Preparation and application of supramolecular radiation cooling material using host-guest inclusion to assist heat absorption

Abstract

The invention discloses preparation and application of a supramolecular radiation cooling material using host-guest inclusion to assist heat absorption. Comprising the following steps: a compound with a macrocyclic structure is self-polymerized or grafted to a high-molecular polymer side chain to form a supramolecular host unit; the method comprises the following steps: assembling a supramolecular host unit and a selected guest unit in a solvent, and forming a stable supramolecular host-guest composite structure through host-guest inclusion; preparing supramolecular host-guest microspheres or aerogel by taking the composite structure as a construction unit and adopting a spray-freeze drying or freeze drying method to form a porous material; the material can effectively dissipate heat through thermal response host-guest interaction between host molecules and guest molecules, so that after the porous material is formed, the material has active heat absorption and passive radiation cooling performance, the problem of performance degradation of a common radiation cooling material in a high-humidity environment is solved, and the service life of the material is prolonged. The excellent cooling effect can still be kept under the humid and hot conditions, and the good application prospect is achieved.

Description

Technical Field

[0001] This invention relates to the field of energy and energy conservation, specifically to the preparation and application of a supramolecular radiative cooling material that utilizes host-guest encapsulation to assist in heat absorption. Background Technology

[0002] In recent years, the massive consumption of fossil fuels has led to a continuous increase in greenhouse gas emissions, exacerbating the global warming problem. Statistics show that since the 20th century, the global average temperature has risen by approximately 0.6°C, and this upward trend is accelerating. This change has not only severely impacted the ecological environment but also made efficient cooling technologies an urgent necessity in daily life and industrial production. According to the International Energy Agency (IEA), global electricity demand related to cooling is projected to nearly triple by 2050, reaching approximately 6200 TWh / year (International Energy Agency, The Future of Cooling - Opportunities for Energy Efficient Air Conditioning, 2018). However, most existing cooling technologies rely on electricity or fossil fuels, resulting in high energy consumption and further increasing greenhouse gas emissions, thus creating a vicious cycle of "high energy consumption - high emissions - climate warming." Therefore, developing a new, green cooling technology that requires no fuel input and produces no greenhouse gas emissions has become a key approach to mitigating global warming and meeting future cooling needs.

[0003] Radiative cooling is a passive cooling method that achieves temperature reduction without external energy input. Its basic principle is to transfer heat directly to outer space in the form of electromagnetic waves through the reflection of sunlight (0.2–2.5 μm) and the efficient emission of infrared radiation within an atmospheric window (8–13 μm) on the material surface (Nature Energy, 2017, 2, 17142; Science 2020, 370, 786). Compared with traditional refrigeration methods, radiative cooling has significant advantages. First, it does not rely on additional energy input and can achieve continuous passive cooling in both day and night environments, exhibiting extremely high energy efficiency. Second, it does not produce greenhouse gas emissions or other pollutants during operation, making it a truly green and environmentally friendly cooling method. Third, radiative cooling can be integrated with various application scenarios such as buildings, vehicles, and energy storage devices, demonstrating broad application potential.

[0004] However, the actual cooling performance of radiative cooling materials is severely limited by various environmental factors, such as high humidity or cloud cover. Increased humidity or cloud cover can reduce or even close the atmospheric transmission window, thereby weakening the radiative cooling performance (International Journal of Heat and Mass Transfer, 2022, 186, 122438.). It has been reported that the theoretical cooling power of radiative cooling can reach 160 W / m² on sunny days. 2 On cloudy days, it drops to 40 W / m 2 (SolarEnergy, 2021, 218, 195-210.)

[0005] To address the technical challenge that the performance of radiative cooling materials is highly dependent on clear, transparent weather conditions, two main improvement approaches exist. The first approach optimizes performance by increasing solar reflectivity and decreasing solar absorptivity. For example, by utilizing the high reflectivity of silver across the entire wavelength spectrum combined with the efficient scattering effect of microporous / nanofibers, a multilayer structure of expanded polytetrafluoroethylene (ePTFE) / silver / glass (ePAG) can be formed. This material exhibits approximately 98% solar reflectivity and approximately 90% thermal emissivity, achieving a cooling effect of approximately 4.0 °C in high-humidity environments (ACS Applied Materials & Interfaces, 2020, 12, 51409-51417). However, such high-reflectivity radiative cooling materials often exhibit overcooling at night, potentially leading to excessively low indoor temperatures. The second approach involves actively regulating solar thermal energy by introducing auxiliary cooling media such as evaporative coolers and phase change materials (PCMs). For example, a radiation / evaporation tandem cooling structure can be used, with a bottom layer of polyvinyl alcohol (PVA)-CaCl2 hydrogel evaporative cooling layer and a top layer of cellulose acetate (CA) fiber network radiative cooling layer. This structure achieves a temperature reduction of more than 7 °C compared to traditional radiative coolers under humid conditions (Science Advances, 2022, 8, eabq0411.). However, this type of structure still has shortcomings in terms of interfacial compatibility between the evaporative cooling layer and the substrate, as well as system cycle stability. Another improvement is to integrate radiative cooling and phase change materials into a single textile using hierarchical core-shell nanofibers, achieving a temperature reduction of approximately 10.7 °C during the day even under conditions where humidity exceeds 50%. Phase change materials (PCMs) such as n-octadecane and polyethylene glycol (PEG) can be encapsulated within the pores of core-shell fibers or aerogels to utilize their phase change behavior for temperature-adaptive thermal regulation, thereby enhancing the cooling performance of radiative cooling materials (Chemical Engineering Journal 2021, 425, 131466; ACS Nano, 2023, 17, 1693-1700.). However, most solid-liquid PCMs are prone to leakage during cyclic phase change processes. Even when converted into solid-solid PCMs through physical encapsulation or chemical bonding, their mechanical properties and latent heat values ​​still decrease significantly.

[0006] The development of supramolecular chemistry has provided new ideas for designing novel radiation cooling materials. For example, host-guest inclusion utilizes the matching of the inner pores of the guest molecule and the host molecule to form a non-covalent inclusion, and the guest unit can undergo reversible construction and dissociation under external stimuli such as temperature and humidity (Journal of the American Chemical Society, 2007, 129, 6396-6397). Through host-guest interactions, not only can highly controllable structural tuning be achieved at the molecular scale, but also multiple functions such as energy transfer, phase regulation, and optical property tuning can be introduced, thereby endowing materials with dynamic environmental responsiveness and self-adaptive capabilities. This provides a new design platform and application possibilities for constructing radiation cooling systems with high efficiency, tunability, and low energy consumption.

[0007] This invention prepares thermally responsive host-guest supramolecular materials into porous structures with micro- and nano-pores. This not only maintains the original high solar reflectivity and infrared emissivity of porous materials but also further endows them with additional energy storage and release properties, thereby assisting in radiative cooling. In practical applications, this supramolecular host-guest porous material can provide continuous and stable cooling effects under high humidity conditions, exhibiting strong environmental adaptability and cooling durability, especially in high-humidity environments. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for the preparation and application of supramolecular radiation cooling materials that utilize host-guest encapsulation to assist heat absorption. The preparation method includes the following steps: (1) Preparation of supramolecular host units: Compounds with macrocyclic structures (such as cyclodextrin, calixarene, cucurbita, etc.) are self-polymerized or grafted onto the side chains of polymers to form supramolecular host units that can be used for subsequent assembly; (2) Assembly of supramolecular host-guest structures: The supramolecular host units and selected guest units are assembled in a suitable solvent to form a stable supramolecular host-guest composite structure through host-guest encapsulation; (3) Preparation of supramolecular radiation cooling materials that utilize host-guest encapsulation to assist heat absorption: Using the supramolecular host-guest structure as the building unit, supramolecular host-guest microspheres or aerogels are prepared by spray-freeze drying or freeze-drying methods to form porous materials. This invention provides a supramolecular porous material for radiative cooling utilizing host-guest inclusion-assisted heat absorption. Because heat dissipation can be effectively achieved through the thermally responsive host-guest interaction between the host and guest molecules, the formation of this porous material cleverly combines the dynamic characteristics of supramolecular chemistry with the physical process of radiative cooling, exhibiting both active heat absorption and passive radiative cooling properties. This overcomes the performance degradation problem of general radiative cooling materials in high humidity environments, maintaining excellent cooling performance even under humid and hot conditions. This invention drives advancements in energy technology through fundamental chemical innovation, possessing significant application value in areas such as building energy conservation, personal thermal management, and electronic device heat dissipation. Furthermore, its preparation method is simple, economical, and efficient, lowering the potential barriers to large-scale production and application, and facilitating technology transfer.

[0009] To achieve the above technical effects, the following technical solution is adopted: A method for preparing a supramolecular radiation cooling material utilizing host-guest inclusion-assisted heat absorption is as follows: Step S1: Preparation of supramolecular host units: The host compound with a macrocyclic structure is formed into an oligomer through self-polymerization or the host compound with a macrocyclic structure is grafted onto the side chain of a polymer to form a supramolecular host unit that can be used for subsequent assembly. Step S2: Assembly of supramolecular host-guest composite structure: The supramolecular host unit obtained in step S1 is assembled with the selected guest unit in a solvent to form a stable supramolecular host-guest composite structure through host-guest inclusion. Step S3: Preparation of supramolecular radiation cooling material with host-guest inclusion and heat absorption: Using supramolecular host-guest composite structure as the building unit, supramolecular host-guest microspheres or aerogels are prepared by spray-freeze drying or freeze-drying method to form porous materials.

[0010] Furthermore, the main compound having a macrocyclic structure in step S1 includes, but is not limited to, cyclodextrin, calixarene, columnar aromatics, cucurbituril, and any one of the derivatives of the above compounds.

[0011] Furthermore, the polymers in step S1 include, but are not limited to, chitosan, sodium alginate, cellulose, hyaluronic acid, pectin, polyacrylic acid, and derivatives of the above polymers.

[0012] Furthermore, in step S2, the guest unit and the supramolecular host unit cavity diameter are matched, enabling them to enclose and form a stable supramolecular host-guest composite structure, and the enclosed structure is temperature responsive.

[0013] Furthermore, the temperature responsiveness specifically means that as the ambient temperature increases from 20 to 50 °C, the inclusion of the supramolecular host-guest composite structure is significantly weakened, or the inclusion is disintegrated.

[0014] Furthermore, the guest unit in step S2 includes, but is not limited to, one or more of polyethylene glycol, shea butter, n-octadecane, n-eicosane, lauryl alcohol, isopropyl stearate, and cocoa butter.

[0015] Furthermore, in step S2, the mass ratio of the supramolecular host unit to the guest unit is 2:8 to 8:2; the assembly in step S2 is achieved by uniform mixing in a solvent, solvent heat treatment, or pH / temperature control to realize the self-assembly of the supramolecular host unit and the guest unit; the solvent is water or a mixture of water and other organic solvents.

[0016] Furthermore, in step S3, the concentration of the supramolecular host-guest composite structure is 20~100 mg / mL; the freeze-drying pressure is 5~20 Pa, the temperature is -40~-20 ℃, and the time is 2-3 days.

[0017] A supramolecular radiation cooling material utilizing host-guest encapsulation to assist heat absorption is prepared using the above-described method. The material has a reflectivity greater than 0.85 in the 0.2-2.5 μm visible light band and an emissivity greater than 0.85 in the 8-13 μm infrared band.

[0018] An application of a supramolecular radiation cooling material that utilizes host-guest encapsulation to assist in heat absorption, wherein the material is used directly as an aerogel for energy-saving cooling of materials, or as an energy-saving cooling component by combining aerogel microspheres with other polymers to form a thin film, thereby achieving zero-energy cooling of materials.

[0019] The beneficial effects of this invention are as follows: (1) Dynamic responsiveness: Guest units can undergo phase transitions or conformational regulation within a temperature range of 20~50 ℃, resulting in reversible molecular slip and unpacking rearrangement. This unique molecular dynamics process provides an additional dissipation channel for energy storage and release, thereby achieving adaptive regulation to changes in ambient temperature and effectively improving the stability and sustainability of the cooling process. (2) Synergistic Energy Regulation: Through the dynamic inclusion between the supramolecular host and guest molecules, the guest molecules can absorb and release latent heat during temperature changes or phase transitions, thereby achieving temporary energy storage and slow release at the molecular scale. This process not only avoids the instantaneous accumulation of heat and reduces the risk of local overheating of the material, but also forms a synergistic effect with the optical reflection and infrared emission properties of porous materials. Specifically, the porous structure provides efficient light scattering, while the energy conversion process of the supramolecular host-guest inclusion structure further enhances the thermal regulation capability of the system. The synergistic effect of the two results in the material having a lower endothermic effect under sunlight irradiation and exhibiting stronger infrared radiation capability within the atmospheric window range, thereby significantly improving radiative cooling efficiency and stability.

[0020] (3) Universality and Designability: Supramolecular host-guest systems offer high flexibility in molecular design. The host framework can be selected from compounds such as cyclodextrins, calixarenes, and cucurbiturates according to different needs, while the guest units can be flexibly configured based on phase transition temperatures and response characteristics. The binding sites and interaction strengths can also be precisely adjusted through chemical modification or structural regulation, enabling these materials to achieve good compatibility with various matrices (such as fibers, aerogels, and thin films) and different functional requirements, thus possessing broad scalability and application prospects.

[0021] (4) Excellent cooling effect under humid and hot conditions: The inherent pore structure of porous materials and the phase keys (CO, CC, etc.) in the system can achieve high reflectivity in the 0.2~2.5 μm band and high emissivity in the 8~13 μm band, achieving a passive radiative cooling effect; while the energy dissipation of the supramolecular host-guest structure serves as an active heat absorption part, achieving an active cooling effect. In supramolecular host-guest porous materials, active cooling and passive cooling complement each other, which can achieve effective cooling under humid and hot conditions. Attached Figure Description

[0022] Figure 1 The microstructure of the supramolecular radiation-cooled aerogel microspheres with host-guest encapsulation and auxiliary heat absorption provided by the present invention is shown at a magnification of 900. Figure 2 The microstructure of the supramolecular radiation-cooled aerogel microspheres with host-guest encapsulation and assisted heat absorption provided by the present invention is shown at a magnification of 4000. Figure 3This is a physical image of the supramolecular radiation-cooled aerogel material with host-guest encapsulation and assisted heat absorption provided by the present invention; Figure 4 This is a microscopic morphology image of the supramolecular radiation-cooled aerogel material with host-guest encapsulation and assisted heat absorption provided by the present invention, magnified at 200 times. Figure 5 A schematic diagram of the testing device for the radiative cooling performance provided by the present invention; Figure 6 A physical diagram of the testing device for the radiative cooling performance provided by the present invention; Figure 7 This is a comparison diagram of the radiation cooling results of the host-guest encapsulation assisted heat absorption supramolecular thin film (Example 1) provided by the present invention and Comparative Example 1; Figure 8 This is a comparison chart of the radiation cooling results of the supramolecular aerogel with host-guest encapsulation and auxiliary heat absorption provided by the present invention (Example 2), the pure polymer aerogel radiation cooling material (Comparative Example 2), and the polymer aerogel radiation cooling material containing guest components (Comparative Example 3). Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0026] Example 1: (1) Preparation of supramolecular host units Self-polymerization of cyclodextrin: 10 g of β-cyclodextrin (β-CD) was dissolved in 16 mL of 20% (w / v) sodium hydroxide solution and stirred at 50 °C for 3 h until completely dissolved. The solution was then cooled to 35 °C. Next, 3.8 mL of epichlorohydrin (EPI), a crosslinking agent, was added, and the mixture was stirred for 4 h to complete the crosslinking reaction. The reaction solution was then dropped into 50 mL of cold acetone, resulting in an oily layer of poly-β-cyclodextrin (P-β-CD). The supernatant was discarded, and the pH of the oily layer was adjusted to neutral with 6 M hydrochloric acid (HCl). Finally, the pH-adjusted product was dialyzed for 5 days in a dialysis bag with a molecular weight cutoff of 8000-14000, and P-β-CD was obtained by rotary evaporation.

[0027] (2) Preparation of supramolecular host-guest complex system Inclusion of polycyclodextrin with polyethylene glycol: 3 g P-β-CD and 1.5 g polyethylene glycol 800 were dissolved together in 50 mL of deionized water and stirred at 25 °C for 24 h to obtain a supramolecular host-guest system solution (P-β-CD@PEG).

[0028] (3) Preparation of supramolecular radiation cooling materials with host-guest encapsulation and auxiliary heat absorption Preparation of supramolecular thin films with host-guest inclusion and assisted endothermic reaction: The above supramolecular host-guest system solution was loaded into a spray gun at a pressure of 0.3 MPa and sprayed into supercooled liquid nitrogen with low surface energy to obtain ice microspheres. The ice microspheres were placed in a freeze dryer at a pressure of 4 Pa ​​and a temperature of -30 °C and dried for 2 days to obtain supramolecular host-guest porous microspheres. Finally, the supramolecular host-guest porous microspheres (1.0 g) were electrostatically sprayed onto a polyacrylonitrile fiber membrane (10 × 10 cm⁻¹). 2 On a substrate, a supramolecular host-guest porous microsphere / polyacrylonitrile cooling film was obtained.

[0029] Example 2: (1) Preparation of supramolecular host units Grafting of calixarenes onto sodium alginate: 1.0 g of sodium alginate (molecular weight approximately 100,000–350,000) was dissolved in 100 mL of deionized water, and a homogeneous, transparent solution was obtained under magnetic stirring. 0.5 g of a carboxymethylated calixarene derivative was slowly added to this solution, along with 0.6 g of N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC HCl) and 0.36 g of N-hydroxysuccinimide (NHS) to activate the calixarene carboxyl groups. The reaction system was stirred at room temperature for 12 hours to allow the calixarenes to covalently graft onto the side chain hydroxyl or carboxyl groups of sodium alginate via amide bonds. After the reaction was complete, the reaction product was dialyzed for 3 days using a dialysis bag (molecular weight cutoff 3 kDa) to remove unreacted reagents and byproducts. After freeze-drying to remove the aqueous solvent, a supramolecular host unit powder was obtained.

[0030] (2) Preparation of supramolecular host-guest complex system Inclusion of calixarene with shea butter: Take 0.8 g of supramolecular host unit obtained in step (1) above, dissolve it in 50 mL of deionized water, slowly add 0.25 g of mixed fatty acid shea butter, and magnetically stir for 6 hours at room temperature to form a stable non-covalent host-guest composite structure, and obtain a homogeneous supramolecular host-guest solution.

[0031] (3) Preparation of supramolecular radiation cooling materials with host-guest encapsulation and auxiliary heat absorption Preparation of supramolecular aerogels with host-guest inclusion-assisted endothermic process: The supramolecular host-guest system solution obtained in step (2) above was placed in a mold and frozen at -20 ℃ for 12 h to obtain a frozen aerogel building block. Finally, the frozen aerogel building block was placed in a freeze dryer at a pressure of 4 Pa ​​and a temperature of -30 ℃ and dried for 3 days to obtain a supramolecular host-guest aerogel.

[0032] Example 3: (1) Preparation of supramolecular host units Grafting of columnar aromatics onto chitosan: 2.0 g of chitosan (molecular weight approximately 50,000 Da) was dissolved in 100 mL of 2wt% acetic acid solution to form a homogeneous chitosan solution. Then, 1.0 g of 1,3,5-trimethyl columnar aromatics was added, along with 0.6 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC HCl) and 0.36 g of N-hydroxysuccinimide (NHS) to activate the carboxyl groups on the columnar aromatics. The reaction system was stirred at room temperature for 12 hours to ensure that the columnar aromatics were grafted onto the chitosan side chains via amide bonds. After the reaction was complete, the reaction product was dialyzed for 3 days using a dialysis bag (molecular weight cutoff 3 kDa) to remove unreacted reagents and byproducts. After freeze-drying to remove the aqueous solvent, supramolecular host unit powder was obtained.

[0033] (2) Preparation of supramolecular host-guest complex system Inclusion of columnar aromatics and n-octadecane: Dissolve 1.5 g of the supramolecular host unit obtained in step (1) above in 50 mL of deionized water, and add 0.8 g of the thermosensitive guest molecule n-octadecane. Stir at room temperature for 6 hours to ensure effective assembly of the host and guest units.

[0034] (3) Preparation of supramolecular radiation cooling materials with host-guest encapsulation and auxiliary heat absorption Preparation of supramolecular thin films with host-guest inclusion and assisted endothermic reaction: The supramolecular host-guest system solution obtained in step (2) above was injected into supercooled liquid nitrogen with low surface energy through a spray gun at a pressure of 0.2 MPa to obtain ice microspheres. The ice microspheres were placed in a freeze dryer at a pressure of 4 Pa ​​and a temperature of -30 ℃ and dried for 2 days to obtain supramolecular host-guest porous microspheres. Then, the supramolecular host-guest porous microspheres (1.2 g) were electrostatically sprayed onto a polyvinylidene fluoride fiber membrane (10 × 10 cm). 2 On a substrate, a supramolecular host-guest porous microsphere / polyvinylidene fluoride cooling film was obtained.

[0035] Example 4: (1) Preparation of supramolecular host units Grafting of cucurbituril onto polyvinyl alcohol: 5.0 g of polyvinyl alcohol (PVA, molecular weight approximately 85,000–124,000, hydroxyl content approximately 98%) was dissolved in 50 mL of deionized water and heated to 80 °C with magnetic stirring until completely dissolved. After cooling the solution to 60 °C, 1.0 g of modified cucurbituril monomer (which may contain active amino or carboxyl functional groups to react with hydroxyl groups) was slowly added, along with N,N'-dicyclohexylcarbodiimide (DCC, 0.5 g) as a condensing agent and 0.05 g of 4-dimethylaminopyridine (DMAP) as a catalyst. The reaction system was stirred continuously for 12 hours under nitrogen protection, allowing the cucurbituril monomer to covalently graft onto the hydroxyl functional groups of the polyvinyl alcohol side chain through esterification or amidation. After the reaction is complete, the polymer product is precipitated by ethanol precipitation of the reaction solution. The product is washed three times to remove unreacted monomers and small molecule byproducts, and the supramolecular host unit grafted with cucurbituril is obtained.

[0036] (2) Preparation of supramolecular host-guest complex system Inclusion of cucurbituril and n-eicosane: Approximately 1.0 g of cucurbituril-grafted polyvinyl alcohol obtained in the examples was dissolved in 20 mL of water and heated to 50 °C with magnetic stirring until completely dissolved. Separately, 0.5 g of n-eicosane was added to the above solution, and the mixture was stirred continuously at 50 °C for 6 hours. This allowed n-eicosane molecules to penetrate into the cavities of the cucurbituril-grafted polymer side chains through hydrophobic interactions and cavity inclusion, forming a stable supramolecular host-guest composite structure. After the reaction was complete, the mixed solution was slowly cooled to room temperature to obtain a cucurbituril-grafted polymer solution containing n-octadecane inclusion.

[0037] (3) Preparation of supramolecular radiation cooling materials with host-guest encapsulation and auxiliary heat absorption Preparation of supramolecular thin films with host-guest inclusion and assisted endothermic reaction: The above supramolecular host-guest system solution was loaded into a spray gun at a pressure of 0.3 MPa and sprayed into supercooled liquid nitrogen with low surface energy to obtain ice microspheres. The ice microspheres were placed in a freeze dryer at a pressure of 4 Pa ​​and a temperature of -30 °C and dried for 2 days to obtain supramolecular host-guest porous microspheres. Then, the supramolecular host-guest porous microspheres (0.8 g) were electrostatically sprayed onto a polylactic acid fiber membrane (10 × 10 cm). 2 On the surface, supramolecular host-guest porous microspheres / polylactic acid cooling films were obtained.

[0038] Example 5: (1) Preparation of supramolecular host units Grafting of cyclodextrin onto sodium polyacrylate: 5.0 g of sodium polyacrylate (PAA, molecular weight approximately 100,000) was dissolved in 50 mL of deionized water and heated to 70 °C with magnetic stirring until completely dissolved. After cooling the solution to 50 °C, 1.2 g of α-cyclodextrin was slowly added, along with 0.6 g of dicyclohexylcarbodiimide (DCC) as a condensing agent and 0.05 g of 4-dimethylaminopyridine (DMAP) as a catalyst. The reaction system was stirred continuously for 10 hours under nitrogen protection, allowing the cyclodextrin to covalently graft onto the carboxyl functional groups of the sodium polyacrylate side chains via amidation. After the reaction was complete, the polymeric product was precipitated by ethanol precipitation, and the mixture was washed three times to remove unreacted monomers and byproducts, yielding the cyclodextrin-grafted supramolecular host unit.

[0039] (2) Preparation of supramolecular host-guest complex system Inclusion of cyclodextrin and lauryl alcohol: 1.2 g of the supramolecular host unit, i.e., cyclodextrin-grafted sodium polyacrylate, was dissolved in 60 mL of water and heated to 50 °C with magnetic stirring until completely dissolved. Separately, 0.5 g of lauryl alcohol was added to the above solution, and the mixture was stirred continuously at 50 °C for 6 hours. This allowed the guest lauryl alcohol to penetrate into the cyclodextrin cavity through hydrophobic interactions and cavity inclusion, forming a stable supramolecular host-guest complex structure. After the reaction was complete, the mixed solution was slowly cooled to room temperature to obtain a cyclodextrin-grafted polymer solution containing lauryl alcohol inclusion.

[0040] (3) Preparation of supramolecular radiation cooling materials with host-guest encapsulation and auxiliary heat absorption Preparation of supramolecular aerogels with host-guest inclusion-assisted endothermic process: The supramolecular host-guest system solution obtained in step (2) above was placed in a mold and frozen at -25 ℃ for 24 h to obtain a frozen aerogel building block. Finally, the frozen aerogel building block was placed in a freeze dryer at a pressure of 2 Pa and a temperature of -30 ℃ and dried for 3 days to obtain a supramolecular host-guest aerogel.

[0041] Example 6: (1) Preparation of supramolecular host units Grafting of cucurbituril onto polylactic acid (PLA): 5.0 g of PLA (molecular weight approximately 50,000) was dissolved in 50 mL of dichloromethane to form a homogeneous solution. After cooling the solution to 30 °C, 1.2 g of cucurbituril was slowly added, along with 0.4 g of dicyclohexylcarbodiimide (DCC) as a condensing agent and 0.02 g of 4-dimethylaminopyridine (DMAP) as a catalyst. The reaction system was stirred continuously for 8 hours under nitrogen protection, allowing cucurbituril to covalently graft onto the carboxyl functional groups of the PLA side chains via an amidation reaction. After the reaction was complete, the dichloromethane solvent was removed, yielding the cucurbituril-grafted supramolecular host unit.

[0042] (2) Preparation of supramolecular host-guest complex system Inclusion of cucurbituril and isopropyl stearate: 1.0 g of the supramolecular host unit, i.e., cyclodextrin-grafted sodium polyacrylate, was dissolved in 60 mL of water and heated to 50 °C with magnetic stirring until completely dissolved. Separately, 0.5 g of isopropyl stearate was added to the above solution, and the mixture was stirred continuously at 50 °C for 6 hours to allow the guest isopropyl stearate to penetrate into the cucurbituril cavity, forming a stable supramolecular host-guest complex structure. After the reaction was complete, the mixed solution was slowly cooled to room temperature to obtain the supramolecular host-guest system.

[0043] (3) Preparation of supramolecular radiation cooling materials with host-guest encapsulation and auxiliary heat absorption Preparation of supramolecular thin films with host-guest encapsulation and assisted endothermic reaction: The above supramolecular host-guest system solution was injected into supercooled, low-surface-energy liquid nitrogen through a spray gun at a pressure of 0.3 MPa to obtain ice microspheres. The ice microspheres were placed in a freeze dryer at a pressure of 4 Pa ​​and a temperature of -30 ℃ and dried for 2 days to obtain supramolecular host-guest porous microspheres. 0.5 g of the supramolecular host-guest porous microspheres were uniformly dispersed in 15 mL of a 5 wt% polyurethane solution (viscosity: <200 mpa.s) (solvent: N,N-dimethylformamide), poured into a glass container, and allowed to evaporate the solvent after 48 h to obtain the supramolecular thin film with host-guest encapsulation and assisted endothermic reaction.

[0044] Example 7: (1) Preparation of supramolecular host units Grafting cyclodextrin onto cellulose: 4.0 g of cellulose (molecular weight approximately 50,000–100,000) was dissolved in 50 mL of deionized water and heated to 60 °C with magnetic stirring until completely dissolved. After cooling the solution to 50 °C, 1.2 g of a cyclodextrin derivative with an active carboxyl group, β-cyclodextrin ethylated derivative, was added, along with 0.5 g of N,N'-dicyclohexylcarbodiimide (DCC) and 0.1 g of 4-dimethylaminopyridine (DMAP, O) as catalysts. The reaction system was continuously stirred for 12 hours under nitrogen protection, allowing cyclodextrin to covalently graft onto the amino functional groups of the chitosan side chains via amidation. After the reaction was complete, the product was precipitated by ethanol precipitation and washed three times to remove unreacted monomers and byproducts, yielding the cyclodextrin-grafted cellulose supramolecular host unit.

[0045] (2) Preparation of supramolecular host-guest complex system Inclusion of cyclodextrin and cocoa butter: 0.9 g of the supramolecular host unit, i.e., sodium polyacrylate grafted with cyclodextrin, was dissolved in 50 mL of water and heated to 50 °C with magnetic stirring until completely dissolved. Separately, 0.5 g of cocoa butter (an inclusion complex of oleic acid, stearic acid, and palmitic acid) was added to the above solution, and the mixture was stirred continuously at 50 °C for 6 hours to allow the guest cocoa butter to penetrate into the cyclodextrin cavity, forming a stable supramolecular host-guest complex structure. After the reaction was complete, the mixed solution was slowly cooled to room temperature to obtain the supramolecular host-guest system.

[0046] (3) Preparation of supramolecular radiation cooling materials with host-guest encapsulation and auxiliary heat absorption Preparation of supramolecular thin films with host-guest encapsulation and assisted endothermic reaction: The above supramolecular host-guest system solution was injected into supercooled low surface energy liquid nitrogen through a spray gun at a pressure of 0.3 MPa to obtain ice microspheres. The ice microspheres were placed in a freeze dryer at a pressure of 4 Pa ​​and a temperature of -30 ℃ and dried for 2 days to obtain supramolecular host-guest porous microspheres. 0.3 g of supramolecular host-guest porous microspheres were uniformly dispersed in 15 mL of a 10 wt% cellulose acetate solution (molecular weight approximately 46,000~60,000) (solvents were water and acetone, water:acetone = 1:19), poured into a glass container, and allowed to evaporate the solvent after 24 h to obtain the supramolecular thin film with host-guest encapsulation and assisted endothermic reaction.

[0047] Comparative Example 1: A polymer porous microsphere thin film radiation cooling material (lacking guest units compared to Example 1) is prepared by the following steps: (1) Preparation of supramolecular host units Self-polymerization of cyclodextrin: 10 g of β-cyclodextrin (β-CD) was dissolved in 16 mL of 20% (w / v) sodium hydroxide solution and stirred at 50 °C for 3 h until completely dissolved. The solution was then cooled to 35 °C. Next, 3.8 mL of epichlorohydrin (EPI), a crosslinking agent, was added, and the mixture was stirred for 4 h to complete the crosslinking reaction. The reaction solution was then dropped into 50 mL of cold acetone, resulting in an oily layer of poly-β-cyclodextrin (P-β-CD). The supernatant was discarded, and the pH of the oily layer was adjusted to neutral with 6 M hydrochloric acid (HCl). Finally, the pH-adjusted product was dialyzed for 5 days in a dialysis bag with a molecular weight cutoff of 8000-14000, and P-β-CD was obtained by rotary evaporation.

[0048] (2) Preparation of polymer porous material radiation cooling material Preparation of porous microsphere films: 4.5 g of P-β-CD was weighed and dissolved in 50 mL of deionized water by stirring. The solution was stirred at 25 °C for 24 h to obtain a homogeneous solution. The polymer solution was then sprayed into supercooled, low-surface-energy liquid nitrogen through a spray gun at a pressure of 0.3 MPa to obtain ice microspheres. The ice microspheres were then placed in a freeze dryer at a pressure of 4 Pa ​​and a temperature of -30 °C for 2 days to obtain polymer porous microspheres. Finally, the supramolecular host-guest porous microspheres were coated onto a polyacrylonitrile fiber membrane by electrostatic spraying to obtain a polymer porous microsphere / polyacrylonitrile cooling film.

[0049] Comparative Example 2: A pure polymer aerogel radiation cooling material (lacking a supramolecular host-guest system compared to Example 2) is prepared by the following steps: 6.0 g of sodium alginate (molecular weight approximately 100,000–350,000) was dissolved in 120 mL of deionized water and stirred at 20 °C for 24 h to obtain a homogeneous solution. The mixture was then placed in a mold and frozen at -20 °C for 24 h to obtain a cryogel building block. Finally, the cryogel building block was placed in a freeze dryer at a pressure of 4 Pa ​​and a temperature of -30 °C for 3 days to obtain a pure polymer aerogel.

[0050] Comparative Example 3: A polymer aerogel radiation cooling material containing a guest component (lacking supramolecular host units compared to Example 2) is prepared by the following steps: 0.25 g of mixed fatty acid shea butter and 1.0 g of sodium alginate (molecular weight approximately 100,000–350,000) were dissolved together in 60 mL of deionized water and stirred at 25 °C for 8 h to obtain a homogeneous mixture. The mixture was then placed in a mold and frozen at -25 °C for 24 h to obtain a cryogel building block. Finally, the cryogel building block was placed in a freeze dryer at a pressure of 2 Pa and a temperature of -30 °C and dried for 3 days to obtain a polymer aerogel radiation cooling material with guest components.

[0051] Experimental results: 1. Microstructure of the porous material of the present invention: (1) Experimental method: The porous microspheres and aerogels prepared in Experimental Example 1 and Experimental Example 3 were sputtered with gold and the microstructure of the samples was analyzed by scanning electron microscopy.

[0052] (2) Experimental results: The microstructure of the porous material is as follows Figure 1 and Figure 2 As shown, where Figure 1 and Figure 2 These are the microstructures of supramolecular host-guest porous aerogel microspheres at different scales. Figure 3 This is a physical image of a supramolecular host-guest aerogel. Figure 4 This is a microscopic morphology image of a supramolecular host-guest aerogel. The supramolecular host-guest porous microspheres exhibit relatively high sphericity, with a diameter distribution of approximately 10-100 μm. The microsphere surface displays a distinct porous structure, which enhances surface light reflection. Supramolecular aerogels can also be customized in size and shape, with a porous surface exhibiting a pore size distribution of approximately 10-200 μm.

[0053] 2. Radiative cooling performance of the porous material of the present invention (1) Experimental Methods: The supramolecular host-guest porous microspheres of Experimental Example 1, the pure polymer porous microspheres of Comparative Example 1, the supramolecular host-guest aerogel of Experimental Example 2, the pure polymer aerogel of Comparative Example 2, and the polymer aerogel containing phase change material of Comparative Example 3 were tested for their radiation cooling performance. The radiation cooling performance tests of the samples were conducted outdoors. The experimental setup consisted of a foam insulation box covered with aluminum foil. A schematic diagram of the setup is shown below. Figure 5 As shown, a physical diagram of the device is as follows. Figure 6 As shown. The aluminum foil serves to prevent heat conduction through its mirror-like reflective surface. An opening is located at the top of the insulating foam box, which is effectively sealed using a size-matched sample. Temperature changes are monitored and recorded in real time using a type K thermocouple attached to the back of the sample. A separate thermocouple is used to measure the ambient temperature in the area of ​​the foam box not covered by the sample. Solar radiation intensity is recorded using an automatic solar radiometer with an accuracy of ±5%.

[0054] (2) Experimental results: The radiative cooling effect of supramolecular host-guest porous materials assisted in refrigeration is as follows: Figure 7 and Figure 8 As shown, where Figure 7 The results of radiation cooling are those of a supramolecular thin film with host-guest encapsulation and assisted heat absorption (Example 1) and Comparative Example 1. Figure 8 The results show the radiation cooling effects of a supramolecular aerogel with host-guest encapsulation and auxiliary heat absorption (Example 2), a pure polymer aerogel radiation cooling material (Comparative Example 2), and a polymer aerogel radiation cooling material containing a guest component (Comparative Example 3). The results were achieved at a relative humidity of 86% and a maximum solar intensity of 1.2 kW / m². 2 In the specified environment, the cooling temperature of the supramolecular microsphere film with host-guest encapsulation and auxiliary heat absorption (Example 1) was consistently higher than that of the polymer porous microsphere film (Comparative Example 1), with a maximum cooling temperature reaching 8.9 °C. These results indicate that supramolecular host-guest porous microspheres can dissipate more energy than pure polymer porous microspheres, achieving a better radiative cooling effect. This was achieved at a relative humidity of 94% and a maximum solar intensity of 0.7 kW / m². 2 In the given environment, the supramolecular aerogel with host-guest encapsulation and auxiliary heat absorption (Example 2) exhibited the highest cooling temperature, reaching 11.6 °C. This was followed by the polymer aerogel radiation cooling material containing guest components (Comparative Example 3), with a maximum cooling temperature of 9.8 °C. Finally, the pure polymer aerogel radiation cooling material (Comparative Example 2) showed the highest cooling temperature at 8.6 °C. The pure polymer aerogel radiation cooling material (Comparative Example 2) demonstrated a certain cooling effect, but it was weaker than the supramolecular aerogel with host-guest encapsulation and auxiliary heat absorption (Example 2) and the polymer aerogel radiation cooling material containing guest components (Comparative Example 3). This is because the pure polymer aerogel radiation cooling material (Comparative Example 2) primarily relies on its porous structure to reflect sunlight for radiation cooling. Compared to the polymer aerogel radiation cooling material containing guest components (Comparative Example 3), it lacks the energy consumed by phase transition, thus its cooling effect is inferior to that of the polymer aerogel containing guest units (Comparative Example 3). For supramolecular aerogels containing equal amounts of guest units with host-guest encapsulation and heat absorption (Example 2) and polymer aerogels containing guest components (Comparative Example 3), the superior radiative cooling performance of the supramolecular aerogel with host-guest encapsulation and heat absorption (Example 2) is attributed to the heat dissipation caused by the slippage and movement of the supramolecular host-guest structure formed between the host and guest molecules. Furthermore, the energy dissipation from the slippage and movement of such supramolecular host-guest structures is unaffected by the environment. Therefore, under conditions of relative humidity above 85%, both the supramolecular film with host-guest encapsulation and heat absorption (Example 1) and the supramolecular aerogel with host-guest encapsulation and heat absorption (Example 2) exhibit excellent radiative cooling performance.

[0055] In summary, this invention discloses the preparation and application of a supramolecular radiative cooling material utilizing host-guest inclusion-assisted heat absorption; comprising: forming a supramolecular host unit by self-polymerization or grafting a compound with a macrocyclic structure onto the side chain of a polymer; assembling the supramolecular host unit and a selected guest unit in a solvent to form a stable supramolecular host-guest composite structure through host-guest inclusion; and preparing supramolecular host-guest microspheres or aerogels using the supramolecular host-guest composite structure as the building block, employing spray-freeze-drying or freeze-drying methods to form a porous material; this material can effectively dissipate heat through the thermally responsive host-guest interaction between the host molecule and the guest molecule, thus possessing both active heat absorption and passive radiative cooling properties after the formation of the porous material, overcoming the performance degradation problem of general radiative cooling materials in high humidity environments, and maintaining excellent cooling effect under humid and hot conditions, showing good application prospects.

[0056] Therefore, those skilled in the art will recognize that although embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Therefore, the scope of the present invention should be understood and recognized as covering all such other variations or modifications.

Claims

1. A method for preparing a supramolecular radiation cooling material utilizing host-guest encapsulation-assisted heat absorption, characterized in that, The preparation method is as follows: Step S1: Preparation of supramolecular host units: The host compound with a macrocyclic structure is formed into an oligomer through self-polymerization or the host compound with a macrocyclic structure is grafted onto the side chain of a polymer to form a supramolecular host unit that can be used for subsequent assembly. Step S2: Assembly of supramolecular host-guest composite structure: The supramolecular host unit obtained in step S1 is assembled with the selected guest unit in a solvent to form a stable supramolecular host-guest composite structure through host-guest inclusion. Step S3: Preparation of supramolecular radiation cooling material with host-guest inclusion and heat absorption: Using supramolecular host-guest composite structure as the building unit, supramolecular host-guest microspheres or aerogels are prepared by spray-freeze drying or freeze-drying method to form porous materials.

2. The method for preparing a supramolecular radiation cooling material utilizing host-guest encapsulation-assisted heat absorption as described in claim 1, characterized in that, The macrocyclic main compound in step S1 includes, but is not limited to, any one of cyclodextrin, calixarene, columnar aromatics, cucurbituril, and derivatives of the above compounds.

3. The method for preparing a supramolecular radiation cooling material utilizing host-guest encapsulation-assisted heat absorption as described in claim 1, characterized in that, The polymers in step S1 include, but are not limited to, chitosan, sodium alginate, cellulose, hyaluronic acid, pectin, polyacrylic acid, and derivatives of the above polymers.

4. The method for preparing a supramolecular radiation cooling material utilizing host-guest encapsulation-assisted heat absorption as described in claim 1, characterized in that, In step S2, the guest unit and the supramolecular host unit cavity diameter are matched, which can enclose and form a stable supramolecular host-guest composite structure, and the enclosed structure has temperature responsiveness.

5. The method for preparing a supramolecular radiation cooling material utilizing host-guest encapsulation-assisted heat absorption as described in claim 4, characterized in that, Specifically, the temperature responsiveness is as follows: as the ambient temperature increases from 20 to 50 °C, the inclusion of the supramolecular host-guest composite structure is significantly weakened, or the inclusion is disintegrated.

6. The method for preparing a supramolecular radiation cooling material utilizing host-guest encapsulation-assisted heat absorption as described in claim 1, characterized in that, The guest unit in step S2 includes, but is not limited to, one or more of polyethylene glycol, shea butter, n-octadecane, n-eicosane, lauryl alcohol, isopropyl stearate, and cocoa butter.

7. The method for preparing a supramolecular radiation cooling material utilizing host-guest encapsulation-assisted heat absorption as described in claim 1, characterized in that, In step S2, the mass ratio of supramolecular host unit to guest unit is 2:8 to 8:2; the assembly in step S2 is achieved by uniform mixing in a solvent, solvent heat treatment, or pH / temperature control to realize the self-assembly of supramolecular host unit and guest unit; the solvent is water or a mixture of water and other organic solvents.

8. The method for preparing a supramolecular radiation cooling material utilizing host-guest encapsulation-assisted heat absorption as described in claim 1, characterized in that, In step S3, the concentration of the supramolecular host-guest composite structure is 20-100 mg / mL; the freeze-drying pressure is 5-20 Pa, the temperature is -40 to -20 ℃, and the time is 2-3 days.

9. A supramolecular radiative cooling material utilizing host-guest encapsulation to assist heat absorption, characterized in that, The material is prepared by any one of the preparation methods described in claims 1-8, and the reflectivity of the material is greater than 0.85 in the visible light band of 0.2-2.5 μm and the emissivity of the material is greater than 0.85 in the infrared band of 8-13 μm.

10. The application of a supramolecular radiation cooling material utilizing host-guest encapsulation-assisted heat absorption as described in claim 9, characterized in that, The material can be used directly as an aerogel for energy-saving cooling of materials, or as an energy-saving cooling component by combining aerogel microspheres with other polymers to form a thin film, thereby achieving zero-energy cooling of materials.

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