A super-hydrophobic coating and a method for making the same

Abstract

The application discloses a super-hydrophobic coating and a preparation method thereof, and relates to the technical field of coatings, in particular to a super-hydrophobic coating preparation method, which is characterized by comprising the following steps: S1, preparing hydrophobic modified nano-silica powder, wherein methyltrimethoxysilane (MTMS) and hexadecyltrimethoxysilane (HDTMS) are used as composite modifiers, the composite modifiers are used for modifying treatment of nano-silica, and the hydrophobic modified nano-silica powder is obtained; S2, preparing a super-hydrophobic topcoat dispersion; and S3, preparing a primer and a coating film forming agent, wherein the MTMS provides a large number of silicon hydroxyl crosslinking sites, can improve the compactness and structural rigidity of the coating, and can improve the grafting efficiency of the HDTMS; the HDTMS introduces long-chain alkyl to reduce surface energy and realize high hydrophobicity; and the two can be compounded to simultaneously obtain a high contact angle and a compact and stable film layer structure, which is superior to a single silane system.

Description

Technical Field

[0001] This invention relates to the field of coating technology, and specifically to a superhydrophobic coating and its preparation method. Background Technology

[0002] Since the early 20th century, against the backdrop of China's rapid economic and urbanization development, the importance of cement concrete in modern construction has been undeniable. As a crucial material in modern construction, concrete's applications have continuously expanded due to its numerous advantages, including abundant raw materials, simple construction processes, high durability, high compressive strength, excellent economic benefits, and low maintenance costs. It is now widely used in basic infrastructure projects such as houses, bridges, dams, roads, airports, and tunnels. According to statistics on national cement production in the first quarter of 2023 released by the China Building Materials Information Network, after the full reopening following the pandemic, national cement production reached 402 million tons in the first quarter of 2023, a year-on-year increase of 4.1%. This demonstrates the gradual recovery in the production and demand of cement concrete, playing a key role in promoting social development and infrastructure construction.

[0003] According to domestic and international surveys, corrosion-related economic losses worldwide account for 1.5% to 4.2% of GDP annually. Currently, the United States faces a severe problem of concrete corrosion, primarily affecting reinforced concrete bridges, highways, parking lots, and harbors, resulting in annual losses of up to $126 billion. The U.S. Technology Assessment Center predicts that hundreds of billions of dollars will be needed annually for repair or reinforcement. A report from the UK Department of Transport indicates that 75% of reinforced concrete structures in England are corroded by chloride ions, with 35% to 40% requiring repair. Therefore, approximately £20 billion is spent annually on reinforced concrete structure maintenance, with repair costs exceeding the initial construction cost. Japan, Canada, and the Middle East also experience varying degrees of building corrosion, with corrosion caused by steel reinforcement requiring frequent maintenance. Concrete plays a crucial role in my country's infrastructure construction, with annual repair costs for concrete corrosion reaching 500 billion yuan, approximately 3.5% to 5% of GDP. Therefore, researching the durability of concrete under different environmental conditions is essential.

[0004] Despite the broad application prospects and development potential of concrete, several problems remain to be addressed, with durability being the most prevalent. As a porous, hydrophilic material, concrete's durability is influenced by a complex array of factors. In particular, water and corrosive substances from the external environment can easily penetrate the concrete structure through capillary action, causing surface deterioration that gradually extends into the matrix, leading to problems such as carbonation, steel corrosion, sulfate corrosion, and freeze-thaw damage. Over time, with the passage of time, concrete structures have suffered severe damage, impairing their function and lifespan, resulting in numerous engineering problems. This not only poses a potential threat to human life and social development but also causes significant economic losses. Therefore, while comprehensively improving concrete durability design and developing appropriate construction methods, it is essential to implement preventative treatments and effective protective measures. This can effectively slow down the erosion process of concrete, improving structural durability and extending its service life. Furthermore, it can save construction costs and reduce maintenance expenses, positively impacting sustainable economic development and environmental protection, and possessing practical significance.

[0005] Theoretical Model of Superhydrophobic Coatings: Superhydrophobic surfaces, typically referring to special wettable surfaces with a water contact angle greater than 150° and a roll-off angle less than 10°, are a highly attractive research direction in the field of biomimetic. The most classic example of this extraordinary water-repellent ability comes from nature, such as the lotus leaf's ability to "emerge from mud unsullied." Through microscopic structural observation, scientists have discovered that the lotus leaf surface has micron-scale papillary structures, and each papilla contains nanoscale waxy crystals. This micro-nano composite hierarchical structure is the physical basis of its superhydrophobicity. Furthermore, water striders can walk freely on water, and their legs also rely on the superhydrophobicity generated by special micron-scale bristle structures. These natural inspirations have inspired researchers to design and fabricate artificial superhydrophobic surfaces using biomimetic methods. In recent years, artificially prepared superhydrophobic surfaces have attracted widespread attention and have broad application prospects in fields such as antifouling, waterproofing, corrosion prevention, fluid drag reduction, oil-water separation, and biomedicine.

[0006] The theoretical basis of superhydrophobicity can be traced back to classical wetting theory. The Young equation describes the contact angle (intrinsic contact angle) on an ideal, smooth, flat surface. However, real solid surfaces are all rough surfaces. The Wenzel and Cassie-Baxter models describe two typical wetting states of liquids on rough surfaces: the Wenzel state (contact angle decreases, droplets penetrate the microstructure) and the Cassie-Baxter state (contact angle increases, droplets suspend on an air pad), respectively. Superhydrophobicity is essentially a stable Cassie-Baxter state, and its realization requires the simultaneous satisfaction of two key conditions: low surface free energy and a suitable micro-rough structure.

[0007] Due to their unique properties, superhydrophobic coatings have been extensively studied by scholars in many fields. For example, the team led by Zhong Minlin at Tsinghua University used ultrafast laser composites to prepare a three-level micro / nano-structured superhydrophobic surface with an ice adhesion strength as low as 1.7 kPa, exhibiting excellent anti-icing and anti-icing properties. The Institute of Oceanology, Chinese Academy of Sciences, and others developed an environmentally friendly Al2O3@PDMS anti-corrosion superhydrophobic coating, providing an effective physical barrier for metal substrates. This coating is simple to prepare, low in cost, and fluorine-free. The team led by Deng Xu at the University of Electronic Science and Technology of China proposed a "decoupling" mechanism and an "armoring" design, using micron-structures for mechanical protection and nano-structures to ensure superhydrophobicity. This solves the problem of achieving both mechanical stability and superhydrophobicity simultaneously, and can be used in solar cell cover plates, utilizing the droplet self-cleaning effect to remove dust and maintain efficient energy conversion. Therefore, developing high-performance, high-durability, low-cost, and easily mass-producible superhydrophobic coatings has become one of the current research hotspots in materials surface science.

[0008] However, despite the existence of various successful preparation strategies in the laboratory, such as sol-gel methods, etching, vapor deposition, and electrospinning, most superhydrophobic coatings still face significant challenges in transitioning from laboratory to practical applications. The core bottleneck lies in insufficient mechanical stability; the fragile micro / nano structures are easily damaged by external friction, scratching, or impact, leading to permanent failure of superhydrophobicity. Furthermore, complex preparation processes, high costs, and long-term environmental durability issues (such as UV aging and chemical corrosion) also hinder their industrialization.

[0009] Therefore, the current research focus is shifting from simply pursuing high contact angles to how to balance the relationship between superhydrophobicity, mechanical robustness, and fabrication process, that is, to develop new coatings that combine excellent superhydrophobic properties with strong mechanical durability.

[0010] Currently, epoxy resin coatings are commonly used for sealing and reinforcing concrete structures to ensure durability. Epoxy resin has strong adhesion, forms a dense film, and provides good protection for concrete, making it a frequently used protective system in engineering projects. To further improve the coating's corrosion resistance, water resistance, and aging resistance, existing technologies often introduce a single silane coupling agent to hydrophobically modify nano-silica, and then combine it with epoxy resin to prepare a superhydrophobic coating.

[0011] While such single-silane modified systems can improve surface hydrophobicity and reduce surface energy to some extent, they still have significant shortcomings in practical applications: Single long-chain silanes (such as HDTMS) have long hydrophobic segments and strong hydrophobicity, but they lack cross-linking sites with inorganic nanoparticles and epoxy resins, resulting in poor coating density and structural stability. (2) Single short-chain silanes (such as MTMS) have many crosslinking sites, good film rigidity, and strong UV resistance and aging resistance, but lack hydrophobic groups, making it difficult to achieve high hydrophobicity and low surface energy. (3) The interfacial bonding between single silane and epoxy resin and nano SiO2 is weak, resulting in insufficient overall durability of the coating and difficulty in simultaneously achieving high hydrophobicity, high density and long-term weather resistance.

[0012] Overall, existing single silane-modified epoxy superhydrophobic coatings generally suffer from technical bottlenecks such as difficulty in achieving both hydrophobicity and structural stability, poor UV aging resistance, and insufficient durability.

[0013] Therefore, a superhydrophobic coating and its preparation method are provided to solve the above-mentioned technical problems. Summary of the Invention

[0014] The purpose of this invention is to provide a superhydrophobic coating and its preparation method to solve the problems of existing single silane-modified epoxy superhydrophobic coatings, such as difficulty in achieving synergistic hydrophobicity and crosslinking stability, poor UV aging resistance, significant hydrophobicity decay after long-term service, and easy aging failure. This invention provides a superhydrophobic coating to achieve the following objectives: (1) overcome the defects of single silanes in simultaneously achieving high hydrophobicity, high interfacial crosslinking, and high density; (2) improve the hydrophobicity retention rate and surface morphology stability of the coating under UV aging conditions; (3) enhance the interfacial bonding force between the silane modifier, nano-SiO2, and epoxy resin matrix, and improve the overall durability of the coating; (4) while maintaining high contact angle superhydrophobicity, significantly improve the coating's UV resistance and environmental aging resistance, and extend the service life of concrete protective coatings.

[0015] The objective of this invention is achieved as follows: A method for preparing a superhydrophobic coating includes the following steps: S1. Prepare hydrophobically modified nano silica powder by using methyltrimethoxysilane (MTMS) and hexadecyltrimethoxysilane (HDTMS) as composite modifiers to modify nano silica and obtain hydrophobically modified nano silica powder. S2. Prepare a superhydrophobic topcoat dispersion by using the hydrophobic modified nano silica powder obtained in S1 as a filler, and adding ethyl acetate, epoxy resin E-44 and phenolic amine epoxy resin curing agent T31. After stirring and dispersing, a superhydrophobic topcoat dispersion is obtained. S3. Preparation of primer and preparation of coating film: Epoxy resin E-44 and phenolic amine epoxy resin curing agent T31 are mixed evenly to obtain primer. After the primer is applied to the surface of the substrate, it is baked until the surface is dry. The superhydrophobic topcoat obtained in S2 is evenly sprayed onto the surface of the primer to obtain a composite coating with superhydrophobic properties, wear resistance and durability.

[0016] The specific operation of S1 is as follows: S1.1 Weigh 0.5g of nano SiO2 powder, add 10g of ethanol and 0.5g of aqueous dispersant BYK-154, and ultrasonically disperse for 30min to obtain nano SiO2 dispersion; S1.2 Using methyltrimethoxysilane (MTMS) and hexadecyltrimethoxysilane (HDTMS) as composite modifiers, with a molar ratio of MTMS to HDTMS of 1:1-4:1, 1 g of the composite modifier was weighed and dissolved in 10 g of anhydrous ethanol, and pre-hydrolyzed for 50 min at 40 °C and pH=5 to obtain MTMS / HDTMS hydrolysate; S1.3 Add the nano-SiO2 dispersion obtained in S1.1 to the MTMS / HDTMS hydrolysate obtained in S1.2, seal and transfer to a water bath, and continuously stir and modify at 60℃ for 2.5–3h; after the reaction is completed, take it out and cool it naturally to room temperature, and obtain wet powder by centrifugation, then dry and grind it thoroughly to obtain hydrophobic modified nano-silica powder.

[0017] The specific operation of S2 is as follows: using 19g of ethyl acetate as solvent, add 0.3-0.7g of the modified nano silica powder obtained in S1, and ultrasonically disperse for 10min to obtain the first mixture. Then add 1g of epoxy resin E-44 to the first mixture, stir until completely dissolved, and continue ultrasonic dispersion for 20min to ensure uniform dispersion. Finally, add 0.35g of phenolic amine epoxy resin curing agent T31, stir evenly at room temperature, and obtain the superhydrophobic topcoat dispersion.

[0018] The specific operation of S3 is as follows: Mix 5g of epoxy resin E-44 and 1.75g ​​of phenolic amine epoxy resin curing agent T31 evenly to obtain a primer. Apply the primer to the surface of the substrate and wait for it to dry. Spray the superhydrophobic topcoat dispersion obtained in S2 evenly onto the surface of the primer. Spray 3-4 times thinly. After curing, a superhydrophobic coating is obtained.

[0019] A superhydrophobic coating obtained by a superhydrophobic coating preparation method.

[0020] The beneficial effects of this invention are: 1. Synergistic effect of dual silanes: The MTMS of this invention provides a large number of silanol crosslinking sites, which not only improves the coating density and structural rigidity, but also improves the grafting efficiency of HDTMS; HDTMS introduces long-chain alkyl groups to reduce surface energy and achieve high hydrophobicity. The combination of the two can simultaneously obtain a high contact angle and a dense and stable film structure, which is superior to a single silane system.

[0021] 2. Enhanced interfacial adhesion: The coating of the present invention has better overall integrity. The bissilane forms a uniform and continuous hydrophobic modified layer on the surface of nano-SiO2, which enhances the compatibility between inorganic particles and epoxy resin, reduces interfacial defects, and makes the coating less prone to delamination and peeling.

[0022] 3. Superior durability and wear resistance: The coating of this invention combines the high adhesion of epoxy resin, the excellent hydrophobicity of bissilane, and the stable cross-linking structure. It is not easy to powder, crack, or lose hydrophobicity under ultraviolet light, temperature change, and other environments, making it more suitable for long-term protection of concrete substrates.

[0023] 4. The process of this invention is simple and highly operable. It can be prepared by conventional hydrolysis, blending and coating, without the need for complex equipment, and is easy to apply in industrial applications. Attached Figure Description

[0024] Figure 1 This is an experimental diagram showing the effect of different dispersion methods on the sedimentation stability of the system according to the present invention; Figure 2 and Figure 3 This is a graph showing the variation of the conductivity of the system over time at different temperatures according to the present invention. Figure 4 and Figure 5 This is a graph showing the change of conductivity of the system over time under different pH conditions according to the present invention; Figure 6 and Figure 7 This is a graph showing the change of conductivity of the system over time under different pH conditions according to the present invention; Figure 8 Water contact angle diagrams of coatings obtained by different mass ratios of SiO2 and HDTMS according to the present invention; Figure 9 Water contact angle diagrams of coatings obtained by adding different amounts of hydrophobically modified nano-silica powder in this invention; Figure 10 This is a water contact angle diagram of the coatings obtained by different molar ratios of HDTMS and MTMS according to the present invention.

[0025] Figure 11 A comparison chart of the initial water contact angle (WCA) of three coatings: pure epoxy (EP), single HDTMS modified epoxy (HDTMS), and dual silane (HDTMS@MTMS) composite modified epoxy. Figure 12 Comparison of total surface energy, dispersion component, and polar component of three coatings: pure epoxy (EP), single HDTMS modified epoxy (HDTMS), and HDTMS@MTMS dual silane composite modified epoxy. Figure 13 The image shows a comparison of the methylene blue wetting behavior of blank concrete (OC), pure epoxy (EP), and HDTMS / MTMS composite modified epoxy (H@M-EP) surfaces according to the present invention. Figure 14 The graph shows the self-cleaning performance test results of blank concrete (OC), pure epoxy (EP), and HDTMS / MTMS composite modified epoxy (H@M-EP) surfaces (fly ash is used as a simulated pollutant). Figure 15 This is a diagram illustrating the self-cleaning process of the H@M-EP coated mortar sample of the present invention; Figure 16 This is a diagram illustrating sandpaper friction. Figure 17 The graph shows the evolution of water contact angle (WCA) as a function of friction distance for two epoxy superhydrophobic coatings: monosilane-modified H-EP and bissilane (MTMS / HDTMS) composite-modified M@H-EP. Figure 18 This is a diagram illustrating tape peeling. Figure 19 The graph shows the evolution of the water contact angle (WCA) of two epoxy superhydrophobic coatings, namely monosilane-modified H-EP and bissilane (MTMS / HDTMS) composite-modified M@H-EP, during repeated peeling of 3M#681 tape. Figure 20 This is a schematic diagram of the scraping cycle; Figure 21 The graph shows the evolution of the water contact angle (WCA) with the number of scratches during the knife scratch test for two epoxy superhydrophobic coatings: monosilane-modified H-EP and bissilane (MTMS / HDTMS) composite-modified M@H-EP. Figure 22 This is a schematic diagram of a freeze-thaw cycle; Figure 23 For illustration purposes only; Figure 24 The graph shows the changes in water absorption rate of four groups of pre-soaked concrete. Figure 25 This is a graph showing the changes in mass loss during freeze-thaw cycles; Figure 26 This is a schematic diagram for determining the dynamic elastic modulus. Figure 27 This is a graph showing the change in relative dynamic elastic modulus during freeze-thaw cycles; Figure 28 This is a schematic diagram of UV aging. Figure 29 This is a graph showing the change in contact angle during UV aging. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] A method for preparing a superhydrophobic coating includes the following steps: S1. Prepare hydrophobically modified nano silica powder by using methyltrimethoxysilane (MTMS) and hexadecyltrimethoxysilane (HDTMS) as composite modifiers to modify nano silica and obtain hydrophobically modified nano silica powder. S2. Prepare a superhydrophobic topcoat dispersion by using the hydrophobic modified nano silica powder obtained in S1 as a filler, and adding ethyl acetate, epoxy resin E-44 and phenolic amine epoxy resin curing agent (T31). After stirring and dispersing, a superhydrophobic topcoat dispersion is obtained. S3. Preparation of primer and preparation of coating film: Epoxy resin E-44 and phenolic amine epoxy resin curing agent (T31) are mixed evenly to obtain primer. After the primer is applied to the surface of the substrate, it is baked until the surface is dry. The superhydrophobic topcoat obtained in S2 is evenly sprayed onto the surface of the primer to obtain a composite coating with superhydrophobic properties, wear resistance and durability.

[0028] The specific operation of S1 is as follows: S1.1 Weigh 0.5g of nano-SiO2 powder, add 10g of ethanol and 0.5g of aqueous dispersant (BYK-154), and ultrasonically disperse for 30min to obtain nano-SiO2 dispersion; S1.2 Using methyltrimethoxysilane (MTMS) and hexadecyltrimethoxysilane (HDTMS) as composite modifiers, with a molar ratio of MTMS to HDTMS of 1:1-4:1, 1 g of the composite modifier was weighed and dissolved in 10 g of anhydrous ethanol, and pre-hydrolyzed for 50 min at 40 °C and pH=5 to obtain MTMS / HDTMS hydrolysate; S1.3 Add the nano-SiO2 dispersion obtained in S1.1 to the MTMS / HDTMS hydrolysate obtained in S1.2, seal and transfer to a water bath, and continuously stir and modify at 60℃ for 2.5–3h; after the reaction is completed, take it out and cool it naturally to room temperature, and obtain wet powder by centrifugation, then dry and grind it thoroughly to obtain hydrophobic modified nano-silica powder.

[0029] The specific operation of S2 is as follows: using 19g of ethyl acetate as solvent, add 0.3-0.7g of the modified nano silica powder obtained in S1, and ultrasonically disperse for 10min to obtain the first mixture. Then add 1g of epoxy resin E-44 to the first mixture, stir until completely dissolved, and continue ultrasonic dispersion for 20min to ensure uniform dispersion. Finally, add 0.35g of phenolic amine epoxy resin curing agent (T31), stir evenly at room temperature, and obtain the superhydrophobic topcoat dispersion.

[0030] The specific operation of S3 is as follows: Mix 5g of epoxy resin E-44 and 1.75g ​​of phenolic amine epoxy resin curing agent (T31) evenly to obtain a primer. Apply the primer to the surface of the substrate and wait for it to dry. Spray the superhydrophobic topcoat dispersion obtained in S2 evenly onto the surface of the primer. Spray 3-4 times thinly. After curing, a superhydrophobic coating is obtained.

[0031] 1. Process optimization 1.1 Dispersion process:

[0032] As shown in Table 1 and Figure 1 As shown, the natural sedimentation group achieved a sedimentation rate of 37.78% after 1 hour, which gradually increased to 43.33% over time (and remained stable after 1 day), indicating that particles easily aggregate and settle rapidly without external force or dispersant action. The group with Byk-154 dispersant alone reduced the sedimentation rate to 30.11% in the initial stage (1 hour), but the sedimentation rate continued to rise to 43.01% over time (stabilizing after 4 days), close to the final sedimentation level of the natural sedimentation group. This indicates that dispersants alone cannot achieve long-term stable dispersion, but still provide a certain dispersion effect. In stark contrast, the ultrasonic dispersion group and the ultrasonic and Byk-154 synergistic treatment group both showed a sedimentation rate of 0% throughout the entire test period from 1 hour to 7 days. This indicates that ultrasonic treatment can effectively break up particle agglomerates, allowing particles to disperse uniformly in the system, and this dispersion state remains stable even after long-term static placement, demonstrating excellent anti-settling performance.

[0033] 1.2 Hydrolysis Process 1.2.1 Effect of Temperature on Conductivity like Figure 2 and Figure 3As shown, the conductivity increases significantly with increasing temperature: at 20℃, the conductivity stabilizes at 60–62 μS / cm; at 30℃, it remains at 73–81 μS / cm; at 40℃, it fluctuates between 85–94 μS / cm; and at 50℃, the conductivity is highest, initially oscillating violently within the 100–111 μS / cm range. With prolonged time, the conductivity in the 20℃, 30℃, and 40℃ groups remains relatively stable, exhibiting only minor fluctuations, indicating a stable ionic environment under low to medium temperature conditions. In contrast, the conductivity in the 50℃ group drops sharply to approximately 85 μS / cm after 110 min, significantly deviating from the previous fluctuation range. This suggests that the system's stability decreases under long-term high-temperature action, possibly due to hindered ion migration, component decomposition, or phase separation, leading to a rapid decline in conductivity.

[0034] Based on the above results, 40℃ is the optimal operating temperature in this study. At this temperature, the system maintains a conductivity level significantly higher than that at 20℃ and 30℃ (85–94 μS / cm), and does not exhibit the long-term stability degradation phenomenon seen at 50℃. This achieves the best balance between conductivity and long-term stability, providing reliable temperature parameters for subsequent process applications.

[0035] 1.2.2 Effect of pH on conductivity like Figure 4 and Figure 5 As shown, the conductivity of different pH groups all exhibited a trend of first fluctuating upward and then gradually decreasing: pH=3: The conductivity fluctuates in the range of 93–103 μS / cm, reaching a peak at 60 min (approximately 103 μS / cm), and decreasing to approximately 92 μS / cm at 120 min.

[0036] pH=4: The conductivity is stable at 95–102 μS / cm with small overall fluctuations, and remains at about 96 μS / cm after 120 min.

[0037] pH=5: The conductivity oscillated in the range of 96–104 μS / cm, reaching the highest value (about 104 μS / cm) at 50 min, which was the highest peak value among the four groups, and remained at a high level throughout, still at about 94 μS / cm at 120 min.

[0038] pH=10: The conductivity fluctuated between 97–103 μS / cm in the early stage, and then dropped sharply after 80 min, dropping to about 84 μS / cm at 120 min, indicating a significant deterioration in the stability of the system.

[0039] Over time, the pH=3, pH=4 and pH=5 groups maintained relatively stable conductivity levels with only slight fluctuations, indicating that the ionic environment of the system is more stable under weak acid to neutral conditions. However, under strongly alkaline conditions (pH=10), the conductivity of the system decreased sharply after 80 minutes, indicating that long-term alkaline environment will destroy the stability of the system and may cause ion precipitation, component aggregation or structural damage, resulting in a significant decrease in conductivity.

[0040] Considering both conductivity and long-term stability, pH=5 is the optimal condition. At this pH, the system exhibits the highest peak conductivity (approximately 104 μS / cm) and maintains a high level of conductivity and good stability throughout the process, without any significant drop. This achieves the best balance between conductivity and long-term stability.

[0041] 1.2.3 Effect of solid content on conductivity like Figure 6 and Figure 7 As shown, the conductivity of each experimental group generally exhibits a trend of first fluctuating upward and then gradually decreasing. The silane content has a significant regulatory effect on the conductivity and long-term stability of the system. 1% silane group: The conductivity fluctuated between 97 and 105 μS / cm, reaching a peak at 80 min and then continuously decreasing, dropping to about 93 μS / cm at 120 min, showing obvious late-stage decay and poor stability.

[0042] 2% silane group: The conductivity remained in the range of 98–107 μS / cm, with the highest peak value among the four groups (about 107 μS / cm), and the smallest fluctuation range throughout the entire process. It was still maintained at about 99 μS / cm at 120 min, showing the best conductivity and stability.

[0043] The 3% silane group showed a peak conductivity of 106 μS / cm, but the conductivity decreased significantly in the later stages, dropping back to about 104 μS / cm at 120 min. Its long-term stability was slightly inferior to that of the 2% group.

[0044] 4% silane group: The initial conductivity level was relatively high (about 99 μS / cm), but it continued to decrease over time, dropping to about 96 μS / cm at 120 min. Overall, it showed a monotonic decay trend and had the worst stability.

[0045] Over time, the conductivity of groups 1%, 3%, and 4% all showed varying degrees of decay, while group 2% maintained a high and stable conductivity level throughout the entire testing period without any significant drop. Considering both peak conductivity and long-term stability, 2% is the optimal silane addition amount: at this content, the system achieves both the highest peak conductivity and ensures long-term stability, achieving the best balance between conductivity and system stability, providing a key basis for optimizing the silane addition process.

[0046] 2. Experimental Variable Design and Control To ensure the reliability and regularity of the experimental results, a single-factor variable experimental design was adopted. All three experimental groups had fixed core baseline conditions, with only a single variable being changed. The specific design is as follows: 2.1. Effect of SiO2:HDTMS mass ratio Core objective: To investigate the effect of the mass ratio of nano-SiO2 to long-chain silane HDTMS on the low-energy modification effect and micro / nano structure construction of the coating surface, and to determine the optimal mass ratio between the two.

[0047] Fixed conditions: The amount of hydrophobically modified nano-silica powder added was 0.4g, the molar ratio of MTMS to HDTMS was 1:1.5, the epoxy resin primer system remained unchanged, and the coating preparation process was consistent.

[0048] Variable range: The SiO2:HDTMS mass ratio was set to 1:0.25, 1:0.5, 1:0.8, and 1:2, respectively. The water contact angle (minimum angle, maximum angle, and average angle) of the coating under different ratios was tested multiple times to analyze the correlation between the ratio and the hydrophobic performance.

[0049] The results are shown in Table 2 and Figure 8 As shown, the coating exhibits the best hydrophobic effect when the SiO2:HDTMS mass ratio is 1:0.8.

[0050] 2.2. Effect of the amount of hydrophobically modified nano-silica powder added The effect of the amount of modified hydrophobic nano-silica powder added on the compactness of the micro-nano rough structure of the coating was investigated, and the optimal amount of powder added was determined to construct a complete micro-nano structure without agglomeration.

[0051] Fixed conditions: SiO2:HDTMS mass ratio is 1:0.8, MTMS:HDTMS molar ratio is 1:1.5, epoxy resin primer system and preparation process remain unchanged.

[0052] Variable range: The amount of hydrophobically modified nano silica powder added was set to 0.3g, 0.4g, 0.5g, 0.6g and 0.7g respectively. By testing the water contact angle of the coating under different addition amounts, the intrinsic relationship between the amount of hydrophobically modified nano silica powder added and the micro-nano structure and hydrophobic properties was analyzed, and the threshold range of the addition amount was clarified. The results are shown in Table 3 and Figure 9 As shown, the coating exhibits the best hydrophobic effect when the amount of hydrophobically modified nano-silica powder added is 0.6g.

[0053] 2.3. Effect of MTMS:HDTMS molar ratio The study investigated the synergistic effects of the amount of short-chain silane MTMS (with a fixed amount of HDTMS) on the coating crosslinking density, micro / nano structure stability, and surface low-energy properties, and optimized the ratio of bissilane compounding.

[0054] Fixed conditions: SiO2:HDTMS mass ratio is 1:0.8, hydrophobic modified nano silica powder addition amount is 0.6g, epoxy resin primer system and preparation process remain unchanged.

[0055] Variable range: The molar ratio of HDTMS:MTMS was set to 1.5:1, 1:1, 1:2, and 1:4, respectively. By testing the water contact angle of the coating under different molar ratios, the synergistic mechanism of short-chain silane crosslinking and long-chain silane low-energy interaction was analyzed, and the optimal compound molar ratio of the two was determined. The results are shown in Table 4 and Figure 10 As shown, the coating exhibits the best hydrophobic effect when the molar ratio of HDTMS to MTMS is 1:2.

[0056] 3. Performance Testing 3.1 Calculation of contact angle and surface energy, from Figure 11 It can be seen that the initial water contact angle (WCA) of the pure EP coating is only 71.6°, exhibiting typical hydrophilic characteristics. This is because the epoxy matrix surface is rich in polar groups such as hydroxyl (-OH), resulting in high surface energy, making it easy for water molecules to spread on its surface. After modification with HDTMS alone, the coating WCA is significantly increased to 148.8°, approaching the superhydrophobic threshold; and after modification with HDTMS@MTMS dual silane composite, the WCA is further increased to 153°, fully meeting the criteria for superhydrophobicity (WCA > 150°), achieving a significant transformation from hydrophilic to superhydrophobic.

[0057] From a mechanistic perspective, for a pure EP matrix, a large number of unreacted epoxy and hydroxyl groups remain on the surface after epoxy curing. These groups are highly polar and have high surface energy. According to Young's equation, the interfacial tension between the high surface energy matrix and water is large, resulting in good wettability and a low contact angle. Essentially, the hydrogen bonding between the polar groups and water molecules drives droplet spreading. For single HDTMS modification, HDTMS (hexadecyltrimethoxysilane), as a long-chain alkyl silane, can undergo a condensation reaction with the hydroxyl groups (-Si-OH) generated by hydrolysis, grafting a layer of long-chain alkyl (-C) groups onto the matrix surface. 16 H 33 The nonpolar properties of long-chain alkyl groups significantly reduce the surface energy of the coating and simultaneously construct a preliminary micro-rough structure, thus greatly improving the contact angle. However, the grafted layer of a single HDTMS has structural defects: the steric hindrance effect of long-chain molecules leads to limited grafting density and can only form a single layer modification, failing to construct a complete micro-nano hierarchical rough structure. Therefore, WCA does not meet the superhydrophobic standard. In contrast, for the HDTMS@MTMS bissilane composite modification, the bissilane system achieves dual optimization of surface energy and microstructure through a synergistic hydrolysis-grafting effect.

[0058] Structural synergy: MTMS (methyltrimethoxysilane) is a short-chain silane with small molecular size and low steric hindrance. It can fill the gaps after the long-chain grafting of HDTMS, improve the grafting density and cross-linking degree of the silane layer, and construct a dense network structure of "short chain filling - long chain support", which greatly enhances the mechanical stability of the coating. Roughness Synergy: During the hydrolysis and polycondensation of bissilanes, the -Si-OH of MTMS preferentially combines with the matrix hydroxyl groups to form a bottom anchor, while the long-chain alkyl of HDTMS extends outward, constructing a hierarchical rough structure on the surface of "nanoscale siloxane network + micron-scale alkyl agglomeration", which conforms to the Cassie-Baxter superhydrophobic model and can trap a large amount of air at the solid-liquid interface, significantly improving the contact angle; Surface energy synergy: The methyl (-CH3) group of MTMS works synergistically with the long-chain alkyl group of HDTMS to further reduce the surface energy of the coating, ultimately achieving superhydrophobic properties with an initial water contact angle (WCA) of >150°.

[0059] Depend on Figure 12It can be seen that the pure EP coating has the highest total surface energy, reaching 42.23 mJ / m², of which the dispersive component is 33.77 mJ / m² and the polar component is 8.46 mJ / m², with the polar component accounting for approximately 20%. This reflects the high surface energy and strong polarity of the epoxy matrix due to its rich surface abundance of polar groups such as hydroxyl (-OH). After modification with HDTMS alone, the total surface energy decreased significantly to 23.52 mJ / m², and the polar component further decreased to 4.49 mJ / m², indicating that the grafting of long-chain alkyl groups effectively shielded the polar groups of the matrix, significantly reducing surface polarity and total surface energy. After modification with HDTMS@MTMS dual silane composite, the total surface energy is 27.67 mJ / m², slightly higher than that of the single HDTMS system, but the polar component is only 6.15 mJ / m², which remains at an extremely low level; its dispersive component (21.52 mJ / m²) accounts for more than 77%, indicating that the dual silane system optimizes the surface energy composition through the construction of micro-nano hierarchical structures while ensuring low polarity, thus achieving a balance between low surface energy and structural stability.

[0060] According to the Young equation and Owens-Wendt theory, the lower the surface energy of a solid and the smaller the proportion of polar components, the worse its wettability with water and the higher its contact angle. In the bissilane system, the short-chain MTMS silane fills the gaps in the long-chain grafts of HDTMS, improving the crosslinking density and grafting integrity of the silane layer. It maintains the low surface energy through the synergistic effect of methyl and long-chain alkyl groups, and constructs a more stable micro-nano rough structure, ultimately achieving a further increase in the contact angle (153°), verifying the synergistic advantage of bissilane modification in wettability regulation.

[0061] 3.2 Self-cleaning effect, by Figure 13-15 It can be seen that, from Figure 13 It can be seen that the methylene blue solution spreads and penetrates rapidly on the surface of the OC sample, showing a completely wetted state; although the droplets on the surface of the EP sample are not completely spread, the contact angle is low and the wettability is still strong; the droplets on the surface of the M@H-SiO2-EP coating are uniformly spherical and there is no wetting or penetration phenomenon, which directly shows that the coating has successfully achieved superhydrophobic properties and can effectively block liquid intrusion.

[0062] Depend on Figure 14It was found that fly ash contaminants on the untreated concrete (OC) surface could not be removed by water washing, and with prolonged soaking time, water rapidly penetrated into the porous matrix, causing the contaminants to firmly bond with the surface. Some contaminants remained on the surface of the epoxy resin primer (EP) sample, and the surface was gradually wetted by water, increasing the adhesion of the contaminants. However, the fly ash contaminants on the surface of the M@H-SiO2-EP superhydrophobic coating sample automatically rolled off with the water flow, maintaining a clean surface throughout the soaking process, without any contaminant residue or water wetting. This result directly demonstrates the excellent self-cleaning properties of the superhydrophobic coating, stemming from its low surface adhesion in the Cassie-Baxter state. Water droplets can carry contaminants away from the surface, achieving a self-cleaning effect while effectively preventing water from contacting the substrate.

[0063] Figure 15 The self-cleaning mechanism of the superhydrophobic coating is visually demonstrated: (b1) In the initial state, fly ash contaminants are uniformly adhered to the coating surface; (b2-b3) Water droplets on the coating surface are spherical with high contact angles, rolling under gravity and carrying the adhered fly ash contaminants; (b4) After the water droplets leave, the contaminants on the coating surface are completely removed, restoring a clean state. This phenomenon stems from the micro-nano rough structure and low surface energy characteristics of the coating surface, which puts the water droplets in a Cassie-Baxter wetting state. During rolling, the surface contaminants can be efficiently peeled off, exhibiting excellent self-cleaning ability.

[0064] 3.3 Mechanical durability 3.3.1 Sandpaper friction The coating was tested according to ISO / TS 10689:2023. Characterization was performed using a linear reciprocating wear test: a 40×40 mm coating sample was fixed on 800-grit sandpaper with the working surface facing down, and a 100 g weight (total pressure approximately 1.4 kPa) was applied. Linear reciprocating friction was performed at a rate of 10 cm / s. After every 5 meters of movement, the change in coating wettability was measured using a contact angle goniometer, marking one wear cycle.

[0065] like Figure 16 and Figure 17As shown, both coatings initially met the superhydrophobic requirements. However, with increasing friction distance, the water-ceiling angle (WCA) of the two coatings showed significant differences. The WCA of the monosilane H-EP coating decreased rapidly and abruptly, fluctuating only slightly within 0-10 m, then dropping sharply after 10 m, reaching 114.09° at around 35 m, completely losing its superhydrophobic properties. This indicates that the mechanical bonding between its surface micro / nano structure and the low surface energy layer is weak, making it easily worn away and failing. In contrast, the WCA of the bissilane M@H-EP coating decreased slowly and gradually, remaining above 147° within 0-50 m, maintaining excellent superhydrophobic properties. The hydrophobic angle only decreased to 114.10° at 120 m, demonstrating mechanical durability far superior to that of the monosilane coating.

[0066] The results show that the dual-silane composite modification constructs a more stable micro-nano hierarchical rough structure and a dense low surface energy graft layer through synergistic effect, which greatly improves the wear resistance of the coating and effectively extends the service life of the superhydrophobic coating, providing a high-performance solution for engineering applications.

[0067] 3.3.2 Tape Peel Test: The adhesive strength of the coating is tested using a tape peel test. 3M #681 tape is firmly adhered to the coating surface and then rapidly peeled off at 180°. The contact angle of the coating is tested after every 5 peels.

[0068] like Figure 18 and Figure 19 As shown, with increasing peeling cycles, the WCA of the monosilane H-EP coating exhibits a rapid and precipitous decline, showing a significant decrease within 0-10 peeling cycles. After 25 peeling cycles, it drops to 121.75°, completely losing its superhydrophobic properties. This indicates weak interfacial adhesion between the coating and the substrate, and the surface low-energy layer and micro / nano structures are easily peeled off by the tape. In contrast, the WCA of the bissilane M@H-EP coating exhibits a slow, gradient decline, remaining above 150° throughout 0-70 peeling cycles, maintaining excellent superhydrophobic properties. After 100 peeling cycles, it still maintains 133.77°, demonstrating significantly superior interfacial stability and peel resistance compared to the monosilane coating.

[0069] The results show that the bissilane composite modification enhances the interfacial bonding between the coating and the epoxy matrix through synergistic effect, constructs a more stable micro-nano hierarchical rough structure and a dense low surface energy graft layer, and effectively resists the mechanical action of repeated peeling.

[0070] 3.3.3 Scraping Cycle: The sharp blade scratching cycle test uses a hand knife to scratch the coating surface at a 45° angle. One complete scratch from top to bottom is one scratching cycle, and the change in contact angle is recorded every 5 cycles.

[0071] like Figure 20 and Figure 21As shown, with the increase of the number of scratches, the WCA of the monosilane H-EP coating decreases rapidly and linearly. After 10 scratches, the WCA has dropped to about 132°, and after 15 scratches, it further decreases to 112.65°, completely losing its superhydrophobic properties. This indicates that the mechanical stability of its surface micro-nano rough structure and low surface energy modification layer is extremely poor. Under the scratching action of sharp blades, the surface structure is rapidly destroyed and the low-energy components are completely stripped off, resulting in irreversible failure of the superhydrophobic properties.

[0072] In contrast, the WCA of the dual-silane M@H-EP coating maintained high stability throughout the scratch test: within the range of 0 to 50 scratches, the WCA fluctuated only slightly between 150.5° and 155.8°, with no obvious attenuation trend; after 50 scratches, the WCA was still as high as 152.97°, maintaining an excellent superhydrophobic state and demonstrating extremely strong scratch resistance and mechanical durability. Combined with the droplet morphology before and after scratching in the illustration, it can be seen that the H-EP coating droplets spread significantly after scratching, while the M@H-EP coating maintained spherical droplets, further verifying the high stability of its surface structure.

[0073] The above results indicate that the dual-silane composite modification, through the synergistic effect of short-chain silanes (MTMS) enhancing the coating crosslinking density and matrix bonding force, and long-chain silanes (HDTMS) maintaining low surface energy properties, constructs a dense protective system with both high mechanical strength and low surface energy. This system can effectively resist scratching damage from sharp tools and significantly improve the coating's resistance to mechanical damage.

[0074] 3.4 Freeze-thaw cycle test: OC corresponds to ordinary concrete, EP corresponds to epoxy primer, H-EP corresponds to single HDTMS modified SiO2 combined with epoxy primer, and H@M-EP corresponds to HDTMS / MTMS composite modified SiO2 combined with epoxy primer.

[0075] Before the freeze-thaw cycle test, in accordance with the requirements of GB / T 50082-2009 rapid freeze-thaw method, four groups of samples were pretreated by soaking in water for 4 days. Figures 22-24 As shown, both groups of samples exhibited water absorption during immersion. The water absorption rate of each group first increased rapidly and then stabilized with the extension of immersion time, showing diffusion-controlled characteristics. After 4 days of immersion, the water absorption rate of blank concrete OC was 4.56%, with well-developed interconnected pores leading to rapid water absorption; pure epoxy EP was 1.84%, with surface sealing reducing water absorption channels; single silane H-EP decreased to 0.79%, with low surface energy further inhibiting water adsorption; and dual silane composite H@M-EP was only 0.28%, with its dense structure and strong hydrophobicity synergistically blocking water intrusion and reducing the driving force of freeze-thaw damage from the source.

[0076] like Figure 25 As shown, with the increase of freeze-thaw cycles, the mass loss of each group gradually increased, and the degree of deterioration was: ordinary concrete OC > pure epoxy EP > single silane H-EP > dual silane composite H@M-EP. After 100 cycles, the mass loss rate of blank concrete reached 5.92%, mainly due to the expansion of water-ice phase transformation leading to matrix cracking and spalling; pure epoxy was 3.04%, although it can seal pores, it is prone to micro-cracks; single silane decreased to 1.46%, the hydrophobic effect reduced water intrusion; dual silane composite was only 0.49%, thanks to the dense cross-linked structure and strong interfacial bonding, which effectively inhibited freeze-thaw erosion and water penetration.

[0077] like Figure 26-27 As shown, the relative dynamic modulus of elasticity continuously decreases with increasing freeze-thaw cycles, reflecting the continuous accumulation of internal damage. After 100 cycles, the OC modulus of blank concrete is only 55.42%, indicating severe damage to the internal structure; the pure epoxy EP is 67.88%, with coating cracking accelerating the deterioration process; the single silane H-EP maintains 80.39%, and its hydrophobic and water-reducing properties mitigate freeze-thaw damage; the dual silane composite H@M-EP remains as high as 90.07%, due to its dense and stable cross-linked network, which significantly delays microcrack propagation and preserves structural integrity and mechanical properties to the greatest extent.

[0078] 3.5 UV aging: such as Figure 28 and Figure 29 As shown, the contact angles of all coatings decreased to varying degrees with prolonged UV aging time. The pure epoxy coating EP exhibited poor UV resistance; under UV irradiation, its surface was easily oxidized and chain-severed, leading to a rapid increase in polar groups. The contact angle decreased rapidly from an initial 72.36° to 52.09° after 48 hours, with significantly enhanced hydrophilicity. The single silane coating H-EP showed excellent initial hydrophobicity, but its alkyl chains were prone to photo-oxidative degradation under UV light, resulting in the destruction of its low surface energy structure. Its contact angle decay rate was significantly faster than that of the bissilane system. The bissilane composite modified coating H@M-EP, due to the formation of a dense cross-linked network, effectively mitigated surface structural damage caused by UV irradiation, exhibiting the most gradual decrease in contact angle, maintaining 148.46° after 48 hours, significantly better than the single silane coating and demonstrating stronger UV aging stability.

Claims

1. A method for preparing a superhydrophobic coating, characterized in that, Includes the following steps: S1. Prepare hydrophobically modified nano silica powder by using methyltrimethoxysilane (MTMS) and hexadecyltrimethoxysilane (HDTMS) as composite modifiers to modify nano silica and obtain hydrophobically modified nano silica powder. S2. Prepare a superhydrophobic topcoat dispersion by using the hydrophobic modified nano silica powder obtained in S1 as a filler, and adding ethyl acetate, epoxy resin E-44 and phenolic amine epoxy resin curing agent T31. After stirring and dispersing, a superhydrophobic topcoat dispersion is obtained. S3. Preparation of primer and preparation of coating film: Epoxy resin E-44 and phenolic amine epoxy resin curing agent T31 are mixed evenly to obtain primer. After the primer is applied to the surface of the substrate, it is baked until the surface is dry. The superhydrophobic topcoat obtained in S2 is evenly sprayed onto the surface of the primer to obtain a composite coating with superhydrophobic properties, wear resistance and durability.

2. The method for preparing a superhydrophobic coating according to claim 1, characterized in that, The specific operation of S1 is as follows: S1.1 Weigh 0.5g of nano SiO2 powder, add 10g of ethanol and 0.5g of aqueous dispersant BYK-154, and ultrasonically disperse for 30min to obtain nano SiO2 dispersion; S1.2 Using methyltrimethoxysilane (MTMS) and hexadecyltrimethoxysilane (HDTMS) as composite modifiers, with a molar ratio of MTMS to HDTMS of 1:1-4:1, 1 g of the composite modifier was weighed and dissolved in 10 g of anhydrous ethanol, and pre-hydrolyzed for 50 min at 40 °C and pH=5 to obtain MTMS / HDTMS hydrolysate; S1.3 Add the nano-SiO2 dispersion obtained in S1.1 to the MTMS / HDTMS hydrolysate obtained in S1.2, seal and transfer to a water bath, and continuously stir and modify at 60℃ for 2.5–3h; after the reaction is completed, take it out and cool it naturally to room temperature, and obtain wet powder by centrifugation, then dry and grind it thoroughly to obtain hydrophobic modified nano-silica powder.

3. The method for preparing a superhydrophobic coating according to claim 1, characterized in that, The specific operation of S2 is as follows: using 19g of ethyl acetate as solvent, add 0.3-0.7g of the modified nano silica powder obtained in S1, and ultrasonically disperse for 10min to obtain the first mixture. Then add 1g of epoxy resin E-44 to the first mixture, stir until completely dissolved, and continue ultrasonic dispersion for 20min to ensure uniform dispersion. Finally, add 0.35g of phenolic amine epoxy resin curing agent T31, stir evenly at room temperature, and obtain the superhydrophobic topcoat dispersion.

4. The method for preparing a superhydrophobic coating according to claim 1, characterized in that, The specific operation of S3 is as follows: Mix 5g of epoxy resin E-44 and 1.75g ​​of phenolic amine epoxy resin curing agent T31 evenly to obtain a primer. Apply the primer to the surface of the substrate and wait for it to dry. Spray the superhydrophobic topcoat dispersion obtained in S2 evenly onto the surface of the primer. Spray 3-4 times thinly. After curing, a superhydrophobic coating is obtained.

5. A superhydrophobic coating, characterized in that, Obtained by any one of the superhydrophobic coating preparation methods according to claims 1-4.

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