Porous P (VDF-HFP) radiation refrigeration film with night heat preservation function as well as preparation method and application of porous P (VDF-HFP) radiation refrigeration film
A porous radiation cooling membrane was prepared by mixing P(VDF-HFP) with SiO2 aerogel particles and treating it with surfactants. This solved the problem of heat preservation in extreme environments and achieved the dual function of cooling during the day and heat preservation at night. It also broke through the stability and cost problems of SiO2 aerogel particles in preparation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUAZHONG UNIV OF SCI & TECH
- Filing Date
- 2026-03-10
- Publication Date
- 2026-05-15
AI Technical Summary
Existing radiation cooling films cannot meet the insulation requirements of cold nights in extreme environments with large day-night temperature differences. Furthermore, SiO2 aerogel particles are prone to breakage or aggregation during the preparation process, resulting in high production costs and making them difficult to apply to environments with drastic temperature changes.
P(VDF-HFP) acetone solution is mixed with SiO2 aerogel particles, and a surfactant is added. By controlling the stirring time and humidity conditions, a porous radiation cooling film is formed. Combining the micro-nano structure of SiO2 aerogel particles and the phase separation of the polymer film, the heat preservation function at night is achieved.
The prepared porous P(VDF-HFP) radiation cooling film exhibits radiative cooling during the day and heat preservation at night, with extremely low thermal conductivity, making it suitable for extreme environments with drastic temperature changes. This achieves bidirectional thermal management and reduces manufacturing costs.
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Figure CN122037286A_ABST
Abstract
Description
Technical Field
[0001] This invention pertains to radiation cooling materials, specifically a porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function, its preparation method, and its application. Background Technology
[0002] Currently, air conditioning and central heating are typical methods of cooling and heating, which result in significant energy waste when cooling or heating large spaces. Therefore, adopting green and sustainable energy technologies in the cooling and heating sectors is crucial for alleviating the energy crisis and reducing greenhouse gas emissions.
[0003] Passive radiative cooling technology can radiate heat into outer space without consuming external energy, showing great potential in addressing the growing energy crisis and the greenhouse effect. However, current radiative cooling films only have a single function of continuous radiative cooling throughout the day, and cannot meet people's needs for warmth on cold nights in extreme environments with drastic temperature changes. For example, patent CN117986672A invented a microporous polymer radiation cooling film prepared using polymers, inorganic oxides, phase change microcapsules, lubricants, and antioxidants. The polymer film prepared in Example 23 achieved a cooling effect of 10°C. Patent CN117164939A invented a micro-nano porous-particulate composite radiation cooling thin film coating prepared using polymer / silane, curing agent / binder / initiator, and dielectric particles. The thin film coating prepared by this invention achieved a cooling effect exceeding 15°C under direct sunlight during the day. Patent CN115928323A invented a PVDF-HFP / PDMS composite fiber membrane with high radiation cooling performance prepared using polyvinylidene fluoride hexafluoropropylene and dimethylsiloxane. This composite membrane achieved a cooling effect of 738 W / m 2 Under sunlight, a cooling effect of 6.4℃ was achieved, and when there is no sunlight at night, a cooling effect of about 7.1℃ can be achieved. Although the aforementioned reported radiative cooling devices have excellent cooling effects, they all only have a single function of continuous day and night cooling. In areas with large temperature differences between day and night, single-function passive radiative cooling films cannot meet people's needs for nighttime heat preservation. In addition, the composite film preparation method of patent CN114702712A does not perform surface activity treatment on SiO2 aerogel particles, which can easily lead to the breakage or aggregation of SiO2 aerogel particles during stirring; the multilayer radiative cooling device of patent CN117804093A uses noble metals and photonic crystal structures, which has high manufacturing costs and complex preparation processes.
[0004] In addition, traditional nighttime insulation methods rely on energy-intensive active heaters, which not only require additional power supply systems but also increase carbon emissions. Summary of the Invention
[0005] To address the shortcomings of most currently prepared radiation-cooling films, such as continuous cooling at night, which fails to meet the insulation needs of people in temperate continental climates with large diurnal temperature differences, this invention provides a porous P(VDF-HFP) radiation-cooling film with nighttime insulation function, its preparation method, and its application. The porous P(VDF-HFP) radiation-cooling film with nighttime insulation function prepared by the method of this invention ensures both radiation cooling in high-temperature environments during the day and energy-free insulation in cold environments at night, achieving a dual-function integration of daytime radiation cooling and nighttime heat insulation. This solves the problems of thermal management and energy consumption in extreme environments with drastic temperature changes, and also overcomes the technical defects of traditional radiation-cooling films, which are difficult to apply effectively in extreme environments with drastic temperature changes. A low-cost, easy-to-operate, and mass-producible radiation-cooling film with nighttime insulation function has been designed and prepared.
[0006] The technical objectives of this invention also include: a) overcoming the shortcomings of current radiation cooling films, such as single function and high manufacturing cost; b) overcoming the problem of SiO2 aerogel particles being easily broken or aggregated in the preparation process; c) overcoming the bottleneck that radiation cooling materials are difficult to apply in extreme environments with drastic temperature changes, so as to obtain radiation cooling films with extremely low thermal conductivity (greatly reducing the heat transfer rate) for application in extreme environments with drastic temperature changes, such as space.
[0007] Based on the above technical objectives, the present invention adopts the following technical solution: This invention protects a method for preparing a porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function, comprising the following steps: When the acetone solution of P(VDF-HFP) is mixed with SiO2 aerogel particles for 0 min to 60 min, a surfactant is added and the mixture is stirred until homogeneous to obtain a suspension.
[0008] The suspension and water are alternately sprayed onto the substrate. At this time, the non-solvent water and the solvent acetone evaporate through non-solvent exchange. The solute in the suspension eventually forms a porous membrane. After drying, a porous P (VDF-HFP) radiation cooling membrane with nighttime heat preservation function is loaded onto the substrate surface.
[0009] Preferably, the acetone solution of P(VDF-HFP) is prepared by dissolving P(VDF-HFP) powder in acetone, and the mass percentage of P(VDF-HFP) powder in the acetone solution is 5wt%~30wt%. If there is too much P(VDF-HFP), the viscosity of the acetone solution of P(VDF-HFP) will increase, making it difficult to spray from the spray gun and easily clogging the nozzle; if there is too little P(VDF-HFP), the viscosity of the acetone solution of P(VDF-HFP) will be low, making it easy to spray from the spray gun, but difficult to form a film on the substrate.
[0010] Preferably, the volume ratio of P(VDF-HFP) powder to SiO2 aerogel particles is 100:30~70. The volume ratio is determined by weighing different amounts of the two materials based on their densities provided by the manufacturers.
[0011] Preferably, the surfactant is selected from Triton X-100, Tween-80, or Brij-35.
[0012] Preferably, the mass ratio of surfactant to SiO2 aerogel particles is 1:0.2~1.2, and the mass ratio of surfactant to suspension is 0.4~0.6:100. When there is too little surfactant, there are insufficient surfactant molecules to protect the SiO2 aerogel particles, making them easily broken during stirring, thus failing to achieve particle size control and affecting the reflectivity in the solar radiation band. When there is too much surfactant, it will change the thermodynamic state of the P(VDF-HFP) acetone solution, affecting the non-solvent exchange phase separation process and pore formation.
[0013] Preferably, the substrate is selected from fabrics, such as polyester, linen, and cotton, and a porous P (VDF-HFP) radiation cooling film with nighttime heat preservation function is loaded on the substrate surface to obtain a porous radiation cooling film.
[0014] Preferably, the spraying is done using a manual electrostatic spray gun or an automatic electrostatic spray gun.
[0015] Preferably, the non-solvent exchange method involves alternately spraying a suspension and water onto a substrate, ensuring the ambient humidity is greater than 50%, and then using water and acetone for non-solvent exchange. When the humidity is less than 50%, the non-solvent water and solvent acetone cannot fully exchange, resulting in fewer pores and hindering sunlight scattering, leading to lower reflectivity in the solar spectrum. In this process, under high humidity, the acetone solvent and non-solvent water exchange and evaporate, ultimately forming a porous membrane. The purpose of spraying water is to increase the ambient humidity, allowing water vapor to exchange with the acetone.
[0016] This invention also protects a porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function, characterized in that the porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function prepared by the above preparation method has a porosity of 50%~70%.
[0017] This invention also protects the application of porous P(VDF-HFP) radiation cooling membranes with nighttime heat preservation function in the preparation of radiation cooling materials.
[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The porous P(VDF-HFP) radiative cooling membrane with nighttime heat preservation function of the present invention uses acetone solution of P(VDF-HFP) and SiO2 aerogel particles as raw materials. When the two are mixed and stirred for 0 min to 60 min, a surfactant is added and mixed evenly. The longer the surfactant is added, the more fragmented the SiO2 aerogel particles are during the stirring process. As a result, the particle size of SiO2 aerogel particles is not controlled within 0.5 μm to 2.5 μm, which prevents effective scattering of sunlight through the Mie scattering effect, resulting in a relatively low solar reflectivity.
[0019] The porous structure formation principle of the porous P(VDF-HFP) radiative cooling membrane with nighttime heat preservation function of this invention is as follows: Under high humidity environment, acetone solvent and water vapor undergo non-solvent interdiffusion and form a double diffusion process. As diffusion proceeds, the polymer membrane system changes from a thermodynamically stable state to an unstable state, resulting in phase separation and obtaining a polymer-rich phase and a polymer-poor phase. The polymer-rich phase further solidifies into a pore support, and after drying, the polymer-poor phase forms pores. The difference in phonon modes at the solid-solid and solid-gas phase interfaces inside the polymer membrane can increase the interfacial thermal resistance, thereby reducing the thermal conductivity of the porous P(VDF-HFP) radiative cooling membrane with nighttime heat preservation function and improving its heat preservation performance.
[0020] According to the theory of Mie scattering, sunlight incident on the surface of micropores and particles of the same size will produce strong scattering. The porous P(VDF-HFP) radiation-cooling film with nighttime heat preservation function can scatter a large amount of sunlight. By controlling the addition time of surfactant, the particle size of SiO2 aerogel particles can be controlled, thus ensuring that the size of the doped SiO2 aerogel particles also meets the scattering conditions of Mie scattering, further enhancing the reflection effect. Since the micro-nano structure of SiO2 aerogel particles is composed of a large number of nano-sized pores, according to the principle of Rayleigh scattering, pores of this size can strongly scatter ultraviolet light, thereby enhancing the overall reflection effect of the solar light band. Therefore, the porous P(VDF-HFP) radiation-cooling film with nighttime heat preservation function prepared by the method of this invention has extremely high solar light band reflectivity.
[0021] The Knudsen diffusion effect describes the diffusion of gas molecules within pores with pore sizes close to or smaller than the mean free path of the gas molecules, resulting from frequent collisions between molecules and pore walls. Based on the Knudsen diffusion effect, micro / nano porous structures can increase the collision frequency between gas molecules and pore walls, blocking heat transfer, inhibiting heat conduction paths, and effectively reducing the heat conduction rate of the bulk phase. Therefore, the porous P(VDF-HFP) radiative cooling film with nighttime heat preservation function prepared using the method of this invention exhibits extremely low thermal conductivity, thereby achieving the nighttime heat preservation function.
[0022] This invention selects P(VDF-HFP) and SiO2 aerogel particles as raw materials. The carbon-hydrogen bonds, carbon-fluorine bonds, and silicon-oxygen bonds contained in P(VDF-HFP) exhibit strong absorption peaks in the atmospheric window wavelength range (8μm~13μm). According to Kirchhoff's law of thermal radiation, absorptivity equals emissivity. Therefore, the porous P(VDF-HFP) radiative cooling film with nighttime heat preservation function prepared using the method of this invention has extremely high emissivity in the atmospheric window wavelength range. According to the theory of radiative cooling, the heat of an object can pass through the 8μm~13μm atmospheric window and radiate to a 3K outer space cold source. Therefore, an object with high emissivity and high solar reflectivity in the atmospheric window can minimize absorption of daytime solar energy input while radiating heat back into space, thus achieving passive radiative cooling below ambient temperature during the day.
[0023] 2. The innovation of this invention compared with the prior art lies in: (1) This invention innovatively proposes and develops a thermal management technology that takes into account both thermal radiation and thermal conduction, so that the thermal management material has both high-performance high-temperature cooling and low-temperature insulation functions, and achieves bidirectional thermal management in extreme environments with drastic temperature changes.
[0024] (2) This invention innovatively develops a porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function, which has a thermal conductivity of 0.035W / (m·K) and can effectively block heat flow, enabling the radiation cooling film to be effectively used in extreme environments such as space where temperature changes are drastic.
[0025] (3) The present invention innovatively introduces surfactants in the preparation process, and achieves structural protection and particle size control of SiO2 aerogel particles by controlling the addition time of activator, thereby improving the porosity of porous P(VDF-HFP) radiation cooling membrane with nighttime heat preservation function.
[0026] (4) The present invention innovatively sprays a porous P (VDF-HFP) radiation cooling film with nighttime heat preservation function onto the surface of fabrics such as cotton, linen, and polyester, which can be used for thermal management in specific scenarios such as outdoor tents.
[0027] 3. Compared with the prior art, the advantages of the present invention are: (1) The porous P(VDF-HFP) radiation cooling film of the present invention has the function of heat preservation at night, which breaks through the problem of the single function of continuous cooling throughout the day of the existing radiation cooling film and realizes the dual function integration of heat insulation and radiation cooling.
[0028] (2) In view of the fact that the current porous radiation cooling film only regulates the temperature from the perspective of single thermal radiation, the present invention introduces a low thermal conductivity function to combine thermal conduction and thermal transfer for thermal management.
[0029] (3) The current application scenarios of radiation cooling films are limited to terrestrial environments with small day-night temperature differences. Since the radiation cooling film prepared by this invention has extremely low thermal conductivity and can block heat flow transfer, it can be applied in terrestrial environments with large day-night temperature differences and space environments with drastic temperature changes, thus meeting the application requirements in extreme environments with drastic temperature changes.
[0030] (4) In view of the shortcomings of the current radiation cooling film preparation process using SiO2 aerogel particles, the structural stability of SiO2 aerogel particles has never been considered. The present invention adds a surfactant to the technical solution to maintain the stability of the structure of some SiO2 aerogel particles and retain some of the characteristics of SiO2 aerogel. This is beneficial to ensure the stability of the optical and thermal properties of the porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function.
[0031] (5) The technical solution of the present invention uses all commercially mature raw materials, and the preparation process adopts simple blending solution and electro-spraying processing technology, realizing the large-scale preparation of radiation cooling film with nighttime heat preservation function, and providing a low-cost method for preparing radiation cooling film with nighttime heat preservation function. Attached Figure Description
[0032] Figure 1 This is a schematic diagram illustrating the structure and function of the porous radiative cooling membrane designed for this invention, which combines daytime radiative cooling and nighttime heat preservation.
[0033] Figure 2 The images show actual photos of the porous radiation cooling films used in Examples 1, 7, and 8.
[0034] Figure 3 Cross-sectional scanning electron microscope images of porous P(VDF-HFP) radiation cooling films with nighttime heat preservation function in Examples 1, 6, and 2.
[0035] Figure 4The reflection and emission spectra of the porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function in Example 1 are shown in the wavelength range of 0.28μm to 15μm.
[0036] Figure 5 The temperature tracking curve of the porous P(VDF-HFP) radiative cooling film with nighttime heat preservation function in Example 1 is shown as a whole day under the condition of isolated convection exchange (Hongshan District, Wuhan, July 7, 2024, 15:45 to July 8, 2024, 15:45). Detailed Implementation
[0037] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.
[0038] The P(VDF-HFP) powder of this invention was purchased from Mingsen Plastics Co., Ltd., model Arkoma 2801; the surfactant was Aladdin, model Triton X-100; the SiO2 aerogel particles were purchased from Tuwang Technology Co., Ltd., with a particle size of 15μm~50μm; the sprayer was Prijet, model SG9618ST.
[0039] Regarding the technical objectives of this invention, a) this invention provides a low-cost method for preparing a radiation-cooling film with nighttime heat preservation function, overcoming the shortcomings of current radiation-cooling films that have single function and high manufacturing cost; b) this invention innovatively adds a surfactant to the preparation process, and by controlling the time of surfactant addition, effectively adjusts the particle size of SiO2 aerogel particles to 0.5μm~2.5μm, overcoming the problem that SiO2 aerogel particles are easily broken or aggregated in the preparation process; c) the porous P(VDF-HFP) radiation-cooling film with nighttime heat preservation function prepared by the method of this invention overcomes the bottleneck of the difficulty in applying radiation-cooling materials in extreme environments with drastic temperature changes, obtaining a radiation-cooling film with extremely low thermal conductivity (greatly reducing the heat transfer rate) for application in extreme environments with drastic temperature changes such as space.
[0040] The technical solution of the present invention will be studied below using examples and comparative examples. The specific research methods and results are shown below: Example 1 A method for preparing a porous radiation-cooling film includes the following steps: S1. Add 23.80g of P(VDF-HFP) powder to 285mL of acetone (the mass percentage of P(VDF-HFP) powder is calculated by dividing the mass of P(VDF-HFP) powder by the total mass of P(VDF-HFP) powder and acetone. The mass of 285mL of acetone is 214.2g after density conversion, so the mass percentage of P(VDF-HFP) is calculated to be 10wt%). Stir magnetically for 30min in a 50℃ water bath until completely dissolved to obtain a P(VDF-HFP) solution with a mass percentage of 10wt%.
[0041] S2. Weigh 1.2g of SiO2 aerogel particles and add them to the above P(VDF-HFP) solution. Mix them evenly by magnetic stirring in a 50℃ water bath for 30min to obtain a P(VDF-HFP) / SiO2 mixture.
[0042] S3. Weigh 1.5g of surfactant and add it to the above P(VDF-HFP) / SiO2 mixture. Stir magnetically for 2 hours in a 50℃ water bath and then sonicate for 10 minutes to form a uniformly dispersed suspension.
[0043] S4. Transfer the suspension to a sprayer, and then spray the suspension onto the polyester surface every 30 minutes at room temperature, while spraying water mist during the intervals to obtain a wet film.
[0044] S5. After the wet film is left to dry in a cool place for 24 hours, a porous P(VDF-HFP) radiation cooling film with a SiO2 aerogel particle volume fraction of 60% and a nighttime heat preservation function is obtained on the polyester plane. The SiO2 aerogel particle volume fraction is calculated by dividing the volume of SiO2 aerogel particles by the total volume of SiO2 aerogel particles and P(VDF-HFP) powder particles, and the porous radiation cooling film is obtained.
[0045] The porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function prepared in this embodiment has the following pore size distribution: nano-sized pores are distributed at 400±230nm, and micro-sized pores are distributed at 7.25±12.86μm.
[0046] The porous P(VDF-HFP) radiation-cooling film with nighttime heat preservation function prepared in this embodiment exhibits a high reflectivity of 97.58% in the 0.3μm~2.5μm solar radiation band; simultaneously, it has a high-mid infrared emissivity of 97.34% in the 8μm~13μm infrared atmospheric window band, and the thermal conductivity test result is 0.035W / (m·K). From the outdoor measured results, compared with the ambient temperature, at 800W / m... 2Under sunlight, it can achieve a cooling effect of 10.3℃; and when there is no sunlight at night, it can achieve a heat preservation effect of 7.0℃.
[0047] Example 2 A method for preparing a porous radiation cooling membrane is the same as the preparation steps in Example 1, except that 23.80g of P(VDF-HFP) powder particles in step S1 are replaced with 24.64g of P(VDF-HFP) powder particles, and 1.2g of SiO2 aerogel particles in step S2 are replaced with 0.36g of SiO2 aerogel particles. A porous P(VDF-HFP) radiation cooling membrane with a nighttime heat preservation function and a SiO2 aerogel particle volume fraction of 30% is obtained on a polyester plane.
[0048] The results show that it has a high reflectivity of 93.63% in the 0.3μm~2.5μm band and a high-mid-infrared emissivity of 96.67% in the 8μm~13μm band, with a thermal conductivity of 0.048 W / (m·K). From outdoor testing, compared to ambient temperature, at 800 W / m... 2 Under sunlight, it can achieve a cooling effect of 6.8℃; and when there is no sunlight at night, it can achieve a heat preservation effect of 4.4℃.
[0049] Example 3 A method for preparing a porous radiation cooling membrane is the same as the preparation steps in Example 1, except that 23.80g of P(VDF-HFP) powder particles in step S1 are replaced with 24.45g of P(VDF-HFP) powder particles, and 1.2g of SiO2 aerogel particles in step S2 are replaced with 0.55g of SiO2 aerogel particles. A porous P(VDF-HFP) radiation cooling membrane with a nighttime heat preservation function and a SiO2 aerogel particle volume fraction of 40% is obtained on a polyester plane.
[0050] The results show that it has a high reflectivity of 94.71% in the 0.3μm~2.5μm band and a high-mid-infrared emissivity of 96.81% in the 8μm~13μm band, with a thermal conductivity of 0.043W / (m·K). From outdoor testing, compared to ambient temperature, at 800W / m... 2 Under sunlight, it can achieve a cooling effect of 7.8℃; and when there is no sunlight at night, it can achieve a heat preservation effect of 4.9℃.
[0051] Example 4 A method for preparing a porous radiation cooling membrane is the same as the preparation steps in Example 1, except that 23.80g of P(VDF-HFP) powder particles in step S1 are replaced with 24.18g of P(VDF-HFP) powder particles, and 1.2g of SiO2 aerogel particles in step S2 are replaced with 0.82g of SiO2 aerogel particles. A porous P(VDF-HFP) radiation cooling membrane with a nighttime heat preservation function and a SiO2 aerogel particle volume fraction of 50% is obtained on a polyester plane.
[0052] The results show that it has a high reflectivity of 96.16% in the 0.3μm~2.5μm band and a high-mid-infrared emissivity of 96.59% in the 8μm~13μm band, with a thermal conductivity of 0.039W / (m·K). From outdoor testing, compared to ambient temperature, at 800W / m... 2 Under sunlight, it can achieve a cooling effect of 8.9℃; and when there is no sunlight at night, it can achieve a heat preservation effect of 5.3℃.
[0053] Example 5 A method for preparing a porous radiation-cooling membrane is the same as the preparation steps in Example 1, except that 23.80g of P(VDF-HFP) powder particles in step S1 are replaced with 23.18g of P(VDF-HFP) powder particles, and 1.2g of SiO2 aerogel particles in step S2 are replaced with 1.82g of SiO2 aerogel particles. A porous P(VDF-HFP) radiation-cooling membrane with a nighttime heat preservation function and a SiO2 aerogel particle volume fraction of 70% is obtained on a polyester plane.
[0054] The results show that it has a high reflectivity of 94.55% in the 0.3μm~2.5μm band and a high-mid-infrared emissivity of 97.19% in the 8μm~13μm band, with a thermal conductivity of 0.041W / (m·K). From outdoor testing, compared to ambient temperature, at 800W / m... 2 Under sunlight, it can achieve a cooling effect of 7.5℃; and when there is no sunlight at night, it can achieve a heat preservation effect of 6.7℃.
[0055] Example 6 A method for preparing a porous radiation cooling membrane is the same as the preparation steps in Example 1, except that the magnetic stirring time in step S2 is replaced by 1 hour instead of 30 minutes. A porous P(VDF-HFP) radiation cooling membrane with nighttime heat preservation function is obtained on a polyester plane, consisting of SiO2 aerogel particle agglomerates (particle size of about 500 nm).
[0056] The results show that it has a high reflectivity of 94.38% in the 0.3μm~2.5μm band and a high-mid infrared emissivity of 96.79% in the 8μm~13μm band, with a thermal conductivity of 0.046 W / (m·K). From outdoor testing, compared to ambient temperature, at 800 W / m... 2 Under sunlight, it can achieve a cooling effect of 6.9℃; and when there is no sunlight at night, it can achieve a heat preservation effect of 5.2℃.
[0057] Example 7 A method for preparing a porous radiation cooling membrane is the same as the preparation steps in Example 1, except that the polyester plane in step S4 is replaced with a flax plane, and a porous P(VDF-HFP) radiation cooling membrane with a SiO2 aerogel particle volume fraction of 60% and a nighttime heat preservation function is obtained on the flax plane.
[0058] Example 8 A method for preparing a porous radiation cooling membrane is the same as the preparation steps in Example 1, except that the polyester plane in step S4 is replaced with a cotton plane, and a porous P(VDF-HFP) radiation cooling membrane with a SiO2 aerogel particle volume fraction of 60% and a nighttime heat preservation function is obtained on the cotton plane.
[0059] Example 9 A method for preparing a porous radiation cooling film is the same as the preparation steps in Example 1, except that the magnetic stirring time in step S2 is replaced by 0 min instead of 30 min, and a porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function is obtained on a polyester plane.
[0060] The results show that it has a high reflectivity of 94.26% in the 0.3μm~2.5μm band and a high-mid-infrared emissivity of 96.92% in the 8μm~13μm band, with a thermal conductivity of 0.049 W / (m·K). From outdoor testing, compared to ambient temperature, at 800 W / m... 2 Under sunlight, it can achieve a cooling effect of 6.5℃; and when there is no sunlight at night, it can achieve a heat preservation effect of 4.7℃.
[0061] Comparative Example 1 A method for preparing a porous radiation cooling film is the same as the preparation steps in Example 1, except that the surfactant in step S3 is not added, and a porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function is obtained on a polyester plane.
[0062] The results show that it has a high reflectivity of 90.77% in the 0.3μm~2.5μm band and a high-mid-infrared emissivity of 95.35% in the 8μm~13μm band, with a thermal conductivity of 0.058 W / (m·K). From outdoor testing, compared to ambient temperature, at 800 W / m... 2 Under sunlight, it can achieve a cooling effect of 5.8℃; and when there is no sunlight at night, it can achieve a heat preservation effect of 2.8℃.
[0063] Comparative Example 2 A method for preparing a porous radiation cooling membrane is the same as the preparation steps in Example 1, except that the magnetic stirring time in step S2 is replaced by 1.5 h instead of 30 min. A porous P(VDF-HFP) radiation cooling membrane with nighttime heat preservation function is obtained on a polyester plane, consisting of SiO2 aerogel particle agglomerates (particle size of about 50 nm).
[0064] The results show that it has a high reflectivity of 92.63% in the 0.3μm~2.5μm band and a high-mid-infrared emissivity of 96.84% in the 8μm~13μm band, with a thermal conductivity of 0.052W / (m·K). From outdoor testing, compared to ambient temperature, at 800W / m... 2 Under solar irradiation, a cooling effect of 6.1℃ can be achieved; and when there is no sunlight at night, a heat preservation effect of 3.8℃ can be achieved. Compared with Example 1, Example 6 and Comparative Example 2 have poor reflectivity in the solar light band. The reason for this defect is that the longer the surfactant is added, the more fragmented the SiO2 aerogel particles are during the stirring process, resulting in the particle size of the SiO2 aerogel particles not being controlled within a suitable range. As a result, they cannot effectively scatter sunlight through the Mie scattering effect, thus causing a relatively low solar reflectivity.
[0065] Analysis of the above examples and comparative examples shows that when the volume fraction of SiO2 aerogel particles is 60% and the stirring time is 30 min, the prepared porous P(VDF-HFP) radiative cooling film with nighttime heat preservation function has the highest infrared emissivity, solar reflectivity, and daytime cooling and nighttime heat preservation effect. However, when the volume fraction of SiO2 aerogel particles is too small, the solar reflectivity of the prepared porous P(VDF-HFP) radiative cooling film with nighttime heat preservation function is low, indicating that a smaller volume fraction of SiO2 aerogel particles is insufficient to increase porosity, resulting in poor reflection at the porous interface. Simultaneously, as the volume fraction of SiO2 aerogel particles increases, porosity increases, thermal conductivity decreases, and the nighttime heat preservation effect is enhanced. Therefore, it is necessary to add SiO2 aerogel particles to improve the reflectivity and thermal conductivity of the porous P(VDF-HFP) radiative cooling film. However, when the amount of SiO2 aerogel particles increases to a certain extent, the content of the polymer backbone relatively decreases, the refractive index difference of the structure decreases, leading to a decrease in solar reflectivity and thus affecting the cooling effect. Furthermore, by comparing the above examples, it was found that the solar reflectivity of the prepared porous P(VDF-HFP) radiative cooling membrane with nighttime heat preservation function decreased with increasing stirring time in step S2. This indicates that the longer the stirring time, the looser the structure and the smaller the size of the SiO2 aerogel particles, resulting in poorer daytime cooling and nighttime heat preservation effects. Therefore, it is necessary to add a surfactant within a suitable time range to protect the SiO2 aerogel particles to ensure excellent thermal management performance.
[0066] Structural Description: The porous radiation cooling film prepared in the above embodiments has a two-layer structure. The bottom layer is made of polyester, cotton, or linen, and the upper layer is a porous PVDF-HFP film doped with SiO2 aerogel particles. Peeling the upper porous PVDF-HFP film doped with SiO2 aerogel particles from the bottom layer yields the porous PVDF-HFP radiation cooling film with nighttime heat preservation function described in this invention. A physical image of the porous radiation cooling film is shown below. Figure 3 As shown, the thickness of the porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function is 300μm~600μm. In the above process, a large number of SiO2 aerogel particles obtained by solution surfactant processing are suspended in the suspension and sprayed out with the suspension through an electric spray gun, forming doped particles in the porous P(VDF-HFP) film. Figure 4 The difference is clearly discernible. Due to the non-solvent exchange between acetone and water vapor in the air, the porous PVDF-HFP film doped with SiO2 aerogel particles contains a large number of micron- and nano-sized air pores, with a porosity of 60%–85%. The microstructure of the cross-section of the porous PVDF-HFP film doped with SiO2 aerogel particles is as follows: Figure 4 As shown.
[0067] Function Introduction: The device designed in this invention achieves a weighted reflectance of up to 97.58% in the solar spectral band (0.28μm~2.5μm) and a maximum emissivity of 97.34% in the infrared atmospheric window band. Based on the spectral performance of the device, it possesses daytime radiative cooling capabilities during hot summers.
[0068] Due to the extremely low thermal conductivity of air, and according to the Knudsen effect, nanoscale air pores can impede the propagation of heat in a medium. Therefore, porous materials are often excellent thermal insulation materials. The device designed in this invention has a porosity exceeding 60%, and the SiO2 aerogel particles themselves are high-quality thermal insulation materials with extremely low thermal conductivity. Therefore, the device exhibits extremely low thermal conductivity, reaching 0.035 W / (m·K), making it a good thermal insulation material that achieves heat preservation effects in cold environments.
[0069] Based on outdoor testing results, compared to ambient temperature, at 800W / m 2 Under sunlight, it can achieve a cooling effect of 10.3℃; and when there is no sunlight at night, it can achieve a heat preservation effect of 7.0℃. Attached image description: Figure 1 This is a schematic diagram illustrating the structure and function of the porous radiative cooling membrane designed for this invention, which combines daytime radiative cooling and nighttime heat preservation. Figure 1 This indicates that the prepared porous radiation-cooling membrane contains pores of various sizes and aerogel particles. When sunlight is incident, the porous structure of the membrane, the aerogel particles, and the pores inside the aerogel particles scatter the sunlight, resulting in high reflectivity in the solar wavelength range. Figure 2 These are physical images of the porous radiation cooling films of Embodiments 1, 7 and 8 of the present invention.
[0071] Figure 3 These are cross-sectional scanning electron microscope (SEM) images of the porous P(VDF-HFP) radiation-cooling films with nighttime heat preservation function prepared in Examples 1, 6, and Comparative Example 2. Figure 3 It can be seen that with the increase of magnetic stirring time, the size of SiO2 aerogel particle aggregates in the porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function gradually decreases. The continuous decrease in the size of SiO2 aerogel particle aggregates will affect the reflectivity of the solar light band. Specifically, its size is too small to meet the size effect of Mie scattering theory, thus failing to effectively reflect sunlight. Therefore, it is necessary to add surfactants to protect its surface and prevent it from being broken down during stirring, thereby controlling its particle size to fall within a suitable range (0.5μm~2.5μm), and synergistically enhancing the reflectivity of sunlight with the porous structure.
[0072] Figure 4 The reflection and emission spectra of the porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function in Example 1 are shown in the wavelength range of 0.28μm to 15μm, demonstrating that its reflectivity in the solar band is 97.58% and its emissivity in the infrared atmospheric window band is 97.34%.
[0073] Figure 5 This is a temperature tracking curve of the porous P(VDF-HFP) radiative cooling film with nighttime heat preservation function in Example 1 under conditions of isolated convection exchange, over a full day (Hongshan District, Wuhan, July 7, 2024, 15:45 to July 8, 2024, 15:45). From... Figure 5 It can be seen that the porous P(VDF-HFP) radiative cooling film with nighttime heat preservation function in Example 1 has a temperature that is always lower than the ambient temperature during the day, with a maximum temperature drop of about 10.3°C, and has a superior radiative cooling effect during the day; at night, its temperature is always higher than the ambient temperature, without a continuous temperature drop, and has a good nighttime heat preservation effect, with a maximum heat preservation of about 7°C.
[0074] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.
Claims
1. A method for preparing a porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function, characterized in that, Includes the following steps: When the acetone solution of P(VDF-HFP) is mixed with SiO2 aerogel particles with a particle size of 15μm~50μm for 0min~60min, a surfactant is added and mixed evenly to obtain a suspension. The suspension and water are alternately sprayed onto the substrate. At this time, the non-solvent water and the solvent acetone evaporate through non-solvent exchange. The solute in the suspension eventually forms a porous membrane. After drying, a porous P (VDF-HFP) radiation cooling membrane with nighttime heat preservation function is loaded onto the substrate surface.
2. The method for preparing a porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function according to claim 1, characterized in that, The acetone solution of P(VDF-HFP) is prepared by dissolving P(VDF-HFP) powder in acetone. The mass percentage of P(VDF-HFP) powder in the acetone solution of P(VDF-HFP) is 5wt%~30wt%.
3. The method for preparing a porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function according to claim 2, characterized in that, The volume ratio of P(VDF-HFP) powder to SiO2 aerogel particles is 100:30~70.
4. The method for preparing a porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function according to claim 1, characterized in that, The surfactant is selected from Triton X-100, Tween-80 or Brij-35.
5. The method for preparing a porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function according to claim 1, characterized in that, The mass ratio of surfactant to SiO2 aerogel particles is 1:0.2~1.2, and the mass ratio of surfactant to suspension is 0.4~0.6:
100.
6. The method for preparing a porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function according to claim 1, characterized in that, The substrate is selected from fabric, and a porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function is loaded on the substrate surface to obtain a porous radiation cooling film.
7. The method for preparing a porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function according to claim 1, characterized in that, The non-solvent exchange method involves alternately spraying the suspension and water onto the substrate, ensuring that the humidity of the spraying environment is greater than 50%, and then using water and acetone for non-solvent exchange.
8. A porous P(VDF-HFP) radiative cooling film with nighttime heat preservation function, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 7.
9. The porous P(VDF-HFP) radiative cooling film with nighttime heat preservation function according to claim 8, characterized in that, The porosity of the porous P(VDF-HFP) radiation cooling film with nighttime heat preservation function is 50%~70%.
10. The application of the porous P(VDF-HFP) radiation cooling membrane with nighttime heat preservation function as described in claim 8 in the preparation of radiation cooling materials.