Preparation method of aerogel confined n-octadecane phase change thermal storage composite material

Abstract

This invention relates to a method for preparing an aerogel-confined n-octadecane phase change thermal storage composite material. The invention uses 4,4′-diaminodiphenyl ether and pyromellitic dianhydride to form a polyamic acid precursor solution, and a bacterial cellulose dispersion to construct a support network. A pre-hydrolyzed siloxane precursor solution is introduced into the polyamic acid / bacterial cellulose wet system for in-situ co-condensation and aging to form a polyamic acid / bacterial cellulose / silica wet cogel. This cogel is then subjected to solvent displacement, directional freezing, freeze-drying, and graded thermal imidization to obtain a polyimide / bacterial cellulose / silica ternary hybrid aerogel framework. The aerogel framework is pre-degassed, and molten n-octadecane is introduced into the pores. After cooling and annealing, the phase change thermal storage composite material is obtained. This invention improves the effective filling and confinement retention of n-octadecane through wet silica cogel, solvent displacement to maintain pore accessibility, graded thermal imidization to stabilize pore walls, and pulsed impregnation.

Description

Technical Field

[0001] This invention relates to the technical fields of phase change thermal storage materials, aerogel composite materials, and building energy-saving / low-temperature thermal management materials, specifically to a method for preparing an aerogel-confined n-octadecane phase change thermal storage composite material; and more particularly to a method for preparing a phase change thermal storage composite material with polyimide, bacterial cellulose, and silica as a ternary hybrid framework and achieving efficient n-octadecane confinement through pore function matching. Background Technology

[0002] Phase change thermal storage materials can absorb or release latent heat during solid-liquid phase change processes, and can be used for peak shaving, passive temperature regulation, low-temperature thermal buffering, and device thermal management. Octadecylene has advantages such as a suitable phase change temperature range, good chemical stability, and low supercooling, but it is prone to flow and leakage in the molten state, leading to phase change enthalpy decay, component contamination, and decreased service reliability.

[0003] Loading n-octadecane into porous support materials is a common technique to improve their morphological stability. Aerogels, due to their low density, high porosity, and tunable pore structure, can restrict the migration of phase change materials through capillary action, surface tension, and interfacial interactions. However, in actual loading processes, simply increasing the specific surface area does not necessarily lead to a higher effective phase change enthalpy; if the pore size is too small, long-chain alkane molecules cannot fully enter the internal channels, while if the pore size is too large, the capillary confinement ability is insufficient, and leakage is prone to occur.

[0004] Polyimide possesses excellent thermal stability and skeletal support capabilities, bacterial cellulose offers a high aspect ratio nanofiber network and a renewable source, and silica exhibits high pore wall rigidity and interfacial stability. Constructing these three components into an organic-inorganic hybrid aerogel is advantageous for balancing a thermally stable framework, a flexible network, and inorganic reinforcing domains. However, if a route of first preparing the polyimide / bacterial cellulose aerogel followed by silica post-treatment is adopted, silica is more likely to remain on local pore walls or in the outer channels, potentially causing neck blockage, reduced pore accessibility, or uneven impregnation. Summary of the Invention

[0005] This invention addresses the technical problems of easy leakage of n-octadecane, insufficient accessibility of porous framework channels, and low utilization rate of effective heat storage space in the prior art. It provides a method for preparing an aerogel-confined n-octadecane phase change heat storage composite material. The method uses wet co-gel as the core, completes the introduction of the silicon-oxygen network before pore formation, and combines it with solvent replacement, directional freeze drying, staged thermal imidization, and pulse impregnation. This allows macropores, mesopores, and narrow pore necks to respectively undertake the functions of transport, capillary storage, and interface anchoring during the infiltration, storage, and confinement of n-octadecane, thereby improving the effective loading capacity and cycle morphology stability of n-octadecane.

[0006] The technical solution of this invention is as follows: This invention provides a method for preparing an aerogel-confined n-octadecane phase change thermal storage composite material, characterized in that the method for preparing the aerogel-confined n-octadecane phase change thermal storage composite material includes the following steps:

[0007] 1) Dissolve 4,4′-diaminodiphenyl ether in N,N-dimethylformamide, add pyromellitic dianhydride to carry out polycondensation reaction to obtain polyamic acid precursor solution;

[0008] 2) Triethylamine was added to the bacterial cellulose dispersion, followed by polyamic acid precursor solution, to form a polyamic acid / bacterial cellulose composite dispersion;

[0009] 3) A mixed silicon source containing tetraethoxysilane and methyltrimethoxysilane is pre-hydrolyzed, and the resulting siloxane pre-hydrolyzed solution is added to a polyamic acid / bacterial cellulose composite dispersion for in-situ co-condensation and aging to form a polyamic acid / bacterial cellulose / silica wet cogel.

[0010] 4) The wet cogel was subjected to solvent replacement, directional freezing and freeze-drying to obtain polyamic acid / bacterial cellulose / silica composite aerogel;

[0011] 5) The composite aerogel was subjected to graded thermal imidization in a nitrogen atmosphere to obtain a polyimide / bacterial cellulose / silica ternary hybrid aerogel framework.

[0012] 6) After pre-degassing the aerogel skeleton, it is placed in molten n-octadecane and loaded with n-octadecane using a pulsed vacuum-compression impregnation method. After cooling and solidification, a phase change thermal storage composite material is obtained.

[0013] Furthermore, in step 1), the molar ratio of 4,4′-diaminodiphenyl ether to pyromellitic dianhydride is 1:0.95~1.10, the solid content of the polyamic acid precursor solution is 3wt%~12wt%, the polycondensation reaction temperature is 0℃~10℃, and the reaction time is 3h~10h.

[0014] Furthermore, in step 2), the mass fraction of the bacterial cellulose dispersion is 0.3wt%~1.5wt%, and 0.2g~2.0g of triethylamine is added to every 100mL of bacterial cellulose dispersion; based on the polyamic acid solid content, a precursor solution containing 0.3g~2.5g of polyamic acid is added.

[0015] Furthermore, in step 3), the volume ratio of tetraethoxysilane to methyltrimethoxysilane is 1:0.2~2.0, the total amount of mixed silicon source is 0.2mL~2.5mL, and the pre-hydrolysis system is a weakly acidic system composed of ethanol, water and acetic acid with a pH of 3.0~5.0.

[0016] Furthermore, in step 3), a pore structure regulator is added to the pre-hydrolysis system. The pore structure regulator is hexadecyltrimethylammonium bromide or polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer (Pluronic F127). The amount of pore structure regulator is 0.01g~0.30g, and the pre-hydrolysis time is 20min~120min. The in-situ co-condensation and aging temperature is 25℃~60℃, and the aging time is 2h~12h.

[0017] Furthermore, in step 4), solvent replacement includes ethanol replacement and tert-butanol replacement. The ethanol replacement time is 12h~48h, and the tert-butanol replacement time is 12h~48h. The replacement solution is changed every 6h~12h.

[0018] Furthermore, in step 4), directional freezing uses a bottom cold source to form a temperature gradient, with a freezing rate of 0.5℃ / min to 5℃ / min, a freeze-drying temperature of -45℃ to -65℃, and a freeze-drying time of 48h to 96h.

[0019] Furthermore, in step 5), the graded thermal imidization includes holding at 100℃~140℃ for 0.5h~1.5h, 170℃~210℃ for 0.5h~1.5h, 230℃~270℃ for 0.5h~1.5h, and 280℃~320℃ for 0.5h~2h, with a heating rate of 2℃ / min~8℃ / min and a nitrogen flow rate of 50mL / min~200mL / min.

[0020] Furthermore, in step 6), the pre-degassing temperature is 60℃~90℃, and the pre-degassing time is 0.5h~3h; the molten n-octadecane temperature is 55℃~85℃; the pulsed vacuum-repressurization impregnation includes 3~8 cycles, each cycle including maintaining at -0.04MPa~-0.095MPa for 10min~40min, and then returning to atmospheric pressure or introducing inert gas for repressurization for 5min~30min.

[0021] This invention provides a method for preparing an aerogel-confined n-octadecane phase change thermal storage composite material. A polyamic acid precursor solution is formed using 4,4′-diaminodiphenyl ether and pyromellitic dianhydride, and a nanofiber support network is constructed using a bacterial cellulose dispersion. The pre-hydrolyzed siloxane precursor solution is introduced into the polyamic acid / bacterial cellulose wet system for in-situ co-condensation and aging to form a polyamic acid / bacterial cellulose / silica wet cogel. This cogel is then subjected to solvent replacement, directional freezing, freeze-drying, and graded thermal imidization under nitrogen protection to obtain a polyimide / bacterial cellulose / silica ternary hybrid aerogel framework. Subsequently, the aerogel framework is pre-degassed, molten n-octadecane is introduced into the pores, and the resulting material is cooled, crystallized, and annealed at low temperature to obtain a morphologically stable phase change thermal storage composite material. The core process of this invention is "wet-state silica co-gelling - solvent replacement - directional freeze-drying - graded thermal imidization - pulsed vacuum impregnation". By introducing pre-hydrolyzed siloxanes into the wet polyamic acid / bacterial cellulose network, the silica reinforcing domains are uniformly incorporated into the pore wall structure before pore formation, avoiding post-processing pore blockage. Furthermore, pulsed impregnation improves the uniformity of the n-octadecane internal filling. Therefore, compared with existing technologies, this invention has the following advantages:

[0022] 1) The present invention moves the silica network introduction step to the wet co-gel stage, so that the silica-reinforcing domains are evenly distributed before the polyamic acid / bacterial cellulose network is formed, which helps to reduce the outer layer deposition and pore neck blockage caused by post-processing.

[0023] 2) This invention reduces the risk of pore wall collapse during freeze-drying by replacing the solvent with ethanol / tert-butanol, maintaining the accessibility of mesopores and the transport capacity of interconnected pores, thereby improving the uniformity of n-octadecane entering the aerogel.

[0024] 3) This invention employs staged thermal imidization, which stabilizes the polyimide skeleton during the gradual dehydration and cyclization process, reducing the risk of structural shrinkage and microcracks caused by a single high-temperature treatment.

[0025] 4) The present invention employs pulsed vacuum-compression impregnation, which allows molten n-octadecane to repeatedly enter the interconnecting holes and mesopores under varying pressure gradients. This is more effective than continuous vacuum impregnation in removing residual gas from the holes and improving the uniformity of internal filling.

[0026] 5) This invention is based on the design of pore function matching, so that macropores / connecting pores play the role of permeation channels, mesopores play the role of capillary storage, and micropores or narrow pore necks play the role of interface anchoring, thereby achieving high loading, low leakage and stable thermal response of n-octadecane. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the preparation process of the present invention.

[0028] Figure 2This is a schematic diagram showing the relationship between aerogel pore structure matching and n-octadecane confined thermal storage.

[0029] Figure 3 This is a schematic diagram of the pore confinement structure of the PBS aerogel framework and PBSO composite material.

[0030] Figure 4 This is a comparison chart of apparent n-octadecane loading and thermal storage response in different embodiments.

[0031] Figure 5 This is a diagram showing the change in mesopore volume before and after octadecane impregnation. Detailed Implementation

[0032] The overall solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings:

[0033] In this invention, all reagents used are commercially available. PI is polyimide, BC is bacterial cellulose, SiO2 is silica, OD is n-octadecane, PBS represents the polyimide / bacterial cellulose / silica ternary hybrid aerogel framework, and PBSO represents the n-octadecane confinement phase change thermal storage composite material.

[0034] See Figure 1 This invention provides a method for preparing an aerogel-confined n-octadecane phase change thermal storage composite material. First, a polyamic acid precursor solution is prepared and then combined with a bacterial cellulose dispersion to form a composite dispersion. Next, a pre-hydrolyzed siloxane is introduced into the composite dispersion to complete wet in-situ co-condensation, allowing the siloxane network to enter the polyamic acid / bacterial cellulose network before pore formation. Subsequently, accessible channels are constructed through solvent replacement, directional freezing, and freeze-drying, followed by staged thermal imidization to obtain a stable aerogel framework. Finally, n-octadecane is confined within the channels using pulsed vacuum-compression impregnation. The specific steps are as follows:

[0035] 1) Dissolve 4,4′-diaminodiphenyl ether in N,N-dimethylformamide, add pyromellitic dianhydride to carry out polycondensation reaction to obtain polyamic acid precursor solution;

[0036] The molar ratio of 4,4′-diaminodiphenyl ether to pyromellitic dianhydride is 1:0.95~1.10, the solid content of the polyamic acid precursor solution is 3wt%~12wt%, the polycondensation reaction temperature is 0℃~10℃, and the reaction time is 3h~10h.

[0037] 2) Triethylamine was added to the bacterial cellulose dispersion, followed by polyamic acid precursor solution, to form a polyamic acid / bacterial cellulose composite dispersion;

[0038] The bacterial cellulose dispersion has a mass fraction of 0.3wt%~1.5wt%, and 0.2g~2.0g of triethylamine is added to every 100mL of bacterial cellulose dispersion; a precursor solution containing 0.3g~2.5g of polyamic acid is added based on the polyamic acid solid content.

[0039] 3) A mixed silicon source containing tetraethoxysilane and methyltrimethoxysilane is pre-hydrolyzed, and the resulting siloxane pre-hydrolyzed solution is added to a polyamic acid / bacterial cellulose composite dispersion for in-situ co-condensation and aging to form a polyamic acid / bacterial cellulose / silica wet cogel.

[0040] The volume ratio of tetraethoxysilane to methyltrimethoxysilane is 1:0.2~2.0, the total amount of mixed silicon source is 0.2mL~2.5mL, and the pre-hydrolysis system is a weakly acidic system composed of ethanol, water and acetic acid with a pH of 3.0~5.0.

[0041] A pore structure modifier is also added to the pre-hydrolysis system. The pore structure modifier is hexadecyltrimethylammonium bromide or polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer (Pluronic F127). The amount of pore structure modifier is 0.01g~0.30g, and the pre-hydrolysis time is 20min~120min. The in-situ co-condensation and aging temperature is 25℃~60℃, and the aging time is 2h~12h.

[0042] 4) The wet cogel was subjected to solvent replacement, directional freezing and freeze-drying to obtain polyamic acid / bacterial cellulose / silica composite aerogel;

[0043] Solvent replacement includes ethanol replacement and tert-butanol replacement. The ethanol replacement time is 12h~48h, and the tert-butanol replacement time is 12h~48h. The replacement solution is changed every 6h~12h.

[0044] Directional freezing uses a bottom cold source to create a temperature gradient, with a freezing rate of 0.5℃ / min to 5℃ / min, a freeze-drying temperature of -45℃ to -65℃, and a freeze-drying time of 48h to 96h.

[0045] 5) The composite aerogel was subjected to graded thermal imidization in a nitrogen atmosphere to obtain a polyimide / bacterial cellulose / silica ternary hybrid aerogel framework.

[0046] The graded thermal imidization process includes holding at 100℃~140℃ for 0.5h~1.5h, 170℃~210℃ for 0.5h~1.5h, 230℃~270℃ for 0.5h~1.5h, and 280℃~320℃ for 0.5h~2h, with a heating rate of 2℃ / min~8℃ / min and a nitrogen flow rate of 50mL / min~200mL / min.

[0047] 6) After pre-degassing the aerogel skeleton, it is placed in molten n-octadecane and loaded with n-octadecane using a pulsed vacuum-compression impregnation method. After cooling and solidification, a phase change thermal storage composite material is obtained.

[0048] The pre-degassing temperature is 60℃~90℃, and the pre-degassing time is 0.5h~3h; the melting temperature of n-octadecane is 55℃~85℃; the pulsed vacuum-repressurization impregnation includes 3~8 cycles, each cycle includes maintaining at -0.04MPa~-0.095MPa for 10min~40min, and then returning to atmospheric pressure or introducing inert gas for repressurization for 5min~30min.

[0049] The aerogel-confined n-octadecane phase change thermal storage composite material prepared by the present invention includes a continuous polyimide skeleton, a bacterial cellulose nanofiber network, a silica inorganic reinforcing domain, and n-octadecane confined in aerogel channels, wherein the interconnecting pores serve as n-octadecane transport channels, the mesopores serve as the main capillary storage space, and the micropores or narrow pore necks serve as interface anchoring points.

[0050] See Figure 2 In the figure, pore structures of different scales serve different functions: macropores or interconnected pores mainly act as low-resistance transport channels for molten n-octadecane to enter the aerogel, which is beneficial to improving impregnation efficiency and filling uniformity; mesopores, as the main capillary storage space, can restrict the migration of n-octadecane during the phase transition process through capillary and interfacial interactions; micropores or narrow pore necks provide interfacial adsorption and anchoring points, further enhancing the confinement effect on n-octadecane molecules. Through the synergistic matching between macropores, mesopores, and micropores, this invention avoids the problem of insufficient utilization of effective heat storage space caused by simply pursuing high specific surface area, and achieves a balance between high loading capacity, low leakage risk, and stable thermal response of n-octadecane.

[0051] See Figure 3 Before impregnation, the aerogel framework of this invention is composed of a continuous polyimide network, a bacterial cellulose nanofiber framework, and silica inorganic reinforcing domains, forming a stable support framework with a hierarchical porous structure. Polyimide provides thermal stability and skeletal support, bacterial cellulose provides the nanofiber network and pore structure template, and silica reinforcing domains improve pore wall rigidity and interfacial stability. After vacuum-assisted impregnation, molten n-octadecane enters the aerogel pores and is confined within the channels, forming a PBSO phase change thermal storage composite material. This structure maintains overall morphological stability during the solid-liquid phase transition of n-octadecane, reducing liquid leakage.

[0052] The following are specific application examples of the present invention.

[0053] Example 1: Preparation of PBSO-1 phase change thermal storage composite material.

[0054] 1) Add 5.71 g of 4,4′-diaminodiphenyl ether to 200 mL of N,N-dimethylformamide and stir until dissolved at 5 °C; add 6.00 g of pyromellitic dianhydride in portions and continue the reaction for 6 h to obtain a polyamic acid precursor solution; wherein, the molar ratio of 4,4′-diaminodiphenyl ether to pyromellitic dianhydride is approximately 1.036:1.000.

[0055] 2) Add 1.0 g of triethylamine to 100 mL of bacterial cellulose dispersion with a mass fraction of 0.8 wt%, and stir for 30 min; add the precursor solution corresponding to 0.5 g of polyamic acid precursor on a dry basis, and stir for 12 h to obtain polyamic acid / bacterial cellulose composite dispersion.

[0056] 3) Mix tetraethoxysilane and methyltrimethoxysilane at a volume ratio of 1:1. Add 0.6 mL of the mixed silicon source to the ethanol / water / acetic acid system and add 0.06 g of hexadecyltrimethylammonium bromide. Pre-hydrolyze for 40 min. Add the resulting siloxane pre-hydrolyzed solution dropwise to the composite dispersion obtained in step 2). Co-condense and age in situ at 40 °C for 6 h to obtain a ternary wet cogel.

[0057] 4) The wet cogel was successively replaced with ethanol and tert-butanol for 24 hours each, and the replacement solution was changed every 12 hours. Then it was frozen in a directional freezing device and freeze-dried at -56℃ for 72 hours to obtain polyamic acid / bacterial cellulose / silica composite aerogel.

[0058] 5) The composite aerogel obtained in step 4) was placed in a nitrogen atmosphere and kept at 120℃, 180℃, 250℃ and 300℃ for 1h in sequence. The heating rate was 5℃ / min and the nitrogen flow rate was 150mL / min to obtain the PBS-1 aerogel framework.

[0059] 6) The PBS-1 aerogel skeleton was pre-degassed at 80℃ and -0.08MPa for 1h; then it was placed in molten n-octadecane at 70℃ for 5 pulse impregnation cycles, each cycle including -0.08MPa for 20min and nitrogen repressurization for 10min; excess n-octadecane on the surface was removed, and after cooling to room temperature, it was annealed at 35℃ for 2h to obtain the PBSO-1 phase change thermal storage composite material.

[0060] Example 2: Preparation of PBSO-2 phase change thermal storage composite material.

[0061] This embodiment is basically the same as Embodiment 1, except that: in step 2), a precursor solution corresponding to 1.0 g of polyamic acid precursor on a dry basis is added, and the resulting aerogel skeleton is denoted as PBS-2. The composite material obtained after pulse impregnation with n-octadecane is denoted as PBSO-2. In this embodiment, the organic skeleton support, mesoporous accessibility, and capillary confinement ability are relatively balanced, and it can be regarded as a preferred embodiment.

[0062] Under optimal testing conditions, the apparent n-octadecane loading of PBSO-2 can reach 82.15 wt%, and it exhibits a high-temperature endothermic response of 202.23 J / g in a test program of 30℃~300℃.

[0063] Example 3: Preparation of PBSO-3 phase change thermal storage composite material.

[0064] This embodiment is basically the same as Example 1, except that: in step 2), a precursor solution corresponding to 1.5g of polyamic acid precursor on a dry basis is added, and the resulting aerogel skeleton is denoted as PBS-3. The composite material obtained after pulse impregnation with n-octadecane is denoted as PBSO-3. A higher polyamic acid content can enhance the integrity of the skeleton, but excessive increase in organic phase may reduce the accessibility of some pores.

[0065] Example 4: Preparation of PBSO-4 phase change thermal storage composite material.

[0066] This embodiment is basically the same as Embodiment 1, except that: in step 2), a precursor solution corresponding to 2.0 g of polyamic acid precursor on a dry basis is added, and the resulting aerogel skeleton is denoted as PBS-4. The composite material obtained after pulse impregnation with n-octadecane is denoted as PBSO-4. This embodiment is used to illustrate that when the amount of polyamic acid continues to increase, the specific surface area, pore volume and effective heat storage response of the aerogel are not simply positively correlated.

[0067] Performance Testing and Results Explanation:

[0068] Nitrogen adsorption-desorption was used to test the specific surface area, pore size distribution, and pore volume of the aerogel skeleton and the impregnated composite material. Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used to characterize the skeleton composition and interface structure. TG-DSC was used to test the thermal response of the composite material. The leakage behavior was evaluated by the heated filter paper method or the weighing method.

[0069] Table 1 Apparent OD loading and high-temperature endothermic response of PBSO composite materials

[0070]

[0071] As shown in Table 1, PBSO-2 exhibits both high apparent n-octadecane loading and thermal storage response, indicating a good match between organic framework support, interconnected pore transport, and mesoporous capillary storage at this ratio.

[0072] See Figure 4 Different amounts of polyamic acid added alter the pore structure and accessibility of the aerogel framework, thus affecting the actual loading capacity and thermal response of n-octadecane. The figure shows that PBSO-2 exhibits a higher apparent n-octadecane loading and a higher high-temperature endothermic response, indicating that its aerogel pore structure is well-matched with the penetration, storage, and confinement behavior of n-octadecane molecules. In contrast, some samples, although potentially possessing higher specific surface area or pore volume, did not show a corresponding increase in effective loading and thermal response due to insufficient coordination in pore size distribution, connectivity, or capillary confinement ability. Therefore, Figure 4 This further illustrates that pore function matching is more effective than single pore structure parameters in determining the thermal storage performance of composite phase change materials.

[0073] Table 2 Pore structure parameters of PBS aerogel skeleton before n-octadecane impregnation

[0074]

[0075] As can be seen from Table 2, the increase in BET specific surface area and pore volume does not necessarily correspond to a higher effective thermal storage response, indicating that the pore accessibility, mesoporous storage capacity and narrow pore neck confinement effect emphasized in this invention are more critical for n-octadecane loading.

[0076] Test results show that wet silica co-gel and solvent replacement processes are beneficial to maintaining the accessibility of interconnected pores and mesopores. The mesopore volume is significantly reduced after n-octadecane impregnation, indicating that n-octadecane mainly enters the mesopore storage space. At the same time, the composite material can maintain the stability of its overall morphology during heating, indicating that the interaction between the micropore or narrow pore neck and pore wall interface has a constraining effect on the molten n-octadecane.

[0077] See Figure 5 Before impregnation, the PBS aerogel framework possesses a certain mesopore volume, providing the main capillary storage space for n-octadecane. After impregnation, the residual mesopore volume of the PBSO composite material significantly decreases, indicating that a large amount of n-octadecane enters and occupies the mesopore region of the aerogel. The degree of mesopore volume reduction varies among different samples, reflecting the differences in the filling efficiency and confinement degree of n-octadecane in frameworks with different pore structures. Among them, the sample with a significant reduction in mesopore volume while still maintaining an appropriate amount of residual accessible pores indicates that it can achieve both high n-octadecane loading and maintain a certain degree of pore stability and confinement effect. This result further demonstrates that the present invention achieves the technical effect of efficient n-octadecane storage and leakage suppression by controlling the hierarchical pore structure of the aerogel.

[0078] This invention emphasizes evaluating carrier effectiveness based on pore function matching, rather than solely on specific surface area. For long-chain n-octadecane, interconnecting pores provide transport channels, mesopores provide the main storage space, and micropores or narrow pore necks provide confined anchoring points; these three elements work together to determine effective loading and leakage prevention capabilities.

[0079] The technical contents of this invention and those not specifically described in the above embodiments are the same as those in the prior art.

[0080] The above are merely specific embodiments disclosed in this invention, but the scope of protection disclosed in this invention is not limited thereto. The scope of protection disclosed in this invention should be determined by the scope of the claims.

Claims

1. A method for preparing an aerogel-confined n-octadecane phase change thermal storage composite material, characterized by: The preparation method of the aerogel-confined n-octadecane phase change thermal storage composite material includes the following steps: 1) Dissolve 4,4′-diaminodiphenyl ether in N,N-dimethylformamide, add pyromellitic dianhydride to carry out polycondensation reaction to obtain polyamic acid precursor solution; 2) Triethylamine was added to the bacterial cellulose dispersion, followed by polyamic acid precursor solution, to form a polyamic acid / bacterial cellulose composite dispersion; 3) A mixed silicon source containing tetraethoxysilane and methyltrimethoxysilane is pre-hydrolyzed, and the resulting siloxane pre-hydrolyzed solution is added to a polyamic acid / bacterial cellulose composite dispersion for in-situ co-condensation and aging to form a polyamic acid / bacterial cellulose / silica wet cogel. 4) The wet cogel was subjected to solvent replacement, directional freezing and freeze-drying to obtain polyamic acid / bacterial cellulose / silica composite aerogel; 5) The composite aerogel was subjected to graded thermal imidization in a nitrogen atmosphere to obtain a polyimide / bacterial cellulose / silica ternary hybrid aerogel framework. 6) After pre-degassing the aerogel skeleton, it is placed in molten n-octadecane and loaded with n-octadecane using a pulsed vacuum-compression impregnation method. After cooling and solidification, a phase change thermal storage composite material is obtained.

2. The method for preparing the aerogel-confined n-octadecane phase change thermal storage composite material according to claim 1, characterized in that: In step 1), the molar ratio of 4,4′-diaminodiphenyl ether to pyromellitic dianhydride is 1:0.95~1.10, the solid content of the polyamic acid precursor solution is 3wt%~12wt%, the polycondensation reaction temperature is 0℃~10℃, and the reaction time is 3h~10h.

3. The method for preparing the aerogel-confined n-octadecane phase change thermal storage composite material according to claim 2, characterized in that: In step 2), the bacterial cellulose dispersion has a mass fraction of 0.3wt% to 1.5wt%, and 0.2g to 2.0g of triethylamine is added to every 100mL of bacterial cellulose dispersion; a precursor solution containing 0.3g to 2.5g of polyamic acid is added based on the polyamic acid solid content.

4. The method for preparing the aerogel-confined n-octadecane phase change thermal storage composite material according to claim 3, characterized in that: In step 3), the volume ratio of tetraethoxysilane to methyltrimethoxysilane is 1:0.2~2.0, the total amount of mixed silicon source is 0.2mL~2.5mL, and the pre-hydrolysis system is a weakly acidic system composed of ethanol, water and acetic acid with a pH of 3.0~5.

0.

5. The method for preparing the aerogel-confined n-octadecane phase change thermal storage composite material according to claim 4, characterized in that: In step 3), a pore structure regulator is added to the pre-hydrolysis system. The pore structure regulator is hexadecyltrimethylammonium bromide or polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer. The amount of pore structure regulator is 0.01g~0.30g, the pre-hydrolysis time is 20min~120min, the in-situ co-condensation and aging temperature is 25℃~60℃, and the aging time is 2h~12h.

6. The method for preparing the aerogel-confined n-octadecane phase change thermal storage composite material according to claim 5, characterized in that: In step 4), solvent replacement includes ethanol replacement and tert-butanol replacement. The ethanol replacement time is 12h~48h, and the tert-butanol replacement time is 12h~48h. The replacement solution is changed every 6h~12h.

7. The method for preparing the aerogel-confined n-octadecane phase change thermal storage composite material according to claim 6, characterized in that: In step 4), directional freezing uses a bottom cold source to form a temperature gradient, with a freezing rate of 0.5℃ / min to 5℃ / min, a freeze-drying temperature of -45℃ to -65℃, and a freeze-drying time of 48h to 96h.

8. The method for preparing the aerogel-confined n-octadecane phase change thermal storage composite material according to claim 7, characterized in that: Step 5) involves graded thermal imidization, which includes holding at 100℃~140℃ for 0.5h~1.5h, 170℃~210℃ for 0.5h~1.5h, 230℃~270℃ for 0.5h~1.5h, and 280℃~320℃ for 0.5h~2h. The heating rate is 2℃ / min~8℃ / min, and the nitrogen flow rate is 50mL / min~200mL / min.

9. The method for preparing the aerogel-confined n-octadecane phase change thermal storage composite material according to claim 8, characterized in that: In step 6), the pre-degassing temperature is 60℃~90℃, and the pre-degassing time is 0.5h~3h; the melting temperature of n-octadecane is 55℃~85℃; the pulsed vacuum-repressurization impregnation includes 3~8 cycles, each cycle including maintaining at -0.04MPa~-0.095MPa for 10min~40min, and then returning to atmospheric pressure or introducing inert gas for repressurization for 5min~30min.

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