A method for preparing a fluorine-free superhydrophobic coating
By using a modified nanopowder spraying method to prepare a fluorine-free superhydrophobic coating, the problems of insufficient rough structure construction and poor functional synergy in the prior art are solved. This results in a coating with high water contact angle, low roll-off angle, excellent anti-icing performance, self-cleaning and good thermal stability. It is suitable for a variety of substrates, low in cost, and easy to apply on a large scale.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HEFEI UNIV OF TECH
- Filing Date
- 2026-04-27
- Publication Date
- 2026-06-09
AI Technical Summary
Existing fluorine-free superhydrophobic coatings suffer from problems such as insufficient rough structure construction, poor functional synergy, and complex or high-cost preparation processes, making it difficult to achieve high water contact angle, low roll-off angle, excellent anti-icing performance, self-cleaning ability, and good thermal stability.
Using stearic acid-modified zinc oxide nanopowder (ZnO@STA) and hexadecyltrimethoxysilane-modified titanium dioxide nanopowder (TiO2@HDTMS) as raw materials, a fluorine-free superhydrophobic coating with a micro-nano composite structure is formed on the substrate surface through a high-atomization spraying method. An air cushion layer is formed on the coating surface to achieve superhydrophobic properties, and a stable Cassie-Baxter state is constructed through particle size differences.
A fluorine-free superhydrophobic coating with a static contact angle as high as 156.7° and a roll-off angle as low as 3.6° was prepared. It has excellent anti-icing performance, self-cleaning ability and good thermal stability. It is suitable for a variety of substrates, has low cost and is easy to apply on a large scale.
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Figure CN122168160A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of hydrophobic coatings, specifically relating to a method for preparing a fluorine-free superhydrophobic coating. Background Technology
[0002] Icing, frosting, and surface contamination are widespread problems in power, transportation, aviation, and photovoltaic industries, easily causing equipment failure, efficiency reduction, and safety hazards. Superhydrophobic coatings, due to their high water contact angle, low roll-off angle, and low solid-liquid adhesion, can achieve passive anti-icing, delayed frosting, and self-cleaning functions, becoming an important technological direction for surface functional protection. Traditional superhydrophobic coatings mostly rely on fluorides to achieve low surface energy, which suffers from high cost, environmental unfriendliness, and biotoxicity, limiting their large-scale application. At the same time, most superhydrophobic coatings suffer from insufficient roughness construction, single composition, and poor structural stability, making it difficult to simultaneously achieve excellent superhydrophobicity, anti-icing, self-cleaning, and thermal stability. In recent years, researchers have attempted to construct fluorine-free superhydrophobic coatings by compositing inorganic nanoparticles (such as SiO2, ZnO, TiO2) with low surface energy organic materials. For example, surface modification of nanoparticles using stearic acid or silane coupling agents can improve their hydrophobic properties to some extent. However, existing fluorine-free systems still have the following shortcomings:
[0003] 1. Insufficient construction of rough structure: Most systems rely on nanoparticles of a single size, making it difficult to form multi-scale micro-nano composite structures. This leads to instability of the Cassie-Baxter state, making it difficult to maintain the water contact angle above 150° and the roll-off angle is also relatively large.
[0004] 2. Poor functional synergy: Existing coatings often only focus on hydrophobicity, neglecting the synergistic optimization of anti-icing performance, self-cleaning performance, and thermal stability. Especially in low-temperature and high-humidity environments, hydrophobic performance is easily degraded, and the effect of delaying icing is limited.
[0005] 3. Complex preparation process or high cost: Although some fluorine-free superhydrophobic coatings have good performance, the preparation process involves multiple reactions, high temperature treatment or special equipment, which is not conducive to large-scale promotion.
[0006] Therefore, developing a fluorine-free, environmentally friendly, easy-to-prepare, and high-performance superhydrophobic coating that achieves high water contact angle (>150°), low roll-off angle (<10°), excellent anti-icing properties, self-cleaning ability, good thermal stability, and strong substrate adhesion is of great significance for meeting the surface protection needs of industrial scenarios. Summary of the Invention
[0007] To address the shortcomings of the prior art, this invention provides a method for preparing a fluorine-free superhydrophobic coating.
[0008] The method for preparing the fluorine-free superhydrophobic coating of the present invention includes the following steps:
[0009] Step 1: Place the substrate in deionized water, acetone and anhydrous ethanol in sequence for ultrasonic cleaning for 15 min each, and dry it with nitrogen gas for later use.
[0010] Step 2: Add 0.75g of stearic acid-modified zinc oxide nanopowder (ZnO@STA) and 0.25g of hexadecyltrimethoxysilane-modified titanium dioxide nanopowder (TiO2@HDTMS) to 10 mL of cyclohexane, then add 1g of polydimethylsiloxane (PDMS) and 0.1g of the matching curing agent. Disperse the mixture ultrasonically at room temperature for 0.5 h and stir magnetically for 2 h to obtain a fluorine-free superhydrophobic coating.
[0011] Step 3: Use a high-atomization spray gun to evenly spray the fluorine-free superhydrophobic coating onto the substrate surface. The spraying pressure is 0.2~0.4 MPa and the spraying distance is 15~25 cm. Place the sprayed sample in a 100℃ oven to cure for 2 h to obtain the fluorine-free superhydrophobic coating.
[0012] In step 1, the substrate includes glass, alumina ceramic, Q235 steel, wood, or glass fiber.
[0013] In step 2, the stearic acid-modified zinc oxide nanopowder is prepared by the following method:
[0014] 4 g of ZnO nanoparticles with a particle size of 50 nm were dispersed in 20 mL of anhydrous ethanol, 4 g of stearic acid were added, the mixture was magnetically stirred at room temperature for 3 h, dried at 75 °C for 5 h, and then ground to obtain the final product.
[0015] In step 2, the hexadecyltrimethoxysilane-modified titanium dioxide nanopowder is prepared by the following method:
[0016] 4 g of TiO2 nanoparticles with a particle size of 5-10 nm were dispersed in 20 mL of anhydrous ethanol, 1 g of hexadecyltrimethoxysilane was added, the mixture was stirred at room temperature for 3 h, dried at 75 °C for 5 h, and then ground to obtain the final product.
[0017] Furthermore, the mass ratio of ZnO@STA to TiO2@HDTMS is 1:3 to 3:1, preferably 3:1. This ratio provides the best hydrophobic properties for the coating, with a water contact angle of up to 156.7°.
[0018] In step 3, the spray gun is a butterfly-shaped high-atomization spray gun with a nozzle diameter of 0.8 mm. Furthermore, the coating method includes, but is not limited to, spraying, brushing, and spin coating, and can be flexibly selected according to the shape of the substrate.
[0019] The beneficial effects of this invention are reflected in:
[0020] This invention uses stearic acid-modified zinc oxide nanopowder (ZnO@STA) and hexadecyltrimethoxysilane-modified titanium dioxide nanopowder (TiO2@HDTMS) as raw materials to prepare a stable fluorine-free composite superhydrophobic material. Using this material, a fluorine-free superhydrophobic coating with excellent superhydrophobic properties and outstanding anti-icing performance can be prepared. Moreover, the preparation process does not involve corrosive chemical raw materials, thus controlling the preparation cost. Furthermore, it can be coated by spraying, which is beneficial for large-scale application.
[0021] This invention utilizes modified nanoparticles of different particle sizes to achieve a coating with higher surface roughness, a static contact angle as high as 156.7°, and a roll-off angle as low as 3.6°, which can greatly delay the freezing time of droplets on the coating surface.
[0022] Compared with general superhydrophobic coatings, the present invention has excellent anti-icing performance. At -20℃, the time for water droplets to freeze completely is extended to 226s, which is 182s longer than bare glass, and the delayed freezing rate is as high as 413.6%.
[0023] The coating preparation method of this invention does not involve the use of corrosive chemical reagents such as acids, alkalis, and salts, and the preparation process is safe and environmentally friendly. This invention uses a spraying method to prepare the coating, which is suitable for various substrate surfaces, and is low in cost, making it easy to apply on a large scale. Attached Figure Description
[0024] Figure 1 These are photos comparing the wetting properties of the nanopowder before and after modification.
[0025] Figure 2 SEM images of the fluorine-free superhydrophobic coating obtained in Example 1 at different magnifications.
[0026] Figure 3 The images show the wetting properties and 3D morphology of the fluorine-free superhydrophobic coating prepared in Example 1.
[0027] Figure 4 The image shows the "silver mirror phenomenon" observed when the fluorine-free superhydrophobic coating prepared in Example 1 is immersed in water.
[0028] Figure 5 The image shows the process of water droplets freezing on the surface of the fluorine-free superhydrophobic coating prepared in Example 1 and its comparison with bare glass.
[0029] Figure 6 Photographs showing the self-cleaning performance of the fluorine-free superhydrophobic coating prepared in Example 1.
[0030] Figure 7 The thermogravimetric analysis curve of the fluorine-free superhydrophobic coating prepared in Example 1 is shown.
[0031] Figure 8The image shows a comparison of the WCA of the coatings obtained in Example 1 and Comparative Examples 1, 2, and 3.
[0032] Figure 9 The frosting rate of bare glass and ZTSC1-ZTSC5 after being placed on a cooling platform at -20°C for 15 minutes in Example 2.
[0033] Figure 10 The contact angle (WCA) is for ZTSC1-ZTSC5 in Example 2. Detailed Implementation
[0034] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.
[0035] Unless otherwise specified, the raw materials, reagents or devices used in the following embodiments can be obtained from conventional commercial sources or by existing known methods; unless otherwise specified, the methods used in the embodiments of the present invention are methods mastered by those skilled in the art.
[0036] Zinc oxide (ZnO) nanoparticles, with an average particle size of 50 nm, were purchased from Shanghai Maclean Biotechnology Co., Ltd.; titanium dioxide (TiO2) nanoparticles, with an average particle size of 5-10 nm, were purchased from Shanghai Aladdin Biotechnology Co., Ltd.; stearic acid (STA), analytical grade, was purchased from Shanghai Maclean Biotechnology Co., Ltd.; hexadecyltrimethoxysilane (HDTMS), analytical grade, was purchased from Shanghai Aladdin Biotechnology Co., Ltd.; polydimethylsiloxane (PDMS), brand name Dow SYLGARD 184, was purchased from Dow Chemical; methyl vinylcyclosiloxane was purchased from Dow Corning, Midland, Michigan, USA.
[0037] Example 1: Preparation of a fluorine-free superhydrophobic coating
[0038] (1) Preparation of modified ZnO powder: 4g of ZnO nanopowder was dispersed in 20mL of anhydrous ethanol, 4g of stearic acid was added, stirred at room temperature for 3h, dried at 75℃ for 5h, and ground to obtain ZnO@STA powder.
[0039] (2) Preparation of modified TiO2 powder: 4g of TiO2 nanopowder was dispersed in 20mL of anhydrous ethanol, 1g of HDTMS was added, stirred at room temperature for 3h, dried at 75℃ for 5h, and then ground to obtain TiO2@HDTMS powder.
[0040] (3) Take 0.75g ZnO@STA powder and 0.25g TiO2@HDTMS powder in a beaker, add 10 mL cyclohexane, then add 1 g PDMS and 0.1 g matching curing agent methyl vinyl cyclosiloxane, ultrasonically disperse at room temperature for 0.5 h, and magnetically stir for 2 h to obtain fluorine-free superhydrophobic coating.
[0041] (4) Use a 0.8mm diameter atomizing spray gun to spray the fluorine-free superhydrophobic coating evenly onto the substrate surface. The spraying air pressure is 0.3MPa and the spraying distance is 20cm. Finally, place it in an oven at 100℃ for 2h to cure and obtain the fluorine-free superhydrophobic coating.
[0042] The SEM image of the fluorine-free superhydrophobic coating prepared in this embodiment is as follows: Figure 2 As shown, the coating surface is very rough, forming a micro-nano composite structure. This structure can trap air and form an air cushion layer, which is the source of the coating's superhydrophobic properties.
[0043] Figure 3 The 3D morphology and wetting performance test diagram of the high-adhesion fluorine-free superhydrophobic coating prepared in this embodiment are shown. Its surface roughness reaches 48.33 μm, WCA is about 156.7°, and WSA is about 3.6°.
[0044] Figure 4 The "silver mirror phenomenon" of the high-adhesion fluorine-free superhydrophobic coating prepared in this embodiment when immersed in water is demonstrated, proving that a stable air cushion layer is formed on its surface.
[0045] Figure 5 This study demonstrates the passive anti-icing performance of the high-adhesion, fluorine-free superhydrophobic coating prepared in this embodiment. The coating was placed on a -20°C cooling platform, and a 10 μL droplet was placed on it. Photographs and freezing times of the droplet were recorded. Using bare glass as a control group, the droplet on the bare glass surface exhibited a diffused pattern and completely froze at 44 seconds; while the droplet on the coated surface was spherical and completely froze at 226 seconds, representing a significant 413.6% increase in freezing time compared to the bare glass.
[0046] Figure 6 The self-cleaning performance of the high-adhesion fluorine-free superhydrophobic coating prepared in this embodiment is demonstrated. It can be seen that dust and contaminants on the coating surface are easily carried away by the rolling droplets.
[0047] Figure 7 The thermogravimetric analysis curves of the high-adhesion fluorine-free superhydrophobic coating prepared in this embodiment are shown. The coating remains stable below 200°C with a weight loss rate of less than 2%, indicating that it has good thermal stability.
[0048] Example 2: Optimization of the ratio of ZnO@STA to TiO2@HDTMS
[0049] Following the method of Example 1, only the ratio of ZnO@STA to TiO2@HDTMS was adjusted to investigate the effect of the change in the ratio on the coating performance. The setting of the ZnO@STA to TiO2@HDTMS ratio is shown in Table 1 below.
[0050]
[0051] The frosting rate and contact angle of the prepared coatings were investigated separately. Figure 9 and Figure 10 The test results show that the mixing ratio of ZnO@STA to TiO2@HDTMS has a significant impact on the hydrophobic and anti-frost properties of the coating.
[0052] Figure 9 The frosting rates of bare glass and ZTSC1-ZTSC5 coatings were measured after being placed on a -20°C cooling platform for 15 minutes. After 15 minutes at -20°C, the frosting rates of all coatings were lower than those of the bare glass, demonstrating that the coatings of this invention have good passive anti-icing / anti-frost capabilities. Among them, the coating with the ZTSC4 formulation had the lowest frosting rate (2.725 mg / cm³). 2 It exhibits the best anti-smoothing effect.
[0053] Figure 10 The contact angles (WCA) for ZTSC1-ZTSC5 are shown. With increasing ZnO@STA content, the static contact angle (WCA) of the coating initially increases and then decreases. When the mass ratio of ZnO@STA to TiO2@HDTMS is 3:1 (i.e., ZTSC4), the coating exhibits optimal superhydrophobic properties, with the contact angle reaching its peak. This indicates that the larger ZnO@STA particles and the smaller TiO2@HDTMS particles work synergistically to construct a micro / nano composite rough structure most conducive to the formation of the Cassie-Baxter state.
[0054] In summary, by adjusting the mass ratio of the two modified nanopowders, the hydrophobic and anti-frost properties of the coating can be synergistically optimized. Experimental data fully demonstrate that when the mass ratio of ZnO@STA to TiO2@HDTMS is 3:1, the coating achieves the best overall surface protection performance.
[0055] Comparative Example 1:
[0056] The coating in this comparative example was prepared using the same method as in Example 1, except that in step (3), only 1g of ZnO@STA powder was used, and TiO2@HDTMS powder was not used.
[0057] The coating prepared in this comparative example was tested according to the test method in Example 1, and the WCA of the coating was found to be 146.4°.
[0058] Comparative Example 2:
[0059] The coating in this comparative example was prepared using the same method as in Example 1, except that in step (3), only 1g of TiO2@HDTMS powder was used, and ZnO@STA powder was not used.
[0060] The coating prepared in this comparative example was tested according to the test method in Example 1, and the WCA of the coating was found to be 103.2°.
[0061] Comparative Example 3:
[0062] The coating in this comparative example was prepared using the same method as in Example 1, except that in step (3), the ZnO and TiO2 powders were not modified, and 0.75g of unmodified ZnO and 0.25g of TiO2 nanopowder were used directly.
[0063] The coating prepared in this comparative example was tested according to the test method in Example 1. It was found that the coating prepared in this comparative example did not have superhydrophobic properties, and the WCA was only 101.9°.
[0064] in conclusion:
[0065] By comparing Comparative Examples 1 and 2 with Example 1, it can be concluded that it is difficult to construct a micro / nano composite structure with sufficient three-dimensional roughness using ZnO@STA or TiO2@HDTMS powder alone, and thus impossible to achieve a stable superhydrophobic state. By combining the two modified powders, the synergistic effect of ZnO@STA (larger particle size) and TiO2@HDTMS (smaller particle size) can be utilized to construct an ideal micro / nano surface morphology with high roughness, thereby achieving excellent superhydrophobic properties.
[0066] By comparing Comparative Example 3 with Example 1, it can be concluded that the unmodified nanopowder does not possess hydrophobic properties and cannot be used to prepare superhydrophobic coatings.
[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for preparing a fluorine-free superhydrophobic coating, characterized in that... Includes the following steps: Step 1: Place the substrate in deionized water, acetone, and anhydrous ethanol in sequence for ultrasonic cleaning, and then dry it with nitrogen gas for later use. Step 2: Add modified zinc oxide nanopowder and modified titanium dioxide nanopowder to cyclohexane, then add polydimethylsiloxane and matching curing agent, disperse evenly to obtain fluorine-free superhydrophobic coating; Step 3: Use a high-atomization spray gun to evenly spray the fluorine-free superhydrophobic coating onto the substrate surface. The spraying pressure is 0.2~0.4MPa and the spraying distance is 15~25 cm. Place the sprayed sample in a 100℃ oven to cure for 2 hours to obtain the fluorine-free superhydrophobic coating.
2. The preparation method according to claim 1, characterized in that: In step 1, the substrate includes glass, alumina ceramic, Q235 steel, wood, or glass fiber.
3. The preparation method according to claim 1, characterized in that: In step 2, the modified zinc oxide nanopowder is stearic acid modified zinc oxide nanopowder.
4. The preparation method according to claim 3, characterized in that: The stearic acid-modified zinc oxide nanopowder was prepared by the following method: ZnO nanoparticles with a particle size of 50 nm were dispersed in anhydrous ethanol, stearic acid was added, the mixture was stirred at room temperature, dried and ground.
5. The preparation method according to claim 4, characterized in that: The mass ratio of ZnO nanopowder to stearic acid is 1:
1.
6. The preparation method according to claim 1, characterized in that: In step 2, the modified titanium dioxide nanopowder is hexadecyltrimethoxysilane modified titanium dioxide nanopowder.
7. The preparation method according to claim 6, characterized in that: The hexadecyltrimethoxysilane-modified titanium dioxide nanopowder was prepared by the following method: TiO2 nanoparticles with a particle size of 5-10 nm were dispersed in anhydrous ethanol, hexadecyltrimethoxysilane was added, stirred at room temperature, dried and ground.
8. The preparation method according to claim 7, characterized in that: The mass ratio of TiO2 nanopowder to hexadecyltrimethoxysilane is 4:
1.
9. The preparation method according to claim 1, characterized in that: The mass ratio of the modified zinc oxide nanopowder to the modified titanium dioxide nanopowder is 1:3 to 3:1.