Thermochromic HPC / PEG hydrogel as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of thermochromic HPC / PEG hydrogel, which comprises the following steps: preparing an aqueous solution of hydroxy propyl cellulose (HPC), and slowly adding potassium persulfate (KPS) and a BIS initiator under a stirring condition to obtain HPC hydrogel; adding PEG (Polyethylene Glycol) into the HPC hydrogel, and carrying out ultrasonic mixing to obtain thermochromic HPC / PEG hydrogel; the molecular weight of the PEG is 400 to 20000; the mass percent of the PEG in the HPC / PEG hydrogel is 0 to 50 percent by weight; the thermochromic intelligent window is obtained by injecting the thermochromic HPC / PEG hydrogel between two pieces of quartz glass, then sealing the periphery and standing. By adding PEG with proper content and molecular weight, dual regulation and control of LCST and optical performance of the HPC hydrogel are realized, the problem that low response temperature and high solar modulation capability of the hydrogel cannot be achieved at the same time is solved, and the obtained HPC / PEG hydrogel has the characteristics of high transmittance, high solar modulation efficiency, low critical transition temperature and long cycle life.

Description

Technical Field

[0001] The invention belongs to the technical field of composite materials, and particularly relates to a thermochromic hydrogel. Background Art

[0002] Surveys have found that total building energy consumption is increasing, accounting for 40% of global energy consumption. Windows are a significant contributor to building energy consumption, accounting for over two-thirds of total energy consumption. Traditional windows, due to their poor insulation, allow heat to flow between indoor and outdoor spaces, increasing energy consumption for heating and air conditioning systems. The research and application of smart window glass can significantly improve this problem.

[0003] Thermochromic hydrogels have attracted considerable attention in the field of smart windows due to their high-performance transparency. The transparency of hydrogels can be reduced by scattering incident light as the ambient temperature changes. These smart windows allow sunlight to enter buildings at room temperature while blocking it at higher temperatures. However, current practical applications of thermochromic hydrogels still face numerous challenges, including low transmittance, low modulation efficiency, high critical transition temperature, and poor cycle life, which hinder their practical application in smart windows.

[0004] In order to make the hydrogel smart window meet the needs of practical applications, the ideal smart window should have a low critical solution temperature (<30°C), high visible light transmittance (T lum >88%), high solar modulation efficiency (ΔT sol >70%), high near-infrared light modulation (ΔT NIR >60%) and high stability.

[0005] HPC hydrogel has become a competitive candidate material for smart window applications. However, there are still several major issues that hinder its application: 1) the response temperature (LCST) is higher than the human body's optimal temperature, exceeding 44°C; 2) the near-infrared light modulation (ΔT) above the response temperature (LCST) is not stable. NIR ) and solar modulation (ΔT sol ) is very limited, resulting in poor energy savings; 3) it is difficult to simultaneously optimize both the high response temperature (LCST) and low solar modulation efficiency through a single approach, often requiring multiple, complex approaches. Therefore, the main research question regarding thermochromic hydrogels is how to achieve both high transmittance and high solar modulation efficiency while maintaining a low critical transition temperature. Summary of the Invention

[0006] The present invention aims to provide a thermochromic HPC / PEG hydrogel. By adding PEG of appropriate content and molecular weight, dual regulation of the LCST and optical properties of the HPC hydrogel is achieved, solving the dilemma of the hydrogel's inability to achieve both low response temperature and high solar modulation ability. The resulting HPC / PEG hydrogel has the characteristics of high transmittance, high solar modulation efficiency, low critical transition temperature, and long cycle life.

[0007] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0008] A method for preparing a thermochromic HPC / PEG hydrogel comprises the following steps:

[0009] (1) preparing an aqueous solution of hydroxypropyl cellulose (HPC), and slowly adding potassium persulfate (KPS) and BIS initiator under stirring to obtain an HPC hydrogel;

[0010] (2) Polyethylene glycol (PEG) was added to the HPC hydrogel and ultrasonically mixed to obtain a thermochromic HPC / PEG hydrogel.

[0011] According to the above scheme, the concentration of HPC hydrogel in step (1) is 2.5wt% to 4wt%.

[0012] According to the above scheme, step (1) also includes introducing inert gas to exhaust air.

[0013] According to the above scheme, in step (1), the amount of KPS added is 4wt% to 6wt% of the hydroxypropyl cellulose, and the amount of BIS added is 4wt% to 6wt% of the hydroxypropyl cellulose.

[0014] According to the above scheme, after adding KPS and BIS in step (1), the stirring speed is greater than 300 r / min and the stirring time is 4h to 6h.

[0015] According to the above scheme, the molecular weight of PEG in step (2) is 400-20000.

[0016] According to the above scheme, the mass percentage of PEG in the thermochromic HPC / PEG hydrogel in step (2) is 0 wt % to 50 wt %.

[0017] In the preferred solution, the added amount of PEG400 is 5wt%-50wt%; the added amount of PEG2000 is 5wt%-35wt%; and the added amount of PEG20000 is 5wt%-10wt%.

[0018] A thermochromic HPC / PEG hydrogel was prepared according to the above scheme.

[0019] A thermochromic smart window is obtained by injecting the above-mentioned HPC / PEG hydrogel between two pieces of quartz glass, then sealing them on all sides and letting them stand.

[0020] According to the above scheme, the thickness of the HPC / PEG hydrogel is 1 to 2 mm.

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

[0022] (1) The present invention adds PEG to the HPC hydrogel. The addition of PEG achieves dual regulation of the LCST and optical properties of the HPC hydrogel, solving the dilemma of the hydrogel being unable to achieve both low response temperature and high solar modulation capability.

[0023] (2) By changing the content and molecular weight of PEG, the LCST of the hydrogel can be lowered to a temperature suitable for the human body (<30°C).

[0024] (3) The addition of PEG significantly improved the optical properties of HPC hydrogels. Under the optimal conditions, the hydrogels obtained had low LCST (<30°C) and excellent optical properties (T lum >88%, ΔT lum >80%, ΔT NIR >60%, ΔT sol >70%), and good cycle stability (optical properties remain unchanged after more than 100 heating and cooling cycles).

[0025] (4) The preparation process of the present invention is simple, low in cost, short in production cycle, good in performance, and can be produced on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 : Transmittance spectrum of HPC / PEG400 hydrogel in Example 1 (2.5wt%).

[0027] Figure 2 : Fourier transform infrared spectrum of HPC / PEG2000 hydrogel in Example 2 (2.5wt%).

[0028] Figure 3 : Transmittance spectrum of HPC / PEG2000 hydrogel in Example 2 (2.5wt%).

[0029] Figure 4 : Relationship between the critical solution temperature (LCST) of HPC / PEG2000 hydrogel (2.5 wt%) and the PEG2000 concentration in Example 2.

[0030] Figure 5 : Performance cycle diagram of the (2.5wt%) HPC / PEG2000 hydrogel in Example 2 under 100 heating and cooling conditions.

[0031] Figure 6 : Transmittance spectrum of HPC / PEG20000 hydrogel in Example 3 (2.5wt%).

[0032] Figure 7 : Transmittance spectrum of HPC / PEG400 hydrogel in Example 4 (4 wt %).

[0033] Figure 8 : Transmittance spectrum of HPC / PEG2000 hydrogel in Example 5 (4 wt %).

[0034] Figure 9 : Transmittance spectrum of (4 wt %) HPC / PEG20000 hydrogel in Example 6. DETAILED DESCRIPTION

[0035] The following examples further illustrate the technical solutions of the present invention but are not intended to limit the scope of protection of the present invention.

[0036] Example 1

[0037] Preparation of (2.5wt%) HPC / PEG400 hydrogel:

[0038] (1) First, 2.5 g of HPC powder was dissolved in 97.5 g of deionized water and stirred in a beaker at room temperature for 24 hours to obtain a uniform and transparent initial solution. The initial solution was added to a three-necked flask, and 4 wt% BIS and 4 wt% KPS were added sequentially to initiate polymerization. The entire polymerization reaction was carried out under nitrogen protection. After stirring at room temperature for 4 hours, an HPC hydrogel with a mass fraction of 2.5% was obtained.

[0039] (2) Several 1g HPC hydrogels were placed in a test tube. PEG400 at varying mass fractions (0wt%-50wt%) was then added to the hydrogels and sonicated in an ice-water bath until completely dissolved. This yielded a series of composite HPC / PEG400 hydrogels. The composite hydrogels were then rapidly injected into a 1-2mm thick layer between two sheets of quartz glass and allowed to stand for a period of time to form a composite hydrogel smart window.

[0040] Figure 1This is the transmittance spectrum of the (2.5wt%) HPC / PEG400 hydrogel prepared in this example. The transmittance of the hydrogel was tested in the 300-2500nm sunlight band using a UV-3600 ultraviolet-visible-near-infrared spectrophotometer. The following examples are the same as above. The solid line represents the transmittance curve of the hydrogel tested at 20°C, and the dotted line represents the transmittance curve corresponding to the test at 40°C. As can be seen from the figure, the HPC / PEG400 hydrogel has a very high visible light transmittance at 20°C, T lum At 40°C, as the PEG400 content increases, the transmittance curve of the HPC / PEG400 hydrogel gradually shifts downward, and the transmittance continues to decrease. This indicates that the introduction of PEG400 improves the optical properties of the HPC hydrogel, with a solar modulation efficiency of 70.09% and a near-infrared modulation rate exceeding 40%.

[0041] Example 2

[0042] Preparation of (2.5 wt%) HPC / PEG2000 hydrogel:

[0043] (1) First, 2.5 g of HPC powder was dissolved in 97.5 g of deionized water and stirred in a beaker at room temperature for 24 hours to obtain a uniform and transparent initial solution. The initial solution was added to a three-necked flask, and 4 wt% BIS and 4 wt% KPS were added sequentially to initiate polymerization. The entire polymerization reaction was carried out under nitrogen protection. After stirring at room temperature for 4 hours, an HPC hydrogel with a mass fraction of 2.5% was obtained.

[0044] (2) Several 1g HPC hydrogels were placed in a test tube. PEG2000 at varying mass fractions (0wt%-35wt%) was then added to the hydrogels and sonicated in an ice-water bath until completely dissolved. This yielded a series of composite HPC / PEG2000 hydrogels. The composite hydrogels were then rapidly injected into a 1-2mm thick interlayer between two sheets of quartz glass and allowed to stand for a period of time to form a composite hydrogel smart window.

[0045] Figure 2 The infrared spectra of (2.5 wt%) HPC and (2.5 wt%) HPC / PEG2000 hydrogels prepared in this example were obtained. The chemical composition of HPC and HPG2000 hydrogels was determined by FTIR spectroscopy. -1 The absorption peak at 2970 cm is caused by the stretching vibration of the hydroxyl group in HPC. -1 and 2874cm -1 The absorption peak at 1047 cm is caused by the CH stretching vibration in HPC. -1The absorption peak at 3424 cm is caused by the stretching vibration of COC in HPC. The presence of these characteristic peaks indicates that the sample is an ideal HPC hydrogel. In the HPG2000 composite hydrogel, with the increase of PEG2000 content, the absorption peak at 3424 cm -1 The absorption peak intensity caused by OH stretching vibration increases near 1467cm -1 The absorption peak caused by the binding vibration of CH was observed near 2888 cm -1 The characteristic peak produced by the methylene stretching vibration can be observed near 1343 cm -1 and 1281cm -1 The absorption peak at is caused by CO stretching vibration, indicating that PEG2000 is successfully incorporated into HPC.

[0046] Figure 3 The transmittance spectrum of the (2.5 wt%) HPC / PEG2000 hydrogel prepared in this example is shown in Figure 2. The solid line represents the transmittance curve of the hydrogel tested at 20°C, and the dotted line represents the transmittance curve of the hydrogel tested at 40°C. As can be seen from the figure, the HPC / PEG2000 hydrogel has a very high visible light transmittance at 20°C. lum At 40°C, as the PEG2000 content increases, the transmittance curve of the HPC / PEG2000 hydrogel gradually shifts downward, and the transmittance continues to decrease. This indicates that the introduction of PEG400 improves the optical properties of the HPC hydrogel, with a solar modulation efficiency of 84.19% and a near-infrared modulation rate exceeding 70%.

[0047] Figure 4 The graph shows the relationship between the critical solution temperature (LCST) and PEG2000 concentration for the (2.5 wt%) HPC / PEG2000 hydrogel prepared in this example. As can be seen from the figure, the critical solution temperature of the (2.5 wt%) HPC / PEG2000 hydrogel decreases with increasing PEG2000 content. At 35 wt% PEG2000, the hydrogel's LCST is 24°C.

[0048] Figure 5 This graph shows the transmittance of the 2.5 wt% HPC / PEG2000 hydrogel prepared in this example after 100 cycles of heating and cooling. As can be seen from the graph, after 100 cycles of heating and cooling, the transmittance of the hydrogel remains essentially unchanged at both 20°C and 40°C, demonstrating the stability of the hydrogel's performance.

[0049] Example 3

[0050] Preparation of (2.5wt%) HPC / PEG20000 hydrogel:

[0051] (1) First, 2.5 g of HPC powder was dissolved in 97.5 g of deionized water and stirred in a beaker at room temperature for 24 hours to obtain a uniform and transparent initial solution. The initial solution was added to a three-necked flask, and 4 wt% BIS and 4 wt% KPS were added sequentially to initiate polymerization. The entire polymerization reaction was carried out under nitrogen protection. After stirring at room temperature for 4 hours, an HPC hydrogel with a mass fraction of 2.5% was obtained.

[0052] (2) Several 1g HPC hydrogels were placed in a test tube. PEG20000 at varying mass fractions (5wt%-10wt%) was then added to the hydrogels and sonicated in an ice-water bath until completely dissolved. This yielded a series of composite (2.5wt%) HPC / PEG20000 hydrogels. The composite hydrogels were then rapidly injected into a 1-2mm thick interlayer between two sheets of quartz glass and allowed to stand for a period of time to form a composite hydrogel smart window.

[0053] Figure 6 The transmittance spectrum of the (2.5 wt%) HPC / PEG20000 hydrogel prepared in this example is shown in Figure 2. The solid line represents the transmittance curve of the hydrogel tested at 20°C, and the dotted line represents the transmittance curve of the hydrogel tested at 40°C. As can be seen from the figure, the HPC / PEG20000 hydrogel has a very high visible light transmittance at 20°C. lum At 40°C, as the PEG20000 content increases, the transmittance curve of the (2.5wt%) HPC / PEG20000 hydrogel gradually shifts downward, and the transmittance continues to decrease. This indicates that the introduction of PEG20000 improves the optical properties of the HPC hydrogel, with a solar modulation efficiency of 80.04% and a near-infrared modulation rate exceeding 60%.

[0054] Example 4

[0055] Preparation of (4 wt%) HPC / PEG400 hydrogel:

[0056] (1) First, 4 g of HPC powder was dissolved in 96 g of deionized water and stirred at room temperature for 24 hours in a beaker to obtain a homogeneous and transparent initial solution. The initial solution was added to a three-necked flask, and 6 wt% BIS and 6 wt% KPS were added sequentially to initiate polymerization. The entire polymerization reaction was carried out under nitrogen protection. After stirring at room temperature for 4 hours, an HPC hydrogel with a mass fraction of 4% was obtained.

[0057] (2) Several 1g HPC hydrogels were placed in a test tube. PEG400 at varying mass fractions (30wt%-50wt%) was then added to the hydrogels and sonicated in an ice-water bath until completely dissolved. This yielded a series of composite (4wt%) HPC / PEG400 hydrogels. The composite hydrogels were then rapidly injected into a 1-2mm thick interlayer between two sheets of quartz glass and allowed to stand for a period of time to form a composite hydrogel smart window.

[0058] Figure 7 The transmittance spectrum of the (4 wt%) HPC / PEG400 hydrogel prepared in this example is shown in Figure 2. The solid line represents the transmittance curve of the hydrogel tested at 20°C, and the dotted line represents the transmittance curve of the hydrogel tested at 40°C. As can be seen from the figure, the HPC / PEG400 hydrogel has a very high visible light transmittance at 20°C. lum At 40°C, as the PEG400 content increases, the transmittance curve of the (4wt%) HPC / PEG400 hydrogel gradually shifts downward, and the transmittance continues to decrease. This indicates that the introduction of PEG400 improves the optical properties of the HPC hydrogel, with a solar modulation efficiency of 77.47% and a near-infrared modulation rate exceeding 40%.

[0059] Example 5

[0060] Preparation of (4 wt%) HPC / PEG2000 hydrogel:

[0061] (1) First, 4 g of HPC powder was dissolved in 96 g of deionized water and stirred at room temperature for 24 hours in a beaker to obtain a homogeneous and transparent initial solution. The initial solution was added to a three-necked flask, and 6 wt% BIS and 6 wt% KPS were added sequentially to initiate polymerization. The entire polymerization reaction was carried out under nitrogen protection. After stirring at room temperature for 4 hours, an HPC hydrogel with a mass fraction of 4% was obtained.

[0062] (2) Several 1g HPC hydrogels were placed in test tubes. PEG2000 at varying mass fractions (10wt%-30wt%) was then added to the hydrogels and sonicated in an ice-water bath until completely dissolved. This yielded a series of composite (4wt%) HPC / PEG2000 hydrogels. The composite hydrogels were then rapidly injected into a 1-2mm thick interlayer between two sheets of quartz glass and allowed to stand for a period of time to form composite hydrogel smart windows.

[0063] Figure 8The transmittance spectrum of the (4 wt%) HPC / PEG2000 hydrogel prepared in this example is shown in Figure 2. The solid line represents the transmittance curve of the hydrogel tested at 20°C, and the dotted line represents the transmittance curve of the hydrogel tested at 40°C. As can be seen from the figure, the HPC / PEG2000 hydrogel has a very high visible light transmittance at 20°C. lum At 40°C, as the PEG2000 content increases, the transmittance curve of the (4wt%) HPC / PEG2000 hydrogel gradually shifts downward, and the transmittance continues to decrease. This indicates that the introduction of PEG2000 improves the optical properties of the HPC hydrogel, with a solar modulation efficiency of 84.24% and a near-infrared modulation rate exceeding 70%.

[0064] Example 6

[0065] Preparation of (4 wt%) HPC / PEG20000 hydrogel:

[0066] (1) First, 4 g of HPC powder was dissolved in 96 g of deionized water and stirred at room temperature for 24 hours in a beaker to obtain a homogeneous and transparent initial solution. The initial solution was added to a three-necked flask, and 6 wt% BIS and 6 wt% KPS were added sequentially to initiate polymerization. The entire polymerization reaction was carried out under nitrogen protection. After stirring at room temperature for 4 hours, an HPC hydrogel with a mass fraction of 4% was obtained.

[0067] (2) Several 1g HPC hydrogels were placed in a test tube. PEG20000 at varying mass fractions (5wt%-10wt%) was then added to the hydrogels and sonicated in an ice-water bath until completely dissolved. This yielded a series of composite (4wt%) HPC / PEG20000 hydrogels. The composite hydrogels were then rapidly injected into a 1-2mm thick interlayer between two sheets of quartz glass and allowed to stand for a period of time to form a composite hydrogel smart window.

[0068] Figure 9 The transmittance spectrum of the (4 wt%) HPC / PEG20000 hydrogel prepared in this example is shown in Figure 2. The solid line represents the transmittance curve of the hydrogel tested at 20°C, and the dotted line represents the transmittance curve of the hydrogel tested at 40°C. As can be seen from the figure, the HPC / PEG20000 hydrogel has a very high visible light transmittance at 20°C. lum At 40°C, as the PEG20000 content increases, the transmittance curve of the (4wt%) HPC / PEG20000 hydrogel gradually shifts downward, and the transmittance continues to decrease. This indicates that the introduction of PEG20000 improves the optical properties of the HPC hydrogel, with a solar modulation efficiency of 81.92% and a near-infrared modulation rate exceeding 70%.

Claims

1. A method for preparing a thermochromic HPC / PEG hydrogel, characterized in that The following steps are involved: (1) preparing an aqueous solution of hydroxypropyl cellulose (HPC), and slowly adding potassium persulfate (KPS) and BIS initiator under stirring to obtain an HPC hydrogel; (2) Polyethylene glycol (PEG) was added to the HPC hydrogel and ultrasonically mixed to obtain a thermochromic HPC / PEG hydrogel.

2. The preparation method of thermochromic HPC / PEG hydrogel as claimed in claim 1, characterized in that The concentration of the HPC hydrogel in step (1) is 2.5 wt% to 4 wt%.

3. The preparation method of thermochromic HPC / PEG hydrogel as claimed in claim 1, characterized in that Step (1) also includes introducing inert gas to exhaust air.

4. The preparation method of thermochromic HPC / PEG hydrogel as claimed in claim 1, characterized in that In step (1), the amount of KPS added is 4wt% to 6wt% of the hydroxypropyl cellulose, and the amount of BIS added is 4wt% to 6wt% of the hydroxypropyl cellulose.

5. The preparation method of thermochromic HPC / PEG hydrogel as claimed in claim 1, characterized in that After adding KPS and BIS in step (1), the stirring speed is greater than 300 r / min and the stirring time is 4 h to 6 h.

6. The method for preparing the thermochromic HPC / PEG hydrogel according to claim 1, wherein The molecular weight of PEG in step (2) is 400-20000; the mass percentage of PEG in the thermochromic HPC / PEG hydrogel is 0wt% to 50wt%.

7. The method for preparing the thermochromic HPC / PEG hydrogel according to claim 6, wherein The added amount of PEG400 is 5wt%-50wt%; the added amount of PEG2000 is 5wt%-35wt%; and the added amount of PEG20000 is 5wt%-10wt%.

8. A thermochromic HPC / PEG hydrogel, characterized in that The thermochromic HPC / PEG hydrogel is prepared by the preparation method of any one of claims 1 to 7.

9. A thermochromic smart window, characterized in that The thermochromic HPC / PEG hydrogel according to claim 8 is injected between two pieces of quartz glass, and then sealed on all sides and left to stand.

10. The thermochromic smart window according to claim 9, characterized in that The thickness of the HPC / PEG hydrogel is 1 to 2 mm.

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