Preparation method and application of self-healing superhydrophobic coating based on ZB@BN / SiO2 bilayer structure

Abstract

The application discloses a preparation method and application of a self-repairing super-hydrophobic coating based on a ZB@BN / SiO2 double-layer structure, and the preparation method comprises the following steps: uniformly mixing ZB@BN composite particles and double-component polyurethane resin in a solvent, and coating on a substrate surface; uniformly mixing micron-grade coupling agent modified SiO2 particles and double-component polyurethane resin in a solvent, and coating on a hydrophilic bottom layer; uniformly mixing nano-grade coupling agent modified SiO2 particles and double-component polyurethane resin in a solvent, and coating on a micron coarse structure layer after semi-curing of the micron coarse structure layer, so that the double-layer structure self-repairing super-hydrophobic coating is obtained after solidification. The innovative double-layer structure combines the rapid active repair of the bottom layer with the long-term passive barrier of the top layer, the top super-hydrophobic layer provides excellent physical barrier and drag reduction functions, the 'labyrinth effect' of the BN nanosheet of the bottom layer prolongs the corrosion path, ZIF-8@BTA provides corrosion protection, and the two cooperate to endow the coating with excellent long-term corrosion resistance, self-repairing and drag reduction performance.

Description

Technical Field

[0001] This invention relates to functional coatings for metal surfaces, specifically to a method for preparing and applying a self-healing superhydrophobic coating based on a ZB@BN / SiO2 bilayer structure. Background Technology

[0002] In the aerospace industry, aluminum alloys are widely used in key structural components such as aircraft skin, frames, and cabins due to their excellent specific strength, machinability, and economy. However, aircraft face a harsh, multi-factor coupled environment during service: ultraviolet radiation in the high-altitude atmosphere, cyclical changes in temperature and pressure, moisture, and corrosive media such as de-icing fluids and salt spray that may be encountered in the airport ground environment can all accelerate the corrosion process of aluminum alloy structures, such as pitting corrosion and stress corrosion cracking, seriously threatening flight safety and structural lifespan, and resulting in high maintenance costs.

[0003] Meanwhile, aircraft manufacturers have a perpetual pursuit of weight reduction and improved fuel economy. Frictional drag on the fuselage surface is one of the important factors affecting aerodynamic efficiency. Superhydrophobic surface technology, inspired by the lotus effect, can theoretically reduce viscous drag at the air-solid interface by constructing micro-nano rough structures and modifying them with low surface energy. It also possesses potential advantages such as waterproofing, anti-icing, and self-cleaning, which is of great significance for improving aircraft performance.

[0004] Currently, the protection of aerospace aluminum alloys mainly relies on chromate conversion coatings or conventional organic coatings. These technologies either have environmental toxicity issues or lack dynamic damage repair capabilities. Existing research on single superhydrophobic coatings largely focuses on static hydrophobic properties; their fragile micro-nano structures are easily damaged by high-speed airflow, sand and gravel impacts, or routine maintenance. Once damaged, they not only lose their superhydrophobic and drag-reduction functions, but the damaged area also becomes the starting point for corrosion, and they cannot repair themselves. Therefore, developing an intelligent coating system that can adapt to the dynamic aerospace environment, rapidly and autonomously repair itself after physical damage, and simultaneously provide long-term corrosion protection and potential aerodynamic drag reduction benefits is a crucial issue urgently needing to be addressed in the field of aerospace materials surface engineering. This will not only extend the lifespan of aircraft structures and reduce maintenance costs, but also have a positive impact on improving the overall performance of aircraft. Summary of the Invention

[0005] To address the problem that aluminum alloy protective coatings cannot repair themselves once damaged, this invention provides a method for preparing and applying a self-healing superhydrophobic coating based on a ZB@BN / SiO2 double-layer structure. This self-healing superhydrophobic coating can achieve intelligent protection effects such as rapid repair of damaged areas and long-term protection of intact areas.

[0006] To achieve the above objectives, the present invention provides a method for preparing a self-healing superhydrophobic coating based on a ZB@BN / SiO2 bilayer structure, comprising the following steps: S1. Mix and disperse ZB@BN composite particles and two-component polyurethane resin in a solvent to form a uniform coating, and coat it on the substrate surface to form a hydrophilic underlayer. S2. Micron-sized coupling agent modified SiO2 particles and two-component polyurethane resin are mixed and dispersed in a solvent to form a uniform coating, which is then coated on a hydrophilic substrate to form a micron-scale rough structure layer. S3. Nanoscale coupling agent-modified SiO2 particles and two-component polyurethane resin are mixed and dispersed in a solvent to form a uniform coating. After the micron-scale rough structure layer is semi-cured, it is coated on the micron-scale rough structure layer to form a nano-coating layer. After curing, a self-healing superhydrophobic coating with a two-layer structure is obtained. The purpose of this step-by-step construction is that micron-scale particles provide macroscopic roughness as the main framework, while nanoscale particles fill the gaps and coat the micron-scale particles to form secondary roughness. Together, they constitute a micro / nano-hierarchical structure. If micron and nanoparticles are mixed and sprayed at once, the nanoparticles tend to accumulate at the bottom of the gaps between the micron particles, making it difficult to form a uniform coating structure and weakening the stabilizing effect of hierarchical roughness on the Cassie-Baxter state. In addition, coating the nano-layer in the semi-cured state allows the nanoparticles to be partially embedded in the incompletely cured micron layer, enhancing the interlayer bonding force. At the same time, during subsequent friction and wear processes, the micron framework can effectively protect the underlying nanostructure, preventing the coating from rapidly losing its superhydrophobic properties due to the shedding of surface nanoparticles, thus giving the coating excellent mechanical wear resistance.

[0007] The superhydrophobic coating of this invention has a hydrophilic ZB@BN (ZIF-8@BTA@BN) self-healing layer as its base layer. This layer utilizes its hydrophilic properties to promote rapid penetration of corrosive media into the damaged area. Traditional superhydrophobic coatings, after being scratched, suffer from a hydrophobic barrier that actually delays the contact between the corrosive media and the underlying repair agent, leading to a delayed release of the corrosion inhibitor. The exposed metal substrate at the scratch site corrodes before the repair process begins. However, this invention, by designing the base layer to be hydrophilic, ensures that after the scratch penetrates the top superhydrophobic layer, the corrosive media can quickly wet and penetrate to the base layer, rapidly triggering the release of the BTA corrosion inhibitor in the ZB@BN composite particles. This allows the repair reaction to be completed before the corrosive media causes significant damage to the metal substrate. In other words, the hydrophilic base layer "accelerates" the repair response process, rather than the corrosion destruction process. Meanwhile, the top superhydrophobic layer provides long-lasting physical barrier in the intact area, and the "maze effect" of the BN nanosheets in the bottom layer continues to delay the diffusion of corrosive media. Together, these two elements ensure reliable protection in both intact and damaged areas, achieving efficient self-healing. The BTA self-healing mechanism mainly involves three steps. First, the ZIF-8 shell undergoes structural dissociation in acidic or alkaline environments, causing the internally loaded BTA molecules to be rapidly released to the scratched area. This process is driven by the local pH change triggered by the exposure of the metal substrate at the scratch. Afterward, the released BTA molecules chemically adsorb onto the exposed aluminum substrate surface through the lone pair electrons in their nitrogen-containing heterocyclic structure, forming a stable BTA-Al coordination complex ([BTA-Al-BTA)). n Simultaneously, BTA can also form a dense adsorption film on the metal surface. This protective film effectively isolates the corrosive medium from direct contact with the metal substrate, inhibiting anodic dissolution and cathodic reactions, thereby preventing further corrosion propagation. Finally, during scratch repair, in addition to the BTA corrosion inhibitor, the HDTMS@SiO2 particles (including micron- and nano-sized particles) in the coating can also migrate to the scratch site while the BTA is released, working together with the protective film formed by the BTA to achieve a dual repair of physical filling and chemical protection for the scratched area.

[0008] Furthermore, in this invention, the bottom layer and the top layer are not simply functional superpositions; rather, there is a synergistic relationship between them that promotes each other, specifically manifested in the following three aspects: 1. Synergistic "Protection-Enhancement" of Top Layer to Bottom Layer: The top superhydrophobic layer not only provides physical barrier but, more importantly, acts as a "protective shield" to prevent the bottom ZB@BN composite particles from direct contact with the external environment. Without top layer protection, the BTA corrosion inhibitor in the bottom layer would be continuously released in trace amounts due to moisture penetration during long-term service, leading to premature depletion of its repair function. The presence of the top superhydrophobic layer keeps the bottom layer in a relatively "dry" environment, where the corrosion inhibitor is only activated and released when scratch damage occurs or the top layer is damaged, thus achieving "on-demand release" of the corrosion inhibitor and significantly improving its utilization efficiency and service life. This mechanism of "top layer protecting bottom layer, bottom layer responding to damage" makes the sustainability of the repair function far exceed that of a single self-healing coating.

[0009] 2. Synergistic Support and Compensation from Bottom Layer to Top Layer: While the micro-nano hierarchical structure of the top superhydrophobic layer provides excellent hydrophobicity and wear resistance, surface nanoparticles inevitably detach due to friction during long-term service, leading to a decrease in hydrophobic performance. At this point, the ZB@BN composite particles in the bottom layer can play a "functional compensation" role: on the one hand, the BTA corrosion inhibitor released from the bottom layer can migrate to structural defects in the top layer, forming a protective adsorption film to compensate for the decrease in barrier performance caused by physical wear; on the other hand, the "maze effect" of the BN nanosheets in the bottom layer can continue to delay the longitudinal penetration of corrosive media even when the barrier capacity of the top layer weakens, ensuring the robustness of the overall protective performance of the coating.

[0010] 3. Trigger-Execution Synergy in Damage Response: Traditional superhydrophobic coatings, after scratch damage, can actually hinder the contact between corrosive media and repair agents due to the hydrophobic barrier, leading to a delayed repair response. In this invention, the hydrophilicity of the bottom layer and the hydrophobicity of the top layer form a "functional complementarity": the top layer provides a hydrophobic barrier over the intact area, while at the scratch site, the hydrophilic surface of the bottom layer is exposed, rapidly attracting the penetration of corrosive media and quickly triggering BTA release. This contrasting design of "top layer hydrophobic - bottom layer hydrophilic" allows the coating to switch functions before and after damage, ensuring both long-term barrier protection during daily service and rapid response after damage occurs—something that cannot be achieved with a single coating or simple hybrid coating.

[0011] In summary, this invention achieves a synergistic effect through the synergistic design of a dual-layer structure, where the top layer stores energy for the bottom layer, the bottom layer fills gaps for the top layer, and the damage response is faster than the corrosion process. It is superior to single-function coatings or simple combinations thereof in terms of long-term corrosion protection, intelligent repair, and wear resistance.

[0012] Specifically, in step S1, the preparation method of the ZB@BN composite particles is as follows: S1.1 Mix and grind 0.5-1 parts by mass of boron nitride nanosheets, 1-2 parts by mass of sodium hydroxide and 1.4-2.5 parts by mass of potassium hydroxide, add water, and hydrothermally react at 180-200℃ for 10-12 h to obtain hydroxylated boron nitride. S1.2 Disperse 2-3 parts by mass of zinc nitrate hexahydrate and 0.4-1 parts by mass of hydroxylated boron nitride in a mixture of methanol and deionized water; S1.3 Dissolve 4.5-5 parts by weight of 2-methylimidazole and 0.05-0.1 parts by weight of benzotriazole in a methanol solution; S1.4 Slowly mix the solutions obtained in steps 1.2 and S1.3 and stir the reaction for 5-6 hours. After centrifugation, washing and drying, the product is ZB@BN composite particles.

[0013] Preferably, in step S1, the mass ratio of the ZB@BN composite particles to the two-component polyurethane resin is 1:(24~30).

[0014] Specifically, the preparation method of micron-sized or nano-sized coupling agent modified SiO2 particles is as follows: micron-sized or nano-sized silica is dispersed in a mixture of ethanol and deionized water, the pH is adjusted to 8-9, and the coupling agent is slowly added dropwise under constant temperature stirring at 40-50℃. The reaction is carried out for 4-5 hours. After centrifugation, washing and drying, the product is obtained as coupling agent modified SiO2 particles. The mass ratio of micron-sized or nano-sized silica to coupling agent is 1:(2-3).

[0015] Preferably, the coupling agent is hexadecyltrimethoxysilane, octyltrimethoxysilane, hexadecyltriethoxysilane, or methyloctadecyldimethoxysilane.

[0016] Preferably, the particle size of the micron-sized silica is 10-20 μm, and the particle size of the nano-sized silica is 20-30 nm.

[0017] Preferably, in steps S1 to S3, the mass ratio of component A to component B in the two-component polyurethane resin is 5:1.

[0018] The second aspect of the present invention provides a self-healing superhydrophobic coating based on a ZB@BN / SiO2 bilayer structure prepared by the above-described preparation method.

[0019] The third aspect of this invention provides the application of the above-mentioned self-healing superhydrophobic coating based on the ZB@BN / SiO2 bilayer structure in the preparation of corrosion-resistant and drag-reducing aluminum alloy surfaces.

[0020] Through the above technical solution, the present invention achieves the following beneficial effects: 1. The innovative double-layer structure of this invention combines the rapid active repair of the bottom layer with the long-term passive barrier of the top layer, overcoming the limitations of single-function coatings and realizing intelligent zoned protection.

[0021] 2. The hydrophilic design of the bottom layer of this invention ensures that the corrosive medium can quickly contact and activate the ZB@BN nano-container at the scratch, avoiding the problem of delayed repair response of traditional superhydrophobic coatings.

[0022] 3. The top superhydrophobic layer of this invention provides excellent physical barrier and drag reduction function; the "maze effect" of the bottom BN nanosheets extends the corrosion path, and ZIF-8@BTA provides corrosion inhibition protection; the two work together to give the coating excellent long-term anti-corrosion, self-healing and drag reduction performance.

[0023] 4. The hydroxylation treatment of BN enhances its compatibility with polymers, improving coating adhesion and density. The two-step spraying process is simple, suitable for surface treatment of complex components, and facilitates industrialization. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating the preparation of the double-layer self-healing superhydrophobic coating of the present invention; Figure 2 Comparison of infrared spectra (a) and XRD patterns (b) of different samples; Figure 3 SEM images of BN powder (a, a1), BN-OH powder (b, b1) and ZB@BN powder (c, c1); Figure 4 Water droplet adhesion test (a~a4), anti-fouling test (b~b3), and self-cleaning performance test (c~c3) of HDTMS@SiO2 / ZB@BN / PU coating. Figure 5 The images show a comparison of the 30-day salt spray test results for each sample. A, B, C, and D are the salt spray test comparison images for Al 1060, PU coating, HDTMS@SiO2 / BN / PU coating, and HDTMS@SiO2 / ZB@BN / PU coating, respectively. Figure 6 The diagrams show the corrosion mechanism of Al 1060 (a), the corrosion protection mechanism of PU coating (b), the corrosion protection mechanism of HDTMS@SiO2 / ZB@BN / PU superhydrophobic coating (c), and the self-healing mechanism (d). Detailed Implementation

[0025] The specific embodiments of the present invention will be described in detail below with reference to examples. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0026] Example 1 like Figure 1 As shown, the preparation method of the self-healing superhydrophobic coating based on the ZB@BN / SiO2 bilayer structure is as follows: Step 1 (Preparation of ZB@BN composite particles): 0.5 g boron nitride (BN) nanosheets, 1.0 g sodium hydroxide, and 1.4 g potassium hydroxide were ground together and mixed with 20 mL deionized water. The mixture was then transferred to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 180 °C for 12 h. The reaction product was repeatedly centrifuged and washed until neutral, and dried at 80 °C to obtain hydroxylated boron nitride (BN-OH). 2.0 g zinc nitrate hexahydrate and 0.4 g BN-OH were added to a mixture of 48 mL methanol and 12 mL deionized water and ultrasonically dispersed for 5 min, denoted as solution A. 4.8 g 2-methylimidazole and 70 mg benzotriazole (BTA) were dissolved in 10 mL methanol and magnetically stirred until dissolved, denoted as solution B. Under continuous stirring, solution B was slowly added dropwise to solution A, and the reaction was continued at room temperature for 5 h. After the reaction was completed, the particles were centrifuged, washed three times with methanol, and dried at 60℃ for 12 h to obtain ZB@BN composite particles. The infrared spectra and XRD patterns of BN powder, BN-OH powder, and ZB@BN powder are shown below. Figure 2 As shown, by Figure 2 The infrared spectral comparison shows that for BN nanosheets, a peak can be observed at 1376 cm⁻¹. -1 The characteristic peak of in-plane stretching vibration at 817 cm⁻¹ is located at the B–N plane. -1 The characteristic peak of the out-of-plane bending vibration of B–N at 3423 cm⁻¹. For BN-OH nanosheets, it is located at 3423 cm⁻¹. -1 The characteristic peak of the O–H stretching vibration at [location missing] indicates successful hydroxylation of the BN nanosheets. The FT-IR spectrum of the ZB particles shows multiple characteristic peaks, including one at 1573 cm⁻¹. -1 The characteristic peak at 1145 cm⁻¹ is the stretching vibration peak of the C=N bond. -1 and 995 cm -1 The characteristic peak at 777 cm⁻¹ is the stretching vibration peak of the CN bond. -1 The characteristic peaks at this location are the stretching vibration peaks of aromatic CH bonds, and the peak at 422 cm⁻¹ is also present. -1 The characteristic peaks are stretching vibration peaks of the Zn-N bond, confirming the presence of ZIF-8 and BTA. For ZB@BN, its FT-IR spectrum contains all the characteristic peaks of both BN and ZB particles, indicating the simultaneous presence of both components in the ZB@BN composite particles. Figure 2XRD spectroscopy revealed that BN nanosheets, BN-OH nanosheets, ZB particles, and ZB@BN all exhibited high crystallinity, displaying clear diffraction peaks. The characteristic diffraction peaks of BN nanosheets matched the JCPDS PDF#34-0421 standard card, with the strong peak at 2θ=26.6° corresponding to the (002) crystal plane of BN. Notably, the characteristic peaks of BN-OH were identical to those of BN, indicating that hydroxylation did not alter the crystal structure of the particles. In the XRD pattern of ZB particles, the diffraction peaks at 2θ=7.4°, 10.4°, 12.8°, 14.8°, 16.5°, and 18.1° corresponded to the (001), (002), (112), (022), (013), and (222) crystal planes of the ZIF-8 crystal structure, respectively, indicating that the introduction of BTA did not change the crystal structure of ZIF-8. For the ZB@BN nanocontainer, its XRD pattern fully retains the characteristic peaks of BN and ZIF-8. In summary, the ZB@BN composite particles were successfully synthesized. SEM images of BN powder, BN-OH powder, and ZB@BN powder are shown below. Figure 3 As shown in the figure, both before and after hydroxylation of BN, the particles exhibit a smooth, lamellar structure. This indicates that hydroxylation of boron nitride nanosheets does not affect their crystal structure, a result consistent with XRD analysis. Furthermore, the lamellar structure is key to BN's excellent barrier properties, effectively preventing the penetration of corrosive media in liquids and achieving effective barrier protection. (Comparison...) Figure 3 As shown in (b) and (c), the microstructure of ZB@BN particles modified with ZIF-8 and BTA is characterized by a large number of regular cubic structures randomly distributed on their surface. This indicates that the ZB particles and BN-OH particles are not simply physically mixed, but rather that the ZB particles grow in situ on the smooth surface of BN-OH.

[0027] Step 2 (Preparation of HDTMS@SiO2 hydrophobic particles): Weigh 1.0 g of micron-sized SiO2 (approximately 10 μm particle size) and 1.0 g of nano-sized SiO2 (approximately 20 nm particle size). Disperse the SiO2 particles in 50 mL of ethanol / water (volume ratio 4:1) mixed solvent, and adjust the pH to 8 with ammonia. Under constant temperature stirring at 40 °C, slowly add 3 mL of hexadecyltrimethoxysilane (HDTMS) to the dispersion, and continue the reaction for 5 h. After the reaction is complete, centrifuge to separate the product, wash three times with ethanol, and dry at 80 °C for 12 h to obtain hydrophobically modified micron-sized HDTMS@SiO2 and nano-sized HDTMS@SiO2 particles, respectively. Step 3 (Preparation of Double-Layer Self-Healing Superhydrophobic Coating): Substrate Pretreatment: Sand the surface of the 1060 aluminum alloy sheet with 400-grit sandpaper, then ultrasonically clean it sequentially with acetone, ethanol, and deionized water, and dry it for later use. Preparation of the Base Coating: Weigh 0.2 g ZB@BN particles, 4.0 g polyurethane component A, 0.8 g polyurethane component B, and 5 mL ethyl acetate, mix, and ultrasonically disperse for 15 min. Preparation of the Top Coating: Micron-layer Coating: Weigh 0.5 g micron-sized HDTMS@SiO2, 2.0 g polyurethane component A, 0.4 g polyurethane component B, and 3 mL ethyl acetate, and mix and disperse. Nano-layer Coating: Weigh 0.3 g nano-sized HDTMS@SiO2, 2.0 g polyurethane component A, 0.4 g polyurethane component B, and 3 mL ethyl acetate, and mix and disperse. Spraying and Curing: Spray the base coating evenly onto the pretreated aluminum sheet surface to form the base layer. After the base layer is surface dry, spray the micron-layer coating onto the base layer. After the micron layer has partially cured (becomes non-sticky to the touch), the nano-layer coating is sprayed onto its surface. The sample is then cured at room temperature for 24 hours to obtain the final double-layer structure coating.

[0028] Example 2 Step 1 (Preparation of ZB@BN composite particles): 1 g boron nitride (BN) nanosheets, 2.0 g sodium hydroxide, and 2.5 g potassium hydroxide were ground together and mixed with 30 mL deionized water. The mixture was then transferred to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 200 °C for 10 h. The reaction product was repeatedly centrifuged and washed until neutral, and dried at 80 °C to obtain hydroxylated boron nitride (BN-OH). 3.0 g zinc nitrate hexahydrate and 1 g BN-OH were added to a mixture of 48 mL methanol and 12 mL deionized water and ultrasonically dispersed for 5 min, denoted as solution A. 4.5 g 2-methylimidazole and 50 mg benzotriazole (BTA) were dissolved in 10 mL methanol and magnetically stirred until dissolved, denoted as solution B. Under continuous stirring, solution B was slowly added dropwise to solution A, and the reaction was continued at room temperature for 6 h. After the reaction was completed, the particles were centrifuged, washed three times with methanol, and dried at 60℃ for 12 h to obtain ZB@BN composite particles. Step 2 (Preparation of HDTMS@SiO2 hydrophobic particles): Weigh 2.5 g of micron-sized SiO2 (particle size approximately 10 μm) and 2.5 g of nano-sized SiO2 (particle size approximately 20 nm). Disperse the SiO2 particles in 50 mL of an ethanol / water mixture (volume ratio 4:1), and adjust the pH to 9 with ammonia. Under constant temperature stirring at 50 °C, slowly add 5.6 mL of hexadecyltriethoxysilane to the dispersion, and continue the reaction for 4 h. After the reaction, centrifuge to separate the product, wash three times with ethanol, and dry at 80 °C for 12 h to obtain hydrophobically modified micron-sized HDTMS@SiO2 and nano-sized HDTMS@SiO2 particles, respectively. Step 3 (Preparation of Double-Layer Self-Healing Superhydrophobic Coating): Substrate Pretreatment: Sand the surface of the 1060 aluminum alloy sheet with 400-grit sandpaper, then ultrasonically clean it sequentially with acetone, ethanol, and deionized water, and dry it for later use. Preparation of the Base Coating: Weigh 0.2 g ZB@BN particles, 5.0 g polyurethane component A, 1.0 g polyurethane component B, and 5 mL ethyl acetate, mix, and ultrasonically disperse for 15 min. Preparation of the Top Coating: Micron-layer Coating: Weigh 1.0 g micron HDTMS@SiO2, 2.0 g polyurethane component A, 0.4 g polyurethane component B, and 3 mL ethyl acetate, and mix and disperse. Nano-layer Coating: Weigh 0.6 g nano HDTMS@SiO2, 2.0 g polyurethane component A, 0.4 g polyurethane component B, and 3 mL ethyl acetate, and mix and disperse. Spraying and Curing: Spray the base coating evenly onto the pretreated aluminum sheet surface to form the base layer. After the base layer is surface dry, spray the micron-layer coating onto the base layer. After the micron layer has partially cured (becomes non-sticky to the touch), the nano-layer coating is sprayed onto its surface. The sample is then cured at room temperature for 24 hours to obtain the final double-layer structure coating.

[0029] Example 3 Step 1 (Preparation of ZB@BN composite particles): 0.8 g boron nitride (BN) nanosheets, 1.5 g sodium hydroxide, and 2.0 g potassium hydroxide were ground together and mixed with 30 mL deionized water. The mixture was then transferred to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 190 °C for 12 h. The reaction product was repeatedly centrifuged and washed until neutral, and dried at 80 °C to obtain hydroxylated boron nitride (BN-OH). 2.5 g zinc nitrate hexahydrate and 0.8 g BN-OH were added to a mixture of 48 mL methanol and 12 mL deionized water and ultrasonically dispersed for 5 min, denoted as solution A. 5 g 2-methylimidazole and 100 mg benzotriazole (BTA) were dissolved in 10 mL methanol and magnetically stirred until dissolved, denoted as solution B. Under continuous stirring, solution B was slowly added dropwise to solution A, and the reaction was continued at room temperature for 6 h. After the reaction was completed, the particles were centrifuged, washed three times with methanol, and dried at 60℃ for 12 h to obtain ZB@BN composite particles. Step 2 (Preparation of HDTMS@SiO2 hydrophobic particles): Weigh 1.6 g of micron-sized SiO2 (particle size approximately 10 μm) and 1.6 g of nano-sized SiO2 (particle size approximately 20 nm). Disperse the SiO2 particles in 50 mL of an ethanol / water mixture (volume ratio 4:1), and adjust the pH to 9 with ammonia. Under constant temperature and stirring at 50 °C, slowly add 5.5 mL of octyltrimethoxysilane to the dispersion, and continue the reaction for 4 h. After the reaction is complete, centrifuge to separate the product, wash three times with ethanol, and dry at 80 °C for 12 h to obtain hydrophobically modified micron-sized HDTMS@SiO2 and nano-sized HDTMS@SiO2 particles, respectively. Step 3 (Preparation of Double-Layer Self-Healing Superhydrophobic Coating): Substrate Pretreatment: Sand the surface of the 1060 aluminum alloy sheet with 400-grit sandpaper, then ultrasonically clean it sequentially with acetone, ethanol, and deionized water, and dry it for later use. Preparation of the Base Coating: Weigh 0.2 g ZB@BN particles, 4.5 g polyurethane component A, 0.9 g polyurethane component B, and 5 mL ethyl acetate, mix, and ultrasonically disperse for 15 min. Preparation of the Top Coating: Micron-layer Coating: Weigh 0.5 g micron-sized HDTMS@SiO2, 2.0 g polyurethane component A, 0.4 g polyurethane component B, and 3 mL ethyl acetate, and mix and disperse. Nano-layer Coating: Weigh 0.3 g nano-sized HDTMS@SiO2, 2.0 g polyurethane component A, 0.4 g polyurethane component B, and 3 mL ethyl acetate, and mix and disperse. Spraying and Curing: Spray the base coating evenly onto the pretreated aluminum sheet surface to form the base layer. After the base layer is surface dry, spray the micron-layer coating onto the base layer. After the micron layer has partially cured (becomes non-sticky to the touch), the nano-layer coating is sprayed onto its surface. The sample is then cured at room temperature for 24 hours to obtain the final double-layer structure coating.

[0030] Comparative Example 1 Other conditions are the same as in Example 1, except that the preparation of the superhydrophobic layer is omitted.

[0031] Comparative Example 2 Other conditions are the same as in Example 1, except that the ZB@BN underlying layer is omitted.

[0032] Comparative Example 3 Other conditions are the same as in Example 1, except that the micron layer coating and the nano layer coating are prepared and sprayed sequentially, instead of being prepared and sprayed together, that is, micron HDTMS@SiO2 and nano HDTMS@SiO2 are mixed with polyurethane resin and solvent to prepare the coating.

[0033] Comparative Example 4 The other conditions are the same as in Example 1, except that the micron layer coating is replaced with a nano layer coating.

[0034] Comparative Example 5 The other conditions are the same as in Example 1, except that the nano-layer coating is replaced with a micro-layer coating.

[0035] Performance testing The coatings obtained in the above embodiments and comparative examples were tested as follows: (1) Wettability: The wettability of the coating was tested by immersing it in a methyl orange solution and removing methylene blue powder from the surface of the coating.

[0036] (2) Corrosion resistance: A traditional three-electrode electrochemical system was used, with a silver / silver chloride electrode (Ag / AgCl) as the reference electrode, a platinum electrode (Pt) as the auxiliary electrode, and each sample as the working electrode. Electrochemical tests were performed in a 3.5 wt.% NaCl solution, and the coating was tested after its open-circuit potential in the 3.5 wt.% NaCl solution stabilized. The frequency range of electrochemical impedance spectroscopy (EIS) was 10 Hz. -2 ~10 5 Hz, disturbance amplitude of 5 mV, and test area of ​​working electrode of 1 cm². 2 Each sample was tested three times.

[0037] (3) Self-healing property: According to GB / T10125-2012 "Artificial Atmosphere Corrosion Test - Salt Spray Test", cross-shaped scratches approximately 40 mm long and 0.2 mm deep were made on the surface of each sample using a knife. An ASR-60A salt spray testing machine was used to simulate a corrosive environment for a neutral salt spray test. The solution used in the test was 3.5 wt.% NaCl, with a pH value of 6.5~7.2. The test chamber temperature was 35 ℃, and the spray volume was 1~2 mL / 80 cm. 2 Between / h. Samples were removed and dried at regular intervals, and then the corrosion on the sample surface and at the scratches was observed using an electron optical microscope.

[0038] (4) Drag Reduction Performance: Drag reduction tests were conducted in a plastic water tank measuring 1.3 × 0.35 × 0.24 m. To study the drag reduction performance of the coating, each model boat was equipped with a 3V battery as its power system and maintained the same weight. The time required for it to complete a 1.2-meter voyage was recorded, and the test was repeated 20 times to calculate the average speed and drag reduction rate of the model boat.

[0039] (5) Environmental stability: To assess physical and chemical stability, acid and alkali resistance tests, UV resistance tests, and abrasion resistance tests were conducted. For the acid and alkali resistance test, solutions with pH values ​​of 1-13 were dropped onto the surface of the superhydrophobic coating, and its WCA and SA were tested after the water droplets stabilized for 0.5 h. For the UV resistance test, the WCA and SA of the sample were tested under UV light irradiation. For the abrasion resistance test, the sample was rubbed on 400-grit sandpaper, and the changes in WCA and SA were measured.

[0040] The results are shown in the table below:

[0041] The results show that: 1. Comparison of the Example and Comparative Example 1: The low-frequency impedance modulus of Comparative Example 1 (without top layer) is 1.13 × 10⁻⁶. 9 Ω·cm 2 The value of Example 1 was increased to 2.68 × 10⁻⁶. 9 Ω·cm 2 This represents an increase of approximately 2.4 times. This indicates that the physical barrier effect of the top superhydrophobic layer significantly enhances the coating's corrosion resistance.

[0042] 2. Comparison of Example 1 and Comparative Example 2: Comparative Example 2 (without underlying layer) has a low-frequency impedance modulus of only 3.87 × 10⁻⁶. 8 Ω·cm 2 This is significantly lower than that of Example 1 (2.68 × 10⁻⁶). 2 Ω·cm 2 Furthermore, no self-healing phenomenon was observed at the scratches after 30 days of salt spray testing. This indicates that the corrosion-inhibiting release and "maze effect" of the underlying ZB@BN composite particles are indispensable for the coating's corrosion protection and self-healing functions.

[0043] 3. Comparison of Example 1 and Comparative Example 3: Comparative Example 3 (micro / nano hybrid spraying) had a water contact angle of 153.2° and a drag reduction rate of 22.10%, both lower than Example 1 (162.9°, 28.85%); moreover, its wear resistance decreased, losing its superhydrophobicity after 100 cm of wear. This indicates that the micro / nano hierarchical structure constructed by stepwise spraying is superior to simple hybrid spraying in terms of hydrophobicity, drag reduction, and wear resistance.

[0044] 4. Comparison of Examples with Comparative Examples 4 and 5: Comparative Example 4 (nanolayer only) showed a drag reduction rate of 16.13%, and Comparative Example 5 (micron layer only) showed a drag reduction rate of 10.16%, both significantly lower than Example 1 (28.85%). This indicates that the composite structure of the micron framework and the nano-coating layer produced a drag reduction and efficiency enhancement effect. Furthermore, Comparative Example 4 lost its superhydrophobicity after 60 cm of wear, and Comparative Example 5 lost its superhydrophobicity after 40 cm of wear, while Example 1 could withstand 160 cm of wear, demonstrating that the protective effect of the micron framework on the nanostructure significantly improved the wear resistance life.

[0045] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0046] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0047] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a self-healing superhydrophobic coating based on a ZB@BN / SiO2 bilayer structure, characterized in that, Includes the following steps: S1. Mix and disperse ZB@BN composite particles and two-component polyurethane resin in a solvent to form a uniform coating, and coat it on the substrate surface to form a hydrophilic underlayer. S2. Micron-sized coupling agent modified SiO2 particles and two-component polyurethane resin are mixed and dispersed in a solvent to form a uniform coating, which is then coated on a hydrophilic substrate to form a micron-scale rough structure layer. S3. Mix and disperse nano-sized coupling agent-modified SiO2 particles and two-component polyurethane resin in a solvent to form a uniform coating. After the micron-rough structure layer is semi-cured, coat it onto the micron-rough structure layer to form a nano-coating layer. After curing, a self-healing superhydrophobic coating with a double-layer structure is obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the preparation method of the ZB@BN composite particles is as follows: S1.1 Mix and grind 0.5-1 parts by mass of boron nitride nanosheets, 1-2 parts by mass of sodium hydroxide and 1.4-2.5 parts by mass of potassium hydroxide, add water, and hydrothermally react at 180-200℃ for 10-12 h to obtain hydroxylated boron nitride. S1.2 Disperse 2-3 parts by mass of zinc nitrate hexahydrate and 0.4-1 parts by mass of hydroxylated boron nitride in a mixture of methanol and deionized water; S1.3 Dissolve 4.5-5 parts by weight of 2-methylimidazole and 0.05-0.1 parts by weight of benzotriazole in a methanol solution; S1.4 Slowly mix the solutions obtained in steps 1.2 and S1.3 and stir the reaction for 5-6 hours. After centrifugation, washing and drying, the product is ZB@BN composite particles.

3. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of the ZB@BN composite particles to the two-component polyurethane resin is 1:(24~30).

4. The preparation method according to claim 1, characterized in that, The preparation method of micron-sized or nano-sized coupling agent modified SiO2 particles is as follows: micron-sized or nano-sized silica is dispersed in a mixture of ethanol and deionized water, the pH is adjusted to 8-9, and the coupling agent is slowly added dropwise under constant temperature stirring at 40-50℃. The reaction is carried out for 4-5 hours. After centrifugation, washing and drying, the product is obtained as coupling agent modified SiO2 particles. The mass ratio of micron-sized or nano-sized silica to coupling agent is 1:(2-3).

5. The preparation method according to claim 4, characterized in that, The coupling agent is hexadecyltrimethoxysilane, octyltrimethoxysilane, hexadecyltriethoxysilane, or methyloctadecyldimethoxysilane.

6. The preparation method according to claim 4, characterized in that, The micron-sized silica has a particle size of 10-20 μm, and the nano-sized silica has a particle size of 20-30 nm.

7. The preparation method according to any one of claims 1 to 6, characterized in that, In steps S1 to S3, the mass ratio of component A to component B in the two-component polyurethane resin is 5:

1.

8. The self-healing superhydrophobic coating based on the ZB@BN / SiO2 bilayer structure prepared by the preparation method of any one of claims 1 to 7.

9. The application of the self-healing superhydrophobic coating based on the ZB@BN / SiO2 bilayer structure as described in claim 8 in the preparation of corrosion-resistant and drag-reducing aluminum alloy surfaces.

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