A biomimetic multilayer structure of nanofiber radiation refrigeration heat insulation film

Abstract

The application belongs to the field of composite materials, and particularly relates to a bionic multilayer structure nanofiber radiation refrigeration and heat insulation film; from outside to inside, the film comprises a bionic antireflection layer, a sunlight spectrum reflection layer, a nanofiber porous heat insulation layer and an atmospheric window radiation layer; the bionic antireflection layer is a subwavelength nanoconvex array imitating the structure of a moth eye, and is formed on the outer surface of the sunlight spectrum reflection layer; the sunlight spectrum reflection layer is a polymer film doped with high reflectivity nano particles; the nanofiber porous heat insulation layer is a porous film formed by interweaving polymer nanofibers prepared by electrospinning technology; and the atmospheric window radiation layer is a functional layer coated or blended with high-emissivity inorganic nano particles on the inner surface of the nanofiber porous heat insulation layer; the film integrates the bionic antireflection, high sunlight reflection, high-efficiency heat radiation and physical heat insulation, and realizes efficient, stable and flexible daytime radiation refrigeration.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of composite materials, and particularly relates to a nano-fiber radiation cooling and heat insulation film with a biomimetic multi-layer structure. BACKGROUND

[0002] With the increasingly severe global energy crisis and climate change, the development of zero / low energy consumption active cooling technology has become one of the key challenges for sustainable development. In this context, passive daytime radiation cooling (PDRC) technology has emerged as the times require, which provides a solution for realizing passive and zero-pollution cooling through the "cosmic cold source", a natural heat sink. The core physical mechanism lies in that the material is designed to have two independent spectral properties: a very high reflectivity in the 0.25-2.5 μm solar spectrum band to minimize the input of solar radiation energy; and a very high emissivity in the 8-13 μm "atmospheric window" band, so that the internal heat of the object can be efficiently transmitted to the outer space near absolute zero in the form of infrared radiation.

[0003] Although the PDRC technology principle is clear and has broad prospects, the existing technology still faces a series of severe challenges and limitations in the process of actual materialization and application:

[0004] 1. The coordination dilemma of spectral performance:

[0005] Current mainstream PDRC materials, such as randomly distributed microporous polymer films (such as PVDF-HFP) or inorganic particle / polymer composite coatings, often have difficulty in achieving perfect coordination in a wide spectral range. For example, in order to pursue a very high solar reflectivity (95%), it is usually necessary to rely on high-concentration, wide-bandgap inorganic scattering particles (such as TiO2), but these particles may have unnecessary phonon resonance absorption in part of the mid-infrared band, which in turn inhibits their ideal emissivity in the atmospheric window. Conversely, some organic polymers with intrinsic high emissivity in the 8-13 μm band often have insufficient solar reflectivity. This "seesaw" effect of spectral performance makes it difficult for the material to approach the theoretical ideal values of solar reflectivity and infrared emissivity at the same time, limiting its maximum cooling efficiency.

[0006] 2. The fatal weakness of environmental thermal interference:

[0007] Most of the studies focus on the radiative properties of the material surface, but generally ignore the interference of heat conduction and convection from the environment side. When the PDRC material is directly attached to the protected object (such as the outer wall of a building, the outer shell of electronic equipment, or the surface of a storage tank), the heat from the high-temperature environment will continuously enter the cooling system through solid conduction and air convection, seriously annihilating or even completely canceling its radiative cooling effect. This coexistence of "cooling" and "heating" leads to a situation where the actual cooling effect is much lower than the theoretical value in practical application scenarios, especially in high-temperature environments during the day. Therefore, the practical application value of PDRC structures lacking efficient thermal insulation design is greatly reduced.

[0008] 3. Comprehensive test of mechanical properties and durability:

[0009] For practical applications, PDRC materials must have excellent mechanical properties and long-term durability. However, there are still many challenges:

[0010] Flexibility: Many PDRC materials based on rigid photonic crystals or silicon structures have excellent performance, but their inherent brittleness makes them unsuitable for flexible or deformable substrates.

[0011] Strength: Although microporous films prepared by phase separation methods are flexible, their mechanical strength is often insufficient, making them prone to tearing, wear, and difficult to withstand installation stress or external physical impact.

[0012] Weather resistance: Materials need to be exposed to ultraviolet light, moisture, temperature cycles, and pollutants for a long time. The polymer matrix may yellow due to ultraviolet radiation, causing an increase in solar absorption, and the nanoparticles may be lost due to rainwater erosion, and the porous structure may fail due to dust blockage. The current material system still faces great challenges in balancing high performance and long service life.

[0013] 4. Cost and process barriers of large-scale production:

[0014] To achieve specific optical structures (such as multi-layer photonic crystals, complex micro-nano gratings, etc.), it is often necessary to rely on advanced micro-nano processing technologies such as electron beam lithography and ion etching. Although these processes can produce samples with excellent performance, they are expensive, complex, and have very low output, completely unable to meet the needs of large-scale applications such as buildings and outdoor equipment. Developing a high-performance PDRC material that is compatible with mature and scalable industrial production processes (such as solution spinning, roll-to-roll coating, etc.) is the only way to achieve industrialization, and it is also a blank and difficulty in the current technical field. SUMMARY

[0015] In order to make up for the deficiencies of the prior art, the application provides a nanofiber radiation refrigeration and heat insulation film with a biomimetic multilayer structure to solve the problems of insufficient spectral performance, easy environmental thermal interference and poor mechanical flexibility of existing radiation refrigeration materials. The film integrates biomimetic antireflection, high solar reflectance, high-efficiency thermal radiation and physical insulation, and realizes efficient, stable and flexible daytime radiation refrigeration.

[0016] The technical scheme adopted by the application to solve the technical problems is that the nanofiber radiation refrigeration and heat insulation film with a biomimetic multilayer structure comprises, from the outside to the inside, a biomimetic antireflection layer, a solar spectrum reflection layer, a nanofiber porous insulation layer and an atmospheric window radiation layer.

[0017] The biomimetic antireflection layer is a subwavelength nanoconvex array simulating the structure of a moth eye, formed on the outer surface of the solar spectrum reflection layer, for reducing the reflection of sunlight and increasing the wide-band antireflection performance.

[0018] The solar spectrum reflection layer is a polymer film doped with high-reflectivity nano particles, for high-reflectivity reflection of sunlight in the 250nm-2.5μm band.

[0019] The nanofiber porous insulation layer is a porous film formed by interweaving polymer nanofibers prepared by electrospinning technology, with a porosity greater than 80%, for blocking heat conduction and convection and allowing infrared radiation in the 8-13μm band to pass through.

[0020] The atmospheric window radiation layer is a functional layer coated or blended with high-emissivity inorganic nano particles on the inner surface of the nanofiber porous insulation layer, for efficiently emitting infrared radiation in the 8-13μm band to the outer space of the atmosphere.

[0021] As a further technical scheme of the application, the nanoconvexes of the biomimetic antireflection layer are conical or hemispherical, with a diameter of 200-500nm and a height of 300-600nm.

[0022] As a further technical scheme of the application, the biomimetic antireflection layer is usually made of a high-refractive, weather-resistant transparent polymer or metal oxide; and the thickness of the biomimetic antireflection layer is 200nm-800nm.

[0023] As a further technical scheme of the application, the solar spectrum reflection layer is composed of a transparent polymer matrix uniformly doped with high-refractive, low-absorption inorganic nano particles.

[0024] As a further technical scheme of the application, the inorganic nano particles are selected from one or more of titanium dioxide, zinc oxide and barium sulfate.

[0025] As a further technical solution of the present application: the particle size of the inorganic nanoparticles is controlled in 50-300 nm to minimize Rayleigh scattering; the thickness of the solar spectrum reflection layer is usually 10-50 μm.

[0026] As a further technical solution of the present application: the thickness of the nanofiber porous thermal insulation layer is 50 μm-300 μm; the polymer nanofiber adopts one or more of polyvinylidene fluoride, polyurethane, and polyacrylonitrile; wherein the single fiber diameter is 100-500 nm, the porosity is >80%, and the thickness is 100-500 μm.

[0027] As a further technical solution of the present application: the high-emissivity inorganic nanoparticles adopt one or more of silicon dioxide, silicon carbide, and boron nitride.

[0028] As a further technical solution of the present application: the thickness of the atmospheric window radiation layer is 10 μm-50 μm, and the particle size of the high-emissivity inorganic nanoparticles is 0.5-5 μm.

[0029] As a further technical solution of the present application: the preparation method of the nanofiber radiation refrigeration and thermal insulation film comprises the following steps:

[0030] Step 1: using electrospinning technology, spinning a polymer solution containing high-emissivity nanoparticles to form a nanofiber porous thermal insulation layer and an atmospheric window radiation layer composite structure directly on a cylindrical metal roller with a diameter of 20 cm and a length of 30 cm, to obtain a nanofiber composite lower layer;

[0031] Step 2: first, a polymer film doped with high-reflectivity nanoparticles is prepared by flow casting, stretching or coating to obtain a solar spectrum reflection layer;

[0032] Then a biomimetic moth eye structure is prepared on the surface of the film by nanoimprinting or self-assembly technology to form a biomimetic composite upper layer;

[0033] Step 3: laminating and compounding the biomimetic composite upper layer prepared above and the nanofiber composite lower layer by using an environmentally friendly adhesive to obtain the final multilayer composite thermal insulation film.

[0034] The beneficial effects of the present application are as follows:

[0035] The present application introduces a moth-eye nanostructure as the outermost layer; the function of this structure is not intuitive antireflection, but greatly reduces surface reflection loss through the principle of gradient refractive index, so that more sunlight enters the internal reflection layer and is reflected out efficiently. This is a strategy of reducing reflection to achieve high reflection, which optimizes the overall solar reflection efficiency from the optical principle.

[0036] This invention uses an electrospun nanofiber membrane as the intermediate layer. Its high porosity gives it an extremely low thermal conductivity, while its polymer fiber skeleton is highly transparent to infrared light in the 8-13μm wavelength band; making it a functional transmission channel that is both heat-insulating and infrared-transmitting, isolating the lower layer's radiative cooling from the upper layer's external environment, ensuring that the radiative cooling effect is not affected by environmental heat.

[0037] This invention achieves a highly efficient, stable, and practical daytime radiation cooling and heat insulation film through a biomimetic antireflective layer (antireflective layer), a solar reflective layer (reflection), a nanofiber heat insulation layer (heat insulation / transmission), and an atmospheric window radiation layer (emission).

[0038] This invention employs a unique four-layer structure, which generates three major physical effects: high reflection, high radiation, and high heat insulation, thereby converging into the advantages of efficient, stable, and zero-energy-consumption cooling. Attached Figure Description

[0039] The invention will now be further described with reference to the accompanying drawings.

[0040] Figure 1 This is a schematic diagram of the structure of a biomimetic multilayer nanofiber radiation cooling and heat insulation film of the present invention;

[0041] In the diagram: 10, biomimetic antireflective layer; 20, solar spectrum reflective layer; 30, nanofiber porous heat insulation layer; 40, atmospheric window radiation layer. Detailed Implementation

[0042] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0043] Example 1

[0044] like Figure 1 As shown in the embodiment of the present invention, a biomimetic multilayer nanofiber radiation cooling and heat insulation film includes, from the outside to the inside: a biomimetic antireflective layer 10, a solar spectrum reflective layer 20, a nanofiber porous heat insulation layer 30, and an atmospheric window radiation layer 40.

[0045] The biomimetic antireflective layer 10 is a subwavelength nano-protrusion array that mimics the structure of a moth's eye. It is formed on the outer surface of the solar spectrum reflective layer 20 to reduce the reflection of sunlight and increase broadband antireflective performance. The thickness of the biomimetic antireflective layer 10 is 200 nm.

[0046] Specifically, the nano-protrusions of the biomimetic antireflection layer 10 are conical or hemispherical, with a diameter of 200 nm and a height of 300 nm;

[0047] The material of the biomimetic antireflection layer 10 is usually composed of high-refractive, weather-resistant transparent polymers (such as UV-cured resin) or metal oxides (such as TiO2); the mass ratio of the weather-resistant transparent polymers to the metal oxides is 100:5;

[0048] The sub-wavelength nano-protrusion array simulating the structure of moth eye is used to reduce the surface reflectivity of the sunlight band (especially the visible light and near-infrared light), increase the incidence of light, and thus indirectly improve the sunlight reflection ability of the overall structure.

[0049] The sunlight spectrum reflection layer 20 is a polymer film doped with high-refractive nanoparticles, which is used to reflect the sunlight of the 250 nm band at a high reflectivity;

[0050] Specifically, the sunlight spectrum reflection layer 20 is composed of a transparent polymer matrix (such as PET) uniformly doped with high-refractive, low-absorption inorganic nanoparticles; the mass ratio of the transparent polymer matrix to the inorganic nanoparticles is 100:5;

[0051] The inorganic nanoparticles are selected from one or more of titanium dioxide (TiO2), zinc oxide (ZnO), and barium sulfate (BaSO4); the particle size is controlled at 50 nm to minimize Rayleigh scattering; the thickness of the sunlight spectrum reflection layer 20 is usually 10 μm.

[0052] It should be noted that the sunlight spectrum reflection layer 20, as the core reflection unit, reflects the sunlight of the 250 nm-2.5 μm band at a high reflectivity (target > 92%) in almost the entire spectrum, thereby minimizing the absorption of solar radiation energy.

[0053] The nanofiber porous thermal insulation layer 30 is a porous membrane formed by the interweaving of polymer nanofibers prepared by electrospinning technology, with a porosity of more than 80%, which is used to block heat conduction and convection and allow the transmission of infrared light of the 8-13 μm band; the thickness of the nanofiber porous thermal insulation layer 30 is 50 μm;

[0054] Specifically, the three-dimensional network structure is formed by the interweaving of polymer nanofibers prepared by electrospinning technology; the polymer nanofibers are made of polyvinylidene fluoride (PVDF) or the like; wherein the diameter of a single fiber is 100 nm, the porosity is 85%, and the thickness is 100 μm.

[0055] It should be noted that the nanofiber porous thermal insulation layer 30 effectively blocks the heat conduction and convection from the external environment through the large number of micron and nanoscale pores inside it; since the intrinsic vibration absorption peak of the polymer constituting the nanofiber is usually not in the 8-13 μm band, this layer is highly transparent to infrared radiation of this band, allowing the radiative cooling of the inner layer to pass unobstructed;

[0056] The atmospheric window radiation layer 40 is a functional layer in which high emissivity inorganic nanoparticles are coated or blended on the inner surface of the nanofiber porous heat insulation layer 30, for efficiently emitting infrared radiation in the 8-13μm band into the outer space of the atmosphere; the thickness of the atmospheric window radiation layer 40 is 10μm.

[0057] Specifically, the high-emissivity inorganic nanoparticles are made of silicon dioxide (SiO2). These materials exhibit intrinsically high emissivity >0.9 in the 8-13 μm wavelength range; particle size: 0.5 μm, to ensure effective infrared emission;

[0058] It should be noted that the atmospheric window radiation layer 40 is made of high emissivity inorganic nanoparticles that are firmly attached to the lower surface (or the entire skeleton) of the nanofiber porous heat insulation layer 30 through coating, impregnation or blending. As the core cooling unit, it efficiently emits infrared radiation in the 8-13 μm band and dissipates heat directly into the cold outer space through the atmospheric window.

[0059] Example 2

[0060] The biomimetic multilayer nanofiber radiation cooling and heat insulation film of the present invention comprises, from the outside to the inside: a biomimetic antireflection layer 10, a solar spectrum reflection layer 20, a nanofiber porous heat insulation layer 30, and an atmospheric window radiation layer 40.

[0061] The biomimetic antireflective layer 10 is a subwavelength nano-protrusion array that mimics the structure of a moth's eye. It is formed on the outer surface of the solar spectrum reflective layer 20 to reduce the reflection of sunlight and increase broadband antireflective performance. The thickness of the biomimetic antireflective layer 10 is 500 nm.

[0062] Specifically, the nano-protrusions of the biomimetic antireflection layer 10 are conical or hemispherical, with a diameter of 350 nm and a height of 450 nm;

[0063] The biomimetic antireflective layer 10 is typically made of a high-refractive-index, weather-resistant transparent polymer (such as a UV-curable resin) or a metal oxide (such as TiO2, Si3N4); the mass ratio of the weather-resistant transparent polymer to the metal oxide is 100:30.

[0064] Among them, the subwavelength nano-protrusion array that mimics the structure of a moth's eye is used to reduce the surface reflectivity of sunlight in the solar spectrum (especially visible and near-infrared light), increase the incident light, and thus indirectly improve the overall structure's ability to reflect sunlight.

[0065] The solar spectral reflective layer 20 is a polymer film doped with high reflectivity nanoparticles, used for high reflectivity reflection of sunlight in the 1.0 μm band;

[0066] Specifically, the solar spectral reflective layer 20 is composed of a transparent polymer matrix (such as TPU) uniformly doped with inorganic nanoparticles with high refractive index and low absorption; the mass ratio of the transparent polymer matrix to the inorganic nanoparticles is 100:40.

[0067] Among them, the inorganic nanoparticles are selected from one or more of titanium dioxide (TiO2), zinc oxide (ZnO), and barium sulfate (BaSO4); the particle size is controlled at 150 nm to minimize Rayleigh scattering; the thickness of the solar spectral reflective layer 20 is usually 30 μm.

[0068] It should be noted that the solar spectral reflective layer 20, as the core reflective unit, provides high reflectivity across almost the entire spectrum of sunlight in the 250nm-2.5μm band (target > 92%), minimizing the absorption of solar radiation energy.

[0069] The nanofiber porous heat insulation layer 30 is a porous membrane formed by interwoven polymer nanofibers prepared by electrospinning technology. Its porosity is greater than 80%, which is used to block heat conduction and convection, and allows infrared light in the 8-13μm band to pass through; the thickness of the nanofiber porous heat insulation layer 30 is 50μm-300μm.

[0070] Specifically, a three-dimensional network structure is formed by interwoven polymer nanofibers prepared by electrospinning technology; the polymer nanofibers are made of polyurethane (PU); wherein, the diameter of a single fiber is 300 nm, the porosity is >88%, and the thickness is 300 μm.

[0071] It should be noted that the nanofiber porous insulation layer 30 effectively blocks heat conduction and convection from the external environment through the large number of micron and nano-sized pores inside it; since the intrinsic vibration absorption peak of the polymer that makes up the nanofiber is usually not in the 8-13μm band, the layer is highly transparent to infrared radiation in this band, allowing the radiation from the inner layer to pass through unimpeded.

[0072] The atmospheric window radiation layer 40 is a functional layer with high emissivity inorganic nanoparticles coated or blended on the inner surface of the nanofiber porous heat insulation layer 30. It is used to efficiently emit infrared radiation in the 8-13μm band into the outer space of the atmosphere. The thickness of the atmospheric window radiation layer 40 is 30μm.

[0073] Specifically, the high-emissivity inorganic nanoparticles are made of silicon carbide (SiC). These materials exhibit intrinsically high emissivity >0.9 in the 8-13 μm wavelength range; particle size: 2.5 μm, to ensure effective infrared emission;

[0074] It should be noted that the atmospheric window radiation layer 40 is made of high emissivity inorganic nanoparticles that are firmly attached to the lower surface (or the entire skeleton) of the nanofiber porous heat insulation layer 30 through coating, impregnation or blending. As the core cooling unit, it efficiently emits infrared radiation in the 8-13 μm band and dissipates heat directly into the cold outer space through the atmospheric window.

[0075] Example 3

[0076] The biomimetic multilayer nanofiber radiation cooling and heat insulation film of the present invention comprises, from the outside to the inside: a biomimetic antireflection layer 10, a solar spectrum reflection layer 20, a nanofiber porous heat insulation layer 30, and an atmospheric window radiation layer 40.

[0077] The biomimetic antireflective layer 10 is a subwavelength nano-protrusion array that mimics the structure of a moth's eye. It is formed on the outer surface of the solar spectrum reflective layer 20 to reduce the reflection of sunlight and increase broadband antireflective performance. The thickness of the biomimetic antireflective layer 10 is 800 nm.

[0078] Specifically, the nano-protrusions of the biomimetic antireflection layer 10 are conical or hemispherical, with a diameter of 500 nm and a height of 600 nm;

[0079] The biomimetic antireflective layer 10 is typically made of a high-refractive-index, weather-resistant transparent polymer (such as a UV-curable resin) or a metal oxide (such as TiO2, Si3N4); the mass ratio of the weather-resistant transparent polymer to the metal oxide is 100:60.

[0080] Among them, the subwavelength nano-protrusion array that mimics the structure of a moth's eye is used to reduce the surface reflectivity of sunlight in the solar spectrum (especially visible and near-infrared light), increase the incident light, and thus indirectly improve the overall structure's ability to reflect sunlight.

[0081] The solar spectral reflective layer 20 is a polymer film doped with high reflectivity nanoparticles, used for high reflectivity reflection of sunlight in the 250nm-2.5μm wavelength band;

[0082] Specifically, the solar spectral reflective layer 20 is composed of a transparent polymer matrix (such as PVDF) uniformly doped with inorganic nanoparticles with high refractive index and low absorption; the mass ratio of the transparent polymer matrix to the inorganic nanoparticles is 100:80.

[0083] Among them, the inorganic nanoparticles are selected from barium sulfate (BaSO4); the particle size is controlled at 300 nm to minimize Rayleigh scattering; the thickness of the solar spectral reflective layer 20 is typically 50 μm.

[0084] It should be noted that the solar spectral reflective layer 20, as the core reflective unit, provides high reflectivity across almost the entire spectrum of sunlight in the 250nm-2.5μm band (target > 92%), minimizing the absorption of solar radiation energy.

[0085] The nanofiber porous heat insulation layer 30 is a porous membrane formed by interwoven polymer nanofibers prepared by electrospinning technology. Its porosity is greater than 80%, which is used to block heat conduction and convection, and allows infrared light in the 8-13μm band to pass through; the thickness of the nanofiber porous heat insulation layer 30 is 300μm.

[0086] Specifically, a three-dimensional network structure is formed by interwoven polymer nanofibers prepared by electrospinning technology; the polymer nanofibers are polyacrylonitrile (PAN); wherein, the diameter of a single fiber is 500 nm, the porosity is >80%, and the thickness is 500 μm.

[0087] It should be noted that the nanofiber porous insulation layer 30 effectively blocks heat conduction and convection from the external environment through the large number of micron and nano-sized pores inside it; since the intrinsic vibration absorption peak of the polymer that makes up the nanofiber is usually not in the 8-13μm band, the layer is highly transparent to infrared radiation in this band, allowing the radiation from the inner layer to pass through unimpeded.

[0088] The atmospheric window radiation layer 40 is a functional layer with high emissivity inorganic nanoparticles coated or blended on the inner surface of the nanofiber porous heat insulation layer 30. It is used to efficiently emit infrared radiation in the 8-13μm band into the outer space of the atmosphere. The thickness of the atmospheric window radiation layer 40 is 50μm.

[0089] Specifically, the high-emissivity inorganic nanoparticles are boron nitride (BN). These materials exhibit intrinsically high emissivity >0.9 in the 8-13 μm wavelength range; particle size: 5 μm, to ensure effective infrared emission;

[0090] It should be noted that the atmospheric window radiation layer 40 is made of high emissivity inorganic nanoparticles that are firmly attached to the lower surface (or the entire skeleton) of the nanofiber porous heat insulation layer 30 through coating, impregnation or blending. As the core cooling unit, it efficiently emits infrared radiation in the 8-13 μm band and dissipates heat directly into the cold outer space through the atmospheric window.

[0091] Example 4

[0092] The method for preparing a biomimetic multilayer nanofiber radiation cooling and heat insulation film according to an embodiment of the present invention includes the following steps:

[0093] Step 1: Using electrospinning technology, a polymer solution containing high emissivity nanoparticles (such as SiO2) is spun directly onto a cylindrical metal roller with a diameter of 20cm and a length of 30cm to form a composite structure of a nanofiber porous heat insulation layer 30 and an atmospheric window radiation layer 40, thus obtaining the nanofiber composite lower layer.

[0094] Step 2: First, a polymer film doped with high-reflectivity nanoparticles is prepared by casting, stretching or coating to obtain a solar spectral reflective layer 20.

[0095] Then, a biomimetic moth-eye structure (i.e., biomimetic antireflective layer 10) is prepared on the surface of the film using nanoimprinting or self-assembly techniques, forming a biomimetic composite upper layer.

[0096] Step 3: The biomimetic composite upper layer and the nanofiber composite lower layer prepared above are laminated together using an environmentally friendly adhesive to obtain the final multilayer composite heat insulation film.

[0097] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A biomimetic multilayer nanofiber radiation cooling and heat insulation film, characterized in that: From the outside to the inside, it includes: a biomimetic anti-reflection layer (10), a solar spectrum reflective layer (20), a nanofiber porous heat insulation layer (30), and an atmospheric window radiation layer (40). The biomimetic antireflective layer (10) is a subwavelength nano-protrusion array that mimics the structure of a moth's eye and is formed on the outer surface of the solar spectrum reflective layer (20) to reduce the reflection of sunlight and increase the antireflective performance of a wide band; the nanofiber radiation cooling and heat insulation film introduces a moth-eye-like nanostructure as the outermost layer. The solar spectrum reflective layer (20) is a polymer film doped with high reflectivity nanoparticles, used for high reflectivity reflection of sunlight in the 250nm-2.5μm band; The nanofiber porous heat insulation layer (30) is a porous membrane formed by interwoven polymer nanofibers prepared by electrospinning technology. Its porosity is greater than 80%, which is used to block heat conduction and convection and allows infrared rays in the 8-13μm band to pass through. The atmospheric window radiation layer (40) is a functional layer with high emissivity inorganic nanoparticles coated or blended on the inner surface of the nanofiber porous heat insulation layer (30) for emitting infrared radiation in the 8-13μm band to the outer space of the atmosphere.

2. The biomimetic multilayer nanofiber radiation cooling and heat insulation film according to claim 1, characterized in that: The nanoprotrusions of the biomimetic antireflective layer (10) are conical or hemispherical, with a diameter of 200-500 nm and a height of 300-600 nm.

3. The biomimetic multilayer nanofiber radiation cooling and heat insulation film according to claim 2, characterized in that: The biomimetic antireflective layer (10) is made of a transparent polymer or metal oxide with high refractive index and weather resistance; the thickness of the biomimetic antireflective layer (10) is 200nm-800nm.

4. The biomimetic multilayer nanofiber radiation cooling and heat insulation film according to claim 1, characterized in that: The solar spectral reflective layer (20) is composed of inorganic nanoparticles with high refractive index and low absorption uniformly doped into a transparent polymer matrix.

5. The biomimetic multilayer nanofiber radiation cooling and heat insulation film according to claim 4, characterized in that: The inorganic nanoparticles are selected from one or more of titanium dioxide, zinc oxide, and barium sulfate.

6. The biomimetic multilayer nanofiber radiation cooling and heat insulation film according to claim 5, characterized in that: The particle size of the inorganic nanoparticles is controlled at 50-300 nm to minimize Rayleigh scattering; the thickness of the solar spectral reflective layer (20) is 10-50 μm.

7. The biomimetic multilayer nanofiber radiation cooling and heat insulation film according to claim 6, characterized in that: The thickness of the nanofiber porous insulation layer (30) is 50μm-300μm; the polymer nanofibers are one or more of polyvinylidene fluoride, polyurethane, and polyacrylonitrile; wherein, the diameter of a single fiber is 100-500 nm, the porosity is >80%, and the thickness is 100-500μm.

8. The biomimetic multilayer nanofiber radiation cooling and heat insulation film according to claim 7, characterized in that: High-emissivity inorganic nanoparticles are made of one or more of silicon dioxide, silicon carbide, and boron nitride.

9. The biomimetic multilayer nanofiber radiation cooling and heat insulation film according to claim 8, characterized in that: The atmospheric window radiation layer (40) has a thickness of 10μm-50μm, and the particle size of the high emissivity inorganic nanoparticles is 0.5-5μm.

10. The biomimetic multilayer nanofiber radiation cooling and heat insulation film according to claim 1, characterized in that: The preparation method of this nanofiber radiation cooling and heat insulation film includes the following steps: Step 1: Using electrospinning technology, a polymer solution containing high emissivity nanoparticles is spun and directly formed on a cylindrical metal roller with a diameter of 20cm and a length of 30cm to form a composite structure of a nanofiber porous heat insulation layer (30) and an atmospheric window radiation layer (40), thus obtaining the nanofiber composite lower layer. Step 2: First, a polymer film doped with high-reflectivity nanoparticles is prepared by casting, stretching or coating to obtain a solar spectral reflective layer (20). Then, a biomimetic moth-eye structure is fabricated on the surface of the film using nanoimprinting or self-assembly techniques to form a biomimetic antireflection layer. Step 3: The biomimetic antireflective layer prepared above is laminated with the nanofiber composite lower layer using an environmentally friendly adhesive to obtain the final nanofiber radiation cooling and heat insulation film.

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