A composite coating based on coffee ring effect enhancement and a preparation method thereof

Abstract

The application provides a composite coating based on coffee ring effect enhancement and a preparation method thereof, and the method comprises the following steps: S1. cleaning a substrate surface; S2. preparing a nano suspension; S3. atomizing the suspension prepared in the step S2 by a spray gun, and depositing the suspension in the form of a micro-droplet group on the cleaned substrate surface to form a nano-particle ring skeleton on the substrate surface; S4. covering the nano-particle ring skeleton with a polymer coating; and S5. solidifying the substrate coated in the step S4 to form a complete nano-composite coating. By converting the coffee ring effect from a "defect" to an "actively utilized tool", a three-dimensional stacked micro-nano topological skeleton composed of a nano-particle ring structure is constructed on the substrate surface through spray-induced micro-droplet group evaporation self-assembly, and the synchronous significant improvement of the coating hardness and the interfacial adhesion strength is realized by utilizing the triple synergistic enhancement effect of mechanical pinning, stress dispersion and topological induction of the ring skeleton.

Description

Technical Field

[0001] This invention belongs to the field of surface treatment and protection technology of metal materials, specifically relating to a composite coating enhanced by the coffee ring effect and its preparation method. This invention constructs discrete stacked ring microstructures by spray-induced evaporation and self-assembly of microdroplets, thereby enhancing the interfacial bonding and mechanical hardness of the composite coating. Background Technology

[0002] Coating metal surfaces with polymer coatings such as polyester, polyurethane, and epoxy is a common method for corrosion protection, wear resistance, and decoration. However, the adhesion strength between polymer coatings and metal substrates is limited, and they are prone to peeling under mechanical stress, thermal cycling, or corrosive environments. Furthermore, pure polymer coatings generally lack sufficient hardness, and their resistance to scratches, erosion, and abrasion needs improvement.

[0003] In existing technologies, the following methods are commonly used to improve this: 1. Surface roughening treatment: such as sandblasting and chemical etching, to increase the surface area of ​​the substrate and the mechanical interlocking effect. Although this method can improve adhesion, it may damage the substrate, the process is complex, and it has limited contribution to improving hardness.

[0004] 2. Adding reinforcing phases: Directly incorporating nanoparticles (such as SiO2, Al2O3, CNTs) into the polymer coating to improve hardness (dispersion strengthening). However, simple blending can easily lead to uneven agglomeration of nanoparticles within the coating, forming stress concentration points, which may weaken interfacial adhesion and even cause premature coating failure.

[0005] 3. Use coupling agents: improve interfacial chemical bonding, but are effective only for specific metal-polymer systems, have limited universality, and increase costs and process steps.

[0006] On the other hand, the coffee ring effect is a common physical phenomenon during droplet evaporation, where solute particles are transported and enriched towards the edges due to contact line pinning and capillary replenishment, resulting in ring-shaped deposits after drying. This effect has long been considered a defect that needs to be actively suppressed or avoided in fields such as inkjet printing, thin film processing, and biosensing, and various technical means are dedicated to eliminating ring-shaped deposits to obtain uniform film layers.

[0007] Therefore, the main problem with existing technology is: 1. It is difficult to significantly improve the coating hardness while simultaneously and effectively enhancing the adhesion strength between the coating and the metal substrate; 2. The dispersibility of nanoparticles and interfacial stress concentration are the core contradictions that traditional blending methods cannot fundamentally solve. 3. The coffee ring effect has long been regarded as a negative phenomenon and has never been used as a proactive design tool to build interface enhancement structures; 4. There is a lack of a method for preparing nanocomposite coatings that combines high performance, high efficiency, low cost, and is compatible with industrial spraying processes. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the technical bottleneck in the prior art where uneven dispersion of nanoparticles and concentration of interfacial stress make it difficult to simultaneously optimize coating hardness and adhesion strength, and to provide a composite coating based on the coffee ring effect.

[0009] The technical problem it aims to solve can be addressed through the following technical solutions.

[0010] A composite coating based on the coffee ring effect enhancement includes a metal substrate, characterized in that protruding nanoparticle ring skeleton units are deposited on the surface of the metal substrate by spraying, and the ring skeleton units are covered and cured by a polymer coating.

[0011] Furthermore, the ring-shaped framework unit is a ring-shaped ridge structure formed by discrete, randomly distributed, and statistically uniform nanoparticles.

[0012] Furthermore, the annular skeleton unit is formed by one or multiple sprayings of droplets.

[0013] Another technical problem to be solved by the present invention is to provide a method for preparing a composite coating enhanced by the coffee ring effect, the method comprising the following steps: S1. Cleaning of the substrate surface; S2. Preparation of nano-suspensions; S3. The suspension obtained in step S2 is atomized by a spray gun and deposited on the cleaned substrate surface in the form of micron-sized droplet groups, forming a nanoparticle ring skeleton on the substrate surface. S4. Cover the nanoparticle ring framework with a polymer coating; S5. Cure the substrate coated in step S4 to form a complete nanocomposite coating.

[0014] Furthermore, in step S2, when preparing the nano suspension, the nanoparticles and volatile solvent are mixed at a mass ratio of 100:(0.5-10), and 0.01-0.5 wt% dispersant is added. The mixture is then subjected to ultrasonic vibration to form a uniform and stable suspension. The nanoparticles have a particle size of 5-500 nm.

[0015] Furthermore, the volatile solvent is selected from one or more of deionized water, ethanol, isopropanol, or a water-ethanol mixture; the dispersant is selected from one or more of sodium polyacrylate, cetyltrimethylammonium bromide, and polyvinylpyrrolidone.

[0016] Furthermore, in step S3, the nanoparticle ring framework is deposited on the substrate surface in a coffee ring effect.

[0017] Furthermore, in step S3, the suspension is atomized by a spray gun and deposited on the substrate surface in the form of micron-sized droplet clusters; the spraying process parameters are controlled as follows: a. Nozzle diameter: 0.1~0.8 mm; b. Spraying pressure: 0.1~0.9 MPa; c. Spraying distance: 5–300 cm; d. Single spray amount: 0.01~2 mL / cm²; Furthermore, the ambient temperature is controlled at 20–50°C, the relative humidity is <50%, and there is little wind and dust, allowing the droplets to spread naturally and evaporate.

[0018] Furthermore, the droplet diameters formed by atomization exhibit a log-normal distribution. Droplets of different sizes evaporate to form coffee-ring skeletal units of varying diameters, constituting a composite reinforced interface with multi-scale ring structures. During atomization, the droplet landing points follow a spatially random distribution, and the number of rings per unit area has a linear relationship with the coating amount, R² > 0.95. 2 It is the coefficient of determination, used to measure the degree of fit of a simulation in statistics.

[0019] Furthermore, in step S3, a nanoparticle ring skeleton is formed on the substrate surface, which is formed by single spraying or multiple spraying and stacking.

[0020] Furthermore, the droplet coverage of a single spray is 10-60%.

[0021] Furthermore, when using a multi-coating stacking molding method, the following control conditions shall be implemented: (1) The subsequent sprayed droplets fall randomly in the existing ring area, the top of the ring ridge, or the blank area between rings, and are distributed in a probabilistic manner; (2) The spatial relationship between the subsequently stacked annular skeleton and the earlier formed annular skeleton is a stacking configuration relationship of filling inside the ring, stacking on the ring, or new formation between the rings.

[0022] Preferably, after multiple spraying and stacking, the stacking configuration of each ring skeleton is: ring filling: ring stacking: inter-ring new formation = 3:4:3.

[0023] Furthermore, in step S4, the polymer coating is applied using a dip coating, spin coating, or spray coating method to form the polymer coating.

[0024] Preferably, the polymer coating is selected from one or more of waterborne polyurethane resin, waterborne acrylic emulsion, waterborne epoxy resin, waterborne alkyd resin, or solvent-based fluorocarbon resin.

[0025] Furthermore, in step S5, the coated substrate is cured at 50–150°C for 0.5–8 hours to form a complete nanocomposite coating. The composite coating and its preparation method provided by this invention creatively transform the coffee ring effect from a "defect that needs to be avoided" into a "manufacturing tool that can be actively utilized." Through spray-induced microdroplet evaporation and self-assembly, a three-dimensional stacked micro-nano topological framework composed of nanoparticle ring structures is randomly, efficiently, and cost-effectively constructed on the substrate surface. By utilizing the triple synergistic enhancement effect of mechanical pinning, stress dispersion, and topological induction of this ring framework, the coating hardness and interfacial adhesion strength are simultaneously and significantly improved.

[0026] Compared with the prior art, the present invention has the following beneficial effects: 1. Transform the "coffee ring defect" into a "reinforced framework"; This invention overturns the traditional perception that the coffee ring effect has long been considered a negative phenomenon, proposing instead that it be used as an active design tool, utilizing ring deposition as an interface-enhancing framework for coatings. This "paradigm shift" not only provides a completely new approach to coating interface strengthening but also opens up new avenues for the functional utilization of other long-avoided physical phenomena.

[0027] 2. Collaborative enhancement mechanism; (1) Mechanical pinning (micro-anchoring): The nanoparticle ring skeleton embedded in the interface, like countless "micro-piles", forms a strong mechanical interlock at the coating / substrate interface. The stacked configuration on the ring increases the local ring height by more than 50%, further strengthening the anchoring effect and effectively resisting shear stress and peeling stress.

[0028] (2) Stress dispersion and transmission: The ring-shaped skeleton structure can effectively disperse and transmit the local concentrated stress (such as scratches and impacts) applied to the coating surface to a larger substrate area; the high rigidity of the nanoparticles themselves can bear the stress and avoid the coating cracking or peeling caused by stress accumulation at a single weak point.

[0029] (3) Topology-induced toughening: The three-dimensional stacked ring skeleton forms a continuous undulating topological morphology at the interface, which increases the crack propagation path length and improves the coating toughness.

[0030] 3. Fundamentally solve the problem of decentralization; This invention utilizes the coffee ring effect to achieve the directional and self-organized arrangement of nanoparticles, fundamentally avoiding the problem of random agglomeration of nanoparticles in traditional blending methods; the statistical uniformity of the spray process ensures the orderly distribution of the reinforcing phase on a macroscopic scale, while overcoming the limitation of large-area preparation by the single-drop precise control method.

[0031] 4. The process is simple and controllable, and is fully compatible with industrial production lines; The method of this invention is simple and fully adaptable to existing industrial spraying production lines, requiring no additional complex equipment. By adjusting the suspension concentration, spraying parameters, and stacking times, statistical control can be achieved on structural parameters such as ring height (adjustable from 200 to 1500 nm), ring diameter (adjustable from 50 to 400 μm), and areal density (adjustable from 30% to >95%), thereby enabling "programmed" design of coating performance.

[0032] 5. Significant performance improvement; Experiments show that the composite coating prepared by this invention is superior to coatings prepared by traditional blending methods: (1) Microhardness increased by 100-200%; (2) The interfacial adhesion was improved from level 2-3 to level 0 (cross-cut test, no peeling). Critical load L c increases by 3 to 6 times.

[0033] 6. It has strong universality and broad application prospects; The method of this invention is applicable to a variety of substrates such as steel, copper, aluminum, stainless steel, and glass; it is applicable to a variety of nanoparticles such as silicon oxide, alumina, silicon carbide, and nano-clay; and it is applicable to a variety of polymer systems such as waterborne polyurethane, waterborne acrylic, waterborne epoxy, and fluorocarbon resin. It has good technical versatility and industrial promotion value, and can be widely used in functional coatings such as anti-corrosion, wear-resistant, and anti-icing coatings in aerospace, marine engineering, automotive industry, and electronics. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the main process flow of the preparation method of the present invention.

[0035] Figure 2 A schematic diagram of the formation of a "coffee ring" structure by the evaporation of a single droplet (particle transport to the edge), illustrating how capillary flow propels particle transport during droplet evaporation to form the coffee ring structure.

[0036] Figures 3-5 This is a schematic diagram comparing the interface structure of the nanocomposite coating of this invention with that of a traditional blending coating. Figure 3 and Figure 4 This is the discrete ring array of the present invention. Figure 4 yes Figure 3 Enlarged view of the area within the Chinese box; Figure 5 The traditional method disperses and enhances randomly agglomerated particles; the figure shows a stable array of silica rings with a spreading diameter (~100 µm) densely arranged on the substrate. No local peeling or agglomeration occurred after the coating was lifted, proving that the prepared composite coating has good adhesion.

[0037] Figure 6 and Figure 7This is a comparison chart of the scratch test results of the coatings in Example 1 and the comparative example. Figure 6 This illustrates the application of a 5N force to the surface of the coffee ring array composite coating of the present invention; Figure 7 The diagram illustrates the application of a 2N force to the surface using the traditional dispersion strengthening method. Test results show that the coffee ring array can effectively disperse stress. In the scratch test, the coating was not penetrated and there was no macroscopically visible peeling. The technical solution of this invention effectively improves the critical load of the coating. Detailed Implementation

[0038] This invention provides a composite coating enhanced by the coffee ring effect and its preparation method, the preparation method comprising the following steps: S1. Surface pre-cleaning: The substrate undergoes degreasing, derusting, and dust removal in sequence: first, grease is removed using an alkaline solution or organic solvent; then, the rust layer is removed by pickling or mechanical grinding; finally, surface dust is removed by high-pressure sandblasting or compressed air blowing to ensure the substrate is clean and dry. This step is basically consistent with the requirements of conventional coating processes. S2. Preparation of nano-suspensions: Nanoparticles are mixed with a volatile solvent at a mass ratio of 100:0.5–10, and 0.01–0.5 wt% dispersant is added. The mixture is then subjected to ultrasonic vibration (power 20–500 W, time 2–10 min) to form a uniform and stable suspension. The nanoparticles have a particle size of 5–500 nm. The volatile solvent is selected from one or more of deionized water, ethanol, isopropanol, or a water-ethanol mixture. The dispersant is selected from one or more of sodium polyacrylate, cetyltrimethylammonium bromide, and polyvinylpyrrolidone.

[0039] S3. Coffee ring framework deposition – microdroplet cluster spray self-assembly: The suspension obtained in step S2 is atomized by a spray gun and deposited on the substrate surface after pretreatment in step S1 in the form of micron-sized droplet clusters; the spraying process parameters are controlled as follows: a. Nozzle diameter: 0.1~0.8 mm; b. Spraying pressure: 0.1~0.9 MPa; c. Spraying distance: 5–300 cm; d. Single spray amount: 0.01~2 mL / cm².

[0040] The ambient temperature is controlled at 20-50℃, the relative humidity is <50%, and there is little wind and dust, allowing the droplets to spread naturally and evaporate and dry. This step is the core step of the technical solution of the present invention, and has the following special technical features: (1) Actively utilize the coffee loop effect: This invention does not inhibit or avoid annular deposition, but actively induces droplets to evaporate in a pinned contact line state by precisely controlling the spraying parameters and evaporation conditions, so that nanoparticles migrate directionally to the droplet periphery to form a complete, continuous, and mechanically stable annular ridge structure as an interface reinforcement skeleton for the coating.

[0041] (2) Control of atomized droplet size distribution: The droplet diameters formed by atomization exhibit a log-normal distribution, with characteristic diameters D50 = 50–200 μm and D90 = 150–400 μm. After evaporation, droplets of different sizes form coffee ring framework units of different diameters, constituting a composite reinforced interface with multi-scale ring structures coexisting.

[0042] (3) Random drop points and statistical uniformity: The droplet landing points follow a spatially random distribution, but in a statistically significant sense, the number of rings per unit area is linearly related to the amount of coating applied (R²>0.95, where R...). 2 It is the coefficient of determination, used to measure the degree of simulation fit in statistics, and can achieve macroscopic uniform and microscopic random ring array coverage.

[0043] S4. Skeleton Stacking and 3D Network Construction: If necessary, step S3 can be repeated 1 to 5 times to achieve multiple spraying and stacking, constructing a three-dimensional coffee ring skeleton network.

[0044] The key technical point of this step is: (1) Spatial inconsistency in stacking: Subsequent sprayed droplets fall randomly into existing ring areas, the top of ring ridges, or blank areas between rings, exhibiting a probabilistic distribution. The droplet coverage of a single spray is approximately 10–60%, and multiple sprays gradually approach full surface coverage through random coverage.

[0045] (2) Three basic stacking configurations: 1) Type I - Ring Filling: Droplets fall into the pits inside the ring, and after evaporation, the particles are deposited inside the ring, reinforcing the weak area in the ring center and improving the integrity of the single ring structure.

[0046] 2) Type II - Ring Stacking: The droplet falls on the top of the existing ring ridge. After evaporation, the ring height increases significantly, forming a multi-level stacked skeleton structure of "ridge on ridge", which is the preferred enhanced configuration of the present invention.

[0047] 3) Type III - Inter-ring regeneration: Droplets fall into the blank area, forming new ecological coffee ring skeleton units, increasing the density of the ring array surface.

[0048] (3) Statistical evolution law of structural parameters: 1) Ring height: As the number of stacking times increases, the probability distribution of ring height shifts to the right and widens; the average ring height increases from 100-400 nm for a single stack to 500-1500 nm for five stacks.

[0049] 2) Ring width: The change is not significant (2-5 μm).

[0050] 3) Areal density: increased from ~20% in a single pass to ~95% in five passes.

[0051] 4) Stacking configuration ratio: The ratio of Type I, Type II and Type III is approximately 3:4:3, with the proportion of Type II increasing with the number of stacking times.

[0052] S5. Polymer coating coverage: After treatment in step S3 or S4, a polymer coating is applied to the substrate surface with a nanoparticle ring framework using a dip-coating, spin-coating, or spray-coating method. The polymer coating is selected from one or more of waterborne polyurethane resin, waterborne acrylic emulsion, waterborne epoxy resin, waterborne alkyd resin, or solvent-based fluorocarbon resin.

[0053] S6. Curing and molding: The substrate coated in step S5 is cured at 50–150°C for 0.5–8 hours to form a complete nanocomposite coating.

[0054] Using the above-described preparation method of the present invention, the nanoparticle ring framework is completely embedded in the interface region between the coating and the substrate. The protruding portion at the top of the ring ridge is anchored into the coating body, and the ring base portion adheres to the substrate surface, forming a three-dimensional interlocking interface structure of "micro-pile anchoring". The coating layer is then cured to form a complete nanocomposite coating; wherein, the nanoparticle ring structure is embedded in the interface region between the coating and the metal, and is partially embedded in the coating layer.

[0055] Furthermore, the nanocomposite coating prepared by the above method has a three-dimensional stacked micro / nano topological framework interface layer between the metal substrate and the main body of the polymer coating. This interface layer is composed of discrete, randomly distributed, and statistically uniform annular ridge structures of nanoparticles. The annular framework units correspond to the positions of the initial droplets, and their diameters are determined by the size of the initial droplets, exhibiting a distribution of 50–400 μm. The ring height is 200–1500 nm, the ring width is 1–10 μm, and the ring array density increases with the number of sprayings, reaching ≥80% after three sprayings. The annular framework is partially embedded in the micro-recessed areas of the substrate surface and partially protruded into the coating body, forming a synergistically enhanced interface with mechanical interlocking, stress dispersion, and topological anchoring.

[0056] The present invention will be further described in detail below with reference to the accompanying drawings and more specific embodiments.

[0057] Example 1: Steel substrate / SiO2 ring / waterborne polyurethane (single spray).

[0058] S1. Substrate Preparation: After grinding a certain type of steel sheet, it was ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes each, and then dried with nitrogen.

[0059] S2. Preparation of suspension: Take SiO2 nanoparticles with an average particle size of 50 nm, disperse them in deionized water, add 0.1 wt% sodium polyacrylate, and sonicate for 5 min (300 W power, 2 s interval) to prepare a stable suspension with a solid content of 2 wt%.

[0060] S3. Coffee ring skeleton deposition: Using a spray gun (nozzle diameter 0.3 mm, spraying pressure 0.2 MPa), perform a single pulse spray at a distance of 20 cm from the substrate, with a spray volume of 0.5 mL / cm². Place the substrate on a 30°C hot table with relative humidity <30% until the droplets completely evaporate and dry, allowing them to self-assemble into a SiO2 nanoparticle ring framework.

[0061] S4. Skeleton Stacking: This embodiment does not involve secondary stacking.

[0062] S5. Polymer coating coverage: Aqueous polyurethane resin (30% solid content) was diluted to 20% with deionized water. Using the dip-coating method, the matrix with the SiO2 ring backbone was immersed in the resin solution at a speed of 100 mm / min and then pulled out of the liquid at a uniform speed to form a wet film.

[0063] S6. Curing and molding: The composite coating was obtained by curing in an oven at 80℃ for 2 hours.

[0064] Performance testing: Microhardness: 0.072 GPa; Adhesion (cross-cut test): Grade 0; Critical load L c: 5.5 N.

[0065] Example 2: Aluminum matrix / Al2O3 ring / waterborne epoxy resin (three-layer spray coating stacking).

[0066] S1. Substrate Preparation: The aluminum alloy sheet was subjected to alkaline degreasing (50 g / L NaOH, 60℃, 2 min), acid pickling and brightening (200 g / L HNO3, room temperature, 30 s), deionized water washing, and nitrogen drying.

[0067] S2. Preparation of suspension: Take α-Al2O3 nanoparticles with an average particle size of 100 nm, disperse them in an ethanol-water (1:1) mixed solvent, add 0.1 wt% polyvinylpyrrolidone, and sonicate for 5 min to prepare a stable suspension with a solid content of 3 wt%.

[0068] S3. First coffee ring skeleton deposition: The spraying parameters are the same as in Example 1, and the evaporation conditions are 25°C and RH 40%.

[0069] S4. Second and third coats stacked: Repeat step S3 twice, allowing each coat to dry completely between applications.

[0070] S5. Polymer coating coverage: Waterborne epoxy resin (40% solids content) and waterborne amine curing agent were mixed at a mass ratio of 4:1 and diluted with deionized water to a solids content of 30%. The mixture was then sprayed to evenly cover the substrate surface, with a wet film thickness of approximately 50 μm.

[0071] S6. Curing and molding: Step curing: 80℃ / 2 h + 120℃ / 1 h.

[0072] Performance testing: Microhardness: 0.098 GPa; Adhesion (cross-cut test): Grade 0; Critical load L c: 8.5 N.

[0073] Comparative example: Traditional blending method (steel matrix / SiO2 / waterborne polyurethane).

[0074] S1. Substrate Preparation: Same as Example 1.

[0075] S2. Formulation of blended coatings: Take SiO2 nanoparticles with an average particle size of 50 nm, add them directly to waterborne polyurethane resin (30% solid content diluted to 20%) with a solid content of 2 wt%, add 0.1 wt% sodium polyacrylate, and ultrasonically vibrate for 20 min to prepare a blend coating.

[0076] S3. Polymer coating coverage: The lifting method was used, with the same parameters as in Example 1.

[0077] S4. Curing and molding: 80℃ / 2 h.

[0078] Performance testing: Microhardness: 0.035 GPa; Adhesion (cross-cut test): Grade 2; Critical load L c:1.5 N。

Claims

1. A composite coating enhanced by the coffee ring effect, comprising a metal substrate, characterized in that, A ring-shaped framework unit with protruding nanoparticles is sprayed and deposited on the surface of a metal substrate, and the ring-shaped framework unit is covered and cured with a polymer coating.

2. The composite coating based on the coffee ring effect enhancement according to claim 1, characterized in that, The ring-shaped framework unit is a ring-shaped ridge structure formed by discrete, randomly distributed, and statistically uniform nanoparticles.

3. The composite coating based on the coffee ring effect enhancement according to claim 1 or 2, characterized in that, The annular skeleton unit is formed by one or more sprays of droplets applied and stacked together.

4. A method for preparing a composite coating enhanced by the coffee ring effect, characterized in that, Includes the following steps: S1. Cleaning of the substrate surface; S2. Preparation of nano-suspensions; S3. The suspension obtained in step S2 is atomized by a spray gun and deposited on the cleaned substrate surface in the form of micron-sized droplet groups, forming a nanoparticle ring skeleton on the substrate surface. S4. Cover the nanoparticle ring framework with a polymer coating; S5. Cure the substrate coated in step S4 to form a complete nanocomposite coating.

5. The preparation method according to claim 4, characterized in that, In step S2, when preparing the nano suspension, the nanoparticles and volatile solvent are mixed at a mass ratio of 100:(0.5-10), and 0.01-0.5 wt% dispersant is added. The mixture is then subjected to ultrasonic vibration to form a uniform and stable suspension. The nanoparticles have a particle size of 5-500 nm.

6. The preparation method according to claim 5, characterized in that, The volatile solvent is selected from one or more of deionized water, ethanol, isopropanol, or a water-ethanol mixture; the dispersant is selected from one or more of sodium polyacrylate, cetyltrimethylammonium bromide, and polyvinylpyrrolidone.

7. The preparation method according to claim 4, characterized in that, In step S3, the nanoparticle ring framework is deposited on the substrate surface in a coffee ring effect.

8. The preparation method according to claim 4 or 7, characterized in that, In step S3, the suspension is atomized by a spray gun and deposited on the substrate surface in the form of micron-sized droplet clusters; The spraying process parameters are controlled as follows: a. Nozzle diameter: 0.1~0.8 mm; b. Spraying pressure: 0.1~0.9 MPa; c. Spraying distance: 5–300 cm; d. Single spray amount: 0.01~2 mL / cm²; Furthermore, the ambient temperature is controlled at 20–50°C, the relative humidity is <50%, and there is little wind and dust, allowing the droplets to spread naturally and evaporate.

9. The preparation method according to claim 8, characterized in that, The droplet diameters formed by atomization follow a log-normal distribution. Droplets of different sizes evaporate to form coffee-ring skeletal units of varying diameters, constituting a composite reinforced interface with multi-scale ring structures. During atomization, the droplet landing points follow a spatially random distribution, and the number of rings per unit area has a linear relationship with the coating amount (R² > 0.95). 2 It is the coefficient of determination, used to measure the degree of fit of a simulation in statistics.

10. The preparation method according to claim 4, characterized in that, In step S3, a nanoparticle ring skeleton is formed on the substrate surface, which is formed by single spraying or multiple spraying and stacking.

11. The preparation method according to claim 10, characterized in that, The droplet coverage of a single spray is 10-60%.

12. The preparation method according to claim 10 or 11, characterized in that, When using a multi-coating stacking molding method, the following control conditions shall be implemented: (1) The subsequent sprayed droplets fall randomly in the existing ring area, the top of the ring ridge, or the blank area between rings, and are distributed in a probabilistic manner; (2) The spatial relationship between the subsequently stacked annular skeleton and the earlier formed annular skeleton is a stacking configuration relationship of filling inside the ring, stacking on the ring, or new formation between the rings.

13. The preparation method according to claim 12, characterized in that, After multiple spraying and stacking, the stacking configuration of each ring skeleton is as follows: Inner ring filling: Upper ring stacking: Inter-ring new formation = 3:4:

3.

14. The preparation method according to claim 4, characterized in that, In step S4, the polymer coating is formed by applying a polymer coating using a dip coating method, spin coating method, or spray coating method.

15. The preparation method according to claim 14, characterized in that, The polymer coating is selected from one or more of waterborne polyurethane resin, waterborne acrylic emulsion, waterborne epoxy resin, waterborne alkyd resin, or solvent-based fluorocarbon resin.

16. The preparation method according to claim 4, characterized in that, In step S5, the coated substrate is cured at 50–150°C for 0.5–8 hours to form a complete nanocomposite coating.

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