Hollow mechanochromic liquid crystal elastic fiber and preparation method thereof

Abstract

This invention provides a hollow mechanochromic liquid crystal elastic fiber and its preparation method. First, a precursor containing a non-chiral nematic liquid crystal monomer and a chiral liquid crystal monomer is prepared. A specific device is used to uniformly coat the precursor onto the surface of a glass capillary. The capillary is then left to stand at room temperature, and secondary cross-linking is achieved by irradiation with an ultraviolet lamp. After removing the glass capillary, the hollow mechanochromic liquid crystal elastic fiber is obtained. This invention achieves liquid crystal-induced assembly and online cross-linking under controlled prepolymerization process, using a specific device to uniformly coat the precursor onto the glass capillary surface, and under static and light-irradiation conditions. A cholesteric planar texture is formed on the glass capillary surface, resulting in a hollow mechanochromic liquid crystal elastic fiber with the liquid crystal helical axis radially distributed along the fiber's radial direction. This invention achieves surface color uniformity and reversible cycle stability of the cholesteric liquid crystal fiber. When subjected to uniaxial tension, the fiber surface color changes significantly, exhibiting high force response sensitivity and promising application prospects.

Description

Technical Field

[0001] This invention relates to the field of mechanochromic fabric technology, and more particularly to a hollow mechanochromic liquid crystal elastic fiber and its preparation method. Background Technology

[0002] Mechanochromic textiles are a class of materials whose optical properties change reversibly upon exposure to external mechanical forces. They enable visual detection and sensing of external forces and are widely used in emerging fields such as rehabilitation therapy and sports. Currently, mechanochromic textiles can be prepared by coating or impregnating the surface of textiles or fibers with a mechanochromic functional coating. For example, an invention patent (application number CN 201811153848.2) discloses a liquid crystal fiber and its preparation method. This method involves impregnating a single core fiber with a liquid crystal-containing finishing solution, drying and fixing it, thus fixing the liquid crystal onto the fiber sheath to form a liquid crystal fiber with a sheath-core structure. However, the functional coating prepared in this way has poor weather resistance and washability, a short service life, and the core fiber used is polyester or nylon, both of which have poor elasticity. Therefore, the mechanochromic performance of this liquid crystal fiber is limited. The invention patent (application number CN 202210936184.7) discloses another type of force-sensitive color-changing polyurethane fiber and its preparation method. First, a fiber-forming polymer containing force-sensitive groups in the main chain is synthesized, and then force-sensitive color-changing fibers are prepared by spinning to prepare force-sensitive textiles. When the fiber is subjected to force, the force-sensitive groups undergo isomerization, and the fiber color changes. However, the pigment color gamut of this fiber is narrow, it is easily bleached by light, and the surface color change is not obvious after the fiber is deformed by force, resulting in low sensitivity.

[0003] To overcome the shortcomings of the aforementioned mechanochromic materials, researchers have conducted extensive fundamental research in the field of structural color-based mechanochromic materials. For example, a Chinese patent (application number CN 202210964511.X) discloses a cellulose nanofiber hydrogel with mechanical color change and its application. This invention achieves the directional deposition and arrangement of cellulose nanofibers through steam bath treatment, thereby preparing the mechanical color-changing hydrogel. However, this hydrogel requires the action of a polarizer to achieve the colorless to colored transition, and the color cycle count is only 1 to 3 times, indicating poor reversible cycle stability.

[0004] In recent years, mechanochromic cholesteric liquid crystal elastomer materials have developed rapidly and become a research hotspot. Their mechanochromic principle is based on Bragg selective reflection. However, preparing cholesteric liquid crystal elastomers into fibers presents certain challenges: firstly, Plateau-Rayleigh instability causes the precursor solution to easily decompose into droplets, making it difficult to prepare uniform fibers; secondly, the fibers are one-dimensional long-range morphology, inevitably undergoing slight twisting during use. This necessitates that different surfaces along the fiber axis exhibit the same color to achieve accurate sensing of external forces, thereby expanding the application range of cholesteric liquid crystal elastomer fibers.

[0005] In view of this, it is necessary to design an improved hollow mechanochromic liquid crystal elastic fiber and its preparation method to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a hollow mechanochromic liquid crystal elastic fiber and its preparation method. By controlling the prepolymerization process of the liquid crystal precursor, a specific preparation device is used to uniformly coat the precursor onto the surface of a glass capillary, thereby achieving induced assembly and online crosslinking. This allows the liquid crystal precursor to form a cholesteric planar texture on the surface of the glass capillary, resulting in a hollow mechanochromic liquid crystal elastic fiber with the liquid crystal helical axis radially distributed along the fiber's radial direction. This overcomes the shortcomings of existing cholesteric liquid crystal elastomer fibers.

[0007] To achieve the above-mentioned objective, this invention provides a method for preparing hollow mechanochromic liquid crystal elastic fibers, comprising the following steps:

[0008] S1. Mix the liquid crystal monomer with an organic solvent, heat to 70-90°C and cool to room temperature, then add a crosslinking agent, chain extender, photoinitiator and catalyst, stir and let stand for 15-25 minutes to obtain a precursor; the liquid crystal monomer includes a non-chiral nematic liquid crystal monomer and a chiral liquid crystal monomer.

[0009] S2. The precursor from step S1 is injected into a preparation apparatus for hollow mechanochromic liquid crystal elastic fibers. The preparation apparatus includes a cylindrical hollow tube, a channel inlet disposed on the surface of the cylindrical hollow tube, and a glass capillary tube sleeved inside the cylindrical hollow tube. The channel inlet forms a certain angle with the cylindrical hollow tube, the glass capillary tube coincides with the axis of the cylindrical hollow tube, and a cavity is formed between the glass capillary tube and the cylindrical hollow tube. After the precursor enters the cavity, the glass capillary tube moves horizontally in the cylindrical hollow tube, so that the precursor is uniformly coated on the surface of the glass capillary tube.

[0010] S3. The glass capillary with surface-coated prepolymer obtained in step S2 is left to stand at room temperature for 22-26 hours, then irradiated with ultraviolet light for 3-7 minutes. The irradiated glass capillary is then immersed in hydrofluoric acid for 1.5-2.5 hours, and washed with water until neutral to obtain the hollow mechanochromic liquid crystal elastic fiber.

[0011] As a further improvement of the present invention, in step S1, the mass ratio of the non-chiral nematic liquid crystal monomer to the chiral liquid crystal monomer is (20-25):1.

[0012] As a further improvement of the present invention, in step S1, the crosslinking agent is pentaerythritol tetrakis(3-mercaptopropionic acid), the chain extender is 3,6-dioxa-1,8-octanedithiol, and the catalyst is di-n-propylamine solution.

[0013] As a further improvement of the present invention, the specific operation process of step S1 is as follows: 2.6-2.7g of non-chiral nematic liquid crystal monomer, 0.1-0.2g of chiral liquid crystal monomer and 0.15-0.25mL of organic solvent are mixed, heated to 70-90°C and cooled to room temperature, and then 12-18μL of pentaerythritol tetrakis(3-mercaptopropionic acid), 68-70mg of 3,6-dioxa-1,8-octanedithiol, 0.2-0.3mg of photoinitiator and 60-70μL of di-n-propylamine solution are added, stirred and allowed to stand for 15-25min to obtain the precursor.

[0014] As a further improvement of the present invention, the non-chiral nematic liquid crystal monomer is 2-methyl-1,4-phenylene bis(4-(3-(acryloyloxy)propoxy)benzoate, and the chiral liquid crystal monomer is (3R,3AR,6S,6AR)-hexahydrofuran[3,2-B]furan-3,6-diylbis(4-((4-((((4-(acryloyloxy)butoxy)carbonyl)oxy)benzoyl)oxy)benzoate).

[0015] As a further improvement of the present invention, in step S1, the organic solvent is dichloromethane and the photoinitiator is 2,2-dimethyl-2-phenylacetophenone.

[0016] As a further improvement of the present invention, the di-n-propylamine solution is prepared by diluting di-n-propylamine by 40 to 60 times with dichloromethane.

[0017] As a further improvement of the present invention, in step S3, the power of the ultraviolet lamp is 50mW / cm². 2 The wavelength is 365nm.

[0018] A hollow mechanochromic liquid crystal elastic fiber prepared by any one of the above methods, wherein the hollow mechanochromic liquid crystal elastic fiber has a hollow thin-walled structure and contains liquid crystals radially distributed along the helical axis of the fiber.

[0019] As a further improvement of the present invention, the hollow mechanochromic liquid crystal elastic fiber has a diameter of 0.5 to 1.5 mm and a hollow thin wall thickness of 40 to 80 μm.

[0020] The beneficial effects of this invention are:

[0021] 1. The hollow mechanochromic liquid crystal elastic fiber and its preparation method of the present invention involve first preparing a precursor containing a non-chiral nematic liquid crystal monomer and a chiral liquid crystal monomer, then uniformly coating the precursor onto the surface of a glass capillary using a specific device, allowing it to stand at room temperature, and then performing secondary crosslinking by irradiation with an ultraviolet lamp. Finally, the glass capillary is removed to obtain the hollow mechanochromic liquid crystal elastic fiber. The present invention controls the prepolymerization process of the liquid crystal precursor, uses a specific preparation device to uniformly coat the precursor onto the surface of the glass capillary, and achieves induced assembly and online crosslinking under standing and light irradiation conditions. This results in the formation of a cholesteric planar texture of the liquid crystal precursor on the surface of the glass capillary, yielding a hollow mechanochromic liquid crystal elastic fiber with the liquid crystal helical axis radially distributed along the fiber's radial direction. This overcomes the shortcomings of existing cholesteric liquid crystal elastomer fiber preparation methods and applications. When the hollow mechanochromic liquid crystal elastic fiber of the present invention is subjected to uniaxial tension, the Poisson effect of the hollow thin-walled structure is significant, the fiber wall is compressed, thereby compressing the pitch inside the fiber to a large extent, generating a large pitch difference, achieving a large chromatographic shift, and the color change on the fiber surface is obvious, thus improving the force response sensitivity of the fiber.

[0022] 2. This invention selects an appropriate amount of chiral liquid crystal monomers to be added to the precursor. This not only adjusts the pitch of the liquid crystal, achieving greater chromatographic movement and improving the force response sensitivity of the fiber, but also induces assembly, which is beneficial for forming a uniform thin-walled fiber structure on the surface of the glass capillary. By controlling the synthesis formula and process of the precursor, this invention enables the precursor to have suitable viscosity and crosslinking degree, promoting secondary crosslinking of the precursor in subsequent processes and avoiding the problem of uneven distribution of the precursor on the surface of the glass capillary due to gravity during the secondary crosslinking process. Using the glass capillary as a circular support substrate, the assembly process is controlled by controlling the solvent evaporation rate, so that the liquid crystal precursor is oriented and assembled on the capillary surface, forming a radially radial distribution. This ensures that the pitch of the hollow mechanochromic liquid crystal elastomer fiber is perpendicular to the surface of the capillary, making the initial color of the fiber uniform in the radial direction. Even if the fiber undergoes a certain degree of twisting, the color perpendicular to the axial direction will not change, achieving the surface color uniformity and reversible cycle stability of the cholesteric liquid crystal fiber.

[0023] 3. This invention employs a specific device to prepare hollow mechanochromic liquid crystal elastic fibers. A cylindrical hollow tube is used in conjunction with a movable glass capillary inside. When the precursor enters the cavity between the two, the glass capillary moves horizontally from one end of the cylindrical hollow tube to the other. Due to the precursor's viscosity and the pressure from the cylindrical hollow tube, uniform coating of the precursor on the capillary surface is achieved. Simultaneously, under the support of the glass capillary, the liquid crystal precursor is oriented and assembled on the capillary surface, forming a radially radiating distribution structure, thus achieving color uniformity in the hollow mechanochromic liquid crystal elastic fibers. Attached Figure Description

[0024] Figure 1 This is a SEM cross-sectional image of the hollow mechanochromic liquid crystal elastic fiber prepared in Example 1.

[0025] Figure 2 This is a schematic diagram illustrating the stretching color-reversible recovery principle of the hollow mechanical color-changing liquid crystal elastic fiber in this invention.

[0026] Figure 3 Optical photographs of the hollow mechanochromic liquid crystal elastic fiber of Example 1 under right-handed polarized light, showing the fiber rotating radially at different angles.

[0027] Figure 4 Optical photographs of the hollow mechanochromic liquid crystal elastic fiber of Example 1 under different stretching states.

[0028] Figure 5 This is a stretch-recovery diagram of the hollow mechanochromic liquid crystal elastic fiber of Example 1.

[0029] Figure 6 The image shows the color change of the hollow mechanical color-changing liquid crystal elastic fiber in Example 1 under different stretching states.

[0030] Figure 7 This is a schematic diagram of the apparatus 100 for preparing hollow mechanochromic liquid crystal elastic fibers.

[0031] Figure Labels

[0032] 100 - Apparatus for preparing hollow mechanochromic liquid crystal elastic fibers; 110 - Cylindrical hollow tube; 120 - Channel inlet; 130 - Glass capillary; 200 - Injector. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0035] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0036] A method for preparing hollow mechanochromic liquid crystal elastic fibers includes the following steps:

[0037] S1. Mix the liquid crystal monomer with an organic solvent, heat to 70-90°C and hold for 5 minutes to dissolve the liquid crystal, cool to room temperature, then add a crosslinking agent, chain extender, photoinitiator and catalyst, stir and let stand for 15-25 minutes to obtain the precursor; the liquid crystal monomer includes non-chiral nematic liquid crystal monomers and chiral liquid crystal monomers.

[0038] S2. Using a syringe 200, the precursor from step S1 is injected into the apparatus 100 for preparing hollow mechanochromic liquid crystal elastic fibers, such as... Figure 7 As shown, the preparation apparatus includes a cylindrical hollow tube 110, a channel inlet 120 disposed on the surface of the cylindrical hollow tube 110, and a glass capillary 130 sleeved inside the cylindrical hollow tube 110. The channel inlet 120 forms a certain angle with the cylindrical hollow tube 110, and the axis of the glass capillary 130 coincides with that of the cylindrical hollow tube 110, forming a cavity between the glass capillary 130 and the cylindrical hollow tube 110. After the precursor enters the cavity, the glass capillary 130 moves horizontally in the cylindrical hollow tube 110, so that the precursor is uniformly coated on the surface of the glass capillary 130.

[0039] Hollow mechanochromic liquid crystal elastic fibers are prepared using a specific device. A cylindrical hollow tube 110 and its internal movable glass capillary 130 cooperate with each other. When the precursor enters the cavity between the two, the glass capillary 130 moves horizontally from one end of the cylindrical hollow tube 110 to the other. Because the precursor has a certain viscosity and is compressed by the cylindrical hollow tube 110, the precursor is uniformly coated on the surface of the capillary, and finally a hollow thin-walled fiber with a uniform arc surface is obtained.

[0040] S3. The glass capillary 130 with surface-coated prepolymer obtained in step S2 is left to stand at room temperature for 22-26 hours, then irradiated with ultraviolet light for 3-7 minutes. The irradiated glass capillary 130 is then immersed in hydrofluoric acid for 1.5-2.5 hours, and washed with water until neutral to obtain hollow mechanochromic liquid crystal elastic fiber.

[0041] In particular, this invention controls the prepolymerization process of the liquid crystal precursor. Prepolymerization can prevent the precursor solution from decomposing into droplets, providing a prerequisite for the preparation of uniform fibers. A specific preparation device is used to uniformly coat the precursor onto the surface of the glass capillary 130. Under static and light-irradiation conditions, induced assembly and online crosslinking are achieved, so that the liquid crystal precursor forms a cholesteric planar texture on the surface of the glass capillary 130. Hollow mechanochromic liquid crystal elastic fibers with the liquid crystal helical axis radially distributed along the fiber are obtained, overcoming the shortcomings of existing cholesteric liquid crystal elastomer fiber preparation methods and applications.

[0042] In step S1, the mass ratio of non-chiral nematic liquid crystal monomers to chiral liquid crystal monomers is (20-25):1. Adding chiral liquid crystal monomers to the precursor and limiting the amount of chiral liquid crystal monomers added can not only adjust the pitch of the liquid crystal, achieve greater chromatographic movement, and improve the force response sensitivity of the fibers, but also induce assembly, which is beneficial to forming a uniform thin-walled fiber structure on the surface of the glass capillary 130.

[0043] Specifically, in step S1, the crosslinking agent is pentaerythritol tetrakis(3-mercaptopropionic acid) ester (PETMP), the chain extender is 3,6-dioxa-1,8-octanedithiol (EDDET), and the catalyst is di-n-propylamine (DPA) solution. The specific operating procedure for step S1 is as follows: 2.6–2.7 g of achiral nematic liquid crystal monomer, 0.1–0.2 g of chiral liquid crystal monomer, and 0.15–0.25 mL of organic solvent are mixed, heated to 70–90 °C, and then cooled to room temperature. Next, 12–18 μL of pentaerythritol tetrakis(3-mercaptopropionic acid) ester, 68–70 mg of 3,6-dioxa-1,8-octanedithiol, 0.2–0.3 mg of photoinitiator, and 60–70 μL of di-n-propylamine solution are added. After stirring, the mixture is allowed to stand for 15–25 min to obtain the precursor. By defining the synthesis formula and process of the precursor, and utilizing the crosslinking effect of the crosslinking agent, the precursor undergoes pre-crosslinking during the standing process. By limiting the standing time, a precursor with suitable viscosity and degree of crosslinking is obtained, which facilitates the subsequent coating process. This promotes the secondary crosslinking of the precursor in the subsequent process and avoids the problem of uneven distribution of the precursor on the surface of the glass capillary 130 due to gravity during the secondary crosslinking process.

[0044] In some specific embodiments, the di-n-propylamine solution is prepared by diluting di-n-propylamine 40 to 60 times with dichloromethane.

[0045] In step S1, the non-chiral nematic liquid crystal monomer is 2-methyl-1,4-phenylenebis(4-(3-(acryloyloxy)propoxy)benzoate (RM257), and the chiral liquid crystal monomer is (3R,3AR,6S,6AR)-hexahydrofuran[3,2-B]furan-3,6-dimethylbis(4-((4-((((4-(acryloyloxy)butoxy)carbonyl)oxy)benzoyl)oxy)benzoate) (LC756). The organic solvent is dichloromethane (DCM), and the photoinitiator is 2,2-dimethyl-2-phenylacetophenone (I-651).

[0046] This invention uses a glass capillary 130 as a circular support substrate. By controlling the solvent evaporation rate, i.e. the settling time in step S3, the assembly process is controlled, allowing the liquid crystal precursor to be oriented and assembled on the capillary surface, forming a radially radial distribution. This ensures that the pitch of the hollow mechanochromic liquid crystal elastomer fibers is perpendicular to the capillary surface, resulting in uniform initial color of the fibers in the radial direction. Even if the fibers undergo a certain degree of twisting, the color in the axial direction will not change, thus achieving uniform surface color and reversible cycle stability of the cholesteric liquid crystal fibers.

[0047] In some specific embodiments, in step S3, the power of the ultraviolet lamp is 50mW / cm². 2 The wavelength is 365nm. In the secondary crosslinking process of the precursor, in addition to the effects of resting time and illumination time on the degree of crosslinking of the precursor, the power of the ultraviolet lamp also has a certain impact, so it needs to be limited.

[0048] A hollow mechanochromic liquid crystal elastic fiber prepared by the above method has a hollow thin-walled structure and contains liquid crystals radially distributed along the helical axis of the fiber. Please refer to [link to relevant documentation]. Figure 2 As shown, when the hollow, force-induced color-changing liquid crystal elastic fiber is subjected to uniaxial tension, the Poisson effect of the hollow thin-walled structure is significant, the fiber wall is compressed, thereby compressing the pitch inside the fiber to a large extent, generating a large pitch difference, achieving a large chromatographic shift, and the color change on the fiber surface is obvious, thus improving the force response sensitivity of the fiber.

[0049] In some specific embodiments, the diameter of the hollow mechanochromic liquid crystal elastic fiber is 0.5 to 1.5 mm, and the thickness of the hollow thin wall is 40 to 80 μm.

[0050] Example 1

[0051] This embodiment provides a method for preparing hollow mechanochromic liquid crystal elastic fibers, including the following steps:

[0052] S1. Mix 2.688g of RM257, 0.119g of LC756 and 0.2mL of DCM, heat to 80℃, cool to 25℃ after 5min, then add 14μL of PETMP, 69.6mg of EDDET, 0.21mg of I-651 and 65μL of DPA solution (diluted 50 times with DCM), stir and let stand for 20min to carry out the prepolymerization reaction to obtain the precursor.

[0053] S2. The precursor from step S1 is injected into the hollow mechanochromic liquid crystal elastic fiber preparation apparatus 100 using a syringe 200. After the precursor enters the cavity between the glass capillary 130 (diameter of 1.10 mm) and the cylindrical hollow tube 110 (inner diameter of 2 mm), the glass capillary 130 moves horizontally in the cylindrical hollow tube 110, so that the precursor is uniformly coated on the surface of the glass capillary 130.

[0054] S3. The glass capillary 130 with the surface-coated prepolymer obtained in step S2 is placed at 25°C in a fume hood for 24 hours, and then subjected to ultraviolet light (wavelength 365nm, power 50mW / cm). 2 Irradiate for 5 minutes, then immerse the irradiated glass capillary 130 in hydrofluoric acid for 2 hours. After washing with water until neutral, hollow mechanochromic liquid crystal elastic fiber is obtained.

[0055] Please see Figure 1 The image shown is a SEM cross-sectional view of the hollow mechanochromic liquid crystal elastic fiber prepared in Example 1. As can be seen from the image, the hollow mechanochromic liquid crystal elastic fiber has a hollow thin-walled structure with relatively uniform wall thickness.

[0056] Please see Figure 3 The image shows optical photographs of the hollow mechanochromic liquid crystal elastic fiber of Example 1 under right-handed polarized light, with the fiber rotated radially at different angles; where (a) represents 0°, (b) 90°, (c) 180°, and (d) 270°. As can be seen from the figures, the surface color of the hollow mechanochromic liquid crystal elastic fiber prepared in Example 1 is basically consistent at different rotation angles, indicating that the liquid crystal assembly structure in the fiber is radially radial. Therefore, the surface color of the fiber is nearly consistent when observed from different radial angles, resulting in color uniformity.

[0057] Please see Figure 4The image shows optical photographs of the hollow, mechanochromic liquid crystal elastic fiber of Example 1 under different tensile conditions. (a) is the unstretched state, (b) is the tensile strain of 17%, (c) is the tensile strain of 34%, and (d) is the tensile strain of 50%. As can be seen from the figures, the fiber exhibits different colors under different tensile strains, and the color changes are significant. This is because the Poisson effect is significant in the hollow, thin-walled structure of the fiber. During stretching, the fiber wall is compressed, resulting in a large pitch difference within the fiber, leading to a large chromatographic shift. This results in a noticeable color change on the fiber surface and high force response sensitivity of the fiber.

[0058] Please see Figure 5 The figure shows the stretch-recovery diagram of the hollow mechanochromic liquid crystal elastic fiber of Example 1. In the diagram, "initial" represents the unstretched initial state, and 25%, 50%, and 65% represent different tensile strains. As can be seen from the figure, the hollow mechanochromic liquid crystal elastic fiber not only exhibits different color changes during stretching but also undergoes corresponding color changes during recovery, indicating that it possesses reversible cycle stability.

[0059] Please see Figure 6 The image shows the color change of the hollow mechanochromic liquid crystal elastic fiber of Example 1 under different tensile conditions. As can be seen from the CIE1931 coordinate graph, with the increase of tensile strain, the color of the fiber surface gradually changes from red to green. This color change allows for the visual sensing of the tensile strain experienced by the fiber.

[0060] Comparative Example 1

[0061] Comparative Example 1 provides a mechanochromic liquid crystal elastic fiber and its preparation method. Ordinary polyester fiber is immersed in the precursor of this application, and then the process of step S3 is performed to obtain a mechanochromic liquid crystal elastic fiber with a surface-loaded precursor.

[0062] Comparative Example 2

[0063] Comparative Example 2 provides a mechanochromic liquid crystal elastic fiber and its preparation method. The difference from Example 1 is that LC756 chiral liquid crystal monomer is not added in step S1. The rest is roughly the same as Example 1, and will not be repeated here.

[0064] Comparative Example 3

[0065] Comparative Example 3 provides a mechanochromic liquid crystal elastic fiber and its preparation method. Compared with Example 1, the difference is that in step S1, LC756 is used to replace all of RM257. The rest is roughly the same as in Example 1, and will not be described again here.

[0066] Comparative Example 4

[0067] Comparative Example 4 provides a mechanochromic liquid crystal elastic fiber and its preparation method. Compared with Example 1, the difference is that in step S1, after stirring, the fiber is allowed to stand for 40 minutes to carry out a prepolymerization reaction, and step S2 is carried out directly. The rest is roughly the same as in Example 1, and will not be repeated here.

[0068] Comparative Example 5

[0069] Comparative Example 5 provides a mechanochromic liquid crystal elastic fiber and its preparation method. Compared with Example 1, the difference is that in step S3, the fiber is not left to stand in a fume hood for 24 hours, but is directly irradiated with ultraviolet light. The rest is roughly the same as Example 1, and will not be described again here.

[0070] Comparative Example 6

[0071] Comparative Example 6 provides a mechanochromic liquid crystal elastic fiber and its preparation method, wherein ordinary polyurethane fiber is immersed in the precursor of this application, and then the process of step S3 is performed to obtain a mechanochromic liquid crystal elastic fiber with a surface-loaded precursor.

[0072] The fibers prepared in Example 1 and Comparative Examples 1-6 were tested for color change properties and reflection wavelength under different stretching conditions. The results are shown in the table below.

[0073] Table 1. Characterization of fiber color-changing properties in Examples 1 and 6 (color / reflection wavelength after stretching with different strains)

[0074] Unstretched Tensile strain 17% Tensile strain 34% 50% tensile strain Example 1 Red (652nm) Orange (602nm) Yellow (559nm) Green (519nm) Comparative Example 1 Red (648nm) Red (648nm) Red (648nm) Red (648nm) Comparative Example 2 transparent transparent transparent transparent Comparative Example 3 transparent transparent transparent transparent Comparative Example 4 White White White White Comparative Example 5 transparent transparent transparent transparent Comparative Example 6 Red (652nm) Red (652nm) Red (645nm) Orange (605nm)

[0075] Table 1 shows that the fibers prepared in Example 1 exhibit excellent color-changing properties under different stretching states. In contrast, in Comparative Example 1, the liquid crystal prepolymer was coated onto the surface of ordinary polyester fibers. Since ordinary polyester fibers are not elastic fibers, they cannot generate significant strain during stretching to change the liquid crystal pitch; therefore, the fiber color remains unchanged, remaining red. Comparative Examples 2 and 3 show that without the addition of chiral liquid crystal monomers, conventional liquid crystal monomers cannot be induced to assemble and form a cholesteric helical structure, thus Bragg reflection cannot be achieved, resulting in only transparent fibers. If all chiral liquid crystal monomers are used, the absence of cholesteric liquid crystal monomers also prevents the formation of a helical structure, thus Bragg reflection cannot occur. Comparative Example 4 shows that if the resting time is too long, the prepolymerization reaction over-exists, resulting in excessive cross-linking. This leads to a high system viscosity, which is detrimental to liquid crystal assembly, preventing the formation of the cholesteric phase and resulting in strong light scattering. Therefore, the fibers appear white and do not change color after stretching. Comparative Example 5 shows that if the solvent in the prepolymer is not allowed to evaporate during standing, it is impossible to induce the orderly assembly of liquid crystal units to form a cholesteric helical structure. The system remains isotropic, exhibiting a transparent color, and does not change color when stretched. Comparative Example 6 shows that if the special device of this invention is not used and only the impregnation coating method is employed, it is impossible to construct a thin layer of liquid crystal elastomer on the surface of polyurethane fiber, and a significant Poisson effect cannot be achieved. The force-sensitive color-changing fiber is not sensitive to strain, and the color-changing effect is not sensitive.

[0076] In summary, this invention provides a hollow mechanochromic liquid crystal elastic fiber and its preparation method. First, a precursor containing both chiral nematic liquid crystal monomers and chiral liquid crystal monomers is prepared. Then, a specific device is used to uniformly coat the precursor onto the surface of a glass capillary. The capillary is then left to stand at room temperature and subjected to secondary cross-linking under ultraviolet light irradiation. Finally, the glass capillary is removed, yielding the hollow mechanochromic liquid crystal elastic fiber. This invention controls the prepolymerization process of the liquid crystal precursor, uses a specific preparation device to uniformly coat the precursor onto the surface of the glass capillary, and achieves induced assembly and online cross-linking under static and light-irradiation conditions. This results in a cholesteric planar texture formed by the liquid crystal precursor on the glass capillary surface, yielding a hollow mechanochromic liquid crystal elastic fiber with the liquid crystal helical axis radially distributed along the fiber's radial direction. This overcomes the shortcomings of existing cholesteric liquid crystal elastomer fiber preparation methods and applications, achieving surface color uniformity and reversible cycle stability in cholesteric liquid crystal fibers. When the hollow mechanochromic liquid crystal elastic fiber of the present invention is subjected to uniaxial tension, the Poisson effect of the hollow thin-walled structure is significant, the fiber wall is compressed, thereby compressing the pitch inside the fiber to a large extent, generating a large pitch difference, achieving a large chromatographic shift, and the color change on the fiber surface is obvious, thus improving the force response sensitivity of the fiber.

[0077] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing hollow mechanochromic liquid crystal elastic fibers, characterized in that, Includes the following steps: S1. Mix the liquid crystal monomer with an organic solvent, heat to 70~90℃ and cool to room temperature, then add a crosslinking agent, chain extender, photoinitiator and catalyst, stir and let stand for 15~25 min to obtain a precursor; the liquid crystal monomer includes a non-chiral nematic liquid crystal monomer and a chiral liquid crystal monomer. The crosslinking agent is pentaerythritol tetrakis(3-mercaptopropionic acid) ester, the chain extender is 3,6-dioxa-1,8-octanedithiol, and the catalyst is di-n-propylamine solution; The non-chiral nematic liquid crystal monomer is 2-methyl-1,4-phenylene bis(4-(3-(acryloyloxy)propoxy)benzoate, and the chiral liquid crystal monomer is (3R,3AR,6S,6AR)-hexahydrofuran[3,2-B]furan-3,6-diylbis(4-((4-((((4-(acryloyloxy)butoxy)carbonyl)oxy)benzoyl)oxy)benzoate); The organic solvent is dichloromethane, and the photoinitiator is 2,2-dimethyl-2-phenylacetophenone; S2. The precursor from step S1 is injected into a preparation apparatus for hollow mechanochromic liquid crystal elastic fibers. The preparation apparatus includes a cylindrical hollow tube, a channel inlet disposed on the surface of the cylindrical hollow tube, and a glass capillary sleeved inside the cylindrical hollow tube. The channel inlet forms a certain angle with the cylindrical hollow tube, and a cavity is formed between the glass capillary and the cylindrical hollow tube. After the precursor enters the cavity, the glass capillary moves horizontally within the cylindrical hollow tube, so that the precursor is uniformly coated on the surface of the glass capillary. S3. The glass capillary with surface-coated prepolymer obtained in step S2 is left to stand at room temperature for 22-26 h, then irradiated with ultraviolet light for 3-7 min. The irradiated glass capillary is then immersed in hydrofluoric acid for 1.5-2.5 h, and washed with water until neutral to obtain the hollow mechanochromic liquid crystal elastic fiber.

2. The method for preparing hollow mechanochromic liquid crystal elastic fibers according to claim 1, characterized in that, In step S1, the mass ratio of the non-chiral nematic liquid crystal monomer to the chiral liquid crystal monomer is (20~25):

1.

3. The method for preparing hollow mechanochromic liquid crystal elastic fibers according to claim 2, characterized in that, The specific operation process of step S1 is as follows: 2.6~2.7 g of non-chiral nematic liquid crystal monomer, 0.1~0.2 g of chiral liquid crystal monomer and 0.15~0.25 mL of organic solvent are mixed, heated to 70~90℃ and cooled to room temperature. Then, 12~18 μL of pentaerythritol tetrakis(3-mercaptopropionic acid), 68~70 mg of 3,6-dioxa-1,8-octanedithiol, 0.2~0.3 mg of photoinitiator and 60~70 μL of di-n-propylamine solution are added. After stirring, the mixture is allowed to stand for 15~25 min to obtain the precursor.

4. The method for preparing hollow mechanochromic liquid crystal elastic fibers according to claim 3, characterized in that, The di-n-propylamine solution was prepared by diluting di-n-propylamine 40 to 60 times with dichloromethane.

5. The method for preparing hollow mechanochromic liquid crystal elastic fibers according to claim 1, characterized in that, In step S3, the power of the ultraviolet lamp is 50 mW / cm². 2 The wavelength is 365 nm.

6. A hollow mechanochromic liquid crystal elastic fiber prepared by the preparation method according to any one of claims 1 to 5, characterized in that, The hollow mechanochromic liquid crystal elastic fiber has a hollow thin-walled structure and contains liquid crystals that are radially distributed along the helical axis of the fiber.

7. The hollow mechanochromic liquid crystal elastic fiber according to claim 6, characterized in that, The hollow mechanochromic liquid crystal elastic fiber has a diameter of 0.5~1.5 mm and a hollow thin wall thickness of 40~80 μm.

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