Super-tensile thermochromic hydrogel as well as preparation method and application thereof

Abstract

The invention discloses super-tensile thermochromic hydrogel as well as a preparation method and application thereof, and belongs to the field of functional materials for intelligent windows. According to the hydrogel, N-isopropylacrylamide (NIPAM) and N, N-diethylacrylamide (DEA) serve as comonomers, DEA-based nanogel serves as a cross-linking agent, the molar ratio of NIPAM to DEA is regulated and controlled to be (1: 1)-(1: 10), the prepared series of temperature-sensitive hydrogel can achieve rapid conversion from transparency to white in a high-temperature environment, and the phase change temperature of the hydrogel is continuously adjustable within the range of 22-35 DEG C; meanwhile, the elongation at break of the hydrogel reaches 2000-4700%, and the hydrogel can meet the temperature response requirements in different climate areas and under different use conditions. The hydrogel can realize reversible conversion between a transparent state and a non-transparent state through temperature regulation and control, provides high-performance material selection for the field of intelligent windows, and has important application value in the field of building energy conservation and low-carbon development.

Description

Technical Field

[0001] This invention belongs to the field of functional materials for smart windows. Specifically, it relates to an ultra-stretched thermochromic hydrogel, its preparation method and application, and a smart window product containing the hydrogel. Background Technology

[0002] Smart window technology is an important development direction in the field of building energy conservation. Traditional windows, due to their high heat conduction efficiency, have become a major source of energy loss in building envelopes. Thermochromic hydrogels, especially poly(N-isopropylacrylamide)-based hydrogels, show potential in smart window applications because their phase transition temperature is close to the human body's comfortable temperature range and they possess passive response and rapid phase change characteristics.

[0003] However, existing thermochromic hydrogels still have the following technical problems: (1) The phase change temperature has a narrow adjustable range, usually less than 10°C, which makes it difficult to adapt to the response temperature requirements of different climate regions; (2) Poor mechanical properties, with elongation at break generally below 300%, making it prone to breakage under external force, which affects the durability of the material; (3) Insufficient long-term cycle stability, and the phase change capability decreases with the number of uses, which restricts its actual service life.

[0004] Therefore, achieving wide-range thermochromic temperature control while simultaneously considering the mechanical properties and long-term stability of hydrogel materials is a key issue that needs to be addressed in this technological field. Summary of the Invention

[0005] This invention addresses the problems of narrow adjustable phase transition temperature range, poor mechanical properties, and insufficient stability of existing thermochromic hydrogels. It provides an ultrastretchable thermochromic hydrogel, its preparation method, and its application. By controlling the monomer ratio, a wide-temperature-range phase transition is achieved, and the mechanical properties are enhanced by cross-linking with nanogels, thus meeting the practical application requirements of smart windows.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: The superstretched thermochromic hydrogel of this invention uses NIPAM and DEA as comonomers and DEA-based nanogels as crosslinking agents. By adjusting the molar ratio of NIPAM to DEA (1:1~1:10), the phase transition temperature can be continuously adjusted from 22-35°C. Utilizing the preferential crosslinking of DEA nanogels with DEA ​​segments, a high-density chemical crosslinking network is formed, significantly improving mechanical properties, with a maximum elongation at break of 4700%. The hydrogel of this invention also exhibits excellent optical properties, with a visible light transmittance (T... lum The solar modulation rate reached 87.7%, and the solar light modulation rate (ΔT) was 87.7%. solThe transmittance can reach up to 78.7%, effectively balancing light transmission and heat insulation functions. At the same time, thanks to the chemical cross-linking effect of DEA nanogel, its mechanical properties are significantly improved, with an elongation at break of ≥2000%, up to 4700% (molar ratio of NIPAM to DEA 1:10). After 100 thermal cycles, the transmittance decay rate is ≤5%, demonstrating excellent stability.

[0007] Its preparation method includes three steps: DEA nanogel synthesis, hydrogel precursor solution preparation and low-temperature polymerization. The process is simple and controllable, and suitable for large-scale production.

[0008] The purpose of this invention is to provide a super-stretchable thermochromic hydrogel, which is polymerized at low temperature using N-isopropylacrylamide (NIPAM) and N,N-diethylacrylamide (DEA) as comonomers and DEA-based nanogels as crosslinking agents; the hydrogel has a phase transition temperature of 22-35℃, an elongation at break ≥2000%, and a visible light transmittance (T0) in a low-temperature transparent state. lum The maximum value can reach 87.7%; among which, the molar ratio of NIPAM to DEA is 1:1 to 1:10.

[0009] Furthermore, when the molar ratio of NIPAM to DEA is 1:9, the visible light transmittance (T) of the hydrogel is... lum The solar modulation rate (ΔT) was 87.7%. sol The figure was 78.7%.

[0010] Furthermore, when the molar ratio of NIPAM to DEA is 1:10, the elongation at break of the hydrogel is ≥4700%.

[0011] Furthermore, the DEA-based nanogel was prepared according to the following steps: DEA monomer was dissolved in deionized water, and N,N'-methylenebisacrylamide, potassium persulfate, and sodium dodecyl sulfonate were added. The mixture was stirred until dissolved and reacted at 40-60°C under nitrogen protection and stirring for 30-45 minutes to obtain DEA nanogel. Among them, N,N'-methylenebisacrylamide accounted for 0.2% of the mass of DEA monomer, potassium persulfate accounted for 0.27% of the mass of DEA monomer, and sodium dodecyl sulfonate accounted for 2.7% of the mass of DEA monomer.

[0012] Furthermore, the particle size of the DEA-based nanogel is 40-200 nm.

[0013] Another object of the present invention is to provide a method for preparing the above-mentioned superstretched thermochromic hydrogel.

[0014] A method for preparing an ultrastretched thermochromic hydrogel includes the following steps: NIPAM and DEA monomers were mixed, and deionized water and DEA-based nanogels were added. The mixture was stirred until homogeneous, and an inert gas was introduced to remove oxygen. The mixture was then injected into a mold and polymerized at 0-5°C to obtain the superstretched thermochromic hydrogel.

[0015] In addition, the use of any of the above-described hydrogels or hydrogels prepared by any of the above methods is also provided, for use as a dimming functional layer of a smart window.

[0016] In addition, a smart window is provided, wherein the dimming function layer of the smart window is made of any of the above-described hydrogels or hydrogels prepared by any of the above-described methods.

[0017] Furthermore, the dimming function layer can remain transparent when the ambient temperature is below 22°C and switch to an opaque state when the ambient temperature is above 35°C, with a response time of less than 10 seconds for the transparent-opaque state transition.

[0018] Furthermore, the light transmittance of the dimming functional layer does not decrease by more than 5% after 100 transparent-opaque thermal cycles.

[0019] Compared with the prior art, the present invention has the following beneficial effects: This invention features a wide temperature range and precisely adjustable phase change performance: by simply changing the monomer ratio of NIPAM to DEA, the phase change temperature can be continuously and precisely controlled within the range of 22-35°C, which can flexibly adapt to the needs of smart windows in different climate regions from temperate to tropical. This invention possesses excellent optical performance: when NIPAM:DEA=1:9, the visible light transmittance (T) lum The solar modulation rate reached 87.7%, and the solar light modulation rate (ΔT) was 87.7%. sol The coverage rate reached 78.7%, which can effectively balance the needs of "lighting-heat insulation"; This invention has ultra-high mechanical strength: thanks to the synergistic effect of the chemical cross-linking network constructed by DEA nanogel and the PNIPAM physical network, the hydrogel exhibits amazing tensile properties, with a minimum elongation at break of 2000% and a maximum of 4700%, far exceeding that of traditional hydrogels (<300%), and can effectively resist mechanical stress during installation and use. This invention features rapid thermal response and excellent cycling stability: the hydrogel's transparent-opaque state transition can be completed within 10 seconds, demonstrating rapid response. After 100 repeated thermal cycling tests, its optical performance degradation rate does not exceed 5%, proving its excellent long-term operational reliability; The preparation process of this invention is simple: solution polymerization combined with nanogel crosslinking, requiring no complex equipment, low cost, and scalable production.

[0020] For a deeper understanding of the features and technical content of this invention, please refer to the accompanying detailed description and drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0021] Figure 1 This is a flowchart of the preparation process of thermochromic hydrogel, where (a) is a schematic diagram of the application of smart window and (b) is a schematic diagram of the cross-linking structure of NIPAM, DEA and DEA nanogel. Figure 2 These are the phase transition temperature control curves of hydrogels with different NIPAM to DEA molar ratios; Figure 3 These are the UV-Vis and near-infrared transmittance curves of the hydrogel with a NIPAM to DEA molar ratio of 1:9 and actual photographs of the hydrogel's thermal response at different temperatures. Figure 4 These are the stress-strain curves of hydrogels with different NIPAM to DEA molar ratios; Figure 5 The phase transition response time of hydrogels with different NIPAM to DEA molar ratios; Figure 6 It is a smart window simulation test of temperature rise and fall curves. Detailed Implementation

[0022] The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but should not be considered as limiting the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0023] Example 1: Step 1: Preparation of DEA nanogels 50 mL of deionized water was poured into a 250 mL three-necked flask, and nitrogen gas was purged (flow rate 50 mL / min) for 15 minutes to remove oxygen. 10 mL of DEA (purity 99%) was added, and the mixture was magnetically stirred (300 rpm) until completely dissolved. 0.020 g of MBA, 0.027 g of KPS, and 0.27 g of SDS were added sequentially, and stirring was continued until dissolved. The flask was placed in a 60°C constant temperature water bath, and the reaction was carried out under nitrogen protection for 45 minutes to obtain a milky white DEA nanogel solution. The particle size was measured to be 40–200 nm by dynamic light scattering (DLS).

[0024] Step 2: Preparation of thermochromic hydrogel with NIPAM:DEA = 1:9 Weigh 0.0595g NIPAM and 0.5355g DEA (molar ratio 1:9) and add them to a 50mL beaker; add 0.1mL deionized water and 0.9mL of the DEA nanogel prepared in step 1, and stir until completely dissolved; after purging with nitrogen for 15 minutes to remove oxygen, inject the solution into a double-layered glass mold (10×10cm) with a spacing of 1mm using a syringe, seal it, and place it in an ice-water bath (0°C) for polymerization for 24h to obtain a transparent hydrogel sample.

[0025] Example 2 differs from Example 1 in that the molar ratio of NIPAM to DEA is 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, or 1:10. Other steps and parameters are the same as in Example 1.

[0026] Performance testing Phase transition temperature test: The hydrogel prepared in the example was placed in a gradient thermostat (20~40°C), and its transmittance abrupt change point at a wavelength of 500 nm was monitored by a UV-Vis spectrophotometer. The phase transition temperature was measured to be 32°C. Mechanical performance testing: The elongation at break was 4620% when tested using a universal testing machine (tensile rate 50 mm / min). Optical performance testing: The visible light transmittance (400~780nm) is 87.7% at 15°C, dropping to 0% at 45°C, and the solar light modulation rate (ΔT) is... sol The figure was 78.7%; Cyclic stability test: The hydrogel sample was alternately placed in a water bath environment of 15°C (transparent) and 45°C (opaque). Each cycle included heating and cooling until the state was stable. After 100 cycles, the transmittance at 15°C was 87.4%.

[0027] Thermal response speed test: The hydrogel sample, initially placed in an ice-water bath, was rapidly transferred to a 45°C constant-temperature water bath, and the time required for its transmittance to decrease from 87.7% to 0% was recorded. The response time of this sample was approximately 9 seconds.

[0028] Smart window temperature control performance demonstration: A 10×10×10cm heat-insulated acrylic glass test chamber was constructed. A 10×10 cm hydrogel sample from Example 1 was installed on one side as a window interlayer, and a 50W sodium lamp was placed on the other side to simulate sunlight. The chamber was kept at a room temperature of 26°C. oIn an indoor environment (C), the light source was turned on and the temperature change inside the test chamber over time was recorded. A water window with deionized water as the interlayer was used as a control. The experimental results show that the hydrogel smart window of this invention can effectively slow down the rate of temperature rise inside the chamber, and its final equilibrium temperature is significantly lower than that of the control group, demonstrating its excellent active thermal insulation and regulation capabilities.

[0029] Phase transition temperature regulation curves of hydrogels with different NIPAM to DEA molar ratios are shown below. Figure 2 As shown, by Figure 2 It is known that the phase transition temperature of the synthesized thermosensitive gel gradually increases with the increase of DEA monomer content. By fixing the NIPAM elastomer content and adjusting the DEA ratio, the phase transition temperature can be precisely controlled within a wide range of 22°-35°C.

[0030] When the molar ratio of NIPAM to DEA is 1:9, the UV-Vis-NIR transmittance curve of this hydrogel is as follows: Figure 3 As shown in Figure A. Figure 3 As can be seen from Figure A, the gel exhibits excellent light transmittance at low temperatures. Integrated calculations show that its transmittance in the visible light band (400~780nm) reaches 87.7%, and its solar modulation efficiency (ΔT) is [missing value]. sol The transmittance was 78.7%; under high temperature conditions, the hydrogel turned white, and the transmittance was 0 in the entire wavelength range tested, indicating that it has excellent light-blocking performance. Figure 3 B shows real-world images of the hydrogel's thermal response at different temperatures under sunny conditions, visually verifying its excellent temperature response characteristics and sunlight modulation effect.

[0031] Stress-strain curves of hydrogels with different NIPAM to DEA molar ratios are shown below. Figure 4 As shown, by Figure 4 As can be seen, the hydrogels prepared by this invention all exhibit excellent tensile properties, with the elongation at break exceeding 2000% for all sample ratios. The curves in the figure further demonstrate the regulatory effect of component ratio on mechanical properties: with the increase of DEA content, the elongation at break and tensile strength of the gel generally show an increasing trend. This phenomenon is closely related to the crosslinking behavior of the nanogel: the nanogel is prepared from DEA monomers, and the difference in hydrophilicity between DEA and NIPAM makes it more inclined to crosslink with DEA ​​segments to form DEA polymer chains; when the DEA ratio is low, the nanogel is prone to uneven dispersion in the system, resulting in insufficient crosslinking density and ultimately a decrease in the tensile strength of the hydrogel.

[0032] Phase transition response times of hydrogels with different NIPAM to DEA molar ratios are as follows: Figure 5As shown, the regulation law of NIPAM:DEA ratio thermochromic response time was quantitatively revealed: with the increase of DEA content, the response time increased from ~6.53 seconds to ~9.43 seconds. The fast response speed of less than 10 seconds meets the requirements of "real-time dynamic dimming" for smart windows.

[0033] The temperature rise curve of the intelligent window simulation test device is as follows: Figure 6 As shown, by Figure 6 It can be seen that the heating rate of the test chamber with the smart window is significantly lower than that of the control group (water window) with a water interlayer. Compared with the smart window (black curve, maximum temperature approximately 36°C), the water window (red curve) has a faster temperature rise rate, reaching a maximum temperature of approximately 38°C. This indicates that the smart window can more efficiently regulate the heat transfer process during the heat input phase, delaying the temperature rise of the test chamber. Compared to the water window, the smart window has superior temperature regulation performance, effectively reducing the magnitude and rate of temperature rise during heat input, providing new possibilities for practical applications in the field of building energy conservation. During the cooling phase, there is no significant difference in cooling speed between the two, a characteristic that gives the smart window a significant advantage in practical application scenarios such as summer energy-saving cooling, providing strong support for the implementation of passive energy-saving technologies in low-carbon buildings.

[0034] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the scope of the present invention.

Claims

1. A superstretchable thermochromic hydrogel, characterized in that, The hydrogel was polymerized at low temperature using N-isopropylacrylamide (NIPAM) and N,N-diethylacrylamide (DEA) as comonomers and DEA-based nanogel as a crosslinking agent. The hydrogel has a phase transition temperature of 22-35℃, an elongation at break ≥2000%, and a visible light transmittance (T0) in its low-temperature transparent state. lum The maximum value can reach 87.7%; among which, the molar ratio of NIPAM to DEA is 1:1 to 1:

10.

2. The hydrogel according to claim 1, characterized in that, When the molar ratio of NIPAM to DEA is 1:9, the visible light transmittance (T) of the hydrogel is... lum The solar modulation rate (ΔT) was 87.7%. sol The figure was 78.7%.

3. The hydrogel according to claim 1, characterized in that, When the molar ratio of NIPAM to DEA is 1:10, the elongation at break of the hydrogel reaches 4700%.

4. The hydrogel according to claims 1-3, characterized in that, DEA-based nanogels were prepared according to the following steps: DEA monomer was dissolved in deionized water, and N,N'-methylenebisacrylamide, potassium persulfate, and sodium dodecyl sulfonate were added. The mixture was stirred until dissolved and reacted at 40-60°C under nitrogen protection and stirring for 30-45 minutes to obtain DEA nanogel. Among them, N,N'-methylenebisacrylamide accounted for 0.2% of the mass of DEA monomer, potassium persulfate accounted for 0.27% of the mass of DEA monomer, and sodium dodecyl sulfonate accounted for 2.7% of the mass of DEA monomer.

5. The hydrogel according to claim 4, characterized in that, The particle size of DEA-based nanogels is 40-200 nm.

6. The method for preparing the hydrogel according to claims 1-5, characterized in that, Includes the following steps: NIPAM and DEA monomers were mixed, and deionized water and DEA-based nanogels were added. The mixture was stirred until homogeneous, and an inert gas was introduced to remove oxygen. The mixture was then injected into a mold and polymerized at 0-5°C to obtain the superstretched thermochromic hydrogel.

7. The hydrogel according to claims 1-5 or the hydrogel prepared by the method of claim 6 is used as the dimming functional layer of a smart window.

8. A smart window, characterized in that, The dimming layer of the smart window is made of the hydrogel described in claims 1-5 or the hydrogel prepared by the method described in claim 6.

9. The smart window according to claim 8, characterized in that, The dimming function layer can remain transparent when the ambient temperature is below 22°C and switch to an opaque state when the ambient temperature is above 35°C, with a response time of less than 10 seconds for the transparent-opaque state transition.

10. The smart window according to claim 8 or 9, characterized in that, The light transmittance of the dimming functional layer does not decrease by more than 5% after 100 transparent-opaque thermal cycles.

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