Preparation method of salvinia natans bionic coating based on reusable thermosensitive softening template and deep pinning
By introducing a reusable thermally softening template and deep pinning technology into the biomimetic coating of Sophora japonica, the problems of template recycling difficulty and coating structure consistency were solved, the wettability gradient stability and air film coverage of the coating were improved, the cost was reduced and the sustainability of the process was enhanced.
Patent Information
- Application Number
- CN202511446786.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-11
- Publication Date
- 2025-12-05
AI Technical Summary
Existing biomimetic coatings for *Lysimachia foenum-graecum* suffer from problems in preparation and application, such as difficulty in template recovery, poor consistency of coating micro-protrusion structure, difficulty in maintaining wettability gradient, decreased air film coverage, and unsustainable drag reduction effect.
By employing a reusable thermosensitive softening template and deep pinning technology, Fe3O4 nano- and micro-sized particles are introduced into the epoxy resin matrix through staged magnetic field control to form a micro-protrusion structure. The template is positioned under thermosensitive conditions, and the template recycling and coating wettability gradient are achieved by combining heating and ultrasonic treatment.
It significantly improves the gas film stability and drag reduction performance of the coating, reduces the preparation cost, enhances the sustainability of the process, and enables multiple recycling of the template.
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Figure CN121064702A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of biomimetic functional coating, and particularly relates to a lotus leaf biomimetic coating based on reusable heat-sensitive softening template and deep pinning and a preparation method thereof. BACKGROUND
[0002] Biomimetic surface functional materials are an important research direction in the field of material science and marine engineering in recent years. The surface of lotus leaf has a special wetting gradient, the base and side wall are hydrophobic, and the top end region remains hydrophilic, so as to be able to maintain a gas film structure underwater and realize the functions of drag reduction and antifouling. Inspired by this phenomenon, researchers have developed various biomimetic coatings and tried to apply them in the fields of ship navigation, marine engineering equipment and underwater protection. The existing lotus leaf biomimetic coating still has limitations in preparation and application. The micro-protrusion structure of the coating often depends on complex templates, and the templates are difficult to recycle after use, increasing the cost of materials and processes. The surface treatment is mostly in the form of overall hydrophobicization, and it is difficult to distinguish the wetting difference of the base, side wall and top end, so that the coating is difficult to form a stable gradient structure. The distribution of magnetic particles is not balanced during the solidification process, the layering effect of nano and micro particles is insufficient, the consistency of the micro-protrusion morphology is difficult to guarantee, and it is more difficult to realize stable construction on a large-area substrate. The coating shows problems such as decrease of gas film coverage, insufficient stability and short-term drag reduction effect in complex marine environment, which limits the popularization and application of lotus leaf biomimetic coating.
[0003] It is urgent to propose a new preparation strategy to realize deep pinning and structure stability through reusable heat-sensitive softening template combined with layered magnetic field regulation, and at the same time to form a persistent wetting gradient on the surface of the coating, so as to improve the stability of the gas film, the drag reduction performance and the environmental adaptability. SUMMARY
[0004] In order to overcome the problems of unstable gas film, difficult to maintain wetting gradient, difficult to recycle template and uneven distribution of particles of the lotus leaf biomimetic coating in the background art, the purpose of the present application is to provide a lotus leaf biomimetic coating based on reusable heat-sensitive softening template and deep pinning and a preparation method thereof. The present application introduces ferroferric oxide nanoparticles and microparticles in the epoxy resin matrix, and makes different size particles layering enrichment through phased magnetic field regulation, to form a magnetic coating with micro-protrusion structure on the surface of the substrate; a heat-sensitive core-shell template with ferroferric oxide particles modified by 3-aminopropyl triethoxysilane as the core and corn starch as the shell is prepared, and the template is positioned and deeply embedded into the micro-protrusion tip under the action of heat-sensitive conditions and magnetic field; the base and side wall are converted into hydrophobic regions and the top end region remains hydrophilic through hydrophobic treatment of the coating under the protection of the template; the template is recycled through heating combined with ultrasonic, so as to form a stable wetting gradient structure on the surface of the coating.
[0005] The application can significantly improve the gas film stability and drag reduction performance of the coating surface, realize the recycling of the heat-sensitive template, reduce the preparation cost and enhance the sustainability of the process.
[0006] The object of the application can be achieved by the following technical solutions: A sophia leaf biomimetic coating based on a reusable heat-sensitive softening template and deep pinning is prepared from the following raw materials by weight: epoxy resin 60-80 parts; acetone 20-40 parts; toluene 10-20 parts; ferroferric oxide nanoparticles 10-20 parts; ferroferric oxide microparticles 5-15 parts; polyvinylpyrrolidone 0.2-1.0 parts; corn starch 10-30 parts; ferroferric oxide particles modified by 3-aminopropyl triethoxysilane 5-15 parts; octadecylamine 1-5 parts; perfluorooctyl triethoxysilane 1-5 parts; deionized water 50-100 parts; wherein the mass ratio of ferroferric oxide nanoparticles to ferroferric oxide microparticles is 1:2-2:1, and the mass ratio of corn starch to magnetic ferroferric oxide particles is 2:1-5:1; after deep pressing protection by magnetic field stratification regulation and heat-sensitive softening template, a sophia leaf biomimetic coating is formed, which has hydrophobic base and sidewall and hydrophilic top end.
[0007] Optionally, the coating surface has an array of micro-protrusions with a diameter of 5-20 microns and a height of 10-50 microns, the contact angle of the base and sidewall is 150-170 degrees, and the contact angle of the top end region is 40-90 degrees, forming a stable wetting gradient.
[0008] Optionally, the coating forms a stable gas film underwater, the gas film coverage is 85%-92%, the drag reduction rate is 32%-42%, and the gas film stability is 30-50 hours.
[0009] Optionally, a preparation method of a sophia leaf biomimetic coating based on a reusable heat-sensitive softening template and deep pinning includes the following steps: S1, mixing epoxy resin with acetone and toluene, adding ferroferric oxide nanoparticles, ferroferric oxide microparticles and polyvinylpyrrolidone, and performing ultrasonic dispersion and mechanical stirring to obtain a uniformly dispersed magnetic spraying slurry; S2, forming a magnetic coating on a hydrophilic pretreated substrate surface by using a pneumatic spraying method, and applying a magnetic field in stages during the curing process to cause stratified migration of the nanoparticles and microparticles and form a particle-rich region at the tip of the micro-protrusion; S3, dissolving corn starch into a heat-sensitive solution, adding ferroferric oxide particles modified by 3-aminopropyl triethoxysilane, performing ultrasonic dispersion and stirring mixing, and using a spray drying process to prepare core-shell structure particles with ferroferric oxide as the core and starch as the shell; S4, disperse the core-shell particles as a template into a suspension, soften under a heat-sensitive condition, and position the tip of the micro-protrusion of the coating under the action of a magnetic field; S5, press the template into the surface of the coating under the action of the magnetic field in the softened state of the template to form a deep pinning structure, and keep the solidified state after cooling; S6, under the protection of the template, place the whole coating in a mixed solution of octadecylamine and perfluorooctyltriethoxysilane to hydrophobize the base and sidewall of the micro-protrusion, and keep the tip area hydrophilic; S7, separate the template from the coating by heating and ultrasonic treatment, and recycle the template for reuse; S8, after recycling the template, the surface of the coating naturally forms a wetting gradient structure with the base and sidewall being hydrophobic and the tip being hydrophilic.
[0010] Optionally, the spraying thickness in step S2 is 50-200 μm, and the phased magnetic field includes a first phase with a strength of 50-120 Gauss and a second phase with a strength of 120-200 Gauss.
[0011] Optionally, the preparation step of the 3-aminopropyltriethoxysilane modified ferroferric oxide particles in step S3 is dispersing the ferroferric oxide particles in an ethanol solution, adding 3-aminopropyltriethoxysilane, stirring and reacting for 1-3 hours, and then washing and drying to obtain; the particle size of the core-shell structure particles in step S3 is 5-15 μm.
[0012] Optionally, the concentration of the suspension in step S4 is 0.3%-1.2%.
[0013] Optionally, the treatment temperature in step S6 is 60-80 °C, and the time is 2-6 hours.
[0014] Optionally, the template recycling temperature in step S7 is 85-120 °C, the ultrasonic frequency is 40-80 kHz, and the template can be recycled for 4-8 times on average.
[0015] The present application has the following beneficial effects: The present application introduces a reusable heat-sensitive softening template to solve the problem of difficult reuse of the existing template, realizes 4-8 times of recycling, and greatly reduces the process cost; the template is stably embedded at the tip of the micro-protrusion in a deep pinning manner, which significantly enhances the durability of the wetting gradient of the coating; the ordered distribution of the nanometer and micrometer ferroferric oxide particles is realized by layered magnetic field regulation, which ensures the consistency and stability of the microstructure morphology, thereby significantly improving the gas film coverage and stability. BRIEF DESCRIPTION OF DRAWINGS
[0016] The present application will be further described below with reference to the accompanying drawings.
[0017] Figure 1 is a schematic diagram of the template thermal softening mechanism and deep indentation pinning process and its micro-SEM characterization; Figure 2 is the EDS fluorine element distribution in the final coating microstructure, i.e., the protrusion structure; Figure 3 is the contact angle and underwater air film demonstration of the embodiment. DETAILED DESCRIPTION
[0018] The application is further illustrated below in conjunction with specific embodiments, but the application is not limited to the following embodiments, and equivalent adjustments made without departing from the spirit and essence of the application shall be deemed to fall within the protection scope of the application.
[0019] Embodiment 1 The purpose of this embodiment is to verify whether the coating prepared under the upper limit condition of each component allocation ratio can realize stable wetting gradient and higher air film coverage.
[0020] S1, 15 parts of ferroferric oxide particles were dispersed in 100 parts of ethanol solution, after ultrasonic treatment for 30 min, 5 parts of 3-aminopropyl triethoxysilane was added, and the reaction was carried out at 70℃ for 3h; after the reaction was completed, filtration, ethanol washing 3 times, and drying in a 80℃ vacuum drying oven for 12h, modified ferroferric oxide particles by 3-aminopropyl triethoxysilane were obtained; S2, 80 parts of epoxy resin, 40 parts of acetone and 20 parts of toluene were mixed uniformly, 20 parts of ferroferric oxide nanoparticles, 15 parts of ferroferric oxide microparticles and 1.0 parts of polyvinylpyrrolidone were added in turn, and a uniform slurry was obtained by ultrasonic treatment for 1h and mechanical stirring for 2h; a coating with a thickness of about 200μm was formed on the surface of the hydrophilic treated substrate by pneumatic spraying, and a magnetic field was applied in stages during the curing process: 120 Gauss in the first stage and 200 Gauss in the second stage; S3, 30 parts of corn starch were dissolved in deionized water, and the modified ferroferric oxide particles by 3-aminopropyl triethoxysilane were added, ultrasonic dispersion for 30 min, and then spray drying was used to prepare core-shell particles with a particle size of about 15μm; the particles were dispersed into a suspension with a concentration of 1.2%, softened under the condition of 75℃ thermal sensitivity, and positioned to the tip of the micro-protrusion of the coating under the action of the magnetic field, and then pressed into the coating by the magnetic field force and cooled and solidified; then the coating was immersed in a mixed solution of octadecylamine and perfluorooctyl triethoxysilane, and reacted at 80℃ for 6h, the base and the sidewall were hydrophobized under the protection of the template, and the top end remained hydrophilic; finally, the template was separated and recovered under the condition of 120℃ and 60kHz ultrasonic, and could be recycled for 8 times.
[0021] Embodiment 2 The purpose of this embodiment is to verify whether the coating prepared under the intermediate ratio condition can balance the air film coverage and the stability of the coating structure.
[0022] S1, 10 parts of Fe304particles were dispersed in 80 parts of ethanol solution, after ultrasonic treatment for 20 min, 3 parts of 3-aminopropyl triethoxysilane was added, and the mixture was stirred at 65°C for 2 h; after reaction, the mixture was filtered, washed with ethanol for 2 times, and dried in a vacuum drying oven at 70°C for 10 h to obtain Fe304particles modified by 3-aminopropyl triethoxysilane; S2, 70 parts of epoxy resin, 30 parts of acetone and 15 parts of toluene were mixed, 15 parts of Fe304nanoparticles, 10 parts of Fe304microparticles and 0.6 parts of polyvinylpyrrolidone were added, and the mixture was ultrasonically treated for 40 min and mechanically stirred for 1.5 h to obtain a uniform slurry; a coating layer with a thickness of about 120 μm was formed on the surface of the hydrophilic treated substrate by pneumatic spraying, and a magnetic field was applied in stages during curing: 90 Gauss in the first stage and 160 Gauss in the second stage; S3, 20 parts of corn starch were dissolved in deionized water, and Fe304particles modified by 3-aminopropyl triethoxysilane were added, and the mixture was ultrasonically dispersed for 20 min and stirred and mixed, and then spray dried to obtain core-shell particles with a particle size of about 10 μm; the particles were dispersed into a suspension with a concentration of 0.8%, softened under a heat-sensitive condition at 70°C, and positioned to the tips of the micro-protrusions under the action of a magnetic field, and then pressed and cooled to solidify; the coating layer was placed in a mixed solution of octadecylamine and perfluorooctyl triethoxysilane, and reacted at 70°C for 4 h to form a hydrophobic base and a hydrophilic top end; finally, the template was separated and recovered under the condition of ultrasonic treatment at 100°C and 60 kHz, and the average recycling times were 6.
[0023] Example 3 The purpose of this example is to verify whether the coating prepared under the component lower limit condition can ensure the wetting gradient and the minimum acceptable gas film stability.
[0024] S1, 10 parts of Fe304particles were dispersed in 80 parts of ethanol solution, after ultrasonic treatment for 20 min, 3 parts of 3-aminopropyl triethoxysilane was added, and the mixture was stirred at 65°C for 2 h; after reaction, the mixture was filtered, washed with ethanol for 2 times, and dried in a vacuum drying oven at 70°C for 10 h to obtain Fe304particles modified by 3-aminopropyl triethoxysilane; S2, 70 parts of epoxy resin, 30 parts of acetone and 15 parts of toluene were mixed, 15 parts of Fe304nanoparticles, 10 parts of Fe304microparticles and 0.6 parts of polyvinylpyrrolidone were added, and the mixture was ultrasonically treated for 40 min and mechanically stirred for 1.5 h to obtain a uniform slurry; a coating layer with a thickness of about 120 μm was formed on the surface of the hydrophilic treated substrate by pneumatic spraying, and a magnetic field was applied in stages during curing: 90 Gauss in the first stage and 160 Gauss in the second stage; S3, 10 parts of corn starch were dissolved in deionized water, and the 3- aminopropyl triethoxysilane modified ferric oxide particles were added, and ultrasonic dispersion was performed for 10 min, stirring and mixing, and spray drying was performed to prepare core-shell particles with a particle size of about 5 μm; the particles were dispersed into a suspension with a concentration of 0.3%, softened under a heat-sensitive condition at 60°C, and positioned to the tips of the coating micro-protrusions under the action of a magnetic field, and pressed into a cold fixed state; then the coating was immersed in a mixed solution of octadecylamine and perfluorooctyl triethoxysilane, and reacted at 60°C for 2 h to form a hydrophobic base and a hydrophilic top end; finally, the template was separated under the condition of ultrasonic at 85°C and 40 kHz, and the average recycling times were 4.
[0025] Comparative Example 1 The purpose of the present comparative example is to verify the difference in coating microstructure stability and wetting gradient retention ability when the traditional surface composite magnetic template method is used.
[0026] S1, 10 parts of ferric oxide particles were dispersed in 80 parts of ethanol solution, and after ultrasonic dispersion for 20 min, 3 parts of 3-aminopropyl triethoxysilane were added, and stirring was performed at 65°C for 2 h; after the reaction, filtration, washing and drying were performed to obtain 3-aminopropyl triethoxysilane modified ferric oxide particles; S2, 70 parts of epoxy resin, 30 parts of acetone and 15 parts of toluene were mixed, 15 parts of ferric oxide nanoparticles, 10 parts of ferric oxide microparticles and 0.6 parts of polyvinylpyrrolidone were added, and slurry was obtained by ultrasonic dispersion for 40 min and mechanical stirring for 1.5 h; a coating with a thickness of about 120 μm was formed on the surface of the hydrophilic treated substrate by pneumatic spraying, and a magnetic field was applied in stages during curing: 90 Gauss in the first stage and 160 Gauss in the second stage; S3, the traditional surface composite magnetic template method was used, that is, the 3-aminopropyl triethoxysilane modified ferric oxide particle suspension was directly added dropwise on the surface of the coating, the particles were allowed to stay on the micro-protrusion surface by magnetic field, and the whole was immersed in a mixed solution of octadecylamine and perfluorooctyl triethoxysilane, and reacted at 70°C for 4 h; the template formed a cover layer on the surface, but failed to embed into the protrusion tip, and could not maintain a stable gradient after cooling.
[0027] Comparative Example 2 The purpose of the present comparative example is to verify the difference in coating gas film coverage and template recycling performance when the traditional polymer template method is used.
[0028] S1, 10 parts of ferric oxide particles were dispersed in 80 parts of ethanol solution, and after ultrasonic dispersion for 20 min, 3 parts of 3-aminopropyl triethoxysilane were added, and stirring was performed at 65°C for 2 h; after the reaction, filtration, washing and drying were performed to obtain 3-aminopropyl triethoxysilane modified ferric oxide particles; S2, 70 parts of epoxy resin, 30 parts of acetone and 15 parts of toluene were mixed, 15 parts of Fe304nanoparticles, 10 parts of Fe304microparticles and 0.6 parts of polyvinylpyrrolidone were added, and a slurry was obtained by ultrasonic treatment for 40 min and mechanical stirring for 1.5 h; a coating layer with a thickness of about 120 μm was formed on the surface of the hydrophilic treated substrate by pneumatic spraying, and a magnetic field was applied during curing in stages: 90 Gauss in the first stage and 160 Gauss in the second stage; S3, a conventional polymer template method was used, i.e. 20 parts of corn starch solution was spray dried to obtain solid spherical particles as templates, which were directly and uniformly spread on the surface of the coating layer and lightly pressed to position, and then the whole was immersed in a mixed solution of octadecylamine and perfluorooctyltriethoxysilane and reacted at 70°C for 4 h; the polymer template did not have the property of thermal softening, and could not achieve deep pinning, and finally the coating surface lacked a clear and stable wetting gradient after the template was removed.
[0029] Performance test 1. Air film coverage test method The sample of the example and the comparative example was cut into a 50 mm x 50 mm sheet and fixed to the bottom of a transparent water tank. By filling air and adjusting the water depth to 0.5 m, a high-definition camera was used to take an image of the air film distribution on the surface of the coating layer at a vertical angle. The air film area ratio was calculated using image analysis software to obtain the air film coverage. Each group of samples was tested in parallel for 3 times during the test, and the average value was taken as the final result.
[0030] 2. Drag reduction performance test method The sample was cut into a 100 mm x 20 mm strip and fixed to the bottom of the test section of the flow tank. The water flow velocity of the water tank was set to 0.5 m / s, 1.0 m / s and 1.5 m / s in three gradients, and a differential pressure meter was used to measure the pressure difference between the sample section and the smooth substrate section. According to the formula for calculating frictional resistance, the drag reduction rate was obtained. Each speed was tested 3 times, and the average value was taken.
[0031] 3. Air film stability test method Under the condition of still water with a water depth of 0.5 m, the sample was placed in a transparent water tank, and the air film retention time was observed and recorded. The air film stability was defined as the time required for the air film coverage to drop to 50%. During the test, an optical microscope was used to monitor the local air film rupture process. Different samples were tested in parallel for 3 times, and the average value was taken as the final air film stability index.
[0032] 4. Template recycling performance test method The template of the example and the comparative example was tested for multiple cycles, each cycle including: template combining with coating, hydrophobization treatment, template separation and recovery. The appearance integrity of the template after each cycle was recorded, and the contact angle and air film coverage of the coating surface were measured. Based on the data at the first use, the retention rate after each cycle was calculated. When the retention rate decreased to below 80%, the template was considered to be invalid. Finally, the average number of cycles that the template could be used was counted as an evaluation index of cycle performance.
[0033] Table 1 Comparison of performance test results of examples and comparative examples
[0034] The samples of examples 1-3 and comparative examples 1-2 were tested for system performance to verify the actual application effect of the present application. The air film coverage and stability test results showed that the examples could all form an integrated and continuous air film under water, among which example 2 performed best, with an air film coverage of 92% and a stable maintenance time of up to 50h, which was significantly better than examples 1 and 3, and much higher than 10-12h of the comparative examples. The results showed that the coating treated by the heat-sensitive softening template and deep pinning could effectively maintain the wetting gradient in the underwater environment, thereby ensuring the long-term existence of the air film.
[0035] The test of drag reduction performance further verified the above results. The drag reduction rates of the examples under water flow conditions were all maintained at 33%-42%, which was significantly higher than the level of less than 20% of the comparative examples. Among them, the drag reduction rate of example 2 was the highest, reaching 42%, which showed that it could still effectively reduce the fluid resistance under high flow rate conditions. This performance advantage was directly related to the stable air film on the surface of the coating, which proved the actual value of the present application in energy saving and protection.
[0036] The present application also showed significant advantages in the cycle performance of the template. The templates of the examples could all be recycled and used for multiple times, with the cycle number being between 4-8 times, among which example 2 could be used for up to 8 times. In contrast, the traditional surface composite magnetic template method could hardly realize the recovery of the template, and the traditional polymer template method could be used at most only once. The recyclable feature of the present application not only reduced the material use cost, but also improved the overall green environmental protection value.
[0037] From Figure 1 The template heat-sensitive softening mechanism and deep pinning process schematic and micro-SEM characterization shown in FIGS. 1-3 can intuitively understand the basis of the structure construction of the coating. Figure 2 The EDS fluorine element distribution results shown in FIG. 4 further verified the effectiveness of the hydrophobic modification in the base and side wall areas, while the top end area remained hydrophilic characteristics, which confirmed the existence of the wetting gradient from the element distribution point of view. Figure 3The contact angle measurement and air film demonstration show the performance of the coating in the actual use environment, especially the air film coverage of the sample of Example 2 is complete, the holding time is the longest, and the data in the table is highly consistent.
[0038] In summary, the present application significantly enhances the wetting gradient stability and underwater air film maintenance ability of the mimosa pudica biomimetic coating through the "heat-sensitive softening template - deep pinning" strategy. Among them, Example 2 performs best in air film coverage, drag reduction rate, stability and template recycling performance, and the overall performance is significantly better than the comparative example, fully proving the innovation and practical value of the present application in energy saving and drag reduction and marine protection applications.
Claims
1. A mimicked lotus leaf biomimetic coating based on recyclable heat-softenable template and deep pinning, characterized in that, Prepared from the following raw materials by weight: epoxy resin 60-80 parts; acetone 20-40 parts; toluene 10-20 parts; Fe3O4 nanoparticles 10-20 parts; Fe3O4 microparticles 5-15 parts; polyvinylpyrrolidone 0.2-1.0 parts; corn starch 10-30 parts; Fe3O4 particles modified by 3-aminopropyl triethoxysilane 5-15 parts; octadecylamine 1-5 parts; perfluorooctyl triethoxysilane 1-5 parts; deionized water 50-100 parts; wherein the mass ratio of Fe3O4 nanoparticles to Fe3O4 microparticles is 1:2-2:1, the mass ratio of corn starch to magnetic Fe3O4 particles is 2:1-5:1, after magnetic field stratification regulation and heat-sensitive softening template deep pressing protection, a lotus leaf fern biomimetic coating is formed, which has hydrophobic base and side wall and hydrophilic top end.
2. A lotus leaf biomimetic coating based on reusable heat-sensitive softening template and deep pinning according to claim 1, characterized in that, The coating surface has a micro-protrusion array with a diameter of 5-20 μm and a height of 10-50 μm, the contact angle of the base and the side wall is 150-170°, and the contact angle of the top end region is 40-90°, forming a stable wetting gradient.
3. A mimicked lotus leaf coating based on reusable heat-sensitive softening template and deep pinning according to claim 1, characterized in that, The coating forms a stable gas film underwater, the gas film coverage is 85%-92%, the drag reduction rate is 32%-42%, and the gas film stability is 30-50 hours.
4. A method for preparing a biomimetic coating based on reusable heat-softened template and deeply pinned Salvinia heptameric a, the biomimetic coating based on reusable heat-softened template and deeply pinned Salvinia heptameric a being as claimed in any one of claims 1 to 3, characterized in that, Comprising the following steps: S1, mixing epoxy resin with acetone and toluene, adding Fe3O4 nanoparticles, Fe3O4 microparticles and polyvinylpyrrolidone, and obtaining a uniformly dispersed magnetic spraying slurry through ultrasonic dispersion and mechanical stirring; S2, forming a magnetic coating on the surface of a substrate pretreated by hydrophilization by using a pneumatic spraying method, and applying a magnetic field in stages during the curing process; S3, dissolving corn starch into a heat-sensitive solution, adding Fe3O4 particles modified by 3-aminopropyl triethoxysilane, mixing through ultrasonic dispersion and stirring, and preparing Fe3O4 core-shell structure particles with Fe3O4 core and starch shell by using a spray drying process; S4, dispersing the core-shell particles into a suspension as a template, softening under heat-sensitive conditions, and positioning at the tip of the coating micro-protrusion under the action of a magnetic field; S5, pressing the template into the coating surface under the action of a magnetic field in the softening state of the template to form a deep pinning structure, and maintaining a solidified state after cooling; S6, under the protection of the template, placing the entire coating in a mixed solution of octadecylamine and perfluorooctyl triethoxysilane to hydrophobize the base and the side wall of the micro-protrusion, and keeping the top end region hydrophilic; S7, separating the template from the coating by heating and ultrasonic treatment, and recycling the template for reuse; S8, after template recycling, the coating surface naturally forms a wetting gradient structure with hydrophobic base and side wall and hydrophilic tip.
5. The method according to claim 4, wherein the method is characterized by, The spraying thickness in step S2 is 50-200 μm, and the staged magnetic field includes a first stage strength of 50-120 Gauss and a second stage strength of 120-200 Gauss.
6. The method according to claim 4, wherein the method is characterized by, The preparation step of the four-iron oxide particles modified by 3-aminopropyl triethoxysilane in the step S3 is dispersing the four-iron oxide particles in an ethanol solution, adding 3-aminopropyl triethoxysilane, stirring and reacting for 1-3 hours, and then washing and drying to obtain; the particle size of the core-shell structure particles in the step S3 is 5-15 μm.
7. The method according to claim 4, wherein the method is characterized by, The concentration of the suspension in the step S4 is 0.3%-1.2%.
8. The method according to claim 4, wherein the method is characterized by, The treatment temperature of the step S6 is 60-80 ℃, and the time is 2-6 hours.
9. The method according to claim 4, wherein the method is characterized by, The template recovery temperature of the step S7 is 85-120 ℃, the ultrasonic frequency is 40-80 kHz, and the template can be recycled for 4-8 times on average.