Thermochromic organic-inorganic hydrogel for intelligent window as well as preparation method and application of thermochromic organic-inorganic hydrogel

Abstract

The invention belongs to the field of bionic photon structure composite materials, and particularly relates to thermochromic organic-inorganic hydrogel for an intelligent window as well as a preparation method and application of the thermochromic organic-inorganic hydrogel. The thermochromic organic-inorganic hydrogel is prepared through multi-scale structural design, and the design synergistically combines the advantages of organic components and inorganic components; the structural design comprises self-densification of a micro scale, thermal response cluster of a nano scale and fine amorphous mineral form regulation of a molecular scale. The preparation method is simple, large-scale preparation of intelligent windows in any prepared shape can be achieved, the excellent energy absorption and adhesion capacity of the obtained organic-inorganic hydrogel layer enables the assembled intelligent window to have remarkably enhanced impact resistance, and the fragile characteristic of a traditional window is avoided.

Description

Technical Field

[0001] The present invention belongs to the field of bionic photon structure composite materials, and particularly relates to a thermochromic organic-inorganic hydrogel for intelligent windows, a preparation method thereof, and an application thereof. Background Art

[0002] Building energy consumption accounts for about 40% of the global energy consumption in developed countries. As one of the components with the lowest energy efficiency, windows cause up to 60% of energy loss due to the increased heat from solar radiation in summer and heat loss in winter. To improve building energy efficiency and reduce carbon emissions, it is crucial to develop intelligent windows that can dynamically adapt to different solar radiation and weather conditions. Currently, researchers have been committed to developing intelligent windows that can dynamically adjust the transmittance of the solar spectrum (0.3 - 2.5 μm) in response to multiple stimuli, including electricity, light, heat, and mechanical action. Electrochromic and photochromic intelligent windows have certain limitations in terms of energy consumption, cost, and practicality. Thermochromic intelligent windows, due to their simple structure, zero energy consumption, and automatic light regulation based on ambient temperature, have become an economical and highly effective option in the application of intelligent windows.

[0003] Thermochromic materials with tunable optical properties are crucial for achieving efficient sunlight modulation ability (ΔT sol ) for thermochromic intelligent windows. Recent research has generally focused on inorganic materials (such as vanadium dioxide (VO2) and perovskites) and organic thermoresponsive materials (such as poly(N-isopropylacrylamide) (pNIPAm) and polymer blends). Inorganic thermochromic materials have excellent durability, long lifespan, resistance to photo-degradation, and high thermal stability. However, their practical applications are limited by disadvantages such as high transition temperature, color, brittleness, potential biotoxicity, and high cost. For example, VO2 exhibits phase change characteristics above the transition temperature, which can significantly reduce the near-infrared transmittance while having little effect on the visible light transmittance, thus having application potential in intelligent windows. However, the yellowish color of VO2, visible light transmittance below 30%, critical temperature (τ c ) as high as 68 °C, and potential biotoxicity limit its practical applications. Perovskite materials have diverse structural types and tunable optical properties, but their limited low-temperature thermochromic performance, environmental toxicity, and insufficient sunlight modulation ability hinder their widespread application in intelligent windows. On the other hand, organic thermochromic materials have advantages such as lower color change temperature, high sensitivity to temperature changes, easy processability, flexibility, and lower cost. However, their limited light modulation ability and easy photo-degradability may lead to shorter cycle stability and decreased overall lifespan. To address the problems of oxidation and durability, recent research has developed polymer blends with enhanced durability, but their transmittance and ΔT solStill relatively limited. Emerging thermochromic materials based on low critical solution temperature (LCST)-type hydrogels, such as pNIPAm hydrogels, have attracted extensive attention due to their high transparency and tunable transition temperature. However, smart windows based on pNIPAm hydrogels usually exhibit low light scattering efficiency due to small pNIPAm chain aggregation, resulting in a low ΔT sol . Therefore, the development of highly flexible thermochromic materials with high visible light transmittance (T lum ), tunable τc, strong ΔT sol and long-term stability is crucial for the preparation of high-performance thermochromic smart windows. SUMMARY OF THE INVENTION

[0004] In order to overcome the disadvantages and deficiencies in the prior art, the primary object of the present invention is to provide a method for preparing a thermochromic organic-inorganic hydrogel for smart windows.

[0005] Another object of the present invention is to provide a thermochromic organic-inorganic hydrogel for smart windows prepared by the above preparation method.

[0006] Another object of the present invention is to provide the application of the above thermochromic organic-inorganic hydrogel for smart windows.

[0007] The object of the present invention is achieved by the following technical solutions:

[0008] A method for preparing a thermochromic organic-inorganic hydrogel for smart windows, comprising the following operating steps: adding a CaCl2 solution with a molar concentration of 0.2 - 0.7 mol / L to a polyacrylic acid (PAA) solution with a molar concentration of 1 mol / L, stirring overnight at room temperature to mix evenly to obtain a mixed solution; subsequently, injecting a Na2CO3 solution with the same molar concentration as the CaCl2 solution into the mixed solution at a rate of 300 mL / h to obtain a turbid and opaque PAA / ACC hydrogel; the CaCl2 solution, PAA solution and Na2CO3 solution are of equal volume; allowing the obtained turbid and opaque PAA / ACC hydrogel to stand for 35 - 40 days, or centrifuging at a centrifugal speed of 10,000 rpm for 30 - 40 minutes, the hydrogel undergoes self-compaction behavior, expelling air bubbles and excess moisture, generating phase separation, with an upper water phase formed and a transparent PAA / ACC hydrogel formed in the lower layer, which is the thermochromic organic-inorganic hydrogel for smart windows.

[0009] A thermochromic organic-inorganic hydrogel for smart windows prepared by the above preparation method, the visible light transmittance T of the thermochromic organic-inorganic hydrogel lum = 99%, has a tunable critical change temperature within 20 - 37 °C, and its temperature-triggered sunlight modulation ability ΔTsol Up to 86.1%, with a rapid temperature response of 3 s; after 3 months of ultraviolet irradiation or after being placed at 100 °C for 24 h, its optical properties remain stable.

[0010] Application of the above thermochromic organic-inorganic hydrogel in the preparation of smart windows.

[0011] Principle of the present invention:

[0012] The present invention designs and prepares a thermochromic organic-inorganic hydrogel through multi-scale structure regulation, which synergistically combines the advantages of organic components and inorganic components. This structural design includes self-densification at the microscale, thermoresponsive clusters at the nanoscale, and regulation of the fine amorphous mineral morphology at the molecular scale. The self-compacting behavior and amorphous minerals can provide high transmittance for the hydrogel, while the thermoresponsive phase separation of the organic-inorganic clusters enables the hydrogel to rapidly transform between transparent and opaque states. The organic-inorganic hydrogel prepared by this method exhibits ultra-high visible light transmittance (T lum = 99%), a widely tunable critical change temperature (20 - 37 °C), excellent ΔT sol (up to 86.1%), rapid responsiveness (about 3 s), and long-term stability in extreme environments (such as strong ultraviolet irradiation and high temperature). In addition, the organic-inorganic hydrogel of the present invention has good fluidity, enabling it to be easily assembled into the interlayer of ordinary optical glass to construct smart windows. The excellent energy absorption and adhesion ability of the organic-inorganic hydrogel layer make the assembled smart windows have significantly enhanced impact resistance, avoiding the fragile characteristics of traditional windows. In addition, due to the inherent self-healing performance of the hydrogel, these hydrogels can be easily recycled and used to prepare new smart windows, which has significant advantages compared with covalently bonded thermochromic materials.

[0013] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0014] (1) The present invention prepares a thermochromic organic-inorganic hydrogel through multi-scale structural design, which synergistically combines the advantages of organic components and inorganic components; this structural design includes self-densification at the microscale, thermoresponsive clusters at the nanoscale, and regulation of the fine amorphous mineral morphology at the molecular scale.

[0015] (2) The preparation method of the present invention is simple and can realize the large-scale preparation of smart windows with any desired shape.

[0016] (3) The excellent energy absorption and adhesion ability of the organic-inorganic hydrogel layer make the assembled smart windows have significantly enhanced impact resistance, avoiding the fragile characteristics of traditional windows. Brief Description of the Drawings

[0017] Figure 1 Schematic diagram of the self - densification process and thermal response process of polyacrylic acid / amorphous calcium carbonate hydrogel in Example 1 of the present invention.

[0018] Figure 2 In the process of standing for 0 - 35 days in Example 1 of the present invention, physical diagram of the appearance and microscopic diagram of polyacrylic acid / amorphous calcium carbonate hydrogel, from top to bottom are the top view, side view of the hydrogel and the corresponding optical microscope photos.

[0019] Figure 3 Graph of the volume and viscosity changes of hydrogels formed by reacting calcium chloride and sodium carbonate with different molar concentrations with 1M polyacrylic acid.

[0020] Figure 4 Schematic diagram and XRD pattern of hydrogels and dispersions formed by reacting calcium chloride and sodium carbonate with different molar concentrations with 1M polyacrylic acid.

[0021] Figure 5 Transmittance of 550nm visible light of polyacrylic acid / amorphous calcium carbonate hydrogels with different amorphous calcium carbonate contents under different temperature conditions.

[0022] Figure 6 Ultraviolet - visible - near - infrared diagram of polyacrylic acid / amorphous calcium carbonate hydrogel and schematic diagram of the temperature - triggered sunlight modulation ability of the hydrogel, where a is the ultraviolet - visible - near - infrared spectrum of 1mm polyacrylic acid / amorphous calcium carbonate hydrogel at different temperatures, b is the ultraviolet - visible - near - infrared spectrum of polyacrylic acid / amorphous calcium carbonate hydrogels with different thicknesses at room temperature, c is the T lum 、ΔT lum and ΔT sol Comparison.

[0023] Figure 7 Comparison chart of the impact resistance performance of ordinary glass, smart window at 20°C and smart window at 50°C.

[0024] Figure 8 Graph of the optical performance change of the smart window made of polyacrylic acid / amorphous calcium carbonate hydrogel of the present invention under extreme environments, where a is placed outdoors for 180 days, b is continuously irradiated with ultraviolet light for three months, c is placed at 100°C for 24h. Detailed Description of the Invention

[0025] The present invention will be further described in detail below in conjunction with the embodiments and the drawings, but the embodiments of the present invention are not limited thereto.

[0026] Example 1:

[0027] A preparation method of a thermochromic organic-inorganic hydrogel for smart windows, and the schematic diagram of the preparation process is as Figure 1 shown, and specifically includes the following operating steps:

[0028] Add 100 mL of CaCl2 solution with a molar concentration of 0.4 mol / L to 100 mL of polyacrylic acid (PAA) solution with a molar concentration of 1 mol / L, stir overnight at room temperature to mix evenly to obtain a mixed solution; subsequently, inject 100 mL of Na2CO3 solution with a molar concentration of 0.4 mol / L into the mixed solution at a rate of 300 mL / h to obtain a turbid and opaque PAA / ACC hydrogel; let the obtained turbid and opaque PAA / ACC hydrogel stand for 35 - 40 days, or centrifuge it at a centrifugal speed of 10,000 rpm for 30 - 40 minutes, the hydrogel undergoes self-compaction behavior, expels air bubbles and excess water, generates phase separation, the upper layer forms an aqueous phase, and the lower layer forms a transparent PAA / ACC hydrogel (polyacrylic acid / amorphous calcium carbonate hydrogel), which is the thermochromic organic-inorganic hydrogel for smart windows. During the process of standing for 0 - 35 days, the appearance and microscopic schematic diagram of the thermochromic organic-inorganic hydrogel are as Figure 2 shown. As time goes by, the hydrogel undergoes self-compaction behavior, and the excess water and air bubbles gradually exclude from the gel, manifested as its top view gradually changing from opaque to transparent, and it can be observed from the side view that the excluded water gradually accumulates on the upper layer of the hydrogel, and it can be observed from the optical microscope photo that the air bubbles therein gradually decrease until they disappear.

[0029] Example 2:

[0030] Other steps are the same as those in Example 1, the difference is that the centrifugation treatment is used to replace the standing treatment for the turbid and opaque PAA / ACC hydrogel. Specifically, centrifuge it at a centrifugal speed of 10,000 rpm for 30 minutes to obtain a transparent PAA / ACC hydrogel (polyacrylic acid / amorphous calcium carbonate hydrogel), which is the thermochromic organic-inorganic hydrogel for smart windows.

[0031] Example 3

[0032] Other steps are the same as those in Example 2, except that the concentrations of the CaCl₂ solution and the Na₂CO₃ solution are 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 mol / L respectively, and the concentrations of the CaCl₂ solution and the Na₂CO₃ solution are kept consistent. Observe and detect the volume and viscosity changes of the finally obtained hydrogel product, and conduct XRD pattern analysis to observe the rheological behavior of the hydrogel and the crystal form of calcium carbonate in the hydrogel. It can be seen from the pictures that when the concentrations of the CaCl₂ solution and the Na₂CO₃ solution are 0.1 mol / L respectively, the finally obtained product is only the PAA / ACC dispersion, and the PAA / ACC hydrogel cannot be formed, that is, the thermochromic organic-inorganic hydrogel for smart windows is not obtained; when the concentrations of the CaCl₂ solution and the Na₂CO₃ solution are 0.2 - 0.4 mol / L respectively, the finally obtained products are the PAA / ACC dispersion and the PAA / ACC hydrogel, and the thermochromic organic-inorganic hydrogel for smart windows can be obtained. When the concentration of the CaCl₂ solution and the Na₂CO₃ solution is 0.4 mol / L, the volume of the obtained PAA / ACC hydrogel is the largest, and the crystal form of calcium carbonate in the hydrogel is amorphous; when the concentrations of the CaCl₂ solution and the Na₂CO₃ solution are 0.5 - 0.7 mol / L respectively, the finally obtained products are the calcite suspension and the PAA / ACC hydrogel, and the thermochromic organic-inorganic hydrogel for smart windows can be obtained; when the concentrations of the CaCl₂ solution and the Na₂CO₃ solution are 0.8 - 1.0 mol / L respectively, the finally obtained products are the calcite suspension and the PAA / calcite hydrogel, and the PAA / ACC hydrogel cannot be formed, that is, the thermochromic organic-inorganic hydrogel for smart windows is not obtained.

[0033] Example 4

[0034] Using the thermochromic organic-inorganic hydrogels prepared with the concentrations of the CaCl₂ solution and the Na₂CO₃ solution being 0.4, 0.5, 0.6, and 0.7 mol / L in Example 3, the mass percentage contents of amorphous calcium carbonate (ACC) in these four hydrogels measured by EDX are 20 wt%, 26 wt%, 33 wt%, and 38 wt% respectively. Measure the transmittance of visible light at 550 nm of these four hydrogels under different temperature conditions, and the results are as Figure 5 shown. The polyacrylic acid / amorphous calcium carbonate hydrogels with different amorphous calcium carbonate contents have a widely adjustable critical change temperature (20 - 37 °C).

[0035] Example 5

[0036] The thermochromic organic-inorganic hydrogel prepared by using the concentrations of CaCl2 solution and Na2CO3 solution in Example 3 as 0.4 mol / L, that is, the transparent polyacrylic acid / amorphous calcium carbonate hydrogel (PAA / ACC hydrogel), is used as the material for preparing the thermochromic smart window. The transparent polyacrylic acid / amorphous calcium carbonate hydrogel is encapsulated between two ordinary optical glasses to obtain the smart window. The following optical performance detection experiments are carried out on the prepared thermochromic smart window:

[0037] Measure the ultraviolet-visible-near-infrared spectra of 1 mm polyacrylic acid / amorphous calcium carbonate hydrogel (PAA / ACC hydrogel) at different temperatures, as Figure 6 shown in a of. The change in the transmittance of 1 mm polyacrylic acid / amorphous calcium carbonate hydrogel at different temperatures is shown, and the wavelength range is 300 - 2500 nm. It can be observed that its transmittance decreases with the increase of temperature; measure the ultraviolet-visible-near-infrared spectra of polyacrylic acid / amorphous calcium carbonate hydrogels with different thicknesses at room temperature, as Figure 6 shown in b of. The transmittance of polyacrylic acid / amorphous calcium carbonate hydrogel in the wavelength range of 300 - 2500 nm decreases with the increase of the hydrogel thickness; 1 mm polyacrylic acid / amorphous calcium carbonate hydrogel has an ultra-high visible light transmittance (T lum = 99%) and excellent ΔT sol (up to 86.1%), as Figure 6 shown in c of.

[0038] Compare the impact resistance of ordinary glass, the smart window at 20 °C, and the smart window at 50 °C, as Figure 7 shown. The ordinary optical glass without the hydrogel layer cracked at an impact strength of 2.4 kJ m -2 , showing typical brittle failure characteristics. In contrast, the smart window encapsulated with PAA / ACC hydrogel can withstand impact strengths of 3.9 kJ m -2 and 4.1 kJ m -2 in the transparent (20 °C) and opaque (50 °C) states respectively, which is significantly higher than that of ordinary glass, indicating that the hydrogel layer effectively improves its impact resistance. After the impact test, the ordinary glass broke into a large number of fragments, while the PAA / ACC hydrogel-based smart window maintained the overall structural integrity, only showing typical "spider web" cracks, which indicates that the hydrogel layer can effectively inhibit the crack propagation, thus improving the safety of the material, making it of great value in fields such as architecture, automotive, and safety protection applications. Polyacrylic acid / amorphous calcium carbonate hydrogel, as the intermediate layer of the smart window, has excellent energy absorption and adhesion capabilities.

[0039] Measure the change in the optical properties of smart windows made of polyacrylic acid / amorphous calcium carbonate hydrogels under extreme conditions, such as Figure 8 shown. a is for outdoor placement for 180 days, b is for continuous UV irradiation for three months, and c is for high-temperature placement at 100 °C for 24 h. The results show good stability under extreme conditions.

[0040] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A preparation method of a thermochromic organic-inorganic hydrogel for intelligent windows, characterized in that It includes the following operation steps: adding a CaCl2 solution with a molar concentration of 0.2 - 0.7 mol / L to a polyacrylic acid solution with a molar concentration of 1 mol / L, stirring overnight at room temperature to mix evenly to obtain a mixed solution; subsequently, injecting a Na2CO3 solution with the same molar concentration as the CaCl2 solution into the mixed solution at a rate of 300 mL / h to obtain a turbid and opaque PAA / ACC hydrogel; the CaCl2 solution, the PAA solution, and the Na2CO3 solution are of equal volume; leaving the obtained turbid and opaque PAA / ACC hydrogel to stand for 35 - 40 days, or centrifuging at a centrifugal speed of 10,000 rpm for 30 - 40 minutes, the hydrogel undergoes self-compaction behavior, discharging air bubbles and excess moisture, generating phase separation, with an aqueous phase formed on the upper layer and a transparent PAA / ACC hydrogel formed on the lower layer, which is the thermochromic organic-inorganic hydrogel for smart windows.

2. A thermochromic organic-inorganic hydrogel for smart windows prepared by the preparation method according to claim 1, characterized in that: The visible light transmittance T of the thermochromic organic-inorganic hydrogel lum = 99%, has an adjustable critical change temperature within 20 - 37 °C, and its temperature-triggered sunlight modulation ability ΔT sol is as high as 86.1%, and it has a fast temperature response of 3 s; Its optical properties remain stable after 3 months of ultraviolet irradiation or after being placed at 100 °C for 24 h.

3. Application of the thermochromic organic-inorganic hydrogel according to claim 2 in the preparation of smart windows.

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