A high-reflective high-emissive prismatic photonic metamaterial film for radiative cooling and a preparation method thereof

Abstract

The application discloses a high-reflective and high-emissive prism photonic metamaterial film for radiation refrigeration and a preparation method thereof, and belongs to the technical field of metamaterials and radiation refrigeration preparation. The film is composed of an organic polymer film layer at the lower layer and a small hole structure layer at the upper layer. The lower surface of the organic polymer film layer is uniformly distributed with three-prism structures. The three-prism structures are arranged in parallel. The bottom side length is 45-55 um, the height is 20-25 um, and the top angle is 85-95 degrees. The small hole structure layer is formed by mixing organic polymer and dielectric microsphere particles. The pore size ranges from 0.1 um to 10 um. Due to the enhanced reflection of the three-prism structure and the resonance of the dielectric microsphere particles, the film shows high reflection in the ultraviolet-visible-near infrared band, and shows high emissivity in the mid-infrared band. Daytime radiation cooling can be effectively realized. Experimental results show that the radiation refrigeration film can reflect most of the sunlight and emit heat outward by emitting mid-infrared and far-infrared rays, thereby achieving heat dissipation. The film is simple to prepare and can be produced on a large scale.

Description

Technical Field

[0001] This invention belongs to the field of metamaterials and radiation cooling preparation technology, specifically relating to a high-reflectivity, high-emission prism photonic metamaterial thin film for radiation cooling and its preparation method. Background Technology

[0002] With global warming and the intensification of extreme weather events, especially in summer, the demand for cooling is continuously increasing, and is projected to increase tenfold by 2050. Traditional refrigeration equipment, such as refrigerators and air conditioners, consumes a large amount of energy and resources during operation, generating additional heat, contributing to the greenhouse effect, urban heat island effect, and harmful gases, thus exacerbating global warming and air pollution. Statistics show that buildings account for 45% of my country's total energy consumption. Buildings, exposed to sunlight, absorb heat from their surfaces, causing their temperature to rise. This heat is then conducted to the building walls, which in turn heat the internal air, resulting in increased indoor air temperature. According to data from international refrigeration research institutions, the electricity consumed by air conditioners and refrigerators currently accounts for approximately 20% of global electricity consumption. Furthermore, the widespread use of air conditioners, refrigerators, and other refrigeration appliances has led to a surge in electricity consumption, and overloaded power usage frequently causes power outages. Therefore, achieving zero-energy active cooling is a crucial goal for energy conservation and carbon reduction in the production sector.

[0003] To achieve high-performance radiative cooling, the cooler must have high solar reflectivity during the day to reduce energy input and high mid-infrared emissivity in the atmospheric transparency window to release as much heat as possible. Current radiative cooling materials mainly include inorganic or metallic porous materials, metal-polymer layered coatings, polymer composites, and porous polymer materials. In recent years, although radiative cooling technology has made great progress, its practical application is limited by complex manufacturing processes, susceptibility to contamination, and high costs. Based on these problems, this invention provides a high-reflectivity, high-emissivity prism photonic metamaterial thin film for radiative cooling and its preparation method. This material exhibits high reflectivity in the ultraviolet-visible-near-infrared band through enhanced reflection via a designed prism structure without adding any metal reflectors, while simultaneously achieving high reflectivity through dielectric microsphere particles. Resonance exhibits high emissivity in the mid-infrared region, enabling effective daytime radiative cooling, making it a highly advantageous radiative cooling film for various applications. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings and deficiencies of existing technologies by providing a high-reflectivity, high-emission prism photonic metamaterial thin film for radiation cooling and its preparation method. The thin film prepared by this invention is a radiation-cooling thin film capable of reflecting most sunlight and dissipating heat by emitting mid- and far-infrared rays. It possesses both high reflectivity and high emission characteristics, enabling low-cost, energy-free cooling and sun protection. Its preparation is simple and suitable for large-scale production.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0006] One objective of this invention is to provide a method for preparing a high-reflectivity, high-emission prism photonic metamaterial thin film for radiation cooling, the method comprising the following steps:

[0007] (1) An organic polymer is added to a double roller with a triangular prism groove on one side, and a thin film A with a triangular prism structure on one side is formed by rolling.

[0008] (2) Add the organic polymer to a mixed solution of organic solvent and water, and stir magnetically in a water bath to obtain solution A;

[0009] (3) Add dielectric microspheres to solution A and stir magnetically in a water bath until they are evenly distributed to obtain solution B;

[0010] (4) Drop-cast solution B onto the side of the previously prepared thin film A without the prism structure to obtain a double-layer film;

[0011] (5) Place the double-layer film obtained in step 4 in a fixed environment and let it stand and dry. After the solution evaporates, the high-reflection and high-emission prism photonic metamaterial thin film is obtained.

[0012] Preferably, the formed prism structures are arranged in parallel at equal intervals, and the base length of the triangle of each prism structure cross section is 45-55 μm, the height is 20-25 μm, and the vertex angle ranges from 85° to 95°.

[0013] Preferably, the stirring time of the mixture of organic polymer, organic solvent and water is 90-120 min until a homogeneous and clear solution A is formed, and the stirring rate is preferably 100-200 r / min, wherein the mass ratio of organic polymer, organic solvent and water is 0.8-1.2:8-11:0.5-2. The water bath temperature is 50-60℃.

[0014] Preferably, dielectric microspheres are slowly added to solution A, and the mixture is magnetically stirred in a water bath at a speed of 100–200 r / min for 30–60 min to obtain solution B. The dielectric microspheres have a particle size of 4–8 μm, and the mass fraction of the dielectric microspheres is 10%–20%. The water bath temperature is 50–60 °C.

[0015] Preferably, the organic polymer is selected from at least one of polydimethylsiloxane, polymethyl methacrylate, polyvinylidene fluoride-hexafluoropropylene, polyethylene oxide, and polylactic acid.

[0016] Preferably, the organic solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, toluene, tetrahydrofuran, and acetone;

[0017] Preferably, the dielectric microspheres are selected from at least one of titanium dioxide, aluminum oxide, silicon dioxide, or barium sulfate;

[0018] Preferably, solution B is drop-cast onto the previously prepared thin film A at a drop volume of 0.08–0.24 ml / cm². 2 This ensures that the distribution is even.

[0019] Preferably, the prepared bilayer membrane is placed in an environment of 20-30°C to allow organic and water solvents to evaporate, and the solvent evaporation time is 24-36 hours. The pore size range of the small pores formed on the surface is 0.1-10 μm.

[0020] The second objective of this invention is to provide a high-reflectivity, high-emission prism photonic metamaterial thin film prepared by any of the above-mentioned preparation methods. This thin film consists of a lower organic polymer film layer and an upper porous structure layer. The lower surface of the organic polymer film layer is uniformly distributed with triangular prism structures arranged in parallel. The base length of the triangle of each triangular prism structure is 45-55 μm, the height is 20-25 μm, and the apex angle is 85°-95°. The porous structure layer is composed of a mixture of organic polymer and dielectric microsphere particles, with a pore size ranging from 0.1 to 10 μm.

[0021] A third objective of this invention is to provide an application of the thin film prepared by any of the above-mentioned methods in the field of radiative cooling. The radiative cooling field includes areas where surface cooling is required, such as automobiles, buildings, and clothing.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) The thin film prepared by the present invention has a prism structure. Due to total internal reflection, the reflection effect can be enhanced. Under direct sunlight, the radiation cooling thin film can achieve a cooling effect of more than 6°C.

[0024] (2) The radiation cooling film prepared by the present invention has good flexibility and hydrophobicity, which expands the application range.

[0025] (3) The radiation cooling film prepared by the present invention has a selective radiation capability of dielectric microspheres with controllable particle size, which is due to the good radiation performance brought about by the film being located at the atmospheric window (8-13 μm).

[0026] (4) All materials used in this invention are industrial grade materials, which are easy to obtain, low in cost, and simple to operate. They can be prepared on a large scale and in large quantities, and have good industrial prospects. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the prism structure prepared in Example 1.

[0028] Figure 2 This is a SEM image of the thin film prepared in Example 1. Figure 2 'a' is a picture of the actual object. Figure 2 b and Figure 2 c is an SEM image of the micropore structure on the upper layer of the thin film. Figure 2 d、 Figure 2 e and Figure 2 f is a SEM image of the triangular prism structure at the bottom of the thin film.

[0029] Figure 3 The reflectance spectra of the thin films prepared in Examples 1-5 in the solar spectral region (0.3-2.5 μm).

[0030] Figure 4 A comparison of the reflectance curves of the thin film prepared in Example 1 and the thin film prepared in Comparative Example 1 in the solar spectral region (0.3-2.5 μm).

[0031] Figure 5 Comparison of the emissivity curves of the thin film prepared in Example 1 and the thin film prepared in Comparative Example 1 in the mid-infrared (2.5-16 μm) range.

[0032] Figure 6 The electric field diagram is shown for the dielectric particles of silicon dioxide in the thin film prepared in Example 1.

[0033] Figure 7 shows the cooling data of the thin film prepared in Example 1 and the thin film prepared in Comparative Example 1 during outdoor testing. Figure 7a This is a diagram showing the cooling effect. Figure 7b The solar power at the time of the test. Figure 7c This is a temperature difference graph.

[0034] Figure 8a The image shows the hydrophobic angle of the thin film prepared in Example 1. Figure 8b Stress-strain curve. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0036] Example 1

[0037] 100g of polyvinylidene fluoride-hexafluoropropylene is added to a double roller with a triangular prism structure on one side. The roller temperature is set to 165℃ and the preferred rotation speed is 20r / min. After rolling, a thin film A with a triangular prism structure on one side is formed. The formed prism structure is evenly spaced and parallel, with a bottom edge length of 50um, a height of 25um, and a apex angle of 90°.

[0038] Add 2g of polyvinylidene fluoride-hexafluoropropylene to a mixed solution of 18g of acetone and 2g of water, and stir magnetically in a water bath for 90min until a uniform and clear solution A is formed. The stirring rate is 150r / min, and the water bath temperature is preferably 55℃.

[0039] Silica was slowly added to solution A to obtain solution B. The solution was then stirred magnetically in a water bath at a speed of 150 r / min for 90 min. The spherical silica particles had a diameter of 5 μm and a mass fraction of 20%.

[0040] Solution B was drop-cast onto the non-prism structure side of the previously prepared thin film A at a volume of 0.24 ml / cm³. 2 To ensure uniform distribution, the prepared bilayer membrane was placed at 25°C to allow acetone and water solvents to evaporate for 24 hours.

[0041] The thin film obtained in this embodiment exhibits a reflectance of 96.4% in the solar spectrum (wavelength 300 to 2500 nm) and an infrared emissivity of 97.2% in the atmospheric window wavelength range (wavelength 2.5 to 16 μm). The pore size distribution is predominantly bimodal, with micron-sized pores mainly at 3 μm and nanopores mainly at 0.3 μm. The structure of the obtained thin film is as follows... Figure 1 , 2 As shown.

[0042] Example 2

[0043] 100g of polyvinylidene fluoride-hexafluoropropylene is added to a double roller with a triangular prism structure on one side. The roller temperature is set to 165℃ and the preferred rotation speed is 20r / min. After rolling, a thin film A with a triangular prism structure on one side is formed. The formed prism structure is evenly spaced and parallel, with a bottom edge length of 50um, a height of 25um, and a apex angle of 90°.

[0044] Add 2g of polyvinylidene fluoride-hexafluoropropylene to a mixed solution of 18g of acetone and 2g of water, and stir magnetically in a water bath for 90min until a uniform and clear solution A is formed. The stirring rate is 150r / min, and the water bath temperature is preferably 55℃.

[0045] Silica was slowly added to solution A to obtain a white solution B. The solution was then stirred magnetically in a water bath at a speed of 150 r / min for 90 min. The spherical silica particles had a diameter of 5 μm and a mass fraction of 20%.

[0046] Solution B was drop-cast onto the non-prism structure side of the previously prepared thin film A at a drop volume of 0.20 ml / cm². 2 To ensure uniform distribution, the prepared bilayer membrane was placed at 25°C to allow acetone and water solvents to evaporate for 24 hours.

[0047] The thin film obtained in this embodiment has a reflectance of 95.4% in the solar spectrum range (wavelength 300 to 2500 nm) and an infrared emissivity of 97% in the atmospheric window wavelength range (wavelength 2.5 to 16 μm). The pore size range mainly exhibits a bimodal distribution, with the micron pore size mainly being 4 μm and the nanopore size mainly being 0.3 μm.

[0048] Example 3

[0049] 100g of polyvinylidene fluoride-hexafluoropropylene is added to a double roller with a triangular prism structure on one side. The roller temperature is set to 165℃ and the preferred rotation speed is 20r / min. After rolling, a thin film A with a triangular prism structure on one side is formed. The formed prism structure is evenly spaced and parallel, with a bottom edge length of 50um, a height of 25um, and a apex angle of 90°.

[0050] Add 2g of polyvinylidene fluoride-hexafluoropropylene to a mixed solution of 18g of acetone and 2g of water, and stir magnetically in a water bath for 90min until a uniform and clear solution A is formed. The stirring rate is 150r / min, and the water bath temperature is preferably 55℃.

[0051] Silica was slowly added to solution A to obtain a white solution B. The solution was then stirred magnetically in a water bath at a speed of 150 r / min for 90 min. The spherical silica particles had a diameter of 5 μm and a mass fraction of 20%.

[0052] Solution B was drop-cast onto the non-prism structure side of the previously prepared thin film A at a drop volume of 0.16 ml / cm². 2 To ensure uniform distribution, the prepared bilayer membrane was placed at 25°C to allow acetone and water solvents to evaporate for 24 hours.

[0053] The thin film obtained in this embodiment has a reflectance of 92.8% in the solar spectrum range (wavelength 300 to 2500 nm) and an infrared emissivity of 96.4% in the atmospheric window wavelength range (wavelength 2.5 to 16 μm). The pore size range mainly exhibits a bimodal distribution, with the micron pore size mainly being 3 μm and the nanopore size mainly being 0.4 μm.

[0054] Example 4

[0055] 100g of polyvinylidene fluoride-hexafluoropropylene is added to a double roller with a triangular prism structure on one side. The roller temperature is set to 165℃ and the preferred rotation speed is 20r / min. After rolling, a thin film A with a triangular prism structure on one side is formed. The formed prism structure is evenly spaced and parallel, with a bottom edge length of 50um, a height of 25um, and a apex angle of 90°.

[0056] Add 2g of polyvinylidene fluoride-hexafluoropropylene to a mixed solution of 18g of acetone and 2g of water, and stir magnetically in a water bath for 90min until a uniform and clear solution A is formed. The stirring rate is 150r / min, and the water bath temperature is preferably 55℃.

[0057] Silica was slowly added to solution A to obtain a white solution B. The solution was then stirred magnetically in a water bath at a speed of 150 r / min for 90 min. The spherical silica particles had a diameter of 5 μm and a mass fraction of 20%.

[0058] Solution B was drop-cast onto the non-prism structure side of the previously prepared thin film A at a drop volume of 0.12 ml / cm². 2 To ensure uniform distribution, the prepared bilayer membrane was placed at 25°C to allow acetone and water solvents to evaporate for 24 hours.

[0059] The thin film obtained in this embodiment has a reflectance of 91.6% in the solar spectrum range (wavelength 300 to 2500 nm) and an infrared emissivity of 95.4% in the atmospheric window wavelength range (wavelength 2.5 to 16 μm). The pore size range mainly exhibits a bimodal distribution, with the micron pore size mainly being 4 μm and the nanopore size mainly being 0.2 μm.

[0060] Example 5

[0061] 100g of polyvinylidene fluoride-hexafluoropropylene is added to a double roller with a triangular prism structure on one side. The roller temperature is set to 165℃ and the preferred rotation speed is 20r / min. After rolling, a thin film A with a triangular prism structure on one side is formed. The formed prism structure is evenly spaced and parallel, with a bottom edge length of 50um, a height of 25um, and a apex angle of 90°.

[0062] Add 2g of polyvinylidene fluoride-hexafluoropropylene to a mixed solution of 18g of acetone and 2g of water, and stir magnetically in a water bath for 90min until a uniform and clear precursor solution A is formed. The stirring rate is 150r / min, and the water bath temperature is preferably 55℃.

[0063] Silica was slowly added to solution A to obtain a white solution B. The solution was then stirred magnetically in a water bath at a speed of 150 r / min for 90 min. The spherical silica particles had a diameter of 5 μm and a mass fraction of 20%.

[0064] Solution B was drop-cast onto the non-prism structure side of the previously prepared thin film A at a drop volume of 0.08 ml / cm². 2 To ensure uniform distribution, the prepared bilayer membrane was placed at 25°C to allow acetone and water solvents to evaporate for 24 hours.

[0065] The thin film obtained in this embodiment has a reflectance of 90.2% in the solar spectrum range (wavelength 300 to 2500 nm) and an infrared emissivity of 95.1% in the atmospheric window wavelength range (wavelength 2.5 to 16 μm). The pore size range mainly exhibits a bimodal distribution, with the micron pore size mainly being 5 μm and the nanopore size mainly being 0.3 μm.

[0066] Example 6

[0067] 100g of polymethyl methacrylate is added to a double roller with a triangular prism structure on one side. The roller temperature is set to 150℃ and the preferred rotation speed is 20r / min. After rolling, a film A with a triangular prism structure on one side is formed. The formed prism structure is evenly spaced and parallel, with a bottom edge length of 50um, a height of 25um, and a apex angle of 90°.

[0068] Add 2g of polyvinylidene fluoride-hexafluoropropylene to a mixed solution of 18g of N,N-dimethylformyl and 2g of water, and stir magnetically in a water bath for 90min until a uniform and clear solution A is formed. The stirring rate is 150r / min, and the water bath temperature is preferably 55℃.

[0069] Alumina was slowly added to solution A to obtain a white solution B. The solution was then stirred magnetically in a water bath at a speed of 150 r / min for 90 min. The alumina particles had a diameter of 5 μm and a mass fraction of 20%.

[0070] Solution B was drop-cast onto the non-prism structure side of the previously prepared thin film A at a volume of 0.24 ml / cm³. 2 To ensure uniform distribution, the prepared bilayer membrane was placed at 25°C to allow N,N-dimethylformyl solvent and water solvent to evaporate for 24 hours.

[0071] The thin film obtained in this embodiment has a reflectance of 94.6% in the solar spectrum range (wavelength 300 to 2500 nm) and an infrared emissivity of 94.3% in the atmospheric window wavelength range (wavelength 2.5 to 16 μm). The pore size range mainly exhibits a bimodal distribution, with the micron pore size mainly being 5 μm and the nanopore size mainly being 0.4 μm.

[0072] Example 7

[0073] 100g of polyethylene oxide is added to a double roller with a triangular prism structure on one side. The roller temperature is set to 90℃ and the preferred rotation speed is 20r / min. After rolling, a film A with a triangular prism structure on one side is formed. The formed prism structure is evenly spaced and parallel, with a bottom edge length of 50um, a height of 25um, and a apex angle of 90°.

[0074] Add 2g of polyvinylidene fluoride-hexafluoropropylene to a mixed solution of 18g of N-methylpyrrolidone and 2g of water, and stir magnetically in a water bath for 90min until a uniform and clear solution A is formed. The stirring rate is 150r / min, and the water bath temperature is preferably 60℃.

[0075] Barium sulfate was slowly added to solution A to obtain a white solution B. The solution was then stirred magnetically in a water bath at a speed of 150 r / min for 90 min. The barium sulfate particles had a diameter of 4 μm and a mass fraction of 20%.

[0076] Solution B was drop-cast onto the non-prism structure side of the previously prepared thin film A at a volume of 0.24 ml / cm³. 2 To ensure uniform distribution, the prepared bilayer membrane was placed at 25°C to allow N-methylpyrrolidone and water solvents to evaporate for 48 hours.

[0077] The thin film obtained in this embodiment has a reflectance of 94.3% in the solar spectrum range (wavelength 300 to 2500 nm) and an infrared emissivity of 95.3% in the atmospheric window wavelength range (wavelength 2.5 to 16 μm). The pore size range mainly exhibits a bimodal distribution, with the micron pore size mainly being 4 μm and the nanopore size mainly being 0.4 μm.

[0078] Comparative Example 1

[0079] This comparative example provides a thin film without a prism photonic structure.

[0080] This comparative example only includes the upper porous membrane, and the preparation method of the porous membrane is the same as step two of Example 1. The solution in step two is prepared at 0.24 ml / cm 2 The film is placed on a clean glass substrate and placed at 25°C to allow the acetone and water solvents to evaporate. The solvent evaporation time is 24 hours. After peeling, a film without a prism structure can be obtained.

[0081] Figure 4 , 5 The figures show a comparison of the reflectance curves in the solar spectral region (0.3–2.5 μm) and the emissivity curves in the mid-infrared region (2.5–16 μm) of the thin films prepared in Example 1 and Comparative Example 1, respectively. It can be seen that the double-layer thin film with the prism structure of the present invention has both better reflectance and emissivity. Figure 6 Figure 7 shows the electric field distribution diagram obtained from the simulation software for the optimal silica particle size. The silica filler with the optimal particle size contributes to the emissivity of the film in the 8-13 μm range. Figure 8 shows the cooling data diagram from outdoor testing, which shows that the bilayer film with the prism structure of this invention has a better cooling effect. Figure 8 shows the water contact angle and stress-strain curve of the radiation cooling film of this invention, which shows that the prepared radiation cooling film not only has good outdoor cooling capability, but also has the potential for use in extreme weather conditions.

[0082] The embodiments described above are some, but not all, embodiments of the present invention, and are not intended to limit the present invention in any way. The present invention is not limited to the above embodiments, and various variations can be made according to the inventive purpose of the present invention. Any modifications, additions, and equivalent substitutions made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-reflectivity, high-emission prism photonic metamaterial thin film for radiative cooling, characterized in that, The film consists of a lower organic polymer film layer and an upper porous structure layer. The lower surface of the organic polymer film layer is uniformly distributed with triangular prism structures. The triangular prism structures are arranged in parallel. The base length of the triangle of each triangular prism structure is 45~55um, the height is 20~25um, and the apex angle is 85°~95°. The porous structure layer is composed of organic polymer and dielectric microsphere particles, with a pore size ranging from 0.1 to 10um.

2. The high-reflectivity, high-emission prism photonic metamaterial thin film for radiative cooling according to claim 1, characterized in that, The organic polymer is at least one of polydimethylsiloxane, polymethyl methacrylate, polyvinylidene fluoride-hexafluoropropylene, polyethylene oxide, and polylactic acid.

3. The high-reflectivity, high-emission prism photonic metamaterial thin film for radiative cooling according to claim 1, characterized in that, The dielectric microspheres are selected from at least one of titanium dioxide, aluminum oxide, silicon dioxide, or barium sulfate, and have a particle size of 4-8 μm.

4. The application of the high-reflectivity, high-emission prism photonic metamaterial thin film for radiative cooling as described in any one of claims 1-3, characterized in that, The thin film is used as a radiation-cooling film in the field of refrigeration.

5. A method for preparing a high-reflectivity, high-emission prism photonic metamaterial thin film for radiation cooling as described in any one of claims 1 to 3, characterized in that, Includes the following steps: (1) An organic polymer is added to a double roller with a prism column structure groove on one side, and a thin film A with a prism structure evenly distributed on one side is formed by roller pressing. (2) Add the organic polymer to a mixed solution of organic solvent and water, and stir magnetically in a water bath to obtain solution A; (3) Add dielectric microspheres to solution A and stir magnetically in a water bath until they are evenly distributed to obtain solution B; (4) Solution B is drop-cast onto the side of the prepared film A without the prism structure to obtain a double film; (5) The obtained double-layer film is left to stand and dry until the solution evaporates to obtain the high-reflection and high-emission prism photonic metamaterial thin film.

6. The method for preparing a high-reflectivity, high-emission prism photonic metamaterial thin film for radiative cooling according to claim 5, characterized in that, In step (2), the mass ratio of organic polymer, organic solvent and water is 0.8~1.2:8~11:0.5~2.

7. The method for preparing a high-reflectivity, high-emission prism photonic metamaterial thin film for radiative cooling according to claim 5, characterized in that, In step (2), the mixture of organic polymer, organic solvent and water is magnetically stirred in a water bath for 90-120 min at a stirring rate of 100-200 r / min and a water bath temperature of 50-60℃.

8. The method for preparing a high-reflectivity, high-emission prism photonic metamaterial thin film for radiative cooling according to claim 5, characterized in that, The organic solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, toluene, tetrahydrofuran, and acetone.

9. The method for preparing a high-reflectivity, high-emission prism photonic metamaterial thin film for radiative cooling according to claim 5, characterized in that, In step (3), the stirring speed is 100~200 r / min, the stirring time is 30~60 min, the water bath temperature is 50~60℃, and the mass fraction of dielectric microspheres in solution B is 10%~20%.

10. The method for preparing a high-reflectivity, high-emission prism photonic metamaterial thin film for radiation cooling according to claim 5, characterized in that, In step (4), the drip casting volume is 0.08~0.24 ml / cm³. 2 To ensure uniform distribution, in step (5), the double-layer membrane is placed in an environment of 20~30℃ to allow organic solvents and water to evaporate, with an evaporation time of 24~36h.

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