Janus type flexible radiation refrigeration material and preparation method thereof

Abstract

The invention discloses a Janus type flexible radiation refrigeration material and a preparation method thereof.The Janus type flexible radiation refrigeration material is characterized in that a modified radiation refrigeration layer and a functional layer are arranged on the upper surface and the lower surface of a substrate fiber layer with specific functional groups, and on one hand, the substrate fiber layer can be subjected to esterification or silanization bonding with the amino silane modified radiation refrigeration layer; the material can be subjected to an esterification reaction with a carboxylation modified functional layer, so that the three-layer material interface is chemically bonded, the bonding force of the interface is effectively improved, the dynamic stability is effectively improved on the basis of ensuring the optical performance and the 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 realize 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 radiation refrigeration 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 electronic device thermal protection, but their commercialization process is limited by material cost and process complexity.

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

[0006] The present application provides a Janus-type flexible radiation refrigeration material to solve the problem of insufficient optical performance and mechanical flexibility of existing radiation refrigeration materials, which limits their large-scale application.

[0007] Therefore, the scheme of the present application is as follows: The first aspect of the present application is to provide a Janus-type flexible radiation refrigeration material, which comprises a radiation refrigeration layer, a base fiber layer and a functional layer stacked from top to bottom; wherein: The radiation refrigeration 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.

[0008] Further, the inorganic particles are selected from one or more of SiO2, TiO2, BN, Al2O3 and CaSO3.

[0009] Further, the amino silane modification includes modifying the surface of inorganic nanoparticles with amino (-NH2) and alkoxysilane (-Si (OR)3) functional groups using a modifier, preferably an amino silane coupling agent.

[0010] Further, the phase change microcapsules are paraffin / SiO2 or polyethylene glycol / cellulose phase change fibers.

[0011] Further, the mass ratio of the polymer to the phase change microcapsules is (3-5):1.

[0012] Further, the fiber diameter of the base fiber layer is 5-200 nm, and the porosity is greater than or equal to 80%.

[0013] Further, the thickness of the functional layer is 10-50 microns.

[0014] Further, the mass ratio of MXene to Fe3O4 in the functional layer is (1-5):1.

[0015] Further, the carboxylated modification process of MXene / Fe3O4 uses an acid anhydride.

[0016] The second aspect of the present application is to provide a preparation method of the Janus-type flexible radiation refrigeration material of the first aspect, comprising the steps of preparing a base fiber layer by centrifugal spinning, and solidifying after spraying a functional layer and a radiation refrigeration layer on the front and back surfaces of the base fiber layer, respectively.

[0017] Further, in the spraying process of the functional layer: The spraying pressure is 0.2-0.5 MPa, and the solidification temperature is 50-80℃; and / or, the spraying process uses a carboxylated modified MXene / Fe3O4 dispersion liquid with a mass concentration of 5-20t%.

[0018] Further, 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.

[0019] The third aspect of the present application is to provide the application of the Janus-type flexible radiation refrigeration material of the first aspect in the preparation of wearable devices, building energy-saving films, or camouflage protective products.

[0020] Compared with the prior art, the present application has the following beneficial effects: The Janus-type flexible radiation refrigeration material provided by the present application sets a modified radiation refrigeration layer and a functional layer on the upper and lower surfaces of a base fiber layer with a specific functional group. The base fiber layer can be esterified or silanized bonded with the amino silane modified radiation refrigeration layer, and can also be esterified with the carboxylated modified functional layer, thereby chemically bonding the interfaces of the three-layer material, effectively improving the bonding force of the interface, effectively improving the dynamic stability on the basis of ensuring the optical performance and mechanical flexibility, and promoting the application of the radiation refrigeration material.

[0021] The Janus-type flexible radiative refrigeration material provided by the present invention contains a hydroxyl-containing base fiber layer, which is prepared by centrifugal spinning of a mixture of a polymer and phase change microcapsules. The polymer surface is rich in hydroxyl or carboxyl groups, which form a strong chemical bonding interface in situ with the complementary functional groups of the functional layer materials on both sides during the spray curing process. It does not require additional plasma treatment or silane coupling agents and is suitable for industrial-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the structure of the Janus-type flexible radiation refrigeration material described in the present invention.

[0023] Figure 2 Schematic diagram of the porous network structure of the base fiber layer under an electron microscope of the present invention. DETAILED DESCRIPTION

[0024] The technical solutions of the present invention will be clearly and completely described below in conjunction with preferred embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0025] In one embodiment, Figure 1 As shown, a Janus-type flexible radiative cooling material is provided, comprising a radiative cooling layer 1, a base fiber layer 2, and a functional layer 3 stacked from top to bottom; wherein: The radiative cooling layer is obtained by modifying inorganic nanoparticles with aminosilane; 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) or polyvinylidene fluoride (PVDF), polymethyl acrylate (PMMA), and polydimethoxysilane (PDMS); The functional layer is carboxyl-modified MXene / Fe3O4.

[0026] In the above embodiment, modified radiant cooling layers and functional layers are arranged on the upper and lower surfaces of the base fiber layer having specific functional groups. The base fiber layer can undergo esterification or silanization bonding with the aminosilane-modified radiant cooling layer, and can also undergo esterification reaction with the carboxyl-modified functional layer, thereby chemically bonding the interfaces of the three layers of materials, effectively improving the bonding strength of the interfaces, and effectively improving the dynamic stability while ensuring optical properties and mechanical flexibility, thereby promoting the application of radiant cooling materials.

[0027] In the above embodiment, the solar reflectivity of the radiation cooling layer 1 is ≥95%, and the infrared emissivity is ≥90%; the base fiber layer 2 is a phase change base material layer, and the functional layer 3 is an electromagnetic shielding layer with an electromagnetic shielding efficiency ≥85 dB and a square resistance ≤10 Ω / sq. Among them, the radiation cooling layer 1 is mainly responsible for dissipating heat in the form of infrared radiation, achieving passive cooling; the phase change base material layer plays a role in buffering temperature changes and providing flexibility; the electromagnetic shielding layer protects the inside from electromagnetic interference, etc. Realize the multifunctional coupling of radiation cooling, joule heating and electromagnetic shielding.

[0028] In the above embodiment, the radiation cooling layer 1 and the functional layer 3 are chemically bonded by spraying on the upper and lower surfaces of the base fiber layer.

[0029] In some embodiments, the base fiber layer prepared by centrifugal spinning of the polymer and phase change microcapsules has a fiber diameter in the range of 50-200 nm, and a porosity ≥80% (. Figure 2 ). The polymer and phase change microcapsules form a "sugar cane stick" composite structure, which improves the bending resistance of the material (tensile strength ≥10 MPa). Through the design of hydrophilic-hydrophobic Janus wettability, one-way moisture transfer is achieved (water evaporation rate 0.31 g / h), improving the wearing comfort.

[0030] In preferred embodiments, the inorganic particles are selected from one or more of SiO2, TiO2, BN, Al2O3, CaSO3.

[0031] In preferred embodiments, the amino silane modification includes modifying the surface of the inorganic nanoparticles with amino (-NH2) and alkoxysilane group (-Si (OR)3) functional groups using a modifier, preferably an amino silane coupling agent such as KH-550, KH-602, KH-551, etc.

[0032] In preferred embodiments, the phase change microcapsules, but not limited to, paraffin@silica core-shell structure, have a phase change enthalpy ≥180 J / g, a particle size of 1-5 μm, and a polyethylene glycol (PEG) / cellulose phase change fiber (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, balancing the environmental temperature fluctuations.

[0033] In preferred embodiments, the mass ratio of the hydroxyl-containing polymer to the phase change microcapsules is (3-5):1. The mass ratio of MXene to Fe3O4 in the functional layer is (1-5):1.

[0034] In preferred embodiments, the carboxylation modification process of MXene / Fe3O4 uses anhydrides of organic dibasic acids to realize the surface grafting of carboxylic acid groups, such as commonly used anhydrides such as succinic anhydride and maleic anhydride.

[0035] The material prepared by the application can achieve passive cooling of 10℃ (solar irradiance ≥ 900 W / m²) and 1.5 V low-voltage driven heating (response time ≤ 130 seconds) in wearable devices, while meeting the complex curved surface fitting requirements (performance decay ≤ 15% after 1000 cycles of bending), and is suitable for the fields of intelligent clothing, building energy-saving films and infrared camouflage protection.

[0036] In another embodiment, a preparation method of the above Janus-type flexible radiative cooling material is provided, comprising the steps of preparing a base fiber layer by centrifugal spinning, and respectively spraying and solidifying a functional layer and a radiative cooling layer on the front and back surfaces of the base fiber layer.

[0037] In a preferred embodiment, during the spraying process of the functional layer, the spraying pressure is 0.2-0.5 MPa, and the solidification temperature is 50-80℃; the spraying process uses a carboxyl-modified MXene / Fe3O4 dispersion liquid with a mass concentration of 5-20t%.

[0038] In a preferred embodiment, the radiative cooling layer is first prepared into a composite sol, and then dried by spraying to form a porous radiative cooling layer.

[0039] In the above embodiment, during the spraying and solidification process, the surface functional groups of the base fiber layer (such as the hydroxyl groups of PVA and the carboxyl groups of PLA) form covalent bonding interfaces (such as ester bonds) with the modified functional groups of the functional layer; the surface of the inorganic nanoparticles of the radiative cooling layer is modified by amino silane, and silanization (such as Si-O-C bond) occurs with the surface functional groups of the base fiber layer, achieving a peeling strength between the base fiber layer and the upper and lower layers of ≥ 5.2 N / cm.

[0040] In a preferred embodiment, the rotation speed of the centrifugal spinning process is 8000-12000 rpm, and the centrifugal spinning process uses a double-nozzle design with a nozzle aperture of 0.3-0.8 mm to improve efficiency and ensure fiber diameter and porosity.

[0041] The Janus-type flexible material prepared by the above method can achieve the following effects: 1. Weather resistance: after 1000 hours of aging at 85℃ / 85% humidity, the interface peeling strength retention rate is ≥ 90%, which is 5 times higher than that of traditional processes; 2. Mechanical properties: interlayer peeling strength 5.2 N / cm, performance decay ≤ 3% after 5000 bends (curvature radius 2 mm); 3. After being applied to a 30-layer residential south window coating material, the indoor temperature is reduced by 4.2℃ in summer afternoon, the air conditioning opening time is reduced by 2.5 hours / day, the monthly electricity saving is 120 degrees, and the energy saving rate is 28%; 4. After the material is applied to the surface of the server cabinet, the 10 GHz electromagnetic shielding efficiency is 88.5 dB, the equipment failure rate is reduced by 60%, the heat dissipation energy consumption is reduced by 22%, and the annual operation and maintenance cost is saved by 850,000 yuan per 10,000 square meters; 5. After being soaked in a 15% NaCl solution for 30 days, the sheet resistance of the MXene / Fe3O4 layer changes by less than or equal to 5%, and the material is suitable for use as an electromagnetic shielding layer for underwater robots, replacing traditional titanium alloy shielding covers to reduce weight by 70%.

[0042] The following is a preferred embodiment of the present application, and the specific embodiments described herein are merely used to explain the present application and do not limit the present application. Unless otherwise specified, the materials used are commercially available, and the experimental methods used are those skilled in the art.

[0043] Example 1

[0044] The preparation method of the Janus-type flexible radiation refrigeration material comprises the following steps: 1) Carboxylation modification of MXene / Fe3O4 dispersion liquid: 5g MXene / Fe3O4 and 10g succinic anhydride are dispersed in 100mL DMF and mixed, stirred at 60°C for 24h, washed by centrifugation, and then washed with DMF for 3 times to obtain carboxylated MXene / Fe3O4 (the measured -COOH grafting rate is 1.5 mmol / g); 2) Amino silane modification of inorganic nanoparticles: SiO2 / TiO2 (molar ratio 1:1) nanoparticles are dispersed in a mixture of ethanol-water (volume ratio 4:1), KH-550 (1.5% of the mass of the particles) is added, and refluxed at 80°C for 4h, and then dried to obtain amino silane modified particles (-NH2 grafting density 0.9 μmol / m 2 ); 3) PVA is dissolved in deionized water (concentration 8 wt.%), paraffin@silica core-shell microcapsules (phase change enthalpy 185J / g, particle size 2μm, mass ratio 4:1) are added, and a fiber membrane with a thickness of 200μm is prepared by centrifugal spinning (rotational speed 10000 rpm); The schematic diagram of the porous network structure of the substrate fiber layer under the electron microscope is shown in Figure 2 As can be seen, the fibers form a random and staggered network structure, the diameter is distributed in the range of 50-200 nm, the fibers are arranged without orientation, and a porous network structure is formed, and the porosity is greater than or equal to 80%; 4) A carboxylated MXene / Fe₃O₄ dispersion (15 wt.%, spray pressure 0.3 MPa) was sprayed onto side A of the fiber membrane and cured at 80°C to form a 10 μm-thick conductive shielding layer. Modified titanium dioxide (TiO₂), silicon dioxide (SiO₂), and polydimethylsiloxane (PDMS) were mixed in a 1:1 mass ratio, and an appropriate amount of n-hexane was added as a solvent. The mixture was stirred to form an aminosilanized SiO₂-TiO₂ sol. The SiO₂-TiO₂ sol (1:1 molar ratio) was then sprayed onto side B of the fiber membrane. After drying, a porous radiative layer was formed, ultimately yielding the Janus-type flexible radiative cooling material.

[0045] Example 2

[0046] A method for preparing a Janus-type flexible radiation cooling material comprises the following steps: 1) Carboxylation modification of the MXene / Fe3O4 dispersion: 8 g of MXene / Fe3O4 (mass ratio 5:1) and 12 g of maleic anhydride were dispersed in 150 mL of N-methylpyrrolidone, stirred at 50°C for 20 h, centrifuged, and washed three times with ethanol to obtain carboxylated MXene / Fe3O4 (-COOH grafting rate 1.2 mmol / g); 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% particle mass) was added, and the mixture was refluxed at 70°C for 5 h. After drying, aminosilane-modified particles (-NH2 grafting density 0.8 μmol / m²) were obtained. 3) Polylactic acid (PLA) was dissolved in dichloromethane (concentration 10 wt.%), and polyethylene glycol / cellulose phase change fiber (latent heat 182 J / g, phase change temperature 30°C, mass ratio 3:1) was added. Centrifugal spinning (8000 rpm, dual nozzle, pore size 0.5 mm) was performed to produce a 180 μm thick fiber membrane (fiber diameter 80-150 nm, porosity 82%). 4) A carboxylated MXene / Fe3O4 dispersion (mass concentration 20 wt.%, spraying pressure 0.2 MPa) was sprayed on the A side 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 in a mass ratio of 2:1, solvent: cyclohexane) was sprayed on the B side of the fiber membrane and dried to form a radiative cooling layer, ultimately obtaining a Janus-type flexible radiative cooling material.

[0047] Example 3

[0048] A preparation method of the Janus-type flexible radiative cooling material, the steps are: 1) Carboxyl modification of MXene / Fe3O4 dispersion liquid: 6 g of MXene / Fe3O4 (mass ratio 3:1) is dispersed in 120 mL of DMSO with 8 g of phthalic anhydride, stirred at 65°C for 22 h, washed by centrifugation, and then washed with acetone for 3 times to obtain carboxylated MXene / Fe3O4 (-COOH grafting rate 1.6 mmol / g); 2) Aminosilane modification of inorganic nanoparticles: CaSO3 / SiO2 (mass ratio 1:2) nanoparticles are dispersed in a mixture of ethanol-water (volume ratio 5:1), KH-551 (1% of the mass of the particles) is added, and refluxed at 85°C for 3 h, and then dried to obtain aminosilane-modified particles (-NH2 grafting density 1.0 μmol / m²); 3) Polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) (mass ratio 1:1) are dissolved in DMF (total concentration 12 wt.%), paraffin@SiO2 microcapsules (phase change enthalpy 180 J / g, particle size 3 μm, mass ratio 5:1) are added, and a fiber membrane with a thickness of 220 μm (fiber diameter 50-180 nm, porosity 85%) is prepared by centrifugal spinning (rotational speed 12000 rpm, double nozzle, pore size 0.3 mm); 4) Spray carboxylated MXene / Fe3O4 dispersion liquid (mass concentration 5 wt.%, spraying pressure 0.5 MPa) on one side of the fiber membrane A, and form a 50 μm thick functional layer after curing at 60°C; spray CaSO3 / SiO2 modified sol (mixed with polymethyl methacrylate at a mass ratio of 1:1, and the solvent is ethyl acetate) on the other side of the fiber membrane B, and dry to form a radiative cooling layer, and finally obtain a Janus-type flexible radiative cooling material.

[0049] Example 4

[0050] A preparation method of the Janus-type flexible radiative cooling material, the steps are: 1) Carboxyl modification of MXene / Fe3O4 dispersion liquid: 6 g of MXene / Fe3O4 (mass ratio 3:1) is dispersed in 120 mL of DMSO with 8 g of phthalic anhydride, stirred at 65°C for 22 h, washed by centrifugation, and then washed with acetone for 3 times to obtain carboxylated MXene / Fe3O4 (-COOH grafting rate 1.6 mmol / g); 2) Aminosilane modification of inorganic nanoparticles: TiO2 / BN (mass ratio 2:1) nanoparticles were dispersed in a mixture of ethanol-water (volume ratio 4:1), KH-550 was added (1.8% of the mass of the particles), and refluxed at 75°C for 3.5 h. After drying, aminosilane-modified particles (-NH2grafting density 0.95 μmol / m²) were obtained; 3) Polydimethylsilane (PDMS) was dissolved in n-hexane (concentration 9 wt.%), and polyethylene glycol / cellulose phase change fibers (latent heat 183 J / g, mass ratio 4:1) were added. A fiber membrane with a thickness of 210 μm (fiber diameter 60-200 nm, porosity 81%) was prepared by centrifugal spinning (rotation speed 11000 rpm, double nozzle, pore size 0.8 mm); 4) A carboxylated MXene / Fe3O4 dispersion (mass concentration 10 wt.%, spraying pressure 0.4 MPa) was sprayed on one side of the fiber membrane A, and a functional layer with a thickness of 20 μm was formed after curing at 70°C. A TiO2 / BN modified sol (mixed with PDMS at a mass ratio of 1.5:1, with n-hexane as the solvent) was sprayed on the other side of the fiber membrane B, and a radiation cooling layer was formed after drying. Finally, a Janus-type flexible radiation cooling material was obtained.

[0051] Comparative Example 1

[0052] The difference from Example 1 is that the inorganic nanoparticles of the radiation cooling layer are not aminosilane-modified (directly using untreated SiO2 / TiO2). The remaining steps and parameters are the same.

[0053] Comparative Example 2

[0054] The difference from Example 1 is that the MXene / Fe3O4 of the functional layer is not carboxylated (directly using untreated MXene / Fe3O4). The remaining steps and parameters are the same.

[0055] Comparative Example 3

[0056] The difference from Example 1 is that the base fiber layer does not add phase change microcapsules (only PVA is used for centrifugal spinning). The remaining steps and parameters are the same.

[0057] Comparative Example 4

[0058] The difference from Example 1 is that the base fiber layer is prepared by electrospinning (rotation speed 2000 rpm, the remaining spinning parameters are the same). The remaining steps and parameters are the same.

[0059] Comparative Example 5

[0060] The difference from Example 1 is that the functional layer is pure MXene (without Fe3O4) and no carboxyl modification is performed. The remaining steps and parameters are the same.

[0061] Comparative Example 6

[0062] The difference from Example 1 is that the radiation cooling layer, the functional layer and the substrate fiber layer are bonded by hot pressing (without chemical bonding). The remaining steps and parameters are the same.

[0063] Test Example

[0064] The above examples and comparative examples are tested for performance, including: solar reflectivity, infrared emissivity, interlayer peeling strength, tensile strength, performance decay rate after bending, electromagnetic shielding efficiency, weather resistance.

[0065] Test standards (methods are): 1. Solar reflectivity: tested by ultraviolet-visible-near infrared spectrophotometer (300-2500 nm band); 2. Infrared emissivity: tested by Fourier transform infrared spectrometer (8-13 μm band); 3. Interlayer peeling strength: tested by universal testing machine according to GB / T 2790-1995 standard; 4. Tensile strength: tested by universal testing machine according to GB / T 1040.3-2006 standard; 5. Performance decay rate after 5000 times of bending: the material is cycled bent 5000 times under the condition of a curvature radius of 2 mm, and the decay rate of solar reflectivity and infrared emissivity before and after bending is tested; 6. Electromagnetic shielding efficiency: tested by vector network analyzer (10 GHz band); 7. Weather resistance: tested by interlayer peeling strength retention rate after aging at 85°C / 85% humidity for 1000 hours.

[0066] The results are shown in Table 1.

[0067] Table 1:

[0068] As can be seen from the test results in Table 1, the various performances of Examples 1-4 are excellent. In terms of solar reflectivity and infrared emissivity, both are maintained at 91% and above, ensuring good radiation cooling effect; the interlayer peeling strength is all above 5.2 N / cm, indicating that the chemical bonding between the three layers is firm and the interfacial bonding force is strong; the tensile strength is 11-12 MPa, showing good mechanical properties; after 5000 times of bending, the performance attenuation rate is only 2%-3%, and the dynamic stability is excellent; the electromagnetic shielding efficiency is not less than 87 dB, which can effectively play a shielding role; after aging for 1000 hours under the condition of 85℃ / 85% humidity, the weather resistance retention rate is still above 90%, and the environmental adaptability is strong. This fully shows that the Janus type flexible radiation cooling material prepared by the present application realizes the good combination of optical properties, mechanical properties, dynamic stability and functional characteristics through reasonable material selection, modification treatment and preparation process.

[0069] Comparative Example 1: Since the inorganic nanoparticles of the radiation cooling layer are not modified by amino silane, they cannot form effective chemical bonding with the substrate fiber layer, and the interlayer mainly relies on physical adsorption, resulting in a significant decrease in interlayer peeling strength to 2.1 N / cm. The performance attenuation rate after 5000 times of bending is 15%, and the weather resistance retention rate is only 60%, which is significantly lower than that of Example 1. This shows that amino silane modification is crucial for improving the interfacial bonding force, dynamic stability and weather resistance of the radiation cooling layer and the substrate fiber layer.

[0070] Comparative Example 2: The MXene / Fe3O4 of the functional layer is not modified by carboxylation, and cannot effectively esterify with the substrate fiber layer, resulting in weak interfacial bonding force and interlayer peeling strength of 2.3 N / cm. The performance attenuation rate after 5000 times of bending is 18%, and the weather resistance retention rate is 58%, which is inferior to Example 1. It can be seen that carboxylation modification is the key to ensuring the firm combination of the functional layer and the substrate fiber layer and maintaining the overall performance stability of the material.

[0071] Comparative Example 3: The substrate fiber layer does not add phase change microcapsules, and only uses PVA for centrifugal spinning, and the tensile strength decreases to 8 MPa, and the mechanical properties decrease significantly. This is because the addition of phase change microcapsules can form a "sugarcane stick" composite structure with polymers, improving the bending resistance and mechanical strength of the material. The lack of phase change microcapsules weakens this enhancement effect, which cannot meet the requirements of the material for flexibility and mechanical properties.

[0072] Comparative Example 4: The base fiber layer is prepared by electrospinning instead of centrifugal spinning, and the uneven fiber diameter leads to a decrease in porosity, and the infrared emissivity decreases to 90%, which is lower than 92% of Example 1. At the same time, the interlayer peeling strength is 3.5 N / cm, the performance attenuation rate after 5000 times of bending is 12%, and the weather resistance retention rate is 75%, all of which are lower than those of Example 1. This reflects the advantages of centrifugal spinning technology in preparing high porosity and uniform fiber structure, which further positively affects the optical properties and interfacial bonding force of the material.

[0073] Comparative Example 5: The functional layer is pure MXene and is not modified by carboxylation, and the electromagnetic shielding efficiency decreases to 70 dB, which is much lower than 89 dB of Example 1. This is because the addition of Fe3O4 helps to improve the electromagnetic shielding performance, and the carboxylation modification ensures the bonding of the functional layer and the substrate, thereby ensuring the stable performance of the shielding function. In addition, its interlayer peeling strength is 2.0 N / cm, the performance attenuation rate after 5000 times of bending is 20%, and the weather resistance retention rate is 55%, all of which are poor, further highlighting the importance of reasonable composition and modification of the functional layer.

[0074] Comparative Example 6: The radiation cooling layer, the functional layer and the base fiber layer are bonded by hot pressing, and no chemical bonding is formed, and the interlayer only relies on physical force, the interlayer peeling strength is only 1.8 N / cm, the performance attenuation rate after 5000 times of bending is as high as 25%, and the weather resistance retention rate is only 45%, all of which are the worst. This fully proves that the way of realizing the chemical bonding of the three-layer material interface through chemical reaction in the present application has significant effects on improving the interfacial bonding force, dynamic stability and weather resistance, which is unmatched by traditional physical bonding process.

[0075] In summary, the present application significantly improves the dynamic stability and comprehensive performance of the material through three-layer chemical bonding and process optimization.

[0076] Although embodiments of the present application 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 therein without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A Janus-type flexible radiation cooling material, characterized in that: It includes a radiation 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 aminosilane; 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 polydimethoxysilane; The functional layer is carboxyl-modified MXene / Fe3O4.

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

3. The Janus-type flexible radiative cooling material according to claim 1, characterized in that: The aminosilane modification uses an amino silane coupling agent.

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

1.

5. The Janus-type flexible radiative cooling material according to claim 1, characterized in that: 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 according to claim 1, characterized in that: The thickness of the functional layer is 10-50 μm; and / or, the mass ratio of MXene to Fe3O4 in the functional layer is (1-5):1; And / or, the MXene / Fe3O4 carboxylation modification process uses anhydride.

7. The method for preparing the Janus-type flexible radiative cooling material according to any one of claims 1 to 6, characterized in that: The method comprises the steps of preparing a base fiber layer by centrifugal spinning, spraying a functional layer and a radiation cooling layer on both sides of the base fiber layer respectively, and then solidifying the layer.

8. The preparation method according to claim 7, characterized in that During the functional layer spraying process: The spraying pressure is 0.2-0.5 MPa and the curing temperature is 50-80°C; And / or, the spraying process uses a carboxyl-modified MXene / Fe3O4 dispersion with a mass concentration of 5-20t%.

9. The preparation method according to claim 7, characterized in that The rotation speed of the centrifugal spinning process is 8000-12000 rpm; and / or, the centrifugal spinning process adopts a double nozzle design with a nozzle aperture of 0.3-0.8 mm.

10. Use of the Janus-type flexible radiative cooling material according to any one of claims 1 to 6 in the preparation of wearable devices, building energy-saving films or camouflage protective products.

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