Temperature-sensitive color-changing material and preparation method thereof

Abstract

The invention relates to the technical field of phase-change materials, and discloses a temperature-sensitive color-changing material and a preparation method thereof, the temperature-sensitive color-changing material comprises an inner core which is cellulose nanocrystal coated with VO2, and a shell which is polydopamine. According to the temperature-sensitive color-changing material provided by the invention, by utilizing the 1D dimension, the internal rigidity, the space supporting property, the biocompatibility and the response optical characteristics of the cellulose nanocrystals, the cellulose nanocrystals and the VO2 are subjected to a synergistic effect, so that the stability of the VO2 is improved; the surface of the cellulose nanocrystal (at) VO2 is coated with polydopamine to form a coating layer, so that the thermal responsiveness of the material can be improved, and the material can be bonded with the cellulose nanocrystal by utilizing multiple functional groups of dopamine, so that the mechanical property is improved.

Description

Technical Field

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

[0002] Thermochromic materials refer to specific substances that change their own color while sensing changes in the external environment temperature. That is, when the temperature is higher or lower than a certain temperature range, the color can change reversibly with the rise and fall of temperature, and the temperature when the color changes is called the color change temperature. Among the many color-changing materials, VO2 has received widespread attention due to its reversible metal-semiconductor phase change temperature that is closest to room temperature and its excellent phase change properties. VO2 thermochromic materials can be used in smart windows, anti-counterfeiting coatings, smart packaging, etc. In the application process of VO2, its inherent characteristics do not meet the requirements of people's use, such as insufficient light transmittance, poor weather resistance, and excessively high phase change temperature. Based on this, there are currently ways to improve VO2 by ion doping and nano-coating, but these methods are insufficient to improve performance. Summary of the invention

[0003] Technical problems solved by the present invention:

[0004] It is used to solve the problems of insufficient light transmittance and poor weather resistance of existing VO2.

[0005] The technical solution adopted by the present invention is:

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

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

[0008] The core, which is cellulose nanocrystals@VO2,

[0009] The outer shell is polydopamine.

[0010] In the above, the preparation method of cellulose nanocrystals @VO2 is as follows: adding ammonium metavanadate to an oxalic acid solution, stirring to obtain a first blended liquid; adding a cellulose nanocrystal dispersion to the first blended liquid, continuing to stir to obtain a second blended liquid; placing the second blended liquid in a high-pressure reactor, the reactor lining is made of polytetrafluoroethylene material, and heat-insulating treatment at 170-200°C for 40-60h, cooling it to room temperature, centrifuging, washing with deionized water and anhydrous ethanol, and obtaining cellulose nanocrystals @VO2. 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 temperature-sensitive color-changing material, comprising the following steps:

[0012] Disperse cellulose nanocrystals @VO2 in DMF to form a first dispersion, wherein cellulose nanocrystals @VO2:DMF=1g:60-100ml, and seal for later use; disperse EDTAD in DMF to form a second dispersion, wherein EDTAD:DMF=0.1-2g:25-50mL, and seal for later use; gradually drip the second dispersion into the first dispersion at 65-80°C and N2 atmosphere, and keep stirring (36-48h). After the dispersion is completed, centrifuge, wash with DMF and distilled water for multiple times, and dry to obtain an intermediate;

[0013] The intermediate prepared above is made into a suspension, Tris is added to the suspension, and the pH value of the suspension is adjusted to 8.5. Then, dopamine is added to the suspension, and the amount of dopamine added is 0.8 to 1.2 times that of cellulose nanocrystals @VO2. Stir at room temperature for 48 hours, and then, after the stirring is completed, filter, place the filtrate in a PVP solution (mass concentration of 1 to 3wt%) and let it stand for 1 to 4 hours, and then wash the filtrate with deionized water to obtain a thermosensitive color-changing material.

[0014] The technical mechanism adopted by the present invention and the beneficial effects achieved are:

[0015] (1) The thermochromic material provided by the present invention utilizes the 1D dimension, intrinsic rigidity, spatial support, biocompatibility and responsive optical properties of cellulose nanocrystals to synergize with VO2, thereby improving the stability of VO2.

[0016] (2) The thermochromic material provided by the present invention partially carboxylates the cellulose nanocrystals, thereby improving the stability of the cellulose nanocrystals@VO2 and avoiding agglomeration; and improving the stability of VO2.

[0017] (3) The thermochromic material provided by the present invention utilizes polydopamine to coat the surface of cellulose nanocrystals@VO2 to form a coating layer, thereby improving the thermal responsiveness of the material, and utilizing the various functional groups of dopamine to bond with cellulose nanocrystals, thereby improving the mechanical properties.

[0018] (4) The temperature-sensitive color-changing material provided by the present invention is used to improve the interface strength of polydopamine by introducing hydrogen bonds between polyvinyl pyrrolidone and polydopamine. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0020] <Example>

[0021] Example 1

[0022] This embodiment provides a method for preparing a temperature-sensitive color-changing material, comprising 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 mixed liquid after stirring; add cellulose nanocrystal dispersion (obtained by dispersing 1 g of cellulose nanocrystals in water) to the first mixed liquid, continue stirring to obtain a second mixed liquid; place the second mixed liquid in a high-pressure reactor, heat-treat at 180°C for 48 hours, cool it to room temperature, centrifuge, and wash with deionized water and anhydrous ethanol to obtain cellulose nanocrystals@VO2.

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

[0026] 1g of cellulose nanocrystals @VO2 was dispersed in 100ml of DMF to form a first dispersion, which was sealed for later use. 0.5g of EDTAD was dispersed in 50ml of DMF to form a second dispersion, which was sealed for later use. Then, at 75°C and in an N2 atmosphere, the second dispersion was gradually dripped into the first dispersion, and stirred for 36 hours. After the dispersion was completed, it was centrifuged, washed with DMF and distilled water for several times, and dried to obtain an intermediate. The intermediate was made into a suspension, Tris was added to the suspension, and the pH value of the suspension was adjusted to 8.5. Then, 1g of dopamine was added to the suspension, and stirred at room temperature for 48 hours. After the stirring was completed, the filtrate was placed in a 3wt% PVP solution and allowed to stand for 2 hours, and the filtrate was washed with deionized water to obtain a thermosensitive color-changing material.

[0027] Example 2

[0028] This embodiment provides a method for preparing a temperature-sensitive color-changing material, comprising the following steps:

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

[0030] 1 g of ammonium metavanadate was dissolved in 0.01 mol / L oxalic acid solution, and the mixture was stirred to obtain a first mixed liquid; a cellulose nanocrystal dispersion (obtained by dispersing 0.8 g of cellulose nanocrystals in water) was added to the first mixed liquid, and the mixture was stirred continuously to obtain a second mixed liquid; the second mixed liquid was placed in a high-pressure reactor, and the mixture was heat-treated at 180°C for 48 h, and then cooled to room temperature. The mixture was centrifuged and washed with deionized water and anhydrous ethanol to obtain cellulose nanocrystals@VO2.

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

[0032] 1g of cellulose nanocrystals @VO2 was dispersed in 120ml of DMF to form a first dispersion, which was sealed for later use. 0.3g of EDTAD was dispersed in 50ml of DMF to form a second dispersion, which was sealed for later use. Then, at 75°C and in an N2 atmosphere, the second dispersion was gradually dripped into the first dispersion, and stirred for 36 hours. After the dispersion was completed, it was centrifuged, washed with DMF and distilled water for several times, and dried to obtain an intermediate. The intermediate was made into a suspension, Tris was added to the suspension, and the pH value of the suspension was adjusted to 8.5. Then, 1g of dopamine was added to the suspension, and stirred at room temperature for 48 hours. After the stirring was completed, the filtrate was placed in a 3wt% PVP solution and allowed to stand for 2 hours, and the filtrate was washed with deionized water to obtain a thermosensitive color-changing material.

[0033] <Comparative Example>

[0034] Comparative Example 1

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

[0036] Comparative Example 2

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

[0038] Comparative Example 3

[0039] The difference between this comparative example and Example 1 is that no PVP is added.

[0040] <Test example>

[0041] The temperature-sensitive color-changing materials prepared in Examples 1-2 and Comparative Examples 1-3 were used as samples for experimental measurements.

[0042] After cleaning and drying the substrate (quartz glass), spin coating the coating solution to obtain a composite film. The coating solution is obtained by mixing 0.2g sample, 0.2g PVP, and 5ml ethanol. Under the conditions of 20℃ and 80℃, keep warm for 0.5h, and measure the visible light transmittance and sunlight regulation efficiency, referring to ISO9050:2003(E). The results are shown in Table 1.

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

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

[0045]

Claims

1. A temperature-sensitive color-changing material, characterized in that: include: The core, which is cellulose nanocrystals@VO2, The outer shell is polydopamine.

2. The temperature-sensitive color-changing material according to claim 1, characterized in that: The preparation method of cellulose nanocrystals @VO2 is as follows: adding ammonium metavanadate into an oxalic acid solution, and obtaining a first mixed solution after stirring; adding the cellulose nanocrystal dispersion to the first mixed solution and continuing stirring to obtain a second mixed solution; The second mixed liquid is placed in a high-pressure reactor, subjected to heat preservation treatment, cooled to room temperature, and centrifuged and washed to obtain cellulose nanocrystals@VO2.

3. The temperature-sensitive color-changing material according to claim 1, characterized in that: Cellulose nanocrystals@VO2 include at least one of the features (1-1) to (1-3): (1-1) Insulation treatment: 170-200°C, 40-60h; (1-2) The mass concentration of oxalic acid solution is 0.01 mol / L; (1-3) The mass ratio of ammonium metavanadate to nanocrystalline cellulose is 1:0.8-1.

5.

4. A method for preparing a temperature-sensitive color-changing material according to any one of claims 1 to 3, characterized in that: The steps include: The cellulose nanocrystals @VO2 are dispersed in DMF to form a first dispersion, and EDTAD is dispersed in DMF to form a second dispersion; the second dispersion is gradually dripped into the first dispersion while stirring, and after completion, the dispersion is centrifuged, washed, and dried to obtain an intermediate; The intermediate is prepared into a suspension, Tris is added to the suspension, and the pH value of the suspension is adjusted to 8.5; then, dopamine is added to the suspension, and the suspension is stirred at room temperature, and then filtered and washed to obtain a thermochromic material.

5. The method for preparing the temperature-sensitive color-changing material according to claim 4, characterized in that: Cellulose nanocrystals @VO2:DMF in the first dispersion = 1 g: 60-100 ml.

6. The method for preparing the temperature-sensitive color-changing material according to claim 4, characterized in that: In the second dispersion, EDTAD:DMF=0.1-2 g:25-50 mL.

7. The method for preparing the thermochromic material according to any one of claims 4 to 6, characterized in that: The dropping process is carried out at 65-80°C and N2 atmosphere; the stirring time is 36-48h.

8. The method for preparing the temperature-sensitive color-changing material according to claim 4, characterized in that: The amount of dopamine added is 0.8 to 1.2 times that of cellulose nanocrystals@VO2.

9. The method for preparing a temperature-sensitive color-changing material according to any one of claims 4 to 6 and 8, characterized in that: After filtration, the filtrate is placed in a PVP solution and allowed to stand for a period of time, and then washed.

10. The method for preparing the temperature-sensitive color-changing material according to claim 9, characterized in that: The mass concentration of PVP is 1 to 3 wt%.

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