Colored heat insulation type radiation refrigeration film based on hollow SiO2 microspheres and preparation method thereof

Abstract

The invention discloses a colored heat insulation type radiation refrigeration film based on hollow SiO2 microspheres and a preparation method thereof, and belongs to the technical field of new materials. The monodisperse hollow SiO2 microspheres are used for preparing a three-dimensional photonic crystal structure color, the hollow structure can form a high refractive index ratio with a polymer and endow the film with a beautiful structural color, the heat conductivity of the material is reduced, the purposes of heat insulation and heat preservation are achieved, and the heat management capacity is effectively improved. The micron-sized particles for reflecting sunlight are large in particle size and cannot be filled in gaps of the photonic crystal structure to damage the structural color, the polymer for film forming permeates into the gaps of the photonic crystal structure, and the micron-sized particles and the photonic crystal are cured in the polymer film, so that the film forming effect is improved. The problem that the structural color and the radiation refrigeration material are poor in bonding strength is solved. The daytime net refrigeration power of the prepared film can reach 95.6 W / m < 2 >, the temperature of a building can be reduced by 9.7 DEG C, raw materials are low in cost and easy to obtain, a metal reflecting layer is not needed, the preparation method is simple, and the film is expected to be applied to energy-saving buildings on a large scale.

Description

Technical Field

[0001] The invention relates to a colorful heat-insulating radiation cooling film based on hollow SiO2 microspheres and a preparation method thereof, belonging to the technical field of new materials. Background Art

[0002] With the development of science and technology and the improvement of material level, people's consumption and demand for fossil energy have increased year by year, and the greenhouse gas emission rate is high, leading to the intensification of severe weather phenomena such as global warming and acid rain. Surveys have found that buildings account for more than 30% of the world's total energy consumption, and this energy consumption is mainly used for heating and cooling. In order to achieve building energy conservation, on the basis of good building insulation, a green, energy-free refrigeration technology or material is also needed to replace high-energy condensers or reduce the refrigeration pressure of condensers. In recent years, passive daytime radiation cooling technology has attracted much attention. This technology reduces heat absorption by reflecting sunlight in the 0.3-2.5 μm band, and uses the atmospheric window in the 8-13 μm band to transfer the heat of earth objects to space (about 3 K) in the form of thermal radiation, without consuming any energy or causing any pollution.

[0003] Some polymer films have high emissivity in the infrared region, and the preparation method of polymer films is simple and can be prepared on a large area. In order to improve the reflectivity of the film in the visible light band, a metal reflective layer such as silver or aluminum is usually superimposed on the back of the film, which undoubtedly increases the cost of the radiative cooling film. Doping particles with sunlight reflection and heat insulation effects in the polymer to prepare a composite film with radiative cooling properties is currently the best choice for cooling buildings.

[0004] In addition to cost issues, there are certain aesthetic requirements for the exterior walls of buildings, but in order to reflect as much sunlight as possible, most radiation cooling materials are white or silver, and these colors are not always popular in practical application scenarios. In essence, based on the interaction between sunlight and materials, colored passive radiation coolers can be divided into two mechanisms: dye coloring and structural coloring. The first uses pigments and dyes to selectively absorb specific parts of the visible spectrum (0.4-0.74 μm) to obtain the desired color through their inherent absorption of chemicals. However, absorbing energy in the visible light band generates a lot of heat, which reduces the efficiency of radiation cooling. Photonic crystals are a material with periodic changes in dielectric constants and have the characteristics of photon bandgap. When the photon bandgap is within the visible light range, visible light of a specific wavelength cannot propagate, so it is reflected and produces structural color. Due to the different principles of color formation, the structural color has little effect on the radiation cooling performance of the composite film, and the color saturation of the structural color is high and relatively stable. In theory, the structure will not be destroyed and will never fade.

[0005] In outdoor applications, the durability of the radiant cooling film should also be considered, such as material structure degradation caused by ultraviolet (UV) radiation, surface contamination caused by wind, sand and dust, and surface damage caused by impact or friction, which will adversely affect the cooling efficiency and color saturation. At present, there are still challenges in obtaining cheap, efficient and durable colored building exterior wall radiant coolers. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the present invention provides a type of colorful heat-insulating radiation cooling film based on hollow SiO2 microspheres and a preparation method thereof. Monodisperse hollow SiO2 microspheres are prepared by a hard template method, and three-dimensional photonic crystal structural colors are constructed by an immersion and pulling method. Due to the presence of the hollow structure, SiO2 (refractive index n≈1.457), air (refractive index n=1) and polymer produce a high refractive index ratio, thereby giving the structural color film a beautiful structural color, and the thermal conductivity of air is lower than that of SiO2. After passing through the hollow structure, part of the heat is blocked, thereby achieving the purpose of heat insulation.

[0007] The technical solution adopted by the present invention is: a colorful heat-insulating radiation cooling film based on hollow SiO2 microspheres, which is composed of photonic crystals formed by assembling hollow SiO2 microspheres capable of producing structural colors and heat-insulating effects, micron-sized particles with sunlight reflection effects, and infrared radiation polymers filled between the hollow SiO2 microspheres and the micron-sized particles. The mass fraction of the micron-sized particles in the film is 30 wt%-70 wt%, the thickness of the hollow SiO2 microsphere structural color layer is 0.5-1.5 μm, and the thickness of the film is 0.5-1.8 mm.

[0008] The micron-sized particles of the present invention include at least one of hollow glass microspheres (HGBs), hollow ceramic microspheres, diatomaceous earth, barium sulfate, titanium dioxide, aluminum oxide, and polytetrafluoroethylene.

[0009] The infrared radiation polymer of the present invention includes at least one of polydimethylsiloxane (PDMS), polyvinylidene fluoride, polymethyl methacrylate, polylactic acid and polyoxymethylene.

[0010] Preferably, the particle size of the monodisperse hollow SiO2 microspheres used is 213 nm-268 nm.

[0011] A method for preparing a colored heat-insulating radiation cooling film based on hollow SiO2 microspheres comprises the following process steps:

[0012] (1) uniformly dispersing micron-sized particles and polymer or micron-sized particles, polymer monomer and initiator in a solvent by ultrasonic or magnetic stirring to form a casting solution;

[0013] (2) adding ethanol to ultrasonically disperse the monodisperse hollow SiO2 microspheres constituting the photonic crystal structural color to obtain a microsphere dispersion, and preparing a three-dimensional photonic crystal by an immersion-pulling method. A clean substrate is vertically immersed in the microsphere dispersion, pulled at room temperature, and dried to obtain a substrate loaded with the photonic crystal structural color;

[0014] (3) Pour the casting liquid onto the substrate loaded with photonic crystal structural color, and peel it off from the substrate after solidification to obtain a colorful heat-insulating radiant cooling film based on hollow SiO2 microspheres.

[0015] In the above technical solution, the solvent is one of n-hexane, acetone, N,N-dimethylformamide, tetrahydrofuran, and hexafluoroisopropanol.

[0016] Preferably, the usage ratio of the micron-sized particles to the polymer is 4:10-23:10, and the usage ratio of the micron-sized particles to the polymer monomer to the initiator is 4:10:1-23:10:1.

[0017] Preferably, the amount of the solvent used is 0.5-2 times the mass of the polymer or polymer monomer and the initiator.

[0018] Preferably, the mass fraction of the hollow SiO2 microsphere dispersion is 5 wt%-10 wt%.

[0019] The beneficial effects of the present invention are as follows: the colorful heat-insulating radiation cooling film based on hollow SiO2 microspheres of the present invention utilizes the high refractive index ratio between the hollow SiO2 microspheres and the polymer to effectively improve the color saturation of the structural color film, and at the same time the hollow structure can achieve the purpose of heat insulation and heat preservation, and can effectively improve the thermal management capability, in the visible light and near-infrared light bands, the micron-sized particles used reflect and scatter most of the sunlight in this band, absorbing less, and the polymer has a high emissivity in the atmospheric window band.

[0020] The polymer used has high emission characteristics in the infrared region, and is doped with micron-sized particles with sunlight reflection effects. Due to the large particle size, the particles will not fill into the gaps in the photonic crystal structure, and therefore will not damage the structural color. The polymer used for film formation penetrates into the gaps in the photonic crystal structure, and both the micron-sized particles and the photonic crystal structure are solidified in the PDMS film. The structural color is transferred from the substrate, solving the problem of poor bonding strength between the structural color and the radiation refrigeration material.

[0021] The present invention controls the reflection, absorption and scattering of the film in a specific band by optimizing the particle size and addition amount of micron-sized particles in the film and the film thickness. After adding micron-sized particles with reflective effect, the film can achieve high reflectivity (96.3%) without a metal reflective layer, and the average emissivity in the atmospheric window band (8 μm-13 μm) can reach 94.9%, and the net cooling power can reach 95.6 W / m at daytime ambient temperature. 2 It can cool down buildings by 9.7℃ and has excellent daytime passive radiation cooling performance. The raw materials are cheap and easy to obtain, the preparation method is simple, and the color saturation is high. It is expected to be used on a large scale in energy-saving buildings.

[0022] All micro-nanoparticles in the film are encapsulated in a polymer with high mechanical strength. At the same time, the film has self-cleaning ability and a water contact angle of up to 119°, which has great potential for application in energy-saving buildings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The solar reflection spectra (0.3 μm-2.5 μm) of the white heat-insulating radiation cooling film and PDMS with different mass fractions of micron-sized particles in Examples 1-5.

[0024] Figure 2 The atmospheric window emission spectra (8 μm-13 μm) of the white heat-insulating radiation cooling film and PDMS with different mass fractions of micron-sized particles in Examples 1-5.

[0025] Figure 3 The solar reflection spectra (0.3 μm-2.5 μm) of the white heat-insulating radiant cooling films of different thicknesses in Examples 6-10.

[0026] Figure 4 : The atmospheric window emission spectra (8 μm-13 μm) of the white heat-insulating radiative cooling films of different thicknesses in Examples 6-10.

[0027] Figure 5 This is a transmission electron microscope photograph of hollow SiO2 in Example 11.

[0028] Figure 6 This is a scanning electron microscope photograph of the green film surface in Example 11.

[0029] Figure 7 This is a scanning electron microscope photograph of the cross section of the green film in Example 11.

[0030] Figure 8 is the solar reflection spectrum (0.3 μm-2.5 μm) of the colored film in Examples 11-13.

[0031] Fig. 9It is the atmospheric window emission spectrum (8μm-13μm) of the color film in Examples 11-13.

[0032] Fig.10 These are digital photos of the colored films in Examples 11-13.

[0033] Fig.11 : This is the CIE chromaticity diagram of the structural colors of the color films in Examples 11-13.

[0034] Fig.12 Graph showing the water contact angle and self-cleaning performance of the colored film in Example 11.

[0035] Fig.13 This is a test diagram of the mechanical strength of the color film in Example 11.

[0036] Fig.14 This is the test device and environmental diagram for the cooling performance of the colored film on a building in Example 11.

[0037] Fig.15 This is a graph showing the test results of the cooling performance of the colored film on a building in Example 11. DETAILED DESCRIPTION

[0038] The following non-limiting embodiments may enable a person skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0039] The test methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0040] Example 1

[0041] (1) 4.3 g of HGBs with a particle size range of 10 μm-40 μm, 10 g of PDMS monomer and 1 g of initiator were added to 30 g of n-hexane solvent and magnetically stirred for 0.5 h to obtain a uniformly dispersed casting solution. The PDMS monomer and initiator were purchased from Dow Corning.

[0042] (2) Pour the casting solution prepared in step (1) evenly onto a clean polytetrafluoroethylene substrate, pre-cure at room temperature for 1 h to allow the n-hexane to evaporate, then heat to 80 °C and continue curing for 1 h. Peel it off from the substrate to obtain a white heat-insulating radiation cooling film with a thickness of 1.2 mm.

[0043] Embodiment 2-5

[0044] The mass of HGBs was changed to 6.7, 10, 15, and 23.3 g, respectively, and other conditions were consistent with those in Example 1, to obtain the corresponding white heat-insulating radiation cooling films.

[0045] Embodiment 6-10

[0046] The mass of HGBs was changed to 15 g, the thickness of the film was changed to 0.5, 0.8, 1.4, 1.6, and 1.8 mm, and the other conditions were consistent with those in Example 1, and the corresponding white heat-insulating radiation cooling films were obtained.

[0047] Embodiment 11

[0048] The polytetrafluoroethylene substrate in step (2) was replaced with a substrate having a structural color, the mass of HGBs was changed to 15 g, the film thickness was changed to 1.6 mm, and the other conditions were consistent with those in Example 1, thereby obtaining a corresponding yellow-green heat-insulating radiation cooling film.

[0049] The specific method for assembling structural color is as follows: after fully grinding the hollow SiO2 microsphere powder with a particle size of 232 nm, disperse it in anhydrous ethanol to obtain a microsphere dispersion with a concentration of 5 wt% for use, and use the immersion pulling method to prepare the three-dimensional photonic crystal of hollow SiO2. A clean polytetrafluoroethylene sheet is vertically immersed in the microsphere dispersion, and pulled 3 times at 30 °C with a speed of 1-2 μm / s to obtain a three-dimensional photonic crystal structural color film of hollow SiO2; the hollow SiO2 is made of polystyrene microspheres as a hard template, and then calcined to remove the polystyrene core.

[0050] Examples 12-13

[0051] The particle sizes of the hollow SiO2 microspheres were changed to 213 nm and 268 nm, respectively, and the other conditions were consistent with those in Example 11, and the corresponding blue and red heat-insulating radiant cooling films were obtained.

[0052] Figure 1 The solar reflection spectra of Examples 1-5 and PDMS are the preferred values ​​for the mass fraction of HGBs. As can be seen from the figure, the average solar reflectivity (0.3 μm-2.5 μm) of PDMS is only 5.9%. After adding HGBs, the reflectivity of the film increases. This is because the hollow structure of HGBs can reflect sunlight multiple times, so less solar energy is absorbed, and the thermal conductivity of HGBs is only 0.03-0.07W / (m·K), thus achieving functions such as reflection and heat insulation. As the mass fraction of HGBs increases, the reflection first increases and then decreases, reaching a maximum value of 95.7% when the mass fraction reaches 60 wt%.

[0053] Figure 2: The atmospheric window emission spectra of Examples 1-5 and PDMS. It can be seen from the figure that the emissivity of PDMS in the atmospheric window is relatively high. This is because the functional groups such as Si-O-Si and Si-C in PDMS have characteristic vibration absorption peaks in the atmospheric window band of 8 μm-14 μm. After adding HGBs, the emissivity increases slightly. This is because HGBs are mainly composed of alkali calcium borosilicate, and the stretching vibration peak of the Si-O-Si bond at 9.7 μm has strong absorption at the atmospheric window. In addition, the Mie resonance can expand infrared absorption and improve the long-wavelength infrared emissivity. As the mass fraction of HGBs increases, the emissivity gradually increases. When the mass fraction of HGBs reaches 40%, the emissivity is 0.936 (higher than the emissivity of PDMS 0.925). When the mass fraction of HGBs is further increased, the emissivity does not increase significantly.

[0054] Figure 3 The solar reflection spectra of Examples 6-10 are the preferred values ​​for the film thickness. As can be seen from the figure, as the film thickness increases, the reflection first increases and then decreases, reaching a maximum value of 96.3% at 1.6 mm.

[0055] Figure 4 2 is the atmospheric window emission spectrum of Examples 6-10. It can be seen from the figure that the emissivity of the films with thicknesses of 0.5, 0.8, 1.4, 1.6, and 1.8 mm is all around 0.94, indicating that the thickness has little effect on the infrared emissivity.

[0056] Figure 5 This is a transmission electron microscope photograph of the monodisperse hollow SiO2 microspheres that are the structural color building units in Example 11. It can be seen that the microspheres have a smooth surface, a hollow structure, a wall thickness of about 48nm, and good monodispersity, so they can produce better structural colors and certain thermal insulation capabilities.

[0057] Figure 6 and Figure 7 The surface and cross-sectional scanning electron micrographs of the colored film in Example 11. As can be seen from the figure, PDMS has penetrated into the gap between HGBs and hollow SiO2 3DPCs, and the cured film has a certain mechanical strength.

[0058] Figure 8 The solar reflection spectra of Examples 11-13 are as follows. In Example 11, the film prepared using hollow SiO2 microspheres with a particle size of 232 nm as the structural color building unit is yellow-green, and the films prepared in Examples 12 and 13 are blue and red, respectively. This is because the position of the photon bandgap changes and the structural color changes as the particle size of the hollow SiO2 microspheres changes. The yellow-green film in Example 1 has the highest average sunlight reflectivity of 96.0%.

[0059] Fig. 911-13 are the atmospheric window emission spectra. It can be seen from the figure that the emissivity of the film with red and green structural colors is about 0.95, indicating that the hollow SiO2 structural color layer can improve the emissivity of the film at the atmospheric window.

[0060] Fig.10 is a digital photo of the splicing pattern of Examples 11-13, Fig.11 This is a chromaticity diagram obtained by converting the reflection peak of the reflection spectrum of Examples 11-13 into the chromaticity value in the CIE color coordinate. The results show that the structural color produced by the colored thermal insulation type radiation cooling film is consistent with the reflection spectrum.

[0061] Fig.12 The water contact angle and self-cleaning performance test diagram of the colored film in Example 11 show that the contact angle of the colored film prepared by the present invention with water can reach 119°, which has a certain degree of hydrophobicity. Soil particles sprinkled on the coating can be washed away by water droplets without leaving any traces on the surface of the film. When edible oil is dropped on the surface of the film and wiped off with paper, no oil film will be left on the surface of the film to contaminate the film.

[0062] Fig.13 This is a mechanical strength test chart of the colored film in Example 11. It can be seen that after the film is placed in 50°C water and ultrasonicated for 12 hours, the structural color will not be damaged at all. After sticking and tearing off with 95N / 25mm tape 20 times, the structural color remains intact. The film is pressed by a 200g weight and rubbed on 1200-mesh sandpaper with a moving distance of 10cm each time. After repeating this 20 times, the surface of the structural color film is worn, indicating that the wear resistance of the film needs to be strengthened, but the color fastness of the structural color is very high.

[0063] A radiant cooling film with an area of ​​10 cm*10 cm was prepared according to the method described in Example 11. In order to evaluate the cooling performance of the colored heat-insulating radiant cooling film applied to buildings, a house model with windows made of cement board material with a size of 10 cm*10 cm*10 cm and a wall thickness of 1 cm was built with reference to the actual building materials and characteristics. The film was covered on the top and exterior walls of the house. In order to more intuitively evaluate the cooling performance of the film, the temperatures of the exposed cement board house model not covered with the film and the cement board house model coated with a green coating were compared. The real-time temperature was recorded with a four-channel temperature recorder. K-type thermocouples were placed inside the above three house models and in a louvered box used to measure the ambient temperature under air circulation conditions. The test was conducted under clear and breezy conditions. The house was placed on a tabletop about 1m above the ground and covered with pearl cotton. The test was conducted in Dalian on September 6, 2024. The test environment and equipment were as follows. Fig.14 shown.

[0064] Depend on Fig.15 It can be seen that when the average solar radiation intensity is 90 mW / cm 2At noon with a relative humidity of 33%, the temperature inside the house covered with the colored heat-insulating radiant cooling film is 9.7°C lower than that inside the house without the film, and 5.7°C lower than that inside the house with the green coating. The radiant cooling film itself is 3.2°C lower than the ambient temperature. This shows that the temperature of the colored heat-insulating radiant cooling film of the invention can be kept below the ambient temperature during use, and it can maintain excellent cooling performance while maintaining color.

[0065] Examples 14-15 The number of immersion and pulling in Example 11 was changed to 2 and 5 times respectively, and the other conditions were consistent with Example 11, to obtain a colorful heat-insulating radiant cooling film with a hollow SiO2 structural color layer thickness of 0.5 μm and 1.5 μm.

[0066] Examples 16-20

[0067] Hollow ceramic microbeads, diatomaceous earth, barium sulfate, titanium dioxide, and aluminum oxide were used to replace HGBs to obtain corresponding colored heat-insulating radiant cooling films. Other conditions were the same as those in Example 11.

[0068] Embodiment 21

[0069] By replacing PDMS with polyvinylidene fluoride, using acetone or N,N-dimethylformamide as solvent, and having a mass ratio of HGBs to polyvinylidene fluoride of 1:2, a corresponding colored heat-insulating radiant cooling film is obtained, and other conditions are consistent with those in Example 1.

[0070] Embodiment 22

[0071] The corresponding colored heat-insulating radiant cooling film was obtained by replacing PDMS with polymethyl methacrylate and using tetrahydrofuran as solvent. Other conditions were the same as those in Example 11.

[0072] Embodiment 23

[0073] The corresponding colored heat-insulating radiant cooling film was obtained by replacing PDMS with polyoxymethylene, replacing HGBs with polytetrafluoroethylene micron particles, and using hexafluoroisopropanol as solvent. Other conditions were the same as those in Example 11.

[0074] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Based on hollow SiO 2 Colored heat-insulating radiation cooling film of microspheres, Features: Hollow SiO2 that can produce structural color and thermal insulation effects 2 Photonic crystals formed by microsphere assembly, micron-sized particles with sunlight reflection effect and infiltration in hollow SiO 2 The infrared radiation polymer between the microspheres and the gaps between the micron-sized particles is composed; the mass fraction of the micron-sized particles in the film is 30 wt%-70 wt%, and the hollow SiO 2 The thickness of the microsphere structure color layer is 0.5-1.5 μm, and the thickness of the film is 0.5-1.8 mm.

2. The hollow SiO based method according to claim 1 2 Colored heat-insulating radiation cooling film of microspheres, Features: The micron-sized particles include at least one of hollow glass microspheres, hollow ceramic microspheres, diatomaceous earth, barium sulfate, titanium dioxide, and aluminum oxide.

3. The hollow SiO based method according to claim 1 2 Colored heat-insulating radiation cooling film of microspheres, Features: The infrared radiation polymer includes at least one of polydimethylsiloxane, polyvinylidene fluoride, polymethyl methacrylate, polylactic acid, polyoxymethylene, and polytetrafluoroethylene.

4. According to claim 1, based on hollow SiO 2 Colored heat-insulating radiation cooling film of microspheres, Features: The hollow SiO 2 The particle size of the microspheres is 213 nm-268 nm.

5. The hollow SiO 2 Preparation method of microsphere colored heat-insulating radiation cooling film, It is characterized in that The following steps are involved: (1) uniformly dispersing micron-sized particles and polymer or micron-sized particles, polymer monomer and initiator in a solvent by ultrasonic or magnetic stirring to form a casting solution; (2) The monodisperse hollow SiO 2 The microspheres are evenly dispersed by ultrasonication in ethanol to obtain a microsphere dispersion, and a three-dimensional photonic crystal is prepared by an immersion-pulling method. A clean substrate is vertically immersed in the microsphere dispersion, pulled at room temperature, and dried to obtain a substrate loaded with photonic crystal structural colors. (3) Pour the casting liquid onto the substrate loaded with photonic crystal structure color, and peel it off from the substrate after solidification to obtain a hollow SiO-based 2 Colored heat-insulating radiant cooling film with microspheres.

6. The hollow SiO based method according to claim 5 2 Preparation method of microsphere colored heat-insulating radiation cooling film, Features: The solvent is one of n-hexane, toluene, acetone, dichloromethane and tetrahydrofuran.

7. The hollow SiO based method according to claim 5. 2 Preparation method of microsphere colored heat-insulating radiation cooling film, Features: The usage ratio of the micron-sized particles to the polymer is 4:10-23:10, and the usage ratio of the micron-sized particles to the polymer monomer and the initiator is 4:10:1-23:10:

1.

8. The hollow SiO based method according to claim 5 2 Preparation method of microsphere colored heat-insulating radiation cooling film, Features: The hollow SiO 2 The mass fraction of the microsphere dispersion is 5 wt%-10 wt%.

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