A core-shell structure bifunctional radiative cooling fiber membrane and a preparation method and application thereof

Abstract

The application discloses a kind of core-shell structure dual-function radiation cooling fiber membrane and preparation method and application thereof, belong to radiation cooling technical field, preparation method is as follows: 1) dianhydride and diacid monomer are dissolved in organic solvent and reacted to obtain polyamic acid, dehydrating agent and catalyst are added to obtain mixed solution, mixed solution is added to non-solvent to obtain fibrous polymer, and shell polymer polyimide is obtained after drying;2) polyimide is dissolved in organic solvent to prepare electrospinning shell layer solution;Phase change material is dissolved in organic solvent to prepare electrospinning core layer solution;3) using coaxial electrospinning technology, the above-mentioned electrospinning shell layer solution and core layer solution are stretched under 10-25kV, and core-shell structure dual-function radiation cooling fiber membrane is obtained.The method solves the problem that existing radiation cooling material is prone to cause severe temperature rise and drop due to external environmental factors, and cannot actively control temperature fluctuation.

Description

Technical Field

[0001] This invention belongs to the field of radiation cooling technology, specifically relating to a core-shell structured bifunctional radiation cooling fiber membrane, its preparation method, and its application. Background Technology

[0002] Refrigeration is an indispensable core technology for ensuring thermal comfort, equipment stability, and transportation and preservation. It not only improves human quality of life but also drives progress in multiple fields such as industry, medicine, and information technology, demonstrating broad and profound scientific and social value. However, current traditional refrigeration technologies rely on fossil fuels. It is projected that by 2050, global electricity demand for refrigeration will account for 20% of total electricity consumption, and direct carbon emissions are expected to account for 45% of the equivalent carbon emissions, hindering global decarbonization goals. To address this challenge, developing energy-saving, environmentally friendly, and high-performance cooling strategies to replace traditional cooling methods is urgently needed.

[0003] Currently, researchers have produced a large number of materials with excellent radiative cooling performance by combining structured photonics engineering and material property design, including biomimetic array thin films, layered porous coatings, and ceramics. However, in practical applications, due to the complexity of environmental and weather changes, relying solely on a single radiative cooling material to achieve a new thermal equilibrium may lead to drastic heating and cooling due to insufficient thermal insulation or a high heat transfer coefficient. Living organisms and precision equipment are highly sensitive to temperature changes, posing a challenge to ensuring thermal comfort. Furthermore, maintaining a stable thermal comfort environment requires external energy support, undoubtedly resulting in increased energy consumption. This phenomenon is prevalent in single-function radiative cooling materials, including coatings, thin films, and fabrics, specifically manifested as drastic temperature fluctuations (>5-10 °C) in a short period of time depending on solar irradiance. Therefore, achieving both thermal comfort and energy efficiency through single-function radiative coolers is extremely challenging.

[0004] Currently, when traditional fiber structures are used as materials for radiative cooling, the heat continuously absorbed from sunlight and the environment through conduction and convection causes the radiative cooler to heat up rapidly to reach thermal equilibrium. On the one hand, although its high reflectivity and high emissivity optical properties can lower the final thermal equilibrium temperature, the heating process is extremely rapid. During this period, a large amount of heat is transferred to the temperature-sensitive internal environment through thermal conduction, causing the internal ambient temperature to deviate from its original temperature. To avoid this phenomenon, more energy is needed for cooling. On the other hand, during cloudy weather, the solar radiation intensity drops sharply, but due to the material's high emissivity, heat is still continuously emitted. At this time, the temperature of the radiative cooler will be lower than the internal ambient temperature, causing the internal ambient temperature to be conducted outward. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a core-shell structured bifunctional radiation cooling fiber membrane, its preparation method and application, overcoming the problem that existing radiation cooling materials are prone to drastic heating and cooling due to external environmental factors and cannot actively control temperature fluctuations.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a core-shell structured bifunctional radiation-cooled fiber membrane and its preparation method, comprising the following steps: 1) Dissolve dianhydride monomer and diamine monomer in an organic solvent to react and obtain polyamic acid. Add a dehydrating agent and a catalyst to react and obtain a mixed solution. Pour the mixed solution into a non-solvent to obtain a fibrous polymer. After drying, obtain a shell polymer polyimide. The mass ratio of the dianhydride and diamine monomer to the organic solvent is 1:(3-5), and the volume ratio of the mixed solution to the non-solvent is >1:10. 2) Dissolve polyimide in an organic solvent to prepare an electrospinning shell solution, wherein the mass ratio of the polyimide to the organic solvent is 1:(2-5); dissolve a phase change material in an organic solvent to prepare an electrospinning core solution, wherein the mass ratio of the phase change material to the organic solvent is (5-10):1; wherein the phase change material includes one of polyethylene glycol, lauric acid, and paraffin wax; 3) Using coaxial electrospinning technology, the shell and core solutions of the electrospinning are stretched at a voltage of 10-25kV to obtain a core-shell structured bifunctional radiation-cooled fiber membrane.

[0007] In the preparation process described above, the selected shell material and phase change material (polyethylene glycol, lauric acid, or paraffin) have a significant impact on the final core-shell structure and radiative cooling performance. Different shell materials exhibit varying optical properties, directly affecting the shell's solar reflectivity, mid-infrared emissivity, and radiative cooling efficiency. Furthermore, different phase change materials have different enthalpy values ​​and phase change temperature ranges, directly influencing the thermal shock resistance of the composite fiber material. Specifically, higher shell material concentrations result in greater viscosity and require a higher voltage for electrospinning. However, excessively high or low concentrations can negatively impact fiber membrane preparation. Too high a concentration prevents spinning, while too low a concentration leads to unstable composite droplets, preventing complete encapsulation of the core phase change material by the shell, thus affecting the fiber membrane's radiative cooling and phase change performance. In addition, the shell material's own optical properties are crucial for its radiative cooling performance; however, excessively thin shells reduce radiative cooling capacity. Phase change materials primarily exhibit phase change properties; the transition from solid to liquid requires heat absorption, while the transition from liquid to solid releases energy. Therefore, a core-shell structure is used to encapsulate the phase change material, preventing it from leaking out in liquid form during the phase change process. With the phase change material incorporated into the fiber membrane of this invention, the heating and cooling processes become more gradual, avoiding abrupt increases and decreases.

[0008] In the above technical solution, the non-solvent in step 1) refers to a solvent that cannot dissolve the solute but is infinitely miscible with the solvent. Its function is to cause the fibrous polymer to precipitate due to decreased solubility. The volume ratio of the mixed solution to the non-solvent needs to be greater than 1:10, and the non-solvent needs to be replaced multiple times. That is, the mixing reaction of the mixed solution and the non-solvent needs to be cyclical multiple times, with the non-solvent replaced once per cycle. Each cycle lasts six hours, for a total of four cycles. The purpose is to remove the organic solvent, catalyst, and dehydrating agent from the original solution. The principle is that organic solvents are infinitely miscible with non-solvents, and organic solvents tend to penetrate into non-solvents, ultimately causing phase separation of the solute in the original solution. In addition, the coaxial electrospinning technology in step 3) must be carried out under a high voltage of 10-25kV. Its principle is to stretch the spinning solution to form nanofibers through electrostatic force. If the voltage is too low, the viscosity between solutions cannot be overcome.

[0009] Preferably, in step 1), the molar ratio of the dianhydride to the diamine monomer is 0.8-1.2. The dianhydride monomer includes one of 4,4′-(hexafluoroisopropene)phthalic anhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and 1,2,3,4-tetramethyl1,2,3,4-cyclobutanetetracarboxylic dianhydride. The diamine monomer includes one of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane, and 2,2'-bis(trifluoromethyl)diaminobiphenyl.

[0010] In a further preferred embodiment, to gel the reaction solution and prevent rapid heat accumulation caused by adding the dianhydride monomer all at once, the dianhydride monomer should be added in batches.

[0011] Preferably, in step 1), the volume ratio of the dehydrating agent to the catalyst is 1:3, the dehydrating agent is acetic anhydride, and the catalyst is a pyridine solution.

[0012] Preferably, in steps 1) and 2), the organic solvent includes one of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone, and the non-solvent includes one of deionized water, methanol and ethanol.

[0013] Preferably, in step 3), the distance between the needle and the receiving platform in the coaxial electrospinning technology is 5~15 cm, the feeding rate is 0.5~2 mL / h, and the spinning temperature is 30~50 ℃.

[0014] In the above technical solution, the main parameters for forming the core-shell structure of the fiber membrane of the present invention are shell layer concentration, core layer concentration, electrostatic voltage, and push rate. The shell layer concentration determines whether it can completely encapsulate the core layer solution; therefore, the shell layer viscosity is usually greater than that of the core layer. The push rate mainly affects the diameter of the core layer in the core-shell fiber structure. The faster the push rate, the larger the core layer diameter, the more energy it can absorb and release, the slower the heating and cooling rates, and the more gradual the heating and cooling. However, an excessively high push rate can also lead to leakage of the core layer phase change material and damage to the core-shell structure.

[0015] Preferably, in step 1), the mixed solution of dianhydride and diamine monomer with organic solvent is fully reacted in a water bath at 0-10 °C for 5-20 h with mechanical stirring at a rate of 200-500 r / min, and then fully reacted at room temperature for 15-40 h after adding dehydrating agent and catalyst; the drying temperature is 60-120 °C.

[0016] Preferably, in step 2), the phase change material and the spinning aid are dissolved in an organic solvent to prepare an electrospinning core layer solution, and the mass ratio of the phase change material to the spinning aid is (5-15):1; the spinning aid includes one of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene oxide and N-methylpyrrolidone.

[0017] In the above technical solutions, different spinning aids have different molecular compatibility and solution viscosity, which directly affect the electrostatic stretching process during spinning and determine whether a robust core-shell microstructure can be formed to prevent leakage of phase change materials.

[0018] More preferably, in step 1), the volume of the non-solvent is 2-3 L.

[0019] More preferably, the organic solvent is 3-8 times the total mass of the phase change material and the spinning aid.

[0020] The present invention also discloses the preparation method of the above-mentioned core-shell structured bifunctional radiation cooling fiber membrane, which has a core-shell structure and a core layer diameter of 232 nm - 786 nm.

[0021] In the above technical solution, the core layer diameter of 232 nm - 786 nm ensures that as much phase change material as possible is coated without reducing the visible light reflectivity and mid-infrared emissivity of the fiber membrane, thus giving it a higher enthalpy. This results in stronger resistance to thermal shock in scenarios involving sudden temperature drops and rapid temperature rises.

[0022] A further preferred embodiment has a core diameter of 786 nm.

[0023] This invention optimizes the core layer structure to 786 nm, introducing a higher content of phase change material while ensuring radiative cooling performance and preventing leakage. This allows for the absorption and release of more heat to mitigate internal temperature changes in the face of complex and changing external environments, effectively achieving thermal shock resistance.

[0024] Further preferred embodiments show that the core-shell structured bifunctional radiation-cooled fiber membrane has a solar reflectance of 90.2–97.5%, a mid-infrared emissivity of 82.1–92.7%, and a thermal conductivity of 0.054–0.091 W·m. -1 ·K -1 The enthalpy value is 18.2~124.3 J / g.

[0025] The present invention also discloses the application of the above-mentioned core-shell structured bifunctional radiation cooling fiber membrane in radiation cooling.

[0026] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing a core-shell structured bifunctional radiation-cooled fiber membrane. Based on the radiation cooling mechanism, the polyimide molecular chain is designed to improve its solar reflectivity and mid-infrared emissivity. Specifically, by introducing a trifluoromethyl functional group into the diamine monomer, the formation of charge-transfer complexes can be effectively suppressed, achieving effective decolorization. This is because the strong electronegativity of fluorine (F) causes the trifluoromethyl group to exhibit a strong electron-withdrawing effect, effectively suppressing the charge-transfer ability of the benzene ring in the diamine monomer as both acceptor and donor, reducing the formation of charge-transfer complexes, and thus endowing the fiber shell with high solar reflectivity and mid-infrared emissivity. Decolorization is mainly related to the visible light reflectivity and mid-infrared emissivity of the material. Different polyimides exhibit yellow hues, causing them to absorb yellow light from sunlight in the visible light spectrum. However, after decolorization using this invention, the fluorinated polyimide becomes white, reflecting all visible light and thus reducing heat absorption. Simultaneously, the absorption wavelength of the CF bond in the trifluoromethyl group coincides with the atmospheric transparency window, increasing the mid-infrared emissivity and emitting more heat into deep space, further reducing temperature. In addition, by encapsulating phase change materials within a shell polymer (polyimide) using coaxial electrospinning technology, the fiber membrane acquires high latent heat. When subjected to external thermal shock, the heat is stored as latent heat, preventing drastic temperature changes. Furthermore, the robust core-shell structure enhances its shape stability and prevents performance degradation due to leakage. In the heat transfer of this core-shell bifunctional radiative cooling fiber membrane, the high latent heat of the phase change material allows heat absorbed from the outside to be stored, maintaining a constant temperature in the phase change layer and continuing to conduct heat downwards to the un-phase-change layer. During this process, the high emissivity of the shell continuously emits heat outwards, slowing the rate of downward heat transfer and minimizing temperature changes at the bottom until the stored energy reaches its limit. When the external energy source is lost, the heat stored at the top is preferentially released, maintaining a constant temperature in the bottom phase change layer, reducing the temperature difference between the inside and outside until all heat is released. This effectively mitigates drastic temperature drops. Therefore, the key advantage of core-shell structured bifunctional radiative cooling fiber membranes lies in the active regulation of temperature fluctuations through the dynamic storage / release of latent heat of phase change. In summary, this invention ingeniously utilizes the core-shell structure of nanofibers to introduce phase change materials. On the one hand, it effectively alleviates the problem of short-term overcooling and overheating of coolers caused by external environmental factors; on the other hand, the core-shell nanofiber structure can effectively encapsulate the phase change material, preventing leakage and other problems that occur during the phase change process. This research enriches the design inspiration and theoretical support for multifunctional, integrated radiative cooling materials, opening up new possibilities for their application in building energy conservation, equipment stability, and transportation and storage.

[0027] Furthermore, the catalyst is a pyridine solution, which promotes the chemical imidization process, causing fluorinated polyamic acid to generate fluorinated polyimide. During this process, cyclization generates water, and acetic anhydride acts as a dehydrating agent, removing water and allowing the reaction to proceed in the forward direction.

[0028] Furthermore, the organic solvent is selected from N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone. These substances are all highly polar aprotic solvents with strong dissolving power, which can effectively dissolve dianhydride monomers, diamine monomers, and polyimide. The non-solvent is selected from deionized water, methanol, and ethanol because deionized water, methanol, and ethanol are all polar solvents with large differences in solubility parameters from the organic solvents of polyamic acid, which can quickly initiate phase separation and form fibrous polymers.

[0029] Furthermore, in the coaxial electrospinning process, by adjusting parameters such as spinning voltage, distance between the needle and the receiving platform, feeding rate, and spinning temperature, the stretching speed and morphology of the shell solution and core solution can be controlled, thereby controlling the core-shell fiber structure.

[0030] Furthermore, by controlling the mechanical stirring rate (200~500 r / min) and the low-temperature water bath (0-10℃), uniform dispersion and slow polymerization of monomers can be achieved in the initial stage of the reaction, reducing side reactions. These conditions help the polyamic acid precursor form polymer chains with uniform molecular weight distribution and regular structure, providing a foundation for subsequent dehydration and ring closure to form the polyimide shell. The staged reaction design (5-20 hours at low temperature and 15-40 hours at room temperature) ensures the full synthesis of the polyamic acid precursor and the formation of a highly stable polyimide structure through dehydration and ring closure at room temperature. The selection of drying temperature (60-120℃) effectively removes residual solvents while avoiding high-temperature damage to the core-shell structure of the fiber. The moderate temperature maintains the uniformity of fiber diameter, thereby ensuring a balance between radiative cooling function (high reflectivity and emissivity) and thermal insulation performance.

[0031] Furthermore, the purpose of vacuum degassing is to remove air from the spinning solution. If there are air bubbles during electrospinning, the resulting fibers will be discontinuous, affecting the fiber morphology and the final properties of the material.

[0032] Furthermore, the spinning aid is mainly used to improve the viscosity of the phase change material so that it can form fibers under the action of electrostatic force. The main reason is that the phase change material itself is as thin as water and has almost no viscosity, so it cannot form fibers. If the phase change material is used directly as the core layer solution, a stable core-shell structure cannot be formed, and the shell may even break, which will lead to a decrease in the radiation cooling performance of the fiber membrane.

[0033] The present invention also provides a core-shell structured bifunctional radiation-cooled fiber membrane prepared by the above preparation method, with a core layer diameter of 232 nm - 786 nm. This core layer diameter ensures that as much phase change material as possible is coated without reducing the visible light reflectance and mid-infrared emissivity of the fiber membrane, so that it has a larger enthalpy, making the fiber membrane more resistant to thermal shock in the face of sudden temperature drops and rapid temperature rises.

[0034] The present invention also provides the application of the above-mentioned core-shell structured dual-function radiation cooling fiber membrane in radiation cooling. When facing external drastic heating or cooling environments, temperature fluctuations can be actively regulated through the shell structure and core structure. Attached Figure Description

[0035] Figure 1 This is a scanned image of the core-shell structured bifunctional radiation-cooled fiber membrane of the present invention; Figure 2 This is an EDS image of the core-shell structured bifunctional radiation-cooled fiber membrane of the present invention; Figure 3 Transmission images of dual-functional radiation-cooled fiber membranes with different core-shell structures according to the present invention; Figure 4a The reflectance spectrum of the FPL0.8 fiber membrane of the present invention in the range of 0.25-2.5 μm is shown. Figure 4b The emissivity spectrum of the FPL0.8 fiber membrane of the present invention in the range of 2.5-20 μm is shown. Figure 4c The graphs show the weighted average reflectance (0.25-2.5 μm) and weighted average emissivity (2.5-20 μm) of the FPL0.8 fiber membrane of this invention. Figure 5 The DSC curves are shown for the first and 100th cycles of the core-shell structure bifunctional radiation-cooled fiber membrane of this invention. Figure 6 This invention demonstrates the radiation cooling performance of the core-shell structure dual-functional radiation-cooled fiber membrane under simulated conditions. Figure 7 This invention relates to the radiation cooling performance of a core-shell structured dual-function radiation-cooled fiber membrane in an outdoor environment. Detailed Implementation

[0036] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0037] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0038] The present invention will be further described in detail below with reference to embodiments: Example 1 Step 1: First, dissolve 10.2 g of 2,2'-bis(trifluoromethyl)diaminobiphenyl in 125.3 g of N,N-dimethylacetamide solution in an ice-water bath at 0 °C with a mechanical stirrer at 500 r / min. Simultaneously, purge the three-necked flask with argon gas until complete dissolution. Add 14.2 g of 4,4′-(hexafluoroisopropene)phthalic anhydride in eight batches, 10 min apart. After all additions are complete, continue stirring for 12 h, then add 16.8 g of acetic anhydride and 6.3 g of pyridine. Continue stirring at room temperature for 24 h to obtain a clear, viscous solution. Slowly pour the clear, viscous solution into a beaker containing 2 L of methanol solution, stirring rapidly with a glass rod during the process, to obtain a fibrous solid. Dry the solid in an oven at 80 °C to obtain a fibrous polymer. Take 5 g of dried fibrous solid and dissolve it in 20 g of N,N-dimethylformamide to obtain a transparent, viscous shell solution with a solid content of 20%, and refrigerate for later use. Dissolve 10 g of lauric acid and 1 g of N-methylpyrrolidone in 4 g of N,N-dimethylformamide at 50 °C to obtain a core solution.

[0039] Step 2: After vacuum degassing the shell and core solutions obtained in Step 1 at 30 °C, they were continuously spun by connecting them to an 18 / 25G coaxial spinning needle on an electrospinning machine using a flexible tube. The spinning voltage was 19 kV, the distance between the needle and the receiving platform was 13 cm, the shell feeding rate was 0.19 mL / h, the core feeding rate was 0.45 mL / h, and the spinning temperature was 30 °C. Under the action of electrostatic force, the composite solution was stretched, and the organic solvent rapidly evaporated to form composite nanofibers with a core-shell structure. The entire spinning process lasted for 12 h.

[0040] The fiber membrane prepared in this embodiment has a core layer diameter of 786 nm, a solar reflectance of 96.7%, a mid-infrared emissivity of 89.6%, and a thermal conductivity of 0.061 W·m. -1 ·K -1 The enthalpy value is 114.2 J / g.

[0041] Example 2 Step 1: First, dissolve 13.7 g of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene in 83.6 g of N,N-dimethylacetamide solution in an ice-water bath at 0 °C with a mechanical stirrer at 500 r / min. Simultaneously, argon gas is bubbled into the three-necked flask until complete dissolution. Then, add 7.2 g of 1,2,4,5-cyclohexanetetracarboxylic dianhydride in six batches, 15 min apart. After the additions are complete, continue stirring for 12 h, then add 15.5 g of acetic anhydride and 5.9 g of pyridine. Continue stirring at room temperature for 24 h to obtain a clear, viscous solution. Slowly pour the clear, viscous solution into a beaker containing 2 L of deionized water, stirring rapidly with a glass rod during the process, to obtain a fibrous solid. Dry the solid in an oven at 80 °C to obtain a fibrous polymer. Take 5 g of dried fibrous solid and dissolve it in 15 g of N,N-dimethylformamide to obtain a transparent, viscous shell solution with a solid content of 25%, and refrigerate for later use. Dissolve 12 g of lauric acid and 0.8 g of N-methylpyrrolidone in 5 g of N,N-dimethylformamide at 50 °C to obtain a core solution.

[0042] Step 2: After vacuum degassing the shell and core solutions obtained in Step 1 at 30 °C, they were continuously spun by connecting them to an 18 / 25G coaxial spinning needle on an electrospinning machine using a flexible tube. The spinning voltage was 20 kV, the distance between the needle and the receiving platform was 12 cm, the shell feeding rate was 0.15 mL / h, the core feeding rate was 0.51 mL / h, and the spinning temperature was 30 °C. Under the action of electrostatic force, the composite solution was stretched, and the organic solvent rapidly evaporated to form composite nanofibers with a core-shell structure. The entire spinning process lasted for 12 h.

[0043] The fiber membrane prepared in this embodiment has a core layer diameter of 613 nm, a solar reflectance of 94.3%, a mid-infrared emissivity of 88.6%, and a thermal conductivity of 0.078 W·m. -1 ·K -1 The enthalpy value is 101.5 J / g.

[0044] Example 3 Step 1: First, dissolve 16.5 g of 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane in 83.6 g of N,N-dimethylacetamide solution in an ice-water bath at 0 °C with a mechanical stirrer at 500 r / min. Simultaneously, argon gas is bubbled into the three-necked flask until complete dissolution. Then, add 8.7 g of 1,2,3,4-tetramethyl1,2,3,4-cyclobutanetetracarboxylic acid dianhydride in four batches, 15 min apart. After the additions are complete, continue stirring for 12 h, then add 16.3 g of acetic anhydride and 6.2 g of pyridine. Continue stirring at room temperature for 24 h to obtain a clear, viscous solution. Slowly pour the clear, viscous solution into a beaker containing 2 L of ethanol, stirring rapidly with a glass rod to obtain a fibrous solid. Dry in an oven at 80 °C to obtain a fibrous polymer. Take 5 g of dried fibrous solid and dissolve it in 15 g of N,N-dimethylformamide to obtain a transparent, viscous shell solution with a solid content of 25%, and refrigerate for later use. Dissolve 9 g of lauric acid and 0.75 g of N-methylpyrrolidone in 5 g of N,N-dimethylformamide at 50 °C to obtain a core solution.

[0045] Step 2: After vacuum degassing the shell and core solutions obtained in Step 1 at 30 °C, they were continuously spun by connecting them to an 18 / 25G coaxial spinning needle on an electrospinning machine using a flexible tube. The spinning voltage was 16 kV, the distance between the needle and the receiving platform was 10 cm, the shell feeding rate was 0.18 mL / h, the core feeding rate was 0.72 mL / h, and the spinning temperature was 30 °C. Under the action of electrostatic force, the composite solution was stretched, and the organic solvent rapidly evaporated to form composite nanofibers with a core-shell structure. The entire spinning process lasted for 12 h.

[0046] The fiber membrane prepared in this embodiment has a core layer diameter of 512 nm, a solar reflectance of 91.3%, a mid-infrared emissivity of 91.1%, and a thermal conductivity of 0.066 W·m. -1 ·K -1 The enthalpy value is 98.2 J / g.

[0047] Example 4 Step 1: First, dissolve 16.5 g of 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane in 83.6 g of N,N-dimethylacetamide solution in an ice-water bath at 0 °C with a mechanical stirrer at 500 r / min. Simultaneously, argon gas is bubbled into the three-necked flask until complete dissolution. Then, add 14.2 g of 4,4′-(hexafluoroisopropene)phthalic anhydride in eight batches, 10 min apart. After the additions are complete, continue stirring for 12 h, then add 18.2 g of acetic anhydride and 8.4 g of pyridine. Continue stirring at room temperature for 24 h to obtain a clear, viscous solution. Slowly pour the clear, viscous solution into a beaker containing 3 L of methanol, stirring rapidly with a glass rod during the process, to obtain a fibrous solid. Dry the solid in an oven at 80 °C to obtain a fibrous polymer. Take another 10 g of dried fibrous solid and dissolve it in 30 g of N,N-dimethylformamide to obtain a transparent, viscous shell solution with a solid content of 25%, and refrigerate it for later use. Then, dissolve 10 g of lauric acid and 1.5 g of N-methylpyrrolidone in 5.5 g of N,N-dimethylformamide at 50 °C to obtain a core solution.

[0048] Step 2: After vacuum degassing the shell and core solutions obtained in Step 1 at 30 °C, they were continuously spun by connecting them to an 18 / 25G coaxial spinning needle on an electrospinning machine using a flexible tube. The spinning voltage was 18 kV, the distance between the needle and the receiving platform was 12 cm, the shell feeding rate was 0.2 mL / h, the core feeding rate was 0.66 mL / h, and the spinning temperature was 30 °C. Under the action of electrostatic force, the composite solution was stretched, and the organic solvent rapidly evaporated to form composite nanofibers with a core-shell structure. The entire spinning process lasted for 12 h.

[0049] The fiber membrane prepared in this embodiment has a core layer diameter of 402 nm, a solar reflectance of 95.1%, a mid-infrared emissivity of 85.4%, and a thermal conductivity of 0.72 W·m. -1 ·K -1 The enthalpy value is 72.6 J / g.

[0050] Example 5 Step 1: First, dissolve 13.7 g of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene in 83.6 g of N,N-dimethylformamide solution in an ice-water bath at 5°C with a mechanical stirrer at 200 r / min. Simultaneously, argon gas is bubbled into the three-necked flask until complete dissolution. Then, add 7.2 g of 1,2,4,5-cyclohexanetetracarboxylic dianhydride in six batches, 15 min apart. After all additions are complete, continue stirring for 5 h, then add 15.5 g of acetic anhydride and 5.9 g of pyridine. Continue stirring at room temperature for another 15 h to obtain a clear, viscous solution. Slowly pour the clear, viscous solution into a beaker containing 2 L of deionized water, stirring rapidly with a glass rod to obtain a fibrous solid. Dry the solid in an oven at 60°C to obtain a fibrous polymer. Take 5 g of dried fibrous solid and dissolve it in 10 g of N,N-dimethylformamide to obtain a transparent, viscous shell solution with a solid content of 33%, and refrigerate for later use. Dissolve 25 g of polyethylene glycol and 0.8 g of polyvinylpyrrolidone in 5 g of N,N-dimethylformamide at 50 °C to obtain a core solution.

[0051] Step 2: After vacuum degassing the shell and core solutions obtained in Step 1 at 20 °C, they were continuously spun by connecting them to an 18 / 25G coaxial spinning needle on an electrospinning machine using a flexible tube. The spinning voltage was 5 kV, the distance between the needle and the receiving platform was 5 cm, the shell feeding rate was 0.15 mL / h, the core feeding rate was 1.25 mL / h, and the spinning temperature was 30 °C. Under the action of electrostatic force, the composite solution was stretched, and the organic solvent rapidly evaporated to form composite nanofibers with a core-shell structure. The entire spinning process lasted for 12 h.

[0052] The fiber membrane prepared in this embodiment has a core layer diameter of 754 nm, a solar reflectance of 95.3%, a mid-infrared emissivity of 88.2%, and a thermal conductivity of 0.055 W·m. -1 ·K -1 The enthalpy value is 103.9 J / g.

[0053] Example 6 Step 1: First, dissolve 13.7 g of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene in 83.6 g of N-methylpyrrolidone in an ice-water bath at 10 °C with a mechanical stirrer at 250 r / min. Simultaneously, argon gas is bubbled into the three-necked flask until complete dissolution. Then, add 7.2 g of 1,2,4,5-cyclohexanetetracarboxylic dianhydride in six batches, 15 min apart. After all additions are complete, continue stirring for 20 h, then add 15.5 g of acetic anhydride and 5.9 g of pyridine. Continue stirring at room temperature for 27 h to obtain a clear, viscous solution. Slowly pour the clear, viscous solution into a beaker containing 2 L of deionized water, stirring rapidly with a glass rod to obtain a fibrous solid. Dry the solid in an oven at 90 °C to obtain a fibrous polymer. Take 5 g of dried fibrous solid and dissolve it in 25 g of N,N-dimethylformamide to obtain a transparent, viscous shell solution with a solid content of 25%, and refrigerate it for later use. Dissolve 50 g of paraffin and 0.8 g of polyvinyl alcohol in 5 g of N,N-dimethylformamide at 50°C to obtain a core solution.

[0054] Step 2: After vacuum degassing the shell and core solutions obtained in Step 1 at 25 °C, they were continuously spun by connecting them to an 18 / 25G coaxial spinning needle on an electrospinning machine using a flexible tube. The spinning voltage was 12 kV, the distance between the needle and the receiving platform was 15 cm, the shell feeding rate was 0.15 mL / h, the core feeding rate was 2.0 mL / h, and the spinning temperature was 30 °C. Under the action of electrostatic force, the composite solution was stretched, and the organic solvent rapidly evaporated to form composite nanofibers with a core-shell structure. The entire spinning process lasted for 12 h.

[0055] The fiber membrane prepared in this embodiment has a core layer diameter of 766 nm, a solar reflectance of 94.8%, a mid-infrared emissivity of 88.6%, and a thermal conductivity of 0.073 W·m. -1 ·K -1 The enthalpy value is 112.9 J / g.

[0056] Example 7 Step 1: First, dissolve 13.7 g of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene in 83.6 g of N,N-dimethylformamide solution in an ice-water bath at 0 °C with a mechanical stirrer at 500 r / min. Simultaneously, argon gas is bubbled into the three-necked flask until complete dissolution. Then, add 7.2 g of 1,2,4,5-cyclohexanetetracarboxylic dianhydride in six batches, 15 min apart. After the additions are complete, continue stirring for 12 h, then add 15.5 g of acetic anhydride and 5.9 g of pyridine. Continue stirring at room temperature for 40 h to obtain a clear, viscous solution. Slowly pour the clear, viscous solution into a beaker containing 2 L of deionized water, stirring rapidly with a glass rod during the process, to obtain a fibrous solid. Dry the solid in an oven at 120 °C to obtain a fibrous polymer. Take 5 g of dried fibrous solid and dissolve it in 15 g of N,N-dimethylformamide to obtain a transparent, viscous shell solution with a solid content of 25%, and refrigerate it for later use. Dissolve 35 g of paraffin and 0.8 g of polyethylene oxide in 5 g of N,N-dimethylformamide at 50°C to obtain a core solution.

[0057] Step 2: After vacuum degassing the shell and core solutions obtained in Step 1 at 30 °C, they were continuously spun by connecting them to an 18 / 25G coaxial spinning needle on an electrospinning machine using a flexible tube. The spinning voltage was 20 kV, the distance between the needle and the receiving platform was 12 cm, the shell feeding rate was 0.15 mL / h, the core feeding rate was 0.51 mL / h, and the spinning temperature was 30 °C. Under the action of electrostatic force, the composite solution was stretched, and the organic solvent rapidly evaporated to form composite nanofibers with a core-shell structure. The entire spinning process lasted for 12 h.

[0058] The fiber membrane prepared in this embodiment has a core layer diameter of 698 nm, a solar reflectance of 95.7%, a mid-infrared emissivity of 83.1%, and a thermal conductivity of 0.058 W·m. -1 ·K -1 The enthalpy value is 112.4 J / g.

[0059] Comparative Example 1 Preparation method of ordinary polyimide fiber membrane: First, 18.4 g of 4,4'-diaminodiphenyl ether was dissolved in N,N-dimethylformamide solution with a mass of 4 times the total mass of monomers. Argon gas was introduced, and the mixture was stirred in a water bath at 0 °C under mechanical stirring at 300 r / min until completely dissolved. 20.2 g of pyromellitic anhydride was added in 6 batches, maintaining a molar ratio of dianhydride to diamine monomer of 1, with each addition 20 min apart. After the addition was complete, stirring was continued for 5 h to obtain a pale yellow, transparent, viscous electrospinning solution with a solid content of 20%, which was refrigerated for later use. The solution was connected to a 22G spinning needle on an electrospinning machine and continuously spun for 8 h to form polyamic acid nanofibers. The spinning voltage was 16 kV, the distance between the needle and the receiving platform was 8 cm, the feed rate was 0.23 mL / h, and the spinning temperature was 30 °C. Polyamic acid nanofibers were placed in a vacuum oven at 120 ℃ to remove organic solvents and moisture. Under an argon atmosphere, the temperature was first raised from 30 ℃ to 200 ℃ at a rate of 5 ℃ / min and held for 1 h, then raised to 320 ℃ and held for 1 h to achieve thermal imidization. Finally, the temperature was allowed to drop naturally to obtain a common polyimide fiber membrane.

[0060] Comparative Example 2 Preparation method of single-function radiative cooling material: First, 10.2 g of 2,2'-bis(trifluoromethyl)diaminobiphenyl was dissolved in 125.3 g of N,N-dimethylacetamide solution in an ice-water bath at 0 °C with a mechanical stirrer at 500 r / min. Argon gas was simultaneously introduced into a three-necked flask until complete dissolution. Then, 14.2 g of 4,4′-(hexafluoroisopropene)phthalic anhydride was added in eight batches, with 10 min intervals between each addition. After the additions were complete, stirring was continued for 12 h, followed by the addition of 16.8 g of acetic anhydride and 6.3 g of pyridine. Stirring was continued at room temperature for 24 h to obtain a transparent viscous solution. This transparent viscous solution was then slowly poured into a beaker containing 2 L of methanol solution, with rapid stirring using a glass rod to obtain a fibrous solid. The solid was dried in an oven at 80 °C to obtain a fibrous polymer. Five g of dried fibrous solid was dissolved in 20 g of N,N-dimethylformamide to obtain a transparent, viscous solution with a solid content of 20%, which was then refrigerated for later use. The resulting shell and core solutions were subjected to vacuum degassing at 30 °C, followed by continuous spinning using a 22G spinning needle on an electrospinning machine. The spinning voltage was 19 kV, the distance between the needle and the receiving platform was 13 cm, the feed rate was 0.19 mL / h, and the spinning temperature was 30 °C. Under the influence of electrostatic force, the solution was stretched, and the entire spinning process lasted 12 h. The organic solvent rapidly evaporated, forming a single-function radiative cooling material.

[0061] like Figure 1As shown, the core-shell nanofibers exhibit a uniform structure with no fiber breakage, demonstrating the stable and successful fabrication of the core-shell structure.

[0062] like Figure 2 As shown in the EDS image, the F element is uniformly dispersed on the surface of the fiber, proving the successful introduction of fluorine-containing functional groups.

[0063] like Figure 3 As shown, with the increase of the core layer push rate, the diameter of the core layer gradually increased from 232 nm to 786 nm. However, when the push ratio (FPL) of the shell layer to the core layer solution is greater than 1, it can be seen that the shell layer with FPL1 cannot completely cover the core layer, and the optimal process for the fiber membrane is FPL of 0.8.

[0064] like Figures 4a-4c The test results show the reflectivity of the FPL0.8 fiber membrane of this invention in the range of 0.25-2.5 μm and the emissivity in the range of 2.5-20 μm, demonstrating its superior optical performance and indirectly proving its radiative cooling properties. Figure 4a As shown, the FPL0.8 fiber membrane exhibits a reflectance >90% in the main energy region of the solar spectrum (0.3–1.5 μm), with a reflectance >90% in the visible light region (0.4–0.7 μm), preventing the material from heating up due to heat absorption. The reflectance in the near-infrared region (0.7–1.5 μm) is also >90%, blocking approximately 50% of the heat energy input from sunlight. This demonstrates that the FPL0.8 fiber membrane possesses high reflectivity to sunlight, effectively reducing heat absorption; Figure 4b As shown, the FPL0.8 fiber membrane exhibits an emissivity of up to 95% in the 8–13 μm wavelength band (the Earth's atmospheric transparency window), allowing the absorbed heat energy to penetrate the atmosphere as infrared radiation and dissipate directly into space. This demonstrates its efficient heat radiation capability, enabling passive radiative cooling. Figure 4c As shown, the blue and red bars represent the absorption or reflection percentages at different wavelengths, indicating that the FPL0.8 fiber membrane almost completely reflects (95%) the solar spectrum, allowing only minimal energy absorption or transmission. This is consistent with... Figure 4a The high reflectivity data is consistent.

[0065] like Figure 5 The test showed 100 cycles of thermal cycling. The DSC curves of the first and 100th cycles almost overlapped, proving that the enthalpy value did not decrease after multiple cycles. This demonstrates that the core-shell structure can effectively encapsulate the phase change material and prevent its leakage.

[0066] like Figure 6As shown, under the same simulated sunlight conditions, the ordinary polyimide fiber membrane (PI) prepared in Comparative Example 1 had a particularly short heating and cooling time and a very high equilibrium temperature of 55°C. However, the FPL0.8 fiber membrane prepared in this invention firstly heated up very slowly and required a longer time to reach the equilibrium temperature. Secondly, the final equilibrium temperature was about 7°C lower than that of PI. Furthermore, after removing the simulated light source, the temperature of PI dropped quickly, but the temperature of FPL dropped at a very slow rate.

[0067] The fiber membrane of FPL0.8 of this invention and the single-function radiative cooling material of Comparative Example 2 were shielded from sunlight, while the control group (without any substance) was exposed to direct sunlight. The temperature changes of the fiber membrane of FPL0.8, the single-function radiative cooling material, and the control group were then observed, leading to the following conclusions: Figure 7 As shown, the yellow background represents sunlight intensity. With increasing sunlight intensity, the temperature of the FPL0.8 fiber membrane of this invention rises more slowly. However, around 10:10, the weather changes drastically, and sunlight intensity drops sharply. The temperature of the blank group and the single-function radiative cooling material drops rapidly, exceeding 15°C. Such a temperature difference would be extremely unfriendly to both humans and equipment. However, the temperature difference of the FPL0.8 fiber membrane of this invention is less than 4°C. Therefore, the fiber membrane prepared by this invention can effectively resist thermal shock.

[0068] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a core-shell structured bifunctional radiative cooling fiber membrane, characterized in that, Includes the following steps: 1) A dianhydride monomer and a trifluoromethyldiamine monomer are dissolved in an organic solvent and reacted to obtain polyamic acid. A dehydrating agent and a catalyst are added to obtain a mixed solution. The mixed solution is added to a non-solvent to obtain a fibrous polymer. After drying, a shell polymer, polyimide, is obtained. The mass ratio of the dianhydride and the trifluoromethyldiamine monomer to the organic solvent is 1:(3-5), and the volume ratio of the mixed solution to the non-solvent is >1:

10. The non-solvent includes one of deionized water, methanol, and ethanol. 2) Dissolve polyimide in an organic solvent to prepare an electrospinning shell solution, wherein the mass ratio of polyimide to organic solvent is 1:(2-5); dissolve a phase change material in an organic solvent to prepare an electrospinning core solution, wherein the mass ratio of phase change material to organic solvent is (5-10):1; wherein the phase change material includes one of polyethylene glycol, lauric acid, and paraffin wax; 3) Using coaxial electrospinning technology, the shell and core solutions of the electrospinning are stretched at a voltage of 10-25kV to obtain a core-shell structured bifunctional radiation-cooled fiber membrane.

2. The method for preparing a core-shell structured bifunctional radiation-cooled fiber membrane according to claim 1, characterized in that, In step 1), the molar ratio of the dianhydride to the trifluoromethyldiamine monomer is 0.8-1.

2. The dianhydride monomer includes one of 4,4′-(hexafluoroisopropene)phthalic anhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and 1,2,3,4-tetramethyl1,2,3,4-cyclobutanetetracarboxylic dianhydride. The trifluoromethyldiamine monomer includes one of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane, and 2,2'-bis(trifluoromethyl)diaminobiphenyl.

3. The method for preparing a core-shell structured bifunctional radiation-cooled fiber membrane according to claim 1, characterized in that, In step 1), the volume ratio of the dehydrating agent to the catalyst is 1:3, the dehydrating agent is acetic anhydride, and the catalyst is a pyridine solution.

4. The method for preparing a core-shell structured bifunctional radiation-cooled fiber membrane according to claim 1, characterized in that, In steps 1) and 2), the organic solvent includes one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

5. The method for preparing a core-shell structured bifunctional radiation-cooled fiber membrane according to claim 1, characterized in that, In step 3), the distance between the needle and the receiving platform in the coaxial electrospinning technology is 5~15 cm, the feeding rate is 0.5~2 mL / h, and the spinning temperature is 30~50 ℃.

6. The method for preparing a core-shell structured bifunctional radiation-cooled fiber membrane according to claim 1, characterized in that, In step 1), the mixed solution of dianhydride monomer, trifluoromethyldiamine monomer and organic solvent is reacted in a water bath at 0-10 ℃ for 5-20 h with mechanical stirring at 200-500 r / min. After adding dehydrating agent and catalyst, the reaction is carried out at room temperature for 15-40 h. The drying temperature is 60-120℃.

7. The method for preparing a core-shell structured bifunctional radiation-cooled fiber membrane according to claim 1, characterized in that, In step 2), the phase change material and the spinning aid are dissolved in an organic solvent to prepare an electrospinning core layer solution. The mass ratio of the phase change material to the spinning aid is (5-15):

1. The spinning aid includes one of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene oxide, and N-methylpyrrolidone.

8. The method for preparing a core-shell structured bifunctional radiation-cooled fiber membrane according to claim 1, characterized in that, In step 3), the electrospinning shell solution and core solution are subjected to vacuum degassing treatment at 20~30 ℃, and then the electrospinning shell solution and core solution are drawn using coaxial electrospinning technology.

9. A core-shell structured bifunctional radiation-cooled fiber membrane prepared by the method for preparing a core-shell structured bifunctional radiation-cooled fiber membrane according to any one of claims 1 to 8, characterized in that, The bifunctional radiation-cooled fiber membrane has a core-shell structure with a core diameter of 232 nm - 786 nm.

10. The application of the core-shell structured bifunctional radiation-cooling fiber membrane of claim 9 in radiation cooling.

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