Hydroxypropyl cellulose-based structural color smart window and preparation method thereof

Abstract

This invention provides a structural color smart window based on hydroxypropyl cellulose and its preparation method, belonging to the field of thermochromic hydrogel technology. The structural color smart window of this invention is prepared by mixing sodium lignosulfonate and hydroxypropyl cellulose, followed by self-assembly and sealing at room temperature. The structural color smart window prepared by this invention achieves synergistic control of the structural color and the lowest critical solution temperature (LCST) of the hydrogel. The process is simple and effectively solves the technical problems of excessively high response temperature and complex color control in traditional materials. By adjusting the content of sodium lignosulfonate, the LCST of the hydrogel can be precisely adjusted to a suitable operating temperature over a wide range, while simultaneously obtaining highly efficient transmittance modulation performance. The introduction of sodium lignosulfonate changes the state and distribution of water molecules in the gel network, achieving multicolor and reversible control of the structural color.

Description

Technical Field

[0001] This invention belongs to the field of thermochromic hydrogel technology, specifically relating to a structural color smart window based on hydroxypropyl cellulose and its preparation method. Background Technology

[0002] With the increasing global demand for energy-efficient and comfortable buildings, smart window technology, as a passive energy-saving solution that can dynamically adjust solar radiation, has received widespread attention from academia and industry. Among them, thermochromic smart windows can autonomously adjust their light transmittance or reflectivity according to changes in ambient temperature without the need for external energy input, making them a highly promising type of smart window material.

[0003] Currently, smart windows based on hydrogel materials are an important research direction in the field of smart windows. These smart windows mainly utilize the interaction between hydrophilic groups and water in the three-dimensional network structure of hydrogels, undergoing a reversible swelling-contraction phase transition when the ambient temperature changes, thereby achieving intelligent regulation of the transmittance of sunlight (especially near-infrared light). Existing technologies include the use of the isotope deuterium water (D2O) to prepare hydrogel smart window systems, solving the problem of strong near-infrared absorption in traditional hydrogels and improving the transmittance modulation rate. Other existing technologies utilize the crosslinking method of hydroxypropyl cellulose and polyethylene glycol to prepare thermochromic hydrogels with high transmittance and high solar modulation rate.

[0004] While hydrogel-based smart window materials have shown potential in thermal response dimming, they still have significant drawbacks: traditional hydrogels (such as PNIPAm) rely on petroleum-based raw materials, making them less environmentally friendly; hydroxypropyl cellulose (HPC) is a promising ideal substrate for constructing green smart windows, but it still faces several key bottlenecks: firstly, its minimum critical melting temperature (LCST) is usually above 44°C, exceeding the range of human comfort temperatures, limiting its applicability in room-temperature energy-saving windows; secondly, its optical state can usually only switch between transparent and milky white, resulting in a single function and lack of color; and thirdly, it is difficult to achieve a lower LCST and higher solar modulation efficiency through a single method, often requiring multi-step modification or composite strategies, which are complex and challenge the reproducibility of the process.

[0005] Therefore, providing a smart window with a simple preparation method, low minimum critical dissolution temperature, high solar modulation rate, and adjustable structural color has become a challenge in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a structural color smart window based on hydroxypropyl cellulose and its preparation method. The preparation method provided by this invention is simple, and the prepared hydrogel smart window has advantages such as tunable structural color, low minimum critical dissolution temperature, and high solar light modulation rate.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a structural color smart window based on hydroxypropyl cellulose, comprising the following steps: (1) Sodium lignosulfonate, water and hydroxypropyl cellulose were mixed to obtain a precursor solution; (2) The precursor solution obtained in step (1) is self-assembled to obtain a structure color smart window based on hydroxypropyl cellulose.

[0008] Preferably, in step (1), the mass ratio of sodium lignosulfonate to water is (1~5) g: (95~99) mL.

[0009] Preferably, in step (1), the mass ratio of sodium lignosulfonate to water is (1~3) g: (97~99) mL.

[0010] Preferably, in step (1), the ratio of the mass of hydroxypropyl cellulose to the total mass of sodium lignosulfonate and water is (5.5~7):(3~4.5).

[0011] Preferably, in step (1), the ratio of the mass of hydroxypropyl cellulose to the total mass of sodium lignosulfonate and water is (6~7):(3~4).

[0012] Preferably, in step (1), the ratio of the mass of hydroxypropyl cellulose to the total mass of sodium lignosulfonate and water is (6~6.5):(3.5~4).

[0013] Preferably, the self-assembly temperature in step (2) is 20~30℃ and the self-assembly time is 5~10min.

[0014] Preferably, the self-assembly in step (2) is carried out under sealed conditions.

[0015] The present invention also provides a structured color smart window based on hydroxypropyl cellulose prepared by the preparation method described above.

[0016] This invention provides a method for preparing a structural color smart window based on hydroxypropyl cellulose, comprising the following steps: (1) mixing sodium lignosulfonate, water, and hydroxypropyl cellulose to obtain a precursor solution; (2) self-assembling the precursor solution obtained in step (1) to obtain a structural color smart window based on hydroxypropyl cellulose. This invention introduces sodium lignosulfonate into the hydroxypropyl cellulose structural color hydrogel system, achieving synergistic regulation of the hydrogel structural color and LCST. The process is simple and effectively solves the technical problems of excessively high response temperature and complex color regulation in traditional materials. By adjusting the content of sodium lignosulfonate, the LCST of the hydrogel can be precisely adjusted to a suitable operating temperature over a wide range, while simultaneously obtaining efficient transmittance modulation performance. The introduction of sodium lignosulfonate changes the state and distribution of water molecules in the gel network, achieving multicolor and reversible regulation of the structural color. The results of the embodiments show that the structural color smart window prepared by this invention can display different colors at different temperatures, and can also display different colors when the ratio of sodium lignosulfonate to hydroxypropyl cellulose is different. It has high transmittance at room temperature and low LCST. Attached Figure Description

[0017] Figure 1 Images of the hydroxypropyl cellulose-based structural color smart window prepared in Example 1 at 25°C and 45°C; Figure 2 The circular dichroism spectrum at multiple temperatures of the hydroxypropyl cellulose-based structural color smart window prepared in Example 1; Figure 3 Transmittance spectra of the hydroxypropyl cellulose-based structural color smart window at multiple temperatures prepared in Example 1; Figure 4 Images of the hydroxypropyl cellulose-based structural color smart windows prepared in Examples 1 and 2 at 25°C; Figure 5 Circular dichroism spectra of the hydroxypropyl cellulose-based structural color smart windows prepared in Examples 1 and 2; Figure 6 Images of the hydroxypropyl cellulose-based structural color smart windows prepared in Examples 2 and 3 at room temperature and 45°C; Figure 7 Circular dichroism spectra of the hydroxypropyl cellulose-based structural color smart windows prepared in Examples 2 and 3; Figure 8 Transmission spectra of the hydroxypropyl cellulose-based structural color smart windows prepared in Examples 2 and 3 at room temperature and 45°C. Detailed Implementation

[0018] This invention provides a method for preparing a structural color smart window based on hydroxypropyl cellulose, comprising the following steps: (1) Sodium lignosulfonate, water and hydroxypropyl cellulose were mixed to obtain a precursor solution; (2) The precursor solution obtained in step (1) is self-assembled to obtain a structure color smart window based on hydroxypropyl cellulose.

[0019] Unless otherwise specified, the present invention does not impose any special restrictions on the source of the raw materials, and commercially available products well known to those skilled in the art can be used.

[0020] This invention involves mixing sodium lignosulfonate, water, and hydroxypropyl cellulose to obtain a precursor solution.

[0021] In this invention, the preferred mass-to-volume ratio of sodium lignosulfonate to water is (1~5) g:(95~99) mL. As one embodiment, the mass-to-volume ratio of sodium lignosulfonate to water can specifically be 1 g:99 mL, 2 g:98 mL, 3 g:97 mL, 4 g:96 mL, or 5 g:95 mL.

[0022] The hydroxypropyl cellulose used in this invention has a viscosity of 3-6 mPa·s at 20°C when its aqueous solution has a mass concentration of 2%. Using hydroxypropyl cellulose of this viscosity allows the prepared smart window to possess structural color, while using hydroxypropyl cellulose of other viscosities would result in the smart window lacking structural color.

[0023] In this invention, the preferred mass ratio of the hydroxypropyl cellulose to the total mass of sodium lignosulfonate and water is (5.5~7):(3~4.5). As one embodiment, the specific mass ratio of the hydroxypropyl cellulose to the total mass of sodium lignosulfonate and water may be 5.5:4.5, 6:4, 6.5:3.5, or 7:3.

[0024] This invention controls the mass-to-volume ratio of sodium lignosulfonate and water, and the mass-to-total mass ratio of hydroxypropyl cellulose to sodium lignosulfonate and water, within the aforementioned ranges. This further reduces the LCST of the hydrogel. Furthermore, by adjusting the ratio of sodium lignosulfonate and hydroxypropyl cellulose, effective control of the structural color and transmittance of the smart window can be achieved.

[0025] In this invention, the preferred method for mixing sodium lignosulfonate, water, and hydroxypropyl cellulose is as follows: sodium lignosulfonate and water are mixed and sonicated at 20-30°C for 20-40 minutes to obtain a sodium lignosulfonate solution. The sodium lignosulfonate solution is then mixed with hydroxypropyl cellulose, stirred, and centrifuged at 8000-10000 r / min for 10-20 minutes.

[0026] After obtaining the precursor solution, the present invention performs self-assembly on the precursor solution to obtain a structure-color smart window based on hydroxypropyl cellulose.

[0027] In this invention, the self-assembly temperature is preferably 20-30°C; the self-assembly time is preferably 5-10 minutes. As one embodiment, the self-assembly temperature can specifically be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, or 30°C; the self-assembly time can specifically be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes. By controlling the self-assembly temperature and time within the above ranges, this invention allows hydroxypropyl cellulose and sodium lignosulfonate to react fully to form a hydrogel.

[0028] In this invention, the self-assembly is preferably carried out under sealed conditions.

[0029] In one embodiment, the present invention involves pouring a precursor solution onto a glass slide, clamping it together with another glass slide, applying a UV-curable adhesive around the glass slides, and then irradiating the adhesive with an ultraviolet lamp to cure it, thereby forming a sealed condition.

[0030] The present invention does not impose any special limitation on the size of the glass sheet; it can be selected according to actual needs.

[0031] The present invention does not have any special limitations on the type of UV curable adhesive or the time of UV lamp irradiation. Commercially available UV curable adhesives known to those skilled in the art can be used, and UV lamp irradiation can be performed until the UV curable adhesive is completely cured.

[0032] This invention introduces sodium lignosulfonate into a hydroxypropyl cellulose structural color hydrogel system, achieving synergistic regulation of the hydrogel's structural color and LCST. This effectively solves the technical problems of excessively high response temperatures and complex color control in traditional materials. By adjusting the content of sodium lignosulfonate, the LCST of the hydrogel can be precisely adjusted to a suitable operating temperature over a wide range, while simultaneously achieving highly efficient transmittance modulation performance. The introduction of sodium lignosulfonate further realizes multicolor and reversible regulation of the structural color by altering the state and distribution of water molecules in the gel network. The preparation method provided by this invention utilizes widely available and inexpensive raw materials, has a simple preparation process, and is environmentally friendly, showing promising application prospects.

[0033] This invention constructs a circularly polarized structural color hydrogel smart window with thermochromic properties by combining sodium lignosulfonate with chiral cellulose derivative hydroxypropyl cellulose. This effectively solves the problem of excessively high LCST in existing hydrogel materials. The prepared hydrogel can not only control the structural color through ion concentration, but also has significant thermochromic response characteristics and a wide transmittance modulation range under high temperature conditions. The prepared hydrogel has advantages such as controllable structural color, low minimum critical dissolution temperature, and high solar light modulation rate.

[0034] The present invention also provides a structured color smart window based on hydroxypropyl cellulose prepared by the preparation method described above.

[0035] The smart window prepared by this invention has significant thermochromic response characteristics and has advantages such as adjustable structural color, low minimum critical dissolution temperature, and high solar light modulation rate.

[0036] The hydrogel structured color smart window prepared by this invention has significant thermochromic response characteristics and a wide transmittance modulation range under high temperature conditions, making it suitable for energy-saving dimming applications such as smart windows.

[0037] The present invention does not impose any special limitations on the operation of the application, and any technical solution known to those skilled in the art can be used.

[0038] In one embodiment, the thickness of the structural color smart window provided by the present invention can be 1~2mm (this thickness does not include the thickness of the glass sheet during the manufacturing process).

[0039] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] The CAS RN of hydroxypropyl cellulose in the example is 9004-64-2, and the product code is H0473.

[0041] Example 1 A method for preparing a structural color smart window based on hydroxypropyl cellulose is as follows: (1) Mix 3g of sodium lignosulfonate with 97mL of distilled water and sonicate in a water bath at 25℃ for 20min to obtain a sodium lignosulfonate solution; (2) Add 4g of sodium lignosulfonate solution obtained in step (1) to a beaker, add 6g of hydroxypropyl cellulose (HPC, the viscosity of an aqueous solution of 2% hydroxypropyl cellulose at 20℃ is 3~6mPa·s) and stir to disperse it, then centrifuge at 10000r / min for 10min to obtain the precursor solution. (3) Pour the precursor solution obtained in step (2) onto a glass slide, clamp it together with another glass slide, apply a UV curable adhesive around the glass slide, and then irradiate it with a UV lamp until the adhesive is completely cured. Let it stand at 25°C for 10 minutes to perform self-assembly and obtain a structure color smart window based on hydroxypropyl cellulose with a thickness of 1 mm.

[0042] Images of the hydroxypropyl cellulose-based structural color smart window prepared in Example 1 at 25°C and 45°C are shown below. Figure 1 As shown. From Figure 1 As can be seen, the structural color of the smart window is green at 25℃, and the color changes as the temperature rises to 45℃, indicating that the structural color smart window has thermochromic properties.

[0043] The circular dichroism (CD) spectrum of the hydroxypropyl cellulose-based structural color smart window prepared in Example 1 was detected, and the resulting circular dichroism spectra at multiple temperatures are shown below. Figure 2 As shown. From Figure 2 As can be seen, the circular dichroism spectrum has a downward peak near 500 nm, indicating that the hydroxypropyl cellulose-based structural color smart window possesses right-handed circularly polarized structural color characteristics. The addition of sodium lignosulfonate does not destroy the original chiral structure of HPC. The CD peak of the hydroxypropyl cellulose-based structural color smart window shows a regular shift at various temperatures, proving its temperature response performance, which is also consistent with... Figure 1 The structural color changes correspond accordingly.

[0044] The transmission spectrum of the hydroxypropyl cellulose-based structural color smart window prepared in Example 1 was detected, and the transmittance spectra at multiple temperatures are shown below. Figure 3 As shown. (Through) Figure 3 It can be seen that the transmittance of the transmission spectrum decreases significantly with increasing temperature, indicating the visible light transmittance modulation characteristics of the temperature response of the circularly polarized structured color smart window based on hydroxypropyl cellulose.

[0045] Example 2 A method for preparing a structural color smart window based on hydroxypropyl cellulose is as follows: (1) Mix 3g of sodium lignosulfonate with 97mL of distilled water and sonicate in a water bath at 25℃ for 20min to obtain a sodium lignosulfonate solution; (2) Add 3.5g of sodium lignosulfonate solution obtained in step (1) to a beaker, add 6.5g of hydroxypropyl cellulose (HPC, the viscosity of 2% hydroxypropyl cellulose aqueous solution at 20℃ is 3~6mPa·s) and stir to disperse it, then centrifuge at 10000r / min for 10min to obtain the precursor solution. (3) Pour the precursor solution obtained in step (2) onto a glass slide, clamp it together with another glass slide, apply a UV curable adhesive around the glass slide, and then irradiate it with a UV lamp until the adhesive is completely cured. Let it stand at 25°C for 10 minutes to perform self-assembly and obtain a structure color smart window based on hydroxypropyl cellulose with a thickness of 1 mm.

[0046] Figure 4 Images of the hydroxypropyl cellulose-based structural color smart windows prepared in Examples 1 and 2 at 25°C, where 60 wt% represents Example 1 and 65 wt% represents Example 2. From Figure 4 As can be seen, when the HPC mass fraction is 60%, the smart window presents a green structural color. When the HPC mass fraction increases to 65%, the smart window color changes significantly and turns purple. This indicates that as the HPC content increases, the periodicity of the chiral nematic structure formed by its self-assembly changes, thus causing a change in structural color.

[0047] Figure 5 Circular dichroism spectra of the hydroxypropyl cellulose-based structural color smart windows prepared in Examples 1 and 2. Figure 5 As can be seen, when the HPC mass fraction is 60%, the CD spectrum shows a corresponding peak at a wavelength of approximately 580 nm. When the mass fraction increases to 65%, this CD peak shifts to approximately 410 nm, indicating a change in the optical activity of its chiral structure. This result is consistent with... Figure 4 The observed color changes are consistent, indicating that the quality fraction of HPC alters the structural color of the smart window.

[0048] Example 3 A method for preparing a structural color smart window based on hydroxypropyl cellulose is as follows: (1) Mix 1g of sodium lignosulfonate with 99mL of distilled water and sonicate in a water bath at 25℃ for 20min to obtain a sodium lignosulfonate solution. (2) Add 3.5g of sodium lignosulfonate solution obtained in step (1) to a beaker, add 6.5g of hydroxypropyl cellulose (HPC, the viscosity of 2% hydroxypropyl cellulose aqueous solution at 20℃ is 3~6mPa·s) and stir to disperse it, then centrifuge at 10000r / min for 10min to obtain the precursor solution. (3) Pour the precursor solution obtained in step (2) onto a glass slide, clamp it together with another glass slide, apply a UV curable adhesive around the glass slide, and then irradiate it with a UV lamp until the adhesive is completely cured. Let it stand at 25°C for 10 minutes to perform self-assembly and obtain a structure color smart window based on hydroxypropyl cellulose with a thickness of 1 mm.

[0049] Images of the hydroxypropyl cellulose-based structural color smart windows prepared in Examples 2 and 3 at room temperature and 45°C are shown below. Figure 6 As shown, 1 wt% represents Example 3, and 3 wt% represents Example 2. From Figure 6 As can be seen, at room temperature, the low-concentration sodium lignin sulfonate hydrogel smart window exhibits a pale purple structural color, while the high-concentration hydrogel smart window has a brownish lignin color with an indistinct structural color. This indicates that the structural color of the HPC smart window can be effectively controlled by adjusting the concentration of sodium lignin sulfonate. At room temperature, both exhibit high light transmittance and can clearly distinguish background text. However, when the ambient temperature rises to 45℃, the low-concentration hydrogel smart window displays a blue-green structural color and still retains some visible light transmittance. In contrast, the high-concentration hydrogel smart window turns purple, and its light transmittance decreases significantly, making it difficult to distinguish background objects. This phenomenon demonstrates that increasing the concentration of sodium lignin sulfonate can effectively reduce the LCST of the hydrogel.

[0050] The circular dichroism spectra of the hydroxypropyl cellulose-based structural color smart windows prepared in Examples 2 and 3 are as follows: Figure 7 As shown. From Figure 7 As can be seen, when the mass fraction of sodium lignosulfonate solution is 3%, the CD spectrum shows a characteristic peak at approximately 410 nm. When the mass fraction decreases to 1%, this CD characteristic peak shifts to approximately 440 nm, indicating a change in the pitch of its chiral structure. This result is consistent with... Figure 6 The color changes observed at room temperature were consistent, confirming that the structural color of the smart window can be effectively controlled by adjusting the mass fraction of the sodium lignosulfonate solution.

[0051] The transmission spectra of the hydroxypropyl cellulose-based structural color smart windows prepared in Examples 2 and 3 at room temperature and 45°C are shown below. Figure 8 As shown. From Figure 8 As can be seen, both mass fraction hydrogels exhibited high transmittance at room temperature. When the temperature rose to 45℃, the transmittance of the hydrogel with the higher mass fraction dropped to near zero, indicating that the temperature had exceeded the LCST of the hydrogel smart window. The hydrogel smart window with the lower mass fraction, however, maintained a certain transmittance, indicating that its LCST had not yet been reached. This result is consistent with... Figure 6This is consistent with the phenomenon that the text can be clearly recognized under room temperature background, confirming that increasing the mass fraction of sodium lignosulfonate solution can effectively reduce the LCST of hydrogel, thereby significantly enhancing the transmittance modulation capability of hydrogel smart windows.

[0052] As demonstrated in the above embodiments, this invention successfully constructs a smart hydrogel smart window material possessing both structural color and thermochromic properties by co-assembling the biomolecule sodium lignin sulfonate with the chiral nematic cellulose derivative hydroxypropyl cellulose. The preparation process utilizes widely available and inexpensive raw materials, involves simple operation steps, and is environmentally friendly, conforming to green chemistry principles.

[0053] The results of the examples confirm that the structural color of the smart window can be effectively controlled by adjusting the mass fraction of hydroxypropyl cellulose and the concentration of sodium lignosulfonate. Furthermore, this material exhibits a sensitive response to external temperature, not only reversibly altering its circularly polarized structural color but also dynamically modulating its transmittance, demonstrating excellent thermochromic properties and optical control capabilities, and showing broad application prospects in the field of smart windows.

[0054] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a structural color smart window based on hydroxypropyl cellulose, comprising the following steps: (1) Sodium lignosulfonate, water and hydroxypropyl cellulose were mixed to obtain a precursor solution; (2) The precursor solution obtained in step (1) is self-assembled to obtain a structure color smart window based on hydroxypropyl cellulose.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of sodium lignosulfonate to water is (1~5) g: (95~99) mL.

3. The preparation method according to claim 2, characterized in that, In step (1), the mass ratio of sodium lignosulfonate to water is (1~3) g: (97~99) mL.

4. The preparation method according to claim 1, characterized in that, In step (1), the ratio of the mass of hydroxypropyl cellulose to the total mass of sodium lignosulfonate and water is (5.5~7):(3~4.5).

5. The preparation method according to claim 4, characterized in that, In step (1), the ratio of the mass of hydroxypropyl cellulose to the total mass of sodium lignosulfonate and water is (6~7):(3~4).

6. The preparation method according to claim 5, characterized in that, In step (1), the ratio of the mass of hydroxypropyl cellulose to the total mass of sodium lignosulfonate and water is (6~6.5):(3.5~4).

7. The preparation method according to claim 1, characterized in that, The self-assembly temperature in step (2) is 20~30℃, and the self-assembly time is 5~10min.

8. The preparation method according to claim 1, characterized in that, The self-assembly in step (2) is carried out under sealed conditions.

9. The structured color smart window based on hydroxypropyl cellulose prepared by the preparation method according to any one of claims 1 to 8.

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