Self-adaptive thermochromic super-hydrophobic self-cleaning radiation cooling coating as well as preparation method and application thereof

Abstract

The invention discloses a self-adaptive thermochromism super-hydrophobic self-cleaning radiation cooling coating as well as a preparation method and application of the self-adaptive thermochromism super-hydrophobic self-cleaning radiation cooling coating. The method comprises the following steps: dissolving a polymer matrix in an organic solvent, and magnetically stirring at room temperature for 0.5-3 hours to obtain a prepolymer solution; the preparation method comprises the following steps: dispersing an optical filler in an organic solvent, and performing ultrasonic treatment for 0.5-3 hours to obtain an emulsion; mixing the prepolymer solution and the emulsion, stirring at room temperature for 10-60 minutes, adding thermochromic phase change microcapsules, and uniformly mixing to obtain a precursor suspension; and spraying the precursor suspension on the surface of a substrate, and curing to obtain the self-adaptive thermochromic super-hydrophobic self-cleaning radiation cooling coating. The preparation method provided by the invention is simple to operate and mild in reaction condition, and the prepared coating has the advantages of self-adaptive radiation cooling, visual attractiveness, super-hydrophobic self-cleaning and mechanical environment durability, and is suitable for energy conservation and protection of building outer walls, roofs and outdoor equipment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of functional materials, in particular to a self-adaptive thermochromic, super-hydrophobic self-cleaning radiative cooling coating and a preparation method and application thereof. BACKGROUND

[0002] Passive radiative cooling technology is a green cooling method relying on the spectral properties of materials to achieve spontaneous heat dissipation. Its basic principle is to achieve direct heat radiation to outer space by high reflection of sunlight (0.3-2.5 μm) and high emission of infrared radiation (8-13 μm) in the atmospheric transmission window, so as to make the surface temperature of the object lower than the ambient temperature. This passive heat dissipation method without external energy input has the advantages of low energy consumption, good environmental protection, wide application range, etc., and is therefore considered as an important way to replace traditional refrigeration methods.

[0003] In recent years, researchers have developed a variety of radiative cooling materials with high reflectivity and high emissivity, including multilayer photonic structure films, nanoporous polymer materials, organic-inorganic composite systems, and biomimetic microstructure fabrics, etc. Although these materials have made significant progress in spectral regulation, there are still many limitations in practical application. The optical properties of most existing radiative cooling materials are fixed and cannot be dynamically adjusted according to the ambient temperature or seasonal changes, which easily leads to excessive cooling in winter or at night; at the same time, their appearance is mostly white, lacking the architectural decorative aesthetic, limiting their promotion in urban landscapes and facades.

[0004] In the prior art, some studies have attempted to introduce thermochromic materials (such as VO2) or phase change materials to achieve adaptive regulation. For example, Chinese invention patent CN 114702850A discloses a vanadium dioxide composite powder temperature control coating, which utilizes the absorption of tungsten bronze to near-infrared light to convert light into heat, thereby promoting the phase change of vanadium dioxide, and then realizing the transmission or shielding of different wavelength light, ultimately realizing room temperature regulation function. However, this scheme often faces problems such as high transition temperature, complex synthesis process, poor chemical stability, or poor compatibility with the matrix. In addition, there are still few reports on coatings that combine efficient cooling, dynamic regulation, mechanical durability, and self-cleaning functions.

[0005] Therefore, the prior art still needs to be improved and developed. SUMMARY

[0006] In view of the deficiencies of the prior art described above, the purpose of the present application is to provide a self-adaptive thermochromic, super-hydrophobic self-cleaning radiative cooling coating and a preparation method and application thereof, aiming to solve the problems of lack of temperature response characteristics, complex preparation process, and single function in the prior art.

[0007] The technical solution of the present application is as follows: In a first aspect, the present invention provides a method for preparing an adaptive thermochromic, superhydrophobic, self-cleaning radiation-cooling coating, comprising: Step S1: Dissolve the polymer matrix in an organic solvent and magnetically stir at room temperature for 0.5–3 h to obtain a prepolymer solution; Step S2: Disperse the optical filler in an organic solvent and sonicate for 0.5–3 hours to obtain an emulsion; Step S3: Mix the prepolymer solution and the emulsion, stir at room temperature for 10-60 min, add thermochromic phase change microcapsules, mix evenly, and obtain a precursor suspension; Step S4: Spray the precursor suspension onto the substrate surface and cure it to obtain the adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coating.

[0008] Optionally, the polymer matrix is ​​a PDMS matrix.

[0009] Optionally, the optical filler is one or more of hexagonal boron nitride, hollow glass microspheres, silicon dioxide, titanium dioxide, calcium titanate, barium sulfate, and aluminum oxide.

[0010] Preferably, the optical filler is hexagonal boron nitride and hollow glass microspheres.

[0011] Preferably, the mass ratio of the hexagonal boron nitride to the hollow glass microspheres can be adjusted as needed, and the mass ratio is 2:8 to 8:2; more preferably, the mass ratio is 7:3.

[0012] Optionally, the hollow glass microspheres have a particle size of 5–30 μm; the hexagonal boron nitride has a particle size of 5–50 μm.

[0013] Optionally, the thermochromic microcapsules have a particle size of 1.5–20 μm.

[0014] Optionally, the organic solvent is one or more selected from ethyl acetate, dichloromethane, chloroform, toluene, xylene, N,N-dimethylformamide, and tetrahydrofuran.

[0015] Optionally, the mass ratio of the polymer matrix to the organic solvent is 1: (5-8); the mass ratio of the polymer matrix to the curing agent is 10: (0.8-1.2); and the mass ratio of the polymer matrix to the optical filler is 1: (1-3).

[0016] Optionally, the mass content of thermochromic microcapsules in the precursor suspension is 1% to 5%.

[0017] Optionally, the color-changing temperature of the thermochromic microcapsule is 25–60°C.

[0018] Optionally, step S3 further includes adding an auxiliary agent when adding the thermochromic phase change microcapsules; the auxiliary agent is one or more of ultraviolet absorbers, light stabilizers, and antioxidants.

[0019] Optionally, in step S4, the spraying process parameters are set as follows: liquid viscosity of 150-300 cP, spraying pressure of 0.6-1.0 MPa, and distance between the spray gun and the substrate of approximately 13-18 cm.

[0020] Optionally, the curing temperature in step S4 is 40–90°C.

[0021] Preferably, the thickness of the adaptive thermochromic, superhydrophobic self-cleaning radiation cooling coating is 200–1000 μm, and more preferably, the thickness is 400 μm.

[0022] In a second aspect, the present invention provides an adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coating prepared by the above-described preparation method.

[0023] A third aspect of the present invention provides an application of the adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coating prepared by the above-described method in the fields of building energy conservation, 5G base stations, outdoor equipment, or vehicle thermal management systems.

[0024] Beneficial effects: This invention provides an adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coating, its preparation method, and its application. Compared with the prior art, the advantages of this invention's adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coating are: (1) Intelligent and adaptive thermal management is achieved: In the adaptive thermochromic, superhydrophobic self-cleaning radiation cooling coating provided by this invention, thermochromic phase change microcapsules (TCMs) are introduced, enabling the coating to have a reversible color-to-white transition capability. When the ambient temperature is higher than the color change temperature, the coating automatically changes to a highly reflective white state, maximizing the radiation cooling efficiency; when the temperature decreases, it restores its original color, effectively absorbing sunlight to suppress the "overcooling" phenomenon, thereby overcoming the inherent defect of traditional static radiation cooling materials that cannot adapt to changes in ambient temperature.

[0025] (2) Combining high-efficiency cooling performance with aesthetic value: The adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coating provided by this invention has high solar reflectivity (≥90%) and high-infrared emissivity (≥90%). By reducing solar energy absorption through high reflectivity and accelerating heat radiation outward using high-infrared emissivity, a stable and efficient passive cooling effect is achieved. In addition, the coating can be customized in various colors such as red, blue, green, and yellow, meeting the urgent needs for color diversity and visual aesthetics in building exteriors, urban landscapes, and other fields, breaking the traditional limitation that high-performance radiation cooling coatings are all white.

[0026] (3) The preparation process is simple and easy to scale up: The adaptive thermochromic, superhydrophobic self-cleaning radiation cooling coating provided by this invention can be achieved through physical blending and conventional spraying processes. The raw materials are readily available, the process is simple, and no complex or expensive equipment is required, which provides a solid guarantee for large-scale practical application and commercial promotion.

[0027] (4) Multifunctional integration: The adaptive thermochromic, superhydrophobic self-cleaning radiation cooling coating provided by this invention successfully integrates the four major functions of "adaptive radiation cooling", "visual aesthetics", "superhydrophobic self-cleaning" and "mechanical environment durability" into a single coating system, providing an advanced material solution of "one material for multiple uses", which significantly enhances the comprehensive competitiveness and application value of the product. Attached Figure Description

[0028] Figure 1 This is a schematic diagram illustrating the working principle of the adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coating prepared according to the present invention.

[0029] Figure 2 This is a SEM image of the superhydrophobic self-cleaning radiation cooling coating prepared in Example 2 of the present invention.

[0030] Figure 3 The solar radiation reflection spectrum and mid-infrared emission spectrum of the superhydrophobic self-cleaning radiation cooling coating prepared in Comparative Example 1 of this invention are shown.

[0031] Figure 4 The solar radiation reflection spectrum and mid-infrared emission spectrum of the superhydrophobic self-cleaning radiation cooling coating prepared in Comparative Example 2 of this invention are shown.

[0032] Figure 5 The solar radiation reflectance spectrum of the blue adaptive thermochromic, superhydrophobic self-cleaning radiation cooling coating prepared in Example 2 of the present invention.

[0033] Figure 6The solar radiation reflectance spectrum of the red adaptive thermochromic, superhydrophobic self-cleaning radiation cooling coating prepared in Example 3 of the present invention.

[0034] Figure 7 The solar radiation reflectance spectrum of the yellow adaptive thermochromic, superhydrophobic self-cleaning radiation cooling coating prepared in Example 4 of the present invention.

[0035] Figure 8 The solar radiation reflectance spectrum of the green adaptive thermochromic, superhydrophobic self-cleaning radiation cooling coating prepared in Example 5 of the present invention.

[0036] Figure 9 The mid-infrared emission spectra of the adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coatings obtained in Examples 1-5 of this invention are shown.

[0037] Figure 10 This is a schematic diagram of the surface and surface contact angle of the superhydrophobic self-cleaning radiation cooling coating obtained in Example 1 of the present invention.

[0038] Figure 11 This is a schematic diagram illustrating the multifunctional application scenarios of the superhydrophobic self-cleaning radiation cooling coating obtained in Embodiment 1 of the present invention.

[0039] Figure 12 These are outdoor thermal images of the coatings obtained in Examples 1-5 of the present invention.

[0040] Figure 13 This is a schematic diagram of the thermochromic transformation process of the coatings obtained in Examples 1-5 of the present invention at temperatures exceeding 45°C.

[0041] Figure 14 The images and temperature change curves of the adaptive thermochromic, superhydrophobic self-cleaning radiation cooling coating, commercial coating, and blank bare aluminum plate prepared in Example 2 of the present invention are shown in indoor simulation tests. Detailed Implementation

[0042] This invention provides an adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coating, its preparation method, and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0043] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0044] This invention provides a method for preparing an adaptive thermochromic, superhydrophobic, self-cleaning radiation-cooling coating, comprising: Step S1: Dissolve the polymer matrix in an organic solvent and magnetically stir at room temperature for 0.5–3 h to obtain a prepolymer solution; Step S2: Disperse the optical filler in an organic solvent and sonicate for 0.5–3 hours to obtain an emulsion; Step S3: Mix the prepolymer solution and the emulsion, stir at room temperature for 10-60 min, add thermochromic phase change microcapsules, mix evenly, and obtain a precursor suspension; Step S4: Spray the precursor suspension onto the substrate surface and cure it to obtain the adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coating.

[0045] The coating provided in this invention uses a polymer matrix as the continuous phase, constructs a highly efficient solar scattering network and a mid-infrared emission framework through optical fillers, and introduces thermochromic phase change microcapsules (TCMs). When the ambient temperature is below the color-changing temperature, the TCMs are in a colored state, and the solar reflectivity of the coating is approximately 70%–90%. When the temperature rises above the color-changing temperature, the TCMs turn white, and the reflectivity increases to 90%–95%, thereby achieving an adaptive radiative cooling effect that automatically adjusts absorption and reflection according to temperature changes.

[0046] In the preparation method of this invention, the polymer matrix and optical filler are dissolved or dispersed in an organic solvent respectively, and then mixed to form a stable composite suspension. This effectively controls the viscosity and dispersion uniformity of the system, avoids the aggregation or sedimentation of the optical filler, and ensures that the optical filler is uniformly distributed in the polymer matrix, forming a stable light scattering and infrared emission structure, thus improving the radiative cooling performance. Adding thermochromic phase change microcapsules to the composite suspension yields a precursor suspension, which ensures the integrity of the thermochromic phase change microcapsule shell structure and the reversibility of the phase change. This allows the resulting coating to undergo a reversible color-to-white transition when the temperature changes, achieving adaptive temperature response and dimming function.

[0047] Furthermore, the method of this invention is simple to operate and the process is controllable. The prepared coating has a uniform structure and stable interface, and has both high reflectivity and high infrared emissivity, resulting in efficient radiative cooling performance. It also has thermochromic adjustment and superhydrophobic self-cleaning characteristics, which can meet the application needs of building exterior walls and outdoor equipment for intelligent temperature regulation, durable anti-fouling and visual aesthetics.

[0048] In some embodiments, the optical filler is one or more of hexagonal boron nitride, hollow glass microspheres, silicon dioxide, titanium dioxide, calcium titanate, barium sulfate, and aluminum oxide.

[0049] In some embodiments, the optical filler is hexagonal boron nitride and hollow glass microspheres; the polymer matrix is ​​a PDMS matrix.

[0050] This invention also incorporates hexagonal boron nitride (hBN) with high refractive index and strong infrared emission, hollow glass microspheres (HGM) with multiple scattering effects and thermal insulation properties, and polydimethylsiloxane (PDMS) with low surface energy and excellent flexibility. These components enhance the optical properties of the coating while imparting excellent mechanical stability and superhydrophobic self-cleaning characteristics. In other words, the superhydrophobic self-cleaning radiation-cooling coating prepared using hBN, HGM, and PDMS substrates exhibits superior superhydrophobicity, self-cleaning function, and long-term durability.

[0051] The working principle of the coating prepared in this embodiment is as follows: Figure 1 As shown, based on the low surface energy of the PDMS substrate and the micro-nano hierarchical rough structure constructed from HGM and hBN, the coating exhibits stable superhydrophobicity (water contact angle >150°), effectively repelling water droplets and allowing them to automatically roll off and remove surface contaminants, thus maintaining the long-term cleanliness of the optical surface. Simultaneously, the coating exhibits a solar reflectance ≥90% above the color-changing temperature and an emissivity of 90%–95% in the mid-infrared region, achieving highly efficient solar reflection and thermal radiation performance. Furthermore, the coating demonstrates excellent mechanical abrasion resistance, chemical stability (resistance to acid and alkali corrosion), and UV aging resistance, ensuring its long service life in harsh outdoor environments.

[0052] Although existing studies have shown that the aforementioned components such as hBN, HGM, and PDMS can improve optical reflection, thermal emission, and surface antifouling properties, it is difficult to achieve a multifunctional integrated coating with tunable spectrum, strong weather resistance, structural stability, and large-area spraying capability in the same system. The preparation method provided in this invention, through stepwise dissolution, dispersion, and mixing process control, enables uniform distribution and interfacial synergy of each component in the same system, thereby preparing a coating with adaptive thermochromic properties, superhydrophobic self-cleaning radiation cooling.

[0053] In some embodiments, the mass ratio of the hexagonal boron nitride to the hollow glass microspheres can be adjusted as needed, and the mass ratio is 2:8 to 8:2 (for example, it can be 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, etc.), more preferably, the mass ratio is 7:3.

[0054] In some embodiments, the hollow glass microspheres have a particle size of 5–30 μm (e.g., 5 μm, 10 μm, 15 μm, 20 μm, 25 μm or 30 μm); the hexagonal boron nitride has a particle size of 5–50 μm (e.g., 5 μm, 10 μm, 20 μm, 30 μm, 40 μm or 50 μm).

[0055] In some embodiments, the thermochromic microcapsules have a particle size of 1.5 to 20 μm (e.g., 1.5 μm, 5 μm, 10 μm, 15 μm or 20 μm).

[0056] In this embodiment of the invention, by utilizing the particle size range of the thermochromic microcapsules, hollow glass microspheres, and hexagonal boron nitride, the dispersion stability and film uniformity of the system can be improved while ensuring the optical control effect.

[0057] In some embodiments, the organic solvent is one or more of ethyl acetate, dichloromethane, chloroform, toluene, xylene, N,N-dimethylformamide, and tetrahydrofuran.

[0058] In some embodiments, the mass ratio of the polymer matrix to the organic solvent is 1:(5-8) (e.g., 1:5, 1:6, 1:7 or 1:8). The mass ratio of polymer matrix to curing agent is 10:(0.8-1.2), preferably 10:1; The mass ratio of polymer matrix to optical filler is 1:(1 to 3) (for example, it can be 1:1, 1:2 or 1:3).

[0059] In some embodiments, the mass content of the thermochromic microcapsules in the precursor suspension is 1% to 5% (e.g., 1%, 2%, 3%, 4%, or 5%). More preferably, the mass content is 1% to 3%.

[0060] In some embodiments, the color-changing temperature of the thermochromic microcapsules is 25–60°C.

[0061] In some embodiments, step S3 further includes adding an auxiliary agent when adding the thermochromic phase change microcapsules; the auxiliary agent is one or more of ultraviolet absorbers, light stabilizers, and antioxidants.

[0062] In some embodiments, in step S4, the spraying process parameters are set as follows: liquid viscosity is 150-300 cP, spraying pressure is 0.6-1.0 MPa, and the distance between the spray gun and the substrate is about 13-18 cm.

[0063] In some embodiments, the curing temperature in step S4 is 40 to 90°C (for example, it can be 40°C, 50°C, 60°C, 70°C, 80°C or 90°C).

[0064] In some embodiments, the thickness of the adaptive thermochromic, superhydrophobic self-cleaning radiation cooling coating is 200~1000μm (e.g., 200μm, 400μm, 600μm, 800μm or 1000μm), preferably 400μm.

[0065] This invention provides a coating with adaptive thermochromic properties, superhydrophobic self-cleaning radiation cooling, prepared by the above-described method.

[0066] This invention provides an application of the adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coating prepared by the above method in the fields of building energy conservation, 5G base stations, outdoor equipment, or vehicle thermal management systems.

[0067] The present invention will be further described below through specific embodiments.

[0068] Example 1 This embodiment provides a superhydrophobic self-cleaning radiation cooling coating and its preparation method, including the following steps: (1) Dissolve 5 g of PDMS matrix in 10 g of ethyl acetate. Stir the mixture magnetically at room temperature for 1 hour to form a homogeneous PDMS prepolymer solution.

[0069] (2) Disperse 3 g of hBN and 2 g of HGM in 20 g of ethyl acetate. Then, sonicate the mixture (ultrasonic frequency 40 kHz, power 540 W) for 1 hour until a uniform and stable white emulsion is formed.

[0070] (3) Mix the solutions obtained in step (1) and step (2) and continue to stir magnetically for 30 minutes at room temperature. Add 0.5 g of curing agent (PDMS to curing agent mass ratio is 10:1) to mix them thoroughly to obtain a composite suspension.

[0071] (4) Using the composite suspension as a precursor suspension, the precursor suspension was sprayed onto a clean aluminum substrate surface using a W-71 spray gun (nozzle diameter 1.0 mm). The optimized spraying process parameters were: liquid viscosity approximately 200 cP, spraying pressure 0.8 MPa, and distance between the spray gun and the substrate approximately 15 cm. The final coating thickness was adjusted to 400 μm by controlling the spraying time.

[0072] (5) Transfer the coated substrate to an oven and heat it at 50°C for 3 hours to form a uniform, superhydrophobic radiation cooling coating.

[0073] Example 2 This embodiment provides an adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coating and its preparation method, including the following steps: (1) Following the steps (1) to (3) in Example 1, a composite suspension was first prepared.

[0074] (2) Add blue TCMs to the above composite suspension (the amount added can be adjusted within the range of 1% to 5%, and 1% is used as an example in this embodiment). At the same time, add 0.5g of curing agent, 0.05g of ultraviolet absorber, 0.05g of light stabilizer and 0.05g of antioxidant.

[0075] (3) Stir the mixture obtained in step (2) at room temperature in the dark for 30 minutes to ensure that the TCMs and the additives are evenly dispersed to obtain a precursor suspension.

[0076] (4) Using the same spraying parameters as in step (4) of Example 1 (viscosity 200 cP, pressure 0.8 MPa, distance 15 cm), the precursor suspension was sprayed onto various substrates such as aluminum substrate, cement board, wood board or glass. The final coating thickness was adjusted to 400 μm by controlling the spraying time.

[0077] (5) Place the sprayed substrate in a 50°C oven for 3 hours to cure, and obtain a radiation cooling coating with adaptive thermochromic properties and superhydrophobic self-cleaning properties.

[0078] Example 3 This embodiment provides an adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coating and its preparation method, including the following steps: (1) Prepare the composite suspension first, following the steps (1) to (3) in Example 1.

[0079] (2) Add red TCMs to the above composite suspension (the amount added can be adjusted in the range of 1% to 5%, and 1% is used as an example in this embodiment). At the same time, add 0.5g of curing agent, 0.05g of ultraviolet absorber, 0.05g of light stabilizer and 0.05g of antioxidant.

[0080] (3) Stir the mixture obtained in step (2) at room temperature in the dark for 30 minutes to ensure that the TCMs and the additives are evenly dispersed to obtain a precursor suspension.

[0081] (4) Using the same spraying parameters as in step (4) of Example 1 (viscosity 200 cP, pressure 0.8 MPa, distance 15 cm), the precursor suspension was sprayed onto various substrates such as aluminum substrate, cement board, wood board or glass. The final coating thickness was adjusted to 400 μm by controlling the spraying time.

[0082] (5) Place the sprayed substrate in a 50°C oven for 3 hours to cure, and obtain a radiation cooling coating with adaptive thermochromic properties and superhydrophobic self-cleaning properties.

[0083] Example 4 This embodiment provides an adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coating and its preparation method, including the following steps: (1) Following the steps (1) to (3) in Example 1, a composite suspension was first prepared.

[0084] (2) Add yellow TCMs to the above composite suspension (the amount added can be adjusted in the range of 1% to 5%, and 1% is used as an example in this embodiment). At the same time, add 0.5g of curing agent, 0.05g of ultraviolet absorber, 0.05g of light stabilizer and 0.05g of antioxidant.

[0085] (3) Stir the mixture obtained in step (2) at room temperature in the dark for 30 minutes to ensure that the TCMs and the additives are evenly dispersed to obtain a precursor suspension.

[0086] (4) Using the same spraying parameters as step (4) in Example 1 (viscosity 200 cP, pressure 0.8 MPa, distance 15 cm), the precursor suspension was sprayed onto various substrates such as aluminum substrate, cement board, wood board or glass. The final coating thickness was adjusted to 400 μm by controlling the spraying time.

[0087] (5) The coated substrate was placed in a 50°C oven for 3 hours to cure, and finally a thermochromic, superhydrophobic, self-cleaning radiation cooling coating was obtained.

[0088] Example 5 This embodiment provides an adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coating and its preparation method, including the following steps: (1) Following the steps (1) to (3) in Example 1, a composite suspension was first prepared.

[0089] (2) Add 1 wt% of green TCMs to the above composite suspension. At the same time, add 0.5 g of curing agent, 0.05 g of ultraviolet absorber, 0.05 g of light stabilizer and 0.05 g of antioxidant.

[0090] (3) Stir the mixture obtained in step (2) at room temperature in the dark for 30 minutes to ensure that the TCMs and the additives are evenly dispersed to obtain a precursor suspension.

[0091] (4) Using the same spraying parameters as step (4) in Example 1 (viscosity 200 cP, pressure 0.8 MPa, distance 15 cm), the precursor suspension was sprayed onto various substrates such as aluminum substrate, cement board, wood board or glass. The final coating thickness was adjusted to 400 μm by controlling the spraying time.

[0092] (5) The coated substrate was placed in a 50°C oven for 3 hours to cure, and finally a thermochromic, superhydrophobic, self-cleaning radiation cooling coating was obtained.

[0093] Comparative Example 1 This embodiment provides a superhydrophobic self-cleaning radiation cooling coating and its preparation method, including the following steps: (1) Weigh 5 g of PDMS matrix and 0.5 g of curing agent and dissolve them together in 10 g of ethyl acetate. Stir the mixture magnetically at room temperature for 1 hour to form a homogeneous PDMS prepolymer solution.

[0094] (2) Weigh 1g, 2g, 3g and 4g of HGM respectively, and disperse them in 20g of ethyl acetate to obtain 4 groups of mixtures. Then, sonicate the 4 groups of mixtures for 1 hour to obtain 4 groups of uniform and stable white emulsions.

[0095] (3) Mix the solutions obtained in step (1) and step (2) and continue to stir magnetically for 30 minutes at room temperature to ensure thorough mixing and obtain 4 sets of stable precursor suspensions.

[0096] (4) Using a W-71 spray gun (nozzle diameter 1.0 mm), the four precursor suspensions were sprayed onto the clean aluminum substrate surface. The optimized spraying process parameters were: liquid viscosity approximately 200 cP, spraying pressure 0.8 MPa, and distance between the spray gun and the substrate approximately 15 cm. By controlling the spraying time, the wet film thickness of the coating was controlled within a certain range, with the aim of achieving a thickness of approximately 400 μm after drying and curing.

[0097] The coated substrate was transferred to an oven and heated at 50°C for 3 hours to obtain four sets of superhydrophobic self-cleaning radiation cooling coatings. The HGM content of the four sets of superhydrophobic self-cleaning radiation cooling coatings was 20%, 40%, 60%, and 80%, respectively.

[0098] Comparative Example 2 This comparative example provides a superhydrophobic self-cleaning radiation cooling coating and its preparation method, including the following steps: (1) Dissolve 5 g of PDMS matrix and 0.5 g of curing agent (the mass ratio of PDMS matrix to curing agent is 10:1) together in 10 g of ethyl acetate. Stir the mixture magnetically at room temperature for 1 hour to form a homogeneous PDMS prepolymer solution.

[0099] (2) Weigh out 0g, 1g, 2g, 3g and 4g of hBN respectively, add 2g of HGM to each, and disperse them in 20g of ethyl acetate to obtain 5 groups of mixtures. Then, sonicate the 5 groups of mixtures for 1 hour to obtain 5 groups of uniform and stable white emulsions.

[0100] (3) Mix the solutions obtained in step (1) and step (2) and continue to stir magnetically for 30 minutes at room temperature to ensure thorough mixing and obtain 5 groups of stable precursor suspensions.

[0101] (4) Five precursor suspensions were sprayed onto a clean aluminum substrate surface using a W-71 spray gun (nozzle diameter 1.0 mm). The optimized spraying process parameters were: liquid viscosity approximately 200 cP, spraying pressure 0.8 MPa, and distance between the spray gun and the substrate approximately 15 cm. By controlling the spraying time, the wet film thickness of the coating was controlled within a certain range, with the aim of achieving a thickness of approximately 400 μm after drying and curing.

[0102] (5) The coated substrate was transferred to an oven and heated and cured at 50°C for 3 hours to obtain 5 groups of superhydrophobic self-cleaning radiation cooling coatings, wherein the hBN content in the 5 groups of superhydrophobic self-cleaning radiation cooling coatings was 0%, 20%, 40%, 60%, and 80%, respectively.

[0103] Test Example 1 This test example analyzes the working principle of the coatings prepared in Examples 2-5 and performs structural characterization tests on the coating prepared in Example 1.

[0104] (1) The working principle of the coatings prepared in Examples 2-5 is as follows: Figure 1 As shown, from Figure 1 As can be seen, relying on the low surface energy and micro-nano hierarchical rough structure of the PDMS matrix, stable superhydrophobicity (water contact angle >150°) and self-cleaning function are achieved, and it also has excellent mechanical wear resistance, chemical stability and UV aging resistance, thus ensuring its long service life in harsh outdoor environments.

[0105] (2) SEM image of the coating prepared in Example 2 is shown below. Figure 2 As shown in the figure, the lamellar hBN, HGM, and TCMs in the PDMS matrix complement and synergize in function and structure, jointly forming the intelligent cooling system of the coating. Among them, the lamellar hBN, with its wide bandgap (5.96 eV), high refractive index, and unique phonon-polariton resonance, enhances ultraviolet-visible light scattering to improve solar reflectivity (contributing ≥90% of the reflectivity) while also providing efficient mid-infrared emission capability (contributing ≥95% of the emissivity), which is the core of broadband optical performance. HGM, with its hollow structure, forms a large number of "shell-air" interfaces in the coating, further enhancing the reflection of sunlight by inducing strong Mie scattering and multiple internal reflections; at the same time, its micron-sized spheres, as the main framework, together with the lamellar hBN structure and solidification pores, construct the key micro-nano hierarchical roughness, which is the structural basis for superhydrophobicity (contact angle >150°) and self-cleaning function.

[0106] Test Example 2 This test example involves measuring the solar radiation reflectance spectrum and mid-infrared emission spectrum of the coatings prepared in Examples 1-5 and Comparative Examples 1-2.

[0107] Test conditions and methods: (1) Characterization of solar reflectivity performance The reflectance spectrum of the coating was tested using a UV / Vis / NIR spectrophotometer (Lambda 950), with a high-reflectivity PTFE white board as the reference substrate. The test wavelength range was set to 0.3–2.5 μm and the sampling interval was 5 nm.

[0108] Derivation of the formula for calculating the average solar reflectivity of radiation-cooled materials:

[0109] R(λ) represents the spectral reflectance at a specific wavelength. IAM1.5(λ) is the solar irradiance (W / (m²)). 2 (·μm), data sourced from ASTM G173-03 (2012). Integration interval is from λ1=0.3μm to λ2=2.5μm.

[0110] (2) Atmospheric window emission performance characterization The mid-infrared reflectance R(λ) and transmittance T(λ) of the coating were determined using a Fourier transform infrared spectrometer (Nicolet IS20, equipped with a gold-plated diffuse reflectance integrating sphere). Based on the law of conservation of energy: reflectance R + transmittance T + absorptivity α = 1. Combining this with Kirchhoff's law of thermal radiation, under thermal equilibrium, the emissivity ε and absorptivity α of an object at the same wavelength are equal. Therefore, the emissivity of the coating ε(λ) = 1 - R(λ) - T(λ), where R(λ) and T(λ) can be directly measured experimentally. The test wavelength range was 2.5–18 μm.

[0111] Derivation of the formula for calculating the mean emissivity of the atmospheric window of a radiation-cooled material:

[0112]

[0113] Where ε(λ) is the spectral emissivity of the radiative cooling material at the corresponding wavelength. BB (λ) is the spectral radiation intensity of an ideal blackbody at the corresponding wavelength at the corresponding temperature, in W / (m²). 2 (·μm). Since the wavelength range of the atmospheric window is 8–13 μm, λ1 and λ2 are 8 μm and 13 μm, respectively.

[0114] Test results: (1) such asFigure 3 As shown, the reflectivity of the coatings prepared in Comparative Example 1 is all below 90% (as shown in Table 1). Figure 4 The results show that adding 60% hBN results in a coating reflectance >90%. This indicates that the coating reflectance only reaches above 80% with increasing HGM content, but further addition weakens the reflectance; therefore, 40% HGM was chosen. Further addition of hBN, reaching a 60% hBN content, maintains a reflectance greater than 90%. (HGM:PDMS = 20%~80%; hBN:PDMS = 0%~80%) In Comparative Example 1, only HGM was added, resulting in low reflectivity of the coating, which significantly affected its cooling effect. Therefore, in Comparative Example 2, hBN was added to the material from Comparative Example 1. The reflectivity of the coating gradually increased with increasing hBN content, reaching over 90% when 60% hBN was added. The sheet-like hBN and hollow spherical HGM, through functional complementarity and synergy in the PDMS matrix, together constitute the intelligent cooling system of the coating, exhibiting a certain cooling effect.

[0115] Table 1. Changes in reflectivity and emissivity in Comparative Example 1

[0116] Table 2. Changes in reflectivity and emissivity in Comparative Example 2

[0117] (2) Compared to the white radiative cooling coatings in Comparative Examples 1 and 2, colored coatings have greater practical value in building applications, such as... Figures 5-8 The radiation-cooling coatings prepared in Examples 2-5 are of different colors. When the ambient temperature is below the color-changing temperature, the coating is in a colored state with a solar reflectivity of approximately 70%–90%. When the temperature rises above the color-changing temperature, the coating turns white, and the reflectivity increases to 90%–95%, thus achieving an adaptive radiation-cooling effect that automatically adjusts absorption and reflection according to temperature changes. This adaptive thermochromic, superhydrophobic, self-cleaning radiation-cooling coating not only possesses the high emissivity and high reflectivity of white paint but also has the function of automatically adjusting its color according to temperature changes.

[0118] Table 3. Changes in reflectivity and emissivity in Examples 1-5

[0119] Figure 9 The figures show the mid-infrared emission spectra of the coatings prepared in Examples 1-5. As can be seen from the figures, the mid-infrared emissivity of the coatings prepared in Examples 1-5 is 90% to 95%.

[0120] Test Example 3 This test example focuses on the surface wetting test of the superhydrophobic self-cleaning radiation cooling coating prepared in Example 1.

[0121] like Figure 10 As shown, the coating prepared in Example 1 was placed horizontally, and water droplets, water droplets with dye, tea, and milk were dropped onto its surface. It can be observed from the figure that all liquids maintained a nearly spherical shape on the coating surface, without wetting or spreading. The water droplets were measured using a contact angle meter, and the left and right contact angles were 152.4° and 151.0°, respectively, i.e., contact angle > 150°. Therefore, the coating prepared in Example 1 exhibits superhydrophobic properties with a contact angle > 150°.

[0122] Test Example 4 In this test example, the coating prepared in Example 1 was applied to the surfaces of cement board, aluminum plate, wood board and glass, respectively, to verify its applicability and functional stability on different substrate materials.

[0123] like Figure 11 As shown, the coating prepared in Example 1 can maintain good adhesion and film uniformity on various substrates, and has superhydrophobic self-cleaning and radiation cooling properties in different scenarios.

[0124] Test Example 5 This test example involves conducting radiation cooling tests on the coatings prepared in Examples 1-5 outdoors.

[0125] The coatings prepared in Examples 1-5 were applied to aluminum plates and placed in an unobstructed outdoor environment (ambient temperature of 20-40°C), and the surface temperature of the coatings was monitored.

[0126] like Figure 12 As shown, the first row represents the coatings prepared in Example 1; the second row represents the coatings prepared in Examples 2-5. Through... Figure 12 It is evident that the aluminum plate coated with the radiation cooling coating has a significantly lower temperature than the surrounding environment. This demonstrates that the coatings prepared in Examples 1-5 exhibit excellent cooling effects outdoors, i.e., they possess superior radiation cooling performance.

[0127] Test Example 6 This test example focuses on the thermochromic testing of the coatings prepared in Examples 1-5.

[0128] The coatings prepared in Examples 1-5 were applied to aluminum plates and placed on a constant temperature heating table. The temperature was gradually increased from room temperature to 50°C and then cooled back to room temperature. The color changes were recorded by taking pictures.

[0129] like Figure 13 As shown, Figure 13The thermochromic transformation process of the coatings prepared in Examples 1-5 is demonstrated, proving that the coatings prepared in Examples 2-5 possess reversible color-to-white transformation capabilities. When the ambient temperature is higher than the critical transition temperature (approximately 45°C), the coatings prepared in Examples 2-5 automatically change to a highly reflective white state, maximizing radiative cooling efficiency; when the temperature decreases, they revert to their original color, effectively absorbing sunlight to suppress the "overcooling" phenomenon, thereby overcoming the inherent defect of traditional static radiative cooling materials that cannot adapt to changes in ambient temperature.

[0130] Test Example 7 In this test example, the coating prepared in Example 2 was subjected to thermal imaging testing in an indoor simulation test.

[0131] The adaptive thermochromic, superhydrophobic, self-cleaning radiation-cooling coating prepared in Example 2 (i.e., the multi-colored radiation-cooling coating in the figure) and a commercial coating were respectively coated onto aluminum plates, and thermal imaging tests were conducted on both the coated and bare aluminum plates in an indoor simulation experiment. Using a xenon lamp to simulate sunlight (approximately 1000W), the coated plates were continuously irradiated, and the temperature change curves were recorded. It was found that the temperature rise of the multi-colored superhydrophobic radiation-cooling coating prepared in Example 2 was significantly lower than the others, and it tended to reach equilibrium after approximately 30°C. This indicates that the coating prepared in Example 2 has superior radiation-cooling performance compared to the commercial coating.

[0132] In summary, the adaptive thermochromic, superhydrophobic, self-cleaning radiation cooling coating provided by this invention possesses high reflectivity and high-to-medium infrared emissivity, enabling efficient passive cooling. By introducing thermochromic phase change microcapsules, the coating can automatically adjust its reflectivity according to changes in ambient temperature, providing adaptive temperature control. The coating also exhibits excellent superhydrophobic and self-cleaning properties. Furthermore, the coating structure is stable, wear-resistant, weather-resistant, and resistant to UV aging, making it suitable for long-term antifouling and thermal management applications on building exteriors, roofs, and outdoor equipment.

[0133] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method of making a self-adapting thermochromic, superhydrophobic self-cleaning radiative cooling coating, characterized in that, The preparation method comprises the following steps: S1, dissolving a polymer matrix in an organic solvent, and stirring magnetically at room temperature for 0.5-3 hours to obtain a prepolymer solution; S2, dispersing optical fillers in an organic solvent, and ultrasonic treating for 0.5-3 hours to obtain an emulsion; S3, mixing the prepolymer solution and the emulsion, and stirring at room temperature for 10-60 minutes to obtain a composite suspension; adding thermochromic phase change microcapsules to the composite suspension, and mixing uniformly to obtain a precursor suspension; S4, spraying the precursor suspension on a substrate surface, and curing to obtain the self-adaptive thermochromic, super-hydrophobic self-cleaning and radiation cooling coating.

2. The production method according to claim 1, characterized by, The optical fillers are one or more of hexagonal boron nitride, hollow glass microbeads, silicon dioxide, titanium dioxide, calcium titanate, barium sulfate and aluminum oxide.

3. The production method according to claim 2, characterized by, The optical fillers are hexagonal boron nitride and hollow glass microbeads.

4. The production method according to claim 3, characterized by, The particle size of the hollow glass microbeads is 5-30 μm, and the particle size of the hexagonal boron nitride is 5-50 μm.

5. The preparation method according to claim 1, characterized in that, The particle size of the thermochromic microcapsules is 1.5-20 μm.

6. The method of claim 1, wherein, The organic solvent is one or more of ethyl acetate, dichloromethane, trichloromethane, toluene, dimethylbenzene, N,N-dimethylformamide and tetrahydrofuran.

7. The production method according to claim 1, characterized by, The mass ratio of the polymer matrix to the organic solvent is 1:(5-8), the mass ratio of the polymer matrix to a curing agent used for curing is 10:(0.8-1.2), the mass ratio of the polymer matrix to the optical fillers is 1:(1-3), and the mass content of the thermochromic microcapsules in the precursor suspension is 1%-5%.

8. The method of claim 1, wherein, In step S3, an additive is further added when the thermochromic phase change microcapsules are added; the additive is one or more of an ultraviolet absorber, a light stabilizer and an antioxidant.

9. A self-adaptive thermochromic, super-hydrophobic self-cleaning and radiation cooling coating prepared by the preparation method in any one of claims 1-8.

10. Application of a self-adaptive thermochromic, super-hydrophobic self-cleaning and radiation cooling coating prepared by the preparation method in any one of claims 1-8 in the field of building energy saving, 5G base station, outdoor equipment or vehicle thermal management system.

Images