MXene / PAO6@SiO2 composite epoxy coating based on Diels-Alder reaction, its preparation method and application

Abstract

This application provides a Diels-Alder reaction-based MXene / PAO6@SiO2 composite epoxy coating, its preparation method, and its application. The method includes: taking bisphenol A diglycidyl ether and polypropylene glycol diglycidyl ether, respectively, adding furfurylamine and N,N-dimethylformamide to obtain solutions A and B, and reacting them at 60°C to obtain BADGE-FA prepolymer and PPGDGE-FA prepolymer, respectively; modifying few-layer MXene with diaminobenzenesulfonic acid; reacting the BADGE-FA prepolymer and PPGDGE-FA prepolymer with 4,4'-bismaleimide diphenylmethane, adding fMXene and PAO6@SiO2 microcapsules, stirring, and ultrasonicating to obtain a composite coating; and coating the composite coating onto the substrate surface to obtain a composite epoxy coating. This application constructs a multifunctional composite epoxy coating with self-healing, corrosion-resistant, and wear-resistant functions.

Description

Technical Field

[0001] This application relates to the technical field of anti-corrosion and wear-resistant functional materials, and in particular to an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction, its preparation method and application. Background Technology

[0002] Corrosion and wear are the main causes of failure in metallic materials, resulting in huge economic losses in my country every year. Therefore, the development of high-performance protective coatings is of great economic and social significance for extending the service life of metal equipment and reducing resource waste.

[0003] Epoxy resin coatings are widely used in corrosion and wear-resistant applications due to their excellent properties such as high mechanical strength, good chemical stability, cross-linking characteristics, strong metal adhesion, low shrinkage, and low water absorption. However, during the curing process, ordinary epoxy coatings can develop pores and conductive channels due to shrinkage or solvent evaporation, allowing corrosive media (such as oxygen, water, and chloride ions) to gradually penetrate to the coating / metal interface, reducing the coating's barrier performance and adhesion. Simultaneously, the inherent brittleness of epoxy resin makes it prone to microcracks under mechanical friction or impact, further accelerating the intrusion of corrosive media. These inherent defects make it difficult for traditional epoxy coatings to simultaneously resist the penetration of corrosive media and damage from mechanical friction during long-term service. Summary of the Invention

[0004] This application provides a Diels-Alder reaction-based MXene / PAO6@SiO2 composite epoxy coating, its preparation method, and its application, in order to solve the problems mentioned in the background art.

[0005] In a first aspect, this application provides a method for preparing an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction, comprising the following steps: (1) Preparation of furan-functionalized epoxy prepolymer: Bisphenol A diglycidyl ether was placed in a dry container, and furfural and N,N-dimethylformamide were added to the container and stirred to obtain solution A. Polypropylene glycol diglycidyl ether was placed in a dry container, and furfural and N,N-dimethylformamide were added to the container and stirred to obtain solution B. Solutions A and B were transferred to a reactor and stirred at 60°C for 4 hours. Solution A reacted to obtain BADGE-FA prepolymer, and solution B reacted to obtain BPPGDGE-FA prepolymer. (2) Modification of few-layer MXene nanosheets: Diaminobenzenesulfonic acid was dissolved in deionized water, stirred and dispersed for 1 hour, then stirred in an oil bath at 80°C for 2 hours, filtered, washed, and dried to finally obtain fMXene nanosheets; (3) Preparation of composite epoxy coating: BADGE-FA prepolymer, PPGDGE-FA prepolymer and 4,4'-bismaleimide diphenylmethane were mixed and stirred at room temperature for 1 hour to obtain a basic epoxy resin coating. Then fMXene nanosheets and PAO6@SiO2 microcapsules were added and uniformly dispersed by mechanical stirring and ultrasonic treatment to obtain a composite coating. The composite coating was coated on the substrate surface and dried to obtain a composite epoxy coating.

[0006] Optionally, in solution A, the mass ratio of bisphenol A diglycidyl ether to furfurylamine is 10:2.56, and the mass ratio of bisphenol A diglycidyl ether to N,N-dimethylformamide is 10:23. In solution B, the mass ratio of polypropylene glycol diglycidyl ether to furfurylamine is 10:1.52, and the mass ratio of polypropylene glycol diglycidyl ether to N,N-dimethylformamide is 10:23.

[0007] Optionally, in the modification step of few-layer MXene nanosheets, the mass ratio of few-layer MXene to diaminobenzenesulfonic acid is 0.4:0.2, and the mass-volume ratio of the sum of the masses of few-layer MXene and diaminobenzenesulfonic acid to deionized water is 0.6 g / 200 mL.

[0008] Optionally, in the preparation step of the composite epoxy coating, the mass ratio of BADGE-FA prepolymer to PPGDGE-FA prepolymer is 1-10:1-10, and the molar ratio of furan groups in BADGE-FA prepolymer to maleimide groups in 4,4'-bismaleimide diphenylmethane is 1:1.

[0009] Optionally, the amount of fMXene nanosheets added is 5 wt% of the composite coating, and the amount of PAO6@SiO2 microcapsules added is 5 wt% of the composite coating.

[0010] Optionally, the preparation methods of PAO6@SiO2 microcapsules include: PAO6 and OP-10 emulsifiers were mixed with deionized water and stirred at high speed at 8000-10000 rpm for 5 minutes to obtain a water-in-oil emulsion. The pH value of the water-in-oil emulsion was then adjusted to >10. Sodium metasilicate nonahydrate was dissolved in deionized water and acidified to pH < 2. Then, it was titrated back with 15 wt% sodium carbonate until the pH value was 2.85-3.00 to obtain a stable and uniform silica sol. The water-in-oil emulsion was transferred to a 60°C oil bath and stirred at 250-300 rpm. Silica sol was then added dropwise to the emulsion at a rate of 1 mL / min using a pump. After the addition was complete, the mixture was stirred at 60°C for 48 h. The mixture was then allowed to stand at 70°C for 6-12 h to mature. Finally, it was cooled to room temperature, the product was filtered out, washed with anhydrous ethanol, and dried at 80°C for 12 h to obtain white PAO6@SiO2 microcapsules.

[0011] Optionally, in the water-in-oil emulsion, the mass ratio of PAO6 to OP-10 emulsifier is 20:1.5, and the mass-volume ratio of PAO6 to deionized water is 20g / 200mL. In the silica sol, the mass-to-volume ratio of sodium metasilicate nonahydrate to deionized water is 15 g / 200 mL.

[0012] Optionally, the thickness of the composite epoxy coating is less than 100 μm.

[0013] Secondly, this application provides an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction, which is obtained by the above-described preparation method.

[0014] Thirdly, this application provides an application of the above-mentioned composite epoxy coating in the fields of lubrication and corrosion prevention of mechanical equipment surfaces.

[0015] This application provides a Diels-Alder reaction-based MXene / PAO6@SiO2 composite epoxy coating, its preparation method, and its application. This achieves the preparation of a composite epoxy coating and, compared to existing technologies, offers the following advantages: (1) This application successfully constructed a multifunctional epoxy coating system with self-healing, anti-corrosion, and wear-resistant functions by combining self-healing resin and filler. Furan groups were introduced into the prepolymer chain segments by ring-opening reactions of the epoxy groups in bisphenol A diglycidyl ether and polypropylene glycol diglycidyl ether with the primary amine groups in furfurylamine. The bisphenol A skeleton in bisphenol A diglycidyl ether provided rigidity, and the polyether chains in polypropylene glycol diglycidyl ether provided flexibility, forming an interpenetrating network or blend system to achieve toughening. A thermally triggered self-healing epoxy network was constructed by reacting BADGE-FA prepolymer and BPGDGE-FA prepolymer with 4,4'-bismaleimide diphenylmethane in a reversible DA covalent reaction, resulting in a basic epoxy resin coating. Simultaneously, two functional fillers, fMXene nanosheets and PAO6@SiO2 microcapsules, are introduced. The fMXene nanosheets form a dense lubricating film in the coating, preventing the intrusion of external corrosive media. At the same time, the PAO6@SiO2 microcapsules release fluid lubricant, filling the pores of the epoxy coating to form a physical barrier, so that the composite epoxy coating has multiple functions such as corrosion resistance, wear resistance and self-repair.

[0016] (2) The functional fillers fMXene nanosheets and PAO6@SiO2 microcapsules significantly improved the wear resistance of the coating. Among them, the MWEP composite coating had the best friction performance, the lowest friction coefficient and a smooth curve, and a significant reduction in wear volume. During the friction process, fMXene can form a solid lubrication transfer film at the interface and bear part of the load, while the lubricant released by the microcapsules provides fluid lubrication. The two work together to construct a composite lubrication system, thereby significantly reducing the friction coefficient and inhibiting wear.

[0017] (3) Corrosion protection tests show that the microcapsules release PAO6 to form a hydrophobic barrier, which can delay the penetration of corrosive media. The "maze effect" constructed by MXene extends the diffusion path of the media, and the overall protection performance is significantly improved. When the coating is damaged, the microcapsules release PAO6 to form a hydrophobic protective layer at the local defect, thus achieving effective protection for the defect area. Therefore, the MWEP coating, combined with the hydrophobic barrier of the microcapsules and the maze effect of fMXene, maintains the highest low-frequency impedance and charge transfer resistance under long-term immersion, and has the best interface stability, achieving long-term protection against both overall and local defects. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a process diagram for preparing a furan-functionalized epoxy prepolymer according to an embodiment of this application; Figure 2 The images show the cross-sectional morphology of the composite epoxy coatings obtained in Example 4 and Comparative Examples 1-3. Figure 3 The adhesion force diagrams are for the composite epoxy coatings obtained in Example 4, Comparative Examples 1-3; Figure 4 Optical microscope images of the composite epoxy coatings obtained in Comparative Examples 2, 3 and 4 before and after scratch self-healing; Figure 5 The images show optical microscope images of the composite epoxy coatings obtained in Comparative Examples 1, 4 and 5 before and after scratch self-healing. Figure 6 (a) is a graph showing the friction coefficient of the composite epoxy coatings obtained in Example 4, Comparative Examples 1-3. Figure 6 (b) is a graph showing the average friction coefficient of the composite epoxy coatings obtained in Example 4, Comparative Examples 1-3; Figure 7 The images show the three-dimensional surface morphology of the wear marks on the composite epoxy coatings obtained in Example 4 and Comparative Examples 1-3. Figure 8 The figures show the salt spray test results of the composite epoxy coatings obtained in Example 4 and Comparative Examples 1-3. Figure 9 Electrochemical impedance spectroscopy (EIS) diagrams of the composite epoxy coatings obtained in Example 4 and Comparative Examples 1-3. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are also within the scope of protection of this application.

[0021] like Figure 1 As shown, in a first aspect, this application provides a method for preparing an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction, comprising the following steps: (1) Preparation of furan-functionalized epoxy prepolymer: Bisphenol A diglycidyl ether was placed in a dry container, and furfural and N,N-dimethylformamide were added to the container and stirred to obtain solution A. Polypropylene glycol diglycidyl ether was placed in a dry container, and furfural and N,N-dimethylformamide were added to the container and stirred to obtain solution B. Solutions A and B were transferred to a reactor and stirred at 60°C for 4 hours. Solution A reacted to obtain BADGE-FA prepolymer, and solution B reacted to obtain BPPGDGE-FA prepolymer. (2) Modification of few-layer MXene nanosheets: Few-layer MXene and diaminobenzenesulfonic acid were placed in deionized water, stirred and dispersed for 1 h, stirred in an oil bath at 80 °C for 2 h, filtered, washed at least three times with anhydrous ethanol, and dried in an oven at 60 °C for 12 h to finally obtain fMXene nanosheets. (3) Preparation of composite epoxy coating: BADGE-FA prepolymer, PPGDGE-FA prepolymer and 4,4'-bismaleimide diphenylmethane were mixed and stirred at room temperature for 1 hour to obtain a basic epoxy resin coating. Then fMXene nanosheets and PAO6@SiO2 microcapsules were added and uniformly dispersed by mechanical stirring and ultrasonic treatment to obtain a composite coating. The composite coating was coated on the substrate surface and dried to obtain a composite epoxy coating.

[0022] Specifically, in the preparation of furan-functionalized epoxy prepolymers, the epoxy groups in bisphenol A diglycidyl ether (BADGE) and polypropylene glycol diglycidyl ether (PPGDGE) undergo ring-opening reactions with the primary amine groups in furfurylamine (FA), respectively, introducing furan groups into the prepolymer chain segments to obtain furan-functionalized epoxy prepolymers (BADGE-FA prepolymer, BPPGDGE-FA prepolymer). The bisphenol A backbone in BADGE provides rigidity, and the polyether chain in PPGDGE provides flexibility, forming an interpenetrating network or blend system to achieve toughening.

[0023] In the modification step of few-layer MXene nanosheets, the surface of few-layer MXene was modified by diaminobenzenesulfonic acid, and nitrogen element was successfully introduced. The benzenesulfonic acid group can enhance the interfacial compatibility with epoxy matrix and form a maze effect in epoxy matrix. This not only improves the dispersibility of fMXene in polymer matrix and the interfacial interaction with epoxy resin, preventing stacking, but also, due to the presence of amino groups, further participates in the epoxy curing reaction, thereby improving the corrosion resistance and wear resistance of the composite epoxy coating.

[0024] Furthermore, the few-layer MXene nanosheets were prepared using a liquid-phase exfoliation method, specifically including the following steps: taking multilayer MXene (Ti3C2T... x The powder was added to dimethyl sulfoxide (DMSO) and magnetically stirred at room temperature for 12 hours to achieve pre-intercalation. Subsequently, the dispersion was centrifuged at 5000 rpm, and the precipitate was collected. The precipitate was redispersed in deionized water and sonicated in a water bath for 6 hours. After sonication, the resulting dispersion was first centrifuged at 3000 rpm for 5 minutes to collect the supernatant to remove unexfoliated thick sheets; then, the supernatant was centrifuged at 10000 rpm for 5 minutes, and the resulting precipitate was the exfoliated few-layer MXene nanosheets. Finally, the precipitate was washed multiple times with anhydrous ethanol and dried in a vacuum drying oven at 80°C for 12 hours to obtain few-layer MXene, which was then sealed and stored for later use.

[0025] The mass ratio of multilayer MXene powder to dimethyl sulfoxide and deionized water is 1:30:500. Room temperature refers to 15-25℃.

[0026] In the preparation steps of the composite epoxy coating, BADGE-FA prepolymer and BPGDGE-FA prepolymer undergo a reversible DA covalent reaction with 4,4'-bismaleimide diphenylmethane to construct a thermally triggered self-healing epoxy network, resulting in a basic epoxy resin coating. Simultaneously, two functional fillers, fMXene nanosheets and PAO6@SiO2 microcapsules, are introduced. The fMXene nanosheets and microcapsules are uniformly dispersed in the epoxy matrix with good interfacial bonding. Due to its two-dimensional layered structure, fMXene forms a solid lubrication transfer film at the interface during friction, simultaneously playing a role in load bearing and friction reduction; the PAO6@SiO2 microcapsules provide fluid lubrication. The synergy of these two fillers significantly reduces the coefficient of friction of the composite epoxy coating, making the wear volume negligible. Furthermore, the two-dimensional layered structure of fMXene creates a "maze effect" within the coating, effectively extending the diffusion path of corrosive media; the PAO6 released from the microcapsules forms a hydrophobic barrier at local defects. The synergy of these two fillers gives the composite epoxy coating excellent long-term protective performance.

[0027] Among them, the reversibility of DA endows the composite epoxy coating with self-healing properties, so that the scratches of the composite epoxy coating are completely closed after the reverse reaction and re-crosslinking. At the same time, the solid lubricating film formed by fMXene nanosheets and the fluid lubricant released by PAO6@SiO2 microcapsules, as well as the mechanical properties of epoxy material, make the composite epoxy coating provided by this application have excellent anti-corrosion, wear resistance and self-lubricating properties.

[0028] Furthermore, the composite coating is applied to the substrate surface by spraying. The substrate is selected from iron, aluminum, magnesium, zinc, and their respective alloys. In this application, Q235 steel plate is selected as the coating substrate. Before use, it undergoes sandblasting roughening treatment, cleaning with deionized water and ethanol, and drying treatment to enhance the coating adhesion. Finally, the prepared composite coating is uniformly sprayed onto the pretreated Q235 steel surface using a spraying method. After spraying, the coating is first placed in a vacuum drying oven at 45°C for 24 hours to allow the solvent to fully evaporate. Then, the coating is transferred to an 80°C oven for curing for 12 hours to obtain the composite coating.

[0029] In the sandblasting process, 100-mesh sand is used, and the average surface roughness (Ra) of the substrate after sandblasting is 2.0-4.5µm. During the spraying process, the spraying pressure is 0.3-0.5MPa, the spraying distance is 15-20cm, and the spraying time is 50s.

[0030] This application, through the aforementioned scheme, successfully constructs a multifunctional epoxy coating system possessing self-healing, corrosion-resistant, and wear-resistant functions by combining self-healing resin and fillers. By allowing the epoxy groups in bisphenol A diglycidyl ether and polypropylene glycol diglycidyl ether to undergo ring-opening reactions with the primary amine groups in furfurylamine, furan groups are introduced into the prepolymer segments, giving the coating the possibility of room-temperature crosslinking. The bisphenol A backbone in bisphenol A diglycidyl ether provides rigidity, while the polyether chains in polypropylene glycol diglycidyl ether provide flexibility, forming an interpenetrating network or blend system to achieve toughening. By further reacting the BADGE-FA prepolymer and BPGDGE-FA prepolymer with 4,4'-bismaleimide diphenylmethane in a reversible DA covalent reaction, a thermally triggered self-healing epoxy network is constructed, yielding the basic epoxy resin coating. Simultaneously, two functional fillers, fMXene nanosheets and PAO6@SiO2 microcapsules, are introduced. The fMXene nanosheets form a dense lubricating film in the coating, preventing the intrusion of external corrosive media. At the same time, the PAO6@SiO2 microcapsules release fluid lubricant, filling the pores of the epoxy coating to form a physical barrier, so that the composite epoxy coating has multiple functions such as corrosion resistance, wear resistance and self-repair.

[0031] Optionally, in solution A, the mass ratio of bisphenol A diglycidyl ether to furfurylamine is 10:2.56, and the mass ratio of bisphenol A diglycidyl ether to N,N-dimethylformamide is 10:23. In solution B, the mass ratio of polypropylene glycol diglycidyl ether to furfurylamine is 10:1.52, and the mass ratio of polypropylene glycol diglycidyl ether to N,N-dimethylformamide is 10:23.

[0032] Optionally, in the modification step of few-layer MXene nanosheets, the mass ratio of few-layer MXene to diaminobenzenesulfonic acid is 0.4:0.2, and the mass-volume ratio of the sum of the masses of few-layer MXene and diaminobenzenesulfonic acid to deionized water is 0.6 g / 200 mL.

[0033] Optionally, in the preparation step of the composite epoxy coating, the mass ratio of BADGE-FA prepolymer to PPGDGE-FA prepolymer is 1-10:1-10, and the molar ratio of furan groups in BADGE-FA prepolymer to maleimide groups in 4,4'-bismaleimide diphenylmethane is 1:1.

[0034] Specifically, by controlling the ratio of prepolymer to BMI, the molar ratio of "furan groups (dienes)" in the prepolymer to "maleimide groups (dienesophiles)" in 4,4'-bismaleimide diphenylmethane (BMI) is 1:1, thereby constructing a three-dimensional network with the highest crosslinking density and self-healing efficiency.

[0035] Preferably, the mass ratio of BADGE-FA prepolymer to PPGDGE-FA prepolymer is 1:9, 3:7, 5:5, 7:3, or 9:1; more preferably, the mass ratio of BADGE-FA prepolymer to PPGDGE-FA prepolymer is 7:3.

[0036] Optionally, the amount of fMXene nanosheets added is 5 wt% of the composite coating, and the amount of PAO6@SiO2 microcapsules added is 5 wt% of the composite coating.

[0037] Optionally, the preparation methods of PAO6@SiO2 microcapsules include: PAO6 and OP-10 emulsifiers were mixed with deionized water and stirred at high speed at 8000-10000 rpm for 5 minutes to obtain a water-in-oil emulsion. The pH value of the water-in-oil emulsion was then adjusted to >10 (using sodium hydroxide or potassium hydroxide). Sodium metasilicate nonahydrate was dissolved in deionized water and acidified (using hydrochloric acid or sulfuric acid) until pH < 2. Then, it was back-titrated with 15 wt% sodium carbonate until the pH value was 2.85-3.00 to obtain a stable and uniform silica sol. The water-in-oil emulsion was transferred to a 60°C oil bath and stirred at 250-300 rpm. Silica sol was then added dropwise to the emulsion at a rate of 1 mL / min using a pump. After the addition was complete, the mixture was stirred at 60°C for 48 h. The mixture was then allowed to stand at 70°C for 6-12 h to mature. Finally, it was cooled to room temperature, the product was filtered out, washed with anhydrous ethanol, and dried at 80°C for 12 h to obtain white PAO6@SiO2 microcapsules.

[0038] Specifically, OP-10 emulsifier forms a water-in-oil emulsion under high-speed shearing. PAO6 (polyalphaolefin) serves as the oil phase core, dispersed into tiny droplets. In an alkaline environment (pH>10), activated silicic acid in the silica sol undergoes a condensation reaction at the oil-water interface, dehydrating to form a three-dimensional -Si-O-Si- network structure. As the reaction time increases (48 hours), this network structure densifies and eventually deposits on the surface of the PAO6 droplets, forming a rigid SiO2 shell. The SiO2 shell physically isolates the core lubricant (PAO6), preventing premature leakage or reaction with the resin during coating formulation and storage. When the coating cracks due to friction or external force, the stress at the crack tip punctures the brittle SiO2 shell, releasing the PAO6 lubricating oil. PAO6 can quickly fill the cracks to form an oil film, providing physical lubrication to reduce the coefficient of friction and blocking corrosion channels.

[0039] Optionally, in the water-in-oil emulsion, the mass ratio of PAO6 to OP-10 emulsifier is 20:1.5, and the mass-volume ratio of PAO6 to deionized water is 20g / 200mL. In the silica sol, the mass-to-volume ratio of sodium metasilicate nonahydrate to deionized water is 15 g / 200 mL.

[0040] Optionally, the thickness of the composite epoxy coating is less than 100 μm.

[0041] Specifically, DA crosslinking relies on the movement of molecular chain segments to repair defects. If the composite epoxy coating is too thick (>100μm), the heat transfer of the inner layer will be delayed during the repair heating, and the internal bubbles will be difficult to escape. Controlling the thickness to within 100μm can ensure that the entire coating layer can be heated evenly at the reverse DA reaction temperature, achieving rapid and thorough self-healing of scratches.

[0042] More preferably, the thickness of the composite epoxy coating is 90-100 μm.

[0043] Secondly, this application provides an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction, which is obtained by the above-described preparation method.

[0044] Thirdly, this application provides an application of the above-mentioned composite epoxy coating in the fields of lubrication and corrosion prevention of mechanical equipment surfaces.

[0045] The following are embodiments and effect test examples of this application, further describing the technical solution and technical effects of the present invention. However, the scope of protection of the present invention is not limited to these embodiments. Any changes or equivalent substitutions that do not depart from the concept of the present invention are within the scope of protection of the present invention. Furthermore, for those embodiments where specific technical operation steps or conditions are not specified, they are performed according to the techniques or conditions described in general literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0046] Example 1 A method for preparing an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction includes the following steps: (1) Preparation of furan-functionalized epoxy prepolymer: Take 10g of bisphenol A diglycidyl ether in a dry container, add 2.56g of furfurylamine and 23g of N,N-dimethylformamide to the container, stir to obtain solution A. Take 10g of polypropylene glycol diglycidyl ether in a dry container, add 1.52g of furfurylamine and 23g of N,N-dimethylformamide to the container, stir to obtain solution B. Transfer solutions A and B to reactors respectively, and stir and react at 60℃ for 4h. Solution A reacts to obtain BADGE-FA prepolymer, and solution B reacts to obtain BPPGDGE-FA prepolymer. (2) Modification of few-layer MXene nanosheets: Take 1g of multilayer MXene (Ti3C2T) x The powder was added to 30g of dimethyl sulfoxide (DMSO) and magnetically stirred at room temperature for 12 hours to achieve pre-intercalation. Subsequently, the dispersion was centrifuged at 5000 rpm, and the precipitate was collected. The precipitate was redispersed in 500g of deionized water and sonicated in a water bath for 6 hours. After sonication, the resulting dispersion was first centrifuged at 3000 rpm for 5 minutes to collect the supernatant to remove unexfoliated thick sheets; then, the supernatant was centrifuged at 10000 rpm for 5 minutes, and the resulting precipitate was the exfoliated few-layer MXene nanosheets. Finally, the precipitate was washed three times with anhydrous ethanol and dried in a vacuum drying oven at 80℃ for 12 hours to obtain few-layer MXene.

[0047] 0.4 g of few-layer MXene and 0.2 g of diaminobenzenesulfonic acid were placed in 200 mL of deionized water, stirred and dispersed for 1 h, stirred in an oil bath at 80 °C for 2 h, filtered, washed three times with anhydrous ethanol, and dried in an oven at 60 °C for 12 h to finally obtain fMXene nanosheets.

[0048] (3) Preparation of PAO6@SiO2 microcapsules: Mix 20g PAO6, 1.5g OP-10 emulsifier with 200mL deionized water and stir at 8000rpm for 5min to obtain a water-in-oil emulsion. Adjust the pH of the water-in-oil emulsion to 11. Take another 15g of sodium metasilicate nonahydrate and dissolve it in 200mL of deionized water. Acidify it to pH 1.2, and then back-titrate it with 15wt% sodium carbonate to pH 2.85 to obtain a stable and uniform silica sol. The water-in-oil emulsion was transferred to a 60°C oil bath and stirred at 250 rpm. Silica sol was then added dropwise to the emulsion at a rate of 1 mL / min using a pump. After the addition was complete, the mixture was stirred at 60°C for 48 h. The mixture was then allowed to stand at 70°C for 6 h to mature. Finally, it was cooled to room temperature, the product was filtered out, washed with anhydrous ethanol, and dried at 80°C for 12 h to obtain white PAO6@SiO2 microcapsules.

[0049] (4) Preparation of composite epoxy coating: BADGE-FA prepolymer, PPGDGE-FA prepolymer, and 4,4'-bismaleimide diphenylmethane were mixed and stirred at room temperature for 1 hour to obtain a basic epoxy resin coating. Then, fMXene nanosheets and PAO6@SiO2 microcapsules were added and uniformly dispersed by mechanical stirring and ultrasonic treatment to obtain a composite coating. The composite coating was applied to the substrate surface and placed in a vacuum drying oven at 45°C for 24 hours to allow the solvent to fully evaporate. Then, the coating was transferred to an oven at 80°C for 12 hours to cure, resulting in a composite coating.

[0050] The mass ratio of BADGE-FA prepolymer to PPGDGE-FA prepolymer is 1:9, and the molar ratio of furan groups in BADGE-FA prepolymer to maleimide groups in 4,4'-bismaleimide diphenylmethane is 1:1. The amount of fMXene nanosheets added is 5 wt% of the composite coating, and the amount of PAO6@SiO2 microcapsules added is 5 wt% of the composite coating.

[0051] In the sandblasting process, 100-mesh abrasive was used, and the average surface roughness (Ra) of the substrate after sandblasting was 2.0µm. During the spraying process, the spraying pressure was 0.3MPa, the spraying distance was 15cm, and the spraying time was 50s.

[0052] Example 2 A method for preparing an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction includes the following steps: The difference from Example 1 is that: (3) Preparation of PAO6@SiO2 microcapsules: Mix 20g PAO6, 1.5g OP-10 emulsifier with 200mL deionized water and stir at 9000rpm for 5min to obtain a water-in-oil emulsion. Adjust the pH of the water-in-oil emulsion to 12. Take another 15g of sodium metasilicate nonahydrate and dissolve it in 200mL of deionized water. Acidify it to pH 1.5, and then back-titrate it with 15wt% sodium carbonate to pH 2.9 to obtain a stable and uniform silica sol. The water-in-oil emulsion was transferred to a 60°C oil bath and stirred at 300 rpm. Silica sol was then added dropwise to the emulsion at a rate of 1 mL / min using a pump. After the addition was complete, the mixture was stirred at 60°C for 48 h. The mixture was then allowed to stand at 70°C for 12 h to mature. Finally, it was cooled to room temperature, the product was filtered out, washed with anhydrous ethanol, and dried at 80°C for 12 h to obtain white PAO6@SiO2 microcapsules.

[0053] (4) Preparation of composite epoxy coating: The mass ratio of BADGE-FA prepolymer to PPGDGE-FA prepolymer is 3:7, and the molar ratio of furan groups in BADGE-FA prepolymer to maleimide groups in 4,4'-bismaleimide diphenylmethane is 1:1. The amount of fMXene nanosheets added is 5 wt% of the composite coating, and the amount of PAO6@SiO2 microcapsules added is 5 wt% of the composite coating.

[0054] In the sandblasting process, 100-mesh abrasive was used, and the average surface roughness (Ra) of the substrate after sandblasting was 3µm. During the spraying process, the spraying pressure was 0.3MPa, the spraying distance was 20cm, and the spraying time was 50s. Example 3

[0055] A method for preparing an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction includes the following steps: The difference from Example 1 is that: (3) Preparation of PAO6@SiO2 microcapsules: Mix 20g PAO6, 1.5g OP-10 emulsifier with 200mL deionized water, and stir at 10000rpm for 5min to obtain a water-in-oil emulsion. Adjust the pH of the water-in-oil emulsion to 13. Take another 15g of sodium metasilicate nonahydrate and dissolve it in 200mL of deionized water. Acidify it to pH 1, and then back-titrate it with 15wt% sodium carbonate until the pH is 3.00 to obtain a stable and uniform silica sol. The water-in-oil emulsion was transferred to a 60°C oil bath and stirred at 280 rpm. Silica sol was then added dropwise to the emulsion at a rate of 1 mL / min using a pump. After the addition was complete, the mixture was stirred at 60°C for 48 h. The mixture was then allowed to stand at 70°C for 10 h to mature. Finally, it was cooled to room temperature, the product was filtered out, washed with anhydrous ethanol, and dried at 80°C for 12 h to obtain white PAO6@SiO2 microcapsules.

[0056] (4) Preparation of composite epoxy coating: BADGE-FA prepolymer, PPGDGE-FA prepolymer, and 4,4'-bismaleimide diphenylmethane were mixed and stirred at room temperature for 1 hour to obtain a basic epoxy resin coating. Then, fMXene nanosheets and PAO6@SiO2 microcapsules were added and uniformly dispersed by mechanical stirring and ultrasonic treatment to obtain a composite coating. The composite coating was applied to the substrate surface and placed in a vacuum drying oven at 45°C for 24 hours to allow the solvent to fully evaporate. Then, the coating was transferred to an oven at 80°C for 12 hours to cure, resulting in a composite coating.

[0057] The mass ratio of BADGE-FA prepolymer to PPGDGE-FA prepolymer is 5:5, and the molar ratio of furan groups in BADGE-FA prepolymer to maleimide groups in 4,4'-bismaleimide diphenylmethane is 1:1. The amount of fMXene nanosheets added is 5 wt% of the composite coating, and the amount of PAO6@SiO2 microcapsules added is 5 wt% of the composite coating.

[0058] During sandblasting, 100-mesh abrasive was used, resulting in an average surface roughness (Ra) of 4.5µm for the substrate. The spraying pressure was 0.4MPa, the spraying distance was 15cm, and the spraying time was 50s. Example 4

[0059] A method for preparing an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction includes the following steps: The difference from Example 3 is that: (4) Preparation of composite epoxy coating: The mass ratio of BADGE-FA prepolymer to PPGDGE-FA prepolymer is 7:3, and the molar ratio of furan groups in BADGE-FA prepolymer to maleimide groups in 4,4'-bismaleimide diphenylmethane is 1:1. The amount of fMXene nanosheets added is 5 wt% of the composite coating, and the amount of PAO6@SiO2 microcapsules added is 5 wt% of the composite coating.

[0060] In the sandblasting process, 100-mesh abrasive was used, resulting in an average surface roughness (Ra) of 2.5µm for the substrate. During the coating process, the coating pressure was 0.3MPa, the coating distance was 15cm, and the coating time was 50s. The resulting composite epoxy coating was named MWEP. Example 5

[0061] A method for preparing an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction includes the following steps: The difference from Example 3 is that: (4) Preparation of composite epoxy coating: The mass ratio of BADGE-FA prepolymer to PPGDGE-FA prepolymer is 9:1, and the molar ratio of furan groups in BADGE-FA prepolymer to maleimide groups in 4,4'-bismaleimide diphenylmethane is 1:1. The amount of fMXene nanosheets added is 5 wt% of the composite coating, and the amount of PAO6@SiO2 microcapsules added is 5 wt% of the composite coating.

[0062] In the sandblasting process, 100-mesh abrasive was used, and the average surface roughness (Ra) of the substrate after sandblasting was 4µm. During the spraying process, the spraying pressure was 0.4MPa, the spraying distance was 18cm, and the spraying time was 50s.

[0063] Comparative Example 1 A method for preparing an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction includes the following steps: The difference from Example 4 is that: (4) Preparation of composite epoxy coating: The composite epoxy coating does not contain fMXene nanosheets and PAO6@SiO2 microcapsules, and the resulting composite epoxy coating is named EP.

[0064] Comparative Example 2 A method for preparing an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction includes the following steps: The difference from Example 4 is that: (4) Preparation of composite epoxy coating: The composite epoxy coating contains fMXene nanosheets but not PAO6@SiO2 microcapsules, and the resulting composite epoxy coating is named MEP.

[0065] Comparative Example 3 A method for preparing an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction includes the following steps: The difference from Example 4 is that: (4) Preparation of composite epoxy coating: The composite epoxy coating contains PAO6@SiO2 microcapsules but not fMXene nanosheets, and the resulting composite epoxy coating is named WEP.

[0066] Experimental Example 1 Composite epoxy coatings were successfully prepared in Examples 1-5. Taking the composite epoxy coating (MWEP) obtained in Example 4 as an example, the performance of the composite epoxy coating was tested and compared with the composite epoxy coatings obtained in Comparative Examples 1-3.

[0067] Coating cross-sectional morphology characterization The cross-sectional morphology of the composite epoxy coatings obtained in Example 4 and Comparative Examples 1-3 was characterized using scanning electron microscopy, and the results are as follows: Figure 2 As shown.

[0068] Figure 2The images show the cross-sectional morphology of the composite epoxy coatings obtained in Example 4 and Comparative Examples 1-3. The first row shows the morphology at 1000x magnification, and the second row shows the morphology at 2000x magnification. The images also show the cross-sectional SEM morphology of the coatings (a1)-(a2)EP (Comparative Example 1), (b1)-(b2)MEP (Comparative Example 2), (c1)-(c2)WEP (Comparative Example 3), and (d1)-(d2)MWEP (Example 4).

[0069] Depend on Figure 2 It can be seen that the surfaces of the four coatings are generally continuous and intact, without cracks or obvious defects. In the pure EP coating, the cross-section exhibits a uniform and dense structure with a complete morphology and no obvious defects. The MEP coating with added fMXene (Comparative Example 2) has a macroscopic surface morphology very similar to the EP coating, and no significant changes in roughness or new surface structures are produced due to the introduction of filler. This is because the lateral dimensions of fMXene nanosheets are typically in the micrometer range and the thickness is in the nanometer range. When it is uniformly dispersed in the resin matrix at a low content (5wt%), it mainly acts on the internal structure and interface of the coating, without significantly changing its surface morphology at low magnification. In the WEP (Comparative Example 3) coating and the MWEP (Example 4) coating, the cross-section exhibits significantly different structural characteristics. Spherical or near-spherical pores with diameters ranging from 20 to 50 μm are visible in the figure. The pore edges are clear, and no radial cracks are observed in the surrounding epoxy matrix, indicating that the interface between the microcapsules and the resin matrix is ​​well bonded, and the introduction of microcapsules has not seriously damaged the overall density of the coating.

[0070] Experiment Example 2 Mechanical property testing of composite epoxy coating The adhesion of the coating was tested using a pull-off test according to standard ISO 4624-2016. Coating thickness was determined using a PosiTector 6000 FNS1 thickness gauge, and pencil hardness was tested using a pencil hardness tester (BGD 507 / S). At least three parallel tests were performed for each group of experiments, and the average value was taken. The coating thickness and pencil hardness results for the composite coating are shown in Table 1, and the adhesion of the composite coating is shown in Table 2. Figure 3 As shown.

[0071] Table 1

[0072] Figure 3 This is an adhesion force diagram of the composite epoxy coatings obtained in Example 4 and Comparative Examples 1-3. (Observation) Figure 3The adhesion of EP was found to be 4.69 ± 0.34 MPa. The coating was uniform and continuous, maintaining stable contact with the substrate and thus maintaining good bonding strength under external forces. After adding microcapsules, the adhesion of the WEP coating decreased to 3.97 ± 0.37 MPa. This is mainly because the microcapsules formed dispersed particle regions in the coating, reducing the effective contact area between the substrate and the matrix, and causing localized stress concentration at the interface, thus reducing the overall adhesion. In the MEP coating, the adhesion was 4.37 ± 0.28 MPa, slightly lower than EP but higher than WEP. This is because while the introduction of MXene improved the internal microstructure of the coating, making the resin contact with the substrate more uniform locally, slight discontinuities still formed at local interfaces, resulting in a slight decrease in adhesion compared to EP. However, compared to WEP containing microcapsules, the two-dimensional structure of MXene helps enhance interfacial bonding and overall coating stability, making the adhesion of MEP still higher than that of WEP. The adhesion of MWEP was 4.15±0.31 MPa, falling between that of MEP and WEP. This indicates that the fMXene nanofiller alleviated the interfacial weaknesses caused by the PAO6@SiO2 microcapsules to some extent, maintaining the adhesion of the composite system at a moderate level. Interfacial observation showed that the nanofiller was uniformly dispersed, improving local contact stability, while the microcapsules still had certain interfacial weaknesses. The combined effect of both factors resulted in the final adhesion performance.

[0073] Table 1 shows that the synergistic effect of fMXene nanosheets and PAO6@SiO2 microcapsules improved the overall hardness of the coating while maintaining good uniformity. Overall, the four coatings showed an increasing trend in both thickness and hardness. The addition of functional fillers effectively improved the mechanical properties and application uniformity of the coatings, providing a reliable guarantee for their durability and application performance.

[0074] Experimental Example 3 Self-healing performance characterization The self-healing properties of the composite epoxy coating were observed using an Olympus BX53M optical microscope. Uniform scratches were made into the prepared coating using a scalpel. The coating was then placed in a 140°C oven for 2 hours to allow the resin to undergo a reverse DA reaction, followed by a curing process in an 80°C oven for 6 hours. The scratches were photographed and their width measured before and after self-healing using an optical microscope. The initial scratches, created manually, ranged in width from 36µm to 100µm and had a length of 2cm.

[0075] Comparative Example 4 A method for preparing an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction includes the following steps: The difference from Example 4 is that: (4) Preparation of composite epoxy coating: The composite epoxy coating is a pure epoxy coating, meaning that the composite epoxy coating does not contain fMXene nanosheets and PAO6@SiO2 microcapsules, and only contains BADGE-FA prepolymer.

[0076] Comparative Example 5 A method for preparing an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction includes the following steps: The difference from Example 4 is that: (4) Preparation of composite epoxy coating: The composite epoxy coating is a pure epoxy coating, meaning that the composite epoxy coating does not contain fMXene nanosheets and PAO6@SiO2 microcapsules, and only contains PPGDGE-FA prepolymer.

[0077] The self-healing properties of the composite epoxy coatings obtained in Example 4 and Comparative Examples 1-5 were characterized, and the results are as follows: Figure 4 , Figure 5 As shown. Figure 4 The images show optical microscope images of the composite epoxy coatings obtained in Comparative Examples 2, 3 and 4 before and after self-healing of scratches: (a1)-(a2) MEP (Comparative Example 2), (b1)-(b2) WEP (Comparative Example 3), (c1)-(c2) MWEP (Example 4), (a1-c1) before self-healing, and (a2-c2) after self-healing.

[0078] Figure 5 The images show optical microscope images of the composite epoxy coatings obtained in Comparative Examples 1, 4 and 5 before and after self-healing of scratches. (d1)-(d2) Comparative Example 4, (e1)-(e2) Comparative Example 5, (f1)-(f2) Comparative Example 1, (d1-f1) before self-healing, and (d2-f2) after self-healing.

[0079] Figure 5In Comparative Example 4 (d1-d2), the width of the scratch decreased from 40.38 μm to 11.36 μm after repair, achieving partial closure, indicating that its DA bond has a certain degree of reversibility. However, the shape recovery was incomplete due to insufficient cross-linking network strength. In Comparative Example 5 (e1-e2), although the scratch could be basically closed, visible repair traces remained on the surface. Comparative Example 1 (f1-f2) exhibited excellent self-healing performance. Its scratch with an initial width of 60.27 μm completely disappeared after repair and was almost invisible under an optical microscope. In Comparative Example 1, when BADGE-FA prepolymer and PPGDGE-FA prepolymer were compounded in a mass ratio of 7:3, the flexible PPGDGE-FA segments provided sufficient molecular mobility for the reversible reaction of the DA bond, while the rigid BADGE-FA units constructed a stable network framework, providing necessary support for interfacial contact and re-crosslinking. This synergistic effect of "combining rigidity and flexibility" allows the network of the composite coating obtained in Comparative Example 1 to achieve full migration and contact of molecular chains after damage, while effectively maintaining the shape stability of the repair interface, thus achieving a better visual repair effect.

[0080] Figure 4 In the study, all composite coatings exhibited excellent self-healing efficiency. Under the same repair conditions, artificial scratches on the surfaces of MEP, WEP, and MWEP coatings almost completely disappeared after repair, becoming indistinguishable under an optical microscope, with visual repair effects comparable to the matrix in Comparative Example 1. This result indicates that the introduction of 5wt% fMXene nanosheets and / or microcapsules did not affect the intrinsic self-healing capability of the epoxy resin matrix based on the DA reaction.

[0081] Experiment Example 4 Tribological property characterization The tribological properties of the composite epoxy coatings obtained in Example 4 and Comparative Examples 1-3 were characterized using a CSM TRB3 tribometer (Anton Paar, Switzerland). The test employed a ball-disc friction mode, using φ6 mm 304 stainless steel balls as the grinding pair, under a load of 5 N, a frequency of 2 Hz, and a friction stroke of 6 mm for 20 min. Subsequently, the surface morphology of the wear tracks was characterized using a DCM8 fully automated true-color confocal microscope, and the three-dimensional morphology of the wear tracks was quantitatively analyzed using accompanying software. The results are shown below. Figure 6 , Figure 7 As shown.

[0082] Figure 6 (a) is a graph showing the friction coefficient of the composite epoxy coatings obtained in Example 4, Comparative Examples 1-3. Figure 6 (b) is a graph showing the average friction coefficient of the composite epoxy coatings obtained in Example 4, Comparative Examples 1-3.

[0083] Figure 6 In (b) of the comparison example 1, the average coefficient of friction of the pure epoxy coating EP was as high as 0.699, indicating severe coating wear. The high coefficient of friction of EP is mainly attributed to the inherent brittleness of the cross-linked network of the pure epoxy coating. During friction, microcracks are prone to initiation and propagation on the brittle surface, leading to the material peeling off in fragments.

[0084] The addition of functional fillers significantly improved the tribological properties of the coatings. Specifically, the WEP coating (Comparative Example 3) with only PAO6@SiO2 microcapsules showed an average friction coefficient of 0.099, while the MEP coating (Comparative Example 2) with only fMXene nanosheets showed a coefficient of friction of 0.120, indicating that both PAO6@SiO2 microcapsules and fMXene nanosheets effectively enhanced the friction-reducing properties of the coatings. Particularly noteworthy was the MWEP coating (Example 4) with both fMXene nanosheets and PAO6@SiO2 microcapsules, which exhibited the best tribological properties, with the lowest average friction coefficient of only 0.054. Furthermore, the curve remained stable throughout the test, demonstrating extremely low friction fluctuations and excellent wear resistance stability.

[0085] Figure 7 The images show the three-dimensional surface morphology of the wear marks on the composite epoxy coatings obtained in Example 4 and Comparative Examples 1-3. Figure 7 (a) is a three-dimensional surface morphology diagram of the wear marks on EP (Comparative Example 1). Figure 7 (b) is a three-dimensional surface morphology diagram of the wear marks on the MEP (Comparative Example 2). Figure 7 (c) is a three-dimensional surface morphology diagram of the wear marks on WEP (Comparative Example 3). Figure 7 (d) is a three-dimensional surface morphology diagram of the wear marks of MWEP (Example 4).

[0086] observe Figure 7The pure EP coating (Comparative Example 1) exhibited deep and wide wear marks, with a significant wear volume. In contrast, the MEP coating only showed minor shallow scratches, with a significantly reduced wear volume. The wear surfaces of the WEP and MWEP coatings (Comparative Example 2) were smoother, consistent with their extremely low coefficients of friction. However, the wear marks on the MWEP surface were not obvious. For fMXene two-dimensional nanosheets, their good mechanical properties and layered structure effectively bear loads and hinder crack propagation during friction, thus enhancing the coating's wear resistance. Secondly, under shearing action, the fMXene nanosheet layers easily spread at the friction interface and form a continuous, dense solid lubricant transfer film. This film effectively isolates the direct contact between the mating parts and the coating substrate, transforming sliding friction into low-shear friction between MXene layers, thereby significantly reducing the coefficient of friction and wear rate. For PAO6@SiO2 microcapsules, when the friction pair slides on the coating surface, the generated mechanical stress causes the microcapsule shell to rupture, releasing the encapsulated PAO6 lubricant to the friction interface. These lubricants can spread rapidly, forming a fluid lubrication film that effectively reduces shear stress at the contact surface, enabling a shift from solid friction to hybrid or fluid lubrication, thereby significantly reducing friction and wear. In the MWEP coating, the solid lubrication and load-bearing properties of fMXene, combined with the fluid lubrication and self-healing properties of the microcapsules, produce a significant synergistic effect: the robust framework constructed by fMXene maintains the integrity of the coating, while the lubricating film provided by the microcapsules further optimizes the interfacial lubrication state. Together, they construct a highly efficient and durable wear-resistant protection system.

[0087] Therefore, by introducing fMXene nanosheets and PAO6@SiO2 microcapsules, not only were the friction coefficient and wear volume of the epoxy coating significantly reduced, but also the tribological properties of the coating were qualitatively improved through the organic combination of solid lubrication, fluid lubrication, and self-healing mechanisms. This demonstrates the great potential of this composite strategy in preparing high-performance wear-resistant coatings.

[0088] Experimental Example 5 Corrosion resistance characterization The corrosion resistance of the composite epoxy coatings obtained in Example 4, Comparative Examples 1-3 were characterized.

[0089] The corrosion resistance of the coating was evaluated by electrochemical impedance spectroscopy (EIS) and neutral salt spray testing. EIS testing was performed using a CHI660e electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd.). Before testing, the sample was sealed with a paraffin-resin mixture, leaving a 1 cm² exposed area, and immersed in 3.5 wt% NaCl solution for 24 h until the open-circuit potential stabilized. A three-electrode system was used: a saturated calomel electrode (reference electrode), a platinum electrode (auxiliary electrode), and the coating sample (working electrode). The testing frequency range was 10 Hz.-2 -10 5 A 10 mV sinusoidal perturbation signal was applied at Hz. Zsimpwin software was used to fit and analyze the EIS data. Salt spray testing was conducted in a KD-HYW150 salt spray chamber according to ISO 7253 standards, with test conditions of 5 wt% NaCl solution and 35℃. The corrosion of the sample surface was observed periodically. To study the self-healing performance of the coating, cross-scratches (deep to the steel substrate) were prepared on the coating surface, followed by heat treatment under the aforementioned self-healing conditions to complete the self-healing process. Subsequently, the repaired samples were subjected to EIS and salt spray tests under the same conditions to evaluate their post-repair protective performance.

[0090] Figure 8 The figures show the salt spray test results of the composite epoxy coatings obtained in Example 4 and Comparative Examples 1-3. Figure 9 The electrochemical impedance diagrams of the composite epoxy coatings obtained in Example 4 and Comparative Examples 1-3 are shown below: (a1-d1) Nyquist diagram, (a2-d2) Bode amplitude diagram, (a3-d3) Bode phase angle diagram, where a represents Comparative Example 1, b represents Comparative Example 2, c represents Comparative Example 3, and d represents Example 4.

[0091] observe Figure 8 It can be seen that all four composite epoxy coatings exhibit good anti-corrosion performance. EP showed corrosion pitting after 15 days, and its protective ability rapidly declined over time, with a significant decrease in interfacial barrier effect. Self-healing alone was insufficient to maintain long-term protection of the metal substrate. WEP showed corrosion pitting after 30 days. During long-term immersion, the microcapsules in the coating ruptured, releasing PAO6, which formed a hydrophobic barrier on the coating surface, effectively preventing corrosive media from penetrating into the substrate. MEP's anti-corrosion effect was far superior to EP and WEP, mainly due to the "maze effect" formed by MXene nanosheets in the coating, which prolonged the diffusion path of corrosive media into the substrate, thus improving the coating's barrier ability. The long-term protective effect of the MWEP composite system stemmed from the synergistic effect of microcapsules and MXene. The PAO6 released from the microcapsules formed a hydrophobic barrier on the coating surface, while the MXene nanosheets prolonged the diffusion path of corrosive media through the maze effect, effectively delaying the penetration of corrosive media, thereby improving the interfacial barrier ability of the coating and enabling it to maintain stable protective performance under long-term salt spray exposure. Although MXene possesses some conductivity, the fMXene used in this application exists in a dispersed form within the epoxy matrix, and the addition amount is low, making it difficult to form a continuous conductive pathway. Therefore, its intrinsic conductivity is significantly limited in the composite system. Consequently, its primary role in the coating is still the physical barrier effect created by the two-dimensional sheet structure, rather than electrochemical conductivity.

[0092] Figure 9The (a1-d1) Nyquist plots show that all systems exhibit large capacitive arcs in the early stages of immersion, with low-frequency impedances reaching the order of 10. 8 Ω·cm 2 This indicates that the coating can effectively prevent corrosive media from contacting the metal substrate in the initial stage. In the MWEP composite coating, the fMXene barrier effect works synergistically with the hydrophobic barrier of the microcapsules to maintain high overall coating impedance and form additional barriers at local microcracks or pores, further improving interface stability.

[0093] The low-frequency impedance of the EP coating is 4.79 × 10⁻⁶ d. 8 Ω·cm² decreased to 1.21×10⁻⁶ at 60 days. 6 Ω·cm 2 This indicates that the shielding ability of the pure epoxy coating weakens rapidly under long-term immersion. Although the coating has a certain self-healing ability, the epoxy system alone cannot effectively prevent corrosive media from penetrating the metal surface. The interface is easily invaded by moisture and ions, leading to an accelerated corrosion reaction. The WEP coating still maintains a strength of 1.01 × 10⁻⁶ after 60 days. 8 Ω·cm 2 The low-frequency impedance of the MEP coating is 1.29 × 10⁻⁶ after 60 days. 8 Ω·cm 2 The MWEP composite coating exhibits a low-frequency impedance of 6.65 × 10⁻⁶ at 1 day. 8 Ω·cm 2 It remained at 2.77 × 10 after 60 days. 8 Ω·cm 2 The results show that the synergistic effect of microcapsules and fMXene forms barriers at both overall and local defects, enabling the coating to maintain high impedance and interfacial stability during long-term immersion.

[0094] Figure 9 The (a3-d3) Bode phase angle plots show that the initial peak values ​​of each coating in the high-frequency region are close to 90°, indicating that the coatings initially possess good capacitance characteristics and shielding capabilities. With increasing immersion time, the peak values ​​generally decrease and shift towards lower frequencies, reflecting the gradual penetration of the corrosive medium into the metal interface and the enhanced interfacial charge transfer reaction. The hydrophobic barrier formed by the microcapsules of the WEP coating provides barrier properties at microcracks, while the MXene nanosheets of the MEP coating extend the medium diffusion path. The MWEP composite coating maintains high impedance and stability in both overall and local defect regions through the synergistic effect of both. These changes directly reflect the interfacial electrochemical properties and barrier capabilities of each coating during the immersion process.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing an MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction, characterized in that, Includes the following steps: (1) Preparation of furan-functionalized epoxy prepolymer: Bisphenol A diglycidyl ether was placed in a dry container, and furfurylamine and N,N-dimethylformamide were added to the container and stirred to obtain solution A. Polypropylene glycol diglycidyl ether was placed in a dry container, and furfurylamine and N,N-dimethylformamide were added to the container and stirred to obtain solution B. Solutions A and B were transferred to reactors respectively and stirred at 60°C for 4 hours. Solution A reacted to obtain BADGE-FA prepolymer, and solution B reacted to obtain BPPGDGE-FA prepolymer. (2) Modification of few-layer MXene nanosheets: Few-layer MXene and diaminobenzenesulfonic acid were placed in deionized water, stirred and dispersed for 1 hour, and then stirred in an oil bath at 80°C for 2 hours. After filtration, washing and drying, fMXene nanosheets were finally obtained. (3) Preparation of composite epoxy coating: BADGE-FA prepolymer, PPGDGE-FA prepolymer and 4,4'-bismaleimide diphenylmethane were mixed and stirred at room temperature for 1 hour to obtain a basic epoxy resin coating. Then, fMXene nanosheets and PAO6@SiO2 microcapsules were added and uniformly dispersed by mechanical stirring and ultrasonic treatment to obtain a composite coating. The composite coating was coated on the substrate surface and dried to obtain the composite epoxy coating.

2. The method for preparing the MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction according to claim 1, characterized in that, In solution A, the mass ratio of bisphenol A diglycidyl ether to furfurylamine is 10:2.56, and the mass ratio of bisphenol A diglycidyl ether to N,N-dimethylformamide is 10:

23. In solution B, the mass ratio of polypropylene glycol diglycidyl ether to furfurylamine is 10:1.52, and the mass ratio of polypropylene glycol diglycidyl ether to N,N-dimethylformamide is 10:

23.

3. The method for preparing the MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction according to claim 1, characterized in that, In the modification step of few-layer MXene nanosheets, the mass ratio of the few-layer MXene to the diaminobenzenesulfonic acid is 0.4:0.2, and the mass-volume ratio of the sum of the masses of the few-layer MXene and the diaminobenzenesulfonic acid to the mass-volume ratio of the deionized water is 0.6 g / 200 mL.

4. The method for preparing the MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction according to claim 1, characterized in that, In the preparation steps of the composite epoxy coating, the mass ratio of the BADGE-FA prepolymer to the PPGDGE-FA prepolymer is 1-10:1-10, and the molar ratio of the furan group in the BADGE-FA prepolymer to the maleimide group in 4,4'-bismaleimide diphenylmethane is 1:

1.

5. The method for preparing the MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction according to claim 1, characterized in that, The amount of fMXene nanosheets added is 5 wt% of the composite coating, and the amount of PAO6@SiO2 microcapsules added is 5 wt% of the composite coating.

6. The method for preparing the MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction according to claim 1, characterized in that, The preparation method of the PAO6@SiO2 microcapsules includes: PAO6 and OP-10 emulsifiers were mixed with deionized water and stirred at 8000-10000 rpm for 5 minutes to obtain a water-in-oil emulsion. The pH of the water-in-oil emulsion was then adjusted to >10. Sodium metasilicate nonahydrate was dissolved in deionized water and acidified to pH < 2. Then, it was titrated back with 15 wt% sodium carbonate until the pH value was 2.85-3.00 to obtain a stable and uniform silica sol. The water-in-oil emulsion was transferred to a 60°C oil bath and stirred at 250-300 rpm. The silica sol was then added dropwise to the water-in-oil emulsion at a rate of 1 mL / min using a pump. After the addition was complete, the mixture was stirred at 60°C for 48 h. The mixture was then allowed to stand at 70°C for 6-12 h to mature. Finally, it was cooled to room temperature, the product was filtered out, washed with anhydrous ethanol, and dried at 80°C for 12 h to obtain white PAO6@SiO2 microcapsules.

7. The method for preparing the MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction according to claim 6, characterized in that, In the water-in-oil emulsion, the mass ratio of PAO6 to the OP-10 emulsifier is 20:1.5, and the mass-to-volume ratio of PAO6 to the deionized water is 20g / 200mL. In the silica sol, the mass-to-volume ratio of sodium metasilicate nonahydrate to deionized water is 15 g / 200 mL.

8. The method for preparing the MXene / PAO6@SiO2 composite epoxy coating based on the Diels-Alder reaction according to claim 1, characterized in that, The thickness of the composite epoxy coating is less than 100 μm.

9. A Diels-Alder reaction-based MXene / PAO6@SiO2 composite epoxy coating, characterized in that, It is obtained by the preparation method according to any one of claims 1-8.

10. The application of the composite epoxy coating as described in claim 9 in the field of lubrication and corrosion protection of mechanical equipment surfaces.

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