Preparation method of a dual-network aerogel phase change composite material

Abstract

The application discloses a preparation method of a double-network aerogel phase change composite material. The double-network aerogel phase change composite material prepared by the method is a double-network aerogel phase change composite material with 'rigid-flexible-hydrophobic' synergy, which can realize manufacturability under normal pressure, efficient and stable packaging of high-load PCM and excellent service reliability while maintaining high porosity and low thermal conductivity. In the application, hydrophobic silicon source and TEOS are used as double precursors, and in the gelation process, the skeleton is embedded in situ to reduce the interfacial free energy and dry tension; boehmite nanofibers are introduced in the sol stage to improve the anti-collapse and anti-crack ability of the skeleton from the source; after gelation, secondary crosslinking is carried out to obtain a flexible through network; low surface tension solvents are replaced step by step, and the material is dried by stepwise heating under normal pressure, so that a double-network, size-stable, light and porous aerogel matrix is obtained; under vacuum conditions, the heat conduction and flame retardant channels are constructed, and the leakage is inhibited, so that the double-network aerogel phase change composite material is obtained.

Description

Technical Field

[0001] This invention relates to a method for preparing a phase change composite material, and more specifically to a method for preparing a dual-network aerogel phase change composite material, belonging to the technical field of preparation of nanoporous materials and composite phase change energy storage materials. Background Technology

[0002] Aerogels are three-dimensional porous amorphous frameworks composed of polymer chains or nanoparticles, characterized by low density, high porosity, and ultra-low thermal conductivity. Among them, SiO2 aerogels can achieve λ < 0.02 W·m⁻¹·K⁻¹ at room temperature, and have shown broad application prospects in aerospace, petrochemical, building insulation, and battery thermal management. However, pure SiO2 aerogels are brittle and prone to shrinkage and structural degradation during wide-temperature and long-term service, which limits their thermal insulation and mechanical reliability. In terms of industrial preparation, although supercritical drying can suppress shrinkage and obtain a high-porosity framework, the equipment investment and process energy consumption are high and the process is complex, making it difficult to support low-cost large-scale production. Atmospheric pressure drying has cost and process advantages, but capillary stress during drying can easily induce framework collapse and cracking. Existing research has shown that by reducing drying stress through silane modification and low surface tension solvent replacement, and by superimposing a fiber framework or a second network to provide structural support, the forming stability of atmospheric pressure drying can be significantly improved (Wu et al., Chemical Industry Progress, 2022, 41(02): 837).

[0003] To meet the integrated need for thermal insulation and heat storage, the combination of phase change materials (PCMs) and aerogels has become a hot topic. However, after impregnation with high-content PCMs, the single-network SiO2 framework often suffers from pore blockage, increased thermal conductivity, framework pulverization, and insufficient support. Meanwhile, combustible organic PCMs pose risks of leakage and flame retardancy, making it difficult to simultaneously achieve high heat storage density, thermal insulation performance, and cycle stability. Therefore, researchers have turned to dual-network reinforced structures, hoping to achieve both high-load PCM and long-term service stability while being manufacturable at atmospheric pressure.

[0004] Current research often focuses on "organic-inorganic" or "inorganic-inorganic" dual-network approaches, but these approaches still struggle to simultaneously meet the requirements of large-scale preparation and complex service applications. For example, with organic polybenzoxazine / SiO2, the asynchronous solubility parameters and gel / crosslinking rates between the two phases easily lead to poor interfacial compatibility and macroscopic phase separation. This results in complex processes, high costs, and significant organic waste, with a narrow window for atmospheric pressure densification (Liu et al., ACS Applied Nano Materials, 2024, 7(16): 19527-19537). Similarly, with inorganic-inorganic interpenetrating networks like SiC / SiO2, the process typically involves first constructing a SiC framework, then growing SiO2 in situ within it, followed by hydrophobication with HMDS and atmospheric pressure drying. This multi-step process is highly dependent on interfacial treatment, and research often focuses on thermal protection or electromagnetic absorption, with insufficient attention paid to the impregnation adaptation and cycle reliability of high-load PCMs (Yan et al., Composites Part A, 2024). 186); Rare earth modified SiO2 inhibits high-temperature shrinkage and crystallization and reduces thermal conductivity by forming Si-O-RE (Y / Yb, etc.) bonds, but it is mainly aimed at improving high-temperature tolerance and mostly relies on supercritical drying. It pays limited attention to the relief of damp heat and drying stress, as well as the synergistic encapsulation with high-content PCM and cycle stability (Wu et al., Ceramics International, 2025, 51(16): 22086-22102); Some elastic high-temperature organic-based composite systems such as PI / SiO2 have the advantages of flexibility and temperature resistance, but they usually still rely on supercritical drying, which increases the complexity of equipment and processes (Sun et al., Materials Today Communications, 2024, 39). In terms of reinforcement selection, boehmite (γ-AlOOH) nanofibers are highly matched in size to the pore size of SiO2 framework (approximately 20 nm in diameter and 0.4-0.5 μm in length). Its surface -OH can form a dense hydrogen bond network with Si-OH, significantly improving the interfacial load-bearing capacity and crack resistance. Compared with micron-sized fibers or macro-fiber mats such as glass fiber and mullite, boehmite has better dispersibility and specific surface area, does not introduce significant macropore stratification, and is more conducive to the uniform impregnation and cycle stability of subsequent PCM. It combines cost and process adaptability and is suitable for low-to-medium temperature thermal protection scenarios (Zhang Jie et al., Journal of Chinese Universities and Colleges Chemistry, 2022, 43(11): 108). Therefore, to achieve low-cost manufacturing and stable composite with high PCM content under normal pressure drying conditions, and to simultaneously solve the coupled problems of brittleness, shrinkage, leakage and flame retardancy, a systematic and synergistic design is needed in the reinforcing phase, interface chemistry, gelation and drying process control, and functional synergy. Thus, it is necessary to develop a preparation method for dual-network aerogel phase change composite materials to solve the problems existing in the current technology. Summary of the Invention

[0005] This invention addresses the problems of inorganic silicon-based aerogels in the prior art, such as easy collapse and high brittleness during normal pressure drying, pore blockage and leakage after being combined with high-content PCM, and insufficient flame retardancy and cycle stability. It provides a method for preparing a dual-network aerogel phase change composite material. The dual-network aerogel phase change composite material prepared by this method is a "rigid-flexible-hydrophobic" synergistic dual-network aerogel phase change composite material. While maintaining high porosity and low thermal conductivity, it achieves manufacturability under normal pressure conditions, efficient and stable encapsulation of high-load PCM, and excellent service reliability.

[0006] This invention employs a hydrophobic silicon source (MTMS and / or MTES) and TEOS as dual precursors to conduct an acid / base catalyzed sol-gel reaction in an alcohol / water system. This allows the -CH3 hydrophobic groups to be in situ embedded into the framework during gelation, reducing interfacial free energy and drying tension. During the sol stage, boehmite (γ-AlOOH) nanofibers are introduced to achieve nanoscale matching with the SiO2 framework pore size and interfacial hydrogen bonding, thereby enhancing the framework's resistance to collapse and cracking from the source. After gelation, the wet gel is placed in an aluminum-containing source solution or a CaCO3-GDL solution system for secondary crosslinking, allowing sodium alginate segments to bind with Al... 3⁺ Or Ca 2+ Coordination forms a flexible, interconnected "egg-box" type ion-crosslinked network to disperse localized stresses caused by drying and impregnation and improve hygrothermal stability. Subsequently, a stepwise low-surface-tension solvent replacement with ethanol and n-hexane is used, followed by stepwise heating and drying at atmospheric pressure to obtain a lightweight, porous aerogel matrix with a dual-network, in-situ hydrophobic, and dimensionally stable structure. Finally, under vacuum conditions, a mixture of molten paraffin (or decane, etc.) and a flame-retardant-thermal-conducting synergist (such as expanded graphite) is impregnated into the pores to construct thermally conductive and flame-retardant channels and suppress leakage, achieving a phase change composite aerogel with high permeability, high heat storage density, low thermal conductivity, and excellent cycling stability.

[0007] This invention is achieved through the following technical solution: The preparation method of the dual-network aerogel phase change composite material of the present invention includes the following steps: 1) Preparation of SiO2-sodium alginate sol and wet gel A hydrophobic silicon source was mixed with tetraethyl orthosilicate, and water and anhydrous ethanol were added. The mixture was then hydrolyzed under acid catalysis while the pH of the system was controlled. The mixture was stirred uniformly to obtain a silicon source precursor sol. Boehmite nanofibers were added to the silicon source precursor sol, and the mixture was ultrasonically treated to obtain a uniformly dispersed mixed sol. The mixed sol was slowly added to a 2 wt% sodium alginate aqueous solution and stirred until homogeneous. Subsequently, a pH adjuster was added dropwise to adjust the pH of the system, and the mixture was stirred to form a wet gel. 2) Construction of a flexible-rigid dual-network structure After the wet gel obtained in step 1) is allowed to stand and age, it is completely immersed in an aluminum source solution or a calcium source solution system to carry out secondary cross-linking. After secondary cross-linking, a flexible-rigid through-network structure is constructed to obtain a composite wet gel. 3) Solvent displacement of composite wet gel The composite wet gel obtained in step 2) is continuously replaced with anhydrous ethanol and n-hexane to remove water and other residual liquids; the solvent replacement process is now complete and the composite wet gel is ready to dry. 4) Drying of the composite wet gel The composite wet gel obtained after solvent replacement in step 3) is first dried for more than 24 hours, then dried at a gradually increasing temperature for more than 12 hours, and finally dried at a high temperature for more than 2 hours to obtain a lightweight and porous double-network aerogel matrix. 5) Preparation of dual-network aerogel phase change composite materials The lightweight, porous dual-network aerogel matrix obtained in step 4) is immersed in a molten phase change material containing phase change material and flame-retardant and thermally conductive additives to fully fill the aerogel pores. After cooling, the surface residue is removed to obtain a dual-network aerogel phase change composite material.

[0008] The preparation method of the above-mentioned dual-network aerogel phase change composite material of the present invention further includes the following technical solution: the temperature at which the hydrophobic silicon source and tetraethyl orthosilicate are mixed in step 1) is 40-50℃, wherein the hydrophobic silicon source is methyltrimethoxysilane or methyltriethoxysilane; the water is deionized water, and the molar ratio of hydrophobic silicon source: tetraethyl orthosilicate: anhydrous ethanol: water is 1:1:9:6; the acid catalyst is hydrochloric acid or acetic acid, and the pH of the system is controlled at 3-4.

[0009] The preparation method of the above-mentioned dual-network aerogel phase change composite material of the present invention may further include the following: the amount of boehmite nanofibers used in step 1) is 1-2 wt% of the sol mass; the volume ratio of the mixed sol to 2 wt% sodium alginate aqueous solution is 3-5:15-20; and the pH adjuster is ammonia or propylene oxide to adjust the pH of the system to 5-6.

[0010] The preparation method of the above-mentioned dual-network aerogel phase change composite material of the present invention can be further described as follows: the aluminum source solution in step 2) is an AlCl3 solution or an Al(NO3)3 solution, the calcium source solution is a CaCl2 solution or a Ca(NO3)2 solution, and the molar concentration of the aluminum source solution or the calcium source solution is 0.1-0.2 mol L⁻¹; the secondary crosslinking temperature is 40-50 ℃, and the secondary crosslinking time is 12-24 h.

[0011] The preparation method of the above-mentioned dual-network aerogel phase change composite material of the present invention can be further described as follows: the composite wet gel described in step 3) is replaced sequentially with anhydrous ethanol and n-hexane at room temperature; the replacement with anhydrous ethanol lasts for 12-24 hours and is replaced 3-4 times; the replacement with n-hexane lasts for 12-24 hours and is replaced 1-4 times.

[0012] The preparation method of the above-mentioned dual-network aerogel phase change composite material of the present invention can be further described as follows: the drying temperature for drying for more than 24 hours in step 4) is 40-50 ℃, the drying temperature for drying for more than 12 hours is 60-70 ℃ for 12 hours, the high temperature drying temperature is 100-110 ℃, and the overall drying process is a step-by-step temperature increase program drying under normal pressure.

[0013] The preparation method of the above-mentioned dual-network aerogel phase change composite material of the present invention may further include the following technical solutions: the phase change material mentioned in step 5) is paraffin or stearic acid; the flame retardant and thermally conductive additive is expanded graphite, graphene or carbon nanotubes, and the amount of flame retardant and thermally conductive additive is 3-5 wt% of the mass of the phase change material; the low pressure conditions for impregnation are a vacuum degree not higher than 0.1 MPa, an impregnation time of 0.5-1 h, and an impregnation temperature of 75-85℃.

[0014] Compared with the prior art, the present invention has the following advantages: In terms of manufacturability under normal pressure, this invention significantly reduces drying stress and avoids supercritical equipment and energy consumption through in-situ hydrophobicity and low surface tension replacement. Regarding structural stability, it relies on the size matching and hydrogen bond network between boehmite nanofibers and the SiO2 framework to enhance interfacial load-bearing capacity and suppress drying shrinkage and cracking. In terms of environmental adaptability, it utilizes sodium alginate-Al... 3 ⁺ (or Ca) 2 + The flexible subnetwork disperses stress and improves hygrothermal stability. In terms of functional synergy, it achieves rapid charge and discharge of high-load PCM, low leakage and flame retardant safety through vacuum impregnation and expanded graphite channels, thereby achieving a balance between cost, process and overall performance, and is suitable for engineering applications for wide-temperature thermal management.

[0015] This invention can be manufactured under normal pressure: It employs in-situ hydrophobic co-condensation of MTMS / (or MTES) and TEOS with ethanol and n-hexane substitution, achieving a SiO2 framework with high porosity, low density, low thermal conductivity, and high hydrophobicity without relying on supercritical drying, significantly reducing equipment and energy consumption; it possesses a rigid-flexible through-structure: γ-AlOOH nanofibers and sodium alginate-Al 3 ⁺ / Ca 2⁺ The "egg box" ion crosslinking forms a dual network, and nanoscale matching and hydrogen bonding effectively disperse drying / impregnation stress, significantly inhibiting shrinkage and cracking, and improving dimensional, mechanical, and hygrothermal / cyclic stability; integrated thermal management with high-load PCM: vacuum impregnation achieves high loading, low leakage, and rapid charge / discharge heat; expanded graphite and other materials synergistically construct thermally conductive and flame-retardant channels, achieving a comprehensive balance between insulation + heat storage and safety; in addition, the process is simple, has a wide window, and is easy to scale up: pH-controlled gelation triggers are optional (ammonia / propylene oxide), and secondary crosslinking ions can be replaced (Al). 3 ⁺ / Ca 2 ⁺), atmospheric pressure step drying is suitable for different sizes and formulations, making it easy to scale up and promote. Attached Figure Description

[0016] Figure 1 SEM image of boehmite fiber composite aerogel in Example 1 Figure 2 BET plot of the boehmite fiber composite aerogel prepared in Example 1 Figure 3 Water contact angle diagram of the composite aerogel prepared in Example 1 Figure 4 SEM image of the aerogel composite material in Example 1 Figure 5 Schematic diagram of a double-network aerogel structure Detailed Implementation Example 1

[0017] Mix 2.6 mL of MTMS and 4 mL of TEOS, then add to a mixture of 9.6 mL of anhydrous ethanol and 2 mL of water. Adjust the pH to 4 by adding HCl solution dropwise. Add 1% boehmite nanofibers to the silicon precursor sol, and obtain a uniformly dispersed mixed sol by ultrasonic treatment. Take 3 mL of the mixed sol and mix it with 15 mL of 2 wt% sodium alginate solution. Stir evenly in a 40 °C water bath. Adjust the pH to approximately 5.0 with propylene oxide and stir evenly to obtain a pre-crosslinked sol. Allow it to stand to obtain a gel. Completely immerse the obtained wet gel in 0.1 mol·L⁻¹ AlCl₃ solution at 40 °C for 24 h for crosslinking. The obtained composite wet gel is then subjected to ethanol replacement for 24 h (twice) and n-hexane replacement for 12 h (twice) at room temperature. The solvent-displaced composite wet gel was subjected to a stepwise temperature-programmed drying process at atmospheric pressure (40℃ for 24 h, 60℃ for 12 h, and 100℃ for 2 h) to obtain an aerogel. This aerogel was then impregnated with paraffin wax containing 3 wt% expanded graphite at 75℃ and 0.08 MPa for 30 min, followed by cooling to remove residual wax, yielding the composite material. The prepared aerogel matrix had a density of 0.0906 g / cm³. 3 The BET specific surface area of ​​the boehmite fiber composite aerogel is 500.672 m².2 / g, the hydrophobic angle of the composite aerogel is 129.4°, and the melting temperature T of the composite aerogel material was measured by DSC. m =59℃, crystallization temperature T c =46℃. The latent heat after compounding is approximately 103.5 J / g.

[0018] Example 2 Mix 3 mL of MTES and 3.4 mL of TEOS, and add them to a mixture of 7.9 mL of anhydrous ethanol and 1.6 mL of water. Adjust the pH to 3.5 by adding HCl solution dropwise. Add 1.5% boehmite nanofibers to the silicon source precursor sol, and obtain a uniformly dispersed mixed sol by sonication. Take 4 mL of the mixed sol and mix it with 18 mL of 2 wt% sodium alginate solution. Stir evenly in a 45°C water bath. Adjust the pH to approximately 5.5 with propylene oxide and stir evenly to obtain a pre-crosslinked sol. Allow it to stand to obtain a gel. Completely immerse the obtained wet gel in 0.15 mol·L⁻¹ AlCl₃ solution at 45°C for crosslinking for 18 h. The obtained composite wet gel is then subjected to ethanol replacement for 12 h (4 times) and n-hexane replacement for 12 h (4 times) at room temperature. The solvent-displaced composite wet gel was subjected to a stepwise temperature-programmed drying process at atmospheric pressure (45℃ for 24 h, 65℃ for 12 h, and 105℃ for 2 h) to obtain an aerogel. This aerogel was then impregnated with stearic acid containing 4 wt% expanded graphite at 85℃ and 0.1 MPa for 45 min, followed by cooling to remove residual liquid, yielding the composite material. The prepared aerogel matrix had a density of 0.0960 g / cm³. 3 The BET specific surface area of ​​the boehmite fiber composite aerogel is 490.822 m². 2 / g, the hydrophobic angle of the composite aerogel is 131.0°.

[0019] Example 3 Mix 5 mL of MTMS and 7.8 mL of TEOS, then add to a mixture of 18.4 mL of anhydrous ethanol and 3.8 mL of water. Adjust the pH to 3 by adding HCl solution dropwise. Add 2% boehmite nanofibers to the silicon precursor sol, and obtain a uniformly dispersed mixed sol by sonication. Take 5 mL of the mixed sol and mix with 20 mL of 2 wt% sodium alginate solution, stirring evenly in a 50°C water bath. Adjust the pH to approximately 6.0 with propylene oxide, and stir evenly to obtain a pre-crosslinked sol. Allow to stand to obtain a gel. Completely immerse the obtained wet gel in 0.2 mol·L⁻¹ AlCl₃ solution at 50°C for crosslinking for 12 h. The obtained composite wet gel is then subjected to ethanol replacement for 18 h (3 times) and n-hexane replacement for 18 h (3 times) at room temperature. The solvent-displaced composite wet gel was subjected to a stepwise temperature-programmed drying process at atmospheric pressure (24 h at 50 °C, 12 h at 70 °C, and 2 h at 110 °C) to obtain an aerogel. This aerogel was then impregnated with paraffin containing 5 wt% expanded graphite at 80 °C and 0.09 MPa for 1 h, followed by cooling to remove residual liquid, yielding the composite material. The prepared aerogel matrix had a density of 0.102 g / cm³. 3 The BET specific surface area of ​​the boehmite fiber composite aerogel is 470.968 m². 2 / g, the hydrophobic angle of the composite aerogel is 130.1°.

[0020] Example 4 Mix 5 mL of MTES and 5.6 mL of TEOS, and add them to a mixture of 13.2 mL of anhydrous ethanol and 2.7 mL of water. Adjust the pH to 4 by adding HCl solution dropwise. Add 1% boehmite nanofibers to the silicon source precursor sol, and obtain a uniformly dispersed mixed sol by sonication. Take 3 mL of the mixed sol and mix it with 15 mL of 2 wt% sodium alginate solution. Stir evenly in a 45°C water bath. Adjust the pH to approximately 5.5 with propylene oxide and stir evenly to obtain a pre-crosslinked sol. Allow it to stand to obtain a gel. Completely immerse the obtained wet gel in 0.1 mol·L⁻¹ CaCl₂ solution at 45°C for crosslinking for 24 h. The obtained composite wet gel is then subjected to ethanol replacement for 24 h (twice) and n-hexane replacement for 24 h (twice) at room temperature. The solvent-displaced composite wet gel was subjected to a stepwise temperature-programmed drying process at atmospheric pressure (40℃ for 24 h, 60℃ for 12 h, and 110℃ for 2 h) to obtain an aerogel. This aerogel was then impregnated with paraffin wax containing 5 wt% expanded graphite at 75℃ and 0.08 MPa for 45 min, followed by cooling to remove residual liquid, yielding the composite material. The prepared aerogel matrix had a density of 0.0895 g / cm³. 3 The BET specific surface area of ​​the boehmite fiber composite aerogel is 517.390 m². 2 / g, the hydrophobic angle of the composite aerogel is 130.5°.

[0021] Example 5 Mix 3.20 mL of MTMS and 5 mL of TEOS, then add to a mixture of 11.8 mL of anhydrous ethanol and 2.4 mL of water. Adjust the pH to 4 by adding HCl solution dropwise. Add 1% boehmite nanofibers to the silicon precursor sol, and obtain a uniformly dispersed mixed sol by sonication. Take 3 mL of the mixed sol and mix with 15 mL of 2 wt% sodium alginate solution, stirring evenly in a 45°C water bath. Adjust the pH to approximately 5.5 with propylene oxide, stir evenly to obtain a pre-crosslinked sol, and allow it to stand to obtain a gel. Completely immerse the obtained wet gel in 0.1 mol·L⁻¹ Ca(NO₃)₂ solution at 45°C for 24 h for crosslinking. The obtained composite wet gel is then subjected to ethanol replacement for 24 h (twice) and n-hexane replacement for 24 h (twice) at room temperature. The solvent-displaced composite wet gel was subjected to a stepwise temperature-programmed drying process at atmospheric pressure (40℃ for 24 h, 60℃ for 12 h, and 110℃ for 2 h) to obtain an aerogel. This aerogel was then impregnated with paraffin wax containing 5 wt% expanded graphite at 75℃ and 0.08 MPa for 45 min, followed by cooling to remove residual liquid, yielding the composite material. The prepared aerogel matrix had a density of 0.0890 g / cm³. 3 The BET specific surface area of ​​the boehmite fiber composite aerogel is 515.609 m². 2 / g, the hydrophobic angle of the composite aerogel is 129.3°.

[0022] Example 6 2.8 mL of MTMS and 4.4 mL of TEOS were mixed and added to a mixture of 10.3 mL of anhydrous ethanol and 2.1 mL of water. The pH was adjusted to 3.5 by adding HCl solution dropwise. 1.5% boehmite nanofibers were added to the silicon precursor sol, and the mixture was sonicated to obtain a uniformly dispersed mixed sol. 3 mL of the mixed sol was taken and mixed with 15 mL of 2 wt% sodium alginate solution and stirred evenly in a 45 ℃ water bath. The pH was adjusted to approximately 5.5 with propylene oxide and stirred evenly to obtain a pre-crosslinked sol. The sol was allowed to stand to obtain a gel. The obtained wet gel was completely immersed in 0.15 mol·L⁻¹ AlCl₃ solution at 45 ℃ for 18 h for crosslinking. The obtained composite wet gel was then subjected to ethanol replacement for 12 h (3 times) and n-hexane replacement for 12 h (3 times) at room temperature. The solvent-displaced composite wet gel was subjected to a stepwise temperature-programmed drying process at atmospheric pressure (45 °C for 24 h, 65 °C for 12 h, and then 105 °C for 2 h) to obtain an aerogel. This aerogel was then impregnated with paraffin containing 3 wt% expanded graphite at 80 °C and 0.09 MPa for 45 min, followed by cooling to remove residual liquid, yielding the composite material. The prepared aerogel matrix had a density of 0.0965 g / cm³. 3The BET specific surface area of ​​the boehmite fiber composite aerogel is 498.450 m². 2 / g, the hydrophobic angle of the composite aerogel is 129.9°.

[0023] Example 7 Mix 3.2 mL of MTES and 3.6 mL of TEOS, and add them to a mixture of 8.4 mL of anhydrous ethanol and 1.7 mL of water. Adjust the pH to 3.0 by adding HCl solution dropwise. Add 1% boehmite nanofibers to the silicon precursor sol, and obtain a uniformly dispersed mixed sol by sonication. Take 4 mL of the mixed sol and mix it with 18 mL of 2 wt% sodium alginate solution. Stir evenly in a 40 ℃ water bath. Adjust the pH to approximately 5.0 with ammonia water and stir evenly to obtain a pre-crosslinked sol. Allow it to stand to obtain a gel. Completely immerse the obtained wet gel in 0.10 mol·L⁻¹ Al(NO₃)₃ solution at 40 ℃ for 24 h for crosslinking. The obtained composite wet gel is then subjected to ethanol replacement for 24 h (twice) and n-hexane replacement for 12 h (twice) at room temperature. The solvent-displaced composite wet gel was subjected to a stepwise temperature-programmed drying process at atmospheric pressure (40 °C for 24 h, 60 °C for 12 h, and then 100 °C for 2 h) to obtain an aerogel. This aerogel was then impregnated with stearic acid containing 4 wt% graphene at 75 °C and 0.08 MPa for 1 h, followed by cooling to remove residual liquid, yielding the composite material. The prepared aerogel matrix had a density of 0.0898 g / cm³. 3 The BET specific surface area of ​​the boehmite fiber composite aerogel is 510.220 m². 2 / g, the hydrophobic angle of the composite aerogel is 131.2°. Example 8

[0024] 3.0 mL of MTMS and 4.7 mL of TEOS were mixed and added to a mixture of 11.1 mL of anhydrous ethanol and 2.3 mL of water. The pH was adjusted to 3.8 by adding HCl solution dropwise. 2% boehmite nanofibers were added to the silicon precursor sol, and the mixture was sonicated to obtain a uniformly dispersed mixed sol. 5 mL of the mixed sol was mixed with 20 mL of 2 wt% sodium alginate solution and stirred evenly in a 50 ℃ water bath. The pH was adjusted to approximately 6.0 with propylene oxide and stirred evenly to obtain a pre-crosslinked sol. The sol was allowed to stand to obtain a gel. The obtained wet gel was completely immersed in 0.20 mol·L⁻¹ AlCl₃ solution at 50 ℃ for 12 h for crosslinking. The obtained composite wet gel was then subjected to ethanol replacement for 18 h (3 times) and n-hexane replacement for 18 h (3 times) at room temperature. The solvent-displaced composite wet gel was subjected to a stepwise temperature-programmed drying process at atmospheric pressure (50 °C for 24 h, 70 °C for 12 h, and then 110 °C for 2 h) to obtain an aerogel. This aerogel was then impregnated with paraffin containing 5 wt% expanded graphite at 85 °C and 0.10 MPa for 30 min, followed by cooling to remove residual liquid, yielding the composite material. The prepared aerogel matrix had a density of 0.105 g / cm³. 3 The BET specific surface area of ​​the boehmite fiber composite aerogel is 465.880 m². 2 / g, the hydrophobic angle of the composite aerogel is 130.2°. Example 9

[0025] Mix 4.0 mL of MTES and 4.5 mL of TEOS, and add them to a mixture of 10.6 mL of anhydrous ethanol and 2.2 mL of water. Adjust the pH to 3.2 by adding HCl solution dropwise. Add 1.2% boehmite nanofibers to the silicon precursor sol. After sonication, obtain a uniformly dispersed mixed sol. Take 3 mL of the mixed sol and mix it with 15 mL of 2 wt% sodium alginate solution. Stir evenly in a 45 ℃ water bath. Adjust the pH to approximately 5.5 with ammonia water and stir evenly to obtain a pre-crosslinked sol. Allow it to stand to obtain a gel. Completely immerse the obtained wet gel in 0.10 mol·L⁻¹ CaCl₂ solution at 45 ℃ for crosslinking for 24 h. The obtained composite wet gel is then subjected to ethanol replacement for 12 h (4 times) and n-hexane replacement for 12 h (4 times) at room temperature. The solvent-displaced composite wet gel was subjected to a stepwise temperature-programmed drying process at atmospheric pressure (45 °C for 24 h, 65 °C for 12 h, and then 105 °C for 2 h) to obtain an aerogel. This aerogel was then impregnated with stearic acid containing 3 wt% carbon nanotubes at 80 °C and 0.09 MPa for 45 min, followed by cooling to remove residual liquid, yielding the composite material. The prepared aerogel matrix had a density of 0.0923 g / cm³. 3 The BET specific surface area of ​​the boehmite fiber composite aerogel is 505.915 m².2 / g, the hydrophobic angle of the composite aerogel is 130.8°. Example 10

[0026] 3.4 mL of MTMS and 5.3 mL of TEOS were mixed and added to a mixture of 12.5 mL of anhydrous ethanol and 2.6 mL of water. The pH was adjusted to 3.5 by adding HCl solution dropwise. 1% boehmite nanofibers were added to the silicon precursor sol, and the mixture was sonicated to obtain a uniformly dispersed mixed sol. 4 mL of the mixed sol was taken and mixed with 18 mL of 2 wt% sodium alginate solution and stirred evenly in a 40 ℃ water bath. The pH was adjusted to approximately 5.0 with propylene oxide and stirred evenly to obtain a pre-crosslinked sol. The sol was allowed to stand to obtain a gel. The obtained wet gel was completely immersed in 0.15 mol·L⁻¹ Ca(NO₃)₂ solution at 40 ℃ for 18 h for crosslinking. The obtained composite wet gel was subjected to ethanol replacement for 24 h (1 time) and 12 h (1 time) at room temperature, and then to n-hexane replacement for 12 h (2 times). The solvent-displaced composite wet gel was subjected to a stepwise temperature-programmed drying process at atmospheric pressure (40 °C for 24 h, 60 °C for 12 h, and then 100 °C for 2 h) to obtain an aerogel. This aerogel was then impregnated with paraffin containing 5 wt% graphene at 75 °C and 0.08 MPa for 1 h, followed by cooling to remove residual liquid, yielding the composite material. The prepared aerogel matrix had a density of 0.0906 g / cm³. 3 The BET specific surface area of ​​the boehmite fiber composite aerogel is 510.880 m². 2 / g, the hydrophobic angle of the composite aerogel is 129.6°. Example 11

[0027] Mix 3.6 mL of MTES and 4.0 mL of TEOS, and add them to a mixture of 9.5 mL of anhydrous ethanol and 2.0 mL of water. Adjust the pH to 3.8 by adding HCl solution dropwise. Add 1.8% boehmite nanofibers to the silicon source precursor sol. After sonication, obtain a uniformly dispersed mixed sol. Take 5 mL of the mixed sol and mix it with 20 mL of 2 wt% sodium alginate solution. Stir evenly in a 50 ℃ water bath. Adjust the pH to approximately 5.8 with ammonia water and stir evenly to obtain a pre-crosslinked sol. Allow it to stand to obtain a gel. Completely immerse the obtained wet gel in 0.20 mol·L⁻¹ Al(NO₃)₃ solution at 50 ℃ for 12 h for crosslinking. The obtained composite wet gel is then subjected to ethanol replacement for 12 h (3 times) and n-hexane replacement for 12 h (3 times) at room temperature. The solvent-displaced composite wet gel was subjected to a stepwise temperature-programmed drying process at atmospheric pressure (50 °C for 24 h, 70 °C for 12 h, and then 110 °C for 2 h) to obtain an aerogel. This aerogel was then impregnated with stearic acid containing 4 wt% carbon nanotubes at 85 °C and 0.10 MPa for 30 min, followed by cooling to remove residual liquid, yielding the composite material. The prepared aerogel matrix had a density of 0.0991 g / cm³. 3 The BET specific surface area of ​​the boehmite fiber composite aerogel is 482.930 m². 2 / g, the hydrophobic angle of the composite aerogel is 131.0°. Example 12

[0028] 2.9 mL of MTMS and 4.5 mL of TEOS were mixed and added to a mixture of 10.7 mL of anhydrous ethanol and 2.2 mL of water. The pH was adjusted to 3.0 by adding HCl solution dropwise. 1.3% boehmite nanofibers were added to the silicon precursor sol, and the mixture was sonicated to obtain a uniformly dispersed mixed sol. 3 mL of the mixed sol was taken and mixed with 16 mL of 2 wt% sodium alginate solution and stirred evenly in a 45 ℃ water bath. The pH was adjusted to approximately 5.2 with propylene oxide and stirred evenly to obtain a pre-crosslinked sol. The sol was allowed to stand to obtain a gel. The obtained wet gel was completely immersed in 0.10 mol·L⁻¹ AlCl₃ solution at 45 ℃ for 24 h for crosslinking. The obtained composite wet gel was then subjected to ethanol replacement for 18 h (twice) and n-hexane replacement for 18 h (twice) at room temperature. The solvent-displaced composite wet gel was subjected to a stepwise temperature-programmed drying process at atmospheric pressure (45 °C for 24 h, 65 °C for 12 h, and then 105 °C for 2 h) to obtain an aerogel. This aerogel was then impregnated with paraffin containing 3 wt% expanded graphite at 80 °C and 0.09 MPa for 1 h, followed by cooling to remove residual liquid, yielding the composite material. The prepared aerogel matrix had a density of 0.0945 g / cm³. 3The BET specific surface area of ​​the boehmite fiber composite aerogel is 500.870 m². 2 / g, the hydrophobic angle of the composite aerogel is 129.5°. Example 13

[0029] Mix 4.5 mL of MTES and 5.0 mL of TEOS, and add them to a mixture of 11.9 mL of anhydrous ethanol and 2.4 mL of water. Adjust the pH to 3.6 by adding HCl solution dropwise. Add 1% boehmite nanofibers to the silicon precursor sol, and obtain a uniformly dispersed mixed sol by sonication. Take 4 mL of the mixed sol and mix it with 19 mL of 2 wt% sodium alginate solution. Stir evenly in a 45 ℃ water bath. Adjust the pH to approximately 5.5 with ammonia water and stir evenly to obtain a pre-crosslinked sol. Allow it to stand to obtain a gel. Completely immerse the obtained wet gel in 0.20 mol·L⁻¹ CaCl₂ solution at 45 ℃ for crosslinking for 12 h. The obtained composite wet gel is then subjected to ethanol replacement for 12 h (4 times) and n-hexane replacement for 12 h (4 times) at room temperature. The solvent-displaced composite wet gel was subjected to a stepwise temperature-programmed drying process at atmospheric pressure (40 °C for 24 h, 60 °C for 12 h, and then 100 °C for 2 h) to obtain an aerogel. This aerogel was then impregnated with stearic acid containing 5 wt% graphene at 75 °C and 0.08 MPa for 45 min, followed by cooling to remove residual liquid, yielding the composite material. The prepared aerogel matrix had a density of 0.0915 g / cm³. 3 The BET specific surface area of ​​the boehmite fiber composite aerogel is 512.741 m². 2 / g, the hydrophobic angle of the composite aerogel is 130.7°. Example 14

[0030] 3.6 mL of MTMS and 5.6 mL of TEOS were mixed and added to a mixture of 13.2 mL of anhydrous ethanol and 2.7 mL of water. The pH was adjusted to 3.3 by adding HCl solution dropwise. 2% boehmite nanofibers were added to the silicon source precursor sol, and the mixture was sonicated to obtain a uniformly dispersed mixed sol. 5 mL of the mixed sol was taken and mixed with 20 mL of 2 wt% sodium alginate solution and stirred evenly in a 40 ℃ water bath. The pH was adjusted to approximately 5.8 with propylene oxide and stirred evenly to obtain a pre-crosslinked sol. The sol was allowed to stand to obtain a gel. The obtained wet gel was completely immersed in 0.15 mol·L⁻¹ Ca(NO₃)₂ solution at 40 ℃ for 18 h for crosslinking. The obtained composite wet gel was subjected to ethanol replacement for 24 h (1 time) and n-hexane replacement for 12 h (3 times) at room temperature. The solvent-displaced composite wet gel was subjected to a stepwise temperature-programmed drying process at atmospheric pressure (45 °C for 24 h, 65 °C for 12 h, and then 105 °C for 2 h) to obtain an aerogel. This aerogel was then impregnated with paraffin containing 3 wt% carbon nanotubes at 85 °C and 0.10 MPa for 30 min, followed by cooling to remove residual liquid, yielding the composite material. The prepared aerogel matrix had a density of 0.103 g / cm³. 3 The BET specific surface area of ​​the boehmite fiber composite aerogel is 466.015 m². 2 / g, the hydrophobic angle of the composite aerogel is 130.2°. Example 15

[0031] Mix 5.0 mL of MTES and 5.6 mL of TEOS, and add them to a mixture of 13.2 mL of anhydrous ethanol and 2.7 mL of water. Adjust the pH to 4.0 by adding HCl solution dropwise. Add 1.6% boehmite nanofibers to the silicon source precursor sol. After sonication, obtain a uniformly dispersed mixed sol. Take 3 mL of the mixed sol and mix it with 15 mL of 2 wt% sodium alginate solution. Stir evenly in a 50 ℃ water bath. Adjust the pH to approximately 6.0 with ammonia water and stir evenly to obtain a pre-crosslinked sol. Allow it to stand to obtain a gel. Completely immerse the obtained wet gel in 0.10 mol·L⁻¹ Al(NO₃)₃ solution at 50 ℃ for 24 h for crosslinking. The obtained composite wet gel is then subjected to ethanol replacement for 12 h (twice) and n-hexane replacement for 24 h (once) at room temperature. The solvent-displaced composite wet gel was subjected to a stepwise temperature-programmed drying process at atmospheric pressure (50 °C for 24 h, 70 °C for 12 h, and then 110 °C for 2 h) to obtain an aerogel. This aerogel was then impregnated with stearic acid containing 4 wt% expanded graphite for 1 h at 80 °C and 0.09 MPa, followed by cooling to remove residual liquid, yielding the composite material. The prepared aerogel matrix had a density of 0.0975 g / cm³. 3The BET specific surface area of ​​the boehmite fiber composite aerogel is 492.390 m². 2 / g, the hydrophobic angle of the composite aerogel is 130.9°.

Claims

1. A method for preparing a dual-network aerogel phase change composite material, characterized in that, Includes the following steps: 1) Preparation of SiO2-sodium alginate sol and wet gel A hydrophobic silicon source was mixed with tetraethyl orthosilicate, and water and anhydrous ethanol were added. The mixture was then hydrolyzed under acid catalysis while the pH of the system was controlled. The mixture was stirred uniformly to obtain a silicon source precursor sol. Boehmite nanofibers were added to the silicon source precursor sol, and the mixture was ultrasonically treated to obtain a uniformly dispersed mixed sol. The mixed sol was slowly added to a 2 wt% sodium alginate aqueous solution and stirred until homogeneous. Subsequently, a pH adjuster was added dropwise to adjust the pH of the system, and the mixture was stirred to form a wet gel. 2) Construction of a flexible-rigid dual-network structure After the wet gel obtained in step 1) is allowed to stand and age, it is completely immersed in an aluminum source solution or a calcium source solution system to carry out secondary cross-linking. After secondary cross-linking, a flexible-rigid through-network structure is constructed to obtain a composite wet gel. 3) Solvent displacement of composite wet gel The composite wet gel obtained in step 2) is continuously replaced with anhydrous ethanol and n-hexane to remove water and other residual liquids; the solvent replacement process is now complete and the composite wet gel is ready to dry. 4) Drying of the composite wet gel The composite wet gel obtained after solvent replacement in step 3) is first dried for more than 24 hours, then dried at a gradually increasing temperature for more than 12 hours, and finally dried at a high temperature for more than 2 hours to obtain a lightweight and porous double-network aerogel matrix. 5) Preparation of dual-network aerogel phase change composite materials The lightweight, porous dual-network aerogel matrix obtained in step 4) is immersed in a molten phase change material containing phase change material and flame-retardant and thermally conductive additives to fully fill the aerogel pores. After cooling, the surface residue is removed to obtain a dual-network aerogel phase change composite material.

2. The preparation method of the dual-network aerogel phase change composite material according to claim 1, characterized in that, The temperature at which the hydrophobic silicon source and tetraethyl orthosilicate are mixed in step 1) is 40-50°C. The hydrophobic silicon source is methyltrimethoxysilane or methyltriethoxysilane. The water is deionized water. The molar ratio of hydrophobic silicon source: tetraethyl orthosilicate: anhydrous ethanol: water is 1:1:9:

6. The acid catalyst is hydrochloric acid or acetic acid. The pH of the system is controlled at 3-4.

3. The method for preparing the dual-network aerogel phase change composite material according to claim 1, characterized in that, In step 1), the amount of boehmite nanofibers used is 1-2 wt% of the sol mass; the volume ratio of the mixed sol to 2 wt% sodium alginate aqueous solution is 3-5:15-20; the pH adjuster is ammonia or propylene oxide, which adjusts the pH of the system to 5-6.

4. The method for preparing the dual-network aerogel phase change composite material according to claim 1, characterized in that, In step 2), the aluminum source solution is an AlCl3 solution or an Al(NO3)3 solution, and the calcium source solution is a CaCl2 solution or a Ca(NO3)2 solution. The molar concentration of the aluminum source solution or the calcium source solution is 0.1-0.2 mol L⁻¹. The secondary crosslinking temperature is 40-50 ℃, and the secondary crosslinking time is 12-24 h.

5. The method for preparing the dual-network aerogel phase change composite material according to claim 1, characterized in that, In step 3), the composite wet gel is sequentially replaced with anhydrous ethanol and n-hexane at room temperature; the replacement with anhydrous ethanol lasts for 12-24 hours and is replaced 3-4 times; the replacement with n-hexane lasts for 12-24 hours and is replaced 1-4 times.

6. The method for preparing the dual-network aerogel phase change composite material according to claim 1, characterized in that, In step 4), the drying temperature for drying for more than 24 hours is 40-50 ℃, the drying temperature for drying for more than 12 hours is 60-70 ℃ for 12 hours, the high temperature drying temperature is 100-110 ℃, and the overall drying process is a step-by-step temperature increase program drying under normal pressure.

7. The method for preparing the dual-network aerogel phase change composite material according to claim 1, characterized in that, The phase change material mentioned in step 5) is paraffin or stearic acid; the flame retardant and thermally conductive additive is expanded graphite, graphene or carbon nanotubes, and the amount of flame retardant and thermally conductive additive is 3-5 wt% of the phase change material; the low pressure conditions for impregnation are a vacuum degree not higher than 0.1 MPa, an impregnation time of 0.5-1 h, and an impregnation temperature of 75-85℃.

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