A reversible thermochromic material and preparation method thereof

Abstract

The present invention discloses a reversible thermochromic material, which is composed of a polyol and at least two color-developing materials. The present invention also discloses a method for preparing the reversible thermochromic material, which is specifically: heating the polyol in a water bath to a molten state; adding two different triarylmethane dyes to the molten polyol, mixing and stirring evenly, and obtaining the reversible thermochromic material. Compared with the existing ternary reversible thermochromic material system, the reversible thermochromic material of the present invention does not contain toxic phenol-based color developers; the reversible thermochromic material of the present invention, under the premise of fixing the type of color-developing agent, can adjust the type of doped dyes to enable the color-changing material to achieve different color changes.

Description

Technical Field

[0001] The invention relates to a reversible thermochromic material and also to a method for preparing the reversible thermochromic material. Background Art

[0002] Reversible thermochromic materials are color-changing materials that change color reversibly with temperature changes. Among them, ternary reversible thermochromic materials have become a hot topic of research due to their bright color change and good reversibility. Ternary reversible thermochromic materials are mainly composed of three parts: color former, color developer, and solvent. The color former is generally a dye that determines the color of the substance, the color developer is generally an acid that determines the depth of the color, and the solvent is generally a phase change material that determines the temperature of the color change.

[0003] Common color developers are generally phenolic acids. Wang Shuoshuo et al. [Wang Shuoshuo, et al. Reversibly thermochromic and high strength core-shell nanofibers fabricated by melt coaxial electrospinning [J]. Journal of Applied Polymer Science, 2021, 138 (21): 50465] prepared a reversible thermochromic material composed of crystal violet lactone / bisphenol A / tetradecanol, which can undergo a reversible color change from blue to white at around 38°C, and the latent heat of phase change is 88.71 J / g. Yuan Yanping et al. [A reversible thermochromic shape-fixed phase change functional material and its preparation method: CN112852384A [P]. 2021-05-28] invented a reversible thermochromic material composed of crystal violet lactone / 4-dodecylphenol / alkane phase change material, which can undergo a reversible color change between blue and white at 18-65°C. Fang Xi [Preparation and Application of Thermochromic Hybrid Silica Sol [D]. Donghua University, 2012] prepared a thermochromic material composed of crystal violet lactone / bisphenol S / hexadecanol and found that the material can undergo reversible color change near the phase transition point of hexadecanol. However, phenolic substances are often accompanied by certain toxicity and have certain toxic effects on nature and even the human body. How to overcome this problem and find a new color change system is a major research hotspot.

[0004] In addition, the color of common reversible thermochromic materials is usually determined only by the chromogen, Wan Zhang et al. [Wan Zhang, et al. A new approach for the preparation of durable and reversible colorchanging polyester fabrics using thermochromic dye-loaded silicone capsules [J]. Journal of Materials Chemistry C, 2017, 5: 8169-8178], Yue Pu et al. [Yue Pu and Jian Fang. Preparation and thermochromic behavior of low-temperature thermochromic microcapsule temperature indicators [J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2022: 129889] and Zetian Zhang et al. [Zetian Zhang, Reversible thermochromic microencapsulated phase change materials for enhancing functionality of silicone rubber materials [J]. Materials Chemistry and Physics, 2022, 290: 126564] Both use crystal violet lactone as the colorant, but use different color developers, and the final materials can reversibly change between blue and white.Honghan Bu et al. [Honghan Bu, et al. Thermochromic and tunable emissivity properties of BCG / CaCl2 / PEG-g-CDA composites for smart adaptive camouflage in visible and infrared wavebands [J]. Optical Materials, 2018, 84: 109-114] and Du Jiangyan et al. [Du Jiangyan et al. Preparation and thermochromic properties of bromocresol green-alkaline earth metal ions-hexadecanol thermochromic composites [J]. Functional Materials, 2000 (05): 554-555 + 557] both used bromocresol green as a colorant, and the prepared reversible thermochromic material was green at low temperatures and yellow at high temperatures. In this case, when the color of the color-changing material needs to be changed, the type of colorant can only be changed. However, sometimes there is a situation where the type of colorant needs to be fixed. Therefore, how to achieve different color changes on the basis of fixed colorants is also a major problem facing today. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a reversible thermochromic material that does not contain toxic phenol-based color developers and can achieve different color changes based on a fixed color developer; another purpose of the present invention is to provide a method for preparing the above-mentioned reversible thermochromic material.

[0006] Technical solution: The reversible thermochromic material of the present invention is composed of polyol and at least two color-developing materials.

[0007] The two color-developing materials are two different triarylmethane dyes, namely triarylmethane dye I and triarylmethane dye II; the mixing mass ratio of the triarylmethane dye I and the triarylmethane dye II is 1:3 to 3:1. If the added masses of the two dyes are very different, the problem of no color change will occur.

[0008] The total mass ratio of the color-developing material to the mass ratio of the polyol is 1:250 to 1500. If the amount of polyol added is too little, the dye cannot be fully dispersed and precipitation will occur in the system.

[0009] The method for preparing the reversible thermochromic material comprises the following steps:

[0010] (1) heating the polyol in a water bath to a molten state;

[0011] (2) Add two different triarylmethane dyes to the molten polyol in step (1), mix and stir evenly to obtain a reversible thermochromic material.

[0012] Wherein, in step (1), the water bath heating temperature is higher than the melting point of the polyol, so that it is in a molten state.

[0013] Wherein, in step (2), the mixing and stirring temperature is consistent with the water bath heating temperature in step (1), and the stirring time is 15 to 30 minutes.

[0014] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) Compared with the existing ternary reversible thermochromic material system, the reversible thermochromic material of the present invention does not contain toxic phenol-based color developers; (2) Under the premise of fixing the type of colorant, the reversible thermochromic material of the present invention can achieve different color changes by adjusting the type of doped dye. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Flow chart for preparing reversible thermochromic materials;

[0016] Figure 2 A schematic diagram of the color change of the reversible thermochromic material prepared in Example 1;

[0017] Figure 3 Schematic diagram of temperature change of the reversible thermochromic material prepared in Example 1;

[0018] Figure 4 A schematic diagram of a device for measuring color change temperature and complex color temperature;

[0019] Figure 5 A schematic diagram of the color change of the reversible thermochromic material prepared in Example 2;

[0020] Figure 6 Schematic diagram of temperature change of the reversible thermochromic material prepared in Example 2;

[0021] Figure 7 A schematic diagram of the color change of the reversible thermochromic material prepared in Example 3;

[0022] Figure 8 A schematic diagram of the color change of the material prepared in Comparative Example 1;

[0023] Fig. 9 Schematic diagram of the color change of the material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0024] Example 1

[0025] The method for preparing the reversible thermochromic material of the present invention comprises the following steps:

[0026] (1) Heat 5 g of stearyl alcohol (SA) in a 70°C water bath until it melts;

[0027] (2) Add 0.01 g of crystal violet lactone (CVL) and 0.01 g of cresol red (CSR) to the molten stearyl alcohol in step (1), respectively, and mix and stir at 70° C. to obtain a reversible thermochromic material.

[0028] Figure 2 Schematic diagram of the color change of the reversible thermochromic material prepared in Example 1. Figure 2 (a) is the initial color of the reversible thermochromic material at room temperature, Figure 2 (b) is the color of the reversible thermochromic material at a high temperature of 70°C. Figure 2 (c) is the color of the reversible thermochromic material when it returns to room temperature. Figure 2 It can be seen that the reversible thermochromic material is in a yellow-green solid state at room temperature, and turns into a red liquid at a high temperature of 70°C. When the temperature drops, the color turns back to a yellow-green solid state, and the color reproduction performance is good.

[0029] Figure 3 This is a temperature change diagram of the reversible thermochromic material prepared in Example 1. Figure 3 (a) is the heating curve of the reversible thermochromic material. Figure 3 As can be seen in (a), when the temperature rises to 53.37°C, the reversible thermochromic material undergoes a phase change from solid to liquid, absorbing heat. Figure 3 (b) is the cooling curve of the reversible thermochromic material. It can be seen from the curve that the reversible thermochromic material undergoes two phase changes and releases heat. The first phase change starts at 56.91°C and the second phase change starts at 50.98°C.

[0030] Figure 4 This is a schematic diagram of the device for measuring the color change temperature and the complex color temperature of Example 1. The actual temperature of the digital display constant temperature water bath will vary greatly due to the influence of the environment. In order to reduce the influence of the ambient temperature, the lid of the digital display constant temperature water bath is covered, leaving only a beaker-sized opening for heating the sample; at the same time, the temperature measuring line of the multi-channel data recorder is inserted into the digital display constant temperature water bath to obtain accurate real-time temperature. In addition, during the test, only a thin layer of sample is left at the bottom of the beaker (the thickness is enough for a water drop to spread out) in order to quickly capture temperature changes. After testing, the color change temperature of the color-changing material in Example 1 is 57.6°C, and the complex color temperature is 56.8°C, which are respectively Figure 3 The starting temperature of the phase change during the heating process is basically the same as the starting temperature of the first phase change during the cooling process.

[0031] Example 2

[0032] The method for preparing the reversible thermochromic material of the present invention comprises the following steps:

[0033] (1) Heat 5 g of myristyl alcohol (MA) in a 50°C water bath until it melts;

[0034] (2) Add 0.01 g of crystal violet lactone (CVL) and 0.01 g of bromophenol blue (BPB) to the molten myristyl alcohol in step (1), respectively, and mix and stir at 50° C. to obtain a reversible thermochromic material.

[0035] Figure 5 Schematic diagram of the color change of the reversible thermochromic material prepared in Example 2. Figure 5 (a) is the initial color of the reversible thermochromic material at room temperature, Figure 5 (b) is the color of the reversible thermochromic material at a high temperature of 50°C. Figure 5 (c) is the color of the reversible thermochromic material when it returns to room temperature. Figure 5 It can be seen that the color is a white-green solid at room temperature, and the color changes to a cyan liquid at high temperature (50°C). When the temperature returns to room temperature, the color changes to a white-green solid again, and the color reproduction performance is good.

[0036] Figure 6 This is a temperature change diagram of the reversible thermochromic material prepared in Example 2. Figure 6 (a) is the temperature rise curve of the reversible thermochromic material. It can be seen from the curve that when the temperature rises to 37.32°C, the reversible thermochromic material undergoes a phase change from solid to liquid, absorbing heat. Figure 6 (b) is the cooling curve of the reversible thermochromic material. It can be seen from the figure that when the temperature drops to 37°C, the material begins to change from liquid to solid, releasing heat.

[0037] pass Figure 4 The color change temperature of the reversible color-changing material was measured using a device. The results showed that the color change temperature of the reversible color-changing material was 37.3°C and the complex color temperature was 36.5°C, which is consistent with Figure 6 The starting phase change temperature during the heating and cooling process is basically the same.

[0038] Example 3

[0039] The method for preparing the reversible thermochromic material of the present invention comprises the following steps:

[0040] (1) Heat 5 g of stearyl alcohol (SA) in a 70°C water bath until it melts;

[0041] (2) Add 0.01 g of crystal violet lactone (CVL) and 0.03 g of cresol red (CSR) to the molten stearyl alcohol in step (1), respectively, and mix and stir at 70° C. to obtain a reversible thermochromic material.

[0042] Figure 7Schematic diagram of the color change of the reversible thermochromic material prepared in Example 3. Figure 7 (a) is the initial color of the reversible thermochromic material at room temperature, Figure 7 (b) is the color of the reversible thermochromic material at a high temperature of 70°C. Figure 7 (c) is the color of the reversible thermochromic material at room temperature. As can be seen from the figure, the reversible thermochromic material has a color change phenomenon, but the color is reddish at low temperatures, and the degree of color change is not as obvious as in Example 1.

[0043] Comparative Example 1

[0044] (1) Heat 5 g of stearyl alcohol (SA) in a 70°C water bath until it melts;

[0045] (2) Add 0.01 g of crystal violet lactone (CVL) and 0.0001 g of cresol red (CSR) to the molten stearyl alcohol in step (1), respectively, and mix and stir at 70° C. until uniform.

[0046] Figure 8 Schematic diagram of the color change of the material prepared in Comparative Example 1. Figure 8 (a) is the initial color of the material at room temperature, Figure 8 (b) is the color of the material at a high temperature of 70°C. Figure 8 (c) is the color of the material when it is restored to room temperature. Figure 8 It can be seen that the material only undergoes phase change without causing color change.

[0047] Comparative Example 2

[0048] (1) Heat 5 g of stearyl alcohol (SA) in a 70°C water bath until it melts;

[0049] (2) Add 0.0001 g of crystal violet lactone (CVL) and 0.01 g of cresol red (CSR) to the molten stearyl alcohol in step (1), respectively, and mix and stir at 70° C. until uniform.

[0050] Fig. 9 Schematic diagram of the color change of the material prepared in Comparative Example 2. Fig. 9 (a) is the initial color of the material at room temperature, Fig. 9 (b) is the color of the material at a high temperature of 70°C. Fig. 9 (c) is the color of the material when it is restored to room temperature. Fig. 9 It can be seen that the material only undergoes phase change without discoloration. Comparative Examples 1 to 2 show that if the added masses of the two dyes are very different, there will be a problem of no discoloration.

Claims

1. A reversible thermochromic material, characterized in that: It is composed of a polyol and at least two color-developing materials; the two color-developing materials are two different triarylmethane dyes, namely triarylmethane dye I and triarylmethane dye II; the mixing mass ratio of the triarylmethane dye I and the triarylmethane dye II is 1:1; the mass ratio of the total mass of the color-developing material to the polyol is 1:250; the polyol is stearyl alcohol; the two different triarylmethane dyes are crystal violet lactone and cresol red; The reversible thermochromic material is a yellow-green solid at room temperature, turns into a red liquid at a high temperature of 70°C, and turns into a yellow-green solid again when the temperature drops.

2. The method for preparing the reversible thermochromic material according to claim 1, characterized in that: The steps include: (1) Heat the polyol in a water bath until it is molten; (2) Add two different triarylmethane dyes to the molten polyol in step (1), mix and stir evenly to obtain a reversible thermochromic material.

3. The method for preparing a reversible thermochromic material according to claim 2, characterized in that: In step (1), the water bath heating temperature is higher than the melting point of the polyol.

4. The method for preparing a reversible thermochromic material according to claim 2, characterized in that: In step (2), the mixing and stirring temperature is consistent with the water bath heating temperature in step (1), and the stirring time is 15 to 30 minutes.

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