Fluorescent porous membrane for daytime radiation cooling

Abstract

The invention discloses a fluorescent porous membrane for daytime radiation cooling, and a preparation method of the fluorescent porous membrane comprises the following steps: dispersing fluorescent polymethyl vinyl microspheres in an organic polymer solution to obtain a membrane casting solution; and coating a substrate with the membrane casting solution, and volatilizing the solvent to obtain the fluorescent porous membrane for daytime radiation cooling, the organic polymer is at least one of polyvinylidene fluoride-hexafluoroethylene, polyvinylidene fluoride and polytetrafluoroethylene; the preparation method of the fluorescent polymethyl vinyl microspheres comprises the following steps: carrying out emulsion polymerization on methyltrimethoxysilane and vinyltrimethoxysilane to prepare the polymethyl vinyl microspheres; and calcining the polymethyl vinyl microspheres to obtain the fluorescent polymethyl vinyl microspheres. The fluorescent porous membrane disclosed by the invention not only has an obvious passive radiation refrigeration effect in the daytime, but also can emit bright blue light under the irradiation of an ultraviolet lamp.

Description

Technical Field

[0001] The invention relates to the technical field of daytime radiation cooling, and in particular to a fluorescent porous membrane used for daytime radiation cooling. Background Art

[0002] Passive solar radiative cooling (PDRC) is a technology that cools objects by reflecting solar energy and emitting radiation. Efficient PDRC materials should have high solar reflectivity in the 0.3-2.5μm solar spectrum range and high emissivity in the 8-13μm atmospheric window range. With the advancement of PDRC materials, various materials such as photonic structures, metamaterials, porous polymers, and nanoparticle doped materials have shown excellent cooling performance.

[0003] Optimal cooling performance usually requires high solar reflection, resulting in the appearance of high-efficiency PDRC materials being white or silver. This optical uniformity problem greatly limits their application. To address this problem, the introduction of pigments and photonic crystal materials into PDRC materials can expand the commercial application of PDRC coatings. Although brightly colored pigments provide a wide range of color options, they result in reduced solar reflectivity. Photonic crystals can display specific colors while reflecting solar energy, but the preparation process is complex and difficult to mass produce. In contrast, self-luminous PDRC materials produce colors without absorbing external solar energy, thus having superior cooling performance.

[0004] A Chinese patent document with publication number CN115434151A discloses a colored passive radiation cooling coating fabric, wherein an inorganic nanoparticle dispersion is first applied to a fiber fabric to obtain a daytime passive radiation coating, and then a modified organic pigment solution is sprayed on the daytime passive radiation coating, and the colored radiation cooling coating fabric is obtained after drying. The colored passive radiation cooling coating fabric has a reflectivity of less than 90% within the solar spectrum range.

[0005] The Chinese patent document with publication number CN115403887A provides a colored daytime passive radiation cooling porous film and a preparation method thereof. The method prepares a colored daytime passive radiation cooling porous film by uniformly dispersing inorganic particles and inorganic pigment particles in an organic polymer. The colored passive radiation cooling coating fabric prepared by the method has a reflectivity of less than 90% within the solar spectrum range. Summary of the invention

[0006] The present invention provides a fluorescent porous membrane for daytime radiation cooling. The fluorescent porous membrane not only has an obvious passive radiation cooling effect during the day, but can also emit bright blue light under the irradiation of ultraviolet lamps and can be patterned under ultraviolet light. It can meet ordinary cooling needs and is also suitable for cooling scenarios that require anti-counterfeiting technology or fluorescent markings.

[0007] The technical solution of the present invention is as follows:

[0008] A fluorescent porous membrane for daytime radiation cooling, the preparation method of which comprises: dispersing fluorescent polymethylvinyl microspheres in an organic polymer solution to obtain a casting solution; coating the casting solution on a substrate, and obtaining the fluorescent porous membrane for daytime radiation cooling after the solvent evaporates;

[0009] The organic polymer is at least one of polyvinylidene fluoride-hexafluoroethylene, polyvinylidene fluoride, and polytetrafluoroethylene;

[0010] The preparation method of the fluorescent polymethylvinyl microspheres comprises: preparing polymethylvinyl microspheres by emulsion polymerization of methyltrimethoxysilane and vinyltrimethoxysilane; and obtaining fluorescent polymethylvinyl microspheres by calcining the polymethylvinyl microspheres.

[0011] The fluorescent porous film of the present invention not only has high reflectivity and high emissivity in the solar spectrum and the atmospheric window range respectively, but also can emit bright blue light under the irradiation of ultraviolet lamp.

[0012] Preferably, in the organic polymer solution, the solvent includes an organic solvent and water; the mass ratio of the organic polymer, the organic solvent, and the water is 1:2-20:0.5-2; more preferably 1:5-10:1-2.

[0013] The organic solvent is acetone.

[0014] Preferably, in the fluorescent porous membrane, the mass ratio of the fluorescent microspheres to the organic polymer is 1:3-20.

[0015] With the increase of the mass fraction of fluorescent microspheres in the fluorescent porous membrane, the reflectivity of the fluorescent porous membrane gradually decreases, but the emissivity gradually increases.

[0016] Further preferably, in the fluorescent porous membrane, the mass ratio of the fluorescent microspheres to the organic polymer is 1:3-10; most preferably 1:4-5.

[0017] Preferably, the thickness of the fluorescent porous membrane is 30-2000 μm.

[0018] As the thickness of the fluorescent porous membrane increases, the reflectivity of the fluorescent porous membrane increases accordingly, and the emissivity remains basically unchanged. However, when the thickness reaches a certain level, the reflectivity remains unchanged and the mechanical properties of the prepared membrane deteriorate.

[0019] More preferably, the thickness of the fluorescent porous membrane is 200-800 μm; more preferably 400-600 μm; most preferably 500 μm.

[0020] Preferably, the particle size of the fluorescent polyvinyl methyl ether microspheres is 20 nm-10 μm; more preferably 50 nm-2 μm.

[0021] Preferably, the preparation method of the fluorescent polyvinyl methyl ether microspheres comprises:

[0022] (i) subjecting the microsphere raw material to emulsion polymerization for 5-20 hours, separating, washing, and drying to obtain polymethylvinyl microspheres;

[0023] In terms of mass percentage, the microsphere raw materials include:

[0024]

[0025] The balance is water;

[0026] (ii) calcining the poly(methyl vinyl) microspheres at 300-500° C. for 1-5 h to obtain fluorescent poly(methyl vinyl) microspheres.

[0027]

[0028] The balance is water.

[0029] Preferably, the surfactant is at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate, and sodium dodecylbenzene sulfonate; the auxiliary agent A is at least one of ammonia water and triethylamine; and the auxiliary agent B is polypyrrolidone.

[0030] The fluorescent porous membrane of the present invention has a fluorescent effect because the polyvinyl methyl ether microspheres filled in the porous membrane have a fluorescent effect, and the fluorescent effect is caused by the defective structure inside the microspheres, such as impurity carbon, oxygen defects, etc. The high reflectivity of the fluorescent porous membrane is the result of the strong scattering of sunlight by the porous structure and the reflection of sunlight by particles of different particle sizes contained therein. On the other hand, it is because the fluorescent microspheres can convert the absorbed ultraviolet light into visible light to improve the overall sunlight reflectivity. The high emissivity of the fluorescent porous membrane is due to the high emission of the organic polymer substrate and the molecular structure of the microspheres in the mid-infrared band.

[0031] The fluorescent porous film of the present invention can be covered on roofs and exterior walls to help cool down buildings, and can also be used to cool down cars and other equipment and outdoor equipment that need cooling. It is suitable for cooling scenes that require patterning and personalization under ultraviolet light, as well as cooling scenes that require anti-counterfeiting technology or fluorescent marking.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The preparation method of the present invention is simple, low-cost, and easy to industrialize;

[0034] (2) The reflectivity and emissivity of the fluorescent porous membrane prepared by the present invention can reach more than 90%;

[0035] (3) The fluorescent porous film prepared by the present invention can emit bright blue under ultraviolet light and can be patterned under ultraviolet light. In addition to ordinary cooling scenarios, it can also be used in cooling scenarios that require anti-counterfeiting technology or fluorescent marking. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a scanning electron microscope image of the fluorescent polyvinyl chloride microspheres prepared in Example 5;

[0037] Figure 2 The reflectivity and emissivity data of the fluorescent porous film prepared in Example 10 in the solar spectrum and mid-infrared spectrum range;

[0038] Figure 3 The scanning electron microscope image of the fluorescent porous membrane prepared in Example 10; wherein (a) is a surface scanning electron microscope image, and (b) is a cross-sectional scanning electron microscope image;

[0039] Figure 4 The temperature change of the fluorescent porous membrane prepared in Example 10 under solar radiation;

[0040] Figure 5 The photo (a) and infrared thermal imaging (b) of the fluorescent porous film prepared in Example 10 coated on a car model;

[0041] Figure 6 These are photos of the fluorescent porous membrane prepared in Example 10 under natural light and ultraviolet light, respectively. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0043] In the following examples, the prepared fluorescent porous membrane was subjected to an ultraviolet-visible-near infrared reflectivity test and an infrared emissivity test, and the reflectivity and emissivity of the sample were calculated.

[0044] Example 1

[0045] Preparation of polyvinyl methyl ether microspheres:

[0046] (1) 160 g of deionized water, 0.05 g of polypyrrolidone (PVP), and 0.1 g of sodium dodecyl sulfate (SDS) were stirred and dissolved in a 500 mL three-necked flask;

[0047] (2) 10 g of methyltrimethoxysilane (MTMS) and 10 g of vinyltrimethoxysilane were added to (1);

[0048] (3) adding 0.04 g of aqueous ammonia to (2), followed by stirring for 10 hours to obtain a polyvinyl methyl ether microsphere emulsion;

[0049] (4) The prepared polymethylvinyl microsphere emulsion is centrifuged and then washed three times with water and ethanol respectively, and then dried at 80° C. to obtain polymethylvinyl microspheres.

[0050] Example 2

[0051] Preparation of polyvinyl methyl ether microspheres:

[0052] (1) 160 g of deionized water, 0.05 g of polypyrrolidone (PVP), and 0.1 g of sodium dodecyl sulfate (SDS) were stirred and dissolved in a 500 mL three-necked flask;

[0053] (2) 20 g of methyltrimethoxysilane (MTMS) and 10 g of vinyltrimethoxysilane were added to (1);

[0054] (3) adding 0.04 g of aqueous ammonia to (2), followed by stirring for 10 hours to obtain a polyvinyl methyl ether microsphere emulsion;

[0055] (4) The prepared polymethylvinyl microsphere emulsion is centrifuged and then washed three times with water and ethanol respectively, and then dried at 80° C. to obtain polymethylvinyl microspheres.

[0056] Example 3

[0057] Preparation of polyvinyl methyl ether microspheres:

[0058] (1) 160 g of deionized water, 0.05 g of polypyrrolidone (PVP), and 0.1 g of sodium dodecyl sulfate (SDS) were stirred and dissolved in a 500 mL three-necked flask;

[0059] (2) 30 g of methyltrimethoxysilane (MTMS) and 10 g of vinyltrimethoxysilane were added to (1);

[0060] (3) adding 0.04 g of aqueous ammonia to (2), followed by stirring for 10 hours to obtain a polyvinyl methyl ether microsphere emulsion;

[0061] (4) The prepared polymethylvinyl microsphere emulsion is centrifuged and then washed three times with water and ethanol respectively, and then dried at 80° C. to obtain polymethylvinyl microspheres.

[0062] Example 4

[0063] Preparation of polyvinyl methyl ether microspheres:

[0064] (1) 160 g of deionized water, 0.05 g of polypyrrolidone (PVP), and 0.1 g of sodium dodecyl sulfate (SDS) were stirred and dissolved in a 500 mL three-necked flask;

[0065] (2) 40 g of methyltrimethoxysilane (MTMS) and 10 g of vinyltrimethoxysilane were added to (1);

[0066] (3) adding 0.04 g of aqueous ammonia to (2), followed by stirring for 10 hours to obtain a polyvinyl methyl ether microsphere emulsion;

[0067] (4) The prepared polymethylvinyl microsphere emulsion is centrifuged and then washed three times with water and ethanol respectively, and then dried at 80° C. to obtain polymethylvinyl microspheres.

[0068] Example 5

[0069] Preparation of fluorescent polyvinyl chloride microspheres:

[0070] The polyvinyl methyl ether microspheres prepared in Example 3 were calcined in a muffle furnace at 400° C. for 2 hours to obtain fluorescent polyvinyl methyl ether microspheres. Figure 1 It can be seen that the fluorescent polyvinyl methyl ether microspheres are spherical particles with a relatively smooth surface and a particle size of 50nm-2μm.

[0071] Example 6

[0072] (1) Weigh 2.5 g of polyvinylidene fluoride-hexafluoroethylene and add it to 20 g of acetone and stir to dissolve;

[0073] (2) Weigh 2.5 g of deionized water and add it to step (1) and stir until the solution is clear;

[0074] (3) Weigh 0.125 g of the fluorescent polyvinyl methyl ether microspheres prepared in Example 5 and evenly disperse them into step (2) to obtain a casting solution;

[0075] (4) The casting solution is poured onto a smooth glass plate and coated with a film casting device of a certain size. After the solvent evaporates, a fluorescent porous film with a thickness of 500 μm is obtained.

[0076] Example 7

[0077] (1) Weigh 2.5 g of polyvinylidene fluoride-hexafluoroethylene and add it to 20 g of acetone and stir to dissolve;

[0078] (2) Weigh 2.5 g of deionized water and add it to step (1) and stir until the solution is clear;

[0079] (3) Weigh 0.25 g of the fluorescent polyvinyl methyl ether microspheres prepared in Example 5 and evenly disperse them into step (2) to obtain a casting solution;

[0080] (4) The casting solution is poured onto a smooth glass plate and coated with a film casting device of a certain size. After the solvent evaporates, a fluorescent porous film with a thickness of 500 μm is obtained.

[0081] Example 8

[0082] (1) Weigh 2.5 g of polyvinylidene fluoride-hexafluoroethylene and add it to 20 g of acetone and stir to dissolve;

[0083] (2) Weigh 2.5 g of deionized water and add it to step (1) and stir until the solution is clear;

[0084] (3) Weigh 0.375 g of the fluorescent polyvinyl methyl ether microspheres prepared in Example 5 and evenly disperse them into step (2) to obtain a casting solution;

[0085] (4) The casting solution is poured onto a smooth glass plate and coated with a film casting device of a certain size. After the solvent evaporates, a fluorescent porous film with a thickness of 500 μm is obtained.

[0086] Example 9

[0087] (1) Weigh 2.5 g of polyvinylidene fluoride-hexafluoroethylene and add it to 20 g of acetone and stir to dissolve;

[0088] (2) Weigh 2.5 g of deionized water and add it to step (1) and stir until the solution is clear;

[0089] (3) Weigh 0.5 g of the fluorescent polyvinyl methyl ether microspheres prepared in Example 5 and evenly disperse them into step (2) to obtain a casting solution;

[0090] (4) The casting solution is poured onto a smooth glass plate and coated with a film casting device of a certain size. After the solvent evaporates, a fluorescent porous film with a thickness of 500 μm is obtained.

[0091] Example 10

[0092] (1) Weigh 2.5 g of polyvinylidene fluoride-hexafluoroethylene and add it to 20 g of acetone and stir to dissolve;

[0093] (2) Weigh 2.5 g of deionized water and add it to step (1) and stir until the solution is clear;

[0094] (3) Weigh 0.625 g of the fluorescent polyvinyl methyl ether microspheres prepared in Example 5 and evenly disperse them into step (2) to obtain a casting solution;

[0095] (4) The casting solution is poured onto a smooth glass plate and coated with a film casting device of a certain size. After the solvent evaporates, a fluorescent porous film with a thickness of 500 μm is obtained.

[0096] Depend on Figure 2It can be seen that the solar reflectivity of the porous film is 95.6%, and the mid-infrared emissivity is 92.2%, which has high solar reflectivity and mid-infrared emissivity. Figure 3 It shows that air pores of different pore sizes are distributed in the porous membrane, and fluorescent polyvinyl methyl ether microspheres are randomly distributed on its polymer skeleton, which is beneficial to improve the reflection of sunlight.

[0097] Embodiment 11

[0098] (1) Weigh 2.5 g of polyvinylidene fluoride-hexafluoroethylene and add it to 20 g of acetone and stir to dissolve;

[0099] (2) Weigh 2.5 g of deionized water and add it to step (1) and stir until the solution is clear;

[0100] (3) Weigh 0.625 g of the fluorescent polyvinyl methyl ether microspheres prepared in Example 5 and evenly disperse them into step (2) to obtain a casting solution;

[0101] (4) The casting solution is poured onto a smooth glass plate and coated with a film casting device of a certain size. After the solvent evaporates, a fluorescent porous film with a thickness of 200 μm is obtained.

[0102] Example 12

[0103] (1) Weigh 2.5 g of polyvinylidene fluoride-hexafluoroethylene and add it to 20 g of acetone and stir to dissolve;

[0104] (2) Weigh 2.5 g of deionized water and add it to step (1) and stir until the solution is clear;

[0105] (3) Weigh 0.625 g of the fluorescent polyvinyl methyl ether microspheres prepared in Example 5 and evenly disperse them into step (2) to obtain a casting solution;

[0106] (4) The casting solution is poured onto a smooth glass plate and coated with a film casting device of a certain size. After the solvent evaporates, a fluorescent porous film with a thickness of 400 μm is obtained.

[0107] Example 13

[0108] (1) Weigh 2.5 g of polyvinylidene fluoride-hexafluoroethylene and add it to 20 g of acetone and stir to dissolve;

[0109] (2) Weigh 2.5 g of deionized water and add it to step (1) and stir until the solution is clear;

[0110] (3) Weigh 0.625 g of the fluorescent polyvinyl methyl ether microspheres prepared in Example 5 and evenly disperse them into step (2) to obtain a casting solution;

[0111] (4) The casting liquid is poured onto a smooth glass plate and coated with a film casting device of a certain size. After the solvent evaporates, a fluorescent porous film with a thickness of 600 μm is obtained.

[0112] Embodiment 14

[0113] (1) Weigh 2.5 g of polyvinylidene fluoride-hexafluoroethylene and add it to 20 g of acetone and stir to dissolve;

[0114] (2) Weigh 2.5 g of deionized water and add it to step (1) and stir until the solution is clear;

[0115] (3) Weigh 0.625 g of the fluorescent polyvinyl methyl ether microspheres prepared in Example 5 and evenly disperse them into step (2) to obtain a casting solution;

[0116] (4) The casting solution is poured onto a smooth glass plate and coated with a film casting device of a certain size. After the solvent evaporates, a fluorescent porous film with a thickness of 800 μm is obtained.

[0117] The fluorescent porous membranes obtained in Examples 7-14 were subjected to UV-visible-near infrared reflectivity test and mid-infrared emissivity test. The test results are shown in Table 1.

[0118] Table 1 Reflectivity and emissivity test results of Examples 7-14 in the solar spectrum and mid-infrared spectrum

[0119]

[0120]

[0121] It can be seen from Table 1 that with the increase of fluorescent polyvinyl methyl ether microspheres in the fluorescent porous membrane, the reflectivity decreases and the emissivity increases; with the increase of the thickness of the fluorescent porous membrane, the reflectivity of the membrane also increases, and the emissivity remains basically unchanged. After reaching a certain thickness, the reflectivity remains unchanged.

[0122] Embodiment 15

[0123] The fluorescent porous membrane prepared in Example 10 was placed under outdoor solar radiation to measure its cooling effect. The results are as follows: Figure 4 As shown. Figure 4 It can be seen that the maximum difference between the temperature of the fluorescent porous membrane and the ambient temperature during the day is 8.5°C. This shows that the fluorescent porous membrane has a significant cooling effect.

[0124] Example 16

[0125] The fluorescent porous membrane prepared in Example 10 was placed on a car model to measure its cooling effect. The results are as follows: Figure 5 As shown. Figure 5It can be seen that the surface temperature of the car model covered with the fluorescent porous film is 39.7°C, which is significantly lower than that of the naked car model, and the surface temperature difference between the two is 11.6°C. This shows that the fluorescent porous film has a wide range of applications.

[0126] Embodiment 17

[0127] The "ZSTU" membrane made from the fluorescent porous membrane prepared in Example 10 was placed under natural light and ultraviolet light respectively to measure its fluorescence effect. The results are as follows: Figure 6 As shown. Figure 6 It can be seen that under ultraviolet light, "ZSTU" emits bright blue light. This shows that the fluorescent porous membrane has an obvious fluorescent effect.

[0128] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A fluorescent porous membrane for daytime radiation cooling, characterized in that: The preparation method comprises: dispersing fluorescent polymethylvinyl microspheres in an organic polymer solution to obtain a casting solution; coating the casting solution on a substrate, and obtaining the fluorescent porous membrane for daytime radiation cooling after the solvent evaporates; The organic polymer is at least one of polyvinylidene fluoride-hexafluoroethylene, polyvinylidene fluoride, and polytetrafluoroethylene; The preparation method of the fluorescent polymethylvinyl microspheres comprises: preparing polymethylvinyl microspheres by emulsion polymerization of methyltrimethoxysilane and vinyltrimethoxysilane; and obtaining fluorescent polymethylvinyl microspheres by calcining the polymethylvinyl microspheres.

2. The fluorescent porous membrane for daytime radiation cooling according to claim 1, characterized in that: In the fluorescent porous membrane, the mass ratio of the fluorescent microspheres to the organic polymer is 1:3-20.

3. The fluorescent porous membrane for daytime radiation cooling according to claim 2, characterized in that: In the fluorescent porous membrane, the mass ratio of the fluorescent microspheres to the organic polymer is 1:3-10.

4. The fluorescent porous membrane for daytime radiation cooling according to claim 1, characterized in that: The thickness of the fluorescent porous membrane is 30-2000 μm.

5. The fluorescent porous membrane for daytime radiation cooling according to claim 4, characterized in that: The thickness of the fluorescent porous membrane is 200-800 μm.

6. The fluorescent porous membrane for daytime radiation cooling according to claim 1, characterized in that: The particle size of the fluorescent polymethylvinyl microspheres is 20nm-10μm.

7. The fluorescent porous membrane for daytime radiation cooling according to claim 1, characterized in that: The preparation method of the fluorescent polyvinyl methyl ether microspheres comprises: (i) subjecting the microsphere raw material to emulsion polymerization for 5-20 hours, separating, washing, and drying to obtain polymethylvinyl microspheres; In terms of mass percentage, the microsphere raw materials include: (ii) calcining the poly(methyl vinyl) microspheres at 300-500° C. for 1-5 h to obtain fluorescent poly(methyl vinyl) microspheres.

8. The fluorescent porous membrane for daytime radiation cooling according to claim 7, characterized in that: The microsphere raw materials include:

9. The fluorescent porous membrane for daytime radiation cooling according to claim 7, characterized in that: The surfactant is at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate and sodium dodecylbenzene sulfonate; the auxiliary agent A is at least one of ammonia water and triethylamine; and the auxiliary agent B is polypyrrolidone.

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