Flexible radiative cooling film with self-cleaning function and preparation method thereof

Abstract

The application provides a flexible radiation refrigeration film with a self-cleaning function and a preparation method thereof, and belongs to the technical field of radiation refrigeration preparation. The preparation method comprises the following steps: selecting and cleaning a base material; configuring a uniform mixed solution of polydimethylsiloxane and aluminum oxide particles; dropping and coating the uniform mixed solution on the surface of the base material, and peeling off the film after solidification to obtain a flexible radiation refrigeration film. The polydimethylsiloxane and the aluminum oxide particles have low absorption rates in the visible light and near-infrared wave bands, and have good emissivity in the mid-infrared wave band, so that the film has good passive radiation refrigeration performance. In addition, the hydrophobicity of the polydimethylsiloxane can enable the film to have a self-cleaning function. The materials used in the application are all industrial raw materials that are easy to obtain, have low cost, are simple to prepare, and can realize large-scale preparation.

Description

Technical Field

[0001] This invention belongs to the field of radiation refrigeration preparation technology, and relates to a flexible radiation refrigeration film with self-cleaning function and cooling without energy input, and its preparation method. Background Technology

[0002] Traditional refrigeration equipment, such as air conditioners, requires energy input and provides excellent cooling, but its widespread use consumes vast amounts of energy. According to statistics, global electricity consumption for refrigeration currently accounts for 15% of total global electricity consumption, while energy demand is primarily met by finite fossil fuels. The combustion of fossil fuels emits large amounts of harmful substances and the greenhouse gas carbon dioxide, causing serious problems such as energy shortages, environmental pollution, and global warming. Furthermore, with continuous societal progress, human demand for energy is increasing, and it is projected that by 2050, the amount of equipment used for refrigeration will be ten times that of today. Given this enormous energy consumption demand, developing a new refrigeration technology, distinct from traditional methods, to significantly alleviate the energy crisis and global warming is of great importance.

[0003] Radiative cooling is a passive cooling technology that requires no energy input, maintaining a temperature lower than ambient temperature even under direct sunlight. The principle of radiative cooling is to reflect most of the sunlight in the 250-2500nm wavelength range, absorbing only a small amount to prevent its own temperature from rising; simultaneously, it emits its own heat through an atmospheric window (8-13μm) into outer space where the temperature is near absolute zero, achieving cooling without energy input. Current radiative cooling materials mainly include inorganic or metallic porous materials, metal polymer layered coatings, polymer composites, and porous polymer materials. In recent years, although radiative cooling technology has made great progress, its practical application is limited by complex manufacturing processes, susceptibility to contamination, and high costs. Based on these problems, this invention provides a method for preparing a flexible radiative cooling film with self-cleaning function. This method achieves good cooling performance while being simple to prepare, self-cleaning, and low in cost. Summary of the Invention

[0004] This invention addresses the limitations of existing radiation cooling materials, such as complex manufacturing processes, susceptibility to contamination, and high costs, by providing a radiation cooling thin film that is simple to prepare, self-cleaning, low-cost, and flexible.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a flexible radiation-cooling film with self-cleaning function includes the following steps:

[0007] Step 1: Clean the substrate surface and dry it for later use.

[0008] Step 2: Blend polydimethylsiloxane, polydimethylsiloxane curing agent, alumina particles and solvent together and stir evenly with a magnetic stirrer to obtain a mixed solution; the mass ratio of polydimethylsiloxane, polydimethylsiloxane curing agent, alumina particles and solvent is 0.15:0.015:1:(1-1.5).

[0009] Step 3: In a fume hood, drop the uniform mixed solution obtained in step 2 onto the substrate surface obtained in step 1; after the solvent evaporates, place the substrate on a heating table to cure, and demold after cooling to obtain a radiation cooling film with self-cleaning and flexibility.

[0010] Furthermore, in step 1, the substrate is an aluminum plate or aluminum alloy plate with various planar shapes; the substrate surface is cleaned sequentially using acetone, deionized water, and anhydrous ethanol. The substrate of this invention is not limited to the above-mentioned substrates, nor is it limited to various shapes and sizes, and different substrates are not limited to the cleaning methods described above.

[0011] Furthermore, in step 2, the present invention is not limited to using alumina particles, but also includes one or more of the following: silicon dioxide particles, titanium dioxide particles, boron nitride particles, zinc oxide particles, magnesium oxide particles, zirconium dioxide particles, and yttrium oxide particles.

[0012] Furthermore, in step 2, the polydimethylsiloxane curing agent is one or more amine curing agents.

[0013] Furthermore, in step 2, the alumina particle size is dispersed between 0.5-5 μm.

[0014] Furthermore, in step 2, the solvent is one or more of butyl acetate, ethyl acetate, and acetone; the stirring time with a magnetic stirrer is 0.5-1 h.

[0015] Furthermore, in step 3, every 10cm 2 Add 1 to 1.6 ml of the mixed solution to the substrate surface.

[0016] Furthermore, in step 3, the solvent evaporation time is 3-5 hours, the heating temperature is 100-150°C, the heating curing time is 10-30 minutes, and the demolding method is the blade demolding method.

[0017] A flexible radiation cooling film with self-cleaning function is prepared by the above-described method.

[0018] The innovation and principle of this invention: A radiation-cooling membrane is prepared using a phase separation method, which is simple and easy to implement. While achieving radiation cooling, it also possesses self-cleaning and flexibility. Polydimethylsiloxane is a transparent hydrophobic polymer material with good flexibility after curing, enabling the radiation-cooling membrane to have excellent self-cleaning and flexibility. Polydimethylsiloxane has low absorption in the visible and near-infrared bands, but good emissivity in the mid-infrared band, giving the membrane radiation cooling function. Alumina has negligible absorption in the visible and near-infrared spectral range, therefore generating almost no heat under direct sunlight. In the mid-infrared band, alumina particles have high emissivity, thereby enhancing the membrane's radiation cooling capability.

[0019] The beneficial effects of this invention are as follows:

[0020] (1) The radiation cooling film prepared by the present invention can achieve a cooling effect of 12°C under direct sunlight.

[0021] (2) The radiation cooling film prepared by the present invention has good flexibility, which expands the application range.

[0022] (3) The contact angle between the surface of the radiation cooling film prepared by the present invention and water is greater than 150°, which has good hydrophobicity and self-cleaning properties, ensuring that the cooling effect of the film surface will not be affected by environmental pollution.

[0023] (4) All materials used in this invention are industrial-grade materials, which are easy to obtain and inexpensive. The preparation method used is drop coating, which is simple and easy to operate. Most traditional radiation cooling films lack flexibility and self-cleaning properties, have complex preparation methods, and are costly. The preparation method of this invention is simple and easy to implement, the materials used are inexpensive, and the prepared film has good self-cleaning properties and flexibility. It can be prepared on a large scale and in large quantities, and has good industrial prospects. Attached image description:

[0024] Figure 1 The image shows the reflectivity data of the radiation-cooling film prepared in Example 1 of the present invention.

[0025] Figure 2 This is a refrigeration data diagram of the radiation-cooling film prepared in Example 1 of the present invention. Figure 2 (a) is a diagram showing the cooling effect. Figure 2 (b) is the solar power during the test. Figure 2 (c) is a temperature difference diagram.

[0026] Figure 3 The surface contact angle of the radiation cooling film prepared in Example 1 of the present invention is shown.

[0027] Figure 4 This is a diagram illustrating the self-cleaning performance of the radiation-cooling film prepared in Example 1 of the present invention. Figure 4 (a) indicates that the membrane surface is contaminated with soil. Figure 4 (b) is the state diagram during self-cleaning. Figure 4 (c) Self-cleaning diagram.

[0028] Figure 5 This is a surface morphology image of the radiation-cooling film prepared in Example 1 of the present invention. Figure 5 (a) is a surface morphology image magnified 1000 times. Figure 5 (b) is a surface morphology image magnified 5000 times.

[0029] Figure 6 This is a flexibility test diagram of the radiation-cooling film prepared in Example 1 of the present invention. Figure 6 (a) involves bending the membrane 180°. Figure 6 (b) is when the membrane returns to its original state after the stress is relieved.

[0030] Specific Implementation Cases

[0031] The technical solution of the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0032] Example 1

[0033] A method for preparing a flexible radiation cooling film with self-cleaning function includes the following specific steps:

[0034] In this implementation case, a 60mm x 60mm x 1mm 1060 aluminum plate was used as the base material. After being cleaned with acetone, deionized water and ethanol, it was dried and placed in a fume hood.

[0035] Mix 1.5g of polydimethylsiloxane with 10g of butyl acetate, add 10g of alumina and 0.15g of polydimethylsiloxane curing agent, and stir with a magnetic stirrer for 1 hour to obtain a homogeneous mixture. Then, drop-coat the resulting mixture onto an aluminum plate.

[0036] Among them, every 10cm 2 1 ml of the mixed solution was dropped onto the substrate surface; after 3 hours, the butyl acetate completely evaporated, and the aluminum plate was placed on a heating table and heated at 150°C for 10 minutes to solidify. After cooling, the film was demolded using a blade to obtain the radiation cooling film.

[0037] Meanwhile, the performance of the prepared radiation-cooling film was tested:

[0038] (1) Testing the cooling performance of radiation cooling films

[0039] The reflectance in the ultraviolet / visible / near-infrared bands was measured using a Lambda 1050+ spectrophotometer with a PTFE-coated integrating sphere as the instrument's standard detector. The test step size was 0.5 nm. The reflectance was calculated to be 0.96 by substituting the test results into formula E1. Here, 300-2500 nm represents the solar spectrum; λ is the wavelength; R... sun (λ) represents the reflectance spectrum of the sample surface; I sun (λ) is the AM 1.5 standard solar spectrum.

[0040]

[0041] The reflectance in the 2.5–15 μm band was measured using a Fourier transform infrared spectrometer (Nicolet iS50) with a Pike gold integrating sphere. Substituting the test results into formula E2, the emissivity was calculated to be 0.95. The 8–13 μm band represents the atmospheric transparency window, and R... TIR (λ) represents the reflectivity of the radiation-cooling film surface in the mid-infrared band. According to Kirchhoff's law of thermal radiation, this is determined by measuring the reflectivity (Ra). TIR (λ) yields the emissivity, while the transmittance is negligible. According to Planck's law (E3), I B (λ,T) represents blackbody radiation at temperature T, where c is the speed of light, λ is the wavelength, h is Planck's constant, and K is the velocity of light. B This is the Boltzmann constant. The test results are as follows: Figure 1 As shown.

[0042]

[0043]

[0044] (2) Outdoor testing of the cooling performance of the radiation cooling film

[0045] The outdoor testing setup for the cooling performance of the radiative cooling film consisted of a 30cm x 20cm x 5cm foam board with four 5cm x 5cm x 1cm grooves. Three of the grooves were covered with the radiative cooling film, a 1060 aluminum plate, and a 1060 aluminum plate covered with the radiative cooling film, respectively. K-type thermocouple sensors were placed in each of the four grooves to measure their temperature. An eight-channel temperature recorder (JINKO, JK-808) was used to record the real-time temperature. The entire foam board was wrapped with aluminum foil to shield it from ambient radiation. To shield against the effects of heat convection, a polyethylene film was placed on top. A solar photometer (TES-132) was used to measure solar power. The test was conducted on November 8, 2022, at the square in front of the Zhifang Building at Dalian University of Technology in Dalian, Liaoning Province, China, lasting four hours from 9:00 AM to 1:00 PM. Figure 2(a) shows the measured cooling effect. The curves from top to bottom represent the aluminum plate temperature, air temperature, temperature of the 1060 aluminum plate covered with the radiative cooling film, and the temperature of the radiative cooling film. Comparing the temperatures of the radiative cooling film and the air, as well as comparing the temperatures of the aluminum plate and the aluminum plate covered with the radiative cooling film, reveals a significant cooling effect. Figure 2 (b) Solar power from 9 a.m. to 1 p.m. during the test. Figure 2 (c) is a temperature difference graph. From top to bottom, it shows the result of subtracting the air temperature from the aluminum plate temperature, the result of subtracting the air temperature from the aluminum plate temperature covered by the radiative cooling film, and the result of subtracting the air temperature from the radiative cooling film temperature. The first two curves show that the radiative cooling film has a significant cooling effect on the aluminum plate, and the last curve shows that the radiative cooling film has good cooling performance. It can be found that the radiative cooling film is effective at solar power of 300-650W / m. 2 It can achieve an average cooling effect of 12℃.

[0046] (3) Testing of the self-cleaning performance of the radiation cooling film

[0047] The contact angle of the samples was measured using a TBU 100 contact angle meter. The water droplet size was 5 μL. Polynomial fitting was used, and the calculation method was the tangent method. Five points were selected for measurement for each sample. All measurements were performed at room temperature. The measured contact angle of the sample surface was 158°. Figure 3 As shown. Figure 4 For the self-cleaning performance test of the radiation cooling film, the sample was first placed on a tilted glass slide in a petri dish, and then soil was placed on the sample. Figure 4 As shown in (a); then, using a dropper, water is dripped above the sample, and it can be seen that the soil on the sample surface will slide off the sample surface with the water droplets, as shown in (a). Figure 4 As shown in (b); as all the soil slides off, the radiative cooling film achieves self-cleaning, leaving the surface smooth and clean as before, as... Figure 4 As shown in (c).

[0048] (4) Surface morphology detection of radiation cooling film

[0049] Characterization was performed using a field emission scanning electron microscope (SEM) SU5000. Figure 5 (a) The microstructure of the film surface is magnified 1000 times. Figure 5 (b) The microstructure of the film surface is magnified 5000 times. The results show that the prepared film surface has an uneven micro-nano-scale rough structure. These micro-nano-rough structures are formed by the bonding of alumina particles with dispersed particle size with polydimethylsiloxane, which provides conditions for hydrophobicity of the sample surface and enhances the reflectivity of the sample in the visible / near-infrared band and the emissivity in the 8-13 μm band.

[0050] (5) Radiative cooling film flexibility test

[0051] like Figure 6 As shown in (a), when the membrane is bent 180°, it does not break or crack; subsequently, when the force is released, the radiative cooling membrane returns to its original shape without any change. Figure 6 As shown in (b).

[0052] Example 2

[0053] A method for preparing a flexible radiation cooling film with self-cleaning function includes the following specific steps:

[0054] In this implementation case, an 80mm x 80mm x 1mm 7075 aluminum alloy sheet was used as the base material. After being cleaned with acetone, deionized water and ethanol, it was dried and placed in a fume hood.

[0055] Mix 3g of polydimethylsiloxane with 24g of ethyl acetate, add 20g of silica and 0.3g of polydimethylsiloxane curing agent, and stir with a magnetic stirrer for 45 minutes to obtain a uniformly mixed solution.

[0056] The resulting mixed solution was dripped onto an aluminum alloy sheet, with each 10cm layer... 2 1.3 ml of the mixed solution was dropped onto the substrate surface; after 4 hours, the ethyl acetate completely evaporated, and the aluminum alloy sheet was placed on a heating table and heated at 120°C for 20 minutes to cure. After cooling, the sheet was demolded using a blade to obtain a flexible radiation cooling film with good self-cleaning properties.

[0057] Example 3

[0058] A method for preparing a flexible radiation cooling film with self-cleaning function includes the following specific steps:

[0059] In this implementation case, a 100mm x 100mm x 1mm 6061 aluminum alloy sheet was used as the base material. After being cleaned with acetone, deionized water and ethanol, it was dried and placed in a fume hood.

[0060] Mix 4.5g of polydimethylsiloxane with 45g of butyl acetate, add 30g of titanium dioxide and 0.45g of polydimethylsiloxane curing agent, and stir with a magnetic stirrer for 30 minutes to obtain a uniformly mixed solution.

[0061] The resulting mixed solution was dripped onto an aluminum alloy sheet, with each 10cm layer... 2 1.6 ml of the mixed solution was dropped onto the substrate surface; after 5 hours, the ethyl acetate completely evaporated, and the aluminum alloy sheet was placed on a heating table and heated at 100°C for 30 minutes to cure. After cooling, the sheet was demolded using a blade to obtain a flexible radiation cooling film with good self-cleaning properties.

[0062] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for preparing a flexible radiation-cooling film with self-cleaning function, characterized in that, Includes the following steps: Step 1: Clean the substrate surface and dry it for later use; Step 2: Polydimethylsiloxane, polydimethylsiloxane curing agent, alumina particles, and solvent are blended and stirred evenly using a magnetic stirrer to obtain a mixed solution; the mass ratio of polydimethylsiloxane, polydimethylsiloxane curing agent, alumina particles, and solvent is 0.15:0.015:1:(1-1.5); the alumina particle size is dispersed between 0.5-5 μm; Step 3: In a fume hood, drop the uniform mixed solution obtained in step 2 onto the substrate surface obtained in step 1; after the solvent evaporates, place the substrate on a heating table to cure, and demold after cooling to obtain a radiation cooling film with self-cleaning and flexibility; the solvent evaporation time is 3-5 hours, the heating temperature is 100-150℃, the curing time is 10-30 minutes, and the demolding method is blade demolding.

2. The method for preparing a flexible radiation-cooling film with self-cleaning function according to claim 1, characterized in that, The substrate is an aluminum plate or an aluminum alloy plate.

3. The method for preparing a flexible radiation-cooling film with self-cleaning function according to claim 1, characterized in that, The alumina particles can be replaced by one or more of the following: silicon dioxide particles, titanium dioxide particles, boron nitride particles, zinc oxide particles, magnesium oxide particles, zirconium dioxide particles, and yttrium oxide particles.

4. The method for preparing a flexible radiation-cooling film with self-cleaning function according to claim 1, characterized in that, The polydimethylsiloxane curing agent is one or more of the amine curing agents.

5. The method for preparing a flexible radiation-cooling film with self-cleaning function according to claim 1, characterized in that, The solvent is one or more of butyl acetate, ethyl acetate, and acetone.

6. The method for preparing a flexible radiation-cooling film with self-cleaning function according to claim 1, characterized in that, In step 3, every 10 cm 2 Add 1~1.6ml of the mixed solution to the substrate surface.

7. A flexible radiative cooling film with self-cleaning function, characterized in that, It is prepared by any one of the preparation methods described in claims 1-6.

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