A color sandwich structure daytime radiative cooler and a preparation method thereof

Abstract

The present application relates to the technical field of passive radiation refrigeration, and specifically discloses a color sandwich structure daytime radiation refrigerator and a preparation method thereof. The refrigerator is a composite sandwich structure, and sequentially comprises an emission layer, a color layer, a separation layer and a porous radiation refrigeration substrate from top to bottom. The color layer is dispersed in a matrix by using an infrared transparent inorganic colorant, so that visible light selective absorption color development is realized, and high reflection in the near-infrared band is maintained. The present application solves the problem of damage of the color layer to the porous structure of the refrigeration layer by the sandwich structure design, and realizes the balance between color performance and refrigeration performance. The solar spectrum reflectivity of the refrigerator can reach 89.9%~91.2%, the mid-infrared emissivity can reach 0.982~0.983, and sub-environmental refrigeration of less than 3.7~5.4℃ below the ambient temperature can be realized during the day. Compared with commercial coatings of the same chroma, the temperature difference reaches 33.3~42.2℃, and the refrigerator has excellent environmental stability and large-scale preparation capacity, and can be widely applied to the fields of building energy saving and outdoor facility cooling, and has significant energy saving and carbon reduction benefits.

Description

Technical Field

[0001] This invention relates to the field of passive daytime radiation cooling technology, and in particular to a colored sandwich structure daytime radiation cooler and its preparation method. Background Technology

[0002] Passive daytime radiative cooling (PDRC) technology achieves high reflectivity in the solar spectrum (0.3~2.5μm) and high emissivity in the mid-infrared band within the atmospheric transparency window (8~13μm) by modulating the spectral properties of materials. This allows heat to be transferred to outer space via thermal radiation, achieving sub-daytime cooling without any energy input. It is a highly promising zero-energy cooling technology. Currently developed PDRC materials, including inorganic dielectric materials, polymer-based composites, and metamaterials, can all achieve efficient sub-daytime cooling. However, to achieve high solar reflectivity, these materials are typically white or silver, lacking aesthetic appeal and exacerbating light pollution, severely limiting their application in scenarios where color is critical, such as building facades and decorative features.

[0003] To achieve colored radiative cooling, existing technologies mainly employ structural color photonic crystals, organic dyes, photoluminescent materials, and inorganic colorants. However, existing solutions have several drawbacks: structural color photonic crystals require complex structural designs and precise fabrication processes, resulting in high costs and difficulty in large-scale production; organic dyes exhibit tail absorption in the near-infrared band, introducing additional heat load and reducing cooling performance; photoluminescent materials lack sufficient color diversity and environmental stability; and existing inorganic colorant-based colored cooling coatings often employ single-layer / double-layer structures where the colorant is directly mixed into the cooling layer or directly coated onto its surface. This can clog or even damage the porous microstructure of the cooling layer, leading to a significant decrease in solar reflectivity and failing to balance color performance with efficient sub-environmental cooling capabilities.

[0004] Patent CN113954453B discloses a colored double-layer radiation cooling film and its preparation method, which includes a layered radiation cooling bottom layer and a colored layer. Although it achieves colored and daytime cooling effects, its bottom layer adopts a conventional structure, and the radiation cooling effect is limited.

[0005] Patent CN115403887A discloses a colored daytime passive radiation cooling porous membrane and its preparation method. It adopts a single-layer structure and disperses inorganic particles and inorganic pigments in an organic polymer. Although it achieves color and daytime cooling effect, its reflectivity is low.

[0006] Therefore, developing a colored radiation cooling material that combines vibrant colors, high efficiency in daytime sub-environmental cooling performance, good environmental stability, and scalability has become a pressing technical challenge in this field. Summary of the Invention

[0007] This invention discloses a colored sandwich structure daytime radiative cooler and its preparation method, aiming to solve the technical problems in the prior art, such as the contradiction between color performance and cooling performance of colored radiative cooling materials, the complexity of the preparation process and the difficulty in scaling up, and the easy damage of the cooling layer structure by the coloring layer leading to performance degradation. Through the composite sandwich structure design, it achieves spectral modulation of selective absorption and color rendering of visible light, high reflectivity in the near-infrared, and high emission in the mid-infrared, while avoiding damage to the microstructure of the cooling layer by the coloring layer. It balances bright colors with efficient sub-environmental cooling performance, and the preparation process is simple, can be mass-produced, and has excellent environmental stability.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A colored sandwich structure daytime radiative cooler, wherein the cooler is a composite sandwich structure, comprising, from top to bottom, an emission layer, a colored layer, an isolation layer and a radiative cooling substrate; The emitting layer is a polydimethylsiloxane (PDMS) film. Using a PDMS film as the emitting layer on the outermost layer of the cooler provides several advantages. First, it exhibits high light transmittance in the 0.3–2.5 μm solar spectrum and high broadband emission characteristics in the 2.5–25 μm mid-infrared band. Second, the PDMS film possesses superhydrophobic properties (water contact angle 139.4°), exhibiting excellent self-cleaning, rain erosion resistance, and acid corrosion resistance, meeting the requirements for long-term outdoor use and ensuring stable cooler performance. Furthermore, the thickness of the emission layer is 2~10μm. For example, the thickness of the emission layer is 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, or any range between any two of the above numbers, such as 2~9.5μm, 2~7.5μm, 2~5.5μm, 2~3.5μm, 3~8μm, 4~6μm, 3~7μm, 4.5~7.5μm. Within this range, the thickness of the emission layer can ensure that the product has excellent emission characteristics, while meeting the requirements of long-term outdoor use and ensuring the stable performance of the cooler. Furthermore, the thickness of the emission layer is 6μm. Within this range, the product can be guaranteed to have excellent emission characteristics, while also meeting the requirements for long-term outdoor use and ensuring stable performance of the cooler. The colored layer is a composite film formed by dispersing an infrared transparent inorganic colorant in a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) matrix. This composite film can selectively absorb specific wavelengths in the visible light band to achieve color development, while having no significant absorption in the near-infrared band, thus avoiding the introduction of additional heat load. Furthermore, the thickness of the color layer is 1~5μm. For example, the thickness of the color layer is 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, or any range between any two of the above numbers, such as 1~4.5μm, 1~4μm, 1~3.5μm, 1~3μm, 1~2μm, 1.5~3.5μm, 1.5~2.5μm, 2.5~4.5μm. Within this range, the thickness of the color layer can ensure that the product can achieve specific color rendering, while ensuring that there is no obvious absorption in the near-infrared band, thus avoiding the introduction of additional heat load. Furthermore, the thickness of the color layer is 2μm. Within this range, the thickness of the color layer can ensure that the product can achieve specific color rendering, while also ensuring that there is no significant absorption in the near-infrared band, thus avoiding the introduction of additional heat load. Further, the particle size of the infrared transparent inorganic colorant is 30~50nm. For example, the particle size of the red transparent inorganic colorant is 30nm, 31nm, 32nm, 33nm, 34nm, 35nm, 36nm, 37nm, 38nm, 39nm, 40nm, 41nm, 42nm, 43nm, 44nm, 45nm, 46nm, 47nm, 48nm, 49nm, 50nm, or a range between any two of the above numbers, such as 30~48nm, 30~46nm, 30~44nm, 30~42nm, 30~40nm, 30~38nm, 30~36nm, 34~46nm, 38~44nm, 40~48nm. The particle size is 40~46nm; the mass fraction of the infrared transparent inorganic colorant in the color layer is 0.1%~0.6%. For example, the mass fraction of the infrared transparent inorganic colorant in the color layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or any two of the above values, such as 0.1%~0.5%, 0.1%~0.4%, 0.1%~0.3%, 0.1%~0.2%, 0.2%~0.5%, 0.2%~0.4%, 0.3%~0.4%. When the particle size and mass fraction of the infrared transparent inorganic colorant are within this range, the colorant can be uniformly dispersed, has excellent color rendering properties, and the color saturation can be controlled without affecting the near-infrared reflectivity. Furthermore, the infrared transparent inorganic colorant is selected from at least one of red, yellow, and blue colorants; using the above colorants can meet different color rendering requirements without affecting the near-infrared reflectivity; Furthermore, the red colorant is iron oxide (Fe2O3), the yellow colorant is nano-silicon (SiNPs), and the blue colorant is Prussian blue (PB). Using the above colorants can meet different color rendering requirements without affecting the near-infrared reflectivity. The isolation layer is a polydimethylsiloxane (PDMS) film; this film has high solar spectrum transmittance and is used to isolate the color layer from the radiation cooling substrate, avoiding blockage and damage to the porous structure of the cooling substrate during the color layer coating process; Furthermore, the thickness of the isolation layer is 5~15μm. For example, the thickness of the isolation layer is 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or any range between any two of the above numbers, such as 5~13μm, 5~11μm, 5~10μm, 5~8μm, 7~14μm, 7~11μm, 9~12μm, 10~14μm. Within this thickness range, the isolation layer can ensure high solar spectral transmittance while effectively isolating the color layer from the radiation cooling substrate, and ensuring the consistency and performance stability of the cooler product. The radiation cooling substrate is a porous thin film formed by the composite of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and alumina nanoparticles (Al2O3NPs). This thin film achieves high reflectivity across the entire solar spectrum through the Mie scattering effect, while also exhibiting high emission characteristics in the mid-infrared band. Further, the thickness of the radiation-cooled substrate is 100~300μm. For example, the thickness of the radiation-cooled substrate is 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, 210μm, 220μm, 230μm, 240μm, 250μm, 260μm, 270μm, 280μm, 290μm, 300μm, or a range between any two of the above numbers, such as 100~280μm, 100~260μm, 100~240μm, 100~220μm. The thickness of the radiation-cooled substrate falls within this range, ensuring uniform dispersion of the nanoparticles, achieving high reflectivity across the entire solar spectrum, and exhibiting high emission characteristics in the mid-infrared band. Furthermore, the thickness of the radiation cooling substrate is 200 μm. Within this range, the uniform dispersion of the dispersed nanoparticles can be ensured, high reflectivity across the entire solar spectrum can be achieved, and high emission characteristics can be maintained in the mid-infrared band. Further, the particle size of the Al2O3 NPs is 300~700nm. For example, the particle size of the Al2O3 NPs is 300nm, 310nm, 320nm, 330nm, 340nm, 350nm, 360nm, 370nm, 380nm, 390nm, 400nm, 410nm, 420nm, 430nm, 440nm, 450nm, 460nm, 470nm, 480nm, 490nm, 500nm, 510nm, 520nm, 530nm, 540nm, 550nm, 560nm, 570nm, 580nm, 590nm, 600nm, 610nm, 620nm, 630nm, etc. nm, 640nm, 650nm, 660nm, 670nm, 680nm, 690nm, 700nm, or any range between any two of the above numbers, such as 300~680nm, 300~660nm, 300~640nm, 300~620nm, 300~600nm, 300~580nm, 300~560nm, 340~560nm, 380~540nm, 400~580nm, 400~560nm, 440~560nm, 480~540nm; the PVDF-HFP and Al2O3 The mass ratio of NPs is 2~4:1. For example, the mass ratio of PVDF-HFP to Al2O3 NPs is 2:1, 2.5:1, 3:1, 3.5:1, 4:1, or any range between any two of the above numbers, such as 2~3.5:1, 2~3:1, 2~2.5:1, 2.5~4:1, 2.5~3.5:1, 2.5~3:1. The particle size and content of Al2O3 NPs are within the above range, which can ensure uniform dispersion of nanoparticles, achieve high reflectivity across the entire solar spectrum, and have high emission characteristics in the mid-infrared band. Furthermore, the particle size of the Al2O3 NPs is 200 nm, and the mass ratio of the PVDF-HFP to the Al2O3 NPs is 2.5:1. The particle size and content of the Al2O3 NPs are within the above range, which can ensure that the nanoparticles are uniformly dispersed, achieve high reflectivity across the entire solar spectrum, and have high emission characteristics in the mid-infrared band. Furthermore, the porous structure is an interconnected hierarchical porous structure with a bimodal pore size distribution. The central pore diameters are 0.4~0.6μm and 2.5~3.5μm, respectively. For example, the central pore diameters are 0.4μm, 0.41μm, 0.42μm, 0.43μm, 0.44μm, 0.45μm, 0.46μm, 0.47μm, 0.48μm, 0.49μm, 0.5μm, 0.51μm, and 0.52μm, respectively. μm, 0.53μm, 0.54μm, 0.55μm, 0.56μm, 0.57μm, 0.58μm, 0.59μm, 0.6μm and 2.5μm, 2.54μm, 2.58μm, 2.6μm, 2.64μm, 2.68μm, 2.7μm, 2.74μm, 2.78μm, 2.8μm, 2.84μm, 2.88μm, 2.9μm, 2.94μm, 2.98μm μm, 3.0μm, 3.04μm, 3.08μm, 3.1μm, 3.14μm, 3.18μm, 3.2μm, 3.24μm, 3.28μm, 3.3μm, 3.34μm, 3.38μm, 3.4μm, 3.44μm, 3.48μm, 3.5μm, or a range between any two of the above numbers, such as 0.4~0.55μm, 0.4~0.5μm, 0.4~0.45μm. The central aperture can be within the range of 0.45~0.55μm, 0.45~0.5μm, 2.5~3.4μm, 2.5~3.2μm, 2.5~3.0μm, 2.5~2.8μm, 2.5~2.6μm, 2.7~3.4μm, 2.7~3.2μm, 2.7~3.0μm, and 2.7~2.8μm. This range ensures efficient light scattering across the entire solar spectrum and improves solar reflectivity.

[0009] Furthermore, the structure of the refrigerator is as follows: Figure 1 As shown, when sunlight is incident on the sandwich structure for color radiation cooling, it first penetrates the color layer without obstruction. After reaching the color layer, the inorganic color nanoparticles in the color layer selectively absorb visible light that is complementary to the desired color. The remaining sunlight penetrates the isolation layer without obstruction and reaches the bottom layer of the cooling layer. The multi-level porous structure and high refractive index nanoparticles of the cooling layer reflect almost all of it backward, eventually reaching the human eye and allowing people to perceive color.

[0010] The emitting layer is highly transparent to sunlight in the 0.3-2.5 micrometer wavelength range, exhibiting no significant absorption. Simultaneously, the broadband high-emissivity generated by the vibration of multiple molecular bonds in the infrared band helps to radiate the heat absorbed by the color layer outwards. The color layer is prepared by uniformly dispersing inorganic color nanoparticles within a polymer matrix. The cooling layer is a multi-level porous polymer composite inorganic dielectric microparticle coating, capable of efficiently reflecting all transmitted sunlight and radiating heat outwards. If the color layer were directly coated onto the surface of the cooling layer, its porous structure would be blocked or damaged (dissolved or swollen) by the inorganic pigments, thus reducing the overall reflectivity. To avoid this problem, a transparent PDMS is used to isolate the color layer from the cooling layer, ensuring the integrity of the multi-level porous structure of the cooling layer.

[0011] This invention also provides a method for preparing a colored sandwich structure daytime radiative cooler, comprising the following steps: S1. Preparation of radiation-cooled substrate: PVDF-HFP is dissolved in a mixed solvent and stirred until homogeneous to obtain a PVDF-HFP solution; Al2O3 NPs are added to the PVDF-HFP solution, and after stirring and dispersing evenly, deionized water is added and stirring is continued to obtain a casting solution; the casting solution is coated on the substrate, and a hierarchical porous radiation-cooled substrate is formed by non-solvent-induced phase separation; S2, Coating of the isolation layer: The PDMS prepolymer and curing agent are mixed and dispersed in isopropanol to obtain a PDMS coating solution; the PDMS coating solution is coated on the surface of the radiation-cooled substrate prepared in step S1, and heated to cure to form an isolation layer; S3, Coating of the colored layer: Dissolve PVDF-HFP in an organic solvent, add an infrared transparent inorganic colorant, stir and disperse evenly to obtain a colored coating liquid; coat the colored coating liquid onto the surface of the isolation layer prepared in step S2, and dry to form a colored layer; S4. Coating of the emission layer: The PDMS prepolymer and curing agent are mixed and dispersed in isopropanol to obtain a PDMS coating liquid; the PDMS coating liquid is sprayed or spin-coated onto the surface of the colored layer prepared in step S3, and heated and cured to form an emission layer, thereby obtaining the colored sandwich structure daytime radiation cooler.

[0012] Further, in steps S1 and S4, the mixed solvent is acetone and N,N-dimethylformamide (DMF), wherein the mass ratio of acetone to DMF is 1:0.5~2, and the mass ratio of PVDF-HFP to the mixed solvent is 1:6~10. Exemplarily, the mass ratio of acetone to DMF is 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, or a range between any two of the above values, such as 1:0.5~1.8, 1:0.5. The mass ratios of PVDF-HFP to the mixed solvent are 1:6, 1:7, 1:8, 1:9, 1:10, or any two of the above values, such as 1:6~9, 1:6~8, 1:6~7, 1:7~9. Mixed solvent ratios and contents within the above ranges can fully dissolve PVDF-HFP and ensure uniform dispersion of nanoparticles. Further, in step S1, the mass ratio of PVDF-HFP to deionized water is 1:1~3, the stirring temperature is 50~70℃, the PVDF-HFP dissolution stirring time is 0.5~2h, the stirring time after adding Al2O3 NPs is 3~5h, and the stirring time after adding deionized water is 0.5~2h; for example, the mass ratio of PVDF-HFP to deionized water is 1:1, 1:2, 1:3, or any range between any two of the above numbers, such as 1:2~3; the stirring temperature is 52℃, 54℃, 56℃, 58℃, 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, or any range between any two of the above numbers, such as 50~68℃, 50~66℃, 50~64℃, 50~62℃, 50~60℃. 50~58℃, 50~56℃, 50~54℃, 56~70℃, 56~66℃, 56~60℃; PVDF-HFP dissolution stirring time is 0.5h, 0.7h, 0.9h, 1.0h, 1.2h, 1.4h, 1.6h, 1.8h, 2.0h, or any range between any two of the above numbers, such as 0.5~1.8h, 0.5~1.4h, 0.5~1.0h, 0.5~0.7h, 0.9~1.8h, 0.9~1.4h, 0.9~1.0h; Al2O3 is added. The stirring time after adding NPs is 3h, 3.2h, 3.4h, 3.6h, 3.8h, 4.0h, 4.2h, 4.4h, 4.6h, 4.8h, 5.0h, or any range between any two of the above numbers, such as 3~4.8h, 3~4.4h, 3~4h, 3~3.6h, 3~3.4h, 3.4~4.4h; the stirring time after adding deionized water is 0.5h, 0.7h, 0.9h, 1.0h, 1.2h, 1.4h, 1.6h, 1.8h, 2.0h, or any range between any two of the above numbers, such as 0.5~1.8h, 0.5~1.4h, 0.5~1.0h, 0.5~0.7h, 0.9~1.8h, 0.9~1.4h, 0.9~1.0h. Furthermore, the coating includes blade coating, spin coating, or spray coating, all of which can achieve meter-scale preparation and are suitable for different substrates and application scenarios; Further, in steps S2 and S4, the mass fraction of the PDMS coating liquid is 5%~15%, and the mass ratio of PDMS prepolymer to curing agent is 7~10:1; the heat curing conditions are 50~70℃ for 1.5~3 hours; for example, the mass fraction of the PDMS coating liquid is 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any range between any two of the above numbers, such as 5%~13%, 5%~10%, 5%~8%, 7%~12%, 8%~11%; the mass ratio of PDMS prepolymer to curing agent is 7:1, 8:1, 9:1, 10:1, or any range between any two of the above numbers, such as 7~9:1, 7~8:1, 8~9:1; heat curing The conditions are 52℃, 54℃, 56℃, 58℃, 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, or any range between any two of the above numbers, such as 50~68℃, 50~66℃, 50~64℃, 50~62℃, 50~60℃, 50~58℃, 50~56℃, 50~54℃, 56~70℃, 56~66℃, 5 6~60℃, keep warm for 1.5h, 1.7h, 1.9h, 2.0h, 2.2h, 2.4h, 2.6h, 2.8h, 3.0h, or any range between any two of the above numbers, such as 1.5~2.8h, 1.5~2.4h, 1.5~2.0h, 1.5~1.7h, 1.9~2.8h, 1.9~2.4h, 1.9~2.0h.

[0013] The present invention also provides an application of a colored sandwich structure daytime radiation cooler, which is coated on the surface of building roofs, building exterior walls, or electronic device housings to achieve zero-energy passive daytime radiation cooling; the cooler has an average reflectivity of ≥89.8% in the 0.3~2.5μm solar spectrum band and an average emissivity of ≥0.982 in the 2.5~25μm mid-infrared band; it can achieve sub-environmental cooling at a temperature 3.7~5.4℃ lower than the ambient temperature during the day, which is 33.3~42.2℃ lower than that of commercial colored coatings of the same chroma.

[0014] Furthermore, when the aforementioned refrigerator is applied to buildings, the annual energy saving per unit area can reach 23.8 MJ·m². -2 The annual CO2 emission reduction per unit area can reach 11.7 kg·m³. -2 .

[0015] Compared with the prior art, the color sandwich structure daytime radiant cooler provided by the present invention has the following technical effects: 1. This invention, through an innovative composite sandwich structure design, perfectly resolves the core contradiction between color performance and cooling performance in the field of color radiative cooling. By isolating the color layer from the radiative cooling substrate with an insulating layer, the blockage, dissolution, and damage to the porous microstructure of the cooling layer during the color layer coating process are completely avoided, ensuring the high solar reflectivity of the cooling layer. At the same time, through the selective visible light absorption of the infrared transparent inorganic colorant, vibrant colors are achieved while minimizing the solar heat load, thus achieving a balance between color rendering and cooling. 2. The cooler of this invention possesses excellent environmental stability and practicality. The outermost PDMS emitting layer endows the material with superhydrophobic properties (water contact angle 139.4°), exhibiting excellent self-cleaning, rain erosion resistance, and acid corrosion resistance. Furthermore, after 60 days of continuous ultraviolet irradiation, the material's solar reflectivity changes by less than 1%, demonstrating excellent aging resistance and meeting the requirements for long-term outdoor use. In addition, the material is compatible with various substrates such as metals, wood, and polymers, exhibiting strong adaptability. 3. The preparation process of the present invention is simple and can be prepared by conventional coating processes such as scraping, spin coating and spraying. It does not require complex and precise equipment, can achieve meter-scale production, and has controllable costs, thus solving the pain point of existing structural color refrigeration materials being difficult to scale up. 4. The cooler of this invention achieves excellent optical and cooling performance, with an average solar spectral reflectance of 89.9%~91.2% and a mid-infrared broadband emissivity of 0.982~0.983, at a daily average of 908.9 W·m -2 Under solar irradiation, it can achieve stable sub-environmental cooling at a temperature 3.7~5.4℃ below ambient temperature during the day. Compared with commercial colored coatings of the same chroma, the temperature difference is as high as 33.3~42.2℃, and the cooling performance far exceeds that of most reported colored radiation cooling materials. 5. The refrigerator of this invention has significant energy-saving and carbon-reduction benefits. When applied on a large scale in the building sector, it can achieve an annual energy saving of 23.8 MJ·m² per unit area. -2 The annual CO2 emission reduction per unit area can reach 11.7 kg·m³. -2 It is adaptable to different climate zones around the world, providing a feasible technical solution for zero-energy buildings, and has broad application prospects. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the colored sandwich structure daytime radiation cooler of the present invention; Figure 2 The following are schematic diagrams of the red-colored sandwich structure daytime radiation cooler of Embodiment 1 of the present invention: (a) is a SEM image; (b) is its elemental distribution diagram. Figure 3 This is a physical image of the yellow-colored sandwich structure daytime radiative cooling device of Embodiment 2 of the present invention; Figure 4 The images show the spectral diagrams of the color sandwich structure daytime radiative coolers of Embodiments 1-3 of the present invention. Figure 5 The outdoor test temperature diagrams are from embodiments 1-3 of this invention. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0018] All raw materials used in the embodiments of this invention are commercially available conventional products. PVDF-HFP (KynarFlex2801) was purchased from Arkema (Shanghai) Chemical Co., Ltd.; PDMS was purchased from Shanghai Smart Technology Co., Ltd.; Al2O3 NPs were purchased from Hangzhou Hengge Nanotechnology Co., Ltd.; Fe2O3, SiNPs, and PB nanoparticles were purchased from Hefei Qianguo New Materials Technology Co., Ltd.; acetone and DMF were of analytical grade and purchased from Beijing Tongguang Fine Chemical Co., Ltd. and Tianjin Fuyu Fine Chemical Co., Ltd.

[0019] like Figure 1 As shown in the schematic diagram of the color sandwich structure daytime radiation cooler of the present invention, when sunlight is incident on the color radiation cooling of the sandwich structure, it first penetrates the color layer without obstruction. After reaching the color layer, the inorganic color nanoparticles in the color layer selectively absorb visible light that is complementary to the desired color. The remaining sunlight penetrates the isolation layer without obstruction and reaches the cooling bottom layer. The multi-level porous structure and high refractive index nanoparticles of the cooling layer will reflect almost all of it backward, and finally reach the human eye, allowing people to perceive color.

[0020] The emitting layer is highly transparent to sunlight in the 0.3-2.5 micrometer wavelength range, exhibiting no significant absorption. Simultaneously, the broadband high-emissivity generated by the vibration of multiple molecular bonds in the infrared band helps to radiate the heat absorbed by the color layer outwards. The color layer is prepared by uniformly dispersing inorganic color nanoparticles within a polymer matrix. The cooling layer is a multi-level porous polymer composite inorganic dielectric microparticle coating, capable of efficiently reflecting all transmitted sunlight and radiating heat outwards. If the color layer were directly coated onto the surface of the cooling layer, its porous structure would be blocked or damaged (dissolved or swollen) by the inorganic pigments, thereby reducing the overall reflectivity. To avoid this problem, this application uses transparent PDMS to isolate the color layer from the cooling layer, ensuring the integrity of the multi-level porous structure of the cooling layer.

[0021] Example 1: Fabrication of the red-colored sandwich structure daytime radiation cooler (CoCooler-R): The specific steps are as follows: Fabrication of S1 radiation-cooled substrate: Weigh out PVDF-HFP and a mixture of acetone and DMF in a mass ratio of 1:8 (where the mass ratio of acetone to DMF is 1:1). Add PVDF-HFP to the mixture of acetone and DMF and stir at 60°C for 1 hour until completely dissolved to obtain a homogeneous PVDF-HFP solution. Add Al2O3 NPs with a particle size of 500 nm to the above solution, wherein the mass ratio of PVDF-HFP to Al2O3 NPs is 2.5:1, and continue stirring at 60°C for 4 h until the nanoparticles are uniformly dispersed. Deionized water was slowly added dropwise to the above dispersion, wherein the mass ratio of PVDF-HFP to deionized water was 1:1. After the addition was completed, stirring was continued for 30 minutes to obtain the casting solution. The casting solution was applied to a clean glass substrate using a doctor blade. Through a non-solvent-induced phase separation process, the solvent and non-solvent rapidly exchanged to form an interconnected hierarchical porous structure. After drying at room temperature, a radiation-cooling substrate with a thickness of 200 μm was obtained. Its pore size exhibited a bimodal distribution, with central pore sizes of 0.49 μm and 2.94 μm, respectively.

[0022] Coating of S2 isolation layer: The PDMS prepolymer and curing agent were mixed evenly at a mass ratio of 8:1, and diluted with isopropanol to obtain a PDMS coating liquid with a mass fraction of 10%. The coating liquid was evenly sprayed onto the surface of the radiation-cooled substrate prepared in step S1, and heated and cured at 60°C for 2 hours to obtain an isolation layer with a thickness of 8 μm.

[0023] S3 red color layer coating: PVDF-HFP was dissolved in a mixed solvent of acetone and DMF to obtain a PVDF-HFP solution with a mass fraction of 10%. Fe2O3 nanoparticles with a particle size of 31 nm were added to the solution, and the mass fraction of Fe2O3 in the system was controlled to be 0.3%. The mixture was stirred and dispersed evenly to obtain a red coating liquid. The red coating liquid was spin-coated onto the surface of the isolation layer prepared in step S2, and dried at room temperature to obtain a red colored layer with a thickness of 2 μm.

[0024] S4 emission layer coating: Using the same PDMS coating solution as in step S2, it was uniformly sprayed onto the surface of the red colored layer prepared in step S3, and heated and cured at 60°C for 2 hours to obtain an emission layer with a thickness of 6 μm. After peeling it off, a red colored sandwich structure daytime radiation cooler was obtained, denoted as CoCooler-R.

[0025] SEM and elemental analysis were performed on the CoCooler-R cooler, such as... Figure 2As shown in (a), the cooler has a four-layer structure, consisting of an emission layer, a color layer, an isolation layer, and a substrate from top to bottom. The substrate has a porous structure, and the layers are tightly bonded together. Figure 2 As shown in (b), the elemental distribution map confirms that the structure has a clear interface. The cooling layer was prepared using a solvent-inducible phase separation method with a two-component good solvent, forming an internally interconnected hierarchical porous structure with a bimodal pore size distribution, concentrated at 0.49 μm and 2.97 μm. Simultaneously, high-refractive-index inorganic dielectric microparticles are uniformly embedded in the hierarchical porous polymer matrix without significant agglomeration, which is also confirmed by the elemental distribution.

[0026] Example 2: Fabrication of a yellow-colored sandwich structure daytime radiation cooler (CoCooler-Y): In this embodiment, the yellow refrigerator is prepared. Except for step S3, the other steps are exactly the same as in Example 1. Step S3 specifically involves: dissolving PVDF-HFP in a mixed solvent of acetone and DMF to obtain a PVDF-HFP solution with a mass fraction of 10%; adding Si nanoparticles with a particle size of 46 nm to the solution, controlling the mass fraction of Si in the system to be 0.3%, and stirring to disperse evenly to obtain a yellow coating liquid; spin-coating the yellow coating liquid onto the surface of the isolation layer prepared in step S2, and drying it at room temperature to obtain a yellow colored layer with a thickness of 2 μm.

[0027] The final product is a yellow-colored sandwich structure daytime radiative cooler, denoted as CoCooler-Y. A physical image of the actual product is shown below. Figure 3 As shown. The left side is a demonstration image of the large-scale preparation of the sandwich structure radiation-cooling coating at Alec's office, and the right side is a demonstration image of commercial colored latex paint exposed outdoors. The temperature comparison through thermal imaging can reflect the cooling performance of the sandwich structure radiation-cooling coating.

[0028] Example 3: Fabrication of the blue-colored sandwich structure daytime radiation cooler (CoCooler-B): The blue refrigerator is prepared in this embodiment. Except for step S3, the other steps are exactly the same as in Example 1. Step S3 specifically involves: dissolving PVDF-HFP in a mixed solvent of acetone and DMF to obtain a PVDF-HFP solution with a mass fraction of 10%; adding Prussian blue (PB) nanoparticles with a particle size of 34 nm to the solution, controlling the mass fraction of PB in the system to be 0.2%, and stirring to disperse evenly to obtain a blue coating liquid; spin-coating the blue coating liquid onto the surface of the isolation layer prepared in step S2, and drying it at room temperature to obtain a blue colored layer with a thickness of 2 μm.

[0029] The final product was a blue-colored sandwich structure daytime radiation cooler, denoted as CoCooler-B.

[0030] Figure 4 The images show the spectra of the colored sandwich structure daytime radiative coolers of Examples 1-3 of this invention. The optimal concentrations of Fe2O3, Si, and PB in the colored layer are 0.3 wt%, 0.3 wt%, and 0.2 wt%, respectively. At these concentrations, the prepared red, yellow, and blue sandwich structure CDRC coatings exhibit vivid colors, and their solar reflectivities reach 90.7%, 91.2%, and 89.9%, respectively. The near-infrared reflectivities are as high as 95.3%, 95.9%, and 90.9%, respectively, which are approximately 30.8%, 32.5%, and 43.1% higher than those of commercial colored latex paints of the same color. This indicates that the sandwich structure plays a dominant role in enhancing near-infrared reflectivity, ensuring that the CDRC coating can reflect the vast majority of sunlight and introduce less heat load.

[0031] Figure 5 The figures show the outdoor test temperature diagrams for Examples 1-3 of this invention. Under cloudy conditions, due to the obstruction of water vapor and clouds, the local atmospheric window transmittance at the experimental site was less than 0.4, which was highly unfavorable for outward scattering of infrared thermal radiation. Although geographical and meteorological conditions have a significant impact on radiative cooling performance, the sandwich structure CDRC coating, thanks to its excellent optical properties, can still maintain a temperature close to the ambient temperature under cloudy conditions, which is 13.7°C lower than that of commercial colored latex paint coatings. o Above C. The above results show that the sandwich structure CDRC coating can also exhibit stable sub-environmental cooling effect under complex weather conditions, and its performance is superior to that of previously reported colored radiative cooling materials.

[0032] Comparative Example 1: Three-layer red radiant cooler: This comparative example prepares a three-layer structure refrigerator without an isolation layer. The remaining raw materials are the same as in Example 1. The specific steps are as follows: 1. Prepare the radiation-cooled substrate using the same method as step S1 in Example 1; 2. Using the same method as step S3 in Example 1, the red coating liquid is directly spin-coated onto the surface of the radiation-cooled substrate to form a colored layer; 3. The emitting layer is coated using the same method as step S4 in Example 1 to obtain a three-layer red radiation cooler.

[0033] Comparative Example 2: Single-layer structure refrigerator: This comparative example prepares a single-layer structure refrigerator, using only the isolation layer as the refrigerator. The same method as step S2 in Example 1 is used to obtain the isolation layer with the same thickness and structure as the refrigerator.

[0034] Comparative Example 3: Commercially available red paint: This comparative example uses a commercially available red exterior wall paint of the same hue as in Example 1, applied to a substrate of the same size, as a control.

[0035] Performance Test Example 1. Optical Performance Test: The reflectance of samples from Examples 1-3 and Comparative Examples 1-3 in the 0.3-2.5 μm solar spectrum was measured using a UV-Vis-NIR spectrophotometer (Shimadzu UV3600Plus) with an integrating sphere. The emissivity of the samples in the 2.5-25 μm mid-infrared band was measured using a Fourier transform infrared spectrometer (Nicoleti S50) with a gold integrating sphere. The results are shown in Table 1 below.

[0036] As shown in Table 1, the tri-color coolers of Examples 1-3 of this invention all have a full solar spectrum reflectance ≥89.8% and a mid-infrared emissivity ≥0.982, which are far higher than the three-layer structure of Comparative Example 1 and the commercial coating of Comparative Example 3. In particular, the reflectance of Example 1 of this invention is much higher than the combination of Comparative Example 1 and Comparative Example 2. Among them, the near-infrared reflectance of the cooler of this invention is more than 30% higher than that of the commercial coating, proving that the sandwich structure design can effectively maintain high near-infrared reflectance and reduce solar heat load.

[0037] Performance Test Example 2. Outdoor Daytime Cooling Performance Test: The test location was a rooftop in Beijing, China (39.85°N, 116.12°E). The test dates were July 16 (sunny), July 26 (cloudy), and July 14 (overcast) in 2024. The test setup used a polystyrene foam insulation box. The sample was attached to the bottom of the box, and a K-type thermocouple was fixed to the back. Aluminum foil was attached to the surface of the box to shield against environmental radiation, and the top was sealed with a polyethylene film to isolate convection. Temperature data was recorded every 10 seconds, along with meteorological data such as solar irradiance, ambient temperature, wind speed, and humidity.

[0038] The test results show that: 1. Under clear weather conditions, the average daily solar irradiance is 908.9 W·m. -2 (11:00~14:00) The daytime steady-state temperatures of the coolers in Examples 1 (CoCooler-R), 2 (CoCooler-Y), and 3 (CoCooler-B) were 5.4℃, 4.5℃, and 3.7℃ lower than the ambient temperature, respectively. They were 10.7℃, 9.4℃, and 8.6℃ lower than Comparative Example 1, respectively, and 33.3℃, ​​40.6℃, and 42.2℃ lower than the commercial coating in Comparative Example 3, respectively. At night, when there was no solar radiation, the cooler temperature was more than 12℃ lower than the ambient temperature.

[0039] 2. Under cloudy weather conditions, the temperature of the cooler is still 7.5℃ lower than that of Comparative Example 1 and 16.6~24.0℃ lower than that of the commercial coating in Comparative Example 3. Under overcast weather conditions, the atmospheric window transmittance is less than 0.4, and the cooler still maintains a temperature close to the ambient temperature, which is 3.5℃ lower than that of Comparative Example 1 and more than 13.7℃ lower than that of the commercial coating in Comparative Example 3. This proves that the cooler of the present invention still has excellent cooling performance under complex weather conditions.

[0040] Performance Test Example 3. Environmental Stability Test: 1. Rain erosion resistance: The solar reflectance of the samples before and after the rain was simulated by 24-hour dynamic jet impact. The reflectance of the cooler in Examples 1-3 changed by less than 1% and there was no structural damage. 2. Acid corrosion resistance: The samples were immersed in an acidic solution with pH=5.6 for 24 hours, and the solar reflectance of the samples before and after the immersion was tested. The reflectance of the coolers in Examples 1-3 changed by less than 1%, and there was no discoloration or peeling. 3. UV aging resistance: The samples were continuously irradiated with UV lamps for 60 days (equivalent to 2 years of outdoor irradiation in Beijing), and the solar reflectance of the samples before and after were tested. The reflectance of the cooler in Examples 1-3 changed by less than 1%, and there was no obvious color decay, which proved the excellent aging resistance. 4. Self-cleaning performance: The sample has a water contact angle of 139.4°, exhibiting superhydrophobic properties. Surface dust can be quickly removed by rainwater without affecting optical performance.

[0041] Performance Test Example 4. Simulation of Building Energy Efficiency and Carbon Reduction Benefits: Using EnergyPlus building energy consumption simulation software, a typical three-story apartment building model was constructed. The refrigerator of this invention and commercial colored paint were used as the building's exterior walls and roof finishes, respectively. The annual cooling energy consumption of the building in 30 typical cities across different climate zones worldwide was simulated. The results show: The refrigerator of this invention achieves an average annual energy saving of 23.8 MJ·m² per unit area globally. -2 The average energy saving rate is 15.5%; the average annual CO2 emission reduction per unit area reaches 11.7 kg·m². -2 In tropical and humid regions, annual CO2 emission reductions can reach 19.5 kg·m³. -2 In cold regions, the energy saving rate can reach more than 20%, proving that the refrigerator of this invention has excellent energy saving and carbon reduction benefits in different climate zones around the world.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A colored sandwich structure daytime radiant cooler, characterized in that, The cooler has a composite sandwich structure, which includes, from top to bottom, an emission layer, a color layer, an isolation layer, and a radiation cooling substrate; The emission layer is a polydimethylsiloxane film; The colored layer is a composite film formed by dispersing an infrared transparent inorganic colorant in a polyvinylidene fluoride-hexafluoropropylene matrix; The isolation layer is a polydimethylsiloxane film; The radiation cooling substrate is a porous thin film formed by a composite of polyvinylidene fluoride-hexafluoropropylene and alumina nanoparticles. The infrared transparent inorganic colorant is selected from at least one of red colorant, yellow colorant and blue colorant; The red colorant is iron oxide, the yellow colorant is nano-silicon, and the blue colorant is Prussian blue.

2. The colored sandwich structure daytime radiant cooler according to claim 1, characterized in that, The thickness of the emitting layer is 2~10μm, the thickness of the color layer is 1~5μm, the thickness of the insulating layer is 5~15μm, and the thickness of the radiation cooling substrate is 100~300μm.

3. The colored sandwich structure daytime radiant cooler according to claim 1, characterized in that, The infrared transparent inorganic colorant has a particle size of 30-50 nm and a mass fraction of 0.1%-0.6% in the color layer.

4. The colored sandwich structure daytime radiant cooler according to claim 1, characterized in that, The alumina nanoparticles have a particle size of 300~700nm; the mass ratio of polyvinylidene fluoride-hexafluoropropylene to alumina nanoparticles is 2~4:1; The porous structure is an interconnected hierarchical porous structure with a bimodal pore size distribution, and the central pore sizes are 0.4~0.6μm and 2.5~3.5μm, respectively.

5. A method for preparing a colored sandwich structure daytime radiative cooler according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Preparation of radiation-cooled substrate: Polyvinylidene fluoride-hexafluoropropylene is dissolved in a mixed solvent and stirred until homogeneous to obtain a polyvinylidene fluoride-hexafluoropropylene solution; alumina nanoparticles are added to the polyvinylidene fluoride-hexafluoropropylene solution, and after stirring and dispersing evenly, deionized water is added and stirring is continued to obtain a casting solution; the casting solution is coated on the substrate, and a hierarchical porous radiation-cooled substrate is formed by non-solvent-induced phase separation; S2, Coating of the isolation layer: The polydimethylsiloxane prepolymer and curing agent are mixed and dispersed in isopropanol to obtain a polydimethylsiloxane coating liquid; the polydimethylsiloxane coating liquid is coated on the surface of the radiation-cooled substrate prepared in step S1, and heated and cured to form an isolation layer; S3, Coating of the colored layer: Polyvinylidene fluoride-hexafluoropropylene is dissolved in an organic solvent, an infrared transparent inorganic colorant is added, and the mixture is stirred and dispersed evenly to obtain a colored coating liquid; the colored coating liquid is coated on the surface of the isolation layer prepared in step S2, and dried to form a colored layer; S4. Coating of the emission layer: The polydimethylsiloxane prepolymer and curing agent are mixed and dispersed in isopropanol to obtain a polydimethylsiloxane coating liquid; the polydimethylsiloxane coating liquid is sprayed or spin-coated onto the surface of the colored layer prepared in step S3, and heated and cured to form an emission layer, thereby obtaining the colored sandwich structure daytime radiation cooler.

6. The preparation method according to claim 5, characterized in that, The mixed solvent in steps S1 and S3 is acetone and N,N-dimethylformamide, wherein the mass ratio of acetone to N,N-dimethylformamide is 1:0.5~2, and the mass ratio of polyvinylidene fluoride-hexafluoropropylene to the mixed solvent is 1:6~10. In step S1, the mass ratio of polyvinylidene fluoride-hexafluoropropylene to deionized water is 1:1~3; the stirring temperature is 50~70℃; the stirring time for dissolving polyvinylidene fluoride-hexafluoropropylene is 0.5~2h; the stirring time after adding alumina nanoparticles is 3~5h; and the stirring time after adding deionized water is 0.5~2h. The coating includes scraping, spin coating, or spraying.

7. The preparation method according to claim 5, characterized in that, In steps S2 and S4, the mass fraction of the polydimethylsiloxane coating liquid is 5%~15%, and the mass ratio of polydimethylsiloxane prepolymer to curing agent is 7~10:1; the heating curing conditions are 50-70℃ for 1.5~3h.

8. The use of a colored sandwich structure daytime radiant cooler prepared by the method of any one of claims 1-4 or claims 5-7, characterized in that, The cooler is coated onto the surface of building roofs, building exterior walls, or electronic device housings to achieve zero-energy passive daytime radiative cooling. The cooler has an average reflectivity of ≥89.8% in the 0.3~2.5μm solar spectrum band and an average emissivity of ≥0.982 in the 2.5~25μm mid-infrared band. It can achieve sub-environmental cooling at a temperature 3.7~5.4℃ lower than the ambient temperature during the day, which is 33.3~42.2℃ lower than that of commercial colored paints of the same chroma.

9. According to claim 8, when the refrigerator is applied to a building, the annual energy saving per unit area can reach 23.8 MJ·m². -2 The annual CO2 emission reduction per unit area can reach 11.7 kg·m³. -2 .

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