A magnesium alloy photothermal super-hydrophobic coating with enhanced stability and a preparation method thereof

Abstract

The present application belongs to the technical field of surface functional coating, and relates to a magnesium alloy photo-thermal super-hydrophobic coating with enhanced stability and a preparation method thereof. In view of the problems that the existing photo-thermal super-hydrophobic coating is prone to structural collapse, interface peeling and performance attenuation during service, a micron column structure is constructed on the surface of a magnesium alloy substrate as a support framework, and a composite coating composed of multi-walled carbon nanotubes, titanium dioxide and modified epoxy resin is sprayed on the surface of the micron column structure. The modified epoxy resin introduces a low surface energy component and enhances the interface bonding capacity of the coating and the substrate. Through the synergistic effect of microstructure support and interface enhancement, the stability of the coating under the action of mechanical wear, chemical corrosion, high-low temperature cycle and water environment is significantly improved. On this basis, the coating still maintains good super-hydrophobicity, photo-thermal performance and anti-icing and deicing performance, and is suitable for magnesium alloy surface protection and anti-icing applications under complex environmental conditions.

Description

Technical Field

[0001] This invention belongs to the field of surface functional coating technology, and particularly relates to a magnesium alloy photothermal superhydrophobic coating with enhanced stability and its preparation method. Background Technology

[0002] Magnesium alloys, due to their low density, high specific strength, and good machinability, have broad application prospects in aerospace, transportation, and energy equipment. In actual service, magnesium alloy components are often exposed to complex environmental conditions, such as mechanical friction and erosion, acid and alkali corrosion, alternating high and low temperature changes, and the effects of rainfall and condensation. In low-temperature and high-humidity environments, icing and de-icing are also prone to occur. The formation and adhesion of ice layers not only affect the normal operation of equipment but may also pose safety hazards. Therefore, developing surface coatings with good stability under complex environmental conditions and combining anti-icing and de-icing functions is of great significance.

[0003] In recent years, photothermal superhydrophobic coatings have attracted widespread attention due to their ability to reduce the solid-liquid contact area by constructing micro / nano-roughened surface structures, while simultaneously converting light energy into heat energy using photothermal materials, thereby delaying icing and achieving active de-icing. These coatings typically rely on nanoscale roughened surface structures and low surface energy interfaces to achieve excellent hydrophobic properties by forming a Cassie-Baxter wetting state, and combine this with photothermal effects to enhance their anti-icing and de-icing capabilities. However, in actual service, these photothermal superhydrophobic coatings are susceptible to damage from friction and wear, fluid erosion, and repeated icing-de-icing cycles, leading to the destruction or peeling of the surface micro / nano-structures. This causes the original Cassie-Baxter wetting state to transform into a Wenzel state, resulting in a decline in the coating's hydrophobic properties and photothermal functions. Furthermore, existing coatings are mostly constructed through spraying or physical adhesion methods, resulting in limited interfacial bonding strength with the substrate. Under complex environmental conditions, they are prone to detachment, making long-term stable service difficult.

[0004] While some existing technologies modify the coating structure by introducing inorganic fillers or resin matrices to improve its overall performance, such modifications mainly focus on the internal structure control of the coating, lacking a systematic design for the synergistic effect between the substrate structure and the coating interface. This makes it difficult to achieve improved coating stability under various service conditions while maintaining photothermal and superhydrophobic properties. Therefore, how to construct a coating system that guarantees photothermal and superhydrophobic properties while possessing both good interfacial bonding ability and structural stability remains a pressing technical problem to be solved in this field.

[0005] The information disclosed in this background section is only intended to enhance the understanding of the background technology of this application and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] To address the issue of insufficient stability of existing photothermal superhydrophobic coatings during actual service, this invention provides a magnesium alloy photothermal superhydrophobic coating with enhanced stability and its preparation method. Instead of simply constructing a superhydrophobic or photothermal coating, it utilizes a composite interface structure that combines the synergistic effect of a micron-structure providing mechanical interlocking support with a modified epoxy resin providing interfacial chemical bonding. This fundamentally solves the problem of coating structural failure under complex environments. Without sacrificing photothermal and superhydrophobic properties, it effectively inhibits structural collapse and interfacial failure of the coating under mechanical wear, chemical corrosion, and cyclic environments, thereby achieving a significant improvement in coating stability.

[0007] This invention proposes a photothermal superhydrophobic coating for magnesium alloys with enhanced stability. The coating is constructed on the surface of a magnesium alloy substrate and includes a micron-sized pillar structure and a photothermal superhydrophobic composite coating covering it. The photothermal superhydrophobic composite coating comprises multi-walled carbon nanotubes, titanium dioxide, a curing agent, and a modified epoxy resin grafted with a silane coupling agent and a fluorinated silane. The silane coupling agent is γ-aminopropyltriethoxysilane, and the fluorinated silane is a fluorinated alkyl silane.

[0008] The γ-aminopropyltriethoxysilane and fluorinated alkylsilane undergo synergistic grafting modification on the epoxy resin molecular chain.

[0009] The composite coating penetrates between the micron-sized pillar structures during the spraying and curing process, and forms an interfacial chemical bond with the magnesium alloy substrate through a silane coupling agent, thereby constructing an interfacial stable structure with synergistic mechanical and chemical bonding.

[0010] The micron-sized pillar structure serves as a supporting framework, and the modified epoxy resin fills the spaces between the micron-sized pillar structures during the curing process to form a continuous phase, thereby achieving structural integration between the coating and the substrate.

[0011] The interfacial chemical bonding effect originates from the hydrolysis and condensation reaction of the silane coupling agent on the magnesium alloy substrate surface and its reaction with epoxy resin. Specifically, after the silane coupling agent is hydrolyzed to form silanol groups, it undergoes a condensation reaction with the hydroxyl groups on the magnesium alloy surface to form Mg-O-Si bonds. Simultaneously, the amino groups in the silane coupling agent molecule undergo a ring-opening reaction with the epoxy resin and participate in the curing process, thereby constructing a "magnesium alloy-silane-resin" chemical bond connection structure between the substrate and the coating. This chemical bonding effect, synergistically with the mechanical interlocking effect provided by the micron-pillar structure, improves the interfacial bonding strength and service stability of the coating.

[0012] Even after mechanical wear, tape peeling, acid and alkali immersion, and exposure to high or low temperature environments, the water contact angle of the magnesium alloy photothermal superhydrophobic coating remains >150° and the roll-off angle remains <10°.

[0013] Preferably, the micron-sized column structure is constructed in situ on the surface of a magnesium alloy substrate by laser processing. The micron-sized column structure is an array structure with a column diameter of 50-100 μm, a column spacing of 50-100 μm, a column height of 10-200 μm, and a column height-to-diameter ratio of 2-5.

[0014] Preferably, the laser processing is nanosecond laser processing, with a pulse width of 50~200 ns, a frequency of 50~200 kHz, and a scanning speed of 50~200 mm / s.

[0015] Preferably, the mass ratio of titanium dioxide to multi-walled carbon nanotubes is 3:1.

[0016] Preferably, the thickness of the photothermal superhydrophobic composite coating is 20~40 μm.

[0017] Furthermore, after at least 50 sandpaper abrasion cycles and at least 70 tape peeling cycles, the magnesium alloy photothermal superhydrophobic coating has a water contact angle >150° and a roll-off angle <10°, and the mass loss rate of the photothermal superhydrophobic composite coating is less than 20%.

[0018] Furthermore, after the magnesium alloy photothermal superhydrophobic coating is immersed in a solution with pH=2 to 13 for 12 h, its water contact angle is >152°.

[0019] Furthermore, after being subjected to high-temperature cycling at 150°C, low-temperature cycling at -15°C, or continuous water droplet rinsing for 12 hours, the magnesium alloy photothermal superhydrophobic coating exhibits a water contact angle >150° and a roll-off angle <7°.

[0020] Furthermore, the magnesium alloy photothermal superhydrophobic coating maintains an ice adhesion strength of 12~19 N / cm after multiple icing-de-icing cycles. 2 .

[0021] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned magnesium alloy photothermal superhydrophobic coating, comprising: (1) Surface pretreatment of magnesium alloy substrate; (2) A micron-sized column structure is constructed on the surface of the magnesium alloy substrate by laser processing; (3) Prepare a coating system comprising multi-walled carbon nanotubes, titanium dioxide, curing agent and modified epoxy resin grafted with silane coupling agent and fluorine-containing silane; (4) The coating system is applied to the surface of the micron column structure, allowing it to penetrate between the micron column structures and solidify, thereby forming an interface bonding structure to obtain the magnesium alloy photothermal superhydrophobic coating.

[0022] Preferably, the coating in step (4) is performed by spraying.

[0023] Preferably, the curing temperature is 90°C and the curing time is 2 hours.

[0024] In this invention, the modified hydrophobic epoxy resin serves as the organic matrix phase of the coating, forming a composite coating system together with TiO2 and multi-walled carbon nanotubes. The modified epoxy resin is a continuous phase used to coat and connect inorganic fillers. During the spraying process, it can penetrate between the micron-sized pillar structures on the magnesium alloy surface and form an interface bonding layer during the curing process, thereby achieving a stable overall structure of the coating.

[0025] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention utilizes the support of the micron-pillar structure for the nano-functional layer and the interfacial enhancement effect of the modified epoxy resin to enable the coating to maintain stable performance under various complex environments. After 50 sandpaper abrasion cycles and 70 tape peeling cycles, the water contact angle of the coating remains above 150°, the roll-off angle is less than 10°, and the mass loss rate is consistently below 20%. Under cycling conditions of 150°C high temperature and -15°C low temperature, the contact angle remains stable at around 155° with no significant attenuation. Furthermore, it retains superhydrophobicity after 12 hours of continuous water droplet rinsing. This indicates that the coating exhibits excellent structural stability and durability under mechanical wear, thermal shock, and fluid action. (2) The modified epoxy resin constructed by synergistic modification of KH-550 and fluorinated silane not only reduced the surface energy, but also significantly enhanced the interfacial bonding ability between the coating and the magnesium alloy substrate. After immersion in solutions with pH=2, 7 and 13 for 12 h, the contact angle of the coating remained above 152° and maintained a stable Cassie-Baxter wetting state, without any obvious failure phenomenon; at the same time, it showed excellent adhesion stability in the tape peeling test, indicating that the interface enhancement strategy effectively suppressed the problem of traditional coating peeling under corrosion and interfacial stress. (3) The L-HET composite coating constructed in this invention exhibits the best overall performance among various comparative systems. Under the same conditions, its water contact angle can reach 157.1°, which is higher than that of the HET coating (154.5°) and the HWCNTs / EP-M coating (153.5°); the surface temperature can rise to about 83.5°C after 180 s of illumination, which is higher than that of the HET coating (80.6°C) and the HWCNTs / EP-M coating (66.9°C), indicating that its photothermal conversion capability is better. At the same time, the ice adhesion strength of this coating is stably maintained in the range of about 12~19 N / cm², which is significantly lower than that of the AZ31B magnesium alloy substrate (109.39 N / cm²), and the water droplet freezing delay time can reach about 1220 s, which is better than the comparative coating without micron structure. This indicates that the synergistic effect of the micron-sized pillar structure and the modified epoxy resin not only did not weaken the original photothermal and superhydrophobic properties of the coating, but also achieved further optimization of its performance, resulting in a synergistic improvement in both stability and functionality. Attached Figure Description

[0026] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the following description is only a part of the embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a flowchart of the L-HET composite coating preparation process.

[0028] Figure 2 Scanning electron microscope (SEM) images and laser confocal images of AZ31B Mg substrate (a), HWCNTs / EP-M coating (b), HET composite coating (c) and L-HET composite coating (d).

[0029] Figure 3 The energy dispersive spectroscopy (EDS) diagrams (a, b, c, d) and elemental content (e) of the L-HET composite coating are shown.

[0030] Figure 4 Infrared thermal imaging of the coating (a), photothermal temperature rise curves of different coatings (b), and photothermal cycling curve of L-HET composite coating (c).

[0031] Figure 5 Image showing the anti-icing properties of the coating.

[0032] Figure 6 Image showing the photothermal de-icing performance of the coating.

[0033] Figure 7The stability tests for the L-HET composite coating include sandpaper abrasion test (a), tape peeling test (b), chemical corrosion resistance test (c), high temperature resistance test (d), low temperature resistance test (e), and water droplet impact resistance test (f).

[0034] Figure 8 Stability test of ice adhesion strength of L-HET composite coating. Detailed Implementation

[0035] This invention proposes a magnesium alloy photothermal superhydrophobic coating with enhanced stability and its preparation method. To facilitate understanding of this invention by those skilled in the art, the specific embodiments of this invention are described below with reference to the accompanying drawings.

[0036] In this invention, unless otherwise specified, the equipment and raw materials used are commercially available or commonly used in the art. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art. Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0037] Example 1: HWCNTs / EP-M@TiO2 photothermal superhydrophobic coating with micron-sized pillar structure (L-HET) The L-HET composite coating preparation process in this embodiment is as follows: Figure 1 As shown.

[0038] (1) Laser processing of micron-sized pillars on magnesium alloy surface: A 20 mm × 20 mm × 1 mm magnesium alloy plate was selected as the substrate material. After polishing with 800#, 1200# and 2000# sandpaper, it was ultrasonically cleaned with anhydrous ethanol and dried with cold air for later use. A nanosecond laser was used to process the magnesium alloy substrate (AZ31B Mg) to prepare a micron-sized pillar array. The nanosecond laser processing parameters were: pulse width: 100 ns, frequency: 100 kHz, power: 30, scanning speed: 100 mm / s, processing distance: 100 μm, processing times: 5 times, pillar diameter: 100 μm, pillar spacing: 100 μm, pillar height: 200 μm, and the ratio of pillar height to diameter was 2.

[0039] (2) Preparation of modified hydrophobic epoxy resin (EP-M): γ-aminopropyltriethoxysilane (KH-550, 0.5 g) was dissolved in 10 mL of anhydrous ethanol containing 0.2 mL of deionized water and stirred at 60 °C for 1 h to allow for complete hydrolysis. Subsequently, 0.5 g of perfluorodecyltrimethoxysilane (FAS) was added, and the mixture was reacted under the same conditions for 1 h to achieve complete grafting of FAS and KH-550, resulting in a translucent fluorinated oligomer. 1 g of the synthesized fluorinated oligomer was mixed with 0.5 g of epoxy resin, stirred for 10 min, and then diluted with 10 mL of ethyl acetate. The mixture was magnetically stirred for 1 h to obtain the modified hydrophobic epoxy resin (EP-M).

[0040] (3) Preparation of HWCNTs / EP-M@TiO2 photothermal superhydrophobic composite coating: TiO2 and multi-walled carbon nanotubes (HWCNTs) were mixed at a mass ratio of 3:1, with a total mass of 0.3 g. 0.4 g of EP-M was added, and the mixture was magnetically stirred for 20 min with 10 mL of ethyl acetate as solvent. After uniform dispersion, 0.2 g of curing agent D230 was added, and stirring was continued for 10 min to obtain the mixture.

[0041] (4) Preparation of L-HET composite coating: The mixture obtained in step (3) was vertically sprayed 15 cm above the surface of the magnesium alloy micron pillar after laser processing. The spraying time was 5 s. The mixture was placed in a drying oven and cured at 90℃ for 2 h to obtain HWCNTs / EP-M@TiO2 photothermal superhydrophobic coating (L-HET) with micron pillar structure.

[0042] Comparative Example 1: HET Composite Coating The difference from Example 1 is that step (1) was not performed, and the mixture obtained in step (3) was directly sprayed onto the surface of the magnesium alloy substrate.

[0043] Comparative Example 2: HWCNTs / EP-M Coating The difference from Example 1 is that step (1) was not performed, and TiO2 was not used in step (3).

[0044] 0.4 g of EP-M was added to 0.3 g of multi-walled carbon nanotubes (MWCNTs) using 10 mL of ethyl acetate as solvent and magnetically stirred for 20 min. After uniform dispersion, 0.2 g of curing agent D230 was added, and stirring was continued for 10 min to obtain a mixture. This mixture was then vertically sprayed onto a magnesium alloy substrate at a distance of 15 cm above the substrate surface and cured in a drying oven at 90 °C for 2 h to obtain an HWCNTs / EP-M coating.

[0045] Comparative Example 3: AZ31B Mg substrate The difference from Example 1 is that the nanosecond laser processing operation in step (1) and steps (2), (3), and (4) were not performed. Only the magnesium alloy surface, i.e., a 20 mm × 20 mm × 1 mm magnesium alloy plate, was used as the base material. After being polished with 800#, 1200# and 2000# sandpaper, it was ultrasonically cleaned with anhydrous ethanol and dried with cold air for later use.

[0046] Material characterization and performance testing Material characterization (1) Surface micromorphology and structural characterization Figure 2 The surface microstructure and roughness of AZ31B magnesium alloy substrates and different modified coatings are shown. Figure 2 As shown in (a), the wear marks distributed in the same direction on the surface of the AZ31B magnesium alloy substrate are clearly visible, with a smooth overall morphology and a surface roughness (Ra) of 1.2 μm. This surface has no obvious nanoscale protrusions or hierarchical structures, and the surface water droplet contact angle (CA) is only 55.7°, exhibiting typical hydrophilic characteristics. The droplet wetting behavior conforms to the Wenzel model; Figure 2 As shown in (b), compared with the AZ31B magnesium alloy substrate, the surface morphology of the HWCNTs / EP-M coating is significantly changed. A large number of irregular micron-sized particles are uniformly covered on the substrate surface. The particles are stacked to form a loose porous structure. A large number of nano-sized nipple-like protrusions are distributed on the surface of the micron particles, forming a typical "particle-nipple" micro / nano multi-level composite structure. Ra is increased to 8.4 μm. This rough interface significantly reduces the actual solid-liquid contact area. The gaps between particles can trap air, which is conducive to the formation of a stable air cushion layer. The coating CA is significantly increased to 153.5°, realizing the transformation from hydrophilic to superhydrophobic state. The wetting behavior conforms to the Cassie-Baxter model. Figure 2 (c) The surface of the HET composite coating exhibits a more uniform and dense multi-level structure. A large number of submicron particles are secondary deposited on the surface of the micron-level skeleton to form a continuously distributed nanopapillary network, giving the surface a typical multi-scale hierarchical rough morphology. Ra is 11.5 μm. Compared with the HWCNTs / EP-M coating, the particle size distribution of this structure is more uniform, the pore structure is finer and the connectivity is better, which is conducive to the formation of a more stable and continuous air interlayer at the interface, further suppressing droplet wetting. Its CA is also further increased to 154.5°, indicating that this coating has a greater structural advantage in constructing a stable superhydrophobic interface. Figure 2(d) The L-HET composite coating has a regularly arranged columnar structure with uniform pore size distribution. The pore walls are formed by the accumulation of rough particles, which simultaneously constructs a multi-level rough structure at both the macroscopic and microscopic scales. This ordered porous structure not only significantly improves the overall surface roughness (Ra 51.5 μm), but also forms a large number of stable air pockets inside the pores. This effectively reduces the solid-liquid contact area while enhancing the stability of the interfacial air cushion layer. The water droplet contact angle of this sample reaches 157.1°, which is the best among the four groups of samples.

[0047] (2) Elemental distribution on the coating surface Energy dispersive spectroscopy (EDS) was performed on the L-HET composite coating, such as... Figure 3 As shown in (a~d), C, O, Ti, and F elements exhibit a uniform distribution on the coating surface, with no obvious element enrichment or severe agglomeration observed. This indicates that the inorganic particles and organic matrix have good dispersibility and compatibility. C and O elements mainly originate from the epoxy resin matrix and HWCNTs, forming a continuous organic-inorganic composite framework. Ti elements show a uniform dotted distribution, indicating that TiO2 particles can be stably embedded in the coating system and play an important structural supporting role in constructing a multi-level rough structure. Meanwhile, F elements are uniformly distributed on the surface, indicating that low surface energy fluorine-containing components have been successfully modified onto the coating surface, providing the necessary chemical basis for achieving a stable hydrophobic interface. Figure 3 As shown in (e), the coating is mainly composed of C (51.35%), O (31.7%), Ti (14.4%), and F (2.56%), further confirming that TiO2 particles and fluorine-containing components have been successfully introduced into the coating system. Although the F content is low, its uniform distribution can significantly reduce the surface free energy and, with... Figure 2 (d) illustrates the synergistic effect of the constructed micro / nano-level roughness structure, which induces the formation of the Cassie-Baxter wetting state. In summary, EDS results demonstrate that this composite coating simultaneously achieves uniform dispersion of inorganic particles and effective modification of low surface energy components, providing a reliable compositional basis for obtaining high contact angles and stable superhydrophobic properties.

[0048] Photothermal performance The temperature rise rate, peak temperature, and cycle stability of the AZ31B magnesium alloy substrate, HWCNTs / EP-M composite coating, HET composite coating, and L-HET composite coating were tested. Figure 4(a) shows the infrared thermal imaging results of the sample under continuous constant illumination. The AZ31B magnesium alloy substrate showed a slow temperature rise throughout the illumination process, with the surface temperature only reaching 31.9 ℃ after 180 s of illumination. This indicates that the bare magnesium alloy has limited absorption and conversion capabilities for light energy and cannot achieve an effective photothermal response. In contrast, the HWCNTs / EP-M coating exhibited significantly enhanced temperature rise behavior, reaching a surface temperature of 66.9 ℃ after 180 s of illumination. This indicates that the introduction of HWCNTs significantly improved the light energy absorption efficiency of the coating. Further comparison revealed that under the same illumination conditions, the photothermal conversion performance of the HET and L-HET composite coatings was superior. After 180 s of illumination, the surface temperature of the HET coating reached 80.6 ℃, while the L-HET coating further increased to 83.5 ℃. Moreover, the high-temperature region was more uniformly distributed in the infrared thermal image, indicating that the synergistic effect of the laser microstructure and the composite filler enhanced the light-harvesting ability and heat accumulation effect of the coating.

[0049] Figure 4 (b) shows the real-time temperature change curves during the illumination switching process of the samples. During the illumination-on phase (0-180 s), the surface temperature of all samples continued to rise. After the illumination was turned off, the surface temperature of each sample dropped rapidly and tended to stabilize. The composite coating showed a faster temperature response during the cooling phase, indicating that the heat generated was mainly concentrated on the surface layer, which is conducive to achieving rapid and controllable photothermal regulation. Figure 4 (c) shows the photothermal response stability test results of the L-HET composite coating under multiple light-on-off cycles. After each light-on cycle, the coating surface temperature can rapidly rise to 80~85℃, and quickly drop back to near the initial temperature after the light is turned off. The peak temperature of each cycle highly coincides with the response curve, with no significant attenuation. This indicates that the L-HET composite coating has excellent photothermal stability and structural reliability under repeated thermal cycling, and its light absorption and heat conversion capabilities do not significantly degrade due to multiple light exposures, demonstrating its potential for long-term service.

[0050] By introducing HWCNTs, inorganic fillers, and laser microstructures, the photothermal conversion efficiency, response rate, and cycle stability of the composite coating are significantly improved. The L-HET composite coating exhibits the best photothermal performance, providing core support for achieving rapid interface heating in low-temperature environments.

[0051] Anti-icing performance The evolution of water droplets freezing on different surfaces was demonstrated through a series of optical photographs. Figure 5It can be seen that the water droplets in the different samples initially exhibited a transparent, regular, spherical shape, indicating that the initial wetting state of liquid water differed among the different substrates, but a phase transition had not yet occurred. With prolonged cooling time, the water droplets on the AZ31B Mg substrate showed obvious freezing characteristics within a short time. Around 78 s, the edges of the droplets became turbid first and gradually expanded inwards, eventually forming completely frozen ice droplets, indicating a rapid freezing induction rate. In contrast, the water droplets on the samples coated with the photothermal superhydrophobic coating remained transparent within the same time frame, and no obvious ice nucleation phenomenon was observed, showing a significant delayed freezing behavior. It wasn't until over 1000 s that the water droplets on the superhydrophobic coating surface gradually showed signs of freezing, and the freezing process was significantly delayed compared to ordinary surfaces. The L-HET composite coating, in particular, only completely froze after 1220 s, indicating that this type of coating can significantly prolong the freezing time of water droplets. This phenomenon demonstrates that the photothermal superhydrophobic coating can effectively inhibit ice nucleus formation and delay ice crystal growth under low-temperature conditions.

[0052] De-icing performance Figure 6 This study illustrates the macroscopic de-icing process of ice on different surfaces under illumination over time. Under the same illumination duration, the melting rates of ice on different surfaces varied significantly. On the AZ31B Mg substrate, ice initially underwent limited edge melting, maintaining a relatively intact overall morphology. At 240 s, the ice still exhibited a distinct blocky structure, indicating limited absorption and transfer of heat from the light. Significant collapse and spreading of the ice only began after 300 s, indicating a slow de-icing process. In contrast, ice on the surfaces of the other three photothermal superhydrophobic coatings showed rapid response characteristics from the initial illumination stage. As illumination time increased, a meltwater layer rapidly appeared at the ice-solid interface, with the bottom of the ice preferentially melting and gradually losing its adhesion support, transforming into a low-height, flattened droplet state within a short time, ultimately achieving rapid detachment. These results demonstrate that the photothermal superhydrophobic coating significantly reduces the stability of ice on the surface and accelerates the light-induced de-icing process.

[0053] Coating stability Figure 7 The wetting stability and environmental adaptability of the L-HET composite coating under various harsh conditions, including mechanical wear, interfacial exfoliation, chemical corrosion, high and low temperature cycling, and long-term water exposure, were characterized. Figure 7As shown in (a) and (b), after 50 sandpaper cycles and 70 tape peel cycles, the contact angle (CA) remained above 150°. Simultaneously, the coating's mass loss rate (k) gradually increased with the number of cycles, but remained below 20%. Throughout the process, the roll-off angle (SA) remained less than 10°, indicating that the coating still possessed superhydrophobicity. These results demonstrate that the pillar-like microstructure on the magnesium alloy substrate and the micro / nano-level structure constructed within the coating were not completely destroyed during wear. Some residual structures effectively maintained the air layer, indicating that the micro / nano structure on the coating surface did not exist solely through weak physical adsorption, but rather formed a relatively strong bonding interface with the substrate. The low surface energy chemical modification continued to play a role after wear, contributing to the coating's excellent wear resistance stability.

[0054] Figure 7 (c) shows the change in contact angle of the coating over time after immersion in solutions with different pH values ​​(pH=2, 7, 13). After immersion in strong acid, neutral, and strong alkali environments for 12 h, the contact angle of the coating remained above 152°. The "silver mirror phenomenon" indicates that the liquid can still stably suspend above the air layer on the coating surface, further verifying the stable existence of the Cassie-Baxter wetting state in different chemical environments. This demonstrates that the chemical composition and micro / nano structure of the coating surface have strong resistance to acid and alkali corrosion.

[0055] like Figure 7 As shown in (d) and (e), after multiple cycles at high temperatures of 150°C and low temperatures of -15°C, the contact angle of the L-HET composite coating remained stable at approximately 155°, while the roll-off angle remained almost unchanged. The high / low temperature treatments did not significantly damage the low surface energy functional groups or micro / nano structural features of the coating. This is mainly attributed to the good stability of the epoxy resin matrix and the supporting effect of the inorganic filler on the structure at high temperatures, enabling the coating to maintain excellent superhydrophobic properties under high-temperature service conditions, providing strong support for its reliability in anti-icing / de-icing applications.

[0056] like Figure 7 As shown in (f), the L-HET composite coating still exhibits superhydrophobicity after 12 hours of continuous water droplet rinsing, indicating that its micro / nano structure and surface chemical properties did not significantly degrade under long-term liquid impact or aquatic environment. This characteristic is of great significance for practical application environments (such as repeated rinsing by rainfall and de-icing water), demonstrating that the coating possesses good long-term service stability and engineering application potential.

[0057] The ice adhesion strength on the AZ31B Mg substrate surface is as high as 109.39 N / cm. 2The composite coating exhibits typical strong ice adhesion characteristics, primarily due to its high surface energy and lack of effective micro / nano structure control, enabling the ice to form large-area solid contact with the substrate, thereby enhancing interfacial adhesion. In contrast, the ice adhesion strength of the composite coating surface after introducing functional fillers is significantly reduced. Specifically, the ice adhesion strength of the HWCNTs / EP-M coating is 15.22 N / cm². 2 The HET composite coating has a strength of 15.88 N / cm. 2 The L-HET coating further reduces the N / cm² to 14.78. 2 The surface energy levels were all more than an order of magnitude lower than those of the AZ31B Mg substrate. This significant difference indicates that constructing superhydrophobic micro / nano structures and introducing low surface energy components can effectively weaken ice-solid interface adhesion. Figure 8 It can be seen that the L-HET composite coating maintained a low ice adhesion strength throughout the 10 consecutive de-icing cycles, with the overall value concentrated between approximately 12 and 19 N / cm. 2 Within the specified range, no significant upward trend was observed, indicating that the coating exhibits good stability and durability under repeated freeze-thaw cycles. This stable low ice adhesion characteristic is mainly attributed to the synergistic effect of the micro / nano hierarchical structure and low surface energy chemical composition of the composite coating surface. On the one hand, the hierarchical rough structure effectively reduces the actual contact area between ice and the solid surface; on the other hand, the low surface energy modified epoxy body reduces the interfacial adhesion work, thereby inhibiting a significant increase in ice adhesion strength. Furthermore, the interlocking structure formed by TiO2 and HWCNTs helps improve the structural integrity of the coating, making it less prone to structural collapse or performance degradation during multiple freeze-thaw cycles.

[0058] Furthermore, in this invention, the laser-constructed micron-sized pillar structure and the modified epoxy resin form a synergistic interface reinforcement effect: on the one hand, the micron-sized pillar structure provides mechanical interlocking for the coating; on the other hand, the modified epoxy resin can penetrate into the gaps between the pillars and cure, thereby forming a stable interfacial bonding layer between the substrate and the coating. This synergistic effect of structural interlocking and chemical bonding enables the coating to maintain its structural integrity under mechanical wear, peeling, and environmental effects, thus significantly improving its stability.

[0059] In summary, this invention constructs a laser-driven micron-shaped pillar structure on the surface of a magnesium alloy and combines it with a modified epoxy resin to form an interface reinforcement layer. This enables the coating to form a composite interface structure on the substrate surface with synergistic effects of structural interlocking and chemical bonding. Without compromising photothermal and anti-icing / de-icing properties, it significantly improves the stability of the coating under mechanical wear, interface delamination, and complex environmental conditions, thus effectively overcoming the problem of insufficient durability in existing photothermal superhydrophobic coatings.

[0060] The embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A stability-enhanced photothermal superhydrophobic coating of a magnesium alloy characterized by: The coating is constructed on the surface of a magnesium alloy substrate and includes a micron-sized pillar structure and a photothermal superhydrophobic composite coating covering it. The photothermal superhydrophobic composite coating comprises multi-walled carbon nanotubes, titanium dioxide, a curing agent, and a modified epoxy resin grafted with a silane coupling agent and a fluorinated silane. The silane coupling agent is γ-aminopropyltriethoxysilane, and the fluorinated silane is a fluorinated alkyl silane.

2. The stability-enhanced, magnesium alloy photothermal superhydrophobic coating of claim 1, wherein: Even after mechanical wear, tape peeling, acid and alkali immersion, and exposure to high or low temperature environments, the water contact angle of the magnesium alloy photothermal superhydrophobic coating remains >150° and the roll-off angle remains <10°.

3. The stability-enhanced, magnesium alloy photothermal superhydrophobic coating of claim 1, wherein: The micron-sized column structure is constructed in situ on the surface of a magnesium alloy substrate by laser processing.

4. The stability-enhanced, magnesium alloy photothermal superhydrophobic coating of claim 3, wherein: The micron-sized column structure is an array structure with a column diameter of 50-100 μm, a column spacing of 50-100 μm, a column height of 10-200 μm, and a column height-to-diameter ratio of 2-5.

5. The stability-enhanced, magnesium alloy photothermal superhydrophobic coating of claim 3, wherein: The laser processing is nanosecond laser processing, with a pulse width of 50~200 ns, a frequency of 50~200 kHz, and a scanning speed of 50~200 mm / s.

6. The stability-enhanced, magnesium alloy photothermal superhydrophobic coating of claim 1, wherein: The mass ratio of titanium dioxide to multi-walled carbon nanotubes is 3:

1.

7. The stability-enhanced, magnesium alloy photothermal superhydrophobic coating of claim 1, wherein: The thickness of the photothermal superhydrophobic composite coating is 20~40 μm.

8. The stability-enhanced photothermal superhydrophobic coating of magnesium alloy according to any one of claims 1-7, characterized in that: After at least 50 sandpaper abrasion cycles and at least 70 tape peeling cycles, the magnesium alloy photothermal superhydrophobic coating has a water contact angle >150° and a roll-off angle <10°, and the mass loss rate of the photothermal superhydrophobic composite coating is less than 20%.

9. A method for preparing a stability-enhanced photothermal superhydrophobic coating of a magnesium alloy according to any one of claims 1 to 7, characterized in that, include: (1) Surface pretreatment of magnesium alloy substrate; (2) A micron-sized column structure is constructed on the surface of the magnesium alloy substrate by laser processing; (3) Prepare a coating system comprising multi-walled carbon nanotubes, titanium dioxide, curing agent and modified epoxy resin grafted with silane coupling agent and fluorine-containing silane; (4) The coating system is applied to the surface of the micron column structure, allowing it to penetrate between the micron column structures and solidify, thereby forming an interface bonding structure to obtain the magnesium alloy photothermal superhydrophobic coating.

10. The method of claim 9, wherein: The coating in step (4) is carried out by spraying, and the curing temperature is 90 ℃ and the curing time is 2 h.

Images