A method for preparing a double-layer dynamic thermal management material

Abstract

The application discloses a preparation method of a double-layer dynamic thermal management material, and comprises the following steps: step 1, preparing a radiation cooling layer: dissolving cellulose acetate in an organic solvent, uniformly dispersing nano-hexagonal boron nitride to form a mixed solution, coating the mixed solution on a substrate, and then treating the mixed solution by a non-solvent induced phase separation method to form a radiation cooling layer with a porous structure; step 2, preparing a phase change heat storage layer: immersing delignified wood in a mixed solution containing a silane coupling agent and a phase change material, and then performing vacuum treatment and drying to form the phase change heat storage layer; and step 3, compounding the radiation cooling layer and the phase change heat storage layer to form the double-layer dynamic thermal management material. The double-layer dynamic thermal management material prepared by the method realizes efficient heat radiation and dynamic temperature regulation through the synergistic effect of the radiation cooling layer and the phase change heat storage layer.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, and in particular to a method for preparing a double-layer dynamic thermal management material. Background Technology

[0002] Energy is crucial for social and economic development. Currently, building energy consumption accounts for half of total energy consumption, with the operational phase consuming the most energy. Upgrading building thermal management using zero-carbon energy and establishing a low-carbon energy transition is essential. Passive radiative cooling technology uses the cold and distant universe (3K) as a cold source to radiate heat, achieving cooling without external energy input, making it a representative of low-carbon thermal management. This technology is key in two aspects: firstly, maximizing the material's reflection in the ultraviolet-visible-near-infrared band (0.3-2.5μm) of the solar spectrum, thus preventing the material from absorbing more light and converting it into more heat; secondly, maximizing the material's emission in the mid-infrared band (8-13 micrometers), the atmospheric window band, where atmospheric transmittance is high, allowing the material to radiate its own heat into the universe as electromagnetic waves.

[0003] Currently, radiative cooling has been developed for use in building materials such as coatings, wood, and insulating foam. However, because the thermal radiation effect of radiative cooling is passive and continuous, and the cooling effect is much greater at night than during the day, this leads to the problem of excessive cooling at night. Especially when radiative cooling materials are used for human body thermal management or building thermal management, people expect their thermal management capabilities to be dynamically adjusted according to the actual outdoor temperature to achieve all-weather dynamic radiative cooling. In addition, due to the structural characteristics of radiative cooling materials, their cooling power has a certain limit. Therefore, improving the cooling performance of radiative cooling materials also needs to be a key focus. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a bilayer dynamic thermal management material. The bilayer dynamic thermal management material prepared by this invention achieves efficient thermal radiation and dynamic temperature control through the synergistic effect of a radiative cooling layer and a phase change thermal storage layer.

[0005] The technical solution of the present invention: a method for preparing a double-layer dynamic thermal management material, comprising the following steps: Step 1: Preparation of radiation cooling layer: Dissolve cellulose acetate in an organic solvent and uniformly disperse nano-hexagonal boron nitride to form a mixed solution. After coating the mixed solution on a substrate, a porous radiation cooling layer is formed by processing it through a non-solvent-induced phase separation method. Step 2, Preparation of phase change heat storage layer: The delignified wood is impregnated in a mixture containing silane coupling agent and phase change material, and then vacuum treated and dried to form a phase change heat storage layer; Step 3: Combine the radiative cooling layer and the phase change thermal storage layer to form a double-layer dynamic thermal management material.

[0006] In the preparation method of the above-mentioned bilayer dynamic thermal management material, in step 1, the organic solvent is composed of N,N-dimethylformamide and acetone; in the mixed solution, the mass ratio of cellulose acetate, nano-hexagonal boron nitride, N,N-dimethylformamide and acetone is 1:0.1-0.3:4-6:4-6.

[0007] In the aforementioned method for preparing a bilayer dynamic thermal management material, in step 1, the acetyl content of the cellulose acetate is 32.0 wt% and the hydroxyl content is 8.7 wt%; the particle size of the nano-hexagonal boron nitride is 500 nm.

[0008] In the aforementioned method for preparing bilayer dynamic thermal management materials, step 1, the non-solvent-induced phase separation method includes: the solution coated on the substrate is naturally air-dried for 3-8 minutes and then immersed in pure water for 15-25 minutes.

[0009] In the aforementioned method for preparing a double-layer dynamic thermal management material, step 2, the delignification treatment of the wood includes: immersing the wood in a sodium chlorite solution, adjusting the pH to 4-5, and heating it in a water bath at 80-90°C for 4-8 hours.

[0010] In the aforementioned method for preparing a double-layer dynamic thermal management material, in step 2, the silane coupling agent is methyltrimethoxysilane, the phase change material is octadecane, and the mass ratio of the silane coupling agent, the phase change material, and water is 1:0.8-1.2:1.5-2.5.

[0011] In the aforementioned method for preparing a bilayer dynamic thermal management material, step 2 involves the following preparation process for the mixture containing the silane coupling agent and the phase change material: First, add hydrochloric acid to the water to adjust the pH value to 3.5-4.5, where the concentration of hydrochloric acid is 0.1 mol / L. Then, add methyltrimethoxysilane and octadecane to blend so that the mass ratio of silane coupling agent, phase change material and water is 1:1:2.

[0012] In the aforementioned method for preparing a double-layer dynamic thermal management material, step 2 involves a vacuum treatment pressure of -0.1 MPa and an impregnation time of 1-3 hours.

[0013] In the aforementioned method for preparing a dual-layer dynamic thermal management material, in step 3, the radiative cooling layer is located on the upper layer, the phase change thermal storage layer is located on the lower layer, and the radiative cooling layer and the phase change thermal storage layer are bonded together by the adhesiveness of the phase change thermal storage layer.

[0014] Compared with existing technologies, this invention, on the one hand, prepares a radiation cooling layer using a solvent-inducing phase separation method, thus exhibiting extremely high porosity with pore sizes mostly distributed in the range of 0.2 μm-2.5 μm. Furthermore, the 500 nm nano-hexagonal boron nitride significantly enhances the reflectivity around 500 nm, thereby achieving high reflectivity across the entire ultraviolet-visible-near-infrared spectrum. Simultaneously, cellulose acetate and nano-hexagonal boron nitride possess a certain mid-infrared emissivity within the atmospheric window band of 8 μm-13 μm. On the other hand, the phase change thermal storage layer is impregnated into delignified wood through the hydrolysis and condensation of methyltrimethoxysilane and the blending of octadecane. The octadecane impregnation endows the phase change thermal storage layer with superior phase change thermal storage capacity, while the hydrolysis and polymerization of methyltrimethoxysilane, followed by impregnation, provides the phase change thermal storage layer with high atmospheric window emissivity to compensate for the insufficient emissivity of the radiation cooling layer. Therefore, the dual-layer dynamic thermal management material of the present invention not only significantly improves the overall emissivity of the material to enhance its radiative cooling capacity, but also enables the material to have a dynamic temperature control effect before and after the octadecane phase transition temperature. Attached Figure Description

[0015] Figure 1 A scanning electron microscope image of the radiation cooling layer of the double-layer dynamic thermal management material in the embodiments of this application; Figure 2 A scanning electron microscope image of the phase change thermal storage layer of the bilayer dynamic thermal management material in the embodiments of this application; Figure 3 The solar spectral reflectance curves of the double-layer dynamic thermal management material in the embodiments of this application are shown in the 0.3μm-2.5μm wavelength band. Figure 4 This is an emissivity curve of the bilayer dynamic thermal management material in the 8μm-13μm atmospheric window band in the embodiments of this application; Figure 5 This is a differential scanning calorimeter test curve of the double-layer dynamic thermal management material in the embodiments of this application. Detailed Implementation

[0016] The following embodiments further illustrate the present invention, but are not intended to limit the scope of the invention.

[0017] Example 1: A method for preparing a bilayer dynamic thermal management material, comprising the following steps: Step 1: Preparation of radiation cooling layer: Dissolve cellulose acetate in an organic solvent and uniformly disperse nano-hexagonal boron nitride to form a mixed solution. After coating the mixed solution on the substrate, a porous radiation cooling layer is formed by processing it through a non-solvent-induced phase separation method. Step 2, Preparation of phase change heat storage layer: The delignified wood is impregnated in a mixture containing silane coupling agent and phase change material, and then vacuum treated and dried to form a phase change heat storage layer; Step 3: Combine the radiative cooling layer and the phase change thermal storage layer to form a double-layer dynamic thermal management material.

[0018] The radiation cooling layer is a porous structure formed by non-solvent-induced phase separation of cellulose acetate and nano-hexagonal boron nitride. Specifically, cellulose acetate is dissolved in a mixed solvent of N,N-dimethylformamide and acetone, and nano-hexagonal boron nitride is dispersed and coated onto a substrate. Phase separation is achieved through immersion in pure water. This structure enhances solar wavelength reflection and mid-infrared emission through its porous morphology, reduces heat absorption, and improves radiative heat dissipation efficiency.

[0019] The phase change thermal storage layer refers to a composite material layer formed by loading silane coupling agents and phase change materials onto delignified wood. Specifically, after removing lignin from the wood with sodium chlorite solution, the wood is impregnated with a mixture of methyltrimethoxysilane and octadecane, followed by vacuum treatment to allow the phase change material to fill the pores of the wood. This layer regulates temperature fluctuations through the storage and release of latent heat from the phase change material, while the silane coupling agent enhances the interfacial stability between the wood and the phase change material.

[0020] Among them, the non-solvent-induced phase separation method involves air-drying a substrate coated with a mixed solution and then immersing it in pure water, where the solvent and non-solvent exchange forms a porous structure. This method optimizes the optical performance of the radiation-cooled layer by controlling the drying time and immersion duration to adjust the pore size and distribution.

[0021] Delignification treatment refers to the process of treating wood with sodium chlorite solution at high temperature under acidic conditions to remove lignin. Specifically, treatment can be carried out at pH 4-5 and 80-90℃ for 4-8 hours. This treatment expands the internal pore volume of the wood, thereby increasing the loading capacity of subsequent phase change materials and the heat storage capacity.

[0022] Vacuum treatment involves placing the wood impregnated with the mixture in a negative pressure environment of -0.1 MPa, using the pressure difference to drive the mixture to penetrate into the pores of the wood. This process ensures that the phase change material fully fills the three-dimensional pore structure of the delignified wood, thereby increasing the heat capacity of the thermal storage layer.

[0023] The core innovation of this invention lies in achieving dynamic thermal management through the synergistic effect of a radiative cooling layer and a phase change thermal storage layer. The radiative cooling layer utilizes its porous structure and the high reflectivity of nano-hexagonal boron nitride in the solar band and the high emission characteristics in the atmospheric window band to continuously dissipate heat. The phase change thermal storage layer actively regulates the diurnal temperature difference by leveraging the latent heat of phase change material. When combined, the phase change material absorbs excess heat during the day to lower the temperature of the radiative layer and enhance heat dissipation efficiency, and releases heat at night to alleviate overcooling, forming a self-regulating temperature mechanism. This structure overcomes the passive limitations of a single radiative cooling material, combining active heat storage and release with passive heat dissipation to achieve all-weather thermal management.

[0024] The working process and principle of this invention are as follows: a dual-layer dynamic thermal management material achieves all-weather dynamic temperature balance through a composite structure of a radiative cooling layer and a phase change thermal storage layer. The radiative cooling layer is composed of cellulose acetate and nano-hexagonal boron nitride, forming a porous structure through a non-solvent-induced phase separation method. The porous structure enhances light scattering and thermal radiation efficiency, while the nano-hexagonal boron nitride optimizes the material's reflection and emission characteristics in specific wavelength bands. The radiative cooling layer reflects ultraviolet-visible-near-infrared light in the solar band to reduce heat absorption, while simultaneously radiating heat outward through atmospheric windows in the mid-infrared band, achieving continuous passive heat dissipation. The phase change thermal storage layer uses delignified wood as a carrier to load the phase change material. The delignified wood has a rich porous structure, and the vacuum impregnation process ensures a high loading capacity of the phase change material. A silane coupling agent enhances the interfacial bonding stability between the wood and the phase change material. The phase change thermal storage layer absorbs excess heat during the day through latent heat of phase change and releases it at night, actively adjusting the heat storage and release rhythm according to changes in ambient temperature. The two-layer structure works synergistically: the radiative cooling layer continuously provides passive heat dissipation, while the phase change thermal storage layer actively adjusts the heat storage and release rhythm according to changes in ambient temperature, together achieving dynamic temperature balance in all weather conditions.

[0025] As a preferred embodiment, the specific implementation of this application is as follows: First, a radiative cooling layer is prepared. Cellulose acetate is dissolved in a mixed solvent of N,N-dimethylformamide and acetone, and nano-hexagonal boron nitride powder is added. The mixture is then ultrasonically dispersed to form a uniform solution. The solution is coated onto a glass substrate, air-dried, and then immersed in pure water for solvent-induced phase separation treatment to form a porous radiative cooling layer. Second, a phase change thermal storage layer is prepared. Poplar wood is selected as the raw material and delignified in a sodium chlorite solution. The treated wood is then impregnated in a mixture containing methyltrimethoxysilane, octadecane, and water under vacuum, followed by drying to form a phase change thermal storage layer. Finally, the radiative cooling layer is placed on top of the phase change thermal storage layer, and the adhesive properties of the phase change thermal storage layer are used for bonding to form a double-layer dynamic thermal management material.

[0026] Through the above-described scheme, this invention solves the problems of radiative cooling materials' inability to dynamically adjust their thermal management capabilities according to actual temperature and excessive cooling at night, while simultaneously improving the cooling performance of radiative cooling materials. The radiative cooling layer continuously provides passive heat dissipation, while the phase change thermal storage layer actively adjusts its heat storage and release rhythm according to changes in ambient temperature; the synergistic effect of both achieves dynamic temperature balance throughout the day. The porous structure of the radiative cooling layer enhances light scattering and thermal radiation efficiency, and the introduction of nano-hexagonal boron nitride further optimizes the material's reflection and emission characteristics in specific wavelength bands, improving cooling performance. The phase change thermal storage layer uses delignified wood as a carrier, possessing a rich porous structure; combined with a vacuum impregnation process, it ensures a high loading capacity of the phase change material, enhancing temperature regulation capabilities. The use of a silane coupling agent improves the interfacial bonding stability between the wood and the phase change material, extending the material's service life.

[0027] Example 2: In some of the above-mentioned solutions in this application, if the type and ratio of organic solvents and the non-solvent-induced phase separation method are not properly selected, problems such as insufficient dissolution of cellulose acetate and uneven dispersion of nanomaterials may occur, thereby affecting the formation of the porous structure of the radiation cooling layer and the final thermal management performance.

[0028] In this regard, the present invention further proposes that the organic solvent is composed of N,N-dimethylformamide and acetone; in the mixed solution, the mass ratio of cellulose acetate, nano-hexagonal boron nitride, N,N-dimethylformamide and acetone is 1:0.1-0.3:4-6:4-6.

[0029] N,N-dimethylformamide, as a highly polar solvent, ensures the full expansion of the cellulose acetate polymer chains through its dissolving power. Acetone, as a low-boiling-point solvent, preferentially evaporates during the subsequent air-drying process, triggering the initial stage of phase separation. The mass ratio of the two solvents is limited to an equilibrium range of 4-6:4-6, ensuring that the solution viscosity meets the leveling requirements of the coating process while preventing solvent residue from causing pore structure collapse. When the amount of nano-hexagonal boron nitride added is controlled at 10%-30% of the mass of cellulose acetate, its solid content in the mixed solution reaches 5%-12wt%. This concentration range ensures that the nanosheets form a continuous reflective network in the matrix while preventing agglomeration caused by excessive addition.

[0030] Specifically, in the coating process, when the mass ratio of N,N-dimethylformamide to acetone is 1:1, the solvent evaporation gradient during the natural air-drying stage causes the cellulose acetate molecular chains to arrange themselves in an orderly manner at the solvent-non-solvent interface, forming interconnected channels with a pore size of 50-200 nm. In the subsequent pure water immersion stage, the remaining N,N-dimethylformamide diffuses into the water, ultimately forming a three-dimensional network structure with a porosity of 85%-92%.

[0031] As a preferred embodiment, the present invention is implemented as follows: When preparing the radiation cooling layer, N,N-dimethylformamide and acetone are selected as organic solvents. First, cellulose acetate is dissolved in N,N-dimethylformamide, then nano-hexagonal boron nitride powder is added, and finally acetone is added for mixing. The mass ratio of cellulose acetate, nano-hexagonal boron nitride, N,N-dimethylformamide, and acetone in the mixed solution can be 1:0.2:5:5. After the mixed solution is thoroughly stirred, it is coated onto a substrate using a blade coating method, and a non-solvent-induced phase separation treatment is performed to form a radiation cooling layer with a porous structure. Through the above technical solution, this application can optimize the dissolution process of cellulose acetate and the dispersion process of nano-hexagonal boron nitride. The combination of N,N-dimethylformamide and acetone can synergistically regulate the polarity and volatility of the solvent, promote the complete dissolution of cellulose acetate, accelerate the solvent evaporation in the subsequent phase separation stage, and thus more efficiently form a uniform porous structure. By controlling the mass ratio of cellulose acetate, nano-hexagonal boron nitride, and the two solvents within a specific range, it is possible to ensure that the dispersion concentration of the nanomaterials enhances the reflectivity of the radiation cooling layer without compromising the stability of the porous structure due to excessive aggregation. Precise control of the solvent ratio balances the solution viscosity and the rate of non-solvent-induced phase separation, preventing problems such as poor leveling or pore structure collapse during coating, ultimately achieving efficient preparation and performance improvement of the radiation cooling layer.

[0032] In a preferred embodiment, cellulose acetate with an acetyl content of 32.0 wt% and a hydroxyl content of 8.7 wt% is selected for preparing the radiation cooling layer, and hexagonal boron nitride nanoparticles with a particle size of 500 nm are used. The acetyl content of cellulose acetate achieves chemical stability by balancing the material's solubility and film-forming properties in organic solvents. For example, when the acetyl content is below 32.0 wt%, insufficient material rigidity may lead to the collapse of the porous structure, while a higher value reduces hydrophilicity and affects phase separation. The hydroxyl content enhances interfacial bonding by providing polar groups; for example, when the hydroxyl content is 8.7 wt%, the intermolecular forces between cellulose acetate and hexagonal boron nitride nanoparticles are optimized. The particle size of the hexagonal boron nitride nanoparticles controls the matching relationship between dispersion stability and optical performance. For example, 500 nm particles avoid agglomeration and sedimentation, and their size matching with the solar wavelength improves scattering efficiency.

[0033] In a preferred embodiment, the substrate coated according to the present invention is first air-dried at room temperature for 5 minutes to form a preliminary phase separation interface on the solution surface. Subsequently, the substrate is immersed in pure water for 20 minutes. During this process, water, acting as a non-solvent, exchanges with the remaining solvent, promoting the final phase separation and solidification of the mixed solution of cellulose acetate and nano-hexagonal boron nitride, forming a porous radiation-cooled layer. Through the above technical solution, the present invention achieves precise control of the non-solvent-induced phase separation process. This avoids the problems of excessive solvent residue leading to pore morphology damage due to insufficient air-drying time, or structural collapse or interlayer delamination caused by excessive immersion time. Furthermore, this method ensures the uniformity and stability of the porous structure, improving the mechanical and optical properties of the radiation-cooled layer.

[0034] Example 3: In some of the above-mentioned schemes in this application, if the delignification treatment is not precisely controlled, or if the type, ratio, and vacuum treatment process parameters of the mixture containing silane coupling agent and phase change material are inappropriate, it may have an adverse effect on the phase change thermal storage layer.

[0035] The delignification treatment of wood according to the present invention includes the following steps: First, a sodium chlorite solution is prepared, and the wood (balsa wood) sample is immersed in the solution. Then, the pH of the solution is adjusted to 4.5 using dilute hydrochloric acid. The solution containing the wood sample is placed in a constant temperature water bath, and the temperature is set to 85°C for 6 hours. After treatment, the wood sample is removed and repeatedly rinsed with deionized water until neutral, and finally dried in a 60°C oven for 24 hours. Through the above technical solution, the present invention achieves a balance between lignin removal efficiency and wood structural integrity during the wood delignification process. Precise control of the sodium chlorite solution concentration, pH value, reaction temperature, and time ensures efficient lignin removal while preserving the porous structure and mechanical strength of the wood. This treatment method forms a uniform porous structure, providing sufficient pores and interfacial bonding sites for subsequent impregnation of phase change materials, thereby improving the heat storage performance and thermal conductivity of the phase change thermal storage layer.

[0036] In a preferred embodiment, methyltrimethoxysilane is selected as the silane coupling agent and octadecane as the phase change material when preparing the phase change thermal storage layer. First, a mixture is prepared by mixing methyltrimethoxysilane, octadecane, and water in a mass ratio of 1:1:2. Specifically, 0.1 mol / L hydrochloric acid is added to 100 g of water to adjust the pH to 4.0, then 50 g of methyltrimethoxysilane and 50 g of octadecane are added and stirred until homogeneous to form the mixture. Delignified wood is then immersed in the mixture and treated under a vacuum of -0.1 MPa for 2 hours. The wood is then removed and dried at 60°C for 24 hours, ultimately forming the phase change thermal storage layer. Through the above technical solution, this invention achieves precise control of the mixture composition and ratio. Methyltrimethoxysilane, as a silane coupling agent, reacts with the methoxy group in its molecular structure to form stable chemical bonds with the hydroxyl groups on the wood surface, enhancing the interfacial bonding between the phase change heat storage layer and the delignified wood matrix, and preventing the phase change material from detaching due to thermal stress or external forces during use. Octadecylane, as a phase change material, has a suitable phase change temperature, enabling efficient heat storage and release through solid-liquid phase change when the ambient temperature changes. By limiting the mass ratio of silane coupling agent, phase change material, and water to 1:1:2, the hydrolysis reaction of the silane coupling agent is fully carried out, forming a homogeneous coupling agent solution, while the phase change material is fully wetted by the coupling agent solution. This avoids stratification of the mixture or uneven dispersion of the phase change material due to imbalance in the ratio, thus ensuring that the final phase change heat storage layer has stable heat storage capacity and durable interfacial bonding performance. By controlling the pH value and component ratio of the mixture, the hydrolysis reaction of the silane coupling agent is promoted, forming a three-dimensional network structure that uniformly coats the phase change material. This structure not only increases the load of phase change material in wood, but also improves the bonding strength between the phase change heat storage layer and the wood matrix.

[0037] In a preferred embodiment, the mixture and wood are placed in a vacuum treatment device, and the vacuum pump is activated to reduce the ambient pressure to -0.1 MPa. This vacuum level is maintained for continuous impregnation, with the impregnation time controlled within the range of 1 to 3 hours. After impregnation, the wood is removed and placed in a drying oven for curing, allowing the silane coupling agent to fully bond with the wood surface while simultaneously ensuring the stable loading of octadecane within the wood pores. Through the above technical solution, the present invention effectively balances the contradiction between the penetration depth of the mixture in the wood pores and the stability of the material structure. Under a vacuum condition of -0.1 MPa, the mixture is driven by the pressure difference to fully penetrate the internal pore structure of the wood, avoiding the collapse of the wood fiber structure due to excessive pressure. The impregnation time of 1-3 hours ensures both the full reaction of the silane coupling agent with the hydroxyl groups on the wood surface and the uniform distribution of the phase change material within the pores. The resulting phase change thermal storage layer has a stable load-bearing capacity, providing a structural basis for the dynamic thermal management performance of the subsequent composite material.

[0038] Example 4: In some of the above-mentioned solutions in this application, a dual-layer dynamic thermal management material is proposed to be formed by combining a radiative cooling layer and a phase change thermal storage layer. However, if an external adhesive or mechanical fixing method is used during the composite process, the interlayer interface thermal resistance may increase, affecting the heat transfer efficiency. In addition, if the interlayer bonding is not stable, it is easy to peel off under thermal stress or environmental changes, leading to material structure failure.

[0039] To address this, the present invention further proposes a radiative cooling layer located on top and a phase change thermal storage layer located on the bottom. The radiative cooling layer and the phase change thermal storage layer are bonded together by the adhesive properties of the phase change thermal storage layer. The upper layer of the radiative cooling layer is positioned to directly face the incident direction of solar radiation. This structural arrangement effectively covers the ultraviolet-visible-near-infrared band of the solar spectrum. For example, when the particle size of the nano-hexagonal boron nitride in the radiative cooling layer is controlled at 500 nm, its scattering characteristics can achieve efficient reflection of the 0.3-2.5 μm band. The lower layer of the phase change thermal storage layer is adapted to its thermal buffering function. When the chemical bonding between the silane coupling agent and the delignified wood fibers in this layer reaches a stable state, the three-dimensional network structure formed inside can effectively load the phase change material octadecane. Through the above technical solution, the present invention solves the problem of increased interfacial thermal resistance caused by external adhesives between composite layers, while avoiding the risk of structural delamination caused by mechanical fixing. The bonding interface forms a stable connection through the chemical bonding between the silane coupling agent and the wood fibers, ensuring efficient heat conduction between the layers. The viscous surface of the phase change thermal storage layer is in direct contact with the radiative cooling layer to form a continuous heat conduction path, which allows the heat reflected during the day to be quickly transferred to the thermal storage layer for storage, and the heat released by the thermal storage layer at night to be conducted back to the radiative cooling layer through the interface to achieve thermal balance.

[0040] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings of the embodiments will be briefly described below. Figure 1 A scanning electron microscope image of the radiation cooling layer of the double-layer dynamic thermal management material in the embodiments of this application; Figure 2 A scanning electron microscope image of the phase change thermal storage layer of the bilayer dynamic thermal management material in the embodiments of this application; Figure 3 The solar spectral reflectance curves of the double-layer dynamic thermal management material in the embodiments of this application are shown in the 0.3μm-2.5μm wavelength band. Figure 4 This is an emissivity curve of the bilayer dynamic thermal management material in the 8μm-13μm atmospheric window band in the embodiments of this application; Figure 5 This is a differential scanning calorimeter (DSC) test curve of the bilayer dynamic thermal management material in the embodiments of this application, wherein the tested bilayer dynamic thermal management materials were all prepared using the process of the preferred embodiment. (Summary) Figures 1 to 5As shown in the accompanying drawings, the bilayer dynamic thermal management material of the present invention has a solar spectral weighted average reflectance of 96.2% in the 0.3μm-2.5μm solar spectral band, a solar spectral weighted average reflectance of 98.4% in the 0.36μm-1.16μm visible-near infrared band, and a weighted average reflectance of 93.8% in the 8μm-13μm atmospheric window band, and has a crystallization enthalpy of 124.578J / g and a melting enthalpy of 126.23J / g.

[0041] In summary, this invention, on the one hand, prepares a radiative cooling layer using a solvent-inducing phase separation method, thus exhibiting extremely high porosity with pore sizes mostly distributed in the range of 0.2 μm to 2.5 μm. Furthermore, the 500 nm nano-hexagonal boron nitride significantly enhances the reflectivity around 500 nm, thereby achieving high reflectivity across the entire ultraviolet-visible-near-infrared spectrum. Simultaneously, cellulose acetate and nano-hexagonal boron nitride possess a certain mid-infrared emissivity within the atmospheric window band of 8 μm to 13 μm. On the other hand, the phase change thermal storage layer is impregnated into delignified wood through the hydrolysis and condensation of methyltrimethoxysilane and the blending of octadecane. The octadecane impregnation endows the phase change thermal storage layer with superior phase change thermal storage capacity, while the hydrolysis and polymerization of methyltrimethoxysilane, followed by impregnation, provides the phase change thermal storage layer with high atmospheric window emissivity to compensate for the insufficient emissivity of the radiative cooling layer. Therefore, the dual-layer dynamic thermal management material of the present invention not only significantly improves the overall emissivity of the material to enhance its radiative cooling capacity, but also enables the material to have a dynamic temperature control effect before and after the octadecane phase transition temperature.

Claims

1. A method for preparing a double-layer dynamic thermal management material, characterized in that, Includes the following steps: Step 1: Preparation of radiation cooling layer: Dissolve cellulose acetate in an organic solvent and uniformly disperse nano-hexagonal boron nitride to form a mixed solution. After coating the mixed solution on a substrate, a porous radiation cooling layer is formed by processing it through a non-solvent-induced phase separation method. Step 2, Preparation of phase change heat storage layer: The delignified wood is impregnated in a mixture containing silane coupling agent and phase change material, and then vacuum treated and dried to form a phase change heat storage layer; Step 3: Combine the radiative cooling layer and the phase change thermal storage layer to form a double-layer dynamic thermal management material; In step 1, the organic solvent is composed of N,N-dimethylformamide and acetone; in the mixed solution, the mass ratio of cellulose acetate, nano-hexagonal boron nitride, N,N-dimethylformamide and acetone is 1:0.1-0.3:4-6:4-6.

2. The method for preparing the double-layer dynamic thermal management material according to claim 1, characterized in that: In step 1, the acetyl content of the cellulose acetate is 32.0 wt%, and the hydroxyl content is 8.7 wt%; the particle size of the nano-hexagonal boron nitride is 500 nm.

3. The method for preparing the double-layer dynamic thermal management material according to claim 1, characterized in that: In step 1, the non-solvent-induced phase separation method includes: the solution coated on the substrate is naturally air-dried for 3-8 minutes and then immersed in pure water for 15-25 minutes.

4. The method for preparing the double-layer dynamic thermal management material according to claim 1, characterized in that: In step 2, the delignification treatment of the wood includes: immersing the wood in a sodium chlorite solution, adjusting the pH to 4-5, and heating it in a water bath at 80-90℃ for 4-8 hours.

5. The method for preparing the double-layer dynamic thermal management material according to claim 1, characterized in that: In step 2, the silane coupling agent is methyltrimethoxysilane, the phase change material is octadecane, and the mass ratio of the silane coupling agent, the phase change material and water is 1:0.8-1.2:1.5-2.

5.

6. The method for preparing the double-layer dynamic thermal management material according to claim 5, characterized in that: In step 2, the preparation process of the mixture containing the silane coupling agent and the phase change material is as follows: First, add hydrochloric acid to the water to adjust the pH value to 3.5-4.5, where the concentration of hydrochloric acid is 0.1 mol / L. Then, add methyltrimethoxysilane and octadecane to blend so that the mass ratio of silane coupling agent, phase change material and water is 1:1:

2.

7. The method for preparing the double-layer dynamic thermal management material according to claim 1, characterized in that: In step 2, the vacuum treatment pressure is -0.1 MPa, and the immersion time is 1-3 hours.

8. The method for preparing the double-layer dynamic thermal management material according to claim 1, characterized in that: In step 3, the radiative cooling layer is located on the upper layer, and the phase change heat storage layer is located on the lower layer. The radiative cooling layer and the phase change heat storage layer are bonded together by the adhesiveness of the phase change heat storage layer.

Images