Electrospinning patterned force-induced color-changing cholesteric liquid crystal elastomer and preparation method thereof

Abstract

The invention discloses an electrospinning patterned force-induced color-changing cholesteric liquid crystal elastomer and a preparation method thereof, and belongs to the technical field of intelligent high polymer materials. The method comprises the following steps: carrying out electrostatic spinning on a cholesteric liquid crystal precursor solution, curing a spun sample under an ultraviolet lamp to form a film, and triggering dynamic key regionalization exchange through external stimulation in a film stretching state to obtain the patterned force-induced color-changing cholesteric liquid crystal elastomer. The precursor solution is prepared by mixing a liquid crystal monomer containing double-arm acrylate groups, chiral molecules, dynamic bond molecules, a chain extender, a base catalyst, a photoinitiator and a solvent. Through specific component proportions and electrostatic spinning process parameters, the patterning and mechanochromic characteristics of the thin film are achieved, and the method is suitable for the field of film materials. The electrostatic spinning preparation method is simple and efficient, is suitable for large-area manufacturing, is flexible in structural design, has remarkable optical anisotropy and stress response characteristics, and enriches the preparation diversity of CLCEs force-induced color-changing materials and color-changing patterns.

Description

Technical Field

[0001] The present invention belongs to the technical field of intelligent polymer materials, and in particular relates to an electrostatically spun patternable mechanochromic cholesteric liquid crystal elastomer and a preparation method thereof. Background Art

[0002] Cholesteric liquid crystal elastomers (CLCEs) are liquid crystal materials with periodic helical structures that exhibit unique optical properties, including selective reflection. Introducing chiral molecules into nematic LCEs can form CLCEs, which, according to Bragg's law, reflect circularly polarized light with the same handedness as the CLCE helices. CLCEs exhibit mechanochromic properties, which arise from changes in the pitch of the helical structure under external forces, thereby affecting light reflection and selective absorption, resulting in a change in color. CLCEs are widely used in smart materials, optical devices, and sensors. Currently, the introduction of dynamic covalent bonds into cross-linked polymers to construct covalently adaptive networks is at the forefront of research. By introducing dynamic covalent bonds into CLCEs, they are activated by external stimuli, causing the network topology to rearrange, thereby fixing the color of the CLCEs under stretching. The unrearranged portions rebound to their original color, thus yielding patterned CLCEs.

[0003] Existing methods for preparing CLCEs primarily include template methods, stress-induced methods, photoresponsive doping methods, and evaporation-induced self-assembly (EIS). However, these methods have limitations in terms of molecular orientation precision, complex patterning capabilities, and mechanical robustness. For example, the template method relies on high-precision molds and complex post-processing, making it difficult to achieve continuous preparation of micro- and nanostructures. While EIS can achieve bright colors, it relies primarily on the slow evaporation of solvents in the natural environment to drive molecular self-assembly. Small changes in ambient temperature, humidity, and airflow can significantly interfere with the solvent evaporation rate, leading to disordered liquid crystal molecular self-assembly and uneven helical structures, resulting in mottled and color-shifting structural colors. Furthermore, the production cycle is long, making it difficult to maintain consistent quality between batches when scaling up, hindering industrial production. Furthermore, limited means of microstructural control make it difficult to precisely construct nanoscale fibers or patterned structures, limiting its application in flexible electronics, biosensors, and other fields. Summary of the Invention

[0004] To address the above technical issues, the present invention proposes an electrospun, patternable mechanochromic cholesteric liquid crystal elastomer and its preparation method. Through electrospinning, droplets are electrostatically dispersed into a jet, rapidly evaporating the solvent. The electric field-assisted molecular orientation coupled with solvent evaporation induces internal molecular self-assembly into a helical structure, reflecting vibrant colors. The electrospun CLCEs are then stretched and subjected to patterned illumination or heating to induce dynamic bond exchange, resulting in a mechanochromic film with a controllable pattern.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the objectives of the present invention is to provide a method for preparing a patternable mechanochromic cholesteric liquid crystal elastomer by electrospinning, comprising the following steps: electrospinning a cholesteric liquid crystal precursor solution, curing the spun sample under an ultraviolet lamp to obtain a film, and performing regionalized dynamic bond exchange on the film under a stretched state to obtain a patternable mechanochromic cholesteric liquid crystal elastomer.

[0007] The present invention is based on electrospinning technology. Specifically, a polymer solution is subjected to electrodynamic stretching under a high-voltage electrostatic field, generating a jet of ultrafine fibers. The rapid stretching effect of the electric field forces the solvent to evaporate within milliseconds, significantly shortening the time window during which the solvent affects molecular arrangement and significantly reducing the interference of the external environment on molecular assembly. This ensures the uniformity of the cholesteric helical structure and produces a material with uniform and stable structural color. During this process, the liquid crystal molecules exhibit orientational order under the influence of an applied electric field and spontaneously form a helical structure. This structure imparts significant optical anisotropy and stress-responsive properties to the material. When the material is subjected to external mechanical stimulation, its photonic band gap undergoes a reversible shift, resulting in a macroscopically visible mechanochromic effect.

[0008] External field synergy can effectively reduce the orientation entropy of liquid crystal molecules and promote the kinetics of the nematic-cholesteric phase transition, thereby optimizing the regularity and long-range order of the helical self-assembled structure. Furthermore, the present invention introduces dynamic covalent bond building units into the spinning precursor solution, spatially selectively regulating the chemical bond recombination process to construct a pre-set pattern with optical contrast on a macroscale. Electrospinning offers the advantages of simple process, scalable production, and flexible structural design. Compared to existing technologies, it is expected to promote the innovative application of CLCEs in intelligent optical devices, biomimetic sensors, and other fields.

[0009] Furthermore, the cholesteric liquid crystal precursor is prepared by mixing a liquid crystal monomer containing a double-arm acrylate group, a chiral molecule, a dynamic bond molecule, a chain extender, a base catalyst, a photoinitiator, and a solvent. The components are present in the following amounts by mass: the molar ratio of the liquid crystal monomer to the chain extender is (1-1.5):1;

[0010] The content of the chiral molecule is 2-5 wt% of the total mass of the liquid crystal monomer and the chain extender;

[0011] The content of the dynamic bond molecules is 1-10 wt% of the total mass of the liquid crystal monomer and the chain extender;

[0012] The content of the base catalyst is 0.5-5 wt% of the total mass of the liquid crystal monomer and the chain extender;

[0013] The content of the photoinitiator is 0.05-5wt% of the total mass of the liquid crystal monomer and the chain extender;

[0014] The concentration of the cholesteric liquid crystal precursor solution is 10-50 wt %.

[0015] Furthermore, the liquid crystal monomer containing a double-arm acrylate group is selected from RM82 (2-methyl-1,4-phenylene bis(4-((6-(acryloyloxy)hexyl)oxy)benzoate), 1,4-bis(4-(6-acryloyloxyhexyloxy)benzyloxy)-2-methylbenzene), RM257 (2-methyl-1,4-phenylene bis(4-(3-(acryloyloxy)propoxy)benzoate), 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene) and LC242 (4-[[[4-[(1-Oxo-2-propenyl)oxy]butoxy]carbonyl]oxy]benzoic acid 2-methyl-1,4-phenylene ester, one or more of 4-[[4-[(1-oxo-2-propenyl)oxy]butoxy]carbonyl]oxy]benzoic acid 2-methyl-1,4-phenylene ester)acyloxy]-2-methylbenzene).

[0016] Furthermore, the chiral molecule is selected from LC756 (1,4:3,6-dianhydro-,2,5-bis[4-[[4-[3-[(1-oxo-2-propen-1-yl)oxy]propoxy]benzoyl]oxy]benzoate], 1,4:3,6-dianhydro-,2,5-bis[4-[[4-[3-[(1-oxo-2-propen-1-yl)oxy]propoxy]benzoyl]oxy]benzoate One or both of: 1,4:3,6-dianhydro-,2,5-bis[4-[[4-[3-[(1-oxo-2-propen-1-yl)oxy]propoxy]benzoyl]oxy]benzoate], 1,4:3,6-dianhydro-2,5-bis[4-[[4-[3-[(1-oxo-2-propen-1-yl)oxy]propoxy]benzoyl]oxy]benzoate]).

[0017] Furthermore, the dynamic bond molecules are selected from light-responsive molecules (such as disulfide bonds, diselenide bonds) or heat-responsive molecules (such as DA bonds, borate bonds, ester bonds, aminoester bonds) or solvent-responsive molecules (such as borate bonds, imine bonds). Among them, cinnamic acid and anthracene can also be used as light-responsive molecules. Although they are not a kind of dynamic covalent bond, they have reversible properties under different wavelengths of light. Photoresponsive dynamic bond molecules are preferred because light has spatial selectivity and can flexibly regionalize induced bond exchange to achieve more refined patterns.

[0018] Furthermore, the chain extender is selected from a chain extender monomer containing a double-arm thiol functional group or an amino functional group, preferably a chain extender monomer containing a double-arm thiol functional group, and more preferably EDDT (3,6-dioxa-1,8-octanedithiol).

[0019] Furthermore, the photoinitiator is selected from one or both of ultraviolet light initiators and visible light initiators, preferably at least one of DMPA (2,2-dimethoxy-1,2-diphenylacetophenone), 819 (phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide), and TPO (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide), more preferably DMPA (2,2-dimethoxy-1,2-diphenylacetophenone).

[0020] Furthermore, the solvent is selected from one or more of toluene, chloroform, ethyl acetate, dichloromethane, tetrahydrofuran, N,N'-dimethylformamide and dimethyl sulfoxide, preferably toluene, chloroform or dichloromethane.

[0021] Furthermore, the electrospinning parameters are: positive high voltage 10-20 kV, negative high voltage 1-10 kV, micro pump injection speed 1.0-1.5 ml / h, drum rotation speed 200-1000 rpm, and spinning time 3-10 h.

[0022] Furthermore, the electrospinning includes single-needle electrospinning, coaxial electrospinning and multi-axis electrospinning.

[0023] When the film is subjected to regionalized dynamic bond exchange, the film is stretched and, at the same time, subjected to regionalized ultraviolet light irradiation, heat treatment or solvent treatment. That is, regionalized dynamic bond exchange is divided into: regionalized photoinduced dynamic bond exchange, regionalized thermally induced dynamic bond exchange and regionalized solvent-induced dynamic bond exchange.

[0024] Furthermore, the process of regionalized photoinduced dynamic bond exchange is: regionalized light irradiation at 365 nm for 30 minutes.

[0025] Furthermore, the process of regionalized thermally induced dynamic bond exchange is: regional heating at 100° C. for 60 minutes.

[0026] Furthermore, the process of regionalized solvent-induced dynamic bond exchange is: regionalized treatment in water or acidic solvent for 60 minutes.

[0027] Furthermore, the film is stretched to a strain range of 10-100%, preferably 80%.

[0028] A second object of the present invention is to provide a patternable mechanochromic cholesteric liquid crystal elastomer prepared by the above-mentioned preparation method.

[0029] A third object of the present invention is to provide a patternable mechanochromic cholesteric liquid crystal elastomer for use in the field of membrane materials.

[0030] Compared with the prior art, the present invention has the following advantages and technical effects:

[0031] The preparation method of the material in the present invention is simple and innovative, suitable for large-area manufacturing, and the uniform thickness of the film material is less than 0.05 mm. Compared with traditional cholesteric liquid crystal films, it breaks through the limitation that thinner films require a substrate, while thicker films are obtained without a substrate.

[0032] During the electrospinning process of the present invention, a high-voltage electric field induces the pre-alignment of liquid crystal molecules along the fiber stretching direction, promoting the directional self-assembly of the cholesteric helical axis (e.g., perpendicular to the fiber axis), thereby enhancing its selective reflectivity. The confined space of the nanofibers inhibits the disordered thermal motion of the liquid crystal molecules, stabilizes the helical pitch, and reduces pitch drift caused by temperature or external forces. The electrospinning process accelerates the solvent evaporation rate and significantly reduces external environmental interference, facilitating the preparation of materials with uniform and stable structural color.

[0033] The present invention realizes patterns with different colors in the membrane material by introducing dynamic bonds and patterned induced bond exchange. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0035] Figure 1 Schematic diagram of the electrospinning operation of the present invention;

[0036] Figure 2 Schematic diagram of the principle of preparing a patternable mechanochromic cholesteric liquid crystal elastomer according to the present invention;

[0037] Figure 3 This is a color display of the patternable mechanochromic cholesteric liquid crystal elastomer prepared in Example 1. DETAILED DESCRIPTION

[0038] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0039] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0040] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0041] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0042] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0043] An embodiment of the present invention provides a method for preparing a patternable mechanochromic cholesteric liquid crystal elastomer by electrospinning, comprising the following steps:

[0044] 1) preparing a cholesteric liquid crystal precursor solution;

[0045] 2) Electrospinning the cholesteric liquid crystal precursor (e.g. Figure 1 shown);

[0046] 3) The spun sample is placed under a UV lamp for curing to obtain a film;

[0047] 4) Performing regional dynamic bond exchange on the film under stretching, and obtaining a film that is a patternable mechanochromic cholesteric liquid crystal elastomer.

[0048] For example, the method for preparing a patternable mechanochromic cholesteric liquid crystal elastomer by electrospinning provided in an embodiment of the present invention comprises the following specific steps:

[0049] (1) Weighing a liquid crystal monomer containing a double-arm acrylate group, a chiral molecule, a dynamic bond molecule, a chain extender, a photoinitiator, triethylamine, and a solvent by mass, stirring and dissolving them to obtain a cholesteric liquid crystal precursor solution;

[0050] (2) transferring the obtained cholesteric liquid crystal precursor solution into a syringe and connecting it to an electrospinning device for electrospinning;

[0051] (3) After the spinning is completed, the sample of the receiver is removed and cured under ultraviolet light. After the curing is completed, the sample is dried to evaporate the solvent and obtain a film;

[0052] (4) The obtained film is uniaxially stretched to 80% strain using a stretching fixture, and then treated under light, heating or solvent conditions. The external force is removed to obtain a patternable mechanochromic cholesteric liquid crystal elastomer (the reaction principle flow chart is shown in FIG. Figure 2 shown).

[0053] In some preferred embodiments, in step (1), the contents of the components are as follows, calculated in percentage by mass: the molar ratio of the liquid crystal monomer to the chain extender is (1-1.5):1;

[0054] The content of the chiral molecule is 2-5 wt% of the total mass of the liquid crystal monomer and the chain extender;

[0055] The content of the dynamic bond molecules is 1-10 wt% of the total mass of the liquid crystal monomer and the chain extender;

[0056] The content of the base catalyst is 0.5-5 wt% of the total mass of the liquid crystal monomer and the chain extender;

[0057] The content of the photoinitiator is 0.05-5wt% of the total mass of the liquid crystal monomer and the chain extender;

[0058] The concentration of the cholesteric liquid crystal precursor solution is 10-50 wt %.

[0059] In some preferred embodiments, in step (1), the liquid crystal monomer containing a double-arm acrylate group can be selected from RM257.

[0060] In some preferred embodiments, in step (1), the chiral molecule can be selected from DK756.

[0061] In some preferred embodiments, in step (1), the dynamic bond molecule can be selected from BISS, diallyl disulfide or BDB.

[0062] The specific preparation steps of the BISS include dissolving sodium hydroxide in methanol, adding L-cystine and stirring to dissolve, then stirring the resulting mixed solution in an ice bath (0°C), dropwise adding acryloyl chloride (Aladdin) while stirring (using a syringe needle with a rubber stopper to prevent explosion, or a constant pressure funnel), allowing the mixture to stand (react for 12 hours), filtering to remove solid byproducts, precipitating the clarified solution in diethyl ether, filtering out the solid precipitant, and drying to obtain N,N'-bis(acryloyl)-(l)-cystine salt. The ratio of sodium hydroxide, methanol, and L-cystine used is 2g:70mL:2.7g.

[0063] The specific preparation steps of the BDB include: using tetrahydrofuran as a solvent and anhydrous magnesium sulfate as a desiccant, reacting 1-thioglycerol and 1,4-phenylenediboronic acid at a certain temperature, vacuum filtering, and finally drying to obtain a mercapto borate compound BDB containing a dynamic bond borate ester bond.

[0064] In some preferred embodiments, in step (1), the chain extender may be EDDT.

[0065] In some preferred embodiments, in step (1), the photoinitiator may be DMPA or 819.

[0066] In some preferred embodiments, in step (1), the solvent may be toluene, chloroform or dichloromethane.

[0067] In some preferred embodiments, in step (2), the electrospinning parameters are: positive high voltage 10-20 kV (such as 12 kV, 16 kV or 20 kV), negative high voltage 1-10 kV (such as 5 kV), micropump injection speed 1.0-1.5 ml / h (such as 1.1 ml / h, 1.2 ml / h or 1.3 ml / h), drum rotation speed 200-1000 rpm (such as 400 rpm, 500 rpm or 600 rpm), spinning time 3-10 h (preferably 4.7 h, 6 h or 7.3 h).

[0068] The electrospinning method includes single-needle electrospinning, coaxial electrospinning and multi-axis electrospinning.

[0069] In some preferred embodiments, in step (4), the irradiation process is: irradiation at 365 nm for 30 min.

[0070] In some preferred embodiments, in step (4), the heating process is: heating at 100° C. for 60 minutes.

[0071] In some preferred embodiments, in step (4), the solvent treatment process is: treating in an ethanol / water solution for 60 minutes. The patternable mechanochromic cholesteric liquid crystal elastomer prepared by the above preparation method can be applied in the field of membrane materials.

[0072] Unless otherwise specified, the "normal temperature" mentioned in the present invention refers to 20-30°C.

[0073] The raw materials used in the present invention are all purchased from the market.

[0074] The electrostatic method selected in the following embodiments of the present invention is single-needle electrospinning.

[0075] The technical solution of the present invention is further illustrated by the following examples.

[0076] Example 1

[0077] A method for preparing a patternable mechanochromic cholesteric liquid crystal elastomer by electrospinning, comprising the following steps:

[0078] S1. Preparation of the dynamic bond molecule BISS: Dissolve 2.0 g of sodium hydroxide in 70 mL of methanol, then add 2.7 g of L-cystine and stir to dissolve. Place the resulting solution in an ice bath at 0°C and stir. Add 2.2 mL of acryloyl chloride dropwise while stirring. Continue the reaction for 12 h. Remove solid byproducts by filtration, precipitate the clarified solution in cold ether, filter out the solid precipitant, and dry under vacuum at room temperature for two days to obtain BISS.

[0079] S2. Preparation of cholesteric liquid crystal precursor: 3.3294 g of RM257, 0.7532 g of EDDT, 0.0533 g of triethylamine, 0.1657 g of BISS, 0.1347 g of DK756, 0.0204 g of DMPA, and 15.956 g of toluene were weighed into a culture bottle and heated and stirred at room temperature for 10 h to dissolve the mixture to obtain a cholesteric liquid crystal monomer precursor.

[0080] S3, electrospinning: 8 mL of pre-polymerized cholesteric liquid crystal monomer precursor solution was transferred into a 10 mL syringe, connected to the electrospinning equipment, and electrospinning was performed using the following parameters: positive high voltage 16 kV, negative high voltage 5 kV, micropump injection speed 1.3 ml / h, drum rotation speed 600 rpm. After 4.7 h, the tin foil on the receiver was removed and the device was cured under a 365 nm UV lamp. After curing, the device was placed in an oven to evaporate the solvent, and the membrane was removed. The membrane thickness was 0.007 mm.

[0081] S4. Patterning treatment: The film is uniaxially stretched to 80% strain using a stretching fixture, and a heating stamp is placed at 100°C for 60 minutes to promote disulfide bond exchange. The external force is removed to obtain a patternable mechanochromic cholesteric liquid crystal elastomer.

[0082] The chiral molecule (DK756) content was adjusted to 0.1347 g, 0.01592 g, 0.1673 g, 0.1796 g, and 0.1918 g, respectively, to obtain patternable mechanochromic cholesteric liquid crystal elastomers with chiral molecule contents of 3.3%, 3.9%, 4.1%, 4.4%, and 4.7%, respectively, wherein the chiral molecule content refers to the percentage of the chiral molecule content in the total mass of the liquid crystal monomer (RM257) and the chain extender (EDDT).

[0083] Figure 3 Color display diagram of the patternable mechanochromic cholesteric liquid crystal elastomer with different chiral molecule contents prepared in Example 1.

[0084] Example 2

[0085] A method for preparing a patternable mechanochromic cholesteric liquid crystal elastomer by electrospinning, comprising the following steps:

[0086] S1. Preparation of dynamic bond molecules: diallyl disulfide;

[0087] S2. Preparation of cholesteric liquid crystal precursor: 3.3639 g of RM82, 0.7532 g of EDDT, 0.2042 g of di-n-propylamine, 0.0408 g of diallyl disulfide, 0.1605 g of DK756, 0.0204 g of 819, and 15.956 g of dichloromethane were weighed into a culture bottle and heated and stirred at room temperature for 10 h to dissolve the cholesteric liquid crystal monomer precursor;

[0088] S3, electrospinning: 8 mL of pre-polymerized cholesteric liquid crystal monomer precursor solution was transferred into a 10 mL syringe, connected to the electrospinning equipment, and electrospinning was performed using the following parameters: positive high voltage 20 kV, negative high voltage 5 kV, micropump injection speed 1.2 ml / h, drum rotation speed 500 rpm. After 6 h, the tin foil on the receiver was removed and the film was cured under a 365 nm UV lamp. After curing, the film was placed in an oven to evaporate the solvent, and the film was removed. The film thickness was 0.012 mm.

[0089] S4. Patternable treatment: The film is uniaxially stretched to 70% strain using a stretching fixture and exposed to 365nm ultraviolet light through a photomask for 30 minutes to promote disulfide bond exchange. The external force is removed to obtain a patternable mechanochromic cholesteric liquid crystal elastomer.

[0090] Example 3

[0091] A method for preparing a patternable mechanochromic cholesteric liquid crystal elastomer by electrospinning, comprising the following steps:

[0092] S1. Preparation of dynamic bond molecule BDB: 21.63 g of 1-thioglycerol, 16.57 g of 1,4-phenylenediboronic acid, and 20 g of anhydrous magnesium sulfate were added to 50 ml of tetrahydrofuran, and reacted at room temperature for 24 h. The anhydrous magnesium sulfate was removed by filtration to obtain a clear solution, and the solvent was removed by vacuum distillation at room temperature using a rotary evaporator. The solution was then dried in a vacuum oven at 70°C for 24 h to obtain a mercapto borate compound BDB containing a dynamic bond borate ester bond.

[0093] S2. Preparation of cholesteric liquid crystal precursor: 3.8284 g of RM257, 0.7532 g of EDDT, 0.0204 g of triethylamine, 0.4082 g of BDB, 0.2.0159 g of LC756, 0.2041 g of DMPA, and 15.956 g of chloroform were weighed into a culture bottle and heated and stirred at room temperature for 10 h to dissolve the mixture to obtain a cholesteric liquid crystal monomer precursor.

[0094] S3, electrospinning: 8 mL of pre-polymerized cholesteric liquid crystal monomer precursor solution was transferred into a 10 mL syringe, connected to the electrospinning equipment, and electrospinning was performed using the following parameters: positive high voltage 12 kV, negative high voltage 5 kV, micropump injection speed 1.1 ml / h, drum rotation speed 400 rpm. After 7.3 h, the tin foil on the receiver was removed and the device was cured under a 365 nm UV lamp. After curing, the device was placed in an oven to evaporate the solvent, and the membrane was removed. The membrane thickness was 0.019 mm.

[0095] S4. Patternable treatment: The film is uniaxially stretched to 50% strain using a stretching fixture, and a pattern is written on the film using an ethanol-water solution for 60 minutes to promote the exchange of borate bonds. The external force is removed to obtain a patternable mechanochromic cholesteric liquid crystal elastomer.

[0096] Comparative Example 1 (no electrospinning)

[0097] S1. Preparation of cholesteric liquid crystal precursor: 3.3294 g of RM257, 0.7532 g of EDDT, 0.0533 g of triethylamine, 0.1657 g of BISS, 0.1347 g of DK756, 0.0204 g of DMPA, and 15.956 g of toluene were weighed into a culture bottle and heated and stirred at room temperature for 10 h to dissolve the mixture to obtain a cholesteric liquid crystal monomer precursor.

[0098] S2, electrospinning: Pour 8 mL of pre-polymerized cholesteric liquid crystal monomer precursor into the mold, evaporate the solvent at room temperature for 24 hours, cure under a 365 nm UV lamp, and place in a 60 ° C oven to evaporate after curing.

[0099] S3. Patterning treatment: The film is uniaxially stretched to 80% strain using a stretching fixture, and a heating stamp is placed at 100°C for 60 minutes to promote disulfide bond exchange. The external force is removed to obtain a patternable mechanochromic cholesteric liquid crystal elastomer.

[0100] Results: The film was relatively thick, the color distribution was uneven, the mechanochromic sensitivity was low, and the pattern contrast was not obvious.

[0101] Comparative Example 2 (without dynamic covalent bond)

[0102] S1. Preparation of cholesteric liquid crystal precursor: 3.3294 g of RM257, 0.7532 g of EDDT, 0.0533 g of triethylamine, 0.1347 g of DK756, 0.0204 g of DMPA, and 15.956 g of toluene were weighed into a culture bottle, heated and stirred at room temperature for 10 h to dissolve, to obtain a cholesteric liquid crystal monomer precursor;

[0103] S2, electrospinning: 8 mL of pre-polymerized cholesteric liquid crystal monomer precursor solution was transferred into a 10 mL syringe, connected to the electrospinning equipment, and electrospinning was performed using the following parameters: positive high voltage 16 kV, negative high voltage 5 kV, micropump injection speed 1.3 ml / h, drum rotation speed 600 rpm. After 4.7 h, the tin foil on the receiver was removed and the device was cured under a 365 nm UV lamp. After curing, the device was placed in an oven to evaporate the solvent, and the membrane was removed. The membrane thickness was 0.007 mm.

[0104] S3. Patterning treatment: The film is uniaxially stretched to 80% strain using a stretching fixture, and a heating stamp is placed at 100°C for 60 minutes to promote disulfide bond exchange. The external force is removed to obtain a patternable mechanochromic cholesteric liquid crystal elastomer.

[0105] Result: The film is relatively uniform and has the same appearance as the product of Example 1. It can be color-changed but cannot be patterned.

[0106] Comparative Example 3 (without chiral molecules)

[0107] S1. Preparation of cholesteric liquid crystal precursor: 3.3294 g of RM257, 0.7532 g of EDDT, 0.0533 g of triethylamine, 0.1657 g of BISS, 0.0204 g of DMPA, and 15.956 g of toluene were weighed into a culture bottle, heated and stirred at room temperature for 10 h to dissolve, to obtain a cholesteric liquid crystal monomer precursor;

[0108] S2, electrospinning: 8 mL of pre-polymerized cholesteric liquid crystal monomer precursor solution was transferred into a 10 mL syringe, connected to the electrospinning equipment, and electrospinning was performed using the following parameters: positive high voltage 16 kV, negative high voltage 5 kV, micropump injection speed 1.3 ml / h, drum rotation speed 600 rpm. After 4.7 h, the tin foil on the receiver was removed and the device was cured under a 365 nm UV lamp. After curing, the device was placed in an oven to evaporate the solvent, and the membrane was removed. The membrane thickness was 0.007 mm.

[0109] S3. Patterning treatment: The film is uniaxially stretched to 80% strain using a stretching fixture, and a heating stamp is placed at 100°C for 60 minutes to promote disulfide bond exchange. The external force is removed to obtain a patternable mechanochromic cholesteric liquid crystal elastomer.

[0110] Result: The film is relatively uniform, white and colorless in appearance, cannot be discolored by force, and cannot be patterned.

[0111] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a patternable mechanochromic cholesteric liquid crystal elastomer by electrospinning, characterized in that: The following steps are involved: The cholesteric liquid crystal precursor liquid is electrospun, and the spun sample is placed under ultraviolet light for curing to obtain a film. The film is stretched and subjected to regional dynamic bond exchange to obtain a patternable mechanochromic cholesteric liquid crystal elastomer.

2. The method for preparing a patternable mechanochromic cholesteric liquid crystal elastomer by electrospinning according to claim 1, characterized in that: The cholesteric liquid crystal precursor solution is prepared by mixing a liquid crystal monomer containing a double-arm acrylate group, a chiral molecule, a dynamic bond molecule, a chain extender, a base catalyst, a photoinitiator and a solvent.

3. The method for preparing a patternable mechanochromic cholesteric liquid crystal elastomer by electrospinning according to claim 2, characterized in that: The molar ratio of the liquid crystal monomer to the chain extender is (1-1.5):1; The content of the chiral molecule is 2-5 wt% of the total mass of the liquid crystal monomer and the chain extender; The content of the dynamic bond molecules is 1-10 wt% of the total mass of the liquid crystal monomer and the chain extender; The content of the base catalyst is 0.5-5 wt% of the total mass of the liquid crystal monomer and the chain extender; The content of the photoinitiator is 0.05-5wt% of the total mass of the liquid crystal monomer and the chain extender; The concentration of the cholesteric liquid crystal precursor solution is 10-50 wt %.

4. The method for preparing a patternable mechanochromic cholesteric liquid crystal elastomer by electrospinning according to claim 3, characterized in that: The liquid crystal monomer containing a double-arm acrylate group is selected from one or more of RM82, RM257 and LC242; and / or, The chiral molecule is selected from one or both of LC756 and DK756; and / or, The dynamic bond molecule is selected from one or more compounds containing disulfide bonds, diselenide bonds, DA bonds, borate bonds, ester bonds, urethane bonds and imine bonds; and / or, The chain extender is selected from chain extender monomers containing a double-arm thiol functional group or an amine functional group; and / or, The photoinitiator is selected from one or both of ultraviolet light initiators and visible light initiators; and / or, The base catalyst is selected from one or more of triethylamine, n-propylamine and di-n-propylamine; and / or, The solvent is selected from one or more of toluene, chloroform, ethyl acetate, dichloromethane, tetrahydrofuran, N,N'-dimethylformamide and dimethyl sulfoxide.

5. The method for preparing a patternable mechanochromic cholesteric liquid crystal elastomer by electrospinning according to claim 1, wherein: The electrospinning parameters are: positive high voltage 10-20 kV, negative high voltage 1-10 kV, micro pump injection speed 1.0-1.5 ml / h, drum rotation speed 200-1000 rpm, and spinning time 3-10 h.

6. The method for preparing a patternable mechanochromic cholesteric liquid crystal elastomer by electrospinning according to claim 1, wherein: The electrospinning method includes single-needle electrospinning, coaxial electrospinning and multi-axis electrospinning.

7. The method for preparing a patternable mechanochromic cholesteric liquid crystal elastomer by electrospinning according to claim 1, wherein: There are three ways to exchange regional dynamic keys: Method 1: Regional illumination at 365 nm for 30 min; Method 2: Regional heating at 100°C for 60 minutes; Method 3: Regional treatment in water or acidic solvent for 60 minutes.

8. The method for preparing a patternable mechanochromic cholesteric liquid crystal elastomer by electrospinning according to claim 1, characterized in that: The strain range of the stretching is 10-100%. 9 . A patternable mechanochromic cholesteric liquid crystal elastomer prepared by the preparation method according to any one of claims 1 to 8 .

10. Use of the patternable mechanochromic cholesteric liquid crystal elastomer according to claim 9 in the field of membrane materials.

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