Porous radiation refrigeration flexible film and preparation method and application thereof

Abstract

The invention provides a porous radiation refrigeration flexible film as well as a preparation method and application thereof, the preparation method comprises the following steps: (1) mixing a NaCl saturated aqueous solution with ethanol, then carrying out ultrasonic treatment on the mixed solution, then centrifugally collecting NaCl to separate out crystals, and drying to obtain superfine NaCl particles; and (2) mixing a PDMS precursor with a curing agent to obtain a PDMS mixed solution, mixing the PDMS mixed solution with the superfine NaCl particles, pouring the mixture into a mold, curing, immersing in a water bath to remove NaCl, and drying to obtain the porous radiation refrigeration flexible film. NaCl particles with small particle size and narrower particle size distribution are prepared by adopting an ultrasonic precipitation method; the porous PDMS film prepared by taking the NaCl particles as a sacrificial template has a better radiation refrigeration effect.

Description

Technical Field

[0001] The invention belongs to the technical field of radiation cooling, and relates to a porous radiation cooling flexible film and a preparation method and application thereof. Background Art

[0002] The use of traditional air conditioning and refrigeration systems has exacerbated the greenhouse effect. In view of the principles of sustainable development, it is crucial to explore alternatives to passive cooling. Radiative cooling technology, which uses the low temperature of outer space to radiate heat, has been increasingly recognized in recent years as a passive cooling solution that can solve urgent problems, and has made significant progress in both theoretical research and practical applications. This cooling technology requires the use of materials and structures with specific optical properties, including high solar reflectivity (0.3-2.5μm) and highly selective infrared (IR) emissivity (8-13μm). Studies have shown that a variety of materials and structures exhibit effective radiative cooling performance, including multilayer photonic structures, hybrid optical metamaterials, hierarchical fiber materials, and porous polymer structures.

[0003] In recent years, there has been increasing interest in the development of materials for large-scale radiative cooling. As a result, research progress has shifted from complex multilayer photonic structures and hybrid optical metamaterials to porous materials that can be prepared in batches. The effectiveness of porous materials in radiative cooling relies on high solar reflectance achieved through Mie scattering, which is affected by the refractive index transition across the polymer-air boundary. This scattering mechanism becomes more pronounced when the pore size of the porous material approaches the target wavelength. Various techniques have been used to fabricate porous polymer materials, including phase inversion, electrospinning, and dielectric embedding-extraction. However, these preparation methods usually require the use of solvents or particles that may pose risks to human health or the environment. To avoid these risks, a recent technique has proposed the use of environmentally friendly water-soluble sodium chloride particles as sacrificial templates to prepare porous materials, and its effectiveness has also been demonstrated. However, it remains a challenge to obtain sodium chloride with smaller, more controllable particle size and narrower particle size distribution to improve the optical properties of the resulting porous structures.

[0004] Therefore, in the art, it is desired to develop a method for preparing sodium chloride with smaller, more controllable particle size and narrower particle size distribution, and use the obtained sodium chloride to prepare a porous radiative cooling flexible film to improve the radiative cooling effect of the film. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a porous radiative cooling flexible film and a preparation method and application thereof. The present invention provides a method for manufacturing a porous PDMS (polydimethylsiloxane) film for radiative cooling using small-sized NaCl particles with a narrower particle size distribution as a sacrificial template. Different from the prior art, the NaCl particles in the present invention are prepared by ultrasonic precipitation, and this method can obtain sodium chloride particles with a small particle size and a narrower particle size distribution.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a porous radiative cooling flexible film, the preparation method comprising:

[0008] (1) mixing a saturated aqueous solution of NaCl with ethanol, then subjecting the obtained mixed solution to ultrasonic treatment, and then collecting the precipitated NaCl crystals by centrifugation and drying them to obtain ultrafine NaCl particles;

[0009] (2) mixing a PDMS precursor and a curing agent to obtain a PDMS mixed solution, mixing the PDMS mixed solution with the ultrafine NaCl particles obtained in step (1), pouring the obtained mixture into a mold, curing it, immersing it in a water bath to remove NaCl, and drying it to obtain the porous radiative cooling flexible film.

[0010] The present invention adopts an ultrasonic precipitation method to prepare NaCl particles with a small particle size and a narrower particle size distribution, and the method is simple, green and environmentally friendly; compared with NaCl particles obtained by static precipitation or static precipitation followed by crushing, the NaCl particles obtained by the method provided by the present invention have a more controllable particle size and a narrower particle size distribution, and the NaCl particles used in a porous PDMS film can also bring about a better radiation cooling effect.

[0011] The ultrafine NaCl particles provided by the present invention are used as sacrificial templates to prepare a small-aperture porous PDMS film, the aperture of which is close to the wavelength of sunlight, so that sunlight can be effectively reflected, thereby reducing the heat absorption of the solar spectrum. In addition, the inherent molecular vibrations of the PDMS polymer (such as Si-C, Si-O-Si and CH) provide a high mid-infrared emissivity, thereby enabling radiative heat dissipation through the atmospheric window, and the synergistic effect of the two spectra can achieve effective daytime radiative cooling.

[0012] The preparation method of the porous radiative cooling flexible film provided by the present invention is simple, scalable and sustainable, the raw materials are easy to obtain, the production cost is low, mass production is possible, and the whole process is green, environmentally friendly and pollution-free.

[0013] Preferably, in step (1), based on 5 mL of saturated aqueous solution of NaCl, the amount of ethanol used is 70-90 mL, for example 70 mL, 75 mL, 80 mL, 85 mL, 90 mL, etc.

[0014] Preferably, the step (1) of mixing the saturated aqueous solution of NaCl with ethanol specifically comprises: gradually adding the saturated aqueous solution of NaCl into ethanol.

[0015] Preferably, the ultrasonic treatment in step (1) is continuous ultrasonic treatment.

[0016] Preferably, the time of the continuous ultrasonic treatment is 150-210 s, for example 150 s, 160 s, 170 s, 180 s, 190 s, 200 s, 210 s, etc.

[0017] Preferably, the drying in step (1) is carried out in an oven or a baking box.

[0018] Preferably, the drying temperature in step (1) is 70-90°C, for example, 70°C, 73°C, 75°C, 78°C, 80°C, 83°C, 85°C, 88°C, 90°C, etc., and the drying time is 18-30h, for example, 18h, 20h, 22h, 24h, 26h, 28h, 30h, etc.

[0019] Preferably, the particle size distribution of the ultrafine NaCl particles in step (1) is concentrated around 6-8 μm, for example, 6 μm, 6.2 μm, 6.4 μm, 6.6 μm, 6.8 μm, 7 μm, 7.2 μm, 7.4 μm, 7.6 μm, 7.8 μm, 8 μm, etc.

[0020] Preferably, the mass ratio of the PDMS precursor and the curing agent in step (2) is (8-12):1, for example 8:1, 8.5:1, 9:1, 9.5:1, 10:1, 10.5:1, 11:1, 11.5:1, 12:1, etc.

[0021] Preferably, the mass ratio of the PDMS mixed solution to the ultrafine NaCl particles in step (2) is (0.8-1.2):1, for example, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, etc.

[0022] Preferably, the mold in step (2) comprises a flat rectangular PTFE mold.

[0023] Preferably, the curing temperature in step (2) is 70-90°C, for example 70°C, 75°C, 80°C, 85°C, 90°C, etc., and the curing time is 2-4h, for example 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0024] Preferably, the temperature of the water bath in step (2) is 70-80°C, for example, 70°C, 73°C, 75°C, 78°C, 80°C, etc.

[0025] Preferably, the immersion time in step (2) is 10-14 hours, for example, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, etc.

[0026] Preferably, the drying in step (2) is carried out in a hot oven.

[0027] Preferably, the drying temperature in step (2) is 70-90°C, for example, 70°C, 73°C, 75°C, 78°C, 80°C, 83°C, 85°C, 88°C, 90°C, etc., and the drying time is 2-4h, for example, 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0028] Preferably, the porous radiative cooling flexible film has a thickness of 500-1000 μm, for example, 500 μm, 550 μm, 600 μm, 650 μm, 700 μm, 750 μm, 800 μm, 850 μm, 900 μm, 950 μm, 1000 μm, etc.

[0029] As a preferred technical solution of the present invention, the preparation method comprises:

[0030] (1) 5 mL of a saturated aqueous solution of NaCl is gradually added to 70-90 mL of ethanol, and then the resulting mixture is subjected to continuous ultrasonic treatment for 150-210 seconds, and then the precipitated NaCl crystals are collected by centrifugation, and dried at 70-90° C. for 18-30 hours to obtain ultrafine NaCl particles with a particle size distribution concentrated at 6-8 μm;

[0031] (2) mixing a PDMS precursor and a curing agent to obtain a PDMS mixed solution, mixing the PDMS mixed solution with the ultrafine NaCl particles obtained in step (1), pouring the obtained mixture into a flat rectangular PTFE mold, then curing the mixture at 70-90° C. for 2-4 hours, taking it out of the mold, and immersing it in a water bath at 70-80° C. for 10-14 hours to remove NaCl, and finally drying it at 70-90° C. for 2-4 hours to eliminate residual moisture, thereby obtaining the porous radiative cooling flexible film.

[0032] In a second aspect, the present invention provides a porous radiative cooling flexible film, wherein the porous radiative cooling flexible film is prepared by the preparation method described in the first aspect.

[0033] In a third aspect, the present invention provides an application of the porous radiative cooling flexible film as described in the second aspect in radiative cooling.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The present invention adopts an ultrasonic precipitation method to prepare NaCl particles with a small particle size and a narrower particle size distribution. The method is simple and environmentally friendly. Compared with NaCl particles obtained by static precipitation or static precipitation followed by crushing, the particle size of the NaCl particles obtained by the method provided by the present invention is more controllable and the particle size distribution is narrower. When used for porous PDMS films, it can also bring about better radiation cooling effects.

[0036] (2) The ultrafine NaCl particles provided by the present invention are used as sacrificial templates to prepare a small-pore porous PDMS film, the pore size of which is close to the wavelength of sunlight, so that sunlight can be effectively reflected, thereby reducing the heat absorption of the solar spectrum. In addition, the inherent molecular vibrations of the PDMS polymer (such as Si-C, Si-O-Si and CH) provide a high mid-infrared emissivity, thereby enabling radiative heat dissipation through the atmospheric window, and the synergistic effect of the two spectra can achieve effective daytime radiative cooling. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is an appearance diagram of the porous radiative cooling flexible film provided in Example 1.

[0038] Figure 2 This is the SEM image of the porous radiative cooling flexible film provided in Example 1.

[0039] Figure 3 This is a SEM image of the ultrafine NaCl particles provided in Example 1.

[0040] Figure 4 This is a graph showing the solar reflectivity test results of the radiative cooling flexible films provided in Example 1 and Comparative Examples 1-6.

[0041] Figure 5 The infrared emissivity test results of the radiative cooling flexible film provided for Example 1 and Comparative Examples 1, 4, 5 and 6 are shown in the figure.

[0042] Figure 6 This is a diagram of the radiative cooling test results of the radiative cooling flexible film provided in Example 1, Comparative Example 3, and a blank control. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0044] Unless otherwise specified, some of the raw material information used in the examples and comparative examples of the present invention is as follows:

[0045] PDMS precursor: Sylgard 184, Dow Corning;

[0046] Curing agent: Sylgard 184, Dow Corning.

[0047] Example 1

[0048] In this embodiment, a method for preparing a porous radiative cooling flexible film is provided, and the preparation method comprises:

[0049] (1) 5 mL of a saturated aqueous solution of NaCl was gradually added to 80 mL of ethanol, and then the resulting mixture was subjected to continuous ultrasonic treatment for 180 seconds. After sufficient precipitation, the white NaCl precipitated crystals were collected by centrifugation, and then dried in an oven at 80° C. for 24 hours to obtain ultrafine NaCl particles with a particle size distribution of about 6-8 μm;

[0050] (2) The PDMS precursor and the curing agent are mixed at a mass ratio of 10:1 to obtain a PDMS mixed solution, and the PDMS mixed solution is mixed with the ultrafine NaCl particles obtained in step (1) at a mass ratio of 1:1 to ensure that the NaCl particles are properly dispersed in the viscous PDMS mixed solution. After sufficient mixing, the obtained mixture is poured into a flat rectangular PTFE mold to control the shape and size of the porous PDMS film, and then the mixture is cured at 80°C for 3 hours, taken out of the mold, and immersed in a water bath at 75°C for 12 hours to remove NaCl, and finally dried in a hot oven at 80°C for 3 hours to eliminate residual moisture, thereby obtaining the porous radiative cooling flexible film with a thickness of 1 mm.

[0051] The porous radiative cooling flexible film provided in this embodiment has excellent flexibility and presents a white appearance (eg Figure 1 ), indicating that it has high reflectivity in the visible light spectrum. Its SEM image is shown in Figure 2 As shown, it can be seen that the radiative cooling flexible film has a porous structure, that is, as expected, NaCl does produce a porous structure in the PDMS film, and the micropores in the sample are consistent with the size of the NaCl template.

[0052] The SEM image of the ultrafine NaCl particles provided in this embodiment is as follows: Figure 3 As shown, it can be seen that the size range of NaCl particles is concentrated around 6-8 μm, and the formation of smaller NaCl crystals is attributed to the effect of ultrasound on the nucleation rate.

[0053] Example 2

[0054] In this embodiment, a method for preparing a porous radiative cooling flexible film is provided, and the preparation method comprises:

[0055] (1) 5 mL of NaCl saturated aqueous solution was gradually added to 70 mL of ethanol, and then the resulting mixture was subjected to continuous ultrasonic treatment for 150 seconds. After sufficient precipitation, the white NaCl precipitated crystals were collected by centrifugation, and then dried in an oven at 70° C. for 18 hours to obtain ultrafine NaCl particles with a particle size distribution of about 6-8 μm;

[0056] (2) The PDMS precursor and the curing agent are mixed at a mass ratio of 10:1 to obtain a PDMS mixed solution, and the PDMS mixed solution is mixed with the ultrafine NaCl particles obtained in step (1) at a mass ratio of 1:1 to ensure that the NaCl particles are properly dispersed in the viscous PDMS mixed solution. After sufficient mixing, the obtained mixture is poured into a flat rectangular PTFE mold to control the shape and size of the porous PDMS film, and then the mixture is cured at 70°C for 2h, taken out of the mold, and immersed in a 70°C water bath for 10h to remove NaCl, and finally dried in a hot oven at 70°C for 2h to eliminate residual moisture, thereby obtaining the porous radiative cooling flexible film with a thickness of 1mm.

[0057] Example 3

[0058] In this embodiment, a method for preparing a porous radiative cooling flexible film is provided, and the preparation method comprises:

[0059] (1) 5 mL of NaCl saturated aqueous solution was gradually added to 90 mL of ethanol, and then the resulting mixture was subjected to continuous ultrasonic treatment for 210 seconds. After sufficient precipitation, the white NaCl precipitated crystals were collected by centrifugation, and then dried in an oven at 90° C. for 30 hours to obtain ultrafine NaCl particles with a particle size distribution of about 6-8 μm;

[0060] (2) The PDMS precursor and the curing agent are mixed at a mass ratio of 10:1 to obtain a PDMS mixed solution, and the PDMS mixed solution is mixed with the ultrafine NaCl particles obtained in step (1) at a mass ratio of 1:1 to ensure that the NaCl particles are properly dispersed in the viscous PDMS mixed solution. After sufficient mixing, the obtained mixture is poured into a flat rectangular PTFE mold to control the shape and size of the porous PDMS film, and then the mixture is cured at 90°C for 4 hours, taken out of the mold, and immersed in a water bath at 80°C for 14 hours to remove NaCl, and finally dried in a hot oven at 90°C for 4 hours to eliminate residual moisture, thereby obtaining the porous radiative cooling flexible film with a thickness of 1 mm.

[0061] Comparative Example 1

[0062] The only difference between this comparative example and Example 1 is that the preparation method of NaCl particles in step (1) is different, as follows:

[0063] 5 mL of NaCl saturated aqueous solution was gradually added to 80 mL of ethanol, and after standing for precipitation, the white NaCl precipitated crystals were collected by centrifugation, and then dried in an oven at 80°C for 24 h to obtain ultrafine NaCl particles with a particle size distribution concentrated around 40-50 μm.

[0064] Comparative Example 2

[0065] The only difference between this comparative example and Example 1 is that the preparation method does not include step (1), and the ultrafine NaCl particles in Example 1 are directly replaced by purchased McLean GR sodium chloride particles (with a particle size concentrated in the range of 100-300 μm).

[0066] Comparative Example 3

[0067] The only difference between this comparative example and Example 1 is that the preparation method does not include step (1), and purchased edible salt particles (with a particle size greater than 500 μm) are directly used to replace the ultrafine NaCl particles in Example 1.

[0068] Comparative Example 4

[0069] The only difference between this comparative example and Example 1 is that the preparation method does not include step (1), and purchased McLean GR sodium chloride particles (with a particle size concentrated in the range of 100-300 μm) are directly used to replace the ultrafine NaCl particles in Example 1, and the mass ratio of sodium chloride particles to PDMS mixed solution is 5:1.

[0070] Comparative Example 5

[0071] The only difference between this comparative example and Example 1 is that the preparation method does not include step (1), and purchased edible salt particles (with a particle size greater than 500 μm) are directly used to replace the ultrafine NaCl particles in Example 1, and the mass ratio of the edible salt particles to the PDMS mixed solution is 5:1.

[0072] Comparative Example 6

[0073] The only difference between this comparative example and Example 1 is that no ultrafine NaCl particles are added in the preparation step, that is, a pure PDMS film is obtained.

[0074] The solar reflectivity test results of the radiative cooling flexible films provided in Example 1 and Comparative Examples 1-6 of the present invention are shown in the figure below: Figure 4 As shown, the infrared emissivity test results of the radiative cooling flexible film provided in Example 1 and Comparative Example 1, Comparative Example 4, Comparative Example 5, and Comparative Example 6 are shown in FIG. Figure 5As shown, it can be seen that the ultrafine porous PDMS film provided in Example 1 can reach a high emissivity of 0.95 in the atmospheric window (8-13 μm) and a reflectivity of 0.85 in the solar spectrum (300-2500 nm). In particular, it has a reflectivity of 0.95 in the visible light range (400-780 nm), which corresponds to the wavelength range with the most solar radiation. And it can be seen that all porous PDMS show higher solar reflectivity and infrared emissivity than pure PDMS, highlighting the role of porous structure in enhancing the optical properties of radiation cooling. In particular, the porous PDMS film prepared with a smaller particle size shows a higher solar reflectivity. This is because as the NaCl particle size decreases, the pore size also decreases and approaches the wavelength of the solar spectrum, thereby improving the solar scattering efficiency. It is worth noting that the solar reflectivity of the ultrafine porous PDMS film even exceeds the solar reflectivity of the film provided by Comparative Examples 4 and 5, and their NaCl to PDMS ratio increases to 5:1. This observation suggests that only a small concentration of ultrafine NaCl particles is required to achieve better optical properties for radiative cooling.

[0075] Under hot sunny weather conditions, the radiative cooling performance of the porous radiative cooling flexible films provided in Example 1 and Comparative Example 3 was evaluated as follows: a wooden building model was placed on the roof, and a thermocouple was placed inside the model. A 5 cm × 5 cm × 1 mm film sample was attached to the top of the building model. For comparison, the temperature of the model covered by the bare model was also recorded, and the results are shown in Figure 1. Figure 6 As shown, it can be seen that during the period of 12:00-13:30, the average temperature of the model covered with the porous radiative cooling flexible film provided in Example 1 is 7°C lower than that of the bare model, and is 3°C lower than that of the model covered with the porous radiative cooling flexible film provided in Comparative Example 3, which indicates that the porous PDMS film prepared by using the ultrafine NaCl particles prepared by ultrasonic precipitation as a template has excellent cooling performance.

[0076] After testing, it was found that the porous radiative cooling flexible film provided in Example 1-2 had similar test results to the porous radiative cooling flexible film provided in Example 1.

[0077] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate the porous radiative cooling flexible film and its preparation method and application, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a porous radiative cooling flexible film, characterized in that: The preparation method comprises: (1) mixing a saturated aqueous solution of NaCl with ethanol, then subjecting the obtained mixed solution to ultrasonic treatment, and then collecting the precipitated NaCl crystals by centrifugation and drying them to obtain ultrafine NaCl particles; (2) mixing a PDMS precursor and a curing agent to obtain a PDMS mixed solution, mixing the PDMS mixed solution with the ultrafine NaCl particles obtained in step (1), pouring the obtained mixture into a mold, curing it, immersing it in a water bath to remove NaCl, and drying it to obtain the porous radiative cooling flexible film.

2. The preparation method according to claim 1, characterized in that: In step (1), based on 5 mL of saturated aqueous solution of NaCl, the amount of ethanol used is 70-90 mL; Preferably, the step (1) of mixing the saturated aqueous solution of NaCl with ethanol specifically comprises: gradually adding the saturated aqueous solution of NaCl into ethanol.

3. The preparation method according to claim 1 or 2, characterized in that: The ultrasonic treatment in step (1) is continuous ultrasonic treatment; Preferably, the time of the continuous ultrasonic treatment is 150-210 s.

4. The preparation method according to any one of claims 1 to 3, characterized in that The drying in step (1) is carried out in an oven or a baking box; Preferably, the drying temperature in step (1) is 70-90° C. and the drying time is 18-30 h; Preferably, the particle size distribution of the ultrafine NaCl particles in step (1) is concentrated in the range of 6-8 μm.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The mass ratio of the PDMS precursor and the curing agent in step (2) is (8-12):1; Preferably, the mass ratio of the PDMS mixed solution to the ultrafine NaCl particles in step (2) is (0.8-1.2):1; Preferably, the mold in step (2) comprises a flat rectangular PTFE mold; Preferably, the curing temperature in step (2) is 70-90° C. and the curing time is 2-4 hours.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The temperature of the water bath in step (2) is 70-80° C. Preferably, the immersion time in step (2) is 10-14 hours; Preferably, the drying in step (2) is carried out in a hot oven; Preferably, the drying temperature in step (2) is 70-90° C. and the drying time is 2-4 h.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The thickness of the porous radiation cooling flexible film is 500-1000 μm.

8. A preparation method according to any one of claims 1 to 7, characterized in that: The preparation method comprises: (1) 5 mL of a saturated aqueous solution of NaCl is gradually added to 70-90 mL of ethanol, and then the resulting mixture is subjected to continuous ultrasonic treatment for 150-210 seconds, and then the precipitated NaCl crystals are collected by centrifugation, and dried at 70-90° C. for 18-30 hours to obtain ultrafine NaCl particles with a particle size distribution concentrated at 6-8 μm; (2) mixing a PDMS precursor and a curing agent to obtain a PDMS mixed solution, mixing the PDMS mixed solution with the ultrafine NaCl particles obtained in step (1), pouring the obtained mixture into a flat rectangular PTFE mold, then curing the mixture at 70-90° C. for 2-4 hours, taking it out of the mold, and immersing it in a water bath at 70-80° C. for 10-14 hours to remove NaCl, and finally drying it at 70-90° C. for 2-4 hours to eliminate residual moisture, thereby obtaining the porous radiative cooling flexible film.

9. A porous radiative cooling flexible film, characterized in that: The porous radiation cooling flexible film is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the porous radiative cooling flexible film according to claim 9 in radiative cooling.

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