Composite porous radiative refrigeration film and preparation method thereof

Abstract

This invention relates to the field of daytime radiative cooling materials technology, and more particularly to a composite porous radiative cooling thin film and its preparation method. The composite porous radiative cooling thin film is mainly composed of four thin film layers bonded together sequentially from the outside to the inside: a solar reflective thin film layer, an infrared emitting thin film layer, an energy storage thin film layer, and a thermally enhanced thin film layer. This invention obtains a composite porous radiative cooling thin film through four thin film layers with different functions. The solar reflective thin film layer has the ability to reflect sunlight in the visible-near infrared region (0.5-2.5 μm), while the infrared emitting thin film layer can enhance the emission performance in the atmospheric window band range (8-13 μm), increasing the ability to exchange heat with cold sources in outer space; the energy storage thin film layer's energy storage phase change material can achieve thermal buffering and enhance the film's resistance to rapid thermal shock through phase change conversion; the thermally enhanced thin film layer can enhance the heat transfer between the film and the covering material, enhancing thermal conductivity to improve the rapid cooling effect.

Description

Technical Field

[0001] This invention relates to the field of daytime radiation cooling materials technology, and in particular to a composite porous radiation cooling thin film and its preparation method. Background Technology

[0002] Daytime radiative cooling technology refers to a passive cooling technique where an object, under direct sunlight, transfers heat directly to the cosmic low-temperature heat sink (3K) through thermal radiation. Its core breakthrough lies in simultaneously resolving the conflicting requirements of solar radiation reflection and atmospheric window emission, utilizing the infrared transparent window (atmospheric window) in the 8-13μm band of Earth's atmosphere to achieve net thermal radiation exchange with space. Since radiative cooling falls under the category of passive cooling, the cooling process does not involve energy consumption, which is conducive to achieving a sustainable, low-carbon thermal management model and mitigating the negative impacts of the greenhouse effect. However, limited by factors such as the selection of precise materials, structural design, and size control, the preparation of traditional radiative cooling films faces challenges such as high cost of large-scale production, insufficient durability, and poor resistance to thermal shock.

[0003] Therefore, existing technologies need to be improved. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a composite porous radiation cooling film and its preparation method, which aims to improve the radiation cooling performance while enhancing the thermal conductivity and heat storage capacity of the film.

[0005] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a composite porous radiation cooling film, comprising the following four film layers bonded together from the outside to the inside: The solar reflective thin film layer consists of a polymer porous substrate film and solar reflective nanoparticles filled inside; The infrared emitting thin film layer consists of a polymer porous substrate film and infrared emitting nanoparticles filled inside; The energy storage thin film layer consists of a polymer porous substrate thin film and energy storage nanoparticles filled inside; The thermally enhanced thin film layer consists of a polymer porous substrate film and thermally enhanced nanoparticles filled inside.

[0006] Optionally, the solar reflective nanoparticles include one or any combination of two of the following: titanium dioxide nanoparticles, alumina nanoparticles, and zirconium oxide nanoparticles.

[0007] Optionally, the infrared emitting thin film layer includes one or any combination of two of the following: silica nanoparticles, barium sulfate nanoparticles, polyvinylidene fluoride-hexafluoropropylene nanoparticles, and polyvinylidene fluoride nanoparticles.

[0008] Optionally, the energy storage nanoparticles include one or any combination of two of the following: paraffin, polyethylene glycol, fatty acid nanoparticles, and polyol nanoparticles.

[0009] Optionally, the thermally enhanced nanoparticles include one or any combination of two of the following: graphene nanoparticles, carbon nanotubes, alumina nanoparticles, and boron nitride nanoparticles.

[0010] Optionally, the polymer porous substrate film is prepared from one of polydimethylsiloxane, polyurethane, polyethylene, polystyrene, polyethylene terephthalate, and polymethyl methacrylate, and the pore size of the polymer porous substrate film is uniform.

[0011] Optionally, the mass ratio of solar reflective nanoparticles to polymer porous substrate film is (1-25):100; the mass ratio of infrared emitting nanoparticles to polymer porous substrate film is (1-25):100; the mass ratio of energy storage nanoparticles to polymer porous substrate film is (1-25):100; and the mass ratio of thermally conductive enhanced nanoparticles to polymer porous substrate film is (1-25):100.

[0012] Optionally, the particle size of the solar reflective nanoparticles, infrared emitting nanoparticles, energy storage nanoparticles, and thermally conductive enhanced nanoparticles is 10-1000 nm.

[0013] Optionally, the thickness of the composite porous radiation cooling film is 50-2000 μm.

[0014] Secondly, the present invention provides a method for preparing a composite porous radiation-cooling thin film, such as... Figure 2 As shown, it includes the following steps: S1. Prepare polymer porous substrate thin films; S2. Solar reflective nanoparticles, infrared emitting nanoparticles, energy storage nanoparticles, and thermally conductive enhanced nanoparticles are respectively filled onto a polymer porous substrate film to obtain a solar reflective film layer, an infrared emitting film layer, an energy storage film layer, and a thermally conductive enhanced film layer. S3. The obtained solar reflective film layer, infrared emitting film layer, energy storage film layer and thermally enhanced film layer are sequentially stacked and bonded to obtain the composite porous radiation cooling film.

[0015] Optionally, in S1, the preparation of the polymer porous substrate film includes the following steps: Polymer particles are dissolved together with low-boiling-point alcohol in a low-boiling-point solvent and stirred until the polymer particles are dissolved. Then, the mixture is poured into a mold and the temperature is controlled at 15-30℃ and the relative humidity at 40-95% to obtain a polymer porous substrate film.

[0016] Optionally, in step S2, filling the polymer porous substrate film with solar reflective nanoparticles, infrared emitting nanoparticles, energy storage nanoparticles, and thermally enhanced nanoparticles respectively includes the following steps: Solar reflective nanoparticles, infrared emitting nanoparticles, energy storage nanoparticles, and thermally conductive enhanced nanoparticles are respectively blended with low surface energy solutions (such as ethanol, acetone, etc.) to form solar reflective nanoparticle mixtures, infrared emitting nanoparticle mixtures, energy storage nanoparticle mixtures, and thermally conductive enhanced nanoparticle mixtures. These mixtures are then applied to a polymer porous substrate film.

[0017] Optionally, in S2, before sequentially stacking and bonding the obtained solar reflective film layer, infrared emitting film layer, energy storage film layer, and thermally enhanced film layer, the solar reflective film layer, infrared emitting film layer, energy storage film layer, and thermally enhanced film layer are respectively subjected to plasma surface treatment, so that hydrophilic groups are distributed on the surface of the solar reflective film layer, infrared emitting film layer, energy storage film layer, and thermally enhanced film layer.

[0018] Beneficial Effects: This invention provides a composite porous radiative cooling film and its preparation method. The composite porous radiative cooling film of this invention integrates four thin film layers with different functions: a solar reflective film layer, an infrared emitting film layer, an energy storage film layer, and a thermally enhanced film layer. The solar reflective film layer has reflective properties of sunlight in the visible-near-infrared region (0.5-2.5 μm), while the infrared emitting film layer enhances the emission performance in the atmospheric window band (8-13 μm), increasing the ability to exchange heat with cold sources in outer space. The energy storage film layer's energy storage phase change material can achieve thermal buffering and enhance the film's resistance to rapid thermal shock through phase change conversion. The thermally enhanced film layer enhances heat transfer between the film and the covering material, improving thermal conductivity and thus improving rapid cooling. The composite porous radiative cooling film can be attached to buildings, tents, factories, heat exchangers, and other objects requiring passive cooling, endowing them with passive zero-energy radiative cooling performance. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the composite porous radiation cooling film in Embodiment 1 of the present invention.

[0020] Figure 2 This is a diagram illustrating the preparation process of the composite porous radiation cooling film in Example 1 of the present invention.

[0021] Figure 3 This is a diagram showing the usage state of the composite porous radiation cooling film in Embodiment 1 of the present invention.

[0022] Figure 4 The images shown are scanning electron microscope (SEM) images of the polymer porous substrate film, the first monolayer film, and the composite porous radiation-cooling film prepared in Example 1 of this invention. (a) is an SEM image of the polymer porous substrate film, (b) is an SEM image of the first monolayer film, and (c) is an SEM image of the composite porous radiation-cooling film.

[0023] Figure 5 This is a graph showing the reflectance of the composite porous radiation-cooling thin film prepared in Example 1 of the present invention in the ultraviolet-visible-near-infrared region.

[0024] Figure 6 This is a diagram illustrating the cooling mechanism of a composite porous radiation-cooling thin film.

[0025] Figure 7 The figure shows the experimental results of the composite porous radiation cooling film prepared in Example 1 of the present invention used in an actual wooden board model.

[0026] Figure 8 This is a daytime outdoor radiation cooling effect test of the composite porous radiation cooling film prepared in Example 1 of the present invention. The upper part is a temperature-time variation graph; the lower part is a real-time solar power measurement. Detailed Implementation

[0027] This invention provides a composite porous radiation-cooling thin film and its preparation method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0028] Compared to traditional cooling methods, composite porous radiation-cooling films based on integrated structural and material design fall into the category of zero-energy consumption, offering significant advantages in mitigating the greenhouse effect and paving the way for sustainable development. Some organisms in nature possess unique multilayered structures on their surfaces. Due to the compositional differences between these multilayered structures, the gradient characteristics facilitate the reflection of specific wavelengths of light and enhance unidirectional thermal conductivity. By orderly stacking these structures, the organism's reflectivity to sunlight can be enhanced, thereby increasing its stability in thermal environments. Inspired by the periodic hierarchical micro / nano structures on the surfaces of some organisms resistant to extreme heat environments (such as the longhorn beetle), composite porous radiation-cooling films may be feasible for fabrication.

[0029] Based on this, this embodiment provides a composite porous radiation cooling thin film, such as... Figure 1 As shown, it consists of the following four thin film layers bonded together from the outside in: The solar reflective thin film layer consists of a polymer porous substrate film and solar reflective nanoparticles filled inside; The infrared emitting thin film layer consists of a polymer porous substrate film and infrared emitting nanoparticles filled inside; The energy storage thin film layer consists of a polymer porous substrate thin film and energy storage nanoparticles filled inside; The thermally enhanced thin film layer consists of a polymer porous substrate film and thermally enhanced nanoparticles filled inside.

[0030] It should be noted that the composite porous radiation cooling film of this embodiment comprises four thin film layers: a solar reflective film layer, an infrared emitting film layer, an energy storage film layer, and a thermally enhanced film layer. The solar reflective film layer enhances the reflection performance of sunlight in the visible-near-infrared region (0.5-2.5 μm), while the infrared emitting film layer enhances the emission performance in the atmospheric window band (8-13 μm), increasing the ability to exchange heat with cold sources in outer space. The energy storage film layer's energy storage phase change material can achieve thermal buffering and enhance the film's resistance to rapid thermal shock through phase change. The thermally enhanced film layer enhances heat transfer between the film and the covering material, improving thermal conductivity and thus improving rapid cooling. Since sunlight reflection occurs on the surface, infrared light emission has a certain degree of penetration and can occur in the sublayer. The phase change of the energy storage material mainly achieves energy conversion between layers, while the thermal enhancement mainly acts on the bonding area between the film and the substrate. Therefore, the four thin film layers in this embodiment must be arranged in a specified order. The composite porous radiative cooling film of this embodiment can be attached to buildings (such as...). Figure 3 The passive zero-energy radiative cooling performance is applied to objects requiring passive cooling, such as the outer surface of a wooden house or the outer surface of a wooden plank, tents, factories, and heat exchangers.

[0031] In some embodiments, the solar reflective nanoparticles include one or any combination of two of the following: titanium dioxide nanoparticles, alumina nanoparticles, and zirconium oxide nanoparticles.

[0032] It should be noted that the solar reflective thin film layer in this embodiment is composed of a polymer porous substrate film and solar reflective nanoparticles filled inside. The solar reflective nanoparticles include one or any combination of two of the following: titanium dioxide nanoparticles, alumina nanoparticles, and zirconium oxide nanoparticles. When the above-mentioned solar reflective nanoparticles (nanoparticles with high dielectric constant) are selected in this embodiment, it can be ensured that the solar reflective thin film layer has strong reflective performance in the ultraviolet / visible-near infrared region (0.3-2.5μm), thereby reducing the adverse effects of solar thermal conversion on film cooling during daytime radiative cooling.

[0033] In some embodiments, the infrared emitting thin film layer includes one or any combination of any two of the following: silica nanoparticles, barium sulfate nanoparticles, polyvinylidene fluoride-hexafluoropropylene nanoparticles, and polyvinylidene fluoride nanoparticles.

[0034] It should be noted that the solar reflective film layer in this embodiment is composed of a polymer porous substrate film and solar reflective nanoparticles filled inside; the infrared emitting film layer includes one or any combination of two of the following: silica nanoparticles, barium sulfate nanoparticles, polyvinylidene fluoride-hexafluoropropylene nanoparticles, and polyvinylidene fluoride nanoparticles. The solar reflective nanoparticles in this embodiment contain active groups, which can absorb light with a wavelength of 8-13 μm through the vibration and deflection of chemical bonds. According to Kirchhoff's law, this absorbed light will eventually be emitted again at its original wavelength, carrying away heat in the process. Selecting the above materials can enhance the emission performance of the radiative cooling film within the atmospheric window wavelength range (8-13 μm), thereby enhancing the daytime radiative cooling effect of the composite porous radiative cooling film.

[0035] In some embodiments, the energy storage nanoparticles include one or any combination of any two of the following: paraffin, polyethylene glycol, fatty acid, and polyol nanoparticles.

[0036] It should be noted that the energy storage thin film layer in this embodiment is composed of a polymer porous substrate film and energy storage nanoparticles filled inside; the energy storage nanoparticles include one or any combination of two of the following: paraffin, polyethylene glycol, fatty acid, and polyol nanoparticles. The energy storage nanoparticles in this embodiment have the characteristic of thermal shock phase transition transformation. They buffer rapid thermal shock through phase transition transformation and slowly restore the initial state through radiative cooling, thus overcoming the defect of traditional radiative cooling thin films that are not resistant to short-term rapid thermal shock.

[0037] In some embodiments, the thermally enhanced nanoparticles include one or any combination of two of the following: graphene nanoparticles, carbon nanotubes, alumina nanoparticles, and boron nitride nanoparticles.

[0038] It should be noted that the thermally enhanced thin film layer of this embodiment consists of a polymer porous substrate film and internally filled thermally enhanced nanoparticles. The thermally enhanced nanoparticles include one or any combination of two of the following: graphene nanoparticles, carbon nanotubes, alumina nanoparticles, and boron nitride nanoparticles. The thermally enhanced nanoparticles of this embodiment effectively compensate for the low thermal conductivity between traditional radiative cooling films and the object acting on them, thus improving continuous thermal conductivity.

[0039] In some embodiments, the polymer porous substrate film is prepared from one of polydimethylsiloxane, polyurethane, polyethylene, polystyrene, polyethylene terephthalate, and polymethyl methacrylate, and the polymer porous substrate film has a uniform pore size.

[0040] In some embodiments, the mass ratio of solar-reflecting nanoparticles to the polymer porous substrate film is (1-25):100, for example, it can be 1:100, 5:100, 10:100, 15:100, 20:100, or 25:100; the mass ratio of infrared-emitting nanoparticles to the polymer porous substrate film is (1-25):100, for example, it can be 1:100, 5:100, 10:100, 15:100, or 20:100. The mass ratio of energy storage nanoparticles to the polymer porous substrate film is (1-25):100, for example, it can be 1:100, 5:100, 10:100, 15:100, 20:100, or 25:100; the mass ratio of thermally conductive nanoparticles to the polymer porous substrate film is (1-25):100, for example, it can be 1:100, 5:100, 10:100, 15:100, 20:100, or 25:100. In this embodiment, the mass ratio of nanoparticles to the polymer porous substrate film is (1-25):100. If the ratio is too low, the effect will not be achieved; if the ratio is too high, the pores will not be able to hold the particles.

[0041] In some embodiments, the particle size of the solar reflective nanoparticles, infrared emitting nanoparticles, energy storage nanoparticles, and thermally conductive enhanced nanoparticles is 10-1000 nm, for example, it can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, etc.

[0042] In some embodiments, the thickness of the composite porous radiation cooling film is 50-2000 μm, for example, it can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, or 2000 μm.

[0043] This embodiment also provides a method for preparing a composite porous radiation-cooling thin film, such as... Figure 2 As shown, it includes the following steps: S1. Prepare polymer porous substrate thin films; S2. Solar reflective nanoparticles, infrared emitting nanoparticles, energy storage nanoparticles, and thermally conductive enhanced nanoparticles are respectively filled onto a polymer porous substrate film to obtain a solar reflective film layer, an infrared emitting film layer, an energy storage film layer, and a thermally conductive enhanced film layer. S3. The obtained solar reflective film layer, infrared emitting film layer, energy storage film layer and thermally enhanced film layer are sequentially stacked and bonded to obtain the composite porous radiation cooling film.

[0044] In some embodiments, in S1, the preparation of the polymer porous substrate film includes the following steps: Polymer particles are dissolved together with low-boiling-point alcohol in a low-boiling-point solvent and stirred until the polymer particles are dissolved. Then, the mixture is poured into a mold and the temperature is controlled at 15-30℃ and the relative humidity at 40-95% to obtain a polymer porous substrate film.

[0045] It should be noted that in this embodiment, polymer particles are mixed with a low-boiling-point alcohol and then dissolved together in a low-boiling-point solvent to form a mixed solution. This involves introducing a low-boiling-point solvent into the mixed solution. During solvent evaporation, the low-boiling-point component interacts with the ordered water droplet array formed by water vapor condensation, resulting in a more regularly shaped, tunable pore size density, and reduced dependence on high humidity. The polymer mass fraction in the polymer solution is 1%-25%, for example, 1%, 5%, 10%, 15%, 20%, or 25%, etc., and the mass fraction of the low-boiling-point component is 0.1%-5%, for example, 0.1%, 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, or 5.0%, etc.

[0046] It should be noted that the polymer described in this embodiment is readily soluble in low-boiling-point solvents to form a polymer solution, and the low-boiling-point alcohol is also readily soluble in low-boiling-point solvents. When the polymer solution is in a high-temperature and high-humidity environment, the surface of the polymer solution cools down due to solvent evaporation, causing water vapor to condense and form an ordered array of water droplets. The water droplets act as dynamic templates to guide the assembly of polymer molecules, leaving a honeycomb-like porous structure after evaporation. The polymer mass fraction in the polymer solution is 1%-25%, for example, it can be 1%, 5%, 10%, 15%, 20%, or 25%. The low-boiling-point solvent can be dichloromethane, trichloromethane, carbon disulfide, etc. The mass fraction of the low-boiling-point alcohol (such as ethanol, ethylene glycol, 1,3-propanediol, glycerol, 1,4-butanediol, etc.) is 0.1%-5%, for example, it can be 0.1%, 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, or 5.0%. Too low or too high a proportion of low-boiling-point alcohol can easily form a non-porous structure, failing to achieve the desired effect.

[0047] In some embodiments, step S2, filling the polymer porous substrate film with solar reflective nanoparticles, infrared emitting nanoparticles, energy storage nanoparticles, and thermally conductive enhanced nanoparticles, respectively, includes the following steps: Solar reflective nanoparticles, infrared emitting nanoparticles, energy storage nanoparticles, and thermally conductive enhanced nanoparticles are respectively blended with low surface energy solutions (such as ethanol, acetone, etc.) to form solar reflective nanoparticle mixtures, infrared emitting nanoparticle mixtures, energy storage nanoparticle mixtures, and thermally conductive enhanced nanoparticle mixtures. These mixtures are then applied to a polymer porous substrate film.

[0048] It should be noted that a mixture of low surface energy solution and solar reflective nanoparticles, infrared emitting nanoparticles, energy storage nanoparticles, and thermally conductive enhanced nanoparticles is formed. Due to the introduction of the low surface energy solution, the mixture is easier to spread. Therefore, a doctor blade can be used to apply the mixture of solar reflective nanoparticles, infrared emitting nanoparticles, energy storage nanoparticles, and thermally conductive enhanced nanoparticles onto the polymer porous substrate film.

[0049] In some embodiments, in S2, before the obtained solar reflective film layer, infrared emitting film layer, energy storage film layer and thermally enhanced film layer are sequentially stacked and bonded, the solar reflective film layer, infrared emitting film layer, energy storage film layer and thermally enhanced film layer are first subjected to plasma surface treatment.

[0050] It should be noted that plasma surface treatment ensures that hydrophilic groups are distributed on the surfaces of the solar reflective film layer, infrared emitting film layer, energy storage film layer, and thermal conductivity enhancement film layer. Then, an adhesive is uniformly coated onto the surface of each single-layer film, ensuring complete wetting. The four film layers with different functions are then neatly arranged in sequence and bonded together. Applying a certain external force enhances the bonding strength. After one hour of bonding, a composite porous radiation cooling film is obtained.

[0051] The present invention will be further described below through specific embodiments.

[0052] Example 1 This embodiment provides a method for preparing a composite porous radiation-cooling thin film, comprising the following steps: Preparation of a polymer porous substrate film: 5g of impact-resistant polystyrene was added to 100mL of dichloromethane solution. The solution was stirred at 1000rpm for 2 hours until the polystyrene was completely dissolved. 1g of 1,3-propanediol was added to the solution, and the mixture was stirred at 1000rpm for 1 hour. 20mL of the solution was poured evenly into an 8×8cm polytetrafluoroethylene mold. The reaction was carried out at 25℃ and 85% humidity for 3 hours to allow natural evaporation and obtain the polymer porous substrate film. The resulting polymer porous substrate film is shown below. Figure 4 As shown in Figure (a), it can be seen from Figure (a) that there are uniform pores on the surface of the thin film.

[0053] Titanium dioxide nanoparticles, silica nanoparticles, polyvinyl alcohol 800, and hexagonal boron nitride particles were added to an ethanol solution at a mass ratio of 1:10. Sodium dodecyl sulfate (0.05% by mass) was added as a surfactant, and the mixture was stirred thoroughly for 1 hour to ensure uniform dispersion. The uniformly dispersed nanoparticle solution was then applied to a porous polymer substrate film. Using a 250-micron doctor blade, the mixture was slowly coated three times and allowed to stand for 30 minutes to dry, thus forming different monolayer films (i.e., solar reflective film layer, infrared emitting film layer, energy storage film layer, and thermally enhanced film layer). Figure 4 Image (b) is a scanning electron microscope image of the first monolayer film, showing that nanoparticles are filled into the pores of the polymer porous substrate film.

[0054] Plasma modification was used to imbue the surfaces of each monolayer film (i.e., the solar reflective film layer, the infrared emitting film layer, the energy storage film layer, and the thermally enhanced film layer) with hydrophilic groups. Ethyl cyanoacrylate adhesive was then coated onto each of the modified monolayer films, and the coating was uniformly applied using a spin coater. The films were then vacuum-treated in a vacuum oven for 15 minutes to obtain bonded monolayer films. A hot press was then applied at room temperature with a pressure of 10 MPa to tightly bond the four monolayer films together. After 24 hours of curing, the composite porous radiation-cooling film was obtained, as shown in the figure. Figure 4 As shown in (c).

[0055] The composite porous radiation cooling film prepared in Example 1 has in-situ modification capabilities and can be directly modified on wood. A photograph of the actual product is shown below. Figure 3 The image shows photographs illustrating the formation of a composite porous radiation cooling film on wooden boards and log cabins. It can be seen that the finished wood surfaces exhibit a regular, snow-white color.

[0056] The scanning electron microscope characterization results of the steps of the preparation method described in Example 1 are as follows: Figure 4 As shown. Figure 4 The surface morphology results of the polymer porous substrate film, the first monolayer film, and the composite porous radiation-cooling film are presented. It can be observed that the pore size of the polymer porous substrate film is between 5 and 10 micrometers, with a uniform and dense pore distribution. In the monolayer film, nanoparticles are uniformly distributed and completely fill the pores. In the composite porous radiation-cooling film, the interfaces of the four monolayer films are clear and firmly bonded, with an overall thickness of approximately 400 micrometers.

[0057] The reflectance results of the composite porous radiation-cooling thin film prepared in Example 1 in the ultraviolet-visible-near-infrared regions are as follows: Figure 5 As shown, the gray background on the left represents the relationship between sunlight intensity and wavelength, while the gray background on the right represents the atmospheric transmission of light of a specific wavelength within the atmospheric window. It is evident that the radiation-cooling film exhibits strong reflectivity in the ultraviolet-visible-near-infrared region, with a comprehensive reflectivity of over 96.4% for sunlight. Simultaneously, within the wavelength range corresponding to the atmospheric window (8-13 μm), the radiation-cooling film exhibits an absorption / emission rate of up to 97%.

[0058] The cooling mechanism of the composite porous radiation-cooling thin film prepared in Example 1 is as follows: Figure 6 As shown. Where, P 太阳 This represents the power that the sun provides to the thin film through light radiation during daytime radiative cooling. P 热辐射 This represents the heat emitted outward through the blackbody radiation mode. P 大气辐射 P represents the radiative heat of the atmosphere on the thin film. 传导+对流This represents heat conduction and heat convection. According to the laws of thermodynamics, the radiative cooling power P... 制冷功率 =P 热辐射 -P 太阳 -P 大气辐射 -P 传导+对流 Based on the excellent solar reflectivity and atmospheric window reflectivity of the radiative cooling film described in Example 1, the film has a strong radiative cooling effect.

[0059] The composite porous radiation-cooling thin film prepared in Example 1 was used for a simulated test in a real house. The test was conducted at midday on a sunny summer day with an average solar irradiance of 837 W·m⁻¹. 2 ( Figure 7 ). Specific photos of the actual product are as follows. Figure 7 As shown, from left to right, the control group consists of wooden boards, and the experimental group consists of wooden boards covered with single-layer (solar reflective layer), double-layer (solar reflective and infrared emission), triple-layer (solar reflective, infrared emission, and energy storage layer), and quadruple-layer (the composite porous radiation cooling film of this embodiment). Both the control and experimental group cabin models were placed under sunlight to allow them to receive ample natural sunlight. Thermocouples were inserted into the surface of the wooden boards to monitor the temperature change over time in real time. Infrared thermal imaging was used to visualize the surface temperature changes of the wooden boards. The results are shown below. Figure 8 As shown, this is a test diagram of the daytime outdoor radiative cooling effect of the radiative cooling film prepared in Example 1 of the present invention. Figure 8 The top center is a temperature-time variation graph; Figure 8 Real-time solar power was measured. The results showed that under 8 hours of irradiation, the composite porous radiation cooling film of this embodiment achieved a temperature difference of up to 10.4°C compared with the control group, single-layer, double-layer and triple-layer films, demonstrating that the composite porous radiation cooling film prepared in Example 1 has excellent radiation cooling effect.

[0060] In summary, this invention provides a composite porous radiative cooling film and its preparation method. The composite porous radiative cooling film of this invention integrates four thin film layers: a solar reflective film layer, an infrared emitting film layer, an energy storage film layer, and a thermally enhanced film layer, resulting in a composite porous radiative cooling film. The solar reflective film layer exhibits excellent solar reflectivity in the visible-near-infrared region (0.5-2.5 μm), while the infrared emitting film layer enhances radiative performance within the atmospheric window wavelength range (8-13 μm), increasing the ability to exchange heat with cold sources in outer space. The energy storage film layer's energy storage phase change material can achieve thermal buffering and enhance the film's resistance to rapid thermal shock through phase change conversion. The thermally enhanced film layer enhances heat transfer between the film and the covering material, improving thermal conductivity and thus improving rapid cooling effects. This composite porous radiative cooling film can be attached to buildings, tents, factories, heat exchangers, and other objects requiring passive cooling, endowing them with passive, zero-energy radiative cooling performance.

[0061] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A composite porous radiation cooling thin film, characterized in that, It is mainly composed of the following four thin film layers bonded together from the outside to the inside: The solar reflective thin film layer consists of a polymer porous substrate film and solar reflective nanoparticles filled inside; The infrared emitting thin film layer consists of a polymer porous substrate film and infrared emitting nanoparticles filled inside; The energy storage thin film layer consists of a polymer porous substrate thin film and energy storage nanoparticles filled inside; The thermally enhanced thin film layer consists of a polymer porous substrate film and thermally enhanced nanoparticles filled inside.

2. The composite porous radiation cooling thin film according to claim 1, characterized in that, The solar reflective nanoparticles include one or any combination of two of the following: titanium dioxide nanoparticles, aluminum oxide nanoparticles, and zirconium oxide nanoparticles. The infrared emitting thin film layer includes one or any combination of any two of the following: silica nanoparticles, barium sulfate nanoparticles, polyvinylidene fluoride-hexafluoropropylene nanoparticles, and polyvinylidene fluoride nanoparticles. The energy storage nanoparticles include one or any combination of two of the following: paraffin, polyethylene glycol, fatty acid and polyol nanoparticles. The thermally enhanced nanoparticles include one or any combination of two of the following: graphene nanoparticles, carbon nanotubes, alumina nanoparticles, and boron nitride nanoparticles.

3. The composite porous radiation cooling thin film according to claim 1, characterized in that, The polymer porous substrate film is prepared from one of polydimethylsiloxane, polyurethane, polyethylene, polystyrene, polyethylene terephthalate, and polymethyl methacrylate, and the pore size of the polymer porous substrate film is uniform.

4. The composite porous radiation cooling thin film according to claim 1, characterized in that, The mass ratio of the solar reflective nanoparticles to the polymer porous substrate film is (1-25):100; the mass ratio of the infrared emitting nanoparticles to the polymer porous substrate film is (1-25):100; the mass ratio of the energy storage nanoparticles to the polymer porous substrate film is (1-25):100; and the mass ratio of the thermally conductive enhanced nanoparticles to the polymer porous substrate film is (1-25):

100.

5. The composite porous radiation cooling thin film according to claim 1, characterized in that, The particle sizes of solar reflective nanoparticles, infrared emitting nanoparticles, energy storage nanoparticles, and thermally conductive enhanced nanoparticles range from 10 to 1000 nm.

6. The composite porous radiation cooling thin film according to claim 1, characterized in that, The thickness of the composite porous radiation cooling film is 50-2000 μm.

7. A method for preparing a composite porous radiation-cooling thin film according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Prepare polymer porous substrate thin films; S2. Solar reflective nanoparticles, infrared emitting nanoparticles, energy storage nanoparticles, and thermally conductive enhanced nanoparticles are respectively filled onto a polymer porous substrate film to obtain a solar reflective film layer, an infrared emitting film layer, an energy storage film layer, and a thermally conductive enhanced film layer. S3. The obtained solar reflective film layer, infrared emitting film layer, energy storage film layer and thermally enhanced film layer are bonded and stacked in sequence to obtain the composite porous radiation cooling film.

8. The preparation method according to claim 7, characterized in that, In S1, the preparation of the polymer porous substrate film includes the following steps: Polymer particles are dissolved together with low-boiling-point alcohol in a low-boiling-point solvent and stirred until the polymer particles are dissolved. Then, the mixture is poured into a mold and the temperature is controlled at 15-30℃ and the relative humidity at 40-95% to obtain a polymer porous substrate film.

9. The preparation method according to claim 7, characterized in that, In S2, the process of filling solar reflective nanoparticles, infrared emitting nanoparticles, energy storage nanoparticles, and thermally conductive enhanced nanoparticles onto a polymer porous substrate film includes the following steps: Solar reflective nanoparticles, infrared emitting nanoparticles, energy storage nanoparticles, and thermally conductive enhanced nanoparticles were respectively blended with a low surface energy solution to form solar reflective nanoparticle mixtures, infrared emitting nanoparticle mixtures, energy storage nanoparticle mixtures, and thermally conductive enhanced nanoparticle mixtures, which were then deposited on a polymer porous substrate film.

10. The preparation method according to claim 7, characterized in that, In S2, before the obtained solar reflective film layer, infrared emitting film layer, energy storage film layer and thermally enhanced film layer are sequentially stacked and bonded, the solar reflective film layer, infrared emitting film layer, energy storage film layer and thermally enhanced film layer are first subjected to plasma surface treatment.

Images