A thermosensitive color-changing material and its preparation method

Abstract

The present invention relates to the technical field of phase change materials, and discloses a temperature-sensitive color-changing material and a preparation method thereof, including: a core, which is cellulose nanocrystal@VO2, and a shell, which is polydopamine. The temperature-sensitive color-changing material provided by the present invention utilizes the 1D dimension, intrinsic rigidity, spatial support, biocompatibility and responsive optical properties of cellulose nanocrystals, and synergistically acts with VO2 to improve the stability of VO2; polydopamine is used to coat the surface of cellulose nanocrystal@VO2 to form a coating layer, thereby improving the thermal responsiveness of the material, and various functional functional groups of dopamine can be used to bond with cellulose nanocrystals, thereby improving the mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of phase change materials, and more specifically, to a temperature-sensitive color-changing material and a preparation method thereof. Background Art

[0002] A temperature-sensitive color-changing material refers to a specific substance whose color changes while sensing the change in the external environmental temperature. That is, when the temperature is higher or lower than a certain specific temperature range, the color can reversibly change with the rise and fall of the temperature, and the temperature at which the color change occurs is called the color-changing temperature. Among many color-changing materials, VO2 has attracted extensive attention due to its reversible metal-semiconductor phase transition temperature being closest to room temperature and its excellent phase transition characteristics. VO2 temperature-sensitive color-changing materials can be applied to smart windows, anti-counterfeiting coatings, smart packaging, etc. During the application of VO2, its inherent properties do not meet the requirements of people's use, such as insufficient light transmittance, poor weather resistance, and too high phase transition temperature. Based on this, currently, there are improvement methods such as ion doping and nano-coating of VO2, but these methods have insufficient performance improvement. Summary of the Invention

[0003] Technical problems to be solved by the present invention:

[0004] To solve the problems of insufficient light transmittance and poor weather resistance existing in the existing VO2.

[0005] Technical solutions adopted by the present invention:

[0006] In view of the above technical problems, the object of the present invention is to provide a temperature-sensitive color-changing material and a preparation method thereof. The specific content is as follows:

[0007] First, the present application provides a temperature-sensitive color-changing material, comprising:

[0008] a core, which is cellulose nanocrystal @VO2,

[0009] a shell, which is polydopamine.

[0010] Among the above, the preparation method of cellulose nanocrystal @VO2 is as follows: ammonium metavanadate is added to an oxalic acid solution, and after stirring, a first blend is obtained; a cellulose nanocrystal dispersion is added to the first blend, and stirring is continued to obtain a second blend; the second blend is placed in a high-pressure reaction kettle with a polytetrafluoroethylene lining, and after heat preservation treatment at 170-200 °C for 40-60 h, it is cooled to room temperature, and after centrifugation, washing with deionized water and absolute ethanol, cellulose nanocrystal @VO2 is obtained. The mass concentration of the oxalic acid solution is 0.01 mol / L, and the mass ratio of ammonium metavanadate to nanocrystalline cellulose is 1:0.8-1.5.

[0011] Second, the present application provides a method for preparing the aforementioned thermochromic material, comprising the following steps:

[0012] Disperse cellulose nanocrystals@VO2 in DMF to form a first dispersion. In the first dispersion, the ratio of cellulose nanocrystals@VO2 to DMF is 1 g:60 - 100 ml. Seal it for standby. Disperse EDTAD in DMF to form a second dispersion. In the second dispersion, the ratio of EDTAD to DMF is 0.1 - 2 g:25 - 50 mL. Seal it for standby. Under the conditions of 65 - 80 °C and N2 atmosphere, gradually drop the second dispersion into the first dispersion while keeping stirring (for 36 - 48 h). After completion, perform centrifugal separation, and then wash it with DMF and distilled water multiple times. After drying, an intermediate is obtained;

[0013] Take the aforementioned prepared intermediate to make a suspension. Add Tris to the suspension and adjust the pH value of the suspension to 8.5. Then, add dopamine to the suspension. The addition amount of dopamine is 0.8 - 1.2 times that of cellulose nanocrystals@VO2. Stir at room temperature for 48 h. After the stirring ends, filter it. Place the filtrate in a PVP solution (mass concentration is 1 - 3 wt%) and let it stand for 1 - 4 h. Then wash the filtrate with deionized water to obtain the thermochromic material.

[0014] Technical mechanism and achieved beneficial effects adopted by the present invention:

[0015] (1) For the thermochromic material provided by the present invention, by utilizing the 1D dimension, inherent rigidity, spatial support, biocompatibility, and responsive optical properties of cellulose nanocrystals, and carrying out synergistic action with VO2, the stability of VO2 is improved.

[0016] (2) For the thermochromic material provided by the present invention, partial carboxylation modification is carried out on cellulose nanocrystals, thereby improving the stability of cellulose nanocrystals@VO2, avoiding agglomeration; and improving the stability of VO2.

[0017] (3) For the thermochromic material provided by the present invention, the surface of cellulose nanocrystals@VO2 is coated with polydopamine to form a coating layer, thereby improving the thermal responsiveness of the material. By using various functional functional groups of dopamine, it can bond with cellulose nanocrystals, thereby improving the mechanical properties.

[0018] (4) For the thermochromic material provided by the present invention, by introducing polyvinylpyrrolidone to form hydrogen bonds with polydopamine, the interfacial strength of polydopamine is improved. Specific embodiments

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0020] <Example>

[0021] Example 1

[0022] This example provides a method for preparing a thermochromic material, including the following steps:

[0023] (1) Preparation of cellulose nanocrystals@VO2:

[0024] Dissolve 1 g of ammonium metavanadate in 0.01 mol / L oxalic acid solution, and obtain a first blend solution after stirring; add a cellulose nanocrystal dispersion (obtained by dispersing 1 g of cellulose nanocrystals in water) to the first blend solution, and continue stirring to obtain a second blend solution; place the second blend solution in a high-pressure reaction kettle, perform heat preservation treatment at 180 °C for 48 h, cool it to room temperature, and after centrifugation, wash it with deionized water and absolute ethanol to obtain cellulose nanocrystals@VO2.

[0025] (2) Preparation of polydopamine-coated cellulose nanocrystals@VO2:

[0026] Disperse 1 g of cellulose nanocrystals@VO2 in 100 ml of DMF to form a first dispersion, seal it for standby, disperse 0.5 g of EDTAD in 50 ml of DMF to form a second dispersion, and seal it for standby; then, at 75 °C under a N2 atmosphere, gradually drop the second dispersion into the first dispersion, keep stirring for 36 h, after completion, perform centrifugal separation, and wash it with DMF and distilled water multiple times, and obtain an intermediate after drying; make the intermediate into a suspension, add Tris to the suspension, and adjust the pH value of the suspension to 8.5. Then, add 1 g of dopamine to the suspension and stir at room temperature for 48 h. After the stirring is completed, after filtration, place the filtrate in a 3 wt% PVP solution and let it stand for 2 h, and then wash the filtrate with deionized water to obtain the thermochromic material.

[0027] Example 2

[0028] This example provides a method for preparing a thermochromic material, including the following steps:

[0029] (1) Preparation of cellulose nanocrystals@VO2:

[0030] Dissolve 1 g of ammonium metavanadate in 0.01 mol / L oxalic acid solution, and obtain the first blend solution after stirring; add the cellulose nanocrystal dispersion (obtained by dispersing 0.8 g of cellulose nanocrystals in water) to the first blend solution, and continue stirring to obtain the second blend solution; place the second blend solution in a high-pressure reaction kettle, keep it at 180 °C for 48 h for heat preservation treatment, cool it to room temperature, and after centrifugation, wash it with deionized water and absolute ethanol to obtain cellulose nanocrystal@VO₂.

[0031] (2) Preparation of polydopamine-coated cellulose nanocrystal@VO₂:

[0032] Disperse 1 g of cellulose nanocrystal@VO₂ in 120 ml of DMF to form the first dispersion solution, seal it for standby; disperse 0.3 g of EDTAD in 50 ml of DMF to form the second dispersion solution, seal it for standby; then, under the condition of 75 °C and N₂ atmosphere, gradually drop the second dispersion solution into the first dispersion solution, keep stirring for 36 h, after completion, carry out centrifugal separation, and then wash it with DMF and distilled water for many times, and obtain the intermediate after drying; make the intermediate into a suspension, add Tris to the suspension, and adjust the pH value of the suspension to 8.5. Then, add 1 g of dopamine to the suspension and stir it at room temperature for 48 h. After that, after the stirring is completed, filter it, place the filtrate in a 3 wt% PVP solution and let it stand for 2 h, and then wash the filtrate with deionized water to obtain the temperature-sensitive color-changing material.

[0033] <Comparative Example>

[0034] Comparative Example 1

[0035] The difference between this comparative example and Example 1 is that cellulose nanocrystal@VO₂ is replaced by VO₂.

[0036] Comparative Example 2

[0037] The difference between this comparative example and Example 1 is that cellulose nanocrystal@VO₂ is not treated with EDTAD.

[0038] Comparative Example 3

[0039] The difference between this comparative example and Example 1 is that PVP is not added.

[0040] <Test Example>

[0041] Use the temperature-sensitive color-changing materials prepared in Examples 1-2 and Comparative Examples 1-3 as samples for test determination.

[0042] After washing and drying the substrate (quartz glass), the coating solution was spin-coated to obtain a composite film. The coating solution was prepared by blending 0.2 g of the sample, 0.2 g of PVP, and 5 ml of ethanol. Under the conditions of 20 °C and 80 °C, it was kept warm for 0.5 h, and the visible light transmittance and the sunlight regulation efficiency were measured with reference to ISO9050:2003(E). The results are shown in Table 1.

[0043] The aforementioned composite film was placed at 60 °C and a relative humidity of 90%, and the enthalpy values of each sample were measured. The results are shown in Table 1.

[0044] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0045]

Claims

1. A temperature-sensitive color-changing material, characterized in that, Comprising: a core, which is cellulose nanocrystal@VO2, a shell, which is polydopamine; A preparation method of a thermosensitive color-changing material, comprising the following steps: Disperse cellulose nanocrystal@VO2 in DMF to form a first dispersion, and disperse EDTAD in DMF to form a second dispersion; gradually drop the second dispersion into the first dispersion, keep stirring, after completion, perform centrifugal separation, and then wash and dry to obtain an intermediate; Take the intermediate to prepare a suspension, add Tris to the suspension, and adjust the pH value of the suspension to 8.5; then, add dopamine to the suspension, stir at room temperature, and then filter and wash to obtain the thermosensitive color-changing material.

2. The thermosensitive discoloring material according to claim 1, wherein The preparation method of cellulose nanocrystal@VO2 is to add ammonium metavanadate to an oxalic acid solution, and obtain a first blend after stirring; Add a cellulose nanocrystal dispersion to the first blend, and continue stirring to obtain a second blend; Place the second blend in a high-pressure reactor, perform heat preservation treatment, cool it to room temperature, and after centrifugation and washing, obtain cellulose nanocrystal@VO2.

3. The thermosensitive discoloring material according to claim 2, wherein Cellulose nanocrystal@VO2 includes at least one of characteristics (1-1) to (1-3): (1-1) Heat preservation treatment: 170~200°C, 40~60h; (1-2) The mass concentration of the oxalic acid solution is 0.01mol / L; (1-3) The mass ratio of ammonium metavanadate to cellulose nanocrystals is 1:0.8~1.

5.

4. The thermochromic material according to claim 1, characterized in that, In the first dispersion, cellulose nanocrystal@VO2:DMF = 1g:60~100ml.

5. The thermosensitive color-changing material according to claim 1, characterized in that, In the second dispersion, EDTAD:DMF = 0.1~2g:25~50mL.

6. The thermochromic material according to any one of claims 1, 4 to 5, characterized in that The dropping process is carried out at 65~80°C in an N2 atmosphere; the stirring time is 36~48h.

7. The thermochromic material according to claim 1, wherein The addition amount of dopamine is 0.8~1.2 times that of cellulose nanocrystal@VO2.

8. The thermochromic material according to any one of claims 1, 4 to 5, and 7, characterized in that, After filtration, place the filtrate in a PVP solution and let it stand for a period of time. After standing, wash it again.

9. The thermosensitive discoloring material according to claim 8, characterized in that, The mass concentration of PVP is 1~3wt%.

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