Visible-near infrared frequency-dividing radiation cooling film based on bionic rose petal micro-nano structure and its preparation method and application

Abstract

The present invention relates to a visible-near-infrared frequency-dividing radiation cooling film based on a bionic rose petal micro-nano structure and a preparation method and application thereof, belonging to the field of radiation cooling technology. In order to solve the problem that existing radiation cooling materials cannot take into account both lighting and cooling performance, the present invention provides a visible-near-infrared frequency-dividing radiation cooling film based on a bionic rose petal micro-nano structure, comprising a transparent bionic micro-nano structure layer and a multilayer film structure layer of a bionic rose petal structure arranged from top to bottom, the surface of the transparent bionic micro-nano structure layer is distributed with a first cone micro-nano structure in an array; the surface of the first cone micro-nano structure is distributed with a second cone micro-nano structure in an array. The present invention realizes the selective transmission of solar radiation energy by the radiation cooling film, realizes the visible-near-infrared band frequency-dividing function and the high emission performance of the atmospheric window, can take into account both lighting and cooling performance, thereby broadening the scope of application of the radiation cooling material.

Description

Technical Field

[0001] The present invention belongs to the field of radiation cooling technology, and in particular relates to a visible-near infrared frequency division type radiation cooling film based on a bionic rose petal micro-nano structure, and a preparation method and application thereof. Background Art

[0002] As an environmentally friendly, zero-energy passive cooling technology, radiation cooling technology can effectively reduce the energy consumption of existing conventional refrigeration, alleviate the energy and environmental crisis, and has broad application prospects. Among them, daytime radiation cooling technology can achieve cooling below air temperature without any energy consumption by strongly reflecting solar radiation energy (0.3-2.5μm) and using atmospheric windows (8-13μm) to exchange heat with outer space through radiation. Existing materials used for daytime radiation cooling include radiation cooling coatings, radiation cooling films, porous polymer structural materials and wooden structural materials. They have been applied to building exterior walls, large oil depots, cold chain transportation, aircraft bridges, human thermal management and other fields, and have achieved considerable cooling power.

[0003] However, existing daytime radiation cooling materials strongly and indiscriminately reflect the full spectrum of solar radiation energy, and fail to consider the requirements of the application scenarios for lighting and appearance. They cannot be applied to scenes such as glass roofs, photovoltaic cells, and car windows that have high requirements for lighting and appearance. The radiation cooling materials used in these scenes not only need to improve the emissivity of the atmospheric window band, but also need to consider the transmittance of the visible light band. The few radiation cooling coatings that consider high transmittance performance of visible light fail to shield the adverse effects of near-infrared heat on the cooling load. Therefore, it is urgent to develop a new type of radiation cooling material that can selectively transmit solar radiation energy and has high emissivity performance of atmospheric windows. Summary of the invention

[0004] In order to solve the problem that existing radiation cooling materials cannot take into account both lighting and cooling performance, the present invention provides a visible-near infrared frequency-dividing radiation cooling film based on a bionic rose petal micro-nano structure, and a preparation method and application thereof.

[0005] The technical solution of the present invention:

[0006] The visible-near infrared frequency-dividing radiation cooling film based on the bionic rose petal micro-nano structure comprises a transparent bionic rose petal structure layer and a multi-layer film structure layer arranged from top to bottom.

[0007] The surface of the transparent bionic micro-nano structure layer is provided with first pyramidal micro-nano structures distributed in an array;

[0008] The surface of the first pyramidal micro-nano structure is distributed with second pyramidal micro-nano structures in an array;

[0009] The height ratio of the first pyramidal micro-nano structure to the second pyramidal micro-nano structure is 5-20:0.5-1.5;

[0010] The multi-layer thin film structure layer comprises a transparent cooling layer, a SiO2 buffer layer, an ITO frequency division layer and a SiO2 substrate layer which are arranged from top to bottom.

[0011] Furthermore, the first pyramidal micro-nanostructure is a pyramidal micro-nanostructure or a conical micro-nanostructure with at least three sides at the bottom, the bottom length of the pyramidal micro-nanostructure is 5-20 μm, and the height is 5-20 μm; the bottom diameter of the conical micro-nanostructure is 4-20 μm, and the height is 5-20 μm; the first pyramidal micro-nanostructure is equidistantly arranged, and the spacing is 4-15 μm;

[0012] The second cone micro-nano structure is a pyramidal micro-nano structure or a conical micro-nano structure with at least three sides on the bottom. The bottom length of the pyramidal micro-nano structure is 0.5-1.5 μm, and the height is 0.5-1.5 μm; the bottom diameter of the conical micro-nano structure is 0.4-1.6 μm, and the height is 0.5-1.5 μm; the second cone micro-nano structure is arranged equidistantly with a spacing of 0.2-1.5 μm.

[0013] Furthermore, the thickness of the transparent cooling layer is 5-100 μm, the thickness of the SiO2 buffer layer is 0.5-5 μm, the thickness of the ITO frequency division layer is 0.5-4 μm, and the thickness of the SiO2 substrate layer is 0.5-5 μm.

[0014] Furthermore, the transparent bionic micro-nano structure layer and the transparent refrigeration layer are both prepared from materials selected from the group consisting of PDMS, PMMA, PVDF and PET.

[0015] A method for preparing a visible-near infrared frequency-dividing radiation cooling film based on a bionic rose petal micro-nano structure, the steps are as follows:

[0016] Step 1: Preparation of transparent bionic micro-nano structure layer:

[0017] A bionic micro-nano structure mold is prepared by wet etching technology and aluminum anodizing method, and a transparent bionic micro-nano structure layer is prepared by hot pressing process based on the obtained bionic micro-nano structure mold;

[0018] Step 2: Preparation of multi-layer thin film structure layer:

[0019] A SiO2 substrate layer, an ITO frequency division layer, a SiO2 buffer layer and a transparent cooling layer are prepared layer by layer by using a vacuum magnetron sputtering method, an electron beam evaporation method, a chemical vapor deposition method or a sol-gel method to obtain a multilayer thin film structure layer;

[0020] Step 3: Radiative cooling film:

[0021] The transparent bionic micro-nano structure layer obtained in step one is laid on the transparent cooling layer of the multilayer film structure layer obtained in step two to obtain a visible-near infrared frequency-divided radiation cooling film with a bionic rose petal micro-nano structure.

[0022] Furthermore, the wet etching technology in step 1 is specifically as follows:

[0023] A micro-nano template with concave cones distributed in an array is prepared on the surface of a silicon wafer by silicon anisotropic wet etching. The etching raw material is 20wt% potassium hydroxide, the etching mask is silicon nitride, and the etching rate of the plate is 1.0-1.5μm / min.

[0024] Furthermore, the aluminum anodizing method described in step 1 is specifically as follows:

[0025] Aluminum is sputtered onto the upper surface of the micro-nano template obtained by wet etching, the thickness of the sputtered aluminum layer is 1 to 2 μm, and a convex micro-nano structure is prepared on the surface of the sputtered aluminum layer by an anodic aluminum oxidation AAO process. The electrolyte is a sulfuric acid solution, an oxalic acid solution or a phosphoric acid solution, the temperature of the electrolyte is -15 to -5°C, the counter electrode of the anodization is titanium, the anodization voltage is 117 to 123 V, the voltage supply time is 2 to 10 min, and the anodization time is 4 to 16 min.

[0026] Furthermore, the hot pressing process in step 1 is specifically as follows:

[0027] The obtained bionic micro-nano structure mold and the transparent organic sheet are stacked in a hot pressing system, the hot pressing temperature is increased from 57-63°C to 127-133°C within 28-32 minutes, an embossing load of 6.0-8.0 kN is applied and maintained for 55-65 seconds, and then the temperature is cooled to 57-63°C within 4-6 minutes to obtain a transparent bionic micro-nano structure layer.

[0028] Furthermore, the specific process parameters of the electron beam evaporation method in step 2 are:

[0029] The coating pressure of SiO2 substrate layer and SiO2 buffer layer is 0.45~0.55Pa, the coating power is 1000~2000W, and the coating time is 3~10h.

[0030] The argon-oxygen ratio of the ITO frequency division layer is 20:1-50:1, the coating power is 1000-2000W, and the coating time is 0.5-3h;

[0031] The coating power of the transparent cooling layer is 500 to 2200 W, and the coating time is 0.5 to 6 hours.

[0032] The application of visible-near-infrared frequency-splitting radiation cooling film based on bionic rose petal micro-nano structure in glass building exterior walls, photovoltaic cells and car windows.

[0033] Beneficial effects of the present invention:

[0034] The present invention utilizes the comprehensive optical properties of the bionic rose petal micro-nano structure and a variety of thin film structures to achieve the selective transmission of solar radiation energy by the radiative cooling film, realize the visible-near infrared band frequency division function and the high emission performance of the atmospheric window, and can take into account both lighting and refrigeration performance, thereby broadening the scope of application of radiative cooling technology.

[0035] The finite difference time domain method (FDTD) based on modern electromagnetic theory calculates that the average transmittance of the radiative cooling film provided by the present invention to near-infrared light is as low as 7.8%, while the average transmittance to visible light can reach up to 85.7%, and the average emissivity of the atmospheric window can reach up to 98.8%. The use of this film can enable the radiative cooling technology to be applied to facilities with high requirements for lighting and appearance, such as various large commercial buildings, solar cells, and car windows. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The schematic diagram of the structure of the visible-near infrared frequency-dividing radiation cooling film based on the micro-nano structure of the bionic rose petals;

[0037] Figure 2 Schematic diagram of the working principle of the visible-near infrared frequency-dividing radiation cooling film based on the micro-nano structure of bionic rose petals;

[0038] Figure 3 The solar spectrum (0.3-2.5 μm) transmittance and atmospheric window (8-13 μm) emissivity curves of the radiative cooling film prepared in Example 1;

[0039] Figure 4 The solar spectrum (0.3-2.5 μm) transmittance and atmospheric window (8-13 μm) emissivity curves of the radiative cooling film prepared in Example 2;

[0040] Figure 5 The solar spectrum (0.3-2.5 μm) transmittance and atmospheric window (8-13 μm) emissivity curves of the radiative cooling film prepared in Example 3;

[0041] Figure 6 The solar spectrum (0.3-2.5 μm) transmittance and atmospheric window (8-13 μm) emissivity curves of the radiative cooling film prepared in Example 4;

[0042] Figure 7A comparison chart of the transmittance curves of the solar spectrum (0.3-2.5 μm) of the radiative cooling film prepared in Example 2 and the radiative cooling film prepared in Comparative Example 1;

[0043] Figure 8 It is a comparison diagram of the atmospheric window (8-13 μm) emissivity curves of the radiative cooling film prepared in Example 2 and the radiative cooling film prepared in Comparative Example 1;

[0044] In the figure, 1. transparent bionic micro-nano structure layer, 1-1. first cone micro-nano structure, 1-2. second cone micro-nano structure, 2. multi-layer thin film structure layer, 2-1. transparent refrigeration layer, 2-2. SiO2 buffer layer, 2-3. ITO frequency division layer, 2-4. SiO2 substrate layer. DETAILED DESCRIPTION

[0045] The technical solution of the present invention is further described below in conjunction with the embodiments, but it is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be included in the protection scope of the present invention. The process equipment or devices not specifically noted in the following embodiments are all conventional equipment or devices in the art. If not specifically specified, the raw materials used in the embodiments of the present invention can be obtained commercially; if not specifically specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0046] Example 1

[0047] The present embodiment provides a visible-near infrared frequency-dividing radiation cooling film based on a bionic rose petal micro-nano structure and a preparation method thereof.

[0048] The radiation cooling film of this embodiment includes a transparent bionic micro-nano structure 1 of a bionic rose petal structure and a multi-layer film structure layer 2.

[0049] The transparent bionic micro-nano structure 1 is a first pyramidal micro-nano structure 1-1 and is distributed in an array on the upper surface of the multilayer thin film structure layer 2; the surface of the first pyramidal micro-nano structure 1-1 is distributed with second pyramidal micro-nano structures 1-2 in an array.

[0050] In this embodiment, the first pyramidal micro-nanostructure 1-1 is a regular quadrangular pyramidal micro-nanostructure with a base length of 10 μm and a height of 11 μm; the second pyramidal micro-nanostructure 1-2 is a regular quadrangular pyramidal micro-nanostructure with a base length of 1 μm and a height of 1.5 μm.

[0051] In this embodiment, the multilayer thin film structure layer 2 includes a transparent cooling layer 2-1, a SiO2 buffer layer 2-2, an ITO (indium tin oxide) frequency division layer 2-3 and a SiO2 base layer 2-4 arranged from top to bottom. The thickness of the transparent cooling layer 2-1 is 15 μm, the thickness of the SiO2 buffer layer 2-2 is 5 μm, the thickness of the ITO frequency division layer 2-3 is 3.5 μm, and the thickness of the SiO2 base layer 2-4 is 5 μm.

[0052] In this embodiment, the transparent bionic micro-nano structure and the transparent refrigeration layer are both made of PDMS (polydimethylsiloxane).

[0053] The steps of the preparation method of the radiation cooling film in this embodiment are as follows:

[0054] Step 1: Preparation of transparent bionic micro-nanostructures:

[0055] (I) Preparation of bionic micro-nanostructure molds:

[0056] Using 20wt% potassium hydroxide as the etching raw material and silicon nitride (Si3N4) as the etching mask, etching was performed on the surface of a 4-inch silicon wafer at 80°C with a flat plate etching rate of 1.1μm / min for 20 minutes to prepare a micro-nano template with concave cones distributed in an array. The size of the concave cones corresponds to the size of the first cone micro-nano structure 1-1. The concave cones on the micro-nano template of this embodiment are equidistantly arranged with a distance of 10μm.

[0057] The silicon nitride mask on the surface of the silicon wafer is removed, and aluminum is sputtered onto the upper surface of the micro-nano template obtained by wet etching. The thickness of the sputtered aluminum layer is 1 μm. An anodic aluminum oxidation (AAO) process is used to prepare a convex micro-nano structure on the surface of the sputtered aluminum layer.

[0058] In this embodiment, the electrolyte of the AAO process is 0.04 mol / L oxalic acid solution, the electrolyte temperature is -10°C, titanium is used as the counter electrode in the anodizing process, the voltage is 120 V, the voltage supply time is 2 min, the anodizing time is 4 min, and the spacing of the convex micro-nano structures distributed in an array on the upper surface of the obtained micro-nano template is 300 nm, and the size of the convex micro-nano structure corresponds to the size of the second cone micro-nano structure 1-2.

[0059] By using the bionic micro-nano structure mold prepared in this embodiment, bionic rose petal structures composed of hierarchical micro-nano structures can be prepared in batches on the surface of PDMS material.

[0060] (II) Preparation of transparent bionic micro-nanostructures:

[0061] The hot pressing system used in this embodiment consists of an upper and lower module and a heating and cooling unit operated by an air compressor. The obtained biomimetic micro-nano structure mold is fixed on the top of the lower module, a PDMS sheet with a thickness of 30 μm is placed on the mold, the temperature of the upper and lower modules is heated, the hot pressing temperature is increased from 60°C to 130°C within 30 minutes, an embossing load of 7.0 kN is applied and maintained for 60 seconds, and then the temperature is cooled to 60°C within 5 minutes, and the hot-pressed PDMS sheet is released from the mold to obtain a transparent biomimetic micro-nano structure layer.

[0062] Step 2: Preparation of multi-layer thin film structure layer:

[0063] In this embodiment, the multi-layer thin film structure layer is prepared by electron beam evaporation method, and the electron beam evaporation equipment is: PVD75Proline SP; manufacturer: Kurt J. Lesker Company, USA).

[0064] The glass substrate is placed in an ultrasonic cleaner for about 25 minutes to remove surface dirt, and then a SiO2 base layer, an ITO frequency division layer, a SiO2 buffer layer and a transparent cooling layer are prepared layer by layer on the glass substrate to obtain a multilayer thin film structure layer.

[0065] Among them, the coating pressure of SiO2 substrate layer and SiO2 buffer layer is 0.5Pa, the coating power is 2000W, and the coating time is 10h; the argon-oxygen ratio of ITO frequency division layer is 50:1, the coating power is 2000W, and the coating time is 2h; the coating power of transparent cooling layer is 1000W, and the coating time is 3h. When replacing the evaporation material, the evaporation should be performed without exposing the multilayer structure sample to ambient air.

[0066] Step 3: Radiative cooling film:

[0067] The transparent bionic micro-nano structure layer obtained in step one is laid on the transparent cooling layer of the multilayer film structure layer obtained in step two to obtain a visible-near infrared frequency-divided radiation cooling film with a bionic rose petal micro-nano structure.

[0068] In this embodiment, the geometric shape and size of the bionic rose petal micro-nano structure are designed based on the natural rose petals, and the surface structure of the natural rose petals is composed of microstructures such as cones and nano-folds. The transparent bionic micro-nano structure prepared by bionics has the effect of reducing the reflection loss of visible light and improving the emissivity of the atmospheric window.

[0069] The SiO2 base layer in the multi-layer thin film structure layer protects the ITO frequency division layer and reduces the visible light reflection loss when the radiation cooling film is bonded to the transparent glass. The ITO frequency division layer blocks the near-infrared radiation in the sunlight. The SiO2 buffer layer reduces the refractive index change inside the radiation cooling film and improves the visible light transmittance. The transparent cooling layer improves the emissivity of the atmospheric window and enhances the cooling effect.

[0070] By utilizing the comprehensive optical properties of the bionic rose petal micro-nano structure and a variety of thin film structures, the radiative cooling film can selectively transmit solar radiation energy, achieve the visible-near infrared band frequency division function and high emission performance of the atmospheric window, so that the radiative cooling film can take into account both lighting and cooling performance.

[0071] Figure 3 The solar spectrum (0.3-2.5μm) transmittance and atmospheric window (8-13μm) emissivity curve of the radiative cooling film prepared in this embodiment are shown in the figure. As shown in the figure, the visible light transmittance of the radiative cooling film is 78.6%, the near infrared transmittance is only 7.8%, and the atmospheric window emissivity is 98.8%. The cooling effect of the radiative cooling film in this embodiment is the best case of the design value.

[0072] Example 2

[0073] The present embodiment provides a visible-near infrared frequency-dividing radiation cooling film based on a bionic rose petal micro-nano structure and a preparation method thereof.

[0074] The radiation cooling film of this embodiment includes a transparent bionic micro-nano structure 1 of a bionic rose petal structure and a multi-layer film structure layer 2.

[0075] The transparent bionic micro-nano structure 1 is a first pyramidal micro-nano structure 1-1 and is distributed in an array on the upper surface of the multilayer thin film structure layer 2; the surface of the first pyramidal micro-nano structure 1-1 is distributed with second pyramidal micro-nano structures 1-2 in an array.

[0076] In this embodiment, the first pyramidal micro-nanostructure 1-1 is a regular quadrangular pyramidal micro-nanostructure with a base length of 8 μm and a height of 6 μm; the second pyramidal micro-nanostructure 1-2 is a regular quadrangular pyramidal micro-nanostructure with a base length of 0.8 μm and a height of 1 μm.

[0077] In this embodiment, the multilayer thin film structure layer 2 includes a transparent cooling layer 2-1, a SiO2 buffer layer 2-2, an ITO (indium tin oxide) frequency division layer 2-3 and a SiO2 base layer 2-4 arranged from top to bottom. The thickness of the transparent cooling layer 2-1 is 5 μm, the thickness of the SiO2 buffer layer 2-2 is 3 μm, the thickness of the ITO frequency division layer 2-3 is 2.5 μm, and the thickness of the SiO2 base layer 2-4 is 3 μm.

[0078] In this embodiment, the transparent bionic micro-nano structure and the transparent refrigeration layer are both made of PDMS (polydimethylsiloxane).

[0079] The steps of the preparation method of the radiation cooling film in this embodiment are as follows:

[0080] Step 1: Preparation of transparent bionic micro-nanostructures:

[0081] (I) Preparation of bionic micro-nanostructure molds:

[0082] Using 20wt% potassium hydroxide as the etching raw material and silicon nitride (Si3N4) as the etching mask, etching was performed on the surface of a 4-inch silicon wafer at 80°C with a flat plate etching rate of 1.1μm / min for 20 minutes to prepare a micro-nano template with concave cones distributed in an array. The size of the concave cones corresponds to the size of the first cone micro-nano structure 1-1. The concave cones on the micro-nano template of this embodiment are equidistantly arranged with a distance of 8μm.

[0083] The silicon nitride mask on the surface of the silicon wafer is removed, and aluminum is sputtered onto the upper surface of the micro-nano template obtained by wet etching. The thickness of the sputtered aluminum layer is 1 μm. An anodic aluminum oxidation (AAO) process is used to prepare a convex micro-nano structure on the surface of the sputtered aluminum layer.

[0084] In this embodiment, the electrolyte of the AAO process is 0.05 mol / L oxalic acid solution, the electrolyte temperature is -10°C, titanium is used as the counter electrode in the anodizing process, the voltage is 120 V, the voltage supply time is 1.5 min, the anodizing time is 3 min, and the spacing of the convex micro-nano structures distributed in an array on the upper surface of the obtained micro-nano template is 200 nm, and the size of the convex micro-nano structure corresponds to the size of the second cone micro-nano structure 1-2.

[0085] By using the bionic micro-nano structure mold prepared in this embodiment, bionic rose petal structures composed of hierarchical micro-nano structures can be prepared in batches on the surface of PDMS material.

[0086] (II) Preparation of transparent bionic micro-nanostructures:

[0087] The hot pressing system used in this embodiment consists of an upper and lower module and a heating and cooling unit operated by an air compressor. The obtained biomimetic micro-nano structure mold is fixed on the top of the lower module, a PDMS sheet with a thickness of 15 μm is placed on the mold, the temperature of the upper and lower modules is heated, the hot pressing temperature is increased from 60°C to 130°C within 30 minutes, an embossing load of 7.0 kN is applied and maintained for 60 seconds, and then the temperature is cooled to 60°C within 5 minutes, and the hot-pressed PDMS sheet is released from the mold to obtain a transparent biomimetic micro-nano structure layer.

[0088] Step 2: Preparation of multi-layer thin film structure layer:

[0089] In this embodiment, the multi-layer thin film structure layer is prepared by electron beam evaporation method, and the electron beam evaporation equipment is: PVD75Proline SP; manufacturer: Kurt J. Lesker Company, USA).

[0090] The glass substrate is placed in an ultrasonic cleaner for about 25 minutes to remove surface dirt, and then a SiO2 base layer, an ITO frequency division layer, a SiO2 buffer layer and a transparent cooling layer are prepared layer by layer on the glass substrate to obtain a multilayer thin film structure layer.

[0091] Among them, the coating pressure of SiO2 substrate layer and SiO2 buffer layer is 0.5Pa, the coating power is 1500W, and the coating time is 6h; the argon-oxygen ratio of ITO frequency division layer is 50:1, the coating power is 1400W, and the coating time is 1.8h; the coating power of transparent cooling layer is 500W, and the coating time is 0.5h. When replacing the evaporation material, the evaporation should be performed without exposing the multilayer structure sample to ambient air.

[0092] Step 3: Radiative cooling film:

[0093] The transparent bionic micro-nano structure layer obtained in step one is laid on the transparent cooling layer of the multilayer film structure layer obtained in step two to obtain a visible-near infrared frequency-divided radiation cooling film with a bionic rose petal micro-nano structure.

[0094] Figure 4 The solar spectrum (0.3-2.5 μm) transmittance and atmospheric window (8-13 μm) emissivity curve of the radiative cooling film prepared in Example 2 are shown; as shown in the figure, the visible light transmittance of the radiative cooling film is 84.1%, the near-infrared transmittance is only 14%, and the atmospheric window emissivity is 95.1%.

[0095] Example 3

[0096] The present embodiment provides a visible-near infrared frequency-dividing radiation cooling film based on a bionic rose petal micro-nano structure and a preparation method thereof.

[0097] The radiation cooling film of this embodiment includes a transparent bionic micro-nano structure 1 of a bionic rose petal structure and a multi-layer film structure layer 2.

[0098] The transparent bionic micro-nano structure 1 is a first pyramidal micro-nano structure 1-1 and is distributed in an array on the upper surface of the multilayer thin film structure layer 2; the surface of the first pyramidal micro-nano structure 1-1 is distributed with second pyramidal micro-nano structures 1-2 in an array.

[0099] In this embodiment, the first pyramidal micro-nanostructure 1-1 is a regular quadrangular pyramidal micro-nanostructure with a base length of 8 μm and a height of 6 μm; the second pyramidal micro-nanostructure 1-2 is a regular quadrangular pyramidal micro-nanostructure with a base length of 0.8 μm and a height of 1 μm.

[0100] In this embodiment, the multilayer thin film structure layer 2 includes a transparent cooling layer 2-1, a SiO2 buffer layer 2-2, an ITO (indium tin oxide) frequency division layer 2-3 and a SiO2 base layer 2-4 arranged from top to bottom. The thickness of the transparent cooling layer 2-1 is 11 μm, the thickness of the SiO2 buffer layer 2-2 is 3 μm, the thickness of the ITO frequency division layer 2-3 is 2 μm, and the thickness of the SiO2 base layer 2-4 is 3 μm.

[0101] In this embodiment, the transparent bionic micro-nano structure and the transparent refrigeration layer are both made of PDMS (polydimethylsiloxane).

[0102] The steps of the preparation method of the radiation cooling film in this embodiment are as follows:

[0103] Step 1: Preparation of transparent bionic micro-nanostructures:

[0104] (I) Preparation of bionic micro-nanostructure molds:

[0105] Using 20wt% potassium hydroxide as the etching raw material and silicon nitride (Si3N4) as the etching mask, etching was performed on the surface of a 4-inch silicon wafer at 80°C with a flat plate etching rate of 1.1μm / min for 20 minutes to prepare a micro-nano template with concave cones distributed in an array. The size of the concave cones corresponds to the size of the first cone micro-nano structure 1-1. The concave cones on the micro-nano template of this embodiment are equidistantly arranged with a distance of 7μm.

[0106] The silicon nitride mask on the surface of the silicon wafer is removed, and aluminum is sputtered onto the upper surface of the micro-nano template obtained by wet etching. The thickness of the sputtered aluminum layer is 1 μm. An anodic aluminum oxidation (AAO) process is used to prepare a convex micro-nano structure on the surface of the sputtered aluminum layer.

[0107] In this embodiment, the electrolyte of the AAO process is 0.05 mol / L oxalic acid solution, the electrolyte temperature is -10°C, titanium is used as the counter electrode in the anodizing process, the voltage is 120 V, the voltage supply time is 1.5 min, the anodizing time is 3 min, and the spacing of the convex micro-nano structures distributed in an array on the upper surface of the obtained micro-nano template is 250 nm, and the size of the convex micro-nano structure corresponds to the size of the second conical micro-nano structure 1-2.

[0108] By using the bionic micro-nano structure mold prepared in this embodiment, bionic rose petal structures composed of hierarchical micro-nano structures can be prepared in batches on the surface of PDMS material.

[0109] (II) Preparation of transparent bionic micro-nanostructures:

[0110] The hot pressing system used in this embodiment consists of an upper and lower module and a heating and cooling unit operated by an air compressor. The obtained biomimetic micro-nano structure mold is fixed on the top of the lower module, a PDMS sheet with a thickness of 20 μm is placed on the mold, the temperature of the upper and lower modules is heated, the hot pressing temperature is increased from 60°C to 130°C within 30 minutes, an embossing load of 7.0 kN is applied and maintained for 60 seconds, and then the temperature is cooled to 60°C within 5 minutes, and the hot-pressed PDMS sheet is released from the mold to obtain a transparent biomimetic micro-nano structure layer.

[0111] Step 2: Preparation of multi-layer thin film structure layer:

[0112] In this embodiment, the multi-layer thin film structure layer is prepared by electron beam evaporation method, and the electron beam evaporation equipment is: PVD75Proline SP; manufacturer: Kurt J. Lesker Company, USA).

[0113] The glass substrate is placed in an ultrasonic cleaner for about 25 minutes to remove surface dirt, and then a SiO2 base layer, an ITO frequency division layer, a SiO2 buffer layer and a transparent cooling layer are prepared layer by layer on the glass substrate to obtain a multilayer thin film structure layer.

[0114] Among them, the coating pressure of SiO2 substrate layer and SiO2 buffer layer is 0.5Pa, the coating power is 1500W, and the coating time is 6h; the argon-oxygen ratio of ITO frequency division layer is 50:1, the coating power is 1000W, and the coating time is 1.5h; the coating power of transparent cooling layer is 1000W, and the coating time is 2h. When replacing the evaporation material, the evaporation should be performed without exposing the multilayer structure sample to ambient air.

[0115] Step 3: Radiative cooling film:

[0116] The transparent bionic micro-nano structure layer obtained in step one is laid on the transparent cooling layer of the multilayer film structure layer obtained in step two to obtain a visible-near infrared frequency-divided radiation cooling film with a bionic rose petal micro-nano structure.

[0117] Figure 5 The solar spectrum (0.3-2.5 μm) transmittance and atmospheric window (8-13 μm) emissivity curve of the radiative cooling film prepared in Example 3 are shown; as shown in the figure, the visible light transmittance of the radiative cooling film is 85.7%, the near-infrared transmittance is 19%, and the atmospheric window emissivity is 96.6%. The lighting effect of the radiative cooling film in this embodiment is the best case of the designed value.

[0118] Example 4

[0119] The present embodiment provides a visible-near infrared frequency-dividing radiation cooling film based on a bionic rose petal micro-nano structure and a preparation method thereof.

[0120] The radiation cooling film of this embodiment includes a transparent bionic micro-nano structure 1 of a bionic rose petal structure and a multi-layer film structure layer 2.

[0121] The transparent bionic micro-nano structure 1 is a first pyramidal micro-nano structure 1-1 and is distributed in an array on the upper surface of the multilayer thin film structure layer 2; the surface of the first pyramidal micro-nano structure 1-1 is distributed with second pyramidal micro-nano structures 1-2 in an array.

[0122] In this embodiment, the first pyramidal micro-nanostructure 1-1 is a regular quadrangular pyramidal micro-nanostructure with a base length of 8 μm and a height of 6 μm; the second pyramidal micro-nanostructure 1-2 is a regular quadrangular pyramidal micro-nanostructure with a base length of 0.8 μm and a height of 1 μm.

[0123] In this embodiment, the multilayer thin film structure layer 2 includes a transparent cooling layer 2-1, a SiO2 buffer layer 2-2, an ITO (indium tin oxide) frequency division layer 2-3 and a SiO2 base layer 2-4 arranged from top to bottom. The thickness of the transparent cooling layer 2-1 is 5 μm, the thickness of the SiO2 buffer layer 2-2 is 3 μm, the thickness of the ITO frequency division layer 2-3 is 2.5 μm, and the thickness of the SiO2 base layer 2-4 is 3 μm.

[0124] In this embodiment, the transparent bionic micro-nano structure and the transparent refrigeration layer are both made of PET (polyethylene terephthalate).

[0125] The steps of the preparation method of the radiation cooling film in this embodiment are as follows:

[0126] Step 1: Preparation of transparent bionic micro-nanostructures:

[0127] (I) Preparation of bionic micro-nanostructure molds:

[0128] Using 20wt% potassium hydroxide as the etching raw material and silicon nitride (Si3N4) as the etching mask, etching was performed on the surface of a 4-inch silicon wafer at 80°C with a flat plate etching rate of 1.1μm / min for 20 minutes to prepare a micro-nano template with concave cones distributed in an array. The size of the concave cones corresponds to the size of the first cone micro-nano structure 1-1. The concave cones on the micro-nano template of this embodiment are equidistantly arranged with a distance of 6μm.

[0129] The silicon nitride mask on the surface of the silicon wafer is removed, and aluminum is sputtered onto the upper surface of the micro-nano template obtained by wet etching. The thickness of the sputtered aluminum layer is 1 μm. An anodic aluminum oxidation (AAO) process is used to prepare a convex micro-nano structure on the surface of the sputtered aluminum layer.

[0130] In this embodiment, the electrolyte of the AAO process is 0.05 mol / L oxalic acid solution, the electrolyte temperature is -10°C, titanium is used as the counter electrode in the anodizing process, the voltage is 120 V, the voltage supply time is 1.5 min, the anodizing time is 3 min, and the spacing of the convex micro-nano structures distributed in an array on the upper surface of the obtained micro-nano template is 200 nm, and the size of the convex micro-nano structure corresponds to the size of the second cone micro-nano structure 1-2.

[0131] By using the bionic micro-nano structure mold prepared in this embodiment, bionic rose petal structures composed of hierarchical micro-nano structures can be prepared in batches on the surface of PDMS material.

[0132] (II) Preparation of transparent bionic micro-nanostructures:

[0133] The hot pressing system used in this embodiment consists of an upper and lower module and a heating and cooling unit operated by an air compressor. The obtained biomimetic micro-nano structure mold is fixed on the top of the lower module, a PDMS sheet with a thickness of 15 μm is placed on the mold, the temperature of the upper and lower modules is heated, the hot pressing temperature is increased from 60°C to 130°C within 30 minutes, an embossing load of 7.0 kN is applied and maintained for 60 seconds, and then the temperature is cooled to 60°C within 5 minutes, and the hot-pressed PDMS sheet is released from the mold to obtain a transparent biomimetic micro-nano structure layer.

[0134] Step 2: Preparation of multi-layer thin film structure layer:

[0135] In this embodiment, the multi-layer thin film structure layer is prepared by electron beam evaporation method, and the electron beam evaporation equipment is: PVD75Proline SP; manufacturer: Kurt J. Lesker Company, USA).

[0136] The glass substrate is placed in an ultrasonic cleaner for about 25 minutes to remove surface dirt, and then a SiO2 base layer, an ITO frequency division layer, a SiO2 buffer layer and a transparent cooling layer are prepared layer by layer on the glass substrate to obtain a multilayer thin film structure layer.

[0137] Among them, the coating pressure of SiO2 substrate layer and SiO2 buffer layer is 0.5Pa, the coating power is 1500W, and the coating time is 6h; the argon-oxygen ratio of ITO frequency division layer is 50:1, the coating power is 1000W, and the coating time is 1.5h; the coating power of transparent cooling layer is 600W, and the coating time is 0.5h. When replacing the evaporation material, the evaporation should be performed without exposing the multilayer structure sample to ambient air.

[0138] Step 3: Radiative cooling film:

[0139] The transparent bionic micro-nano structure layer obtained in step one is laid on the transparent cooling layer of the multilayer film structure layer obtained in step two to obtain a visible-near infrared frequency-divided radiation cooling film with a bionic rose petal micro-nano structure.

[0140] Figure 6 The solar spectrum (0.3-2.5 μm) transmittance and atmospheric window (8-13 μm) emissivity curve of the radiative cooling film prepared in Example 4 are shown; as shown in the figure, the visible light transmittance of the radiative cooling film is 80.9%, the near-infrared transmittance is 13.7%, and the atmospheric window emissivity is 94.2%.

[0141] Comparative Example 1

[0142] This comparative example provides a radiation cooling film without a bionic rose petal micro-nano structure and a preparation method thereof.

[0143] The radiation cooling film of this comparative example only has a multi-layer film structure layer, which includes a transparent cooling layer, a SiO2 buffer layer, an ITO (indium tin oxide) frequency division layer and a SiO2 base layer arranged from top to bottom. The thickness of the transparent cooling layer is 5 μm, the thickness of the SiO2 buffer layer is 3 μm, the thickness of the ITO frequency division layer is 2.5 μm, and the thickness of the SiO2 base layer is 3 μm. In this embodiment, the transparent cooling layer is prepared from PDMS (polydimethylsiloxane).

[0144] The steps of the preparation method of the radiation cooling film of this comparative example are as follows:

[0145] The multilayer thin film structure layer was prepared by electron beam evaporation method, and the electron beam evaporation equipment was PVD 75Proline SP; manufacturer: Kurt J. Lesker Company, USA).

[0146] The glass substrate is placed in an ultrasonic cleaner for about 25 minutes to remove surface dirt, and then a SiO2 base layer, an ITO frequency division layer, a SiO2 buffer layer and a transparent cooling layer are prepared layer by layer on the glass substrate to obtain a multilayer thin film structure layer.

[0147] Among them, the coating pressure of SiO2 substrate layer and SiO2 buffer layer is 0.5Pa, the coating power is 1500W, and the coating time is 6h; the argon-oxygen ratio of ITO frequency division layer is 50:1, the coating power is 1400W, and the coating time is 1.8h; the coating power of transparent cooling layer is 500W, and the coating time is 0.5h. When replacing the evaporation material, the evaporation should be performed without exposing the multilayer structure sample to ambient air.

[0148] Figure 7 and Figure 8The solar spectrum (0.3-2.5 μm) transmittance curve comparison and atmospheric window (8-13 μm) emissivity curve comparison of the radiative cooling film prepared in Example 2 and the radiative cooling film prepared in Comparative Example 1; the visible light transmittance of the radiative cooling film without bionic micro-nano structure in Comparative Example 1 is 83.07%, while the visible light transmittance of the radiative cooling film with bionic micro-nano structure in Example 2 is 84.1%; the atmospheric window emissivity of the radiative cooling film without bionic micro-nano structure in Comparative Example 1 is 91%, while the atmospheric window emissivity of the radiative cooling film with bionic micro-nano structure in Example 2 is 95.1%. By comparison, it can be seen that the bionic micro-nano structure can simultaneously improve the lighting performance and cooling performance of the radiative cooling film.

Claims

1. A visible-near infrared frequency-dividing radiation cooling film based on the bionic rose petal micro-nano structure, characterized in that: It comprises a transparent bionic micro-nano structure layer (1) and a multi-layer thin film structure layer (2) arranged from top to bottom in a bionic rose petal structure. The surface of the transparent bionic micro-nanostructure layer (1) is provided with first pyramidal micro-nanostructures (1-1) distributed in an array; The surface of the first pyramidal micro-nanostructure (1-1) is provided with second pyramidal micro-nanostructures (1-2) distributed in an array; The height ratio of the first pyramidal micro-nanostructure (1-1) to the second pyramidal micro-nanostructure (1-2) is 5-20:0.5-1.5; The multilayer thin film structure layer (2) comprises a transparent cooling layer (2-1), a SiO2 buffer layer (2-2), an ITO frequency division layer (2-3) and a SiO2 base layer (2-4) arranged from top to bottom; The thickness of the transparent cooling layer (2-1) is 5-100 μm, the thickness of the SiO2 buffer layer (2-2) is 0.5-5 μm, the thickness of the ITO frequency division layer (2-3) is 0.5-4 μm, and the thickness of the SiO2 substrate layer (2-4) is 0.5-5 μm; the first pyramidal micro-nanostructure (1-1) is a pyramidal micro-nanostructure or a circular micro-nanostructure with at least three sides at the bottom, the bottom length of the pyramidal micro-nanostructure is 5-20 μm, and the height is 5-20 μm; the bottom diameter of the circular micro-nanostructure is 4-20 μm, and the height is 5-20 μm; the first pyramidal micro-nanostructure (1-1) is equidistantly arranged, with a spacing of 4-15 μm; The second pyramidal micro-nanostructure (1-2) is a pyramidal micro-nanostructure or a circular cone micro-nanostructure with at least three sides at the bottom, the length of the bottom side of the pyramidal micro-nanostructure is 0.5-1.5 μm, and the height is 0.5-1.5 μm; the bottom diameter of the circular cone micro-nanostructure is 0.4-1.6 μm, and the height is 0.5-1.5 μm; the second pyramidal micro-nanostructure (1-2) is equidistantly arranged, with a spacing of 0.2-1.5 μm; The transparent bionic micro-nano structure layer (1) and the transparent refrigeration layer (2-1) are both prepared from raw materials selected from the group consisting of PDMS, PMMA, PVDF and PET.

2. A method for preparing a visible-near infrared frequency-dividing radiation cooling film based on a bionic rose petal micro-nano structure as claimed in claim 1, characterized in that: Here are the steps: Step 1: Preparation of transparent bionic micro-nano structure layer: A bionic micro-nano structure mold is prepared by wet etching technology and aluminum anodizing method, and a transparent bionic micro-nano structure layer is prepared by hot pressing process based on the obtained bionic micro-nano structure mold; Step 2: Preparation of multi-layer thin film structure layer: A SiO2 substrate layer, an ITO frequency division layer, a SiO2 buffer layer and a transparent cooling layer are prepared layer by layer by using a vacuum magnetron sputtering method, an electron beam evaporation method, a chemical vapor deposition method or a sol-gel method to obtain a multilayer thin film structure layer; Step 3: Radiative cooling film: The transparent bionic micro-nano structure layer obtained in step one is laid on the transparent cooling layer of the multilayer film structure layer obtained in step two to obtain a visible-near infrared frequency-divided radiation cooling film with a bionic rose petal micro-nano structure.

3. The method for preparing the visible-near infrared frequency division type radiation cooling film based on the bionic rose petal micro-nano structure according to claim 2 is characterized in that: The wet etching technology described in step 1 is specifically as follows: Silicon anisotropic wet etching was used to prepare a micro-nano template with concave cones distributed in an array on the surface of a silicon wafer. The etching raw material was 20wt% potassium hydroxide, the etching mask was silicon nitride, and the etching rate of the plate was 1.0~1.5 μm / min.

4. The method for preparing the visible-near infrared frequency division type radiation cooling film based on the bionic rose petal micro-nano structure according to claim 3 is characterized in that: The aluminum anodizing method described in step 1 is specifically as follows: Aluminum is sputtered onto the upper surface of the micro-nano template obtained by wet etching, the thickness of the sputtered aluminum layer is 1~2μm, and a convex micro-nano structure is prepared on the surface of the sputtered aluminum layer by an anodic aluminum oxidation AAO process. The electrolyte is a sulfuric acid solution, an oxalic acid solution or a phosphoric acid solution. The temperature of the electrolyte is -15~-5°C, the counter electrode of the anodization is titanium, the anodization voltage is 117~123V, the voltage supply time is 2~10min, and the anodization time is 4~16min.

5. The method for preparing the visible-near infrared frequency division type radiation cooling film based on the bionic rose petal micro-nano structure according to claim 4 is characterized in that: The hot pressing process in step 1 is specifically as follows: The obtained bionic micro-nano structure mold and transparent organic sheet are stacked in a hot pressing system, the hot pressing temperature is increased from 57-63°C to 127-133°C within 28-32 minutes, an embossing load of 6.0-8.0 kN is applied and lasts for 55-65 seconds, and then the temperature is cooled to 57-63°C within 4-6 minutes to obtain a transparent bionic micro-nano structure layer.

6. The method for preparing the visible-near infrared frequency division type radiation cooling film based on the bionic rose petal micro-nano structure according to claim 5, characterized in that: The specific process parameters of the electron beam evaporation method in step 2 are: The coating pressure of SiO2 substrate layer and SiO2 buffer layer is 0.45~0.55Pa, the coating power is 1000~2000W, and the coating time is 3~10h. The argon-oxygen ratio of the ITO frequency division layer is 20:1-50:1, the coating power is 1000-2000W, and the coating time is 0.5-3h; The coating power of the transparent cooling layer is 500~2200W, and the coating time is 0.5~6h.

7. Application of the visible-near infrared frequency-divided radiation cooling film based on the bionic rose petal micro-nano structure as claimed in claim 1 in glass building exterior walls, photovoltaic cells, and automobile windows.

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