Construction method of high-selectivity radiation refrigeration metasurface

Abstract

The invention discloses a construction method of a high-selectivity radiation refrigeration metasurface, which comprises the following steps: a polymer, a curing agent and an organic solvent are uniformly mixed in proportion to obtain a mixed solution, the curing agent accounts for 5-20wt% of the polymer, and the organic solvent accounts for 0-50wt% of the mixed solution; preparing a metal film layer with the thickness of 50-200nm on the substrate; coating the mixed solution on the metal film layer and drying to form a polymer film layer; and the dielectric microspheres are trapped into the polymer film layer through a one-way friction method, a single-layer dielectric microsphere array is formed, and the high-selectivity radiation refrigeration metasurface is obtained. The average solar reflectivity and the atmospheric transparent window emissivity can reach 0.96, the spectral selectivity of 8-13 [mu] m can reach 1.50, and the cooling effect lower than 12.8 DEG C of the environment can be achieved under direct sunlight at noon.

Description

Technical Field

[0001] The present invention relates to the technical field of radiative cooling, and in particular to a method for constructing a highly selective radiative cooling super surface. Background Art

[0003] Refrigeration technology plays an important role in many aspects of human daily life, such as buildings, vehicles, clothing, electronic products, etc. According to statistics, the existing refrigeration methods consume 15% of the world's electricity and emit 10% of the world's greenhouse gases, causing serious environmental and economic problems. It is inconsistent with the current national strategic development goals of "carbon peak and carbon neutrality" and urgently needs to be replaced. The daytime passive radiative cooling (PDRC) technology uses the principle of highly reflecting sunlight in the 0.3-2.5μm band and transmitting infrared radiation of a specific wavelength to the cold outer space through an atmospheric transparent window of 8-13μm. It has the advantages of no electric refrigeration, zero pollution, and zero carbon source, and is expected to reduce or replace traditional electric refrigeration technology.

[0004] Radiative cooling is divided into two types according to the spectrum. One is a broadband radiator, which has a blackbody-like emissivity in the thermal wavelength range of 5-30μm; the other is a selective radiator, whose emissivity is close to 1 in 8-13μm and 0 in the rest of the band. Compared with broadband radiators, highly selective radiators can suppress the absorption of downward radiation from the atmosphere outside the transparent window, thereby achieving a lower steady-state temperature, which is suitable for refrigeration applications below ambient temperature. However, the development of selective radiative cooling nowadays faces many problems. For example, the use of micro-nano photonic structures, metasurfaces, metamaterials, etc. can achieve better spectral selectivity and cooling limits, but the materials and processing technologies are complex and expensive, and it is difficult to achieve large-scale preparation. Therefore, the construction of large-scale, low-cost selective radiative cooling bodies is a major challenge. Summary of the invention

[0006] In order to solve the above technical problems, an embodiment of the present invention provides a method for constructing a highly selective radiative cooling metasurface. The specific technical solution is as follows: In order to solve the above-mentioned technical problems, the present invention is achieved as follows: Provided is a method for constructing a highly selective radiation cooling super surface, comprising the following steps: uniformly mixing a polymer, a curing agent, and an organic solvent in proportion to obtain a mixed solution, wherein: the curing agent accounts for 5-20wt% of the polymer, and the organic solvent accounts for 0-50wt% of the mixed solution; preparing a metal film layer with a thickness of 50-200nm on a substrate; coating the mixed solution on the metal film layer and drying it to form a polymer film layer; sinking dielectric microspheres into the polymer film layer by a unidirectional friction method to form a single-layer dielectric microsphere array, thereby obtaining a highly selective radiation cooling super surface.

[0007] In one embodiment, the polymer is any one of PDMS prepolymer, water-based silicone resin, polyurethane (PU), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), silicone rubber and polyethylene oxide (PEO); the organic solvent includes one or more of toluene, chloroform and tetrahydrofuran.

[0008] In one embodiment, the polymer, curing agent and organic solvent are mixed evenly by magnetic stirring, mechanical stirring, homogenous stirring or ultrasonic stirring.

[0009] In one embodiment, the substrate is made of glass, ceramic, wood or metal; and the metal film layer is made of gold, silver or aluminum.

[0010] In one embodiment, the metal film layer is formed on the substrate by thermal evaporation, electroplating, chemical plating or vapor deposition.

[0011] In one embodiment, the mixed solution is coated on the metal film layer by spraying, pouring, roller coating or spin coating.

[0012] In one embodiment, the thickness of the mixed solution after being coated on the metal film layer is 5-30 μm.

[0013] In one embodiment, the dielectric microspheres include silicon dioxide (SiO 2 ) microspheres, polymethyl methacrylate (PMMA) microspheres, polystyrene (PS) microspheres, silicon nitride (Si 3 N 4 )Microspheres, alumina (Al 2 O 3 ) microspheres, zirconium oxide (ZrO 2 ) microspheres, silicon carbide (SiC) microspheres, barium titanate (BaTiO 3 ) microspheres, germanium (Ge) microspheres, yttrium oxide (Y 2 O 3 ) microspheres and boron nitride (BN) microspheres; the size of the dielectric microspheres is 2-20 μm.

[0014] In one embodiment, the depth of the dielectric microspheres embedded in the polymer film layer is between 0 and the diameter of the microspheres.

[0015] In one embodiment, the average solar reflectivity of the highly selective radiation cooling metasurface is ≥ 0.92, the atmospheric transparent window selective emissivity is ≥ 0.92, and the 8-13 μm infrared selectivity is ≥ 1.40. It can reduce the temperature by an average of 5-10°C during the day and by a maximum of 10-15°C at noon.

[0016] In an embodiment of the present invention, a mixed solution is obtained by mixing a polymer, a curing agent and an organic solvent, and a metal film layer is formed on a substrate at the same time. Then, the mixed solution is coated on the metal film layer and dried into a polymer film, and finally, dielectric microspheres are trapped on the polymer film layer, so as to form a three-layer structure of a highly selective radiation cooling metasurface. The phonon polarization resonance of the dielectric microspheres of the highly selective radiation cooling metasurface of the present invention and the inherent absorption characteristics of the polymer layer can enhance the selective emission of the atmospheric transparent window, and the metal film layer can highly reflect sunlight. The synergistic effect of the three-layer structure of the highly selective radiation cooling metasurface of the present invention can make its average solar reflectivity and atmospheric transparent window emissivity as high as 0.96, and the spectral selectivity of 8-13μm is as high as 1.50. Under direct sunlight at noon, a cooling effect of 12.8°C below the environment can be achieved. At the same time, the preparation process of the construction method of the highly selective radiation cooling metasurface of the present invention does not require complex and expensive processing equipment and harsh processing conditions, and can be mass-produced. In addition, the highly selective radiation cooling metasurface prepared by the construction method of the present invention can be easily integrated into various application scenarios, such as building roofs and exterior walls, water tanks, car bodies, etc., and has broad practical application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 A flowchart of the steps of the method for constructing a highly selective radiation cooling metasurface of the present invention; Figure 2 Schematic diagram of the structure of the highly selective radiation cooling super surface in Example 1 of the present invention and SiO 2 Electron micrograph of microsphere array; Figure 3 The reflection spectrum of the highly selective radiation cooling metasurface at a wavelength of 0.3-2.5 μm and the emission spectrum at a wavelength of 5-16 μm in Example 1 of the present invention; Figure 4 The SiO used in Example 1 of the present invention2 , refractive index (n) and extinction coefficient (k) of PDMS; Figure 5 This is the temperature curve of the highly selective radiative cooling metasurface in Example 1 of the present invention under direct sunlight at noon. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] See also Figure 1 , which is a flow chart of the steps of the construction method of the highly selective radiation cooling super surface of the present invention; as shown in the figure, the construction method of the highly selective radiation cooling super surface of the present embodiment includes the following steps S1 to S4. In step S1, the polymer, the curing agent, and the organic solvent are mixed evenly in proportion to obtain a mixed solution. Wherein: the proportion of the curing agent to the polymer is 5-20wt%, and the proportion of the organic solvent to the mixed solution is 0-50wt%. In this embodiment, the polymer, the curing agent and the organic solvent are mixed evenly by magnetic stirring, mechanical stirring, homogeneous stirring or ultrasonic stirring. The polymer is any one of PDMS prepolymer, water-based silicone resin, polyurethane (PU), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), silicone rubber (SiliconeRubber) and polyethylene oxide (PEO). The organic solvent includes one or more of toluene, chloroform and tetrahydrofuran.

[0022] Then, in step S2, a metal film layer with a thickness of 50-200nm is formed on the substrate. In this embodiment, the metal film layer is formed on the substrate by thermal evaporation, electroplating, chemical plating or vapor deposition. The coating equipment used is any one of a physical vapor coating apparatus, a chemical vapor coating apparatus, a magnetron sputtering coating apparatus, an ion coating apparatus, etc. The material of the substrate is glass, ceramic, wood or metal. The material of the metal film layer is gold, silver or aluminum. Then, in step S3, the mixed solution is applied to the metal film layer and dried to form a polymer film layer. The mixed solution is applied to the metal film layer by spraying, pouring, roller coating or spin coating, and the thickness of the film formed after the mixed solution is applied to the metal film layer is 5-30μm. The drying method can be selected to dry in an indoor environment or in an oven. The coating equipment used is any one of a spray coater, an automatic coating apparatus, a roller coater or a spin coater.

[0023] Finally, in step S4, the dielectric microspheres are sunk into the polymer film layer by a unidirectional friction method to form a single-layer dielectric microsphere array, thereby obtaining a highly selective radiation cooling metasurface. In this embodiment, the depth of the dielectric microspheres sunk into the polymer film layer is between 0 and the diameter of the microspheres. The size of the dielectric microspheres is 2-20 μm. The dielectric microspheres include silicon dioxide (SiO 2 ) microspheres, polymethyl methacrylate (PMMA) microspheres, polystyrene (PS) microspheres, silicon nitride (Si 3 N 4 )Microspheres, alumina (Al 2 O 3 ) microspheres, zirconium oxide (ZrO 2 ) microspheres, silicon carbide (SiC) microspheres, barium titanate (BaTiO 3 ) microspheres, germanium (Ge) microspheres, yttrium oxide (Y 2 O 3 ) microspheres and boron nitride (BN) microspheres.

[0024] The highly selective radiation cooling metasurface obtained in the above step S4 is a three-layer structure. The phonon polarization resonance of the dielectric microspheres of the highly selective radiation cooling metasurface of this embodiment and the inherent absorption characteristics of the polymer layer can enhance the selective emission of the atmospheric transparent window, and the metal film layer can highly reflect sunlight. The synergistic effect of the three-layer structure can make the average solar reflectivity of the highly selective radiation cooling metasurface ≥ 0.92, the selective emissivity of the atmospheric transparent window ≥ 0.92, and the 8-13μm infrared selectivity ≥ 1.40. The average temperature can be reduced by 5-10°C during the day, and the maximum temperature can be reduced by 10-15°C at noon. Under direct sunlight at noon, a cooling effect of 12.8°C below the environment can be achieved. The highly selective radiation cooling metasurface prepared in this embodiment has good hydrophobicity (water contact angle of 149°), excellent flexibility, processing performance and wide integration. At the same time, the preparation process of the construction method of the highly selective radiation cooling metasurface of this embodiment does not require complex and expensive processing equipment and harsh processing conditions, and can be mass-produced. In addition, the highly selective radiative cooling metasurface prepared by the construction method of this embodiment can be easily integrated into various application scenarios, such as building roofs and exterior walls, water tanks, car bodies, etc., and has broad practical application prospects.

[0025] The beneficial effects of the method for constructing a highly selective radiative cooling metasurface of the present invention will be described below with specific examples.

[0026] Example 1 1. Weigh 5 g of polydimethylsiloxane prepolymer (PDMS) and 0.5 g of curing agent (SYLGARD184) in 2.5 mL of chloroform (CHCI 3) solvent, stirred at room temperature for 5 min, and PDMS / CHCI was obtained. 3 Mixing solutions; 2. Use a physical vapor coating apparatus to thermally evaporate a 100nm thick silver film on the glass substrate; 3. Spin the mixed solution on the glass substrate covered with the silver film at a speed of 6000 r / s for 300 s using a spin coater. After the solution is naturally leveled, put it into an air blower at 80°C for drying. Take it out after 12 hours to obtain a PDMS / Ag coating. 4. Then use the unidirectional friction method to make SiO with a particle size of 10μm 2 The microspheres are evenly rubbed on the PDMS film to make 3 / 4 of the SiO 2 The microspheres are embedded in the PDMS film and arranged in a hexagonal array to obtain SiO-based 2 / PDMS / Ag highly selective radiative cooling supersurface film.

[0027] See also Figure 2 As shown, it is a schematic diagram of the structure of the highly selective radiation cooling super surface in Example 1 of the present invention and SiO 2 Electron micrograph of the microsphere array; As shown in the figure, the single-layer SiO 2 The hexagonal arrays are closely arranged and evenly micro-sunk into the PDMS layer.

[0028] See also Figure 3 As shown, it is the reflection spectrum of the highly selective radiation cooling metasurface at a wavelength of 0.3-2.5 μm and the emission spectrum at a wavelength of 5-16 μm in Example 1 of the present invention; as shown in the figure, due to SiO 2 / PDMS's Si-O-Si and Si-C molecular structures and their various vibration modes, the selective wide-angle radiation cooling thin film coating has multiple strong absorption peaks at the atmospheric transparent window, and their intrinsic absorption peaks are mainly located at around 9.16μm and 12.5μm in the atmospheric window, which ensures that it can release a large amount of infrared light in the atmospheric transparent window and keep its own heat at the lowest level.

[0029] See also Figure 4 As shown, it is SiO used in Example 1 of the present invention. 2 , the refractive index (n) and extinction coefficient (k) of PDMS; as shown in the figure, the average solar reflectivity of the highly selective radiation cooling metasurface prepared above is as high as 0.96, indicating that it hardly absorbs sunlight, and the 8-13μm selective emissivity is also as high as 0.96, indicating that a large amount of infrared light can be emitted through the atmospheric transparent window, and the infrared selectivity of this window is 1.5 (with 5-16μm band as a reference), which makes the actual cooling performance better.

[0030] See also Figure 5 As shown, it is a temperature curve of the highly selective radiation cooling metasurface in Example 1 of the present invention under direct sunlight at noon; as shown in the figure, the highly selective radiation cooling metasurface prepared above is under direct sunlight at noon, and the temperature of the highly selective radiation cooling metasurface itself is always lower than the ambient temperature, with an average temperature drop of about 9.7°C.

[0031] Embodiment 2: The difference between this embodiment and the above-mentioned embodiment 1 is that CHCI in embodiment 1 is replaced by 3 Replace with toluene (C 7 H 8 ), SiO 2 The particle size of the microspheres was changed to 5 μm, and the metallic silver was replaced by metallic aluminum.

[0032] 1. Weigh 5 g PDMS and 0.5 g SYLGARD 184 in 3 g C 7 H 8 The PDMS / C 7 H 8 dispersion; 2. Use a physical vapor coating apparatus to thermally evaporate a 100nm thick aluminum film on the glass substrate; 3. Spin the above dispersion onto a glass substrate covered with an aluminum film. After the solution is naturally leveled, place it in an air blower at 80°C for drying. Take it out after 12 hours to obtain a PDMS / Ag coating. Then, use the unidirectional friction method to coat the SiO 2 The microspheres are evenly rubbed on the PDMS film to make 1 / 2 of the SiO 2 The microspheres are embedded in the PDMS film and arranged in a hexagonal array to obtain SiO 2 / PDMS / Al highly selective radiative cooling supersurface film.

[0033] In summary, the present invention provides a method for constructing a highly selective radiation cooling metasurface, wherein a mixed solution is obtained by mixing a polymer, a curing agent and an organic solvent, and a metal film layer is formed on a substrate at the same time, and then the mixed solution is coated on the metal film layer and dried into a polymer film, and finally a dielectric microsphere is trapped on the polymer film layer, so as to form a three-layer structure of a highly selective radiation cooling metasurface. The phonon polarization resonance of the dielectric microspheres of the highly selective radiation cooling metasurface of the present invention and the inherent absorption characteristics of the polymer layer can enhance the selective emission of the atmospheric transparent window, and the metal film layer can highly reflect sunlight. The synergistic effect of the three-layer structure of the highly selective radiation cooling metasurface of the present invention can make its average solar reflectivity and atmospheric transparent window emissivity as high as 0.96, and the spectral selectivity of 8-13μm is as high as 1.50. Under direct sunlight at noon, a cooling effect of 12.8°C below the environment can be achieved. At the same time, the preparation process of the method for constructing the highly selective radiation cooling metasurface of the present invention does not require complex and expensive processing equipment and harsh processing conditions, and can be mass-produced. In addition, the highly selective radiation cooling metasurface prepared by the construction method of the present invention can be easily integrated into various application scenarios, such as building roofs and exterior walls, water tanks, car bodies, etc., and has broad practical application prospects.

[0034] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0035] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A method for constructing a highly selective radiative cooling metasurface, characterized in that: The following steps are involved: The polymer, the curing agent and the organic solvent are mixed uniformly in proportion to obtain a mixed solution, wherein: the curing agent accounts for 5-20wt% of the polymer, and the organic solvent accounts for 0-50wt% of the mixed solution; Preparing a metal film layer with a thickness of 50-200 nm on a substrate; coating the mixed solution on the metal film layer, and drying to form a polymer film layer; The dielectric microspheres are sunk into the polymer film layer by a one-way friction method to form a single-layer dielectric microsphere array, thereby obtaining the highly selective radiation cooling super surface.

2. The method for constructing a highly selective radiative cooling metasurface according to claim 1, characterized in that: The polymer is any one of PDMS prepolymer, water-based silicone resin, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber and polyethylene oxide; the organic solvent includes one or more of toluene, chloroform and tetrahydrofuran.

3. The method for constructing a highly selective radiative cooling metasurface according to claim 1, characterized in that: The polymer, the curing agent and the organic solvent are mixed uniformly by means of magnetic stirring, mechanical stirring, homogeneous stirring or ultrasonic stirring.

4. The method for constructing a highly selective radiative cooling metasurface according to claim 1, characterized in that: The material of the substrate is glass, ceramic, wood or metal; the material of the metal film layer is gold, silver or aluminum.

5. The method for constructing a highly selective radiative cooling metasurface according to claim 1, characterized in that: The metal film layer is formed on the substrate by thermal evaporation, electroplating, chemical plating or vapor deposition.

6. The method for constructing a highly selective radiative cooling metasurface according to claim 1, characterized in that: The mixed solution is coated on the metal film layer by spraying, pouring, roller coating or spin coating.

7. The method for constructing a highly selective radiative cooling metasurface according to claim 1, characterized in that: The thickness of the film formed after the mixed solution is coated on the metal film layer is 5-30 μm.

8. The method for constructing a highly selective radiative cooling metasurface according to claim 1, characterized in that: The dielectric microspheres include any one of silica microspheres, polymethyl methacrylate microspheres, polystyrene microspheres, silicon nitride microspheres, alumina microspheres, zirconium oxide microspheres, silicon carbide microspheres, barium titanate microspheres, germanium microspheres, yttrium oxide microspheres and boron nitride (BN) microspheres; and the size of the dielectric microspheres is 2-20 μm.

9. The method for constructing a highly selective radiative cooling metasurface according to claim 1, characterized in that: The depth of the dielectric microspheres embedded in the polymer film layer is between 0 and the diameter of the microspheres.

10. The method for constructing a highly selective radiative cooling metasurface according to claim 1, characterized in that: The highly selective radiation cooling metasurface has an average solar reflectivity of ≥0.92, an atmospheric transparent window selective emissivity of ≥0.92, and an 8-13 μm infrared selectivity of ≥1.

40. It can reduce the temperature by an average of 5-10°C during the day and by a maximum of 10-15°C at noon.

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