MAC intelligent window and preparation method thereof

Abstract

The invention relates to an intelligent window, in particular to an MAC intelligent window and a preparation method thereof. According to the MAC intelligent window developed by the invention, an anti-freezing hydrogel electrolyte is adhered to the intelligent window based on a UCST mechanism and is combined with cesium tungsten bronze (Cs0. 33WO3) to form a novel intelligent window, and the problem that a traditional thermochromic intelligent window cannot give consideration to energy saving, privacy protection and long-term stability is effectively solved. The P (AM-co-AA) hydrogel disclosed by the invention has excellent adhesion performance, and the optimal adhesion strength of the P (AM-co-AA) hydrogel on glass can reach 0.43 MPa; and meanwhile, KCl endows the P (AM-co-AA) hydrogel with excellent freezing resistance, and the MAC intelligent window has long-term stability due to good adhesion and freezing resistance, and does not have obvious light transmittance fluctuation after 100 cycles. In an outdoor test, the MAC intelligent window shows excellent refrigeration performance, and compared with a common window, the MAC intelligent window has the advantages that the maximum refrigeration effect can reach 3.2 DEG C, and the annual average energy is saved by 163.82 MJ m <-2 >.

Description

Technical Field

[0001] This invention relates to smart windows, and more particularly to a MAC smart window and its manufacturing method. Background Technology

[0002] With the continuous growth of global energy consumption, building energy consumption accounts for approximately 40% of the total global energy consumption. Windows are among the least energy-efficient components of building structures. To save energy as much as possible, smart windows capable of flexibly changing optical properties have been designed. Based on different external stimuli, smart windows can be categorized into thermochromic windows, electrochromic windows, mechanochromic windows, and photochromic windows. Among them, thermochromic windows dynamically adjust their transparency through temperature changes caused by sunlight, requiring no additional energy input, making them not only low-cost but also effectively energy-saving. Currently, some thermochromic windows are mainly based on inorganic thermochromic materials. However, the phase transition temperatures of these materials are generally higher than the conventional ambient temperature range, limiting their practical application under normal climatic conditions. Thermochromic hydrogels are considered ideal candidate materials for smart windows due to their good tunability of transition temperatures and low cost. However, traditional hydrogels have weak adhesion and are not freeze-resistant, greatly limiting their application in smart windows.

[0003] Currently, most thermochromic hydrogel smart windows achieve optical modulation primarily based on the low critical solution temperature (LCST) mechanism. When the ambient temperature is high, these smart windows become opaque to block sunlight, thus regulating the temperature. For example, smart windows based on PNIPAm hydrogels have achieved visible light transmittance as high as 91.3% (T0). lum ) and 88.84% solar modulation capability (ΔT) sol The PHPA smart windows prepared by Zhu et al. exhibit good solar modulation capabilities (1-93%) and fast light response speeds (from seconds to tens of seconds). However, the opaque state of these LCST smart windows during the day hinders the transmission of natural sunlight, leading to the need for additional lighting energy in the room and thus increasing energy consumption. Furthermore, they become transparent at night (at low ambient temperatures), failing to provide nighttime privacy.

[0004] In contrast, thermochromic hydrogels with an upper critical solution temperature (UCST) can meet these requirements. These hydrogels remain transparent at high temperatures and become opaque at low temperatures. From a thermodynamic perspective, this phase separation phenomenon is caused by the Gibbs free energy (ΔG). m =ΔH m -TΔS m The change in ΔG determines this. m When the value is greater than 0, the system tends to undergo phase separation. The difference between UCST and LCST is essentially due to the enthalpy change (ΔH) in the Gibbs free energy change.m ) and entropy change (ΔS) m The competition mechanism between them. The behavior of LCST is mainly determined by ΔS. m Drive, TΔS m (ΔS m <0, -TΔS m The term >0) dominates at high temperatures and increases sharply with increasing temperature. When |TΔS m |Exceeds|ΔH m |When, ΔG m It becomes positive and entropy-driven phase separation occurs. This is mainly due to ΔS. m The LCST behavior of the driven components differs, while the UCST behavior is mainly determined by ΔH. m This is caused by the weaker interaction between polymer chains and water molecules at low temperatures (ΔH). m >0, endothermic effect). Due to the effect of low temperature, TΔS m The contribution of the term is limited, and the phase transition is ΔH m Primarily. When |ΔH m |Exceeds|TΔS m |When, ΔG m When the temperature changes to positive, enthalpy-driven phase separation occurs, and the hydrogel becomes opaque. Therefore, unlike traditional LCST hydrogel smart windows, UCST hydrogel smart windows can meet the dual requirements of energy saving and privacy protection. For example, Lai et al. developed a bidirectional temperature-sensitive smart window using acrylamide (AM), acrylic acid (AA), and N-isopropylacrylamide (NIPAM). This innovation simultaneously achieves energy saving and privacy protection effects for smart windows. However, this type of smart window only has high transparency within a specific temperature range, which limits its practical application. Long and colleagues also proposed a UCST smart window composed of polyethylene (PE) sheets, UCST zwitterionic hydrogels, and silver nanowires (Ag NWs). This smart window can not only balance appropriate light transmittance and cooling effect during the day, but also provide privacy protection at night. However, the preparation process of Ag NWs is complex and costly, making it unsuitable for large-scale applications. At the same time, the adhesion and antifreeze properties of the hydrogels in the above-mentioned smart windows are poor, and insufficient adhesion and antifreeze properties of the hydrogels will lead to poor long-term stability of the smart window. Therefore, existing smart windows struggle to balance the multiple requirements of visibility, energy saving, privacy protection, and long-term stability.

[0005] Here, this application develops a temperature-dependent phase-separation adhesive antifreeze hydrogel electrolyte and assembles it into a novel smart window that is transparent and cool during the day, opaque at night to protect privacy, and possesses long-term stability. The smart window structure consists of a glass sheet, P(AM-co-AA) hydrogel, and cesium tungsten bronze (Cs). 0.33The composition is WO3. Among them, the P(AM-co-AA) hydrogel possesses solar modulation capability (ΔT) due to the upper critical solution temperature (UCST) mechanism. sol ) and adjustable transition temperature (T c ); Cs 0.33 WO3 effectively blocks near-infrared radiation. Adjusting the monomer ratio of the hydrogel improved its solar light modulation capability and allowed for regulation of the critical transition temperature. The fabricated smart window achieved good visible light transmittance during the day (T0). lum ≥70.12%), solar modulation capability (ΔT) sol ≥70.1%) and extremely low near-infrared transmittance (T NIR With a transmittance of ≤0.6%, it provides good visibility and suppresses thermal gain, becoming opaque at night to offer privacy. Thanks to the excellent adhesion and freeze-thaw resistance of the P(AM-co-AA) hydrogel, the smart window maintained essentially unchanged transmittance after 100 cycles of transmittance switching tests and being placed outdoors for 15 days, demonstrating excellent reversibility and long-term stability. In outdoor tests, the smart window achieved a maximum cooling effect of 3.2°C compared to a normal window. Simulation experiments were conducted in three cities with different climates—Dalian, Shanghai, and Guangzhou—and the simulation results showed significant energy-saving effects using the smart window. This opens a new path for developing novel smart windows that can meet the energy-saving needs and privacy protection under different climatic conditions, contributing to global building energy conservation and promoting a low-carbon economy. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, this invention provides a MAC smart window and its preparation method.

[0007] This invention is achieved through the following technical solution:

[0008] In a first aspect, the present invention provides a MAC smart window, the smart window structure of which consists of a glass sheet, P(AM-co-AA) hydrogel, and cesium tungsten bronze Cs. 0.33 Composed of WO3.

[0009] Secondly, the present invention provides a method for preparing a MAC smart window, comprising the following steps:

[0010] Step 1: Preparation of P(AM-co-AA) hydrogel

[0011] P(AM-co-AA) hydrogels were prepared by free radical polymerization. First, acrylamide (AM) and acrylate (AA) were dissolved in 10g of salt solutions of different concentrations at room temperature according to different monomer ratios. Then, 0.1wt% of N,N-methylenebisacrylamide (MBA), a crosslinking agent, was added to the mixture and stirred at room temperature to obtain a homogeneous aqueous solution. Next, 1wt% of α-ketoglutaric acid (KGA), a photoinitiator, was added to the homogeneous aqueous solution and stirred until completely dissolved to obtain a precursor solution. Finally, the precursor solution was injected into a mold and irradiated with ultraviolet (UV) light.

[0012] Step 2: Cs 0.33 WO3 coated glass (glass-Cs) 0.33 Preparation of WO3

[0013] Cs 0.33 A solution of WO3 nanoparticles mixed with acrylic resin and toluene in a mass ratio of toluene:acrylic resin:Cs 0.33 Mix WO3 in a ratio of 0.9:0.85:0.16 and stir further to obtain a uniform dispersion; apply the dispersion onto ordinary glass using a coating machine.

[0014] Step 3: Assemble the Mac Smart Window

[0015] The precursor solution obtained in step 1 was injected into a Cs-type membrane consisting of ordinary glass and silicone rubber as a spacer. 0.33 The MAC smart window is then cross-linked by irradiation with ultraviolet (UV) light in a mold composed of WO3-coated glass.

[0016] Preferably, in step 1, the mass ratio of acrylamide AM to acrylic acid monomer is 9:1, 7:3, 5:5, 3:7, or 1:9.

[0017] Preferably, in step 1, the salt solutions of different concentrations are potassium chloride solutions with concentrations of 0, 1, 2, and 3 M, respectively.

[0018] Preferably, in step 1, the light is irradiated with ultraviolet (UV) light for 10 minutes (365nm, 20W).

[0019] Preferably, in step 2, the depth of the coating machine concave is 22 μm.

[0020] Preferably, in step 3, the thickness of the silicone rubber is 2 mm.

[0021] Preferably, in step 3, the light is irradiated under ultraviolet (UV) light for 15 minutes (365nm, 20W).

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

[0023] This invention develops a MAC smart window based on an adhesive antifreeze hydrogel electrolyte with a UCST mechanism, and incorporates cesium tungsten bronze (Cs). 0.33 The combination of WO3 and other components forms a new type of smart window, which effectively solves the problem that traditional thermochromic smart windows cannot simultaneously achieve energy saving, privacy protection, and long-term stability.

[0024] (1) The transmittance and solar light modulation ability (ΔT) of P(AM-co-AA) hydrogel can be adjusted by changing the monomer ratio. sol ) and critical transition temperature (T c ), Cs 0.33 WO3 can effectively block near-infrared light.

[0025] (2) The manufactured smart window has excellent visible light transmittance (T) during the day. lum ≥70.12%), solar modulation capability (ΔT) sol ≥70.1%) and extremely low near-infrared transmittance (T NIR It has a low visible light transmittance of ≤0.6% and achieves a low visible light transmittance of 0.02% at night, providing privacy protection.

[0026] (3) P(AM-co-AA) hydrogel exhibits excellent adhesion properties, with its optimal adhesion strength on glass reaching 0.43 MPa. Simultaneously, KCl imparts excellent antifreeze properties to the P(AM-co-AA) hydrogel, achieving a conductivity of 3.53 mS / cm at -30℃. -1 Excellent adhesion and freeze resistance give MAC Smart Window long-term stability, with no significant fluctuation in light transmittance after 100 cycles.

[0027] (4) In outdoor testing, the MAC smart window demonstrated excellent cooling performance, achieving a maximum cooling effect of 3.2℃ compared to ordinary windows, with an average annual energy saving of 163.82 MJ / m³. -2 Energy-saving simulation experiments were conducted in three cities with different climates, and the results showed that the energy-saving requirements under different climatic conditions can be met. Attached Figure Description

[0028] The invention will now be further described with reference to the accompanying drawings.

[0029] Figure 1 (a) Schematic diagram of the preparation of hydrogel electrolyte; (b) FTIR spectrum of P(AM-co-AA) hydrogel;

[0030] Figure 2 Transmittance curves of P(AM-co-AA) hydrogels with different monomer concentrations at high temperature (35℃) and low temperature (20℃);

[0031] Figure 3 Effect of different monomer ratios on the transmittance of P(AM-co-AA) hydrogels. (a) Optical images of P(AM-co-AA) hydrogels with different monomer ratios at different temperatures; transmittance curves of P(AM-co-AA) hydrogels with different monomer ratios at (b) 35℃ and (c) 20℃;

[0032] Figure 4 The effect of thickness on the optical properties of hydrogels. (a) Transmittance curves of P(AM-co-AA) hydrogels of different thicknesses; (b) Comparison of transmittance of P(AM-co-AA) hydrogels of different thicknesses at different temperatures;

[0033] Figure 5 The effect of monomer ratio on the transmittance and upper critical dissolution temperature of hydrogels. (a) Infrared spectra of P(AM-co-AA) hydrogels with different monomer ratios; (b) DSC curves of P(AM-co-AA) hydrogels with different monomer ratios.

[0034] Figure 6 Thermochromic mechanism of P(AM-co-AA) hydrogel;

[0035] Figure 7 (a) Optical images of P(AM-co-AA) hydrogel at different temperatures; (b) SEM images of P(AM-co-AA) hydrogel at 35℃ and 20℃, respectively;

[0036] Figure 8 (a) Temperature-dependent rheological spectra of G', G” and tanδ of P(AM-co-AA) hydrogel; XPS spectra of (b) C 1s, (c) O 1s and (d) N 1s of P(AM-co-AA) hydrogel.

[0037] Figure 9 Photos of hydrogels adhering to glass, wood, metal, and rubber;

[0038] Figure 10 The adhesion strength of P(AM-co-AA) hydrogel to different substrates;

[0039] Figure 11 Antifreeze properties of P(AM-co-AA) hydrogel. (a) Tensile photographs of P(AM-co-AA) hydrogel at room temperature and -30°C; (b) DSC curves of P(AM-co-AA) hydrogel with different salt concentrations; (c) Ionic conductivity of P(AM-co-AA) hydrogel at different temperatures;

[0040] Figure 12The structure of the MAC smart window based on P(AM-co-AA) hydrogel electrolyte assembly;

[0041] Figure 13 The light modulation capability of MAC smart windows. (a) Transmittance curves of MAC smart windows with different cesium tungsten bronze contents; (b) transmittance curves and (c) optical photographs of MAC smart windows during the day and at night;

[0042] Figure 14 MAC Smart Window, pure hydrogel, ordinary glass, and glass containing Cs 0.33 Comparison of the optical properties of WO3-coated glass;

[0043] Figure 15 Long-term stability of MAC smart windows. (a) Light transmittance of MAC smart windows at 500 nm after 100 cycles; (b) Light transmittance of MAC smart windows after 84 hours and 15 days; (c) Comparison of light transmittance and sunlight modulation capabilities of this work with other smart windows;

[0044] Figure 16 (a) Schematic diagram of the outdoor temperature measurement device; (b) Photograph of the outdoor temperature measurement device;

[0045] Figure 17 Outdoor temperature test. (a) Relative humidity and light intensity curves in Jinan on the day of temperature measurement; (b) Temperature change curves of three different window types under solar radiation.

[0046] Figure 18 Energy-saving simulation calculation in Jinan. (a) Schematic diagram of the building model used in the energy-saving simulation calculation; (b) Simulation calculation of the energy-saving effects of MAC smart windows, commercial insulated glass and ordinary glass under Jinan's climate conditions;

[0047] Figure 19 Energy-saving effects were simulated in three Chinese cities with significant climate differences. Monthly energy consumption of ordinary glass, commercial insulated glass, and MAC smart windows were calculated under climatic conditions in (a) Dalian, (b) Shanghai, and (c) Guangzhou. Detailed Implementation

[0048] The invention will now be further described with reference to the accompanying drawings.

[0049] Raw materials and reagents

[0050] Table 1 Main Raw Materials and Reagents

[0051]

[0052]

[0053] Experimental instruments and equipment

[0054] Table 2 Main Experimental Instruments and Equipment

[0055]

[0056] Experimental sample preparation

[0057] Step 1: Preparation of P(AM-co-AA) hydrogel

[0058] P(AM-co-AA) hydrogels were prepared by free radical polymerization. First, acrylamide (AM) and acrylic acid (AA) were dissolved in 10g of salt solutions of different concentrations (0, 1, 2, and 3 M potassium chloride solutions) at room temperature according to different monomer ratios. Then, 0.1 wt% of the total monomer mass of N,N-methylenebisacrylamide (MBA) as a crosslinking agent was added, and the mixture was stirred at room temperature to obtain a homogeneous aqueous solution. Next, 1 wt% of the total monomer mass of α-ketoglutaric acid (KGA) as a photoinitiator was added to the above solution, and the mixture was stirred until completely dissolved. Finally, the precursor solution was injected into a mold and irradiated with ultraviolet (UV) light (365 nm, 20 W) for 10 min.

[0059] Step 2Cs 0.33 WO3 coated glass (glass-Cs) 0.33 Preparation of WO3

[0060] Cs 0.33 A solution of WO3 nanoparticles mixed with acrylic resin and toluene in a mass ratio of toluene:acrylic resin:Cs 0.33 WO3 was mixed in a ratio of 0.9:0.85:0.16 and stirred for 1 hour to obtain a uniform dispersion. The dispersion was then applied to ordinary glass using a coater with a concave depth of 22 μm.

[0061] Step 3: Assemble the MAC Smart Window

[0062] The precursor solution obtained in step 1 was injected into a Cs system consisting of ordinary glass and spacers made of 2mm silicone rubber. 0.33 The assembled MAC smart window is placed in a mold made of WO3-coated glass. Then, it is cross-linked by irradiating it with ultraviolet (UV) light for 15 minutes (365nm, 20W).

[0063] Example 2

[0064] Test characterization

[0065] Optical performance testing

[0066] The transmittance of P(AM-co-AA) hydrogel and MAC smart window samples in the wavelength range of 0.3–2.5 μm was measured using a UV-vis-NIR spectrophotometer (Carry 7000, Agilent) equipped with an integrating sphere at 20 °C and 35 °C. The transmittance of the hydrogel in the visible light range (380–780 nm) was measured (T... lum ), near-infrared range (780-2500nm) (T NIR ) and the range of sunlight (280-2500nm) (T sol The transmittance within the range is calculated using the following formula:

[0067]

[0068] Where T() is the transmittance at wavelength, lum() is the standard luminous efficacy function for photosensitive vision, and sol() is the AM1.5 solar radiation spectrum.

[0069] Solar modulation capability (ΔT) sol It is calculated using the following formula:

[0070] ΔT sol =T sol，35℃ -T sol，20℃

[0071] Adhesion performance test

[0072] Overlap shear tests were performed using a computer-controlled universal testing machine (Hensgrand, WDW-02, China) to characterize the adhesion strength of the hydrogel. Before each test, a hydrogel sample, trimmed to 10 mm × 25 mm and 1 mm thick, was sandwiched between two substrates. The sample was then subjected to a 50 mm shear test. -1 The crosshead is stretched vertically at high speed.

[0073] Mechanical property testing

[0074] The mechanical properties of the materials were tested using a computer-controlled universal testing machine (Hensgrand, WDW-02, China). The tensile specimens were cuboids with a length of 50 mm, a width of 7 mm, and a thickness of 3 mm. The tensile speed was 50 mm / min. -1 Mechanical performance testing involves taking the median data from the dataset with the most frequent measurements and then analyzing and plotting it.

[0075] Conductivity testing of hydrogel electrolytes

[0076] Ionic conductivity (σ, mS cm) of hydrogel electrolyte -1Electrochemical impedance spectroscopy (EIS) measurements were performed using a CHI 660E electrochemical workstation. First, the hydrogel electrolyte was filled into a CR927 battery case and stabilized at different temperatures for two hours. Then, the EIS of the hydrogel electrolyte was measured at the corresponding temperatures. At least three measurements were performed for each sample, and the average value was used to reduce error. The ionic conductivity was calculated using the following formula:

[0077]

[0078] Where R is the resistance (Ω) and S is the cross-sectional area (cm²) of the hydrogel electrolyte sample. 2 ), where L is the thickness of the sample (cm).

[0079] Differential scanning calorimetry (DSC)

[0080] DSC was performed using a TA2500 instrument. For testing the hydrogel phase transition temperature, 20-30 mg of all hydrogel samples were weighed and sealed in an aluminum pan, with an empty pan used as a reference. The samples were cooled from room temperature to -60°C under a nitrogen atmosphere, stabilized for 5 min, and then heated from -60°C to 40°C at a rate of 2°C / min.

[0081] Outdoor temperature measurement test

[0082] In outdoor temperature measurement tests, a sample measuring 24×14×12cm was created. 3 A polystyrene foam model house. The polystyrene foam model house is wrapped in aluminum foil to completely isolate it from the environment. The MAC smart window measures 8×6cm. 2 The gap between the glass panes was set to 2 mm for injecting the hydrogel precursor solution. A thermocouple thermometer (TES-132) was used to monitor the temperature inside the model chamber. Ordinary glass and commercially available insulated glass were used for comparison.

[0083] Energy-saving performance simulation

[0084] Using EnergyPlus software and an "ideal load-air system" model, a full-building cooling capacity simulation of the district cooling system was performed. In the model, the glass system is evenly distributed on the four walls, with a total window glass area of ​​42 m². 2 The thermochromic properties of the MAC Smart Window were modeled using the EnergyPlus built-in program: "Window Material: Glazing Group: Thermochromic" object. A series of material layers with variable optical parameters were designed for simulation within each specified temperature range.

[0085] Other testing methods

[0086] Fourier transform infrared spectrometer (Nicolet 10, USA) was used at 4000–500 cm⁻¹ -1 Fourier transform infrared (FTIR) spectra of the samples were measured within the wavenumber range. AFM phase images were obtained by atomic force microscopy (Multimode 8). The morphology of freeze-dried P(AM-co-AA) hydrogels at different temperatures was studied using scanning electron microscopy (Hitachi Regulus 8220). Rheological characterization was performed on a rotationally controlled rheometer (Anton Paar, MCR302, Germany).

[0087] Results and Discussion of Example 3

[0088] Design and preparation of hydrogel electrolytes

[0089] This application first develops a temperature-mediated phase separation adhesive antifreeze hydrogel electrolyte. Based on the UCST mechanism, two hydrophilic monomers, AM and AA, were selected. Figure 1 a) First, 0M, 1M, 2M, and 3M salt solutions (LiCl, NaCl, KCl) were prepared. AM and AA were dissolved in 10g of the above salt solutions at a molar ratio of 5:5 and stirred until homogeneous. The total monomer concentration was controlled at 2M. Crosslinking agent MBA (equivalent to 0.1wt% of the total monomer mass) and photoinitiator KGA (equivalent to 1wt% of the total monomer mass) were added and stirred continuously. Subsequently, the precursor solution was injected into a glass mold and sonicated for 10min to remove air bubbles and impurities. Finally, crosslinking was performed by irradiation with ultraviolet light (UV) for 10min to obtain the thermosensitive copolymer P(AM-co-AA). The chemical composition of P(AM-co-AA) hydrogel was verified by Fourier transform infrared (FTIR) spectroscopy. The P(AM-co-AA) hydrogel still showed similarities to PAM hydrogel (1672cm⁻¹). -1 ) and PAA hydrogel (1736cm) -1 The carbonyl stretching vibrations associated with PAM hydrogels were not observed. However, no -NH2 (1612 cm⁻¹) vibrations associated with PAM hydrogels were observed in P(AM-co-AA) hydrogels. -1 The stretching vibrations of the amide group in P(AM-co-AA) are restricted. This means that the stretching vibrations of the amide group in P(AM-co-AA) are restricted. Figure 1 b).

[0090] Investigation into the ratio of electrolyte monomers in hydrogels

[0091] The phase transition of P(AM-co-AA) hydrogels originates from the intermolecular hydrogen bonds formed between polyacrylamide (PAM) and polyacrylic acid (PAA) at low temperatures, which dissociate when the temperature rises to a specific value. The optical transition of the hydrogel caused by the formation and dissociation of hydrogen bonds depends on the hydrogen bond density, network structure, and temperature changes, and the hydrogen bond density and network structure are closely related to the concentration and composition ratio of macromolecular chains in the hydrogel. In the preparation of P(AM-co-AA) hydrogels, the transmittance and upper critical dissolution temperature of the P(AM-co-AA) hydrogel can be precisely adjusted by controlling the monomer concentration and molar ratio of acrylamide (AM) to acrylic acid (AA). Figure 2 The effect of AM and AA monomer concentrations on the transmittance of P(AM-co-AA) hydrogel under high temperature (35℃) and low temperature (20℃) conditions was demonstrated. When the monomer concentrations of AM and AA reached 2M, the transmittance of the P(AM-co-AA) hydrogel in the visible light range reached a maximum of 87.35%. At 20℃, the transmittance approached 0%.

[0092] Figure 3 The results show that when the AM:AA ratio is 1:9 and 9:1, no phase transition occurs in the P(AM-co-AA) hydrogel within the temperature range of 5–35 °C; however, reversible phase transitions occur when the AM:AA ratio is 3:7, 5:5, and 7:3. This phenomenon demonstrates that the optical transition of the P(AM-co-AA) hydrogel is significantly affected by the monomer ratio. Furthermore, this application further confirms this by testing the transmittance of P(AM-co-AA) hydrogels with different monomer ratios. Figure 3 As shown in b, at 35℃, the transmittance curves of P(AM-co-AA) hydrogels with five different monomer ratios showed little difference. (Comparison...) Figure 3 b and Figure 3 As can be seen from c, at 20℃, the transmittance curves of P(AM-co-AA) hydrogels with AM:AA ratios of 1:9 and 9:1 are consistent with those at 35℃, showing no significant change; when AM:AA is 7:3, the transmittance decreases slightly; when AM:AA is 3:7 and 5:5, the transmittance approaches 0%.

[0093] Meanwhile, the transmittance curves of P(AM-co-AA) hydrogels with different thicknesses (1 mm, 2 mm, and 3 mm) were measured when the monomer ratio of AM:AA was 5:5. Figure 4 a). The results show that at 35℃, the To of the P(AM-co-AA) hydrogel increases with increasing hydrogel thickness. lum Almost no change, while T NIR Gradually decreasing. Among them, T... NIRThe percentage decreased from 35.12% for 1mm samples to 12.84% for 2mm samples, and further to 5.26% for 3mm samples, while T lum Maintaining approximately 87.2% ( Figure 4 b). Therefore, increasing the thickness of the P(AM-co-AA) hydrogel at high temperatures can reduce T. NIR And it has little impact on visible light. For example... Figure 4 As shown in b, when the temperature is reduced to 20℃, the T values ​​of the 1mm, 2mm, and 3mm samples are... lum and T NIR All values ​​approach 0%. These results indicate that at lower temperatures, the thickness of the P(AM-co-AA) hydrogel has little effect on visible and near-infrared transmittance.

[0094] To further investigate the influence mechanism of the monomer ratio of AM to AA on the transmittance and upper critical dissolution temperature of the hydrogel, this application conducted Fourier transform infrared (FTIR) spectroscopy and low-field nuclear magnetic resonance (LF-NMR) spectroscopy. Figure 5 The FTIR spectrum shown in figure a indicates that the wavenumbers of both the -COOH and C=O stretching vibrations in the amide groups are lowest at an AM:AA ratio of 5:5, suggesting that the hydrogen bonding between AM and AA is strongest at this monomer ratio.

[0095] Furthermore, as a thermochromic hydrogel, the upper critical dissolution temperature (UCST) is a key parameter affecting the performance of P(AM-co-AA). Differential scanning calorimetry (DSC) is typically used to measure the thermal effects associated with the UCST, thereby indirectly calculating the UCST. The transition temperature (Ti) of the smart window... c The default UCST is the same as that of P(AM-co-AA) hydrogel. DSC test results are as follows: Figure 5 As shown, the upper critical dissolution temperature was 28.9℃ when AM:AA was 5:5.

[0096] Analysis of temperature-mediated hydrogen bond interaction mechanism

[0097] Based on the results of transmittance tests, this application found that the optical properties of P(AM-co-AA) hydrogel exhibit significant differences with temperature. At high temperatures (>28.9℃), the hydrogel is transparent, while it becomes opaque when exposed to lower ambient temperatures. Notably, when the hydrogel is exposed to a high-temperature environment again, it becomes transparent again, demonstrating remarkable reversible optical properties. Figure 6As shown, the hydrogen bonding between polymer chains and water molecules weakens significantly at low temperatures, while the hydrogen bonding between polymer chains strengthens, promoting contraction to form a polymer-rich region, resulting in the opaque state of the P(AM-co-AA) hydrogel. With increasing temperature, the hydrogen bonds between polymer chains dissociate, intermolecular forces weaken, thereby improving the solubility and compatibility of the polymer chains in water, ultimately leading to the end of phase separation and the system returning to a homogeneous, transparent state.

[0098] Furthermore, optical photographs show that the P(AM-co-AA) hydrogel is homogeneous and transparent at high temperatures (35°C), but when exposed to an ambient temperature of 20°C, the P(AM-co-AA) hydrogel undergoes phase separation and becomes opaque overall. Figure 7 a). For example Figure 7 As shown in the scanning electron microscope (SEM) images, the P(AM-co-AA) hydrogel freeze-dried at 35°C exhibits a porous, sheet-like structure, while shrinkage occurs at 20°C, leading to the formation of a filamentous structure. These phenomena also demonstrate that the polymer is completely soluble in water at high temperatures, and when the temperature decreases, aggregation is driven by strong intermolecular forces, resulting in self-assembly to form polymer-rich regions.

[0099] To further reveal the key mechanism of temperature-driven hydrogen bonding interactions and explore the effect of temperature on the optical properties of hydrogels, this application used a rheometer to determine the viscoelastic behavior of P(AM-co-AA) hydrogels and conducted tests and analyses using X-ray photoelectron spectroscopy (XPS). Figure 8 The temperature-varying rheological spectrum of a shows that, throughout the temperature range of 0–60 °C, G' is consistently significantly higher than G'', and the loss factor (tanδ) is consistently less than 1. This indicates that the P(AM-co-AA) hydrogel remains in an elastic gel state with a stable three-dimensional network structure, and temperature changes do not alter its gel state. This characteristic allows the P(AM-co-AA) hydrogel to maintain good mechanical stability under temperature variations, making it suitable as a smart window material. G' exhibits a significant change near 29 °C, compared to... Figure 5 The upper critical dissolution temperature (UCST ≈ 29 ℃) measured by the DSC curve in b is consistent with the phase transition temperature of the P(AM-co-AA) hydrogel.

[0100] like Figure 8XPS spectra of b, c, and d show that as the temperature decreases, the peaks of COOH / CONH2 (C 1s), O=C-NH2 / O=C-OH and C-OH (O 1s), and H2N-C=O (N 1s) all shift to lower binding energies. This indicates that low temperature enhances hydrogen bonding interactions, and more hydrogen bonds are formed between the amino groups on PAM and the carboxyl groups in PAA, causing phase separation of the P(AM-co-AA) hydrogel at low temperatures.

[0101] Adhesion and antifreeze properties of hydrogel electrolytes

[0102] The adhesion properties and freeze resistance of hydrogels directly affect the long-term stability and reliability of smart windows. With the dissociation of hydrogen bonds, a large number of active groups (-COOH and -NH2) in the P(AM-co-AA) hydrogel are exposed. As shown in the figure, it can be observed that the P(AM-co-AA) hydrogel can firmly adhere to various materials, exhibiting strong and stable adhesion to glass, wood, metal, and rubber substrates.

[0103] To further quantitatively evaluate the adhesiveness of P(AM-co-AA) hydrogel, the adhesion strength of P(AM-co-AA) hydrogel to four representative materials—glass, wood, metal, and rubber—was determined using an lap shear strength test. Notably, the hydrogel exhibited the highest adhesion strength with glass, reaching 0.43 MPa, while the adhesion strengths with wood, metal, and rubber were 0.27 MPa, 0.11 MPa, and 0.22 MPa, respectively. These results demonstrate that P(AM-co-AA) hydrogel possesses broad-spectrum, universal adhesive properties.

[0104] This application also investigated the effect of KCl on the antifreeze properties of P(AM-co-AA) hydrogels. The inorganic salt was used to break the hydrogen bonds between water molecules, thereby lowering the freezing point of the hydrogel. A 3 M KCl concentration P(AM-co-AA) hydrogel was placed at -30 °C for 12 hours. Figure 11 As shown in figure a, the hydrogel remains elastic and can be stretched to a certain extent without breaking, exhibiting excellent freeze resistance. Differential scanning calorimetry (DSC) was used to further investigate the effect of KCl concentration on the freezing point of the P(AM-co-AA) hydrogel. Figure 11 As shown in b, the freezing points of the P(AM-co-AA) hydrogel were -1.8, -11.2, -18.7, and -31.2 °C, respectively, when the KCl concentrations were 0, 1, 2, and 3 M. This application also indirectly characterized the antifreeze performance by testing the conductivity at different KCl concentrations at low temperatures. Figure 11As shown in Figure c, the P(AM-co-AA) hydrogel with a KCl concentration of 0 M exhibits poor low-temperature conductivity. When the KCl concentration is increased to 3 M, the conductivity of the P(AM-co-AA) hydrogel at -30 °C reaches 3.53 mS / cm. -1 .

[0105] Smart windows based on hydrogel electrolyte assembly

[0106] Taking all factors into consideration, this application selected P(AM-co-AA) hydrogel with an AM:AA ratio of 5:5 and a KCl concentration of 3M as the thermochromic smart window. The P(AM-co-AA) hydrogel was synthesized in situ in a mold composed of two glass layers, one of which was coated with a layer of cesium tungsten bronze (Cs). 0.33 WO3), the two glass elements are separated by a silicone spacer. The P(AM-co-AA) hydrogel provides solar modulation capabilities and an adjustable transition temperature (T). c The glass panel serves as the mechanical support for the smart window, Cs 0.33 WO3 further blocks near-infrared radiation. This smart window is named MAC Smart Window, and its structure is as follows... Figure 12 As shown.

[0107] Generally, solar heating is primarily contributed by heat transfer in the visible light (Vis, 380-780nm) and near-infrared light (NIR, 780-2500nm) ranges, accounting for 44% and 53% of the total, respectively. Therefore, achieving low near-infrared transmittance (T) during the day... NIR Near-infrared light blocking is crucial for reducing energy consumption. According to the near-infrared light blocking mechanism, the following two strategies are mainly adopted to effectively block near-infrared light: near-infrared reflection and near-infrared absorption

[112] . However, it should be noted that near-infrared reflection, due to its strong solar infrared reflection capability, may cause excessive heat loss in winter, which is not conducive to indoor heating. In addition, studies have also found that reflected solar heat may exacerbate the urban heat island effect and cause thermal degradation problems to the surrounding building structures. [113,114] In contrast, materials that absorb near-infrared light can overcome the drawbacks of near-infrared reflection, among which Cs 0.33 WO3 is considered an ideal candidate material for near-infrared shielding.

[0108] like Figure 13 As shown in a, with Cs 0.33 The increase in WO3 content affects the T in MAC Smart Window. NIR The value is getting lower and lower, but T lum It also gradually decreases. To ensure good daytime visibility, a layer of Cs was chosen. 0.33 Further testing was conducted on the Mac Smart Window in WO3. The Mac Smart Window achieved a 70.12% Tilting spectral density during the day.lum and 0.6% T NIR It effectively reduces near-infrared transmittance while maintaining visibility, and becomes opaque at night, achieving a low visible light transmittance of 0.02%, thus providing privacy protection. Figure 13 b). Similarly from Figure 13 c. It can be observed that the MAC Smart Window has high transparency during the day, allowing a clear view of what is behind it, while it becomes opaque at night, demonstrating good light modulation capabilities.

[0109] In addition, this application compares MAC smart windows, P(AM-co-AA) hydrogel, ordinary glass, and Cs. 0.33 WO3 coated glass (Glass-Cs) 0.33 Optical properties between WO3 and WO4. Figure 14 As shown, at 35 ℃, due to Cs 0.33 The presence of the WO3 coating, and the T in the MAC Smart Window lum Lower than that of corresponding hydrogels and ordinary glass. Compared to 90.46% of ordinary glass, T... NIR Compared to P(AM-co-AA) hydrogel and Glass-Cs 0.33 WO3 showed relatively low T values ​​of 12.84% and 4.45%, respectively. NIR This indicates that P(AM-co-AA) hydrogel and Cs 0.33 WO3 coatings can block near-infrared light. Meanwhile, the T-shaped coating on the MAC Smart Window... NIR It is significantly lower than other materials, demonstrating excellent near-infrared light blocking ability.

[0110] To evaluate the long-term stability of the MAC Smart Window during transitions between high-temperature, high-transmittance and low-temperature, low-transmittance operation, this application underwent 100 transmittance switching cycles. Figure 15 As shown in Figure a. The results show that the sunlight modulation capability of the MAC smart window is stable, with no significant fluctuation in transmittance after 100 cycles. To further investigate the long-term durability of the MAC smart window, it was placed outdoors in Jinan for 84 hours and 15 days. The transmittance of the MAC smart window remained basically unchanged under high and low temperatures. Figure 15 b). These results indicate that the MAC smart window exhibits excellent optical reversibility and long-term stability due to the superior adhesion of its P(AM-co-AA) hydrogel, making it durable for long-term building temperature regulation. Compared with other reported smart windows, its T... lum and ΔT sol Compared to MAC Smart Window, it has superior T... lum and ΔT sol ,like Figure 15 As shown in c.

[0111] Intelligent window outdoor temperature measurement and energy-saving simulation

[0112] To study the temperature regulation and energy-saving performance of the MAC smart window, this application constructed a model house outdoors in Jinan during the summer. For example... Figure 16 As shown in a, this application will have an 8×6cm 2 The MAC Smart Window is fixed in a 24×14×12cm area. 3 The polystyrene foam model house was insulated from the environment by wrapping it with tin foil. Furthermore, to demonstrate the superior energy-saving performance of the MAC smart window, this application selected ordinary glass and commercial insulated glass as comparisons in outdoor temperature measurement tests. Photos of the outdoor tests are shown below. Figure 16 As shown in b.

[0113] like Figure 17 As shown in Figure a, weather data for the day of the outdoor temperature test is provided, including changes in relative humidity and solar radiation intensity. The test results show that from 8:00 AM, the indoor temperatures of all three model houses increased significantly with increasing solar radiation intensity. The indoor temperatures of all model houses reached their maximum at 1:20 PM. At this time, the indoor temperature of the ordinary glass model house was 52.2℃, and the indoor temperature of the commercial insulated glass model house was 51℃. In contrast, the indoor temperature of the MAC smart window model house was 49℃, which was 3.2℃ and 2℃ lower than the former two, respectively. Figure 17 b). This result strongly confirms that MAC Smart Window has excellent indoor temperature regulation performance.

[0114] To further explore the energy-saving performance of MAC Smart Window, energy-saving simulation calculations were performed using EnergyPlus software. Figure 18 Shown as a schematic diagram of the building model used in energy-saving simulation calculations. Because Figure 17 In section b, the temperature regulation performance of three types of windows was tested in Jinan during the summer; therefore, Jinan was chosen as the simulated city for energy conservation evaluation. The annual HVAC energy consumption of ordinary glass is 761.97 MJ / m³. -2 Based on ordinary glass, commercial insulated glass can save 115.16 MJ / m² per year. -2 Regarding HVAC energy consumption, MAC Smart Window can save 163.82 MJ / m² per year. -2 HVAC energy consumption ( Figure 18 b).

[0115] To demonstrate that MAC Smart Window can efficiently regulate temperature and save energy across a wide range of climates and geography, this application selected three typical cities in China and conducted a series of energy-saving simulations: Dalian (121.45 °E, 39.02 °N), Shanghai (120.55 °E, 30.45 °N), and Guangzhou (112.57 °E, 22.26 °N). Figure 19 a, b, and c describe the monthly HVAC energy consumption of MAC smart windows, commercial insulated glass, and ordinary glass in three cities. In all three cities, the annual monthly HVAC energy consumption of MAC smart windows is lower than that of commercial insulated glass and ordinary glass. These results demonstrate that MAC smart windows have good energy-saving performance in buildings in cities with different climates.

Claims

1. A MAC smart window characterized in that, The smart window structure consists of a glass pane, P(AM-co-AA) hydrogel, and cesium tungsten bronze Cs. 0.33 Composed of WO3.

2. A method for preparing the MAC smart window according to claim 1, characterized in that, Includes the following steps: Step 1: Preparation of P(AM-co-AA) hydrogel P(AM-co-AA) hydrogels were prepared by free radical polymerization. First, acrylamide (AM) and acrylic acid (AA) were dissolved in 10 g of salt solutions of different concentrations at room temperature according to different monomer ratios. Then, 0.1 wt% of N,N-methylenebisacrylamide (MBA), a crosslinking agent, was added and stirred at room temperature to obtain a homogeneous aqueous solution. Next, 1 wt% of α-ketoglutaric acid (KGA), a photoinitiator, was added to the obtained homogeneous aqueous solution and stirred until completely dissolved to obtain a precursor solution. Finally, the precursor solution was injected into a mold and irradiated with ultraviolet (UV) light. Step 2: Cs 0.33 WO3 coated glass (glass-Cs) 0.33 Preparation of WO3 Cs 0.33 A solution of WO3 nanoparticles mixed with acrylic resin and toluene in a mass ratio of toluene:acrylic resin:Cs 0.33 Mix WO3 in a ratio of 0.9 : 0.85 : 0.16 and stir further to obtain a uniform dispersion; apply the dispersion onto ordinary glass using a coating machine. Step 3: Assemble the Mac Smart Window The precursor solution obtained in step 1 was injected into a Cs-type membrane consisting of ordinary glass and silicone rubber as a spacer. 0.33 The assembled MAC smart window is placed in a mold made of WO3-coated glass; then it is cross-linked by irradiation under ultraviolet (UV) light.

3. The method according to claim 1, characterized in that, In step 1, the mass ratios of acrylamide AM and acrylic acid monomer are 9:1, 7:3, 5:5, 3:7, and 1:9, respectively.

4. The method according to claim 1, characterized in that, In step 1, the salt solutions of different concentrations are potassium chloride solutions with concentrations of 0, 1, 2, and 3 M, respectively.

5. The method according to claim 1, characterized in that, In step 1, the light is irradiated with ultraviolet (UV) light for 10 min (365 nm, 20 W).

6. The method according to claim 1, characterized in that, In step 2, the depth of the coating machine concave is 22 µm.

7. The method according to claim 1, characterized in that, In step 3, the silicone rubber thickness is 2 mm.

8. The method according to claim 1, characterized in that, In step 3, the sample is irradiated with ultraviolet (UV) light for 15 min (365nm, 20 W).

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