Janus flexible radiative cooling material and method of making the same

Abstract

The application discloses a Janus type flexible radiation refrigeration material and a preparation method thereof, wherein a modified radiation refrigeration layer and a functional layer are arranged on the upper and lower surfaces of a base fiber layer with specific functional groups, the base fiber layer can be esterified or silylated and bonded with the amino silane modified radiation refrigeration layer, and can also be esterified with the carboxyl modified functional layer, so that the interfaces of the three layers are chemically bonded, the bonding force of the interfaces is effectively improved, the dynamic stability is effectively improved on the basis of guaranteeing the optical performance and mechanical flexibility, and the application of the radiation refrigeration material is promoted.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible functional materials, in particular to a Janus-type flexible radiative cooling material and a preparation method thereof. BACKGROUND

[0002] With the intensification of global warming and the increasingly severe energy crisis, developing efficient and energy-saving refrigeration technology has become a key research direction in the fields of material science and energy engineering. Traditional refrigeration technology relies on compressor refrigeration, which has high energy consumption and requires the use of greenhouse gas refrigerants, exacerbating energy consumption and environmental pollution. In this context, radiative cooling technology has received widespread attention due to its zero-energy consumption and pollution-free characteristics. This technology uses the high emissivity of the material surface in the 8-13 μm atmospheric transparent window band to directly dissipate heat in the form of infrared radiation to the low-temperature outer space, thereby achieving passive cooling. However, existing radiative cooling materials still face many technical bottlenecks: first, most materials rely on rigid substrates (such as metals, ceramics) or complex multi-layer structures (such as photonic crystals, metamaterials), which are difficult to meet the demand for flexibility and conformability of emerging fields such as flexible electronics and wearable devices; second, traditional preparation processes (such as photolithography, vapor deposition) are costly and inefficient, making it difficult to achieve large-scale production; third, single-function design cannot balance radiative cooling performance and environmental adaptability, for example, the back of the material is easily disturbed by external heat sources, reducing the cooling efficiency.

[0003] In recent years, research and development of flexible radiative cooling materials have made some progress, such as porous polymer films based on electrospinning, nanofiber composite fabrics, etc., but their cooling performance (usually less than 100 W / m 2 ) and mechanical strength are still difficult to balance. In addition, conventional single-sided radiative cooling materials are easily affected by ground heat radiation, air convection, and other factors in outdoor applications, resulting in a decrease in effective cooling power. For this reason, researchers have proposed a Janus-type (double-sided heterogeneous) structure design concept, which differentially regulates different waveband spectra on the surface of the material to achieve directional management of heat. For example, the front side is designed as a high infrared emission layer to enhance radiative cooling, and the back side is designed as a high solar reflectance layer to reduce external heat absorption. However, existing Janus materials mostly use coating, lamination, and other processes to combine, relying on physical adsorption or external aids (such as plasma treatment, silane coupling agent) at the interface, with weak interfacial bonding and limited flexibility. In particular, in dynamic bending or stretching scenarios, the interfacial bonding between the functional layer and the substrate is weak, which easily leads to interlayer peeling, resulting in a decrease in optical and electrical performance.

[0004] As a high-efficiency process for preparing nanofibers, centrifugal spinning technology has the advantages of controllable fiber diameter (50-500 nm) and fast production rate (more than 10 times higher than electrospinning), and can construct a three-dimensional network structure with high porosity, which is beneficial to enhancing the efficiency of infrared radiation and heat conduction. Spray technology can achieve precise loading of functional components (such as reflective particles and hydrophobic agents) through layer-by-layer deposition, and endow the material surface with multifunctional properties. The combination of the two processes is expected to break through the bottleneck of the difficulty in optimizing structure and function in the preparation of traditional Janus materials, while meeting the needs of flexibility, high refrigeration efficiency and environmental stability. In addition, flexible radiative cooling materials have broad application prospects in the fields of building energy saving (such as intelligent window film), personal thermal management (such as cooling clothing), and thermal protection of electronic devices, but their commercialization process is limited by material cost and process complexity.

[0005] Therefore, developing a Janus-type flexible radiative cooling material based on a centrifugal spinning-spray composite process not only can promote the practical breakthrough of radiative cooling technology, but also will provide an innovative solution for green energy and sustainable development. SUMMARY

[0006] The present application provides a Janus-type flexible radiative cooling material to solve the defects of the prior art radiative cooling material that the optical performance is insufficient and the mechanical flexibility is insufficient, which limits the large-scale application.

[0007] Therefore, the scheme of the present application is as follows:

[0008] The first aspect of the present application is to provide a Janus-type flexible radiative cooling material, which comprises a radiative cooling layer, a base fiber layer and a functional layer stacked from top to bottom; wherein:

[0009] The radiative cooling layer is obtained by modifying inorganic nanoparticles with amino silane;

[0010] The base fiber layer is obtained by centrifugal spinning of a polymer and phase change microcapsules; the polymer is selected from one or more of polyvinyl alcohol, polylactic acid, polyacrylonitrile, polyvinylidene fluoride, polymethyl acrylate or polydimethyl siloxane;

[0011] The functional layer is carboxylated MXene / Fe3O4.

[0012] Further, the inorganic particles are selected from one or more of SiO2, TiO2, BN, Al2O3 and CaSO3.

[0013] Further, the amino silane modification includes modifying the surface of the inorganic nanoparticles with amino (-NH2) and alkoxysilane (-Si (OR)3) functional groups using a modifier, preferably an amino silane coupling agent.

[0014] Furthermore, the phase change microcapsules are paraffin@SiO2 or polyethylene glycol / cellulose phase change fibers.

[0015] Furthermore, the mass ratio of the polymer to the phase change microcapsules is (3-5):1.

[0016] Furthermore, the fiber diameter of the base fiber layer is 5-200 nm, and the porosity is ≥80%.

[0017] Furthermore, the thickness of the functional layer is 10-50 μm.

[0018] Furthermore, the mass ratio of MXene to Fe3O4 in the functional layer is (1-5):1.

[0019] Furthermore, the MXene / Fe3O4 carboxylation modification process uses acid anhydrides.

[0020] A second aspect of the present invention is to provide a method for preparing the Janus-type flexible radiation cooling material described in the first aspect, comprising the steps of preparing a base fiber layer by centrifugal spinning, and spraying a functional layer and a radiation cooling layer onto both sides of the base fiber layer respectively, followed by curing.

[0021] Furthermore, during the functional layer spraying process:

[0022] The spraying pressure is 0.2-0.5 MPa, and the curing temperature is 50-80℃; and / or, the spraying process uses a carboxylated modified MXene / Fe3O4 dispersion with a mass concentration of 5-20t.

[0023] Furthermore, the centrifugal spinning process rotates at a speed of 8000-12000 rpm; and / or, the centrifugal spinning process uses a dual-nozzle design with a nozzle orifice diameter of 0.3-0.8 mm.

[0024] A third aspect of the invention is to provide the use of the Janus-type flexible radiative cooling material described in the first aspect in the preparation of wearable devices, building energy-saving films, or camouflage and protective products.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The Janus-type flexible radiation cooling material provided by this invention has modified radiation cooling layers and functional layers on the upper and lower surfaces of a base fiber layer with specific functional groups. The base fiber layer can undergo esterification or silanization bonding with the aminosilane-modified radiation cooling layer, and can also undergo esterification reaction with the carboxyl-modified functional layer, thereby chemically bonding the three-layer material interface, effectively improving the interfacial bonding force. While ensuring optical performance and mechanical flexibility, it effectively improves dynamic stability and promotes the application of radiation cooling materials.

[0027] The Janus-type flexible radiative cooling material provided by this invention is prepared by centrifugal spinning of polymer and phase change microcapsules. The polymer surface is rich in hydroxyl or carboxyl groups, which complement the functional groups of the functional layer materials on both sides. During the spraying and curing process, a strong chemical bonding interface is formed in situ, without the need for additional plasma treatment or silane coupling agents, making it suitable for industrial-scale production. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the Janus-type flexible radiative cooling material structure described in this invention.

[0029] Figure 2 This is a schematic diagram of the porous network structure of the substrate fiber layer under an electron microscope according to the present invention. Detailed Implementation

[0030] The technical solution of the present invention will now be clearly and completely described in conjunction with preferred embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] In one embodiment, such as Figure 1 As shown, a Janus-type flexible radiative cooling material is provided, comprising a radiative cooling layer 1, a substrate fiber layer 2, and a functional layer 3 stacked from top to bottom; wherein:

[0032] The radiation cooling layer is obtained by modifying inorganic nanoparticles with aminosilane;

[0033] The base fiber layer is obtained by centrifugal spinning of a polymer and phase change microcapsules; the polymer is selected from one or more of polyvinyl alcohol (PVA), polylactic acid (PLA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polymethyl acrylate (PMMA), and polydimethoxysilane (PDMS).

[0034] The functional layer is carboxylated modified MXene / Fe3O4.

[0035] In the above embodiments, modified radiation cooling layers and functional layers are disposed on the upper and lower surfaces of a base fiber layer containing specific functional groups. The base fiber layer can undergo esterification or silanization bonding with the aminosilane-modified radiation cooling layer and can also undergo esterification reaction with the carboxyl-modified functional layer, thereby chemically bonding the three-layer material interface, effectively improving the interfacial bonding force, and effectively improving dynamic stability while ensuring optical performance and mechanical flexibility, thus promoting the application of radiation cooling materials.

[0036] In the above embodiments, the solar reflectivity of the radiation cooling layer 1 is ≥95%, and the infrared emissivity is ≥90%; the substrate fiber layer 2 is a phase change substrate layer, and the functional layer 3 is an electromagnetic shielding layer with an electromagnetic shielding efficiency ≥85dB and a sheet resistance ≤10Ω / sq. The radiation cooling layer 1 is primarily responsible for dissipating heat in the form of infrared radiation, achieving passive cooling; the phase change substrate layer buffers temperature changes and provides flexibility; and the electromagnetic shielding layer protects the interior from electromagnetic interference. This achieves multifunctional coupling of radiation cooling, Joule heating, and electromagnetic shielding.

[0037] In the above embodiments, the radiation cooling layer 1 and the functional layer 3 are chemically bonded by spraying onto the upper and lower surfaces of the substrate fiber layer.

[0038] In some embodiments, the base fiber layer, prepared by centrifugal spinning of polymers and phase change microcapsules, has a fiber diameter ranging from 50 to 200 nm and a porosity ≥80%. Figure 2 The polymer and phase change microcapsules form a "candied hawthorn stick" composite structure, improving the material's flexural strength (tensile strength ≥10 MPa). Combined with a hydrophilic-hydrophobic Janus wettability design, it achieves one-way moisture wicking (water evaporation rate 0.31 g / h), enhancing wearing comfort.

[0039] In a preferred embodiment, the inorganic particles are selected from one or more of SiO2, TiO2, BN, Al2O3, and CaSO3.

[0040] In a preferred embodiment, the aminosilane modification includes modifying the surface of inorganic nanoparticles with amino (-NH2) and alkoxysilane (-Si(OR)3) functional groups using a modifier. Preferably, the modifier is an aminosilane coupling agent, such as KH-550, KH-602, KH-551, etc.

[0041] In a preferred embodiment, the phase change microcapsules are, but are not limited to, a paraffin@silica core-shell structure, with a phase change enthalpy ≥180 J / g, a particle size of 1-5 μm, and polyethylene glycol (PEG) / cellulose phase change fibers (latent heat ≥180 J / g, phase change temperature 28-32℃). The addition of the phase change microcapsules can absorb / release heat through solid-liquid phase change, thus balancing ambient temperature fluctuations.

[0042] In a preferred embodiment, the mass ratio of the hydroxyl-containing polymer to the phase change microcapsule is (3-5):1. The mass ratio of MXene to Fe3O4 in the functional layer is (1-5):1.

[0043] In a preferred embodiment, the MXene / Fe3O4 carboxylation modification process uses an anhydride of an organic dicarboxylic acid to achieve surface grafting of carboxylic acid groups, such as using common anhydrides like succinic anhydride and maleic anhydride.

[0044] The material prepared by this invention can achieve passive cooling of 10℃ (solar irradiance ≥900W / m²) and low-voltage driven heating of 1.5V (response time ≤130 seconds) in wearable devices, while meeting the requirements for bonding to complex curved surfaces (performance degradation ≤15% after 1000 cycles of bending). It is suitable for smart clothing, building energy-saving films and infrared camouflage protection.

[0045] In another embodiment, a method for preparing the above-mentioned Janus-type flexible radiation cooling material is provided, including the steps of preparing a base fiber layer by centrifugal spinning, and spraying a functional layer and a radiation cooling layer onto both sides of the base fiber layer and then curing it.

[0046] In a preferred embodiment, during the functional layer spraying process, the spraying pressure is 0.2-0.5 MPa and the curing temperature is 50-80℃; the spraying process uses a carboxylated modified MXene / Fe3O4 dispersion with a mass concentration of 5-20t.

[0047] In a preferred embodiment, the radiation cooling layer is first made into a composite sol, which is then sprayed and dried to form a porous radiation cooling layer.

[0048] In the above embodiments, during the spraying and curing process, the functional groups on the surface of the base fiber layer (such as the hydroxyl groups of PVA and the carboxyl groups of PLA) form a covalent bond interface (such as ester bonds) with the functional groups modified in the functional layer; after the inorganic nanoparticles of the radiation cooling layer are modified by aminosilanization, they undergo silanization with the functional groups on the surface of the base fiber layer (such as Si-OC bonds), achieving a peel strength ≥5.2 N / cm between the base fiber layer and the upper and lower layers.

[0049] In a preferred embodiment, the centrifugal spinning process rotates at 8000-12000 rpm and uses a dual-nozzle design with nozzle orifice diameters of 0.3-0.8 mm to improve efficiency and ensure fiber diameter and porosity.

[0050] The above methods can achieve the following effects with Janus-type flexible materials:

[0051] 1. Weather resistance: After aging at 85℃ / 85% humidity for 1000 hours, the interfacial peel strength retention rate is ≥90%, which is 5 times higher than that of traditional processes;

[0052] 2. Mechanical properties: interlaminar peel strength 5.2 N / cm, performance degradation ≤3% after 5000 bending cycles (radius of curvature 2 mm);

[0053] 3. After the material was applied to the south-facing windows of a 30-story residential building, the indoor temperature in the summer afternoons decreased by 4.2℃, the air conditioning usage time decreased by 2.5 hours / day, the average monthly electricity saving was 120 kWh, and the energy saving rate was 28%.

[0054] 4. When applied to the surface coating material of server racks, the electromagnetic shielding efficiency at 10 GHz is 88.5 dB, the equipment failure rate is reduced by 60%, the heat dissipation energy consumption is reduced by 22%, and the annual maintenance cost is reduced by 850,000 yuan per 10,000 square meters.

[0055] 5. After soaking in 15% NaCl solution for 30 days, the sheet resistance change of the MXene / Fe3O4 layer is ≤5%, which is suitable for electromagnetic shielding layers of underwater robots and can replace traditional titanium alloy shielding covers with a weight reduction of 70%.

[0056] The following are preferred embodiments of the present invention. The specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Unless otherwise specified, all materials used are commercially available, and all experimental methods used are those skilled in the art.

[0057] Example 1

[0058] The preparation method of Janus-type flexible radiative cooling material includes the following steps:

[0059] 1) Carboxylation modification of MXene / Fe3O4 dispersion: 5g MXene / Fe3O4 and 10g succinic anhydride were dispersed in 100mL DMF and mixed. The mixture was stirred at 60℃ for 24h. After centrifugation and washing, it was washed 3 times with DMF to obtain carboxylated MXene / Fe3O4 (the -COOH grafting rate was measured to be 1.5 mmol / g).

[0060] 2) Aminosilane modification of inorganic nanoparticles: SiO2 / TiO2 (molar ratio 1:1) nanoparticles were dispersed in an ethanol-water (volume ratio 4:1) mixture, KH-550 (1.5% of particle mass) was added, and the mixture was refluxed at 80℃ for 4 h. After drying, aminosilane-modified particles (-NH2 grafting density 0.9 μmol / m³) were obtained. 2 );

[0061] 3) PVA was dissolved in deionized water (concentration 8 wt.%), and paraffin@silica core-shell microcapsules (phase change enthalpy 185 J / g, particle size 2 μm, mass ratio 4:1) were added. The mixture was then centrifuged and spun (speed 10000 rpm) to obtain a fiber membrane with a thickness of 200 μm.

[0062] A schematic diagram of the porous network structure of the substrate fiber layer under an electron microscope is shown below. Figure 2 As shown, the fibers exhibit a randomly interwoven network structure with diameters ranging from 50 to 200 nm. The fibers are arranged without orientation, forming a porous network structure with a porosity ≥80%.

[0063] 4) A carboxylated MXene / Fe3O4 dispersion (15 wt.%, spraying pressure 0.3 MPa) was sprayed onto side A of the fiber membrane and cured at 80℃ to form a 10 μm thick conductive shielding layer. Modified titanium dioxide (TiO2), silicon dioxide (SiO2), and polydimethylsiloxane (PDMS) were mixed at a mass ratio of 1:1, and an appropriate amount of n-hexane was added as a solvent. The mixture was stirred evenly to form an aminosilanized SiO2-TiO2 sol. Then, the SiO2-TiO2 sol (molar ratio 1:1) was sprayed onto side B of the fiber membrane. After drying, a porous radiation layer was formed, ultimately yielding the Janus-type flexible radiative cooling material.

[0064] Example 2

[0065] The preparation method of Janus-type flexible radiative cooling material includes the following steps:

[0066] 1) Carboxylation modification of MXene / Fe3O4 dispersion: 8g of MXene / Fe3O4 (mass ratio 5:1) and 12g of maleic anhydride were dispersed in 150mL of N-methylpyrrolidone, stirred at 50℃ for 20h, centrifuged and washed three times with ethanol to obtain carboxylated MXene / Fe3O4 (-COOH grafting rate 1.2mmol / g).

[0067] 2) Aminosilane modification of inorganic nanoparticles: BN / Al2O3 (mass ratio 3:2) nanoparticles were dispersed in an isopropanol-water (volume ratio 3:1) mixture, KH-602 (2% of particle mass) was added, refluxed at 70℃ for 5 h, and dried to obtain aminosilane modified particles (-NH2 grafting density 0.8 μmol / m²).

[0068] 3) Dissolve polylactic acid (PLA) in dichloromethane (concentration 10wt.%), add polyethylene glycol / cellulose phase change fiber (latent heat 182J / g, phase change temperature 30℃, mass ratio 3:1), and centrifuge spinning (speed 8000rpm, dual nozzles, pore size 0.5mm) to obtain a fiber membrane with a thickness of 180μm (fiber diameter 80-150nm, porosity 82%).

[0069] 4) A carboxylated MXene / Fe3O4 dispersion (20 wt.% mass concentration, 0.2 MPa spraying pressure) is sprayed onto side A of the fiber membrane and cured at 50°C to form a 30 μm thick functional layer; a BN / Al2O3 modified sol (mixed with PDMS at a mass ratio of 2:1, with cyclohexane as the solvent) is sprayed onto side B of the fiber membrane and dried to form a radiation cooling layer, thus obtaining the Janus-type flexible radiation cooling material.

[0070] Example 3

[0071] The preparation method of Janus-type flexible radiative cooling material includes the following steps:

[0072] 1) Carboxylation modification of MXene / Fe3O4 dispersion: 6g MXene / Fe3O4 (mass ratio 3:1) and 8g phthalic anhydride were dispersed in 120mL DMSO, stirred at 65℃ for 22h, centrifuged and washed three times with acetone to obtain carboxylated MXene / Fe3O4 (-COOH grafting rate 1.6mmol / g).

[0073] 2) Aminosilane modification of inorganic nanoparticles: CaSO3 / SiO2 (mass ratio 1:2) nanoparticles were dispersed in an ethanol-water (volume ratio 5:1) mixture, KH-551 (1% of particle mass) was added, refluxed at 85℃ for 3 h, and dried to obtain aminosilane modified particles (-NH2 grafting density 1.0 μmol / m²).

[0074] 3) Polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) (mass ratio 1:1) were dissolved in DMF (total concentration 12wt.%), and paraffin@SiO2 microcapsules (phase change enthalpy 180J / g, particle size 3μm, mass ratio 5:1) were added. The mixture was then centrifuged (12000rpm, dual nozzles, pore size 0.3mm) to obtain a fiber membrane with a thickness of 220μm (fiber diameter 50-180nm, porosity 85%).

[0075] 4) A carboxylated MXene / Fe3O4 dispersion (5 wt.% concentration, 0.5 MPa spraying pressure) is sprayed onto side A of the fiber membrane and cured at 60°C to form a 50 μm thick functional layer; a CaSO3 / SiO2 modified sol (mixed with polymethyl methacrylate at a mass ratio of 1:1, with ethyl acetate as the solvent) is sprayed onto side B of the fiber membrane and dried to form a radiation cooling layer, thus obtaining the Janus-type flexible radiation cooling material.

[0076] Example 4

[0077] The preparation method of Janus-type flexible radiative cooling material includes the following steps:

[0078] 1) Carboxylation modification of MXene / Fe3O4 dispersion: 4g MXene / Fe3O4 (mass ratio 1:1) and 9g succinic anhydride were dispersed in 120mL DMF, stirred at 65℃ for 22h, centrifuged and washed, and then washed 3 times with DMF to obtain carboxylated MXene / Fe3O4 (-COOH grafting rate 1.3mmol / g).

[0079] 2) Aminosilane modification of inorganic nanoparticles: TiO2 / BN (mass ratio 2:1) nanoparticles were dispersed in an ethanol-water (volume ratio 4:1) mixture, KH-550 (1.8% of particle mass) was added, refluxed at 75℃ for 3.5 h, and dried to obtain aminosilane modified particles (-NH2 grafting density 0.95 μmol / m²).

[0080] 3) Dissolve polydimethoxysilane (PDMS) in n-hexane (concentration 9 wt.%), add polyethylene glycol / cellulose phase change fiber (latent heat 183 J / g, mass ratio 4:1), and centrifuge spinning (speed 11000 rpm, dual nozzles, pore size 0.8 mm) to obtain a fiber membrane with a thickness of 210 μm (fiber diameter 60-200 nm, porosity 81%).

[0081] 4) A carboxylated MXene / Fe3O4 dispersion (10 wt.% concentration, 0.4 MPa spraying pressure) is sprayed onto side A of the fiber membrane and cured at 70°C to form a 20 μm thick functional layer; a TiO2 / BN modified sol (mixed with PDMS at a mass ratio of 1.5:1, with n-hexane as the solvent) is sprayed onto side B of the fiber membrane and dried to form a radiation cooling layer, thus obtaining the Janus-type flexible radiation cooling material.

[0082] Comparative Example 1

[0083] The difference from Example 1 is that the inorganic nanoparticles in the radiation cooling layer were not modified with aminosilane (untreated SiO2 / TiO2 was used directly). The remaining steps and parameters are the same.

[0084] Comparative Example 2

[0085] The difference from Example 1 is that the MXene / Fe3O4 in the functional layer was not modified by carboxylation (untreated MXene / Fe3O4 was used directly). The remaining steps and parameters are the same.

[0086] Comparative Example 3

[0087] The difference from Example 1 is that no phase change microcapsules were added to the base fiber layer (only PVA was used for centrifugal spinning). The remaining steps and parameters are the same.

[0088] Comparative Example 4

[0089] The difference from Example 1 is that the base fiber layer was prepared by electrospinning (2000 rpm, with the other spinning parameters being the same). The remaining steps and parameters are the same.

[0090] Comparative Example 5

[0091] The difference from Example 1 is that the functional layer is pure MXene (without Fe3O4) and has not undergone carboxylation modification. The remaining steps and parameters are the same.

[0092] Comparative Example 6

[0093] The difference from Example 1 is that the radiation cooling layer, functional layer, and substrate fiber layer are bonded together by thermoforming (without chemical bonding). The remaining steps and parameters are the same.

[0094] Test case

[0095] Performance tests were conducted on the above embodiments and comparative examples, including: solar reflectivity, infrared emissivity, interlayer peel strength, tensile strength, performance degradation rate after bending, electromagnetic shielding efficiency, and weather resistance.

[0096] Test standards (methods):

[0097] 1. Solar reflectance: measured using an ultraviolet-visible-near-infrared spectrophotometer (300-2500nm band);

[0098] 2. Infrared emissivity: Measured using a Fourier transform infrared spectrometer (8-13μm band);

[0099] 3. Interlayer peel strength: Tested using a universal testing machine according to GB / T 2790-1995 standard;

[0100] 4. Tensile strength: Tested using a universal testing machine in accordance with GB / T 1040.3-2006 standard;

[0101] 5. Performance degradation rate after 5000 bends: The material was cyclically bent 5000 times with a curvature radius of 2mm, and the degradation rate of solar reflectivity and infrared emissivity before and after bending was tested.

[0102] 6. Electromagnetic shielding efficiency: tested using a vector network analyzer (10GHz band);

[0103] 7. Weather resistance: After aging for 1000 hours at 85℃ / 85% humidity, the interlayer peel strength retention rate is tested.

[0104] The results are shown in Table 1.

[0105] Table 1:

[0106]

[0107] As can be seen from the test results in Table 1, Examples 1-4 exhibit excellent performance in all aspects. In terms of solar reflectivity and infrared emissivity, all remain at 91% or higher, ensuring good radiative cooling effect; the interlayer peel strength all reach above 5.2 N / cm, indicating strong chemical bonding and interfacial adhesion between the three layers; the tensile strength is 11-12 MPa, demonstrating good mechanical properties; after 5000 bending cycles, the performance degradation rate is only 2%-3%, showing excellent dynamic stability; the electromagnetic shielding efficiency is not less than 87 dB, effectively playing a shielding role; after aging for 1000 hours at 85℃ / 85% humidity, the weather resistance retention rate is still above 90%, demonstrating strong environmental adaptability. This fully demonstrates that the Janus-type flexible radiative cooling material prepared in this invention, through reasonable material selection, modification treatment, and preparation process, achieves a good combination of optical performance, mechanical properties, dynamic stability, and functional characteristics.

[0108] Comparative Example 1: Because the inorganic nanoparticles in the radiation cooling layer were not modified with aminosilane, they could not form effective chemical bonds with the substrate fiber layer. Interlayer bonding relied mainly on physical adsorption, resulting in a significant decrease in interlayer peel strength to 2.1 N / cm. After 5000 bending cycles, the performance degradation rate reached 15%, and the weather resistance retention rate was only 60%, significantly lower than in Example 1. This indicates that aminosilane modification is crucial for improving the interfacial bonding, dynamic stability, and weather resistance between the radiation cooling layer and the substrate fiber layer.

[0109] Comparative Example 2: The MXene / Fe3O4 functional layer was not carboxylated and could not undergo effective esterification with the substrate fiber layer, resulting in weak interfacial adhesion and an interlayer peel strength of 2.3 N / cm. After 5000 bending cycles, the performance degradation rate reached 18%, and the weather resistance retention rate was 58%, which is inferior to that of Example 1. Therefore, carboxylation modification is crucial for ensuring a strong bond between the functional layer and the substrate fiber layer and maintaining the overall stability of the material's performance.

[0110] Comparative Example 3: Without phase change microcapsules added to the base fiber layer, centrifugal spinning using only PVA resulted in a decrease in tensile strength to 8 MPa and a significant decline in mechanical properties. This is because the addition of phase change microcapsules can form a "candied hawthorn stick" composite structure with the polymer, improving the material's bending resistance and mechanical strength. The lack of phase change microcapsules weakens this reinforcing effect, failing to meet the material's requirements for flexibility and mechanical properties.

[0111] Comparative Example 4: The base fiber layer was prepared by electrospinning instead of centrifugal spinning. The uneven fiber diameter led to reduced porosity, and the infrared emissivity decreased to 90%, lower than the 92% in Example 1. Simultaneously, the interlayer peel strength was 3.5 N / cm, the performance degradation rate after 5000 bends was 12%, and the weather resistance retention rate was 75%, all lower than in Example 1. This demonstrates the advantages of centrifugal spinning technology in preparing high-porosity, uniform fiber structures, thus positively impacting the optical properties and interfacial bonding of the material.

[0112] Comparative Example 5: The functional layer was pure MXene without carboxylation modification, resulting in a significant drop in electromagnetic shielding efficiency to 70 dB, far lower than the 89 dB of Example 1. This is because the addition of Fe3O4 helps improve electromagnetic shielding performance, and carboxylation modification ensures the bonding between the functional layer and the substrate, thereby ensuring stable shielding function. Furthermore, its interlayer peel strength (2.0 N / cm), 5000-cycle bending performance degradation rate (20%), and weather resistance retention rate (55%) were all poor, further highlighting the importance of a reasonable composition and modification of the functional layer.

[0113] Comparative Example 6: The radiation cooling layer, functional layer, and base fiber layer were bonded together by hot pressing, but no chemical bonding was formed. The interlayer relied solely on physical forces, resulting in an interlayer peel strength of only 1.8 N / cm. After 5000 bending cycles, the performance degradation rate reached as high as 25%, and the weather resistance retention rate was only 45%, with all performance characteristics being the worst. This fully demonstrates the significant effect of the chemical bonding method of the three-layer material interface achieved through chemical reaction in this invention in improving interfacial adhesion, dynamic stability, and weather resistance, which is unmatched by traditional physical bonding processes.

[0114] In summary, this invention significantly improves the dynamic stability and overall performance of the material through three-layer chemical bonding and process optimization.

[0115] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A Janus-type flexible radiative cooling material, characterized in that, The Janus-type flexible radiative cooling material comprises a radiative cooling layer, a base fiber layer and a functional layer stacked from top to bottom; wherein: The radiative cooling layer is obtained by modifying inorganic nanoparticles with amino silane; The base fiber layer is obtained by centrifugal spinning of a polymer and phase change microcapsules; the polymer is selected from one or more of polyvinyl alcohol, polylactic acid, polyacrylonitrile, polyvinylidene fluoride, polymethyl acrylate or polydimethyl siloxane; The functional layer is carboxylated MXene / Fe3O4; The preparation method of the Janus-type flexible radiative cooling material comprises: preparing a base fiber layer by centrifugal spinning, then spraying and solidifying a functional layer and a radiative cooling layer on the front and back surfaces of the base fiber layer respectively; during the spraying of the functional layer, the spraying pressure is 0.2-0.5 MPa, and the solidification temperature is 50-80℃.

2. The Janus-type flexible radiative cooling material of claim 1, wherein, The inorganic nanoparticles are selected from one or more of SiO2, TiO2, BN, Al2O3 and CaSO3.

3. The Janus-type flexible radiative cooling material of claim 1, wherein, The amino silane modification uses an amino silane coupling agent.

4. The Janus-type flexible radiative cooling material of claim 1, wherein, The phase change microcapsules are paraffin@SiO2 or polyethylene glycol / cellulose phase change fibers; The mass ratio of the polymer to the phase change microcapsules is (3-5):

1.

5. The Janus-type flexible radiative cooling material of claim 1, wherein, The fiber diameter of the base fiber layer is 5-200 nm, and the porosity is ≥80%.

6. The Janus-type flexible radiative cooling material of claim 1, wherein, The thickness of the functional layer is 10-50 μm. The mass ratio of MXene to Fe3O4 in the functional layer is (1-5):

1. The carboxylation modification of MXene / Fe3O4 uses an acid anhydride.

7. The Janus-type flexible radiative cooling material of claim 1, wherein, The spraying process of the functional layer uses a carboxylated MXene / Fe3O4 dispersion liquid with a mass concentration of 5-20 t%.

8. The Janus-type flexible radiative cooling material of claim 1, wherein, The rotation speed of the centrifugal spinning process is 8000-12000 rpm; and / or the centrifugal spinning process uses a double-jet design with a jet aperture of 0.3-0.8 mm.

9. Use of the Janus-type flexible radiative cooling material according to any one of claims 1-8 in the preparation of wearable devices, building energy-saving films or camouflage protective products.

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