Composite coating with gradient pore structure as well as preparation method and application of composite coating

Abstract

The invention discloses a composite coating with a gradient hole structure and a preparation method and application thereof, and belongs to the technical field of composite coatings, the composite coating comprises a base material, a radiation cooling layer arranged on the base material and a temperature response layer arranged on the radiation cooling layer; the radiation cooling layer is prepared from a phase change microcapsule and a first polymer solution, and the temperature response layer is prepared from a phase change microcapsule, a thermochromic microcapsule and a second polymer solution; wherein the radiation cooling layer and the temperature response layer have different average pore diameters, and jointly form a gradient pore structure. The technical problem that an existing composite layer structure lacks waterproof performance is solved.

Description

Technical Field

[0001] This invention belongs to the field of functional coating technology, specifically relating to a composite coating with a gradient pore structure, its preparation method, and its application. Background Technology

[0002] Global warming has exacerbated climate system instability and led to more frequent extreme weather events. In particular, persistent high temperatures pose a serious health threat to people working or engaging in outdoor activities. Radiative cooling technology, as a passive cooling method, can dissipate radiant heat into outer space through atmospheric windows of 8-13 μm and reflect solar radiation (0.25-2.5 μm), thus achieving self-cooling. Currently, radiative cooling technology is widely used in textiles, building facades, and solar cells, with a wide range of materials and diverse manufacturing processes. Porous radiative cooling coatings have attracted considerable attention due to their efficient reflection of sunlight, ease of fabrication, and wide applicability. However, they still face some limitations in practical applications. Radiative cooling coatings need high emissivity in the atmospheric window band to enhance mid-infrared radiative heat dissipation. This characteristic can cause them to continuously radiate heat into the cold outer space during non-daytime environments (such as low-temperature nighttime environments), potentially leading to overcooling and limiting their practical application in regions with large diurnal temperature variations.

[0003] To ensure high reflectivity of the coating to sunlight, most coatings are white or silver. This is because the absorption of visible light by dyes or pigments reduces the material's reflectivity to sunlight, thus affecting its radiative cooling effect. This drawback makes it difficult to meet the color requirements of architecture and clothing, limiting its application.

[0004] As an outdoor material, porous coatings are susceptible to contamination from rainwater, dirt, and other liquids, weakening their long-term cooling performance. For example, rainwater seeping into a wall not only contaminates the surface but, if difficult to remove, can lead to dampness and mold. If used as a fabric, liquid seeping into its interior can cause an uncomfortable sticky feeling and even stuffiness during prolonged wear, affecting comfort. Waterproof and breathable coatings prevent liquid water (such as rainwater and snowmelt) from penetrating the material from the external environment while allowing internal water vapor (such as sweat) to diffuse and escape. Integrating waterproof and breathable functionality into radiative cooling coatings can effectively improve their susceptibility to moisture contamination and performance degradation, but it also has limitations. This function relies on constructing a microporous structure with pore sizes between water molecules and water droplets; smaller pore sizes result in better waterproofing, but excessively small pores weaken sunlight scattering, reducing cooling efficiency; excessively large pore sizes easily lead to leakage. Ensuring high waterproofing requires optimizing the pore size to maintain efficient optical properties. Therefore, it is of great significance to develop a porous radiation cooling coating that can solve the problems of non-daytime supercooling and poor waterproof and moisture-permeability, which can broaden its application range.

[0005] Chinese patent CN118087280A discloses an intelligent bidirectional temperature adaptive thermal management fabric, its preparation method, and its application. By coating the surface of the fiber fabric with a radiation cooling layer and a thermochromic phase change microcapsule functional surface layer, the thermochromic phase change microcapsules exhibit colorless or black color at different temperatures, thus adjusting the reflection and absorption rates of sunlight and mid-infrared radiation to achieve intelligent bidirectional temperature adaptive thermal management. However, the composite layer structure of this patent lacks waterproof performance, which limits its practicality and durability in outdoor applications. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide a composite coating with a gradient pore structure, its preparation method and application, so as to solve the technical problem that the existing composite layer structure lacks waterproof and breathable performance.

[0007] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a composite coating with a gradient pore structure, comprising a substrate, a radiation cooling layer disposed on the substrate, and a temperature-responsive layer disposed on the radiation cooling layer; the radiation cooling layer is prepared by phase change microcapsules and a first polymer solution, and the temperature-responsive layer is prepared by phase change microcapsules, thermochromic microcapsules, and a second polymer solution; wherein the average pore size of the radiation cooling layer is smaller than that of the temperature-responsive layer and they have different average pore sizes, together constituting a gradient pore structure.

[0008] Preferably, the pore size of the radiative cooling layer is 0.5μm to 2μm, and the pore size of the temperature response layer is 5μm to 10μm.

[0009] Preferably, the mass fraction of the first polymer solution is 15wt%~40wt%, and the content of phase change microcapsules in the radiation cooling layer is 10wt%~40wt% of the first polymer solution. The second polymer solution has a mass fraction of 10wt% to 30wt%, the phase change microcapsules have a content of 5wt% to 10wt% of the second polymer solution, and the thermochromic microcapsules have a content of 8wt% to 15wt% of the second polymer solution.

[0010] Preferably, the polymers in the first polymer solution and the second polymer solution are each selected from one or a mixture of any two of polyurethane, cellulose acetate, polyvinylidene fluoride, and cellulose acetate butyrate; when the polymer in the first polymer solution is a mixture of any two of polyurethane, cellulose acetate, polyvinylidene fluoride, and cellulose acetate butyrate, the mass ratio of the two polymers is (1-5):(1-5); when the polymer in the second polymer solution is a mixture of any two of polyurethane, cellulose acetate, polyvinylidene fluoride, and cellulose acetate butyrate, the mass ratio of the two polymers is (1~3):(3~1).

[0011] Preferably, the phase transition temperature of the phase change microcapsules is 28~40℃, and the particle size is 300nm~800nm; the phase transition temperature of the thermochromic microcapsules is 28~40℃, and the particle size is 800~1500nm. The color change mechanism is: colorless at high temperatures and color developed at low temperatures. Specifically, if thermochromic microcapsules with a phase transition temperature of 40℃ are selected, the composite coating will be colorless when the external temperature is above 40℃, and will develop color when the external temperature is below 40℃. The color change mechanism of thermochromic microcapsules with a phase transition temperature of 28~40℃ is the same.

[0012] Preferably, the substrate includes any one of fabric, leather, ceramic and polyvinyl chloride board.

[0013] Preferably, the thickness of the radiative cooling layer is 300μm~500μm, and the thickness of the temperature response layer is 100μm~200μm.

[0014] The present invention also provides a method for preparing the above-mentioned composite coating with a gradient pore structure, comprising the following steps: Step 1: Add the first polymer to the mixed solvent and stir to form a first polymer solution. Disperse the phase change microcapsules into the mixed solvent and mix them with the first polymer solution to obtain composite solution A. Step 2: Add the second polymer to the mixed solvent and stir to form a second polymer solution. Disperse the phase change microcapsules and thermochromic microcapsules into the mixed solvent and mix them with the second polymer solution to obtain composite solution B. Step 3: Apply composite solution A to the surface of the substrate and place it in a constant temperature and humidity environment for 10-20 minutes. Then remove it and vacuum dry it to form a radiation cooling layer. Apply composite solution B to the surface of the radiation cooling layer and place it in a constant temperature and humidity environment for 15-30 minutes. After soaking, remove it and vacuum dry it to form a temperature response layer. This yields a composite coating with a gradient pore structure.

[0015] Preferably, in step 3, during the formation of the radiative cooling layer, the constant temperature is 30~50℃ and the constant humidity is 60~90%; during the formation of the temperature response layer, the constant temperature is 30~50℃ and the constant humidity is 70~90%.

[0016] Further preferably, the mixed solvents in both the first and second polymer solutions comprise a mixture of any two of N,N-dimethylformamide, N-methylpyrrolidone, N,N-dimethylacetamide, and dimethyl sulfoxide. In the first polymer solution, the mass ratio of any two solvents is (1~3):(1~3), and in the second polymer solution, the mass ratio of any two solvents is (1~3):(1~3). The function of the mixed solvents is to ensure that the phase change microcapsules or thermochromic microcapsules achieve a high degree of uniform dispersion in the final composite solution A or composite solution B, preventing agglomeration caused by directly adding a high-viscosity polymer solution.

[0017] The present invention also provides applications of the above-mentioned composite coating with gradient pore structure in the fields of building energy conservation, smart textiles, outdoor equipment, or energy thermal management.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a composite coating with a gradient pore structure, comprising a substrate, a radiative cooling layer, and a temperature-responsive layer. The average pore size of the radiative cooling layer is smaller than that of the temperature-responsive layer, forming a gradient pore structure that achieves both radiative cooling and waterproof / breathable functionality. The gradient pore structure manages moisture penetration through a gradual distribution of pore size: smaller pores in the radiative cooling layer effectively block liquid water intrusion, while larger pores in the temperature-responsive layer allow water vapor to pass through, thus achieving a balance between waterproofing and breathability. Simultaneously, the predominantly large pore size of the temperature-responsive layer enhances the scattering and reflection of sunlight, improving radiative cooling performance. This structure reduces moisture accumulation and prevents coating failure due to water immersion. Furthermore, the presence of phase change microcapsules in both layers aids in temperature regulation, reducing condensation caused by temperature fluctuations through phase change heat absorption or release, indirectly enhancing waterproof durability. Because the radiative cooling layer has a small pore structure, it allows water vapor to escape smoothly while blocking external liquid water penetration, achieving excellent waterproof and breathable performance and mitigating the drawbacks of large pores in the temperature-responsive layer that allow water seepage. This gradient pore structure spatially coordinates the conflicting pore size requirements of radiative cooling and waterproofing / permeability. It avoids the problem of poor radiative cooling performance caused by weak reflection in a single small pore structure, and also overcomes the water seepage defect of a single large pore structure, significantly expanding the applicability of the material in complex outdoor environments.

[0019] The gradient pore structure also achieves high solar reflectivity, which, combined with the high infrared emissivity of the polymer, can play a role in radiative cooling. At the same time, the phase change microcapsules in the composite coating can achieve daytime cooling and alleviate nighttime overcooling by storing and releasing heat. Thermochromic microcapsules can switch colors according to the ambient temperature. When the temperature is high (such as during the day), they become light-colored or transparent to maintain high solar reflectivity and ensure radiative cooling performance. When the temperature is low (such as at night), they become colored, which not only meets the need for coloring but also inhibits radiative heat dissipation and enhances the heat preservation effect. The two work together to achieve dual adaptive radiative cooling.

[0020] Furthermore, the pore size of the radiative cooling layer is 0.5μm~2μm, and the pore size of the temperature-responsive layer is 5μm~10μm. The large pore size of the temperature-responsive layer enhances the scattering and reflection of sunlight, improving radiative cooling performance, and also provides an efficient channel for water vapor molecules to escape. The small pore structure of the radiative cooling layer, while blocking the penetration of external liquid water, still allows internal water vapor to escape, thus synergistically achieving excellent waterproof and breathable functions.

[0021] Furthermore, the mass fraction range of the first and second polymer solutions ensures that the solutions can form a continuous and uniform film, creating a waterproof barrier through the interweaving of polymer chains. The microcapsule content of the radiative cooling layer is 10-40 wt%, and the microcapsule content of the temperature-responsive layer is 5-15 wt%. These two content ranges provide phase change functionality without excessively compromising coating integrity. The high polymer content enhances the mechanical strength and hydrophobicity of the coating, while the uniform dispersion of the microcapsules prevents localized weaknesses, thereby improving overall waterproof performance.

[0022] The mass fraction of the first polymer solution, due to its slower exchange rate between solvent and water (non-solvent) during phase separation, facilitates the formation of a dense microporous structure. The small pore size contributes to waterproofing and moisture permeability, blocking liquid water while allowing water vapor to pass through. The content of phase change microcapsules in the radiant cooling layer ensures sufficient loading to provide heat storage and release functions, mitigating nighttime overcooling issues without excessively interfering with the phase separation process of the polymer solution. Excessive content may damage the pore structure, while insufficient content may weaken the phase change effect; a range of 10wt%-40wt% optimizes the balance between function and structure.

[0023] During phase separation, the exchange rate between solvent and water (non-solvent) in the second polymer solution is faster, making it easier to form a macroporous structure. The large pore size helps enhance solar reflection and scattering, improving radiative cooling performance. The content of phase change microcapsules and thermochromic microcapsules in the temperature-responsive layer ensures sufficient thermochromic and phase change functions without significantly affecting the formation of the macroporous structure. Thermochromic microcapsules become light-colored or transparent at high temperatures, maintaining high reflectivity; they develop color at low temperatures, meeting color requirements and suppressing heat dissipation. Phase change microcapsules provide additional thermal management.

[0024] Furthermore, both the first and second polymers possess inherent hydrophobic or waterproof properties. Polyurethane, due to its elastomer properties and water resistance, is suitable for waterproof coatings, while cellulose acetate can form a dense film. The combined use of these two polymers can enhance the hydrolytic stability and flexibility of the coating, preventing water molecule penetration through hydrogen bonds or hydrophobic interactions, thereby directly strengthening the waterproofing effect.

[0025] The mass ratio of the two polymers in the first polymer solution is (1-5):(1-5). By adjusting the ratio, a higher proportion of the polymer with good miscibility with water (non-solvent) can be selected, thereby forming finer pores and enhancing waterproof and breathable properties. In addition, this ratio range also provides flexibility, allowing optimization based on the specific polymer's effect on miscibility.

[0026] The mass ratio of the two polymers in the second polymer solution is (1~3):(3~1). By adjusting the ratio, a higher proportion of the polymer with poor miscibility with water (a non-solvent) can be selected, thereby forming larger pores and enhancing radiative cooling performance. This ratio range ensures the controllability of the upper pore structure.

[0027] Furthermore, the phase change temperature (28-40°C) matches the ambient temperature range. When the temperature changes, the phase change material absorbs or releases latent heat, reducing microcracks in the coating caused by thermal stress and thus preventing water molecule intrusion. The particle size of the phase change microcapsules and thermochromic microcapsules ensures uniform dispersion of the microcapsules without compromising the continuity of the coating.

[0028] Furthermore, one of the following materials—fabric, leather, ceramic, and PVC board—is selected as the substrate. These substrates are commonly used in outdoor settings and frequently face challenges such as high temperatures and rain erosion. The coating provides additional functional enhancements. The gradient pore structure of the coating not only bonds with the substrate to form an overall waterproof barrier but also reduces the surface temperature of the substrate through radiative cooling, thereby improving the environmental durability of the substrate.

[0029] Furthermore, the varying thicknesses of the radiative cooling and temperature-responsive layers ensure that the coatings are of sufficient quality to prevent water penetration while avoiding excessive thickness that could lead to cracking or reduced breathability. The thicker radiative cooling layer provides the primary waterproof barrier, while the thinner temperature-responsive layer allows vapor to pass through, balancing waterproofing and comfort.

[0030] This invention also provides a method for preparing the aforementioned composite coating. First, two polymer solutions are prepared, and phase change microcapsules and thermochromic microcapsules are added to each to form a composite solution. Then, a layer-by-layer coating process is performed (first, composite solution A containing phase change microcapsules is coated onto the substrate surface to form a radiation-cooled layer, then composite solution B containing both phase change and thermochromic microcapsules is coated onto it to form a temperature-responsive layer). Phase separation is carried out under constant temperature and humidity conditions. Finally, after vacuum drying, a composite coating with a gradient pore structure is obtained. This method ensures the formation of the gradient pore structure by controlling the coating process. The coating technique allows for uniform coating application and avoids defects; the constant temperature and humidity environment (10-20 min) controls the solvent evaporation rate, affecting the formation of the pore structure; slower evaporation leads to denser pores, enhancing water resistance. Vacuum drying removes residual solvent, strengthens the coating structure, and prevents water molecule penetration.

[0031] Furthermore, constant temperature and humidity conditions (temperature 30-50°C, humidity 60-90%) optimized the polymer gelation and pore formation process. Higher humidity (70-90%) facilitated phase separation, resulting in a more uniform pore structure and thus enhancing water resistance; temperature control ensured that the phase change microcapsules were not damaged.

[0032] This invention also provides applications of the above-mentioned composite coating in the fields of building energy conservation, smart textiles, outdoor equipment, or energy thermal management, specifically including: 1) Building exterior walls: Coated to building exterior walls, it can significantly reflect solar radiation and reduce indoor temperature in summer, reducing air conditioning energy consumption; in winter, the phase change material in the coating can alleviate nighttime cold, and the thermochromic properties can regulate the heat absorption / dissipation balance. Its waterproof and breathable properties can prevent rainwater intrusion while allowing water vapor inside the wall to escape, preventing condensation and mold, and protecting the building structure; 2) Outdoor clothing: Used in mountaineering clothing, protective clothing, sportswear, etc., it can effectively reduce the body surface temperature during the day and prevent excessive cold at night; the waterproof and breathable function ensures that the wearer stays dry and comfortable during exercise; 3) Outdoor equipment: Used in outdoor tents, warehouse tarpaulins, etc., it can reflect sunlight, reduce the temperature inside the tent, prevent internal condensation, and resist rainwater erosion; 4) Energy equipment: Coated on the outer shell of communication base stations, distribution boxes, etc., it can prevent the equipment from performance degradation or shutdown due to high temperature overheating, while protecting the equipment from rain and humid environment erosion. Attached Figure Description

[0033] Figure 1 This is a schematic diagram illustrating the principle of radiation cooling and waterproofing / breathability of the composite coating of the present invention. Figure 2 Infrared thermal imaging image of the composite coating prepared in Example 3 of this invention; Figure 3 The water contact angle of the composite coating prepared in Example 3 of this invention; Figure 4 a is a SEM image of the radiation cooling layer of the composite coating prepared in Example 3 of the present invention. Figure 4 b is a SEM image of the temperature-responsive layer of the composite coating prepared in Example 3 of the present invention. Detailed Implementation

[0034] To enable those skilled in the art to understand the features and effects of the present invention, the following descriptions and definitions are only general descriptions of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in the event of any conflict, the definitions in this specification shall prevail.

[0035] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0036] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0037] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0038] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0039] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0040] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents parts by weight, and "ratio" represents weight proportion.

[0041] Example 1 First, a polyurethane solution with a mass fraction of 15 wt% was prepared using N,N-dimethylformamide and dimethyl sulfoxide in a mass ratio of 1:3 as a mixed solvent. Then, phase change microcapsules with a phase change temperature of 28°C and a particle size of 500 nm were added, with a mass fraction of 20 wt% of the polyurethane solution. After thorough mixing, composite solution A was obtained.

[0042] Simultaneously, using N,N-dimethylformamide and dimethyl sulfoxide in a mass ratio of 1:3 as a mixed solvent, a polyurethane solution with a mass fraction of 20 wt% was prepared. Phase change microcapsules with a phase change temperature of 28℃ and a particle size of 500 μm and thermochromic microcapsules with a phase change temperature of 28℃ and a particle size of 800 μm were added, with their mass fractions being 5 wt% and 10 wt% of the polyurethane solution, respectively. After mixing evenly, composite solution B was obtained.

[0043] Subsequently, composite solution A was scraped onto the leather surface and placed in an environment with a temperature of 30°C and a humidity of 50% for 10 minutes. It was then removed and vacuum dried to obtain composite coating A with a thickness of 400 μm. Next, composite solution B was scraped onto the surface of composite coating A, controlling the coating thickness to 200 μm, and placed in an environment with a temperature of 40°C and a humidity of 70% for 15 minutes. It was then immersed in deionized water for 1 hour, removed, and vacuum dried to obtain a dual adaptive radiative cooling-waterproof and breathable composite coating with a gradient pore structure. This coating achieves dual adaptive radiative cooling within a 28°C phase transition range, with a solar reflectance of 92% and a mid-infrared emissivity of 96%, and can withstand solar irradiance of 500 W / m². 2 A temperature drop of 5℃ was achieved, with a static water contact angle of 115°, a hydrostatic pressure of 65.1 kPa, and a moisture permeability of 8.42 kg·m³. -2 ·d -1 .

[0044] Example 2 First, a polymer solution with a mass fraction of 20 wt% was prepared by dissolving polyvinylidene fluoride and cellulose acetate in a mass ratio of 2:1 using N,N-dimethylacetamide and N-methylpyrrolidone as a mixed solvent. Then, phase change microcapsules with a phase change temperature of 37°C and a particle size of 700 nm were added, with a mass fraction of 40 wt% of the polymer solution. After thorough mixing, composite solution A was obtained.

[0045] Simultaneously, using N,N-dimethylacetamide and N-methylpyrrolidone in a mass ratio of 1:2 as a mixed solvent, polyvinylidene fluoride and cellulose acetate in a mass ratio of 3:1 were dissolved to prepare a polymer solution with a mass fraction of 25 wt%. Subsequently, phase change microcapsules with a phase change temperature of 37°C and a particle size of 700 μm and thermochromic microcapsules with a phase change temperature of 33°C and a particle size of 1000 μm were added, with mass fractions of 6 wt% and 12 wt% of the polymer solution, respectively. After thorough mixing, composite solution B was obtained.

[0046] Subsequently, composite solution A was applied to the surface of a PVC board and placed in an environment with a temperature of 40°C and a humidity of 70% for 10 minutes. After removal and vacuum drying, a composite coating A with a thickness of 300 μm was obtained. Next, composite solution B was applied to the surface of composite coating A, controlling the coating thickness to 100 μm. The board was then placed in an environment with a temperature of 50°C and a humidity of 90% for 20 minutes, immersed in deionized water for 2 hours, and then removed and vacuum dried to obtain a dual adaptive radiative cooling-waterproof and breathable composite coating with a gradient pore structure. This coating achieves dual adaptive radiative cooling within a 37°C phase transition range, with a solar reflectance of 94% and a mid-infrared emissivity of 97%, and can withstand solar irradiance of 700 W / m². 2 A temperature drop of 7°C was achieved, with a static water contact angle of 127°, a hydrostatic pressure of 71.3 kPa, and a moisture permeability of 9.06 kg·m³. -2 ·d -1 .

[0047] Example 3 First, a polymer solution with a mass ratio of 25 wt% was prepared by dissolving polyurethane and cellulose acetate in a 1:1 mass ratio using N,N-dimethylformamide and N-methylpyrrolidone as a mixed solvent. Then, phase change microcapsules with a phase change temperature of 40°C and a particle size of 600 nm were added, with a mass fraction of 30 wt% of the polymer solution. After thorough mixing, composite solution A was obtained.

[0048] Simultaneously, using N,N-dimethylformamide and N-methylpyrrolidone in a 1:1 mass ratio as a mixed solvent, polyurethane and cellulose acetate in a 3:1 mass ratio were dissolved to prepare a polymer solution with a mass fraction of 30 wt%. Subsequently, phase change microcapsules with a phase change temperature of 40℃ and a particle size of 600 μm and thermochromic microcapsules with a phase change temperature of 40℃ and a particle size of 1500 μm were added, with mass fractions of 10 wt% and 10 wt% of the above polymer solution, respectively. After thorough mixing, composite solution B was obtained.

[0049] Subsequently, composite solution A was applied to the fabric surface and placed in an environment with a temperature of 45℃ and a humidity of 80% for 20 minutes. After removal and vacuum drying, a composite coating A with a thickness of 300 μm was obtained. Next, composite solution B was applied to the surface of composite coating A, controlling the coating thickness to 200 μm. This coating was then placed in an environment with a temperature of 50℃ and a humidity of 90% for 30 minutes, immersed in deionized water for 1 hour, and then removed and vacuum dried to obtain a dual adaptive radiative cooling-waterproof and breathable composite coating with a gradient pore structure. This coating achieves dual adaptive radiative cooling within a 40℃ phase transition range, has a solar reflectivity of 95%, a mid-infrared emissivity of 98%, and can withstand solar irradiance of 800 W / m². 2A temperature drop of 10℃ was achieved, with a hydrostatic pressure of 75.2 kPa and a moisture permeability of 11.47 kg·m³. -2 ·d -1 .like Figure 1 As shown, the large-pore structure of the temperature-responsive layer can reflect sunlight and change color according to temperature changes, achieving efficient radiative cooling; the small-pore structure of the radiative cooling layer blocks external liquid water penetration while allowing internal water vapor to escape, and the internal phase change microcapsules also cool down through phase change heat storage / release. The two work synergistically to achieve both radiative cooling and waterproof / breathable effects; Figure 2 As shown, the fabric with composite coating prepared in this embodiment has a more significant heat insulation effect compared to the cotton fabric control group; as Figure 3 As shown, the static water contact angle of the composite coating obtained in this embodiment is 131°, thus proving that it has a certain degree of waterproof performance. Figure 4 Figure a shows a SEM image of the composite coating radiation cooling layer of this invention. This layer exhibits a dense, sponge-like microporous structure with an average pore size distribution between 0.5 μm and 2 μm. This precise pore structure effectively blocks the permeation of external liquid water while allowing water vapor to pass through. Furthermore, the phase change microcapsules in the coating achieve temperature regulation through heat storage / release. Figure 4 Figure b shows a SEM image of the temperature-responsive composite coating layer of this invention. This layer forms an open, interconnected pore structure with an average pore size distribution of 5μm-10μm. This pore structure can reflect sunlight and efficiently remove water vapor. Furthermore, the synergistic effect of phase change microcapsules and thermochromic microcapsules within the coating achieves radiative cooling and waterproof / breathable functions.

[0050] Example 4 First, a polymer solution with a mass fraction of 40 wt% was prepared by dissolving polyvinylidene fluoride and cellulose acetate butyrate in a mass ratio of 1:3 in a mixed solvent of N-methylpyrrolidone and dimethyl sulfoxide in a mass ratio of 2:5. Then, phase change microcapsules with a phase change temperature of 37°C and a particle size of 800 nm were added, with a mass fraction of 15 wt% of the polymer solution. After thorough mixing, composite solution A was obtained.

[0051] Simultaneously, a polymer solution with a mass ratio of 20 wt% was prepared by dissolving polyvinylidene fluoride and cellulose acetate butyrate in a mass ratio of 3:1 in a mixed solvent of N-methylpyrrolidone and dimethyl sulfoxide in a mass ratio of 3:2. Subsequently, phase change microcapsules with a phase change temperature of 37°C and a particle size of 800 μm and thermochromic microcapsules with a phase change temperature of 37°C and a particle size of 1000 μm were added, with mass fractions of 8 wt% and 15 wt% of the polymer solution, respectively. After thorough mixing, composite solution B was obtained.

[0052] Subsequently, composite solution A was applied to the ceramic surface and placed in an environment with a temperature of 45℃ and a humidity of 80% for 10 minutes. After removal and vacuum drying, a composite coating A with a thickness of 500 μm was obtained. Next, composite solution B was applied to the surface of composite coating A, controlling the coating thickness to 100 μm. This coating was then placed in an environment with a temperature of 50℃ and a humidity of 90% for 15 minutes, immersed in deionized water for 1 hour, and then removed and vacuum dried to obtain a dual adaptive radiative cooling-waterproof and breathable composite coating with a gradient pore structure. This coating achieves dual adaptive radiative cooling within a 37℃ phase transition range, with a solar reflectivity of 94% and a mid-infrared emissivity of 96%, and can withstand solar irradiance of 900 W / m². 2 A temperature drop of 6℃ was achieved, with a static water contact angle of 121°, a hydrostatic pressure of 80.6 kPa, and a moisture permeability of 10.08 kg·m³. -2 ·d -1 .

[0053] Example 5 First, a polymer solution with a mass fraction of 40 wt% was prepared by dissolving polyvinylidene fluoride and cellulose acetate butyrate in a mass ratio of 1:3 in a mixed solvent of N-methylpyrrolidone and dimethyl sulfoxide in a mass ratio of 2:5. Then, phase change microcapsules with a phase change temperature of 37°C and a particle size of 300 nm were added, with a mass fraction of 10 wt% of the polymer solution. After thorough mixing, composite solution A was obtained.

[0054] Simultaneously, using N-methylpyrrolidone and dimethyl sulfoxide in a mass ratio of 3:2 as a mixed solvent, polyvinylidene fluoride and cellulose acetate butyrate in a mass ratio of 3:1 were dissolved to prepare a polymer solution with a mass fraction of 10 wt%. Subsequently, phase change microcapsules with a phase change temperature of 37°C and a particle size of 800 μm and thermochromic microcapsules with a phase change temperature of 37°C and a particle size of 1000 μm were added, with mass fractions of 8 wt% and 8 wt% of the above polymer solution, respectively. After thorough mixing, composite solution B was obtained.

[0055] Subsequently, composite solution A was applied to the ceramic surface and placed in an environment with a temperature of 45°C and a humidity of 80% for 10 minutes. It was then removed and vacuum dried to obtain a composite coating A with a thickness of 500 μm. Next, composite solution B was applied to the surface of composite coating A, controlling the coating thickness to 100 μm. It was then placed in an environment with a temperature of 50°C and a humidity of 90% for 15 minutes. After immersing it in deionized water for 1 hour, it was removed and vacuum dried to obtain a dual adaptive radiation cooling-waterproof and breathable composite coating with a gradient pore structure.

[0056] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A composite coating with a gradient pore structure, characterized in that, The invention includes a substrate, a radiation cooling layer disposed on the substrate, and a temperature-responsive layer disposed on the radiation cooling layer; the radiation cooling layer is prepared by phase change microcapsules and a first polymer solution, and the temperature-responsive layer is prepared by phase change microcapsules, thermochromic microcapsules, and a second polymer solution; wherein the average pore size of the radiation cooling layer is smaller than the average pore size of the temperature-responsive layer, together forming a gradient pore structure.

2. The composite coating with a gradient pore structure according to claim 1, characterized in that, The pore size of the radiative cooling layer is 0.5μm~2μm, and the pore size of the temperature response layer is 5μm~10μm.

3. A composite coating with a gradient pore structure according to claim 1, characterized in that, The mass fraction of the first polymer solution is 15wt%~40wt%, and the content of phase change microcapsules in the radiation cooling layer is 10wt%~40wt% of the first polymer solution. The second polymer solution has a mass fraction of 10wt% to 30wt%, the phase change microcapsules have a content of 5wt% to 10wt% of the second polymer solution, and the thermochromic microcapsules have a content of 8wt% to 15wt% of the second polymer solution.

4. The composite coating with a gradient pore structure according to claim 3, characterized in that, The polymers in the first polymer solution and the second polymer solution are each selected from one or a mixture of any two of polyurethane, cellulose acetate, polyvinylidene fluoride and cellulose acetate butyrate; when the polymer in the first polymer solution is a mixture of any two of polyurethane, cellulose acetate, polyvinylidene fluoride and cellulose acetate butyrate, the mass ratio of the two polymers is (1-5):(1-5); when the polymer in the second polymer solution is a mixture of any two of polyurethane, cellulose acetate, polyvinylidene fluoride and cellulose acetate butyrate, the mass ratio of the two polymers is (1~3):(3~1).

5. A composite coating with a gradient pore structure according to claim 1, characterized in that, The phase change microcapsules have a phase change temperature of 28~40℃ and a particle size of 300nm~800nm; the thermochromic microcapsules have a phase change temperature of 28~40℃ and a particle size of 800~1500nm.

6. The composite coating with a gradient pore structure according to claim 1, characterized in that, The substrate includes any one of fabric, leather, ceramic and polyvinyl chloride board.

7. The composite coating with a gradient pore structure according to claim 1, characterized in that, The thickness of the radiation cooling layer is 300μm~500μm, and the thickness of the temperature response layer is 100μm~200μm.

8. A method for preparing a composite coating with a gradient pore structure according to any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Add the first polymer to the mixed solvent and stir to form a first polymer solution. Disperse the phase change microcapsules into the mixed solvent and mix them with the first polymer solution to obtain composite solution A. Step 2: Add the second polymer to the mixed solvent and stir to form a second polymer solution. Disperse the phase change microcapsules and thermochromic microcapsules into the mixed solvent and mix them with the second polymer solution to obtain composite solution B. Step 3: Apply composite solution A to the surface of the substrate and place it in a constant temperature and humidity environment for 10-20 minutes. Then remove it and vacuum dry it to form a radiation cooling layer. Composite solution B is applied to the surface of the radiation cooling layer and placed in a constant temperature and humidity environment for 15-30 minutes. After soaking, it is removed and vacuum dried to form a temperature-responsive layer, thereby obtaining a composite coating with a gradient pore structure.

9. The method for preparing a composite coating with a gradient pore structure according to claim 8, characterized in that, In step 3, during the formation of the radiative cooling layer, the constant temperature is 30~50℃ and the constant humidity is 60~90%; during the formation of the temperature response layer, the constant temperature is 30~50℃ and the constant humidity is 70~90%.

10. The application of a composite coating with a gradient pore structure as described in any one of claims 1 to 7 in the fields of building energy conservation, smart textiles, outdoor equipment, or energy thermal management.

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