Stretchable color-changing liquid crystal polymer optical driver, preparation method and application thereof

Abstract

The application belongs to the field of liquid crystal polymer material preparation, and discloses a stretchable color-changing photo-induced deformation cholesteric liquid crystal polymer film as well as a preparation method and application thereof. Polymerizable azobenzene molecules with photo-responsive characteristics are introduced into the liquid crystal polymer to prepare a liquid crystal polymer film capable of photo-induced deformation, which can be applied to the preparation of photo-driven devices, bionic multifunctional materials and artificial soft robots. The preparation method is simple and easy to operate, and is safe. The ultraviolet light used is a clean energy, which has the advantages of being simple and easy to obtain, capable of non-contact remote control, and easy to control in time and space. The film material prepared by the application can change the structural color under stress, and can also produce deformation under ultraviolet light. The structural color and deformation can be adjusted by the stress size and the ultraviolet light intensity, and no further processing is required.

Description

Technical Field

[0001] This invention belongs to the field of liquid crystal polymer material preparation, specifically relating to a stretchable and color-changing photodeformable cholesteric phase liquid crystal polymer film, its preparation method, and its application. Background Technology

[0002] Photodeformable liquid crystal polymers are materials that can move under light-driven conditions, directly converting light energy into the material's mechanical energy. Ultraviolet light is a clean energy source with advantages such as ease of availability, non-contact remote control, and good biocompatibility. It is also easy to control in time and space, making it an ideal driving method.

[0003] Azobenzene molecules are among the most widely used liquid crystal polymer actuators. Under ultraviolet light irradiation, they undergo cis-trans isomerization, leading to a decrease in the orderliness of liquid crystal molecules and even phase transitions. The molecular-scale cis-trans isomerism of azobenzene can be amplified into macroscopic deformation of the entire liquid crystal material through the synergistic effect of liquid crystal building blocks. This greatly enhances the application of this molecule in practical production and daily life. The structural color of cholesteric liquid crystals is determined by the microstructure of the liquid crystal polymer film and does not depend on pigments or dyes. Therefore, how to prepare photosensitive polymer films with stretch-induced color change has become a key issue. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a stretchable, color-changing, photodeformable cholesteric phase liquid crystal polymer film, its preparation method, and its application. Specifically, the following technical solution is adopted: According to a first aspect of the present invention, a method for preparing a stretchable, color-changing photodeformable cholesteric liquid crystal polymer film is provided, comprising the following steps: First, the liquid crystal monomer and azobenzene molecules are mixed evenly. Then, 3,6-dioxa-1,8-octanedithiols, pentaerythritol tetra(3-mercaptopropionate), chiral molecules and free radical photoinitiators are added. After mixing, the mixture is dropped onto a glass slide, and then another glass slide is placed on top to carry out the polymerization reaction. After the reaction is completed, a stretchable and color-changing photodeformable cholesteric liquid crystal polymer film is obtained.

[0005] This invention introduces polymerizable azobenzene molecules with photoresponsive properties into liquid crystal polymers, preparing a light-controlled deformation-inducible liquid crystal polymer film. The added azobenzene molecules undergo cis-trans isomerization under ultraviolet light irradiation, leading to a decrease in the orderliness of the liquid crystal molecules and even a phase transition. The molecular-scale cis-trans isomerization of azobenzene can be amplified into macroscopic deformation of the entire liquid crystal material through the synergistic effect of the liquid crystal building blocks. This preparation method is simple to operate, easy to implement, and highly safe. Furthermore, the ultraviolet light used is a clean energy source with advantages such as easy availability, non-contact remote control, and ease of control in time and space.

[0006] This invention also introduces 3,6-dioxa-1,8-octanedithiol molecules into the liquid crystal polymer to prepare a liquid crystal polymer film with good stretching properties. The added chiral molecule, R5011, has a large HTP (heavy thiol content), and only a small amount is needed to impart a distinct structural color to the material. Uniaxial stretching can achieve a blue shift of the structural color of the liquid crystal polymer film, thereby achieving the purpose of programming the structural color.

[0007] The aforementioned free radical photoinitiator is bis(1-(2,4-difluorophenyl)-3-pyrrolithyl)titanium, which can generate free radicals under green light irradiation and initiate the polymerization of polymer monomers, but will not cause material deformation. The above-mentioned mixed liquid crystal is poured into a liquid crystal cell with two sides rubbed parallel alignment to form a liquid crystal film. The PET spacer is controlled to have a thickness of 120 μm, a length of 0.5 cm-6 cm, and a width of 0.2 cm-4 cm. Excessive or insufficient thickness will affect the photoresponse speed and deformation of the film.

[0008] Preferably, the mass ratio of liquid crystal monomer to azobenzene molecules is (80-95):(5-25). When there is no azobenzene molecules or the content is too low, no photoresponse effect will occur.

[0009] Preferably, the mass fraction ratio of 3,6-dioxa-1,8-octanedithiol, pentaerythritol tetra(3-mercaptopropionate), chiral molecule, and free radical photoinitiator is (8%-14%):(1%-6%):(2%-2.5%):(1%-5%). When the contents of 3,6-dioxa-1,8-octanedithiol and pentaerythritol tetra(3-mercaptopropionate) are too high or too low, a liquid crystal film cannot be formed.

[0010] Preferably, the liquid crystal monomer is selected from at least one of the following compounds: , , ; Where R is n is any positive integer from 1 to 12. The above-mentioned liquid crystal polymer has dual functional groups, and can simultaneously possess liquid crystal and reactive functional groups. Therefore, it can be further cross-linked and cured through chemical reactions to improve its performance and stability.

[0011] More preferably, the liquid crystal monomer structure is as shown in Formula I: Formula I. This structure exhibits good chiral self-assembly properties and high stability.

[0012] Preferably, the azobenzene molecule is selected from at least one of the following compounds: , , , ; Where R is selected from , , or n is any positive integer from 1 to 12.

[0013] More preferably, the molecular structure of azobenzene is shown in Formula II: Formula II. This structure can be covalently crosslinked into liquid crystal polymer materials and exhibits the property of undergoing cis-trans isomerization under ultraviolet light excitation.

[0014] Preferably, the polymerization reaction temperature is 50 °C and the time is 8 h-24 h. If the polymerization temperature is too high or too low, the structural color of the liquid crystal film will be indistinct. If the polymerization time is too short, the liquid crystal film will not form; if the polymerization time is too long, the film will have an excessively high degree of cross-linking, making it hard, brittle, and easily damaged.

[0015] According to a second aspect of the present invention, a stretchable, color-changing, photodeformable cholesteric liquid crystal polymer film prepared by the above method is also provided. The film material prepared by the present invention can undergo structural color changes under stress and can also deform under ultraviolet light irradiation. It can return to its initial shape upon heating. The structural color and deformation can be adjusted by the stress magnitude and ultraviolet light intensity without further processing. The film thickness is controlled to be 80 μm-500 μm; excessively large or small thicknesses will affect the film's photoresponse speed and deformation magnitude.

[0016] According to a third aspect of the present invention, the application of the above-mentioned photodeformable polymer film in the preparation of optical actuators, biomimetic multifunctional materials, and artificial soft robots is also provided. The liquid crystal polymer film prepared by the present invention exhibits a blue shift in its structural color under applied stress. The structural color of the film can be programmed by controlling the stretching position and stress magnitude, demonstrating significant application potential in the fields of soft actuators and biomimetic devices. Furthermore, the deformation and structural color change functions can be achieved without further processing, playing a crucial role in the fields of smart materials and light-controlled robot materials.

[0017] The beneficial effects of this invention are as follows: This invention introduces polymerizable azobenzene molecules with photoresponsive properties into liquid crystal polymers, thus preparing a liquid crystal polymer film capable of photo-controlled deformation. The preparation method of this invention is simple and easy to operate, and highly safe. The ultraviolet light used is a clean energy source with advantages such as easy availability, non-contact remote control, and ease of control in time and space. The film material obtained by this invention can change its structural color under stress and can also deform under ultraviolet light irradiation. Heating restores it to its initial shape. The structural color and deformation can be adjusted by the stress magnitude and ultraviolet light intensity without further processing. It can be applied to the preparation of optical actuators, biomimetic multifunctional materials, and artificial soft robots. Attached Figure Description

[0018] Figure 1 The diagram shown is a schematic of the stretchable and color-changing photodeformable polymer film prepared in Example 1. Figure 2 The image shown is a stretch color change test diagram of the stretchable color-changing cholesteric liquid crystal polymer film prepared in Comparative Example 1. Figure 3 The figure shown is a test result of the photoresponse time of the stretchable and color-changing photodeformable polymer film prepared in Example 1 under different ultraviolet light intensities. Figure 4 The image shown is an image of the stretchable, color-changing photodeformable polymer film prepared in Example 1 bending under ultraviolet light irradiation.

[0019] Figure 5 The image shown is of the cholesteric liquid crystal polymer film with structural color prepared in Comparative Example 1, which did not undergo any deformation under ultraviolet light irradiation. Detailed Implementation The following will provide a clear and complete description of the concept and technical effects of the present invention in conjunction with the embodiments and accompanying drawings, so as to fully understand the purpose, solution and effects of the present invention. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0020] Example 1 A stretchable, color-changing, photodeformable cholesteric liquid crystal polymer film, the preparation method of which includes the following steps: First, the liquid crystal monomer and azobenzene molecules were mixed at a mass ratio of 90:10. Then, the mixture was mixed with 13.69% 3,6-dioxa-1,8-octanedithiol, 6.1% pentaerythritol tetra(3-mercaptopropionate), 2.29% chiral molecule R5011, and 1% photoinitiator Irg784 by mass fraction. The mixture was then dropped onto a glass slide that had been treated with parallel orientation. Another glass slide with parallel orientation was then placed on top. The thickness was controlled at 120 μm using PET spacers. The polymerization temperature was 50 ℃, and the polymerization time was 8 h. After polymerization, the liquid crystal cell was opened to obtain a cholesteric phase liquid crystal polymer film.

[0021] The liquid crystal monomer structure used in this embodiment is as follows: ; The molecular structure of the azobenzene used in this embodiment is as follows: .

[0022] Example 2 This embodiment tests the cholesteric liquid crystal polymer film prepared in Example 1 under ultraviolet light irradiation. The obtained polymer film was irradiated with ultraviolet light of different intensities, and the results are as follows. Figure 3 As shown, the thin film can generate an ultraviolet light response, and the light response time decreases as the light intensity increases.

[0023] Example 3 This embodiment tests the stretchability and color change of the cholesteric liquid crystal polymer film prepared in Example 1. The obtained polymer film was stretched using a stretching instrument, and the results are as follows: Figure 1 and Figure 4 As shown, when stretched to 150% of its initial length, the structural color of the film changes from red to green. The film is then cured by irradiating it with 520 nm green light at an intensity of 1 mW / cm². 2 A curing time of 2 hours yields a film with a fixed green structural color. One end of the film is clamped and fixed, and the film is irradiated with 365 nm ultraviolet light at an intensity of 1800 μW / cm². 2 The thin film can produce local deformation, which accumulates into bending deformation, with the bending direction along the long axis of the liquid crystal molecules in the thin film.

[0024] Comparative Example 1 A stretchable, color-changing cholesteric phase liquid crystal polymer film is prepared by the following steps: 73.56% monomer C6M, 16.69% 3,6-dioxa-1,8-octanedithiol, 7.1% pentaerythritol tetra(3-mercaptopropionate), 1.65% chiral molecule R5011, and 1% photoinitiator Irg784 were mixed and dropped onto a glass slide that had undergone parallel orientation treatment. Then, another glass slide with parallel orientation was placed on top, and the thickness was controlled at 120 μm using PET spacers. The polymerization temperature was 50 ℃, and the polymerization time was 8 h. After polymerization, the liquid crystal cell was opened to obtain a polymer liquid crystal film.

[0025] The liquid crystal monomer structure used in this embodiment is as follows: .

[0026] The cholesteric liquid crystal polymer film prepared in this comparative example was subjected to a stretchability color change test. The obtained polymer film was stretched using a stretching instrument, and the results are as follows. Figure 2 As shown, when the film is stretched from its initial length of 1 cm to 2 cm, its structural color changes from red to green; upon further stretching to 3.5 cm, the structural color changes to blue-green. The film is cured by irradiating it with 520 nm green light at an intensity of 1 mW / cm². 2 A curing time of 2 hours yields a film with a fixed structural color of blue-green.

[0027] The cholesteric liquid crystal polymer film prepared in this comparative example was subjected to photoinduced deformation testing. One end of the film was clamped and fixed, and the film was irradiated with 365 nm ultraviolet light at an intensity of 1800 μW / cm. 2 The result is as follows Figure 5 As shown, the film did not produce any deformation effect.

[0028] In summary, the cholesteric liquid crystal polymer films prepared by adding azobenzene molecules have a thickness of 80 μm-500 μm; they can achieve structural color transformation under stretching and exhibit deformation function under ultraviolet light irradiation.

[0029] Although the description of the invention has been quite detailed and particularly of several described embodiments, it is not intended to limit it to any of these details or embodiments or any particular embodiment, but should be considered as providing a broad possible interpretation of the claims by referring to the appended claims and taking into account the prior art, thereby effectively covering the intended scope of the invention. Furthermore, the invention has been described above with respect to embodiments foreseeable by the inventors in order to provide a useful description, and non-substantial modifications to the invention that have not yet been foreseen may still represent equivalent modifications.

Claims

1. A method for preparing a stretchable, color-changing, photodeformable cholesteric phase liquid crystal polymer film, characterized in that, Includes the following steps: First, the liquid crystal monomer and azobenzene molecules are mixed evenly. Then, 3,6-dioxa-1,8-octanedithiols, pentaerythritol tetra(3-mercaptopropionate), chiral molecules and free radical photoinitiators are added. After mixing, the mixture is dropped onto a glass slide. Then, another glass slide is placed on top to carry out the polymerization reaction. After the reaction is completed, a stretchable and color-changing photodeformable cholesteric liquid crystal polymer film is obtained. The structure of the liquid crystal monomer is shown in Formula I: Formula I; The molecular structure of the azobenzene is shown in Formula II: Formula II.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the liquid crystal monomer to the azobenzene molecule is (80-95):(5-25).

3. The preparation method according to claim 1, characterized in that, The mass ratio of the 3,6-dioxa-1,8-octanedithiol, the pentaerythritol tetra(3-mercaptopropionate), the chiral molecule, and the free radical photoinitiator is (8%-14%):(1%-6%):(2%-2.5%):(1%-5%).

4. The preparation method according to claim 1, characterized in that, The polymerization reaction was carried out at a temperature of 50 °C for 8-24 hours.

5. A stretchable, color-changing, photodeformable cholesteric liquid crystal polymer film, characterized in that, It is prepared by the preparation method according to any one of claims 1-4.

6. The application of the photodeformable cholesteric liquid crystal polymer film according to claim 5 in the preparation of optical actuators, biomimetic multifunctional materials, and artificial soft robots.

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