Thermochromic intelligent window based on vanadium dioxide nanoparticle film concentration gradient structure and preparation method of thermochromic intelligent window

Abstract

The invention belongs to the technical field of glass for buildings, and discloses a thermochromic intelligent window based on a vanadium dioxide nanoparticle film concentration gradient structure and a preparation method thereof.The preparation method comprises the steps that firstly, two parts of W-VO2 nanoparticles with different masses and PVP are added into absolute ethyl alcohol to be subjected to ultrasonic oscillation, and the W-VO2 nanoparticles and PVP are stirred to be evenly distributed and then stand for use; the method comprises the following steps: sequentially coating the surface of a pretreated glass substrate with W-VO2amp with relatively high concentration from bottom to top; a PVP dispersion liquid, a PMMA dispersion liquid, and low-concentration W-VO2amp are added; a PVP dispersion liquid; therefore, a W-VO2 gradient structure with low concentration at the top layer and high concentration at the bottom layer is formed on the surface of the glass substrate. The visible light transmittance of the thermochromic intelligent window is greatly improved, meanwhile, the solar modulation capacity is improved, the antagonism between the two optical properties of the visible light transmittance and the solar modulation efficiency is weakened or even broken through, and thermochromic development of the intelligent window and the radiation refrigeration field is further promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of architectural glass, and in particular relates to a concentration gradient enhanced vanadium dioxide nanoparticle film thermochromic smart window and a preparation method thereof. Background Art

[0002] With the continuous advancement of globalization and industrialization, the imbalance between global energy supply and demand has sharply intensified. International energy prices fluctuate frequently, and energy demand continues to increase worldwide, leading to increasing global warming and greenhouse effects. Energy conservation has become urgent. Buildings account for the vast majority of energy consumption. Effectively controlling energy loss in buildings can significantly improve energy utilization and promote energy efficiency. The majority of building energy consumption is used to maintain internal temperature and power electrical equipment. However, because wall materials, windows, and other structures are crucial for heat exchange with the outside world, significant energy waste results, leading to reduced energy utilization. Windows are the most important heat exchange channels, and air conditioning is required to regulate indoor temperatures, whether in the sweltering summer or the freezing winter. During this process, the temperature difference between indoors and outdoors is significant. Since windows are essential components connecting the interior of a building to the external environment, heat loss through them accounts for approximately half of the total heat exchanged within the building. Therefore, reducing building energy consumption should prioritize window energy conservation. The application of smart windows is a key approach to reducing energy consumption.

[0003] Smart windows are primarily categorized by their excitation source: thermochromic, electrochromic, and photochromic. However, their widespread adoption is hampered by performance requirements such as switching rate, cycle life, durability, optical performance, and environmental friendliness, as well as the need for large size and low cost. Therefore, developing a feasible, low-cost, multi-band modulated, high-performance, tunable radiative cooling thermochromic smart window is an urgent challenge.

[0004] Vanadium dioxide (VO2) is a transition metal oxide semiconductor material that undergoes a reversible metal-semiconductor phase transition at 68°C. In the semiconductor (insulating) phase, vanadium dioxide is relatively transparent to infrared radiation, while the transition to the metallic phase results in infrared absorption. When the ambient temperature exceeds a critical threshold, the transmittance of the near-infrared spectrum decreases significantly, while the transmittance of visible light is basically unaffected. This effectively blocks heat-generating infrared radiation while maintaining sunlight exposure, thereby achieving indoor temperature regulation. Based on these optoelectronic properties, VO2 has become an ideal material for thermochromic smart window applications. In the research on VO2 thermochromic smart windows, how to simultaneously improve visible light transmittance (Tlum), solar energy modulation capability (△Tsol) and lower the phase transition temperature has become the main problem hindering its development. Researchers have developed various methods to improve performance, including element doping, core-shell structures, and multilayer film structures. Element doping involves incorporating elements (such as tungsten, hydrogen, zirconium, magnesium, hafnium, and tantalum) into the vanadium dioxide preparation process. These elements occupy or influence the positions of V and O atoms, disrupting or distorting the V–V chains in the monoclinic structure, reducing the orbital splitting gap, and enhancing the electron concentration in the vanadium dioxide, thereby lowering the thermal driving force for electron motion. Tungsten doping lowers the phase transition temperature of vanadium dioxide to 28°C, which is well-suited for practical applications. However, element doping often reduces the thermochromic performance of smart windows. While lowering the phase transition temperature, it also reduces visible light transmittance and solar modulation efficiency, making them unsuitable for practical applications. Both visible light transmittance and solar modulation efficiency are crucial for thermochromic smart windows. Researchers have proposed addressing this performance challenge through multilayer film design. Multilayer film structures often incorporate antireflection layers based on the principle of refractive index gradients, which can improve Tlum to a certain extent. However, this often results in insufficient solar modulation capability, preventing them from effectively regulating room temperature. Summary of the Invention

[0005] In view of the problem that dimming devices based on vanadium dioxide materials currently used in microelectronics fields such as smart windows and radiative cooling cannot simultaneously improve visible light transmittance and solar energy modulation efficiency, the present invention provides a thermochromic smart window based on a concentration gradient structure of vanadium dioxide nanoparticle film and a preparation method thereof. While greatly improving the visible light transmittance of the W-VO2 / PVP thermochromic smart window, it also improves the solar energy modulation capability, weakens or even breaks the antagonism between the two optical properties of visible light transmittance and solar energy modulation efficiency, and further promotes the development of thermochromism in the fields of smart windows and radiative cooling.

[0006] According to one aspect of the present invention, a thermochromic smart window based on a vanadium dioxide nanoparticle film concentration gradient structure is provided, which is prepared by the following process:

[0007] Two W-VO2 nanoparticles of different masses were taken, and the two W-VO2 nanoparticles were added to anhydrous ethanol with PVP, ultrasonically vibrated, and then evenly distributed by magnetic stirring before being allowed to stand for use. A W-VO2 & PVP dispersion with a higher concentration and a W-VO2 & PVP dispersion with a lower concentration were obtained.

[0008] Add PMMA particles to acetone, subject them to ultrasonic oscillation, and then stir them magnetically to uniformly distribute them before allowing them to stand for use to obtain a PMMA dispersion.

[0009] On the surface of the pretreated glass substrate, the W-VO2&PVP dispersion with higher concentration, the PMMA dispersion, and the W-VO2&PVP dispersion with lower concentration are sequentially coated from bottom to top; thereby forming a W-VO2 gradient structure with low concentration on the top layer and high concentration on the bottom layer on the surface of the glass substrate.

[0010] According to another aspect of the present invention, a method for preparing a thermochromic smart window based on a vanadium dioxide nanoparticle film concentration gradient structure is provided, comprising the following steps:

[0011] Two W-VO2 nanoparticles of different masses were taken, and the two W-VO2 nanoparticles were added to anhydrous ethanol with PVP, ultrasonically vibrated, and then evenly distributed by magnetic stirring before being allowed to stand for use. A W-VO2 & PVP dispersion with a higher concentration and a W-VO2 & PVP dispersion with a lower concentration were obtained.

[0012] Add PMMA particles to acetone, subject them to ultrasonic oscillation, and then stir them magnetically to uniformly distribute them before allowing them to stand for use to obtain a PMMA dispersion.

[0013] On the surface of the pretreated glass substrate, the W-VO2&PVP dispersion with higher concentration, the PMMA dispersion, and the W-VO2&PVP dispersion with lower concentration are sequentially coated from bottom to top; thereby forming a W-VO2 gradient structure with low concentration on the top layer and high concentration on the bottom layer on the surface of the glass substrate.

[0014] Regarding the above-mentioned thermochromic smart window based on the concentration gradient structure of vanadium dioxide nanoparticle film and its preparation method:

[0015] Preferably, the concentration difference between the W-VO2 & PVP dispersion with a higher concentration and the W-VO2 & PVP dispersion with a lower concentration is in the range of 2%-6%.

[0016] Preferably, the concentrations of the W-VO2 & PVP dispersion with a higher concentration and the W-VO2 & PVP dispersion with a lower concentration are 0.2%-1.2%.

[0017] Preferably, the mass ratio of W-VO2 nanoparticles to PVP in the W-VO2&PVP dispersion is 1:20-200.

[0018] Preferably, the pretreatment of the glass substrate comprises: firstly, ultrasonically cleaning the glass substrate in acetone, then ultrasonically cleaning the glass substrate in anhydrous ethanol, and finally ultrasonically cleaning the glass substrate in deionized water, and then drying the glass substrate for later use.

[0019] Preferably, the coating includes: first dropping the W-VO2 & PVP dispersion with a higher concentration on the surface of the pretreated glass substrate, and then using a glue spreader to spin coat it, first rotating at a low speed, then rotating at a high speed, and finally drying it for use; then dropping the PMMA dispersion on the coated glass sample surface, and then using a glue spreader to spin coat it, first rotating at a low speed, then rotating at a high speed, and finally drying it for use; then dropping the W-VO2 & PVP dispersion with a lower concentration on the coated glass sample surface, and then using a glue spreader to spin coat it, first rotating at a low speed, then rotating at a high speed, and finally drying it for use.

[0020] The beneficial effects of the present invention are:

[0021] The present invention provides a thermochromic smart window based on a concentration gradient structure of a vanadium dioxide nanoparticle film. On the one hand, the introduction of PVP material can not only serve as a dispersant but also as a transparent material to increase the visible light transmittance. On the other hand, the performance is improved by constructing a concentration gradient difference. The less W-VO2 & PVP layer on the surface can improve the visible light transmittance; the more W-VO2 & PVP layer in the inner layer can enhance the ability to regulate infrared light.

[0022] Based on this, the present invention fabricates a thermochromic smart window with a comprehensive, high-performance W-VO2 / PVP concentration gradient structure that is more practical for practical applications. This significantly improves the solar modulation efficiency of the W-VO2 / PVP thermochromic smart window while maintaining a high visible light transmittance. This weakens or even breaks the antagonistic effect between the two optical properties of visible light transmittance and solar modulation efficiency, further promoting the development of thermochromic smart windows and radiative cooling. With the development of microelectronic devices toward miniaturization and reliability, the W-VO2 / PVP concentration gradient structure has become an important means of improving microelectronic device performance, providing preparation experience for experimental results and promoting the development of microelectronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart for preparing the thermochromic smart window sample of Example 1 of the present invention.

[0024] Figure 2Visible-near infrared spectra of the thermochromic smart window sample prepared in Example 1 of the present invention; (a)(c)(e)(g) show the transmittance in the 380-2500nm band with a concentration gradient of 0.56%, 0.45%, 0.34%, and 0.22%; (b)(d)(f)(h) show the thermochromic performance with a concentration gradient of 0.56%, 0.45%, 0.34%, and 0.22% according to the data obtained by the spectrophotometer.

[0025] Figure 3 This is a scanning electron microscope image of the thermochromic smart window sample prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments and accompanying drawings.

[0027] like Figure 1 As shown, the present invention provides a thermochromic smart window based on the concentration gradient structure of vanadium dioxide nanoparticle film and a preparation method thereof, proposes a W-VO2&PVP concentration gradient structure model through the concentration gradient theory, optimizes the drug mass ratio and method, provides a higher visible light transmittance, and improves its ability to modulate thermal radiation and near-infrared regulation.

[0028] Example 1

[0029] The specific steps of its preparation are as follows:

[0030] Step 1: Preparation before synthesis

[0031] A1: Cleaning experimental equipment and substrates

[0032] Ultrasonic cleaning was performed on the beaker, spoon, glass substrate, and magnet to ensure surface cleanliness. The substrate cleaning process was as follows: an appropriate amount of anhydrous ethanol was poured into the beaker and ultrasonically cleaned for 15 minutes to remove any impurities or dust. The substrate was then placed in a clean beaker and ultrasonically cleaned for 15 minutes each in acetone and anhydrous ethanol. Finally, the cleaned substrate was removed, transferred to a tray, and dried in an oven for 15 minutes.

[0033] A2: Weighing, PVP, W-VO2 nanoparticles, PMMA particles

[0034] Use a high-precision electronic scale to weigh 5 mg, 30 mg, and 35 mg of W-VO2 nanoparticles, 100 mg of PMMA particles, and 1000 mg of PVP powder, respectively. Use a measuring cylinder to measure 5 ml of anhydrous ethanol and 7.5 ml of acetone, respectively.

[0035] Step 2: Preparation of PMMA dispersion:

[0036] A1: Preparation of dispersion

[0037] 100 mg of PMMA particles were dissolved in 7.5 ml of acetone and dispersed by ultrasonication at 25-40°C for 1 h to uniformly disperse the PMMA, and finally stirred by a magnetic stirrer for 4 h.

[0038] Step 3: Preparation of W-VO2(NP)&PVP dispersion:

[0039] A1: Preparation of W-VO2 dispersion:

[0040] 5 mg, 30 mg, and 35 mg of W-VO2 nanoparticles were added to 5 ml of anhydrous ethanol, respectively, and ultrasonically dispersed at 50 °C for 30 min to form three dispersions.

[0041] A2: Preparation of W-VO2(NP) & PVP dispersion:

[0042] 1000 mg of PVP was added to each of the three dispersions, and ultrasonic oscillation was continued for 1 h. Finally, the mixture was stirred for 3 h using a magnetic stirrer, and then allowed to stand for 24 h for use.

[0043] Step 3: Preparation of composite layer:

[0044] A1: Spin coating and heating W-VO2 & PVP layer

[0045] Using a pipette, 200 μL of the W-VO2 & PVP dispersion corresponding to 30 mg and 35 mg of W-VO2 nanoparticles, respectively, was dropped onto two transparent glass substrates. Spin coating parameters were adjusted to a low speed of 800 rpm for 10 seconds and a high speed of 2000 rpm for 20 seconds. After spin coating, the composite layer was heated at 60°C for 5 minutes to dry it. The composite layer corresponding to the 35 mg W-VO2 nanoparticles is designated sample S1.

[0046] A2: Spin coating and heating PMMA layer

[0047] Use a pipette to measure 200 μL of the PMMA dispersion and drop it onto the 30 mg W-VO2 & PVP layer obtained in step A1. Spin coating parameters are adjusted to a low speed of 800 rpm for 10 seconds and a high speed of 3000 rpm for 20 seconds. After spin coating, heat the composite layer at 120°C for 5 minutes to remove surface haze and dry it.

[0048] A3: Spin coating and heating W-VO2&PVP / PMMA / W-VO2&PVP layer

[0049] Using a pipette, 200 μL of the W-VO2 & PVP dispersion corresponding to 5 mg of W-VO2 nanoparticles was dripped onto the composite layer prepared in A2. Spin coating parameters were adjusted to a low speed of 800 rpm for 10 seconds and a high speed of 2000 rpm for 20 seconds. After spin coating, the composite layer was heated at 60°C for 5 minutes to dry it. The resulting sample was designated S11. The concentration difference between the two W-VO2 & PVP layers in S11 was 0.22%.

[0050] Example 2

[0051] A composite layer was prepared on a transparent glass substrate according to the specific steps of Example 1, with the following differences:

[0052] In step 1, the W-VO2 used in A2 was 10 mg, 30 mg, and 40 mg;

[0053] In step 3, 30 mg and 40 mg of W-VO2 nanoparticles corresponding to the W-VO2 & PVP dispersion were measured in A1; among them, the composite layer corresponding to 40 mg of W-VO2 nanoparticles was sample numbered S2;

[0054] In step 3, the PMMA dispersion in A2 was dropped onto the 30 mg W-VO2 & PVP layer obtained in A1;

[0055] In step 3, 10 mg of the W-VO2 & PVP dispersion corresponding to the W-VO2 nanoparticles was measured in A3, and the obtained sample was numbered S22; the concentration difference between the two W-VO2 & PVP layers in S22 was 0.34%.

[0056] Example 3

[0057] A composite layer was prepared on a transparent glass substrate according to the specific steps of Example 1, with the following differences:

[0058] In step 1, the W-VO2 used in A2 was 15 mg, 30 mg, and 45 mg;

[0059] In step 3, 30 mg and 45 mg of W-VO2 nanoparticles corresponding to the W-VO2 & PVP dispersion were weighed from A1; the composite layer corresponding to 45 mg of W-VO2 nanoparticles was sampled as S3;

[0060] In step 3, the PMMA dispersion in A2 was dropped onto the 30 mg W-VO2 & PVP layer obtained in A1;

[0061] In step 3, 15 mg of the W-VO2 & PVP dispersion corresponding to the W-VO2 nanoparticles was measured in A3, and the obtained sample was numbered S33; the concentration difference between the two W-VO2 & PVP layers in S33 was 0.45%.

[0062] Example 4

[0063] A composite layer was prepared on a transparent glass substrate according to the specific steps of Example 1, with the following differences:

[0064] In step 1, the W-VO2 used in A2 was 20 mg, 30 mg, and 50 mg;

[0065] In step 3, 30 mg and 50 mg of W-VO2 nanoparticles corresponding to the W-VO2 & PVP dispersion were measured in A1; among them, the composite layer corresponding to 50 mg of W-VO2 nanoparticles was sample numbered S4;

[0066] In step 3, the PMMA dispersion in A2 was dropped onto the 30 mg W-VO2 & PVP layer obtained in A1;

[0067] In step 3, 20 mg of the W-VO2 & PVP dispersion corresponding to the W-VO2 nanoparticles was measured in A3, and the obtained sample was numbered S44; the concentration difference between the two W-VO2 & PVP layers in S44 was 0.56%.

[0068] The thermochromic smart window samples (S1, S11, S2, S22, S3, S33, S4, S44) prepared in Examples 1-4 of the present invention were tested using an ultraviolet-near infrared-visible spectrophotometer at 20°C and 90°C, respectively. Figure 2 Visible-mid-infrared infrared spectra of the samples. (a)(c)(e)(g) show the transmittance at concentration gradients of 0.56%, 0.45%, 0.34%, and 0.22% over the 380-2500nm range. (b)(d)(f)(h) show the thermochromic properties at concentration gradients of 0.56%, 0.45%, 0.34%, and 0.22%, as determined by a spectrophotometer.

[0069] like Figure 2 As shown in the figure, when the total W-VO2 concentration of the single-layer structure (S1, S2, S3, S4) and the double-layer structure (S11, S22, S33, S44) is the same, the tested samples all show that the visible light transmittance of the double-layer structure is better than that of the single-layer structure, and the solar energy modulation ability of some double-layer structure samples is slightly improved compared with the single-layer structure.

[0070] The transmittance of the S44 double-layer structure is 60.75%, and the transmittance of the S4 single-layer structure is 57.79%. It can be seen that when the W-VO2 concentration difference is 0.56%, the visible light transmittance of the double-layer structure is 5.12% higher than that of the single-layer structure.

[0071] The transmittance of the S33 double-layer structure is 59.52%, while the transmittance of the S3 single-layer structure is 56.06%. This shows that at a W-VO2 concentration gradient of 0.45%, the visible light transmittance of the double-layer structure is 6.20% higher than that of the single-layer structure. At the same time, the solar energy modulation capability of the double-layer structure is 18.8% higher than that of the single-layer structure.

[0072] The transmittance of the S22 double-layer structure is 58.53%, while the transmittance of the S2 single-layer structure is 50.33%. This shows that when the W-VO2 concentration difference is 0.34%, the visible light transmittance of the double-layer structure is 16.27% higher than that of the single-layer structure. At the same time, the solar energy modulation capability of the double-layer structure is 5.47% higher than that of the single-layer structure.

[0073] The transmittance of the S11 double-layer structure is 53.43%, while the transmittance of the S1 single-layer structure is 48.52%. This indicates that when the W-VO2 concentration difference is 0.22%, the visible light transmittance of the double-layer structure is 10.12% higher than that of the single-layer structure. Furthermore, the solar energy modulation capability of the double-layer structure is 4.79% higher than that of the single-layer structure.

[0074] This is because the uniform distribution of W-VO2 in a single-layer structure means that light passing through the material interacts with W-VO2 of the same concentration, resulting in greater absorption loss. In a double-layer structure, a low-concentration W-VO2 layer is placed on the light-incident side, while a high-concentration W-VO2 layer is placed on the light-exiting side. Light first passes through the low-concentration layer with less absorption before entering the high-concentration layer with greater absorption. This design reduces overall absorption and thus improves transmittance.

[0075] Therefore, constructing a concentration gradient structure can optimize light transmission and thermal insulation performance. A smaller surface W-VO2 layer can improve visible light transmittance. As the concentration gradient difference continues to increase, the relative increase in transmittance first increases and then decreases, from a maximum of 16.27%. The relative increase in solar modulation power first increases and then decreases, with a maximum of 18.8%. This is because as the concentration gradient increases to a certain extent, the low-concentration layer gradually becomes thicker, and the increased absorption of light causes the overall transmittance to decrease (the appropriate concentration gradient range is 2%-6%).

[0076] Figure 3 This is a picture of the sample taken by a field emission scanning electron microscope (SEM). It can be seen that the layers are clearly stratified, and PMMA plays a good separating role, effectively preventing the layers from dissolving each other.

[0077] It can be seen that the preparation method based on the W-VO2&PVP concentration gradient structure provided by the present invention can be effectively applied to radiative cooling smart windows. According to the characterization of its spectral characteristics, it can improve the ability to modulate thermal radiation and near-infrared regulation, meeting the performance requirements of the smart window and radiative cooling fields. The process is simple and the preparation cost is reduced, thus promoting the development of microelectronic devices.

[0078] The technical solutions disclosed and proposed by the present invention can be implemented by those skilled in the art by drawing on the content of this document and appropriately changing the conditions, routes, and other aspects. Although the methods and preparation techniques of the present invention have been described through preferred embodiments, it is obvious that those skilled in the art can modify or recombine the methods and technical routes described herein without departing from the content, spirit, and scope of the present invention to achieve the ultimate preparation technology. It is particularly important to point out that all similar substitutions and modifications that are obvious to those skilled in the art are considered to be included in the spirit, scope, and content of the present invention.

Claims

1. A thermochromic smart window based on a concentration gradient structure of vanadium dioxide nanoparticle film, characterized in that: Obtained by the following preparation process: Two W-VO2 nanoparticles of different masses were taken, and the two W-VO2 nanoparticles were added to anhydrous ethanol with PVP, ultrasonically vibrated, and then evenly distributed by magnetic stirring before being allowed to stand for use. A W-VO2 & PVP dispersion with a higher concentration and a W-VO2 & PVP dispersion with a lower concentration were obtained. Add PMMA particles to acetone, subject them to ultrasonic oscillation, and then stir them magnetically to uniformly distribute them before allowing them to stand for use to obtain a PMMA dispersion. On the surface of the pretreated glass substrate, the W-VO2&PVP dispersion with higher concentration, the PMMA dispersion, and the W-VO2&PVP dispersion with lower concentration are sequentially coated from bottom to top; thereby forming a W-VO2 gradient structure with low concentration on the top layer and high concentration on the bottom layer on the surface of the glass substrate.

2. The thermochromic smart window based on the concentration gradient structure of vanadium dioxide nanoparticle film according to claim 1, characterized in that: The concentration difference between the W-VO2 & PVP dispersion with a higher concentration and the W-VO2 & PVP dispersion with a lower concentration is in the range of 2%-6%.

3. The thermochromic smart window based on the concentration gradient structure of vanadium dioxide nanoparticle film according to claim 1, characterized in that: The concentrations of the W-VO2 & PVP dispersion with a higher concentration and the W-VO2 & PVP dispersion with a lower concentration are 0.2%-1.2%.

4. The thermochromic smart window based on the concentration gradient structure of vanadium dioxide nanoparticle film according to claim 1, characterized in that: The mass ratio of W-VO2 nanoparticles to PVP in the W-VO2&PVP dispersion is 1:20-200.

5. The thermochromic smart window based on the concentration gradient structure of vanadium dioxide nanoparticle film according to claim 1, characterized in that: The pretreatment of the glass substrate comprises: firstly placing the glass substrate in acetone for ultrasonic cleaning, then placing the glass substrate in anhydrous ethanol for ultrasonic cleaning, and finally placing the glass substrate in deionized water for ultrasonic cleaning, and then drying for standby use.

6. The thermochromic smart window based on the concentration gradient structure of vanadium dioxide nanoparticle film according to claim 1, characterized in that: The coating includes: first dropping the W-VO2&PVP dispersion with a higher concentration on the surface of the pretreated glass substrate, then using a spin coater to perform spin coating, first rotating at a low speed, then rotating at a high speed, and finally drying for use; then dropping the PMMA dispersion on the coated glass sample surface, then using a spin coater to perform spin coating, first rotating at a low speed, then rotating at a high speed, and finally drying for use; then dropping the W-VO2&PVP dispersion with a lower concentration on the coated glass sample surface, then using a spin coater to perform spin coating, first rotating at a low speed, then rotating at a high speed, and finally drying for use.

7. A method for preparing a thermochromic smart window based on a vanadium dioxide nanoparticle film concentration gradient structure, characterized in that: The steps include: Two W-VO2 nanoparticles of different masses were taken, and the two W-VO2 nanoparticles were added to anhydrous ethanol with PVP, ultrasonically vibrated, and then evenly distributed by magnetic stirring before being allowed to stand for use. A W-VO2 & PVP dispersion with a higher concentration and a W-VO2 & PVP dispersion with a lower concentration were obtained. Add PMMA particles to acetone, subject them to ultrasonic oscillation, and then stir them magnetically to uniformly distribute them before allowing them to stand for use to obtain a PMMA dispersion. On the surface of the pretreated glass substrate, the W-VO2&PVP dispersion with higher concentration, the PMMA dispersion, and the W-VO2&PVP dispersion with lower concentration are sequentially coated from bottom to top; thereby forming a W-VO2 gradient structure with low concentration on the top layer and high concentration on the bottom layer on the surface of the glass substrate.

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