A thermochromic cholesteric liquid crystal material and a preparation method thereof

Abstract

A thermochromic cholesteric liquid crystal material is composed of a matrix liquid crystal and a chiral agent. The matrix liquid crystal includes mixture A and mixture B, both of which are hydrogen-bonded liquid crystals. Among them: The clearing point of mixture A is 120°C to 180°C, and it is a mixture of at least two benzoic acid derivatives; the crystallization point of mixture B is -30°C to 0°C, and it is a mixture of at least two cyclohexanecarboxylic acid derivatives. The cholesteric liquid crystal material of the present invention has the characteristics of high sensitivity and wide color gamut. It can achieve continuous color change of structural color from red to blue within a very narrow temperature range. Optimally, the change of structural color from red to blue can be achieved within 3°C to 5°C, which is much more sensitive than traditional cholesteric liquid crystals, and has a wide color change range. It has great application potential in temperature display, anti-counterfeiting technology and other aspects.

Description

Technical Field

[0001] The present invention relates to the technical field of thermochromic materials, and particularly relates to a thermochromic cholesteric liquid crystal material and a preparation method thereof. Background Art

[0002] Most animals and plants in nature have rich colors, and they can convey information and adapt to the environment through colors. Many colors are manifested because certain compounds in animals and plants absorb or reflect light of specific wavelengths, and this kind of color is called dye color (or chemical color), such as the colors of most flowers. In addition to dye colors, there is also a kind of color widely present in nature, which is caused by the microstructures on the surfaces of animals and plants, making light undergo physical processes such as interference and diffraction, and this kind of color is called structural color (or physical color), such as the colors of butterfly wings and beetle shells. And the colors of some animals and plants can also change with external stimuli, or actively change colors to convey information and disguise themselves, such as chameleons.

[0003] Due to its special helical structure, cholesteric liquid crystal has strong optical rotation performance and selective reflection performance, and can show very bright colors. Similarly, cholesteric liquid crystal can also achieve light regulation through various external stimuli. At different temperatures, the cholesteric liquid crystal selectively reflects different wavelengths, which is called the thermochromic effect of cholesteric phase. Compared with other stimulation methods, thermal stimulation widely exists in nature, and it is pollution-free and easy to operate. Therefore, using the thermochromic effect of cholesteric liquid crystal to regulate the reflected color has gradually attracted the attention of researchers, and corresponding applicable devices have been made, such as liquid crystal thermometers, color-changing fabrics, infrared detectors, etc. However, usually the color change sensitivity of cholesteric liquid crystal with temperature is not high, which affects the sensitivity of liquid crystal thermometers. Therefore, preparing a cholesteric liquid crystal with simple components, fewer processes, continuous color change, wide color change range, high sensitivity, and good stability is of great significance for thermochromic cholesteric liquid crystal. Summary of the Invention

[0004] The present invention aims to provide a thermochromic cholesteric liquid crystal material highly sensitive to temperature and a preparation method thereof, so as to solve the technical problems existing in traditional cholesteric liquid crystals, such as low sensitivity of color change with temperature and narrow color change range. In addition to the characteristic of high sensitivity, the most important point of the thermochromic cholesteric liquid crystal material of the present invention is that the color change range can be controlled near room temperature, and human body temperature can be used to make it change color.

[0005] To achieve the above object, the present invention provides a thermochromic cholesteric liquid crystal material, which is composed of a matrix liquid crystal and a chiral agent. It obtains structural color by adding a chiral agent, and adjusts the temperature range of the cholesteric liquid crystal by adjusting the types and proportions of liquid crystal monomers in the matrix liquid crystal. Utilizing the high sensitivity of the molecular arrangement mode in the system to temperature, the change in temperature causes the periodicity of the cholesteric liquid crystal to change, thereby changing the reflected color.

[0006] Specifically, the matrix liquid crystal includes mixture A and mixture B, both of which are hydrogen-bond liquid crystals. The functions of mixture A and B are to enable the liquid crystal to have a relatively wide temperature range. The blending ratio of the two mainly adjusts the covered color-changing temperature range, and the selection of the type and content of the chiral agent will have a great impact on the system sensitivity.

[0007] The clearing point of mixture A is 120°C to 180°C, and it is a mixture of at least two benzoic acid derivatives. The structural general formula of the benzoic acid derivative is:

[0008]

[0009] Wherein, R is OCH2 or CH2; n is an integer from 0 to 17;

[0010] The crystallization point of mixture B is -30°C to 0°C, and it is a mixture of at least two cyclohexanecarboxylic acid derivatives. The structural general formula of the cyclohexanecarboxylic acid derivative is:

[0011]

[0012] Wherein, R is OCH2 or CH2; m is an integer from 0 to 17.

[0013] As a further preferred technical solution of the present invention, the mass ratio of the total mass of mixture A and mixture B to the mass of the chiral agent is 9:1 to 1:9.

[0014] As a further preferred technical solution of the present invention, the mass ratio of mixture A to mixture B is 9:1 to 1:9.

[0015] As a further preferred technical solution of the present invention, the chiral agent is a common chiral agent, which includes and is not limited to one or more of S811, R811, S1011, R1011, S5011, R5011, BDH1281, CB15 mixed in any proportion.

[0016] According to another aspect of the present invention, the present invention also provides a preparation method of a thermochromic cholesteric liquid crystal material, which includes the following steps:

[0017] (1) Take at least two benzoic acid derivatives and mix them to obtain mixture A with a clearing point of 120°C to 180°C;

[0018] (2) Take at least two cyclohexanecarboxylic acid derivatives and mix them to obtain mixture B with a crystallization point of -30°C to 0°C;

[0019] (3) Heat mixture A and mixture B to the clear state respectively, then mix them evenly and add a chiral agent to obtain a cholesteric liquid crystal, that is, a thermochromic cholesteric liquid crystal material.

[0020] The thermochromic cholesteric liquid crystal material and its preparation method of the present invention can achieve the following beneficial effects by adopting the above technical solutions: It has the characteristics of high sensitivity and wide color gamut, and can realize the continuous color change of structural color from red to blue within a very narrow temperature range. Optimally, the change of structural color from red to blue can be achieved within 3°C to 5°C, which is much more sensitive than traditional cholesteric liquid crystals, and has a wide color change range; The temperature range covered by the color change is close to room temperature, and it can be applied to products that change color at room temperature according to different usage requirements; The thermochromic cholesteric liquid crystal material with high sensitivity and wide color change range obtained by the present invention has great application potential in temperature display, color-changing fabrics, sensors, anti-counterfeiting technologies, etc. Description of the Drawings

[0021] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0022] Figure 1 It is the polarized light diagram of the cholesteric liquid crystal at different temperatures in Example 1.

[0023] Figure 2 It is the reflection spectrum diagram of the cholesteric liquid crystal at different temperatures in Example 1.

[0024] Figure 3 It is the polarized light diagram of the cholesteric liquid crystal at different temperatures in Example 2.

[0025] Figure 4 It is the reflection spectrum diagram of the cholesteric liquid crystal at different temperatures in Example 2.

[0026] Figure 5 It is the polarized light diagram of the cholesteric liquid crystal at different temperatures in Example 3.

[0027] Figure 6 It is the reflection spectrum diagram of the cholesteric liquid crystal at different temperatures in Example 3.

[0028] Figure 7 It is the chemical structural formula of each material component in Table 1.

[0029] Figure 8 It is the chemical structural formula of each material component in Table 2.

[0030] Figure 9 They are the chemical structural formulas of the material components in Table 3.

[0031] The realization of the object, functional features and advantages of the present invention will be further described with reference to the embodiments and the accompanying drawings. Embodiment

[0032] The following further details the specific embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for explaining and illustrating the present invention, and are not used to limit the present invention.

[0033] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which the present invention pertains. The test reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified. Example

[0034] Select the materials and mixing ratios as shown in Table 1. The chemical structural formulas of the material components are as Figure 7 shown. Heat mixture A and mixture B to the clear state respectively, then mix them evenly, and then add a chiral agent to obtain a cholesteric liquid crystal, also known as a thermochromic cholesteric liquid crystal material. Among them, the clearing point of mixture A is 140 °C, and the crystallization point of mixture B is -20 °C.

[0035] Use the reflection mode (RL mode) of a polarized light microscope (POM) to preliminarily observe the reflection color and texture of the cholesteric liquid crystal, and use the transmission mode (TL mode) of a polarized light microscope (POM) to further observe the texture of the liquid crystal. The test results are as Figure 1 and 2 shown.

[0036] The prepared cholesteric liquid crystal has excellent thermochromic ability. Obvious reflection colors can be observed from the polarized light microscope, and as the temperature rises, the reflection color changes from red to orange, green, and finally to blue at 60 °C.

[0037] Table 1. Sample formula of the cholesteric liquid crystal material in Example 1

[0038]

[0039] Select the materials and mixing ratios as shown in Table 2. The chemical structural formulas of the material components are as Figure 8 shown. Heat mixture A and mixture B to the clear state respectively, then mix them evenly, and then add a chiral agent to obtain a cholesteric liquid crystal, that is, a thermochromic cholesteric liquid crystal material. Among them, the clearing point of mixture A is 138 °C, and the crystallization point of mixture B is -15 °C.

[0040] The reflection color and texture of the cholesteric liquid crystal were preliminarily observed using the reflection mode (RL mode) of a polarized light microscope (POM), and the texture of the liquid crystal was further observed using the transmission mode (TL mode) of the polarized light microscope (POM). The test results are as Figure 3 and 4 shown.

[0041] The prepared cholesteric liquid crystal has excellent thermochromic ability. Obvious reflection colors can be observed through a polarized light microscope, with bright and uniform colors and relatively high color change sensitivity; the reflection wavelengths of its colors can cover 674 nm to 450 nm. At 30 °C, the initial central wavelength of the cholesteric liquid crystal is 674 nm, and its color is red. When the temperature rises to 32 °C, the color changes from red to orange. The increase in temperature will cause a blue shift of the reflection band gap. When the temperature rises to 36 °C and 44 °C, the corresponding reflection colors are green and blue respectively.

[0042] Table 2. Sample formula of the cholesteric liquid crystal material in Example 2

[0043]

[0044] As a better choice of the technical solution of the present invention, the materials and mixing ratios shown in Table 3 are selected. The chemical structural formulas of each material component are as Figure 9 shown. The mixture A and the mixture B are respectively heated to the clear state, then mixed evenly, and then a chiral agent is added to obtain a cholesteric liquid crystal, that is, a thermochromic cholesteric liquid crystal material. Among them, the clearing point of the mixture A is 120 °C, and the crystallization point of the mixture B is -10 °C.

[0045] The reflection color and texture of the cholesteric liquid crystal were preliminarily observed using the reflection mode (RL mode) of a polarized light microscope (POM), and the texture of the liquid crystal was further observed using the transmission mode (TL mode) of the polarized light microscope (POM). The test results are as Figure 5 and 6 shown. The cholesteric liquid crystal presents an oil streak texture at room temperature, and the structural color is bright.

[0046] At 27 °C, the initial central wavelength of the cholesteric liquid crystal is about 690 nm. When the temperature rises from 27 °C to 28 °C, the reflection band gap of the cholesteric liquid crystal moves from 680 nm to 590 nm. The increase in temperature will cause a blue shift of the reflection band gap. Finally, the cholesteric liquid crystal turns green at 29 °C and blue at 30 °C. This fully demonstrates that the present invention has obtained a thermochromic cholesteric liquid crystal material with high sensitivity, and the color change range can be controlled near room temperature.

[0047] Table 3. Sample formula of the cholesteric liquid crystal material in Example 3

[0048]

[0049] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that these are only examples, and various changes or modifications can be made to this embodiment without departing from the principles and essence of the present invention. The protection scope of the present invention is only defined by the appended claims.

Claims

1. A thermochromic cholesteric liquid crystal material, which is composed of a parent liquid crystal and a chiral agent, is characterized in that The matrix liquid crystal includes mixture A and mixture B, where: The clearing point of mixture A is 120°C to 180°C, and it is a mixture of at least two benzoic acid derivatives. The structural general formula of the benzoic acid derivative is: ； where R is OCH2 or CH2, and n is an integer from 0 to 17; The crystallization point of mixture B is -30°C to 0°C, and it is a mixture of at least two cyclohexanecarboxylic acid derivatives. The structural general formula of the cyclohexanecarboxylic acid derivative is: ； where R is OCH2 or CH2, and m is an integer from 0 to 17; The chiral agent is one or a mixture of more than one of S811, R811, S1011, R1011, S5011, R5011, BDH1281, and CB15.

2. The thermochromic cholesteric liquid crystal material according to claim 1, characterized in that, The mass ratio of the total mass of mixture A and mixture B to the mass of the chiral agent is 9:1 to 1:

9.

3. The thermochromic cholesteric liquid crystal material according to claim 1, wherein The mass ratio of mixture A to mixture B is 9:1 to 1:

9.

4. A method for preparing a thermochromic cholesteric liquid crystal material according to any one of claims 1-3, characterized in that, It includes the following steps: (1) Take at least two benzoic acid derivatives and mix them to obtain mixture A with a clearing point of 120°C to 180°C; (2) Take at least two cyclohexanecarboxylic acid derivatives and mix them to obtain mixture B with a crystallization point of -30°C to 0°C; (3) Heat mixture A and mixture B to the clear state respectively, then mix them evenly and add the chiral agent to obtain the thermochromic cholesteric liquid crystal material.

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