High-reflection composite disordered superstructure material and preparation method and application thereof

Abstract

The application belongs to the technical field of thermal control materials, and discloses a high-reflection composite disordered superstructure material and a preparation method and application thereof. The material comprises a light-heat regulation superstructure composed of two highly disordered long-wave reflection layers and short-wave reflection layers. The material has a highly disordered spatial distribution of scattering particles in the interior, a white appearance, a thickness of 200-1000 microns, a solar spectrum band-weighted average reflectivity of 0.8-0.97, a regulation reflection band of 0.2-8 microns, an infrared emissivity of 0.75-0.92, and advantages of wide band, high reflection, simple construction, low cost, and scalability. Meanwhile, due to the characteristics of the secondary flow casting in-situ solidification forming technology, the formed composite superstructure is easy to be mechanically processed, thereby ensuring the applicability of the composite highly disordered scattering superstructure to irregular surfaces and curved surfaces.

Description

Technical Field

[0001] This invention belongs to the field of selective radiation thermal control materials technology, specifically relating to a broadband high-reflectivity composite disordered superstructure material, its preparation method, and its application. Background Technology

[0002] Considering the environmental impact, radiative cooling, as a novel space cooling method that requires no energy input and only utilizes the properties of the surface material to control the heat of the covered object, has become a highly promising solution.

[0003] The fundamental idea behind efficient space cooling or device cooling is to isolate external solar radiation heat sources while dissipating its own heat as much as possible. Using high-reflectivity materials can improve the efficiency of heat dissipation, but for broadband solar radiation with energy distribution covering the ultraviolet, visible, and even infrared bands, achieving high reflectivity within that broadband band becomes crucial for efficient space cooling. Currently, based on the different reflectance spectral ranges, radiation cooling materials are generally classified into two main types: narrowband radiation cooling materials that concentrate reflection of solar radiation in the 0.2–2.5 μm band, and broadband radiation cooling materials that uniformly reflect the entire 0.2–8 μm band. The former has high emissivity in bands greater than 2.5 μm, while the latter only has high emissivity in the 8–13 μm atmospheric window band.

[0004] Superstructures, as a novel functional material design concept that integrates the intrinsic properties of materials such as high refractive index and low absorption coefficient with the advantages of artificial configuration, have shown great application potential in spectral modulation and selective radiation. For example, Chinese patent CN112460836 A, "Passive Radiation Cooling Composite Film," proposes a metal-based film combined with patterned metasurface configuration to achieve spectral performance modulation in different bands. However, this scheme is limited by the intrinsic ultraviolet absorption characteristics of metals, and the reflectivity cannot be further improved. Moreover, the high cost and scalability of metal-based film preparation limit the widespread application of this scheme. Another example is Chinese patent CN109343159A, "A Nonlinear Laser Constriction Structure Based on a One-Dimensional Photonic Crystal," which constructs a one-dimensional photonic crystal superstructure by stacking multiple layers of dielectrics. Although customized band photothermal performance modulation can be achieved through photonic bandgap modulation, problems such as the small thickness of each dielectric layer and high requirements for fabrication precision also urgently need to be solved.

[0005] In comparison, scattering superstructures that achieve broadband high reflectivity by utilizing the highly disordered spatial distribution of scattering units are highly practical. By analyzing the coupling relationship between the target radiation wavelength, target bandwidth, and scattering unit structural parameters, the geometry, size, content, and even spatial distribution of the scattering units can be precisely designed and controlled. When the scattering units whose geometry and size match the target control band have site coordinates in three-dimensional space that conform to the Percus–Yevick hard sphere model, their spatial distribution is highly disordered. Photothermal controllable scattering superstructures constructed based on Mie scattering theory can achieve broadband high reflectivity targets. Since the reflectivity originates from the disordered distribution of scattering units with specific structural parameters in three-dimensional space, this type of superstructure has lower processing precision requirements. Combined with the selection of low-cost materials, highly disordered scattering superstructures are expected to achieve low-cost, large-scale production without sacrificing performance.

[0006] Currently, most publicly reported highly disordered scattering superstructures are monolayer coatings or thin films. This singular structural design limits the further extension of the reflection band, often resulting in poor reflection in the infrared band, typically achieving high reflectivity only in the 0.2-2.5 μm band. Therefore, while ensuring low cost and large-scale production of highly disordered scattering superstructures, further extending the superstructure form to prepare highly efficient radiation thermal control materials with a reflection bandwidth extending to the infrared band has significant engineering application background and research value. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a high-reflectivity composite disordered superstructure material, its preparation method, and its applications. This material possesses high reflectivity across a wide wavelength range and is a superstructure composed of highly disordered spatial structures.

[0008] The design concept of scattering superstructures is reflected in both the geometric structural parameters and spatial distribution of the scattering units. Based on the coupling relationship between the target wavelength, bandwidth, and structural parameters, the geometry and structural parameters of the scattering particles can be rationally designed to match their strong scattering band with the target modulation band, thereby generating the strongest spectral response. Simultaneously, when the distribution of these scattering particles in three-dimensional space conforms to the Percus–Yevick hard-sphere model, the degree of disorder is high. The scattering artificial superstructure constructed in this way, targeting photothermal modulation, will achieve broadband high-reflectivity targets based on Mie theory and the principle of multiple scattering. Currently reported scattering superstructures are mainly in the form of single-layer thin films or coatings. While this single form achieves efficient reflection in the ultraviolet and visible bands, the structural parameters of the scattering particles limit their effectiveness in scattering near-infrared and mid-infrared bands, severely restricting the expansion of the reflection bandwidth. By designing structural parameters for different scattering efficiencies using a bilayer composite highly disordered superstructure, the reflection bandwidth can be effectively broadened. This approach can maintain the original advantages of disordered scattering superstructures while introducing new selective radiation photothermal modulation concepts, thereby further promoting the practical application of superstructures.

[0009] The technical solution of the present invention is as follows:

[0010] This invention discloses a highly reflective composite disordered superstructure material, comprising a photothermal modulating superstructure composed of two highly disordered long-wavelength reflective layers and a short-wavelength reflective layer. The long-wavelength reflective layer is the bottom layer, with a modulating wavelength range of 1–8 μm, and is made of scattering particles with an average structural size of 5–20 μm and a structural size distribution range of 3–50 μm. The short-wavelength reflective layer is the top layer, with a modulating wavelength range of 0.2–1 μm, and is made of scattering particles with an average structural size of 0.1–2 μm and a structural size distribution range of 0.02–5 μm.

[0011] The superstructure material has a highly disordered spatial distribution of internal scattering particles, is white in appearance, has a thickness of 200–1000 μm, a weighted average reflectance of 0.8–0.97 in the solar spectrum band, an infrared emissivity of 0.75–0.92, and a modulated reflection band of 0.2–8 μm.

[0012] The scattering particles are silicon dioxide, yttrium oxide, magnesium aluminum spinel, zirconium oxide, zinc sulfide, aluminum oxynitride, or yttrium aluminum garnet.

[0013] This invention also discloses a method for preparing the above-mentioned high-reflectivity composite disordered superstructure material, comprising the following steps:

[0014] (1) Prepare two slurries of scattering particles with different structural sizes: Disperse dried scattering particles with an average structural size of 5-20 μm and a structural size distribution range of 3-50 μm, and an average structural size of 0.1-2 μm and a structural size distribution range of 0.02-5 μm, respectively, in a mixed solution containing a dispersant and a binder, and then add an antifoaming agent and mix well to obtain slurries of scattering particles with large structural size and slurries of scattering particles with small structural size;

[0015] (2) Long-wave reflective layer forming: Large-size scattering particle slurry is cast on a cast base film, cured in situ at 10-40℃, and dried for 3-24 hours to obtain a long-wave reflective layer as the bottom layer.

[0016] (3) Short-wave reflective layer forming: small-sized scattering particle slurry is cast onto the long-wave reflective layer in a secondary casting process, cured in situ at 10-40℃, and dried for 1-24 hours to obtain a surface layer that is a short-wave reflective layer.

[0017] (4) Preparation of composite disordered superstructure material: After the composite disordered superstructure blank with two highly disordered long-wave reflective layers and short-wave reflective layers is dried and debonded, it is processed into materials of specific shape and / or size as needed, and then sintered at high temperature to obtain composite disordered superstructure material.

[0018] Two structural sizes of the scattering particles are selected. To match the response to short-wavelength incident radiation, the average particle size of the small-sized scattering particles is preferably in the range of 0.1 to 2 μm. To form a highly disordered spatially distributed superstructure and avoid the ordered spontaneous assembly of particles with similar sizes, the structural size distribution range of the small-sized scattering particles is 0.02 to 5 μm. To match the response to long-wavelength incident radiation, the average particle size of the large-sized scattering particles is preferably in the range of 5 to 20 μm. To form a highly disordered spatially distributed superstructure and avoid the ordered spontaneous assembly of particles with similar sizes, the structural size distribution range of the large-sized scattering particles is 3 to 50 μm. Two uniform, stable, and disordered dispersed ceramic slurries are prepared using scattering particles of the two structural sizes respectively.

[0019] In one embodiment of the present invention, the total thickness of the long-wave reflective layer and the short-wave reflective layer after secondary casting is preferably 600-1400 μm. When the surface short-wave reflective layer is prepared by secondary casting, the casting machine scraper is 50-100 μm higher than the bottom long-wave reflective layer. The two highly disordered reflective structures, which are assembled from scattering particles of specific size, together constitute a composite photothermal control superstructure.

[0020] In one embodiment of the present invention, in preferred step (4), the high-temperature sintering temperature is 700-1200°C, the sintering atmosphere is air or oxygen, and the sintering time is 2-8 hours.

[0021] In one embodiment of the present invention, in preferred step (1), the dispersant is dispersed in distilled water, mixed well, and then a pre-prepared binder solution is added to obtain a mixed solution containing the dispersant and the binder.

[0022] In one embodiment of the present invention, the solvent of the binder solution is preferably distilled water, the amount of binder solution added is 5-10 wt% of the slurry mass, and the solid content of the binder in the binder solution is 10-16 wt%. The binder is one or both of polyvinyl alcohol or polyvinyl butyral, used to fix the spatial distribution of disordered scattering particles in situ.

[0023] In one embodiment of the present invention, the amount of the scattering particles added is preferably 75-85 wt% of the slurry mass.

[0024] In one embodiment of the present invention, the dispersant is preferably one or more of polyvinylpyrrolidone, a copolymer of isobutylene and maleic anhydride, sodium dodecyl sulfonate, or polyethylene glycol, used to ensure that large and small scattering particles are uniformly and randomly distributed in the slurry; the amount of the dispersant added is 0.2 to 1.2 wt% of the mass of the scattering particles.

[0025] In one embodiment of the present invention, the defoamer is preferably one or more of n-propanol, isopropanol, n-butanol, isobutanol or tert-butanol; the amount of the defoamer added is 0.2 to 1 wt% of the mass of the scattering particles.

[0026] This invention also discloses the application of the aforementioned high-reflectivity composite disordered superstructure material as a radiative cooling substrate in atmospheric-protected surface environments or un-atmospheric space environments. The application of radiative cooling and heat control in substrates facing solar radiation includes surface building exterior walls, surface building roofs, the outer surfaces of fixed or non-fixed surface facilities, space device shells, and spacecraft skins.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention discloses a high-reflectivity composite disordered superstructure material. By effectively combining two reflective layers with different structural parameters, and controlling the spectral ranges of 0.2–1 μm and 1–8 μm, the high-reflectivity band of the superstructure is greatly expanded, with the reflection band controlled to 0.2–8 μm. Simultaneously, while improving the superstructure's spectral control capability and radiative thermal control performance (solar reflectivity, mid-infrared emissivity), it offers advantages such as simple construction, low cost, and scalability. Furthermore, due to the characteristics of the secondary casting in-situ curing molding technology, the molded composite superstructure is easy to machine, ensuring the applicability of the composite highly disordered scattering superstructure to irregular and curved surfaces. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of a broadband high-reflectivity composite disordered superstructure material of the present invention, wherein 1 is a surface short-wave reflective layer composed of disordered distribution of small-sized scattering particles, 2 is a bottom long-wave reflective layer composed of disordered distribution of large-sized scattering particles, and 3 is the air medium in the gaps between the scattering particles.

[0030] Figure 2 This is a schematic diagram of a physical photograph of a high-reflectivity composite disordered superstructure material according to Embodiment 1 of the present invention;

[0031] Figure 3 This is a schematic diagram of the microscopic cross-sectional structure of a high-reflectivity composite disordered superstructure material according to Embodiment 3 of the present invention. Detailed Implementation

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0033] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0034] The present invention discloses a method for preparing a high-reflectivity composite disordered superstructure material, comprising the following steps:

[0035] (1) Prepare two slurries of scattering particles with different structural sizes: First, transfer scattering particles with an average structural size of 5-20 μm and a structural size distribution range of 3-50 μm and an average structural size of 0.1-2 μm into a vacuum drying oven for drying and use; Dispersant is ultrasonically dispersed in distilled water, stirred evenly, and then a certain amount of pre-prepared binder solution is added and stirred until uniform. Then, the dried scattering particles are added, ultrasonically dispersed and stirred until uniformly mixed. Then, an appropriate amount of defoamer is added and stirred thoroughly until the slurry is stable and uniform, thus obtaining a slurry of scattering particles with a large structural size; Slurry of scattering particles with an average structural size of 0.1-2 μm and a structural size distribution range of 0.02-5 μm is selected and prepared according to the above method to obtain a slurry of scattering particles with a small structural size.

[0036] (2) Long-wave reflective layer forming: Large-size scattering particle slurry is cast on a cast base film, cured in situ at 10-40℃, and dried for 3-24 hours to obtain a long-wave reflective layer as the bottom layer.

[0037] (3) Short-wave reflective layer forming: small-sized scattering particle slurry is cast onto the long-wave reflective layer in a secondary casting process, cured in situ at 10-40℃, and dried for 1-24 hours to obtain a surface layer that is a short-wave reflective layer.

[0038] (4) Preparation of composite disordered superstructure material: After the composite disordered superstructure preform with two highly disordered long-wave reflective layers and a short-wave reflective layer is dried and debonded, it is processed into materials of specific shapes and / or sizes as needed, and then sintered at high temperature to obtain the composite disordered superstructure material. Its structural schematic diagram is shown in the figure. Figure 1 As shown.

[0039] Example 1

[0040] A method for preparing a high-reflectivity composite disordered superstructure material according to Embodiment 1 of the present invention includes the following steps:

[0041] In this embodiment, the scattering particles of the composite disordered superstructure material are zirconium oxide, the dispersant is a copolymer of isobutylene and maleic anhydride, the binder is a 12wt% aqueous solution of polyvinyl alcohol, and the defoamer is n-propanol.

[0042] (1) Prepare ceramic slurries with two different structural size scattering particles: Weigh small-sized zirconia particles with an average structural size of 0.5 μm and a structural size distribution range of 0.2 to 1.5 μm and place them in a vacuum drying oven and dry them at 50°C for later use, so that the zirconia scattering particles account for 75 wt% of the slurry mass; Weigh a copolymer of isobutylene and maleic anhydride as a dispersant, with a mass of 0.5 wt% of the scattering particle mass, add the dispersant to distilled water and ultrasonically disperse it evenly; Weigh a binder solution, with a mass of 7 wt% of the scattering particle mass, add it to distilled water mixed with the dispersant, and ultrasonically stir it evenly and mix it thoroughly; Add the dried small-sized scattering particles to the above solution, ultrasonically disperse and stir until they are evenly mixed; Add n-propanol as a defoamer, with a mass of 4 wt% of the scattering particle mass, and stir it thoroughly until the slurry is stable and uniform, thus obtaining a slurry with small-sized scattering particles.

[0043] Weigh large-sized zirconia particles with an average structural size of 8 μm and a structural size distribution range of 3–15 μm. Make the zirconia scattering particles account for 75 wt% of the slurry mass. Repeat the above slurry preparation process to obtain a slurry with large-sized scattering particles.

[0044] (2) Forming of long-wave reflective layer: ceramic slurry prepared from large-sized zirconia particles with an average particle size of 8 μm and a structural size distribution range of 3 to 15 μm is cast onto a casting base film. The thickness of the cast wet film is controlled to be 1200 μm. The film is cured in situ at 30°C and dried for 5 hours to obtain the bottom long-wave reflective layer.

[0045] (3) Forming of short-wave reflective layer: A ceramic slurry prepared from small-sized zirconia particles with an average particle size of 0.5 μm and a structural size distribution range of 0.2 to 1.5 μm is cast onto the long-wave reflective layer in a secondary casting process. The total thickness of the cast wet film is controlled to be 1000 μm. The film is cured in situ at 30°C and dried for 2 hours to obtain a short-wave reflective layer on the surface.

[0046] (3) Preparation of the composite disordered superstructure: After the composite disordered superstructure blank with an upper short-wavelength reflective layer and a lower long-wavelength reflective layer is completely dried and debonded at 55℃, it is mechanically cut into 45mm×25mm blank pieces and then transferred to a high-temperature muffle furnace for sintering at 1300℃ for 5 hours to obtain the aforementioned wide-band high-reflectivity composite disordered superstructure. A schematic diagram of the physical object is shown below. Figure 2 As shown.

[0047] The broadband high-reflectance composite disordered superstructure prepared in this embodiment was measured to have a thickness of 800 μm using a thickness gauge. Its diffuse reflectance spectrum in the 0.2–8 μm band was measured using a UV-Vis-NIR spectrophotometer and a Fourier transform infrared spectrometer. When the material prepared in this embodiment is applied to substrate radiative cooling in a surface environment, the reflectance across the entire solar spectrum is calculated using the intensity of the solar spectrum absorbed by the atmosphere. A weighted integral calculation based on the AM1.5 standard solar spectral intensity yields a weighted reflectance of 0.96. The diffuse reflectance spectrum above 8 μm was measured using a Fourier transform infrared spectrometer. Since this sample is opaque, the emissivity spectrum can be further calculated using the formula "emissivity = 1 - reflectivity". Then, the blackbody radiation intensity at 300 K, calculated using Planck's blackbody radiation formula, is weighted and integrally calculated to yield an infrared emissivity of 0.82 in the atmospheric window 8–13 μm band.

[0048] Example 2

[0049] A method for preparing a high-reflectivity composite disordered superstructure material according to Embodiment 2 of the present invention includes the following steps:

[0050] In this embodiment, the scattering particles involved in the composite disordered superstructure are magnesium aluminum spinel particles, the dispersant is sodium dodecyl sulfonate, the binder is a 16wt% aqueous solution of polyvinyl alcohol, and the defoamer is n-butanol.

[0051] (1) Prepare ceramic slurries with two different structural size scattering particles: Weigh small-sized magnesium aluminum spinel particles with an average structural size of 0.3 μm and a structural size distribution range of 0.1 to 1 μm and place them in a vacuum drying oven. Dry them at 50°C for later use, so that the magnesium aluminum spinel particles account for 80 wt% of the slurry mass; Weigh sodium dodecyl sulfonate dispersant, which is 0.8 wt% of the scattering particle mass. Add the dispersant to distilled water and ultrasonically disperse it evenly; Weigh binder solution, which is 10 wt% of the scattering particle mass. Add it to distilled water containing the dispersant and ultrasonically stir it evenly to mix it thoroughly; Add the dried small-sized scattering particles to the above solution and ultrasonically disperse and stir until they are evenly mixed; Add n-butanol as an antifoaming agent, which is 4 wt% of the scattering particle mass. Stir it thoroughly until the slurry is stable and uniform to obtain a slurry with small-sized scattering particles.

[0052] Weigh large-sized magnesium aluminum spinel particles with an average structural size of 15 μm and a structural size distribution range of 5–25 μm. Make the magnesium aluminum spinel scattering particles account for 80 wt% of the slurry mass. Repeat the above slurry preparation process to obtain a slurry with large-sized scattering particles.

[0053] (2) Forming of long-wave reflective layer: Ceramic slurry prepared from large-sized magnesium aluminum spinel particles with an average particle size of 15 μm and a structural size distribution range of 5 to 25 μm is cast onto a casting base film. The thickness of the cast wet film is controlled to be 1000 μm. The film is cured in situ at 20°C and dried for 10 hours to obtain the bottom long-wave reflective layer.

[0054] (3) Forming of short-wave reflective layer: A ceramic slurry prepared from small-sized magnesium aluminum spinel particles with an average particle size of 0.3 μm and a size distribution range of 0.1 to 1 μm is cast onto the long-wave reflective layer in a secondary casting process. The total thickness of the cast wet film is controlled to be 900 μm. The film is cured in situ at 20°C and dried for 4 hours to obtain a short-wave reflective layer on the surface.

[0055] (4) Preparation of composite disordered superstructure: After the composite disordered superstructure blank with the upper layer being a short-wave reflective layer and the lower layer being a long-wave reflective layer is completely dried and debonded at 60℃, it is mechanically cut into 40mm×40mm blank pieces and then transferred to a high-temperature muffle furnace for sintering at 1000℃ for 4 hours to obtain the wide-band high-reflectivity composite disordered superstructure.

[0056] The thickness of the broadband high-reflectance composite disordered superstructure prepared in this embodiment was measured to be 730 μm using a thickness gauge. Its diffuse reflectance spectrum in the 0.2–8 μm band was measured using a UV-Vis-NIR spectrophotometer and a Fourier transform infrared spectrometer. When the material prepared in this embodiment is used for substrate radiative cooling in a space environment, due to the loss of atmospheric protection, solar irradiance energy is not attenuated. Therefore, its solar weighted reflectance is calculated to be 0.94 based on the weighted integral of the AMO standard solar spectral intensity. Its diffuse reflectance spectrum above 8 μm was measured using a Fourier transform infrared spectrometer. Since this sample is opaque, the emissivity spectrum can be further calculated using "emissivity = 1 - reflectivity". Again, due to the absence of atmospheric protection, calculations are not limited to the 8–13 μm band. Based on the blackbody radiation intensity at 300 K calculated using Planck's blackbody radiation formula, the infrared emissivity above 8 μm is calculated to be 0.88 using weighted integral.

[0057] Example 3

[0058] A method for preparing a high-reflectivity composite disordered superstructure material according to Embodiment 3 of the present invention includes the following steps:

[0059] In this embodiment, the scattering particles involved in the composite disordered superstructure are yttrium oxide particles, the dispersant is a copolymer of isobutylene and maleic anhydride, the binder is a 14wt% aqueous solution of polyvinyl alcohol, and the defoamer is n-propanol.

[0060] (1) Prepare ceramic slurries with two different structural size scattering particles: Weigh small-sized yttrium oxide particles with an average structural size of 0.4 μm and a structural size distribution range of 0.1 to 1.2 μm and place them in a vacuum drying oven. Dry them at 50°C for later use, so that the yttrium oxide scattering particles account for 78 wt% of the slurry mass; Weigh a copolymer of isobutylene and maleic anhydride as a dispersant, with a mass of 0.3 wt% of the scattering particle mass. Add the dispersant to distilled water and ultrasonically disperse it evenly; Weigh a binder solution, with a mass of 10 wt% of the scattering particle mass. Add it to distilled water containing the dispersant and ultrasonically stir it evenly to mix it thoroughly; Add the dried small-sized scattering particles to the above solution and ultrasonically disperse and stir until they are evenly mixed; Add n-propanol as a defoamer, with a mass of 4 wt% of the scattering particle mass, and stir it thoroughly until the slurry is stable and uniform to obtain a slurry with small-sized scattering particles.

[0061] Weigh large-sized yttrium oxide particles with an average structural size of 29 μm and a structural size distribution range of 10–45 μm. Make the yttrium oxide scattering particles account for 75 wt% of the slurry mass, and repeat the above slurry preparation process to obtain a slurry with large-sized scattering particles.

[0062] (2) Forming of long-wave reflective layer: Ceramic slurry prepared from large-sized yttrium oxide particles with an average particle size of 29 μm and a structural size distribution range of 10 to 45 μm is cast onto a casting base film. The thickness of the cast wet film is controlled to be 900 μm. The film is cured in situ at 30°C and dried for 6 hours to obtain the bottom long-wave reflective layer.

[0063] (3) Forming of short-wave reflective layer: Ceramic slurry prepared from small-sized yttrium oxide particles with an average particle size of 0.4 μm and a size distribution range of 0.1 to 1.2 μm is cast onto long-wave reflective layer in a secondary casting process. The total thickness of the cast wet film is controlled to be 800 μm. The film is cured in situ at 30°C and dried for 2 hours to obtain short-wave reflective layer on the surface.

[0064] (4) Preparation of the composite disordered superstructure: After the composite disordered superstructure blank with an upper short-wavelength reflective layer and a lower long-wavelength reflective layer is completely dried and debonded at 60℃, it is mechanically cut into 40mm×40mm blank pieces and then transferred to a high-temperature muffle furnace for sintering at 1050℃ for 6 hours to obtain the aforementioned wide-band high-reflectivity composite disordered superstructure. Its microscopic cross-sectional structure is shown in the figure below. Figure 3 As shown, the double-layer composite structure is clearly visible.

[0065] The broadband high-reflectance composite disordered superstructure prepared in this embodiment was measured to have a thickness of 550 μm using a thickness gauge. Its diffuse reflectance spectrum in the 0.2–8 μm band was measured using a UV-Vis-NIR spectrophotometer and a Fourier transform infrared spectrometer. When the material prepared in this embodiment is applied to substrate radiative cooling in a surface environment, the reflectance across the entire solar spectrum is calculated using the intensity of the solar spectrum absorbed by the atmosphere. A weighted integral calculation based on the AM1.5 standard solar spectral intensity yields a weighted reflectance of 0.95. The diffuse reflectance spectrum above 8 μm was measured using a Fourier transform infrared spectrometer. Since this sample is opaque, the emissivity spectrum can be further calculated using the formula "emissivity = 1 - reflectivity". Then, the blackbody radiation intensity at 300 K, calculated using Planck's blackbody radiation formula, is weighted and integrated to calculate the infrared emissivity in the atmospheric window 8–13 μm band, which is 0.84.

[0066] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A highly reflective composite disordered superstructure material, characterized in that, The superstructure comprises a photothermal modulating layer consisting of two highly disordered long-wavelength reflective layers and a short-wavelength reflective layer. The long-wavelength reflective layer, the bottom layer, has a modulating wavelength range of 1–8 μm and is made of scattering particles with an average structural size of 5–20 μm and a structural size distribution range of 3–50 μm. The short-wavelength reflective layer, the top layer, has a modulating wavelength range of 0.2–1 μm and is made of scattering particles with an average structural size of 0.1–2 μm and a structural size distribution range of 0.02–5 μm. The superstructure material has a highly disordered spatial distribution of internal scattering particles, is white in appearance, has a thickness of 200–1000 μm, a weighted average reflectance of 0.8–0.97 in the solar spectrum band, an infrared emissivity of 0.75–0.92, and a modulated reflection band of 0.2–8 μm. The scattering particles are silicon dioxide, yttrium oxide, magnesium aluminum spinel, zirconium oxide, zinc sulfide, aluminum oxynitride, or yttrium aluminum garnet.

2. A method for preparing a high-reflectivity composite disordered superstructure material as described in claim 1, characterized in that, It is prepared by the following steps: (1) Prepare two slurries of scattering particles with different structural sizes: Disperse dried scattering particles with an average structural size of 5-20 μm and a structural size distribution range of 3-50 μm, and an average structural size of 0.1-2 μm and a structural size distribution range of 0.02-5 μm, respectively, in a mixed solution containing a dispersant and a binder, and then add an antifoaming agent and mix well to obtain slurries of scattering particles with large structural size and slurries of scattering particles with small structural size; (2) Long-wave reflective layer forming: Large-size scattering particle slurry is cast on a cast base film, cured in situ at 10-40℃, and dried for 3-24 hours to obtain a long-wave reflective layer as the bottom layer. (3) Short-wave reflective layer forming: small-sized scattering particle slurry is cast onto the long-wave reflective layer in a secondary casting process, cured in situ at 10-40℃, and dried for 1-24 hours to obtain a surface layer that is a short-wave reflective layer. (4) Preparation of composite disordered superstructure material: After the two highly disordered long-wave reflective layers and short-wave reflective layers are dried and debonded, the composite disordered superstructure material is obtained by high-temperature sintering.

3. The method for preparing the high-reflectivity composite disordered superstructure material according to claim 2, characterized in that, The total thickness of the long-wave reflective layer and the short-wave reflective layer after the secondary casting is 600-1400 μm. When the surface short-wave reflective layer is prepared by secondary casting, the casting machine scraper is 50-100 μm higher than the bottom long-wave reflective layer.

4. The method for preparing the high-reflectivity composite disordered superstructure material according to claim 2, characterized in that, In step (4), the high-temperature sintering temperature is 700-1200℃, the sintering atmosphere is air or oxygen, and the sintering time is 2-8 hours.

5. The method for preparing the high-reflectivity composite disordered superstructure material according to claim 2, characterized in that, In step (1), the dispersant is dispersed in distilled water, mixed well, and then a pre-prepared binder solution is added to obtain a mixed solution containing the dispersant and the binder.

6. The method for preparing the high-reflectivity composite disordered superstructure material according to claim 5, characterized in that, The solvent of the adhesive solution is distilled water, the amount of adhesive solution added is 5-10 wt% of the slurry mass, the solid content of the adhesive in the adhesive solution is 10-16 wt%, and the adhesive is one or both of polyvinyl alcohol or polyvinyl butyral.

7. The method for preparing the high-reflectivity composite disordered superstructure material according to claim 2, characterized in that, The amount of the scattering particles added is 75-85 wt% of the slurry mass.

8. The method for preparing the high-reflectivity composite disordered superstructure material according to claim 2, characterized in that, The dispersant is one or more of polyvinylpyrrolidone, a copolymer of isobutylene and maleic anhydride, sodium dodecyl sulfonate, or polyethylene glycol; the amount of the dispersant added is 0.2 to 1.2 wt% of the mass of the scattering particles.

9. The method for preparing the high-reflectivity composite disordered superstructure material according to claim 2, characterized in that, The defoamer is one or more of n-propanol, isopropanol, n-butanol, isobutanol, or tert-butanol; The amount of defoamer added is 0.2 to 1 wt% of the mass of the scattering particles.

10. The application of the high-reflectivity composite disordered superstructure material of claim 1 as a radiation cooling substrate in an atmospheric-protected surface environment or an un-atmospheric space environment.

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