Preparation and application of porous polymethyl methacrylate composite film

Abstract

This invention relates to the field of materials technology, specifically disclosing the preparation and application of a porous polymethyl methacrylate (PMMA) composite film. The preparation method includes the following steps: using PMMA as a raw material, adding dimethylformamide and mixing evenly; then adding perfluoropolyether and hollow silica, mixing evenly to obtain a coating solution; coating the coating solution onto a substrate, and drying to obtain the porous PMMA composite film. This preparation method is simple, the resulting film has high whiteness, good radiative cooling effect, and good thermal insulation effect. It exhibits excellent radiative cooling in summer and heat preservation under conditions of internal heat sources in winter, making it suitable for widespread application.

Description

Technical Field

[0001] This invention belongs to the field of materials technology and relates to the problems of heat preservation and radiation cooling, specifically to the preparation and application of a porous polymethyl methacrylate composite film. Background Technology

[0002] Radiative cooling is a technology that cools objects based on the principle of thermal radiation. As a novel green cooling technology, its core mechanism is to reduce the temperature of an object by radiating energy from its surface into outer space. The material needs to possess both high reflectivity to sunlight (especially in the 0.3-2.5μm wavelength range) and high infrared emissivity to atmospheric windows (8-13μm wavelength range) to radiate sunlight and heat as much as possible, thereby achieving cooling. This green and energy-free technology is considered one of the most promising solutions to alleviate the global cooling energy crisis.

[0003] CN120648141A discloses a SiO2 / TiO2 / PMMA radiation cooling thin film and its preparation method. The film is made of N,N-dimethylformamide, polymethyl methacrylate, silicon dioxide, and titanium dioxide. It exhibits high reflectivity in the ultraviolet-visible-near-infrared band and high emissivity in the infrared band, achieving sub-environmental cooling at 8.4℃. However, this thin film has a single function, possessing only radiation cooling performance and lacking effective heat transfer blocking capabilities, making it difficult to meet the practical application needs of different seasons (such as summer cooling and winter insulation). Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for preparing and applying a porous polymethyl methacrylate composite film. The preparation method is simple, the prepared film has high whiteness, good radiation cooling effect, and good heat insulation effect, and it has diverse application scenarios.

[0005] The technical solution of the present invention is a method for preparing a porous polymethyl methacrylate composite film, comprising the following steps: S1. Using polymethyl methacrylate as raw material, add dimethylformamide and mix evenly; S2. Add perfluoropolyether and hollow silica to the liquid obtained in S1, and mix evenly to obtain the coating solution. S3. Apply the coating solution onto the substrate by scraping, and after drying, a porous polymethyl methacrylate composite film is obtained.

[0006] Furthermore, the mass ratio of polymethyl methacrylate to dimethylformamide is 1:4; the mixing temperature is 60℃; and the mixing time is 1h.

[0007] Furthermore, the mass ratio of polymethyl methacrylate to perfluoropolyether and hollow silica in S2 is 1:0.2-1:0.2-0.5.

[0008] Furthermore, the mass ratio of polymethyl methacrylate to perfluoropolyether and hollow silica in S2 is 1:0.8:0.4.

[0009] Furthermore, the hollow silica has a spherical outer shell and an internal cavity, and the outer shell is an amorphous silica layer.

[0010] Furthermore, the overall particle size of the hollow silica is 0.8~2μm, and the outer shell wall thickness is 50~200nm.

[0011] Furthermore, the mixing temperature in S2 is 60°C, and the mixing time is 2 hours.

[0012] Furthermore, the substrate in S3 is an acrylic sheet or a glass sheet; the coating thickness is 500~1000μm, preferably 800μm.

[0013] The present invention also relates to porous polymethyl methacrylate composite films prepared by the aforementioned preparation method.

[0014] The present invention also relates to the application of the aforementioned porous polymethyl methacrylate composite film in radiation cooling and / or thermal insulation materials.

[0015] The present invention has the following beneficial effects: Existing technologies often use low-boiling-point solvents such as deionized water and ethanol as pore-forming agents, inducing phase separation through solvent evaporation to form a porous structure. However, these methods are extremely sensitive to environmental temperature and humidity, leading to film shrinkage, cracking, and low film formation rates after formation. This invention, in preparing porous polymethyl methacrylate (PMMA) composite films, incorporates perfluoropolyether as a pore-forming agent, along with a certain amount of hollow silica. Perfluoropolyether exhibits significant compatibility differences with the PMMA / dimethylformamide system. During coating and drying, the solvent evaporates, forming a three-dimensional interconnected porous network. Compared to traditional pore-forming agents, perfluoropolyether has low surface tension, is less prone to polymerization, and allows for controllable pore size. The pore-forming process does not require strict temperature and humidity conditions, significantly improving process stability. Furthermore, the porous structure formed by perfluoropolyether pore-forming itself has low thermal conductivity, imparting thermal insulation properties to the film and achieving a synergistic effect of radiative cooling and thermal insulation.

[0016] Meanwhile, this invention introduces hollow silica to replace conventional solid silica filler. The shell and internal cavity of the hollow silica form a core-shell structure, significantly improving scattering efficiency. Simultaneously, it creates a refractive difference with the polymethyl methacrylate matrix, resulting in stronger backscattering according to Mie scattering theory. Experiments show that, at the same addition amount, the reflectivity of the hollow silica system in the visible-near-infrared band is significantly improved compared to the solid silica system. Furthermore, this invention limits the overall particle size of the hollow silica to 0.8–2 μm and the outer shell wall thickness to 50–200 μm. The particle size range of nm is on the same order of magnitude as the wavelength of the solar spectrum, which can generate strong Mie scattering to maximize reflection efficiency. If the particle size is too small, the scattering cross section will be insufficient, and if it is too large, sedimentation or agglomeration will easily occur. The shell thickness is controlled within the above range to ensure the mechanical strength of the microspheres to prevent breakage during the preparation process, and to maintain a sufficiently large cavity volume to reduce the equivalent refractive index. Their synergistic effect ensures that the infrared emissivity of the film in the atmospheric window band is not significantly weakened by the introduction of fillers, achieving a balance between high reflectivity and high emissivity. Thirdly, the cavity structure of hollow silica itself has extremely low thermal conductivity. Together with the porous structure formed by perfluoropolyether pores, it forms a double thermal barrier. The overall thermal conductivity of the film can be reduced to 0.035 W / (m·K), which is far lower than that of traditional radiation cooling films.

[0017] The porous polymethyl methacrylate composite film prepared by this invention has high reflectivity in the visible light band and high emissivity in the atmospheric window band; it also has good radiative cooling effect and heat preservation ability, and can be applied and promoted in scenarios where cooling is required in summer and heat preservation is required when there is an internal heat source in winter. Attached Figure Description

[0018] Figure 1 The graph shows the reflectance of porous radiation-cooling films with different mass ratios of perfluoropolyether doped in Example 1.

[0019] Figure 2 The graph shows the emissivity of porous radiation-cooling films with different mass ratios of perfluoropolyether doped in Example 1.

[0020] Figure 3 The graph shows the reflectance of porous polymethyl methacrylate@hollow silica films with different mass ratios of hollow silica in Example 2.

[0021] Figure 4 Emissivity curves of porous polymethyl methacrylate@hollow silica films with different mass ratios of hollow silica are shown in Example 2.

[0022] Figure 5 The reflectance curves of porous polymethyl methacrylate doped with hollow silica and solid silica respectively in Example 3 are shown.

[0023] Figure 6 The emissivity curves of porous polymethyl methacrylate doped with hollow silica and solid silica respectively are shown in Example 3.

[0024] Figure 7 This is a photograph of a porous polymethyl methacrylate (PMMA) @ 6wt% hollow silica film with the optimal mass ratio of doped perfluoropolyether and hollow silica, as shown in Example 2.

[0025] Figure 8 This is a schematic diagram of the heating device in Example 4.

[0026] Figure 9 The curves showing the temperature change of the upper surface of different coatings in Example 4 are shown.

[0027] Figure 10 This is an electron microscope image of the porous polymethyl methacrylate @ 6wt% hollow silica film of Example 2.

[0028] Figure 11 This is the temperature drop testing device for the outdoor porous polymethyl methacrylate@6wt% hollow silica film used in Example 6. Figure 11 A represents the test site for the test kit. Figure 11 B is a schematic diagram of the temperature drop test box.

[0029] Figure 12 The temperature drop curve and solar irradiance of the porous polymethyl methacrylate@6wt% hollow silica film in Example 6 were tested outdoors.

[0030] Figure 13 The temperature difference test curve of the porous polymethyl methacrylate@6wt% hollow silica film in Example 6 placed outdoors.

[0031] Figure 14 The test site and test apparatus for the outdoor porous polymethyl methacrylate@6wt% hollow silica film of Example 7.

[0032] Figure 15 Example 7 shows the thermal insulation test curve and solar irradiance of a porous polymethyl methacrylate @ 6wt% hollow silica film placed outdoors.

[0033] Figure 16 This is a comparison chart of the thermal conductivity of the various films in Example 8. Detailed Implementation

[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, all raw materials and reagents used are commercially available.

[0035] In the following examples, polymethyl methacrylate (PMMA) was purchased from Shanghai Maclean Biotechnology Co., Ltd., and was of analytical grade (AR); perfluoropolyether (PFMA) was purchased from Shanghai Maclean Biotechnology Co., Ltd., with a weight-average molecular weight of 630 g / mol, and was a colorless and transparent liquid at room temperature; hollow silica was purchased from Shanghai Maclean Biotechnology Co., Ltd., and was a white powder product with an overall particle size distribution of 0.8–2 μm, a median particle size of approximately 1 μm, an outer shell wall thickness of 50–200 nm, a cavity diameter to overall particle size ratio of 0.5–0.8, a tap density of 0.2–0.4 g / cm³, and a specific surface area of ​​300–600 m² / g.

[0036] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.

[0037] Example 1 This invention presents experiments on porous radiation-cooling thin films doped with different mass ratios of perfluoropolyether. The specific preparation method is as follows: (1) According to the mass ratio of polymethyl methacrylate to dimethylformamide of 1:4, weigh 4g of polymethyl methacrylate and 16g of dimethylformamide into a weighing bottle and stir magnetically at 60℃ for 1h to make them fully mixed.

[0038] (2) According to the mass ratio of polymethyl methacrylate and perfluoropolyether is 1:0-1, weigh 0g, 2g, 3.2g and 4g of perfluoropolyether respectively, add them to the mixture in step (1) and continue to stir magnetically at 60℃ for 2h to make it uniform, so as to obtain transparent coating stock solution.

[0039] (3) The transparent coating solution from step (2) was applied to the acrylic substrate using a dropper to form a smooth coating with a thickness of 800 μm. After standing indoors for 12 hours, porous radiation-cooling films with different doping ratios were obtained. The reflectance and emissivity of the obtained films were tested. Specifically, the reflectance and transmittance (0.3-2.5 μm) of the prepared samples were tested and analyzed using a Lambda750 UV-VIS-NIR spectrophotometer from PE Corporation, USA. The emissivity was indirectly measured using a Spectrum Two Fourier Transform Infrared Spectrometer from PE Corporation, USA.

[0040] according to Figure 1 , 2It can be observed that different doping ratios result in corresponding differences in reflectivity and emissivity. Higher doping ratios lead to increased reflectivity and emissivity. When the mass ratio of polymethyl methacrylate (PMMA) to perfluoropolyether (PFPO) is 1:0.8, the film exhibits an average reflectivity of 89% in the solar radiation band (0.3-2.5 μm), approximately 52 times that of pure PMMA (1.7%), while the emissivity also increases from 93.5% to 96.1%. Further addition of PFPO leads to a decrease in both average reflectivity and emissivity; therefore, a mass ratio of PMMA to PFPO of 1:0.8 is chosen.

[0041] Example 2 This invention presents experiments on porous polymethyl methacrylate@hollow silica films doped with different mass ratios of hollow silica. The specific preparation method is as follows: (1) According to the mass ratio of polymethyl methacrylate to dimethylformamide of 1:4, weigh 4g of polymethyl methacrylate and 16g of dimethylformamide into a weighing bottle and stir magnetically at 60℃ for 1h to make them fully mixed.

[0042] (2) According to the mass ratio of polymethyl methacrylate and perfluoropolyether is 1:0.8, and the mass fraction of hollow silica in the total solution is 3wt%, 5wt%, 6wt% and 8wt%, respectively, weigh 3.2g of perfluoropolyether and 0.8g, 1.2g, 1.6g and 2g of hollow silica, add them to the mixture in step (1) and continue to stir magnetically at 60℃ for 2h to make it uniform, so as to obtain white coating stock solution.

[0043] (3) The white coating solution from step (2) was applied to the acrylic substrate using a dropper. A smooth coating with a thickness of 800 μm was obtained by scraping. After standing indoors for 12 hours, porous polymethyl methacrylate films with different hollow silica doping ratios were obtained. The reflectivity and emissivity of the obtained films were tested, and the results were based on... Figure 3 , 4 It can be observed that different doping ratios of hollow silica result in corresponding differences in reflectivity and emissivity. As the doping ratio increases, both reflectivity and emissivity continuously improve, reaching a peak after adding 6 wt% hollow silica. Further addition leads to a decrease in reflectivity, at which point the film's average reflectivity is 94% and its average emissivity is 97.2%, compared to... Figure 1 , 2 The porous radiation-cooled thin film showed a 5% increase in average reflectivity and a 1.1% increase in average emissivity. The surfaces of the thin films with different proportions were nearly identical. Figure 7 A photograph of a porous polymethyl methacrylate (PMMA) @ 6wt% hollow silica film obtained after doping with 6wt% hollow silica.

[0044] Example 3 The effect of porous polymethyl methacrylate doped with hollow silica and solid silica respectively on its optical properties.

[0045] The preparation steps (1) and (2) are the same as in Example 1, resulting in a porous radiation-cooling film with a mass ratio of pure polymethyl methacrylate and perfluoropolyether of 1:0 and 1:0.8, respectively. Preparation step (3) is the same as in Example 2, resulting in a porous polymethyl methacrylate film with 6 wt% hollow silica added. The hollow silica in step (3) is replaced with solid silica, while other parameters remain unchanged, resulting in a porous polymethyl methacrylate film with 6 wt% solid silica added. The reflectivity and emissivity of the obtained film are tested, and based on… Figure 5 , 6 It can be observed that porous radiation-cooling films with added hollow silica exhibit higher reflectivity and emissivity than those with added solid silica. This is primarily due to the low refractive index, strong multiple scattering and interface reflection resulting from the hollow structure, as well as the efficient coupling of infrared radiation by the porous network. Compared to solid particles, the hollow structure creates a synergistic enhancement effect in both optical and thermal properties.

[0046] Example 4 The effect of different mass ratios of perfluoropolyether and hollow silica on the thermal insulation performance of porous polymethyl methacrylate hollow silica films.

[0047] The preparation steps (1) and (2) are the same as in Example 1, resulting in porous radiation cooling films with pure polymethyl methacrylate and perfluoropolyether in mass ratios of 1:0 and 1:0.8, respectively. The preparation step (3) is the same as in Example 2, resulting in porous polymethyl methacrylate films with added hollow silica in mass fractions of 3 wt% and 6 wt%.

[0048] use Figure 8 The heating device was used to place the four sample films on a 50W heating pad, maintaining the temperature at 60℃. The surface temperature change curves are shown in the figure. Figure 9 .according to Figure 9 As can be seen, after heating on the heating pad for one hour, the porous radiative cooling film with 6 wt% hollow silica had the lowest upper surface temperature, followed by the film with 3 wt% hollow silica, while pure polymethyl methacrylate had the highest temperature. This indicates that the thermal insulation performance of the film was improved after the addition of perfluoropolyether, making it more difficult for heat to be transferred to the upper surface. Then, the addition of 3 wt% and 6 wt% hollow silica respectively significantly improved the thermal insulation performance, and the more silica added, the better the thermal insulation performance and the lower the upper surface temperature of the film.

[0049] Example 5 The surface morphology of a porous radiation-cooling thin film doped with 6 wt% hollow silica and with a thickness of 800 μm was studied. The specific preparation method is as follows: (1) According to the mass ratio of polymethyl methacrylate to dimethylformamide of 1:4, weigh 4g of polymethyl methacrylate and 16g of dimethylformamide into a weighing bottle and stir magnetically at 60℃ for 1h to make them fully mixed.

[0050] (2) According to the mass ratio of polymethyl methacrylate and perfluoropolyether is 1:0.8, and the mass fraction of hollow silica is 6wt%, weigh 3.2g of perfluoropolyether and 1.6g of hollow silica, add them to the mixture in step (1), and continue to stir magnetically at 60℃ for 2h to make it uniform, so as to obtain white coating stock solution.

[0051] (3) The white coating solution from step (2) was applied to the acrylic substrate using a dropper. A smooth coating with a thickness of 800 μm was obtained by scraping. After standing indoors for 12 hours, a porous polymethyl methacrylate (PMMA)@6wt% hollow silica film was obtained. Its electron microscope image is shown below. Figure 10 ,according to Figure 10 A. It can be clearly observed that the surface microstructure of this radiation-cooling film consists of a large number of micro- and nano-porous particles, which are relatively uniformly distributed. According to Figure 10 B, the same is true on the side, which also suggests that its porous structure is connected.

[0052] Example 6 Study on the outdoor cooling performance of porous radiation cooling films doped with hollow silica at a mass fraction of 6wt% and a thickness of 800μm.

[0053] The porous polymethyl methacrylate (PMMA) @ 6wt% hollow silica film was prepared using the same method as in Example 5. A porous PMMA film (prepared using the same method as in Example 1) and commercial white paint (350g of metal anti-rust white paint from Muyaju Sanitary Ware Co., Ltd.) were selected as the control group. The specifications of the experimental temperature measuring box are as follows... Figure 11 Box A has the same dimensions of 16×16cm and an opening of 5×5cm. The interior is filled with polyethylene foam, and the outer wall is wrapped with thin aluminum foil for insulation, reducing the impact of heat convection. On August 17, 2025, a temperature drop experiment was conducted on the rooftop of the School of Materials and Chemical Engineering at Three Gorges University in Yichang City. The experimental site is as follows: Figure 11As shown in Figure B, the experimental film was placed at the cavity opening and sealed with a PE film to reduce the influence of external wind, humidity, and heat flow. A thermocouple was connected to the substrate to record temperature data. A solar irradiance meter was placed next to the experimental box to record the solar irradiance during the measurement period of the day. The average solar irradiance during the period from 11:00 to 14:00 on that day was 827 W / m². 2 The porous polymethyl methacrylate (PMMA)@6wt% hollow silica film exhibits a maximum temperature drop of 20.6℃ and an average temperature drop of approximately 15.7℃ compared to sub-ambient temperature. This temperature difference is higher than that of commercial white paint and porous PMMA film. Specifically... Figure 12 , 13 As shown.

[0054] Example 7 This study investigates the thermal insulation performance of a porous radiative cooling film doped with 6 wt% hollow silica and with a thickness of 800 μm when there is an internal heat source in winter.

[0055] The preparation method of the porous polymethyl methacrylate (PMMA) @ 6wt% hollow silica film is the same as in Example 5. Pure PMMA film (prepared using the same method as in Example 1, except without the addition of perfluoropolyether) and commercial white paint (350g of metal anti-rust white paint from Muyaju Sanitary Ware Co., Ltd.) were selected as control groups. The test site and experimental temperature measuring box are as follows. Figure 14 The box measures 16×16cm in length and width, with an opening of 5×5cm. The interior is filled with polyethylene foam, and the outer wall is wrapped with thin aluminum foil for insulation, reducing the impact of heat convection. On January 8, 2026, an insulation experiment was conducted on the rooftop of the School of Materials and Chemical Engineering at Three Gorges University in Yichang City. The experimental film was placed at the opening and sealed with PE film to reduce the influence of external wind, humidity, and heat flow. A hot-coupled device was connected to the substrate to record temperature data. A 40W heating device was placed at the bottom of the cavity to heat it to a constant temperature of 60℃. A solar irradiance meter was placed next to the experimental box to record the solar irradiance during the measurement period. The average solar irradiance during the period from 11:00 to 14:00 on that day was 277W / m². 2 The porous polymethyl methacrylate (PMMA)@6wt% hollow silica film maintained its highest temperature throughout the testing process, and even after the test, the temperature remained around 60°C. See details... Figure 15 This indicates that the target coating has a good heat insulation effect when there is a heat source inside.

[0056] Example 8 Preparation of polymethyl methacrylate film: The mass ratio of polymethyl methacrylate to dimethylformamide is 1:4. Weigh 4g of polymethyl methacrylate and 16g of dimethylformamide into a weighing bottle and stir magnetically at 60℃ for 1h to ensure thorough mixing. Apply the mixture to an acrylic substrate using a dropper and obtain a smooth coating by scraping. The coating thickness is 800μm. After standing indoors for 12h, the polymethyl methacrylate film is obtained.

[0057] The porous polymethyl methacrylate film was prepared using the same method as in Example 1, with a mass ratio of polymethyl methacrylate to perfluoropolyether of 1:0.8.

[0058] The preparation method of porous polymethyl methacrylate@hollow silica films doped with different hollow silica is the same as in Example 2, wherein the doping ratio of hollow silica is 3wt% and 6wt%, respectively; that is, porous polymethyl methacrylate@3wt% hollow silica films and porous polymethyl methacrylate@6wt% hollow silica films.

[0059] The thermal conductivity of the above-mentioned polymethyl methacrylate (PMMA) film, porous PMMA film, porous PMMA@3wt% hollow silica film, and porous PMMA@6wt% hollow silica film was tested. Specifically, a laser thermal conductivity meter was used to test the above samples, and the test results are shown below. Figure 16 The thermal conductivity of the polymethyl methacrylate film can be observed to be 0.25 W / m. - ¹K - ¹, while the porous polymethyl methacrylate film prepared using perfluoropolyether has a thermal conductivity of only 0.091 W / m². - ¹K - ¹ This is because the porous structure disrupts the continuous stacking of PMMA molecular chains, further hindering heat conduction. Adding hollow silica to a porous polymethyl methacrylate film further reduces the thermal conductivity. This is due to the multiple inhibitory effects of its unique hollow structure on heat transfer; firstly, its own thermal conductivity is already low (approximately 0.15~0.20 W / m²). - ¹K - ¹), and secondly, multiple interfaces are formed inside the film to suppress heat transfer. Furthermore, the thermal conductivity decreases with increasing amounts of hollow silica; the thermal conductivity of porous polymethyl methacrylate@6wt% hollow silica film is only 0.035 W / m². - ¹K - ¹ is an excellent thermal insulation material.

[0060] The above embodiments describe preferred embodiments of the present invention, but the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other way. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for preparing a porous polymethyl methacrylate composite film, characterized in that, Includes the following steps: S1. Using polymethyl methacrylate as raw material, add dimethylformamide and mix evenly; S2. Add perfluoropolyether and hollow silica to the liquid obtained in S1, and mix evenly to obtain the coating solution. S3. Apply the coating solution onto the substrate by scraping, and after drying, a porous polymethyl methacrylate composite film is obtained.

2. The preparation method according to claim 1, characterized in that: The mass ratio of polymethyl methacrylate to dimethylformamide is 1:4; the mixing temperature is 60-70℃, and the mixing time is 1-2 hours.

3. The preparation method according to claim 1, characterized in that: The mass ratio of polymethyl methacrylate to perfluoropolyether and hollow silica in S2 is 1:0.2-1:0.2-0.

5.

4. The preparation method according to claim 3, characterized in that: In S2, the mass ratio of polymethyl methacrylate to perfluoropolyether and hollow silica is 1:0.8:0.

4.

5. The preparation method according to claim 1, characterized in that: The hollow silica has a spherical outer shell and an internal cavity, and the outer shell is an amorphous silica layer.

6. The preparation method according to claim 5, characterized in that: The hollow silica has an overall particle size of 0.8~2μm and an outer shell thickness of 50~200nm.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The mixing temperature in S2 is 60-70℃, and the mixing time is 1-2 hours.

8. The preparation method according to claim 1, characterized in that: The substrate for S3 can be acrylic, glass, aluminum, or wood; the coating thickness is 500~1000μm.

9. The porous polymethyl methacrylate composite film prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the porous polymethyl methacrylate composite film according to claim 9 in radiation cooling and thermal insulation materials.

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