VO2-based thermochromic composite film with gradient regulation and control of visible and near-infrared dual wavebands and preparation method of VO2-based thermochromic composite film

Abstract

The invention belongs to the field of preparation of thermochromic films, and particularly relates to a VO2-based thermochromic composite film with gradient regulation and control of visible and near-infrared dual wavebands and a preparation method of the VO2-based thermochromic composite film with gradient regulation and control of visible and near-infrared dual wavebands. In order to solve the problem that visibility is sacrificed when an existing thermochromic material co-modulates a visible-near-infrared band, the visible-near-infrared dual-band gradient regulation thermochromic composite film based on VO2 is provided and comprises a film forming substrate, a phase change material and a phase change latent heat material, wherein the phase change material and the phase change latent heat material are distributed in the film forming substrate; the phase change material is tungsten-doped vanadium dioxide nano powder; the phase change latent heat material comprises at least one of n-hexadecane, n-octadecane, stearic acid, palmitic acid and paraffin. According to the invention, visible-near infrared dual-band temperature gradient regulation and control can be realized.

Description

Technical Field

[0001] This invention relates to a visible-near-infrared dual-band gradient-controlled thermochromic composite film based on VO2 and its preparation method, including the preparation of tungsten-doped vanadium dioxide nanopowder and the preparation of paraffin / polyvinyl alcohol organic film, belonging to the field of thermochromic film preparation. Background Technology

[0002] Energy is a crucial foundation for maintaining a nation's sustained economic development and ensuring people's material well-being. Today, energy shortages and environmental pollution are becoming increasingly severe. While developing new energy sources, scientists are also striving to find ways to conserve energy and reduce consumption. Buildings are one of the main places where humans conduct production and daily life activities. Building energy consumption accounts for a large proportion of total energy consumption in human production and daily life. Within building energy consumption, the energy consumption of lighting and air conditioning systems, used to improve building comfort, accounts for over 75% of total building energy consumption. Both of these energy consumption components are related to window and door glass; therefore, developing energy-efficient architectural glass is an important way to achieve building energy conservation.

[0003] Current methods for controlling energy loss in architectural glass are static. For example, Low-E glass, which has high reflectivity in the infrared band, blocks infrared rays from passing through windows; double-glazed windows utilize the low thermal conductivity of air to reduce heat conduction between the indoor and outdoor environments. In recent years, with technological advancements, the concept of "smart windows" has emerged. These windows can dynamically adjust the intensity of light entering the room based on differences in indoor and outdoor environments, reducing the use of air conditioning and lighting systems. Thermally responsive materials, due to their ability to respond to ambient temperature and the absence of additional energy input, have become the preferred material system for smart windows.

[0004] Vanadium dioxide (VO2) undergoes a phase transition from monoclinic to tetragonal near 68℃ when excited by a thermal field, accompanied by abrupt changes in its optical and electrical properties. As temperature increases, vanadium dioxide undergoes a phase transition, during which its optical properties change dramatically, particularly its transmittance in the near-infrared band. Below the phase transition temperature, vanadium dioxide exhibits high transmittance in the near-infrared band; however, after the phase transition, its transmittance in this band decreases sharply. Based on this inherent property of vanadium dioxide, it can respond automatically to environmental changes, and its ability to block near-infrared light after a high-temperature phase transition makes it a promising candidate for applications in smart windows, contributing to energy conservation and emission reduction in response to the "dual-carbon" policy.

[0005] However, the phase transition temperature of VO2 is close to 68℃, which is relatively high compared to the comfortable temperature range for normal human living. To lower the phase transition temperature of VO2 and improve its applicability, much research has been conducted on doping it with transition metal ions, such as W. 6+ Mo 6+ 、Nb 5+This reduces the phase transition temperature to near room temperature. However, the VO2 modulation band is limited to the near-infrared region of the solar spectrum, which still limits the energy-saving effect. In the solar spectrum, the visible light region accounts for a larger proportion of energy than the infrared region; therefore, to further improve the energy-saving effect, the modulation wavelength range of the thermochromic material system is extended from the near-infrared region to the visible-near-infrared region. For example, the poly(N-isopropylacrylamide) (PNIPAM) hydrogel proposed by Yi Long et al. (Adv. Funct. Mater. 2018, 28, 1705365 DOI: 10.1002 / adfm.201705365) modulates the visible and near-infrared bands of the solar spectrum through a thermally responsive sol-gel transition. Below the phase transition temperature, PNIPAM is in a sol state, with small molecules uniformly dispersed in the solvent, resulting in high transmittance in the visible-near-infrared band. As the temperature increases, the molecular chains aggregate and swell, enriching into large particles. At this point, due to strong scattering, the transmittance in the visible-near-infrared band decreases sharply, thus achieving temperature-responsive visible-near-infrared modulation and enhancing energy-saving effects. However, the modulation of this material system is limited to the co-modulation of visible and near-infrared light, i.e., two states where the transmittance in the visible-near-infrared band is simultaneously high or simultaneously low. Therefore, the resulting modulation effect inevitably leads to unnecessary sacrifice of visibility under certain conditions. Summary of the Invention

[0006] To address the issue that existing thermochromic materials sacrifice visibility when co-modulated in the visible-near-infrared bands, this invention proposes a thermochromic composite film based on VO2 with visible-near-infrared dual-band gradient modulation and its preparation method, achieving temperature gradient modulation in both the visible-near-infrared bands.

[0007] On one hand, the present invention provides a visible and near-infrared dual-band gradient-controlled thermochromic composite film based on VO2, comprising: a film-forming matrix, and a phase change material and a phase change latent heat material distributed in the film-forming matrix; The phase change material is vanadium dioxide powder; the latent heat material of the phase change includes at least one of n-hexadecane, n-octadecane, stearic acid, palmitic acid, and paraffin.

[0008] This invention provides a gradient control scheme for the visible and near-infrared bands based on thermochromic properties, which to some extent solves the problem of sacrificing visibility to increase energy-saving effects. Specifically, this invention mixes and disperses phase change materials (such as tungsten-doped vanadium dioxide) and latent heat materials (such as paraffin wax) into a film-forming matrix (such as polyvinyl alcohol), combining two phase change materials with different temperature thermal responses to achieve gradient control of the visible and near-infrared bands. Based on the principle of refractive index matching, the latent heat material paraffin wax is made to have the characteristics of low-temperature high transmittance and high-temperature low transmittance, changing from opaque at low temperatures to transparent at high temperatures. As the ambient temperature rises, tungsten-doped vanadium dioxide first undergoes a phase change, blocking near-infrared light. Before the phase change, the refractive indices of solid paraffin wax and polyvinyl alcohol are approximately equal, maintaining a high transmittance. At this point, ensuring high transmittance in the visible light region guarantees visibility. As the temperature continues to rise, paraffin wax undergoes a phase change, its refractive index changes, and it no longer matches the refractive index of polyvinyl alcohol, resulting in strong scattering and reducing visible light transmittance, thereby improving energy-saving efficiency.

[0009] Preferably, the film-forming matrix includes at least one of polyvinyl butyral (PVB), polyvinylpyrrolidone (PVP), and polyvinyl alcohol (PVA); preferably, the degree of alcoholysis of the polyvinyl alcohol is 87% to 89%, and the molecular weight is 15,000 to 20,000.

[0010] Preferably, the refractive index of the phase change latent heat material in the solid state is 1.508 to 1.512, and the refractive index after liquefaction is 1.435 to 1.448, and the refractive index of the film-forming matrix is ​​1.502 to 1.507.

[0011] Preferably, the vanadium dioxide powder is tungsten-doped vanadium dioxide nanoparticles, with a W doping content not exceeding 2 at%; the particle size of the vanadium dioxide nanoparticles is in the range of 30 to 70 nm, and the phase transition temperature is 29°C to 55°C.

[0012] Preferably, the phase transition temperature of the tungsten-doped vanadium dioxide nanopowder is lower than that of paraffin.

[0013] Preferably, the thickness of the VO2-based visible-near-infrared dual-band gradient-controlled thermochromic composite film is 40 μm to 200 μm.

[0014] Preferably, the mass ratio of the phase change material to the film-forming matrix is ​​1:(396.2~773.6); the mass ratio of the latent heat of phase change material to the film-forming matrix is ​​1:(3.0~7.0). When (2) vanadium dioxide is in excess, due to its inherent absorption, it will significantly reduce the transmittance of the film at low temperatures. On the one hand, it will seriously affect the modulation rate between the lowest and highest temperatures, and on the other hand, it will seriously damage the visibility at low and medium temperatures, which is contrary to the problem of sacrificing visibility in this invention. When paraffin is in excess, the paraffin particles undergo heating and cooling cycles. After melting, they are easy to aggregate. After solidification, they form large particles to micron-sized particles. The size of the paraffin particles is no longer nanometer-sized, which leads to a significant reduction in transmittance at low temperatures. On the one hand, it will seriously affect the modulation rate between the lowest and highest temperatures, and on the other hand, it will seriously damage the visibility at low and medium temperatures, which is contrary to the problem of sacrificing visibility in this invention.

[0015] Furthermore, preferably, the mass ratio of the phase change material to the latent heat material is (4.0 to 10.8): 1000.

[0016] Preferably, the properties of the VO2-based visible-near-infrared dual-band gradient-controlled thermochromic composite film include: Below the vanadium dioxide phase transition temperature, the visible transmittance is 44.7%–65.07%, and the near-infrared transmittance is 44.74%–65.84%. Alternatively, when the temperature is above the vanadium dioxide phase transition temperature but below the melting point of the latent heat material, vanadium dioxide undergoes a phase transition, with a visible transmittance of 40.38%–56.42% (still with good visibility) and a near-infrared transmittance of 39.66%–57.53%. Alternatively, when the temperature is above the melting point of the latent heat of phase change material, the latent heat of phase change material changes from solid to liquid, and the refractive index changes. This causes a mismatch in refractive index between the latent heat of phase change material and the film-forming matrix, resulting in strong scattering of light. The shorter the wavelength, the greater the degree of scattering. The visible transmittance is 18.00% to 14.33%, and the near-infrared transmittance is 19.43% to 34.76%.

[0017] In another aspect, the present invention provides a method for preparing a VO2-based visible and near-infrared dual-band gradient-controlled thermochromic composite film, comprising: preparing the VO2-based visible and near-infrared dual-band gradient-controlled thermochromic composite film by at least one of the following methods: blade coating, spray gun coating, and vacuum drying.

[0018] The beneficial effects of this invention are: 1. In this invention, based on the principle of refractive index matching, the organic thin film prepared by combining phase change material paraffin with a polymer film-forming agent can achieve modulation of the visible light band. 2. This invention combines an organic thin film that modulates the visible light band with vanadium dioxide that modulates the near-infrared band, thereby achieving dual-band modulation of visible and near-infrared light. 3. This invention reduces the phase transition temperature of vanadium dioxide by doping with tungsten, making it lower than that of paraffin. This enables preferential modulation of the near-infrared band in the composite thin film, and as the temperature increases, it achieves a combined modulation effect of the visible and near-infrared bands. 4. This invention regulates the content ratio of each component to optimize the optical properties of the composite film; 5. The preparation method of this invention is simple and easy to operate, with low process precision requirements, making it suitable for large-scale production; the paraffin phase change material used is low in cost, readily available, and pollution-free. 6. In the thermal response material system, this invention is the first to propose the use of gradient modulation of the visible-near infrared band, which makes it more intelligent. Attached Figure Description

[0019] Figure 1 The DSC curve of the tungsten-doped vanadium dioxide powder prepared in Example 1; Figure 2 The transmittance of the thermochromic composite film prepared in Example 1 at different temperatures. Detailed Implementation

[0020] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0021] Thermosensitive materials that respond to ambient temperature have received limited research attention due to the potential sacrifice in visibility. This paper proposes a strategy to prepare a VO2-based thermochromic organic composite film, enabling temperature gradient modulation across the visible-near-infrared dual-band. This broadens the modulation range to the visible-near-infrared band, enhancing energy efficiency, while simultaneously addressing the issue of unnecessary visibility sacrifice. This invention achieves two-stage thermal drive and gradient modulation of the visible-near-infrared band by lowering the phase transition temperature of vanadium dioxide (VOD) to below that of paraffin wax through tungsten doping. During the heating process, the temperature first reaches the VOD phase transition temperature (intermediate temperature state), where near-infrared modulation is primarily achieved, while visible light transmittance remains high, ensuring visibility. Further temperature increases to the paraffin wax phase transition temperature achieve co-modulation of the visible-near-infrared band (low transmittance in both visible and near-infrared), with a modulation rate reaching 34.7%. Pure VOD or pure paraffin wax, with only one phase transition temperature, cannot achieve gradient modulation.

[0022] Specifically, this invention combines tungsten-doped vanadium dioxide modulation in the near-infrared band with paraffin / polyvinyl alcohol modulation in the visible light band, resulting in superior energy-saving performance. Specifically, tungsten doping lowers the phase transition temperature of vanadium dioxide to approximately 35°C, with the phase transition occurring before that of paraffin, thus blocking near-infrared light. Based on the principle of refractive index matching, an organic thin film is prepared by combining the thermally responsive phase change material paraffin with the film-forming agent polyvinyl alcohol (PVA). The refractive index of solid paraffin is approximately equal to that of PVA, resulting in high transmittance in the visible and near-infrared bands. As the temperature increases, paraffin undergoes a phase transition from solid to liquid, changing its refractive index, which is no longer approximately equal to that of PVA. At this point, the thin film exhibits strong scattering in the visible and near-infrared bands, resulting in low transmittance in these bands and effectively blocking solar radiation.

[0023] Compared with previous thermochromic films, this invention has the advantage of visible light and near-infrared gradient regulation, which to some extent solves the problem of sacrificing visibility to improve energy saving, expands the applicable temperature range, is more intelligent, and has a simple preparation process and low cost.

[0024] The following exemplifies the preparation method of a VO2-based visible-near-infrared dual-band gradient-controlled thermochromic composite film.

[0025] Vanadium pentoxide is dissolved in distilled water, and then an alkaline solution is added to adjust the pH to 7.5–8.5 (e.g., 8). A strong reducing agent (e.g., hydrazine) is added and mixed (e.g., magnetically stirred for 30 min). Ammonium paratungstate ((NH4)), a hexavalent tungsten compound, is added at a total molar amount of 0.5–2% of the total vanadium content. 10 (H2W 12 O 42 A suspension of tungsten-doped vanadium dioxide precursor was obtained by reacting sodium hydroxide (4·H₂O) with water. The alkaline solution was sodium hydroxide or ammonia. The molar ratio of the strong reducing agent hydrazine to the raw material vanadium pentoxide was 2:1.

[0026] A suspension of tungsten-doped vanadium dioxide precursor was transferred to a reaction vessel and subjected to hydrothermal treatment, followed by natural cooling to room temperature to obtain tungsten-doped vanadium dioxide nanoparticles. The hydrothermal treatment temperature could be 250–350°C for 18–26 hours. Preferably, the reaction was carried out at 280°C for 24 hours. More preferably, the temperature was increased to 280°C at a rate of 8.5°C / min and held at 280°C for 24 hours. Finally, the nanoparticles were centrifuged, washed, dried at 60°C for 24 hours, ground, and stored and packaged for later use. As an example, centrifugation and washing were performed using deionized water three times and anhydrous ethanol twice, with a centrifuge speed of 11000 r / min, resulting in tungsten-doped vanadium dioxide nanoparticles with a particle size of 30 nm–70 nm.

[0027] Paraffin wax is dispersed in an aqueous solution of polyvinyl alcohol (e.g., concentration 1 wt%) at a mass ratio of 1 g to 5 g: 40 ml to obtain a paraffin / polyvinyl alcohol dispersion ①. The dispersion method can be water bath stirring and / or ultrasonic dispersion. The degree of alcoholysis of polyvinyl alcohol is 87% to 89%. The melting point of paraffin wax is 58 to 60 °C, and its phase transition temperature is higher than that of tungsten-doped vanadium dioxide. For example, the dispersion method includes: (1) first stirring magnetically in a water bath at 65 °C for 10 min, with the speed of the magnetic stirrer being 600 r / min; (2) then ultrasonically dispersing at 50 to 60 °C for 40 min; repeating steps (1)-(2) 2 to 4 times.

[0028] A paraffin / polyvinyl alcohol dispersion ① is mixed with a 10 wt% aqueous solution of polyvinyl alcohol at a volume ratio of 1:1.5–5.5 to obtain a paraffin / polyvinyl alcohol mixture ②. The mixing method includes magnetic stirring and / or ultrasound. For example, the magnetic stirrer is used at a speed of 600 r / min for 20 min, followed by ultrasound for 30 min.

[0029] Tungsten-doped vanadium dioxide nanoparticles were dispersed in a paraffin / polyvinyl alcohol mixture ② at a ratio of 3.0 mg to 6.0 mg: 40 ml to obtain the mixture. The dispersion method could be ultrasonication, for example, ultrasonication for 20 minutes.

[0030] After preparing a wet film from the mixture, it is then dried (e.g., vacuum drying) to obtain a thermochromic composite film. The film can be prepared by various methods, such as multi-layer coating and drying (single layer thickness 60 μm–150 μm), spray gun coating and drying (spray gun nozzle diameter 2 μm–5 μm), and vacuum drying using a custom mold (drying temperature 60°C, drying time 6–24 h).

[0031] In this invention, the thermochromic composite film exhibits high transmittance in the visible and near-infrared bands at low temperatures. As the temperature rises, the tungsten-doped vanadium dioxide undergoes a phase transition first, resulting in high transmittance in the visible and low transmittance in the infrared bands. With further temperature increases, paraffin undergoes a phase transition, changing from a solid to a liquid state, altering its refractive index. The refractive index mismatch between paraffin and polyvinyl alcohol leads to strong light scattering; the shorter the wavelength, the greater the scattering, resulting in low transmittance in both the visible and near-infrared bands. This thermochromic composite film can gradient-control the visible-near-infrared bands, enhancing energy-saving effects, resolving unnecessary sacrifices in visibility, and exhibiting good thermal and cycling stability.

[0032] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0033] Example 1 Vanadium pentoxide (V₂O₅) was dissolved in deionized water, and then the pH was adjusted to 8 by adding alkaline ammonia solution. A strong reducing agent, hydrazine, was added, and the mixture was magnetically stirred for 30 minutes. Ammonium paratungstate ((NH₄⁺), a hexavalent tungsten compound comprising 1.5% of the total molar amount of vanadium, was then added. 10 (H2W 12 O 42 The vanadium dioxide nanoparticles were reacted with 4H₂O at 280°C for 24 hours, then naturally cooled to room temperature. After centrifugation, washing, and drying at 60°C for 24 hours, tungsten-doped vanadium dioxide nanoparticles were obtained. Paraffin wax was dispersed in a 1 wt% aqueous solution of polyvinyl alcohol at a ratio of 3 g:40 ml, stirred in a 65°C water bath for 10 minutes, and then ultrasonically dispersed at 60°C for 40 minutes. This process was repeated three times to obtain a paraffin / polyvinyl alcohol dispersion ①. This dispersion was then mixed with a 10 wt% polyvinyl alcohol solution at a ratio of 1:3 (volume ratio), stirred for 20 minutes, and ultrasonically dispersed for 30 minutes to obtain a paraffin / polyvinyl alcohol dispersion ②. Tungsten-doped vanadium dioxide nanoparticles were dispersed in the paraffin / polyvinyl alcohol dispersion ② at a ratio of 5.3 mg:40 ml (mass ratio), and ultrasonically dispersed for 20 minutes to obtain a mixed solution. A mold of the required size was customized, and the mixed solution was cast. The mixture was then vacuum dried at 60°C for 24 hours to obtain the gradient-controlled thermochromic composite film proposed in this invention. The phase transition temperature of the tungsten-doped film is 32.9°C. Figure 1 As shown, the modulation rate between the lowest and highest temperatures of the composite thin film is 34.7%, and the gradient-tuned spectrum in the visible-infrared band is as follows. Figure 2 As shown.

[0034] Example 2 Vanadium pentoxide (V₂O₅) was dissolved in deionized water, and then the pH was adjusted to 8 by adding alkaline ammonia solution. A strong reducing agent, hydrazine, was added, and the mixture was magnetically stirred for 30 minutes. Ammonium paratungstate ((NH₄⁺), a hexavalent tungsten compound comprising 1.5% of the total molar amount of vanadium, was then added. 10 (H2W 12 O 42The vanadium dioxide nanoparticles were reacted with 4H₂O in a reactor at 280℃ for 24 hours, then naturally cooled to room temperature. After centrifugation, washing, and drying at 60℃ for 24 hours, tungsten-doped vanadium dioxide nanoparticles were obtained. Paraffin wax was dispersed in a 1wt% polyvinyl alcohol aqueous solution at a ratio of 3g:40ml, stirred in a 65℃ water bath for 10 minutes, and then ultrasonically dispersed at 60℃ for 40 minutes. This process was repeated three times to obtain a paraffin / polyvinyl alcohol dispersion ①. This dispersion was then mixed with a 10wt% polyvinyl alcohol solution at a volume ratio of 1:3, stirred for 20 minutes, and ultrasonically dispersed for 30 minutes to obtain a paraffin / polyvinyl alcohol dispersion ②. Tungsten-doped vanadium dioxide nanoparticles were dispersed in the paraffin / polyvinyl alcohol dispersion ② at a ratio of 5.3mg:40ml, and ultrasonically dispersed for 20 minutes to obtain a mixture. This mixture was then sprayed onto a polyethylene terephthalate (PET) substrate using a 5μm nozzle and dried at 60℃ for 2 hours. This process was repeated four times. The gradient-controlled thermochromic composite film proposed in this invention can then be obtained. The modulation rate between the lowest and highest temperatures of the composite film is 24.2%.

[0035] Example 3 Vanadium pentoxide (V₂O₅) was dissolved in deionized water, and then the pH was adjusted to 8 by adding alkaline ammonia solution. A strong reducing agent, hydrazine, was added, and the mixture was magnetically stirred for 30 minutes. Ammonium paratungstate ((NH₄⁺), a hexavalent tungsten compound comprising 1.5% of the total molar amount of vanadium, was then added. 10 (H2W 12 O 42 The vanadium dioxide nanoparticles were reacted with 4H₂O in a reactor at 280°C for 24 hours, then naturally cooled to room temperature. After centrifugation, washing, and drying at 60°C for 24 hours, tungsten-doped vanadium dioxide nanoparticles were obtained. Paraffin wax was dispersed in a 1 wt% aqueous solution of polyvinyl alcohol at a ratio of 3 g:40 ml, stirred in a water bath at 65°C for 10 minutes, and then ultrasonically dispersed at 60°C for 40 minutes. This process was repeated three times to obtain a paraffin / polyvinyl alcohol dispersion ①. This dispersion was then mixed with a 10 wt% polyvinyl alcohol solution at a volume ratio of 1:3, stirred for 20 minutes, and ultrasonically dispersed for 30 minutes to obtain a paraffin / polyvinyl alcohol dispersion ②. Tungsten-doped vanadium dioxide nanoparticles were dispersed in the paraffin / polyvinyl alcohol dispersion ② at a ratio of 5.3 mg:40 ml, and ultrasonically dispersed for 20 minutes to obtain a mixed solution. This solution was then coated onto a polyethylene terephthalate (PET) substrate using a 120 μm doctor blade and dried at 60°C for 6 hours. The gradient-controlled thermochromic composite film proposed in this invention was thus obtained. The modulation rate between the lowest and highest temperatures of the composite film is 24.3%.

[0036] Example 4 The preparation process of the thermochromic composite film in Example 4 is the same as in Example 1, except that: ammonium paratungstate ((NH4)), a hexavalent tungsten compound, is added at a molar weight of 1.0% of the total vanadium content. 10(H2W 12 O 42 The phase transition temperature of the obtained vanadium dioxide nanopowder was 39.8℃.

[0037] Example 5 The preparation process of the thermochromic composite film in Example 5 is the same as in Example 1, except that: ammonium paratungstate ((NH4)), a hexavalent tungsten compound, is added at a molar weight of 2.0% of the total vanadium content. 10 (H2W 12 O 42 The phase transition temperature of the obtained vanadium dioxide nanopowder was 29.3℃.

[0038] Example 6 The preparation process of the thermochromic composite film in Example 6 is the same as in Example 1, except that paraffin is dispersed in a 1 wt% aqueous solution of polyvinyl alcohol at a ratio of 2 g: 40 ml. The modulation rate between the lowest and highest temperatures of the resulting composite film is 27.8%.

[0039] Example 7 The preparation process of the thermochromic composite film in Example 7 is the same as in Example 1, except that paraffin was dispersed in a 1 wt% aqueous solution of polyvinyl alcohol at a ratio of 4 g: 40 ml. The modulation rate of the resulting composite film between the low and high temperatures was 31.4%.

[0040] Example 8 The preparation process of the thermochromic composite film in Example 8 is the same as in Example 1, except that: the paraffin / polyvinyl alcohol dispersion ① is mixed with 10 wt% polyvinyl alcohol solution at a ratio of 1:2 (volume ratio), stirred for 20 min, and sonicated for 30 min. The modulation rate between the lowest and highest temperatures of the resulting composite film is 29.5%.

[0041] Example 9 The preparation process of the thermochromic composite film in Example 9 is the same as in Example 1, except that: 1 wt% paraffin / polyvinyl alcohol dispersion ① and 10 wt% polyvinyl alcohol solution are mixed at a ratio of 1:5 (volume ratio), stirred for 20 min, and sonicated for 30 min. The modulation rate between the lowest and highest temperatures of the resulting composite film is 26.5%.

[0042] Example 10 The preparation process of the thermochromic composite film in Example 10 is the same as in Example 1, except that tungsten-doped vanadium dioxide nanoparticles are dispersed in a paraffin / polyvinyl alcohol dispersion at a ratio of 4.0 mg: 40 ml. The modulation rate between the lowest and highest temperatures of the resulting composite film is 27.5%.

[0043] Example 11 The preparation process of the thermochromic composite film in Example 11 is the same as in Example 1, except that tungsten-doped vanadium dioxide nanoparticles are dispersed in a paraffin / polyvinyl alcohol dispersion ② at a ratio of 6.0 mg: 40 ml. The modulation rate between the lowest and highest temperatures of the resulting composite film is 31.5%.

[0044] Example 12 The preparation process of the thermochromic composite film in Example 12 is the same as in Example 2, except that the nozzle diameter of the spray gun used for spraying is 2 μm. The modulation rate between the lowest and highest temperatures of the resulting composite film is 23.3%.

[0045] Example 13 The preparation process of the thermochromic composite film in Example 13 is the same as in Example 2, except that the nozzle diameter of the spray gun used for spraying is 4 μm. The modulation rate between the lowest and highest temperatures of the resulting composite film is 23.6%.

[0046] Example 14 The preparation process of the thermochromic composite film in Example 14 is the same as in Example 3, except that the doctor blade used for coating is 60 μm. The modulation rate between the lowest and highest temperatures of the resulting composite film is 23.8%.

[0047] Example 15 The preparation process of the thermochromic composite film in Example 15 is the same as in Example 3, except that the doctor blade used for coating is 80 μm. The modulation rate between the lowest and highest temperatures of the resulting composite film is 23.9%.

[0048] Comparative Example 1 The preparation process of the composite film in Comparative Example 1 is the same as that in Example 1, except that paraffin was dispersed in an aqueous solution of 1 wt% polyvinyl alcohol at a ratio of 10 g: 40 ml.

[0049] Comparative Example 2 The preparation process of the composite film in Comparative Example 2 is the same as that in Example 1, except that: tungsten-doped vanadium dioxide nanoparticles are dispersed in paraffin / polyvinyl alcohol dispersion ② at a ratio of 20.0 mg: 40 ml.

[0050] Comparative Example 3 The preparation process of the composite film in Comparative Example 3 is the same as that in Example 1, except that no paraffin was added.

[0051] Comparative Example 4 The preparation process of the composite film in Comparative Example 4 is the same as that in Example 1, except that W was not added to dope VO2.

[0052] Comparative Example 5 The preparation process of the composite thin film in Comparative Example 5 is the same as that in Example 1, except that VO2 is not doped with W.

[0053] Comparative Example 6 The preparation process of the composite film in Comparative Example 6 is the same as that in Example 1, except that the film-forming matrix is ​​polyethylene glycol.

[0054] Table 1 shows the composition and performance parameters of the thermochromic composite film prepared according to the present invention: The first mass ratio refers to the mass ratio of the phase change material to the film-forming matrix. The second mass ratio refers to the mass ratio of the latent heat of the phase change material to the film-forming matrix.

[0055] from Figure 1 As can be seen from the data, tungsten-doped vanadium dioxide nanopowder with a phase transition temperature of 33℃ was selected. Figure 2 The results show that the film exhibits high visible-near-infrared transmittance at room temperature. As temperature increases, it first reaches the phase transition temperature of vanadium dioxide, at which point the near-infrared transmittance decreases significantly, while the visible light transmittance remains relatively unchanged. With further temperature increases, paraffin undergoes a phase transition, changing from a solid to a liquid state, altering its refractive index. The refractive index mismatch between paraffin and polyvinyl alcohol leads to strong light scattering; the shorter the wavelength, the greater the scattering, resulting in a significant decrease in visible-near-infrared transmittance. This VO2-based thermochromic organic composite film achieves gradient modulation of the visible-near-infrared band.

Claims

1. A thermochromic composite film based on VO2 with visible and near-infrared dual-band gradient modulation, characterized in that, include: Film-forming matrix, and phase change materials and latent heat of phase change materials distributed in the film-forming matrix; The phase change material is tungsten-doped vanadium dioxide nanopowder; The latent heat material of phase change includes at least one of n-hexadecane, n-octadecane, stearic acid, palmitic acid, and paraffin.

2. The visible-near-infrared dual-band gradient-controlled thermochromic composite film based on VO2 according to claim 1, characterized in that, The film-forming matrix includes at least one of polyvinyl butyral (PVB), polyvinylpyrrolidone (PVP), and polyvinyl alcohol (PVA); preferably, the degree of alcoholysis of the polyvinyl alcohol is 87% to 89%, and the molecular weight is 15,000 to 20,000.

3. The visible-near-infrared dual-band gradient-controlled thermochromic composite film based on VO2 according to claim 1 or 2, characterized in that, The refractive index in the solid state is 1.508–1.512, the refractive index after liquefaction is 1.435–1.448, and the refractive index of the film-forming matrix is ​​1.502–1.

507.

4. The visible-near-infrared dual-band gradient-controlled thermochromic composite film based on VO2 according to any one of claims 1-3, characterized in that, The tungsten-doped vanadium dioxide powder has a W doping content of no more than 2.0 at%; the particle size of the vanadium dioxide nanoparticles is in the range of 30 to 70 nm, and the phase transition temperature is 29°C to 55°C.

5. The visible-near-infrared dual-band gradient-controlled thermochromic composite film based on VO2 according to claim 4, characterized in that, The phase transition temperatures of the tungsten-doped vanadium dioxide nanopowder are all lower than those of paraffin.

6. The visible-near-infrared dual-band gradient-controlled thermochromic composite film based on VO2 according to any one of claims 1-5, characterized in that, The thickness of the VO2-based visible and near-infrared dual-band gradient-controlled thermochromic composite film is 40 μm to 200 μm.

7. The visible-near-infrared dual-band gradient-controlled thermochromic composite film based on VO2 according to any one of claims 1-6, characterized in that, The mass ratio of the phase change material to the film-forming matrix is ​​1:(396.2~773.6); the mass ratio of the phase change latent heat material to the film-forming matrix is ​​1:(3.0~7.0).

8. The visible-near-infrared dual-band gradient-controlled thermochromic composite film based on VO2 as described in claim 7, characterized in that, The mass ratio of the phase change material to the latent heat material is (4.0–10.8):1000.

9. The visible-near-infrared dual-band gradient-controlled thermochromic composite film based on VO2 according to any one of claims 1-8, characterized in that, The properties of the VO2-based visible-near-infrared dual-band gradient-controlled thermochromic composite film include: Below the vanadium dioxide phase transition temperature, the visible transmittance is 44.7%–65.07%, and the near-infrared transmittance is 44.74%–65.84%. Alternatively, vanadium dioxide undergoes a phase transition when the temperature is above the vanadium dioxide phase transition temperature but below the melting point of the latent heat material, with a visible transmittance of 40.38%–56.42% and a near-infrared transmittance of 39.66%–57.53%. Alternatively, when the temperature is above the melting point of the latent heat of phase change material, the latent heat of phase change material changes from solid to liquid, and the refractive index changes. This causes a mismatch in refractive index between the latent heat of phase change material and the film-forming matrix, resulting in strong scattering of light. The shorter the wavelength, the greater the degree of scattering. The visible transmittance is 18.00% to 14.33%, and the near-infrared transmittance is 19.43% to 34.76%.

10. A method for preparing a visible-near-infrared dual-band gradient-controlled thermochromic composite thin film based on VO2, as described in any one of claims 1-9, characterized in that, include: The thermochromic composite film with visible and near-infrared dual-band gradient modulation based on VO2 was prepared by at least one of the following methods: blade coating, spray gun coating, and vacuum drying.

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