An optically invisible colored radiation cooling coating and its preparation method and application

Abstract

The present invention discloses an optically invisible colored radiation cooling coating and a preparation method and application thereof, and relates to the technical field of optically invisible materials. The coating raw material comprises the following components in mass percentage: 30-50% of nanoparticles wrapped in fluorescent silica shells, 30-35% of polydimethylsiloxane, 5-10% of auxiliary agent, and 30-40% of ethyl acetate, and the sum of the mass percentages of each component is 100%; the present invention not only avoids the fluorescence aggregation quenching effect of the organic dye and improves the maximum fluorescence intensity of the dye by doping the organic fluorescent dye in mesoporous silica and using the silica shell for coating, but also the outer silica shell layer also acts as a protective layer, shielding the oxidation of the dye by ultraviolet rays, solvents and oxygen, and improving the photostability of the dye.

Description

Technical Field

[0001] The present invention relates to the technical field of optical stealth materials, and in particular to an optical stealth colored radiation refrigeration coating and a preparation method and application thereof. Background Art

[0002] Radiative cooling technology refers to the spontaneous radiation of heat from objects on the earth's surface into outer space through the "atmospheric window" (mainly in the 8-13μm band), thereby helping objects to cool down without the need for external energy input.

[0003] At present, in order to improve the performance of radiation cooling materials, metals such as gold, silver or ultra-white materials are often used as substrates to achieve higher reflectivity, thereby reducing the absorption of sunlight. However, these radiation cooling materials with white or silvery white surfaces will produce strong light pollution in practical applications and cannot meet the requirements of target concealment. Therefore, the development of radiation cooling materials that can effectively reduce temperature while maintaining concealment has become a problem that needs to be solved urgently. Summary of the invention

[0004] In view of the deficiencies in the above-mentioned background technology, the present invention mainly solves the problems in the prior art that the radiation refrigeration materials are lighter in color, the color radiation refrigeration coating has low refrigeration power and cannot meet the concealment requirements. The present invention provides an optically invisible color radiation refrigeration coating and its preparation method and application. The main components of the coating are nanoparticles wrapped in fluorescent silica shells, polydimethylsiloxane and additives. By doping organic fluorescent dyes in mesoporous silica and coating them with silica shells, not only the fluorescence aggregation quenching effect of the organic dye is avoided and the maximum fluorescence intensity of the dye is increased, but also the outer silica shell layer also acts as a protective layer, shielding the oxidation of the dye by ultraviolet rays, solvents and oxygen, and improving the photostability of the dye.

[0005] The first object of the present invention is to provide an optically invisible colored radiation cooling coating, wherein the coating raw material comprises the following components in mass percentage:

[0006] 30-50% of nanoparticles wrapped in fluorescent silica shells, 30-35% of polydimethylsiloxane, 1-5% of additives, 30-40% of ethyl acetate, and the sum of the mass percentages of the components is 100%;

[0007] The nanoparticles wrapped in fluorescent silica shells include inorganic nanoparticles, and mesoporous silica and silica shells coated on the surface of the inorganic nanoparticles, wherein the mesoporous silica is also loaded with a dye, and the dye is an organic fluorescent dye;

[0008] The inorganic nanoparticles are one or more of Al2O3, TiO2, CaCO3, MgCO3 and BaSO4;

[0009] The auxiliary agents include dispersants and film-forming auxiliary agents.

[0010] Preferably, the mass ratio of the dispersant to the film-forming aid is 1-2:1; wherein the dispersant is polyacrylic acid; and the film-forming aid is dodecyl alcohol ester.

[0011] Preferably, the size of the inorganic nanoparticles is 0.2-15 μm.

[0012] Preferably, the fluorescent silica shell-wrapped nanoparticles are prepared according to the following steps:

[0013] The organic fluorescent dye and the template agent A are dissolved in a water solvent, and then the inorganic nanoparticles are added and mixed evenly to obtain a mixed solution;

[0014] NaOH solution is added to the mixed solution, and after mixing evenly, tetraethyl orthosilicate is added for the first time at 75-85°C. After reacting for 1-3 hours, template B is added, and tetraethyl orthosilicate is added for the second time. The reaction is continued at 25-35°C for 3-5 hours to obtain fluorescent silica shell-wrapped nanoparticles.

[0015] Preferably, the organic fluorescent dye is one or more of rhodamine B, brilliant green SF, coumarin, and nigrosine; the template agent A is CTAB, and the template agent B is PVP.

[0016] The mass ratio of the organic fluorescent dye, template A, template B and inorganic nanoparticles is (0.1-0.5):3:1:1.

[0017] Preferably, the amount of tetraethyl orthosilicate added for the first time accounts for 3-5% of the total volume of the reaction solution; and the amount of tetraethyl orthosilicate added for the second time accounts for 2-4% of the total volume of the reaction solution.

[0018] Preferably, the color radiation cooling coating has a sunlight reflectivity of ≥80%, and an emissivity at an atmospheric transparent window of ≥90%.

[0019] The second object of the present invention is to provide a method for preparing an optically invisible colored radiation cooling coating, comprising the following steps:

[0020] The nanoparticles wrapped in fluorescent silica shells, ethyl acetate, polydimethylsiloxane and additives are added into anhydrous ethanol and mixed evenly to obtain a coating of a color radiation cooling layer;

[0021] The coating of the color radiation cooling layer is applied to the surface of the substrate and dried to obtain the color radiation cooling coating.

[0022] Preferably, the color radiation cooling coating has a thickness of 300-800 μm.

[0023] The third object of the present invention is to provide an optically invisible colored radiation cooling coating for use in optically invisible applications.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention provides an optically invisible colored radiation cooling coating and a preparation method and application thereof. The present invention wraps mesoporous silica doped with organic fluorescent dyes on the surface of highly reflective nanoparticles and uses a silica shell for coating. This not only avoids the fluorescence aggregation quenching effect of the organic dye through the coating of the mesoporous silica, and improves the maximum fluorescence intensity of the dye, but also the outer silica shell layer also acts as a protective layer, shielding the oxidation of the dye by ultraviolet rays, solvents and oxygen, and improving the light stability of the dye. The present invention can solve the problem that the color radiation cooling coating made of inorganic dyes is light in color and cannot meet the military camouflage color standard. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of the fluorescent particles in the present invention.

[0027] Figure 2 The SEM images of the fluorescent particles in Comparative Example 1 (A) and Example 1 (B) of the present invention are shown.

[0028] Figure 3 This is a comparison chart of the emerald green radiation cooling coating prepared in Example 1 of the present invention and in Comparative Example 2 after 72 hours of UV aging experiment.

[0029] Figure 4 The solar reflectivity of the emerald green radiative cooling coatings prepared in Example 1 of the present invention and Comparative Example 2.

[0030] Figure 5 The mid-infrared emissivity of the emerald green radiative cooling coatings prepared in Example 1 and Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0032] The purpose of the present invention is to solve the problems in the prior art that the color of the radiation cooling material is light, the cooling power of the colored radiation cooling coating is low, and the concealment cannot be satisfied. The present invention dopes the organic fluorescent pigment into the mesoporous silica and wraps it on the nanoparticles, uses the silica shell for coating, and directly adds it into the coating as the coloring filling particles to prepare the radiation cooling coating. The present invention has the advantages of simple preparation method, convenient construction method, meeting the color requirements of the equipment digital, long-lasting color and excellent cooling effect.

[0033] In order to achieve the above-mentioned object, the first aspect of the present invention provides an optically invisible colored radiation cooling coating, wherein the coating raw material comprises the following components in mass percentage:

[0034] 30-50% of nanoparticles wrapped in fluorescent silica shells, 30-35% of polydimethylsiloxane, 1-5% of additives, 30-40% of ethyl acetate, and the sum of the mass percentages of the components is 100%;

[0035] See also Figure 1 As shown, the nanoparticles wrapped in fluorescent silica shells include inorganic nanoparticles, and mesoporous silica and silica shells coated on the surface of the inorganic nanoparticles, wherein the mesoporous silica is also loaded with a dye, and the dye is an organic fluorescent dye;

[0036] The inorganic nanoparticles are one or more of Al2O3, TiO2, CaCO3, MgCO3 and BaSO4;

[0037] The auxiliary agents include dispersants and film-forming auxiliary agents.

[0038] The coating provided by the present invention mainly comprises nanoparticles wrapped in fluorescent silica shells, polydimethylsiloxane and additives. By doping organic fluorescent dyes in mesoporous silica and coating them with silica shells, not only the fluorescence aggregation quenching effect of organic dyes is avoided, the maximum fluorescence intensity of the dyes is improved, and the outer silica shell layer also acts as a protective layer, shielding the oxidation of the dyes by ultraviolet rays, solvents and oxygen, and improving the photostability of the dyes. In addition, the presence of a silica layer of suitable thickness can also increase the mid-infrared emissivity of the coating, ensuring the cooling effect of the colored daytime radiation cooling coating. The present invention provides a new idea for solving the problems of lighter color of radiation cooling materials, low cooling power of colored radiation cooling coatings and failure to meet concealment in the prior art. The coating preparation method is simple, the color is controllable and durable, it has a high reflectivity in the visible light band, and a high emissivity in the 8-13μm atmospheric window band, achieving an excellent radiation cooling effect.

[0039] The mass ratio of the dispersant to the film-forming aid is 1-2:1, and the preferred mass ratio is 2:1; wherein the dispersant is polyacrylic acid (PAA), and the film-forming aid is dodecyl alcohol ester, such as Texanol ester or alcohol ester-12. The size of the inorganic nanoparticles is 0.2-15 μm.

[0040] The fluorescent silica shell-wrapped nanoparticles are prepared according to the following steps:

[0041] The organic fluorescent dye and the template agent A are dissolved in a water solvent, and then the inorganic nanoparticles are added and mixed evenly to obtain a mixed solution;

[0042] NaOH solution is added to the mixed solution, and after mixing evenly, tetraethyl orthosilicate is added for the first time at 75-85°C. After reacting for 1-3 hours, template B is added, and tetraethyl orthosilicate is added for the second time. The reaction is continued at 25-35°C for 3-5 hours to obtain fluorescent silica shell-wrapped nanoparticles.

[0043] The organic fluorescent dye is one or more of rhodamine B, brilliant green SF, coumarin, and nigrosine; the template agent A is cetyltrimethylammonium bromide (CTAB), and the template agent B is polyvinyl pyrrolidone (PVP);

[0044] The mass ratio of the organic fluorescent dye, template A, template B and inorganic nanoparticles is (0.1-0.5):3:1:1.

[0045] It should be noted that CTAB and PVP are both templates and surfactants, which can form silica with different morphologies, one is mesoporous and the other is a shell. For this purpose, CTAB is added first and then PVP.

[0046] The amount of the tetraethyl orthosilicate added for the first time accounts for 3-5% of the total volume of the reaction solution; the amount of the tetraethyl orthosilicate added for the second time accounts for 2-4% of the total volume of the reaction solution.

[0047] Exemplarily, fluorescent silica shell-wrapped nanoparticles are prepared by the following method:

[0048] (1) Weigh a certain amount of organic fluorescent dye, template A and nanoparticles, dissolve them in deionized water, and mix them thoroughly under ultrasonication for 30 minutes; wherein the mass ratio of the organic fluorescent dye, template A, nanoparticles and deionized water is 0.1-0.5:3:1:100.

[0049] (2) Add NaOH solution to the solution at room temperature, mix well, set the reaction temperature to 80°C, slowly add 3-5% tetraethyl orthosilicate (TEOS) to the total volume of the solution under vigorous stirring, and react for 2 hours;

[0050] (3) Then, PVP of template B was added, with a mass ratio of PVP to CTAB of 1:3. After dissolution, 3% TEOS was added dropwise again. The reaction temperature was set at 30°C. The hydrolysis and condensation reaction was carried out for 4 hours, then cooled to room temperature and centrifuged to obtain the reactants. The reactants were washed three times with anhydrous ethanol and deionized water by alternating ultrasonic centrifugation, and freeze-dried to obtain nanoparticles wrapped with fluorescent silica shells.

[0051] The color radiation cooling coating has a sunlight reflectivity of ≥80% and an emissivity of ≥90% in the atmospheric transparent window. The color difference between the color radiation cooling coating and the standard background is less than 2 , the visible light brightness contrast is less than 0.3.

[0052] A second aspect of the present invention provides a method for preparing an optically invisible colored radiation cooling coating, comprising the following steps:

[0053] The nanoparticles wrapped in fluorescent silica shells, ethyl acetate, polydimethylsiloxane and additives are added into anhydrous ethanol and mixed evenly to obtain a coating of a color radiation cooling layer;

[0054] The coating of the color radiation cooling layer is applied to the surface of the substrate and dried to obtain the color radiation cooling coating.

[0055] The thickness of the colored radiation cooling coating is 300-800 μm.

[0056] Exemplarily, a method for preparing an optically invisible colored radiation cooling coating comprises the following steps:

[0057] (1) Add the fluorescent silica shell-wrapped nanoparticles into anhydrous ethanol at room temperature and disperse them by ultrasonic at room temperature and pressure for 20 min;

[0058] (2) Then, add ethyl acetate at room temperature and pressure for 5 minutes with a stirring speed of 200 to 400 r / min;

[0059] (3) adding liquid polydimethylsiloxane and an auxiliary agent, stirring and mixing at room temperature and pressure for 20 minutes, with a stirring speed of 200 to 400 r / min, to obtain a coating for preparing a colored radiation cooling layer; wherein the auxiliary agent includes a dispersant and a film-forming auxiliary agent. The dispersant is polyacrylic acid (PAA), and the film-forming auxiliary agent is dodecyl alcohol ester, and the mass ratio of the two is 2:1;

[0060] (4) The colored radiation cooling layer coating is sprayed on the surface of the substrate and dried at room temperature for 8 hours to obtain the colored radiation cooling coating.

[0061] The third aspect of the present invention provides an application of an optically invisible colored radiation cooling coating in optical invisibility. The coating can be applied to the outside of buildings in hot areas to maintain the building's concealment and low cost while efficiently maintaining the internal temperature.

[0062] It should be noted that the experimental methods used in the present invention are all conventional methods unless otherwise specified; the reagents and materials used are all commercially available unless otherwise specified.

[0063] Example 1

[0064] 0.1 g of brilliant green SF, 6 g of CTAB and 2 g of nanoparticles were weighed and dissolved in 2000 mL of deionized water, ultrasonicated for 30 min, and NaOH solution (16 Mm, 1.75 mL) was added dropwise. After mixing evenly, the reaction temperature was set to 80 ° C. 10 mL of LTEOS was slowly added dropwise under vigorous stirring and reacted for 2 h. Then 2 g of PVP was added and dissolved. 6 mL of LTEOS was added dropwise. The reaction temperature was set at 30 ° C. After reacting again for 4 h, it was cooled to room temperature and centrifuged to obtain the reactant. The reactant was washed three times with anhydrous ethanol and deionized water by alternating ultrasonic centrifugation. The fluorescent silica shell-wrapped nanoparticles were obtained by freeze-drying. Its SEM is as follows: Figure 2 As shown in (B).

[0065] 3g of nanoparticles wrapped in fluorescent silica shells were added to anhydrous ethanol and ultrasonically dispersed for 20min; then 3g of ethyl acetate, 3g of liquid polydimethylsiloxane, 0.3g of film-forming agent, and 0.1g of dispersant were added in sequence and stirred for 20min at room temperature and pressure, with a stirring speed of 200-400r / min to obtain a coating for preparing a color radiation cooling layer. Finally, the color radiation cooling layer coating was sprayed on the surface of the substrate and dried at room temperature for 8h to obtain a color radiation cooling coating. The surface photo of the coating is shown in Figure 2. Figure 3 shown.

[0066] Example 2

[0067] This embodiment is the same as the embodiment 1, except that the organic fluorescent dye is 0.06 g of rhodamine B and 0.036 g of brilliant green SF; the other preparation steps are the same as the embodiment 1, that is, a yellow-brown radiation cooling coating is prepared.

[0068] Example 3

[0069] This embodiment is the same as the embodiment 1, except that the organic fluorescent dye is 0.06 g of rhodamine B, 0.03 g of coumarin and 0.002 g of nigrosine, and the other preparation steps are the same as the embodiment 1, that is, a brown radiation cooling coating is prepared. It should be noted that in order to meet the camouflage color requirement, nigrosine is added to reduce the brightness.

[0070] Comparative Example 1

[0071] The emerald green radiation cooling material was prepared by the same method as in Example 1, except that PVP was not added when preparing the silica shell, but an equal amount of CTAB was used, and the other process steps were the same as in Example 1. The SEM images of the nanoparticles prepared in this comparative example 1 are as follows: Figure 2 As shown in (A).

[0072] See also Figure 2 As shown, Figure 2 (A) is the particle prepared in Comparative Example 1, which has a rough surface and is coated with a layer of mesoporous silica; Figure 2 The particles (B) in the middle are prepared in Example 1, and their surface is smooth, indicating that a layer of silica shell is evenly coated on the surface of the mesoporous silica.

[0073] Comparative Example 2

[0074] The emerald green radiative cooling material was prepared by the same method as in Example 1, except that no organic fluorescent dye was added when preparing the nanoparticles wrapped in the mesoporous silica shell. To ensure similar colors, 0.0047 g of brilliant green SF was added when preparing the coating, and the other process steps were the same as in Example 1.

[0075] The present invention selects three common color blocks, among which the standard color blocks of different colors are The values ​​are: ① emerald green (38.3, -12.8, 17.5); ② khaki (47.1, -0.4, 20.1); ③ dark brown (34.7, 1.1, 4.6).

[0076] After testing and comparison with the colorimeter, the experimental results are as follows:

[0077] The sample thickness is 500 nm;

[0078] In Example 1, the color difference with the emerald green background is 1.7 , visible light brightness contrast 0.21;

[0079] In Example 2, the color difference from the yellow-brown background is 2.3 , visible light brightness contrast 0.17;

[0080] In Example 3, the color difference from the brown background is 2.1 , visible light brightness contrast 0.32.

[0081] The experimental results show that the colored radiation cooling coatings of Examples 1 to 3 meet the use requirements.

[0082] It should be noted that are three basic coordinates representing the brightness of the color; among them, =0 produces black and =100 indicates white; Negative values ​​indicate green and positive values ​​indicate magenta, somewhere between red / magenta and green; Negative values ​​indicate blue and positive values ​​indicate yellow, somewhere in between yellow and blue.

[0083] See also Figure 3 As shown, there is no obvious difference between Example 1 and Comparative Example 2 before the UV aging experiment. Through the colorimeter detection and analysis, the color difference between Comparative Example 2 and Example 1 is 0.13 , the visible light brightness contrast is 0.052, which shows that the color of comparative example 2 is similar to that of example 1. After 72 hours of UV aging test (implemented in accordance with ASTM G154-2023), the color of comparative example 1 sample is yellowish after the test, indicating that the Lab value of the sample after irradiation is compared with the standard background. The value increases, while the color of Example 1 is not significantly different from that before irradiation.

[0084] Figure 4 and Figure 5 It shows that compared with directly adding fluorescent pigments into the coating, the coating sprayed with nanoparticles wrapped in mesoporous silica shells doped with pigments exhibits superior daytime radiative cooling capabilities.

[0085] Specifically, for the radiation cooling coatings of Examples 1 to 3 and Comparative Example 2, the thickness was fixed at 500 μm, and then the solar reflectivity test and the mid-infrared emissivity test were performed. The results are shown in Table 1.

[0086] Table 1 shows the average solar reflectivity and mid-infrared emissivity of different color radiative cooling coatings

[0087]

[0088] As can be seen from Table 1, the coatings prepared by the present invention all have a high solar reflectivity, and compared with direct doping of pigments, the pigments loaded in mesoporous silica have less impact on the overall solar reflectivity of the coating. In addition, the emissivity of the prepared radiation cooling coating in the mid-infrared stage is also at a high level, and the embodiment has shown certain advantages over the comparative example. In summary, the coating exhibits good radiation cooling performance.

[0089] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An optically invisible colored radiation cooling coating, characterized in that: The coating material includes the following components in percentage by weight: 30-50% of nanoparticles wrapped in fluorescent silica shells, 30-35% of polydimethylsiloxane, 5-10% of additives, and 30-40% of ethyl acetate, the sum of the mass percentages of each component being 100%; The nanoparticles wrapped in fluorescent silica shells include inorganic nanoparticles, and mesoporous silica and silica shells sequentially coated on the surface of the inorganic nanoparticles, wherein the mesoporous silica is also loaded with a dye, and the dye is an organic fluorescent dye; The inorganic nanoparticles are one or more of Al2O3, TiO2, CaCO3, MgCO3 and BaSO4; The auxiliary agent includes a dispersant and a film-forming auxiliary agent; The fluorescent silica shell-wrapped nanoparticles are prepared according to the following steps: The organic fluorescent dye and the template agent A are dissolved in a water solvent, and then the inorganic nanoparticles are added and mixed evenly to obtain a mixed solution; Add NaOH solution to the mixed solution, mix well, add tetraethyl orthosilicate for the first time at 75-85°C, react for 1-3 hours, add template B, and add tetraethyl orthosilicate for the second time, and continue to react for 3-5 hours at 25-35°C to obtain fluorescent silica shell-wrapped nanoparticles; The organic fluorescent dye is one or more of rhodamine B, brilliant green SF, coumarin, and nigrosine; the template agent A is CTAB; and the template agent B is PVP; The mass ratio of the organic fluorescent dye, template A, template B and inorganic nanoparticles is (0.1-0.5):3:1:

1.

2. The optically invisible colored radiation cooling coating according to claim 1, characterized in that: The mass ratio of the dispersant to the film-forming aid is 1-2:1; wherein the dispersant is polyacrylic acid; and the film-forming aid is dodecyl alcohol ester.

3. The optically invisible colored radiation cooling coating according to claim 1, characterized in that: The size of the inorganic nanoparticles is 0.2-15 μm.

4. The optically invisible colored radiation cooling coating according to claim 1, characterized in that: The amount of the tetraethyl orthosilicate added for the first time accounts for 3-5% of the total volume of the reaction solution; the amount of the tetraethyl orthosilicate added for the second time accounts for 2-4% of the total volume of the reaction solution.

5. The optically invisible colored radiation cooling coating according to claim 1, characterized in that: The color radiation cooling coating has a sunlight reflectivity of ≥80% and an emissivity in an atmospheric transparent window of ≥90%.

6. A method for preparing the optically invisible colored radiation cooling coating according to any one of claims 1 to 5, characterized in that: The following steps are involved: The nanoparticles wrapped in fluorescent silica shells, ethyl acetate, polydimethylsiloxane and additives are added into anhydrous ethanol and mixed evenly to obtain a coating of a color radiation cooling layer; The coating of the color radiation cooling layer is applied to the surface of the substrate and dried to obtain the color radiation cooling coating.

7. The method for preparing the optically invisible colored radiation cooling coating according to claim 6, characterized in that: The thickness of the colored radiation cooling coating is 300-800 μm.

8. Use of the optically invisible colored radiation cooling coating according to any one of claims 1 to 5 in optical stealth.

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