Force- and acid-induced color changeable liquid crystal elastomer films, methods of making and uses thereof

Abstract

The application discloses a force-induced color change and acid-induced color change liquid crystal elastomer film and a preparation method and application thereof, and belongs to the technical field of liquid crystal elastomers. The method comprises the following steps: mixing an acrylic ester liquid crystal monomer, an acrylic ester acid-induced color change dye and a liquid crystal chiral agent, and then standing at room temperature to form a first mixture; mixing a polysulfane, a dithiol, a photoinitiator and a pre-diluted thermal initiator in a toluene solution to form a second mixture; mixing the first mixture and the second mixture, and then sequentially performing a parallel orientation click reaction and a self-polymerization reaction in a light-shielded and ultraviolet light irradiation environment, so that the force-induced color change and acid-induced color change liquid crystal elastomer film is obtained. The method can make the liquid crystal elastomer have both the force-induced structural color performance and the acid-induced color change pigment color performance, has a wide color change range and rich color information, and can effectively improve the mechanical performance of the liquid crystal elastomer, so that the liquid crystal elastomer can maintain good reversibility when the stretching length is 100%.

Description

Technical Field

[0001] This application belongs to the field of liquid crystal elastomer technology, and particularly relates to mechanochromic and acid-chromic liquid crystal elastomer films, their preparation methods and applications. Background Technology

[0002] Liquid crystal elastomers combine the properties of liquid crystals and elastomers, and can undergo reversible deformation in response to external stimuli, making them suitable as smart materials for applications in sensing, anti-counterfeiting, and information storage. However, as research into the applications of liquid crystal elastomers continues to deepen, single-response liquid crystal elastomers no longer meet application requirements. Therefore, developing liquid crystal elastomers with multiple responsive properties is essential to satisfying these application needs.

[0003] Mechanochromatic properties offer significant advantages in detecting surface damage or stress release in materials, making the development of multi-responsive liquid crystal elastomers with mechanochromatic capabilities a promising area of ​​research. Currently, research on the development of mechanochromatic liquid crystal elastomers primarily focuses on either structural color change or pigment color change.

[0004] However, both single-structure color change and single-pigment color change are prone to the problem of limited color information. Furthermore, single-structure color change suffers from a small color change range, severely restricting the application of multi-responsive liquid crystal elastomers with mechanochromic properties in multi-layered anti-counterfeiting applications. In addition, there are currently no publicly reported examples of dual-responsive liquid crystal elastomers combining mechanochromic structural color change and acid-induced pigment color change. Summary of the Invention

[0005] The purpose of this application is to disclose a mechanochromic and acid-chromic liquid crystal elastomer film, its preparation method, and its application, aiming to solve the technical problems of limited color information for single structural color change or single pigment color change, small range of single structural color change, and the lack of simultaneous mechanochromic structural color change and acid-chromic pigment color change liquid crystal elastomers.

[0006] To achieve the above objectives, the technical solution of this application is:

[0007] The first aspect of this application provides a method for preparing a mechanochromic and acid-chromic liquid crystal elastomer film. The preparation method of this application includes:

[0008] After thermally mixing acrylate liquid crystal monomers, acrylate acid-induced color-changing dyes and liquid crystal chiral agents, the mixture is allowed to stand at room temperature to form a first mixture.

[0009] Dithiol, polythiol, photoinitiator, and pre-diluted thermal initiator are mixed in a toluene solution to form a second mixture;

[0010] The first mixture and the second mixture are mixed evenly to form a third mixture;

[0011] The third mixture is subjected to a parallel-oriented click reaction in a light-protected environment to obtain an oligomer;

[0012] The oligomers undergo a parallel-oriented self-polymerization reaction under ultraviolet light irradiation, resulting in megochromic and acid-chromic liquid crystal elastomer films.

[0013] Preferably, in conjunction with the first aspect, the acrylate liquid crystal monomer is one or more of 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene, 2-methyl-1,4-phenylenebis(4-(4-(acryloyloxy)butoxy)benzoate, 2-methyl-1,4-phenylenebis(4-((6-(acryloyloxy)hexyl)oxy)benzoate, 2-methyl-1,4-phenylenebis(4-(4-(vinyloxy)butoxy)benzoate, and (4-(((4-(acryloyloxy)butoxy)carbonyl)oxy)benzoic acid 2-methyl-1,4-diphenol ester.

[0014] Preferably, in conjunction with the first aspect, the acrylate acid-induced color-changing dye contains rhodamine lactam.

[0015] Preferably, in conjunction with the first aspect, the dithiol is one or more of ethylene glycol dimercaptoacetate, di(mercaptoacetic acid)-1,4-butanediol, 2,2'-(1,2-ethylenedioxy)bis(ethanedithiol), and ethylenedithiol.

[0016] Preferably, in conjunction with the first aspect, the polythiol is one of pentaerythritol tetra-3-mercaptopropionate or trimethylolpropane tris(3-mercaptopropionate).

[0017] Preferably, in conjunction with the first aspect, the photoinitiator is one or more of benzoin dimethyl ether, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-hydroxy-methylphenylpropane-1-one, bis(2,6-difluoro-3-pyrrolidinyldicenoctane) and 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone.

[0018] More preferably, in conjunction with the first aspect, the thermal initiator is one of alkoxides, basic amines, metal hydrides, and amine lithium.

[0019] Preferably, in conjunction with the first aspect, the basic amine is one or a combination of several of di-n-propylamine, ethanolamine, ethylenediamine, diethanolamine, and N,N-dimethylethylamine.

[0020] The second aspect of this application provides mechanochromic and acid-chromic liquid crystal elastomer films prepared by the method described in the first aspect.

[0021] A third aspect of this application provides the application of the mechanochromic and acid-chromic liquid crystal elastomer film described in the second aspect in the preparation of multiple anti-counterfeiting materials.

[0022] Compared with the prior art, the advantages or beneficial effects of the embodiments of this application include at least the following:

[0023] The preparation method of this application enables the conversion of acrylate liquid crystal monomers into a cholesteric phase liquid crystal elastomer matrix while simultaneously dispersing and compounding acrylate acid-induced color-changing dyes into the cholesteric phase liquid crystal elastomer matrix. On the one hand, this allows the liquid crystal elastomer film to simultaneously possess both mechanotropic structural color-changing and acid-induced color-changing properties, and the mechanotropic structural color and acid-induced color-changing dye can produce a sufficient synergistic effect, allowing the color-changing range of the liquid crystal elastomer film to span the entire visible light region and produce variable fluorescence under ultraviolet light. This endows the liquid crystal elastomer film with rich color information and a large color-changing range, which helps to improve the information storage capacity and complexity of the liquid crystal elastomer film, enhancing its application in information storage and multi-layer anti-counterfeiting. On the other hand, it can effectively improve the mechanical properties of the formed liquid crystal elastomer film, enabling the liquid crystal elastomer film to maintain good reversibility when the stretching length is 100%. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The reflectance spectra of the mechanochromic and acid-chromic liquid crystal elastomer film CLCE1 provided in the embodiments of this application under different external forces;

[0026] Figure 2 Transmittance of the mechanochromic and acid-chromic liquid crystal elastomer film CLCE1 provided in the embodiments of this application under tension;

[0027] Figure 3 Transmittance of the mechanochromic and acid-chromic liquid crystal elastomer film CLCE1 provided in the embodiments of this application under tension;

[0028] Figure 4 Absorption spectra of the mechanochromic and acid-chromic liquid crystal elastomer film CLCE1 provided in the embodiments of this application when stimulated by acid.

[0029] Figure 5 Fluorescence spectrum of the mechanochromic and acid-chromic liquid crystal elastomer film CLCE1 provided in the embodiments of this application when stimulated by acid;

[0030] Figure 6 Fluorescence spectrum of the non-stretchable single acid-induced color-changing liquid crystal material A1 after acid fumigation, provided in the embodiments of this application;

[0031] Figure 7 Fluorescence spectrum of the stretchable single-mechanical-chromic liquid crystal elastomer A2 after acid fumigation, provided in the embodiments of this application;

[0032] Figure 8 The fluorescence intensity spectra of the mechanochromic and acid-chromic liquid crystal elastomer film CLCE1 provided in the embodiments of this application are shown at different reflection wavelengths. Detailed Implementation

[0033] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0034] 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.

[0035] 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.

[0036] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means three 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.

[0037] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0038] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0039] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within the scope of this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0040] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0041] In a first aspect, embodiments of this application provide a method for preparing mechanochromic and acid-chromic liquid crystal elastomer films. The preparation method of this application includes:

[0042] After thermally mixing acrylate liquid crystal monomers, acrylate acid-induced color-changing dyes and liquid crystal chiral agents, the mixture is allowed to stand at room temperature to form a first mixture.

[0043] Dithiol, polythiol, photoinitiator, and pre-diluted thermal initiator are mixed in a toluene solution to form a second mixture;

[0044] Mix the first mixture and the second mixture thoroughly to form a third mixture;

[0045] The third mixture is subjected to a parallel-oriented click reaction in a light-protected environment to obtain oligomers;

[0046] The oligomers undergo a parallel-oriented self-polymerization reaction under ultraviolet light, resulting in megochromic and acid-chromic liquid crystal elastomer films.

[0047] The preparation method disclosed in this application includes a click reaction between acrylate liquid crystal monomers and acrylate acid-chromic dyes with thiols, and a UV-induced self-polymerization reaction of cholesteric liquid crystal elastomers. Specifically, under the catalysis of an alkaline thermal initiator, the acrylate liquid crystal monomers and acrylate acid-chromic dyes undergo Michael addition with thiols, transforming the polymer network from a liquid crystal polymer to a cholesteric liquid crystal elastomer. After generating the cholesteric liquid crystal elastomer through the click reaction, a further self-polymerization reaction is initiated by UV light, further increasing the crosslinking density of the cholesteric liquid crystal elastomer and forming a liquid crystal elastomer film with better mechanical properties. The mechanical properties of the liquid crystal elastomer film can be further optimized by adjusting the ratio of acrylate groups in the acrylate liquid crystal monomers and acrylate acid-chromic dyes to thiol groups in the thiols, as well as the content ratio of polythiols to dithiols.

[0048] The synergistic combination of click reaction and self-polymerization reaction described above enables the formed cholesteric liquid crystal elastomer to possess a periodic helical structure at the nanoscale. This structure selectively reflects chiral circularly polarized light, with the reflected wavelength following the Bragg equation for crystal reflection. When the cholesteric liquid crystal elastomer is stretched, the periodic arrangement of the liquid crystals is subjected to axial stretching and normal compression, resulting in a shorter pitch and a change in the color of the reflected light. Specifically, this manifests as a blue shift in the reflection bandgap and an apparent blue shift in color, causing regions with shorter exposure times to exhibit two different structural colors compared to regions with longer exposure times. After the external force is removed, the color of the cholesteric liquid crystal elastomer gradually recovers, demonstrating dynamically reversible color control capabilities.

[0049] It should be noted that the thermal mixing in the embodiments of this application should be understood as temperature-conditional mixing, which can be stirring and mixing under certain temperature conditions to ensure the uniformity of the mixture. For example, the components are mixed according to mass percentage and then stirred evenly at a temperature of 60-120°C. The preferred temperature is 80°C.

[0050] It should be noted that the pre-diluted thermal initiator in the embodiments of this application should be understood as a thermal initiator diluted with a solvent. For example, it can be diluted 50 times by mass using toluene solution to effectively control the reaction rate and ensure the formation of cholesteric liquid crystal. Acrylic liquid crystal monomers and acrylate acid-induced color-changing dyes are both understood as the corresponding liquid crystal monomers and acid-induced color-changing dyes containing acrylate groups.

[0051] It should be noted that the liquid crystal chiral agent in the embodiments of this application should be understood as a polymerizable liquid crystal chiral agent, including (3R,3AR,6S,6AR)-hexahydrofuran[3,2-B]furan-3,6-dimethylbis(4-((acryloyloxy)butoxy)carbonyl)oxy)benzoyl)oxy)benzoate), which can be purchased directly from the market or synthesized according to methods known in the art. The embodiments of this application do not impose any special restrictions on its specific chemical structure and source.

[0052] It should be noted that, in the embodiments of this application, the parallel orientation click reaction and self-polymerization reaction are carried out sequentially according to the liquid crystal alignment technology known in the art. For example, the third mixture can be uniformly coated on the glass substrate that has been treated with parallel alignment, and then placed in a light-proof environment at room temperature for 4 hours to carry out the click reaction. The side of the oligomer generated by the click reaction that is away from the glass substrate is irradiated for 1-5 minutes. The sample after the first irradiation is peeled off from the glass substrate, and the other side is irradiated for 1-5 minutes in the same way, so that the parallel orientation self-polymerization reaction occurs on both sides of the oligomer.

[0053] In specific embodiments, the acrylate liquid crystal monomer is preferably one or more of the following: 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene, 2-methyl-1,4-phenylenebis(4-(4-(acryloyloxy)butoxy)benzoate, 2-methyl-1,4-phenylenebis(4-((6-(acryloyloxy)hexyl)oxy)benzoate, 2-methyl-1,4-phenylenebis(4-(4-(vinyloxy)butoxy)benzoate, and (4-(((4-(acryloyloxy)butoxy)carbonyl)oxy)benzoic acid 2-methyl-1,4-diphenol ester.

[0054] These acrylate-based liquid crystal monomers act as liquid crystal building blocks.

[0055] In a specific embodiment, the acrylate acid-induced color-changing dye preferably contains rhodamine lactam, the chemical name of which is 2-acrylamido-3'-(diethylamino)-3-carbonylspirocyclic-[isoindololinone-1,9'-oxanthracene]-6'-acrylate.

[0056] Rhodamine lactam is a leuco closed-ring form containing acrylate groups. When unstimulated, it exhibits a pale yellow color, weak absorption, and no fluorescence. Upon acid stimulation, it transforms from a closed-ring form to an open-ring form, exhibiting a red, strongly absorbed, orange fluorescent state. Therefore, this application selects rhodamine lactam containing acrylate groups and acrylate liquid crystal monomers as chromogenic raw materials. This allows rhodamine lactam to be incorporated into the acrylate liquid crystal monomers to form a cholesteric phase liquid crystal elastomer. This not only gives the mechanochromic liquid crystal elastomer acid-induced chromogenic properties, enabling the superposition of the pigment color induced by rhodamine lactam and the structural color reflected by the cholesteric phase liquid crystal elastomer to form a dual pattern distribution, but also allows the liquid crystal elastomer film to possess the characteristic of rhodamine lactam acid-responsive pigment color. This allows it to display previously hidden information, while the acid-treated area also exhibits unique fluorescence characteristics under ultraviolet light. This makes it suitable as a multi-functional anti-counterfeiting material for applications such as force detectors, surface functional coatings, and information storage.

[0057] In a specific embodiment, the dithiol is preferably one or more of ethylene glycol dimercaptoacetate, di(mercaptoacetic acid)-1,4-butanediol, 2,2'-(1,2-ethylenedioxy)bis(ethanedithiol), and ethylenedithiol.

[0058] These dithiols act as chain extenders, reacting with acrylate liquid crystal monomers to increase the chain length of the polymer network, thereby lowering the glass transition temperature of the polymer material and increasing its tensile properties.

[0059] In a specific embodiment, the polythiol crosslinking agent is preferably one of pentaerythritol tetra-3-mercaptopropionate and trimethylolpropane tris(3-mercaptopropionate).

[0060] These polythiols act as crosslinking agents, transforming the polymer network from a linear to a three-dimensional structure by adding additional reaction sites.

[0061] In a specific embodiment, the photoinitiator is preferably one or more of the following: benzoin dimethyl ether, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-hydroxy-methylphenylpropane-1-one, bis(2,6-difluoro-3-pyrrolidinyldicenoctane) and 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone.

[0062] These photoinitiators play a role in inducing the self-polymerization reaction of acrylates.

[0063] In a specific embodiment, the thermal initiator is preferably one of alkoxides, basic amines, metal hydrides, and amine lithium.

[0064] These thermal initiators play a role in inducing the first-stage click reaction.

[0065] In a specific embodiment, the basic amine is preferably one or a combination of di-n-propylamine, ethanolamine, ethylenediamine, diethanolamine, and N,N-dimethylethylamine.

[0066] These basic amines play a role in inducing the first-stage click reaction.

[0067] Secondly, embodiments of this application also provide mechanochromic and acid-chromic liquid crystal elastomer films prepared by the method described in the first aspect. Based on the method described above, the mechanochromic and acid-chromic liquid crystal elastomer films can exhibit color-changing ranges across the entire visible light region and produce fluorescence properties that can vary under ultraviolet light. Therefore, these mechanochromic and acid-chromic liquid crystal elastomer films possess rich color information and a wide color-changing range, while maintaining good reversibility at 100% stretch length.

[0068] Thirdly, based on the aforementioned mechanochromic and acid-chromic liquid crystal elastomer films, which utilize the synergistic effect of structural and pigment colors in their color-changing mechanism, and considering that the pigment color can reveal previously hidden information, and that the acid-treated regions exhibit unique fluorescence characteristics under ultraviolet light, these mechanochromic and acid-chromic liquid crystal elastomer films, when used in the preparation of multiple anti-counterfeiting materials, can effectively improve the anti-counterfeiting performance of these materials. This has a significant impact on the anti-counterfeiting of force detectors, surface functionalized coatings, and stored information.

[0069] The technical solution of this application will be further described below with reference to specific embodiments.

[0070] Example 1

[0071] This embodiment provides a method for preparing a mechanochromic and acid-chromic liquid crystal elastomer film CLCE1, specifically including:

[0072] S101: 94.8 wt% of 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene, 4.7 wt% of (3R,3AR,6S,6AR)-hexahydrofuran[3,2-B]furan-3,6-dimethylbis(4-((acryloyloxy)butoxy)carbonyl)oxy)benzoyl)oxy)benzoate, and 0.5 wt% of rhodamine lactam were mixed and stirred evenly at 80°C, and then allowed to stand at room temperature to obtain the first mixture;

[0073] S102: Dissolve 46 wt% of 2,2-(1,2-ethylenedioxy)diethylthiol, 7 wt% of pentaerythritol tetra-3-mercaptopropionate, 1 wt% of bis(2,6-difluoro-3-pyrrolephenyl)titanium ether and 46 wt% of pre-diluted dipropylamine in toluene solution and stir until homogeneous to obtain a second mixture.

[0074] S103: Pour 61.5 wt% of the first mixture and 38.5 wt% of the second mixture into the first mixture, and sonicate at room temperature for 5-10 min to obtain the third mixture;

[0075] S104: The third mixture is evenly coated onto a glass substrate that has been parallel oriented, and left to stand at room temperature in a dark environment for 4 hours to obtain the oligomer.

[0076] S105: After irradiating the side of the oligomer facing away from the glass substrate with 520nm green light for 1-5 minutes, peel the sample off the glass substrate and irradiate the other side of the sample for 1-5 minutes in the same way, thus obtaining the gel-chromic and acid-chromic liquid crystal elastomer film CLCE1.

[0077] Example 2

[0078] This embodiment provides a method for preparing a mechanochromic and acid-chromic liquid crystal elastomer film CLCE2, specifically including:

[0079] S201: 94.8 wt% of 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene, 4.7 wt% of (3R,3AR,6S,6AR)-hexahydrofuran[3,2-B]furan-3,6-dimethylbis(4-((acryloyloxy)butoxy)carbonyl)oxy)benzoyl)oxy)benzoate, and 0.5 wt% of rhodamine lactam were mixed and stirred evenly at 80°C, and then allowed to stand at room temperature to obtain the first mixture;

[0080] S202: Dissolve 46 wt% of 2,2-(1,2-ethylenedioxy)diethylthiol, 7 wt% of pentaerythritol tetra-3-mercaptopropionate, 1 wt% of benzoin diethyl ether and 46 wt% of pre-diluted dipropylamine in toluene solution and stir until homogeneous to obtain a second mixture;

[0081] S203: Pour 61.5 wt% of the first mixture and 38.5 wt% of the second mixture into the first mixture, and sonicate at room temperature for 5-10 min to obtain the third mixture;

[0082] S204: The third mixture is evenly coated onto a glass substrate that has been parallel oriented, and left to stand at room temperature in a dark environment for 4 hours to obtain the oligomer;

[0083] S205: After irradiating the side of the oligomer facing away from the glass substrate with 365nm green light for 1-5 minutes, peel the sample off the glass substrate and irradiate the other side of the sample for 1-5 minutes in the same way. This yields the gel-chromic and acid-chromic liquid crystal elastomer film CLCE2.

[0084] To verify the technical effect of this application, the mechanochromic and acid-chromic liquid crystal elastomer film CLCE1 prepared in Example 1 was subjected to spectral analysis, and the results were as follows: Figures 1 to 5 As shown. Among them, Figure 1 The reflectance spectra of the mechanochromic and acid-chromic liquid crystal elastomer film CLCE1 under different external forces; Figure 2 The reversibility of the mechanochromic and acid-chromic liquid crystal elastomer film CLCE1 when stretched to 100%; Figure 3 The transmittance of the methanogenic and acid-induced color-changing liquid crystal elastomer film CLCE1 under stretching; Figure 4 The absorption spectra of the methanogenic and acid-induced color-changing liquid crystal elastomer film CLCE1 when stimulated by acid. Figure 5 The fluorescence spectrum of the methanogenic and acid-induced color-changing liquid crystal elastomer film CLCE1 under acid stimulation.

[0085] according to Figure 1 It can be seen that when stretched by external force, the change in pitch causes a blue shift in the reflection bandgap, and the blue shift of the reflection bandgap can span the entire visible light region, exhibiting a wide range of color changes.

[0086] according to Figure 2 It can be seen that when the mechanochromic and acid-chromic liquid crystal elastomer film CLCE1 is stretched to 100% of its length and then relaxed, it exhibits good reversibility, indicating that the mechanochromic and acid-chromic liquid crystal elastomer film CLCE1 has excellent dynamic reflection bandgap control capability.

[0087] according to Figure 3 It is known that the mechanochromic and acid-chromic liquid crystal elastomer film CLCE1 exhibits excellent mechanochromic ability, which can achieve the phenomenon of blue shift of the reflection bandgap from 590nm to 410nm and the apparent color of the film changing from red to blue.

[0088] according to Figures 4 to 5 It can be seen that after the content of rhodamine lactam is fixed, with the increase of trifluoroacetic acid fumigation time, the absorption spectrum and fluorescence spectrum of the mechanochromic and acid-chromic liquid crystal elastomer film CLCE1 show strong characteristic peaks. The apparent color of the mechanochromic and acid-chromic liquid crystal elastomer film CLCE1 changes from the initial structural color to the pigment color dominated by rhodamine lactam and emits orange-yellow fluorescence.

[0089] To verify the synergistic effect of mechanochromism and acid-chromism, this application prepared an instretchable single acid-chromic liquid crystal material A1 and a stretchable single mechanochromic liquid crystal elastomer A2 as comparisons, and tested their fluorescence intensity under the same acid immersion time. The results are as follows: Figures 6 to 7 As shown. Among them, Figure 6The fluorescence spectrum of Al after acid fumigation of the non-stretchable, single-acid-induced color-changing liquid crystal material; Figure 7 The fluorescence spectrum of stretchable, single-mechanically-sensitive color-changing liquid crystal elastomer A2 after acid fumigation.

[0090] according to Figure 6 It is known that the fluorescence intensity of non-stretchable single acid-induced color-changing liquid crystal materials does not change with external conditions, but is only related to the concentration of rhodamine lactam and the acid immersion time.

[0091] according to Figure 7 It can be seen that the stretchable single-mechanical color-changing liquid crystal elastomer A2 is related to the stretching length. As the stretching length increases, the fluorescence intensity gradually increases and then decreases, thus converting the stretching length into the displacement of the reflection peak.

[0092] In addition, this application also tested the fluorescence intensity of the mechanochromic and acid-chromic liquid crystal elastomer film CLCE1 at different reflection wavelengths, and the results were as follows: Figure 8 As shown. Among them, Figure 8 The fluorescence intensity spectra of the methanogenic and acid-induced chromogenic liquid crystal elastomer film CLCE1 at different reflection wavelengths are shown.

[0093] according to Figure 8 It is known that the fluorescence intensity of rhodamine lactam changes when the reflection peak of the cholesteric liquid crystal elastomer matrix is ​​at different wavelengths, indicating that the fluorescence intensity is affected by the stretching length, i.e., the reflection band gap. The reason for this may be that during stretching, the change in reflectivity of the cholesteric liquid crystal elastomer itself and the shift of its reflection band gap lead to changes in fluorescence intensity. Specifically, during stretching, the reflectivity decreases, meaning more light passes through the cholesteric liquid crystal elastomer, resulting in a decrease in the excitation light intensity received by the fluorescent molecules and a decrease in fluorescence intensity. When the band gap edge moves to the position of the fluorescence peak, the "band gap edge effect" increases the fluorescence intensity. These two effects compete synergistically, causing the fluorescence intensity of the cholesteric liquid crystal elastomer to show a trend of first increasing and then decreasing.

[0094] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0095] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for preparing a mechanochromic and acid-chromic liquid crystal elastomer film, characterized in that, include: After thermally mixing acrylate liquid crystal monomers, acrylate acid-induced color-changing dyes and liquid crystal chiral agents, the mixture is allowed to stand at room temperature to form a first mixture. Dithiol, polythiol, photoinitiator, and pre-diluted thermal initiator are mixed in a toluene solution to form a second mixture; The first mixture and the second mixture are mixed evenly to form a third mixture; The third mixture is subjected to a parallel-oriented click reaction in a light-protected environment to obtain an oligomer; The oligomers undergo a parallel-oriented self-polymerization reaction under ultraviolet light irradiation, resulting in megalochromic and acid-chromic liquid crystal elastomer films. The acrylate liquid crystal monomer is 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene; the acrylate acid-induced color-changing dye contains rhodamine lactam.

2. The preparation method according to claim 1, characterized in that, The dithiol is one or more of the following: ethylene glycol dimercaptoacetate, di(mercaptoacetic acid)-1,4-butanediol, 2,2'-(1,2-ethylenedioxy)bis(ethanedithiol), and ethylenedithiol.

3. The preparation method according to claim 1, characterized in that, The polythiol is one of pentaerythritol tetra-3-mercaptopropionate or trimethylolpropane tris(3-mercaptopropionate).

4. The preparation method according to claim 1, characterized in that, The photoinitiator is one or more of the following: benzoin dimethyl ether, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-hydroxy-methylphenylpropane-1-one, bis(2,6-difluoro-3-pyrrolidinyldicenoctane) and 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone.

5. The preparation method according to claim 1, characterized in that, The thermal initiator is one of alkoxides, basic amines, metal hydrides, and amine lithium.

6. The preparation method according to claim 5, characterized in that, The basic amine is one or a combination of di-n-propylamine, ethanolamine, ethylenediamine, diethanolamine, and N,N-dimethylethylamine.

7. A mechanochromic and acid-chromic liquid crystal elastomer film prepared by the method according to any one of claims 1-6.

8. The application of the mechanochromic and acid-chromic liquid crystal elastomer film according to claim 7 in the preparation of multiple anti-counterfeiting materials.

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