Preparation method and application of modified bionic coating with drag reduction and synergistic performance

Abstract

The invention provides a preparation method and application of a modified bionic coating with resistance reduction and efficiency improvement performance, and belongs to the technical field of ship and ocean engineering coatings. The preparation method comprises the steps that a bionic fish scale array layer is printed on a substrate; carrying out cleaning pretreatment on the substrate to obtain an oil-free and water-free surface to be coated; the preparation method comprises the following steps: dissolving 1H, 1H, 2H, 2H-tridecafluoro-N-octyl silane in absolute ethyl alcohol, carrying out ultrasonic dilution, adding ZIF-8 particles, carrying out magnetic stirring and uniform dispersion, adding a waterborne polyurethane binder, and carrying out ultrasonic treatment to prepare a composite anti-drag spraying liquid; the surface of the bionic structure is evenly coated with the spraying liquid in a surface spray deposition mode, and the bionic drag reduction surface is formed after drying. The bionic anti-drag surface provided by the invention has a remarkable low-resistance characteristic, and the anti-drag rate can exceed 90% under the condition of simulating water flow; meanwhile, the surface has excellent super-hydrophobicity and environmental durability, the water contact angle is larger than 150 degrees, and good self-cleaning and anti-icing performance is shown in the marine environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of surface processing and coating technology, and particularly relates to a preparation method of a modified biomimetic coating with drag reduction and performance enhancement performance and application thereof. BACKGROUND

[0002] Marine transportation is one of the most important transportation modes in international trade. Fuel consumption during the sailing of a ship is mainly used to overcome frictional resistance. At the same time, global warming and energy crisis are becoming major challenges faced by mankind, and the transportation field is one of the important factors leading to these problems.

[0003] Under this background, reducing the greenhouse gas emissions and energy consumption of ships has become an important research topic, and drag reduction technology as a key means to improve the performance of ships and marine engineering equipment has received widespread attention in recent years. From an economic point of view, effective drag reduction can significantly reduce the sailing resistance of a ship, improve the streamline characteristics of the ship surface, thereby improving fuel efficiency and reducing energy consumption; at the same time, the application of drag reduction coating or surface treatment technology also helps to delay material corrosion and reduce maintenance costs. In terms of ecological environment, the energy efficiency improvement brought by drag reduction directly reduces greenhouse gas emissions; in addition, optimizing fluid dynamic performance also helps to reduce disturbance to the marine ecological environment and reduce the potential threat of alien species transferred by ships to local biodiversity.

[0004] The widely used ship drag reduction surface is prone to surface property degradation or physical damage during long-term operation, resulting in unstable drag reduction effect, and even increasing additional resistance, which is not conducive to improving energy efficiency and reducing carbon emissions.

[0005] Therefore, there is an urgent need in this field to develop a new drag reduction surface with sustained stability, environmental friendliness and long-term low resistance performance to reduce energy consumption and environmental impact during ship operation. SUMMARY

[0006] This section aims to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification to avoid obscuring the purpose of this section, abstract and title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0007] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0008] Therefore, the purpose of the present application is to overcome the deficiencies in the prior art, and to provide a green marine biomimetic drag reduction surface formula and manufacturing method which is convenient for construction.

[0009] To solve the above technical problems, the application provides the following technical scheme: a modified bionic surface with drag reduction and efficiency improvement performance, comprising the following steps: (1) dissect real tuna to obtain fish scale layer skin tissue, scan the tuna skin sample to obtain point cloud data model, pre-process and simplify the point cloud data to establish a bionic model, so as to construct a bionic fish scale entity model with array-like structure; the tuna is obtained from a seafood market; (2) a bionic fish scale layer with fish scale array-like arrangement is manufactured on a substrate by an SLA stereolithography process through a 3D printer; after printing, the bionic fish scale surface is repeatedly cleaned by ultrasonic ethanol; the substrate is high-toughness photosensitive resin; (3) 1H, 1H, 2H, 2H-tridecafluoro-N-octylsilane (PFOTS) is ultrasonically diluted in anhydrous ethanol, and then dry ZIF-8 particles are dispersed in the solution and magnetically stirred; (4) water-based polyurethane is added to the above solution, and the mixed solution is ultrasonically treated and then poured into a sprayer; (5) after controlling the spraying distance, the ultrasonically treated ZIF-8 solution is repeatedly sprayed on the bionic surface in a spray deposition manner; after completion, the bionic drag reduction surface is obtained by drying in a drying box.

[0010] The drag reduction mechanism of the application mainly originates from the synergistic effect of the unique surface structure design and functional materials. Based on the reconstruction of the array-like arrangement of tuna scale, combined with low surface energy chemical modification and micro-nano composite coating, the fusion of multiple drag reduction mechanisms is realized. The biomimetic scale layer is precisely manufactured by SLA process using high-toughness photosensitive resin, and the array-like arrangement of the scale structure can effectively guide the water flow and reduce the wall friction resistance. The microstructure can inhibit the formation of turbulent boundary layer and reduce vortex generation, thereby significantly reducing the surface viscous drag. ZIF-8 particles are introduced into the spraying solution to construct a micro-nano composite rough structure, which significantly enhances the hydrophobic performance of the surface. On this basis, 1H, 1H, 2H, 2H-tridecafluoro-N-octylsilane is used as a low surface energy modifier to form a stable perfluoroalkyl monolayer on the biomimetic surface through chemical bonding, thereby greatly reducing the surface free energy. Waterborne polyurethane is used as an adhesive to ensure the firm combination of ZIF-8 particles and the substrate, and also maintains the flexibility of the coating as a whole. The finally constructed biomimetic drag reduction surface combines the dual mechanisms of physical microstructure flow guiding and chemical hydrophobicity and adhesion resistance: the microscale scale structure effectively regulates the near-wall flow field distribution, and the superhydrophobic surface significantly reduces the solid-liquid contact area through stable gas film. What is particularly prominent is that the synergistic effect of the above three functional materials makes the prepared surface show unexpected technical effects in terms of drag reduction performance - compared with the surface treated only with a single hydrophobic material or conventional roughening, the drag reduction rate of the present application is increased by more than expected under the same flow rate conditions, verifying the non-obvious synergistic effect between the structure design and the material combination.

[0011] As a preferred scheme of the biomimetic drag reduction surface described in the application, wherein: the inclination angle of the fish scale of the 3D printed biomimetic scale layer with fish scale array-like arrangement is in the range of 10-30 degrees relative to the scale of the substrate surface.

[0012] As a preferred scheme of the biomimetic drag reduction surface described in the application, wherein: the mass ratio of 1H, 1H, 2H, 2H-tridecafluoro-N-octylsilane to anhydrous ethanol is 1:65~75.

[0013] As a preferred scheme of the biomimetic drag reduction surface described in the application, wherein: the mass ratio of ZIF-8 particles to waterborne polyurethane is 1:0.65~0.8, and the concentration of the ZIF-8 solution is 35mg / mL.

[0014] As a preferred scheme of the biomimetic drag reduction surface described in the application, wherein: the particle size of ZIF-8 is not more than 0.2μm, and the spraying distance is not more than 20cm.

[0015] The application has the following beneficial effects: (1) The bionic drag reduction surface provided by the application can significantly reduce the frictional resistance and viscous resistance in ship navigation through the synergistic effect of the array-shaped microstructure and the low surface energy coating; the bionic model is introduced into the real tuna scale morphological characteristics, so that the drag reduction structure has biological rationality and engineering feasibility, and the optimization effect of fluid mechanics is improved.

[0016] (2) The ZIF-8 reinforced composite coating has excellent hydrophobicity, mechanical durability and marine environment adaptability, effectively prolonging the service life of the drag reduction surface; the environment-friendly formula provided by the application uses water-based polyurethane as the bonding matrix, greatly reducing the use and emission of volatile organic compounds, and meets the green marine equipment manufacturing requirements. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor. Among them: Figure 1 It is a schematic diagram for testing the drag reduction performance of the modified bionic pipeline in the embodiment.

[0018] Figure 2 It is a schematic diagram of the self-cleaning property of the bionic drag reduction surface.

[0019] Figure 3 It is a schematic diagram of the scanning electron microscope of the bionic drag reduction surface before and after sandpaper abrasion.

[0020] Figure 4 It is a schematic diagram of the adhesion performance test of the bionic drag reduction surface.

[0021] Figure 5 It is a schematic diagram of the water erosion performance test of the bionic drag reduction surface.

[0022] Figure 6 It is a schematic diagram of the process of ice formation on the bionic drag reduction surface and the smooth surface. DETAILED DESCRIPTION

[0023] In order to make the above-mentioned purposes, features and advantages of the application more obvious and easy to understand, the specific embodiments of the application will be described in detail in conjunction with the description of the embodiments.

[0024] The polyvinylpyrrolidone in the embodiment of the application is purchased from Shanghai Maikelin Biochemical Technology Co., Ltd., and the batch is C15207561; 1H,1H,2H,2H-tetrafluoro-N-octylsilane was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., batch number K2415035; 2-Methylimidazolium zinc salt (ZIF-8 granules) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., batch number C17171434; The waterborne polyurethane was purchased from Shanghai McLean Biochemical Technology Co., Ltd., batch number C17454501.

[0025] The modified biomimetic surface of this invention, which has drag-reducing and efficiency-enhancing properties, is achieved through, for example... Figure 1 The process shown involves using a high-toughness photosensitive resin as the research substrate. The biomimetic surface of the 3D-printed high-toughness photosensitive resin substrate is cleaned, and then the prepolymer is uniformly sprayed onto the substrate surface. Finally, the substrate is placed in a drying oven for drying to obtain the surface.

[0026] In this embodiment of the invention, the high-toughness photosensitive resin substrate has a size of 32×22×1.5mm, the cross-sectional size of a single biomimetic scale is 2×1.15mm, and the particle size of ZIF-8 is 0.1-0.2μm. In order to comprehensively evaluate the drag reduction performance of the ZIF-8 modified surface, the drag reduction performance was evaluated using a specially made extended biomimetic fish scale pipe.

[0027] (1) Drag reduction performance test in this invention: Based on the original sample, the size was increased to 300×60×1.5mm. Due to the thermal self-healing properties of the material, the sample was bent to form a water delivery pipe, and a ZIF-8 modified coating was sprayed on the center line of the inner wall of the pipe to control the water droplets to flow along a consistent path.

[0028] 100 μL water droplets were introduced into smooth pipes, modified smooth pipes, 10-degree modified pipes, 15-degree modified pipes, 20-degree modified pipes, and 30-degree modified pipes at a 45-degree angle, respectively, and the time taken for the droplet to travel through the entire pipe was recorded. The experiment was repeated multiple times, and the median time was taken to ensure data accuracy.

[0029] (2) Self-cleaning performance test: In drag reduction applications for underwater vehicles, the self-cleaning performance of biomimetic modified coatings is particularly important to ensure more effective resistance to various marine pollutants. In the self-cleaning performance test, mud and dust, two common outdoor pollutants, were selected, and a mixture of the two was used as the pollutant for experimental testing.

[0030] The mixture of ash and soil was evenly spread on both uncoated and coated biomimetic surfaces. The changes in the state of water droplets rolling onto the surfaces were recorded by a camera to compare and determine its self-cleaning performance.

[0031] (3) Durability test: To evaluate the durability of the modified coating, a sandpaper abrasion test was conducted. First, samples were prepared by applying the modified coating to a biomimetic surface. During testing, 800-grit sandpaper was fixed flat on a worktable. Each sample was then placed coating-side down on the sandpaper and securely held in a custom-designed clamp to prevent slippage during the experiment. A 50g weight was placed on the sample as a pressure source. The sample was then dragged across the sandpaper at a constant speed, with each 5cm slip defined as one abrasion cycle. The sample mass was weighed periodically, specifically before testing and after every 100 cycles. Mass loss and retention were calculated based on these measurements to determine the coating's abrasion resistance.

[0032] (4) Adhesion performance test: Since the adhesion between the modified coating and the specimen is a key parameter for evaluating coating durability, a tape peel test was performed according to the ASTM D3359 classification standard to evaluate this critical parameter. Adhesion performance was assessed from the tape peel test methodology using the ASTM D3359 rating scale. Following the standard protocol, the coated surface on the steel plate was prepared by creating a uniform cross-shading pattern. Subsequently, 3M tape was firmly adhered to the prepared area and then quickly removed. A standard comparative inspection of the coated surface was performed to determine the appropriate adhesion rating.

[0033] (5) Erosion performance test: The effect of nanoparticle addition on the erosion resistance of the modified coating was evaluated using a water erosion test. Samples were exposed to a sand-laden cement slurry containing 14% by weight of sand, and impacted at a 60-degree angle and a speed of 14 meters per second. The total duration of the erosion test was 12 hours. Samples were extracted every 3 hours throughout the test. After each extraction, the sample was weighed and then subjected to ultrasonic cleaning for 3 to 5 minutes to remove loosely attached debris. The surface morphology after cleaning was then recorded, and the evaluation criterion was the material mass loss rate.

[0034] (6) Anti-icing performance test: In addition to its application in drag reduction, the anti-icing performance of samples was tested through an icing test to evaluate the surface morphology of the samples in extreme temperature environments, given the thermal self-healing properties of the high-toughness resin material.

[0035] 40 μL water droplets were dropped onto both uncoated and coated biomimetic surfaces, and then placed in ultra-low temperature freezers at -10°C, -15°C, and -20°C for testing. Throughout the experiment, the morphological changes of the water droplets and the time of these changes were recorded until freezing. The anti-icing performance of the surfaces was evaluated based on the freezing time of the water droplets.

[0036] Example 1 (1) A biomimetic fish scale layer with an array of fish scales was manufactured by 3D printing of resin material using SLA stereolithography process. The substrate was a resin substrate, the stereolithography 3D printer was a UnionTech G1400, the laser power was controlled at 200±10mW, the spot diameter was 80±5μm, the single layer curing thickness was set to 50μm, and the scanning speed was set to 6000 mm / s. The resin type is high-toughness standard photosensitive resin, with a surface heat distortion temperature of 58 ℃, water absorption of 0.26%, tensile modulus of 2600MPa, tensile strength of 52.3MPa, fracture strain of 11%, yield strain of 3.4%, and dimensions of 32×22×1.5mm. See fish scale structure Figure 1 (b) Its three-dimensional morphology is a micro-protrusion structure with a specific curvature, and the top has an approximately elliptical outline. The fish scale is 2 mm long, 1.15 mm wide, and 0.3 mm high (i.e., thick). The scale tilt angle (the acute angle formed by the raised part of the fish scale structure and the base plane) is 10 degrees. Rinse repeatedly with deionized water and dry.

[0037] (2) In 50 o C. Prepare a PFOTS solution with a concentration of 12.8 mg / mL at 800 rpm, and disperse 1.2 g of dried ZIF-8 particles in the above solution with a PFOTS content of 310 μL and stir magnetically. (3) Prepare ZIF-8 particles and waterborne polyurethane at a mass ratio of 1:0.75. After mixing thoroughly, add 0.9g of waterborne polyurethane. After ultrasonic treatment of the mixed solution, pour it into a sprayer. (4) After controlling the spraying distance, ZIF-8 solution was repeatedly sprayed evenly onto the oil-free and water-free biomimetic fish scale substrate. After observing that the sprayed material covered the substrate, the sample was placed in a drying oven to dry and obtain a biomimetic drag-reducing surface with a thickness of 1.5 mm, which was named MBS10°.

[0038] Example 2 (1) A biomimetic fish scale layer with an array of fish scales was manufactured by 3D printing of resin material using SLA stereolithography process. The printing process was the same as in Example 1. The size was 32×22×1.5mm and the fish scale tilt angle was 15 degrees. The material was repeatedly rinsed with deionized water and dried.

[0039] (2) In 50 oC. Prepare a PFOTS solution with a concentration of 12.8 mg / mL at 800 rpm, and disperse 1.2 g of dried ZIF-8 particles in the above solution with a PFOTS content of 310 μL and stir magnetically. (3) Prepare ZIF-8 particles and waterborne polyurethane at a mass ratio of 1:0.75. After mixing thoroughly, add 0.9g of waterborne polyurethane. After ultrasonic treatment of the mixed solution, pour it into a sprayer. (4) After controlling the spraying distance, ZIF-8 solution was repeatedly sprayed evenly onto the oil-free and water-free biomimetic fish scale substrate. After observing that the sprayed material covered the substrate, the sample was placed in a drying oven to dry and obtain a biomimetic drag-reducing surface with a thickness of 1.6 mm, which was named MBS15°.

[0040] Example 3 (1) A biomimetic fish scale layer with an array of fish scales was manufactured by 3D printing of resin material using SLA stereolithography process. The printing process was the same as in Example 1. The size was 32×22×1.5mm and the fish scale tilt angle was 20 degrees. The scales were repeatedly rinsed with deionized water and dried. (2) In 50 o C. Prepare a PFOTS solution with a concentration of 12.8 mg / mL at 800 rpm, and disperse 1.2 g of dried ZIF-8 particles in the above solution with a PFOTS content of 310 μL and stir magnetically. (3) Prepare ZIF-8 particles and waterborne polyurethane at a mass ratio of 1:0.75. After mixing thoroughly, add 0.9g of waterborne polyurethane. After ultrasonic treatment of the mixed solution, pour it into a sprayer. (4) After controlling the spraying distance, ZIF-8 solution was repeatedly sprayed evenly onto the oil-free and water-free biomimetic fish scale substrate. After observing that the sprayed material covered the substrate, the sample was placed in a drying oven to dry and obtain a biomimetic drag-reducing surface with a thickness of 1.7 mm, which was named MBS20°.

[0041] Example 4 (1) A biomimetic fish scale layer with an array of fish scales was manufactured by 3D printing of resin material using SLA stereolithography process. The printing process was the same as in Example 1. The size was 32×22×1.5mm and the fish scale tilt angle was 30 degrees. The scales were repeatedly rinsed with deionized water and dried. (2) In 50 o C. Prepare a PFOTS solution with a concentration of 12.8 mg / mL at 800 rpm, and disperse 1.2 g of dried ZIF-8 particles in the above solution with a PFOTS content of 310 μL and stir magnetically. (3) Prepare ZIF-8 particles and waterborne polyurethane at a mass ratio of 1:0.75. After mixing thoroughly, add 0.9g of waterborne polyurethane. After ultrasonic treatment of the mixed solution, pour it into a sprayer. (4) After controlling the spraying distance, ZIF-8 solution was repeatedly sprayed evenly onto the oil-free and water-free biomimetic fish scale substrate. After observing that the sprayed material covered the substrate, the sample was placed in a drying oven to dry and obtain a biomimetic drag-reducing surface with a thickness of 1.9 mm, which was named MBS30°.

[0042] Table 1. Characterization of various properties of modified biomimetic surfaces with drag reduction and efficiency enhancement properties

[0043] As shown in Table 1, the biomimetic drag-reducing surface prepared by the formulation in Example 4 of the present invention has the highest drag reduction rate. The test schematic diagram is shown below. Figure 1 As shown in (a), the appropriate fish scale tilt angle and the modified coating work together to greatly enhance the surface’s ability to reduce resistance underwater. As shown in Table 1, the biomimetic drag-reducing surfaces prepared by the formulations in the embodiments of the present invention all possess extremely high surface dirt removal rates and can play a self-cleaning role. Figure 2 As shown, where Figure 2 (a) Bionic surface samples with modified coating and uncoated bionic surface, (b) and (c) Self-cleaning performance of ZIF-8 modified coating.

[0044] As shown in Table 1, the biomimetic drag-reducing surface prepared by the formulation in Example 1 of the present invention has the highest sandpaper wear quality retention rate, indicating that the coating has excellent wear resistance. Figure 3 As shown, (a) to (d) are SEM images of MBS samples with tilt angles of 10°, 15°, 20° and 30° before the test; (e) to (h) are SEM images of MBS samples with tilt angles of 10°, 15°, 20° and 30° after the test at a wear distance of 4000cm.

[0045] As shown in Table 1, the biomimetic drag-reducing surfaces prepared by the formulations in the embodiments of the present invention all have an ASTM adhesion rating of 4B, indicating that the coating has excellent adhesion. Figure 4 As shown, the test was conducted according to ASTM D3359 standard on the modified biomimetic surface (MBS 30°) with a scale tilt angle of 30° prepared in Example 4. Figure 4As shown, (a) untested MBS sample; (b) before tape peeling (showing 3M tape pressed onto the coated surface); (c) tape peeling (showing the process of quickly tearing off at a 180° angle); (d) scratches left when cutting the surface with a cutter (showing standard square scratches); (e) after tape peeling (showing no coating peeling at the intersection of scratches). As shown in Table 1, the biomimetic drag-reducing surface prepared by the formulation in Example 4 of the present invention exhibits the best mass loss rate in the water erosion test, indicating that the coating has excellent corrosion resistance. Figure 5 As shown; As shown in Table 1, the biomimetic drag-reducing surface prepared by the formulation in Example 4 of the present invention exhibits the best anti-icing performance. This study aims to systematically evaluate the ability of biomimetic surfaces to inhibit or delay ice formation and reduce ice adhesion strength, thereby mitigating the impact of low-temperature underwater environments on the biomimetic surface. Figure 6 As shown, (a) and (b) are optical photographs of the biomimetic surface samples with modified coating and uncoated biomimetic surface samples during the freezing process at -10°C.

[0046] Comparative Example 1 (1) A biomimetic fish scale layer with an array of fish scales was manufactured by 3D printing of resin material using SLA stereolithography process. The size was 32×22×1.5mm and the fish scale tilt angle was 30 degrees. The scale was repeatedly rinsed with deionized water and dried. (2) In 50 o C. Prepare a PFOTS solution with a concentration of 12.8 mg / mL at 800 rpm, and disperse 1.2 g of dried ZIF-8 particles in the solution and stir magnetically. (3) Prepare ZIF-8 particles and waterborne polyurethane at a mass ratio of 1:0.75. After mixing thoroughly, add 0.9g of waterborne polyurethane. After ultrasonic treatment of the mixed solution, pour it into a sprayer. (4) After controlling the spraying distance, ZIF-8 solution was repeatedly sprayed evenly onto the oil-free and water-free biomimetic fish scale substrate. After observing that the sprayed material covered the substrate, the sample was placed in a drying oven to dry and obtain a biomimetic drag-reducing surface with a thickness of 1.9 mm, named MBS30°. (5) To evaluate the effect of the biomimetic drag-reducing surface on drag reduction performance after sandpaper abrasion test, the sample was dragged on 800-grit sandpaper at a constant speed, and each 5cm slide was defined as a wear cycle. The mass of the sample was weighed periodically, specifically before the test and after every 500cm of cumulative wear (i.e., every 100 cycles). After the wear distance reached 4000cm, the sample was taken out for drag reduction performance test.

[0047] Compared with Example 4, this comparative example includes a sandpaper abrasion test, but otherwise remains the same as Example 4.

[0048] The test showed that the drag reduction effect of the coating decreased. The reason was that the biomimetic fish scale layer was worn. However, the surface coating was worn very little and still maintained an excellent drag reduction and efficiency enhancement effect.

[0049] Comparative Example 2 (1) A biomimetic fish scale layer with an array of fish scales was manufactured by 3D printing of resin material using SLA stereolithography process. The size was 32×22×1.5mm and the fish scale tilt angle was 30 degrees. The scale was repeatedly rinsed with deionized water and dried. (2) In 50 o C. Prepare a PFOTS solution with a concentration of 12.8 mg / mL at 800 rpm, and disperse 1.2 g of dried ZIF-8 particles in the above solution with a PFOTS content of 310 μL and stir magnetically. (3) Prepare ZIF-8 particles and waterborne polyurethane at a mass ratio of 1:0.75. After mixing thoroughly, add 0.9g of waterborne polyurethane. After ultrasonic treatment of the mixed solution, pour it into a sprayer. (4) After controlling the spraying distance, ZIF-8 solution was repeatedly sprayed evenly onto the oil-free and water-free biomimetic fish scale substrate. After observing that the sprayed material covered the substrate, the sample was placed in a drying oven to dry and obtain a biomimetic drag-reducing surface with a thickness of 1.9 mm, named MBS30°. (5) To evaluate the effect of the biomimetic drag-reducing surface on drag reduction performance after immersion in a strong acid solution, the sample was immersed in a strong acid solution with pH=1 for 12 hours and then taken out for drag reduction performance testing.

[0050] Compared with Example 4, this comparative example was tested by immersion in a strong acid solution, but otherwise it was the same as Example 4.

[0051] The test showed a slight decrease in the drag reduction effect of the coating. It was determined that the strong acid immersion had some impact on the coating, but the surface coating was less affected, and the biomimetic fish scale layer structure on the surface was not affected, so it still maintained an excellent drag reduction and efficiency enhancement effect.

[0052] Comparative Example 3 (1) A biomimetic fish scale layer with an array of fish scales was manufactured by 3D printing of resin material using SLA stereolithography process. The size was 32×22×1.5mm and the fish scale tilt angle was 30 degrees. The scale was repeatedly rinsed with deionized water and dried. (2) In 50 o C. Prepare a PFOTS solution with a concentration of 12.8 mg / mL at 800 rpm, and disperse 1.2 g of dried ZIF-8 particles in the above solution with a PFOTS content of 310 μL and stir magnetically. (3) Prepare ZIF-8 particles and waterborne polyurethane at a mass ratio of 1:0.75. After mixing thoroughly, add 0.9g of waterborne polyurethane. After ultrasonic treatment of the mixed solution, pour it into a sprayer. (4) After controlling the spraying distance, ZIF-8 solution was repeatedly sprayed evenly onto the oil-free and water-free biomimetic fish scale substrate. After observing that the sprayed material covered the substrate, the sample was placed in a drying oven to dry and obtain a biomimetic drag-reducing surface with a thickness of 1.9 mm, named MBS30°. (5) To evaluate the effect of the biomimetic drag-reducing surface on drag reduction performance after immersion in a weak acid solution, the sample was immersed in a strong acid solution with pH=4 for 12 hours and then taken out for drag reduction performance testing.

[0053] Compared with Example 4, this comparative example was tested by soaking in a weak acid solution, but otherwise it was the same as Example 4.

[0054] The test showed a slight decrease in the drag reduction effect of the coating. The reason was that the weak acid immersion had a slight impact on the coating, but the surface coating was minimally affected, and the biomimetic fish scale layer structure on the surface was not affected, so it still maintained an excellent drag reduction and efficiency enhancement effect.

[0055] Comparative Example 4 (1) A biomimetic fish scale layer with an array of fish scales was manufactured by 3D printing of resin material using SLA stereolithography process. The size was 32×22×1.5mm and the fish scale tilt angle was 30 degrees. The scale was repeatedly rinsed with deionized water and dried. (2) In 50 o C. Prepare a PFOTS solution with a concentration of 12.8 mg / mL at 800 rpm, and disperse 1.2 g of dried ZIF-8 particles in the above solution with a PFOTS content of 310 μL and stir magnetically. (3) Prepare ZIF-8 particles and waterborne polyurethane at a mass ratio of 1:0.75. After mixing thoroughly, add 0.9g of waterborne polyurethane. After ultrasonic treatment of the mixed solution, pour it into a sprayer. (4) After controlling the spraying distance, ZIF-8 solution was repeatedly sprayed evenly onto the oil-free and water-free biomimetic fish scale substrate. After observing that the sprayed material covered the substrate, the sample was placed in a drying oven to dry and obtain a biomimetic drag-reducing surface with a thickness of 1.9 mm, named MBS30°. (5) To evaluate the effect of the biomimetic drag-reducing surface on drag reduction performance after immersion in a weak alkaline solution, the sample was immersed in a strong alkaline solution with pH=9 for 12 hours and then taken out for drag reduction performance testing.

[0056] Compared with Example 4, this comparative example was tested by soaking in a weak alkaline solution, but otherwise it was the same as Example 4.

[0057] The test showed a slight decrease in the drag reduction effect of the coating. The reason was that the weak alkali soaking had a slight impact on the coating, but the surface coating was minimally affected, and the biomimetic fish scale layer structure on the surface was not affected, so it still maintained an excellent drag reduction and efficiency enhancement effect.

[0058] Comparative Example 5 (1) A biomimetic fish scale layer with an array of fish scales was manufactured by 3D printing of resin material using SLA stereolithography process. The size was 32×22×1.5mm and the fish scale tilt angle was 30 degrees. The scale was repeatedly rinsed with deionized water and dried. (2) In 50 o C. Prepare a PFOTS solution with a concentration of 12.8 mg / mL at 800 rpm, and disperse 1.2 g of dried ZIF-8 particles in the above solution with a PFOTS content of 310 μL and stir magnetically. (3) Prepare ZIF-8 particles and waterborne polyurethane at a mass ratio of 1:0.75. After mixing thoroughly, add 0.9g of waterborne polyurethane. After ultrasonic treatment of the mixed solution, pour it into a sprayer. (4) After controlling the spraying distance, ZIF-8 solution was repeatedly sprayed evenly onto the oil-free and water-free biomimetic fish scale substrate. After observing that the sprayed material covered the substrate, the sample was placed in a drying oven to dry and obtain a biomimetic drag-reducing surface with a thickness of 1.9 mm, named MBS30°. (5) To evaluate the effect of the biomimetic drag-reducing surface on drag reduction performance after immersion in a strong alkaline solution, the sample was immersed in a strong alkaline solution with pH=13 for 12 hours and then taken out for drag reduction performance testing.

[0059] Compared with Example 4, this comparative example was tested by soaking in a strong alkaline solution, but otherwise it was the same as Example 4.

[0060] The test showed a slight decrease in the drag reduction effect of the coating. It was determined that the strong alkali soaking had some impact on the coating, but the surface coating was less affected, and the biomimetic fish scale layer structure on the surface was not affected, so it still maintained an excellent drag reduction and efficiency enhancement effect.

[0061] Table 2. Drag reduction rate after testing of biomimetic drag-reducing coating.

[0062] Comparative Example 6 Under the same preparation process conditions as in Example 4, this comparative example only changed the scale tilt angle from 30° to 40°, while keeping the other structural parameters and processing methods unchanged.

[0063] Performance test results show that the drag reduction effect of the 40° tilt angle structure is significantly lower than that of Example 4, specifically, the drag reduction rate drops from 92.1% in Example 4 to 67.3%, a decrease of 24.8%. At the same time, after mechanical wear testing under the same conditions, the coating damage on the surface of this structure is significantly aggravated. After a 4000 cm wear test, the mass loss reaches 63.5 mg, which is about 49.8% higher than 42.4 mg in Example 4, showing poor durability. In addition, the 40° tilt angle sample shows obvious coating cracks and local peeling on the surface, while the sample in Example 4 only shows uniform surface wear.

[0064] Analysis suggests that a 40° tilt angle deteriorates the surface micro-stress distribution, directly weakening its drag-reduction function and adversely affecting the coating's mechanical stability. These results demonstrate that the scale tilt angle has a defined optimization range in this invention; parameter settings exceeding this range lead to a significant deterioration in overall performance indicators such as drag reduction and durability.

[0065] Comparative Example 7 While fully following the preparation process of Example 4, only PFOTS was replaced in equal molar amounts with hexadecyltrimethoxysilane, a hydrophobic modifier commonly used in the art.

[0066] Performance test results show that the hydrophobic properties of the obtained coating are significantly reduced, specifically, the water contact angle decreases from 152.9°±2° in the PFOTS system to 128.4°±3°; the underwater gas film maintenance ability is significantly weakened, and the gas film stabilization time is shortened from >120 minutes to <20 minutes; its final drag reduction effect is not only far lower than that of the embodiment of the present invention using PFOTS, but the drag reduction rate is only 58.5%, which is significantly lower than the 92.1% of the PFOTS system.

[0067] This phenomenon proves that conventional silane materials, lacking the specific perfluorinated chain structure of PFOTS, cannot achieve the same level of surface energy reduction and gas film stabilization.

[0068] Comparative Example 8 This comparative study aims to verify the synergistic effect of ZIF-8 and PFOTS in functional coatings. Three parallel experiments were conducted for comparison. Group A uses a pure ZIF-8 material system; Group B uses a pure PFOTS material system; Group C is the ZIF-8 / PFOTS composite system of the present invention; All experimental groups maintained a consistent total solids content of 1.5g, and each system contained waterborne polyurethane (WPU) as a binder, with the amount of WPU used consistent with that in Example 4. Group A consisted of 1.5g of ZIF-8 / WPU composite, with a ZIF-8 to WPU ratio of 1:0.75; Group B consisted of PFOTS / WPU composite, with a PFOTS to WPU ratio of 1:2.75; and Group C consisted of a composite of ZIF-8 and PFOTS / WPU mixed according to the ratio in Example 4, with a ZIF-8 to PFOTS and WPU ratio of 1:0.75:0.9. The same spraying process parameters were used, including a spraying distance of 20 cm, a carrier gas pressure of 0.3 MPa, and post-treatment conditions of heat treatment at 80°C for 2 h.

[0069] Under strict control of the total solids content, the system performance test results show that the drag reduction performance of the composite system is significantly better than the expected linear superposition of the performance of each single component system. Specifically, group A has a drag reduction rate of 65.1%, group B 59.3%, while group C reaches 92.1%, significantly higher than the theoretical superposition value of 76.3%, exhibiting a synergistic gain effect of 20.6%, demonstrating a typical "1+1>2" synergistic enhancement effect. This non-linear performance improvement fully demonstrates that the synergistic effect of ZIF-8 and PFOTS under specific ratios is non-obvious, reflecting the unexpected technical effects brought about by the material compounding scheme of this invention.

[0070] In summary, the biomimetic drag-reducing surface prepared by this invention exhibits excellent drag-reduction stability and durability under various harsh environments. After sandpaper abrasion tests and immersion treatment in strong acid, strong alkali, weak acid, and weak alkali solutions, the surface still maintains extremely low flow resistance and highly efficient drag-reduction and enhancement performance. The synergistic effect of its biomimetic microstructure and low surface energy coating does not show significant attenuation, demonstrating good mechanical strength and chemical stability.

[0071] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for preparing a modified biomimetic coating with drag-reducing performance, characterized in that: Comprising, 3D printing a biomimetic fish scale structure layer on a substrate, wherein the biomimetic fish scale has a scale inclination angle of 10°-30° relative to the surface of the substrate; Pre-treating the surface of the substrate to ensure no oil stains and no water residue; Dissolving 1H, 1H, 2H, 2H-tridecafluoro-N-octylsilane in anhydrous ethanol, adding dry ZIF-8 particles after ultrasonic dilution, and magnetically stirring to disperse uniformly; Adding aqueous polyurethane to the above solution, and ultrasonic treatment again to form a composite spraying liquid; Spraying the composite liquid uniformly on the surface of the biomimetic fish scale structure by the way of spray deposition surface, and forming the drag reduction biomimetic surface after drying treatment.

2. The production method according to claim 1, characterized by: The pre-treatment of the surface of the substrate comprises, Cleaning the surface of the substrate with anhydrous ethanol and deionized water in sequence, and performing ultrasonic cleaning to obtain an oil-free and water-free substrate to be sprayed.

3. The production method according to claim 1 or 2, characterized by: The substrate comprises common surface materials such as resin, polyurethane, polyethylene and polyamide.

4. The production method according to claim 1, wherein: The high-toughness resin substrate has a tensile modulus of not more than 2600 MPa and a tensile strength of not more than 52.3 MPa.

5. The production method according to claim 1, wherein: The biomimetic fish scale has a scale inclination angle of 10°-30° relative to the surface of the substrate.

6. The production method according to claim 1, wherein: The mass ratio of 1H, 1H, 2H, 2H-tridecafluoro-N-octylsilane to anhydrous ethanol is 1:65-75.

7. The production method according to claim 1, wherein: The mass ratio of ZIF-8 particles to aqueous polyurethane is 1:0.65-0.8, and the concentration of the ZIF-8 solution is 35 mg / mL.

8. The production method according to claim 1, wherein: The particle size of the ZIF-8 is not more than 0.2 μm, and the spraying distance is not more than 20 cm.

9. The modified biomimetic coating with drag reduction and efficiency enhancement performance prepared by the preparation method of any one of claims 1-8.

10. The application of the biomimetic drag reduction coating of claim 9 in drag reduction and efficiency enhancement of underwater vehicles.

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