A copolymer hydrogel coating capable of realizing efficient transparent passive cooling and a preparation method and application thereof

Abstract

The application discloses a copolymer hydrogel coating capable of realizing efficient transparent passive cooling and a preparation method and application thereof, and belongs to the technical field of passive radiation cooling, wherein the main body is poly(N-isopropyl acrylamide-acrylamide) copolymer hydrogel, and the copolymer hydrogel is prepared by using a photopolymerization method with N-isopropyl acrylamide and acrylamide in a copolymerization ratio of 1:1. The copolymer hydrogel coating has high light transmittance and efficient cooling capacity, the transmittance of the coating is 92%-98% in the ultraviolet-visible light band with a wavelength of 0.5 microns-1.1 microns, the emissivity of the coating is 88%-95% in the infrared band with a wavelength of 2.5-16.0 microns, and the infrared emissivity of the coating in the atmospheric transparent window (8-13 micron band) is 92%-95%. The method has the advantages of simple preparation process, short period, greenness and no pollution, and can realize mass industrial production.

Description

A copolymer hydrogel coating capable of achieving efficient, transparent, and passive cooling, its preparation method, and its application. Technical Field

[0001] This invention belongs to the field of passive radiation cooling technology, and particularly relates to a copolymer hydrogel coating that can achieve efficient and transparent passive cooling, its preparation method and application. Background Technology

[0002] The demands for energy efficiency and environmental protection have spurred the development of passive cooling technologies that do not consume fossil fuels. Radiative cooling is of great significance to passive cooling. Since the average temperature of the Earth's surface (approximately 290 K) is significantly higher than the average temperature of outer space (approximately 2.7 K), infrared radiation radiated from the Earth into space can be used to cool objects on the Earth's surface. Particularly in the 8-13 μm wavelength range (atmospheric window), where the atmosphere absorbs almost no heat, thermal radiation from objects can be emitted into outer space, effectively dissipating heat energy.

[0003] On the other hand, inspired by mammals and plants cooling themselves through evaporation of water, the concept of evaporative cooling was proposed. Evaporative cooling releases a large amount of latent heat through the evaporation of water. The high enthalpy of vaporization of water allows it to efficiently transfer heat to the surrounding environment when it vaporizes, while the moisture in the surrounding air gives evaporative cooling a regenerative capacity. Evaporative cooling is very effective in areas with high temperature and low humidity. In areas with high humidity and harsh climatic conditions, radiative cooling can also be effective, making the cooling effects of both methods complement each other.

[0004] Passive radiative cooling is typically achieved by combining high reflectivity with high emissivity, but this can obstruct vision and information reception. Therefore, transparent cooling materials are in high demand in several critical applications. For example, solar cells require both high solar transmittance and efficient cooling capabilities; transparent cooling additives are also attractive in outdoor displays. In these applications, effective cooling within the transparent layer is particularly important for offsetting the heat generated during light transmission. While hydrogel-based cooling materials can effectively achieve evaporative cooling, they are difficult to maintain indefinitely. Therefore, fabricating hydrogel materials with high transmittance and efficient cooling capabilities is extremely challenging. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a copolymer hydrogel coating capable of achieving efficient, transparent, and passive cooling, along with its preparation method and applications.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A copolymer hydrogel coating capable of achieving efficient, transparent, and passive cooling, the main body of which is a poly(N-isopropylacrylamide-acrylamide) copolymer hydrogel, comprising N-isopropylacrylamide segments and acrylamide segments;

[0008] The thickness of the copolymer hydrogel coating is 2.0-2.5 mm.

[0009] Furthermore, the copolymer hydrogel coating has a transmittance of 92%-98% in the ultraviolet-visible band with wavelengths between 0.5 micrometers and 1.1 micrometers; the copolymer hydrogel coating has an emissivity of 88%-95% in the infrared band with wavelengths between 2.5 and 16.0 micrometers, wherein the infrared emissivity in the atmospheric transparency window (8-13 micrometer band) is 92%-95%.

[0010] The copolymer hydrogel coating of this invention possesses both high light transmittance and efficient cooling capacity. Test results show that the visible light transmittance of the copolymer hydrogel coating of this invention is as high as 98% in the sunlight region, and remains above 92%. Unlike pure poly(N-isopropylacrylamide) hydrogel, it does not turn white above 31°C, demonstrating excellent transparency. Furthermore, the infrared emissivity of the copolymer hydrogel coating of this invention is as high as 95%. Simultaneously, the enthalpy of vaporization of the copolymer hydrogel coating of this invention is 1798.91 J·g. -1 The concentration was higher than that of pure poly(N-isopropylacrylamide) hydrogel (1708.91 J·g). -1 ) and pure acrylamide hydrogel (1643.89 J·g) -1 The thermal conductivity of the copolymer hydrogel coating of this invention is 0.4645 W·m. -1 ·K -1 The concentration is lower than that of pure poly(N-isopropylacrylamide) hydrogel (0.515 W·m). -1 ·K -1 ) and pure acrylamide hydrogel (0.5287 W·m -1 ·K -1 A high enthalpy of vaporization means that a higher evaporation energy is required, which is beneficial for evaporative cooling; low thermal conductivity helps maintain thermal equilibrium when the ambient temperature varies greatly.

[0011] The present invention also provides a method for preparing the copolymer hydrogel coating that can achieve efficient, transparent, and passive cooling, wherein a photoinitiated polymerization method is used to introduce acrylamide segments with hydrophilic groups into the N-isopropylacrylamide molecular chain to obtain a copolymer hydrogel coating that achieves efficient, transparent, and passive cooling.

[0012] Furthermore, the preparation method of the copolymer hydrogel coating that can achieve efficient transparent passive cooling includes: mixing an N-isopropylacrylamide monomer solution and an acrylamide monomer solution to obtain a precursor solution, adding a photoinitiator to the precursor solution, and performing photopolymerization to obtain a copolymer hydrogel coating that achieves efficient transparent passive cooling.

[0013] Furthermore, the mass fraction of both the N-isopropylacrylamide monomer solution and the acrylamide monomer solution is 25-30%.

[0014] Furthermore, the method for preparing the N-isopropylacrylamide monomer solution is as follows: dissolving N-isopropylacrylamide monomer powder in deionized water to obtain an N-isopropylacrylamide monomer solution; the method for preparing the acrylamide monomer solution is as follows: dissolving acrylamide monomer powder in deionized water to obtain an acrylamide monomer solution.

[0015] Furthermore, the volume ratio of the N-isopropylacrylamide monomer solution to the acrylamide monomer solution is 1:1.

[0016] Furthermore, the precursor solution can also be prepared by mixing N-isopropylacrylamide monomer powder and acrylamide monomer powder, adding deionized water, and dissolving them completely at room temperature to obtain the precursor solution.

[0017] Furthermore, the photoinitiator is 0.5-1.5 wt% of the precursor solution.

[0018] Furthermore, the photoinitiator is ammonium persulfate.

[0019] Furthermore, the photopolymerization time is 22-30 minutes.

[0020] Furthermore, the preparation method of the copolymer hydrogel coating capable of achieving efficient, transparent, and passive cooling is as follows:

[0021] N-isopropylacrylamide monomer powder and acrylamide monomer powder were dissolved in deionized water to obtain their respective monomer solutions.

[0022] The N-isopropylacrylamide monomer solution and the acrylamide monomer solution were mixed to obtain the precursor solution of the copolymer hydrogel;

[0023] Ammonium persulfate, a photoinitiator, was added to the precursor solution, transferred to a petri dish, and subjected to photopolymerization under a UV lamp to obtain a copolymer hydrogel coating. The thickness of the copolymer hydrogel coating is determined by the amount of polymerization solution in the petri dish and the size of the petri dish.

[0024] Furthermore, during photopolymerization under a UV lamp, the precursor solution was kept 10 cm away from the UV lamp.

[0025] The present invention also provides the application of the copolymer hydrogel coating in passive cooling of photovoltaic panels.

[0026] The present invention also provides the application of the copolymer hydrogel coating in passive cooling of flexible LED displays.

[0027] The copolymer hydrogel coating of this invention exhibits high adhesion and can adhere to a predetermined surface. A 2000g weight was attached to a 2mm thick copolymer hydrogel coating, allowing it to be stably suspended and remaining firmly adhered even after vigorous shaking. Quantitative measurements show that the adhesion strength of the copolymer hydrogel coating of this invention is 37.8 ± 2.18 kPa, which is 45% and 119% stronger than that of pure poly(N-isopropylacrylamide) and polyacrylamide hydrogels, respectively. Furthermore, the copolymer hydrogel of this invention maintains long-term transparency. After 10 months of exposure to the environment, the transparency remains almost unchanged. In contrast, pure poly(N-isopropylacrylamide) and polyacrylamide hydrogels gradually yellow after only one month.

[0028] Compared with the prior art, the present invention has the following advantages and technical effects:

[0029] 1. The copolymer hydrogel coating prepared by the present invention changes the phase transition temperature by introducing acrylamide segments with hydrophilic groups into N-isopropylacrylamide. After optimization testing, a monomer ratio of 25-30% and a copolymerization ratio of 1:1 were determined. The copolymer hydrogel coating prepared under this special ratio has a micro-phase separation structure at the microscopic level and maintains a transparent appearance at the macroscopic level. It also has high solar transmittance and high-to-medium infrared emissivity, and exhibits the best passive cooling capability compared with other copolymerization ratios.

[0030] 2. The copolymer hydrogel coating prepared by this invention has a higher enthalpy of vaporization than pure poly(N-isopropylacrylamide) and polyacrylamide hydrogels, resulting in stronger evaporative cooling capacity. The combination of evaporative cooling and radiative cooling further improves the cooling efficiency of the hydrogel coating. Simultaneously, the copolymer hydrogel coating prepared by this invention has a lower thermal conductivity than pure poly(N-isopropylacrylamide) and polyacrylamide hydrogels, which helps to mitigate the effects of ambient temperature fluctuations and maintain thermal stability.

[0031] 3. The copolymer hydrogel coating prepared by this invention has strong adhesion and can be pasted on common substrates (glass, plastic, cement, etc.), making it easy to apply; it also has good durability and can maintain its original transparency for a long time without affecting the reception of visual information or the appearance.

[0032] 4. The copolymer hydrogel coating prepared by this invention has high transparency and high adhesion, and can be applied to the passive cooling of photovoltaic panels and flexible LED displays without consuming additional energy, which is of great significance for saving energy consumption.

[0033] 5. The preparation method provided by the present invention uses photo-initiated free radical copolymerization to prepare a copolymer hydrogel coating that can achieve efficient, transparent and passive cooling. The preparation process is simple and easy to operate, with a short cycle, is green and pollution-free, and can realize large-scale industrial production. Attached Figure Description

[0034] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0035] Figure 1 is a scanning electron microscope image of the surface of the copolymer hydrogel coating prepared in Example 1;

[0036] Figure 2 is a scanning electron microscope image of the cross section of the copolymer hydrogel coating prepared in Example 1;

[0037] Figure 3 shows the transmittance curves (UV-Vis band) and mid-infrared emissivity curves (infrared band) of the copolymer hydrogel coatings (thickness of 2 mm and 2.5 mm) prepared in Examples 1 and 2.

[0038] Figure 4 is a comparison of the thermal conductivity values ​​of the copolymer hydrogel coating of Example 1, the polyacrylamide hydrogel coating of Comparative Example 1, and the poly(N-isopropylacrylamide) hydrogel coating of Comparative Example 2.

[0039] Figure 5 is a comparison of the enthalpy of vaporization of the copolymer hydrogel coating of Example 1, the polyacrylamide hydrogel coating of Comparative Example 1, and the poly(N-isopropylacrylamide) hydrogel coating of Comparative Example 2. Detailed Implementation

[0040] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0041] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0042] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0043] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0044] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0045] Unless otherwise specified, the room temperature in the embodiments of the present invention is 25±2℃.

[0046] All raw materials used in this invention were purchased commercially. For example, N-isopropylacrylamide monomer was purchased from Shanghai McLean Biochemical Technology Co., Ltd., acrylamide monomer was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and ammonium persulfate was purchased from Xilong Scientific Co., Ltd.

[0047] The technical solution of the present invention will be further illustrated by the following embodiments.

[0048] Example 1

[0049] (1) Weigh 4g of N-isopropylacrylamide monomer powder, add 10mL of deionized water to it, and let it dissolve completely at room temperature to obtain a well mixed N-isopropylacrylamide monomer solution.

[0050] (2) Weigh 4g of acrylamide monomer powder, add 10mL of deionized water to it, and let it dissolve completely at room temperature to obtain a well mixed acrylamide monomer solution.

[0051] (3) Use a pipette to transfer 5 mL of N-isopropylacrylamide monomer solution and 5 mL of acrylamide monomer solution into centrifuge tubes, let stand until they are fully mixed, and obtain a transparent and stable precursor solution.

[0052] (4) Add 0.1g of initiator ammonium persulfate powder to the precursor solution, wait for the powder to dissolve completely, then take 2mL of the solution and transfer it to a 35mm diameter petri dish. Adjust the solution thickness in the petri dish to 2mm by measurement.

[0053] (5) Place the petri dish under ultraviolet light, 10 cm away from the ultraviolet lamp, and photopolymerize for 25 min to obtain a 2 mm thick copolymer hydrogel coating that can achieve efficient, transparent, and passive cooling (i.e., poly(N-isopropylacrylamide-acrylamide) copolymer hydrogel coating).

[0054] Example 2

[0055] (1) Weigh 4g of N-isopropylacrylamide monomer powder, add 10mL of deionized water to it, and let it dissolve completely at room temperature to obtain a well mixed N-isopropylacrylamide monomer solution.

[0056] (2) Weigh 4g of acrylamide monomer powder, add 10mL of deionized water to it, and let it dissolve completely at room temperature to obtain a well mixed acrylamide monomer solution.

[0057] (3) Use a pipette to transfer 5 mL of N-isopropylacrylamide monomer solution and 5 mL of acrylamide monomer solution into centrifuge tubes, let stand until they are fully mixed, and obtain a transparent and stable precursor solution.

[0058] (4) Add 0.1g of initiator ammonium persulfate powder to the precursor solution, wait for the powder to dissolve completely, then take 2.5mL of the solution and transfer it to a 35mm diameter culture dish, and adjust the solution thickness in the culture dish to 2.5mm by measurement;

[0059] (5) Place the petri dish under ultraviolet light, 10 cm away from the ultraviolet lamp, and photopolymerize for 25 min to obtain a poly(N-isopropylacrylamide-acrylamide) copolymer hydrogel coating with a thickness of 2.5 mm.

[0060] Example 3

[0061] (1) Weigh 4g of N-isopropylacrylamide monomer powder and 4g of acrylamide monomer powder and mix them. Add 20mL of deionized water to dissolve them completely at room temperature. After they are fully mixed, a transparent and stable precursor solution is obtained.

[0062] (2) Add 0.2g of initiator ammonium persulfate powder to the precursor solution, wait for the powder to dissolve completely, and then transfer 2.5mL of the solution to a 35mm diameter petri dish;

[0063] (3) Place the petri dish under ultraviolet light, 10 cm away from the ultraviolet lamp, and photopolymerize for 27 min to obtain a copolymer hydrogel coating that can achieve efficient, transparent and passive cooling.

[0064] Example 4

[0065] (1) Weigh 2g of N-isopropylacrylamide monomer powder, add 10mL of deionized water to it, and let it dissolve completely at room temperature to obtain a well mixed N-isopropylacrylamide monomer solution.

[0066] (2) Weigh 2g of acrylamide monomer powder, pour it into N-isopropylacrylamide monomer solution, and let it dissolve completely at room temperature to obtain a well-mixed precursor solution;

[0067] (3) Add 0.1g of initiator ammonium persulfate powder to the precursor solution, wait for the powder to dissolve completely, and then transfer 2.5mL of the solution to a 35mm diameter petri dish;

[0068] (4) Place the petri dish under ultraviolet light, 10 cm away from the ultraviolet lamp, and photopolymerize for 22 min to obtain a copolymer hydrogel coating that can achieve efficient, transparent and passive cooling.

[0069] Comparative Example 1

[0070] (1) Weigh 4g of acrylamide monomer powder, add 10mL of deionized water to it, and let it dissolve completely at room temperature to obtain a well mixed acrylamide monomer solution.

[0071] (2) Add 0.1g of initiator ammonium persulfate powder to the acrylamide monomer solution, wait for the powder to dissolve completely, then take 2mL of solution and transfer it to a 35mm diameter petri dish. After measurement, adjust the solution thickness in the petri dish to 2mm.

[0072] (3) Place the petri dish under ultraviolet light, 10 cm away from the ultraviolet lamp, and photopolymerize for 20 min to obtain a pure polyacrylamide hydrogel coating with a thickness of 2 mm.

[0073] Comparative Example 2

[0074] (1) Weigh 4g of N-isopropylacrylamide monomer powder, add 10mL of deionized water to it, and let it dissolve completely at room temperature to obtain a well mixed N-isopropylacrylamide monomer solution.

[0075] (2) Add 0.1g of initiator ammonium persulfate powder to the N-isopropylacrylamide monomer solution, wait for the powder to dissolve completely, then take 2mL of solution and transfer it to a 35mm diameter petri dish. After measurement, adjust the solution thickness in the petri dish to 2mm.

[0076] (3) Place the petri dish under ultraviolet light, 10 cm away from the ultraviolet lamp, and photopolymerize for 45 min to obtain a pure poly(N-isopropylacrylamide) hydrogel coating with a thickness of 2 mm.

[0077] The poly(N-isopropylacrylamide-acrylamide) copolymer hydrogel coating obtained in Example 1 was subjected to a temperature of -50°C. After 10 hours of freeze-drying, the scanning electron microscope images obtained are shown in Figure 1 (surface) and Figure 2 (cross-section). Small round pores and strip-shaped pores are randomly distributed on the surface of the copolymer hydrogel coating, which are characteristic pore morphologies of polyacrylamide hydrogel and poly(N-isopropylacrylamide) hydrogel, respectively. The special microscopic features of the copolymer hydrogel coating indicate that it is successfully copolymerized from acrylamide and N-isopropylacrylamide monomers. On the other hand, comparing the cross-sections of the three hydrogels, the P(NIPAm-co-AM) copolymer hydrogel also exhibits characteristic pore morphologies (large round pores and densely packed small pores) of both PAM and PNIPAm, and the size of the pores aggregated in different regions varies significantly. Therefore, the copolymerization of AM and NIPAm monomers here may be a random block copolymerization. Although the copolymer hydrogel appears uniform, the presence of a two-phase structure can still be observed microscopically. In polymer-water (hydrogel) systems, due to the different interaction energies between the two phases and water during the water absorption-desorption process, microphase separation occurs; therefore, the copolymer hydrogel possesses a microphase-separated structure.

[0078] Figure 3 shows the transmittance in the ultraviolet-visible band and the infrared emissivity in the infrared band for copolymer hydrogel coatings with thicknesses of 2.0 mm and 2.5 mm. It can be seen that the emissivity of the copolymer hydrogel coating of this invention is higher than 88.6% and 87.7% in the entire infrared range (2.5-16 μm), respectively, and higher than 92.4% and 91.9% in the atmospheric window (8-13 μm), respectively, reaching a maximum of 95.1% and 94.9%. Its transmittance is consistently higher than 96.1% and 92.2% in the visible light wavelength range (390-780 nm), reaching a maximum of 98.3% and 97.6%, making it a promising transparent cooling material. The copolymer hydrogel coating prepared by this invention can reduce the temperature by approximately 3-7°C compared to an uncovered surface under the same sunlight conditions. In actual outdoor tests, the copolymer hydrogel coating prepared by this invention can reduce the average temperature of photovoltaic panel surfaces by approximately 6-10°C and the average temperature of flexible LED screens by approximately 4-8°C.

[0079] Figure 4 is a comparison of the thermal conductivity values ​​of the copolymer hydrogel coating of Example 1, the polyacrylamide hydrogel coating of Comparative Example 1, and the poly(N-isopropylacrylamide) hydrogel coating of Comparative Example 2. It can be seen that the copolymer hydrogel coating has the lowest thermal conductivity, which is 0.4645 W·m. -1 ·K -1Low thermal conductivity helps maintain a relatively stable internal temperature when the ambient temperature fluctuates significantly.

[0080] Figure 5 is a comparison of the enthalpy of vaporization of the copolymer hydrogel coating of Example 1, the polyacrylamide hydrogel coating of Comparative Example 1, and the poly(N-isopropylacrylamide) hydrogel coating of Comparative Example 2. It can be seen that the copolymer hydrogel has the highest enthalpy of vaporization, which is 1798.91 J·g. -1 This means that higher evaporation energy is required to help remove more heat and alleviate the temperature rise. Therefore, the high enthalpy of vaporization of copolymer hydrogels gives them excellent evaporative cooling capabilities.

[0081] The present invention also tested the application-related properties of the copolymer hydrogel coating, and the results are as follows:

[0082] Adhesion strength: An overlap shear test was conducted by placing the hydrogel between two relatively rigid substrate specimens. Glass was used as the substrate, and the relationship between adhesive force and displacement was obtained using a universal testing machine. The formula is: Adhesion strength = F max The adhesion strength of the hydrogel is calculated using the area. F max The maximum adhesion force is represented by Area, which is the contact area between the hydrogel and the substrate. In this test, the thickness of the hydrogel affects the results; therefore, the hydrogel thickness needs to be controlled to <2 mm, and all test samples should be kept at the same thickness level as much as possible. Water content also affects viscosity results; therefore, different hydrogel samples were placed in a well-ventilated area for the same amount of time to allow their quality to stabilize before testing. The copolymer hydrogel coating of Example 1 in this invention exhibits an adhesion strength of 37.8 ± 2.18 kPa, which is 45% and 119% stronger than the pure poly(N-isopropylacrylamide) hydrogel coating and the polyacrylamide hydrogel coating, respectively.

[0083] Mechanical strength: The mechanical properties of the samples were tested using a microcomputer-controlled electronic universal testing machine at a displacement rate of 5 mm / min. -1 The hydrogel used in the test had dimensions of 20×40×1.5mm. 3 Tensile testing reveals the material properties of hydrogels under axial tensile loads, i.e., the stress-strain curve. Average tensile strength measures a material's ability to withstand tensile forces; a higher average tensile strength indicates greater tensile strength. Its value can be expressed by the formula: Tensile Strength = F max / Area is derived, where F maxThe maximum tensile force is represented by Area, which is the original cross-sectional area of ​​the hydrogel. Toughness represents a material's ability to resist fracture; the more energy absorbed before actual fracture, the stronger the toughness. It can be derived from the formula toughness = Energy absorption / Volume, where Energy absorption is the area under the stress-strain curve before fracture. The copolymer hydrogel coating of Example 1 has the highest average tensile strength (0.06 ± 0.01 MPa), higher than that of the pure poly(N-isopropylacrylamide) hydrogel coating (0.03 ± 0.01 MPa) and the polyacrylamide hydrogel coating (0.04 ± 0.01 MPa); the copolymer hydrogel coating of Example 1 also exhibits the strongest toughness (80.5 ± 18.1 MJ·m). -3 The efficiency was higher than that of pure poly(N-isopropylacrylamide) hydrogel coating (10.58±5.35 MJ·m). -3 ) and polyacrylamide hydrogel coating (7.05±3.54MJ·m -3 ).

[0084] Stability: In indoor simulated environment (<500W·m) -2 The cooling performance of the copolymer hydrogel (AM 1.5, 10%-15% relative humidity) was monitored for several days without the addition of water. Taking the copolymer hydrogel prepared in Example 1 as an example, its diameter was 35 mm. As the experimental time increased, the cooling performance of the copolymer hydrogel decreased. Within one day, compared to the reference value (without cooling material), the temperature dropped from 6.5℃ to 2.6℃ (the lowest point). This performance decline was due to the loss of water from the hydrogel. The cooling performance of the copolymer hydrogel tended to stabilize after one day, and even slightly recovered in the following days (this is related to changes in ambient temperature and humidity). Within half a month, its cooling performance remained above 2.6℃.

[0085] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A copolymer hydrogel coating capable of achieving efficient, transparent, and passive cooling, characterized in that, It is composed of poly(N-isopropylacrylamide-acrylamide) copolymer hydrogel, which is composed of N-isopropylacrylamide segments and acrylamide segments. The preparation method is as follows: N-isopropylacrylamide monomer solution and acrylamide monomer solution are mixed to obtain a precursor solution. A photoinitiator is added to the precursor solution to carry out photopolymerization and obtain the copolymer hydrogel coating that can achieve efficient, transparent and passive cooling. The mass fractions of the N-isopropylacrylamide monomer solution and the acrylamide monomer solution are both 25-30%; the volume ratio of the N-isopropylacrylamide monomer solution and the acrylamide monomer solution is 1:1; the thickness of the copolymer hydrogel coating is 2.0-2.5 mm; the transmittance of the copolymer hydrogel coating in the ultraviolet-visible band with wavelengths between 0.5 μm and 1.1 μm is 92%-98%; the emissivity of the copolymer hydrogel coating in the infrared band with wavelengths between 2.5-16.0 μm is 88%-95%, of which the infrared emissivity in the atmospheric transparent window is 92%-95%; the copolymer hydrogel coating that enables efficient transparent passive cooling is used for passive cooling of photovoltaic panels and flexible LED displays.

2. A method for preparing a copolymer hydrogel coating capable of efficient, transparent, and passive cooling as described in claim 1, characterized in that, An N-isopropylacrylamide monomer solution and an acrylamide monomer solution are mixed to obtain a precursor solution. A photoinitiator is added to the precursor solution to carry out photopolymerization, thereby obtaining a copolymer hydrogel coating that can achieve efficient, transparent, and passive cooling.

3. The method for preparing a copolymer hydrogel coating capable of efficient, transparent, and passive cooling according to claim 2, characterized in that, The photoinitiator is 0.5-1.5 wt% of the precursor solution.

4. The method for preparing a copolymer hydrogel coating capable of efficient, transparent, and passive cooling according to claim 2, characterized in that, The photopolymerization time is 22-30 minutes.

5. The application of the copolymer hydrogel coating according to claim 1 in passive cooling of photovoltaic panels.

6. The application of the copolymer hydrogel coating of claim 1 in passive cooling of flexible LED displays.

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