A thermochromic composite film and its preparation method

Abstract

The present invention relates to the technical field of phase change materials, specifically a thermochromic composite membrane and its preparation method. The membrane is formed by casting a membrane solution, wherein cellulose nanocrystals and VO2@SiO2 are dispersed in a film-forming matrix to obtain the membrane solution. By utilizing the inherent rigidity, spatial support, biocompatibility, and optical properties of cellulose nanocrystals, their application in the composite membrane can enhance the mechanical strength, thermochromic performance, and stability of the composite membrane.

Description

Technical Field

[0001] The present invention relates to the technical field of phase change materials, in particular to a thermochromic composite film and a preparation method thereof. Background Art

[0002] Thermochromic materials are substances that change color in response to changes in ambient temperature. Specifically, when the temperature rises or falls below a specific range, the color changes reversibly. The temperature at which this color change occurs is called the color change temperature. This property of thermochromic materials has applications in smart windows, sensors, solar collectors, medical devices, and other fields.

[0003] VO2 is a typical thermochromic material. Its reversible metal-semiconductor phase transition shifts its transmittance from high transmittance at low temperatures to high reflectivity at high temperatures. This thermochromic property has led to its widespread application in smart windows. One of the main methods for preparing VO2 smart windows is to combine VO2 nanopowders with polymer materials to form films or coatings. When VO2 is used in smart windows, high requirements are placed on the weather resistance and stability of the smart windows. Summary of the Invention

[0004] Technical problems solved by the present invention:

[0005] It is used to solve the problem that the existing temperature-sensitive and temperature-color films made of VO2 materials cannot take into account both weather resistance and stability when applied to smart windows.

[0006] The technical solution adopted in the present invention is:

[0007] In response to the above technical problems, the present invention aims to provide a thermochromic composite film and a method for preparing the same. The specific contents are as follows:

[0008] First, the present invention provides a thermochromic composite film, including a film layer and a thermochromic coating coated on the surface of the film layer; the preparation method of the thermochromic coating film liquid is that cellulose nanocrystals and VO2@SiO2 are dispersed in a film-forming matrix to obtain a film liquid.

[0009] In the above, the preparation method of the liquid for thermochromic coating is as follows:

[0010] (1) Preparation of VO2@SiO2: After VO2 was dispersed in ethanol, 30% by mass of NH3·H2O was added to form a first dispersion; the ratio of VO2:ethanol:NH3·H2O in the first dispersion was 1g:150-200ml:6-10ml; tetraethyl orthosilicate was dispersed in ethanol to form a second dispersion; the ratio of tetraethyl orthosilicate:ethanol in the second dispersion was 1g:10ml; the second dispersion was added dropwise to the first dispersion at a ratio of V(first dispersion):V(second dispersion) = 10:1, and the mixture was allowed to react at room temperature for 10-15 hours. After the reaction, the mixture was centrifuged, washed with deionized water, washed with anhydrous ethanol, and then dried to obtain VO2@SiO2.

[0011] (2) Cellulose nanocrystal modification:

[0012] The cellulose nanocrystals were dispersed in a solvent (the solvent was pyridine) by ultrasonic dispersion to obtain a treatment liquid. An acid anhydride solution (the acid anhydride was dodecenylsuccinic anhydride and the solvent was pyridine) was added dropwise to the treatment liquid under a nitrogen atmosphere. The acid anhydride accounted for 2-10 wt % of the cellulose nanocrystals. After treatment at 75-95°C for 3-7 hours, the product was precipitated with distilled water and then treated with distilled water and acetone aqueous solution (V 丙酮 :V 水 =1:1) and washed to obtain modified cellulose nanocrystals.

[0013] (3) Preparation of membrane solution:

[0014] Polyvinyl alcohol and polyurethane are mixed to form a film-forming matrix, and modified cellulose nanocrystals and VO2@SiO2 are added to the film-forming matrix and ultrasonically dispersed. The mass ratio of polyvinyl alcohol, polyurethane, modified cellulose nanocrystals, and VO2@SiO2 is 3-7:3-7:1-3:3-10.

[0015] The technical mechanism adopted by the present invention and the beneficial effects achieved are:

[0016] (1) The thermochromic composite membrane provided by the present invention utilizes the intrinsic rigidity, spatial support, biocompatibility and optical properties of cellulose nanocrystals and applies them to the composite membrane, which can improve the mechanical strength, thermochromic performance and stability of the composite membrane.

[0017] (2) The thermochromic composite film provided by the present invention is modified by treating cellulose nanocrystals, i.e., grafting long carbon chains, which can increase the hydrophobicity while at the same time enhancing the binding force between the modified carboxyl groups and the nanoparticles. The improvement of hydrophobicity can enhance the interfacial interaction between the cellulose nanocrystals and the film-forming matrix.

[0018] (3) The thermochromic material provided by the present invention coats VO2 with SiO2 to isolate VO2 from adverse substances in the outside world (such as oxygen, water vapor, etc.), thereby improving the stability of VO2. DETAILED DESCRIPTION

[0019] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0020] <Example>

[0021] Example 1

[0022] This embodiment provides a method for preparing a thermochromic composite film, comprising the following steps:

[0023] (1) Preparation of VO2@SiO2: 1 g of VO2 was dispersed in 150 ml of ethanol and ultrasonically dispersed for 15 min. Then, 6 ml of 30% NH3·H2O was added to form a first dispersion. 1 g of tetraethyl orthosilicate was dispersed in 10 ml of ethanol and ultrasonically dispersed to form a second dispersion. The second dispersion was slowly added dropwise to the first dispersion at a ratio of V(first dispersion):V(second dispersion) = 10:1. The mixture was allowed to react at room temperature for 15 h. After the reaction, the mixture was centrifuged, washed with deionized water and anhydrous ethanol, and then dried to obtain VO2@SiO2.

[0024] (2) Cellulose nanocrystal modification:

[0025] Cellulose nanocrystals were dispersed in pyridine by ultrasonic dispersion to obtain a treatment solution. Then, an acid anhydride solution (the acid anhydride was dodecenylsuccinic anhydride and the solvent was pyridine) was added dropwise to the treatment solution under a nitrogen atmosphere. The acid anhydride accounted for 5 wt% of the cellulose nanocrystals. After treatment at 80°C for 5 h, the product was precipitated with distilled water and then treated with distilled water and acetone aqueous solution (V 丙酮 :V 水 =1:1) and washed to obtain modified cellulose nanocrystals.

[0026] (3) Preparation of membrane solution:

[0027] Polyvinyl alcohol was dissolved in deionized water and heat-treated at 80°C to form a polyvinyl alcohol solution with a mass concentration of 20%. The polyvinyl alcohol solution was then mixed with polyurethane with a solid content of 30wt% to obtain a film-forming matrix. The VO2@SiO2 prepared in (1) and the modified cellulose nanocrystals prepared in (2) were added to the film-forming matrix and then ultrasonically dispersed to obtain a membrane solution. The mass ratio of polyvinyl alcohol, polyurethane, modified cellulose nanocrystals, and VO2@SiO2 was 5:5:3:7. After vacuum degassing, the membrane solution was cast into a film. The film thickness was controlled at 150μm, the visible light transmittance was 69.4%, the phase transition temperature was 48°C, and the thermal insulation performance was △=6°C. After an aging test at 60°C and 90%, the enthalpy value of 72h was measured to be 12.7J / g.

[0028] Example 2

[0029] This example differs from Example 1 in that the mass ratio of polyvinyl alcohol, polyurethane, modified cellulose nanocrystals, and VO2@SiO2 is 5:5:1:9. The film thickness is controlled at 150 μm, with a visible light transmittance of 68.7%, a phase transition temperature of 48°C, and a thermal insulation performance of Δ=6°C. After aging at 60°C and 90% humidity, the measured enthalpy after 72 hours was 12.4 J / g.

[0030] <Comparative Example>

[0031] Comparative Example 1

[0032] This comparative example differs from Example 1 in that no cellulose nanocrystals were added. The film thickness was controlled at 150 μm, with a visible light transmittance of 62.1%, a phase transition temperature of 54°C, and a thermal insulation performance of Δ=3°C. After aging at 60°C and 90% saturation, the measured enthalpy after 72 hours was 9.6 J / g.

[0033] Comparative Example 2

[0034] This comparative example differs from Example 1 in that modified cellulose nanocrystals are replaced with cellulose nanocrystals. The film thickness was controlled at 150 μm, with a visible light transmittance of 66.7%, a phase transition temperature of 50°C, and a thermal insulation performance of Δ=5°C. After aging at 60°C and 90% humidity, the measured enthalpy after 72 hours was 11.4 J / g.

[0035] Comparative Example 3

[0036] This comparative example differs from Example 1 in that VO2@SiO2 is replaced with VO2. The film thickness is controlled at 150 μm, with a visible light transmittance of 59.4%, a phase transition temperature of 55°C, and a thermal insulation performance of Δ=4°C. After aging at 60°C and 90% stagnation, the measured enthalpy after 72 hours was 11.1 J / g.

[0037] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A thermochromic composite film, characterized in that: The membrane is formed by casting a membrane solution, wherein the membrane solution is prepared by dispersing modified cellulose nanocrystals and VO2@SiO2 in a membrane-forming matrix to obtain a membrane solution; the mass ratio of the membrane-forming matrix, modified cellulose nanocrystals, and VO2@SiO2 is 10:1~3:3~10; The preparation method of the membrane solution comprises the following steps: (1) Preparation of VO2@SiO2; (2) Modified cellulose nanocrystal treatment; (3) Adding modified cellulose nanocrystals and VO2@SiO2 into the film-forming matrix and dispersing them to obtain a membrane solution; (2) In the step of dispersing cellulose nanocrystals in a solvent to obtain a treatment solution, an acid anhydride solution is added dropwise to the treatment solution, and the product is precipitated with distilled water after heat treatment and then washed to obtain modified cellulose nanocrystals.

2. The thermochromic composite film according to claim 1, characterized in that In (1), VO2 is dispersed in ethanol, and then NH3·H2O is added to form a first dispersion; tetraethyl orthosilicate is dispersed in ethanol to form a second dispersion; the second dispersion is added dropwise to the first dispersion, and the mixture is reacted at room temperature. After the reaction is completed, VO2@SiO2 is obtained by centrifugation, washing, and drying.

3. The thermochromic composite film according to claim 2, characterized in that (1) includes at least one of features (1-1) to (1-4): (1-1) In the first dispersion, the ratio of VO2:ethanol:NH3·H2O is 1 g:150-200 ml:6-10 ml; (1-2) The ratio of tetraethyl orthosilicate to ethanol in the second dispersion is 1 g:10 ml; (1-3) The volume ratio of the first dispersion liquid to the second dispersion liquid is 10:1; (1-4) The reaction time is 10~15h.

4. The thermochromic composite film according to claim 1, characterized in that Film-forming matrices include polyvinyl alcohol and polyurethane.

5. The thermochromic composite film according to claim 4, characterized in that: The polyvinyl alcohol adopts a polyvinyl alcohol aqueous solution with a mass concentration of 10-30%; the solid content of the polyurethane is 15-35%.

6. The thermochromic composite film according to claim 1, characterized in that: (2) includes at least one of features (2-1) to (2-3): (2-1) The anhydride is dodecenylsuccinic anhydride; (2-2) Acid anhydride accounts for 2~10wt% of cellulose nanocrystals; (2-3) Heat treatment: 75~95℃ for 3~7h.

7. The method for preparing a thermochromic composite film according to any one of claims 1 to 6, comprising the steps of dispersing modified cellulose nanocrystals and VO2@SiO2 in a film-forming matrix to obtain a film liquid, vacuum degassing the film liquid, and then casting the film by solution casting.