties. A schematic diagram illustrating the effect of shear flow on the polymer crystallization mechanism is shown below. Figure 4 As shown, shear flow control techniques influence the crystallization process from two aspects: polymer nucleation and crystal growth. Figure 4 Previous studies have shown that flow promotes crystal conformational rearrangement, which can be categorized into disordered, isotropic, random coiled states (Coil) and ordered, oriented helical states (Helix). Directional-induced flow causes shear stress to stretch polymer chains, inducing the formation of oriented helical states with lower free energy. The attraction, orientation, and clustering of oriented chains are essential for polymer nucleation; therefore, the generation and orientation of helical states induced by shear flow can significantly promote crystal nucleation. Figure 4A). After crystal nuclei form, the helical state of other polymer chains adsorbed causes the crystal to extend longitudinally, while the lateral shear force stretches the remaining polymer chains, promoting the lateral generation and expansion of crystal nuclei, thereby accelerating the lateral growth of the crystal and significantly improving the crystallization rate. Figure 4 B).

[0053] The high dielectric polymer film of this invention is prepared by the above-described method.

[0054] The following are non-limiting embodiments and comparative examples of the present invention. It should be noted that the schemes in the comparative examples are not prior art, but are only set up for comparison with the schemes in the embodiments, and are not intended to limit the present invention. Unless otherwise stated, all raw materials used in the embodiments and comparative examples are conventional commercially available products, or can be prepared by known methods.

[0055] Example 1 This embodiment provides a method for preparing a polymer thin film with high dielectric properties, including the following steps: (1) Prepare a DMF solution containing 15 wt% PVDF: Using polyvinylidene fluoride (PVDF, purchased from Piezotech Arkema) as the solute and N,N-dimethylformamide (DMF, ACS spectral grade, concentration ≥99.8%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) as the solvent, the preparation process includes the following steps: a. Add 1 mL of DMF to a centrifuge tube beforehand, then accurately weigh 1.2 g of PVDF powder using an analytical balance and add it to the test tube. Continue to add DMF to the centrifuge tube and bring the volume to 8 mL. b. Tighten the test tube cap, shake the test tube to mix the solution in the centrifuge tube, then place the centrifuge tube in the centrifuge and centrifuge at 4000 rpm for 10 minutes. c. Open the test tube cap and stir with an ultrasonic stirrer for 2 minutes; d. Use DMF to bring the volume to 8 mL to make up the difference in dissolution volume; e. Repeat steps bd until the viscosity of the upper and lower layers of the mixed solution in the centrifuge tube is uniformly distributed when the centrifuge tube is inverted, thus obtaining a DMF solution of 15wt% PVDF.

[0056] (2) Shear coating – A 15wt% PVDF DMF solution is shear coated to form a film precursor: S1: Start the coating device, turn on the high-magnification lens and fill light, and start the connected display to ensure normal output of the magnified image. Then preheat the heating plate to 70°C, and then fix the silicon wafer substrate on the preheated heating plate; S2: Place the pre-made coating blade (rectangular, 1cm wide, with 200mm wide grooves distributed longitudinally in the middle parallel to the coating direction) in acetone for ultrasonic cleaning for 5 minutes, then remove it with tweezers and fix it on the blade holder, being careful not to rub the groove surface excessively; then adjust the lens focus to observe the blade, adjust the blade holder so that the blade is at an angle of about 10° to the coating plane, with the long side parallel to the side of the silicon substrate and placed in the center, and the blade tip parallel to the plane of the silicon substrate; then, raise the blade to drip a 15wt% PVDF DMF solution into the reserved space. S3: Use a pipette to take 100μL of 15wt% PVDF DMF solution and drop it onto the silicon substrate directly below the blade tip. Then lower the blade until it slightly touches the droplet. Observe the display screen and slowly lower the blade so that the blade tip touches the substrate. Repeat the slight up and down movement of the blade to continuously squeeze the droplet until it is fully and evenly spread under the blade. S4: Slightly move the blade upwards to disengage from the silicon substrate, then set the blade movement speed to 150-8000μm / s (which changes in real time over time) and begin coating until the blade reaches the end of the motor stroke.

[0057] (3) Evaporation deposition: After coating is completed, slowly lift the coating squeegee, remove the silicon wafer substrate, keep the coated film horizontal, and quickly transfer it to a preheated 70°C heating plate for evaporation deposition for 2 hours to form a structurally stable PVDF film.

[0058] Example 2 This embodiment is basically the same as that of embodiment 1, except that in step (1) of this embodiment, an ACE solution of 15wt% PVDF is prepared.

[0059] Example 3 This embodiment is basically the same as embodiment 1, except that in step (1) of this embodiment, a 15wt% PVDF-TrfE DMF solution is prepared, that is, 1.2g of PVDF-TrfE powder is accurately weighed using an analytical balance in step a.

[0060] Example 4 This embodiment is basically the same as embodiment 3, except that in step (1) of this embodiment, a 15wt% PVDF-TrfE ACE solution is prepared.

[0061] Example 5 This embodiment is basically the same as embodiment 1, except that in step (1) of this embodiment, a 15wt% PVDF-HFP DMF solution is prepared, that is, 1.2g of PVDF-HFP powder is accurately weighed using an analytical balance in step a.

[0062] Example 6 This embodiment is basically the same as embodiment 5, except that in step (1) of this embodiment, a 15wt% PVDF-HFP ACE solution is prepared.

[0063] Example 7 This embodiment is basically the same as embodiment 1, except that: in step (1) of this embodiment, a 15wt% DMF solution of PVDF-TrfE-CTFE is prepared, that is, 1.2g of PVDF-TrfE-CTFE powder is accurately weighed using an analytical balance in step a.

[0064] Example 8 This embodiment is basically the same as embodiment 7, except that in step (1) of this embodiment, a 15wt% PVDF-TrfE-CTFE ACE solution is prepared.

[0065] Example 9 This embodiment is basically the same as embodiment 5, except that: in step (1) of this embodiment, a 15wt% PVDF-HFP (DMF+ACE) solution is prepared, that is, a compound solution of DMF and ACE in which the volume fraction of DMF is 20% and the volume fraction of ACE is 80%.

[0066] Example 10 This embodiment is basically the same as embodiment 9, except that in step (1) of this embodiment, the volume fraction of DMF is 40% and the volume fraction of ACE is 60%.

[0067] Example 11 This embodiment is basically the same as embodiment 9, except that in step (1) of this embodiment, the volume fraction of DMF is 60% and the volume fraction of ACE is 40%.

[0068] Example 12 This embodiment is basically the same as embodiment 9, except that in step (1) of this embodiment, the volume fraction of DMF is 80% and the volume fraction of ACE is 20%.

[0069] Example 13 This embodiment is basically the same as embodiment 5, except that: after step (3), the thin film is annealed in step (4). The specific steps are as follows: the thin film deposited in step (3) is removed from the heating plate and cooled to room temperature; then the temperature of the heating plate is set to 60°C, preheated for 10 minutes, and then the cooled thin film is placed on the heating plate and heated for 3 hours for annealing; after annealing, the thin film is removed from the heating plate and cooled to room temperature.

[0070] Example 14 This embodiment is basically the same as embodiment 13, except that the annealing heating plate temperature in step (4) of this embodiment is 90°C.

[0071] Example 15 This embodiment is basically the same as embodiment 13, except that the annealing heating plate temperature in step (4) of this embodiment is 120°C.

[0072] Example 16 This embodiment is basically the same as embodiment 13, except that the annealing heating plate temperature in step (4) of this embodiment is 150°C.

[0073] Example 17 This embodiment is basically the same as that of embodiment 15, except that: in step (1) of this embodiment, a 15wt% PVDF-HFP (DMF+ACE) solution is prepared, that is, a compound solution of DMF and ACE in which the volume fraction of DMF is 20% and the volume fraction of ACE is 80%.

[0074] Example 18 This embodiment is basically the same as embodiment 15, except that in step (1) of this embodiment, the volume fraction of DMF is 40% and the volume fraction of ACE is 60%.

[0075] Example 19 This embodiment is basically the same as embodiment 15, except that in step (1) of this embodiment, the volume fraction of DMF is 60% and the volume fraction of ACE is 40%.

[0076] Example 20 This embodiment is basically the same as embodiment 15, except that in step (1) of this embodiment, the volume fraction of DMF is 80% and the volume fraction of ACE is 20%.

[0077] Comparative Example 1 This comparative example is basically the same as Example 2, except that step (2) of this comparative example uses the conventional casting method, and the specific preparation process is as follows: (1) Prepare an ACE solution containing 15 wt% PVDF: Using polyvinylidene fluoride (PVDF, purchased from Piezotech Arkema) as the solute and acetone (ACE) as the solvent, the preparation process includes the following steps: a. Add 1 mL of ACE to the centrifuge tube beforehand, then accurately weigh 1.2 g of PVDF powder using an analytical balance and add it to the test tube. Continue to add ACE to the centrifuge tube and bring the volume to 8 mL. b. Tighten the test tube cap, shake the test tube to mix the solution in the centrifuge tube, then place the centrifuge tube in the centrifuge and centrifuge at 4000 rpm for 10 minutes. c. Open the test tube cap and stir with an ultrasonic stirrer for 2 minutes; d. Use ACE to bring the volume to 8 mL to make up the difference in dissolution volume; e. Repeat steps bd until the viscosity of the upper and lower layers of the mixed solution in the centrifuge tube is uniformly distributed when the centrifuge tube is inverted, thus obtaining an ACE solution with 15wt% PVDF.

[0078] (2) Coating by casting S1: Take a regular square silicon wafer with a size of 2cm×2cm, place it in acetone solution and ultrasonically clean it for 2min; then take out the silicon wafer and rinse it with high-pressure nitrogen for 30s; then preheat the heating plate to 70℃ and fix the silicon wafer substrate on the preheated heating plate. S2: Use a pipette to take 300 μL of ACE solution of 15 wt% PVDF and slowly drop it onto the center of the substrate, allowing the droplet to spread naturally, fully and evenly. (3) Evaporation deposition: After coating is completed, the silicon wafer substrate is removed, the coated film is kept horizontal, and it is quickly transferred to a preheated 70°C heating plate for evaporation deposition for 2 hours to form a structurally stable PVDF film.

[0079] Comparative Example 2 This comparative example is basically the same as Comparative Example 1, except that: this comparative example is prepared with a 15wt% PVDF (DMF+ACE) solution, that is, a compound solution of DMF and ACE in which the volume fraction of ACE is 80% and the volume fraction of DMF is 20%.

[0080] Comparative Example 3 This comparative example is basically the same as Comparative Example 1, except that in step (1) of this comparative example, a 15wt% PVDF-TrfE ACE solution is prepared.

[0081] Comparative Example 4 This comparative example is basically the same as Comparative Example 3, except that in step (1) of this comparative example, a 15wt% PVDF-TrfE (DMF+ACE) solution is prepared, that is, a compound solution of DMF and ACE in which the solvent is 80% by volume and 20% by volume of DMF.

[0082] Comparative Example 5 This comparative example is basically the same as Comparative Example 1, except that in step (1) of this comparative example, a 15wt% PVDF-HFP ACE solution is prepared.

[0083] Comparative Example 6 This comparative example is basically the same as Comparative Example 5, except that in step (1) of this comparative example, a 15wt% PVDF-HFP (DMF+ACE) solution is prepared, that is, a compound solution of DMF and ACE in which the volume fraction of ACE is 80% and the volume fraction of DMF is 20%.

[0084] Comparative Example 7 This comparative example is basically the same as Comparative Example 1, except that in step (1) of this comparative example, a 15wt% PVDF-TrfE-CTFE ACE solution is prepared.

[0085] Comparative Example 8 This comparative example is basically the same as Comparative Example 7, except that in step (1) of this comparative example, a 15wt% PVDF-TrfE-CTFE (DMF+ACE) solution is prepared, that is, a compound solution of DMF and ACE in which the solvent is 80% by volume and 20% by volume of DMF.

[0086] Comparative Example 9 This comparative example is basically the same as Comparative Example 1, except that: in step (1) of this comparative example, a 15wt% PVDF-HFP DMF solution is prepared; and the film prepared by casting method is annealed in this comparative example, the annealing process is the same as in Example 13.

[0087] Comparative Example 10 This comparative example is basically the same as Comparative Example 9, except that the annealing heating plate temperature in this comparative example is 90℃.

[0088] Comparative Example 11 This comparative example is basically the same as Comparative Example 9, except that the annealing heating plate temperature in this comparative example is 120℃.

[0089] Comparative Example 12 This comparative example is basically the same as Comparative Example 9, except that the annealing heating plate temperature in this comparative example is 150℃.

[0090] Comparative Example 13 This comparative example is basically the same as Example 11, except that: in step (1) of this comparative example, a 15wt% PVDF-HFP (DMF+ACE) solution is prepared, that is, a compound solution of DMF and ACE in which the solvent is 20% by volume and 80% by volume.

[0091] Comparative Example 14 This comparative example is basically the same as Comparative Example 11, except that in step (1) of this comparative example, the volume fraction of DMF is 40% and the volume fraction of ACE is 60%.

[0092] Comparative Example 15 This comparative example is basically the same as Comparative Example 11, except that in step (1) of this comparative example, the volume fraction of DMF is 60% and the volume fraction of ACE is 40%.

[0093] Comparative Example 16 This comparative example is basically the same as Comparative Example 11, except that in step (1) of this comparative example, the volume fraction of DMF is 80% and the volume fraction of ACE is 20%.

[0094] Fourier transform infrared (FTIR) spectroscopy was performed on the polymer films prepared in Examples 1-8 and Comparative Examples 1-8 using shear flow control methods or casting methods in different solute or solvent systems. The results are as follows: Figure 5 As shown.

[0095] The proportions of orientation states (α, β, and γ states) of the polymer film were calculated based on FTIR spectra. (The proportion of each phase state was approximated by the peak-to-valley difference near the characteristic peaks of the α, β, and γ phases in the measured FTIR spectrum, which was then divided by the sum of the three phase values.) The results are as follows: Figure 6 As shown. Existing research indicates that the β phase of PVDF has an all-trans configuration, with each monomer in its chain having a completely uniform orientation, thus exhibiting strong orientation and electric dipole moment, which can improve the dielectric constant of the finished product, but also increases dielectric loss. The γ phase monomers exhibit periodic small-angle deflections relative to the β phase, representing a strong orientation state, providing both a high dielectric constant and lower dielectric loss; therefore, these two phases are considered the desired states during preparation. From Figure 6 As can be seen from this, the application of shear regulation can increase the proportion of β or γ phase in the finished product in most cases.

[0096] Figure 7This is a phase distribution diagram of the polymer solution at different coating speeds when coating a 15wt% PVDF-HFP DMF solution using a shear flow control method in Example 5 of this invention. As a key variable in the coating process, the coating speed controls the intensity of directional flow, thereby altering the shear force and influencing the crystallization process. Rapid coating induces strong shear, which promotes the formation of oriented states, but this process involves a certain degree of relaxation. If the coating speed is too fast, the solution evaporates prematurely, and the crystalline phase precipitates before the orientation transformation occurs; however, if the coating speed is too slow, the driving force for orientation formation is insufficient, and high-purity oriented crystals cannot be obtained. Therefore, with increasing coating speed, the fractions of β and γ phases show a single peak, while the α phase exhibits a single valley.

[0097] Figure 8 This diagram shows the crystal size of polymer films under different solutes and coating speeds in Examples 2, 4, 6, and 8 of this invention. Crystal size is another microscopic variable affecting dielectric properties; the smaller the size, the lower the resistance to polarization reversal, and consequently, the lower the dielectric loss. When the shear force matches the evaporation rate, the molecular chains are more likely to form large clusters (crystal nuclei) during crystallization, resulting in large crystals. Conversely, evaporation transport and shear force interfere with each other, preventing the crystal nuclei from concentrating and resulting in small crystals. Similar to the trend of orientation states, crystal size also exhibits a single peak. During high-speed coating, as the coating speed increases, the decrease in crystal size and the reduction in orientation states antagonize each other, causing the dielectric properties to exhibit a single-peak curve. Under experimental conditions, as the coating speed increases, PVDF-HFP 15wt% (acetone) achieves the best dielectric properties around 2 mm / s, subsequently decreasing continuously.

[0098] Figure 9 The figures show the energy density of polymer films prepared using either the shear flow control method or the casting method in Examples 6 and 8 and Comparative Examples 5 and 7 of this invention at different coating speeds. As can be seen from the figures, the coating product based on the shear flow method has an average energy density 20% higher than that of the casting method.

[0099] Figure 10 The figures show the dielectric loss of the PVDF-TrFE-CFE films prepared in Example 8 and Comparative Example 7 of this invention. As can be seen from the figures, the dielectric loss of the PVDF-TrFE-CFE film prepared by the shear flow method is reduced by at least 15% compared with that prepared by the casting method, and the electric field threshold for leakage current is significantly increased (from 120MV / m to 200MV / m).

[0100] Figure 11 The figures show the phase distribution of PVDF-HFP films prepared in different solvent systems in Examples 9-11 of this invention. As can be seen from the figures, when the solvent system contains more polar and volatile components (such as acetone), it is more conducive to guiding the formation of orientation states.

[0101] Figure 12 The figures show the phase distribution diagrams of PVDF-HFP / DMF films prepared at different annealing temperatures for Examples 13-16 and Comparative Examples 9-12, and the energy density diagrams of PVDF-HFP films prepared in different solvent systems for Examples 17-20 and Comparative Examples 13-16. As can be seen from the figures, higher annealing temperatures result in stronger stress-induced recrystallization and phase transformation, but at high temperatures, the melting temperature is easily reached, leading to crystal destruction. Increased evaporation rates hinder the phase transformation process, resulting in a decrease in the overall proportion of oriented states after annealing, which is more pronounced at high temperatures. Appropriate control of these two factors can significantly increase the proportion of high-dielectric phases, further enhancing the dielectric properties of the film.

[0102] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0103] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0104] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0105] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a polymer thin film with high dielectric properties, characterized in that, The steps include the following: (1) Prepare a polymer solution using polymer powder as the solute and organic liquid as the solvent; (2) The polymer solution is coated onto the substrate using a shear flow control method; (3) Evaporate and deposit the coating product on the substrate until the film is fixed to obtain the high dielectric polymer film.

2. The method for preparing a high-dielectric-performance polymer thin film according to claim 1, characterized in that, It also includes annealing the film obtained after evaporation deposition in step (3). The annealing process is as follows: after the deposited film is cooled to room temperature, it is annealed and then cooled to room temperature.

3. The method for preparing a high-dielectric-performance polymer thin film according to claim 2, characterized in that, The annealing temperature is 60-150℃, and the annealing time is 2-4 hours.

4. The method for preparing a high-dielectric-performance polymer thin film according to claim 1, characterized in that, In step (1), the polymer powder includes at least one of polyvinylidene fluoride powder, polyvinylidene fluoride-trifluoroethylene powder, polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene powder, and polyvinylidene fluoride-hexafluoropropylene powder. And / or, the organic liquid includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, triethyl phosphate, and acetone; And / or, the mass-volume fraction of the polymer solution is 10-20%.

5. The method for preparing a high-dielectric-performance polymer thin film according to claim 1, characterized in that, In step (1), the preparation process of the polymer solution includes the following steps: a. First, add a small amount of the organic liquid to the centrifuge tube, then add the polymer powder, and then use the organic liquid to make up the volume. b. Tighten the test tube cap and perform shaking and centrifugation in sequence; c. Open the test tube cap and stir using an ultrasonic stirrer; d. Use the organic liquid to make up the volume difference and replenish the dissolved volume. e. Repeat steps bd until the viscosity of the upper and lower layers of the mixed solution in the centrifuge tube is uniformly distributed when the centrifuge tube is inverted, thus obtaining the polymer solution.

6. The method for preparing a high-dielectric-performance polymer thin film according to claim 5, characterized in that, In step b, the centrifugation speed is 3000-5000 rpm and the centrifugation time is 5-10 min; And / or, in step c, the stirring time is 2-5 minutes.

7. The method for preparing a high-dielectric-performance polymer thin film according to claim 1, characterized in that, In step (2), the polymer solution is coated onto the substrate using a shear flow control method, which includes the following steps: S1: Fix the substrate onto the preheated heating plate; S2: Place the coating scraper in acetone for ultrasonic cleaning, and then fix the cleaned coating scraper on the scraper holder; S3: Use a pipette to drop the polymer solution onto the substrate directly below the blade head of the coating doctor blade, then lower the blade until it slightly contacts the polymer droplet; then slowly lower the blade again until the blade head contacts the substrate; repeat the slight up-and-down movement of the blade to continuously squeeze the polymer droplet until it is evenly spread under the blade. S4: Move the blade head up to disengage from the substrate and begin coating until the coating blade reaches the end of the motor stroke.

8. The method for preparing a high-dielectric-performance polymer thin film according to claim 7, characterized in that, In step S1, the substrate is a silicon wafer or a quartz glass plate, and the preheating temperature of the heating plate is 50-90℃. And / or, in step S2, the coating blade is rectangular with a width of 1 cm, and has a 200 μm wide groove distributed longitudinally in the middle parallel to the coating direction; the coating blade on the blade holder forms a 10° angle with the coating plane; the long side of the coating blade is parallel to the side of the substrate and is placed in the center, and the blade tip is parallel to the plane of the substrate. And / or, in step S4, during the coating process, the moving speed of the coating blade is 150-8000 μm / s.

9. The method for preparing a high-dielectric-performance polymer thin film according to claim 1, characterized in that, In step (3), the temperature of the evaporation deposition is 50-90℃.

10. A polymer thin film with high dielectric properties, characterized in that, The high dielectric polymer film is prepared by the preparation method according to any one of claims 1-9.

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