CN114805941A - A kind of directional thermal conduction porous radiation refrigeration film material and preparation method thereof - Google Patents

Abstract

The invention discloses a directional heat-conducting porous radiation refrigeration film material and a preparation method thereofThe oriented heat conducting film is prepared by dispersing MXene oriented heat conducting materials into cellulose and performing oriented freeze drying. The reflectivity of the material to sunlight is 95-99%, the emissivity of the material in an atmospheric window of 8-13 mu m is 94-98%, and the emissivity in solar irradiance is 700-1200W/m ² The temperature can be reduced by 10-25 ℃, so that the internal heat can be quickly and directionally transferred to the outside, and the directional regulation and control of the internal heat of the building can be realized. The invention solves the problems that heat transfer is reduced only from the outside without paying attention to internal heat regulation and control and the like in the prior art, has excellent daytime cooling performance, and can be applied to the fields of building energy conservation, wearable equipment, photovoltaics, 5G base stations, mobile intelligent terminals and the like.

Description

A kind of directional thermal conduction porous radiation refrigeration film material and preparation method thereof

technical field

The invention belongs to the technical field of radiation refrigeration materials, and in particular relates to a directional thermal conduction porous radiation refrigeration film material and a preparation method thereof.

Background technique

Traditional refrigeration equipment such as air conditioners and fans are driven by electricity. Although they can achieve a certain cooling effect, the consumption of electricity and energy increases during use, resulting in negative impacts such as greenhouse effect, air pollution and even acid rain. Therefore, it is of great significance to develop green materials with good cooling effect. The new radiant cooling technology has the advantages of zero energy consumption, no pollution, high cooling performance, etc., and is considered to be an ideal choice to replace energy-intensive cooling methods at this stage. The emergence of various materials and new preparation methods has played a huge role in promoting the development of refrigeration materials. Therefore, passive radiation refrigeration technology is expected to be widely used in building energy saving, wearable devices, photovoltaics, 5G base stations, mobile smart terminals and other fields. .

Cellulose has a unique three-dimensional void network structure, with multi-scale optical fibers and channels as disordered scattering units to scatter sunlight, and the absorption vibration of chemical bonds in cellulose produces high infrared emissivity, but it is not perfect. Covering the entire atmospheric transparent window (8-13 μm), therefore, only through reasonable molecular structure design and synthesis, and the aggregation of various characteristic functional groups can be achieved, high infrared emissivity at 8-13 μm can be achieved. Nanoparticles with a special hollow structure (SiO ₂ , HfO ₂ , TiO ₂ , ZrO ₂ , etc.) can further improve the infrared emissivity of the material. Such semiconductor nanoparticles have a special surface plasmon effect. After the infrared radiation is absorbed by the material , resulting in collective oscillation of electrons on the particle surface, high emissivity can be obtained in the mid- and far-infrared bands, and hollow microspheres with good sealing can also improve the scattering of solid-phase phonons in the shell, thereby reducing the heat transfer of solid-phase phonons. After being transferred to the spherical shell, it needs to pass through the interior of the hollow microsphere and undergo a gas phase heat transfer, thus greatly reducing the thermal conductivity. Evenly dispersing the nanoparticles in the cellulose substrate can efficiently achieve the cooling effect.

Patent CN110317521A discloses a selective radiation refrigeration coating. The selective radiation refrigeration coating includes a radiation refrigeration functional layer with a special structure particle filler, which is used to reflect ultraviolet light and/or visible light and/or near-infrared light in sunlight, and It emits heat through the atmospheric window in the form of infrared radiation. The radiative cooling functional layer includes a rod-shaped structure particle filler and a radiative cooling functional layer resin. The particle filler is distributed in the radiative cooling functional layer resin, and finally achieves >80% reflectivity and >80% reflectivity. infrared emissivity. Patent CN113372612A discloses a preparation method of a cellulose-based radiation temperature-regulating material, by functionalizing cellulose to prepare a cellulose aerogel with a three-dimensional porous structure, showing nearly 94% solar reflectance and 95% solar reflectance. % infrared emissivity. However, the currently developed radiative cooling materials only focus on reducing the heat input from the outside, and lack effective means of regulating the thermal radiation generated in the internal space (the backside of solar radiation). The key to solving this problem is to develop a material that can achieve rapid and directional heat transfer from the inside to the outside, so as to achieve the ideal cooling effect of the interior space.

Patent CN106631082A discloses a directional high thermal conductivity carbon nanotube composite material and a preparation method thereof. The thermal conductivity of the composite material in the axial direction is >100W/m·k by magnetically regulating the directional arrangement of carbon nanotubes, and the thermal conductivity in the non-axial direction is higher than 100W/m·k. The difference is more than 50W/m·k. However, the methods for preparing aligned carbon nanotube arrays are complicated and demanding. Two-dimensional transition metal carbides (MXenes) not only have the excellent properties of traditional two-dimensional nanomaterials, but also have the high electrical conductivity (~8000S/cm) of metals. According to the Weidmann-Franz law, thermal conductivity and electrical conductivity are known. The ratio is proportional to temperature, so MXene also exhibits high thermal conductivity. Single-layer MXene materials have the characteristics of large sheets, single layers and low defects. Due to the reduction of structural defects, the thermal conductivity parallel to the direction of the thermally conductive material is increased, and the interlayer spacing of the material is increased, reducing the thermal conductivity perpendicular to the direction of the thermally conductive material. rate, resulting in its thermal conductivity anisotropy.

SUMMARY OF THE INVENTION

Purpose of the invention: In order to solve the problems that the existing radiation refrigeration materials only focus on the reflection of sunlight, but lack effective control means for the thermal radiation generated in the internal space (the back of the solar radiation), the present invention provides a directional thermal conduction porous radiation refrigeration film material. and its preparation method. Construct the inner side with high directional thermal conductivity to realize the rapid transfer of heat from the inside to the outside, and at the same time construct the outer side with high solar reflectivity and high infrared emissivity, so that the external heat enters the interior as little as possible and the internal heat is converted into heat. The form of radiation is selectively emitted into outer space, and the effective combination and synergy of the inner and outer films make the radiation refrigeration material show a good cooling effect, which is an ideal choice for a new type of high-efficiency radiation refrigeration material.

Technical solution: The directional thermal conductivity porous radiation refrigeration film material of the present invention is formed by superimposing an outer high reflectivity film and an inner directional thermal conductivity film; the high reflectivity film is made of hollow nano-microspheres dispersed in cellulose It is prepared by phase inversion; the oriented thermally conductive film is prepared by dispersing MXene oriented thermally conductive material into cellulose through directional freeze-drying.

Further, the hollow nano-microspheres use polystyrene as a template.

Further, the MXene directional thermal conductive material is prepared by using an in-situ growth hydrofluoric acid method to selectively etch the MAX precursor, ultrasonic peeling, and vacuum filtration.

The invention also discloses a method for preparing a directional thermally conductive porous radiation refrigeration film material, comprising the following steps:

Step 1. Preparation of directional thermal conductivity material: At room temperature, according to the mass ratio of MAX precursor, LiF, and 37wt% dilute hydrochloric acid of 1:2:20 to 1:3:60, mix MAX precursor, LiF and 37wt% dilute hydrochloric acid Add to the reaction kettle, mix well, react for 24~48h, centrifuge, wash the precipitate with deionized water until the pH of the washing solution is >6, and add to the precipitate according to the mass ratio of the precipitate and deionized water to be 1:2~1:3. Ionized water, 900W～1320W ultrasonic for 6h～12h, suction filtration under vacuum, and the filter cake is dried at 60～80℃ for 12～24h to obtain MXene directional thermal conductive material;

Step 2. Preparation of directional thermal conductive film: the mixed solution is NaOH, urea, and aqueous solution with a mass ratio of 1:2:4 to 1:4:10. At room temperature, the mass ratio of MXene directional thermal conductive material, cellulose, and mixed solution is 1 :5:30～1:10:80, add the MXene directional thermal conductive material, cellulose and mixed solution obtained in step 1 into the reaction kettle and mix well, according to the mass ratio of the mixture to absolute ethanol is 1:2～1:4 , add absolute ethanol to the above mixture, let stand for 8 to 16 hours to obtain wet gel, according to the mass ratio of wet gel and deionized water to be 1:2 to 1:3, add deionized water to the wet gel Water, let stand for 2-4 hours, filter to get the hydrogel, transfer the hydrogel to the mold, freeze at -80--20 ℃ for 1-3 hours, and dry it at -80--40 ℃ for 24-48 hours , to obtain a directional thermal conductive film with a film thickness of 0.2 to 0.5 mm;

Step 3. Preparation of hollow nano-microspheres: at room temperature, add polyvinylpyrrolidone, water and anhydrous ethanol into the reaction kettle according to the mass ratio of polyvinylpyrrolidone, water and anhydrous ethanol of 1:1:10 to 1:2:30 Mix well to obtain a mixture, according to the mass ratio of azobisisobutyronitrile, styrene and the mixture of 1:5:25 to 1:7:50, add azobisisobutyronitrile and styrene to the mixture, and at 60 React at ~80 ° C for 10 ~ 14 h, filter, according to the mass ratio of the filter cake to absolute ethanol 1:2 ~ 1:3, wash the filter cake with absolute ethanol 3 ~ 4 times, and dry at 60 ~ 80 ° C for 24 ~ 48h, polystyrene microspheres were obtained; at room temperature, ammonia water, ester precursors, and absolute ethanol were added to the reaction kettle according to the volume ratio of ammonia water, precursor, and absolute ethanol of 1:2:30 to 1:3:50. In the process, mix well to obtain a mixed solution. According to the mass ratio of surfactant, polystyrene microspheres, and mixed solution of 1:3:40 to 1:5:80, add the surfactant and the above prepared polymer to the mixed solution. Styrene microspheres, react for 24～48h, filter, according to the mass ratio of filter cake and deionized water is 1:2, wash the filter cake with deionized water, dry, according to the heating rate of 1～5℃/min, rise to calcined at 400-700 ℃ for 1-3 hours, and then lowered to room temperature to obtain hollow nano-microspheres;

Step 4. Preparation of porous radiation refrigeration film material: the mixed solvent is acetone and N-methylpyrrolidone solvent with a volume ratio of 1:2 to 1:9. At room temperature, the mass ratio of hollow nano-microspheres to cellulose is 1:2 to 1:9. From 10 to 1:30, add the hollow nano-microspheres and cellulose prepared in step 3 into the mixed solvent, stir well to obtain a mixture, pour the mixture into a glass mold, and cover the bottom of the glass mold with the mixture prepared in step 2. Orientation heat conduction film, acetone volatilizes to obtain a laminated film, soak the laminated film in absolute ethanol for 2-6 hours, take it out, and dry it at 60-80 ℃ for 3-6 hours to obtain a porous radiation refrigeration film material, the film of the film material The thickness is 0.3 to 1.1 mm.

Further, in step 1, the MAX precursor is Ti ₃ AlC ₂ or Ti ₂ AlC.

Further, in step 3, the ester precursor is ethyl orthosilicate or tetrabutyl titanate.

Further, in step 3, the surfactant is cetyltrimethylammonium bromide or sodium dodecylsulfonate.

Further, in step 3, the cellulose is bacterial cellulose or lignocellulose.

Principle of Invention: The present invention is formed by superimposing a high reflectivity film and a directional thermal conductive film, wherein the high reflectivity film is prepared by uniformly dispersing hollow nano-microspheres into cellulose to reflect or scatter sunlight as much as possible , reduce the heat input, and at the same time have a high emissivity in the transparent window of the atmosphere, which can selectively emit its own heat to outer space. The directional thermal conductivity film is prepared by dispersing directional thermal conductivity material into cellulose and directional freeze-drying, which is used to absorb the infrared heat radiation in the inner space and transfer the energy directionally to the outer film, so as to reduce the inward emission of infrared radiation. The synergistic effect of the two-layer film improves the reflectivity of the composite material to sunlight, reduces its inward emission of energy, and also improves the orientation of its outward transmission of thermal radiation, so that heat can be quickly and directionally transferred from the inside of the material to the outside. It exhibits excellent daytime cooling performance and is an ideal choice for new high-efficiency radiation refrigeration materials.

The invention induces high-orientation arrangement of the directional heat-conducting material in the cellulose by controlling the direction of freezing and solidification, strengthens the outward heat transfer efficiency, weakens the inward heat radiation effect, and obtains the directional heat-conducting film after freeze-drying. Then, on this basis, through the characteristic structure design of cellulose, the hollow nano-microspheres with matching properties are selected as the filling medium, and the outer side with high solar reflectivity and high infrared emissivity is constructed to improve the material's reflectivity to sunlight and improve the efficiency of the material. Enhances its ability to emit thermal radiation into space. The synergistic effect of the two films is beneficial to the directional conduction of internal heat and enhances the passive radiative cooling effect.

Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

1. In the present invention, the two-dimensional transition metal carbide ( _MXene ) prepared by in-situ generation of hydrofluoric acid etching _Ti3AlC2 has the characteristics of large sheets, monolayers and low defects, and improves the thermal conductivity parallel to the direction of MXene. , by controlling the interlayer spacing of the material, the thermal conductivity perpendicular to the MXene direction is reduced, resulting in anisotropy of thermal conductivity. The use of MXene as a directional thermal conductive material avoids the traditional use of graphene and other carbon materials for complex preparation processes and harsh preparation conditions. The surface of the single-layer MXene sheet will introduce more active groups such as hydroxyl groups, so that the surface presents a negative charge, and there is electrostatic repulsion between the sheets, so it can maintain a stable state for a long time. The thermal conductivity and mechanical strength of the oriented thermally conductive film were investigated.

2. By dispersing MXene directional thermal conductivity material in cellulose and using directional freeze-drying technology to obtain a film with directional thermal conductivity as the inner side, by controlling the temperature gradient during the freezing process, the directional thermal conductivity material is directionally grown in the vertical direction, Due to the anisotropy of thermal conductivity, the directional transfer of heat from the inside to the outside is realized, so that the interior achieves an ideal cooling effect, which solves the problem of the lack of directional heat conduction in the existing radiation refrigeration materials, resulting in excessive heat radiation inwards. problem, reducing inward heat radiation.

3. Select cellulose as the polymer substrate, and use phase conversion technology to obtain a porous structure. By adjusting the pore size, it is concentrated at about 5 μm. The perfect match of the pore size can effectively scatter all wavelengths of sunlight, and to a greater extent. It reduces the heat of solar radiation and solves the drawback that traditional radiation refrigeration materials need sputtering metal layers to improve the reflectivity of sunlight. The existence of porous structures improves the reflectivity of materials to sunlight.

4. Nano-microspheres with hollow structure are obtained by the polystyrene template method. The microspheres have a special surface plasmon effect. After the infrared radiation is absorbed by the material, the surface electrons collectively oscillate. High emissivity, and the hollow structure reflects and scatters the incident sunlight multiple times, thereby weakening the absorption of solar radiation and improving the cooling effect, solving the reflection caused by the absorption of sunlight of a specific wavelength by the original nano-microspheres problems such as low efficiency and poor cooling effect. The hollow nano-microspheres are dispersed in the cellulose substrate as a filling medium, which further improves the infrared emissivity and solar reflectance of the material.

5. The cellulose is activated by sodium hydroxide solution, which destroys the hydrogen bonds in the crystalline area of cellulose and increases the accessibility to the hydroxyl groups of cellulose. There is an electrostatic effect between the hydroxyl groups of cellulose and the dispersion medium, which makes the dispersion medium It can be evenly loaded in the cellulose molecule, overcomes the disadvantage of less free hydroxyl groups in the crystalline region of the cellulose molecule, and increases the active side chain hydroxyl groups. By using materials with special properties to design and modify the side chain hydroxyl groups, cellulose cellulose-derived polymer substrates with high infrared emissivity and high directional thermal conductivity were obtained.

6. The surface of the directional thermal conductive film is constructed by the phase conversion method with cellulose as the polymer substrate, hollow nano-microspheres as the filling medium with high refractive index and high infrared emissivity, and the cavity of a specific size is the high reflectivity of the scattering filling medium film to achieve superimposition with the inner oriented thermally conductive film. Using the same cellulose as the substrate, the cellulose molecular chains are hydrogen-bonded at the interface, and the mechanical interlacing force makes the two layers of membranes tightly bond. The micro/nano-rough structure surface further enhances the interface bonding strength by the surface roughness between the interfaces. The process of directional transfer of heat from the inner side to the outer side is realized, and then the heat is emitted to the outer space in the form of thermal radiation from the outer side, which solves the problem that the existing radiation refrigeration materials only focus on the reflection of sunlight and ignore the inner space. Thermal radiation leads to the problem that high-efficiency radiative cooling cannot be achieved, which improves the cooling power and efficiency of radiative cooling materials.

Description of drawings

Figure 1 is a microscopic topography (SEM) of the directional thermally conductive porous radiation refrigeration film material;

Figure 2 is the actual cooling diagram of the directional thermal conductivity porous radiation refrigeration film material.

Detailed ways

The technical solutions of the present invention will be further described below with reference to the accompanying drawings.

Example 1

a) Preparation of directional thermal conductive material: At room temperature, according to the mass ratio of MAX precursor, LiF and 37wt% dilute hydrochloric acid as 1:2:20, put MAX precursor, LiF and 37wt% dilute hydrochloric acid into the reaction kettle, mix well , react for 24h, centrifuge, wash with deionized water to pH>6, according to the mass ratio of precipitation and deionized water is 1:2, add deionized water to the precipitation, 900W ultrasonic for 6h, suction filtration under vacuum, filter cake in Dry at 60°C for 12h to obtain MXene directional thermally conductive material;

b) Preparation of directional thermal conductive film: the mixed solution is NaOH, urea, and aqueous solution with a mass ratio of 1:2:4. At room temperature, the mass ratio of MXene directional thermal conductive material, cellulose, and mixed solution is 1:5:30. a) The prepared MXene directional thermal conductive material, cellulose, and mixed solution were added to the reaction kettle and mixed. According to the mass ratio of the mixture to absolute ethanol of 1:2, absolute ethanol was added to the above mixture, and allowed to stand for 12 hours to obtain Wet gel, according to the mass ratio of wet gel and deionized water is 1:2, add deionized water to the wet gel, let stand for 2h, filter to obtain hydrogel, transfer the hydrogel to the mold, After freezing at -80°C for 1h, and drying at -80°C for 24h, a directional thermal conductive film with a film thickness of 0.24mm was obtained;

c) Preparation of hollow nano-microspheres: at room temperature, according to the mass ratio of polyvinylpyrrolidone, water and absolute ethanol as 1:1:10, add polyvinylpyrrolidone, water and absolute ethanol into the reaction kettle and mix to obtain a mixed solution, According to the mass ratio of azobisisobutyronitrile, styrene and mixed solution of 1:5:25, add azobisisobutyronitrile and styrene to the mixed solution, react at 60°C for 10h, filter, press the filter cake The mass ratio to absolute ethanol is 1:2, the filter cake is washed 3 times with absolute ethanol, and dried at 60 °C for 24 hours to obtain polystyrene microspheres; The ratio is 1:2:30, ammonia water, lipid precursor and absolute ethanol are added to the reaction kettle, and mixed to obtain a mixed solution. The mass ratio of surfactant, polystyrene microspheres, and mixed solution is 1:3: 40. Add surfactant and polystyrene microspheres to the mixed solution, react for 24 hours, filter, and according to the mass ratio of filter cake and deionized water to be 1:2, wash the filter cake with deionized water, dry, and press the heating rate At 1°C/min, calcined at 400°C for 1 h to obtain hollow nano-microspheres;

d) Preparation of porous radiation refrigeration film material: the mixed solvent is acetone and N-methylpyrrolidone with a volume ratio of 1:2. At room temperature, the mass ratio of hollow nano-microspheres to cellulose is 1:10. Step c) The hollow nano-microspheres and cellulose prepared in 2 are added to the mixed solvent, and the mixture is stirred evenly. The mixture is poured into a glass mold. The bottom of the glass mold is covered with the directional thermal conductive film prepared in step b), and the acetone is volatilized to form a stack. The laminated film was soaked in absolute ethanol for 2 hours, taken out, and dried at 60°C for 3 hours to obtain a porous radiation refrigeration film material. As shown in Figure 1, the film thickness of the film material was 0.6 mm.

The cooling properties of the obtained materials were tested by a temperature tester and a solar irradiance meter. The reflectivity of the material to sunlight is 95%, and the emissivity in the atmospheric window of 8-13 μm is 94%. As shown in Figure 2, the film can achieve a temperature drop of 13°C under the solar irradiance of 700W/m ² .

Comparative Example 1

a) Preparation of hollow nano-microspheres: at room temperature, according to the mass ratio of polyvinylpyrrolidone, water and absolute ethanol as 1:1:10, add polyvinylpyrrolidone, water and absolute ethanol into the reaction kettle and mix to obtain a mixed solution, According to the mass ratio of azobisisobutyronitrile, styrene and mixed solution of 1:5:25, add azobisisobutyronitrile and styrene to the mixed solution, react at 60°C for 10h, filter, press the filter cake The mass ratio to absolute ethanol is 1:2, the filter cake is washed 3 times with absolute ethanol, and dried at 60 °C for 24 hours to obtain polystyrene microspheres; The ratio is 1:2:30, ammonia water, lipid precursor and absolute ethanol are added to the reaction kettle, and mixed to obtain a mixed solution. The mass ratio of surfactant, polystyrene microspheres, and mixed solution is 1:3: 40. Add surfactant and polystyrene microspheres to the mixed solution, react for 24 hours, filter, and according to the mass ratio of filter cake and deionized water to be 1:2, wash the filter cake with deionized water, dry, and press the heating rate At 1°C/min, calcined at 400°C for 1 h to obtain hollow nano-microspheres;

b) Preparation of porous radiation refrigeration film material: the mixed solvent is acetone and N-methylpyrrolidone with a volume ratio of 1:2. At room temperature, the mass ratio of hollow nano-microspheres to cellulose is 1:10. Step a) The hollow nano-microspheres and cellulose prepared in 2000 were added to the mixed solvent, stirred well to obtain a mixture, poured the mixture into a glass mold, and the acetone was volatilized to obtain a film. The film was soaked in absolute ethanol for 2 h, taken out, and placed in The porous radiation refrigeration film material was obtained by drying at 60° C. for 3 hours, and the film thickness of the film material was 0.36 mm.

The cooling properties of the obtained materials were tested by a temperature tester and a solar irradiance meter. The reflectivity of the material to sunlight is 86%, and the emissivity of the material in an atmospheric window of 8-13 μm is 88%. The film can achieve a temperature reduction of 4°C under the solar irradiance of 700W/m ² . It can be seen that changing the structure of the porous radiative cooling film material and the lack of a directional heat-conducting film result in the inability of the internal heat to be directionally transferred to the outside, and the excess thermal radiation inwards forms heat accumulation, which greatly reduces the radiative cooling effect.

Example 2

a) Preparation of directional thermal conductive material: at room temperature, according to the mass ratio of MAX precursor, LiF and 37wt% dilute hydrochloric acid as 1:2:30, put MAX precursor, LiF and 37wt% dilute hydrochloric acid into the reaction kettle, mix well , react for 30h, centrifuge, wash with deionized water to pH>6, according to the mass ratio of precipitation and deionized water is 1:3, add deionized water to the precipitation, 1000W ultrasonic for 7h, suction filtration under vacuum, filter cake in Dry at 60°C for 14h to obtain MXene directional thermal conductivity material;

b) Preparation of directional thermal conductive film: the mixed solution is NaOH, urea, and aqueous solution with a mass ratio of 1:3:5. At room temperature, the mass ratio of MXene directional thermal conductive material, cellulose, and mixed solution is 1:6:40. a) The prepared MXene directional thermally conductive material, cellulose and mixed solution were added to the reaction kettle and mixed well. According to the mass ratio of the mixture to absolute ethanol of 1:3, absolute ethanol was added to the above mixture, and allowed to stand for 10 hours to obtain Wet gel, according to the mass ratio of wet gel and deionized water is 1:2, add deionized water to the wet gel, let stand for 2h, filter to obtain hydrogel, transfer the hydrogel to the mold, After freezing at -60°C for 1h, and drying at -80°C for 24h, a directional thermal conductive film with a film thickness of 0.3mm was obtained;

c) Preparation of hollow nano-microspheres: at room temperature, according to the mass ratio of polyvinylpyrrolidone, water, and anhydrous ethanol to be 1:1:15, add polyvinylpyrrolidone, water, and anhydrous ethanol into the reaction kettle and mix to obtain a mixed solution, According to the mass ratio of azobisisobutyronitrile, styrene and mixed solution of 1:5:30, add azobisisobutyronitrile and styrene to the mixed solution, react at 60°C for 12h, filter, press the filter cake The mass ratio to absolute ethanol is 1:2, the filter cake is washed with absolute ethanol for 3 times, and dried at 60 °C for 30 h to obtain polystyrene microspheres; The ratio is 1:2:35, ammonia water, lipid precursor and absolute ethanol are added to the reaction kettle, and mixed to obtain a mixed solution. The mass ratio of surfactant, polystyrene microspheres, and mixed solution is 1:3: 50. Add surfactant and polystyrene microspheres to the mixed solution, react for 30 hours, filter, according to the mass ratio of filter cake and deionized water to be 1:2, wash the filter cake with deionized water, dry, and press the heating rate At 2°C/min, calcined at 500°C for 1 h to obtain hollow nano-microspheres;

d) Preparation of porous radiation refrigeration film material: the mixed solvent is acetone and N-methylpyrrolidone solvent with a volume ratio of 1:8. At room temperature, the mass ratio of hollow nano-microspheres to cellulose is 1:15. Step c) The hollow nano-microspheres and cellulose prepared in 2 are added to the mixed solvent, and the mixture is stirred evenly. The mixture is poured into a glass mold. The bottom of the glass mold is covered with the directional thermal conductive film prepared in step b), and the acetone is volatilized to form a stack. The laminated film was soaked in absolute ethanol for 3 hours, taken out, and dried at 60° C. for 4 hours to obtain a porous radiation refrigeration film material with a film thickness of 0.5 mm.

The cooling properties of the obtained materials were tested by a temperature tester and a solar irradiance meter. The reflectivity of the material to sunlight is 96%, the emissivity of the 8-13 μm atmospheric window is 95%, and the temperature can be lowered by 14°C under the solar irradiance of 800W/m ² .

Comparative Example 2

a) Preparation of directional thermal conductive material: At room temperature, according to the mass ratio of MAX precursor, LiF and 37wt% dilute hydrochloric acid of 1:1:10, put MAX precursor, LiF and 37wt% dilute hydrochloric acid into the reaction kettle, mix well , react for 20h, centrifuge, wash with deionized water to pH>6, according to the mass ratio of precipitation and deionized water is 1:3, add deionized water to the precipitation, 1000W ultrasonic for 7h, suction filtration under vacuum, filter cake in Dry at 60°C for 14h to obtain MXene directional thermal conductivity material;

b) Preparation of directional thermal conductive film: the mixed solution is NaOH, urea, and aqueous solution with a mass ratio of 1:1:1. At room temperature, the mass ratio of MXene directional thermal conductive material, cellulose, and mixed solution is 1:3:5. a) The prepared MXene directional thermally conductive material, cellulose and mixed solution were added to the reaction kettle and mixed well. According to the mass ratio of the mixture to absolute ethanol of 1:3, absolute ethanol was added to the above mixture, and allowed to stand for 10 hours to obtain Wet gel, according to the mass ratio of wet gel and deionized water is 1:2, add deionized water to the wet gel, let stand for 2h, filter to obtain hydrogel, transfer the hydrogel to the mold, After freezing at -60°C for 1h, and drying at -80°C for 24h, a directional thermal conductive film with a film thickness of 0.3mm was obtained;

c) Preparation of hollow nano-microspheres: at room temperature, according to the mass ratio of polyvinylpyrrolidone, water and absolute ethanol to be 1:1:5, add polyvinylpyrrolidone, water and absolute ethanol into the reaction kettle and mix to obtain a mixed solution, According to the mass ratio of azobisisobutyronitrile, styrene and mixed solution of 1:1:10, add azobisisobutyronitrile and styrene to the mixed solution, react at 60°C for 12h, filter, press the filter cake The mass ratio to absolute ethanol is 1:2, the filter cake is washed with absolute ethanol for 3 times, and dried at 60 °C for 30 h to obtain polystyrene microspheres; The ratio is 1:1:20, ammonia water, lipid precursor and absolute ethanol are added to the reaction kettle, and mixed to obtain a mixed solution. The mass ratio of surfactant, polystyrene microspheres, and mixed solution is 1:3: 50. Add surfactant and polystyrene microspheres to the mixed solution, react for 30 hours, filter, according to the mass ratio of filter cake and deionized water to be 1:2, wash the filter cake with deionized water, dry, and press the heating rate At 2°C/min, calcined at 500°C for 1 h to obtain hollow nano-microspheres;

d) Preparation of porous radiation refrigeration film material: the mixed solvent is acetone and N-methylpyrrolidone solvent with a volume ratio of 1:1. At room temperature, the mass ratio of hollow nano-microspheres to cellulose is 1:5. Step c) The hollow nano-microspheres and cellulose prepared in 2 are added to the mixed solvent, and the mixture is stirred evenly. The mixture is poured into a glass mold. The bottom of the glass mold is covered with the directional thermal conductive film prepared in step b), and the acetone is volatilized to form a stack. The laminated film was soaked in absolute ethanol for 3 hours, taken out, and dried at 60° C. for 4 hours to obtain a porous radiation refrigeration film material with a film thickness of 0.5 mm.

The cooling properties of the obtained materials were tested by a temperature tester and a solar irradiance meter. The reflectivity of the material to sunlight is 87%, the emissivity of the material is 90% in the atmospheric window of 8-13 μm, and the temperature can be lowered by 7°C under the solar irradiance of 800W/m ² . It can be seen that under the condition that other conditions remain unchanged, changing the material preparation ratio, the cooling performance of the porous radiation refrigeration film material prepared by the ratio outside the scope of protection of this patent is significantly reduced.

Example 3

a) Preparation of directional thermal conductive material: At room temperature, according to the mass ratio of MAX precursor, LiF and 37wt% dilute hydrochloric acid to 1:3:50, put MAX precursor, LiF and 37wt% dilute hydrochloric acid into the reaction kettle, mix well , react for 36h, centrifuge, wash with deionized water to pH>6, according to the mass ratio of precipitation and deionized water is 1:3, add deionized water to the precipitation, 1100W ultrasonic for 10h, suction filtration under vacuum, filter cake in Dry at 70℃ for 20h to obtain MXene directional thermal conductive material;

b) Preparation of directional thermal conductive film: the mixed solution is NaOH, urea, and aqueous solution with a mass ratio of 1:4:7. At room temperature, the mass ratio of MXene directional thermal conductive material, cellulose, and mixed solution is 1:8:60. a) The prepared MXene directional thermally conductive material, cellulose, and mixed solution were added to the reaction kettle and mixed. According to the mass ratio of the mixture to absolute ethanol of 1:3, absolute ethanol was added to the above mixture, and allowed to stand for 14 hours to obtain For wet gel, according to the mass ratio of wet gel and deionized water as 1:2, add deionized water to the wet gel, let stand for 3 hours, filter to obtain hydrogel, transfer the hydrogel to the mold, After freezing at -60 °C for 2 hours, and drying at -40 °C for 36 hours, a directional thermal conductive film with a film thickness of 0.4 mm was obtained;

c) Preparation of hollow nano-microspheres: at room temperature, according to the mass ratio of polyvinylpyrrolidone, water, and anhydrous ethanol as 1:2:20, add polyvinylpyrrolidone, water, and anhydrous ethanol into the reaction kettle and mix to obtain a mixed solution, According to the mass ratio of azobisisobutyronitrile, styrene and mixed solution of 1:6:35, add azobisisobutyronitrile and styrene to the mixed solution, react at 70°C for 12h, filter, press the filter cake The mass ratio to absolute ethanol is 1:2, the filter cake is washed 4 times with absolute ethanol, and dried at 70 °C for 36 h to obtain polystyrene microspheres; The ratio is 1:3:30, ammonia water, lipid precursor and absolute ethanol are added to the reaction kettle, and mixed to obtain a mixed solution. The mass ratio of surfactant, polystyrene microspheres, and mixed solution is 1:4: 60. Add surfactant and polystyrene microspheres to the mixed solution, react for 36h, filter, and according to the mass ratio of the filter cake to deionized water is 1:2, wash the filter cake with deionized water, dry, and press the heating rate At 3°C/min, calcined at 600°C for 2h to obtain hollow nano-microspheres;

d) Preparation of porous radiation refrigeration film material: The mixed solvent is acetone and N-methylpyrrolidone solvent with a volume ratio of 1:6. At room temperature, the mass ratio of hollow nano-microspheres to cellulose is 1:20. Step c) The hollow nano-microspheres and cellulose prepared in 2 are added to the mixed solvent, and the mixture is stirred evenly. The mixture is poured into a glass mold. The bottom of the glass mold is covered with the directional thermal conductive film prepared in step b), and the acetone is volatilized to form a stack. The laminated film was soaked in absolute ethanol for 4 hours, taken out, and dried at 70°C for 5 hours to obtain a porous radiation refrigeration film material with a film thickness of 0.8 mm.

The cooling properties of the obtained materials were tested by a temperature tester and a solar irradiance meter. The reflectivity of the material to sunlight is 97%, the emissivity of the material is 96% in the atmospheric window of 8-13 μm, and the temperature can be lowered by 19°C under the solar irradiance of 950W/m ² .

Example 4

a) Preparation of directional thermal conductive material: At room temperature, according to the mass ratio of MAX precursor, LiF and 37wt% dilute hydrochloric acid as 1:3:60, put MAX precursor, LiF and 37wt% dilute hydrochloric acid into the reaction kettle, mix well , react for 48h, centrifuge, wash with deionized water to pH>6, according to the mass ratio of precipitation and deionized water is 1:3, add deionized water to the precipitation, 1320W ultrasonic for 12h, suction filtration under vacuum, filter cake in Dry at 80°C for 24h to obtain MXene directional thermal conductivity material;

b) Preparation of directional thermal conductive film: the mixed solution is NaOH, urea, and aqueous solution with a mass ratio of 1:4:10. At room temperature, the mass ratio of MXene directional thermal conductive material, cellulose, and mixed solution is 1:10:80. a) The prepared MXene directional thermally conductive material, cellulose and mixed solution were added to the reaction kettle and mixed well. According to the mass ratio of the mixture to absolute ethanol of 1:4, absolute ethanol was added to the above mixture, and allowed to stand for 12 hours to obtain Wet gel, according to the mass ratio of wet gel and deionized water is 1:3, add deionized water to the wet gel, let stand for 4 hours, filter to obtain hydrogel, transfer the hydrogel to the mold, After freezing at -20°C for 3h, and drying at -40°C for 48h, a directional thermal conductive film with a film thickness of 0.5mm was obtained;

c) Preparation of hollow nano-microspheres: at room temperature, according to the mass ratio of polyvinylpyrrolidone, water, and absolute ethanol as 1:2:30, add polyvinylpyrrolidone, water, and absolute ethanol into the reaction kettle and mix to obtain a mixed solution, According to the mass ratio of azobisisobutyronitrile, styrene and mixed solution of 1:7:50, add azobisisobutyronitrile and styrene to the mixed solution, react at 80°C for 14h, filter, press the filter cake The mass ratio to absolute ethanol is 1:3, the filter cake is washed with absolute ethanol for 4 times, and dried at 80 °C for 48 hours to obtain polystyrene microspheres; The ratio is 1:3:50, ammonia water, lipid precursor and absolute ethanol are added to the reaction kettle, and mixed to obtain a mixed solution. The mass ratio of surfactant, polystyrene microspheres, and mixed solution is 1:5: 80. Add surfactant and polystyrene microspheres to the mixed solution, react for 48h, filter, according to the mass ratio of filter cake and deionized water to be 1:2, wash the filter cake with deionized water, dry, and press the heating rate At 5°C/min, calcined at 700°C for 3h to obtain hollow nano-microspheres;

d) Preparation of porous radiation refrigeration film material: the mixed solvent is acetone and N-methylpyrrolidone solvent with a volume ratio of 1:9. At room temperature, the mass ratio of hollow nano-microspheres to cellulose is 1:30. Step c) The hollow nano-microspheres and cellulose prepared in 2 are added to the mixed solvent, and the mixture is stirred evenly. The mixture is poured into a glass mold. The bottom of the glass mold is covered with the directional thermal conductive film prepared in step b), and the acetone is volatilized to form a stack. The laminated film was soaked in absolute ethanol for 6 hours, taken out, and dried at 80° C. for 6 hours to obtain a porous radiation refrigeration film material with a film thickness of 1.1 mm.

The cooling properties of the obtained materials were tested by a temperature tester and a solar irradiance meter. The reflectivity of the material to sunlight is 99%, the emissivity of the 8-13 μm atmospheric window is 98%, and the temperature can be lowered by 25°C under the solar irradiance of 1200W/m ² .

Claims (8)

1. A directional thermally conductive porous radiation refrigeration film material is characterized in that, the material is formed by superimposing an outer high-reflectivity film and an inner directional thermal-conducting film; the high-reflectivity film is dispersed into fibers by hollow nano-microspheres. The oriented thermal conductive film is prepared by dispersing the MXene oriented thermal conductive material into cellulose through directional freeze-drying. 2 . The directional thermally conductive porous radiation refrigeration film material according to claim 1 , wherein the hollow nano-microspheres take polystyrene as a template. 3 . 3. The directional thermally conductive porous radiation refrigeration thin film material according to claim 1, wherein the MXene directional thermally conductive material is made by using in-situ growth hydrofluoric acid method to selectively etch MAX precursor, ultrasonic peeling, vacuum filtration prepared. 4. A method for preparing a directional thermally conductive porous radiation refrigeration film material according to claim 1, characterized in that, comprising the steps of: Step 1. Preparation of directional thermal conductivity material: At room temperature, according to the mass ratio of MAX precursor, LiF, and 37wt% dilute hydrochloric acid of 1:2:20 to 1:3:60, mix MAX precursor, LiF and 37wt% dilute hydrochloric acid Add to the reaction kettle, mix well, react for 24~48h, centrifuge, wash the precipitate with deionized water until the pH of the washing solution is >6, and add to the precipitate according to the mass ratio of the precipitate and deionized water to be 1:2~1:3. Ionized water, 900W～1320W ultrasonic for 6h～12h, suction filtration under vacuum, and the filter cake is dried at 60～80℃ for 12～24h to obtain MXene directional thermal conductive material; Step 2. Preparation of directional thermal conductive film: the mixed solution is NaOH, urea, and aqueous solution with a mass ratio of 1:2:4 to 1:4:10. At room temperature, the mass ratio of MXene directional thermal conductive material, cellulose, and mixed solution is 1 :5:30～1:10:80, add the MXene directional thermal conductive material, cellulose and mixed solution obtained in step 1 into the reaction kettle and mix well, according to the mass ratio of the mixture to absolute ethanol is 1:2～1:4 , add absolute ethanol to the above mixture, let stand for 8 to 16 hours to obtain wet gel, according to the mass ratio of wet gel and deionized water to be 1:2 to 1:3, add deionized water to the wet gel Water, let stand for 2-4 hours, filter to get the hydrogel, transfer the hydrogel to the mold, freeze at -80--20 ℃ for 1-3 hours, and dry it at -80--40 ℃ for 24-48 hours , to obtain a directional thermal conductive film with a film thickness of 0.2 to 0.5 mm; Step 3. Preparation of hollow nano-microspheres: at room temperature, add polyvinylpyrrolidone, water and anhydrous ethanol into the reaction kettle according to the mass ratio of polyvinylpyrrolidone, water and anhydrous ethanol of 1:1:10 to 1:2:30 Mix well to obtain a mixture, according to the mass ratio of azobisisobutyronitrile, styrene and the mixture of 1:5:25 to 1:7:50, add azobisisobutyronitrile and styrene to the mixture, and at 60 React at ~80 ° C for 10 ~ 14 h, filter, according to the mass ratio of the filter cake to absolute ethanol 1:2 ~ 1:3, wash the filter cake with absolute ethanol 3 ~ 4 times, and dry at 60 ~ 80 ° C for 24 ~ 48h, polystyrene microspheres were obtained; at room temperature, ammonia water, ester precursors, and absolute ethanol were added to the reaction kettle according to the volume ratio of ammonia water, precursor, and absolute ethanol of 1:2:30 to 1:3:50. In the process, mix well to obtain a mixed solution. According to the mass ratio of surfactant, polystyrene microspheres, and mixed solution of 1:3:40 to 1:5:80, add the surfactant and the above prepared polymer to the mixed solution. Styrene microspheres, react for 24～48h, filter, according to the mass ratio of filter cake and deionized water is 1:2, wash the filter cake with deionized water, dry, according to the heating rate of 1～5℃/min, rise to calcined at 400-700 ℃ for 1-3 hours, and then lowered to room temperature to obtain hollow nano-microspheres; Step 4. Preparation of porous radiation refrigeration film material: the mixed solvent is acetone and N-methylpyrrolidone solvent with a volume ratio of 1:2 to 1:9. At room temperature, the mass ratio of hollow nano-microspheres to cellulose is 1:2 to 1:9. From 10 to 1:30, add the hollow nano-microspheres and cellulose prepared in step 3 into the mixed solvent, stir well to obtain a mixture, pour the mixture into a glass mold, and cover the bottom of the glass mold with the mixture prepared in step 2. Orientation heat conduction film, acetone volatilizes to obtain a laminated film, soak the laminated film in absolute ethanol for 2-6 hours, take it out, and dry it at 60-80 ℃ for 3-6 hours to obtain a porous radiation refrigeration film material, the film of the film material The thickness is 0.3 to 1.1 mm. 5 . The method for preparing a directional thermally conductive porous radiation refrigeration thin film material according to claim 4 , wherein, in step 1, the MAX precursor is Ti ₃ AlC ₂ or Ti ₂ AlC. 6 . 6 . The method for preparing a directional thermally conductive porous radiation refrigeration film material according to claim 4 , wherein, in step 3, the ester precursor is ethyl orthosilicate or tetrabutyl titanate. 7 . 7. The method for preparing a directional thermally conductive porous radiation refrigeration film material according to claim 4, wherein in step 3, the surfactant is cetyltrimethylammonium bromide or dodecylsulfonic acid Sodium. 8 . The method for preparing a directional thermally conductive porous radiation refrigeration film material according to claim 4 , wherein in step 3, the cellulose is bacterial cellulose or lignocellulose. 9 .

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