Evaporative cooling-based synergistically enhanced radiation refrigeration material and preparation method and application thereof

Abstract

The invention discloses a radiation refrigeration material based on evaporative cooling synergistic enhancement and a preparation method and application thereof.The material comprises a radiation refrigeration layer, a moisture power generation layer and a base material supporting layer, and integration of three passive cooling and energy collection functions of passive refrigeration, evaporative cooling and moisture power generation is achieved on fabric; the limitation that all functions exist independently and are difficult to cooperate in the prior art is broken through, the three functions are organically combined and synergistically interacted on the same fabric platform, a complete energy closed-loop system of passive cooling, energy collection and active adjustment / sensing is achieved, energy circulation of the environment and the human body is completely relied on, and the energy utilization rate is improved. And a brand-new functional solution is provided for the wearable device.

Description

Technical Field

[0001] This invention relates to the field of refrigeration materials technology, specifically to evaporative cooling-enhanced radiative refrigeration materials, their preparation methods, and applications. Background Technology

[0002] Radiation cooling technology has evolved over many years, from early single-material reflective cooling to today's spectrally selective radiative cooling. While its technological concepts have continuously innovated, practical application bottlenecks persist. Early radiation cooling materials primarily relied on high-reflectivity metal coatings for passive cooling; however, the high infrared absorption characteristics of metals limited cooling efficiency and their poor flexibility made them unsuitable for wearable applications. With the development of nanotechnology, researchers have developed spectrally selective radiation cooling materials based on photonic crystals and nanoparticles. These materials exhibit high emissivity in the 8-13 μm atmospheric window and high reflectivity in the solar spectrum, theoretically achieving cooling temperature differences exceeding 10°C. However, breakthroughs in adaptability to complex environments have yet to be achieved.

[0003] A deeper analysis of the physical mechanisms reveals that high temperature and humidity environments have multi-dimensional effects on the performance degradation of radiation-cooling materials. Water vapor forming a film on the material surface alters its optical properties; studies show that the absorption rate of solar radiation by the water film is 20%-30% higher than that of a dry surface. Simultaneously, the infrared absorption characteristics of water significantly weaken the material's infrared radiation capability. Internally, water vapor condensation fills the porous structure, disrupting the periodic arrangement of photonic crystals and leading to a decrease in spectral selectivity. Tests conducted in a laboratory on commercial nanoparticle radiation-cooling coatings showed that in an environment of 35℃ and 90% relative humidity, the material's infrared emissivity decreased from 0.92 to 0.65, with a cooling efficiency degradation of 30.4%. This performance degradation is particularly pronounced in practical applications in tropical climates.

[0004] In the field of materials durability research, the operating environment of wearable devices places stringent demands on materials. Traditional physical coating processes used for radiative cooling materials have inherent flaws, resulting in weak interfacial adhesion between the coating and the substrate, making them prone to peeling during repeated bending, stretching, and washing. Comparative test data shows that after 50 standard washes, the functional layer retention rate of traditional coated radiative cooling fabrics is less than 50%. While materials using chemical bonding processes offer improved durability, the complex manufacturing process increases costs by 3-5 times, hindering large-scale production. Although the aerospace field has mastered high-performance durable coating technology, this technology system is based on rigid substrates and cannot meet the flexibility requirements of wearable devices, presenting a fundamental obstacle to technology transfer.

[0005] The development of fabric-based moisture power generation technology has evolved from laboratory prototypes to practical products. Professor Tao Xiaoming's team's breakthrough achievement marks a crucial stage in the industrial application of this technology. Their developed printable hydrogel fabric achieves highly efficient synergy between water vapor adsorption, ion migration, and charge separation through molecular design, improving energy conversion efficiency by an order of magnitude compared to traditional structures. However, in-depth research revealed a humidity threshold effect on the energy output stability of this technology. When the ambient humidity is below 40%, the ionic conductivity of the hydrogel decreases by more than 50%, leading to a sharp decline in output power. This humidity dependence stems from the physical properties of the hydrogel; in low-humidity environments, its swelling degree is insufficient, preventing the formation of continuous ion transport channels. This technological bottleneck limits its application and promotion in arid regions.

[0006] Compared to other energy harvesting technologies, wet power generation has advantages such as strong environmental adaptability and no mechanical loss, but its single function limits the expansion of its application scenarios. The 3D-SMEG technology developed by Nanjing University achieves stable operation over a wide humidity range through biomimetic structural design, but its core objective is to optimize energy output characteristics, without considering integration with other functions. Currently, energy-function integration in wearable devices faces severe challenges. Separately equipping cooling and power generation modules increases system weight by more than 40% and energy consumption by 25%-30%. Furthermore, the operating environment requirements of different modules conflict; for example, cooling modules require good breathability, while traditional power generation modules require sealing and moisture protection.

[0007] From the perspective of energy-thermal management system integration, existing technologies face three core contradictions: first, the contradiction between the high efficiency and environmental adaptability of radiative cooling; second, the contradiction between the energy output and humidity stability of wet power generation; and third, the contradiction between functional integration and system lightweighting. The essence of these contradictions is that the performance optimization of single-function materials cannot meet the comprehensive needs of complex scenarios, necessitating the construction of a multi-functional, synergistic material system.

[0008] Therefore, it is necessary to propose a preparation method for radiation cooling materials based on synergistic enhancement of evaporative cooling, so as to achieve synergistic enhancement of radiation cooling and moisture power generation, and provide a new technical path for solving the energy supply and thermal management problems of wearable devices. Summary of the Invention

[0009] This invention provides a radiation refrigeration material based on evaporative cooling synergistic enhancement to solve the problems of low refrigeration efficiency and poor durability of existing radiation refrigeration materials in high temperature and high humidity environments, as well as insufficient stability and energy conversion efficiency and single function of fabric moisture generators. It realizes the synergistic optimization of material refrigeration and energy harvesting, and expands its application in wearable systems and other fields.

[0010] In view of this, the solution of the present invention is as follows: The first aspect of the present invention is to provide a method for preparing a radiative cooling material based on evaporative cooling synergistic enhancement, the steps of which include: A breathable and hydrophilic fabric is used as the substrate support layer, and then treated with a silane coupling agent and dried. The hydrogel precursor liquid is applied to the substrate support layer, and two electrodes are laid on the coating layer and then cross-linked and cured to form a moisture power generation layer. Aqueous dispersions of radiative cooling particles at various concentrations were prepared, and water-absorbing polymers were added to each aqueous dispersion, followed by heating and stirring to obtain various core-shell structure mixtures. Various precursor mixtures were prepared by adding metal nanowire pre-dispersion liquid to each core-shell structure mixture and adjusting the viscosity. Precursor mixtures were sequentially applied to the wet gas power generation layer in order of increasing concentration of radiative cooling particles, and then dried by gradient heating to obtain the radiative cooling layer, thus obtaining a radiative cooling material based on synergistic enhancement of evaporative cooling.

[0011] Furthermore, the breathable hydrophilic fabric is selected from cotton fabric, hydrophilic modified polyester fabric, or blended fabric, wherein the polyester fabric or blended fabric is hydrophilicated by a silane coupling agent.

[0012] Preferably, the silane coupling agent is selected from KH550 or KH560. The hydrophilicity of ester fabrics or blended fabrics can be improved by impregnating them with a silane coupling agent alcohol solution at a higher temperature, such as impregnating them with a 1-5 wt% silane coupling agent alcohol solution at 40-65°C for 10-40 minutes.

[0013] Furthermore, the hydrogel precursor solution is obtained by crosslinking at least one monomer selected from acrylamide, N-vinylpyrrolidone, acrylic acid, hydroxyethyl methacrylate, and polyvinyl alcohol under the action of an initiator and a catalyst. The electrode is fixed to the hydrogel layer by free radical polymerization reaction, and a lead interface is reserved for current conduction. And / or, the electrode is at least one of a carbon nanotube thin film electrode, a copper electrode, a silver electrode, and a platinum electrode.

[0014] Furthermore, the concentrations of the multiple concentrations of the radiative cooling particles are selected from multiple concentrations between 5% and 15%; such as two or three concentrations, forming a concentration gradient, with two concentrations being preferred. And / or, the preparation method of the core-shell structured mixture is as follows: adding radiation-cooling particles to deionized water, treating it under ultrasonic conditions of 20-25kHz for 30-60min, then adding a water-absorbing polymer, and stirring at 55-60℃ for 30-40min; core-shell structured mixtures with different radiation-cooling particle contents are prepared by using radiation-cooling particles of various concentrations. And / or, the mass ratio of the radiative cooling particles to the water-absorbing polymer is (1.5-5):1.

[0015] Furthermore, the radiation cooling particles are selected from at least one of silica microspheres, aluminum nitride particles, titanium dioxide, or boron nitride; And / or, the water-absorbing polymer is selected from at least one of sodium polyacrylate and chitosan derivatives; And / or, the absorbent polymer also contains a solid hygroscopic agent, such as inorganic hygroscopic agents like calcium chloride or lithium chloride, in an amount of 15-35% of the mass of the absorbent polymer, for dispersion in the core-shell structure gaps.

[0016] Furthermore, the diameter of the metal nanowire is 50-100 nm, and the aspect ratio is 50-100; And / or, the metal nanowires are selected from at least one of silver nanowires and copper nanowires; And / or, the amount of the metal nanowires added is 1-3% of the mass of the core-shell structured mixture; And / or, the viscosity adjustment process uses a water-based adhesive, including but not limited to water-based polyurethane, polyvinyl alcohol, etc., which are used to increase the viscosity of the water-based system and have strong adhesive properties.

[0017] Furthermore, the wet film thickness in the preparation process of the moisture power generation layer is 100-150 μm; and / or, the wet film thickness in the preparation process of the radiation cooling layer is 100-200 μm.

[0018] A second aspect of the present invention is to provide a radiative cooling material based on evaporative cooling synergistic enhancement, prepared by the method described in the first aspect.

[0019] Furthermore, in the material obtained by the preparation method described in the first aspect, the thickness of the substrate support layer is 30-60 μm; And / or, the final thickness of the moisture-generating layer is 80-120 μm; And / or, the final thickness of the radiation cooling layer is 30-60 μm.

[0020] A third aspect of the present invention is the application of the evaporative cooling synergistic enhanced radiative cooling material obtained by the preparation method described in the first aspect above, or the evaporative cooling synergistic enhanced radiative cooling material described in the second aspect, in the preparation of wearable devices.

[0021] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a radiation cooling material based on evaporative cooling synergistic enhancement, comprising a radiation cooling layer, a moisture power generation layer, and a substrate support layer. It integrates three passive cooling and energy harvesting functions—passive cooling, evaporative cooling, and moisture power generation—on a fabric, breaking through the limitations of traditional technologies where each function exists independently and is difficult to coordinate. By organically combining the three functions on the same fabric platform, they synergistically enhance each other, realizing a complete energy closed-loop system of "passive cooling-energy harvesting-active regulation / sensing." It relies entirely on the energy cycle of the environment and the human body, providing a brand-new functional solution for wearable devices.

[0022] The preparation method of the present invention adopts a microstructure design of "radiation cooling particles as the core and water-absorbing polymer as the shell". Through in-situ polymerization process, the water-absorbing polymer molecular chains are uniformly wrapped and coated on the surface of the radiation cooling particles to form a dense and hydrophilic shell structure. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of the evaporative cooling-enhanced radiative cooling material described in one embodiment of the present invention.

[0024] Figure 2 This is a TEM image representing the core-shell structure in one embodiment of the present invention.

[0025] Figure 3 This is a SEM image of the radiation cooling layer described in one embodiment. Detailed Implementation

[0026] The technical solution of the present invention will now be clearly and completely described in conjunction with preferred embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] In one embodiment, a method for preparing a synergistically enhanced radiative cooling material based on evaporative cooling is provided, comprising the following steps: S1. Prepare the substrate support layer by taking a breathable fabric as the substrate support layer, treating it with a silane coupling agent and then drying it. S2. Preparation of the moisture-generating layer: The hydrogel precursor liquid is applied to the substrate support layer, and two electrodes are laid on the coating layer and then cross-linked and cured to form the moisture-generating layer. S3. Fabrication of the radiation cooling layer, including: S31. Prepare aqueous dispersions of radiation-cooling particles of various concentrations, add water-absorbing polymers to each aqueous dispersion and heat and stir to obtain various core-shell structure mixtures; S32. Add metal nanowire pre-dispersion liquid to each core-shell structure mixture and adjust to a suitable viscosity to obtain a variety of precursor mixtures; S33. The precursor mixture was applied to the wet gas power generation layer in order of increasing concentration of the radiative cooling particles, and then dried by gradient heating to obtain the radiative cooling layer, thus obtaining the radiative cooling material based on synergistic enhancement of evaporative cooling.

[0028] The material structure obtained by the above preparation method is as follows: Figure 1 As shown, from top to bottom, the layers are: a radiative cooling layer 3, a moisture-generating layer 2, and a substrate support layer 1. The radiative cooling layer 3 has a core-shell structure with radiative cooling particles as the core and a water-absorbing polymer as the shell, exhibiting a concentration gradient distribution. The moisture-generating layer 2 contains a hydrogel network and carbon nanotube thin-film electrodes. Metal nanowires are dispersed in the radiative cooling layer to enhance conductivity. This system integrates three passive cooling and energy harvesting functions—passive cooling, evaporative cooling, and moisture-generating power—on the substrate support layer. This overcomes the limitations of traditional technologies where each function exists independently and is difficult to coordinate. By organically combining the three on the same fabric platform, they synergistically enhance each other, achieving a complete energy closed-loop system of "passive cooling - energy harvesting - active regulation / sensing." This system relies entirely on the energy cycle of the environment and the human body, providing a novel functional solution for wearable devices.

[0029] The specific collaborative enhancement or collaborative optimization mechanism is as follows: 1) Synergistic effect of radiative cooling layer and evaporative cooling: The water-absorbing polymer shell of the radiative cooling layer adsorbs water vapor from the environment and human sweat. The evaporation of water vapor takes away the surface heat. At the same time, the radiative cooling particles radiate heat through the 8-13μm atmospheric window. The combination of the two increases the cooling efficiency by 25-30% compared with radiative cooling alone. 2) Synergistic effect of evaporative cooling and moisture power generation: During the water vapor evaporation process, the ion migration rate of the hydrogel layer increases by 30-40% due to the humidity gradient, which promotes charge separation in the moisture power generation layer, resulting in a 15-20% increase in output power compared to moisture power generation alone; 3) Energy closed-loop synergy: The electrical energy generated by the moisture power generation layer can drive the micro-sensing module (such as temperature and humidity sensors) integrated into the fabric. The environmental parameters fed back by the sensors can adjust the evaporation rate through the material's own humidity response characteristics, forming a dynamic adjustment closed loop.

[0030] In the above embodiments, the TEM image of the core-shell structured mixture is as follows: Figure 2As shown in the TEM image, this invention visually verifies the successful preparation of a core-shell structured mixture with "radiative cooling particles as the core and a hygroscopic polymer as the shell." Morphologically, the particles are regularly spherical, with a clear boundary between the core and shell, and no agglomeration or structural defects. In terms of size, the particle diameter perfectly matches the design parameters for the radiative cooling particles and the shell thickness. This structure is the core guarantee for achieving synergistic functionality and high durability in "radiative cooling-evaporative cooling-moisture power generation": the high infrared emissivity particles in the core region support efficient cooling, the highly hygroscopic polymer in the shell enables synergistic evaporative cooling and power generation, and the "rigid core + flexible shell" design significantly improves the structural stability and flexibility of the material, ultimately resulting in a significant synergistic enhancement effect in cooling efficiency, power generation stability, and durability.

[0031] In the above embodiments, the SEM image of the radiation cooling layer is as follows: Figure 3 As shown in the image, the microstructure of the radiation-cooling layer exhibits a continuous, uniform, and interconnected porous network structure. This structure is formed by the synergistic effect of gradient dispersion of radiation-cooling particles, cross-linking of water-absorbing polymers, and doping with silver nanowires. It displays a gradient distribution with smaller pores at the surface / edges and larger pores at the bottom / center, either in thickness or within the plane. This porous gradient structure, on the one hand, reduces infrared scattering absorption and utilizes the low infrared absorption characteristics of the air layer to ensure that the emissivity of the radiation-cooling particles in the 8-13 μm band is ≥0.9, enabling a cooling temperature difference of 9.8-12.0℃. On the other hand, it provides a rapid transport channel for water vapor, supporting evaporative cooling and driving ion movement in the humidification power generation layer, thereby increasing the output power density. It achieves a 15-20% increase in efficiency, while maintaining a performance retention rate of ≥84.5% after 1000 bends and a functional retention rate of ≥85% after 50 washes thanks to its excellent mechanical buffering properties. Compared with non-gradient porous structures, its uniform porous structure makes radiative cooling, evaporative cooling, and humidification power generation more efficient. The gradient design can store excess water vapor in high humidity environments and slowly release the stored water vapor in low humidity environments, achieving a high-temperature and high-humidity attenuation rate of ≤10.5% and a low-humidity power retention rate of ≥62.4%. It is the key to achieving multi-dimensional synergistic enhancement of "cooling-power generation-environmental adaptability-durability". Its microstructure and performance data are completely matched, verifying the rationality and effectiveness of the process design.

[0032] Example 1 A method for preparing radiative cooling materials based on synergistic enhancement of evaporative cooling, comprising the following steps: 1) Substrate pretreatment: Take a polyester fabric (10cm×10cm), immerse it in 200mL of 2% KH550 silane coupling agent ethanol solution (ethanol:water = 3:1), stir at 60℃ for 30 minutes, take it out and rinse it 3 times with deionized water, dry it in an oven at 80℃ for 1 hour, and set it aside. 2) Preparation of the moisture-generating layer: Weigh 5g of acrylamide (monomer) and 0.05g of N,N'-methylenebisacrylamide (crosslinking agent), add 45g of deionized water, and stir until completely dissolved to obtain the hydrogel precursor solution. Add 0.1g of ammonium persulfate (initiator) and 0.05mL of tetramethylethylenediamine (catalyst) to the precursor solution, stir evenly, and then coat it on the surface of the pretreated polyester fabric (central area, 8cm×8cm), controlling the thickness to 150μm. Cut two 8cm×1cm carbon nanotube films as electrodes, and attach them to both ends of the hydrogel layer (6cm apart), leaving lead interfaces. Let it stand at room temperature for 30 minutes to allow the hydrogel to crosslink and solidify, forming a "hydrogel network + electrode" moisture-generating layer. 3) Dispersion of radiation-cooled particles: Weigh 7.2g and 10.8g of silica microspheres (average particle size 500nm) respectively, add them to 90g of deionized water, and treat them with a 20kHz high-frequency ultrasonic instrument for 45 minutes (power 300W) to form radiation-cooled particle dispersions with different concentrations (concentration 12% and 8%). 4) Construction of the "core-shell" structure: Add 3g of sodium polyacrylate and 1g of lithium chloride to the above dispersion, heat to 60℃, and stir continuously for 30 minutes; 5) Adhesive mixing: Take silver nanowires (diameter 50-100nm, aspect ratio 50-100), disperse them in 10mL of deionized water at a ratio of 2.5% of the total mass of the mixture, and sonicate them at 15kHz for 10 minutes (power 100W) to form a uniform dispersion. Add the dispersion to the core-shell structure mixture with low-speed stirring. After stirring for 10 minutes, weigh 15g of waterborne polyurethane and slowly add it to the core-shell structure mixture. Continue stirring for 1.5 hours. 6) Gradient coating: The pretreated polyester fabric is laid flat on the coating platform. An adjustable squeegee (blade width 10cm) is used to uniformly coat the low-concentration radiation cooling particle mixture onto the fabric surface. The squeegee height is controlled to make the coating thickness 100μm. During the coating process, the edge pressure is maintained at 5N and the center pressure at 3N. 7) Low-temperature drying: Place the coated fabric in the drying oven and set the program: 60℃ pre-dry for 1 hour → 70℃ dry for 2 hours, then let it cool naturally to room temperature; 8) Take out 7), then uniformly coat the high-concentration radiation cooling particle mixture onto the low-concentration surface layer, and repeat step 7) to obtain the integrated fabric based on the three-function synergistic enhancement of evaporative cooling-radiative cooling-moisture power generation.

[0033] Example 2 A method for preparing radiative cooling materials based on synergistic enhancement of evaporative cooling, comprising the following steps: 1) Substrate pretreatment: Take cotton fabric (10cm×10cm, 100g / m), ultrasonically clean it with deionized water for 15 minutes (power 200W), and dry it in a 60℃ oven for 1 hour. (Cotton fabric is naturally hydrophilic and does not require modification with silane coupling agents). The preparation of the moisture-generating layer is the same as in Example 1.

[0034] 2) Dispersion of radiation-cooled particles: Weigh 5.4g and 9g of aluminum nitride particles respectively, and add them to 90g of deionized water respectively. Treat them with a 25kHz high-frequency ultrasonic instrument (power 250W) for 50 minutes to form radiation-cooled particle dispersions with different concentrations (10% and 6%).

[0035] 3) Construction of the "core-shell" structure: Add 2g of chitosan derivative (90% degree of deacetylation) and 1g of lithium chloride to the above dispersion, heat to 55℃, and continue stirring for 40 minutes.

[0036] 4) Adhesive mixing: Take silver nanowires (diameter 50-100nm, aspect ratio 50-100), disperse them in 10mL of deionized water at a ratio of 1.5% of the total mass of the mixture, and sonicate them at 15kHz for 10 minutes to form a uniform dispersion. Add the dispersion to the core-shell structure mixture with low-speed stirring. After stirring for 10 minutes, weigh 12g of polyvinyl alcohol and slowly add it to the core-shell structure mixture. Continue stirring for 2 hours.

[0037] 5) Gradient coating: The pretreated cotton fabric is laid flat on the coating platform. An adjustable scraper (blade width 10cm) is used to uniformly coat the low-concentration radiation cooling particle mixture onto the fabric surface. The coating thickness is controlled to be 80μm (error ±3μm). During the coating process, the edge pressure is maintained at 4N and the center pressure at 2N.

[0038] 6) Low-temperature drying: Place the coated fabric into a forced-air drying oven and set the program: 55℃ pre-dry for 1.5 hours → 65℃ dry for 2 hours and then allow it to cool naturally to room temperature.

[0039] 7) Take out 6), then uniformly coat the high-concentration radiation cooling particle mixture onto the low-concentration surface layer, and repeat step 6) to obtain the integrated fabric based on the three-function synergistic enhancement of evaporative cooling-radiative cooling-moisture power generation.

[0040] Example 3 A method for preparing radiative cooling materials based on synergistic enhancement of evaporative cooling, comprising the following steps: 1) Substrate pretreatment: Take a cotton / polyester blended fabric (10cm×10cm, mass ratio 3:7, 110g / m), immerse it in 200mL of 2% KH550 silane coupling agent ethanol solution (ethanol:water = 3:1), stir at 60℃ for 30 minutes, remove and rinse 3 times with deionized water, dry in an oven at 80℃ for 1 hour, and set aside. The preparation of the moisture-generating layer is the same as in Example 1.

[0041] 2) Dispersion of radiation-cooled particles: Weigh 5g of silica microspheres + 4g of aluminum nitride particles and 3g of silica microspheres + 2.4g of aluminum nitride particles respectively, add them to 90g of deionized water, and treat them with a 22kHz high-frequency ultrasonic instrument (power 350W) for 55 minutes to form radiation-cooled particle dispersions with different concentrations (10% and 6%).

[0042] 3) Construction of the "core-shell" structure: Add 2g sodium polyacrylate (molecular weight 8 million) + 1g chitosan derivative (2:1 compound) + 1g lithium chloride to the above dispersion, heat to 60℃, and continue stirring for 35 minutes.

[0043] 4) Adhesive mixing: Take silver nanowires (diameter 50-100nm, aspect ratio 50-100), disperse them in 10mL of deionized water at a ratio of 1% of the total mass of the mixture, and sonicate them at 15kHz for 10 minutes to form a uniform dispersion. Add the dispersion to the core-shell structure mixture with low-speed stirring. After stirring for 10 minutes, weigh out 12g of waterborne polyurethane and 3g of polyvinyl alcohol, and slowly add them to the core-shell structure mixture. Continue stirring for 1.2 hours.

[0044] 5) Gradient coating: The pretreated blended fabric is laid flat on the coating platform. An adjustable scraper (blade width 10cm) is used to uniformly coat the low-concentration radiation cooling particle mixture onto the fabric surface. The thickness is controlled at 120μm (error ±3μm) by a laser thickness gauge. During the coating process, the edge pressure is maintained at 5N and the center pressure at 3N.

[0045] 6) Low-temperature drying: Place the coated fabric in a forced-air drying oven and set the program: 60℃ pre-dry for 1 hour → 75℃ dry for 1.5 hours, then let it cool naturally to room temperature.

[0046] 7) Take out 6), then uniformly coat the high-concentration radiation cooling particle mixture onto the low-concentration surface layer, and repeat step 6) to obtain the integrated fabric based on the three-function synergistic enhancement of evaporative cooling-radiative cooling-moisture power generation.

[0047] Example 4 A method for preparing radiative cooling materials based on synergistic enhancement of evaporative cooling, comprising the following steps: 1) Substrate pretreatment: Take polyester fabric (10cm×10cm, 120g / m) and pretreat it with KH550 silane coupling agent according to the method in Example 1, and set it aside. The preparation of the moisture-generating layer is the same as in Example 1.

[0048] 2) Dispersion of radiation-cooled particles: Weigh 7.2g and 10.8g of silica microspheres respectively, add them to 90g of deionized water, and treat them with a 20kHz high-frequency ultrasonic instrument (power 300W) for 60 minutes to form radiation-cooled particle dispersions with different concentrations (concentration 12% and 8%).

[0049] 3) Construction of the "core-shell" structure: Add 5g of sodium polyacrylate and 1g of lithium chloride to the above dispersion, heat to 60℃, and continue stirring for 40 minutes.

[0050] 4) Adhesive mixing: Take silver nanowires (diameter 50-100nm, aspect ratio 50-100), disperse them in 10mL of deionized water at a ratio of 2.5% of the total mass of the mixture, and sonicate them at 15kHz for 10 minutes (power 100W) to form a uniform dispersion. Add the dispersion to the core-shell structure mixture at a low speed of 200r / min and stir for 10 minutes. Then weigh 20g of waterborne polyurethane and slowly add it to the core-shell structure mixture. Continue stirring for 2 hours.

[0051] The subsequent coating and drying steps are the same as in Example 1.

[0052] Example 5 A method for preparing radiative cooling materials based on synergistic enhancement of evaporative cooling, comprising the following steps: 1) Substrate pretreatment: Take a thin polyester fabric (10cm×10cm, 80g / m) and pretreat it with KH550 silane coupling agent according to the method in Example 1. The moisture-generating layer is prepared in the same way as in Example 1.

[0053] 2) Dispersion of radiation-cooled particles: Same as in Example 1.

[0054] 3) Construction of the "core-shell" structure: Same as in Example 1.

[0055] 4) Adhesive mixing: The only difference from Example 1 is that the amount of waterborne polyurethane is changed to 10g.

[0056] The subsequent coating and drying steps are the same as in Example 1.

[0057] Comparative Example 1 A method for preparing a radiation cooling material, comprising the following steps: Except for the core-shell structure construction steps, the rest are the same as in Example 1. The specific difference in steps is that steps 3) to 5) are: 10g of silica microspheres and 3g of sodium polyacrylate are physically mixed and then added to 90g of deionized water without coating and stirring (no heating or shell formation process), and then the binder is added according to step 5).

[0058] Comparative Example 2 A method for preparing a radiation cooling material, comprising the following steps: Except for the radiation-cooled particle dispersion step, the rest is the same as in Example 1. The specific differences are: in step 3), the ultrasonic time is shortened to 20 minutes (power 300W), no concentration gradient is formed (the concentration of the surface layer and the bottom layer is 10%), and the pressure during coating is uniform (4N).

[0059] Comparative Example 3 A method for preparing a radiation cooling material includes the following steps: first, coating a radiation cooling layer, curing it, then coating a power generation layer, and finally cross-linking and curing it.

[0060] Comparative Example 4 A method for preparing a radiation cooling material, comprising the following steps: Except for the substrate pretreatment step, the rest is the same as in Example 1. The specific difference is that in step 1), the polyester fabric is directly coated to prepare the moisture-generating layer without being treated with KH550 silane coupling agent.

[0061] Comparative Example 5 A method for preparing a radiation cooling material, comprising the following steps: A polyester fabric (10cm×10cm) was coated with an aluminum layer (50μm thick) using a vacuum evaporation method. No other functional layers were applied.

[0062] Comparative Example 6 A method for preparing a radiation cooling material, comprising the following steps: The radiation cooling layer was prepared using the exact same materials and processes as in Example 1, but without the integration of the moisture power generation unit (no electrodes and hydrogel layer).

[0063] Performance tests were conducted on the above embodiments and comparative examples, including: cooling temperature difference test, high temperature and high humidity attenuation rate test (environmental adaptability - high humidity stability), output power density test (energy harvesting performance), function retention rate test after 50 washes (durability), low humidity adaptability test (environmental adaptability - low humidity stability), and flexibility (performance retention rate after 1000 bends) test.

[0064] Test standards (methods): 1. The cooling temperature difference was measured using an infrared thermal imager (FLIRE85); the high temperature and high humidity decay rate was the ratio of the cooling temperature difference to the initial state after the material was placed in an environment of 35℃ / 90%RH for 24 hours. 2. Output power density was measured using a Keithley 2450 source meter; 3. The washing test shall be performed in accordance with GB / T3921-2008 "Textiles - Tests for color fastness - Color fastness to washing with soap" standard; 4. Low humidity adaptability is the ratio of output power in a 30% RH environment to that in a 60% RH environment.

[0065] 5. The flexibility (performance retention rate after 1000 bends) test shall be performed in accordance with GB / T24452-2009 "Determination of bending properties of textiles".

[0066] The results are shown in Table 1.

[0067] Table 1: ; As can be seen from the table above, Examples 1-5 (the solutions of this invention) are significantly superior to Comparative Examples 1-6 (comparative solutions) in all five core performance dimensions: refrigeration, power generation, durability, environmental adaptability, and flexibility. This verifies the synergistic advantages of the "core-shell structure + gradient coating + reasonable layer sequence + silane coupling agent modification" design. The relative advantages of the examples are specifically manifested in the following aspects: (a) Cooling performance: The example unit is highly efficient and stable, while the comparative unit shows a significant decrease in performance. Cooling temperature difference: The cooling temperature difference of Examples 1-5 is 9.8-12.0℃, with an average of 10.86℃; the difference of Comparative Examples 1-6 is 5.2-9.0℃, with an average of 6.95℃. The overall improvement of Examples is 56.3%.

[0068] Reasons for the advantage: The "radiative cooling particle core-water-absorbing polymer shell" structure enables synergistic effect between radiative cooling and evaporative cooling, improving the cooling efficiency by 25-30% compared to single radiative cooling.

[0069] Comparative examples show the following shortcomings: Comparative example 1 (no core and shell) has low infrared emissivity due to particle agglomeration; Comparative example 5 (aluminum coating) has strong infrared absorption but weak basic cooling capacity; Comparative example 3 (inverted layer sequence) blocks the synergistic path, resulting in a sharp drop in cooling efficiency.

[0070] High temperature and high humidity attenuation rate: The attenuation rate of the example was only 7.8-10.5%, with an average of 9.0%; the attenuation rate of the comparative example was 15.3-35.2%, with an average of 27.8%, and the attenuation of the example was reduced by 67.6%.

[0071] Advantages: The core-shell structure of the radiation cooling layer can block water vapor intrusion and reduce damage to optical performance; the reasonable layer sequence avoids excessive swelling of the moisture power generation layer.

[0072] Comparative examples have shortcomings: In Comparative Example 3 (layer sequence reversed), the outer hydrogel is prone to excessive swelling, and water vapor penetration damages the radiation cooling layer; In Comparative Example 1 (no core and shell), the particles are not protected by polymers and are easily affected by water vapor.

[0073] (ii) Power generation performance: The output of the example is stable, but the adaptability of the comparative example is poor. Output power density: 6.8-8.0 μW / cm² for the examples, with an average of 7.46 μW / cm²; 3.8-5.1 μW / cm² for Comparative Examples 1-4, and 0 for Comparative Examples 5-6. The power generation efficiency of the examples is improved by 46.3% (compared to the average of Comparative Examples 1-4).

[0074] Advantages: Evaporative cooling promotes ion migration in the hydrogel layer, increasing charge separation efficiency by 15-20%; a reasonable layer sequence allows the moisture-generating layer to be close to the substrate, efficiently adsorbing water vapor.

[0075] Shortcomings of the comparative examples: Comparative example 3 (layer sequence reversed) has insufficient water vapor replenishment and low hydrogel swelling degree; Comparative example 6 (no power generation layer) and comparative example 5 (aluminum coating) have no power generation function module.

[0076] Low humidity adaptability: The power retention rate of the Example at 30%RH was 62.4-72.1%, with an average of 66.6%; the Comparative Examples 1-4 were 32.6-40.8%, with an average of 35.7%. The Example showed an 86.5% improvement in low humidity stability.

[0077] Advantages: The water-absorbing polymer in the radiative cooling layer can store water vapor and slowly release it to the moisture-generating layer, alleviating the problem of low humidity and water loss.

[0078] Comparative examples have shortcomings: Comparative Example 3 (layer sequence reversed) has water vapor in the outer hydrogel that evaporates easily and has no reserve or replenishment; Comparative Example 1 (no core and shell) has no polymer water vapor reserve structure.

[0079] (iii) Durability: The embodiment has a stable structure, while the comparative example is prone to failure. Function retention rate after 50 washes: 85.0-90.1% for the example, with an average of 87.0%; 38.8-70.2% for the comparative example, with an average of 51.3%, the example showed a 69.6% improvement in retention rate.

[0080] Advantages: Silane coupling agent modification enhances the interfacial bonding between the substrate and the functional layer; the core-shell structure improves the integrity of the functional layer and provides strong resistance to washing and peeling.

[0081] Comparative Example Shortcomings: Comparative Example 4 (without coupling agent) has only physical adsorption between layers, which is easy to peel off; Comparative Example 1 (without core and shell) has a loose functional layer structure, which agglomerates and fails after washing.

[0082] Flexibility (performance retention rate after 1000 bends): Examples: 84.5-91.3%, average 87.66%; Comparative examples: 0-76.8%, average 52.4%, with examples showing a 67.3% increase in flexibility.

[0083] Reasons for the advantages: ①The substrate is treated with silane coupling agent, resulting in strong interlayer bonding and making it less prone to delamination when bent; ②The water-absorbing polymers in the core-shell structure are elastic and can buffer bending stress; ③ Gradient coating avoids stress concentration caused by uneven thickness of functional layers.

[0084] Comparison of shortcomings: ① Comparative Example 5 (aluminum coating) has high rigidity. After 1000 bending cycles, the coating breaks, and the performance retention rate is 0. ②Comparative Example 3 (layer sequence reversed) showed poor interlayer compatibility, cracking and detaching after bending, with a retention rate of only 58.3%; ③Comparative Example 4 (without coupling agent) has weak interlayer bonding, and the functional layer peels off after bending, with a retention rate of 52.6%.

[0085] In summary, this invention, through the design of "core-shell structure + gradient coating + reasonable layer sequence + silane coupling agent modification", achieves simultaneous improvement in refrigeration, power generation, durability, environmental adaptability and flexibility, and completely solves the problems of functional synergy failure, structural instability and poor environmental adaptability existing in the comparison, and has extremely strong practical application value.

[0086] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing radiative cooling materials based on synergistic enhancement of evaporative cooling, characterized by the following steps: include: Breathable and hydrophilic fabrics are used as the substrate support layer; The hydrogel precursor liquid is applied to the substrate support layer, and two electrodes are laid on the coating layer and then cross-linked and cured to form a moisture power generation layer. Aqueous dispersions of radiative cooling particles at various concentrations were prepared, and water-absorbing polymers were added to each aqueous dispersion, followed by heating and stirring to obtain various core-shell structure mixtures. Metal nanowire pre-dispersion liquid was added to each core-shell structure mixture and the viscosity was adjusted to obtain various precursor mixtures; Precursor mixtures were sequentially applied to the wet gas power generation layer in order of increasing concentration of radiative cooling particles, and then dried by gradient heating to obtain the radiative cooling layer, thus obtaining a radiative cooling material based on synergistic enhancement of evaporative cooling.

2. The preparation method according to claim 1, characterized in that, The breathable hydrophilic fabric is selected from cotton fabric, hydrophilic modified polyester fabric, or blended fabric.

3. The preparation method according to claim 1, characterized in that, The hydrogel precursor solution is obtained by crosslinking at least one monomer selected from acrylamide, N-vinylpyrrolidone, acrylic acid, hydroxyethyl methacrylate, and polyvinyl alcohol under the action of an initiator and a catalyst. And / or, the electrode is at least one of a carbon nanotube thin film electrode, a copper electrode, a silver electrode, and a platinum electrode.

4. The preparation method according to claim 1, characterized in that, The concentrations of the various radiative cooling particles are selected from multiple concentrations ranging from 5% to 15%. And / or, the preparation method of the core-shell structured mixture is as follows: adding radiation-cooling particles to deionized water, treating it under ultrasonic conditions of 20-25kHz for 30-60min, then adding a water-absorbing polymer to it, and stirring at 55-60℃ for 30-40min to obtain the mixture; And / or, the mass ratio of the radiative cooling particles to the water-absorbing polymer is (1.5-5):

1.

5. The preparation method according to claim 1, characterized in that, The radiation cooling particles are selected from at least one of silica microspheres, aluminum nitride particles, titanium dioxide, or boron nitride. And / or, the water-absorbing polymer is selected from at least one of sodium polyacrylate and chitosan derivatives; And / or, the absorbent polymer may also contain calcium chloride or lithium chloride as a moisture-absorbing enhancer.

6. The preparation method according to claim 1, characterized in that, The diameter of the metal nanowire is 50-100 nm, and the aspect ratio is 50-100. And / or, the metal nanowires are selected from at least one of silver nanowires and copper nanowires; And / or, the amount of the metal nanowires added is 1-3% of the mass of the core-shell structured mixture; And / or, the viscosity adjustment process uses an aqueous adhesive.

7. The preparation method according to claim 1, characterized in that, The wet film thickness during the preparation process of the moisture power generation layer is 100-150 μm; and / or, the wet film thickness during the preparation process of the radiation cooling layer is 100-200 μm.

8. A radiation refrigeration material based on evaporative cooling synergistic enhancement, prepared by the preparation method described in any one of claims 1-7.

9. The evaporative cooling-enhanced radiative cooling material according to claim 1, characterized in that, The thickness of the substrate support layer is 30-60 μm; And / or, the thickness of the moisture-generating layer is 80-120 μm; And / or, the thickness of the radiation cooling layer is 30-60 μm.

10. The application of the evaporative cooling synergistic enhanced radiation cooling material prepared by the preparation method according to any one of claims 1-7 or the evaporative cooling synergistic enhanced radiation cooling material according to any one of claims 8-9 in the preparation of wearable devices.

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