Highly transparent passive temperature regulating single layer thermochromic window and method of making and use thereof

Abstract

The application discloses a kind of high light transmission passive temperature regulating single-layer thermochromic windows and its preparation method and application.The high light transmission passive temperature regulating single-layer thermochromic window includes transparent glass substrate, light adjusting layer and encapsulation layer which are sequentially stacked;Light adjusting layer is the hydrogel network formed by polymerization reaction of N-isopropyl acrylamide, N,N-dimethyl acrylamide and 2-hydroxyethyl acrylate mixed monomers in the presence of crosslinking agent and initiator;The modulation amplitude of solar transmittance of light adjusting layer is 80~90%;Encapsulation layer is used to block the transmission of water vapor and small molecules.The present application constructs uniform transparent network through PNIPAm-DMAA-HEA synergistic copolymerization, so that the visible light transmittance of material in transparent state is stable more than 97%;Reversible phase separation occurs after warming and forms efficient scattering structure, and the transmittance is reduced to below 20%, which can realize passive cooling effect above 6℃.

Description

Technical Field

[0001] This invention belongs to the field of intelligent dimming materials and building energy conservation, and particularly relates to a high-transmittance passive temperature-regulating single-layer thermochromic window, its manufacturing method and application. Background Technology

[0002] With the increasing demands for energy conservation and comfort in the construction, transportation, and agriculture sectors, smart windows that can automatically adjust incident light and heat according to environmental changes have gradually become a research and application hotspot. Among these, thermochromic materials, due to their temperature-driven operation and ability to achieve optical control without external energy consumption, are considered an ideal approach to realizing passively temperature-controlled smart windows. Existing thermochromic window materials include VO2 thin films, metal oxide doped systems, and polymer gels, with hydrogels attracting attention due to their excellent optical transparency, tunable structural design, and adjustable response temperature range. However, the development of hydrogel-based smart windows is still constrained by limitations in their structural design, mechanical properties, and fabrication methods, and a mature system suitable for widespread commercial use has not yet been established.

[0003] Currently, most hydrogel smart windows employ a double-glass sandwich structure, where thermochromic gel is sandwiched between two panes of glass, forming a light-adjusting window through lamination equipment and adhesives. While this structure can achieve a certain degree of transparency-to-shade conversion, it has significant drawbacks: First, the sandwich structure is complex to manufacture, requiring multiple defoaming, lamination, and curing steps, resulting in high production costs and difficulty in achieving roll-to-roll or continuous production, hindering large-scale adoption. Second, the presence of multiple interfaces causes light to undergo multiple refractions, scattering, or absorptions in the transparent state, resulting in visible light transmittance generally below 80-85%, failing to meet the building's demand for natural lighting. Furthermore, traditional hydrogels have weak mechanical properties and cannot form films independently on the glass surface, requiring glass clamping to maintain structural stability, further limiting design freedom. More importantly, hydrogels are prone to water loss, aging, and the presence of volatile small molecules, making them susceptible to shrinkage, discoloration, or odor development during long-term outdoor use, necessitating effective encapsulation to ensure durability.

[0004] In summary, existing smart window technologies struggle to simultaneously meet key application requirements such as high light transmittance (high transmittance in the transparent state), efficient passive temperature regulation, simplified structure, high mechanical stability, large-area mass production potential, and excellent long-term weather resistance. Therefore, there is an urgent need to develop a new thermochromic hydrogel smart window material. By improving the material's mechanical properties, it can be directly coated onto the surface of a single pane of glass to form a stable functional layer, avoiding the traditional sandwich structure. Simultaneously, structural design and encapsulation technologies are needed to improve the transmittance in the transparent state, thermal regulation efficiency, and outdoor lifespan, thereby achieving a low-cost, simplified, and easily industrialized smart window solution. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a high-transmittance passively temperature-controlled single-layer thermochromic window, its manufacturing method, and its application.

[0006] The objective of this invention is achieved through the following technical solution: A single-layer thermochromic window with high light transmittance and passive temperature control includes a transparent glass substrate, a dimming layer and an encapsulation layer stacked sequentially. The light-modulating layer is a hydrogel network formed by the polymerization reaction of a mixture of N-isopropylacrylamide, N,N-dimethylacrylamide, and 2-hydroxyethyl acrylate monomers in the presence of a crosslinking agent and an initiator; the solar transmittance modulation range of the light-modulating layer is 80-90%. The encapsulation layer is used to block the permeation of water vapor and small molecules.

[0007] The preparation method of the above-mentioned high-transmittance passively temperature-controlled single-layer thermochromic window includes the following steps: A hydrogel precursor solution was obtained by adding a crosslinking agent, water, and an initiator to a mixture of N-isopropylacrylamide (NIPAm), N,N-dimethylacrylamide (DMAA), and 2-hydroxyethyl acrylate (HEA) as monomers. The hydrogel precursor liquid is coated on the surface of the transparent glass substrate and allowed to stand at room temperature to form a film, thus obtaining the dimming layer. By attaching the encapsulation layer to the surface of the dimming layer, a single-layer thermochromic window with high light transmittance and passive temperature control is obtained.

[0008] Preferably, in the preparation step of the hydrogel precursor solution, the mass ratio of N-isopropylacrylamide, N,N-dimethylacrylamide, 2-hydroxyethyl acrylate and water is 1.6:045~0.65:0.10~0.20:8~10.

[0009] Preferably, in the preparation step of the hydrogel precursor solution, the amount of the crosslinking agent is 0.4~1.0 wt% of the total monomer.

[0010] Preferably, the crosslinking agent is N,N'-methylenebisacrylamide (MBA).

[0011] Preferably, the preparation step of the hydrogel precursor solution also includes 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), the amount of which is 1 to 5 wt% of the total monomer.

[0012] Preferably, in the preparation step of the hydrogel precursor solution, the initiator includes sodium bisulfite (NaHSO3) and ammonium persulfate (APS); the molar ratio of sodium bisulfite to ammonium persulfate is 1:1~2, and the amount of ammonium persulfate is 0.3~1.7 mol of the total molar amount of the monomer.

[0013] Preferably, in the preparation step of the dimming layer, the hydrogel precursor liquid is coated on the surface of the transparent glass substrate to form a wet film of 100~300μm.

[0014] Preferably, in the preparation step of the dimming layer, the hydrogel precursor liquid is coated onto the surface of the transparent glass substrate by scraping, spraying, or roller coating.

[0015] Preferably, in the preparation step of the dimming layer, the film formation at room temperature refers to allowing the coating layer to stand at 20~30℃ for 0.5~12h to form a dry film of 50~200μm in situ.

[0016] Preferably, the encapsulation layer is made of polyvinylidene chloride and has a thickness of 20~40μm.

[0017] The above-mentioned high-transmittance passive temperature-regulating single-layer thermochromic window is used in the manufacture of energy-saving windows for buildings, vehicle windows, or light transmission and temperature regulation systems for agricultural greenhouses.

[0018] Compared with the prior art, the beneficial effects of the present invention include: (1) The present invention constructs a uniform transparent network by synergistic copolymerization of PNIPAm-DMAA-HEA, so that the visible light transmittance of the smart window in the transparent state is stable at more than 97%; after heating, the material undergoes reversible phase separation and forms an efficient scattering structure, the transmittance drops to below 20%, the solar radiation modulation exceeds 80%, and a passive cooling effect of more than 6°C can be achieved. It has significant energy-saving and temperature-regulating capabilities under different climatic conditions.

[0019] (2) The present invention utilizes hydrogen bond enhancement and covalent cross-linking to form a stable three-dimensional network, so that the film still has sufficient mechanical strength and adhesion in the range of 50~200μm. It can be directly coated on the surface of a single glass without the need for traditional sandwich structure, which significantly simplifies the configuration of smart window, reduces manufacturing cost, and facilitates continuous and large-area preparation, with outstanding engineering feasibility.

[0020] (3) This invention reduces the residual volatile small molecules in the material through formulation purification and structural regulation, and effectively restricts the migration of moisture and small molecules by combining a polyvinylidene chloride (PVDC) high-barrier encapsulation layer, so that the coating remains stable and basically odorless during long-term use; at the same time, the encapsulation layer significantly improves the material's anti-aging, anti-drying and anti-pollution capabilities, so that the smart window can still maintain excellent optical control performance and mechanical integrity in environments such as high temperature, humid heat and long-term sunlight, thereby greatly extending its outdoor service life. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the mold for the PDH smart window prepared in Example 1. Figure 2 This is a schematic diagram of the structure of the PHPF smart window prepared in Example 1.

[0022] Figure 3 These are photographs of the PDH smart window described in Example 2, in both transparent and completely opaque states.

[0023] Figure 4 This is a transmittance curve of the solar band for the PDH smart window described in Example 2, in both transparent and completely opaque states. Figure 5 This is a photograph of the actual response process of the PDH smart window described in Example 3, which completes the reversible process of "transparency-opaqueness".

[0024] Figure 6 The figures show stress-strain diagrams for P-hydrogel, PD-hydrogel, and PDH-hydrogel, with the inset showing the adhesion strength test diagram of PDH-hydrogel on the glass surface.

[0025] Figure 7 Comparison curves of the quality stability test between the PHPF smart window (PHPF SW) prepared in Example 1 and the PHF smart window (PHF SW) prepared in Comparative Example 4.

[0026] Figure 8 This is a comparison chart of GC-MS analysis of the PHPF smart window (PHPF SW) prepared in Example 1 and the PHF smart window (PHF SW) prepared in Comparative Example 4.

[0027] Figure 9 Photos of the PHPF smart window (PHPF SW) prepared for Example 1, the conventional single-layer transparent glass of Comparative Example 5, and the Low-E glass of Comparative Example 6 in outdoor scene experiments.

[0028] Figure 10 The indoor temperature change curves of the PHPF smart window (PHPF SW) prepared in Example 1, the conventional single-layer transparent glass of Comparative Example 5, and the Low-E glass of Comparative Example 6 in an outdoor scene experiment within one day. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0030] Thermochromic materials, due to their temperature-driven nature and ability to achieve optical modulation without external energy consumption, are considered an ideal approach to realizing passively temperature-controlled smart windows. Among existing thermochromic window materials, the development of hydrogel-based smart windows is still limited by their structural design, mechanical properties, and preparation methods, and a mature system that can be widely used commercially has not yet been formed.

[0031] Currently, most hydrogel smart windows are double-glass sandwich structures, which sandwich thermochromic gel between two pieces of glass and form a light-adjusting window through lamination equipment and adhesive. Although this structure can achieve a certain transparency-shading conversion, it has the following obvious defects: (1) The sandwich structure process is complicated, the production cost is high, and it is difficult to achieve roll-to-roll or continuous preparation; (2) The presence of multiple interfaces causes light to be refracted, scattered or absorbed multiple times in the transparent state, and the visible light transmittance is generally less than 80~85%, which is difficult to meet the building's demand for natural lighting; (3) The hydrogel has weak mechanical properties and it is difficult to form a film independently on the glass surface. It needs to rely on glass clamping to maintain structural stability; Hydrogel has the characteristics of easy water loss, easy aging and the presence of volatile small molecules. When used outdoors for a long time, it is easy to shrink, discolor or produce odor. Effective encapsulation is required to ensure its durability.

[0032] To address the shortcomings and deficiencies of the existing technology, the present invention provides a high-transmittance passive temperature-controlled single-layer thermochromic window, comprising a transparent glass substrate, a dimming layer, and an encapsulation layer stacked sequentially. The light-modulating layer is a hydrogel network formed by the polymerization reaction of a mixture of N-isopropylacrylamide (NIPAm), N,N-dimethylacrylamide (DMAA), and 2-hydroxyethyl acrylate (HEA) monomers in the presence of a crosslinking agent and an initiator; the solar transmittance modulation range of the light-modulating layer is 80-90%. The encapsulation layer is used to block the permeation of water vapor and small molecules.

[0033] This invention uses PNIPAm (polymerized from NIPAm) as the core thermochromic matrix and introduces hydrophilic monomers such as DMAA and HEA to synergistically construct a uniform and stable polymeric network. This results in a transparent film with extremely low interfacial scattering and excellent visible light transmittance (over 97%). The hydrogen bonding enhancement of DMAA and the flexible segments of HEA not only improve the mechanical properties of the thin film, enabling it to form a self-supporting coating directly on the glass surface, but also significantly reduce the residue of volatile small molecules at the network structure level, thereby reducing the inherent odor of hydrogel materials at their source. Combined with post-treatment and solvent exchange steps, the polymerized and demolded hydrogel film is first immersed in deionized water at constant temperature multiple times to initially remove unreacted monomers and initiator residues. Subsequently, solvent exchange is completed through gradient concentration ethanol-water solutions to gradually extract low molecular weight oligomers and volatile impurities within the network. Finally, vacuum drying completely removes residual solvents and stabilizes the material structure, further ensuring that the material remains "virtually odorless" during long-term use, thus meeting the high-level air quality requirements of buildings and residential environments.

[0034] The preparation method of the above-mentioned high-transmittance passively temperature-controlled single-layer thermochromic window includes the following steps: A hydrogel precursor solution was obtained by adding a crosslinking agent, water, and an initiator to a mixture of N-isopropylacrylamide, N,N-dimethylacrylamide, and 2-hydroxyethyl acrylate as monomers. The hydrogel precursor liquid is coated on the surface of the transparent glass substrate and allowed to stand at room temperature to form a film, thus obtaining the dimming layer. By attaching the encapsulation layer to the surface of the dimming layer, a single-layer thermochromic window with high light transmittance and passive temperature control is obtained.

[0035] This invention employs a process combining wet coating and room-temperature in-situ polymerization. A precursor solution is uniformly applied to a glass substrate, and a rapid gelation and cross-linking curing process is achieved through an initiation system, enabling controllable film thickness, uniformity, and optical quality. To ensure the long-term outdoor stability of the material, this invention further introduces an encapsulation layer on the outer layer of the hydrogel. This layer, with its low water vapor permeability, suppresses water loss, shrinkage, and leakage of volatile substances, thereby significantly extending service life and improving resistance to yellowing, aging, and contamination. This allows the smart window to maintain stable optical control capabilities even under complex environments such as high temperature, humidity, and prolonged sunlight.

[0036] Preferably, in the preparation step of the hydrogel precursor solution, the mass ratio of N-isopropylacrylamide, N,N-dimethylacrylamide, 2-hydroxyethyl acrylate and water is 1.6:045~0.65:0.10~0.20:8~10.

[0037] In some embodiments of the present invention, the mass ratio of N-isopropylacrylamide, N,N-dimethylacrylamide, 2-hydroxyethyl acrylate, and water is 1.6:0.45~0.65:0.10~0.20:8~10; for example, it can be 1.6:0.65:0.1:9. Thus, the present invention uses a monomer with N-isopropylacrylamide as the thermochromic group, and two hydrophilic monomers, N,N-dimethylacrylamide and 2-hydroxyethyl acrylate, to construct a uniform and stable polymeric network through synergistic effects.

[0038] Preferably, in the preparation step of the hydrogel precursor solution, the amount of the crosslinking agent is 0.4~1.0 wt% of the total monomer.

[0039] In some embodiments of the present invention, the amount of crosslinking agent is 0.5 to 1.0 wt% of the total monomer; for example, it can be 0.4 wt%. Thus, a suitable amount of crosslinking agent allows the resulting polymeric network to maintain excellent swelling properties while possessing sufficient mechanical strength and stability.

[0040] Preferably, the crosslinking agent is N,N'-methylenebisacrylamide (MBA).

[0041] In some embodiments of the present invention, N,N'-methylenebisacrylamide is selected as the crosslinking agent because it has high crosslinking efficiency, low dosage, and excellent hydrophilicity and biocompatibility; in addition, it is inexpensive and readily available.

[0042] Preferably, the preparation step of the hydrogel precursor solution also includes 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), the amount of which is 1 to 5 wt% of the total monomer.

[0043] In some embodiments of the present invention, the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) is introduced as a functional additive. It can improve the solvation state of polymer segments through ion-hydrogen bonding interactions, promoting the formation of a more uniform and dense hydrogel network structure, thereby significantly improving the visible light transmittance in the transparent state and enhancing the reversibility and stability of the thermally induced phase separation process. Furthermore, BMIMBF4 has low volatility and good water retention capacity, effectively slowing down the water loss rate of the hydrogel in the air environment and improving the long-term thermochromic durability of the material under outdoor conditions.

[0044] Preferably, in the preparation step of the hydrogel precursor solution, the initiator includes sodium bisulfite (NaHSO3) and ammonium persulfate (APS); the molar ratio of sodium bisulfite to ammonium persulfate is 1:1~2, and the amount of ammonium persulfate is 0.3~1.7 mol of the total molar amount of the monomer.

[0045] In some embodiments of the present invention, the amount of ammonium persulfate is 0.3 to 1.7 mol% of the total molar amount of monomer; for example, it can be 1.62 mol%. This ratio can ensure a faster polymerization rate and a higher conversion rate, while avoiding excessive polymer molecular weight or excessive side reactions due to excessive initiator.

[0046] Preferably, in the preparation step of the dimming layer, the hydrogel precursor liquid is coated on the surface of the transparent glass substrate to form a wet film of 100~300μm.

[0047] Preferably, in the preparation step of the dimming layer, the hydrogel precursor liquid is coated onto the surface of the transparent glass substrate by scraping, spraying, or roller coating.

[0048] In some embodiments of the present invention, the coating method is a continuous mode such as scraping, spraying, or roller coating, which facilitates large-area, low-cost mass production.

[0049] Preferably, in the preparation step of the dimming layer, the film formation at room temperature refers to allowing the coating layer to stand at 20~30℃ for 0.5~12h to form a dry film of 50~200μm in situ.

[0050] Preferably, the encapsulation layer is made of polyvinylidene chloride (PVDC) and has a thickness of 20~40μm.

[0051] The high-barrier encapsulation layer (PVDC) introduced in this invention plays a crucial role in improving overall performance. By significantly reducing the permeation rate of water vapor and low-molecular-weight substances, it effectively inhibits water loss, shrinkage, and the release of volatile residues from the hydrogel, enabling the material to maintain stable structure and optical properties under outdoor service conditions and remain virtually odorless over a long period. The addition of encapsulation not only extends the lifespan of the hydrogel dimming layer but also ensures air quality safety when the smart window is used in civil buildings and transportation applications.

[0052] The above-mentioned high-transmittance passive temperature-regulating single-layer thermochromic window is used in the manufacture of energy-saving windows for buildings, vehicle windows, or light transmission and temperature regulation systems for agricultural greenhouses.

[0053] The single-layer thermochromic window material prepared by this invention maintains extremely high light transmittance in its transparent state. As the temperature rises to the response range, reversible phase separation occurs within the material, rapidly forming a microscale scattering structure. This causes the transmittance to decrease rapidly from >97% to <20%, while modulating solar radiation by over 80%, achieving a significant cooling effect without energy consumption. Thanks to uniform film formation and the material's excellent adhesion, the coating exhibits stable adhesion to the glass surface, making it resistant to peeling or cracking.

[0054] Example 1 A method for preparing a high-transmittance, passively temperature-controlled single-layer thermochromic window, the specific steps of which are as follows: (1) Thoroughly clean the glass substrate (5mm thick, with a visible light transmittance ≥91.5%, preferably a commercially available product with a transmittance of 91.5%~92.5%, purchased from JD.com Hardware Tools Specialty Store) to ensure stable adhesion of the subsequent coating: Rinse with deionized water and dry, then thoroughly remove organic contaminants from the surface of the glass substrate with ethanol or isopropanol. Subsequently, set a 1.0mm gap strip at the edge of the glass to control the final hydrogel film thickness. After the substrate treatment is completed, start preparing the precursor solution. Place 9.00g of ultrapure water on a stirrer, add NIPAm (1.60g) and DMAA (0.65g) in sequence and dissolve them completely, then add BMIMBF4 (0.10mL) to make the system uniform. Then add crosslinking agent MBA (0.010g) and HEA (0.100g) and continue stirring until completely mixed. After ensuring the solution is homogeneous, APS (0.08g) and NaHSO3 (0.04g) are added to obtain the precursor liquid, forming a redox initiation system to initiate the free radical polymerization reaction. After this, the coating stage should be started quickly to avoid premature gelation of the solution.

[0055] (2) Quickly pour the precursor solution that has just started polymerization into the preset mold and directly coat it onto the surface of the treated glass substrate. Use a flat plate to control the wet film thickness to 100 μm. After coating, gently remove air bubbles to ensure that the film surface is uniform and flat. Place the cast film at room temperature for 12 h to allow the hydrogel to fully gel and form a stable network. In the laboratory characterization stage, after gel solidification, the hydrogel film can be carefully removed and repeatedly washed with ultrapure water at least three times (soaking for 10-30 min each time) to remove soluble impurities such as unreacted monomers, residual initiators, and ionic liquids. Then, it is lightly dried at room temperature or 40°C until there is no free water on the surface. In actual smart window applications, the precursor solution can be directly coated onto the surface of the glass substrate and cured in situ to form a film. The hydrogel layer forms a stable bond with the glass. This structure is subsequently covered and sealed by a PVDC film (10 μm thick) to isolate the migration of residual small molecules, so there is no need for a demolding and cleaning step. The hydrogel prepared in Example 1 is referred to as PDH hydrogel, and the high-transmittance passively temperature-controlled single-layer thermochromic window prepared therefrom is referred to as PHPF smart window (PHPF SW).

[0056] Figure 2 This is a schematic diagram of the PHPF smart window prepared in Example 1. From... Figure 2 We can see that the PHPF smart window includes a transparent glass plate, a dimming layer and an encapsulation layer stacked in sequence; the dimming layer is a PDH hydrogel film and the encapsulation layer is a PVDC encapsulation film.

[0057] Example 2 Ultraviolet-Visible-Near Infrared Transmittance Test (Spectral Transmittance, 200~2500nm) Characterizes wavelength-dependent transmittance in both transparent and opaque states, used to calculate visible light transmittance (T0). lum ), solar transmittance (T) sol ) and solar modulation capability (ΔT) sol Before testing, the sample was cut to fit the sample holder and its thickness was measured, with air used as a baseline control. Measurements were performed using a UV-Vis-NIR spectrophotometer with a coverage of 200–2500 nm and equipped with an integrating sphere. Instrument calibration was completed first, and the baseline was recorded. Subsequently, measurements were taken at low temperatures (room temperature or below the phase transition temperature τ). c ) Measure the transmittance spectrum T in the range of 200~2500 nm low (λ), and then the sample is heated to a high temperature state (above τ). c (Using a constant temperature water bath) and collecting the corresponding transmittance spectrum T after the temperature stabilizes. high (λ). Each temperature condition was tested three times, and the average value was taken. Complete spectral curves, test temperatures and times, sample thickness, and other information were recorded. Finally, the transmittance spectrum was integrated according to the AM1.5G standard solar spectrum to calculate the visible light transmittance T. lum (380~750nm) and solar transmittance T sol (200~2500nm), and further calculate the solar modulation amount ΔT. sol =T sol,low -T sol,high At the same time, the integration interval and the solar spectrum standard adopted are clearly defined.

[0058] Figure 3 These are photographs of the PDH smart window described in Example 2, showing it in both transparent and completely opaque states. Figure 3 As shown, at 2 PM, the outdoor ambient temperature was higher than the phase transition temperature of the hydrogel, which induced reversible phase separation and the formation of a micron-scale scattering structure in the hydrogel, resulting in a significant decrease in light transmittance and the material becoming opaque. However, at 6 PM, as the ambient temperature dropped below the phase transition temperature, the hydrogel returned to a completely transparent state.

[0059] The test results are as follows: By measuring the spectral transmittance of the PDH hydrogel smart window (i.e., the PHPF SW prepared in Example 1) in the 200~2500nm wavelength range, a significant optical switching behavior between the low-temperature transparent state and the high-temperature scattering state can be clearly observed. Under low-temperature conditions (T<τ... c The sample maintains a highly uniform hydrogel network structure with extremely low light scattering. Its visible light transmittance remains above 97% throughout the 380–750 nm range, exhibiting near-completely transparent optical properties. Figure 4 As shown. When the temperature rises above the phase transition temperature τ c At this time, the PNIPAm backbone undergoes reversible phase separation and forms a microscale scattering structure, resulting in a significant decrease in transmittance across the entire spectrum, with visible light transmittance dropping below 20%. This significant spectral change is also reflected in the modulation capability of solar light flux: solar transmittance at low temperatures is significantly higher than at high temperatures, with the difference (ΔT) being substantial. sol The transmittance can reach 80%. Furthermore, the spectral curves show that the transmittance curve at low temperatures is smooth with no obvious scattering peaks, while the high-temperature state exhibits significant transmittance attenuation in both the visible and near-infrared regions. This indicates that the material not only modulates visible light transmission but also possesses a broad-spectrum control capability over total solar energy (UV-Vis-NIR). Repeated tests show good consistency in the spectral morphology of both the transparent and scattering states, with minimal deviation between the three repetitions, indicating stable optical performance and good test repeatability.

[0060] Example 3 Response time test of reversible loop To evaluate the rapid optical switching capability and cycling stability of the PDH smart window (i.e., the PHPF SW prepared in Example 1), the sample was placed in a temperature-controlled hot stage or a rapid hot water bath, and kept in a transparent state (T < τ). c Record its initial transmittance; then rapidly heat the sample to a temperature above τ. c The temperature was monitored, and the transmittance was recorded in real time as it decreased over time to determine the time required for the sample to transition from a transparent state to an opaque steady state. Similarly, the transmittance recovery process was recorded when the sample was rapidly cooled from a high-temperature environment to a low-temperature environment, and the time corresponding to the transmittance recovering to 10% of the initial transparent state threshold was taken as the opaque-to-transparent response time. The experiment was repeated three times and the average was taken to ensure data reliability. Based on this, the sample was subjected to a cyclic switching test, continuously switching between a preset low temperature and a high temperature up to 1000 times, while the time-transmittance curves and transmittance changes at high and low states were recorded in typical cycles to evaluate long-term cyclic stability.

[0061] Test results are as follows Figure 5 As shown, the PDH hydrogel can rapidly complete the "transparent-opaque" phase transition within ten seconds after being heated; the "opaque-transparent" recovery process during cooling is also relatively rapid, with an average response time of about twenty seconds. After thousands of continuous cycles, the bidirectional response time shows no significant change, and the transmittance in the transparent state remains above 90%, without significant attenuation or hysteresis expansion. This indicates that the smart window possesses excellent rapid response characteristics and long-term cycle durability, meeting the repeated dimming needs in actual building environments.

[0062] Comparative Example 1 Comparative Example 1 provides a P-hydrogel, which differs from Example 1 only in that it is a pure PNIPAm system. The preparation steps are as follows: 9.00 g of ultrapure water was placed on a stirrer, 1.60 g of NIPAm was added and fully dissolved, and then 0.10 mL of BMIMBF4 was added to homogenize the system. Subsequently, 0.010 g of crosslinking agent MBA was added and stirring was continued until completely mixed. After ensuring the solution was homogeneous, 0.08 g of APS and 0.04 g of NaHSO3 were added to obtain a precursor fluid, forming a redox initiation system, which initiated a free radical polymerization reaction to obtain the P-hydrogel. The P-hydrogel is a pure PNIPAm (Poly(N-isopropylacrylamide)) system, free of comonomers such as DMAA and HEA. Its network structure mainly relies on the hydrophobic interactions between PNIPAm segments and the formation of a small number of crosslinking points. It has low mechanical strength and is prone to brittle fracture during stretching, making it difficult to meet the toughness requirements for repeated deformation in smart window applications.

[0063] Comparative Example 2 Comparative Example 1 provides a PD hydrogel, which differs from Example 1 only in that it is copolymerized from PNIPAm and DMAA (N,N-dimethylacrylamide). The preparation steps are as follows: 9.00 g of ultrapure water was placed on a stirrer, and 1.60 g of PNIPAm and 0.65 g of DMAA were added sequentially and dissolved completely. Then, 0.10 mL of BMIMBF4 was added to homogenize the system. Subsequently, 0.010 g of crosslinking agent MBA was added and stirring was continued until completely mixed. After ensuring the solution was homogeneous, 0.08 g of APS and 0.04 g of NaHSO3 were added to obtain a precursor fluid, forming a redox initiation system, which initiated a free radical polymerization reaction to obtain the PD hydrogel. The introduction of DMAA enhances the hydrogen bonding interactions of the network, improving its flexibility and deformation resistance to a certain extent, resulting in higher elongation at break and toughness compared to P hydrogels. However, due to the lack of auxiliary network-forming effect of HEA, its overall mechanical properties remain limited, making it difficult to maintain structural stability under large-area coating or long-term cyclic loading conditions.

[0064] Mechanical property testing To evaluate the mechanical stability of hydrogels in practical smart window applications, standard strip samples (according to standard laboratory dimensions) were prepared from P-hydrogel, PD-hydrogel, and PDH-hydrogel (PDH-hydrogel prepared in Example 1). After equilibration under uniform humidity conditions, tensile tests were conducted using an electronic universal testing machine (with a tensile rate set to 10 mm / min). Stress-strain curves were obtained, and the elastic modulus (slope of the linear region), maximum stress, and elongation at break were calculated. The test results are as follows: Figure 6 The display shows that from Figure 6 We can see that the P hydrogel has a low elastic modulus; after adding N,N-dimethylacrylamide, the PD hydrogel network forms more reversible hydrogen bonds and chain segment synergy, and the elastic modulus is similar to that of the P hydrogel, but the extensibility is improved; and after further introducing hydroxyl-containing 2-hydroxyethyl acrylate, the elastic modulus of the PDH hydrogel is significantly improved, indicating that 2-hydroxyethyl acrylate effectively enhances the structural stability of the material by constructing a strong polar hydrogen bond network.

[0065] Meanwhile, to evaluate the adhesion of the hydrogel directly coated on glass, the PDH hydrogel was uniformly coated onto the surface of a standard glass substrate (the transparent glass substrate described in Example 1) and cured into a film. Peel strength tests were conducted using a universal testing machine with a 180° peel fixture. Peel force-displacement curves were recorded at a constant peel rate, and the maximum peel force and average adhesion force were calculated. The test results are as follows: Figure 6 The results show that the average adhesion strength of PDH hydrogel on glass can reach over 50 kPa, which is far superior to the adhesion performance of traditional poly(N-isopropylacrylamide) hydrogel. This is because its polar groups can form a stable hydrogen bond network with the groups on the glass surface, allowing it to be directly coated onto a single pane of glass without an additional adhesive layer. Furthermore, in repeated peel tests, the PDH hydrogel maintained stable adhesion without rapid interfacial debonding, verifying its long-term adhesion reliability in building smart window applications.

[0066] Comparative Example 3 The smart window (PNIPAm SW) was prepared using traditional PNIPAm hydrogel. The preparation steps are as follows: 9.00 g of ultrapure water was placed on a stirrer, 1.60 g of PNIPAm was added and fully dissolved, and then 0.10 mL of BMIMBF4 was added to homogenize the system. Subsequently, 0.010 g of crosslinking agent MBA was added and stirring was continued until completely mixed. After ensuring the solution was homogeneous, 0.08 g of APS and 0.04 g of NaHSO3 were added to obtain the precursor liquid, forming a redox initiation system that initiated a free radical polymerization reaction. This was then rapidly coated onto a monolithic glass substrate. The network structure of this smart window relies primarily on single hydrogen bonds, lacking multiple synergistic cross-linking points, resulting in poor environmental stability. Under outdoor conditions, the smart window is affected by temperature, humidity, and wind speed, leading to rapid moisture evaporation, structural shrinkage and hardening, and a gradual weakening of its thermochromic behavior. Test results show that under average relative humidity of 50% and wind speed of 0.3 m / s, the thermochromic switching capability of the PNIPAm smart window can only be maintained for 60 hours, and the quality retention rate also decreases significantly in the early stages, failing to maintain stable optical control functions, exhibiting typical characteristics of rapid water loss and short lifespan.

[0067] Comparative Example 4 A smart window sample (denoted as PHF SW) was prepared by directly coating a glass substrate with PDH hydrogel. The only difference from Example 1 was that the PVDC high-barrier encapsulation film used in Example 1 was not introduced, nor were any additional barrier encapsulation structures employed. This allowed the hydrogel layer to be directly exposed to the air environment, thus comparing and verifying the impact of encapsulation measures on environmental stability and durability. Although PHF SW possesses superior mechanical properties and thermochromic amplitude, its direct exposure to air inevitably leads to the effects of moisture evaporation and environmental disturbances, causing its optical performance to gradually degrade over time. In outdoor testing (average relative humidity 50%, wind speed 0.3 m / s), PHF SW initially achieved stable solar control capabilities, but as water loss intensified, its light scattering ability and phase separation behavior gradually weakened, and its thermochromic contrast decreased. The results showed that its effective thermochromic lifetime was 120 hours, significantly better than PNIPAm SW, but still insufficient for long-term use. The quality retention rate also decreased significantly in the later stages, indicating that the environmental stability of the unencapsulated PHF SW remains limited.

[0068] Water loss / aging test (quality retention rate and environmental stability) The PHPF smart window (PHPF SW) prepared in Example 1 and the PHF SW prepared in Comparative Example 4 were subjected to quality stability tests. The test steps were as follows: both samples were cut to the same size and their initial mass m0 and initial optical properties were recorded. They were then continuously exposed to an outdoor environment with a temperature cycle of 25-40℃ and a relative humidity of 40%-60%. The temperature of the samples was measured every 12 hours, and their transparent-to-opaque reversible transition behavior was recorded to determine the functional failure time. At the same time, the sample mass m was weighed and the mass retention rate R=m / m0 was calculated. The functional stability and environmental stability of the two samples were comprehensively compared and analyzed to evaluate the effect of the high-barrier encapsulation structure on the durability of the hydrogel smart window. The change in mass over time was recorded and a curve was plotted. The test curve is shown below. Figure 7 As shown. From Figure 7 We can see that PHPF maintained about 90% of its quality during long-term water loss testing, indicating that the packaging strategy significantly improved its environmental stability, optical durability, and actual service life.

[0069] In addition, the test results show that compared with the unencapsulated PHF SW, the PHPF SW can achieve better solar regulation effect during the day, with an average indoor temperature reduction of >3°C, and can maintain a stable thermochromic switching capability for about 264 hours under the same environmental conditions, which is 4.4 times and 2.2 times that of Comparative Example 3 (60 h) and Comparative Example 4 (120 h), respectively. Tests on the suppression of volatile odor substances from PDH hydrogels by encapsulation (GC-MS analysis) To evaluate the effect of encapsulation structure on the release of volatile organic compounds (VOCs) and odor suppression of PDH hydrogels, gas chromatography-mass spectrometry (GC-MS) was used to qualitatively analyze unencapsulated PHF SW (prepared from Comparative Example 4) and the PHPF smart window (PHPF SW) prepared in Example 1 after encapsulation with a high-barrier film. During the test, the samples were placed in sealed sampling containers, and the released volatile components were collected under the same temperature and time conditions. The peak areas of each characteristic peak were normalized to achieve semi-quantitative comparative analysis.

[0070] The above test analysis results are as follows: Figure 8 As shown, from Figure 8 It can be seen that the unencapsulated PDH hydrogel sample exhibited multiple distinct chromatographic peaks with high intensity within the retention time range of 30-40 min, indicating the release of a certain amount of small molecule volatiles from the environment. In contrast, the encapsulated PHPF smart window sample showed a significantly weakened overall chromatographic response, retaining only a few low-intensity characteristic peaks, and the area of ​​the main peaks was significantly reduced. Normalized peak area results showed that the total volatile organic compound release of the encapsulated sample was reduced to less than 30% of the original amount compared to the unencapsulated sample, indicating that the high-barrier encapsulation structure can effectively inhibit the release of residual small molecules and volatile substances from the hydrogel.

[0071] The above results show that by introducing a high-barrier encapsulation layer, not only can the odor release level of PDH hydrogel be significantly reduced, improving its environmental friendliness and comfort in indoor application scenarios, but it can also further enhance the safety and acceptability of the material in actual building smart window applications, providing an important guarantee for its large-scale application.

[0072] Comparative Example 5 Comparative Example 5 uses commercially available single-layer transparent glass (specifically 5mm thick, with a visible light transmittance ≥91.5%, preferably a commercially available product with a transmittance of 91.5%~92.5%) as the base control window. This glass does not have any dimming, heat insulation, or selective spectral control functions.

[0073] Comparative Example 6 Comparative Example 6 used commercially available Low-E (low-emissivity coated) glass (the Low-E coating was purchased from Jiangxi Kewei Thin Film New Material Co., Ltd., with a thickness of 0.04 mm, and the Low-E glass thickness was 5 mm) as a high-performance control group. Low-E glass relies on a metal or metal oxide film layer to reduce infrared radiation transmission and has a certain heat insulation capability.

[0074] Outdoor real-world scenario testing The PHPF smart window (PHPF SW) prepared in Example 1, the conventional single-pane transparent glass of Comparative Example 5, and the Low-E glass of Comparative Example 6 were installed in three identical test buildings. To ensure comparability, the PHPF smart window used the same conventional single-pane glass as Comparative Example 5 as its substrate. Subsequently, the three test buildings were placed in the same location and under the same environmental conditions for a two-day outdoor test. Photos of the test buildings are available in [link to photo]. Figure 9 .

[0075] The indoor temperature change curves of the three test buildings in the actual outdoor scenario test within one day (day 2 outdoor test) were statistically analyzed, and the results are as follows: Figure 10 As shown. From Figure 10 It can be seen that the average daytime indoor temperature of the PHPF smart window group is around 43℃, which is more than 6℃ lower than that of single-pane glass and more than 2℃ lower than that of Low-E glass, making it the best in terms of cooling effect among the three types of windows. Based on calculations combining temperature difference and measured irradiance data, using single-pane glass as a benchmark, the PHPF smart window can reduce the cooling load by hundreds of kilojoules per square meter under typical sunny conditions, corresponding to an annual energy saving potential of over 100 megajoules per square meter. This meets the "high-level energy saving" standard in the field of building energy conservation, fully verifying the efficient solar regulation capabilities and significant energy-saving application value of the PHPF smart window.

[0076] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A single-layer thermochromic window with high light transmittance and passive temperature regulation, characterized in that, It includes a transparent glass substrate, a dimming layer, and an encapsulation layer stacked in sequence; The light-modulating layer is a hydrogel network formed by the polymerization reaction of a mixture of N-isopropylacrylamide, N,N-dimethylacrylamide, and 2-hydroxyethyl acrylate monomers in the presence of a crosslinking agent and an initiator; the solar transmittance modulation range of the light-modulating layer is 80-90%. The encapsulation layer is used to block the permeation of water vapor and small molecules.

2. The method for preparing the high-transmittance passively temperature-controlled single-layer thermochromic window according to claim 1, characterized in that, Includes the following steps: A hydrogel precursor solution was obtained by adding a crosslinking agent, water, and an initiator to a mixture of N-isopropylacrylamide, N,N-dimethylacrylamide, and 2-hydroxyethyl acrylate as monomers. The hydrogel precursor liquid is coated on the surface of the transparent glass substrate and allowed to stand at room temperature to form a film, thus obtaining the dimming layer. By attaching the encapsulation layer to the surface of the dimming layer, a single-layer thermochromic window with high light transmittance and passive temperature control is obtained.

3. The method for preparing the high-transmittance passively temperature-controlled single-layer thermochromic window according to claim 2, characterized in that, In the preparation step of the hydrogel precursor solution, the mass ratio of N-isopropylacrylamide, N,N-dimethylacrylamide, 2-hydroxyethyl acrylate and water is 1.6:045~0.65:0.10~0.20:8~10.

4. The method for preparing a high-transmittance, passively temperature-controlled single-layer thermochromic window according to claim 2, characterized in that, In the preparation step of the hydrogel precursor solution, the amount of the crosslinking agent is 0.4~1.0 wt% of the total monomer; and / or The crosslinking agent is N,N'-methylenebisacrylamide.

5. The method for preparing a high-transmittance, passively temperature-controlled single-layer thermochromic window according to claim 2, characterized in that, The preparation step of the hydrogel precursor solution also includes 1-butyl-3-methylimidazolium tetrafluoroborate, which is added in an amount of 1 to 5 wt% of the total monomer.

6. The method for preparing a high-transmittance, passively temperature-controlled single-layer thermochromic window according to claim 2, characterized in that, In the preparation step of the hydrogel precursor solution, the initiator includes sodium bisulfite and ammonium persulfate; the molar ratio of sodium bisulfite and ammonium persulfate is 1:1~2, and the amount of ammonium persulfate is 0.3~1.7 mol of the total molar amount of the monomer.

7. The method for preparing a high-transmittance passively temperature-controlled single-layer thermochromic window according to claim 2, characterized in that, In the preparation step of the dimming layer, the hydrogel precursor solution is coated on the surface of the transparent glass substrate to form a wet film of 100~300μm; and / or The hydrogel precursor liquid is coated onto the surface of the transparent glass substrate by means of scraping, spraying, or roller coating.

8. The method for preparing a high-transmittance, passively temperature-controlled single-layer thermochromic window according to claim 2, characterized in that, In the preparation step of the dimming layer, the film formation at room temperature refers to allowing the coating layer to stand at 20~30℃ for 0.5~12h to form a dry film of 50~200μm in situ.

9. The method for preparing a high-transmittance, passively temperature-controlled single-layer thermochromic window according to claim 2, characterized in that, The encapsulation layer is made of polyvinylidene chloride and has a thickness of 20~40μm.

10. The application of the high-transmittance passive temperature-regulating single-layer thermochromic window of claim 1 in the manufacture of light-transmittance and temperature-regulating systems for building energy-saving windows, vehicle windows, or agricultural greenhouses.

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