Azobenzene liquid crystal film as well as preparation method and application thereof

Abstract

The invention relates to the technical field of azobenzene liquid crystal materials, and discloses an azobenzene liquid crystal film and a preparation method and application thereof.The azobenzene liquid crystal film is obtained by dissolving a chiral agent, nematic liquid crystals and azobenzene derivative monomers in a solvent and volatilizing the solvent, and the azobenzene derivative monomers have the structure as follows: R1 is selected from C1-20 alkyl; mixing the liquid crystal solution with the polymer solution for reaction to obtain polymer dispersed liquid crystal; and coating the polymer dispersed liquid crystal on a substrate, and drying to obtain the azobenzene liquid crystal film. The optical isomerization characteristic of azobenzene is used for driving the orientation change of liquid crystal molecules, high optical contrast ratio, high optical response speed and good mechanical stability and long-term use performance are achieved, the non-contact light-operated switch function is achieved, and energy consumption and equipment complexity are reduced.

Description

Technical Field

[0001] This invention relates to the field of azobenzene liquid crystal materials technology, specifically to an azobenzene liquid crystal thin film, its preparation method, and its application. Background Technology

[0002] In existing technologies, photoresponsive materials, due to their ability to undergo reversible physical or chemical changes in response to external light stimulation, have shown broad application prospects in fields such as optical switches, information storage, and flexible displays. Among them, azobenzene compounds, as a typical photochromic molecule, are widely recognized as ideal candidate materials for constructing intelligent light-controlled systems due to their efficient and reversible trans-cis photoisomerization properties. However, how to effectively transform the photoresponsive properties of azobenzene molecules into functional performance at the macroscopic material level, while taking into account the material's flexibility, processability, and long-term stability, remains a key challenge for current technological development.

[0003] Traditional azobenzene liquid crystal films often suffer from complex fabrication processes, limited compatibility, insufficient optical contrast, or poor mechanical properties, restricting their practical applications in flexible electronics, wearable devices, and precision optical components. Therefore, developing a novel azobenzene liquid crystal composite film material that integrates high photosensitivity, excellent mechanical properties, good processability, and controllable microstructure molding capabilities is of significant practical importance for advancing related technological fields.

[0004] Chinese patent application "201010541482.3" discloses a method for controlling the optical properties of liquid crystals using azobenzene. The method involves uniformly mixing a liquid crystal compound, a chiral compound, and azobenzene, then filling the mixture into a liquid crystal cell to form a hybrid system. Irradiation of the hybrid system with ultraviolet light causes the azobenzene to change from a trans structure to a cis structure; irradiation with visible light causes the azobenzene to change from a cis structure to a trans structure. The light transmittance and reflectance of the hybrid system reversibly change with the photoisomerization of the azobenzene. Experimental results show that ultraviolet light irradiation requires tens of seconds or even longer to cause the liquid crystal system to lose its liquid crystal phase transition and become isotropic. Furthermore, the irradiation time to recover to the smectic phase under natural light also takes several hours. This indicates a slow light response speed and high power consumption, limiting its applications. Therefore, it is necessary to develop a novel azobenzene liquid crystal thin film with a faster light response speed to achieve low power consumption, ultrafast speed, and reversible light switching functionality. Summary of the Invention

[0005] The main objective of this invention is to provide an azobenzene liquid crystal film, its preparation method, and its application, aiming to solve the problems of complex preparation process, difficult performance control, and slow photoresponse speed of light-driven liquid crystal films in the prior art.

[0006] To achieve the above objectives, the present invention provides a method for preparing an azobenzene liquid crystal thin film, characterized by comprising the following steps:

[0007] S1. Prepare azobenzene derivative monomers with the following structures:

[0008] Among them, R1 is selected from C 1~20 alkyl;

[0009] S2. Dissolve the chiral agent, nematic liquid crystal and azobenzene derivative monomer in a solvent at a mass ratio of 1:(25.87~31.85):(0.5~6.47), and then evaporate the solvent to obtain a liquid crystal solution;

[0010] S3. The liquid crystal solution is mixed with the polymer solution to obtain a polymer-dispersed liquid crystal;

[0011] S4. The polymer-dispersed liquid crystal is coated onto a substrate and dried to obtain an azobenzene liquid crystal film.

[0012] The solvent used in step S2 above to dissolve the chiral agent, nematic liquid crystal, and azobenzene derivative monomer is preferably at least one of the following: water, methanol, ethanol, acetonitrile, tetrahydrofuran, acetone, cyclopentanone, cyclohexanone, dichloromethane, chloroform, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, dioxane, hexafluoroisopropanol, sulfolane, N-methyl-2-pyrrolidone, m-cresol, xylenol, benzene, toluene, xylene, N-vinyl-2-pyrrolidone, butyrolactone, and butyl acetate.

[0013] As a further preferred embodiment of the present invention, the azobenzene derivative monomer is prepared by the following method:

[0014] (1) Disperse p-cyanoaniline uniformly in an acidic solvent, and slowly add an ice-water solution of sodium nitrite dropwise to carry out a diazotization reaction to obtain a diazonium salt solution;

[0015] (2) Phenol and Lewis base are mixed, and diazonium salt solution is slowly added dropwise. After the reaction is complete, the product A is obtained by washing with deionized water and drying.

[0016] (3) Compound A and haloalkane compounds are dissolved in a solvent and halogenated under the action of a catalyst. After washing and drying, the azobenzene derivative monomer is obtained by recrystallization.

[0017] Preferably, the general structural formula of the haloalkane compound is RX, where R is a straight-chain alkyl group and X is a halogen atom (F, Cl, Br, I).

[0018] As a further preferred embodiment of the present invention, the acidic solvent includes at least one of hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, perchloric acid, nitric acid, trifluoroacetic acid, formic acid, dimethyl sulfate, ferric chloride, boron tribromide, aluminum tribromide, or boron trifluoride ether.

[0019] And / or, the Lewis base comprises at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, lithium carbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, rubidium carbonate, cesium carbonate, beryllium carbonate, magnesium carbonate, calcium carbonate, strontium carbonate, barium carbonate, sodium hydride, and calcium hydride;

[0020] And / or, the catalyst comprises any one of potassium carbonate, sodium carbonate, potassium hydroxide, sodium hydroxide, potassium iodide, triethylamine, pyridine, sodium acetate, potassium acetate, potassium phosphate, and tetramethylammonium chloride;

[0021] And / or, the solvent in step (3) is at least one of water, methanol, ethanol, acetonitrile, tetrahydrofuran, acetone, cyclopentanone, cyclohexanone, dichloromethane, chloroform, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, dioxane, hexafluoroisopropanol, sulfolane, N-methyl-2-pyrrolidone, m-cresol, xylenol, benzene, toluene, xylene, N-vinyl-2-pyrrolidone, butyrolactone, and butyl acetate.

[0022] As a further preferred technical solution of the present invention, in step (1), the molar ratio of p-cyanoaniline, sodium nitrite and acidic solvent is 1: (1~1.5):(0.02~0.05); the temperature of the diazotization reaction is 0~5℃, and the reaction time is 0.5~2 h;

[0023] And / or, in step (2), the molar ratio of diazonium salt solution, phenol and Lewis base is 1: (1.0 ~ 2.0): (2.0 ~ 3.0); the reaction temperature is 0 ~ 5 ℃, and the reaction time is 1 ~ 3 h;

[0024] And / or, in step (3), the molar ratio of compound A, haloalkane compound, solvent and catalyst is 1:(1.0~1.5):(0.5~1.0):(1.5~3); the temperature of the halogenation reaction is 50~70 ℃, and the reaction time is 5~15 h.

[0025] As a further preferred embodiment of the present invention, the mass ratio of the chiral agent, nematic liquid crystal, azobenzene derivative monomer and solvent is 1:(25.87~31.85):(0.5~6.47):(16~100); and / or, the temperature at which the solvent evaporates is 70~100 ℃ and the evaporation time is 5~24h.

[0026] As a further preferred technical solution of the present invention, the chiral agent includes at least one of R / S1011, R / S2011, (R)- / (S)-4-(2-methylbutoxy)-4′-cyanobiphenyl (CB15), R / S-5,6-dihydro-5-(trans-4-propylcyclohexyl)-4H-dinaphtho[2,1-f:1',2'-h][1,5]dioxanetraene (R / S5011), isosorbide di(4-cyanobenzoate), cholesterol benzoate, menthyl-4-(4-cyanophenyl)benzoate, menthol-4-(4-cyanophenyl)benzoate, or (R)-1,1′-binaphthol-2,2′-di(4-cyanobenzoate);

[0027] And / or, the nematic liquid crystal includes 4′-cyano-4-pentylbiphenyl, 4′-cyano-4-hexylbiphenyl, 4′-cyano-4-heptylbiphenyl, 4′-cyano-4-octylbiphenyl, 4′-cyano-4-butoxybiphenyl, 4′-cyano-4-pentoxybiphenyl, 4′-cyano-4-hexyloxybiphenyl, 4′-cyano-4-octyloxybiphenyl, 4-pentyl-4′-butoxybiphenyl, 4-hexyl-4′-pentoxybiphenyl, 2-fluoro At least one of the following: -4′-pentyl-[1,1′-biphenyl]-4-carboxylonitrile, 2,3-difluoro-4′-hexyl-[1,1′-biphenyl]-4-carboxylonitrile, 4-(4-cyano-3,5-difluorophenyl)-4′-pentyl terphenyl, 4-cyano-4′-pentyl-1,1′-bicyclohexane, 4-cyano-4′-heptyl-1,1′-bicyclohexane, 5-octyl-2-(4-cyanophenyl)pyrimidine, and E7 liquid crystal mixture.

[0028] As a further preferred embodiment of the present invention, the polymer solution comprises at least one of the following polymers: polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), polyurethane (PU), epoxy resin, polyurethane acrylate (UA), epoxy acrylate (EA), bisphenol A epoxy (DGEBA), polyhydroxyethyl methacrylate (PHEMA), polyethylene glycol dimethacrylate (PEGDMA), polyvinyl acetate (PVAc), ethylene-vinyl acetate copolymer (EVA), polydimethylsiloxane (PDMS), and polyethylene glycol (PEG).

[0029] And / or, the polymer solution has a mass fraction of 5-15%;

[0030] And / or, the volume ratio of the polymer solution to the liquid crystal solution is 100:(1~4).

[0031] And / or, the temperature for mixing the polymer solution with the liquid crystal solution is 25~80 ℃, and the reaction time is 2~20 h.

[0032] According to a second aspect of the present invention, the present invention also provides an azobenzene liquid crystal film prepared by the above-described preparation method.

[0033] According to a third aspect of the invention, the present invention also provides the application of azobenzene liquid crystal thin film in pattern encryption through ultraviolet exposure using a photomask. Specifically, the azobenzene liquid crystal thin film is subjected to ultraviolet exposure under a photomask with a pattern to transfer the pattern onto the film. The ultraviolet exposure time is at least 0.5 s, preferably 0.5 to 10 s, and the wavelength of the ultraviolet light used is 365 nm with an intensity of 1 to 10 mW. The ultraviolet-exposed azobenzene liquid crystal thin film can repeatedly display and hide the pattern, that is, the pattern is displayed above a specific temperature and hidden below that temperature. In addition, after the ultraviolet-exposed azobenzene liquid crystal thin film is irradiated with visible light for a certain period of time (several hours), the pattern written on the film can be completely erased, restoring the film to its initial state before exposure, and a new pattern can be written by re-exposing the film with a photomask.

[0034] By using short-duration, low-intensity ultraviolet mask exposure on an azobenzene liquid crystal film, patterned microstructures are constructed on its surface. Combined with visible light or thermal relaxation, these patterns can be revealed, hidden, and erased. Azobenzene liquid crystal films can be used in pattern display and pattern encryption, for example, as anti-counterfeiting labels after mask exposure. The pattern exposed by the mask can be text, images, or a combination of both; furthermore, the pattern can be a scannable QR code, barcode, or other pattern containing encrypted information.

[0035] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0036] The preparation process of this invention is simple, easy to prepare on a large scale, and improves production efficiency.

[0037] This invention utilizes the photoisomerization properties of azobenzene to drive the orientation change of liquid crystal molecules, resulting in high optical contrast, fast light response speed, good mechanical stability and long-term performance. It realizes a non-contact light-controlled switch function, reducing energy consumption and equipment complexity. Attached Figure Description

[0038] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0039] Figure 1 The following are experimental results of information storage of the thin film prepared in Example 1 after mask exposure: a. before UV exposure, b. after 1 second of UV exposure;

[0040] Figure 2 The following are polarized light micrographs of the liquid crystal state of the azobenzene liquid crystal prepared in Example 1: a. Smectic phase (SmA) texture at 20℃, b. Cholesteric phase (Ch) texture at 21℃.

[0041] Figure 3 A polarized light microscope image of the liquid crystal state of the azobenzene liquid crystal prepared in Example 2;

[0042] Figure 4 A polarized light microscope image of the liquid crystal state of the azobenzene liquid crystal prepared in Example 4;

[0043] Figure 5 A polarized light microscope image of the liquid crystal state of the azobenzene liquid crystal prepared in Example 5;

[0044] Figure 6 The images shown are polarized light micrographs of the azobenzene liquid crystal prepared in Comparative Example 1: a. before UV exposure, b. after UV exposure for 3 min.

[0045] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0046] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0047] In the following description of this embodiment, the terms "including", "comprising", "having", and "containing" are all open-ended terms, meaning that they include but are not limited to.

[0048] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0049] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0050] 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 this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0051] Example 1

[0052] This embodiment provides a method for preparing an azobenzene-derived monomer and an azobenzene liquid crystal film, including:

[0053] S1, dissolve 12.85 mmol sodium nitrite in 15 ml deionized water and store at 0°C for later use. Then, dissolve 12.85 mmol p-cyanoaniline uniformly in a mixture of 3 ml hydrochloric acid and 8 ml deionized water. Slowly add an ice-water solution of sodium nitrite dropwise to the mixture and stir at 0°C for 1 h. After the reaction is complete, a diazonium salt solution is formed and stored at 0°C.

[0054] S2, maintaining at 0℃, added 12.85 mmol phenol, 14.90 mmol sodium hydroxide, 13.02 mmol sodium bicarbonate, and 10 ml deionized water to a beaker. A diazonium salt solution was then slowly added dropwise, and the reaction was allowed to proceed for 2 hours. After the reaction was complete, the mixture was washed repeatedly with deionized water, filtered, and the solid was obtained. The solid was then dried under vacuum for 12 hours to obtain product A.

[0055] S3, 12.85 mmol of product A, 15.42 mmol of bromooctane, 25.7 mmol of potassium carbonate, 5.14 mmol of potassium iodide, and 40 mL of acetone were added to a flask, and the mixture was refluxed at 60 °C for 12 h. After the reaction, the product was cooled, washed several times with acetone, filtered, dried with a small amount of anhydrous sodium sulfate, evaporated by rotary evaporation, recrystallized with ethanol, and dried under vacuum to obtain product B.

[0056] S4. Chiral agent R5011, nematic liquid crystal 8CB (4'-octyl-4-cyanobiphenyl), product B and chloroform were added to a glass bottle in a mass ratio of 1:30.07:2.26:66.67 and mixed evenly. The bottle was opened at 80°C and the solvent was evaporated for 12 hours to obtain an azobenzene liquid crystal solution.

[0057] S5, take 25 μl of azobenzene liquid crystal solution and 1 ml of 10 wt% polyvinyl alcohol solution prepared in advance, react at 70℃ for 12 h to obtain polymer-dispersed liquid crystal, then take 200 μl and uniformly coat it on the substrate, and dry it to obtain azobenzene liquid crystal film.

[0058] The process for synthesizing product B in Example 1 is shown below:

[0059]

[0060] Inject the azobenzene liquid crystal obtained in step S4 of Example 1 into a liquid crystal cell. The texture of the liquid crystal state can be observed under a polarizing microscope. When the temperature is raised from 20 °C to 21 °C, the smectic phase changes to the cholesteric phase. The results are as Figure 2 shown. The SmA-Ch phase transition temperature of the azobenzene liquid crystal film in Example 1 is 21 °C.

[0061] Press the azobenzene liquid crystal film obtained in Example 1 closely against a film with the pattern of the Chinese character "Fu" at a temperature below 21 °C (such as 20 °C). After exposure to ultraviolet light with a wavelength of 365 nm and a low light intensity of 5 mW for 1 s, a hidden-pattern azobenzene liquid crystal film is obtained. As shown in Figure 1 a in, the pattern information cannot be observed by the naked eye; when the film is heated to above 21 °C, a clear pattern of the Chinese character "Fu" can be observed on the film surface, as shown in Figure 1 b in. When the film with the clearly visible pattern of the Chinese character "Fu" is cooled to below 21 °C, the pattern on the film disappears and returns to the state of Figure 1 a in. In this state, the pattern is temporarily hidden. When the temperature is raised to 21 °C and above again, the pattern of the Chinese character "Fu" appears again, thus achieving a reversible change effect; in the state where the pattern is visible or hidden, after being irradiated with visible light for several hours or strong white light for more than a few minutes, when the temperature is raised to 21 °C and above, the pattern no longer appears, and the pattern completely disappears. The film returns to the state before exposure.

[0062] Furthermore, in order to explore the application of the azobenzene liquid crystal film of the present invention in information encryption, replace the pattern of the Chinese character "Fu" on the above film with a two-dimensional code or barcode with preset encoded information. When the pattern of the two-dimensional code or barcode is clearly visible, it can be successfully scanned and recognized by a scanning device; when the pattern disappears, it cannot be scanned and recognized. In addition, by repeatedly heating and cooling the film above and below 21 °C, the azobenzene liquid crystal film can repeatedly show and disappear the pattern. After repeating 100 times, when the temperature is raised to above 21 °C, the pattern can still be clearly visible and can be successfully scanned and recognized by a scanning device. It can be seen that the azobenzene liquid crystal film of the present invention has excellent stability.

[0063] Example 2

[0064] Steps S1 - S3 and S5 for preparing the azobenzene liquid crystal film in Example 2 are the same as those in Example 1; the difference from Example 1 is only that the mass ratios of the components in step S4 are different. Specifically: the mass ratio of the chiral agent R_5011, the nematic liquid crystal 8CB, product B, and chloroform is 1:27.48:4.85:66.67.

[0065] Inject the azobenzene liquid crystal obtained in step S4 of Example 2 into a liquid crystal cell. The texture of the liquid crystal state can be observed under a polarizing microscope. The results are as Figure 3As shown. The SmA-Ch phase transition temperature of the azobenzene liquid crystal film in Example 2 is 17°C.

[0066] Example 3

[0067] In Example 3, steps S1-S3 and S5 for preparing the azobenzene liquid crystal film were the same as in Example 1. The only difference was the mass ratio of the components in step S4. Specifically, the chiral agent R5011, nematic liquid crystal 8CB, product B, and chloroform were in a mass ratio of 1:25.87:6.47:66.67. The SmA-Ch phase transition temperature of the azobenzene liquid crystal film in Example 3 was measured to be 16.5℃.

[0068] A comparison of Examples 1-3 shows that the SmA-Ch phase transition temperature of the azobenzene liquid crystal film can be controlled by changing the ratio of each component in the liquid crystal solution.

[0069] Example 4

[0070] In Example 4, the steps S1-S2 and S4-S5 for preparing the azobenzene liquid crystal film were the same as in Example 1; the only difference was in step S3, specifically: 12.85 mmol of product A, 15.42 mmol of n-hexane bromide, 25.7 mmol of potassium carbonate, 5.14 mmol of potassium iodide, and 40 ml of acetone were added to a flask, and the mixture was refluxed at 60 °C for 12 h. After the reaction, the product was cooled, washed repeatedly with acetone, filtered, dried with a small amount of anhydrous sodium sulfate, evaporated by rotary evaporation, recrystallized with ethanol, and dried under vacuum to obtain product B.

[0071] The process for synthesizing product B in Example 4 is shown below:

[0072]

[0073] The azobenzene liquid crystal obtained in step S4 of Example 4 was injected into a liquid crystal cell. The texture of the liquid crystal state could be observed under a polarizing microscope, and the results are as follows. Figure 4 As shown.

[0074] The azobenzene liquid crystal film obtained in Example 4 was subjected to the mask exposure test as described in Example 1. The exposure parameters were: ultraviolet light exposure at a wavelength of 365 nm and a low light intensity of 5 mW for 1 second, resulting in a SmA-Ch phase transition temperature of 23°C. Below 23°C (e.g., 20°C), the pattern on the exposed film disappeared and became invisible. Upon heating above 23°C, the pattern reappeared clearly. Whether the pattern was visible or hidden, after irradiation with visible light for several hours or with strong white light for several minutes or more, the pattern completely disappeared, and the film returned to its pre-exposure state.

[0075] Example 5

[0076] In Example 5, the steps S1-S2 and S4-S5 for preparing the azobenzene liquid crystal film were the same as in Example 1. The only difference was in step S3, which involved adding 12.85 mmol of product A, 15.42 mmol of 6-chlorohexanol, 25.7 mmol of potassium carbonate, 5.14 mmol of potassium iodide, and 40 ml of acetone to a flask and refluxing at 60°C for 12 h. After the reaction, the product was cooled, washed repeatedly with acetone, filtered, dried with a small amount of anhydrous sodium sulfate, evaporated by rotary evaporation, recrystallized with ethanol, and dried under vacuum to obtain product B.

[0077] The process for synthesizing product B in Example 5 is shown below:

[0078]

[0079] The azobenzene liquid crystal obtained in step S4 of Example 5 was injected into a liquid crystal cell. The texture of the liquid crystal state could be observed under a polarizing microscope, and the results are as follows. Figure 5 As shown.

[0080] The azobenzene liquid crystal film obtained in Example 5 was subjected to the mask exposure test as described in Example 1. The exposure parameters were: ultraviolet light exposure at a wavelength of 365 nm and a low light intensity of 5 mW for 1 second, resulting in a SmA-Ch phase transition temperature of 17°C. Below 17°C (e.g., 16°C), the pattern on the exposed film disappeared and became invisible. Upon heating above 17°C, the pattern reappeared clearly. Whether the pattern was visible or hidden, the pattern completely disappeared after exposure to visible light for several hours or strong white light for several minutes or more, and the film returned to its pre-exposure state.

[0081] To further demonstrate the beneficial technical effects of the present invention, based on the preparation method of Example 1, azobenzene liquid crystal films were prepared by changing only R1 in the azobenzene derivative monomer to different carbon chain lengths for comparative testing, and the SmA-Ch phase transition temperatures (°C) of each were summarized in Table 1.

[0082] Table 1

[0083]

[0084] As shown in Table 1, the azobenzene derivatives with different carbon chain lengths synthesized in this invention have different SmA-Ch phase transition temperatures. With the increase of carbon chain length, the onset temperature decreases to varying degrees.

[0085] Comparative Example 1

[0086] As a control experiment for Example 1, the only difference was that product B used to prepare the azobenzene liquid crystal was replaced with 3.45 mmol of azobenzene (CAS: 103-33-3). Then, 25 μl of the prepared azobenzene liquid crystal and 1 ml of pre-prepared 10 wt% polyvinyl alcohol were reacted at 70°C for 12 h to obtain a polymer-dispersed liquid crystal. 200 μl of this liquid crystal was uniformly coated onto a substrate and dried to obtain an azobenzene liquid crystal film.

[0087] The azobenzene liquid crystal obtained in Comparative Example 1 was injected into a liquid crystal cell, and the texture of the liquid crystal state could be observed under a polarizing microscope, such as... Figure 6 As shown in a; then, after exposing the film to 20mW light for 3 minutes, the results were observed under a polarizing microscope as follows. Figure 6 As shown in b, the color change of the liquid crystal particles is not uniform, and the film recovers its color within seconds under natural conditions after exposure. This is because the azobenzene has poor compatibility with the liquid crystal system. The color change after UV exposure is not caused by the isomerization of azobenzene, but by the heat accompanying UV exposure. Mask exposure experiments revealed that the film in Comparative Document 1 could not achieve reversible pattern display and hiding through short-time (1-second) mask exposure, and even long-time (30 seconds or 3 minutes) mask exposure could not achieve reversible pattern display and hiding.

[0088] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A method for producing an azobenzene liquid crystal film, characterized by, The method comprises the following steps: S1, preparing an azobenzene derivative monomer with the following structure: wherein R1is selected from C 1~20 alkyl; S2, dissolving a chiral agent, a nematic liquid crystal and the azobenzene derivative monomer in a solvent according to a mass ratio of 1:(25.87-31.85):(0.5-6.47), and then evaporating the solvent to obtain a liquid crystal solution; S3, mixing and reacting the liquid crystal solution and a polymer solution to obtain a polymer dispersed liquid crystal; S4, coating the polymer dispersed liquid crystal on a substrate, and drying to obtain an azobenzene liquid crystal film.

2. The method of claim 1, wherein the azobenzene liquid crystal film is prepared by the steps of: The azobenzene derivative monomer is prepared by the following method: (1) uniformly dispersing p-cyanylaniline in an acidic solvent, slowly adding an ice water solution of sodium nitrite drop by drop into the acidic solvent, and performing a diazotization reaction to obtain a diazonium salt solution; (2) mixing phenol and a Lewis base, slowly adding the diazonium salt solution drop by drop into the mixture, and after the reaction is completed, washing and drying the product A obtained through deionized water multiple times; (3) dissolving compound A and a halogenated alkane compound in a solvent, and under the action of a catalyst, a halogenation reaction occurs, and after washing and drying, the azobenzene derivative monomer is obtained through recrystallization.

3. The method of claim 2, wherein the photoalignment layer is formed by irradiating the substrate with polarized light. The acidic solvent comprises at least one of hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, perchloric acid, nitric acid, trifluoroacetic acid, formic acid, dimethyl sulfate, ferric chloride, boron tribromide, aluminum tribromide or boron trifluoride ether; And / or, the Lewis base comprises at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, lithium carbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, rubidium carbonate, cesium carbonate, beryllium carbonate, magnesium carbonate, calcium carbonate, strontium carbonate, barium carbonate, sodium hydride, calcium hydride; And / or, the catalyst comprises any one of potassium carbonate, sodium carbonate, potassium hydroxide, sodium hydroxide, potassium iodide, triethylamine, pyridine, sodium acetate, potassium acetate, potassium phosphate, tetramethylammonium chloride; And / or, the solvent in step (3) is at least one of water, methanol, ethanol, acetonitrile, tetrahydrofuran, acetone, cyclopentanone, cyclohexanone, dichloromethane, chloroform, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, dioxane, hexafluoroisopropanol, cyclobutan sulfone, N-methyl-2-pyrrolidone, m-cresol, dimethylphenol, benzene, toluene, xylene, N-vinyl-2-pyrrolidone, butyrolactone, butyl acetate.

4. The method of claim 2, wherein the photoalignment layer is formed by applying a solution of a photoalignment material onto the substrate and then irradiating the solution with polarized light. In step (1), the molar ratio of p-cyanylaniline, sodium nitrite and the acidic solvent is 1:(1-1.5):(0.02-0.05); the temperature of the diazotization reaction is 0-5 ℃, and the reaction time is 0.5-2 h; And / or, in step (2), the molar ratio of the diazonium salt solution, phenol and the Lewis base is 1:(1.0-2.0):(2.0-3.0); the reaction temperature is 0-5 ℃, and the reaction time is 1-3 h; And / or, in step (3), the molar ratio of compound A, the halogenated alkane compound, the solvent and the catalyst is 1:(1.0-1.5):(0.5-1.0):(1.5-3); the temperature of the halogenation reaction is 50-70 ℃, and the reaction time is 5-15 h.

5. The method for preparing the azobenzene liquid crystal thin film according to claim 1, characterized in that, The mass ratio of the chiral agent, the nematic liquid crystal, the azobenzene derivative monomer and the solvent is 1: (25.87~31.85): (0.5~6.47): (16~100); And / or, the temperature of the solvent is 70~100 ℃, and the volatilization time is 5~24h.

6. The method of claim 1, wherein the azobenzene liquid crystal film is prepared by the steps of: The chiral agent includes at least one of R / S1011, R / S2011, (R)- / (S)-4-(2-methylbutoxy)-4'-cyano biphenyl, R / S-5,6-dihydro-5-(trans-4-propylcyclohexyl)-4H-dinaphtho[2,1-f:1',2'-h][1,5]dioxetene, isosorbide di(4-cyanobenzoate), cholesteryl benzoate, menthyl-4-(4-cyanophenyl)benzoate, menthol-4-(4-cyanophenyl)benzoate or (R)-1,1'-binaphthyl-2,2'-di(4-cyanobenzoate); And / or, the nematic liquid crystal includes at least one of 4'-cyano-4-pentylbiphenyl, 4'-cyano-4-hexylbiphenyl, 4'-cyano-4-heptylbiphenyl, 4'-cyano-4-octylbiphenyl, 4'-cyano-4-butoxybiphenyl, 4'-cyano-4-pentyloxybiphenyl, 4'-cyano-4-hexyloxybiphenyl, 4'-cyano-4-octyloxybiphenyl, 4-pentyl-4'-butoxybiphenyl, 4-hexyl-4'-pentyloxybiphenyl, 2-fluoro-4'-pentyl-[1,1'-biphenyl]-4-carbonitrile, 2,3-difluoro-4'-hexyl-[1,1'-biphenyl]-4-carbonitrile, 4-(4-cyano-3,5-difluorophenyl)-4'-pentylterphenyl, 4-cyano-4'-pentyl-1,1'-bicyclohexane, 4-cyano-4'-heptyl-1,1'-bicyclohexane, 5-octyl-2-(4-cyanophenyl)pyrimidine, E7 liquid crystal mixture.

7. The method for preparing the azobenzene liquid crystal thin film according to claim 1, characterized in that, The polymer of the polymer solution includes at least one of polymethyl methacrylate, polyvinyl alcohol, polyurethane, epoxy resin, polyurethane acrylate, epoxy acrylate, bisphenol A type epoxy, polyhydroxyethyl methacrylate, polyethylene glycol dimethacrylate, polyvinyl acetate, ethylene-vinyl acetate copolymer, polydimethylsiloxane, polyethylene glycol; And / or, the mass fraction of the polymer solution is 5~15%; And / or, the volume ratio of the polymer solution to the liquid crystal solution is 100: (1~4); And / or, the temperature of the mixing reaction of the polymer solution and the liquid crystal solution is 25~80 ℃, and the reaction time is 2~20h.

8. The azobenzene liquid crystal film prepared by the preparation method of any one of claims 1-7.

9. The application of the azobenzene liquid crystal film of claim 8 in pattern encryption by photomask ultraviolet exposure.

10. Use according to claim 9, characterized in that, The pattern adopted by the mask plate of the photomask ultraviolet exposure is a character, a pattern, or a combination of a character and a pattern.

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