A photothermal dual-driven color-changing composite film and its preparation method

Abstract

The present invention discloses a photo-thermal dual-driven color-changing composite film and a preparation method thereof. Vanadyl oxalate, polyvinylpyrrolidone, and ammonium metatungstate are mixed in deionized water, and after sufficient stirring, ultrasonic treatment is carried out to obtain a vanadium coating solution; tungsten hexachloride and absolute ethanol are used as raw materials, and titanium tetrachloride is used as the Ti source, and Ti-doped W 18 O 49 particles are prepared by a solvothermal method; they are mechanically ball-milled until the nanoparticles are mixed with ethanol to obtain a tungsten oxide coating solution; the obtained vanadium coating solution is formed into a film by spin coating and dried to obtain a precursor film; it is annealed in a tube furnace to obtain a tungsten-doped monodisperse vanadium dioxide nanoparticle film; the tungsten oxide coating solution is formed into a film on the tungsten-doped monodisperse vanadium dioxide nanoparticle film by spin coating; the present invention has excellent sunlight regulation efficiency and a low VO2 phase transition temperature under the condition of maintaining a high visible light transmittance; at the same time, due to the attachment of the W 18 O 49 -based film, the oxidation and denaturation of VO2 can be inhibited.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials, and particularly relates to a VO2 / W photothermal dual-driven color-changing 18 O 49 -based composite film and a preparation method thereof. Background Art

[0002] Windows are one of the components with the lowest energy efficiency in buildings. Research shows that for every 0.1 increase in the light transmittance of glass, the annual system energy consumption per unit area in the air-conditioning and heating systems will be reduced by 1254.4 KJ / m 2 , but the cooling energy consumption will also increase accordingly, greatly reducing the energy-saving efficiency of the total building energy. Energy-saving intelligent windows can autonomously adjust the solar radiation passing through the building windows, reduce the double-sided energy consumption of air-conditioning cooling and heating, and achieve breakthrough energy savings.

[0003] Electrochromic, thermochromic, and photochromic intelligent windows are the three main types for realizing building energy conservation, and the former has been installed in buildings. However, electrochromic devices have high costs, complex structures, and require additional energy input to function. The most studied thermochromic intelligent window at present is the VO2-based thermochromic intelligent window, but it has disadvantages such as high phase transition temperature (T c ), low visible light transmittance (T lum ), and low solar energy regulation efficiency (ΔT sol ). Summary of the Invention

[0004] In the prior art, electrochromic devices have high costs, complex structures, require additional energy input to function, and have low energy utilization efficiency; thermochromic intelligent windows have disadvantages such as high phase transition temperature (T c ), low visible light transmittance (T lum ), and low solar energy regulation efficiency (ΔT sol ). At the same time, problems such as difficult preparation and uncontrollable morphology also hinder the development of energy-saving thin film manufacturing technology.

[0005] The applicant's research found that applying stress or doping certain impurity elements on the VO2 lattice can reduce the phase transition temperature of VO2. In terms of improving the visible light transmittance, it can be achieved by preparing a porous discrete film. In terms of improving the solar energy regulation efficiency, it can be achieved by compounding with other materials, such as compounding with W 18 O 49 . In the lattice of W 18 O 49 , there are simultaneously mixed valence states of W 5+ and W 6+ , resulting in local surplus electrons and lattice distortion. These surplus electrons and defect structures can rapidly induce W 5+ and W6+ transform into each other, so W 18 O 49 can theoretically be called a kind of photochromic material. In addition, W 18 O 49 has the advantages of simple preparation and controllable morphology.

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a VO2 / W composite film with photo-thermal dual-driven color change and a preparation method thereof. Under the condition of maintaining a high visible light transmittance, the film has excellent solar light regulation efficiency and a low VO2 phase transition temperature; at the same time, due to the attachment of the W 18 O 49 -based film, the oxidation and denaturation of VO2 can be inhibited; compared with the pure VO2 film, the composite film has excellent optical properties, outstanding energy-saving effects, a lower phase transition temperature and a longer service life. 18 O 49 -based film, the oxidation and denaturation of VO2 can be inhibited; compared with the pure VO2 film, the composite film has excellent optical properties, outstanding energy-saving effects, a lower phase transition temperature and a longer service life.

[0007] To achieve the above purpose, the following technical solutions are adopted:

[0008] A photo-thermal dual-driven color-changing composite film is composed of a W-doped VO2 film with a molar ratio of 2%-5% and a Ti-doped W 18 O 49 film with a molar ratio of 4%-20% by spin coating; the thickness of the VO2 film is 50-100 nm, and the thickness of the W 18 O 49 film is 1-100 μm.

[0009] A preparation method of a photo-thermal dual-driven color-changing composite film includes the following steps:

[0010] (1) Mix vanadyl oxalate, polyvinylpyrrolidone (PVP) and ammonium metatungstate in deionized water, stir well and then perform ultrasonic treatment to obtain a vanadium coating solution;

[0011] (2) Using tungsten hexachloride (WCl6) and absolute ethanol as raw materials and titanium tetrachloride (TiCl4) as the Ti source, prepare Ti-doped W 18 O 49 particles by the solvothermal method; mechanically ball mill to obtain a tungsten oxide coating solution by mixing the nanoparticles with ethanol;

[0012] (3) Spin coat the obtained vanadium coating solution to form a film, dry it to obtain a precursor film; anneal it in a tube furnace to obtain a tungsten-doped monodisperse vanadium dioxide nanoparticle film;

[0013] (4) Spin coat the tungsten oxide coating solution on the tungsten-doped monodisperse vanadium dioxide nanoparticle film to form a film, and perform a drying treatment to obtain a photo-thermal dual-driven color-changing composite film.

[0014] According to the above scheme, in step (1), the concentration of the vanadyl oxalate aqueous solution is 0.1 mol / L; the addition amount of PVP is 3% - 12% of the mass of vanadyl oxalate; the addition amount of ammonium metatungstate is 2% - 5% of the molar amount of vanadium in vanadyl oxalate.

[0015] According to the above scheme, in step (2), the mass ratio of titanium tetrachloride to tungsten hexachloride is 1:(10 - 50).

[0016] According to the above scheme, in step (2), the solvothermal reaction temperature is 100 - 200 °C, the time is 3 - 48 h, and after the reaction, Ti-doped W 18 O 49 particles are obtained by centrifugal collection, washing and drying.

[0017] According to the above scheme, in step (2), the rotation speed of the ball mill is 500 r / min, and one cycle is that the ball milling for 30 - 60 minutes is stopped for 5 - 10 minutes, and a total of 10 - 20 cycles are carried out to further reduce the particle size.

[0018] According to the above scheme, in step (2), the mass ratio of the Ti-doped W 18 O 49 particles to ethanol is 1:(4 - 10).

[0019] According to the above scheme, the spin coating method in step (3) includes two-step spin coating. The rotation speed of the first step is 500 r / min, the time is 5 - 15 s, the rotation speed of the second step is 2000 - 5000 r / min, and the time is 20 - 30 s; the drying temperature is 70 - 100 °C.

[0020] According to the above scheme, in step (3), the annealing temperature of the tube furnace is 500 - 600 °C, the annealing time is 60 - 120 min, and the air pressure in the tube is 2 - 6 Torr.

[0021] According to the above scheme, the spin coating method in step (4) includes two-step spin coating. The rotation speed of the first step is 500 - 1000 r / min, the time is 5 - 15 s, the rotation speed of the second step is 500 - 3000 r / min, and the time is 20 - 30 s; the drying temperature of the film is 70 - 100 °C.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) The raw materials are simple and easy to obtain, and the cost is low. The film is prepared on the glass substrate from the coating solution by the template-free solution method, which has low requirements for equipment and is easy to operate.

[0024] (2) The phase transition temperature of the pure VO2 thin film (near 68 °C) is much higher than room temperature. Doping with 3 at.% of W element can lower the phase transition temperature of VO2 to near room temperature (25.8 °C), and the regulation effect is significant.

[0025] (3) Through the annealing process, part of the PVP in the thin film is burned out and particle voids are generated in the thin film. Vanadyl oxalate is decarbonized and oxidized to VO2, thus forming a VO2 discrete particle film, providing attachment sites for W 18 O 49 particles.

[0026] (4) The nano-VO2 particles in the thin film are highly dispersed, have good crystallinity, small particle sizes, and high porosity. When the ambient temperature rises, the VO2 phase transforms into the metallic phase, showing excellent local surface plasmon resonance effects and increasing the absorption in the near-infrared light band; the photochromic performance and bleaching speed of 10 at.% Ti element-doped W 18 O 49 particles are significantly improved and filled in the particle voids of the VO2 thin film; after solar irradiation, due to the 18 O 49 photochromic phenomenon occurs in W 18 O 49 and most of the near-infrared light is absorbed, causing the VO2 particles near the W 18 O 49 nano-particles to rapidly heat up, promoting VO2 to reach the phase transition temperature and undergo a phase change, further reducing the transmittance in the near-infrared band range, thus greatly improving the solar light regulation efficiency of the composite film; the photo-thermal dual-drive effect enables the composite thin film to achieve a solar light regulation efficiency of 25%-40% while maintaining a high visible light transmittance of 70%-85%, which is superior to the thin films for building energy-saving glass currently available on the market. The excellent optical properties enable this composite thin film to meet the application requirements of building energy-saving glass.

[0027] (5) While ensuring the visible light transmittance of the composite thin film, the number of layers and thickness of the tungsten oxide nanoparticle thin film can be increased spatially, effectively improving the solar light regulation efficiency.

[0028] (6) When the conventional VO2 thin film is exposed to the external environment for a long time, it is prone to oxidation reactions, resulting in damage to the film function. By attaching the tungsten oxide thin film to the outer layer of the VO2 thin film, the service life of the thin film product can be extended. Description of the Drawings

[0029] Figure 1 : High and low temperature ultraviolet-visible-near infrared transmittance spectra of the glass coated with the photo-thermal dual-drive composite thin film in Example 1.

[0030] Figure 2 : Comparison chart of the glass surface temperature changes between the glass coated with the photo-thermal dual-drive composite thin film in Example 1 and ordinary glass under xenon lamp irradiation.

[0031] Figure 3 : Example 1: Comparison of the temperature changes of the solution under the glass coated with the photothermal dual-driven composite film and the ordinary glass under the irradiation of a xenon lamp.

[0032] Figure 4 : Example 2 High and low temperature ultraviolet-visible-near infrared transmittance spectra of glass coated with light-thermal dual-driven composite film.

[0033] Figure 5 : Example 3 High and low temperature ultraviolet-visible-near infrared transmittance spectra of glass coated with light-thermal dual-driven composite film. DETAILED DESCRIPTION

[0034] The following examples further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0035] Example 1

[0036] 1) Weigh 0.4760g of tungsten hexachloride, stir evenly with 40mL of ethanol and 13.2μL of titanium tetrachloride for solvothermal reaction at a temperature of 180°C for 12h. After the reaction, the solid product is collected by centrifugation, washed and dried at a drying temperature of 60°C for 12h to obtain W 18 O 49 Powder;

[0037] 2) Add 0.8 g W 18 O 49 The powder, 0.8 g PVP and 10 mL ethanol were ball milled at a ball mill speed of 500 r / min. The ball milling was repeated for 30 minutes and then stopped for 10 minutes for a total of 20 times. The solution after ball milling was centrifuged at a speed of 10000 r / min for 5 minutes. After centrifugation, the suspension was dried and collected to obtain W 18 O 49 Nanoparticles.

[0038] 3) 0.8g W 18 O 49 The nanoparticles were mixed with 4.0 g of ethanol solution, and the mixed solution was fully magnetically stirred to obtain a uniform tungsten oxide coating solution.

[0039] 4) Take 3 mL of 0.5 mol / L vanadium oxalate aqueous solution with a pipette, add 12 mL of ultrapure water to mix to obtain a 0.1 mol / L vanadium oxalate aqueous solution, add 6% of PVP by mass and 3% of ammonium metatungstate by molar amount of vanadium to the vanadium oxalate aqueous solution, stir thoroughly at 750 r / min for 1 h and ultrasonicate for 1 h until PVP and ammonium metatungstate are completely dissolved, to obtain a uniform vanadium coating solution.

[0040] 5) The obtained vanadium coating solution was evenly dropped on a cleaned glass substrate, and spin-coated by a process of rotating at 500 r / min for 10 s and then at 3000 r / min for 20 s. The coated glass substrate was placed on a heating table and dried at 80 °C for 20 min to obtain a dried precursor film, which was annealed in a tube furnace at an annealing temperature of 550 °C for 1 h to obtain a monodisperse vanadium dioxide nanoparticle film.

[0041] 6) The tungsten oxide coating solution was evenly and rapidly dropped on the film obtained in step 5), and spin-coated by a process of rotating at 500 r / min for 10 s and then at 1500 r / min for 20 s. After coating, it was placed on a heating table and dried at 80 °C for 20 min to obtain a photo-thermal dual-driven VO2 / W 18 O 49 -based photochromic-thermochromic composite film.

[0042] Figure 1 Fig. shows the high and low temperature ultraviolet-visible-near infrared transmittance spectra of the glass coated with the photo-thermal dual-driven VO2 / W 18 O 49 -based photochromic-thermochromic composite film obtained in Example 1. As can be seen from the figure, the visible light transmittance (380 - 780 nm) of the film is relatively high. And because the vanadium dioxide nanoparticles in the film are in a monodisperse state, it has an excellent local surface plasmon resonance effect, manifested as an obvious absorption peak valley in the near infrared light region (75 °C) of the transmittance spectrum. By calculating the visible light transmittance and the solar modulation efficiency of the film, the visible light transmittance was calculated to be 79.47%, and the solar modulation efficiency was 28.68%.

[0043] Figure 2 Fig. shows the comparison chart of the glass surface temperature changes of the glass coated with the photo-thermal dual-driven VO2 / W 18 O 49 -based photochromic-thermochromic composite film obtained in Example 1 and ordinary glass under xenon lamp irradiation. As can be seen from the figure, under the same irradiation time and irradiation power, the surface temperature of the glass coated with the composite film is higher than that of ordinary quartz glass, because the photo-thermal dual-driven VO2 / W 18 O 49 -based photochromic-thermochromic composite film has a strong absorption ability for near infrared light and ultraviolet light, which will increase the temperature of the glass surface.

[0044] Figure 3 Fig. shows the glass coated with the photo-thermal dual-driven VO2 / W 18 O 49Comparison of the temperature change of the solution under the glass of the photochromic-thermochromic composite film glass and ordinary glass under the irradiation of a xenon lamp. As can be seen from the figure, under the same irradiation time and irradiation power, the temperature of the solution under the glass coated with the composite film is 4°C lower than that of the solution under ordinary quartz glass. This is due to the VO2 / W 18 O 49 The photochromic-thermochromic composite film has a strong absorption capacity for near-infrared light and ultraviolet light, and can adjust the energy of sunlight passing through the glass to achieve the purpose of regulating indoor temperature and meet the application needs of building energy-saving glass.

[0045] Example 2

[0046] 1) Weigh 0.4860g of tungsten hexachloride, stir evenly with 40mL of ethanol and 14.1μL of titanium tetrachloride to carry out solvent thermal reaction at a reaction temperature of 180°C for 12h. After the reaction, the solid product is collected by centrifugation, washed and dried at a drying temperature of 60°C for 12h to obtain W 18 O 49 Powder;

[0047] 2) Add 0.8 g W 18 O 49 The powder, 0.8 g PVP and 10 mL ethanol were ball milled at a ball mill speed of 500 r / min. The ball milling was repeated for 30 minutes and then stopped for 10 minutes for a total of 20 times. The solution after ball milling was centrifuged at a speed of 10000 r / min for 5 minutes. After centrifugation, the suspension was dried and collected to obtain W 18 O 49 Nanoparticles;

[0048] 3) 0.8g W 18 O 49 The nanoparticles are mixed with 3.5g of ethanol solution, and the mixed solution is fully magnetically stirred to obtain a uniform tungsten oxide coating solution.

[0049] 4) Take 3 mL of 0.5 mol / L vanadium oxalate aqueous solution with a pipette, add 12 mL of ultrapure water to mix to obtain a 0.1 mol / L vanadium oxalate aqueous solution, add 9% of PVP by mass and 4% of ammonium metatungstate by molar amount of vanadium to the vanadium oxalate aqueous solution, stir thoroughly at 750 r / min for 1 h and ultrasonicate for 1 h until PVP and ammonium metatungstate are completely dissolved, to obtain a uniform vanadium coating solution.

[0050] 5) The obtained vanadium coating solution was evenly dropped on a cleaned glass substrate, and spin-coated by a process of rotating at 500 r / min for 5 s and then at 4500 r / min for 20 s. The coated glass substrate was placed on a heating table and dried at 80 °C for 20 min to obtain a dried precursor film, which was annealed in a tube furnace at an annealing temperature of 500 °C for 1.5 h to obtain a monodisperse vanadium dioxide nanoparticle film.

[0051] 6) The tungsten oxide coating solution was evenly and rapidly dropped on the film obtained in step 5), and spin-coated by a process of rotating at 800 r / min for 5 s and then at 2500 r / min for 25 s. After coating, it was placed on a heating table and dried at 80 °C for 20 min to obtain a photo-thermal dual-driven VO2 / W 18 O 49 -based photochromic-thermochromic composite film.

[0052] Figure 4 It is the high and low temperature ultraviolet-visible-near infrared transmittance spectra of the glass coated with the photo-thermal dual-driven VO2 / W 18 O 49 -based photochromic-thermochromic composite film obtained in Example 2. Compared with Example 1, in Example 2, the spin-coating speed is faster and the thickness of the coated film is thinner, so the visible light transmittance is higher, the sunlight regulation efficiency is lower, and the maximum temperature difference between the glass surface temperature and the solution is smaller. By calculating the visible light transmittance and sunlight modulation efficiency of the film, the visible light transmittance is calculated to be 84.07%, and the sunlight modulation efficiency is 26.11%.

[0053] Example 3

[0054] 1) Weigh 0.4700 g of tungsten hexachloride, mix it evenly with 40 mL of ethanol and 13.5 μL of titanium tetrachloride for a solvothermal reaction. The reaction temperature is 180 °C and the time is 12 h. After the reaction, the solid product is collected by centrifugation, washed and dried. The drying temperature is 60 °C and the time is 12 h to obtain WO 18 O 49 powder;

[0055] 2) Add 0.8 g of WO 18 O 49 powder, 0.8 g of PVP and 10 mL of ethanol into the ball mill for ball milling. The rotation speed of the ball mill is 500 r / min. One cycle is to mill for 30 minutes and stop for 10 minutes, and a total of 20 cycles are carried out; after ball milling, the solution is centrifuged at a speed of 10000 r / min for 5 min, and the suspension is taken after centrifugation, dried and collected to obtain WO 18 O 49 nanoparticles;

[0056] 3) 0.8 g of W 18 O 49The nanoparticles are mixed with 5.0g of ethanol solution, and the mixed solution is fully magnetically stirred to obtain a uniform tungsten oxide coating solution.

[0057] 4) Take 3 mL of 0.5 mol / L vanadium oxalate aqueous solution with a pipette, add 12 mL of ultrapure water to mix to obtain a 0.1 mol / L vanadium oxalate aqueous solution, add 7% of PVP by mass and 4% of ammonium metatungstate by molar amount of vanadium to the vanadium oxalate aqueous solution, stir thoroughly at 750 r / min for 1 h and ultrasonicate for 1 h until PVP and ammonium metatungstate are completely dissolved, to obtain a uniform vanadium coating solution.

[0058] 5) The obtained vanadium coating liquid is evenly dropped on a cleaned glass substrate, and the coating is performed by spin coating at 500 r / min for 15 s and then at 2500 r / min for 20 s. The coated glass substrate is placed on a heating table and dried at 85° C. for 20 min to obtain a dry precursor film, which is then annealed in a tubular furnace at a temperature of 500° C. for 2 h to obtain a monodisperse vanadium dioxide nanoparticle film.

[0059] 6) The tungsten oxide coating solution was evenly and quickly dropped on the film obtained in step 5), and the film was spin-coated at 500 r / min for 15 s and then 1000 r / min for 20 s. After coating, the film was placed on a heating table at 85°C and dried for 20 min to obtain the photothermal dual-driven VO2 / W 18 O 49 Photochromic-thermochromic composite films.

[0060] Figure 5 VO2 / W coated with light-thermal dual drive obtained in Example 3 18 O 49 High and low temperature UV-visible-near infrared transmittance spectra of photochromic-thermochromic composite film glass. Example 3 uses a lower rotation speed, the thickness of the coating is thicker, the visible light transmittance is lower, and the sunlight modulation efficiency is higher. The maximum temperature difference between the glass surface temperature and the solution is larger. By calculating the visible light transmittance of the film and the sunlight modulation efficiency, it is calculated that the visible light transmittance is 72.18% and the sunlight modulation efficiency is 37.68%.

[0061] VO2 / W driven by light and heat obtained in the above examples 18 O 49 The characterization parameters of the base color-changing composite film are shown in Table 1. The characterization methods of each characterization item are as follows:

[0062] Visible light transmittance (T lum ) and T sol The calculation formula is as follows:

[0063] T lum / sol =∫δ lum / sol (λ)T(λ)dλ / ∫δ lum / sol(λ)dλ (1)

[0064] where T(λ) is the transmittance corresponding to different wavelengths, and δ lum (λ) is the standard luminous efficiency function of the human eye's light perception vision, and δ sol (λ) is the AM 1.5 solar spectral irradiance. The solar energy regulation efficiency (ΔT sol ) is calculated as ΔT sol = T sol (M phase) - T sol (R phase), that is, the difference in T sol of the thin film before and after the phase change.

[0065] Two identical solutions are placed under the photothermal dual-driven composite thin film glass and ordinary glass. Under xenon lamp irradiation, the surface temperature of the glass and the solution temperature are measured in real time using a thermocouple, and the temperature difference on the glass surface and the maximum temperature difference of the solution are obtained through calculation. Among them, the solution is prepared by mixing 200 μL ATO and 10 μL deionized water.

[0066] Table 1

[0067] Visible light transmittance Sunlight regulation efficiency Temperature difference on the glass surface Maximum temperature difference of the solution Example 1 79.47％ 28.68％ 41℃ 4℃ Example 2 84.07％ 26.11％ 36℃ 3.0℃ Example 3 72.28％ 37.68％ 56℃ 6.1℃

[0068] Each raw material listed in the present invention, as well as the upper and lower limits and interval values of each raw material of the present invention, and the upper and lower limits and interval values of process parameters (such as temperature, rotation speed, time, etc.) can all implement the present invention, and the embodiments are not listed one by one here.

Claims

1. A preparation method of a photothermal dual-driven color-changing composite film, characterized in that It includes the following steps: (1) Mix vanadyl oxalate, polyvinylpyrrolidone, and ammonium metatungstate in deionized water, stir well, and then perform ultrasonic treatment to obtain a vanadium coating solution; (2) Using tungsten hexachloride and absolute ethanol as raw materials, and titanium tetrachloride as the Ti source, Ti-doped W 18 O 49 particles were prepared by a solvothermal method; the tungsten oxide coating solution was obtained by mechanically ball-milling the nanoparticles and ethanol; (3) Use the spin coating method to form a film with the obtained vanadium coating solution, and dry it to obtain a precursor film; anneal it in a tube furnace to obtain a W-doped monodisperse vanadium dioxide nanoparticle film with a molar ratio of 2% - 5%, and the thickness is 50 - 100 nm; (4) The tungsten oxide coating solution is spin-coated on the W-doped monodisperse vanadium dioxide nanoparticle film to form a Ti-doped WO film with a molar ratio of 4% - 20%. 18 O 49 The thickness of the Ti-doped WO 18 O 49 film is 1 - 100 μm, and after drying treatment, a photothermal dual-driven color-changing composite film is obtained.

2. The preparation method of the photothermal dual-driven color-changing composite film according to claim 1, wherein In step (1), the concentration of the vanadyl oxalate aqueous solution is 0.1 mol / L; the addition amount of PVP is 3% - 12% of the mass of vanadyl oxalate; the addition amount of ammonium metatungstate is 2% - 5% of the vanadium molar amount in vanadyl oxalate.

3. The preparation method of the photothermal dual-driven color-changing composite film according to claim 1, wherein In step (2), the mass ratio of titanium tetrachloride to tungsten hexachloride is 1:(10 - 50).

4. The preparation method of the photothermal dual-driven color-changing composite film according to claim 1, characterized in that In step (2), the solvothermal reaction temperature is 100 - 200 °C, and the time is 3 - 48 h. After the reaction, Ti-doped W 18 O 49 particles are collected by centrifugation, washed, and dried.

5. The preparation method of the photothermal dual-driven color-changing composite film according to claim 1, characterized in that In step (2), the rotation speed of the ball mill is 500 r / min. One cycle is that the ball milling lasts for 30 - 60 minutes and then stops for 5 - 10 minutes. A total of 10 - 20 cycles are carried out to further reduce the particle size.

6. The preparation method of the optothermal dual-driven color-changing composite film according to claim 1, characterized in that The mass ratio of the Ti-doped W described in step (2) 18 O 49 particles to ethanol is 1:(4 - 10).

7. The preparation method of the photothermal dual-driven color-changing composite film according to claim 1, characterized in that The spin coating method in step (3) includes two-step spin coating. The rotation speed in the first step is 500 r / min, and the time is 5 - 15 s. The rotation speed in the second step is 2000 - 5000 r / min, and the time is 20 - 30 s; the drying temperature is 70 - 100°C.

8. The preparation method of the photo-thermal dual-driven color-changing composite film according to claim 1, characterized in that In step (3), the annealing temperature of the tube furnace is 500 - 600°C, the annealing time is 60 - 120 min, and the gas pressure in the tube is 2 - 6 Torr.

9. The preparation method of the photothermal dual-driven color-changing composite film according to claim 1, wherein The spin coating method in step (4) includes two-step spin coating. The rotation speed in the first step is 500 - 1000 r / min, and the time is 5 - 15 s. The rotation speed in the second step is 500 - 3000 r / min, and the time is 20 - 30 s; the film drying temperature is 70 - 100°C.

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