A photonic crystal hydrogel-based thermochromic smart window material, its preparation method and application

Abstract

This invention discloses a photonic crystal hydrogel-based thermochromic smart window material, its preparation method, and its application. The photonic crystal hydrogel-based thermochromic smart window material is obtained by filling a three-dimensional photonic crystal structure with a temperature-sensitive hydrogel prepolymer and then curing it. The temperature-sensitive hydrogel prepolymer is prepared by ultrasonically dispersing a temperature-sensitive monomer, modified cellulose, and a crosslinking agent in deionized water, stirring under ice bath conditions until completely dissolved, adding an initiator and stirring until dissolved, and then adding N,N,N',N'-tetramethylethylenediamine and stirring until homogeneous. The photonic crystal hydrogel-based thermochromic smart window material prepared by this invention can adjust the window transmittance in real time according to the ambient temperature, exhibiting a sensitive thermochromic effect and excellent infrared shielding performance.

Description

Technical Field

[0001] This invention relates to a thermochromic material, and more particularly to a photonic crystal hydrogel-based thermochromic smart window material, its preparation method and application, belonging to the field of smart heat-insulating window technology. Background Technology

[0002] Buildings account for approximately 36% of global energy consumption, with heating, ventilation, and air conditioning (HVAC) systems accounting for about 40-50% of that. Windows significantly impact indoor heating, cooling, and lighting; therefore, optimizing windows is an essential step in reducing building energy consumption. To improve energy efficiency and living comfort, research on smart windows has garnered widespread attention. Smart windows can adjust their transmittance based on factors such as light intensity and ambient temperature, maintaining indoor temperature within a comfortable range and reducing HVAC system energy consumption.

[0003] Currently, the most researched smart windows include electrochromic windows and thermochromic windows. Electrochromic windows precisely control the window's transmittance and color by adjusting the voltage. However, electrochromic windows are actively controlled and require manual intervention. Furthermore, they require power, which further increases energy consumption. On the other hand, thermochromic windows are passively controlled and can adaptively adjust the window's transmittance according to the ambient temperature, achieving the color-changing effect without additional power.

[0004] Chinese invention patent CN 116284850 B discloses a method for preparing an ion-hydrogel electrolyte and applying it to an electrochromic smart window. This method involves mixing lithium chloride and acrylamide to prepare a deep eutectic solvent, then adding the deep eutectic solvent to a hydrogel precursor solution containing N-isopropylamide, sodium dodecyl sulfate, and bis-tert-butylperoxyisopropylbenzene. The hydrogel precursor solution is then filled into a hollow glass interlayer composed of conductive glass containing a WO3 film for curing, resulting in an electrochromic smart window. However, this technology requires an additional power supply to achieve the window's color-changing effect, and relying solely on hydrogel for electrochromism results in poor sunlight modulation capability, while also leading to higher energy consumption.

[0005] Chinese invention patent CN 114573756 B discloses a method for preparing a thermosensitive gel for use in thermochromic smart windows. This technology modifies N-isopropylacrylamide with hydroxypropyl methylcellulose, and obtains a poly(N-isopropylacrylamide / hydroxypropyl methylcellulose) thermosensitive composite gel through redox-initiated free radical polymerization at low temperatures. While this technology achieves a hydrogel phase transition temperature close to room temperature and offers relatively energy-efficient thermochromic properties, the thermochromic effect, prepared solely from thermosensitive monomers such as N-isopropylacrylamide, only changes from a transparent to a white opaque state. Furthermore, in winter, the low temperature prevents the thermosensitive monomers from reaching their phase transition temperature, hindering the hydrogel's phase transition and resulting in excessive indoor light intensity, significantly reducing winter living comfort.

[0006] Chinese invention patent application CN 104129121 A discloses a thermochromic window whose solar transmittance can be adjusted according to temperature. The thermochromic window includes a flexible substrate, a thermochromic thin film disposed on the flexible substrate, and a thermally processed substrate bonded to the thermochromic thin film. The thermochromic material is selected from one of vanadium dioxide (VO2), titanium dioxide (III) (Ti2O3), niobium dioxide (NbO2), and nickel sulfide (NiS). The phase transition temperature of the thermochromic material is controlled by doping it with a dopant. While the phase transition temperature of the thermochromic material decreases with increasing dopant ratio, the thermochromic material is a metal oxide, and the dopant selected from Mo, W, Nb, Ta, Fe, Al, Ti, Sn, and Ni is also a metal, resulting in a generally high color transition temperature and difficulty in controlling low-temperature color change. Moreover, the inherent yellowish-brown color of VO2, which is preferred by this technology, seriously affects the aesthetics and visible light transmittance of the thermochromic window. Furthermore, due to the excessively high phase transition temperature of VO2, the thermochromic window is difficult to effectively control the transmittance of sunlight in everyday use scenarios.

[0007] Overall, existing thermochromic windows struggle to control color changes across a wide temperature range, have limited color-changing temperature ranges, offer fewer color variations, and lack infrared shielding functionality. Summary of the Invention

[0008] This invention addresses the problems existing in the prior art by providing a photonic crystal hydrogel-based thermochromic smart window material with infrared shielding properties, capable of color changing over a wide operating temperature range and displaying a variety of colors, as well as its preparation method.

[0009] Another objective of this invention is to provide the application of the aforementioned photonic crystal hydrogel-based thermochromic smart window material in the fabrication of smart windows.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] A photonic crystal hydrogel-based thermochromic smart window material is obtained by filling a three-dimensional photonic crystal structure with a temperature-sensitive hydrogel prepolymer and then curing it. The temperature-sensitive hydrogel prepolymer is obtained by ultrasonically dispersing a temperature-sensitive monomer, modified cellulose, and a crosslinking agent in deionized water, stirring until completely dissolved in an ice bath, adding an initiator and stirring until dissolved, and then adding N,N,N',N'-tetramethylethylenediamine and stirring until homogeneous. The temperature-sensitive monomer has both hydrophilic and hydrophobic groups, and its LCST is -5 to 70 °C. The three-dimensional photonic crystal structure is obtained by coating a modified colloidal crystal (obtained by adding a dispersion of transparent conductive oxide nanoparticles to a colloidal crystal) onto a carrier using a blade coating or spin coating method. The colloidal crystal is obtained by pre-assembling the colloidal particle dispersion on a tube wall after centrifugation. After pre-assembly, the colloidal crystal forms hierarchical light spots.

[0012] To further achieve the objectives of this invention, preferably, the amounts of the thermosensitive monomer, crosslinking agent, and initiator are 7-15 wt%, 0.05-0.1 wt%, and 0.2-0.3 wt% of the raw material of the thermosensitive hydrogel prepolymer, respectively; the mass ratio of the thermosensitive monomer to the modified cellulose is 10:1-40:1; the molar ratio of N,N,N',N'-tetramethylethylenediamine to the initiator is 2:1-1:1; and the mass ratio of the three-dimensional photonic crystal structure to the thermosensitive hydrogel prepolymer is 7-12:100.

[0013] Preferably, the thermosensitive monomer is one or more of N-isopropylacrylamide, N-tert-butylacrylamide, N,N-diethylacrylamide, N-propylacrylamide, N,N-dimethylacrylamide, dimethylaminopropylacrylamide, and ethoxyethoxyethyl acrylate.

[0014] Preferably, the modified cellulose is obtained by esterification or etherification of cellulose.

[0015] Preferably, the modified cellulose is one or more of methylcellulose, carboxymethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, and cellulose nanofibers.

[0016] Preferably, the crosslinking agent is one or more of N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, and allyl methacrylate; the initiator is one or more of ammonium persulfate, potassium persulfate, and sodium persulfate; the transparent conductive oxide nanoparticles are one or more of indium tin oxide (ITO), antimony tin oxide (ATO), and aluminum zinc oxide (AZO); the colloidal particle dispersion is prepared by dispersing colloidal particle powder in deionized water; and the colloidal particles are polystyrene microspheres, polymethyl methacrylate microspheres, SiO2 microspheres, TiO2 microspheres, or ZnO2 microspheres.

[0017] Preferably, the colloidal particles account for 20-30 wt% of the dispersion; the particle size of the colloidal particles is 160-280 nm.

[0018] Preferably, the curing temperature is 4~15 °C, and the curing time is 12~24 h; the stirring involved in the process of stirring until completely dissolved under ice bath conditions, adding the initiator and stirring until dissolved, and adding N,N,N',N'-tetramethylethylenediamine is all done using magnetic stirring at a speed of 500-1000 rpm; the stirring time for adding N,N,N',N'-tetramethylethylenediamine is 30~60 s; the ultrasonic dispersion time is 60~120 min; the centrifugation speed is 4000~8000 rpm, and the centrifugation time is 40~60 min; the carrier is glass.

[0019] The preparation method of the aforementioned photonic crystal hydrogel-based thermochromic smart window material includes the following steps:

[0020] (1) Centrifuge the colloidal particle dispersion until pre-assembled hierarchical light spots of different colors are formed on the wall of the centrifuge tube to obtain colloidal crystals;

[0021] (2) Add transparent conductive oxide nanoparticle dispersion to the colloidal crystal in step (1), and disperse by ultrasonication to obtain modified colloidal crystal;

[0022] (3) Modified colloidal crystals are self-assembled on a carrier by scraping or spin coating to form a periodically ordered three-dimensional photonic crystal structure;

[0023] (4) Add the thermosensitive monomer, modified cellulose and crosslinking agent to deionized water, disperse by ultrasonication, and stir under ice bath conditions until the monomer is completely dissolved. Add the initiator and stir until dissolved. Add the catalyst N,N,N',N'-tetramethylethylenediamine and stir evenly to obtain the thermosensitive hydrogel prepolymer.

[0024] (5) After filling the three-dimensional photonic crystal structure obtained by self-assembly on the carrier in step (3) with the thermosensitive hydrogel prepolymer liquid from step (4), solidify it to obtain the photonic crystal hydrogel-based thermochromic smart window material.

[0025] The application of the aforementioned photonic crystal hydrogel-based thermochromic smart window material in the fabrication of smart windows.

[0026] Compared with existing color-changing windows, the advantages of this invention are:

[0027] 1. This invention utilizes a rapidly fabricated three-dimensional photonic crystal structure combined with a thermosensitive hydrogel to prepare a thermochromic smart window. The interparticle spacing in the photonic crystal hydrogel thermochromic smart window material changes in real time according to the ambient temperature, realizing multiple color-changing effects and sensitive temperature response of the thermochromic window. This improves upon the shortcomings of ordinary thermochromic windows, which can only change from colorless to white and have a single color-changing effect, and has good privacy protection and decorative functions.

[0028] 2. This invention can precisely control the phase transition temperature of thermosensitive hydrogel by adjusting the ratio of thermosensitive monomer to modified cellulose, so that the color change range of the thermochromic window is within the temperature range that is comfortable for the human body.

[0029] 3. This invention introduces transparent conductive oxide nanoparticles for modification, which improves the shortcomings of ordinary thermochromic windows in low-temperature climates such as winter, where the photothermal conversion efficiency is low. The addition of transparent conductive oxide nanoparticles endows the thermochromic window with excellent photothermal response efficiency and near-infrared shielding performance. Attached Figure Description

[0030] Figure 1 Optical photographs of the three-dimensional photonic crystal structures prepared in Examples 1 and 2.

[0031] Figure 2 An optical photograph of the photonic crystal hydrogel-based thermochromic smart window material prepared in Example 3.

[0032] Figure 3 This is an electron microscope image of the photonic crystal hydrogel-based thermochromic smart window material prepared in Example 3.

[0033] Figure 4 The transmittance spectra of Example 3 and Comparative Example 1 at 20°C and 40°C are compared.

[0034] Figure 5 This is a comparison of the visible light modulation rate between Example 3 and Comparative Example 1.

[0035] Figure 6 The DSC curves are for Examples 3 and 7.

[0036] Figure 7 This is a comparison of the heat insulation effects of Example 3 and Comparative Example 2.

[0037] Figure 8 This is a comparison of the solar transmittance of Example 3 and Comparative Example 2 at 20°C.

[0038] Figure 9 This is a comparison of optical photographs taken at 20°C and 40°C for Example 3.

[0039] Figure 10Example 3: A comparison of simulated heat insulation effects between ordinary glass and Low-E glass.

[0040] Figure 11 The reflectance spectrum of Example 3 at 24°C to 32°C.

[0041] Figure 12 This is an optical photograph of Example 3 taken at temperatures ranging from 24°C to 40°C. Detailed Implementation

[0042] To better understand the present invention, the invention is further described below with reference to the accompanying drawings and embodiments. However, the embodiments do not constitute a limitation on the scope of protection of the claims of the present invention. Other embodiments obtained by those skilled in the art based on the embodiments without creative effort are all within the scope of protection of the present invention.

[0043] This invention addresses the limitations of existing thermochromic windows, which struggle to control color changes across a wide temperature range, have a limited color-changing temperature range, and offer only a limited number of color options. The invention discovers that combining a three-dimensional photonic crystal structure with a temperature-sensitive hydrogel can effectively solve these problems, resulting in a photonic crystal hydrogel-based thermochromic smart window that changes color according to ambient temperature and light intensity. In this invention, the spacing between colloidal particles changes in real-time according to ambient temperature, enabling multiple color-changing effects and sensitive temperature response. This overcomes the shortcomings of ordinary thermochromic windows, which only change from colorless to white and offer limited color-changing effects. It achieves multiple color-temperature matching, providing excellent privacy protection and decorative appeal.

[0044] Meanwhile, the thermosensitive hydrogel of this invention differs from existing thermosensitive materials. Firstly, the thermosensitive monomer possesses both hydrophilic and hydrophobic groups, with a LCST of -5 to 70 °C. Secondly, the thermosensitive hydrogel material contains modified cellulose; adjusting the ratio of the thermosensitive monomer to the modified cellulose can adjust the phase transition temperature of the thermosensitive hydrogel, thus resulting in a photonic crystal hydrogel-based thermochromic window with different color change ranges.

[0045] Meanwhile, in addition to colloidal particles, the three-dimensional photonic crystal structure material of the present invention also contains transparent conductive oxide nanoparticles. By introducing transparent conductive oxide nanoparticles to modify the colloidal particles, the present invention endows the thermochromic window with excellent photothermal response efficiency and near-infrared shielding performance, which can improve the problem of thermochromic windows being difficult and slow to change color under low temperature conditions such as winter.

[0046] Therefore, this invention provides a photonic crystal hydrogel-based thermochromic smart window material, which is obtained by filling a three-dimensional photonic crystal structure with a temperature-sensitive hydrogel prepolymer and then curing it. The temperature-sensitive hydrogel prepolymer is obtained by ultrasonically dispersing a temperature-sensitive monomer, modified cellulose, and crosslinking agent in deionized water, stirring under ice bath conditions until completely dissolved, adding an initiator and stirring until dissolved, and then adding N,N,N',N'-tetramethylethylenediamine and stirring evenly. The temperature-sensitive monomer has both hydrophilic and hydrophobic groups, and the LCST is -5~70 °C. The three-dimensional photonic crystal structure is obtained by coating a modified colloidal crystal, obtained by adding a transparent conductive oxide nanoparticle dispersion to a colloidal crystal, onto a carrier by a scraping or spin coating method. The colloidal crystal is obtained by pre-assembling the colloidal particle dispersion on the tube wall after centrifugation, which will form hierarchical light spots after pre-assembly. The transparent conductive oxide nanoparticle dispersion is obtained by dispersing transparent conductive oxide nanoparticles in deionized water.

[0047] Therefore, the main characteristic of the photonic crystal hydrogel-based thermochromic smart window material of the present invention lies in the raw material composition of the thermosensitive hydrogel prepolymer and the three-dimensional photonic crystal structure itself. The amounts of thermosensitive monomer, modified cellulose, crosslinking agent, and N,N,N',N'-tetramethylethylenediamine in the thermosensitive hydrogel prepolymer, as well as the amounts of colloidal particles and transparent conductive oxide nanoparticles in the three-dimensional photonic crystal structure, can be obtained experimentally according to the present invention. The specific selection of the thermosensitive monomer, modified cellulose, and crosslinking agent involved in the present invention can also be optimized experimentally according to the present invention. Of course, the thermosensitive monomer of the present invention is required to have both hydrophilic and hydrophobic groups, and the LCST is -5 to 70 °C.

[0048] Example 1: Fabrication of a three-dimensional photonic crystal structure

[0049] (1) Preparation of colloidal crystals

[0050] A soap-free emulsion polymerization method was used. 8 g of styrene, 1 g of methyl methacrylate, and 100 g of deionized water were added to a flask equipped with a mechanical stirrer, thermometer, and condenser. The mixture was heated in a water bath at 75 °C for 30 min. Then, 5 mL of a 3% ammonium persulfate solution was added, and the reaction proceeded for 7.5 h to obtain a carboxylated polystyrene (PS) microsphere dispersion. The PS microsphere dispersion was then centrifuged at 8000 rpm for 60 min. The PS microspheres pre-assembled into PS colloidal crystals at the bottom of the centrifuge tube, at which point a bright structural color could be observed.

[0051] (2) Preparation of modified colloidal crystals (PS@ATO)

[0052] Take 5 ml of the pre-assembled PS colloidal crystals from step (1), add 0.05 g of ATO dispersion (50 wt%), add deionized water to prepare a dispersion with a mass fraction of 20 wt%, and after ultrasonic dispersion for 60 min, obtain modified colloidal crystals (PS@ATO).

[0053] (3) Fabrication of three-dimensional photonic crystal structures

[0054] The modified colloidal crystal was coated onto a 100 mm × 100 mm × 1 mm glass slide using a four-sided fabrication apparatus, with a coating thickness of 25 μm. After self-assembly, a crack-free, uniformly colored three-dimensional photonic crystal structure was obtained.

[0055] Example 2: Fabrication of a three-dimensional photonic crystal structure

[0056] (1) Preparation of colloidal crystals

[0057] A soap-free emulsion polymerization method was used. 8 g of styrene, 1 g of methyl methacrylate, and 100 g of deionized water were added to a flask equipped with a mechanical stirrer, thermometer, and condenser. The mixture was heated in a water bath at 75 °C for 30 min. Then, 5 mL of a 3% ammonium persulfate solution was added, and the reaction proceeded for 7.5 h to obtain a carboxylated polystyrene (PS) microsphere dispersion. The PS microsphere dispersion was then centrifuged at 8000 rpm for 60 min. The PS microspheres pre-assembled into PS colloidal crystals at the bottom of the centrifuge tube, at which point a bright structural color could be observed.

[0058] (2) Preparation of modified colloidal crystals (PS@ATO)

[0059] Take 5 ml of the pre-assembled PS colloidal crystals from step (1), add 0.05 g of ATO dispersion (50 wt%), add an appropriate amount of deionized water to prepare a dispersion with a mass fraction of 25 wt%, and after ultrasonic dispersion for 60 min, obtain modified colloidal crystals (PS@ATO).

[0060] (3) Fabrication of three-dimensional photonic crystal structures

[0061] The modified colloidal crystal was coated onto a 100 mm × 100 mm × 1 mm glass slide using a four-sided fabrication apparatus, with a coating thickness of 25 μm. After self-assembly, a crack-free, uniformly colored three-dimensional photonic crystal structure was obtained.

[0062] Figure 1These are optical photographs of the three-dimensional photonic crystal structures from Examples 1 and 2. The images show that modified colloidal crystals with mass fractions of 20 wt% and 25 wt% can be rapidly prepared into crack-free, uniformly colored, and high-contrast three-dimensional photonic crystal structures via blade coating. This is because when the mass fraction of the modified colloidal crystal exceeds a critical mass fraction, the microspheres within the colloidal crystal undergo partial pre-assembly. This allows for rapid and uniform three-dimensional photonic crystal structures to be obtained through blade coating, improving the low efficiency of the "drop coating method" for preparing three-dimensional photonic crystal structures.

[0063] Example 3: Preparation of Photonic Crystal Hydrogel-Based Thermochromic Smart Window Material

[0064] (1) Preparation of colloidal crystals

[0065] A soap-free emulsion polymerization method was employed. 8 g of styrene, 1 g of methyl methacrylate, and 100 g of deionized water were added to a flask equipped with a mechanical stirrer, thermometer, and condenser. The mixture was heated in a water bath at 75 °C for 30 min. Then, 5 mL of a 3% ammonium persulfate solution was added, and the reaction proceeded for 7.5 h to obtain a carboxylated polystyrene (PS) microsphere dispersion. The PS microsphere dispersion was then centrifuged at 6000 rpm for 40 min. The PS microspheres pre-assembled into PS colloidal crystals at the bottom of the centrifuge tube, at which point a vibrant structural color was observed.

[0066] (2) Preparation of modified colloidal crystals (PS@ATO)

[0067] Take 5 ml of the pre-assembled PS colloidal crystals from step (1), add 0.15 g of ATO dispersion (50 wt%), add an appropriate amount of deionized water to prepare a dispersion with a mass fraction of 25 wt%, and after ultrasonic dispersion for 60 min, obtain modified colloidal crystals (PS@ATO).

[0068] (3) Fabrication of three-dimensional photonic crystal structures

[0069] The modified colloidal crystal was coated onto a 100 mm × 100 mm × 1 mm glass slide using a four-sided fabrication apparatus, with a coating thickness of 25 μm. After self-assembly, a crack-free, uniformly colored three-dimensional photonic crystal structure was obtained.

[0070] (4) Preparation of photonic crystal hydrogel-based thermochromic smart window materials

[0071] 1 g of N-isopropylacrylamide, 0.03 g of carboxymethyl cellulose, and 0.01 g of N,N'-methylenebisacrylamide were dissolved in 10 g of deionized water. After ultrasonic dispersion, the solution was magnetically stirred for 30 min in an ice bath. Then, 0.025 g of ammonium persulfate was added to the solution, and the mixture was magnetically stirred for 10 min. Finally, 25 μl of N,N,N',N'-tetramethylethylenediamine was added, and the mixture was magnetically stirred for 30 s to obtain a thermosensitive hydrogel prepolymer. The hydrogel prepolymer was then quickly poured into a hollow glass mold made of a glass slide with a three-dimensional photonic crystal structure deposited on it and a blank glass slide sandwiched between them with a silicone frame. The glass mold was then sealed with sealant, and the mold was placed at 4 °C for 24 h to prepare a photonic crystal hydrogel-based thermochromic smart window material.

[0072] Figure 2 The image shows an optical photograph of the photonic crystal hydrogel-based thermochromic smart window material prepared in Example 3. It can be seen from the image that the structure color of the smart window material is uniform. Figure 3 The image shows an electron microscope image of the photonic crystal hydrogel-based thermochromic smart window material of Example 3. It can be seen from the image that the hydrogel encapsulates the PS microspheres and fills the gaps between the PS microspheres. The arrangement of the PS microspheres still maintains an ordered three-dimensional photonic crystal structure. This structural order is the source of the structural color of the thermochromic smart window material.

[0073] Example 4: Preparation of Photonic Crystal Hydrogel-Based Thermochromic Smart Window Material

[0074] (1) Preparation of colloidal crystals

[0075] A soap-free emulsion polymerization method was employed. 9 g of styrene, 1 g of methyl methacrylate, and 100 g of deionized water were added to a flask equipped with a mechanical stirrer, thermometer, and condenser. The mixture was heated in a water bath at 75 °C for 30 min. Then, 5 mL of a 3% ammonium persulfate solution was added, and the reaction proceeded for 7.5 h to obtain a carboxylated polystyrene (PS) microsphere dispersion. The PS microsphere dispersion was then centrifuged at 4000 rpm for 60 min. The PS microspheres pre-assembled into PS colloidal crystals at the bottom of the centrifuge tube, at which point a vibrant structural color was observed.

[0076] (2) Preparation of modified colloidal crystals (PS@ATO)

[0077] Take 5 ml of the pre-assembled PS colloidal crystals from step (1), add 0.1 g of ATO dispersion (50 wt%), add an appropriate amount of deionized water to prepare a dispersion with a mass fraction of 30 wt%, and after ultrasonic dispersion for 120 min, obtain modified colloidal crystals (PS@ATO).

[0078] (3) Fabrication of three-dimensional photonic crystal structures

[0079] The modified colloidal crystal was coated onto a 100 mm × 100 mm × 1 mm glass slide using a four-sided fabrication apparatus, with a coating thickness of 25 μm. After self-assembly, a crack-free, uniformly colored three-dimensional photonic crystal structure was obtained.

[0080] (4) Preparation of photonic crystal hydrogel-based thermochromic smart window materials

[0081] 1.5 g of N-isopropylacrylamide, 0.1 g of carboxymethyl cellulose, and 0.01 g of polyethylene glycol diacrylate were dissolved in 10 g of deionized water. After ultrasonic dispersion, the solution was magnetically stirred for 30 min in an ice bath. Then, 0.025 g of sodium persulfate was added to the solution, and the mixture was magnetically stirred for 10 min. Finally, 25 μl of N,N,N',N'-tetramethylethylenediamine was added, and the mixture was magnetically stirred for 30 s to obtain a thermosensitive hydrogel prepolymer. The hydrogel prepolymer was then quickly poured into a hollow glass mold made of a glass slide with a three-dimensional photonic crystal structure deposited on it and a blank glass slide sandwiched between them with a silicone frame. The glass mold was then sealed with sealant, and the mold was placed at 4 °C for 24 h to prepare a photonic crystal hydrogel-based thermochromic smart window material.

[0082] Example 5: Preparation of Photonic Crystal Hydrogel-Based Thermochromic Smart Window Material

[0083] (1) Preparation of colloidal crystals

[0084] A soap-free emulsion polymerization method was employed. 11 g of styrene, 1 g of methyl methacrylate, and 100 g of deionized water were added to a flask equipped with a mechanical stirrer, thermometer, and condenser. The mixture was heated in a water bath at 75 °C for 30 min. Then, 5 mL of a 3% ammonium persulfate solution was added, and the reaction proceeded for 7.5 h to obtain a carboxylated polystyrene (PS) microsphere dispersion. The PS microsphere dispersion was then centrifuged at 8000 rpm for 40 min. The PS microspheres pre-assembled into PS colloidal crystals at the bottom of the centrifuge tube, at which point a vibrant structural color was observed.

[0085] (2) Preparation of modified colloidal crystals (PS@ATO)

[0086] Take 5 ml of the pre-assembled PS colloidal crystals from step (1), add 0.05 g of ATO dispersion (50 wt%), add an appropriate amount of deionized water to prepare a dispersion with a mass fraction of 25 wt%, and after ultrasonic dispersion for 60 min, obtain modified colloidal crystals (PS@ATO).

[0087] (3) Fabrication of three-dimensional photonic crystal structures

[0088] The modified colloidal crystal was coated onto a 100 mm × 100 mm × 1 mm glass slide using a four-sided fabrication apparatus, with a coating thickness of 25 μm. After self-assembly, a crack-free, uniformly colored three-dimensional photonic crystal structure was obtained.

[0089] (4) Preparation of photonic crystal hydrogel-based thermochromic smart window materials

[0090] 1 g of N-isopropylacrylamide, 0.06 g of carboxymethyl cellulose, and 0.005 g of allyl methacrylate were dissolved in 10 g of deionized water. After ultrasonic dispersion, the solution was magnetically stirred for 30 min in an ice bath. Then, 0.02 g of potassium persulfate was added to the solution, and the mixture was magnetically stirred for 10 min. Finally, 25 μl of N,N,N',N'-tetramethylethylenediamine was added, and the mixture was magnetically stirred for 30 s to obtain a thermosensitive hydrogel prepolymer. The hydrogel prepolymer was then quickly poured into a hollow glass mold made of a glass slide with a three-dimensional photonic crystal structure deposited on it and a blank glass slide sandwiched between them with a silicone frame. The glass mold was then sealed with sealant, and the mold was placed at 4 °C for 24 h to prepare a photonic crystal hydrogel-based thermochromic smart window material.

[0091] Example 6: Preparation of Photonic Crystal Hydrogel-Based Thermochromic Smart Window Material

[0092] (1) Preparation of colloidal crystals

[0093] A soap-free emulsion polymerization method was employed. 12 g of styrene, 1 g of methyl methacrylate, and 100 g of deionized water were added to a flask equipped with a mechanical stirrer, thermometer, and condenser. The mixture was heated in a water bath at 75 °C for 30 min. Then, 5 mL of a 3% ammonium persulfate solution was added, and the reaction proceeded for 7.5 h to obtain a carboxylated polystyrene (PS) microsphere dispersion. The PS microsphere dispersion was then centrifuged at 6000 rpm for 40 min. The PS microspheres pre-assembled into PS colloidal crystals at the bottom of the centrifuge tube, at which point a vibrant structural color was observed.

[0094] (2) Preparation of modified colloidal crystals (PS@ATO)

[0095] Take 5 ml of the pre-assembled PS colloidal crystals from step (1), add 0.15 g of ATO dispersion (50 wt%), add an appropriate amount of deionized water to prepare a dispersion with a mass fraction of 25 wt%, and after ultrasonic dispersion for 60 min, obtain modified colloidal crystals (PS@ATO).

[0096] (3) Fabrication of three-dimensional photonic crystal structures

[0097] The modified colloidal crystal was coated onto a 100 mm × 100 mm × 1 mm glass slide using a four-sided fabrication apparatus, with a coating thickness of 25 μm. After self-assembly, a crack-free, uniformly colored three-dimensional photonic crystal structure was obtained.

[0098] (4) Preparation of photonic crystal hydrogel-based thermochromic smart window materials

[0099] 1 g of N-isopropylacrylamide, 0.09 g of carboxymethyl cellulose, and 0.01 g of N,N'-methylenebisacrylamide were dissolved in 10 g of deionized water. After ultrasonic dispersion, the solution was magnetically stirred for 30 min in an ice bath. Then, 0.02 g of ammonium persulfate was added to the solution, and the mixture was magnetically stirred for 10 min. Finally, 25 μl of N,N,N',N'-tetramethylethylenediamine was added, and the mixture was magnetically stirred for 30 s to obtain a thermosensitive hydrogel prepolymer. The hydrogel prepolymer was then quickly poured into a hollow glass mold made of a glass slide with a three-dimensional photonic crystal structure deposited on it and a blank glass slide sandwiched between them with a silicone frame. The glass mold was then sealed with sealant, and the mold was placed at 4 °C for 24 h to prepare a photonic crystal hydrogel-based thermochromic smart window material.

[0100] The color of the photonic crystal hydrogel-based thermochromic smart window material can be adjusted by synthesizing colloidal particles of different sizes. The particle size of the colloidal particles synthesized in Examples 3-6 was tested using a Malvern particle size analyzer (Zetasizer Nano S), and the test results are shown in Table 1. Table 1 shows that as the particle size of the colloidal particles increases, the color of the photonic crystal hydrogel-based thermochromic smart window material changes from blue to green, yellow, and red. This is because the interplanar spacing of the three-dimensional photonic crystal structure assembled by different colloidal particles is different. As the particle size of the colloidal particles increases, the interplanar spacing of the three-dimensional photonic crystal structure increases, and its reflection peak increases accordingly, thus changing the structural color.

[0101] Table 1

[0102] Example 3 Example 4 Example 5 Example 6 Colloidal particle size (nm) 180 210 225 245 Photonic crystal hydrogel-based thermochromic smart window material color blue green yellow red

[0103] Example 7: Preparation of Photonic Crystal Hydrogel-Based Thermochromic Smart Window Material

[0104] (1) Preparation of colloidal crystals

[0105] A soap-free emulsion polymerization method was used. 8 g of styrene, 1 g of methyl methacrylate, and 100 g of deionized water were added to a flask equipped with a mechanical stirrer, thermometer, and condenser. The mixture was heated in a water bath at 75 °C for 30 min. Then, 5 mL of a 3% ammonium persulfate solution was added, and the reaction proceeded for 7.5 h to obtain a carboxylated polystyrene (PS) microsphere dispersion. The PS microsphere dispersion was then centrifuged at 8000 rpm for 60 min. The PS microspheres pre-assembled into PS colloidal crystals at the bottom of the centrifuge tube, at which point a bright structural color could be observed.

[0106] (2) Preparation of modified colloidal crystals (PS@ATO)

[0107] Take 5 ml of the pre-assembled PS colloidal crystals from step (1), add 0.05 g of ATO dispersion (50 wt%), add an appropriate amount of deionized water to prepare a dispersion with a mass fraction of 25 wt%, and after ultrasonic dispersion for 60 min, obtain modified colloidal crystals (PS@ATO).

[0108] (3) Fabrication of three-dimensional photonic crystal structures

[0109] The modified colloidal crystal was coated onto a 100 mm × 100 mm × 1 mm glass slide using a four-sided fabrication apparatus, with a coating thickness of 25 μm. After self-assembly, a crack-free, uniformly colored three-dimensional photonic crystal structure was obtained.

[0110] (4) Preparation of photonic crystal hydrogel-based thermochromic smart window materials

[0111] 1 g of N-isopropylacrylamide, 0.09 g of carboxymethyl cellulose, and 0.01 g of N,N'-methylenebisacrylamide were dissolved in 10 g of deionized water. After ultrasonic dispersion, the solution was magnetically stirred for 30 min in an ice bath. Then, 0.025 g of ammonium persulfate was added to the solution, and the mixture was magnetically stirred for 10 min. Finally, 25 μl of N,N,N',N'-tetramethylethylenediamine was added, and the mixture was magnetically stirred for 30 s to obtain a thermosensitive hydrogel prepolymer. The hydrogel prepolymer was then quickly poured into a hollow glass mold made of a glass slide with a three-dimensional photonic crystal structure deposited on it and a blank glass slide sandwiched between them with a silicone frame. The glass mold was then sealed with sealant, and the mold was placed at 4°C for 24 h to prepare a photonic crystal hydrogel-based thermochromic smart window material.

[0112] Example 8: Preparation of Photonic Crystal Hydrogel-Based Thermochromic Smart Window Material

[0113] (1) Preparation of colloidal crystals

[0114] Monodisperse SiO2 microsphere dispersions were prepared using the Stober method. The SiO2 microsphere dispersions were then centrifuged at 8000 rpm for 60 min. The SiO2 microspheres pre-assembled into SiO2 colloidal crystals at the bottom of the centrifuge tube, at which point a vibrant structural color could be observed.

[0115] (2) Preparation of modified colloidal crystals (SiO2@ITO)

[0116] Take 5 ml of the pre-assembled SiO2 colloidal crystals from step (1), add 0.1 g of ITO dispersion (50 wt%), add an appropriate amount of deionized water to prepare a dispersion with a mass fraction of 25 wt%, and after ultrasonic dispersion for 120 min, obtain modified colloidal crystals (SiO2@ITO).

[0117] (3) Fabrication of three-dimensional photonic crystal structures

[0118] The modified colloidal crystal was coated onto a 100 mm × 100 mm × 1 mm glass slide using a four-sided fabrication apparatus, with a coating thickness of 25 μm. After self-assembly, a crack-free, uniformly colored three-dimensional photonic crystal structure was obtained.

[0119] (4) Preparation of photonic crystal hydrogel-based thermochromic smart window materials

[0120] 1 g of N-isopropylacrylamide, 0.01 g of N-tert-butylacrylamide, 0.03 g of carboxymethyl cellulose, and 0.01 g of N,N'-methylenebisacrylamide were dissolved in 10 g of deionized water. After ultrasonic dispersion, the solution was magnetically stirred for 30 min in an ice bath. Then, 0.025 g of ammonium persulfate was added to the solution, and the mixture was magnetically stirred for 10 min. Finally, 25 μl of N,N,N',N'-tetramethylethylenediamine was added, and the mixture was magnetically stirred for 30 s to obtain a thermosensitive hydrogel prepolymer. The hydrogel prepolymer was then quickly poured into a hollow glass mold made of a glass slide with a three-dimensional photonic crystal structure deposited on it and a blank glass slide sandwiched between them with a silicone frame. The glass mold was then sealed with sealant, and the mold was placed at 15°C for 24 h to prepare a photonic crystal hydrogel-based thermochromic smart window material.

[0121] Example 9: Preparation of Photonic Crystal Hydrogel-Based Thermochromic Smart Window Material

[0122] (1) Preparation of colloidal crystals

[0123] Monodisperse SiO2 microsphere dispersions were prepared using the Stober method. The SiO2 microsphere dispersions were then centrifuged at 8000 rpm for 60 min. The SiO2 microspheres pre-assembled into SiO2 colloidal crystals at the bottom of the centrifuge tube, at which point a vibrant structural color could be observed.

[0124] (2) Preparation of modified colloidal crystals (SiO2@ITO)

[0125] Take 5 ml of the pre-assembled SiO2 colloidal crystals from step (1), add 0.1 g of ITO dispersion (50 wt%), add an appropriate amount of deionized water to prepare a dispersion with a mass fraction of 25 wt%, and after ultrasonic dispersion for 120 min, obtain modified colloidal crystals (SiO2@ITO).

[0126] (3) Fabrication of three-dimensional photonic crystal structures

[0127] The modified colloidal crystal was coated onto a 100 mm × 100 mm × 1 mm glass slide using a four-sided fabrication apparatus, with a coating thickness of 25 μm. After self-assembly, a crack-free, uniformly colored three-dimensional photonic crystal structure was obtained.

[0128] (4) Preparation of photonic crystal hydrogel-based thermochromic smart window materials

[0129] 1 g of N-isopropylacrylamide, 0.5 g of ethoxyethoxyethyl acrylate, 0.06 g of cellulose nanofibers, and 0.01 g of N,N'-methylenebisacrylamide were dissolved in 10 g of deionized water. After ultrasonic dispersion, the solution was magnetically stirred for 30 min in an ice bath. Then, 0.025 g of ammonium persulfate was added to the solution, and the mixture was magnetically stirred for 10 min. Finally, 25 μl of N,N,N',N'-tetramethylethylenediamine was added, and the mixture was magnetically stirred for 30 s to obtain a thermosensitive hydrogel prepolymer. The hydrogel prepolymer was then rapidly poured into a hollow glass mold made of a glass slide with a three-dimensional photonic crystal structure deposited on it and a blank glass slide sandwiched between them with a silicone frame. The glass mold was then sealed with sealant, and the mold was placed at 15°C for 24 h to prepare a photonic crystal hydrogel-based thermochromic smart window material.

[0130] Comparative Example 1

[0131] Comparative Example 1 is basically the same as Example 3, except that no modified cellulose was added during the preparation of Comparative Example 1, and the remaining steps and process conditions are the same as those of Example 3.

[0132] 1 g of N-isopropylacrylamide and 0.01 g of N,N'-methylenebisacrylamide were dissolved in 10 g of deionized water. After ultrasonic dispersion, the mixture was magnetically stirred for 30 min in an ice bath. Then, 0.025 g of ammonium persulfate was added to the solution, and the mixture was magnetically stirred for 10 min. Finally, 25 μl of N,N,N',N'-tetramethylethylenediamine was added, and the mixture was magnetically stirred for 30 s to obtain a thermosensitive hydrogel prepolymer. The hydrogel prepolymer was then quickly poured into a hollow glass mold made of a glass slide with a three-dimensional photonic crystal structure deposited on it and a blank glass slide sandwiched between them and a silicone frame. The glass mold was then sealed with sealant, and the mold was placed at 4°C for 24 h to react.

[0133] Figure 4 The transmittance spectra of Example 3 and Comparative Example 1 at 20°C and 40°C are shown in the figures. It can be seen from the figures that the addition of carboxymethyl cellulose can improve the transmittance of the thermochromic smart window, and from... Figure 5 It can be seen that carboxymethyl cellulose can improve the visible light modulation rate of thermochromic smart windows.

[0134] Comparative Example 2

[0135] Comparative Example 2 is basically the same as Example 3, except that the three-dimensional photonic crystal structure used in Comparative Example 2 was not modified by transparent conductive oxide nanoparticles, and the remaining steps and process conditions are the same as in Example 3.

[0136] Unmodified PS colloidal crystals were coated onto a 100 mm × 100 mm × 1 mm glass slide using a BGD tetrahedral fabrication apparatus to a thickness of 25 μm. After self-assembly, a PS photonic crystal template was obtained.

[0137] 1 g of N-isopropylacrylamide, 0.03 g of carboxymethyl cellulose, and 0.01 g of N,N'-methylenebisacrylamide were dissolved in 10 g of deionized water. After ultrasonic dispersion, the solution was magnetically stirred for 30 min in an ice bath. Then, 0.025 g of ammonium persulfate was added to the solution, and the mixture was magnetically stirred for 10 min. Finally, 25 μl of N,N,N',N'-tetramethylethylenediamine was added, and the mixture was magnetically stirred for 30 s to obtain a thermosensitive hydrogel prepolymer. The hydrogel prepolymer was then rapidly poured into a hollow glass mold made of a glass slide with a three-dimensional photonic crystal structure deposited on it and a blank glass slide sandwiched between them and a silicone frame. The glass mold was then sealed with sealant, and the mold was placed at 4°C for 24 h to react.

[0138] Comparative Example 3

[0139] Comparative Example 3 is basically the same as Example 3, except that the hollow glass mold used in the preparation process of Comparative Example 3 does not contain a three-dimensional photonic crystal structure, but is a mold composed of two ordinary glass pieces. The remaining steps and process conditions are the same as those in Example 3.

[0140] 1 g of N-isopropylacrylamide, 0.03 g of carboxymethyl cellulose, and 0.01 g of N,N'-methylenebisacrylamide were dissolved in 10 g of deionized water. After ultrasonic dispersion, the solution was magnetically stirred for 30 min in an ice bath. Then, 0.025 g of ammonium persulfate was added to the solution, and the mixture was magnetically stirred for 10 min. Finally, 25 μl of N,N,N',N'-tetramethylethylenediamine was added, and the mixture was magnetically stirred for 30 s to obtain a thermosensitive hydrogel prepolymer. The hydrogel prepolymer was then quickly poured into a hollow glass mold made of two blank glass slides sandwiching a silicone frame. The mold was then sealed with sealant, and the mold was placed at 4°C for 24 h to react.

[0141] In this embodiment of the invention, a differential scanning calorimeter (DSC250) was used to determine the phase transition temperature (LCST) of the thermosensitive hydrogel. The heating rate was 1 °C / min, the test temperature range was 25 °C to 50 °C, and both the protective gas and the purge gas were N2 with a flow rate of 60 mL / min.

[0142] In this embodiment of the invention, the transmittance spectra of the thermosensitive hydrogel at 20 °C and 40 °C were measured using a UV-Vis-NIR spectrophotometer (Lambda 1050+), and the transmittance in different wavelength bands (visible light band 380~780 nm, solar light band 280~2500 nm) was calculated. The calculation methods are shown in equations (1), (2), (3) and (4).

[0143]

[0144] in The transmittance spectrum was measured in the experiment. It is the standard luminous efficiency function for human photopic vision. It is the solar irradiance spectrum with an atmospheric mass of AM 1.5. It refers to the transmittance of visible light (380~780 nm band). It refers to the transmittance of sunlight (280~2500 nm band).

[0145] In this embodiment of the invention, a temperature measuring box is used to test the heat insulation effect of different windows. The temperature measuring box is 20cm*20cm*15cm in size and is surrounded by aluminum foil on the outside.

[0146] Figure 6These are the DSC curves of Examples 3 and 7. By adjusting the ratio of N-isopropylacrylamide to modified cellulose, the phase transition temperature of the hydrogel can be adjusted from 34.84°C to 35.51°C. This shows that by adjusting the ratio of the temperature-sensitive monomer to modified cellulose, the phase transition temperature of the photonic crystal hydrogel-based thermochromic window material can be precisely controlled, allowing residents to select the "temperature-controlled color change range" of the thermochromic window according to their own needs.

[0147] Figure 7 This figure compares the heat insulation effects of Example 3 and Comparative Example 2. As can be seen from the figure, after 60 minutes of continuous xenon lamp irradiation, the internal temperature of the temperature measuring chamber in Example 3 remained below 35.6 °C, within the comfortable temperature range for the human body. The temperature inside the temperature measuring chamber in Comparative Example 2 reached a maximum of 37.8 °C, exceeding human body temperature and causing a stuffy feeling. The maximum temperature difference between the temperature measuring chambers in Example 3 and Comparative Example 2 reached 3.4 °C, indicating that transparent conductive oxide nanoparticles can improve the photothermal conversion efficiency of the thermochromic smart window. Figure 8 The comparison shows that Example 3 has a solar transmittance as low as 37%, while Comparative Example 2 has a solar transmittance as high as 58%. In summary, this demonstrates that the photonic crystal hydrogel-based thermochromic window material made with transparent conductive oxide nanoparticles possesses excellent thermal insulation and infrared shielding properties, enabling the interior of a house to maintain a comfortable temperature and thus effectively reducing the energy consumption of the HVAC system.

[0148] Figure 9 These are optical photographs of the smart window in Example 3 at 20°C and 40°C. The images show that the smart window has good transmittance at 20°C, but becomes opaque at 40°C due to a phase change in the hydrogel, thus blocking sunlight. This thermochromic smart window's ability to maintain good transmittance at low temperatures and adaptively become opaque at high temperatures demonstrates its potential application in the field of smart thermal insulation.

[0149] Figure 10This study compares the simulated heat insulation effects of the smart window (Example 3), ordinary glass, and Low-E glass (5+9A+5, with 5mm thickness on both sides and a 9mm thick hollow interlayer). The center temperature of the temperature measuring chamber for the smart window in Example 3 reached 40.8 °C, while the center temperatures for the ordinary glass and Low-E glass reached 45.7 °C and 44.9 °C, respectively. At 10:00, the smart window in Example 3 underwent a phase change, effectively blocking direct sunlight, thus maintaining a lower center temperature in its measuring chamber. At 11:10, the temperature difference between the smart window in Example 3 and the temperature measuring chambers containing ordinary glass and Low-E glass was the greatest, achieving a cooling effect of 7.2 °C and 5.1 °C, respectively. This demonstrates that the photonic crystal hydrogel-based thermochromic material exhibits excellent performance in regulating indoor temperature and saving energy, overcoming the shortcomings of insufficient heat insulation in traditional glass and commercially available insulated glass.

[0150] Figure 11 The image shows the reflection spectrum of the smart window in Example 3 at temperatures ranging from 24°C to 32°C. It can be seen that the reflection peak of the thermochromic smart window red-shifts as the temperature increases, indicating an increase in the interplanar spacing of the photonic crystal.

[0151] Figure 12 These are optical photographs of the thermochromic smart window in Example 3 at different temperatures. Between 24°C and 32°C, the volume of the hydrogel swells or contracts with temperature changes, causing variations in the interplanar spacing of the photonic crystal structure. Consequently, the structural color of the photonic crystal changes, achieving the effect of the thermochromic smart window's color adaptively changing with ambient temperature. At 40°C, the PNIPAm polymer chains collapse into a "spherical" shape, increasing the scattering ability of visible light, thus becoming opaque.

[0152] Table 2 compares the optical colors of the photonic crystal hydrogel-based thermochromic smart window of Example 3 and the conventional thermochromic window of Comparative Example 3 at different temperatures. Compared to the conventional thermochromic window, which can only change between colorless and white, the photonic crystal hydrogel-based thermochromic smart window can change its color according to minute temperature variations, making it more precise and sensitive. By observing the changes in window color, residents can intuitively perceive changes in indoor temperature. Furthermore, the diversity of window color changes provides excellent privacy and decorative functions. The adaptive transmittance of the photonic crystal hydrogel-based thermochromic smart window also provides superior heat insulation.

[0153] Table 2

[0154] Temperature (°C) 24 26 28 30 32 40 Example 3 Optical Color green yellow-green yellow-green Orange red White Comparative Example 3 Optical Color Colorless and transparent Colorless and transparent Colorless and transparent Slightly whitened Localized whitening White

[0155] The phase transition temperature of the thermosensitive hydrogel can be adjusted by changing the ratio of the thermosensitive monomer to the modified cellulose, resulting in photonic crystal hydrogel-based thermochromic windows with different color change ranges. In Example 8, the addition of N-tert-butylacrylamide increased the overall hydrophobicity of the thermosensitive hydrogel, lowering its phase transition temperature. Table 3 shows that Example 8 achieved color change at a lower temperature than Example 3, turning completely red at 30 °C and achieving a phase transition at 36 °C. In Example 9, the addition of the hydrophilic monomer ethoxyethoxyethyl acrylate and cellulose nanofibers increased the overall hydrophilicity of the hydrogel, increasing its phase transition temperature. Table 4 shows that Example 9 required an even higher temperature to achieve the window color change, reaching 42 °C. By adjusting the ratio of the thermosensitive monomer to the modified cellulose, photonic crystal hydrogel-based thermochromic windows that change color within different temperature ranges can be obtained, allowing residents to choose according to their needs.

[0156] Table 3

[0157]

[0158] Table 4

[0159]

[0160] Compared to the electrochromic window in Chinese invention patent CN 116284850 B, the photonic crystal hydrogel-based thermochromic window of this invention can adaptively adjust the window's transmittance and color change according to changes in ambient temperature, requiring no additional power supply and consuming less energy. Furthermore, because the photonic crystal hydrogel-based thermochromic window combines a photonic crystal structure with structural colors on the basis of a temperature-sensitive hydrogel, the thermochromic window of this invention offers more diverse window color change effects compared to the ordinary thermochromic window in CN 114573756 B, providing both temperature indication and privacy protection, significantly enhancing its practicality.

[0161] Chinese invention patent application CN104129121A utilizes metal oxides such as VO2 to prepare thermochromic windows. Compared with this, the present invention has a lower phase transition temperature range, can achieve thermochromic effect at a lower temperature, and avoids the influence of the inherent color of metal oxides on the aesthetics of thermochromic windows.

[0162] In summary, this invention combines a photonic crystal structure with a temperature-sensitive hydrogel to create a smart window whose color adapts to temperature, overcoming the limitation of ordinary thermochromic windows with their limited color-changing effect. Furthermore, the introduction of transparent conductive oxide nanoparticles, combined with the temperature-sensitive hydrogel, endows this thermochromic window with excellent infrared shielding properties, improving upon the previous problems of difficult and slow color-changing in low-temperature conditions such as winter.

[0163] It should be noted that the embodiments of the present invention are not limited to the above-described examples. Various changes and modifications can be made to the present invention without departing from the spirit and scope thereof. All such changes and modifications fall within the scope of protection of the present invention as defined by the claims.

Claims

1. A photonic crystal hydrogel-based thermochromic smart window material, characterized in that, The three-dimensional photonic crystal structure is obtained by filling a three-dimensional photonic crystal structure with a thermosensitive hydrogel prepolymer and then curing it. The thermosensitive hydrogel prepolymer is obtained by ultrasonically dispersing a thermosensitive monomer, modified cellulose, and crosslinking agent in deionized water, stirring under ice bath conditions until completely dissolved, adding an initiator and stirring until dissolved, and then adding N,N,N',N'-tetramethylethylenediamine and stirring evenly. The thermosensitive monomer has both hydrophilic and hydrophobic groups, and the LCST is -5~70 °C. The three-dimensional photonic crystal structure is obtained by coating a modified colloidal crystal, obtained by adding a transparent conductive oxide nanoparticle dispersion to a colloidal crystal, onto a carrier by a blade coating or spin coating method. The colloidal crystal is obtained by pre-assembling the colloidal particle dispersion on the tube wall after centrifugation. The amounts of the thermosensitive monomer, crosslinking agent, and initiator are 7-15 wt%, 0.05-0.1 wt%, and 0.2-0.3 wt% of the raw material of the thermosensitive hydrogel prepolymer, respectively. The mass ratio of the thermosensitive monomer to the modified cellulose is 10:1-40:1, and the molar ratio of N,N,N',N'-tetramethylethylenediamine to the initiator is 2:1-1:

1. The mass ratio of the three-dimensional photonic crystal structure to the thermosensitive hydrogel prepolymer is 7-12:

100. The transparent conductive oxide nanoparticles are one or more of indium tin oxide, antimony tin oxide, and zinc aluminum oxide; the modified cellulose is obtained by esterification or etherification of cellulose.

2. The photonic crystal hydrogel-based thermochromic smart window material according to claim 1, characterized in that, The thermosensitive monomer is one or more of N-isopropylacrylamide, N-tert-butylacrylamide, N,N-diethylacrylamide, N-propylacrylamide, and N,N-dimethylacrylamide.

3. The photonic crystal hydrogel-based thermochromic smart window material according to claim 1, characterized in that, The modified cellulose is one or more of methylcellulose, carboxymethylcellulose, hydroxypropylcellulose, and hydroxypropylmethylcellulose.

4. The photonic crystal hydrogel-based thermochromic smart window material according to claim 1, characterized in that, The crosslinking agent is one or more of N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, and allyl methacrylate; the initiator is one or more of ammonium persulfate, potassium persulfate, and sodium persulfate; the colloidal particle dispersion is prepared by dispersing colloidal particle powder in deionized water; the colloidal particles are polystyrene microspheres, polymethyl methacrylate microspheres, SiO2 microspheres, or TiO2 microspheres.

5. The photonic crystal hydrogel-based thermochromic smart window material according to claim 4, characterized in that, The colloidal particles account for 20-30 wt% of the dispersion; the particle size of the colloidal particles is 160-280 nm.

6. The photonic crystal hydrogel-based thermochromic smart window material according to claim 1, characterized in that, The curing temperature is 4~15 °C, and the curing time is 12~24 h; the stirring process involving stirring until completely dissolved under ice bath conditions, adding the initiator and stirring until dissolved, and adding N,N,N',N'-tetramethylethylenediamine is all done using magnetic stirring at a speed of 500-1000 rpm; the stirring time for adding N,N,N',N'-tetramethylethylenediamine is 30~60 s; the ultrasonic dispersion time is 60~120 min; the centrifugation speed is 4000~8000 rpm, and the centrifugation time is 40~60 min; the carrier is glass.

7. The method for preparing the photonic crystal hydrogel-based thermochromic smart window material according to any one of claims 1-6, characterized in that... Includes the following steps: (1) Centrifuge the colloidal particle dispersion until pre-assembled layers of different colors are formed on the wall of the centrifuge tube to obtain colloidal crystals; (2) Add transparent conductive oxide nanoparticles to the colloidal crystal in step (1) and disperse by ultrasonication to obtain modified colloidal crystal; (3) Modified colloidal crystals are self-assembled on a carrier by scraping or spin coating to form a periodically ordered three-dimensional photonic crystal structure; (4) Add the thermosensitive monomer, modified cellulose and crosslinking agent to deionized water, disperse by ultrasonication, and stir under ice bath conditions until the monomer is completely dissolved. Add the initiator and stir until dissolved. Add the catalyst N,N,N',N'-tetramethylethylenediamine and stir evenly to obtain the thermosensitive hydrogel prepolymer. (5) After filling the three-dimensional photonic crystal structure obtained by self-assembly on the carrier in step (3) with the thermosensitive hydrogel prepolymer liquid from step (4), solidify it to obtain the photonic crystal hydrogel-based thermochromic smart window material.

8. The application of the photonic crystal hydrogel-based thermochromic smart window material according to any one of claims 1-6 in the preparation of smart windows.

Images