Temperature control composite structure material with photo-thermal absorption and radiation cooling functions and preparation method of temperature control composite structure material

Abstract

The invention provides a temperature control composite structure material with photo-thermal absorption and radiation cooling functions and a preparation method of the temperature control composite structure material, and belongs to the technical field of temperature control materials. The temperature-control composite structure material comprises a Fe3O4 photo-thermal unit and a BaSO4 radiation cooling unit, wherein the Fe3O4 photo-thermal unit is formed by combining a high-temperature color-changing layer, a Fe3O4 photo-thermal layer and a substrate layer, and the BaSO4 radiation cooling unit is formed by combining a low-temperature color-changing layer, a BaSO4 radiation cooling layer and the substrate layer. The Fe3O4 photo-thermal unit and the BaSO4 radiation cooling unit are arranged together in an array mode. Or the system comprises a Fe3O4 photo-thermal unit formed by combining a high-temperature color-changing layer and a Fe3O4 photo-thermal layer and a BaSO4 radiation cooling unit formed by combining a low-temperature color-changing layer and a BaSO4 radiation cooling layer, wherein the Fe3O4 photo-thermal unit and the BaSO4 radiation cooling unit are arranged together in an array. The invention provides a preparation method of a temperature control composite structure material with photo-thermal absorption and radiation cooling. The prepared temperature control composite structure material can realize temperature self-adaptive switching, so that environmental energy can be efficiently utilized, and the material has good environmental adaptability.

Description

Technical Field

[0001] This invention relates to the field of temperature control materials technology, and in particular to a temperature control composite structural material with photothermal absorption and radiative cooling, and its preparation method. Background Technology

[0002] Climate change is primarily driven by greenhouse gas emissions, which are closely linked to the continued growth in global energy consumption. Traditional heating and cooling technologies consume significant amounts of energy in the thermal management of human living environments. According to the International Energy Agency, approximately 21.5% of global energy is used for heating or cooling in residential and commercial buildings, and in developed regions, energy invested in temperature management can exceed 40% of a country's total energy consumption. Solar thermal heating and passive radiative cooling (PDRC) are sustainable thermal management technologies that can alleviate the current global energy consumption problem without additional energy consumption. Solar heating relies on objects absorbing the solar spectrum (300–2500 nm) and converting it into heat energy. On the other hand, passive radiative cooling materials enhance the reflectivity of the solar spectrum (300–2500 nm) and the emissivity of the atmospheric window spectrum (8–13 μm), helping to reduce heat gain and allow thermal radiation to escape through atmospheric windows—that is, reducing the temperature of objects by reflecting sunlight and emitting long-wave infrared (LWIR) radiation into the cold universe (approximately 3 K). Therefore, by using temperature-intelligent adaptive thermal management technology to cope with fluctuating ambient temperatures, materials can switch between heating and cooling modes, which can meet the temperature management needs of production and daily life.

[0003] In recent years, researchers have developed a large number of photothermal materials to suit various applications. These photothermal materials can be divided into four functional categories: metal nanoparticles, carbon-based materials, organic polymers, and semiconductor materials. The photothermal conversion mechanisms of these different types of materials vary considerably.

[0004] When metal nanoparticles interact with light of appropriate wavelengths, their surface free electrons are excited, and the conduction band electrons oscillate collectively at the same frequency, forming localized surface plasmon resonance (LSPR). These materials exhibit high photothermal conversion efficiency and strong heating capacity. The most commonly used plasma metals are gold, silver, and other precious metals with nanostructures, but their high cost makes large-scale application difficult. If cheaper metals such as aluminum and copper are used instead, their nanomaterial properties make them prone to oxidation, leading to decreased material stability and performance. Furthermore, some metal nanoparticles possess biotoxicity, posing potential hazards to organisms.

[0005] Carbon-based materials (such as carbon nanotubes, graphene, carbon black, graphite, and carbon composites) exhibit strong light absorption and high photothermal conversion efficiency over a wide wavelength range. Although these materials possess excellent performance and relatively low raw material costs, they suffer from poor dispersibility and require chemical modification to achieve stable dispersion in water or other application environments. Furthermore, the preparation of high-quality graphene requires highly precise control conditions, and its complex preparation process also limits its application.

[0006] Organic polymer materials have been extensively studied due to their excellent photothermal conversion efficiency and biocompatibility. Typical organic polymers include polyaniline, polypyrrole, metal-organic frameworks (MOFs), covalent organic frameworks (COFs), polydopamine, and polymer molecules with donor-acceptor structures. Although the research on organic materials is quite mature and they have shown excellent performance in some scenarios, they still have shortcomings such as poor thermal stability and high synthesis difficulty (the preparation of COFs and MOFs is complex and the chemical reaction conditions are harsh), which prevent them from being used as materials for large-area applications.

[0007] For semiconductor materials, when irradiated with incident light of energy equal to or greater than the band gap, they absorb photons and generate active electron-hole pairs. Photoexcitation generates electrons in the conduction band and leaves electron vacancies or holes in the valence band. The subsequent relaxation from a higher excited state to a lower energy state can occur either through radiated photons or non-radiative phonon vibrations. Non-radiative relaxation releases heat as charge carriers distribute some of their energy to the lattice. Various narrow-bandgap semiconductors have been studied as photothermal materials, such as transition metal sulfides like CuS and Cu. 2x Se, WS2, TiO2 and Ti2O3 nanoparticles with oxygen vacancies, nanostructured MoO3, and magnetic microspheres Fe3O4. Fe3O4, as a narrow bandgap semiconductor, absorbs photons and generates electron-hole pairs when irradiated with light of energy equal to or greater than its bandgap, releasing heat through nonradiative relaxation. It is widely used in photothermal material research.

[0008] Fe3O4 is a popular new research material in photothermal conversion due to its low cost, wide absorption wavelength range, high energy content, and ease of functionalization. Furthermore, Fe3O4 nanoparticles possess both near-infrared absorption and magnetic properties. Therefore, magnetite is commonly used as the heating element in thermal management systems.

[0009] The rotation and vibration of chemical bonds in materials generate ubiquitous thermal radiation. This radiation, a technology that utilizes the thermal radiation balance between Earth and the cold universe, can be considered a new form of renewable energy as important as solar energy. It can directly radiate excess heat into outer space without additional energy consumption, thus having significant energy-saving and environmental protection implications.

[0010] Common cooling materials, such as refrigerants, often pose problems such as flammability, explosiveness, and pollution. Research on passive radiative cooling materials lays the foundation for large-scale applications in construction, industry, agriculture, and urban environmental management. Radiative cooling technology achieves significant cooling effects through various mechanisms and materials, including those based on random photonic structures and porous designs, such as metal oxides, semiconductors, and microporous glass coatings. Layered porous ceramics exhibit near-perfect reflectivity in the ultraviolet, visible, and near-infrared bands. For example, Kaixin Lin et al. proposed a honeycomb ceramic material that provides over 130 W / m² in outdoor environments. 2 Its cooling power demonstrates great energy-saving potential.

[0011] Research by Yao Zhai et al. indicates that daytime radiative cooling requires controlling the solar energy absorption rate of materials, as even a mere 10% solar energy absorption can significantly impact cooling efficiency. Therefore, polymer metamaterial thin films, which achieve daytime and nighttime cooling through high solar reflectivity and long-wave infrared emission, are a major research direction. Natural materials and biomimetic design provide inspiration for low solar absorptivity and high infrared emissivity, such as the hair structure of Sahara silver ants and delignified wood; innovative applications of polymers and aerogels further enhance the manufacturability and environmental adaptability of materials. BaSO4 has a reflectivity of over 95% in the solar radiation band, demonstrating high efficiency in radiative cooling. Yan et al. applied BaSO4 to cement-based materials, combining efficient daytime radiative cooling characteristics with building compatibility. Therefore, BaSO4 can be used as a cooling component in thermal management.

[0012] Fe3O4 and BaSO4 exhibit significant temperature-regulating effects under specific conditions, but their adaptability to complex weather conditions remains limited. Specifically, they cannot flexibly adjust temperature in response to environmental changes. Current methods using only Fe3O4 photothermal coatings for heating fail to provide cooling in summer, and the singular cooling function of BaSO4 at night in winter may exacerbate building heating loads. Therefore, a temperature-adaptive intelligent thermal management technology needs to be developed to cope with fluctuating environmental conditions. This technology should be able to switch between cooling and heating modes according to changes in the required temperature, thereby meeting current demands for efficient, intelligent, and energy-saving applications.

[0013] Currently, many types of intelligent windows have been developed, which can be divided into three categories based on the excitation source: electrochromic, photochromic, and thermochromic. Electrochromic materials, such as WO3 and NiO, are actively controlled by an electric field, exhibiting fast response speed, large modulation range, and good cycle stability, but their complex structure requires additional energy and manpower. Photochromic materials, such as metal oxides, Schiff bases, and spiropyran-based organic compounds, are passively driven by light, possessing simple structures, requiring no energy consumption, and can automatically adjust, but they cannot be user-controlled, have poor modulation capabilities, and slow color-changing speed. Thermochromic materials, such as VO2 and thermosensitive hydrogels, are temperature-driven, possessing simple structures, requiring no energy consumption, and can dynamically adapt to thermal changes. Therefore, thermochromic materials can be used as the intelligent control component in thermal management.

[0014] In existing technologies, photothermal absorption coatings mainly achieve efficient absorption of sunlight through graphene, multilayer metals, carbon nanotubes, or ceramic structures, and are only suitable for heating scenarios. Radiation cooling coatings rely on high-reflectivity ceramic particles to achieve strong visible light reflection and infrared radiation through the atmospheric window, and are only suitable for cooling scenarios. Even when photothermal and cooling layers are simply superimposed, their functions remain independent, unable to automatically switch from heating to cooling according to ambient temperature, and without incorporating high-temperature and low-temperature thermochromic materials for adaptive adjustment of the optical path. Furthermore, most existing materials are continuous coating structures, lacking designs that achieve in-plane thermal synergistic control through functional unitization and array arrangement. Therefore, existing technologies generally only meet single thermal management needs and are difficult to simultaneously achieve comprehensive temperature control capabilities for low-temperature heating, high-temperature cooling, and environmental adaptation.

[0015] Therefore, in order to meet the dual goals of high efficiency and energy saving and intelligent response to environmental changes, a new type of photofunctional mineral composite material and structural design is needed. Magnetite and barite are structurally optimized and modularized, and then covered with two different thermochromic materials with different properties: high-temperature color change (low-temperature transparent to high-temperature opaque) and low-temperature color change (high-temperature transparent to low-temperature opaque). The composite of magnetite (photothermal response), barite (radiative cooling), and thermochromic material (temperature-responsive photochromic layer), combined with a multi-structure modular design, can realize the adaptive temperature control function of the material to generate heat at low temperatures and dissipate heat at high temperatures. It is expected to be practically applied in green building, smart wearables and other fields, and can provide technical support for a low-carbon society. Summary of the Invention

[0016] Existing photothermal or radiative cooling materials are mostly single-function, capable of only heating or cooling. Even if the photothermal layer and radiative cooling layer are simply stacked or mixed, it is difficult to provide sufficient heating capacity in low-temperature environments and maintain effective cooling capacity in high-temperature environments. Furthermore, they cannot achieve spontaneous and reversible switching between heating and cooling modes according to the ambient temperature, resulting in limited temperature management range, low energy utilization efficiency, and insufficient environmental adaptability in practical applications.

[0017] The technical problem to be solved by the present invention is to provide a temperature-controlled composite structural material with photothermal absorption and radiation cooling functions and its preparation method. The material can achieve reversible adaptive switching of hot and cold modes according to the ambient temperature, thereby making efficient use of environmental energy and having good environmental adaptability.

[0018] To solve the above-mentioned technical problems, the present invention provides a temperature-controlled composite structural material with photothermal absorption and radiation cooling. The temperature-controlled composite structural material includes a first Fe3O4 photothermal unit composed of a high-temperature color-changing layer, a Fe3O4 photothermal layer and a base layer arranged in an array, and a first BaSO4 radiation cooling unit composed of a low-temperature color-changing layer, a BaSO4 radiation cooling layer and a base layer. The Fe3O4 is Fe3O4 with controlled particle size, and the BaSO4 is BaSO4 with surface modification. The Fe3O4 has a particle size of 10–100 nm, and the BaSO4 has a particle size of 0.2–2.5 μm. The arrangement array of the first Fe3O4 photothermal unit and the first BaSO4 radiation cooling unit is a geometric array arranged regularly or irregularly in a plane, including but not limited to regular hexagonal honeycomb array, square array, equilateral triangle array and regular hexagonal honeycomb-equilateral triangle combination array; The high-temperature color-changing layer is transparent / high light transmittance when the temperature T < T1, and opaque / low light transmittance when T ≥ T1; The low-temperature color-changing layer is opaque / low-transmittance when T < T2, and transparent / high-transmittance when T ≥ T2; The temperatures T1 and T2 are between 15 and 65°C, and the difference between T1 and T2 does not exceed 10°C. This invention provides another temperature-controlled composite structural material with photothermal absorption and radiative cooling. The temperature-controlled composite structural material includes an array of two units: a second Fe3O4 photothermal unit composed of a high-temperature color-changing layer and a Fe3O4 photothermal layer, and a second BaSO4 radiative cooling unit composed of a low-temperature color-changing layer and a BaSO4 radiative cooling layer. The Fe3O4 is Fe3O4 with controlled particle size, and the BaSO4 is BaSO4 with surface modification. The Fe3O4 has a particle size of 10–100 nm, and the BaSO4 has a particle size of 0.2–2.5 μm. The arrangement array of the second Fe3O4 photothermal unit and the second BaSO4 radiation cooling unit is a geometric array arranged regularly or irregularly in a plane, including but not limited to regular hexagonal honeycomb array, square array, equilateral triangle array and regular hexagonal honeycomb-equilateral triangle combination array; The high-temperature color-changing layer is transparent / high light transmittance when the temperature T < T1, and opaque / low light transmittance when T ≥ T1; The low-temperature color-changing layer is opaque / low-transmittance when T < T2, and transparent / high-transmittance when T ≥ T2; The temperatures T1 and T2 are between 15 and 65°C, and the difference between T1 and T2 does not exceed 10°C.

[0019] This invention also provides a method for preparing a temperature-controlled composite material with photothermal absorption and radiative cooling, comprising the following steps: By mass percentage, 10%–30% of high-temperature thermochromic microcapsules and 10%–30% of low-temperature thermochromic microcapsules were mixed with 40%–80% of matrix, 0.5%–3% of dispersant, and 0.1%–1% of ultraviolet absorber at 10–65°C for 10–60 min to obtain a high-temperature thermochromic mixture system and a low-temperature thermochromic mixture system. The high-temperature color-changing mixture system and the low-temperature color-changing mixture system were respectively coated on polyethylene terephthalate film or glass surface, and then dried at 50-80℃ for 10-30 min to obtain a high-temperature color-changing layer and a low-temperature color-changing layer with a thickness of 50-200 μm. Fe3O4 powder and BaSO4 powder were added to deionized water and dispersant respectively and stirred and dispersed. Then, a binder was added dropwise and ultrasonic water bath treatment was performed to form a colloidal dispersion. Ethanol and acid were added to the colloidal dispersion to obtain Fe3O4 suspension and BaSO4 suspension with pH value of 3 to 6. Fe3O4 suspension and BaSO4 suspension were sprayed onto the substrate surface multiple times with a thickness of 5-100 μm each time. After each spraying, the substrate was dried at 60-80℃ for 30-90 min to form a Fe3O4 photothermal layer and a BaSO4 radiation cooling layer with a thickness of 0.05-1.5 mm on the substrate surface. A first Fe3O4 photothermal composite material consisting of a high-temperature color-changing layer, a Fe3O4 photothermal layer, and a substrate layer is formed by bonding the high-temperature color-changing layer and the Fe3O4 photothermal layer together with an adhesive. A first BaSO4 radiation cooling composite material is formed by bonding a low-temperature color-changing layer and a BaSO4 radiation cooling layer on a substrate layer with an adhesive. The first Fe3O4 photothermal composite material and the first BaSO4 radiation cooling composite material are cut into predetermined shapes to obtain the first Fe3O4 photothermal unit and the first BaSO4 radiation cooling unit, respectively. The first Fe3O4 photothermal unit and the first BaSO4 radiation cooling unit are arranged in an array and bonded together to form a temperature-controlled composite material with photothermal absorption and radiation cooling. The high-temperature color-changing layer is transparent / high light transmittance when the temperature T < T1, and opaque / low light transmittance when T ≥ T1; The low-temperature color-changing layer is opaque / low-transmittance when T < T2, and transparent / high-transmittance when T ≥ T2; The temperatures T1 and T2 are between 15 and 65°C, and the difference between T1 and T2 does not exceed 10°C.

[0020] This invention also provides another method for preparing a temperature-controlled composite material with photothermal absorption and radiative cooling, comprising the following steps: The Fe3O4 suspension was sprayed onto the surface of the high-temperature color-changing layer multiple times with a thickness of 5-100 μm each time. After each spraying, the surface was dried at a constant temperature of 40-80°C for 5-90 min to form a Fe3O4 photothermal layer with a thickness of 0.05-1.5 mm on the high-temperature color-changing layer, thus obtaining a second Fe3O4 photothermal composite material with a high-temperature color-changing layer and a Fe3O4 photothermal layer structure. The BaSO4 suspension is sprayed onto the surface of the low-temperature color-changing layer multiple times with a thickness of 5-100 μm each time. After each spraying, it is dried at a constant temperature of 40-80℃ for 5-90 min to form a BaSO4 radiation cooling layer with a thickness of 0.05-1.5 mm on the low-temperature color-changing layer, thus obtaining a second BaSO4 radiation cooling composite structure material with a low-temperature color-changing layer and a BaSO4 radiation cooling layer. The second Fe3O4 photothermal composite material and the second BaSO4 radiation cooling composite material are cut into predetermined shapes to obtain the second Fe3O4 photothermal unit and the second BaSO4 radiation cooling unit, respectively. The second Fe3O4 photothermal unit and the second BaSO4 radiation cooling unit are arranged in an array and bonded together to form a temperature-controlled composite material with photothermal absorption and radiation cooling. The high-temperature color-changing layer is transparent / high light transmittance when the temperature T < T1, and opaque / low light transmittance when T ≥ T1; The low-temperature color-changing layer is opaque / low-transmittance when T < T2, and transparent / high-transmittance when T ≥ T2; The temperatures T1 and T2 are between 15 and 65°C, and the difference between T1 and T2 does not exceed 10°C.

[0021] Furthermore, the color-changing temperature of the high-temperature thermochromic microcapsules and the low-temperature thermochromic microcapsules is 15–65°C; the matrix is ​​an aqueous polyurethane dispersion or an acrylic emulsion; the dispersant includes at least one of sodium polyacrylate, polyethylene glycol, polycarboxylate, phosphate, polyethyleneimine, sodium silicate, citric acid, polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, and sodium hexametaphosphate; the ultraviolet absorber is at least one of benzotriazole compounds, triazine compounds, zinc oxide, and titanium dioxide.

[0022] Furthermore, the preparation of the Fe3O4 powder includes the following steps: 1) Prepare a mixed solution of ferrous salt and ferric salt by dissolving ferrous salt and ferric salt in distilled water at a molar ratio of 1:1 to 1:3; 2) Adjust the pH of the mixed solution of ferrous and ferric salts by adding alkali solution dropwise to obtain the reaction system, which is then adjusted to 8.5–10.5. 3) Heat the reaction system to 65-85℃ and react for 0.75-1.5h. After the reaction is completed, filter the mixture, wash the separated precipitate until it is neutral, and then dry it to obtain Fe3O4 powder with a particle size of 10-100nm and an anti-spinel structure on the (220), (311), and (400) crystal planes. The preparation of the BaSO4 powder further includes the following steps: 1) A mixed powder was obtained by adding 0.5-7 wt% of SiO2, Al2O3, ZrO2 and Y2O3 powders with a particle size of 10-200 nm to BaSO4 powder with an average particle size of 0.5 μm; 2) Add distilled water to the mixed powder and stir to disperse it to obtain a mixed slurry; 3) After evaporating and drying the mixed slurry at 60-100℃, it is subjected to solid-phase heat treatment at 400-1000℃ for 0.5-3 hours to obtain heat-treated material blocks; 4) Grind the heat-treated material blocks to obtain modified BaSO4 powder with a particle size of 0.2 to 2.5 μm.

[0023] Further, the adhesive is a polyvinyl alcohol solution with a mass concentration of 4-6 wt%, or polyacrylamide or hydroxypropyl methylcellulose; the base layer material is stainless steel sheet, copper foil, titanium foil, glass fiber reinforced plastic, cement, ceramic or other metal or non-metal substrates with certain mechanical strength and temperature resistance; the adhesive is selected from pressure-sensitive adhesives, polyurethane adhesives or other weather-resistant structural adhesives with temperature resistance of -20 to 80℃, bonding strength ≥0.5MPa and resistance to ultraviolet aging.

[0024] Furthermore, when the Fe3O4 photothermal unit and the BaSO4 radiation cooling unit array are arranged, the misalignment angle between adjacent units does not exceed 5°.

[0025] Furthermore, the Fe3O4 photothermal unit and the BaSO4 radiative cooling unit are bonded together with a heat-resistant polyurethane structural adhesive or thermally conductive silicone grease with a temperature resistance range of -30 to 100℃ and a shear strength ≥0.6MPa, and then cured under pressure at room temperature for 50 to 70 minutes.

[0026] This invention provides a temperature-controlled composite material with photothermal absorption and radiative cooling, and its preparation method. It innovatively arranges magnetite (Fe3O4), which has excellent broad-spectrum light absorption and high photothermal conversion efficiency, and barite (BaSO4), which has high reflectivity (over 95%) in the solar band and strong radiative heat dissipation performance in the mid-infrared band, together in an array. Combining this with the temperature-responsive adaptive adjustment characteristics of thermochromic materials, Fe3O4 and BaSO4 are respectively combined with high-temperature and low-temperature thermochromic materials to obtain a temperature-controlled composite material with dual photothermal absorption and radiative cooling properties. This achieves adaptive temperature switching of the material, solving the problems of significant energy waste and insufficient environmental adaptability in practical applications.

[0027] This invention provides a temperature-controlled composite structural material with photothermal absorption and radiative cooling, and its preparation method. The magnetite (Fe3O4) photothermal unit and barite (BaSO4) radiative cooling unit constituting the temperature-controlled composite structural material both employ a layered structure. Specifically, a high-temperature thermochromic material layer and a low-temperature thermochromic material layer are respectively bonded to the Fe3O4 photothermal material layer and the BaSO4 radiative cooling material layer, achieving dynamic thermal management of the temperature-controlled composite structural material. At low temperatures (≤threshold change temperature), the high-temperature thermochromic material (low-temperature transparent to high-temperature opaque) is translucent, allowing the Fe3O4 photothermal material layer to absorb sunlight and convert it into heat energy, increasing the system temperature. At high temperatures (≥threshold change temperature), the high-temperature thermochromic material becomes opaque, preventing light from entering the Fe3O4 photothermal material layer. Simultaneously, at high temperatures, the low-temperature thermochromic material (high-temperature transparent to low-temperature opaque) on the BaSO4 radiative cooling material layer is translucent, reflecting sunlight and enhancing long-wave infrared radiative cooling to lower the temperature. By utilizing the photothermal conversion of Fe3O4 photothermal material, the radiative cooling of BaSO4 radiative cooling material, and the light transmission regulation of thermochromic material, the composite structure material can intelligently adjust its light absorption and heat dissipation behavior according to the ambient temperature. This achieves multifunctional synergistic optimization of thermal management performance, reduces reliance on traditional heating and cooling equipment, and improves energy utilization efficiency.

[0028] This invention provides a temperature-controlled composite material with photothermal absorption and radiative cooling, and its preparation method. The magnetite (Fe3O4) photothermal material not only possesses a broad spectral absorption range (covering visible to near-infrared light), but also, due to its low cost, abundant reserves, excellent chemical stability, and convenient functionalization potential, is easy to mass-produce and apply in practice. Meanwhile, barite (BaSO4) radiative cooling material, due to its non-toxicity, high reflectivity, high thermal radiation capacity, and excellent compatibility with various substrates, can be widely used in various architectural coatings, textiles, and agricultural production films. Furthermore, the thermochromic material selected in this invention can achieve dynamic and intelligent environmental temperature response without external energy input, significantly improving the overall energy efficiency of the material system.

[0029] This invention provides a temperature-controlled composite structural material with photothermal absorption and radiative cooling, and its preparation method. Through the synergistic effect of Fe3O4 photothermal material, BaSO4 radiative cooling material, and thermochromic material, it not only overcomes the limitations of existing thermal management materials operating in a single mode, but also effectively solves the problems of excessive energy consumption and insufficient environmental adaptability. Furthermore, the temperature-controlled composite structural material with photothermal absorption and radiative cooling, and its preparation method, provided by this invention, have significant advantages such as simple process, low production cost, stable performance, and rapid response. It is suitable for a wide range of fields, including energy-saving exterior wall coatings for green buildings, thermal management fabrics for smart wearable devices, and temperature-controlled films for agricultural facilities. Its widespread application can provide important technical support and a foundation for reducing global energy consumption, promoting low-carbon development, and facilitating the achievement of energy conservation and emission reduction goals. Attached Figure Description

[0030] Figure 1 This is a cross-sectional view of a temperature-controlled composite structural material with photothermal absorption and radiation cooling provided in an embodiment of the present invention. A is a Fe3O4 photothermal unit, B is a BaSO4 radiation cooling unit, 1 and 6 are base layers, 2 is a magnetite photothermal layer, 3 is a high-temperature color-changing layer, 4 is a low-temperature color-changing layer, and 5 is a barite radiation cooling layer. Figure 2 This is a cross-sectional view of another temperature-controlled composite structural material with photothermal absorption and radiation cooling provided in an embodiment of the present invention. C is Fe3O4 photothermal unit, D is BaSO4 radiation cooling unit, 1 is high-temperature color-changing layer, 2 is magnetite photothermal layer, 3 is barite radiation cooling layer, and 4 is low-temperature color-changing layer. Figure 3 is an array arrangement diagram of Fe3O4 photothermal unit and BaSO4 radiation cooling unit of two temperature-controlled composite structural materials with photothermal absorption and radiation cooling provided in the embodiments of the present invention. Figure 4The XRD pattern of Fe3O4 obtained in the preparation method of a temperature-controlled composite material with photothermal absorption and radiation cooling provided in an embodiment of the present invention; Figure 5 Transmittance diagrams of high-temperature and low-temperature color-changing layers obtained in the preparation method of a temperature-controlled composite material with photothermal absorption and radiation cooling provided in an embodiment of the present invention at different temperatures when the threshold temperature is 30°C. Figure 6 Temperature test curve of the temperature-controlled composite material prepared in the preparation method of the temperature-controlled composite material with photothermal absorption and radiation cooling provided in Embodiment 1 of the present invention; Figure 7 The temperature test curve of the temperature-controlled composite material at low temperature obtained in the preparation method of the temperature-controlled composite material with photothermal absorption and radiation cooling provided in Embodiment 1 of the present invention. Figure 8 This is a schematic diagram showing the planar location distribution of the six thermal insulation foam boxes used in the numerical simulation models of Embodiment 1 and Comparative Examples 1–5 of the present invention, and their temperature distribution at 13:00 in the afternoon. Figure 9(a) is a simulated curve of the surface temperature of each box under summer conditions in Embodiment 1 and Comparative Examples 1–5 of the present invention. Figure 9(b) is a simulated curve of the surface temperature of each box in Autumn working conditions of Embodiment 1 and Comparative Examples 1–5 of the present invention as a function of time. Figure 9(c) is a simulated curve of the surface temperature of each box under winter conditions in Embodiment 1 and Comparative Examples 1–5 of the present invention. Figure 10(a) shows the surface temperature distribution of the GFRP substrate in Embodiment 2 of the present invention under solar irradiation conditions; Figure 10(b) shows the surface temperature distribution of the aluminum foil substrate of Comparative Example 6 of the present invention under solar irradiation conditions; Figure 10(c) shows the surface temperature distribution of the ceramic substrate of Comparative Example 7 of the present invention under solar irradiation conditions; Figure 10(d) shows the surface temperature distribution of the cement substrate of Comparative Example 8 of the present invention under solar irradiation conditions. Figure 11 The simulated curves of the surface temperature of each box under solar irradiation conditions for different substrates in Embodiment 2 and Comparative Examples 6–8 of the present invention are shown. Figure 12(a) shows the surface temperature distribution of the regular hexagonal honeycomb array in Embodiment 3 of the present invention under solar irradiation conditions; Figure 12(b) shows the surface temperature distribution of the square array of Comparative Example 9 of the present invention under solar irradiation conditions; Figure 12(c) shows the surface temperature distribution of the equilateral triangular array of Comparative Example 10 of the present invention under solar irradiation conditions; Figure 12(d) shows the surface temperature distribution of the hexagonal honeycomb-equilateral triangle combined array of Comparative Example 11 of the present invention under solar irradiation conditions; Figure 13 The above are simulated curves showing the change of surface temperature of each box under solar irradiation conditions in Embodiment 3 and Comparative Examples 9–11 of the present invention. Detailed Implementation

[0031] See Figure 1 This invention provides a temperature-controlled composite structural material with photothermal absorption and radiative cooling, comprising an array of Fe3O4 photothermal units A and BaSO4 radiative cooling units B. The Fe3O4 photothermal unit A is composed of a substrate layer 1, a magnetite photothermal layer 2, and a high-temperature color-changing layer 3 bonded together. The BaSO4 radiative cooling unit B is composed of a low-temperature color-changing layer 4, a BaSO4 radiative cooling layer 5, and a substrate layer 6 bonded together.

[0032] Among them, the Fe3O4 in the Fe3O4 photothermal unit A is Fe3O4 with controlled particle size, and the BaSO4 in the BaSO4 radiation cooling unit B is BaSO4 prepared by surface modification.

[0033] The particle size of Fe3O4 is 10–100 nm, and the particle size of BaSO4 is 0.2–2.5 μm.

[0034] Among them, the high-temperature color-changing layer 3 is transparent / high light transmittance when the temperature T < T1, and opaque / low light transmittance when T ≥ T1; The low-temperature color-changing layer 4 is opaque / low-transmittance when T < T2, and transparent / high-transmittance when T ≥ T2; Among them, T1 and T2 are between 15 and 65°C, and the difference between T1 and T2 does not exceed 10°C.

[0035] The Fe3O4 photothermal unit A and the BaSO4 radiative cooling unit B can be arranged in various geometric arrays in a plane. Preferred arrangements include the regular hexagonal honeycomb array shown in Figure 3(a), the square array shown in Figure 3(b), the equilateral triangle array shown in Figure 3(c), and the combined hexagonal honeycomb-equilateral triangle array shown in Figure 3(d). See also Figure 2As another specific embodiment of the present invention, the temperature-controlled composite structural material with photothermal absorption and radiative cooling provided in this embodiment is also composed of Fe3O4 photothermal units C and BaSO4 radiative cooling units D arranged together in an array. However, the structure of the Fe3O4 photothermal unit C and BaSO4 radiative cooling unit D in this embodiment differs from the structure of the Fe3O4 photothermal unit A and BaSO4 radiative cooling unit B described above. In this embodiment, the Fe3O4 photothermal unit C is formed by directly bonding a high-temperature color-changing layer 1 and a Fe3O4 photothermal layer 2 together, and the BaSO4 radiative cooling unit D is formed by directly bonding a low-temperature color-changing layer 4 and a BaSO4 radiative cooling layer 3 together.

[0036] Among them, the Fe3O4 in the Fe3O4 photothermal unit C is Fe3O4 obtained by particle size control, and the BaSO4 in the BaSO4 radiation cooling unit D is BaSO4 prepared by surface modification.

[0037] The particle size of Fe3O4 is 10–100 nm, and the particle size of BaSO4 is 0.2–2.5 μm.

[0038] Among them, the high-temperature color-changing layer 1 is transparent / high light transmittance when the temperature T < T1, and opaque / low light transmittance when T ≥ T1; The low-temperature color-changing layer 4 is opaque / low-transmittance when T < T2, and transparent / high-transmittance when T ≥ T2; Among them, T1 and T2 are between 15 and 65°C, and the difference between T1 and T2 does not exceed 10°C.

[0039] The Fe3O4 photothermal unit C and BaSO4 radiation cooling unit D in this embodiment of the invention can be arranged in a variety of geometric arrays in the plane. Preferred arrangement forms include the regular hexagonal honeycomb array shown in Figure 3(a), the square array shown in Figure 3(b), the equilateral triangle array shown in Figure 3(c), and the regular hexagonal honeycomb-equilateral triangle combined array shown in Figure 3(d).

[0040] Since the size of a photothermal material largely determines its light absorption characteristics and photothermal conversion efficiency, the specific surface area of ​​the Fe3O4 photothermal material provided in this invention increases significantly with decreasing particle size, as well as the surface active sites and defect states (such as oxygen vacancies, Fe²⁺, Fe³⁺ ... + / Fe³ +The increasing unevenness in the proportion of Fe3O4 particles can broaden its light absorption range to some extent, especially exhibiting enhanced optical absorption in the visible to near-infrared region. Furthermore, the nano-sizing process of Fe3O4 can introduce localized surface plasmon-like behavior, further improving its light response. Studies have shown that when the Fe3O4 particle size is controlled between 10 and 100 nm, it can significantly improve the thermal conversion rate per unit mass of material while maintaining strong light absorption. This not only gives Fe3O4 good dispersibility and stability, but also its low thermal conductivity contributes to local heat accumulation, thereby improving photothermal efficiency or solar thermal utilization efficiency. However, when the Fe3O4 particle size decreases to below 10 nm, its light absorption capacity decreases, which may be related to its reduced carrier concentration and enhanced surface heat dissipation.

[0041] Therefore, in the temperature-controlled composite structural materials with photothermal absorption and radiation cooling provided by the present invention, the particle size of the Fe3O4 obtained is controlled to be 10-100 nm by adjusting the synthesis conditions during the preparation of Fe3O4.

[0042] Specifically, the preparation process of Fe3O4 in the Fe3O4 photothermal unit of the two temperature-controlled composite structural materials with photothermal absorption and radiative cooling provided by the present invention includes the following steps: (1) Raw material ratio and dissolution: Weigh one or more of ferrous sulfate (FeSO4), ferrous chloride (FeCl2), and ferrous nitrate (Fe(NO3)2), and dissolve them in distilled water with one or more of ferric sulfate (Fe2(SO4)3), ferric chloride (FeCl3), and ferric nitrate (Fe(NO3)3) in a molar ratio of 1:1 to 1:3 to prepare a uniform and transparent iron salt mixed solution.

[0043] (2) Alkalinity adjustment: Under continuous stirring, add 2.5-5.0 mol / L sodium hydroxide (NaOH), ammonia, or other alkaline solutions dropwise to the above iron salt mixture to adjust the pH of the system to 8.5-10.5. During the adjustment process, it is necessary to keep the stirring uniform and monitor the pH change in real time, and accurately control the dropping rate of NaOH to optimize the precipitate particle size and crystal quality.

[0044] (3) Control of reaction conditions: The reaction system is heated to 65-85℃ and maintained for 0.75-1.5h to promote the formation and uniformity of Fe3O4 crystals. The precipitation rate is controlled by adjusting the dropping rate of NaOH or ammonia (controlled within the range of 6-300 mL / min), thereby affecting the microstructure and crystallization properties of the final product.

[0045] (4) Separation and washing: After the reaction is completed, the precipitate is separated by filtration and washed repeatedly with distilled water until the pH of the washing solution is close to neutral in order to remove residual ionic impurities.

[0046] (5) Drying treatment: Place the washed wet Fe3O4 sample in a forced-air drying oven at 40-100℃ and dry for 1-4 hours to obtain dried Fe3O4 powder.

[0047] See Figure 4 The obtained Fe3O4 was subjected to phase analysis by X-ray diffraction (XRD) and compared with the standard card (JCPDS No. 97-063-3020). The results showed that the obtained Fe3O4 exhibited a typical inverse spinel structure on the (220), (311), and (400) crystal planes, indicating that the product has high purity and good crystallinity. Further calculation of the diffraction peaks using the Scherrer formula estimated the average grain size of the obtained magnetite powder to be 47–85 nm, with a narrow grain size distribution, indicating that the obtained Fe3O4 has good dispersibility and a moderate to uniform degree of crystallinity.

[0048] Because BaSO4 has a band gap (Eg) exceeding 5.7–6 eV, it absorbs almost no solar radiation (approximately 98%), resulting in a low absorption coefficient αs of only 0.06–0.07. However, to reduce the absorption coefficient αs, its reflectivity (ρ) can be increased outside the main absorption boundary of the solar spectrum or in longer wavelength regions. The reflectivity ρ of BaSO4 is affected by the particle size; the more suitable the particle size, the better the scattering and reflection of sunlight. Scattering efficiency is highly dependent on the relationship between particle size and the wavelength of incident light: for visible light (wavelength approximately 400–700 nm), when the particle size of BaSO4 is close to or slightly larger than the wavelength, the scattering efficiency is high (i.e., Mie scattering is dominant). Excessively large particle sizes (such as agglomerated particles of 10–20 μm) cause photons to penetrate deep into the particle interior, resulting in energy loss after multiple reflections and absorptions, thus reducing surface reflectivity. While small particle sizes (<100 nm) offer high specific surface area, the scattering ability of individual particles is weak, resulting in a decrease in overall reflectivity. To achieve high reflectivity ρ over a wider spectral range (e.g., 0.2–2.5 μm in the solar spectrum), the particle size of BaSO4 should be controlled between 0.2 and 2.5 μm. Simultaneously, impurities in the powder also affect reflectivity because they introduce absorption phenomena at different wavelengths, thus impacting the overall optical properties of the material. Therefore, the powder needs to possess high purity and a particle size distribution matching the spectral range.

[0049] However, it is currently difficult to find suitable BaSO4 products with particle sizes concentrated between 0.2 and 2.5 μm on the market. Therefore, in the temperature-controlled composite structural materials with photothermal absorption and radiative cooling provided by the present invention, the particle size of the obtained BaSO4 is controlled to be 0.2–2.5 μm through surface modification during the preparation of BaSO4.

[0050] Specifically, the preparation process of BaSO4 in the BaSO4 radiation cooling unit of the two temperature-controlled composite structural materials with photothermal absorption and radiation cooling provided by the present invention includes the following steps: 1) Take BaSO4 powder with an average particle size of 0.5 µm, add 0.5 to 7 wt% of SiO2, Al2O3, ZrO2, Y2O3 and other nanoparticles with an average particle size of 10 to 200 nm to obtain a mixed powder.

[0051] 2) Add an appropriate amount of distilled water to the mixed powder and disperse it fully in a magnetic stirrer to obtain a mixed slurry.

[0052] 3) After the mixed slurry is evaporated and dried at 60-100℃, it is subjected to solid-phase heat treatment in a muffle furnace at 400-1000℃ for 0.5-3h, taking into account both structural stability and particle size adjustment, without causing crystal transformation. After heat treatment, heat-treated blocks are obtained.

[0053] 4) The heat-treated material blocks are ground to obtain modified BaSO4 powder with a particle size in the range of 0.2 to 2.5 μm.

[0054] The particle size distribution of BaSO4 changed from being predominantly 0.5 μm to concentrated in the range of 0.2–2.5 μm. This is mainly due to the dual effects of nanoparticle processing: firstly, nanoparticles can uniformly coat the surface of BaSO4 microparticles or embed themselves between particles, forming new small aggregates and increasing the apparent size of individual particles; secondly, they cause the original larger aggregates (10–20 μm) to disintegrate into multiple smaller particles, while also acting as "fillers" and "cementing" between particles, stabilizing the newly formed structure. This series of processes leads to the overall particle size distribution converging towards the median size, ultimately forming a distribution range predominantly 0.2–2.5 μm, effectively enhancing the powder's multi-scale scattering ability of sunlight and improving reflectivity.

[0055] Furthermore, the introduction of SiO2, Al2O3, ZrO2, and Y2O3 nanoparticles into BaSO4 not only regulates the particle size distribution of BaSO4 but also significantly enhances the material's thermal emissivity in the mid-infrared band (especially within the 8–13 μm atmospheric window). These oxides themselves possess strong infrared emission capabilities, and their phonon resonance characteristics enable them to efficiently release thermal radiation energy in this band, thus endowing the material with excellent radiative cooling performance. Among them, SiO2 and Al2O3 exhibit good spectral emission characteristics and chemical stability, while ZrO2 and Y2O3, due to their high refractive index, enhance the multiple scattering effect, further improving the overall emission efficiency. The multi-scale structure formed by the nanoparticles on or between the BaSO4 particles not only contributes to enhanced solar reflection but also optimizes the infrared thermal radiation path, resulting in a composite powder with both high reflectivity and high emissivity, exhibiting spectral selectivity, making it particularly suitable for passive radiative cooling applications.

[0056] This invention also provides a method for preparing a temperature-controlled composite material with photothermal absorption and radiative cooling, comprising the following steps: The Fe3O4 and BaSO4 prepared by this invention have significant temperature regulation effects under specific conditions, but their adaptability in complex environments is poor and it is difficult to achieve bidirectional temperature control. This invention optimizes the dispersion and surface modification process of thermochromic microcapsules and combines them with an aqueous polymer matrix system to prepare thermochromic film materials with good dispersibility, UV resistance and temperature response sensitivity.

[0057] (a) Preparation of high-temperature color-changing layer 3 and low-temperature color-changing layer 4 (1) Preparation of thermochromic capsule composite matrix: The thermochromic microcapsules used in this invention are existing, commercially available, and mature products, all with a color-changing temperature range of 15–65 °C. To better adapt the thermochromic microcapsules to their application fields, they are first modified through dispersion and surface coating.

[0058] By weight percentage, 10%–30% of high-temperature thermochromic microcapsules and 10%–30% of low-temperature thermochromic microcapsules were added to 40%–80% of the matrix to obtain a high-temperature thermochromic microcapsule mixture system and a low-temperature thermochromic microcapsule mixture system, respectively.

[0059] The matrix is ​​an aqueous polyurethane dispersion or an acrylic emulsion.

[0060] (2) Add dispersant and ultraviolet absorber: To improve the stability of capsule dispersion, 0.5%–3% dispersant was added to each of the two aforementioned mixing systems. Then, 0.1%–1% ultraviolet absorber was added to enhance the lightfastness of the film after subsequent film formation, thereby effectively improving the material's UV resistance. This resulted in a high-temperature color-changing mixing system and a low-temperature color-changing mixing system.

[0061] The dispersant includes at least one of sodium polyacrylate, polyethylene glycol, polycarboxylate, phosphate, polyethyleneimine, sodium silicate, citric acid, polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, and sodium hexametaphosphate; the ultraviolet absorber is at least one of benzotriazole compounds, triazine compounds, zinc oxide, and titanium dioxide.

[0062] (3) The membrane fabrication process enables the construction of functional membrane layers: The obtained high-temperature and low-temperature color-changing mixtures were stirred within a temperature range of 10–65°C for 10–60 minutes to ensure thorough and uniform mixing of all components. After stirring, the mixtures were degassed to remove air bubbles and prevent pores or defects from forming during film formation.

[0063] Subsequently, the treated high-temperature color-changing mixture and low-temperature color-changing mixture were uniformly coated onto the pre-cleaned polyethylene terephthalate (PET) film or glass substrate using a blade coating method. The coating thickness was controlled between 50 and 200 μm to ensure the density and uniformity of the film layer. After coating, the substrates coated with the high-temperature color-changing mixture and the substrates coated with the low-temperature color-changing mixture were dried at a constant temperature of 50–80 °C for 10–30 min to allow the solvent in the film layer to fully evaporate, forming a continuous and uniform thermochromic film layer. This yielded a high-temperature color-changing layer 3 and a low-temperature color-changing layer 4 with thicknesses of 50–200 μm, respectively.

[0064] Among them, the high-temperature color-changing layer 3 is transparent / high light transmittance when the temperature T < T1, and opaque / low light transmittance when T ≥ T1; The low-temperature color-changing layer 4 is opaque / low-transmittance when T < T2, and transparent / high-transmittance when T ≥ T2; Wherein, T1 and T2 are between 15 and 65 ℃, and the difference between T1 and T2 does not exceed 10 ℃.

[0065] The light transmittance properties of the prepared high-temperature color-changing layer 3 and low-temperature color-changing layer 4 at different temperatures are as follows: Figure 5 As shown. Figure 5 The transmittance curves of the material are shown within the wavelength range of 400–1400 nm, at temperatures below and above the critical temperature (30 °C in this example). Figure 5As can be seen, the transmittance gradually increases with increasing wavelength. Below the critical temperature (dashed line), the overall transmittance of the material is low, with a maximum transmittance of less than 35%; while above the critical temperature (solid line), the transmittance of the material increases significantly, reaching over 60% in the near-infrared region.

[0066] and, Figure 5 The photographs of the samples shown further verify the changes in the optical properties of the aforementioned materials: at low temperatures, the film appears dark and opaque; while at high temperatures, it transforms into a light color and exhibits good transparency, demonstrating a significant thermochromic effect.

[0067] (II) Preparation of Fe3O4 photothermal layer 2 and BaSO4 radiation cooling layer 5 (1) Pretreatment of basal layers 1 and 6: The base layers 1 and 6 are made of stainless steel sheets, copper foil, titanium foil, glass fiber reinforced plastic, cement, ceramics, or other metal or non-metal substrates with certain mechanical strength and temperature resistance.

[0068] In one specific embodiment of the present invention, aluminum foil with a thickness of 50 to 150 μm is preferably used as substrate layer 1 and 6.

[0069] First, the aluminum foil is ultrasonically cleaned in deionized water for 8–12 minutes to remove surface oil and some oxide layer. It is then rinsed with anhydrous ethanol and ultrasonically treated for another 4–6 minutes. After completion, it is allowed to air dry in a clean environment. To further enhance the adhesion between the coating and the substrate, the surface of the aluminum foil is lightly sanded with 500–1200 grit sandpaper.

[0070] (2) Preparation of spraying liquid: Weigh 15–25 g of pre-prepared Fe3O4 powder with a particle size of 10–100 nm and 15–25 g of pre-prepared modified BaSO4 powder with a particle size of 0.2–2.5 μm, respectively, and add them to 40–45 mL of deionized water. Simultaneously, add 0.1–2.0 g of dispersant and stir continuously under magnetic stirring for 25–35 min to promote thorough dispersion of the powders. Then, slowly add 8–12 mL of binder. Place the mixture in an ultrasonic water bath for 25–35 min to form a homogeneous colloidal dispersion. To adjust its rheological properties, add 8–12 mL of ethanol to control the viscosity to the range of 80–550 mPa·s. Finally, adjust the pH of the mixture to 3–6 using 0.01–1 mol / L acetic acid or hydrochloric acid solution to obtain stable Fe3O4 and BaSO4 suspensions, respectively.

[0071] The dispersant includes at least one of sodium polyacrylate, polyethylene glycol, polycarboxylate, phosphate, polyethyleneimine, sodium silicate, citric acid, polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, and sodium hexametaphosphate; the ultraviolet absorber is at least one of benzotriazole compounds, triazine compounds, zinc oxide, and titanium dioxide.

[0072] The adhesive is a polyvinyl alcohol solution with a mass concentration of 4-6 wt%, or polyacrylamide or hydroxypropyl methylcellulose.

[0073] (3) Spraying process: The Fe3O4 and BaSO4 suspensions prepared above were loaded into spray guns with nozzle diameters set to 0.4–1.2 mm. Atomization spraying under constant air pressure control was used, but methods such as ultrasonic atomization and high-pressure micro-spraying can be substituted. The suspensions were uniformly sprayed onto the surfaces of pretreated aluminum foil substrates 1 and 6, with a coating thickness of approximately 5–100 μm. After each spraying, the substrates were dried at a constant temperature of 60–80 °C for 30–90 min to obtain a dense, uniform, crack-free coating. A layered construction strategy of alternating multiple sprayings and intermediate low-temperature drying was adopted to prevent internal stress cracks caused by thickness accumulation. Finally, a Fe3O4 photothermal layer 2 and a BaSO4 radiative cooling layer 5 with a thickness of 0.05–1.5 mm were formed on the surfaces of substrates 1 and 6, respectively.

[0074] (iii) The Fe3O4 photothermal layer 2 is combined with the high-temperature color-changing layer 3, and the BaSO4 radiation cooling layer 5 is combined with the low-temperature color-changing layer 4. The high-temperature color-changing layer 3 and the Fe3O4 photothermal layer 2 on the substrate layer 1 are bonded together with an adhesive, and a pressure of 0.1 to 0.3 MPa is applied and maintained for 30 to 60 seconds to ensure full adhesion, thereby forming a Fe3O4 photothermal composite structure material composed of the high-temperature color-changing layer 3, the Fe3O4 photothermal layer 2 and the substrate layer 1.

[0075] Similarly, the low-temperature color-changing layer 4 and the BaSO4 radiation cooling layer 5 on the substrate layer 6 are bonded together with an adhesive, and a pressure of 0.1 to 0.3 MPa is applied and maintained for 30 to 60 seconds to ensure full adhesion, thus forming a BaSO4 radiation cooling composite structure material consisting of the low-temperature color-changing layer 4, the BaSO4 radiation cooling layer 5, and the substrate layer 6.

[0076] The adhesive used is a pressure-sensitive adhesive, polyurethane adhesive, or other weather-resistant structural adhesive with a temperature resistance of -20 to 80℃, a bonding strength of ≥0.5MPa, and resistance to ultraviolet aging.

[0077] (iv) The Fe3O4 photothermal composite material and the BaSO4 radiation cooling composite material are cut into predetermined shapes to obtain Fe3O4 photothermal unit A and BaSO4 radiation cooling unit B, respectively, as follows: Figure 1 As shown.

[0078] (V) Array layout design of Fe3O4 photothermal unit A and BaSO4 radiation cooling unit B Fe3O4 photothermal unit A and BaSO4 radiation cooling unit B are arranged in an array and bonded together to form a temperature-controlled composite material with photothermal absorption and radiation cooling.

[0079] As another specific embodiment of the present invention, the present invention provides a method for preparing a temperature-controlled composite material with photothermal absorption and radiative cooling, comprising the following steps: The prepared Fe3O4 suspension was directly sprayed onto the surface of the high-temperature color-changing layer 1 in multiple applications with a thickness of 5–100 μm each time. After each spraying, the layer was dried at a constant temperature of 40–80℃ for 5–90 min, forming a Fe3O4 photothermal layer 2 with a thickness of 0.05–1.5 mm on the high-temperature color-changing layer 1, thus obtaining a Fe3O4 photothermal composite material with the structure of high-temperature color-changing layer 1 and Fe3O4 photothermal layer 2.

[0080] The prepared BaSO4 suspension was directly sprayed onto the surface of the low-temperature color-changing layer 4 in multiple applications with a thickness of 5–100 μm each time. After each application, the layer was dried at a constant temperature of 40–80 °C for 5–90 min, forming a BaSO4 radiation cooling layer 3 with a thickness of 0.05–1.5 mm on the low-temperature color-changing layer 4, thus obtaining a BaSO4 radiation cooling composite material with the structure of low-temperature color-changing layer 4 and BaSO4 radiation cooling layer 3.

[0081] Fe3O4 photothermal composite material and BaSO4 radiation-cooled composite material were cut into predetermined shapes to obtain Fe3O4 photothermal unit C and BaSO4 radiation-cooled unit D, respectively. Figure 2 As shown.

[0082] Fe3O4 photothermal unit C and BaSO4 radiation cooling unit D are arranged in an array and bonded together to form a temperature-controlled composite material with photothermal absorption and radiation cooling.

[0083] In this invention, when the Fe3O4 photothermal units A and C and the BaSO4 radiative cooling units B and D are arranged in an array, the misalignment angle between adjacent units does not exceed 5°, providing uniformity while ensuring array isotropy and overall heat flux continuity.

[0084] Meanwhile, during the fixing process, the two temperature-controlled composite structural materials of the present invention are bonded together by heat-resistant polyurethane structural adhesive or thermally conductive silicone grease with a temperature resistance range of -30 to 100℃ and a shear strength ≥0.6 MPa, and then cured under pressure at room temperature for 50 to 70 minutes. The resulting temperature-controlled composite structural material has good consistency in the direction of thermal diffusion, which helps to suppress thermal stress concentration and improve the response speed of the heat-cold conversion zone.

[0085] In this invention, the Fe3O4 photothermal units A and C and the BaSO4 radiative cooling units B and D in the two temperature-controlled composite structural materials are arranged in a geometric array that is regular or irregular in a plane. Specific forms include, but are not limited to, regular hexagonal honeycomb arrays, square arrays, equilateral triangle arrays, and combinations of regular hexagonal honeycomb and equilateral triangle arrays. Specifically, referring to Figure 3(a), the Fe3O4 photothermal units and BaSO4 radiative cooling units can be arranged in a regular hexagonal honeycomb array: each unit is tightly arranged in a honeycomb pattern, exhibiting high isotropy, suitable for enhancing multidirectional heat diffusion and heat flow uniformity. The alternating pattern arrangement of the Fe3O4 photothermal units and BaSO4 radiative cooling units can quickly establish a local thermal gradient, reducing the risk of thermal stress concentration.

[0086] Referring to Figure 3(b), the Fe3O4 photothermal unit and BaSO4 radiative cooling unit can also be arranged in a square array: the functional units are arranged in a right-angled grid, resulting in a regular structure that is easy to manufacture modularly. This structure also has good space-filling and heat flow control performance, making it suitable for large-area deployment scenarios.

[0087] Referring to Figure 3(c), the Fe3O4 photothermal unit and the BaSO4 radiative cooling unit can also be arranged in an equilateral triangle array: using equilateral triangles as the basic unit for assembly facilitates the construction of a high-density thermal control network. Its high boundary density helps to achieve fine-grained temperature control zoning, making it suitable for areas with high local temperature gradient requirements.

[0088] Referring to Figure 3(d), the Fe3O4 photothermal unit and BaSO4 radiative cooling unit can also be arranged in a combination of a hexagonal honeycomb array and an equilateral triangle array: the coupling arrangement of the hexagonal honeycomb unit and the equilateral triangle unit combines the heat diffusion capability of the hexagonal honeycomb structure with the heat channel guiding capability of the equilateral triangle structure, enabling flexible control of complex heat flow. This combined structure improves the coupling efficiency between the heat and cold modules, which helps to achieve rapid response and energy balance in non-uniform heat source environments.

[0089] This invention provides a temperature-controlled composite material with photothermal absorption and radiative cooling, and its preparation method. It innovatively arranges magnetite (Fe3O4), which has excellent broad-spectrum light absorption and high photothermal conversion efficiency, and barite (BaSO4), which has high reflectivity (over 95%) in the solar band and strong radiative heat dissipation performance in the mid-infrared band, together in an array. Combining this with the temperature-responsive adaptive adjustment characteristics of thermochromic materials, Fe3O4 and BaSO4 are respectively combined with high-temperature and low-temperature thermochromic materials to obtain a temperature-controlled composite material with dual photothermal absorption and radiative cooling properties. This achieves adaptive temperature switching of the material, solving the problems of significant energy waste and insufficient environmental adaptability in practical applications.

[0090] The following examples illustrate a temperature-controlled composite structural material with photothermal absorption and radiative cooling provided by the present invention, and its preparation method.

[0091] Example 1 27.8 g of ferrous sulfate heptahydrate (FeSO4·7H2O) and 54.1 g of ferric chloride hexahydrate (FeCl3·6H2O) were weighed and dissolved in 1000 mL of distilled water. The solution was magnetically stirred (400 rpm) for 10 min until a clear orange-yellow solution was formed. While stirring continuously, 2.5 mol / L NaOH solution was added at a rate of 10 mL / min via a burette, with pH monitored in real time. The addition was stopped when the pH stabilized at 9.0 ± 0.2, and the entire addition process lasted approximately 30 min. The reaction system containing the precipitate was then heated to 75 °C and maintained at this temperature for 1 h to promote the formation of Fe3O4 crystals. After the reaction, the solution was allowed to cool naturally to room temperature. The precipitate was separated by vacuum filtration and washed five times with 100 mL of distilled water each time until the pH of the washings was close to neutral. Finally, the obtained precipitate was transferred to a desiccator and dried in an 80 °C oven for 2 h to obtain approximately 11 g of black Fe3O4 powder.

[0092] 100 g of BaSO4 powder with an average particle size of 0.5 μm was weighed, and 1 g of nano-SiO2 with an average particle size of approximately 50 nm (mass fraction 1 wt%) was added. 35 mL of distilled water was added to the mixture, and the mixture was stirred at 600 rpm for 20 min on a magnetic stirrer to obtain a homogeneous slurry. The slurry was dried in a 90 ℃ electric heating oven for 10 h, and then placed in a muffle furnace for heat treatment at 600 ℃ for 2 h at a heating rate of 10 ℃ / min. The mixture was then cooled to room temperature. The heat-treated solid material was ball-milled using zirconia balls for 90 min at a ball-to-material ratio of 1:8 to obtain modified BaSO4 powder with a D50 particle size of 1.4 μm and a particle size distribution concentrated between 0.2 and 2.2 μm. This powder exhibits excellent visible light reflectivity and good mid-infrared emission properties, making it suitable for integrated light reflection and thermal control coatings.

[0093] Two types of thermochromic microcapsules (color-changing temperatures 27 ℃ and 27 ℃) were weighed out and slowly added to 60 g of aqueous polyurethane dispersion, respectively. The mixture was stirred for 20 min at room temperature using a high-speed disperser (1000 rpm) to achieve initial dispersion. Then, 2.0 g of polyvinylpyrrolidone (PVP) was added as a dispersant, and 0.5 g of benzotriazole UV absorber [2-(2-hydroxy-5-tert-butylphenyl)benzotriazole] was added, and stirring continued for 20 min to ensure the additives were fully dissolved and uniformly mixed with the microcapsules. The total mass of the mixture was controlled to be approximately 100 g, with the thermochromic microcapsules accounting for 20%, the matrix for 60%, and the additives for approximately 2.5%. After stirring, the mixture was allowed to stand for 10 min to remove air bubbles. The degassed mixture was then uniformly coated onto the surface of a PET film pre-cleaned and dried with anhydrous ethanol using a scraping method, controlling the wet film thickness to 150 μm. After coating, the film material was placed in a 60 ℃ constant temperature oven for 20 min to dry. After the film surface was no longer sticky and the appearance was uniform and continuous, it was taken out to obtain a high temperature color-changing layer and a low temperature color-changing layer with dense structure, good adhesion, and thermosensitive color-changing and UV resistance properties.

[0094] Aluminum foil with a thickness of 100 μm was selected as the substrate material. First, it was placed in deionized water and ultrasonically cleaned for 10 min to remove surface oil and oxide layers. Then, it was rinsed with anhydrous ethanol and ultrasonically treated for another 5 min to thoroughly clean the surface. After removal, it was allowed to air dry in a clean environment. After drying, the surface of the aluminum foil was lightly sanded with 800-grit sandpaper to enhance surface roughness and improve coating adhesion. Next, 20 g of magnetite (Fe3O4) powder and 20 g of modified barite (BaSO4) powder were weighed and added to 45 mL of deionized water, along with 1.0 g of polyvinylpyrrolidone (PVP) as a dispersant. The mixture was stirred continuously in a magnetic stirrer for 30 min to form a uniform dispersion. Then, 10 mL of a 5 wt% polyvinyl alcohol (PVA) solution was slowly added dropwise, and stirring was continued for 10 min. Finally, the mixture was treated in an ultrasonic water bath for 30 min to obtain a stable colloidal dispersion. Next, 10 mL of ethanol was added to adjust the system viscosity to approximately 350 mPa·s, and the pH was adjusted to 4.5 using 0.1 mol / L acetic acid solution to form a uniform suspension suitable for spraying. The above spraying solution was loaded into a spray gun with a nozzle diameter of 0.8 mm, and uniformly atomized and sprayed onto the pretreated aluminum foil substrate surface at a pressure of 0.25 MPa. After each spraying, the substrate was dried at 70 °C for 60 min. This process of spraying and intermediate drying was repeated three times, ultimately forming a dense and uniform coating with a total thickness of 0.15 mm. The prepared magnetite photothermal film was then cut into rectangular sheets matching the dimensions of the high-temperature color-changing layer. Polyurethane structural adhesive was used as the bonding agent, and the sheets were bonded to a pre-made high-temperature color-changing film at room temperature. After alignment and bonding, a pressure of 0.2 MPa was applied and held for 40 seconds, completing the construction of the three-layer composite structure of the high-temperature color-changing layer, magnetite layer, and aluminum substrate. Using the same method, after bonding the barite coating to the low-temperature color-changing film, a three-layer composite temperature control structure with excellent radiative cooling effect can be formed: low-temperature color-changing layer—barium sulfate layer—aluminum foil base layer.

[0095] The prepared magnetite and barite three-layer composite temperature control structure functional units were cut into square structures with a side length of 30mm, and their edges were trimmed to ensure that the dimensional accuracy of the splicing boundary was within ±0.2mm. The square pieces were arranged sequentially according to the XY rectangular coordinate grid, with magnetite / barite alternately arranged in each row. They were bonded using a heat-resistant polyurethane structural adhesive by dotting and pressing, as shown in Figure 3(b). The constructed square array exhibited excellent modular layout and heat flow uniformity in large-area thermal control applications.

[0096] The following are temperature tests conducted on the temperature-controlled composite material with photothermal absorption and radiative cooling prepared in Example 1 of this invention, and the resulting temperature test curves are shown below. Figure 6As shown, this invention constructs a three-layer composite temperature-controlled structure material of magnetite / barite-thermochromic aluminum foil, which exhibits excellent temperature regulation capabilities in thermal response testing. It can effectively reduce surface temperature in high-temperature environments, demonstrating good radiative cooling performance; while in low-temperature environments, it can rapidly heat up and maintain temperature, showcasing adaptive control functionality. The modular unit array arrangement helps improve the thermal field uniformity of large-area structures, and the thermochromic layer enables visualization of temperature changes, demonstrating significant engineering application value.

[0097] Figure 6 The graph shows the measured temperature curves of the samples under natural light conditions. The blue curve represents the adaptive structure with thermochromic material attached to the surface, while the green curve represents the composite structure of pure magnetite and barium sulfate. At lower temperatures (e.g., before 10:00 AM), the thermochromic material is black and has a stronger ability to absorb sunlight, resulting in a faster temperature rise and a surface temperature higher than that of the pure barium sulfate structure. As the temperature rises to approximately 28°C, the transparency of the thermochromic material changes, its color gradually lightens, and it even approaches transparency. Its reflectivity increases significantly, and its light absorption decreases, leading to a decrease in heating efficiency. The temperature curve is overtaken by the green pure barium sulfate structure, and the gap widens further with subsequent temperature increases. Subsequently, as the external temperature drops below the critical point (e.g., after 3:00 PM), the thermochromic material returns to a low-temperature state (dark color), with enhanced light absorption. Therefore, its cooling rate is relatively slow, and its temperature approaches that of the pure barium sulfate structure again. This process clearly demonstrates the reversible controllability of the optical properties of the thermochromic material within different temperature ranges, achieving dynamic adjustment of heat input. And when the ambient temperature is too low, such as Figure 7 As shown, the designed thermochromic magnetite / barite-aluminum foil three-layer temperature-controlled composite structure can effectively improve the surface heating rate and significantly delay heat loss, exhibiting good heating response and heat preservation capabilities. It is suitable for use in the morning, winter or cold environment, which is conducive to improving the all-weather thermal regulation adaptability of the material.

[0098] To verify the rationality of the structural design and parameter selection of the present invention and their impact on temperature control performance, several comparative examples were set in addition to Example 1.

[0099] Except for differences specifically stated, the raw material ratios, process conditions, and test methods for the comparative examples are the same as in Example 1. By comparing the preparation results and temperature control performance of samples under different conditions, the superiority and synergistic effect of the present invention are further illustrated.

[0100] Comparative Example 1: Radiation-cooled array with thermochromic properties removed The thermochromic layer was removed, and only the "BaSO4 layer - aluminum foil base layer" functional unit was prepared. The preparation methods for BaSO4 modification and particle size, coating thickness, substrate and bonding steps were the same as those in the radiation cooling module in Example 1. All units in the array were of this structure and did not alternate with Fe3O4 units.

[0101] Comparative Example 2: No two alternating arrays, only a radiation-cooled array. Only the "low-temperature color-changing layer - BaSO4 layer - aluminum foil base layer" functional unit was prepared. The preparation methods for BaSO4 modification and particle size, coating thickness, substrate and bonding steps were the same as those in the radiation cooling module in Example 1. All units in the array have this structure and do not alternate with Fe3O4 units.

[0102] Comparative Example 3: Photothermal Array Only (without Thermochromic Coating) Remove the thermochromic layer and prepare only the "Fe3O4 layer - aluminum foil base layer" functional unit. The preparation methods for Fe3O4 powder, thermochromic layer, substrate pretreatment, spraying / thickness, bonding and cutting conditions are the same as those for the photothermal module in Example 1. All units in the array have this structure and do not alternate with BaSO4 units.

[0103] Comparative Example 4: No two alternating arrays, only photothermal array Only the "high-temperature color-changing layer - Fe3O4 layer - aluminum foil base layer" functional unit was prepared. The preparation methods for Fe3O4 powder, color-changing layer, substrate pretreatment, spraying / thickness, bonding and cutting conditions were the same as those for the photothermal module in Example 1. All units in the array have this structure and do not alternate with BaSO4 units.

[0104] Comparative Example 5: Thermochromic effects were removed, and two alternating arrays were retained. The thermochromic layers of the two types of units were removed. The thickness of the Fe3O4 layer and the BaSO4 layer, the substrate pretreatment, the bonding and cutting conditions were the same as in Example 1. The bonding was changed to "functional layer - aluminum foil". The array was still arranged alternately with Fe3O4 and BaSO4, and the size and spacing were the same as in Example 1.

[0105] To evaluate the impact of the structure of this invention on thermal regulation performance, six numerical models composed of insulating foam boxes were established using COMSOL. The geometric dimensions, boundary and material thermal properties, environmental conditions, and solution settings of each box were identical; except for variables specifically mentioned, all other parameters were consistent with Example 1. The six models were arranged in the following planar positions and numbered as follows: the top row, from left to right, consisted of box 1 (Comparative Example 1) – box 3 (Comparative Example 3) – box 5 (Comparative Example 5); the bottom row, from left to right, consisted of box 2 (Comparative Example 2) – box 4 (Comparative Example 4) – box 6 (Example 1), as shown below. Figure 8 As shown.

[0106] To evaluate the adaptive performance of the temperature-controlled composite structure under different climatic conditions, three sets of environmental temperature boundary conditions were set: summer condition 20–30 ℃, corresponding to a high-temperature environment; autumn condition 10–20 ℃, corresponding to a moderate-temperature and transitional season environment; and winter condition... 10~0 ℃, corresponding to a low-temperature environment. Other boundary conditions (including solar irradiance (1000W / m²)) 2 The convective heat transfer coefficient (W / (m²·K)) and radiation background temperature were kept consistent to compare the surface temperature variation and temperature control effect of each structure (comparative example and embodiment) under different seasonal temperature conditions. The material physical properties were all derived from the COMSOL built-in material library. The surface temperature of the six structures was dynamically simulated for 24 hours. The temperature curves under the three seasonal conditions are shown in Figure 9(a), (b), and (c).

[0107] Under summer, autumn, and winter environmental conditions, the surface temperature of six models was dynamically simulated for 24 hours, and the results are shown in Figures 9(a), (b), and (c). The simulations for all three seasons showed a consistent trend: Comparative Examples 3 and 5 experienced significant temperature increases during the day due to solar radiation, with peak temperatures exceeding 60 °C in summer, remaining as high as 55–60 °C in autumn, and reaching 40–45 °C in winter, exhibiting strong heat absorption characteristics. In contrast, Box 6 of Example 1 demonstrated significantly better temperature control capabilities than the comparative examples in all three seasons: in summer, its peak surface temperature was only about 35–37 °C, significantly lower than the continuous high emissivity structures (Comparative Examples 3 and 5), effectively suppressing overheating under high-temperature conditions; in autumn, its peak temperature remained around 30 °C, with significantly reduced temperature fluctuations compared to the comparative examples; and in winter, it achieved significant warming in low-temperature environments, with the highest daytime temperature reaching 26–28 °C, close to the target temperature control temperature (approximately 27 °C), significantly better than the other comparative examples. The above results show that Box No. 6 in Example 1 has good cooling capacity in high-temperature seasons and significant heating capacity in low-temperature seasons. Its thermal regulation performance is significantly better than that of Comparative Examples 1–5, demonstrating excellent seasonal adaptive temperature control characteristics.

[0108] Example 2 12.6 g of ferrous chloride tetrahydrate (FeCl2·4H2O) and 80.8 g of ferric nitrate nonahydrate (Fe(NO3)3·9H2O) were weighed and dissolved in 1200 mL of distilled water. The solution was stirred for 10 min until completely dissolved, resulting in a light brown mixed solution. Under vigorous stirring (600 rpm), a 5 mol / L NaOH solution was rapidly added dropwise at a rate of 50 mL / min to quickly raise the pH to 10.5 ± 0.2. A pH meter was used to monitor the pH throughout the process to control the risk of over-alkalinity. The reaction solution was then heated to 80 °C and maintained at this temperature for 1 h to promote crystallization and control particle size. After the reaction, the solution was allowed to cool naturally. The precipitate was separated by filtration and washed six times with 100 mL of distilled water each time until the washings were neutral. Finally, the solution was dried in an 80 °C drying oven for 3 h to obtain approximately 13 g of dried Fe3O4 powder.

[0109] 100g of BaSO4 powder was weighed and 3g of nano-Al2O3 (3 wt%) with a particle size of approximately 100nm was added. 40 mL of deionized water was added, and the mixture was stirred at 800 rpm for 30 min on a magnetic stirrer, followed by ultrasonic assisted stirring for 10 min to form a uniform dispersion system. The slurry was dried with hot air at 80℃ for 12 h, then placed in a muffle furnace and held at 700℃ for 1.5 h. After cooling, a heat-treated block was obtained. 4) The mixture was ball-milled for 1 h using a planetary ball mill with ceramic balls as the grinding media, ultimately obtaining modified BaSO4 powder with a particle size concentrated between 0.6 and 2.0 μm and an average particle size of approximately 1.2 μm. In this material, nano-Al2O3 acts as a thermal radiation-enhancing phase, exhibiting high emissivity within an 8–13 μm atmospheric window, making it suitable for application in the field of passive cooling building materials.

[0110] 30 g of thermochromic microcapsules (color-changing temperature approximately 27 °C) were weighed and dispersed in 50 g of acrylic emulsion. The mixture was stirred for 15 min at room temperature using a mechanical stirrer (800 rpm). After initial dispersion, 1.5 g of sodium polyacrylate was added as a dispersant, and stirring continued for 10 min to enhance the stability of the capsules in the system. Subsequently, 0.8 g of zinc oxide powder was added as an inorganic ultraviolet absorber, and the mixture was treated with an ultrasonic-assisted disperser for 5 min to ensure uniform dispersion of the ZnO particles and the formation of a stable mixture. The overall system consisted of 30% thermochromic capsules, 50% acrylic matrix, and approximately 2.3% additives. After vacuum degassing for 5 min, the mixture was coated onto a glass substrate using a blade coating method, controlling the coating thickness to 100 μm. The coating was then dried in a 70 °C hot air circulating oven for 25 min to obtain a composite thermochromic film layer with good optical uniformity and sensitive color-changing response.

[0111] A 100 μm thick glass fiber reinforced plastic (GFRP) sheet was selected as the base material, cut into 100 mm × 100 mm sheets, and then cleaned in deionized water using an ultrasonic device for 10 min, followed by cleaning with anhydrous ethanol for 4 min to remove surface residues. After drying, the sheets were uniformly roughened using 600-grit sandpaper to improve adhesion. Subsequently, 18 g of magnetite powder and 22 g of modified barite powder were weighed and added to 45 mL of deionized water, along with 0.8 g of sodium dodecylbenzenesulfonate (SDBS) as a surfactant dispersant. The mixture was stirred for 30 min to ensure thorough wetting and dispersion, obtaining a stable dispersion system. Then, 10 mL of a 4 wt% hydroxypropyl methylcellulose (HPMC) aqueous solution was slowly added as a binder, and the mixture was stirred before being subjected to an ultrasonic water bath for 25 min to obtain a stable colloidal dispersion. To improve spray flowability, 8 mL of ethanol was added to adjust the viscosity to approximately 400 mPa·s, and the pH was adjusted to 4.0 with 0.1 mol / L acetic acid. The mixture was uniformly sprayed onto the GFRP surface using a high-pressure micro-spray gun (1.0 mm nozzle diameter), controlling the single-layer film thickness to approximately 60 μm. After each spraying, the film was dried at 80 °C for 45 min, and a total of three sprayings were applied to form a multilayer composite coating with a thickness of approximately 180 μm. Subsequently, the magnetite layer and the thermochromic film were cut to the same size and bonded together using pressure-sensitive adhesive, with a pressure of 0.15 MPa applied for 30 seconds to obtain a thermochromic / magnetite / GFRP three-layer structure. Similarly, the prepared barite film and the thermochromic film can be bonded together in the same way to achieve a low-temperature reflective temperature-controlled composite structure.

[0112] The prepared magnetite and barite three-layer composite temperature control structure functional units were cut into square structures with a side length of 30mm, and their edges were trimmed to ensure that the dimensional accuracy of the splicing boundary was within ±0.2mm. The square pieces were arranged sequentially according to the XY rectangular coordinate grid, with magnetite / barite alternately arranged in each row. They were bonded using a heat-resistant polyurethane structural adhesive by dotting and pressing, as shown in Figure 3(b). The constructed square array exhibited excellent modular layout and heat flow uniformity in large-area thermal control applications.

[0113] To further verify the influence of the substrate material on the temperature-controlled functional structure of this invention, after calibrating the model in Example 1, and while keeping the physical field settings, solution parameters, and solar irradiation conditions unchanged, Example 2 uniformly replaced the upper surface coating structure with "GFRP substrate + thermochromic layer + (Fe3O4 unit / BaSO4 unit) square array". Based on this, only the substrate materials were changed in Comparative Example 6 (using an aluminum foil substrate), Comparative Example 7 (using a ceramic substrate), and Comparative Example 8 (using a cement substrate), while the Fe3O4 / BaSO4 ratio, thermochromic layer structure, spray thickness, and bonding method remained consistent. By using "substrate thermal conductivity and heat capacity" as the only variable factor, the influence of different substrates on the temperature rise-fall mode switching behavior can be systematically evaluated, and the superiority and universality of this invention can be further verified by combining COMSOL numerical simulations.

[0114] As shown in Figures 10(a), (b), (c), and (d), under the same external meteorological conditions and boundary settings, the temperature distribution on each structural surface at 13:00 exhibits an approximately uniform field dominated by the array units. Only slight temperature gradients exist at the unit edges and in the transition area between the array and the surrounding insulation layer. This indicates that there are no obvious local overheating zones or cold spots between the Fe3O4 / BaSO4 square array and the thermochromic layer used in this invention. In different comparative examples, the temperature gradient decreases as the substrate material is changed from polymer to cement, ceramic, or aluminum foil, while maintaining a continuous and smooth temperature field overall. This demonstrates that the temperature control structure of this invention has good adaptability to different substrate types.

[0115] from Figure 11 The surface temperature cloud maps and temperature-time variation curves of different substrate structures show that, under the same solar irradiance and ambient temperature boundary conditions, the surface temperature curves of the temperature-controlled composite structures of the present invention, constructed from aluminum foil substrates, ceramic substrates, cement substrates, and plastic substrates (Example 2), exhibit essentially the same overall shape and peak temperature, with the four curves highly overlapping and minimal differences in daytime temperature fluctuations. This indicates that, when using the same Fe3O4 / BaSO4 ratio, thermochromic layer structure, coating thickness, and bonding method, the differences in thermal conductivity and heat capacity of the substrate materials have a limited impact on the overall temperature control performance. The temperature response of the structure of the present invention is mainly determined by the surface functional units, and it possesses good adaptability to different substrate materials and a stable and consistent temperature control effect. In comparison, Box 6 of Example 2 of the present invention demonstrates superior thermal control capabilities compared to Comparative Examples 1–5.

[0116] Combining Figure 10 and Figure 11It can be seen that the Fe3O4 / BaSO4 square array combined with the thermochromic layer used in this invention forms a continuous and nearly uniform temperature field on different substrates (polymers, cement, ceramics, aluminum foil). As the thermal conductivity of the substrate increases, the local temperature gradient further decreases and the temperature distribution becomes smoother, indicating that high thermal conductivity is beneficial to improving the temperature uniformity within the array. At the same time, the curves of temperature change over time on the surface of each chamber are basically consistent in shape and peak value, indicating that the overall temperature control level is mainly determined by the surface functional unit. The structure of this invention has good adaptability and stable temperature control effect on a variety of substrate materials.

[0117] Example 3 13.9 g of ferrous chloride tetrahydrate, 13.9 g of ferrous nitrate hexahydrate, and 54.1 g of ferric chloride hexahydrate were weighed and dissolved in 1500 mL of distilled water. The solution was stirred for 10 min until a uniform, brownish-yellow, transparent solution was formed. Then, under stirring (450 rpm), 3.5 mol / L NaOH solution was added dropwise at a rate of 15 mL / min to adjust the pH to 9.2 ± 0.2. After adjustment, the reaction system was heated to 85 °C and reacted at this temperature for 45 min, maintaining medium-speed stirring to ensure uniform temperature and crystal quality. After the reaction was complete, the mixture was cooled to room temperature, and the precipitate was separated by vacuum filtration. The precipitate was washed five times with 120 mL of distilled water until neutral. The precipitate was dried at 80 °C for 2.5 h to obtain approximately 12.5 g of dried Fe3O4 powder.

[0118] 100 g of BaSO4 powder was weighed and mixed with 1.5 g of nano-SiO2 (30 nm particle size) and 1.5 g of nano-Al2O3 (70 nm particle size) at a ratio of 1.5 wt% each. 40 mL of distilled water was added to the mixture, and the mixture was stirred magnetically (700 rpm) for 30 min, followed by ultrasonic water bath treatment for 20 min. The resulting slurry was dried in an 85 ℃ constant temperature oven for 10 h, then heat-treated at 700 ℃ for 2 h, cooled, and pulverized. Zirconia balls were used as the grinding medium, and the mixture was ball-milled for 1 h to obtain a uniform powder with a particle size concentrated between 0.5 and 1.8 μm and an average particle size of 1.3 μm. The synergistic doping of SiO2 and Al2O3 not only modulates the particle size distribution but also enhances infrared emissivity through synergistic phonon emission while maintaining good spectral selectivity, making it suitable for radiative cooling applications such as infrared windows and roof cooling.

[0119] 20 g of magnetite (Fe3O4) powder and 20 g of modified barite (BaSO4) powder were weighed separately and added to 45 mL of deionized water. Simultaneously, 1.0 g of polyvinylpyrrolidone (PVP) was added as a dispersant. The mixture was stirred continuously on a magnetic stirrer for 30 min to achieve uniform powder dispersion. Then, 10 mL of a 5 wt% polyvinyl alcohol (PVA) solution was slowly added dropwise, and stirring was continued for 5 min. The mixture was then treated in an ultrasonic water bath for 30 min to form a stable colloidal dispersion. To adjust the rheological properties of the spray solution, 10 mL of anhydrous ethanol was added to control the system viscosity at approximately 300 mPa·s. Finally, the pH was adjusted to 4.8 using a 0.1 mol / L acetic acid solution to obtain a stable suspension suitable for spraying.

[0120] 70 g of aqueous polyurethane dispersion was used as the matrix, and 20 g of thermochromic microcapsules (color change temperature 28℃) were added. The mixture was dispersed for 20 min under stirring to obtain the basic composite dispersion system. Subsequently, 1.4 g of polyvinylpyrrolidone (PVP) was added as a dispersant (approximately 2% of the total mass), and 0.5 g of benzotriazole UV absorber [2-(2-hydroxy-5-tert-butylphenyl)benzotriazole] was added to enhance the UV resistance of the film. Stirring was continued for 10 min to form the thermochromic capsule composite system. The resulting composite mixture was stirred for 30 min at room temperature to 40℃ to ensure uniform fusion of all components, and then vacuum degassing was performed for 5 min to remove air bubbles. The mixture was then coated onto a pre-cleaned PET film surface using a blade coating method, with a coating thickness controlled at 120 μm. After coating, the film was dried in a 70℃ constant temperature oven for 20 min to form a continuous, defect-free thermochromic film layer. Next, the prepared magnetite spraying liquid was loaded into a pneumatic spray gun with a nozzle diameter set to 0.8 mm. The dried thermochromic film was then atomized and sprayed under constant pressure. After each spraying, the film was dried at 60 °C for 30 min. This spraying and drying process was repeated three times, controlling the total film thickness to approximately 0.15 mm. The magnetite layer and the thermochromic film achieved in-situ bonding through spray deposition, without the need for adhesives, forming a dense, thermally efficient bilayer composite film. The resulting film exhibits excellent near-infrared absorption and colorimetric thermal response, making it suitable for dynamic temperature control applications. Similarly, using the same method, barite spraying liquid was sprayed onto the surface of another set of low-temperature thermochromic films. After drying, a high-reflectivity radiation cooling film layer was obtained, forming a low-temperature thermochromic-BaSO4 bilayer structure, as shown below. Figure 2 As shown.

[0121] This embodiment provides a method for constructing a temperature-controlled composite structure with a regular hexagonal honeycomb array. First, prefabricated Fe3O4 photothermal units and BaSO4 radiative cooling units are cut into regular hexagonal sheets with a side length of 30 mm. Laser cutting is used to ensure that the edge size error does not exceed ±0.2 mm, and the edges are polished to improve the tightness of the splicing. Then, following the regular hexagonal honeycomb array pattern shown in Figure 3(a), the units are densely arranged on a clean and flat ceramic or metal substrate surface. Magnetite units and barite units are arranged in an alternating pattern, for example, nested with one Fe3O4 unit surrounding six BaSO4 units, constructing a local gradient network structure with alternating hot and cold temperatures. Each unit is edge-bonded using a heat-resistant polyurethane structural adhesive. A pressure of 0.2 MPa is applied and held for 60 s before being released. After completion of the arrangement, the structure is cured at room temperature for 4 h to obtain a dense, uniform, and stable honeycomb array structure. This structure is highly isotropic, which can significantly enhance multidirectional heat diffusion and heat flow uniformity. The modular arrangement of localized hot and cold alternation helps to quickly establish a thermal gradient field and reduce the risk of thermal stress concentration. It is suitable for large-area thermal regulation, heat-resistant coatings and energy management systems.

[0122] To verify the advantages of the temperature control structure of this invention in terms of geometric arrangement, Example 3 and Comparative Examples 9-11 all use the same magnetite / barite double-layer composite temperature control functional unit, the same size specifications (30 mm side length), and the same bonding process and substrate conditions, only changing the array arrangement of the functional unit. Example 3 uses a regular hexagonal honeycomb array configuration, while Comparative Examples 9, 10, and 11 use a square array, an equilateral triangular array, and a triangular-hexagonal interlocking combination array, respectively. By changing the array method individually under the same material system and geometric scale, the influence of different layout structures on the heat diffusion path, thermal coupling mode, and overall temperature control performance can be accurately evaluated.

[0123] Comparative Example 9: Square Array The prepared magnetite and barite double-layer composite temperature control structure functional units were cut into square structures with a side length of 30 mm, and their edges were trimmed to ensure that the dimensional accuracy of the splicing boundary was within ±0.2 mm. The square pieces were arranged sequentially according to the XY rectangular coordinate grid, with magnetite / barite alternately arranged in each row. They were bonded using a heat-resistant polyurethane structural adhesive by dotting and pressing, as shown in Figure 3(b). The constructed square array exhibited excellent modular layout and heat flow uniformity in large-area thermal control applications.

[0124] Comparative Example 10: Equilateral Triangle Array The prepared magnetite and barite bilayer composite temperature control structure functional units were cut into triangular structures with a side length of 30 mm, and their edges were trimmed to ensure that the dimensional accuracy of the splicing boundary was within ±0.2 mm. The triangular functional units were assembled into a continuous network according to the equilateral connection method, and the error at the unit joint was controlled within 0.1 mm, as shown in Figure 3(c). This structure has a high boundary density, which can realize precise regional temperature control, and is particularly suitable for microscale or local high heat flux density areas such as chip surface thermal management.

[0125] Comparative Example 11: Hexagonal honeycomb-equilateral triangle combination array The prepared magnetite and barite double-layer composite temperature control structure functional units were cut into triangular structures with a side length of 30 mm and hexagonal structures with a side length of 30 mm. The edges were trimmed to ensure that the dimensional accuracy of the splicing boundary was within ±0.2 mm. A honeycomb structure was used as the main frame, with the triangular units embedded in the boundary gaps of the honeycomb units to form an interlocking composite network structure. During the arrangement process, the honeycomb magnetite modules were assembled first, and then the barite triangular modules were embedded in the structural gaps and fixed with adhesive, as shown in Figure 3(d). This composite structure exhibits better hot and cold channel guidance capabilities under non-uniform heat sources, enabling spatial coupling and dynamic energy balance in thermal response.

[0126] Figure 12 illustrates the surface temperature distribution of different array structures under solar irradiation conditions in Embodiment 3 and Comparative Examples 9–11 of the present invention. Figure 12(a) shows a regular hexagonal honeycomb array, Figure 12(b) a square array, Figure 12(c) a triangular array, and Figure 12(d) a hexagonal honeycomb-triangular interlocking array. All four arrangements use the same magnetite / barite three-layer composite temperature control unit, the same material parameters, and boundary conditions; only the array geometry differs, allowing for individual observation of the influence of the array arrangement on the temperature field morphology. As seen in Figures 12(a–d), different array forms form a complete and continuous heat diffusion network under solar irradiation, exhibiting a stable and uniform temperature distribution. Although slight differences exist in local temperature gradients and isotherm morphologies due to different geometric structures, the overall temperature rise and temperature field uniformity remain on the same order of magnitude. This indicates that the temperature control unit of the present invention can achieve effective heat diffusion and thermal regulation functions under various array arrangements, achieving good temperature control performance without relying on a specific arrangement structure.

[0127] Figure 13The surface temperature of the enclosure under different arrays during a 24-hour solar irradiation cycle is presented. The temperature variation patterns of each array are generally consistent, with temperatures increasing with increasing irradiation, reaching a peak around noon, and then gradually decreasing. There are some differences in the peak temperatures of the different arrays, with the hexagonal honeycomb array exhibiting a slightly higher peak temperature. This is mainly because the hexagonal honeycomb array has a relatively higher proportion of photothermal component (magnetite) at 70%, while the proportion of barium sulfate radiative cooling units is correspondingly reduced, resulting in a stronger photothermal response of the overall structure under solar irradiation. This phenomenon also indicates that the ratio of magnetite-barium sulfate functional units in this invention can be adjusted according to different regional climatic conditions: in high-latitude or low-temperature regions, the proportion of magnetite can be appropriately increased to obtain stronger heating capacity; in hot regions, the proportion of barium sulfate can be increased to enhance the cooling effect, thereby achieving regionalized and seasonal temperature control adaptation.

[0128] In summary, regardless of whether a regular hexagon, square, equilateral triangle, or interlocking array is used, the composite temperature control unit of the present invention can construct a stable and efficient temperature control network, and can further adapt to different environmental temperature requirements by adjusting the ratio of photothermal / cooling components, exhibiting good array compatibility and climate adaptability.

[0129] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A temperature-controlled composite structural material with photothermal absorption and radiative cooling, characterized in that, The temperature-controlled composite structure material includes an array of two components: a first Fe3O4 photothermal unit consisting of a high-temperature color-changing layer, a Fe3O4 photothermal layer, and a base layer, and a first BaSO4 radiation cooling unit consisting of a low-temperature color-changing layer, a BaSO4 radiation cooling layer, and a base layer. The Fe3O4 is Fe3O4 with controlled particle size, and the BaSO4 is BaSO4 with surface modification. The Fe3O4 has a particle size of 10–100 nm, and the BaSO4 has a particle size of 0.2–2.5 μm. The arrangement array of the first Fe3O4 photothermal unit and the first BaSO4 radiation cooling unit is a geometric array arranged regularly or irregularly in a plane, including but not limited to regular hexagonal honeycomb array, square array, equilateral triangle array and regular hexagonal honeycomb-equilateral triangle combination array; The high-temperature color-changing layer is transparent / high light transmittance when the temperature T < T1, and opaque / low light transmittance when T ≥ T1; The low-temperature color-changing layer is opaque / low-transmittance when T < T2, and transparent / high-transmittance when T ≥ T2; The temperatures T1 and T2 are between 15 and 65 °C, and the difference between T1 and T2 does not exceed 10 °C.

2. The temperature-controlled composite structural material with photothermal absorption and radiative cooling according to claim 1, characterized in that, The temperature-controlled composite structure material includes a second Fe3O4 photothermal unit composed of a high-temperature color-changing layer and a Fe3O4 photothermal layer arranged in an array, and a second BaSO4 radiative cooling unit composed of a low-temperature color-changing layer and a BaSO4 radiative cooling layer. The arrangement array of the second Fe3O4 photothermal unit and the second BaSO4 radiation cooling unit is a geometric array arranged regularly or irregularly in a plane, including but not limited to regular hexagonal honeycomb array, square array, equilateral triangle array and regular hexagonal honeycomb-equilateral triangle combination array.

3. A method for preparing a temperature-controlled composite structural material with photothermal absorption and radiative cooling as described in claim 1 or 2, characterized in that, Includes the following steps: By mass percentage, 10%–30% of high-temperature thermochromic microcapsules and 10%–30% of low-temperature thermochromic microcapsules were mixed with 40%–80% of matrix, 0.5%–3% of dispersant, and 0.1%–1% of ultraviolet absorber at 10–65°C for 10–60 min to obtain a high-temperature thermochromic mixture system and a low-temperature thermochromic mixture system. The high-temperature color-changing mixture system and the low-temperature color-changing mixture system were respectively coated on polyethylene terephthalate film or glass surface, and then dried at 50-80℃ for 10-30 min to obtain a high-temperature color-changing layer and a low-temperature color-changing layer with a thickness of 50-200 μm. Fe3O4 powder and BaSO4 powder were added to deionized water and dispersant respectively and stirred and dispersed. Then, a binder was added dropwise and ultrasonic water bath treatment was performed to form a colloidal dispersion. Ethanol and acid were added to the colloidal dispersion to obtain Fe3O4 suspension and BaSO4 suspension with pH value of 3 to 6. Fe3O4 suspension and BaSO4 suspension were sprayed onto the substrate surface multiple times with a thickness of 5-100 μm each time. After each spraying, the substrate was dried at 60-80℃ for 30-90 min to form a Fe3O4 photothermal layer and a BaSO4 radiation cooling layer with a thickness of 0.05-1.5 mm on the substrate surface. A first Fe3O4 photothermal composite material consisting of a high-temperature color-changing layer, a Fe3O4 photothermal layer, and a substrate layer is formed by bonding the high-temperature color-changing layer and the Fe3O4 photothermal layer together with an adhesive. A first BaSO4 radiation cooling composite material is formed by bonding a low-temperature color-changing layer and a BaSO4 radiation cooling layer on a substrate layer with an adhesive. The first Fe3O4 photothermal composite material and the first BaSO4 radiation cooling composite material are cut into predetermined shapes to obtain the first Fe3O4 photothermal unit and the first BaSO4 radiation cooling unit, respectively. The first Fe3O4 photothermal unit and the first BaSO4 radiation cooling unit are arranged in an array and bonded together to form a temperature-controlled composite material with photothermal absorption and radiation cooling. The high-temperature color-changing layer is transparent / high light transmittance when the temperature T < T1, and opaque / low light transmittance when T ≥ T1; The low-temperature color-changing layer is opaque / low-transmittance when T < T2, and transparent / high-transmittance when T ≥ T2; The temperatures T1 and T2 are between 15 and 65°C, and the difference between T1 and T2 does not exceed 10°C.

4. The method for preparing the temperature-controlled composite structural material with photothermal absorption and radiative cooling according to claim 3, characterized in that, Includes the following steps: The Fe3O4 suspension was sprayed onto the surface of the high-temperature color-changing layer multiple times with a thickness of 5-100 μm each time. After each spraying, the surface was dried at a constant temperature of 40-80°C for 5-90 min to form a Fe3O4 photothermal layer with a thickness of 0.05-1.5 mm on the high-temperature color-changing layer, thus obtaining a second Fe3O4 photothermal composite material with a high-temperature color-changing layer and a Fe3O4 photothermal layer structure. The BaSO4 suspension is sprayed onto the surface of the low-temperature color-changing layer multiple times with a thickness of 5-100 μm each time. After each spraying, it is dried at a constant temperature of 40-80℃ for 5-90 min to form a BaSO4 radiation cooling layer with a thickness of 0.05-1.5 mm on the low-temperature color-changing layer, thus obtaining a second BaSO4 radiation cooling composite structure material with a low-temperature color-changing layer and a BaSO4 radiation cooling layer. The second Fe3O4 photothermal composite material and the second BaSO4 radiation cooling composite material are cut into predetermined shapes to obtain the second Fe3O4 photothermal unit and the second BaSO4 radiation cooling unit, respectively. The second Fe3O4 photothermal unit and the second BaSO4 radiation cooling unit are arranged in an array and bonded together to form a temperature-controlled composite material with photothermal absorption and radiation cooling. The high-temperature color-changing layer is transparent / high light transmittance when the temperature T < T1, and opaque / low light transmittance when T ≥ T1; The low-temperature color-changing layer is opaque / low-transmittance when T < T2, and transparent / high-transmittance when T ≥ T2; The temperatures T1 and T2 are between 15 and 65°C, and the difference between T1 and T2 does not exceed 10°C.

5. The method for preparing a temperature-controlled composite material with photothermal absorption and radiative cooling according to claim 3 or 4, characterized in that, The color-changing temperature of the high-temperature thermochromic microcapsules and the low-temperature thermochromic microcapsules is 15–65°C; the matrix is ​​an aqueous polyurethane dispersion or an acrylic emulsion; the dispersant includes at least one of sodium polyacrylate, polyethylene glycol, polycarboxylate, phosphate, polyethyleneimine, sodium silicate, citric acid, polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, and sodium hexametaphosphate; the ultraviolet absorber is at least one of benzotriazole compounds, triazine compounds, zinc oxide, and titanium dioxide.

6. The method for preparing a temperature-controlled composite material with photothermal absorption and radiative cooling according to claim 3 or 4, characterized in that, The preparation of the Fe3O4 powder includes the following steps: 1) Prepare a mixed solution of ferrous salt and ferric salt by dissolving ferrous salt and ferric salt in distilled water at a molar ratio of 1:1 to 1:3; 2) Adjust the pH of the mixed solution of ferrous and ferric salts by adding alkali solution dropwise to obtain the reaction system, which is then adjusted to 8.5–10.

5. 3) Heat the reaction system to 65-85℃ and react for 0.75-1.5h. After the reaction is completed, filter the mixture, wash the separated precipitate until it is neutral, and then dry it to obtain Fe3O4 powder with a particle size of 10-100nm and an anti-spinel structure on the (220), (311), and (400) crystal planes.

7. The method for preparing a temperature-controlled composite material with photothermal absorption and radiative cooling according to claim 3 or 4, characterized in that, The modification of the BaSO4 powder includes the following steps: 1) A mixed powder was obtained by adding 0.5-7 wt% of SiO2, Al2O3, ZrO2 and Y2O3 powders with a particle size of 10-200 nm to BaSO4 powder with an average particle size of 0.5 μm; 2) Add distilled water to the mixed powder and stir to disperse it to obtain a mixed slurry; 3) After evaporating and drying the mixed slurry at 60-100℃, it is subjected to solid-phase heat treatment at 400-1000℃ for 0.5-3 hours to obtain heat-treated material blocks; 4) Grind the heat-treated material blocks to obtain modified BaSO4 powder with a particle size of 0.2 to 2.5 μm.

8. The method for preparing the temperature-controlled composite structural material with photothermal absorption and radiative cooling according to claim 3, characterized in that, The adhesive is a polyvinyl alcohol solution with a mass concentration of 4-6 wt%, or polyacrylamide or hydroxypropyl methylcellulose; the base layer material is stainless steel sheet, copper foil, titanium foil, glass fiber reinforced plastic, cement, ceramic or other metal or non-metal substrates with certain mechanical strength and temperature resistance; the adhesive is selected from pressure-sensitive adhesives, polyurethane adhesives or other weather-resistant structural adhesives with temperature resistance of -20 to 80℃, bonding strength ≥0.5MPa and resistance to ultraviolet aging.

9. The method for a temperature-controlled composite structural material with photothermal absorption and radiative cooling according to claim 3 or 4, characterized in that, When the Fe3O4 photothermal unit and the BaSO4 radiation cooling unit array are arranged, the misalignment angle between adjacent units does not exceed 5°.

10. The method for preparing the temperature-controlled composite structural material with photothermal absorption and radiative cooling according to claim 9, characterized in that, The Fe3O4 photothermal unit and the BaSO4 radiative cooling unit are bonded together with a heat-resistant polyurethane structural adhesive or thermally conductive silicone grease with a temperature resistance range of -30 to 100℃ and a shear strength ≥0.6MPa, and cured under pressure at room temperature for 50 to 70 minutes.

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