Optical functional thin film capable of reflecting solar spectrum in two wavebands and preparation method of optical functional thin film

Abstract

The invention discloses an optical functional film capable of reflecting solar spectrum in two wavebands and a preparation method thereof, the film comprises high-refractive-index layers and low-refractive-index layers which are alternately arranged from bottom to top in sequence, the optical refractive index difference value of the high-refractive-index layers and the low-refractive-index layers in the visible light waveband is 0.13-0.30, and the total number of the layers is 30-60; the high refractive index layer and the low refractive index layer are both made of organic polymer films. According to the optical functional film capable of reflecting the solar spectrum in the two wave bands, the solar spectrum in a green light area (0.4-0.63 mu m) and a near-infrared light area (1.1-1.8 mu m) is selectively filtered out, light of other wavelengths is allowed to penetrate through, and excessive solar radiation heat can be effectively shielded; the method has a wide application prospect in the fields of energy conservation and environmental protection, such as greenhouse planting and novel plastic containers.

Description

Technical Field

[0001] The invention relates to the technical field of thin films, and in particular to an optical functional film capable of reflecting a solar spectrum in dual bands and a preparation method thereof. Background Art

[0002] With the progress and development of human society, energy consumption has gradually increased, and the trend of global warming has become more and more obvious. In order to prevent the increasing threat of global warming, the international community is committed to achieving carbon neutrality and significantly reducing carbon dioxide emissions. Therefore, energy conservation and emission reduction are particularly important. In people's daily lives, there is a great demand for refrigeration, and how to effectively reduce excessive solar radiation without wasting electricity is of great significance to reducing carbon dioxide emissions and global warming. Excessive solar radiation can also affect crop planting and beverage storage. For example, if a plastic container is placed outdoors in direct sunlight, it may heat up quickly, which may easily cause the stored beverage to deteriorate. Similarly, for some open greenhouse plantings, only some passive cooling solutions can be adopted for excessive solar radiation, such as increasing airflow or using gray plastic film to block part of the sunlight. However, the gray film has no selectivity for the wavelength of the incident sunlight. Specifically, the gray film prevents most of the visible light from irradiating the plant, seriously affecting the photosynthesis of the plant and seriously reducing the crop yield. If we can selectively filter out the green light region (0.4-0.57 μm) and near-infrared light region (1.1-1.8 μm) of the solar spectrum, and allow other wavelengths, especially blue and red light, to irradiate the crops, we can prevent excessive solar radiation while maximizing crop yields. In summary, achieving selective shielding of the solar spectrum is of great practical significance for reducing carbon dioxide emissions and achieving carbon neutrality.

[0003] Application No. CN202210967856.0 discloses "a colored daytime passive radiation cooling porous film and its preparation method". The porous polymer film containing inorganic nanoparticles disclosed in the application has a good cooling effect. The porous structure can reflect sunlight well and improve the emissivity and cooling effect of the atmospheric window (8-13μm). However, in fact, the incident solar spectrum is totally reflected without distinction. At the same time, the atmospheric window of the film has a high emissivity, which is mainly used for passive radiation cooling. It cannot achieve selective reflection and transmission of the solar spectrum.

[0004] Application No. CN201810389757.2 discloses "a passive radiation cooling film and its preparation method". The radiation cooling film published is composed of a radiation base film layer and an aluminum film layer, and the aluminum film layer covers the surface of the radiation base film layer to reflect sunlight. The polyethylene resin and the composite filler are composed of silicon dioxide and silicon carbide to achieve a high emissivity of the atmospheric window, thereby achieving passive radiation cooling. It can be seen that the film is mainly used for passive radiation cooling, and cannot achieve selective reflection and transmission of the solar spectrum. Summary of the invention

[0005] Purpose of the invention: The first purpose of the present invention is to provide an optical functional film with a dual-band reflection of the solar spectrum, which selectively over-reflects the solar spectrum in the green light region (0.4-0.63 μm) and the near-infrared light region (1.1-1.8 μm), while allowing other wavelengths of solar light to pass through; The second purpose of the present invention is to provide a method for preparing the optical functional film with a dual-band reflection of the solar spectrum.

[0006] Technical solution: The dual-band optical functional film for reflecting the solar spectrum described in the present invention comprises high refractive index layers and low refractive index layers alternately arranged from bottom to top, the optical refractive index difference between the high refractive index layers and the low refractive index layers in the visible light band is 0.13 to 0.30, and the total number of layers is 30 to 60; the materials of the high refractive index layers and the low refractive index layers are both organic polymer films.

[0007] A specific refractive index difference is formed by the high refractive index and low refractive index layers to achieve the set dual-band reflection.

[0008] The film selectively reflects the solar spectrum in the wavebands of 0.4-0.63 μm and 1.1-1.8 μm, and simultaneously realizes high transmittance of the solar spectrum in other wavebands.

[0009] Preferably, the material of the low refractive index layer is cellulose acetate or perfluorosulfonic acid ionomer dispersion (Aquivion D79-25BS).

[0010] Preferably, the material of the high refractive index layer is polystyrene (PS), polymethyl methacrylate (PMMA) or poly(N-vinylcarbazole) (PVK).

[0011] Preferably, the refractive index of the high refractive index layer in the visible light band of the solar spectrum ranges from 1.48 to 1.66.

[0012] Preferably, the refractive index of the low refractive index layer in the visible light band of the solar spectrum ranges from 1.35 to 1.46.

[0013] Preferably, the thickness of the high refractive index layer is 10 to 30 nm. Preferably, the thickness of the low refractive index layer is 10 to 40 nm. The thickness of a single layer affects the phase change of the incident light wave, thereby affecting the transmission or reflection of a specific wavelength band.

[0014] The method for preparing the dual-band optical functional film reflecting the solar spectrum of the present invention comprises the following steps:

[0015] (1) dissolving the high refractive index layer and the low refractive index layer in solvents to form solutions;

[0016] (2) The high refractive index layer solution and the low refractive index layer solution are alternately spin-coated on the substrate to obtain the thin film.

[0017] Preferably, the substrate is a single crystal silicon substrate.

[0018] Invention Mechanism: The mechanism of the present invention is to use two films with high refractive index and low refractive index to be arranged alternately to form a periodic refractive index distribution. This structure will selectively reflect or transmit light of wavelengths in a specific band, and the principle is based on the interference effect of light waves. That is, when light is incident on this specially designed multilayer film structure, part of the light is reflected and transmitted at the interface of each layer. Due to the difference in layer thickness and refractive index, the phase difference between the reflected light will cause certain wavelengths of light to constructively interfere (enhanced transmission) or destructively interfere (enhanced reflection). Therefore, by accurately designing the refractive index and thickness of each thin film layer, it is possible to block wavelengths in a specific band while allowing wavelengths in other specific bands to pass through.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The dual-band optical functional film reflecting the solar spectrum selectively filters out the solar spectrum in the green light region (0.4-0.63 μm) and the near-infrared light region (1.1-1.8 μm), and allows other wavelengths of light to pass through; (2) The special dual-band optical functional film reflecting the solar spectrum is used for crops, filters out green light and near-infrared light, and allows other light to pass through, especially blue light and red light to irradiate the crops, which can prevent excessive solar radiation while maximizing crop yield; (3) The dual-band optical functional film reflecting the solar spectrum can also be used in plastic containers for food storage to reduce excessive solar radiation heat; (4) The preparation method is simple and easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the structure of an optical functional film that reflects the solar spectrum in dual bands;

[0021] Figure 2 is a solar spectrum reflection curve diagram of the film prepared in Example 1;

[0022] Figure 3 is a solar spectrum reflection curve diagram of the film prepared in Example 2;

[0023] Figure 4 This is a solar spectrum reflection curve diagram of the film prepared in Example 3. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described below in conjunction with embodiments.

[0025] Example 1

[0026] The dual-band optical functional film for reflecting the solar spectrum described in the present invention comprises a high refractive index layer made of polymethyl methacrylate (PMMA, purchased from Mitsubishi Rayon of Japan, IRK-304), and a low refractive index layer made of perfluorosulfonic acid ionomer dispersion (AQ, purchased from Jingbang New Composite Materials). The refractive index of the material PMMA in the visible light band is 1.48, and the refractive index of the material AQ is 1.35. At this time, the difference in optical refractive index between the high refractive index layer PMMA and the low refractive index layer AQ in the visible light band is 0.13.

[0027] Preparation method:

[0028] (1) First, 4 g of PMMA particles were weighed using an electronic balance, placed in a ground glass container containing 100 ml of glacial acetic acid, and sealed for 5 days to obtain a polymer solution, and then ultrasonically dispersed in an ultrasonic container for 15 minutes to make it evenly dispersed, thereby obtaining a polymer solution with a PMMA concentration of about 40 mg / ml;

[0029] (2) taking a perfluorosulfonic acid ionomer dispersion (AQ) aqueous dispersion solution (30 mg / ml);

[0030] (3) After ultrasonically cleaning the quartz glass substrate with acetone, anhydrous ethanol, and deionized water for 15 minutes, the PMMA solution was spin-coated using a conventional spin coating method with a rotation speed of 10,000 rpm. After drying, the film thickness was about 10 nm. Then, the AQ aqueous dispersion solution was spin-coated. After drying, the film thickness was also about 10 nm. Each solution was spin-coated 15 times in this alternating manner to obtain a film with a total of 30 layers.

[0031] The solar spectrum reflectivity of the film is shown in Figure 2. As can be seen from the figure, the film reflects sunlight in the 0.42μm to 0.63μm band and the 1.16μm to 1.81μm band of the solar spectrum, with an average reflectivity of about 35% and 56%, while the solar spectrum in the remaining bands is almost unobstructed, so it can achieve the reduction of excessive solar radiation heat. At the same time, it can be seen from the figure that blue light and red light can pass through the film. If the film is used for agricultural planting, because blue light and red light can be irradiated on the plants, it can reduce excessive heat radiation while maximizing crop yields.

[0032] Example 2

[0033] The dual-band optical functional film reflecting the solar spectrum described in the present invention comprises a high refractive index layer made of polystyrene (PS, particle size 5 to 8 microns, purchased from Hongyu Plastics), a low refractive index layer made of cellulose acetate (CA, purchased from Shanghai Sinopharm Reagent, 39.8 wt%), a refractive index of material PS in the visible light band of 1.57, and a refractive index of material CA of 1.43, and a difference in optical refractive index between the high refractive index layer PS and the low refractive index layer CA in the visible light band of 0.14.

[0034] Preparation method:

[0035] (1) dissolving polystyrene (PS) microsphere particles in a toluene solution, and obtaining a polymer solution by magnetic stirring and ultrasonic dispersion in an ultrasonic container, so that the concentration of the polymer solution is 40 mg / ml;

[0036] (2) dissolving cellulose acetate (CA) in an organic solvent, 4-hydroxy-4-methyl-2-pentanone, to a concentration of 35 mg / ml;

[0037] (3) After ultrasonically cleaning the single crystal silicon substrate with acetone, anhydrous ethanol, and deionized water for 10 minutes in sequence, the conventional spin coating method is still used with a rotation speed set to 8000 rpm to spin-coat the PS solution. After drying to form a film, the film thickness is about 20 nm; then, the CA solution is spin-coated. After drying to form a film, the film thickness is also about 20 nm. This process is repeated alternately, with each solution spin-coated 20 times to obtain a thin film with a total of 40 layers.

[0038] The solar spectrum reflectivity of the film is shown in Figure 3. As can be seen from the figure, the film reflects sunlight in the 0.42μm~0.61μm band and the 1.2μm~1.8μm band of the solar spectrum, with average reflectivity of approximately 57% and 68%, while the solar spectrum in the remaining bands is transmitted almost unobstructed, achieving selectable dual-band reflection, thereby achieving the reduction of excessive solar radiation heat.

[0039] Example 3

[0040] The dual-band optical functional film for reflecting the solar spectrum described in the present invention comprises a high refractive index layer made of poly(N-vinyl carbazole) (PVK, purchased from Shanghai McLean Reagent), and a low refractive index layer made of perfluorosulfonic acid ionomer dispersion (AQ, purchased from Jingbang New Composite Materials). The refractive index of the material PVK in the visible light band is 1.65, and the refractive index of the material AQ is 1.35. At this time, the optical refractive index difference between the high refractive index layer PVK and the low refractive index layer AQ in the visible light band is 0.3.

[0041] Preparation method:

[0042] (1) dissolving poly(N-vinyl carbazole) (PVK) in a toluene solution to obtain a mixed solution with a concentration of 50 mg / ml;

[0043] (2) preparing a water dispersion solution of perfluorosulfonic acid ionomer dispersion (AQ) at a concentration of 30 mg / ml;

[0044] (3) After ultrasonically cleaning the quartz glass substrate with acetone, anhydrous ethanol, and deionized water for 15 minutes, the conventional spin coating method was also used, with the rotation speed set to 6000 rpm, to spin-coat a mixed solution of PVK and toluene. After drying to form a film, the film thickness was about 30 nm; then, the AQ aqueous dispersion solution was spin-coated. After drying to form a film, the film thickness was also about 30 nm. Each solution was spin-coated 30 times in this way, and a thin film with a total number of layers of 60 was obtained (it should be pointed out that in the actual industrial production process, the film can also be prepared by melt extrusion or coating according to the film thickness of the material).

[0045] The solar spectrum reflectivity of the film is shown in Figure 4. As can be seen from the figure, the film reflects sunlight in the 0.41μm~0.60μm band and the 1.15μm~1.75μm band of the solar spectrum, with an average reflectivity of approximately 71% and 82%, while the solar spectrum in the remaining bands is transmitted almost unobstructed, achieving selectable dual-band reflection.

Claims

1. An optical functional film with dual-band reflection of solar spectrum, characterized in that: It comprises high refractive index layers and low refractive index layers alternately arranged from bottom to top, the optical refractive index difference between the high refractive index layers and the low refractive index layers in the visible light band is 0.13 to 0.30, and the total number of layers is 30 to 60; the materials of the high refractive index layers and the low refractive index layers are both organic polymer films.

2. The dual-band optical functional film reflecting the solar spectrum according to claim 1, characterized in that: The film selectively reflects the solar spectrum in the wavebands of 0.4 to 0.063 μm and 1.1 to 1.8 μm, and simultaneously realizes high transmittance of the solar spectrum in other wavebands.

3. The dual-band optical functional film reflecting the solar spectrum according to claim 1, characterized in that: The material of the low refractive index layer is cellulose acetate or perfluorosulfonic acid ionomer dispersion.

4. The dual-band optical functional film reflecting the solar spectrum according to claim 1, characterized in that: The material of the high refractive index layer is polystyrene, polymethyl methacrylate or poly (N-vinyl carbazole).

5. The dual-band optical functional film reflecting the solar spectrum according to claim 1, characterized in that: The refractive index of the high refractive index layer in the visible light band of the solar spectrum ranges from 1.48 to 1.

66.

6. The dual-band optical functional film reflecting the solar spectrum according to claim 1, characterized in that: The refractive index of the low refractive index layer in the visible light band of the solar spectrum ranges from 1.35 to 1.

46.

7. The dual-band optical functional film reflecting the solar spectrum according to claim 1, characterized in that: The thickness of the high refractive index layer is 10-30nm.

8. The dual-band optical functional film reflecting the solar spectrum according to claim 1, characterized in that: The thickness of the low refractive index layer is 10-40nm.

9. A method for preparing a dual-band optical functional film reflecting the solar spectrum according to any one of claims 1 to 8, characterized in that: The following steps are involved: (1) dissolving the high refractive index layer and the low refractive index layer in solvents to form solutions; (2) The high refractive index layer solution and the low refractive index layer solution are alternately spin-coated on the substrate to obtain the thin film.

10. The method for preparing the dual-band optical functional film reflecting the solar spectrum according to claim 9, characterized in that: The base is a single crystal silicon substrate.

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