A porous radiative cooling performance material and a method of making the same

Abstract

The application provides a kind of porous radiation cooling performance material and its preparation method, the components of the material mainly include high molecular polymer with infrared emission characteristics itself, micro-nano filler, modifier and solvent, after the above components are uniformly mixed, bubble is removed, and then the porous radiation cooling performance material is prepared by blade coating and phase separation process.The uniform porous structure formed in the polyurethane matrix by the phase separation process and the nano filler embedded in the pore wall make the light path refract and Mie scattering effect inside the pore multiple times, improve the solar reflectivity and atmospheric window emissivity of the obtained porous radiation cooling performance material, so as to improve the radiation cooling performance, and the good application potential is proved by weather resistance test.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer materials technology, specifically relating to a porous radiative cooling material and its preparation method. This material possesses high solar reflectivity and atmospheric window infrared emissivity, enabling passive radiative cooling without consuming external energy. It is suitable for thermal management needs in areas such as building temperature control, outdoor equipment heat dissipation, and transportation. Background Technology

[0002] Passive radiative cooling (PRC) technology leverages the spectral properties of materials to reflect short-wave solar radiation (0.3–2.5 μm) back into the atmosphere through highly reflective surfaces without consuming external energy. Simultaneously, it efficiently emits long-wave infrared radiation into outer space (around 3 K blackbody cold sources) via atmospheric window wavelengths (8–13 μm), continuously removing heat and achieving passive cooling below ambient temperature. In the context of global energy structure transformation and the "dual-carbon" strategy, PRC, as a zero-energy, zero-carbon emission cooling method, is considered an important alternative or supplement to traditional active cooling (such as vapor compression refrigeration and air conditioning systems). It has significant strategic value in reducing building operating energy consumption, mitigating the urban heat island effect, ensuring the thermal safety of outdoor electronic equipment, and reducing greenhouse gas emissions.

[0003] In recent years, with the rapid development of spectrally selective optical materials, micro-nano structure fabrication processes, and polymer processing technologies, passive radiative cooling materials have shown broad application prospects in fields such as building temperature control (e.g., radiative cooling coatings, membrane coverings for roofs and curtain walls), outdoor equipment heat dissipation (e.g., 5G communication base stations, photovoltaic module backsheets, energy storage power cabinets), and transportation (e.g., vehicle roofs, cold chain logistics containers, aerospace vehicle enclosures). However, these application scenarios place multi-dimensional and systematic stringent requirements on radiative cooling materials: not only do they require materials to possess excellent solar reflectivity (>0.95) and atmospheric window emissivity (>0.95) to achieve high cooling power, but they also require materials to have lightweight structures to reduce additional loads, flexible characteristics to adapt to complex irregular curved surfaces, long-term environmental weather resistance to resist ultraviolet aging and damp heat cycling, good mechanical properties to meet assembly, bending, and service reliability requirements, and low-cost continuous fabrication processes to support large-scale engineering applications.

[0004] Currently, existing passive radiation cooling technologies mainly focus on two major technical routes: thin-film coating and foamed structure. In the thin-film coating route, for example, Chinese patent document CN210390369U (publication date: April 24, 2020) discloses an antioxidant radiation cooling film. This film, by introducing an antioxidant functional layer into a multilayer composite structure, improves the lifespan of the radiation cooling film under ultraviolet light irradiation to a certain extent. However, these types of thin-film cooling materials are typically thin (tens to hundreds of micrometers) and have short optical paths. To ensure high reflectivity, they often rely on high-concentration inorganic fillers (such as TiO2, SiO2, BaSO4, etc.) or precise multilayer interference optical structures. This makes it difficult to balance the material's surface density, flexibility, and optical properties, and the film is prone to brittleness. On the other hand, the interfacial adhesion between the film and the substrate, scratch resistance, and long-term outdoor weather resistance (such as resistance to damp heat and salt spray) still face severe challenges. In addition, when film materials are laid over large areas or bonded to irregular curved surfaces, construction defects such as wrinkles, bubbles, and stress concentration are prone to occur, which limits mechanical compatibility and construction reliability.

[0005] In foamed structural technology, for example, Chinese patent document CN117126451B (publication date: January 5, 2024) discloses a passive radiation cooling foamed polypropylene bead material. This material utilizes the porous structure inside the foamed polypropylene matrix to introduce a large number of gas-solid scattering interfaces, enhancing the scattering efficiency of sunlight within the material. Simultaneously, it leverages the infrared vibration characteristics of the polypropylene polymer chains to achieve long-wave infrared radiation. However, the density of foamed polypropylene bead materials is typically greater than 20 kg / m³. 3 Furthermore, the foaming ratio is limited by melt strength and molding process, making it difficult to meet the requirements of extreme lightweighting (such as density below 10 kg / m³) in fields such as aerospace, portable electronic devices, and flexible wearable devices. 3 The demand for ultra-thin and flexible materials is increasing; however, the polyolefin matrix and foamed pore structure are not resistant to ultraviolet radiation, high temperature and humid environment. During long-term outdoor service, molecular chain breakage, yellowing, powdering and pore structure collapse are likely to occur, resulting in a significant decrease in cooling performance. In addition, the molding process of foamed beads often depends on intermittent molding sintering or steam thermoforming, which has a long molding cycle, high mold cost, and is difficult to achieve continuous, roll-to-roll large-area preparation, which seriously restricts low-cost large-scale application.

[0006] In summary, although existing passive radiative cooling technologies have made some progress in specific performance indicators, various materials still have significant performance shortcomings and application limitations: thin-film materials are insufficient in terms of weather resistance, mechanical compatibility, large-area construction reliability, and flexible bending performance; foamed materials are limited in terms of lightweight limits, long-term weather resistance stability, maintenance of pore structure integrity, and low-cost continuous preparation. To date, no technical solution can simultaneously meet the multiple requirements of lightweight flexible structure, hyperspectral selective cooling performance, excellent environmental weather resistance, good mechanical compatibility, and low-cost large-scale preparation, thus limiting the in-depth application and industrialization of passive radiative cooling technology in a wider range of engineering scenarios. Therefore, developing a passive radiative cooling material and its preparation method that can integrate the above-mentioned multiple performance advantages is of great practical significance for promoting the practical application of radiative cooling technology and achieving the "dual carbon" goal. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a porous radiative cooling material and its preparation method, effectively reducing preparation costs and improving the overall performance of the radiative cooling material. This invention is implemented through the following technical means:

[0008] This invention first discloses a porous material with radiative cooling properties, comprising:

[0009] 1-50 parts of polymer; 0.1-20 parts of micro / nano filler; 0.1-1 part of modifier; 10-500 parts of solvent; wherein:

[0010] The average particle size of the micro / nano filler is 0.01-20 μm.

[0011] Furthermore, the polymer can be selected from those known in the art and conventional polymers available on the market, or a suitable polymer can be selected based on the actual application requirements of the spectral selectivity of the radiative cooling material and cost considerations. To better illustrate the invention and provide several preferred technical solutions for reference, the polymer can be selected from any one of polymethyl methacrylate, thermoplastic polyurethane, polyvinylidene fluoride, polylactic acid, and polydimethylsiloxane.

[0012] Furthermore, the selection of the micro / nano fillers includes those known in the art and those commonly available on the market. Suitable fillers can also be selected based on the actual requirements for spectral selectivity of the radiative cooling material, particle size, and cost. Generally, the micro / nano fillers of this invention can be selected from any one or more of titanium dioxide, silicon dioxide, zinc oxide, aluminum oxide, kaolin, glass microspheres, and rutile titanium dioxide coated mica, or two-dimensional nanosheets containing the above-mentioned micro / nano fillers can be selected.

[0013] Furthermore, the modifier can be selected based on the requirement to improve the compatibility of the filler with the matrix. Those skilled in the art can also select commonly known and commercially available organic reagents based on the actual performance improvement requirements. Generally, the modifier of the present invention can be selected from any one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, isopropyltris(dioctylphosphoyloxy)titanate, hexamethyldisilazane, n-octyltriethoxysilane, hexadecyltrimethoxysilane, and heptadecafluoro-1,1,2,2-tetradecyltrimethoxysilane.

[0014] Furthermore, the solvent is selected based on the solubility of the matrix in the solvent. Generally, any one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, chloroform, toluene, and carbon tetrachloride can be selected.

[0015] This invention also discloses a method for preparing any of the above-mentioned porous radiative cooling materials, comprising the following steps:

[0016] (1) By weight, 0.1 to 1 part of the modifier is placed in a mixed solution of water and ethanol for 10 to 60 min for pre-hydrolysis, with a volume ratio of water to ethanol of 9:1; then micro-nano fillers are introduced into the mixed solution system and stirred at 50 to 80 °C for 3 to 6 h. After the reaction is completed, the mixed solution is filtered and washed, and dried at 40 to 60 °C to obtain the reaction product.

[0017] (2) Place 0.1 to 20 parts of the modified filler from step (1) into 10 to 500 parts of solvent and disperse it fully in an ultrasonic vibration environment for 1 to 2 hours. Then introduce 1 to 50 parts of polymer and stir at a speed of 300 to 600 r / min to obtain a mixture in which the filler is uniformly dispersed.

[0018] (3) Place the uniformly dispersed filler mixture obtained in step (2) under a negative pressure bar (<-0.8MPa) at room temperature. After the air bubbles in the mixture are completely removed, adjust the coating thickness to 400~1200 μm by a scraper at room temperature. After coating into a film, soak it in a solvent and water mixture of different ratios (9:1, 8:2, 7:3, 6:4) for 10~15 min, then transfer it to an aqueous solution for soaking for 24~48 h, and then dry it at 30~60 ℃ for 4~8 h to obtain a porous radiative cooling material.

[0019] Furthermore, the volume ratio of the solvent to the water mixture in step (3) is 6:4.

[0020] The beneficial effects of this invention are:

[0021] (1) This invention provides a porous radiation cooling material and its preparation method, which is prepared by solvent exchange induced phase separation method. The preparation method is simple and low cost.

[0022] (2) This invention provides a porous radiation cooling material and its preparation method. The uniform porous structure and the internally doped nanofillers with their own reflective effect are used to improve the average reflectivity of the film in the solar radiation band (0.25–2.5 μm). Among them, the smaller-sized nanofillers are uniformly and randomly distributed in the porous film, forming an optical structure composed of three media with different optical properties: polymer, nanofillers, and air. This optical structure is used to achieve effective reflection and absorption of radiation in a specific wavelength band.

[0023] (3) The present invention provides a porous radiation cooling material and its preparation method. The synergistic effect of the selective molecular vibration of the specific functional groups of the polymer of the film and the nanofiller doped inside it establishes a new absorption-emission balance relationship in the atmospheric window band (8–14 μm), so that the radiation cooling film has a high average emissivity. Attached Figure Description

[0024] Figure 1 A schematic diagram illustrating the mechanism of action of the pretreatment filler with the modifier and the interaction between the filler and the matrix;

[0025] Figure 2 Image of the porous radiative cooling material prepared in Example 1;

[0026] Figure 3 Figures (a) and (b) are 200X and 4000X scanning electron microscope images of the cross section of the porous radiation cooling material prepared in Comparative Example 1, respectively.

[0027] Figure 4 Figures (a) and (b) are 200X and 1000X scanning electron microscope images of the rutile titanium dioxide coated mica filler (TiO2@Mica) used in Example 1 and Comparative Example 2, respectively.

[0028] Figure 5 Figures (a), (b), and (c) are 200X, 1000X, and 4000X scanning electron microscope images of the cross-section of the porous radiation cooling material prepared in Comparative Example 2, respectively.

[0029] Figure 6 Figures (a), (b), and (c) are 200X, 1000X, and 4000X scanning electron microscope images of the cross-section of the porous radiation cooling material prepared in Example 1, respectively.

[0030] Figure 7 The UV-Vis-NIR reflectance diagrams of the porous radiation cooling materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 are shown.

[0031] Figure 8 Infrared emissivity diagrams of the porous radiation cooling materials prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0032] Figure 9 The diagram shows the indoor cooling performance of the test room to simulate radiation illumination (Solar-1000 solar evaporation photothermal conversion experimental platform of Beijing Newbi Technology Co., Ltd.).

[0033] Figure 10 Detailed images of the sample's indoor cooling performance test (left: schematic diagram; right: actual test photo). Detailed Implementation

[0034] To further illustrate the advantages of the present invention, the technical solution of the present invention will be described in detail below through specific embodiments.

[0035] Example 1

[0036] A porous material with radiative cooling properties, comprising:

[0037] 20 parts polymer matrix, 6 parts micro / nano filler, 0.2 parts modifier, and 100 parts solvent.

[0038] The polymer matrix is ​​selected as thermoplastic polyurethane;

[0039] The micro-nano filler is selected as rutile titanium dioxide coated mica sheet with an average particle size of 10~20μm.

[0040] The modifier selected is γ-aminopropyltriethoxysilane;

[0041] The solvent is N,N-dimethylformamide.

[0042] A method for preparing a porous material with radiative cooling properties includes the following steps:

[0043] (1) By weight, the above-proportioned modifier was placed in a mixed solution of water and ethanol (water: ethanol = 1: 9) for pre-hydrolysis for 30 min. Then, the corresponding proportion of filler was introduced into the mixed solution system and stirred at 60 °C for 4 h. After the reaction was completed, the mixed solution was filtered and washed, and dried at 40 °C to obtain the reaction product.

[0044] (2) The modified filler in step (1) is placed in a solvent and fully dispersed in an ultrasonic vibration environment for 1 h. Then, a polymer is introduced and stirred at a speed of 300 r / min to obtain a mixture in which the filler is uniformly dispersed.

[0045] (3) The mixture of filler uniformly dispersed in step (2) is placed under negative pressure (<-0.8MPa) at room temperature. After the bubbles in the mixture are completely removed, the coating thickness is adjusted to 600 μm by a scraper at room temperature. After coating into a film, it is immersed in a solvent and water mixture with a ratio of (6:4) for 15 min and then transferred to an aqueous solution for 24 h. Subsequently, it is dried at 40 ℃ for 6 h to obtain a porous radiative cooling material.

[0046] Example 2

[0047] A porous material with radiative cooling properties, comprising:

[0048] 20 parts polymer matrix, 2 parts micro / nano filler, 0.2 parts modifier, and 100 parts solvent.

[0049] The polymer matrix is ​​selected as polymethyl methacrylate;

[0050] The micro / nano filler is selected from zinc oxide with an average particle size of 90±10 nm;

[0051] The modifier selected is hexadecyltrimethoxysilane;

[0052] The solvent is N,N-dimethylformamide.

[0053] A method for preparing a porous material with radiative cooling properties includes the following steps:

[0054] (1) By weight, the above-proportioned modifier is placed in a mixed solution of water and ethanol (water: ethanol = 1: 9) for pre-hydrolysis for 30 min, and then introduced into the corresponding proportion of filler in the mixed solution system. The mixture is stirred and mixed at 60 °C for 4 h. After the reaction is completed, the mixed solution is filtered and washed, and dried at 40 °C to obtain the reaction product.

[0055] (2) The modified filler in step (1) is placed in a solvent and fully dispersed in an ultrasonic vibration environment for 2 h. Then, a polymer is introduced and stirred at a speed of 300 r / min to obtain a mixture in which the filler is uniformly dispersed.

[0056] (3) The mixture of filler uniformly dispersed in step (2) is placed under negative pressure (<-0.8MPa) at room temperature. After the bubbles in the mixture are completely removed, the coating thickness is adjusted to 600 μm by a scraper at room temperature. After coating into a film, it is immersed in a solvent and water mixture with a ratio of (6:4) for 15 min and then transferred to an aqueous solution for 24 h. Subsequently, it is dried at 40 ℃ for 6 h to obtain a porous radiative cooling material.

[0057] Example 3

[0058] A porous material with radiative cooling properties and its preparation method, comprising:

[0059] 1 part of polymer; 0.1 part of micro / nano filler; 0.1 part of modifier; 10 parts of solvent;

[0060] The polymer matrix is ​​selected as thermoplastic polyurethane;

[0061] The micro / nano filler is selected from zinc oxide with an average particle size of 90±10 nm;

[0062] The modifier is selected as isopropyl tris(dioctylphosphoyloxy)titanate;

[0063] The solvent is dimethyl sulfoxide.

[0064] (1) By weight, the above-proportioned modifier is placed in a mixed solution of water and ethanol (water: ethanol = 1: 9) for pre-hydrolysis for 30 min, and then introduced into the corresponding proportion of filler in the mixed solution system. The mixture is stirred and mixed at 60 °C for 4 h. After the reaction is completed, the mixed solution is filtered and washed, and dried at 60 °C to obtain the reaction product.

[0065] (2) Place 0.1 parts of the modified filler from step (1) into 10 parts of solvent and disperse it fully in an ultrasonic vibration environment for 2 hours. Then introduce 1 part of polymer and stir at a speed of 600 r / min to obtain a mixture in which the filler is uniformly dispersed.

[0066] (3) The mixture of filler uniformly dispersed in step (2) is placed under negative pressure (<-0.8MPa) at room temperature. After the bubbles in the mixture are completely removed, the coating thickness is adjusted to 800 μm by a scraper at room temperature. After coating into a film, it is immersed in a solvent and water mixture of different ratios (6:4) for 15 min and then transferred to an aqueous solution for 36 h. Subsequently, it is dried at 30 ℃ for 6 h to obtain a porous radiative cooling material.

[0067] Example 4

[0068] A porous material with radiative cooling properties and its preparation method, comprising:

[0069] 50 parts of polymer; 20 parts of micro / nano filler; 1 part of modifier; 500 parts of solvent;

[0070] The polymer matrix is ​​selected as polymethyl methacrylate;

[0071] The micro / nano filler is titanium dioxide with an average particle size of 0.2 μm;

[0072] The modifier is selected as isopropyl tris(dioctylphosphoyloxy)titanate;

[0073] The solvent is dimethyl sulfoxide.

[0074] (1) By weight, the above-proportioned modifier is placed in a mixed solution of water and ethanol (water: ethanol = 1: 9) for pre-hydrolysis for 30 min, and then introduced into the corresponding proportion of filler in the mixed solution system. The mixture is stirred and mixed at 60 °C for 4 h. After the reaction is completed, the mixed solution is filtered and washed, and dried at 60 °C to obtain the reaction product.

[0075] (2) Place 1 part of the modified filler from step (1) into 500 parts of solvent and disperse it fully in an ultrasonic vibration environment for 1 h. Then introduce 50 parts of polymer and stir at a speed of 400 r / min to obtain a mixture in which the filler is uniformly dispersed.

[0076] (3) Place the uniformly dispersed filler mixture obtained in step (2) under a negative pressure bar (<-0.8MPa) at room temperature. After the air bubbles in the mixture are completely removed, adjust the coating thickness to 1200 μm by a scraper at room temperature. After coating into a film, soak it in a solvent and water mixture of different ratios (6:4) for 10 min and then transfer it to an aqueous solution for 24 h. Then dry it at 60 ℃ for 4~8 h to obtain a porous radiative cooling material.

[0077] Mechanism analysis of solvent exchange-induced phase separation: The system is first immersed in a mixed solvent (e.g., 7:3 or 8:2) to allow delayed phase separation in the metastable region, forming a thin, dense surface layer and inhibiting macropore formation. Then, it is rapidly solidified in pure water, locking in a uniform porous structure. Different solvent / water ratios directly control the delay time and phase separation rate. The resulting uniform porous structure, along with the nanofiller enriched in the pore walls, synergistically enhances optical path extension and scattering efficiency through Mie scattering (filler size ≈ light wavelength) and multiple refractions at the polymer-filler-air three-phase interface, achieving structural-functional integration.

[0078] Figure 1The diagram illustrates the mechanism of action of pretreated fillers with modifiers and the interaction between fillers and the matrix: The addition of modifiers effectively improves the compatibility of the inorganic-organic interface and reduces particle agglomeration. For example, γ-aminopropyltriethoxysilane reacts with the hydroxyl groups on the surface of rutile titanium dioxide-coated mica flakes to form siloxane bonds, while the other end forms hydrogen bonds with the TPU matrix, enabling the filler to achieve uniform single-particle dispersion in the TPU matrix.

[0079] Figure 2 The image shows the actual porous radiative cooling material prepared in Example 1. The prepared porous radiative cooling material is white, with a thickness of 100~300 μm and a smooth surface.

[0080] Figure 3 Figures (a) and (b) are 200X and 4000X magnification scanning electron microscope images of the cross-section of the porous radiation cooling material prepared in Comparative Example 1, respectively; it can be seen that it has a porous structure and uniform pore size.

[0081] Figure 4 Figures (a) and (b) are 200X and 1000X scanning electron microscope images of the rutile titanium dioxide coated mica filler (TiO2@Mica) used in Example 1 and Comparative Example 2, respectively. Statistical analysis shows that the micro-nano filler has a sheet structure and its particle size is mainly distributed in the range of 10~20 μm.

[0082] Figure 5 Figures (a), (b), and (c) are 200X, 1000X, and 4000X scanning electron microscope images of the cross-section of the porous radiative cooling material prepared in Comparative Example 2, respectively. They show that the introduction of micro- and nano-fillers significantly affects the formation of the pore structure of the polymer matrix in the porous radiative cooling material prepared without the addition of modifiers. The pore size formed is significantly larger, and the micro- and nano-fillers are unevenly dispersed and loosely bonded in the polymer matrix, accumulating inside the pore structure formed in the polymer matrix.

[0083] Figure 6 Figures (a), (b), and (c) are 200X, 1000X, and 4000X scanning electron microscope images of the cross-section of the porous radiation cooling material prepared in Example 1, respectively. The addition of the modifier effectively improved the compatibility of the inorganic-organic interface and reduced particle agglomeration. The porous radiation cooling material prepared in Example 1 not only improved the interfacial bonding between the micro / nano fillers and the polymer matrix, but also maintained the uniform porous structure formed by the polymer matrix through phase separation.

[0084] Figure 7The images show the UV-Vis-NIR reflectance of the porous radiative cooling materials prepared in Examples 1, 1, and 2. The average solar reflectance of Comparative Example 1 is 91.3%, mainly attributed to multiple reflections and Mie scattering effects generated by its air pores in the 5-8 µm wavelength range. The introduction of rutile titanium dioxide-coated mica filler creates an additional reflective interface through the difference in refractive indices between the polymer matrix, the TiO2 contained in the filler, and the mica sheets, significantly improving the reflectance of Examples 1 and 2. After filler modification, the retention of the uniform porous structure of the polymer matrix increases the reflectance of the film in Example 3 to 91.82%.

[0085] Figure 8 Infrared emissivity diagrams of the porous radiative cooling materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 are shown. Comparative Example 1 exhibits weak LWIR emission, with an average emissivity of 83.46% within the atmospheric window (8-13 μm). In contrast, the porous radiative cooling material containing rutile titanium dioxide-coated mica filler demonstrates significantly improved infrared emissivity. This is attributed to the synergistic effect of selective molecular vibrations between TPU (C=O, NH) and TiO2@Mica-APTES (Si-O, Ti-O), establishing a new absorption-emission balance, resulting in a more complex curve shape and a stronger emission signal in the 8-13 µm atmospheric window region. Notably, Example 1, due to filler modification, achieves an average emissivity of 90.21%, a 6.75% increase compared to the TPU film.

[0086] Comparative Example 1

[0087] A porous material with radiative cooling properties, comprising:

[0088] 20 parts polymer matrix, 0 parts micro / nano filler, 0 parts modifier, 100 parts solvent.

[0089] The polymer matrix is ​​selected as thermoplastic polyurethane;

[0090] The solvent is N,N-dimethylformamide.

[0091] A method for preparing a porous material with radiative cooling properties includes the following steps:

[0092] (1) The polymer was placed in a solvent and stirred at 300 r / min to obtain a homogeneous mixture. The mixture was placed under negative pressure at room temperature. After the air bubbles in the mixture were completely removed, the coating thickness was adjusted to 600 μm by a scraper at room temperature. After coating, the film was immersed in a solvent and water mixture with a ratio of (6:4) for 15 min and then transferred to an aqueous solution for 24 h. Subsequently, it was dried at 40 ℃ for 6 h to obtain a porous radiative cooling material.

[0093] Comparative Example 2

[0094] A porous material with radiative cooling properties, comprising:

[0095] 20 parts polymer matrix, 6 parts micro / nano filler, 0 parts modifier, 100 parts solvent.

[0096] The polymer matrix is ​​selected as thermoplastic polyurethane;

[0097] The micro-nano filler is selected as rutile titanium dioxide coated mica sheet with an average particle size of 10~20μm.

[0098] The solvent is N,N-dimethylformamide.

[0099] A method for preparing a porous material with radiative cooling properties includes the following steps:

[0100] (1) By weight, the filler is placed in the solvent and fully dispersed in an ultrasonic vibration environment for 1 h. Then, a polymer is introduced and stirred at a speed of 300 r / min to obtain a mixture in which the filler is uniformly dispersed.

[0101] (2) Place the uniformly dispersed filler mixture obtained in step (1) under negative pressure at room temperature. After the bubbles in the mixture are completely removed, adjust the coating thickness to 600 μm by a scraper at room temperature. After coating into a film, immerse it in a solvent and water mixture with a ratio of (6:4) for 15 min, then transfer it to an aqueous solution for 24 h. Finally, dry it at 40 ℃ for 6 h to obtain the porous radiative cooling material.

[0102] Comparative Example 3

[0103] The preparation method involves dissolving 95 wt% polyurethane in N,N-dimethyldiamide and mixing it with 5 wt% hollow TiO2 microspheres, followed by thorough ultrasonic dispersion to obtain a hollow TiO2 microsphere / TPU composite. 10 g of the obtained hollow TiO2 microsphere / TPU composite is poured into a grooved mold and allowed to stand at room temperature for 10 minutes. The entire mold is then immersed in water to initiate phase separation. After 5 hours of phase separation, the film is removed from the mold and dried at 20°C for 24 hours to finally obtain a hierarchical porous TiO2-TPU radiation-cooling film. (Comparative document: CN 116813975 A 2023.08.01 A method for preparing a hierarchical porous radiation-cooling film material)

[0104] Comparative Example 4

[0105] The preparation method involves mixing 10g of TPU particles, 30g of PE particles, and 160g of ethyl acetate. The mixture is stirred at 40℃ until a homogeneous polyethylene solution is obtained. This solution is then mixed with 10wt% hollow silica microspheres and thoroughly ultrasonically dispersed to obtain a hollow SiO2 microsphere / PE composite. 10g of the obtained hollow SiO2 microsphere / PE composite is poured into a grooved mold and allowed to stand at room temperature for 40 minutes. The entire mold is then immersed in water to begin phase separation. After 10 hours of phase separation, the film is removed from the mold and dried at 60℃ for 48 hours to finally obtain a hierarchical porous SiO2-PE radiation-cooling film. (Comparative document: CN 116813975 A2023.08.01 A method for preparing a hierarchical porous radiation-cooling film material).

[0106] The average infrared emissivity and average UV-Vis-NIR reflectivity before and after aging of the materials prepared in the embodiments and comparative examples of the present invention are compared, and the results are detailed in Table 1.

[0107] Table 1. Average infrared emissivity and average UV-Vis-NIR reflectivity before and after aging of porous radiative cooling materials

[0108] Sample Name Average infrared emissivity (%) Average UV-Vis-NIR reflectance (%) Average UV-Vis-NIR reflectance (%) after 100 hours of aging Example 1 90.21 91.82 89.17 Example 2 88.15 92.33 87.47 Comparative Example 1 83.46 91.33 86.70 Comparative Example 2 83.65 92.61 85.82 Comparative Example 3 84 95 \ Comparative Example 4 84 92 \

[0109] According to the results in Table 1, Example 1 had an average infrared emissivity of 90.21% and an initial average UV-Vis-NIR reflectivity of 91.82%. After 100 hours of UV aging, the average UV-Vis-NIR reflectivity remained at 89.2%, with a full-spectrum reflectance attenuation of only 2.62 percentage points. Example 2 had an average infrared emissivity of 88.15% and an initial average UV-Vis-NIR reflectivity of 92.33%. After 100 hours of UV aging, the average UV-Vis-NIR reflectivity decreased to 85.8%, with a full-spectrum reflectance attenuation of 6.53 percentage points. Comparative Examples 1, 2, 3, and 4 all had average infrared emissivity of only 83-84% and initial average UV-Vis-NIR reflectivity of 91-95%, respectively, and no 100-hour UV aging performance test was conducted. The test results show that, compared with the comparative example, the embodiments of the present invention can significantly improve the infrared radiation heat dissipation capability of the thin film, while also possessing excellent UV aging resistance. In particular, Example 1 has both high infrared emission efficiency and extremely low solar full-band reflection attenuation amplitude, resulting in better radiation cooling stability under long-term outdoor conditions. Its overall performance is significantly better than the existing comparative formulation system.

[0110] It should be noted that the above description is only used to illustrate the preferred solution of the present invention and is not intended to limit the present invention. Although the foregoing embodiments have provided a detailed description of the present invention, those skilled in the art should know that any modifications or substitutions made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A porous material with radiative cooling properties, comprising: 1-50 parts of polymer; 0.1-20 parts of micro / nano fillers; Modifier 0.1~1 part; Solvent: 10-500 parts; of which: The average particle size of the micro / nano filler is 0.1-20 μm.

2. The porous radiative cooling material according to claim 1, wherein: The polymer is selected from any one of the following: polymethyl methacrylate, thermoplastic polyurethane, polyvinylidene fluoride, polylactic acid, and polydimethylsiloxane.

3. The porous radiative cooling material according to claim 1, wherein: The micro / nano filler is selected from any one or more of titanium dioxide, silicon dioxide, zinc oxide, aluminum oxide, and kaolin.

4. The porous radiative cooling material according to claim 1, wherein: The modifier is selected from any one of the following: γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, isopropyltris(dioctylphosphoyloxy)titanate, hexamethyldisilazane, n-octyltriethoxysilane, hexadecyltrimethoxysilane, and heptadecafluoro-1,1,2,2-tetradecyltrimethoxysilane.

5. The porous radiative cooling material according to claim 1, wherein: The solvent is selected from any one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, chloroform, toluene, and carbon tetrachloride.

6. A method for preparing a porous radiative cooling material according to any one of claims 1 to 5, comprising the following steps: (1) By weight, the modifier was placed in a mixed solution of water and ethanol for pre-hydrolysis, and then micro-nano fillers were introduced into the mixed solution system. The mixture was stirred under heating conditions. After the reaction was completed, the mixed solution was filtered, washed, and dried to obtain the reaction product. (2) Place 0.1 to 20 parts of the reaction product obtained in step (1) in a solvent, disperse it by ultrasonic vibration, then introduce the polymer and stir to mix, so as to obtain a mixture in which the filler is uniformly dispersed; (3) Place the mixture obtained in step (2) under negative pressure at room temperature. After the bubbles in the mixture are completely removed, adjust the coating thickness by scraping with a scraper at room temperature. After coating into a film, place it in a solvent and water mixture for 10-15 minutes and then transfer it to an aqueous solution for 24-48 hours. After drying, the porous radiation cooling material is obtained.

7. The preparation method according to claim 6, wherein: In step (1), the volume ratio of water to ethanol is 9:1, and the pre-hydrolysis time is 10~60 min; The stirring and mixing conditions under the heating conditions are: stirring and mixing at 50~80℃ for 3~6 h; The drying temperature is 40~60℃.

8. The preparation method according to claim 6, wherein: The ultrasonic oscillation dispersion time in step (2) is 1~2 h, and the stirring speed is 300~600 r / min.

9. The preparation method according to claim 6, wherein: The negative pressure condition in step (3) is < -0.8 MPa; The coating thickness is 400~1200 μm; The drying conditions are: drying at 30~60 ℃ for 4~8 h.

10. The preparation method according to claim 6, wherein: The volume ratio of the solvent to water mixture in step (3) is 6:4.

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