A method for preparing SiO2-based bicovalent network superhydrophobic composite coating

Abstract

This invention relates to the field of superhydrophobic composite coating technology, and discloses a method for preparing a SiO2-based bicovalent network superhydrophobic composite coating. This method uses tetraethoxysilane to synthesize silica nanoparticles to construct surface roughness, and utilizes the long fluorocarbon chain of perfluorooctyltriethoxysilane (POTS) to modify it with low surface energy. A silane coupling agent and aluminum nitrate are introduced to generate a Si-O-Si covalent network as molecular bridges and an Al-O-Al covalent network as a framework, respectively. An epoxy resin (EP) is used as a bonding layer to adhere the coating to a substrate. The SiO2-based bicovalent network superhydrophobic composite coating prepared by this method exhibits excellent superhydrophobicity, mechanical stability, chemical stability, and thermal stability, providing a simple manufacturing strategy for the industrial application of superhydrophobic materials.

Description

Technical Field

[0001] This invention relates to the field of superhydrophobic composite coating technology, and in particular to a method for preparing a SiO2-based bicovalent network superhydrophobic composite coating. Background Technology

[0002] Since the late 1990s, inspired by natural organisms such as lotus leaves and insect wings, superhydrophobic surfaces have attracted widespread attention due to their self-cleaning, corrosion resistance, oil-water separation, anti-icing, anti-fogging, drag reduction, directional liquid transport, photocatalysis, and enhanced buoyancy properties, demonstrating enormous application potential in various fields. Typically, water droplets on superhydrophobic surfaces have a contact angle (CA) greater than 150° and a roll-off angle (RA) less than 10°, allowing the droplets to roll freely and maintain an approximately spherical shape. Surface roughness and low surface energy are essential factors for the artificial construction of superhydrophobic surfaces. Appropriate surface roughness is usually achieved through micro / nanostructures, supporting droplets to reach the Cassie-Baxter state; while low surface energy ensures a sufficiently large contact angle, preventing droplets from wetting the micro / nanostructures due to capillary forces. While research on constructing superhydrophobic surfaces is relatively mature, significant challenges remain regarding their stability and large-scale fabrication.

[0003] Mechanical stability is a key characteristic determining whether a superhydrophobic surface can be practically applied. The micro / nano-rough structures of superhydrophobic surfaces are typically very fragile and easily damaged, causing the coating to lose its superhydrophobic effect and thus its functional properties. Several strategies have been developed to improve mechanical strength using adhesives such as epoxy resins, silicone resins, and commercial adhesives. Common methods for improving the mechanical strength of superhydrophobic surfaces involve coating a layer of adhesive between the micro / nano coating and the substrate. During the curing process, the micro / nano particles partially embed themselves in the adhesive. This method only guarantees the mechanical strength of a small layer of coating particles in contact with the adhesive, and essentially cannot simultaneously achieve both mechanical strength and superhydrophobic properties. Another method involves mixing adhesives into the hydrophobic particles to act as a binder between the superhydrophobic micro / nano particles. However, this method requires a very small amount of adhesive, otherwise, the nanoparticles will be completely encapsulated, causing the surface to lose roughness and weakening the hydrophobic properties. Therefore, the superhydrophobic properties are often lost before the mechanical strength is significantly improved, and the dual benefits of both properties cannot be achieved.

[0004] Therefore, it is essential to explore a low-cost, easily scalable method for preparing superhydrophobic surfaces that can balance superhydrophobic properties and mechanical durability. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing a SiO2-based bicovalent network superhydrophobic composite coating.

[0006] The method for preparing SiO2-based dual covalent network superhydrophobic composite coatings provided by this invention includes the following steps:

[0007] 1. Tetraethoxysilane was added to ethanol to form component A, while ammonia and water were added to another ethanol to form component B. After each component was thoroughly mixed, component A was added dropwise to component B under magnetic stirring at 500 rpm to prepare a hydrophilic SiO2 sol.

[0008] S2. Perfluorooctyltriethoxysilane, vinyltriethoxysilane and aluminum nitrate nonahydrate are added to hydrophilic SiO2 sol, and then ultrasonic treatment is performed to obtain an integrated superhydrophobic coating.

[0009] S3. Then, the epoxy resin and the curing agent polyamide resin are mixed and dissolved in ethanol. After mixing evenly, a solution with an epoxy resin concentration of 0.1 g / mL is formed. Then, it is sprayed on the pretreated substrate at a spraying distance of 20 cm. After initial curing at room temperature, an epoxy resin coating is obtained.

[0010] S4. Using a spray gun, spray the prepared superhydrophobic coating onto the epoxy resin coating from a distance of 20cm. After spraying, place the prepared sample in a 150℃ oven overnight to allow the solvent ethanol to completely evaporate and the epoxy resin and aluminum nitrate to cure, ultimately obtaining a superhydrophobic surface with a bicovalent network, labeled F-SiO2 / VTES / AlO2. x / EP coating.

[0011] Preferably, in step S1, the amount of tetraethoxysilane in component A is 1 mL and the amount of ethanol is 5 mL; in component B, the amount of ammonia is 0.36 mL, the amount of water is 0.6 mL, and the amount of ethanol is 5 mL.

[0012] Preferably, in step S2, the amount of perfluorooctyltriethoxysilane used is 0.1 mL, the amount of vinyltriethoxysilane used is 0.4 mL, the amount of aluminum nitrate nonahydrate used is 0.0425 g, and the ultrasonic treatment temperature is 45°C and the time is 1 h.

[0013] Preferably, in step S3, the epoxy resin and the curing agent polyamide resin are mixed at a mass ratio of 1:1, and the initial curing time at room temperature after spraying is 3 hours.

[0014] Preferably, the substrate is one of glass slide, silicon wafer, 1060 pure aluminum sheet, 6061 aluminum alloy sheet, copper sheet and ceramic sheet. Metal substrates are polished sequentially with 600-grit and 2000-grit SiC sandpaper along the surface texture direction, then ultrasonically cleaned with ethanol, and dried in an oven at 60°C. Non-metallic substrates only need to be ultrasonically cleaned with ethanol.

[0015] Compared with related technologies, the method for preparing SiO2-based bicovalent network superhydrophobic composite coatings provided by this invention has the following advantages:

[0016] The prepared coating exhibits excellent superhydrophobicity, with a contact angle greater than 162° and a roll-off angle of approximately 6°.

[0017] The coating exhibits good mechanical stability and can withstand wear exceeding 5600 cm under a pressure of 541 Pa.

[0018] The coating exhibits excellent chemical stability and retains its superhydrophobicity even after being immersed in acidic or alkaline solutions for several hours.

[0019] The coating exhibits excellent thermal stability and maintains its superhydrophobicity at temperatures up to 300°C.

[0020] The coating preparation method is simple and suitable for large-scale industrial manufacturing. Attached Figure Description

[0021] Figure 1 The structural formulas of (a) TEOS, (b) POTS, and (c) VTES in this invention are shown below.

[0022] Figure 2 Schematic diagrams of contact angle and roll-off angle for different coatings: (a) F-SiO2 (RA=5.05°); (b) F-SiO2 / VTES (RA=4.80°); (c) F-SiO2 / VTES / AlO x (RA=2.94°); (d) F-SiO2 / VTES / AlO x / EP (RA=6.62°); (e) SiO2; (f) Bare glass plate;

[0023] Figure 3 SEM images of different surfaces: (a) SiO2 coating; (b) F-SiO2 coating; (c) F-SiO2 / VTES coating; (d) F-SiO2 / VTES / AlO x Coating; (e) F-SiO2 / VTES / AlO x / EP coating;

[0024] Figure 4 EDS test results and elemental mass and atomic number ratios (embedded tables): (a) SiO2 coating; (b) F-SiO2 coating; (c) F-SiO2 / VTES coating; (d) F-SiO2 / VTES / AlO x coating;

[0025] Figure 5For SiO2 nanocomposites, F-SiO2 nanocomposites, F-SiO2 / VTES nanocomposites, F-SiO2 / VTES / AlO x FTIR spectrum of nanocomposite materials;

[0026] Figure 6 The diagram shows: (a) an experimental diagram of the self-cleaning ability of the composite coating; and (b) a schematic diagram of its self-cleaning properties.

[0027] Figure 7 The following are examples: (a) Schematic diagram of abrasion test on superhydrophobic coated sandpaper; (b) Changes in contact angle and roll-off angle of different surfaces with the number of abrasion cycles;

[0028] Figure 8 The following are: (a) the contact angles of droplets with different pH values ​​on the superhydrophobic surface; (b) the curves showing the changes in the contact angle and roll-off angle of the coating with immersion time; and (c) the curves showing the changes in the contact angle and roll-off angle with temperature.

[0029] Figure 9 The following are: (a) the preparation mechanism of SiO2 superhydrophobic composite coating; (b) a schematic diagram of the self-similarity characteristics of failure;

[0030] Figure 10 For example: photographs of water droplets (5.0 μL) on different substrates; the value below each photograph is the corresponding contact angle;

[0031] Figure 11 A schematic diagram of the preparation process of a SiO2-based bivalent covalent network superhydrophobic composite coating provided by the present invention: (a) SiO2 nanoparticles; (b) nanoparticle surface modification and covalent coupling; (c) F-SiO2 / VTES / AlO x / EP composite coating. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] This paper proposes a two-step spraying method to prepare superhydrophobic surfaces with self-similar structures and high wear resistance. Figure 11 As shown, this invention proposes a method for preparing a SiO2-based bicovalent network superhydrophobic composite coating. Using tetraethoxysilane as a raw material, silica nanoparticles are first prepared via the Stöber method. Perfluorooctyltriethoxysilane (POTS) is then used as a surface modifier to obtain superhydrophobic silica nanoparticles. Vinyltriethoxysilane (VTES) and aluminum nitrate nonahydrate (Al(NO3)3·9H2O) are introduced to generate silicon-oxygen and aluminum-oxygen covalent networks, respectively. Simultaneously, low-cost epoxy resin is used as an adhesive layer between the nanoparticles and the substrate to improve the adhesion of the nanocoating.

[0034] The results show that the composite coating exhibits excellent superhydrophobicity, a high contact angle, low rolling resistance, and good mechanical stability. Simultaneously, the coating demonstrates excellent chemical and thermal stability, as well as effective self-cleaning properties. Furthermore, a sol-gel method is employed to deposit micro / nanoparticles onto the substrate surface via spraying. This method offers greater flexibility in material selection, fewer substrate limitations, and lower costs, making it suitable for large-scale industrial manufacturing. This invention not only provides a robust and wear-resistant superhydrophobic surface material but also offers a simplified manufacturing strategy for future industrial applications.

[0035] Next, the preparation method of SiO2-based bicovalent network superhydrophobic composite coating proposed in this invention will be described in detail through the following experimental methods.

[0036] 1. Experiment

[0037] 2.1. Materials

[0038] The reagents required for the experiment are shown in the table below:

[0039] Table 1 Summary of Chemicals Used in the Experiment

[0040]

[0041] Glass slides (76.2 mm × 25.4 mm × 1 mm) were used as the primary substrates for subsequent experiments. Silicon wafers, 1060 pure aluminum wafers, 6061 aluminum alloy wafers, copper wafers, and ceramic wafers were also used, all measuring 20 mm × 20 mm (≈1 mm thickness). All metal substrates were sequentially polished along the surface texture using 600-grit and 2000-grit SiC sandpaper, then ultrasonically cleaned with ethanol, and dried in a 60°C oven. Non-metallic substrates were cleaned using the same method.

[0042] 1.2 Preparation of SiO2-based superhydrophobic composite coating

[0043] First, 1 mL of TEOS was added to 5 mL of EtOH to form component A. Simultaneously, 0.36 mL of ammonia and 0.6 mL of water were added to another 5 mL of EtOH to form component B. After thoroughly mixing each component, component A was added dropwise to component B under magnetic stirring at 500 rpm. After preparing SiO2 nanoparticles, 0.1 mL of POTS, 0.4 mL of VTES, and 0.0425 g of Al(NO3)3·9H2O were added to a hydrophilic SiO2 sol. The mixture was then sonicated at 45 °C for 1 h to obtain an integrated superhydrophobic coating.

[0044] Then, epoxy resin and curing agent polyamide resin were mixed at a mass ratio of 1:1 and dissolved in ethanol. After thorough mixing, an epoxy resin solution with a concentration of 0.1 g / mL was formed. This solution was then sprayed onto the pretreated substrate at a distance of 20 cm. After initial curing at room temperature for 3 hours, the prepared superhydrophobic coating was sprayed onto the epoxy resin coating using a spray gun at a distance of 20 cm. After spraying, the prepared sample was placed in a 150°C oven overnight to allow the solvent ethanol to completely evaporate and the epoxy resin and aluminum nitrate to cure, ultimately obtaining a superhydrophobic surface with a bicovalent network, labeled F-SiO2 / VTES / AlO2. x / EP coating.

[0045] To analyze the specific effects of several different additives, we also prepared F-SiO2 coatings, F-SiO2 / VTES coatings, and F-SiO2 / VTES / AlO2 coatings. x The coatings were compared. The F-SiO2 coating was formed by spraying a hydrophobic SiO2 sol that had only undergone fluorination treatment. The F-SiO2 / VTES coating was formed by adding POTS and VTES to a hydrophilic SiO2 sol before spraying. Both coatings, after adding additives, required ultrasonic treatment at 45°C for 1 hour. After spraying, no curing was required; drying at 60°C for 1 hour was sufficient. F-SiO2 / VTES / AlO x The coating preparation process is the same as that for F-SiO2 / VTES / AlO x / EP coating, the only difference is that it does not use epoxy resin as an adhesive.

[0046] 1.3 Characterization and Testing

[0047] 1.3.1 Surface Characterization Methods

[0048] Wettability analysis method:

[0049] The contact angle and roll-off angle of the prepared surface were measured using an optical tensiometer (older model OneAttension Theta) manufactured by Biolin AG, Sweden, to characterize the wettability of the coating. A 5 μL droplet of deionized water was used for contact angle measurement, and a 10 μL droplet of deionized water was used for roll-off angle measurement.

[0050] Surface morphology analysis methods:

[0051] The surface morphology of the prepared coating was observed using a Field Emission Scanning Electron Microscope (FESEM or SEM) (model JSM-7500) provided by JEOL (Beijing) Science & Trade Co., Ltd. Accelerating voltage ranged from 0.1 to 30 kV, and magnification ranged from 25 to 1,000,000. Gold sputtering was performed before testing to improve the conductivity of the sample surface.

[0052] Elemental composition analysis methods:

[0053] The elemental composition of the prepared sample was analyzed by line scanning using the energy-dispersive spectrometry (EDS) probe built into the field emission scanning electron microscope.

[0054] Methods for analyzing chemical bond composition:

[0055] The chemical group types of the superhydrophobic coating were determined using an Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR or FTIR) instrument (Nicolet 6700) provided by Thermo Fisher Scientific, USA, to verify the surface modification results and the formation of covalent networks. The spectral range was 400–4000 cm⁻¹. -1 The spectral resolution is better than 0.09 cm⁻¹. -1 The scanning speed is no less than 65 images per second (16 cm). -1 ).

[0056] 1.3.2 Performance Testing Methods

[0057] Self-cleaning performance test method:

[0058] The self-cleaning performance was tested using dust. First, dust powder was sprinkled onto the prepared superhydrophobic surface. Then, during the self-cleaning process, deionized water was continuously dripped onto the contaminated surface, and the cleanliness of the surface was observed. Similar tests were performed on the four coatings and bare glass slides for comparison.

[0059] Mechanical stability test method:

[0060] The mechanical stability of different coated samples was verified using a sandpaper abrasion tests. The sample, with the superhydrophobic coating facing down, was placed in direct contact with 2000-grit SiC sandpaper. A 100 g weight was placed on the back of the sample, providing a pressure of 541 Pa. The sample was then dragged 10 cm along a straight line, and then moved 10 cm in the opposite direction along the same path on the sandpaper. This process was considered a wear cycle. The contact angle and roll-off angle of the coating were measured and recorded at regular intervals of wear cycles. Mechanical stability was evaluated using the wear distance, which is the maximum frictional distance the coating can withstand without losing its superhydrophobicity. SEM images of the coating after wear were observed to compare changes in the coating surface morphology.

[0061] Chemical stability testing methods:

[0062] To verify the chemical stability of the coating, the contact angle and roll-off angle of deionized water droplets at different pH values ​​(1–13) on the prepared superhydrophobic coating surface were measured. Aqueous solutions with different pH values ​​were prepared using HCl and NaOH. Furthermore, the prepared coating samples were immersed in acidic and alkaline solutions with different pH values. After a certain time interval, the sample slides were removed, washed with deionized water, dried, and then the contact angle and roll-off angle were measured and recorded using deionized water droplets to observe the effect of immersion in acidic and alkaline solutions with different pH values ​​on the wettability of the coating.

[0063] Thermal stability test method:

[0064] To verify the thermal stability of the prepared superhydrophobic coatings, samples of these coatings were placed in a muffle furnace and heated to different temperatures for 1 hour. After each annealing, the contact angle and roll-off angle of the coatings were measured and recorded using deionized water.

[0065] 2. Results and Discussion

[0066] 2.1. Wettability Analysis

[0067] The contact angle and roll-off angle of the prepared coating are as follows: Figure 2As shown in the figure, the contact angles of the bare glass sheet and the epoxy resin surface were first tested, and the values ​​were 28.62° and 71.39°, respectively. The water droplet could not roll freely, indicating that both were hydrophilic surfaces (contact angle less than 90°). The contact angle of the unmodified SiO2 coating was only about 14.65°, close to the superhydrophilic range (contact angle less than 10°). Upon contact with the coating surface, the water droplet was rapidly absorbed, spread out on the coating surface, and penetrated in all directions. This is because the accumulation of SiO2 nanoparticles forms a nano-rough structure, and the prepared SiO2 nanoparticles have hydrophilic hydroxyl groups on their surface. When the water droplet contacts the coating surface, it is in a Wenzel wetting state. This conforms to Wenzel theory, that is, roughness makes the contact angle of the hydrophilic surface smaller.

[0068] A POTS film was deposited on a glass slide by spraying a solution of POTS, water, and ethanol, followed by ultrasonic treatment for 1 h. The POTS film exhibited a contact angle of 105.53°, indicating that water droplets were hydrophobic, demonstrating the low surface energy of POTS. However, water droplets could not roll freely on this surface because there was no rough structure, preventing the formation of an air cushion beneath the droplets. In contrast, the coating sprayed from POTS-modified SiO2 nanoparticles showed superhydrophobicity, with a contact angle of 168.32° and a roll-off angle of 5.05°. Water droplets formed spherical shapes on the coating surface. This is attributed to the combined effect of the roughness generated by the accumulation of SiO2 nanoparticles and the low surface energy of the conformal POTS layer on the SiO2 particle surface.

[0069] Adding additives to the coating does not affect its superhydrophobicity, such as F-SiO2 / VTES / AlO x The / EP coating maintains a contact angle of approximately 162.83°, allowing water droplets to roll freely on the surface, demonstrating excellent superhydrophobicity. Figure 3 The SEM images show that the cavitation in the nanoscale rough structure is caused by the Si-O-Si covalent polymer and AlO2. x The crystalline filling reduces surface roughness, and the covalent bonds of the nanoparticles contribute to excellent superhydrophobicity. Generally, excessively high or low surface roughness reduces the contact angle.

[0070] 2.2. Surface morphology and chemical properties

[0071] Surface morphology analysis

[0072] The surface morphology of the prepared coating was observed using field emission scanning electron microscopy (SEM), such as... Figure 3 As shown. From Figure 3As can be seen, the SiO2 nanoparticles are all spherical and exhibit good monodispersity, consistent with previous reports. The accumulation of hydrophobic nanoparticles creates a Cassie-Baxter wetting state on the prepared surface. The average particle size was measured to be approximately 400 nm using Nano Measurer software.

[0073] By comparison Figure 3 a and Figure 3 SEM images of b revealed that simple POTS modification barely altered the surface morphology of the nanoparticles. SiO2 microspheres provided nanoscale surface roughness, allowing droplets to be supported and form air cushions, while POTS modification provided low surface energy. Together, these factors resulted in a Cassie-Baxter wetting state of the droplets on the prepared surface. However, when VTES was added, a Si-O-Si covalent network formed between the particles, such as... Figure 3 As shown in c, SiO2 nanoparticles are encapsulated by polysilsesquioxane matrix. When aluminum nitrate is added to form an Al-O-Al covalent network, comparisons show... Figure 3 c and Figure 3 As can be seen in d, some new AlO₂ particles have been added between the particles. x Crystals. Through comparison Figure 3 d and Figure 3 It can be observed that the use of epoxy resin has almost no effect on the surface morphology of the coating; only the SiO2 nanoparticles are partially embedded in the epoxy resin layer. Scanning electron microscopy (SEM) tests demonstrate the effectiveness of using a composite method to enhance mechanical stability through the coating's micro / nanostructure, providing theoretical support for the design of micro / nanostructures.

[0074] Elemental composition analysis

[0075] In addition to surface morphology and wettability, this paper also uses energy-dispersive spectroscopy (EDS) to analyze the surface elemental composition and distribution of a series of POTS-modified coatings. Figure 4 As shown, line scanning was used to analyze the SiO2 coating, F-SiO2 coating, F-SiO2 / VTES coating, and F-SiO2 / VTES / AlO2 coating, respectively. x Elemental composition of nanocomposite materials.

[0076] For the SiO2 nanocoating, elemental peaks for Si and O were observed, with an atomic ratio of 25.45:75.45, close to the theoretical value of 1:2 for SiO2 nanoparticles. This indicates that TEOS completed the hydrolysis-condensation reaction, while the slightly higher O content may be due to the presence of a certain amount of water in the SiO2 nanoparticles. Compared to SiO2, the F-SiO2 nanocoating contains additional C and F elements, with a C:F atomic ratio of 13.92:20.36, very close to the 8:13 C:F atomic ratio on the POTS molecular side chains. This indicates that POTS was successfully modified onto the surface of the silica nanoparticles, meaning the fluorocarbon long chains were successfully grafted onto the particle surface. The introduction of C and F elements lowered the surface energy, transforming the coating from superhydrophilic to superhydrophobic. Compared to the F-SiO2 coating, the F-SiO2 / VTES nanocomposite material did not introduce any new elements, and elemental peaks for Si, O, C, and F were observed. The F-SiO2 / VTES / Al ... x Then, an elemental peak of Al can also be observed. This indicates that Al(NO3)3·9H2O fully decomposes under heating conditions to form AlO. x The covalent network improves the mechanical strength of the coating. The chemical reaction equation for the decomposition of Al(NO3)3·9H2O is shown in Equation 1. The absence of N element may be due to its overflow with NO2.

[0077] 4Al(NO3)3·9H2O→2Al2O3+12NO2+3O2+36H2O (1)

[0078] Chemical bond composition analysis

[0079] Chemical bond composition analysis was performed on a series of POTS-modified coatings prepared using ATR-FTIR, such as... Figure 5 As shown. 3423 cm -1 The absorption peak at 1633 cm⁻¹ is formed by the stretching vibration of the hydroxyl group (-OH). -1 The presence of a bending vibration absorption peak (HOH) at 1100 cm⁻¹ indicates that a small amount of moisture remains within the SiO₂ particles. -1 and 456 cm -1 The two absorption peaks at 801 cm⁻¹ correspond to the stretching and bending vibrations of the Si-O-Si bond, respectively, while the peaks at 801 cm⁻¹... -1 The vibration at 957 cm⁻¹ represents the stretching vibration of the Si-O bond. -1 The absorption peak at 1243 cm⁻¹ represents the bending vibration of the Si-OH group, indicating that some unmodified hydroxyl groups (-OH) still exist on the surface of the prepared SiO₂ nanoparticles. -1 The peak represents the stretching vibration of the CF bond, indicating that the fluorocarbon long chain of POTS has been successfully grafted onto the surface of SiO2 nanoparticles. 3062 cm⁻¹ -1and 2958 cm -1 The peaks represent the asymmetric and symmetric stretching vibrations of the -CH2 group, at 1647 cm⁻¹. -1 and 750 cm -1 The peaks represent stretching vibrations of C=C and Si-C bonds, indicating that VTES was successfully introduced into the system, improving the mechanical strength of the coating. It can be seen that with the addition of different reactants, corresponding chemical groups were successfully introduced into the coating prepared in this paper, demonstrating that the introduction of these groups can reduce the surface energy of nanoparticles while improving the mechanical strength of the coating. The test results are in line with expectations.

[0080] 2.3. Self-cleaning performance analysis

[0081] The self-cleaning properties of superhydrophobic surfaces have significant practical applications, such as reducing maintenance costs for solar panels, air conditioners, and building facades by addressing particulate contamination. Figure 6 As shown, this experiment uses dust to contaminate the superhydrophobic surface.

[0082] Tilt the sample at a 10° angle and continuously drop deionized water onto the superhydrophobic surface, such as... Figure 6 As shown in Figure a, water droplets continuously carry away surface dust and powder as they roll off. The self-cleaning properties of superhydrophobic surfaces are similar to the formation of a superhydrophobic wetting state. On one hand, the superhydrophobic surface has low surface energy; on the other hand, the air cushion formed by the nanoscale rough structure of the surface provides a smaller contact area between dust particles and the superhydrophobic surface. These two factors combined result in very low adhesion between the superhydrophobic surface and dust particles, far less than the adhesion between water droplets and dust particles. Therefore, water droplets can carry away dust particles as they roll off. A schematic diagram of the self-cleaning property is shown below. Figure 6 As shown in b.

[0083] In contrast, the experiment was also conducted on bare glass slides; however, the dust and powder were wetted and remained on the glass surface, such as... Figure 6 As shown in figure a. It is worth noting that on the F-SiO2 coating surface in the figure, some of the superhydrophobic SiO2 white powder is also carried away when water droplets roll. This is because no mechanical strength enhancer is added to the coating, and the binding force between nanoparticles is low. This also indirectly confirms that the coating still has good self-cleaning properties when contaminated by hydrophobic particles.

[0084] 2.4. Coating stability and durability

[0085] Mechanical stability analysis

[0086] This article uses sandpaper polishing to analyze the mechanical stability of the coating. For example... Figure 7As shown in Figure a, the sample sheet with the coated side facing down is in direct contact with the gauze paper. A 100 g weight is placed on the back of the sample sheet. The sample sheet is moved back and forth with tweezers. The contact angle and roll-off angle of the coating are measured every certain wear cycle interval. Figure 7 The results in b show that the superhydrophobic coating modified with POTS alone is the most fragile. After 6 wear cycles, the contact angle of the coating drops below 150°, losing its superhydrophobic properties. Furthermore, water droplets can no longer roll freely on the coating surface after 6 wear cycles. When VTES is added, the coating loses its superhydrophobicity after approximately 1000 cm of wear cycles (50 wear cycles), indicating enhanced mechanical strength. Adding VTES along with aluminum nitrate increases the wear distance to approximately 2000 cm, further enhancing the coating's mechanical strength. When epoxy resin is used as an adhesive layer between the coating and the surface, the contact angle drops below 150° after 280 wear cycles, and the coating can withstand a wear distance of approximately 5600 cm. Compared to simple physical deposition, the use of an adhesive layer significantly improves the coating's mechanical strength.

[0087] Chemical stability analysis

[0088] The widespread application of superhydrophobic coatings relies heavily on their highly stable chemical properties. This paper measures the acid and alkali corrosion resistance of the prepared coating by measuring the contact angle of water droplets with different pH values ​​on the surface of the superhydrophobic coating, and by immersing it in strong acids and alkalis. Although such extreme conditions are not common in daily life, this method can effectively test the corrosion resistance of the coating.

[0089] First, measure the contact angle of water droplets with different pH values ​​on the coating, such as... Figure 8 As shown in Figure a, acidic and alkaline water droplets stained with litmus in different colors all exhibit a spherical shape. The contact angle of the water droplets at different pH values ​​is not significantly different, decreasing only in the alkaline region, but still exceeding 160°. This indicates that the acidity or alkalinity of the droplets has little effect on the wettability of the coating.

[0090] To further investigate the coating's resistance to acidic and alkaline solutions, this paper also conducted immersion experiments in acidic and alkaline solutions. From Figure 8 b shows that acidic solutions have a negative impact on the preparation of F-SiO2 / VTES / AlO2. xThe / EP composite coating showed little effect on wettability. After soaking in HCl solutions at pH=1 and pH=2 for over 30 hours, the coating maintained a contact angle exceeding 150° and a roll-off angle less than 10°, retaining its superhydrophobic properties. After soaking in NaOH solution at pH=12 for over 36 hours, the coating maintained a contact angle of 162.28° and a roll-off angle of 2.13°, continuing its superhydrophobic properties. However, after soaking in NaOH solution at pH=13 for 40 minutes, the contact angle dropped to 136.02°, and the superhydrophobic properties were lost. This phenomenon is because the coating is based on SiO2 nanoparticles, which can react with strongly alkaline substances.

[0091] Thermal stability analysis

[0092] To verify the thermal stability of the coating, repeated heating and annealing experiments were conducted on the coating in a muffle furnace. Figure 8 As shown in Figure c, below 300 ℃, the contact angle and roll-off angle of the coating do not change significantly, indicating that the wettability remains almost unchanged. However, starting from 300 ℃, the hydrophobicity of the coating begins to decrease, the contact angle drops sharply, and the coating cannot roll freely on the surface, although it still retains hydrophobicity. When the temperature reaches 400 ℃, the coating completely loses its hydrophobicity and spreads directly on the surface. This change in wettability at high temperatures may be due to the decomposition of organic matter on the SiO2 nanoparticles.

[0093] 2.5. Stability Mechanism Analysis

[0094] This paper addresses the mechanical durability issues faced by traditional superhydrophobic coatings through two strategies: self-similarity and adhesive layers. Figure 9 As shown, the self-similarity property is achieved in two ways. The first is by using VTES, which, after hydrolysis and condensation, forms a three-dimensional covalent network—a polysilsesquioxane network—between SiO2 nanoparticles through cross-linking. A similar method is vapor deposition, which can directly form nanoparticles cross-linked by Si-O-Si bonds, but this method is costly and has limited scalability. The second method uses aluminum nitrate, which decomposes into Al2O3 (AlO2) under heating conditions. x The covalent network, besides acting as a framework to hold the particles in place, also supports the coating. Epoxy resin, as an adhesive layer, enhances the adhesion between the coating and the substrate. Simultaneously, as an elastomer, epoxy resin can also reduce the peak stress generated during sandpaper abrasion to some extent.

[0095] 2.6. Basis Universality Analysis

[0096] In addition to glass slides, this paper also used several other types of solid materials as substrates to verify the generalizability of the coating. As shown in Figure 10, the same treatment was performed on surfaces such as aluminum, aluminum alloys, silicon, pure copper, and ceramics. The test results showed that the prepared coating exhibited good superhydrophobic properties on these types of substrates, with a contact angle exceeding 165° and a roll-off angle of approximately 2-3°.

[0097] 3. Conclusion

[0098] In summary, we have successfully developed a fluorinated silica-based bicovalent network superhydrophobic composite coating with excellent mechanical, chemical, and thermal stability. Silica nanoparticles were prepared using the Stöber method and modified with POTS, VTES, and aluminum nitrate to prepare the superhydrophobic coating. This superhydrophobic composite coating was constructed by spraying it onto an epoxy resin-treated substrate, exhibiting a contact angle exceeding 165° and a roll-off angle of approximately 2–3°, demonstrating excellent superhydrophobicity. The epoxy resin serves as the binder layer under the composite coating, while VTES and aluminum nitrate form Si-O-Si and AlO-Si layers, respectively. x The network, working together, ensures the mechanical and chemical stability of the coating, enabling it to withstand 541 Pa of pressure on 2000-grit sandpaper for over 5600 cm of wear, and maintain its superhydrophobicity even after immersion in acidic or alkaline solutions for tens of hours. Furthermore, its self-cleaning properties, anti-fouling properties, substrate universality, and heat resistance up to 300°C further enhance its practicality. This work not only provides a robust and wear-resistant superhydrophobic surface material but also offers a new strategy for the design of superhydrophobic coatings.

[0099] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a SiO2-based bicovalent network superhydrophobic composite coating, characterized in that, Includes the following steps: S1. Tetraethoxysilane is added to ethanol to form component A, while ammonia and water are added to another ethanol to form component B. After each component is thoroughly mixed, component A is added dropwise to component B under magnetic stirring at 500 rpm to prepare a hydrophilic SiO2 sol. S2. Perfluorooctyltriethoxysilane, vinyltriethoxysilane and aluminum nitrate nonahydrate are added to hydrophilic SiO2 sol, and then ultrasonic treatment is performed to obtain an integrated superhydrophobic coating. S3. Then, the epoxy resin and the curing agent polyamide resin are mixed and dissolved in ethanol. After mixing evenly, a solution with an epoxy resin concentration of 0.1 g / mL is formed. Then, it is sprayed on the pretreated substrate at a spraying distance of 20 cm. After initial curing at room temperature, an epoxy resin coating is obtained. S4. Using a spray gun, spray the prepared superhydrophobic coating onto the epoxy resin coating from a distance of 20cm. After spraying, place the prepared sample in a 150℃ oven overnight to allow the solvent ethanol to completely evaporate and the epoxy resin and aluminum nitrate to cure, ultimately obtaining a superhydrophobic surface with a bicovalent network, labeled F-SiO2 / VTES / AlO2. x / EP coating.

2. The method for preparing a SiO2-based bicovalent network superhydrophobic composite coating according to claim 1, characterized in that, In step S1, component A contains 1 mL of tetraethoxysilane and 5 mL of ethanol; component B contains 0.36 mL of ammonia, 0.6 mL of water, and 5 mL of ethanol.

3. The method for preparing a SiO2-based bicovalent network superhydrophobic composite coating according to claim 1, characterized in that, In step S2, the amount of perfluorooctyltriethoxysilane used is 0.1 mL, the amount of vinyltriethoxysilane used is 0.4 mL, the amount of aluminum nitrate nonahydrate used is 0.0425 g, and the ultrasonic treatment temperature is 45℃ for 1 h.

4. The method for preparing a SiO2-based bicovalent network superhydrophobic composite coating according to claim 1, characterized in that, In step S3, epoxy resin and curing agent polyamide resin are mixed at a mass ratio of 1:1, and the initial curing time at room temperature after spraying is 3 hours.

5. The method for preparing a SiO2-based bicovalent network superhydrophobic composite coating according to claim 1, characterized in that, The substrate is made of one of the following: glass slide, silicon wafer, 1060 pure aluminum sheet, 6061 aluminum alloy sheet, copper sheet, and ceramic sheet. Metal substrates are polished sequentially with 600-grit and 2000-grit SiC sandpaper along the surface texture direction, then ultrasonically cleaned with ethanol, and dried in an oven at 60°C. Non-metallic substrates only require ultrasonic cleaning with ethanol.

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