A passive radiative cooling super-hydrophobic composite film based on a bionic water strider leg structure and a preparation method and application thereof

Abstract

The application discloses a kind of passive radiative cooling super-hydrophobic composite film based on bionic water strider leg structure and its preparation method and application, belong to functional material technical field, including the following steps: the template with micron-level conical hole is soaked using the alcohol solution of silane, P(VDF-HFP) mixed colloid is evenly spread on template after, through phase separation process, solidification, i.e. the passive radiative cooling super-hydrophobic composite film described;0.5wt.% Including nano-aluminum oxide powder and nano-hydroxyapatite powder in the P(VDF-HFP) mixed colloid.The application is based on bionic water strider leg structure, simultaneously combining P(VDF-HFP) mixture containing nano-aluminum oxide and nano-hydroxyapatite, obtain composite film with super-hydrophobic performance, anti-icing performance and passive refrigeration effect.The composite film obtained by the application can be applied to passive radiative cooling, surface protection, self-cleaning surface, deicing and ice prevention and other fields, can effectively improve the passive radiative refrigeration capacity in polluted environment, enhance the overall energy efficiency and sustainability of system in low-temperature environment.With lower cost and better effect, energy saving and cooling effect is achieved.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, and in particular relates to a passive radiation cooling superhydrophobic composite thin film based on a biomimetic water strider leg structure, its preparation method and application. Background Technology

[0002] With global warming and the energy crisis becoming increasingly severe, the high energy consumption of traditional refrigeration technologies is becoming more prominent, while human technological progress and industrial capacity have significantly improved. However, these advancements have also brought adverse factors, such as the global greenhouse effect and the energy crisis. Therefore, cooling is becoming increasingly important for human life. Passive daytime radiative cooling (PDRC) utilizes the huge temperature difference between the Earth (~300 K) and outer space (~3 K) to transfer excess heat to the cold outer space through thermal radiation, thus achieving passive cooling. Passive radiative cooling (PRC) has attracted much attention as a zero-energy passive cooling technology (Science). However, the accumulation of dust, rainwater, and other contaminants on the surface of outdoor cooling materials can reduce their optical performance, ultimately leading to severe damage to their solar reflectivity. Therefore, developing self-cleaning PDRC materials is the first step in advancing radiative cooling applications in outdoor settings.

[0003] Superhydrophobic materials, due to their unique surface properties, have demonstrated significant application value and broad development prospects in numerous fields. In recent years, inspired by natural plants such as lotus leaves, superhydrophobic surfaces have gradually come into focus. These are special surfaces with a water contact angle (WCA) greater than 150° and a sliding angle (SA) less than 10°, finding wide applications in self-cleaning, corrosion prevention, oil-water separation, and mist collection. For example, in the field of self-cleaning glass, superhydrophobic coatings endow glass surfaces with excellent self-cleaning capabilities. When rainwater or dust falls on glass with a superhydrophobic coating, due to the large contact angle and small roll-off angle between the superhydrophobic surface and water, water droplets can quickly roll off and carry away surface dust particles, achieving self-cleaning of the glass. This greatly reduces the frequency and cost of manual cleaning, improves the light transmittance and aesthetics of the glass, and is widely used in building curtain walls, automotive glass, and other applications.

[0004] Furthermore, the unique micro-nano structure of the superhydrophobic surface has the ability to trap air and form an air layer that can bounce off impacted or condensed water droplets before freezing. As raindrops roll on the surface, they pick up and carry away dust and other contaminants, thus ensuring the long-term optical function of PDRC materials in outdoor environments (Bioinspired Superhydrophobic All-In-One Coating for Adaptive Thermoregulation, Advanced Materials).

[0005] However, in existing technologies, the practical application of radiation cooling materials remains limited by their complex manufacturing processes and poor durability. Furthermore, when most coatings are exposed to the natural environment, their surfaces are inevitably affected by environmental factors such as dust accumulation, rainwater erosion, and microbial growth. These contaminants significantly degrade their surface optical properties, leading to a decline in cooling performance. Therefore, integrating self-cleaning capabilities into radiation cooling coatings is crucial for improving their long-term reliability in real-world outdoor environments. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a passive radiation cooling superhydrophobic composite thin film based on a biomimetic water strider leg structure, its preparation method, and its application.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing a passively radiatively cooled superhydrophobic composite thin film based on a biomimetic water strider leg structure includes the following steps:

[0009] After soaking a template with micron-sized conical pores in an alcohol solution of silane, a P(VDF-HFP) poly(vinylidene fluoride-hexafluoropropylene) copolymer mixture is uniformly spread on the template. After phase separation and curing, the passive radiation cooling superhydrophobic composite film is obtained.

[0010] The P(VDF-HFP) mixed colloid includes 0.5 wt.% nano-alumina powder and 0.5 wt.% nano-hydroxyapatite powder.

[0011] Beneficial Effects: The surface of a water strider's leg is covered with thousands of bristles arranged regularly in the same direction. These bristles further form a spiral-shaped nanoscale groove structure. This dual-scale structure effectively adsorbs air to form a stable gas film, resulting in a water contact angle exceeding 150° and producing a superhydrophobic effect. Simultaneously, this structure can support a load 15 times its own weight without being damaged by water flow fluctuations. This invention, by employing a template with micron-sized conical pores, mimics the microstructure of a water strider's leg, endowing the composite film with superhydrophobic properties. This results in an extremely low surface energy, allowing water droplets to easily roll off, effectively preventing moisture adhesion and wetting, and improving the film's stability and lifespan in humid environments. Furthermore, this microstructure helps enhance the film's scattering and reflection of sunlight, reducing heat absorption and providing a structural basis for passive radiative cooling. Furthermore, the nano-alumina powder and nano-hydroxyapatite powder added to the P(VDF-HFP) mixed colloid can synergistically optimize the optical and thermal properties of the film, enhance the passive radiation cooling effect, and help improve the mechanical strength and wear resistance of the film.

[0012] Preferably, the size of the micron-scale conical aperture is 20-30 micrometers.

[0013] Beneficial effects: The micron-scale conical pores in this size range can accurately mimic the microstructural features of water strider legs, enabling the composite film to achieve optimal superhydrophobic properties, maximizing the contact angle between water droplets and the film surface, minimizing the roll-off angle, achieving efficient self-cleaning and moisture-proof functions, while significantly improving passive radiative cooling efficiency.

[0014] Preferably, the volume concentration of the silane alcohol solution is 0.1-2%, and the silane includes one of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, trifluoropropyltrimethoxysilane, and perfluorobutylethyltrimethoxysilane.

[0015] Beneficial effects: This silane solution can form a uniform low surface energy molecular layer on the template surface. In subsequent preparation processes, this molecular layer helps the P(VDF-HFP) mixed colloid to spread and demold better on the template, while giving the composite film surface a lower surface energy, further enhancing the superhydrophobic properties, and enabling the film to maintain good waterproof and self-cleaning effects in various complex environments.

[0016] Preferably, the preparation method of the P(VDF-HFP) mixed colloid includes the following steps:

[0017] P(VDF-HFP) powder is dissolved in a mixed solvent of acetone and water, and then nano-alumina powder and nano-hydroxyapatite powder are added and stirred evenly to obtain the P(VDF-HFP) mixed colloid.

[0018] Preferably, the mass ratio of the nano-alumina powder to the nano-hydroxyapatite powder is 1:1.

[0019] Beneficial effects: Nano-alumina powder possesses high thermal conductivity and excellent optical properties, which helps to rapidly conduct heat away from the film and modulate the film's absorption and reflection characteristics for different wavelengths of light. Nano-hydroxyapatite powder, on the other hand, has a unique crystal structure and chemical properties, which can enhance the film's ability to exchange heat with the surrounding environment through radiation, while also improving the film's biocompatibility and chemical stability. By rationally controlling the mass ratio of the two, the composite film can achieve an optimal balance in terms of passive radiative cooling performance, mechanical properties, and chemical stability.

[0020] Preferably, the mass ratio of the P(VDF-HFP) powder, acetone, and water is 1:10:1.

[0021] The above raw materials are commonly used in P(VDF-HFP) films. They can fully cure the P(VDF-HFP) mixed colloid under relatively mild conditions (such as the curing temperature and time mentioned later), forming a composite film with stable performance and moderate mechanical strength. Using these film raw materials makes the preparation process easy to operate, while ensuring that the final product has excellent comprehensive performance, meeting the application requirements of passive radiation cooling superhydrophobic composite films.

[0022] Preferably, the stirring temperature is 60°C and the stirring time is 6 hours.

[0023] Preferably, the curing temperature is 30°C and the curing time is 4 hours.

[0024] Beneficial effects: Under the above conditions, the chemical reaction in the P(VDF-HFP) mixed colloid can proceed fully and appropriately. Appropriate curing conditions avoid problems such as excessive internal stress and brittleness of the film caused by excessively high temperature or time, as well as defects such as incomplete curing and unstable performance caused by excessively low temperature or time, thus ensuring the stability and reliability of the composite film quality.

[0025] The present invention also discloses a passive radiation cooling superhydrophobic composite film based on a biomimetic water strider leg structure prepared by the above preparation method.

[0026] Beneficial Effects: The composite film provided by this invention combines the superhydrophobic properties of a biomimetic water strider leg structure with passive radiative cooling functionality, exhibiting unique performance advantages. Its superhydrophobic surface effectively prevents the adhesion of moisture, dust, and other contaminants, achieving self-cleaning and reducing manual maintenance costs. Simultaneously, its excellent passive radiative cooling performance makes it suitable for various cooling scenarios, helping to improve energy efficiency and reduce energy consumption. Furthermore, the film's good mechanical properties and chemical stability ensure its long-term reliability under different environmental conditions.

[0027] This invention also discloses the application of a passive radiation cooling superhydrophobic composite film based on a biomimetic water strider leg structure in passive radiation cooling, surface protection, surface self-cleaning, or de-icing and anti-icing.

[0028] Compared with the prior art, the present invention has the following advantages and technical effects:

[0029] This invention provides a passive radiative cooling superhydrophobic composite thin film based on a biomimetic water strider leg structure, its preparation method, and its applications. Based on this biomimetic water strider leg structure, and combined with a PDMS mixture containing nano-alumina and nano-hydroxyapatite, a composite thin film with superhydrophobic properties and passive cooling effect is obtained. The composite thin film obtained by this invention can be applied to passive radiative cooling, surface protection, self-cleaning surfaces, de-icing and anti-icing, etc., effectively improving passive radiative cooling capacity and achieving energy-saving and cooling effects at a lower cost and with better results. Attached Figure Description

[0030] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0031] Figure 1 This is a schematic diagram of the preparation process of the passive radiation cooling superhydrophobic composite film based on the biomimetic water strider leg structure of the present invention;

[0032] Figure 2 (a) and (b) show the microstructure of the water strider's legs at different magnifications; (c) is an energy dispersive spectroscopy (EDS) image of the water strider's legs.

[0033] Figure 3(a) is a scanning electron microscope (SEM) image of the composite film obtained in Example 1, top view; (b) is an enlarged top view of the SEM image of the composite film obtained in Example 1; (c) is an oblique view of the SEM image of the composite film obtained in Example 1; (d) is an enlarged side view of the SEM image of the composite film obtained in Example 1; (e) is a side view of the SEM image of the bottom cross section of the composite film obtained in Example 1; (f) is an enlarged side view of the SEM image of the cross section of the composite film obtained in Example 1.

[0034] Figure 4 (a) shows a schematic diagram and data of sunlight reflection on the surface of the composite film obtained in Comparative Example 1; (b) shows a schematic diagram and data of sunlight reflection on the surface of the composite film obtained in Comparative Example 2; and (c) shows a schematic diagram and data of sunlight reflection on the surface of the composite film obtained in Example 1.

[0035] Figure 5 (a) shows the mechanism by which the water strider's legs achieve superhydrophobicity; (b) shows the contact angle of water droplets on the surface of the water strider's legs, the biomimetic composite film obtained in Example 1, and the composite film obtained in Comparative Example 1; (c) shows the impact behavior of water droplets on the surface of the water strider's legs, the biomimetic composite film obtained in Example 1, and the composite film obtained in Comparative Example 1.

[0036] Figure 6 (a) shows the rolling angle test process of water droplets on the surface of a water strider's leg; (b) shows the rolling angle test process of water droplets on the surface of the composite film obtained in Comparative Example 1; (c) shows the rolling angle test process of water droplets on the surface of the biomimetic composite film obtained in Example 1; (d) shows the self-cleaning effect test of water droplets on the surface of the composite film obtained in Comparative Example 2; (e) shows the self-cleaning effect test of water droplets on the surface of the biomimetic composite film obtained in Comparative Example 3.

[0037] Figure 7 (a) shows the icing of water droplets on the biomimetic composite film obtained in Example 1; (b) shows the icing of water droplets on the surface of the composite film obtained in Comparative Example 1.

[0038] Figure 8 (a) shows the effect of tape adhesion test on the contact angle of water droplets on the composite film obtained in Example 1; (b) shows the effect of sand impact on the contact angle of water droplets on the composite film obtained in Example 1; and (c) shows the effect of cyclic stretching on the contact angle of water droplets on the composite film obtained in Example 1. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] Unless otherwise specified, room temperature or normal temperature in the embodiments of the present invention refers to 25±3℃.

[0042] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels;

[0043] The aluminum alloy is a 6061 series aluminum alloy.

[0044] The particle size of nano-alumina powder is 200-300 nanometers;

[0045] The particle size of nano-hydroxyapatite powder is 300-400 nanometers.

[0046] Example 1

[0047] A method for preparing a passively radiatively cooled superhydrophobic composite thin film based on a biomimetic water strider leg structure, such as... Figure 1 As shown, it includes the following steps:

[0048] (1) A biomimetic aluminum alloy template (2 cm × 2 cm) with a micron-sized conical hole (hole diameter 20-30 microns, the same below) was manufactured by femtosecond laser processing and the template was ultrasonically cleaned with anhydrous ethanol for 15 minutes.

[0049] (2) Prepare a 0.1% (v / v) ethanol solution of 1H,1H,2H,2H-perfluorodecyltriethoxysilane and stir for 1 hour to promote the hydrolysis of triethoxysilane to generate silanol (-Si-OH). Immerse the template obtained in step (1) in the above silane ethanol solution and let it stand at room temperature for 2 hours. After removing the template, allow the solvent to evaporate naturally at room temperature.

[0050] (3) Dissolve P(VDF-HFP) powder in a mixed solvent of acetone and water, then add 0.5 wt.% nano-alumina powder and 0.5 wt.% nano-hydroxyapatite powder respectively, and stir at 60℃ for 6 h until homogeneous to obtain P(VDF-HFP) mixed colloid. The mass ratio of P(VDF-HFP) powder, acetone and water is 1:10:1. Among them, the mass ratio of nano-alumina powder and nano-hydroxyapatite powder is 1:1.

[0051] (4) Drop 15 mL of P(VDF-HFP) mixed colloid into the center of the biomimetic aluminum alloy template, place it in a tabletop spin coater and spin it evenly (110 Hz / s, 20 s) to spread the mixed colloid evenly on the biomimetic template, and then transfer it to an oven at 30°C for 4 hours to undergo phase separation and curing process to obtain a passive radiation cooling superhydrophobic composite film based on the biomimetic water strider leg structure.

[0052] Comparative Example 1

[0053] The only difference from Example 1 is that step (4) is adjusted, specifically including the following steps:

[0054] (1) A biomimetic aluminum alloy template (2 cm × 2 cm) with micron-level conical holes was manufactured by femtosecond laser processing and the template was ultrasonically cleaned with anhydrous ethanol for 15 minutes.

[0055] (2) Prepare an ethanol solution of 1H,1H,2H,2H-perfluorodecyltriethoxysilane with a concentration of 0.1%-2% (v / v) and stir for 1 hour to promote the hydrolysis of triethoxysilane to generate silanol (-Si-OH). Immerse the template obtained in step (1) in the above silane ethanol solution and let it stand at room temperature for 2 hours. After removing the template, allow the solvent to evaporate naturally at room temperature.

[0056] (3) Dissolve P(VDF-HFP) powder in a mixed solvent of acetone and water, then add 0.5 wt.% nano-alumina powder and 0.5 wt.% nano-hydroxyapatite powder respectively, and stir at 60℃ for 6 h until homogeneous to obtain P(VDF-HFP) mixed colloid. The mass ratio of P(VDF-HFP) powder, acetone and water is 1:10:1. Among them, the mass ratio of nano-alumina powder and nano-hydroxyapatite powder is 1:1.

[0057] (4) Drop 15 mL of P(VDF-HFP) mixed colloid into a common polytetrafluoroethylene mold, place it in a tabletop spin coater and spin it evenly (110 Hz / s, 20 s) to spread the mixed colloid evenly on the polytetrafluoroethylene mold, and then transfer it to an oven at 30°C for 4 hours to undergo phase separation and curing process to obtain a composite film.

[0058] Comparative Example 2

[0059] The only difference from Example 1 is that step (4) is adjusted, and a layer of dust is evenly sprinkled on the surface of the prepared composite film to simulate the composite film under polluted conditions. Specifically, the following steps are included:

[0060] (1) A biomimetic aluminum alloy template (2 cm × 2 cm) with micron-level conical holes was manufactured by femtosecond laser processing and the template was ultrasonically cleaned with anhydrous ethanol for 15 minutes.

[0061] (2) Prepare a 0.1% (v / v) ethanol solution of 1H,1H,2H,2H-perfluorodecyltriethoxysilane and stir for 1 hour to promote the hydrolysis of triethoxysilane to generate silanol (-Si-OH). Immerse the template obtained in step (1) in the above silane ethanol solution and let it stand at room temperature for 2 hours. After removing the template, allow the solvent to evaporate naturally at room temperature.

[0062] (3) Dissolve P(VDF-HFP) powder in a mixed solvent of acetone and water, then add 0.5 wt.% nano-alumina powder and 0.5 wt.% nano-hydroxyapatite powder respectively, and stir at 60℃ for 6 h until homogeneous to obtain P(VDF-HFP) mixed colloid. The mass ratio of P(VDF-HFP) powder, acetone and water is 1:10:1. Among them, the mass ratio of nano-alumina powder and nano-hydroxyapatite powder is 1:1.

[0063] (4) Drop 15 mL of P(VDF-HFP) mixed colloid into a common polytetrafluoroethylene mold, place it in a tabletop spin coater and spin it evenly (110 Hz / s, 20 s) to spread the mixed colloid evenly on the polytetrafluoroethylene mold, and then transfer it to an oven at 30°C for 4 hours to undergo phase separation and curing process to obtain a composite film.

[0064] (5) Sprinkle a layer of dust evenly on the surface of the prepared composite film so that the dust blocks the sunlight from directly hitting the surface of the composite film, thus simulating the working conditions of the composite film in a polluted environment.

[0065] Comparative Example 3

[0066] The only difference from Example 1 is the addition of step (5), which mimics the working condition of the biomimetic composite film in a polluted environment, specifically including the following steps:

[0067] (1) A biomimetic aluminum alloy template (2 cm × 2 cm) with micron-level conical holes was manufactured by femtosecond laser processing and the template was ultrasonically cleaned with anhydrous ethanol for 15 minutes.

[0068] (2) Prepare a 0.1% (v / v) ethanol solution of 1H,1H,2H,2H-perfluorodecyltriethoxysilane and stir for 1 hour to promote the hydrolysis of triethoxysilane to generate silanol (-Si-OH). Immerse the template obtained in step (1) in the above silane ethanol solution and let it stand at room temperature for 2 hours. After removing the template, allow the solvent to evaporate naturally at room temperature.

[0069] (3) Dissolve P(VDF-HFP) powder in a mixed solvent of acetone and water, then add 0.5 wt.% nano-alumina powder and 0.5 wt.% nano-hydroxyapatite powder respectively, and stir at 60℃ for 6 h until homogeneous to obtain P(VDF-HFP) mixed colloid. The mass ratio of P(VDF-HFP) powder, acetone and water is 1:10:1. Among them, the mass ratio of nano-alumina powder and nano-hydroxyapatite powder is 1:1.

[0070] (4) Drop 15 mL of P(VDF-HFP) mixed colloid into the center of the biomimetic aluminum alloy template, place it in a tabletop spin coater and spin it evenly (110 Hz / s, 20 s) to spread the mixed colloid evenly on the biomimetic template, and then transfer it to an oven at 30°C for 4 hours to undergo phase separation and curing process to obtain a passive radiation cooling superhydrophobic composite film based on the biomimetic water strider leg structure.

[0071] (5) Sprinkle a layer of dust evenly on the surface of the prepared biomimetic composite film so that the dust blocks the sunlight from directly shining on the surface of the biomimetic composite film, thus mimicking the working conditions of the biomimetic composite film in a polluted environment.

[0072] Technical effects:

[0073] Figure 2 (a) and (b) show the microstructure of the water strider's legs at different magnifications; (c) is an energy dispersive spectroscopy (EDS) image of the water strider's legs. It can be seen that the water strider's legs have many micron-sized setae, which play a very important role in the water strider's walking on the water surface.

[0074] Figure 3 (a) is a scanning electron microscope (SEM) image of the composite film obtained in Example 1, top view; (b) is a magnified top view of the SEM image of the composite film obtained in Example 1; (c) is an oblique view of the SEM image of the composite film obtained in Example 1; (d) is a magnified side view of the SEM image of the composite film obtained in Example 1; (e) is a side view of the bottom cross-section of the composite film obtained in Example 1; (f) is a magnified side view of the cross-section of the composite film obtained in Example 1. It can be seen that: Example 1 of the present invention successfully prepared a biomimetic composite surface with a micron-level conical structure on the surface, and the cross-section contains abundant multi-level microporous structures. These structures play an important role in achieving good solar light reflection and superhydrophobic properties.

[0075] Figure 4(a) shows a schematic diagram and data of sunlight reflection on the surface of the composite film obtained in Comparative Example 1; (b) shows a schematic diagram and data of sunlight reflection on the surface of the composite film obtained in Comparative Example 2; and (c) shows a schematic diagram and data of sunlight reflection on the surface of the composite film obtained in Example 1. It can be seen that the composite film obtained in Comparative Example 2 significantly reduces solar reflectivity, indicating that dust is detrimental to the passive radiative cooling performance of the material surface. However, the biomimetic composite film obtained in Example 1 exhibits excellent solar reflectivity, demonstrating that the biomimetic structure can enhance solar reflectivity while possessing self-cleaning properties, thus improving passive radiative cooling performance in polluted environments.

[0076] Figure 5 (a) shows the mechanism by which the water strider's legs achieve superhydrophobicity; (b) shows the contact angle of water droplets on the surface of the water strider's legs, the biomimetic composite film obtained in Example 1, and the composite film obtained in Comparative Example 1; (c) shows the impact behavior of water droplets on the surface of the water strider's legs, the biomimetic composite film obtained in Example 1, and the composite film obtained in Comparative Example 1. It can be seen that the contact angle of the biomimetic composite film obtained in Example 1 is approximately 154.5°, corresponding to the Cassie state and exhibiting superhydrophobic properties. In contrast, due to the presence of micropores, water droplets exhibit a Wenzel state on the surface of the film obtained in Comparative Example 1, making it susceptible to contamination in outdoor environments and adversely affecting its radiative cooling performance. On the surface of the biomimetic composite film obtained in Example 1, water droplets spread out after impact, then retract and bounce, eventually detaching from the surface, indicating a good self-cleaning effect. The biomimetic composite film obtained in Example 1 possesses excellent self-cleaning properties, enhancing solar reflectivity while maintaining self-cleaning characteristics, thus improving passive radiative cooling performance in polluted environments.

[0077] Figure 6 (a) shows the roll-off angle test process of water droplets on the surface of a water strider's leg; (b) shows the roll-off angle test process of water droplets on the surface of the composite film obtained in Comparative Example 1; (c) shows the roll-off angle test process of water droplets on the surface of the biomimetic composite film obtained in Example 1; (d) shows the self-cleaning effect test of water droplets on the surface of the composite film obtained in Comparative Example 2; and (e) shows the self-cleaning effect test of water droplets on the surface of the biomimetic composite film obtained in Comparative Example 3. As a key parameter for evaluating the ease with which water droplets roll off a solid surface, the roll-off angle directly reflects the surface's self-cleaning ability. In the roll-off angle tests of these surfaces, the sample stage was gradually tilted, and the critical angle at which the water droplets began to roll was recorded. The results show that the roll-off angle of the surface obtained in Example 1 is less than 10°, indicating that the water droplets can easily roll off the surface, exhibiting good self-cleaning performance. In contrast, the roll-off angle value of the surface obtained in Comparative Example 1 is approximately 40°, indicating that the water droplets are difficult to remove from the surface, resulting in poor dehumidification performance. Therefore, this surface is more prone to accumulating dust and other contaminants, and has weak anti-fouling ability.

[0078] The experiment simulated the working conditions of the composite film in a real outdoor environment by observing the flow behavior of blue water droplets on a contaminated surface. On the surface obtained in Comparative Example 1, the water droplets directly mixed with dust and dirt, forming immobilized contaminated water droplets that adhered to the surface and could not detach on their own. This significantly weakened the solar reflection and heat radiation function of the cooling surface. In contrast, on the surface obtained in Example 1, the water droplets could quickly carry away and remove contaminants, demonstrating excellent self-cleaning ability. This characteristic is of great significance for ensuring that the radiative cooling film maintains stable and efficient cooling performance in outdoor applications over a long period of time.

[0079] Figure 7 (a) shows the freezing of water droplets on the biomimetic composite film obtained in Example 1; (b) shows the freezing of water droplets on the surface of the composite film obtained in Comparative Example 1. It can be seen that freezing delay time experiments were conducted on the surfaces obtained in Example 1 and Comparative Example 1. When the relative humidity was 65%, the complete freezing times were 210 seconds and 60 seconds, respectively. The experimental results show that the surface obtained in Example 1 has a significant advantage in delaying ice crystal formation. The freezing time of the surface obtained in Comparative Example 1 is 3.5 times that of the surface obtained in Example 1, which clearly indicates that the surface obtained in Example 1 can effectively inhibit the nucleation and growth of ice crystals. Further observation of the dynamic evolution of the freezing process revealed that at 300 seconds, only a small number of ice crystals formed on the surface obtained in Example 1, and the droplet morphology remained basically intact; while on the surface obtained in Comparative Example 1, the water droplets completely froze in about 60 seconds, accompanied by rapid ice layer spread. This difference mainly stems from the biomimetic conical structure of the surface obtained in Example 1. This structure endows the surface with superhydrophobicity, greatly reducing the effective contact area between the droplet and the solid surface. This weakens the interfacial interaction and effectively inhibits ice crystal nucleation and subsequent growth. Meanwhile, the superhydrophobic conical array structure forms an air layer between the surface and the droplet, hindering the transfer of heat from the droplet to the surface, thereby prolonging the freezing time.

[0080] Figure 8 (a) shows the effect of tape adhesion test on the contact angle of water droplets on the composite film obtained in Example 1; (b) shows the effect of sand impact on the contact angle of water droplets on the composite film obtained in Example 1; and (c) shows the effect of cyclic stretching on the contact angle of water droplets on the composite film obtained in Example 1. It can be seen that the surface obtained in Example 1 possesses good mechanical stability and is suitable for long-term outdoor working conditions.

[0081] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a passively radiatively cooled superhydrophobic composite thin film based on a biomimetic water strider leg structure, characterized in that, Includes the following steps: After soaking a template with micron-sized conical pores in an alcohol solution of silane, a P(VDF-HFP) mixed colloid is uniformly spread on the template. After phase separation and curing, the passive radiation cooling superhydrophobic composite film is obtained. The P(VDF-HFP) mixed colloid includes 0.5 wt.% nano-alumina powder and nano-hydroxyapatite powder; The size of the micron-scale conical aperture is 20-30 micrometers; The mass ratio of the nano-alumina powder to the nano-hydroxyapatite powder is 1:

1.

2. The method for preparing a passive radiative cooling superhydrophobic composite thin film based on a biomimetic water strider leg structure according to claim 1, characterized in that, The volume concentration of the alcoholic solution of the silane is 0.1-2%, and the silane includes one of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, trifluoropropyltrimethoxysilane, and perfluorobutylethyltrimethoxysilane.

3. The method for preparing a passive radiative cooling superhydrophobic composite thin film based on a biomimetic water strider leg structure according to claim 1, characterized in that, The preparation method of the P(VDF-HFP) mixed colloid includes the following steps: P(VDF-HFP) powder is dissolved in a mixed solvent of acetone and water, and then nano-alumina powder and nano-hydroxyapatite powder are added and stirred evenly to obtain the P(VDF-HFP) mixed colloid.

4. The method for preparing a passive radiative cooling superhydrophobic composite thin film based on a biomimetic water strider leg structure according to claim 3, characterized in that, The mass ratio of the P(VDF-HFP) powder, acetone, and water is 1:10:

1.

5. The method for preparing a passive radiative cooling superhydrophobic composite thin film based on a biomimetic water strider leg structure according to claim 3, characterized in that, The stirring temperature was 60°C and the stirring time was 6 hours.

6. A passively radiatively cooled superhydrophobic composite film based on a biomimetic water strider leg structure, prepared by the preparation method according to any one of claims 1-5.

7. The application of a passive radiation cooling superhydrophobic composite film based on a biomimetic water strider leg structure as described in claim 6 in passive radiation cooling, surface self-cleaning, and de-icing / anti-icing.

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