Super-reflective radiative cooling film with super-hydrophobicity, preparation method and application

Abstract

The application discloses an ultra-reflection radiative cooling film with superhydrophobicity, a preparation method and application. The preparation method comprises the following steps: uniformly mixing DCPDA monomers, graphene quantum dot dispersion, fumed silica and an ultraviolet curing agent to obtain a casting solution; coating the casting solution on the surface of a substrate to obtain a wet film; and performing ultraviolet curing on the wet film to obtain the ultra-reflection radiative cooling film with superhydrophobicity. The graphene quantum dot dispersion and the fumed silica are introduced into the DCPDA monomers, and the ultraviolet curing agent is added, so that high solar reflectivity and high infrared emissivity are realized through ultraviolet curing induced phase separation, the formed film has excellent radiative cooling and self-cleaning performance, and is suitable for building energy saving, cold chain transportation and the like. The application adopts the light polymerization induced phase separation mode, and has the advantages of simple process, low energy consumption and suitability for large-scale application.

Description

Technical Field

[0001] This invention relates to the field of passive radiative cooling materials, and more particularly to a superhydrophobic, superreflective radiative cooling thin film, its preparation method, and its application. Background Technology

[0002] Radiation cooling is a method of cooling that utilizes the radiation of heat from an object to an atmospheric window (8-13 μm). It is of great significance for alleviating energy consumption and reducing air conditioning load. However, in existing technologies, radiation cooling films often struggle to maintain superhydrophobic properties while improving solar reflectivity and infrared emissivity. Furthermore, introducing superhydrophobic structures or functional layers can easily affect the optical properties and stability of the film, thus hindering the widespread application of radiation cooling films.

[0003] Therefore, there is an urgent need to provide a radiation-cooling thin film that can simultaneously achieve high solar reflectivity, high infrared emissivity, and superhydrophobic properties, as well as a method for its preparation. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned technical deficiencies and propose a superhydrophobic, superreflective radiation cooling thin film, its preparation method, and its application, thereby solving the technical problem that radiation cooling thin films in the prior art cannot simultaneously achieve high solar reflectivity, high infrared emissivity, and superhydrophobic properties.

[0005] In a first aspect, the present invention provides a method for preparing a superhydrophobic, superreflective radiation-cooling thin film, comprising the following steps: S1. Mix DCPDA monomer, graphene quantum dot dispersion, fumed silica and UV curing agent evenly to obtain casting solution; S2. Apply the casting solution to the substrate surface to obtain a wet film; S3. The wet film is cured with ultraviolet light to obtain a super-hydrophobic, super-reflective radiation cooling film. The solvent for the graphene quantum dot dispersion is an alcohol solvent.

[0006] In a second aspect, the present invention provides a superhydrophobic superreflectivity radiation cooling film, which is obtained by the preparation method of the superhydrophobic superreflectivity radiation cooling film provided in the first aspect of the present invention.

[0007] Thirdly, the present invention provides an application of a superhydrophobic, superreflective radiation cooling film, which is applied in fields such as building energy conservation and cold chain transportation.

[0008] Compared with the prior art, the beneficial effects of the present invention include: This invention achieves a balance between high solar reflectivity and high infrared emissivity by introducing graphene quantum dot dispersion and fumed silica into DCPDA monomers and adding a UV curing agent. This UV-curing-induced phase separation results in a thin film with excellent radiative cooling and self-cleaning properties, suitable for applications such as building energy conservation and cold chain transportation. The invention employs a photopolymerization-induced phase separation method, which is simple, energy-efficient, and suitable for large-scale applications. Attached Figure Description

[0009] Figure 1 These are optical photographs of presamples prepared with different contents of good solvent in Example 1 of the present invention under an incandescent lamp; wherein (a), (b), (c), (d), and (e) are presample 1, presample 2, presample 3, presample 4, and presample 5, respectively. Figure 2 These are optical photographs of samples prepared from graphene quantum dot dispersions with different contents in Example 2 of the present invention under incandescent light; wherein (a), (b), and (c) are sample 3, sample 5, and sample 7, respectively. Figure 3 These are solar reflectance spectra of samples prepared with good solvents in Example 2 of this invention, samples prepared with graphene quantum dot dispersions of different contents, and commercial white paint. Figure 4 These are optical photographs of samples prepared with different contents of fumed silica in Example 3 of the present invention under an incandescent lamp; wherein (a), (b), (c), (d), (e), and (f) are, in order, samples 8, 9, 10, 11, 12, and 13. Figure 5 These are hydrophobic angle images of samples prepared with different contents of fumed silica in Example 3 of the present invention; wherein (a), (b), (c), (d), (e), and (f) are, in order, samples 8, 9, 10, 11, 12, and 13. Figure 6 These are optical photographs of the commercial white paint of the present invention and samples 5 and 10 in the embodiments under 365nm light irradiation; wherein (a), (b), and (c) are the commercial white paint, sample 5, and sample 10, respectively. Figure 7 These are solar reflectance spectra of samples prepared with different contents of fumed silica in Example 3 of this invention; Figure 8 These are near-infrared emissivity images of samples prepared with different contents of fumed silica in Example 3 of this invention; Figure 9 These are the outdoor cooling curves of commercial white paint and samples 1, 5, and 10 in the examples. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0011] In a first aspect, the present invention provides a method for preparing a superhydrophobic, superreflective radiation-cooling thin film, comprising the following steps: S1. Mix DCPDA (tricyclodecanedimethylethanol diacrylate) monomer, graphene quantum dot dispersion, fumed silica and UV curing agent evenly to obtain casting solution; S2. Apply the casting solution to the substrate surface to obtain a wet film; S3. The wet film is cured under ultraviolet light and cured by photopolymerization-induced phase separation to obtain a superhydrophobic, superreflective radiation cooling film. The solvent for the graphene quantum dot dispersion is an alcohol solvent.

[0012] In this invention, by adding graphene quantum dot dispersion to DCPDA monomer, a good solvent (alcohol solvent) for DCPDA curing monomer is introduced. The polymerized DCPDA formed after UV curing is insoluble in alcohol solvent, precipitates out and forms a porous and fluffy structure, thereby obtaining extremely high reflectivity. On the other hand, graphene quantum dots can convert high-energy short-wavelength light into low-energy visible light, thereby producing a cooling effect. By introducing fumed silica, the luminescence efficiency of graphene quantum dots can be increased and heat conversion can be reduced. On the other hand, reflectivity can be increased through Mie scattering. In addition, the introduction of fumed silica can also improve hydrophobicity by increasing roughness.

[0013] In this embodiment, the alcohol solvent is at least one of methanol, ethanol, and ethylene glycol.

[0014] In this embodiment, the mass fraction of the graphene quantum dot dispersion is 0.0005%~0.002%, and more specifically 0.0008%~0.0012%.

[0015] In this embodiment, the preparation process of the graphene quantum dot dispersion includes: dispersing o-phenylenediamine (OPD) and a catalyst in an alcohol solvent, followed by a solvothermal reaction to obtain the graphene quantum dot dispersion.

[0016] Preferably, the catalyst is at least one of oxalic acid and acetic acid.

[0017] Preferably, the mass ratio of o-phenylenediamine to catalyst is 1:(0.3~3), more preferably 1:(0.8~1.2).

[0018] Preferably, the ratio of o-phenylenediamine to alcohol solvent is 0.1~0.3 mg: 1 mL.

[0019] Preferably, the temperature of the solvothermal reaction is 80~200℃, more preferably 140~180℃, the time of the solvothermal reaction is 4~36h, more preferably 20~30h, and the heating rate is 5~10℃ / min.

[0020] In this embodiment, the mass ratio of DCPDA monomer to graphene quantum dot dispersion is 1:(1~2), preferably 1:(1.4~2).

[0021] In this embodiment, the average particle size of fumed silica is 200~800nm, and more specifically 500nm.

[0022] In this embodiment, the mass ratio of DCPDA monomer to fumed silica is 1:(0.01~0.05).

[0023] In this embodiment, the UV curing agent is ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L).

[0024] In this embodiment, the mass ratio of DCPDA monomer to UV curing agent is 1:(0.01~0.02).

[0025] In this embodiment, the process of uniformly mixing DCPDA monomer, graphene quantum dot dispersion, fumed silica and UV curing agent includes: mixing DCPDA monomer, graphene quantum dot dispersion, fumed silica and UV curing agent, stirring at 40~60 ℃ in the dark for 1~3 h, and then sonicating at 40~60 ℃ in the dark for 1~3 h.

[0026] This invention does not limit the coating method, and those skilled in the art can choose according to the actual situation. For example, spraying, scraping, dipping, spin coating, etc. can be used.

[0027] In this embodiment, the substrate is glass.

[0028] In this embodiment, the thickness of the wet film is 200~800 μm, and more specifically 400 μm.

[0029] In this embodiment, during the UV curing process, the UV wavelength is 365~405 nm, the curing distance (i.e., the distance between the curing lamp and the wet film surface) is 6~24 cm, preferably 18 cm, the curing time is 5~10 s, preferably 10 s, and the curing power is 70%~100% of the maximum power, preferably 100%; the maximum power is 1500 mW / cm 2 .

[0030] In a second aspect, the present invention provides a superhydrophobic superreflectivity radiation cooling film, which is obtained by the preparation method of the superhydrophobic superreflectivity radiation cooling film provided in the first aspect of the present invention.

[0031] In some preferred embodiments of the present invention, by controlling the mass ratio of DCPDA monomer to graphene quantum dot dispersion and the mass ratio of DCPDA monomer to fumed silica, the solar reflectivity of the superhydrophobic superreflectivity radiation cooling film can be controlled to be above 95%, and the visible light reflectivity can be controlled to be above 98%.

[0032] Thirdly, the present invention provides an application of a superhydrophobic, superreflective radiation cooling film, which is applied in fields such as building energy conservation and cold chain transportation.

[0033] To avoid redundancy, the preparation methods of graphene quantum dot dispersions in the following embodiments of the present invention are as follows: 5 mg of OPD and 5 mg of oxalic acid were dissolved in 25 mL of ethanol. The resulting mixture was transferred to a polytetrafluoroethylene (PTFE)-lined high-pressure reactor and sonicated for 5 min. The reactor was then placed in an oven and heated at a rate of 8 °C / min until it reached 160 °C. The reaction time was 24 h. After the reaction was completed, the reactor was cooled to room temperature and removed to obtain a graphene quantum dot dispersion (approximately 0.001% by mass).

[0034] Example 1 Example 1 was used to investigate the effect of different good solvent contents on film-forming properties. The specific steps included: (1) Add DCPDA monomer and good solvent (anhydrous ethanol) to a weighing bottle. The mass of DCPDA and good solvent are 10g:0g, 8g:2g, 6g:4g, 4g:6g, and 2g:8g, respectively, and name them as: presample 1, presample 2, presample 3, presample 4 and presample 5. Then add UV curing agent (TPO-L) of 0.15g, 0.12g, 0.09g, 0.06g and 0.03g, respectively. Then stir and sonicate in the dark in sequence to make the system evenly dispersed and obtain casting solution. The temperature of stirring and sonication is 50℃ and the time of stirring and sonication is 2h. (2) The casting liquid is applied to the glass surface by scraping, and the wet film thickness is controlled to be 400 μm by adjusting the scraper scale; (3) Transfer the wet film to a UV curing chamber (Shanghai Runduo, model: UVK80), set the curing distance to 18 cm, the curing time to 10 s, and the curing power to 100% of the maximum power, with the maximum power being 1500 mW / cm. 2Ultraviolet curing was performed to obtain a superreflective radiation cooling film.

[0035] Example 2 Example 2 investigated the effect of different graphene quantum dot dispersion contents on reflectivity. The specific steps included: (1) 10g of DCPDA monomer and 14g of anhydrous ethanol were added to a weighing bottle as a control group and named Sample 1; DCPDA and graphene quantum dot dispersion were added to a weighing bottle in the following ratios: 10g:10g, 10g:12g, 10g:14g, 10g:16g, 10g:18g and 10g:20g, and named Sample 2, Sample 3, Sample 4, Sample 5, Sample 6 and Sample 7, respectively; then 0.15g of UV curing agent (TPO-L) was added to each sample, and then the system was stirred and sonicated in the dark in sequence to make the system uniformly dispersed and to obtain the casting solution; the temperature of stirring and sonication was 50℃ and the time of stirring and sonication was 2 h. (2) The casting liquid is applied to the glass surface by scraping, and the wet film thickness is controlled to be 400 μm by adjusting the scraper scale; (3) Transfer the wet film to a UV curing chamber (Shanghai Runduo, model: UVK80), set the curing distance to 18 cm, the curing time to 10 s, and the curing power to 100% of the maximum power, with the maximum power being 1500 mW / cm. 2 Ultraviolet curing was performed to obtain a superreflective radiation cooling film.

[0036] Table 1. Relevant preparation parameters and test results for different samples in Example 2.

[0037] Note: The solar reflectance in Table 1 is the weighted average reflectance of the sample calculated using the AM1.5 solar spectrum in the 300~2500nm wavelength range, and the visible reflectance is the weighted average reflectance calculated using the AM1.5 solar spectrum in the visible light range of 380~760nm wavelength range.

[0038] As can be seen from Table 1, within the range of 5:5 to 5:10, the weighted reflectance of the samples in the visible light range reached over 97%.

[0039] Example 3 Example 3 is used to improve reflectivity in the solar radiation band and impart superhydrophobic properties. The specific steps are as follows: (1) Add 10 g of DCPDA monomer, 16 g of graphene quantum dot dispersion, 0.15 g of UV curing agent (TPO-L) and 0~0.5 g of fumed silica (average particle size of 500 nm) to a weighing bottle. The mass of fumed silica is 0 g, 0.1 g, 0.2 g, 0.3 g, 0.4 g and 0.5 g respectively, and they are named sample 8 (same as sample 5), sample 9, sample 10, sample 11, sample 12 and sample 13 respectively. Then, stir and sonicate in the dark in sequence to make the system uniformly dispersed to obtain casting solution. The temperature of stirring and sonication is 50℃ and the time of stirring and sonication is 2 h. (2) The casting liquid is applied to the glass surface by scraping, and the wet film thickness is controlled to be 400 μm by adjusting the scraper scale; (3) Transfer the wet film to a UV curing chamber (Shanghai Runduo, model: UVK80), set the curing distance to 18 cm, the curing time to 10 s, and the curing power to 100% of the maximum power, with the maximum power being 1500 mW / cm. 2 UV curing was performed to obtain a super-reflective radiation cooling film with superhydrophobicity.

[0040] Table 2. Relevant preparation parameters and test results for different samples in Example 3.

[0041] Note: The solar reflectance in Table 2 is the weighted average reflectance of the sample calculated using the AM1.5 solar spectrum in the 300~2500nm wavelength range, and the visible reflectance is the weighted average reflectance calculated using the AM1.5 solar spectrum in the visible light range of 380~760nm wavelength range.

[0042] As can be seen from Table 2, by introducing fumed silica and controlling the proportion of fumed silica, the weighted reflectance of the samples in the sunlight range reached over 96%.

[0043] Performance testing (1) Film formation effect: The film formation effect of the film was observed by optical photographs. See the optical photographs below. Figure 1 , Figure 2 , Figure 4 and Figure 6 .

[0044] (2) UV-Vis-NIR reflectance: Measured using a UV-Vis-NIR spectrophotometer (PE, USA) (0.3~2.5 μm). The test results are shown in […]. Figure 3 and 7 And Tables 1 and 2.

[0045] (3) Mid-infrared emissivity: The emissivity of the infrared spectrum (2.5~16 μm) was measured using a Fourier transform near-infrared spectrometer (PE, USA). The test results are shown in […]. Figure 8 .

[0046] (4) Thin film surface wettability: The water contact angle was recorded using a static water droplet contact angle meter (Beijing Zhongchen Digital Instrument Co., Ltd.). The water droplet size was 10 μL. The test results are shown in the figure. Figure 5 .

[0047] (5) Thin film radiation cooling capacity: The size of a single test device is 15×15×15 cm. 3 A square piece of polystyrene foam, with a 5×5×5 cm cutout in the center of the top. 3 The cavity was designed to mitigate the effects of surrounding heat conduction. The outer surface of the polystyrene foam was covered with aluminum foil tape to reduce its absorption of solar radiation. A 5×5 cm... 2 The sample was placed 4 cm from the bottom of the cavity, and a thermocouple was securely connected to the inner surface of the sample within the cavity. The cavity opening was sealed with a PE film. The temperature inside the test cavity was measured to determine the sample cooling efficiency. The light intensity was measured using a solar densitometer and radiometer; the test results are shown below. Figure 9 .

[0048] Please see Figure 1 ,pass Figure 1 It can be seen that when the ratio of DCPDA to a good solvent is 4:6, a smooth and flat white film can be formed, indicating that the film formation effect is best at this ratio. When the mass ratio is 10:0 and 8:2, the film is transparent; while when the mass ratio is 6:4 and 2:8, cracks appear on the film surface.

[0049] Please see Figure 2 ,pass Figure 2 It can be seen that smooth and flat films can be prepared within the above ratio range.

[0050] Please see Figure 3 ,pass Figure 3 It can be seen that without the addition of graphene quantum dots, the reflectance of the sample at 430 nm even exceeds 100%, which is due to the reflectance of the sample at this time exceeding the reflectance of the BaSO4 background in the UV-Vis-NIR spectrophotometer. After adding graphene quantum dot dispersion, the reflectance at around 430 nm decreases. This is because the graphene quantum dots absorb this part of the light and convert it into 544 nm light. Since the current instrument is a single dichroic spectrometer, it cannot effectively detect this conversion. At the same time, compared with the sample without graphene quantum dot dispersion, the reflectance in the near-infrared band is higher after adding graphene quantum dot dispersion.

[0051] Please see Figure 4 ,pass Figure 4 It can be seen that samples 8 to 13 all have good film-forming effects; and combined with Table 2, it can be seen that sample 10 has the best reflectivity.

[0052] Please see Figure 5 ,pass Figure 5 It can be seen that the hydrophobic angle of the sample without the addition of fumed silica is only 115±0.5°, while the hydrophobic angle increases to 158.5±0.5° after the addition of fumed silica nanoparticles.

[0053] Please see Figure 6 ,pass Figure 6 It can be seen that the color brightness of both Sample 5 and Sample 10 is greater than that of commercial white paint. The reason is that Sample 5 can not only reflect some light, but also absorb some ultraviolet light and emit it in the form of visible light instead of converting it into heat. Furthermore, Sample 10 contains fumed silica, which can not only increase the diffuse reflection of the sample surface, but also increase the optical path, making it appear as a brighter pale yellow than the pale blue of Sample 5.

[0054] Please see Figure 7 ,pass Figure 7 It can be seen that, compared with sample 8 which did not contain fumed silica, samples 9-13 which contained fumed silica compensated for the decrease in reflectance in the ultraviolet region, resulting in a further increase in reflectance.

[0055] Please see Figure 8 ,pass Figure 8 It can be seen that the emissivity of different samples in the mid-infrared is not significantly different. Combined with Table 2, it can be seen that sample 10 has the highest visible light reflectivity, indicating that sample 10 has the best optical performance.

[0056] Please see Figure 9 ,pass Figure 9 It can be seen that the back surface temperatures of samples 1, 5, and 10 are significantly lower than those of the commercial white paint. This is because the reflectivity of samples 1, 5, and 10 is significantly higher than that of the commercial white paint. The reason why samples 5 and 10 have lower temperatures than sample 1 is twofold. Firstly, samples 5 and 10 contain graphene quantum dots, which can convert light from 300 to 490 nm into visible light instead of heat, thus producing a cooling effect. Secondly, fumed silica not only increases the luminous efficiency of graphene quantum dots by increasing the path length of the converted light and reducing heat conversion, but also increases reflectivity through Mie scattering. Ultimately, this results in both samples having lower back surface temperatures than sample 1, and sample 10 having a lower back surface temperature than sample 5.

[0057] In summary, this invention achieves a cooling effect by introducing graphene quantum dots to convert high-energy short-wavelength light into low-energy visible light; the introduction of fumed silica enhances the reflectivity and hydrophobicity of the film; and the DCPDA exhibits high emissivity in the 8-13 μm band, enabling the film to reflect light during the day and radiate strongly in the atmospheric window band, thus achieving efficient cooling. This invention employs a solution-based preparation method, similar to the preparation processes of existing radiation-cooled films and fluorescent long-afterglow films, eliminating the need for complex micro / nano etching or vacuum deposition equipment, making it suitable for mass production. The films of this invention can be made with thicknesses of 200-800 μm, suitable for surfaces such as glass windows and car roofs, offering energy-saving and environmental benefits.

[0058] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a superhydrophobic, superreflective, radiation-cooling thin film, characterized in that, Includes the following steps: DCPDA monomer, graphene quantum dot dispersion, fumed silica and UV curing agent are mixed evenly to obtain casting solution; The casting solution is applied to the substrate surface to obtain a wet film; The wet film is then subjected to ultraviolet curing to obtain a superhydrophobic, superreflective radiation-cooling thin film; wherein... The solvent for the graphene quantum dot dispersion is an alcohol solvent.

2. The method for preparing a superhydrophobic, superreflective, radiation-cooling thin film according to claim 1, characterized in that, The alcohol solvent is at least one selected from methanol, ethanol, and ethylene glycol; and / or, The graphene quantum dot dispersion has a mass fraction of 0.0005%~0.002%; and / or, The mass ratio of the DCPDA monomer to the graphene quantum dot dispersion is 1:(1~2).

3. The method for preparing a superhydrophobic, superreflective, radiation-cooling thin film according to claim 1, characterized in that, The preparation process of the graphene quantum dot dispersion is as follows: o-Phenylenediamine and a catalyst were dispersed in an alcohol solvent, followed by a solvothermal reaction to obtain a graphene quantum dot dispersion; wherein, The catalyst is at least one of oxalic acid and acetic acid; and / or, The mass ratio of o-phenylenediamine to catalyst is 1:(0.3~3); and / or, The ratio of o-phenylenediamine to alcohol solvent is 0.1~0.3 mg:1 mL; and / or, The temperature of the solvothermal reaction is 80~200℃, the time of the solvothermal reaction is 4~36h, and the heating rate is 5~10℃ / min.

4. The method for preparing the superhydrophobic, superreflective radiation-cooling thin film according to claim 1, characterized in that, The average particle size of the fumed silica is 200–800 nm; and / or, The mass ratio of the DCPDA monomer to fumed silica is 1:(0.01~0.05).

5. The method for preparing a superhydrophobic, superreflective, radiation-cooling thin film according to claim 1, characterized in that, The UV curing agent is ethyl 2,4,6-trimethylbenzoylphenylphosphonate; and / or... The mass ratio of the DCPDA monomer to the UV curing agent is 1:(0.01~0.02).

6. The method for preparing the superhydrophobic, superreflective, radiation-cooling thin film according to claim 1, characterized in that, The process of uniformly mixing DCPDA monomer, graphene quantum dot dispersion, fumed silica and UV curing agent includes: mixing DCPDA monomer, graphene quantum dot dispersion, fumed silica and UV curing agent, stirring at 40~60 ℃ in the dark for 1~3 h, and then sonicating at 40~60 ℃ in the dark for 1~3 h.

7. The method for preparing a superhydrophobic, superreflective, radiation-cooling thin film according to claim 1, characterized in that, The substrate is glass; and / or, The thickness of the wet film is 200~800 μm.

8. The method for preparing the superhydrophobic, superreflective, radiation-cooling thin film according to claim 1, characterized in that, During the UV curing process, the UV wavelength is 365~405 nm, the curing distance is 6~24 cm, the curing time is 5~10 s, and the curing power is 70%~100% of the maximum power; wherein, the maximum power is 1500 mW / cm. 2 .

9. A superreflective radiative cooling thin film with superhydrophobicity, characterized in that, The superhydrophobic superreflectivity radiation cooling film is obtained by the preparation method of the superhydrophobic superreflectivity radiation cooling film according to any one of claims 1 to 8.

10. An application of the superhydrophobic, superreflective radiation-cooling thin film as described in claim 9, characterized in that, The superhydrophobic, superreflective radiation cooling film is used in building energy conservation and / or cold chain transportation.

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