Thermochromic hydrogel shielding ultraviolet and near infrared light and preparation method and application thereof

Abstract

The application belongs to the technical field of preparation of thermochromic hydrogel, and discloses a thermochromic hydrogel for shielding ultraviolet and near-infrared light and a preparation method and application thereof. The thermochromic hydrogel is prepared by one-pot low-temperature crosslinking with N-isopropyl acrylamide as a temperature-sensitive matrix, hydroxypropyl methyl cellulose as a modified component, titanium dioxide and cesium tungsten bronze as functional fillers, N, N-methylene bisacrylamide as a crosslinking agent, ammonium persulfate and sodium bisulfite as an initiation system. The thermochromic hydrogel realizes full-band regulation of sunlight by using the ultraviolet shielding of titanium dioxide and the near-infrared heat insulation performance of cesium tungsten bronze. The prepared hydrogel has the characteristics of high visible light transmittance, excellent solar light modulation efficiency and suitable critical transition temperature, and makes up for the defect of insufficient spectral shielding capacity of traditional single PNIPAM hydrogel. The process is mild and simple, the raw materials are cheap and easy to obtain, and the hydrogel is easy to form a film in a large area and to be prepared on a large scale, so the hydrogel can be widely applied to the fields of energy-saving and light-regulating such as intelligent windows of buildings, vehicle-mounted light-regulating glass and the like.

Description

Technical Field

[0001] This invention belongs to the field of thermochromic hydrogel preparation technology, specifically relating to a thermochromic hydrogel that shields against ultraviolet and near-infrared rays, its preparation method, and its applications. This method helps to achieve hydrogels with excellent ultraviolet blocking, near-infrared heat insulation, and thermochromic light transmittance. Background Technology

[0002] Sunlight is rich in ultraviolet (UV) and near-infrared (NIIR) rays. UV rays accelerate the aging and fading of indoor furniture and decorative materials, and cause irreversible damage to human skin. NIIR rays, as a major source of heat radiation, are the core reason for the rapid increase in indoor temperatures and the significant rise in building air conditioning energy consumption in summer. Currently, traditional ordinary glass only provides basic light transmission and cannot effectively block UV and NIIR rays. With the increasing demands for building energy conservation, intelligent vehicle lighting, and healthy and comfortable living environments, smart windows, as a core component of building envelopes for energy saving and consumption reduction, can actively adjust indoor temperature by controlling sunlight transmittance. They have become a key research focus in green building, smart home, and intelligent dimming vehicle windows. While existing commercial coated glass, electrochromic glass, and photochromic glass can achieve a certain degree of light dimming, they generally suffer from low UV shielding efficiency, poor NIIR heat insulation, high raw material and manufacturing costs, complex manufacturing processes, high operating energy consumption, and limited lifespan. They struggle to simultaneously meet the demands for high light transmittance, strong heat insulation, UV protection, and low-cost large-scale application.

[0003] To overcome the technological shortcomings of traditional ordinary glass and existing smart glass materials, thermochromic hydrogels are gradually becoming a preferred new substrate in the field of smart windows. Thermochromic hydrogels rely on their temperature-sensitive phase transition properties, undergoing reversible structural and light-transmitting changes in response to ambient temperature variations. At low temperatures, they maintain high transparency, ensuring sufficient natural indoor lighting. At high temperatures, molecular chain conformational changes and microphase separation occur, blocking sunlight and significantly reducing near-infrared heat radiation entering the room, effectively suppressing room temperature rise and reducing air conditioning energy consumption. Furthermore, through the compounding of functional components, highly efficient ultraviolet shielding and near-infrared heat insulation can be achieved simultaneously before and after the gel phase transition, perfectly meeting the multifunctional application requirements of smart windows in buildings and vehicles. Summary of the Invention

[0004] The present invention aims to provide a thermochromic hydrogel that shields against ultraviolet and near-infrared radiation, its preparation method, and its applications. This invention achieves control over the critical phase transition temperature (LCST) and optical properties of PNIPAM hydrogels by adding appropriate amounts of titanium dioxide (TiO2) and cesium tungsten bronze (Cs). 0.33WO3) achieves shielding against ultraviolet and near-infrared rays, and the resulting PNIPAM / HPMC hydrogel has the characteristics of high transmittance, high solar modulation rate and low critical transition temperature.

[0005] To achieve the above objectives, the following technical solution is adopted:

[0006] In a first aspect, the present invention provides a method for preparing a thermochromic hydrogel that shields against ultraviolet and near-infrared radiation, using N-isopropylacrylamide (NIPAM) as a thermosensitive monomer, hydroxypropyl methylcellulose (HPMC) as a modifying component, and adding titanium dioxide (TiO2) and cesium tungsten bronze (Cs). 0.33 After adding WO3 and water bath conditions, the mixture was allowed to stand at room temperature until it became clear. Then, under stirring, N,N-methylenebisacrylamide (MBA), ammonium persulfate (APS), and sodium bisulfite (NaHSO3) were added as crosslinking agents. After low-temperature crosslinking, PNIPAM / HPMC thermochromic hydrogel was obtained.

[0007] Preferably, the preparation method of the thermochromic hydrogel that shields against ultraviolet and near-infrared rays includes the following specific steps:

[0008] (1) Add N-isopropylacrylamide (NIPAM), hydroxypropyl methylcellulose (HPMC), titanium dioxide (TiO2) and cesium tungsten bronze (Cs) to deionized water. 0.33 WO3), mixed;

[0009] (2) The mixture obtained in step (1) is heated and stirred in a water bath to obtain TiO2 / Cs. 0.33 WO3 mixed with PNIPAM / HPMC turbid solution;

[0010] (3) Let the product obtained in step (2) stand at room temperature until it becomes clear;

[0011] (4) Add the crosslinking agent N,N'-methylenebisacrylamide (MBA), the initiator ammonium persulfate (APS), and sodium bisulfite (NaHSO3) to the clear solution obtained in step (3) with vigorous stirring to obtain a mixed solution;

[0012] (5) Inject the mixture obtained in step (4) into the mold and crosslink it at low temperature to obtain PNIPAM / HPMC thermochromic hydrogel.

[0013] Preferably, in step (1), the TiO2 has a mass fraction of 0.5wt%-3wt%, a rutile crystal form, a particle size of 20-50nm, and Cs... 0.33 The mass fraction of WO3 is 0.5wt%-3wt%, and the particle size is 30-60nm. The mass ratio of NIPAM to HPMC is (3-4):(0.3-0.4).

[0014] Preferably, in step (2), the water bath temperature is 70℃, the rotation speed is 300~400r / min, and the time is 1h.

[0015] Preferably, in step (4), the mass fraction of MBA in the hydrogel is 0.03-0.1 wt%, the mass fraction of APS is 0.03-0.1 wt%, the mass fraction of NaHSO3 is 0.01-0.05 wt%, the stirring speed is 500-600 r / min, and the stirring time is 1-3 min.

[0016] Preferably, in step (5), the temperature for low-temperature crosslinking is 0-3℃ and the crosslinking time is 1h.

[0017] Secondly, the present invention provides a thermochromic hydrogel that shields against ultraviolet and near-infrared rays, which is prepared by the above-described method for preparing thermochromic hydrogels.

[0018] Thirdly, the present invention provides the application of the thermochromic hydrogel described above, which shields against ultraviolet and near-infrared rays, in the preparation of smart windows.

[0019] Preferably, it is used to prepare a thermochromic smart window that shields against ultraviolet and near-infrared rays. The thermochromic smart window is obtained by injecting the thermochromic hydrogel that shields against ultraviolet and near-infrared rays into two pieces of quartz glass sealed with silicone and allowing it to stand.

[0020] Preferably, the thickness of the thermochromic hydrogel is 1-2 mm.

[0021] Compared with the prior art, the present invention has the following effects:

[0022] (1) In this invention, PNIPAM is used as a temperature-sensitive matrix and HPMC is used as an interpenetrating network reinforcing component. NaHSO3 is added to precisely control the critical phase transition temperature (LCST) of the hydrogel, making it suitable for the room temperature range of human dwelling (<30℃). At the same time, the optical properties of the gel are optimized to achieve a reversible response effect of low temperature high light transmittance and high temperature automatic light adjustment and heat insulation.

[0023] (2) Introduce appropriate amounts of TiO2 and Cs 0.33 WO3 functional filler works synergistically to achieve efficient ultraviolet shielding and near-infrared blocking, making up for the lack of intrinsic spectral shielding capability of traditional PNIPAM hydrogels. It can effectively block ultraviolet light damage and near-infrared photothermal effects, greatly improving human health protection and building energy efficiency.

[0024] (3) The preparation process of this invention is mild, the raw materials are readily available, the formulation is compatible, no complex and energy-intensive preparation equipment is required, the operation is simple and controllable, and it is easy to form films on a large area and scale up production. Attached Figure Description

[0025] Figure 1 The doped TiO2 and Cs obtained in Example 1 0.33 UV-Vis-NIR transmittance spectrum of PNIPAM / HPMC hydrogel (PHTC) under WO3.

[0026] Figure 2 This is the UV-Vis-NIR transmittance spectrum of the PNIPAM / HPMC hydrogel (PH) obtained in Comparative Example 1.

[0027] Figure 3 The UV-Vis-NIR transmittance spectrum of the TiO2-doped PNIPAM / HPMC hydrogel (PHT) obtained in Comparative Example 2 is shown.

[0028] Figure 4 Cs obtained from Comparative Example 3 0.33 UV-Vis-NIR transmittance spectrum of WO3-doped PNIPAM / HPMC hydrogel (PHC).

[0029] Figure 5 The doped TiO2 and Cs obtained in Example 1 0.33 DSC phase transition curve of PNIPAM / HPMC hydrogel (PHTC) under WO3.

[0030] Figure 6 This is a SEM image of the thermochromic hydrogel material prepared in Example 1 after freeze-drying.

[0031] Figure 7 These are actual images of the thermochromic hydrogel (PHTC hydrogel) of Example 1 at different temperatures, from 10°C to 40°C and then to 20°C. Detailed Implementation

[0032] The present invention will now be described in detail through specific embodiments. These embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art. As used throughout the specification and claims, the terms "comprising" or "including" are open-ended and are interpreted as "comprising but not limited to". The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are intended to illustrate the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of the invention is determined by the appended claims. Unless otherwise specified, all reagents and materials used in the present invention are commercially available.

[0033] Example 1

[0034] Using NIPAM as the matrix material, HPMC, TiO2 and Cs were added. 0.33 WO3 successfully prepared a thermochromic PNIPAM hydrogel using a simple one-pot method.

[0035] (1) Add 14 mL of deionized water, 3.2 g of N-isopropylacrylamide, 0.3 g of hydroxypropyl methylcellulose, 0.1 g of titanium dioxide powder and 0.1 g of cesium tungsten bronze powder to a beaker;

[0036] (2) Stir at 70°C and 300 r / min for 1 h in a water bath;

[0037] (3) Let the product after heating (2) stand at room temperature until it becomes a clear solution;

[0038] (4) Add 10.6 mg N,N'-methylenebisacrylamide, 10.6 mg ammonium persulfate and 6 mg sodium bisulfite to the clear solution obtained in (3), and stir at 600 r / min for 1 min on a magnetic stirrer;

[0039] (5) The gel obtained in (4) was injected into a glass mold and crosslinked at 0-3℃ for 1 h to obtain TiO2 and Cs 0.33 WO3-doped PNIPAM / HPMC hydrogel smart window.

[0040] Comparative Example 1: Synthesis of PNIPAM / HPMC Hydrogel

[0041] A thermochromic PNIPAM hydrogel was successfully prepared by a simple one-pot method using NIPAM as the matrix material and adding HPMC.

[0042] (1) Add 14 mL of deionized water, 3.2 g of N-isopropylacrylamide, and 0.3 g of hydroxypropyl methylcellulose to a beaker;

[0043] (2) Stir at 70°C and 300 r / min for 1 h in a water bath;

[0044] (3) Let the product after heating (2) stand at room temperature until it becomes a clear solution;

[0045] (4) Add 10.6 mg N,N'-methylenebisacrylamide, 10.6 mg ammonium persulfate and 6 mg sodium bisulfite to the clear solution obtained in (3), and stir at 600 r / min for 1 min on a magnetic stirrer;

[0046] (5) The gel obtained in (4) is injected into a glass mold and crosslinked at 0-3℃ for 1h to obtain a PNIPAM / HPMC hydrogel smart window.

[0047] Comparative Example 2: Synthesis of TiO2-doped PNIPAM / HPMC hydrogel

[0048] A thermochromic PNIPAM hydrogel was successfully prepared by a simple one-pot method using NIPAM as the matrix material and adding HPMC and TiO2.

[0049] (1) Add 14 mL of deionized water, 3.2 g of N-isopropylacrylamide, 0.3 g of hydroxypropyl methylcellulose and 0.1 g of titanium dioxide powder to a beaker;

[0050] (2) Stir at 70°C and 300 r / min for 1 h in a water bath;

[0051] (3) Let the product after heating (2) stand at room temperature until it becomes a clear solution;

[0052] (4) Add 10.6 mg N,N'-methylenebisacrylamide, 10.6 mg ammonium persulfate and 6 mg sodium bisulfite to the clear solution obtained in (3), and stir at 600 r / min for 1 min on a magnetic stirrer;

[0053] (5) The gel obtained in (4) is injected into a glass mold and crosslinked at 0-3℃ for 1h to obtain a TiO2-doped PNIPAM / HPMC hydrogel smart window.

[0054] Comparative Example 3 Cs 0.33 Synthesis of WO3-doped PNIPAM / HPMC hydrogel

[0055] Using NIPAM as the matrix material, HPMC and Cs were added. 0.33 WO3 successfully prepared a thermochromic PNIPAM hydrogel using a simple one-pot method.

[0056] (1) Add 14 mL of deionized water, 3.2 g of N-isopropylacrylamide, 0.3 g of hydroxypropyl methylcellulose and 0.1 g of cesium tungsten bronze powder to a beaker;

[0057] (2) Stir at 70°C and 300 r / min for 1 h in a water bath;

[0058] (3) Let the product after heating (2) stand at room temperature until it becomes a clear solution;

[0059] (4) Add 10.6 mg N,N'-methylenebisacrylamide, 10.6 mg ammonium persulfate and 6 mg sodium bisulfite to the clear solution obtained in (3), and stir at 600 r / min for 1 min on a magnetic stirrer;

[0060] (5) The gel obtained in (4) was injected into a glass mold and crosslinked at 0-3°C for 1 h to obtain Cs. 0.33 WO3-doped PNIPAM / HPMC hydrogel smart window.

[0061] Experimental results

[0062] The hydrogel materials prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were characterized by UV-VIS-NIR detection. The results are as follows: Figure 1 , 2 As shown in Figures 3 and 4, it can be seen that, compared to pH hydrogels, the addition of TiO2 powder enhances the gel's ability to shield against ultraviolet radiation, and the addition of Cs... 0.33 WO3 powder can effectively enhance the near-infrared shielding ability of gels, when TiO2 powder and Cs are simultaneously incorporated. 0.33 The PHTC gel prepared from WO3 powder not only achieves the ability to shield near-infrared rays but also enhances its ability to shield ultraviolet rays.

[0063] The lowest critical dissolution temperature (LCST) of the PHTC hydrogel was determined by differential scanning calorimetry for the material in Example 1, and the results are as follows: Figure 5 As shown, the phase transition temperature of PHTC hydrogel is approximately 24℃, which is lower than that of pure PNIPAM hydrogel (~32℃). This allows for earlier phase transition and effectively improves building energy efficiency.

[0064] The material from Example 1 was subjected to vacuum freeze-drying, and the dried sample was characterized by SEM. The results are as follows: Figure 6 As shown, the PHTC gel exhibits a porous network structure, consisting of TiO2 powder and Cs. 0.33 WO3 powder provides numerous anchoring points, allowing it to be uniformly embedded in the pore walls without agglomeration or sedimentation. This effectively improves the stability of the PHTC hydrogel, giving it excellent optical transmittance and shielding effect.

[0065] The thermochromic smart window prepared in Example 1 was subjected to temperature rise and fall monitoring. Figure 7 The transparent state of the thermochromic hydrogel changes with temperature. When the temperature is raised from 10℃ to 40℃, the gel gradually undergoes a phase transition, and the PHTC gel gradually changes from a transparent state to an opaque state. After the temperature is lowered from 40℃ to 20℃, the gel changes from an opaque state to a transparent state again.

[0066] It is understood that the above specific description of the present invention is only for illustrating the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention to achieve the same technical effect; as long as the use needs are met, they are all within the protection scope of the present invention.

Claims

1. A method for preparing a thermochromic hydrogel that shields against ultraviolet and near-infrared radiation, characterized in that: Using N-isopropylacrylamide (NIPAM) as the thermosensitive monomer and hydroxypropyl methylcellulose (HPMC) as the modifying component, titanium dioxide and cesium tungsten bronze were added. After being placed in a water bath and allowed to stand at room temperature until clear, N,N-methylenebisacrylamide (NIPAM) and ammonium persulfate and sodium bisulfite (HPMC) were added under stirring. After low-temperature crosslinking, PNIPAM / HPMC thermochromic hydrogel was obtained.

2. The method for preparing the thermochromic hydrogel that shields against ultraviolet and near-infrared rays according to claim 1, characterized in that, The specific steps include the following: (1) Add N-isopropylacrylamide (NIPAM), hydroxypropyl methylcellulose (HPMC), titanium dioxide, and cesium tungsten bronze to deionized water and mix. (2) The mixture obtained in step (1) is heated and stirred in a water bath to obtain a turbid solution of titanium dioxide / cesium tungsten bronze mixed PNIPAM / HPMC; (3) Let the product obtained in step (2) stand at room temperature until it becomes clear; (4) Add the crosslinking agent N,N'-methylenebisacrylamide, the initiator ammonium persulfate and sodium bisulfite to the clear solution obtained in step (3) with vigorous stirring to obtain a mixed solution; (5) Inject the mixture obtained in step (4) into the mold and crosslink it at low temperature to obtain PNIPAM / HPMC thermochromic hydrogel.

3. The method for preparing the thermochromic hydrogel that shields against ultraviolet and near-infrared rays according to claim 2, characterized in that: In step (1), the mass fraction of titanium dioxide is 0.5wt%-3wt%, the mass fraction of cesium tungsten bronze is 0.5wt%-3wt%, and the mass ratio of N-isopropylacrylamide to hydroxypropyl methylcellulose is (3-4):(0.3-0.4).

4. The preparation method of the thermochromic hydrogel bar that shields ultraviolet and near-infrared rays according to claim 2, characterized in that: In step (2), the water bath temperature is 70℃, the rotation speed is 300~400r / min, and the time is 1h.

5. The method for preparing the thermochromic hydrogel that shields ultraviolet and near-infrared rays according to claim 2, characterized in that: In step (4), the mass fraction of N,N'-methylenebisacrylamide in the hydrogel is 0.03-0.1 wt%, the mass fraction of ammonium persulfate initiator is 0.03-0.1 wt%, the mass fraction of sodium bisulfite is 0.01-0.05 wt%, the stirring speed is 500-600 r / min, and the stirring time is 1-3 min.

6. The method for preparing the thermochromic hydrogel that shields ultraviolet and near-infrared rays according to claim 2, characterized in that: In step (5), the temperature for low-temperature crosslinking is 0-3℃, and the crosslinking time is 1h.

7. A thermochromic hydrogel that shields against ultraviolet and near-infrared radiation, characterized in that: It is prepared by the method for preparing thermochromic hydrogel according to any one of claims 1-6.

8. The application of the thermochromic hydrogel that shields ultraviolet and near-infrared rays as described in claim 7 in the preparation of smart windows.

9. The application according to claim 8, characterized in that: This invention is applied to the preparation of a thermochromic smart window that shields against ultraviolet and near-infrared radiation. The thermochromic smart window is obtained by injecting the thermochromic hydrogel that shields against ultraviolet and near-infrared radiation into two pieces of quartz glass sealed with silicone and allowing it to stand.

10. The application according to claim 9, characterized in that: The thickness of the thermochromic hydrogel is 1–2 mm.

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