Liquid dual-network thermochromic hydrogel and preparation method thereof

Abstract

The invention discloses liquid dual-network thermochromic hydrogel and a preparation method thereof. The preparation method specifically comprises the following steps: S01, preparing dual-network isopropyl acrylamide PNIPAm hydrogel; s02, preparing carrageenan KCA into a KCA solution, uniformly mixing and stirring the PNIPAm hydrogel prepared in the step S01 and the KCA solution according to a certain proportion, then adding a sodium silicate Na2SiO3 solution, and mixing and stirring to obtain the liquid dual-network thermochromic hydrogel. The carrageenan and Na2SiO3 are introduced into the PNIPAm hydrogel, so that the technical effects of low LCST, excellent visible light transmittance and long-term stability of the liquid dual-network thermochromic hydrogel are realized. The method can be applied to manufacturing of intelligent doors and windows or photovoltaic glass on a large scale.

Description

Technical Field

[0001] The invention relates to the field of polymer materials, and in particular to a liquid double-network thermochromic hydrogel and a preparation method thereof. Background Art

[0002] Smart windows can adjust indoor temperature and lighting according to external conditions, which helps to save energy in buildings and has been vigorously developed. Smart windows are classified according to external stimuli, including mechanical color change, electrochromic change, photochromic change and thermochromic change. Among them, thermochromic self-responsive smart windows are favored due to their simple structure. The main working principle of thermochromic smart windows depends on high-performance thermochromic materials.

[0003] At present, reported thermochromic materials mainly include inorganic vanadium dioxide and various organic compounds such as poly n -isopropylacrylamide (PNIPAm), poly n -vinylcaprolactam, chitosan, hydroxypropylmethylcellulose and polythiophene. Among them, PNIPAm polymer stands out for its excellent switching properties and lower critical solution temperature (LCST) of 32 °C.

[0004] However, the inventors of this application found that the above technology has at least the following technical problems in the process of implementing the technical solution of the invention in the embodiment of this application: 1. The phase change of pure PNIPAm thermochromic material at 32°C cannot meet the human body's comfortable adaptive temperature requirement of 22-27°C.

[0005] 2. The existing technology is to dope inorganic salts into PNIPAm thermochromic material hydrogel to reduce the LCST of pure PNIPAm thermochromic material hydrogel and improve its cooling performance. However, the aggregation of PNIPAm molecules caused by inorganic salts in pure PNIPAm thermochromic material hydrogel reduces the stability of PNIPAm hydrogel, and also reduces the visible light transmittance and durability of PNIPAm smart window. Summary of the invention

[0006] The embodiments of the present application provide a liquid double-network thermochromic hydrogel and a preparation method thereof, thereby solving the problems of high LCST and poor visible light transmittance of thermochromic PNIPAm hydrogel in the prior art. By introducing carrageenan and Na2SiO3 into the PNIPAm hydrogel, the technical effects of low LCST, excellent visible light transmittance and long-term stability of the liquid double-network thermochromic hydrogel are achieved.

[0007] The present application provides a method for preparing a liquid double-network thermochromic hydrogel, which specifically includes the following steps: S01 Preparation of double network isopropyl acrylamide PNIPAm hydrogel; S02 Carrageenan KCA is made into a KCA solution, the PNIPAm hydrogel prepared in step S01 and the KCA solution are mixed and stirred evenly in a certain proportion, and then sodium silicate Na2SiO3 solution is added, and the mixture is mixed and stirred to obtain a double-network thermochromic liquid double-network hydrogel.

[0008] Preferably, in step S02, the ratio of the PNIPAm hydrogel to the carrageenan KCA is 1:1 to 1:3.

[0009] Preferably, the concentration of the sodium silicate Na2SiO3 solution is 0.2~0.7wt%.

[0010] Preferably, the preparation method of double network isopropyl acrylamide PNIPAm hydrogel is as follows: Step 1: Mix the monomer isopropyl acrylamide, the cross-linking agent and ultrapure water to prepare a solution A for standby use, wherein the content of the monomer isopropyl acrylamide in the solution A is 9.1% to 16%; Step 2: Weigh out monomer isopropyl acrylamide, crosslinking agent and ultrapure water, dissolve them in a beaker and stir to mix evenly, wherein the monomer isopropyl acrylamide accounts for 0.25% to 0.45% of the total solution in the beaker, and after being fully dissolved, N2 is continuously introduced, and the water bath is heated and stirred continuously. N, N, N'N'-tetramethylethylenediamine is slowly added to the beaker, and then ammonium sulfate solution is added, the temperature is increased, and the solution A is slowly added dropwise using a peristaltic pump after continuous stirring. After a period of time, heating and N2 introduction are stopped to obtain a double network isopropyl acrylamide PNIPAm hydrogel.

[0011] Preferably, the carrageenan KCA in step S02 can be replaced by sodium alginate.

[0012] Preferably, the sodium silicate Na2SiO3 in step S02 can be replaced by potassium silicate.

[0013] The present application example also provides a liquid double-network thermochromic hydrogel, as prepared in the present application example.

[0014] The embodiment of the present application also provides an application of a liquid double-network thermochromic hydrogel, and the application of the liquid double-network thermochromic hydrogel in smart windows or photovoltaic glass cooling materials.

[0015] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages: 1. The liquid double network thermochromic hydrogel is prepared by introducing carrageenan solution or sodium alginate solution and Na2SiO3 solution or K2SiO3 solution into the double network PNIPAm hydrogel. KCA or sodium alginate enhances the T of the liquid double network thermochromic hydrogel.lum and ΔT sol Na2SiO3 solution or K2SiO3 solution reduces LCST and promotes phase transition at low temperature, thus effectively solving the problem of high LCST and low visible transmittance of PNIPAm hydrogel in the prior art, thereby achieving the technical effect of low LCST and excellent visible transmittance of liquid double-network thermochromic hydrogel. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The experimental effect diagram of the liquid hydrogel injected into the double-layer glass in Example 1 of the present application, wherein the left diagram is a schematic diagram of the light transmission of the glass at low temperature, and the right diagram is a schematic diagram of the light transmission of the glass at high temperature; Figure 2 This is a scanning electron microscope morphology image of the liquid hydrogel in Example 1 of the present application; Figure 3 This is a pore size distribution diagram of a liquid hydrogel in Example 1 of the present application; Figure 4 This is a diagram of the experimental results of using liquid hydrogel in smart windows for outdoor cooling according to Example 1 of the present application. DETAILED DESCRIPTION

[0017] The embodiments of the present application provide a liquid double-network thermochromic hydrogel and a preparation method thereof, thereby solving the problems of high LCST and poor visible light transmittance of thermochromic PNIPAm hydrogel in the prior art. By introducing carrageenan and Na2SiO3 into the PNIPAm hydrogel, the LCST of the liquid double-network thermochromic hydrogel is reduced, thereby improving the stability and transmittance of the liquid double-network thermochromic hydrogel.

[0018] The technical solution in the embodiment of the present application is to solve the above problems, and the overall idea is as follows: The network stability of PNIPAm hydrogel was enhanced by preparing a double-crosslinked PNIPAm polymer network system; then carrageenan or sodium alginate and Na2SiO3 or K2SiO3 were introduced into the double-crosslinked network system PNIPAm hydrogel to obtain a liquid double-network hydrogel. The sodium ions or potassium ions in Na2SiO3 or K2SiO3 can destroy hydrogen bonds, reduce LCST and promote phase transition at low temperatures. The Si-O bond vibration in Na2SiO3 or K2SiO3 silicate ions showed strong absorption in the 10 μm band and had a high atmospheric window emissivity (0.962); at the same time, the addition of KCA or sodium alginate enhanced Tlum and ΔTsol; due to the combined effect, the temperature dropped by 12.3°C under direct sunlight, and remained highly stable even after 100 high and low temperature durability cycle tests.

[0019] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods. Embodiment 1

[0020] S01. Weigh 3.5 g of monomer isopropyl acrylamide, 0.168 g of cross-linking agent N,N'-methylenebisacrylamide and 25 mL of ultrapure water in a beaker and stir for 30 min to obtain solution A.

[0021] S02, add 115 mL of ultrapure water, 0.4 g of monomer isopropyl acrylamide and 0.007 g of cross-linking agent N,N'-methylenebisacrylamide into a three-necked flask. After fully dissolved, continue to introduce N2, adjust the water bath heating temperature to 50 °C, and continue stirring for 1 hour.

[0022] S03. Slowly add 0.6 mL of N, N, N'N'-tetramethylethylenediamine into the flask, followed by 0.8 mL of 10 wt% ammonium sulfate solution, raise the temperature to 70 °C, continue stirring for 1 min, and then slowly add solution A using a peristaltic pump. After 2 h, stop heating and stop passing N2 to obtain isopropylacrylamide PNIPAm hydrogel.

[0023] S04. Weigh 0.25 g of KCA and dissolve it in 50 mL of ultrapure water. Stir and swell at 50 °C for 1 h, then raise the temperature to 75 °C, stir again for 1 h, and finally cool to 40 °C for use.

[0024] S05. The PNIPAm hydrogel prepared in S03 and the carrageenan KCA solution prepared in S04 were mixed in a ratio of 1:2 and stirred for 1 h, and then 0.3 wt% Na2SiO3 solution was added and stirred to obtain a liquid double network hydrogel①.

[0025] The liquid double network hydrogel ① obtained in Example 1 was injected into a double-layer window and tested under simulated sunlight of AM 1.5G. The test results showed that the liquid double network hydrogel ① could reduce the temperature by 12.3°C and the low-temperature transmittance was 89%. Embodiment 2

[0026] The preparation process of this embodiment is the same as the process S01 to S05 of the embodiment 1, except that in S05, the concentration of sodium silicate is increased to 0.6 wt %, to obtain a liquid double network hydrogel ②.

[0027] The liquid double network hydrogel ② obtained in Example 2 was injected into a double-layer window and tested under simulated sunlight of AM 1.5G. The test results showed that the liquid double network hydrogel ② could reduce the temperature by 25.4°C, and the low-temperature transmittance was 78%. Embodiment 3

[0028] The preparation process of this embodiment is the same as the process S01 to S05 of the first embodiment, except that the carrageenan KCA solution is replaced with a sodium alginate solution, and the sodium silicate is replaced with potassium silicate to obtain a liquid double network hydrogel ③.

[0029] The liquid double network hydrogel ③ obtained in Example 3 was injected into a double-layer window and tested under simulated sunlight of AM 1.5G. The test results showed that the liquid double network hydrogel ③ could reduce the temperature by 11.5°C and the low-temperature transmittance was 87%. Embodiment 4

[0030] The preparation process of this embodiment is the same as the process S01 to S05 of the embodiment 1, except that sodium silicate is replaced with potassium silicate to obtain a liquid double network hydrogel ④.

[0031] The liquid double network hydrogel ④ obtained in Example 4 was injected into a double-layer window and tested under simulated sunlight of AM 1.5G. The test results showed that the liquid double network hydrogel ④ could reduce the temperature by 11.9°C and the low-temperature transmittance was 87.6%. Embodiment 5

[0032] The preparation process of this embodiment is the same as the process S01 to S05 of the first embodiment, except that the carrageenan KCA solution is replaced with a sodium alginate solution to obtain a liquid double network hydrogel ⑤.

[0033] The liquid double network hydrogel ⑤ obtained in Example 5 was injected into a double-layer window and tested under simulated sunlight of AM 1.5G. The test results showed that the liquid double network hydrogel ⑤ could reduce the temperature by 12°C, and the low-temperature transmittance was 88.5%.

[0034] The technical solutions in the above embodiments of the present application have at least the following technical effects: The liquid double network thermochromic hydrogel was prepared by introducing carrageenan solution or sodium alginate solution and Na2SiO3 solution or K2SiO3 solution into the double network PNIPAm hydrogel. The T of the liquid double network thermochromic hydrogel was enhanced by KCA or sodium alginate. lum and ΔT sol Na2SiO3 solution or K2SiO3 solution reduces LCST and promotes phase transition at low temperature, thus effectively solving the problem of high LCST and low visible transmittance of PNIPAm hydrogel in the prior art, thereby achieving the technical effect of low LCST and excellent visible transmittance of liquid double-network thermochromic hydrogel.

[0035] The double-network thermochromic hydrogel provided in the embodiment of the present application can be applied to photovoltaic glass due to its excellent technical effects of low LCST and excellent visible light transmittance, thereby achieving the technical effect of cooling the photovoltaic glass.

[0036] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0037] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a liquid double-network thermochromic hydrogel, wherein: The specific steps include: S01 Preparation of double network isopropyl acrylamide PNIPAm hydrogel; S02 Carrageenan KCA is made into a KCA solution, the PNIPAm hydrogel prepared in step S01 and the KCA solution are mixed and stirred evenly in a certain proportion, and then sodium silicate Na2SiO3 solution is added, and the mixture is mixed and stirred to obtain a liquid double network thermochromic hydrogel.

2. The preparation method according to claim 1, wherein The ratio of the PNIPAm hydrogel to the carrageenan KCA in step S02 is 1:1 to 1:

3.

3. The preparation method according to claim 1, wherein The concentration of the sodium silicate Na2SiO3 solution is 0.2-0.7wt%.

4. The preparation method according to claim 1, wherein The preparation method of double network isopropyl acrylamide PNIPAm hydrogel is as follows: Step 1: Mix the monomer isopropyl acrylamide, the cross-linking agent and ultrapure water to prepare a solution A for standby use, wherein the content of the monomer isopropyl acrylamide in the solution A is 9.1% to 16%; Step 2: Weigh out monomer isopropyl acrylamide, crosslinking agent and ultrapure water and dissolve them in a beaker, stir and mix them evenly, wherein the monomer isopropyl acrylamide accounts for 0.25% to 0.45% of the total solution in the beaker, and after it is fully dissolved, N2 is continuously introduced, and the water bath is heated and stirred continuously. N, N, N'N'-tetramethylethylenediamine is slowly added to the beaker, and then ammonium sulfate solution is added. The temperature is increased, and the solution A is slowly added dropwise using a peristaltic pump after continuous stirring. After a period of time, the heating and the introduction of N2 are stopped to obtain a liquid double-network isopropyl acrylamide PNIPAm hydrogel.

5. The preparation method according to claim 1, wherein The carrageenan KCA in step S02 can be replaced by sodium alginate.

6. The preparation method according to claim 1, wherein The sodium silicate Na2SiO3 in step S02 can be replaced by potassium silicate.

7. A liquid double-network thermochromic hydrogel, wherein: It is prepared by the preparation method described in any one of claims 1 to 6 above.

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