Preparation method and application of liquid crystal elastomer plant bionic tendrils

Abstract

The present invention discloses a method for preparing and applying liquid crystal elastomer (LCE) plant bionic tendrils, wherein a liquid crystal monomer, a chain extender / cross-linking agent, and a photothermal filler are dissolved / uniformly dispersed in a volatile organic solvent, and reacted at a relatively low temperature to obtain a liquid crystal elastomer prepolymer; the liquid crystal elastomer prepolymer is added to a 3D printer barrel, and a single-domain liquid crystal elastomer fiber is obtained by extrusion printing, and the fiber is further cross-linked by subsequent heating to fix the orientation structure, thereby obtaining a liquid crystal elastomer plant bionic tendril. The present invention overcomes the problem of a single orientation structure of LCE fibers prepared by existing printing methods, and provides a method for the personalized and large-scale production of liquid crystal elastomer fibers with a skin-core structure. The present invention reduces the process of setting up a stretching device to stretch the fiber precursor and the investment in the stretching equipment, simplifies the production process, improves production efficiency, and reduces production costs. The preparation method is simple and has strong repeatability in large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of liquid crystal elastomer fibers and discloses a preparation method and application of a liquid crystal elastomer plant bionic tendril, in particular, discloses a preparation method and application of a liquid crystal elastomer plant bionic tendril with a skin-core structure. Background Art

[0002] In nature, organisms are able to perform complex and precise biological movements in response to environmental stimuli such as humidity, temperature, or touch, enabling a variety of important life activities. These include the folding of mimosa leaves, the dispersal of seeds, the coiling of cucumber tendrils, the spreading of wheat awns, the opening of chiral seed pods, and the capture of Venus flytraps. These behaviors are primarily derived from the complex hierarchical structures of organisms and their interactions with their environments. By studying the fundamental principles of structure-function relationships in biology, scientists have recently begun designing and fabricating various stimuli-responsive shape-shifting materials, hoping for their widespread application in various biomimetic fields.

[0003] Liquid crystal elastomers (LCEs) are intelligent polymers capable of undergoing reversible changes in physical or chemical properties in response to external stimuli, such as heat, light, and electricity. Due to their convenient preparation process and reversible deformation, LCEs have become an ideal two-way shape memory material. In 1991, Finkelmann et al. prepared the first single-domain nematic LCE by introducing a two-stage hydrogenated polysilane method, capable of actuation under thermal stimulation. This method became the preferred approach for preparing single-domain LCEs for the next two decades. In this method, a lightly cross-linked liquid crystal gel is stretched to align the mesogens along the stretching direction, and then further cross-linking is performed while maintaining the stretching to permanently fix the alignment. However, this approach often presents significant challenges in practice. The pre-cross-linked liquid crystal gel has poor mechanical properties, making it difficult to impart a high degree of alignment through significant stretching. Furthermore, uniaxial mechanical stretching limits the preparation of complex alignment structures. These factors reduce the applicability of LCEs in applications involving shape deformation and actuation. However, biological systems often exhibit more complex three-dimensional deformations, such as the spiral coiling of plant tendrils. Despite recent exciting achievements in the preparation of LCE actuators inspired by natural organisms, fabricating LCE artificial tendrils by fundamentally mimicking the asymmetric hierarchical structure based on basic structure-function principles remains a major scientific challenge. Through scientists' research on tendril anatomy, they found that the helical structure of plant tendrils occurs through lignification and the corresponding asymmetric contraction of specialized glia (g-fiber) cells in the inner layer. Therefore, the most vexing challenge in fabricating LCE artificial tendrils is to fully mimic the asymmetric hierarchical structure of plant tendrils based on biological mechanisms. Summary of the Invention

[0004] The present invention aims to address at least one of the technical problems existing in the aforementioned prior art. To this end, the present invention provides a method for preparing and applying a liquid crystal elastomer plant-inspired tendril with an asymmetric skin-core structure. The liquid crystal elastomer plant-inspired tendril and its composite material can achieve three-dimensional spiral deformation under the stimulation of heat or light, structurally mimicking the asymmetric layered structure of plant tendrils. This overcomes the drawback of existing liquid crystal elastomer materials, which suffer from a single deformation mode, and exhibits rapid deformation speed and large deformation amplitude.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing liquid crystal elastomer fibers, comprising:

[0007] (1) dissolving / uniformly dispersing a liquid crystal monomer, a chain extender / crosslinking agent, and a photothermal filler in a volatile organic solvent and reacting them at a low temperature to prepare a liquid crystal elastomer prepolymer;

[0008] (2) adding a liquid crystal elastomer prepolymer into a 3D printer barrel, and obtaining a single-domain liquid crystal elastomer fiber by extrusion printing;

[0009] (3) The single-domain liquid crystal elastomer is subjected to heat cross-linking treatment to obtain a liquid crystal elastomer plant bionic tendril with a skin-core structure.

[0010] Furthermore, the end group of the liquid crystal monomer in step (1) is acrylate, including any one or more of liquid crystal monomer RM82, liquid crystal monomer RM257, liquid crystal monomer RM006, liquid crystal monomer RM021, liquid crystal monomer RM010, liquid crystal monomer HCM009, liquid crystal monomer HCM008, liquid crystal monomer HCM020, and liquid crystal monomer HCM021.

[0011] Furthermore, the chain extender in step (1) includes one or more of dipropylamine, benzylamine, triethylamine, and diethylamine; and the cross-linking agent includes one or more of dipropylamine, benzylamine, triethylamine, and diethylamine.

[0012] Furthermore, the photothermal filler in step (1) includes one or more of carbon-based graphene, carbon nanotubes or carbon black materials, metal nanoparticles and small molecule organic dyes.

[0013] Furthermore, the volatile organic compound in step (1) includes one or more of dimethylformamide, tetrahydrofuran, dichloromethane and chloroform.

[0014] Furthermore, the molar ratio of the liquid crystal monomer to the chain extender / cross-linking agent in step (1) is 1:0.2-1.5;

[0015] The photothermal filler accounts for 0-10% of the mass ratio of the liquid crystal elastomer prepolymer; and the volatile organic solvent accounts for 0-50% of the mass ratio of the liquid crystal elastomer prepolymer.

[0016] Furthermore, the 3D printer in step (2) includes: a printer based on fused deposition modeling technology, a printer based on selective laser sintering technology, a printer based on photo-stereolithography technology, and a printer based on thin-film lamination manufacturing technology; the printing temperature is 50-100°C, the printing pressure is 0-8 bar, and the printing speed is 1-30 mm / s.

[0017] Furthermore, the heating temperature in step (3) is 60-120° C., and the heating time is 5-48 hours.

[0018] The present invention also discloses a liquid crystal elastomer plant bionic tendril fiber with a skin-core structure, which is prepared according to any of the above preparation methods.

[0019] The invention also discloses an application of the liquid crystal elastomer fiber in preparing a composite material.

[0020] The invention also discloses an application of the liquid crystal elastomer fiber in preparing a driver.

[0021] The invention also discloses an application of the composite material in preparing a driver.

[0022] The Michael addition reaction between diamines and liquid crystal monomers, and the addition of acrylates to primary amines, is essentially a two-stage reaction. In the first stage, the hydrogen atoms on the primary amine (fast, k1) react rapidly with double bonds to extend the chain, producing a liquid crystal prepolymer. The hydrogen atoms on the resulting secondary amine (slower, k2) then react with double bonds in the second stage to achieve crosslinking. The reaction kinetics between the primary and secondary amine hydrogen atoms with the acrylate differ significantly, with k1 being two orders of magnitude greater than k2. The first hydrogen is almost completely consumed before the second hydrogen slowly begins to react. Therefore, mixing the diamine and diacrylate-based liquid crystal monomers at a relatively low temperature yields a liquid crystal prepolymer ink. The slower second-stage crosslinking process allows for a wider time window for printing. After printing, the printed sample is placed in a high-temperature oven to ensure the second-stage crosslinking reaction proceeds. In this process, the diamine acts as both a chain extender and a crosslinker, eliminating the need for additional reagents and equipment such as crosslinkers, initiators, and UV light generators.

[0023] During the printing process, viscous liquid crystal oligomers are extruded from the print nozzle, and the liquid crystal elements are aligned under the shear force of the nozzle and the tensile force as the nozzle moves along a predetermined path. Subsequently, the printed fibers are exposed to room temperature, where the surface cools more rapidly, resulting in a temperature gradient between the exterior and interior of the fiber. Simultaneously, the solvent on the surface evaporates more rapidly, quickly solidifying the ordered structure formed by printing. In contrast, the liquid crystal molecular chains within the fiber experience slower cooling and solvent evaporation, giving them ample time to rearrange themselves driven by thermal motion. As a result, the printed fibers exhibit a skin-core structure, with a highly oriented skin enveloping a less oriented core. Furthermore, during the subsequent cross-linking process, since the sample is printed on a glass substrate, solvent evaporation causes the printed sample to undergo an anisotropic deswelling process, resulting in the formation of a semi-elliptical fiber cross-section.

[0024] The liquid crystal elastomer fibers and their composite materials prepared by the present invention will undergo a liquid crystal phase transition under thermal or light stimulation, and the liquid crystal units will change from anisotropy to isotropy. This phase transition will cause the liquid crystal elastomer fibers to quickly transform from a vertical state to a three-dimensional spiral structure, and return to the original vertical structure after the stimulation is removed.

[0025] The beneficial effects of the present invention are:

[0026] 1. The synthesis process of the present invention adopts a one-step method, which is simple and efficient, and does not require additional cross-linking agents, initiators and ultraviolet rays. The liquid crystal prepolymer ink and LCE fiber suitable for printing can be obtained by a two-stage reaction of acrylate-based liquid crystal monomers and diamines.

[0027] 2. The 3D printing method proposed in the present invention has a simple process and can continuously prepare liquid crystal elastomer fibers with uniform and controllable diameter and orientation degree by controlling the printing path and printing speed. It breaks through the problem of single orientation structure of liquid crystal elastomer fibers prepared by existing printing methods, and provides ideas for the personalized and large-scale production of liquid crystal elastomer fibers with skin-core structure.

[0028] 3. The 3D printing method proposed in the present invention can directly design the orientation structure of the material in one step through a 3D printer, reducing the process of setting up a stretching device to stretch the fiber precursor and the investment in stretching equipment, and does not require other steps such as twisting and ultraviolet light irradiation. It simplifies the production process, improves production efficiency, and reduces production costs. The preparation method is simple and has strong repeatability in large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 To print the schematic diagram;

[0030] Figure 2 The printed fiber shows its semi-elliptical cross-section and skin-core structure under a polarizing microscope;

[0031] Figure 3 The printed fiber shows its semi-elliptical cross-sectional structure under a scanning electron microscope;

[0032] Figure 4 The printed fibers exhibit spiral deformation under heating and cooling stimulation;

[0033] Figure 5 To print CNT-LCE fiber composites that exhibit helical deformation under near-infrared light stimulation;

[0034] Figure 6 The fibers prepared by mechanical stretching only exhibit simple, small-amplitude bending deformations;

[0035] Figure 7 This is the spiral structure of a plant tendril in real life. DETAILED DESCRIPTION

[0036] In order to make the technical solutions of the present invention more clearly understood by those skilled in the art, the following examples are given for illustration. It should be noted that the following examples are only preferred embodiments of the present invention and do not limit the scope of protection claimed by the present invention. Any modification, substitution, or combination made without violating the spirit and principle of the present invention is included in the scope of protection of the present invention.

[0037] The preparation method of the liquid crystal elastomer plant bionic tendril fiber with a skin-core structure and the composite material thereof provided in an embodiment of the present invention comprises the following steps:

[0038] Example 1

[0039] A method for preparing LCE fiber, comprising:

[0040] (1) 0.14 g of liquid crystal monomer RM82, 0.019 g of 1,5-diaminopentane, and 0.025 g of DMF were added to a glass bottle, heated to 80 °C, and mixed evenly with a mixer to obtain a liquid crystal oligomer ink suitable for 3D printing.

[0041] (2) Liquid crystal elastomer materials were printed using a commercial 3D bioprinter (Regenovo, Bio-Printer-WS). The ink was loaded into the printing barrel, and then the temperature was set to 50°C, and the printing platform temperature was maintained at 15°C. The ink was extruded using a nozzle with a diameter of 0.31 mm under nitrogen pressure, while the nozzle moved in a predetermined direction to deposit the polymer ink on the platform. The printing path was controlled by the structural model generated by the printer software. After printing was completed within 30 minutes, the printed sample was placed in an 85°C oven for 12 hours to complete further cross-linking.

[0042] Figure 1 Schematic diagram of 3D printing of LCE fibers in Example 1 of the present invention. Figure 2 This is a polarizing microscope photograph of the cross section of the LCE fiber in Example 1 of the present invention, illustrating that the fiber has a semi-elliptical cross section and a skin-core structure. Figure 3 This is a scanning electron microscope photograph of the LCE fiber in Example 1 of the present invention, illustrating its semi-elliptical cross-sectional structure. Figure 4 In Example 1 of the present invention, the LCE fiber exhibits spiral deformation under heating and cooling stimulation. The vertical fiber with a length of 30 mm is transformed into a spiral structure with a length of 7 mm after heating, and recovers the initial vertical structure after cooling.

[0043] Example 2

[0044] A method for preparing CNT-LCE composite fiber, comprising:

[0045] (1) First, 0.14 g of liquid crystal monomer RM82 was dissolved in 6 mL of tetrahydrofuran, followed by the addition of 0.0015 g of carbon nanotubes. The mixture was stirred for 30 min and ultrasonicated for 120 min to achieve uniform dispersion of the carbon nanotubes. Finally, the mixed solution was poured into a PTFE mold and placed in a 60 °C oven for 1 hour to evaporate the solvent. The prepared CNT-RM82 mixture, 0.019 g of 1,5-diaminopentane, and 0.035 g of DMF were added to a glass bottle, heated to 80 °C, and mixed evenly with a mixer to obtain an ink suitable for 3D printing.

[0046] (2) CNT-LCE composite fiber printing was performed using a commercial 3D bioprinter (Regenovo, Bio-Printer-WS). The ink was loaded into the printing barrel, and then the temperature was set to 50°C, and the printing platform temperature was maintained at 15°C. The ink was extruded using a nozzle with a diameter of 0.41 mm under nitrogen pressure, while the nozzle moved in a predetermined direction to deposit the polymer ink on the platform. The printing path was controlled by a structural model generated by the printer software. After printing was completed within 30 minutes, the printed sample was placed in an 85°C oven for 12 hours to complete further cross-linking.

[0047] Figure 5 This is a photograph of the CNT-LCE composite fiber in Example 2 of the present invention exhibiting spiral deformation under near-infrared light stimulation.

[0048] Comparative Example 1

[0049] The method disclosed in application number: 202110972433.3 (A spirally bendable liquid crystal elastomer fiber, its preparation method and application) was used to prepare a liquid crystal prepolymer using liquid crystal monomers, thiol, Michael addition reaction catalyst and photoinitiator. The prepolymer was drawn into a filament, twisted and fixed, and polymerized using ultraviolet light irradiation to fix the twisted structure, thereby obtaining a liquid crystal elastomer fiber with spiral deformation.

[0050] In the present invention, a two-stage reaction of acrylate-based liquid crystal monomers and diamines is utilized, without the need for additional cross-linking agents, initiators, and ultraviolet rays, to prepare liquid crystal elastomers and composite materials having a skin-core structure through 3D printing. These liquid crystal elastomers are capable of exhibiting rapid and substantial spiral deformation under heat or light stimulation, and do not require steps such as filament drawing, twisting, and ultraviolet light irradiation. This simplifies the production process, improves production efficiency, and reduces production costs.

[0051] Comparative Example 2

[0052] (1) 0.14 g of liquid crystal monomer RM82, 0.019 g of 1,5-diaminopentane, and 0.025 g of DMF were added to a glass bottle, heated to 80 °C, mixed with a mixer, and then heated for 10 minutes.

[0053] (2) The liquid crystal prepolymer in the glass bottle was pulled into fibers using tweezers, and the stretched fibers were placed in an oven at 85°C for 12 hours while maintaining the tension to complete further cross-linking.

[0054] The mechanically stretched fibers only exhibit simple bending deformations with a small amplitude under heating stimulation, and cannot exhibit the large deformations and complex orientation structures that can be achieved through 3D printing, such as Figure 6 shown.

Claims

1. A method for preparing a liquid crystal elastomer plant bionic tendril, comprising: (1) dissolving / uniformly dispersing a liquid crystal monomer, 1,5-diaminopentane, and a photothermal filler in a volatile organic solvent and reacting them at 80° C. to prepare a liquid crystal elastomer prepolymer; (2) adding a liquid crystal elastomer prepolymer into a 3D printer barrel, then setting the temperature to 50°C and maintaining the printing platform temperature at 15°C, and obtaining a single-domain liquid crystal elastomer fiber by extrusion printing; (3) The single-domain liquid crystal elastomer fiber was subjected to a heat cross-linking treatment at a temperature of 85°C for 12 h to obtain a liquid crystal elastomer plant bionic tendril with a skin-core structure; Wherein: the end group of the liquid crystal monomer in step (1) is acrylate, including: Any one or more of the liquid crystal monomer RM82, the liquid crystal monomer RM257, the liquid crystal monomer RM006, the liquid crystal monomer RM021, the liquid crystal monomer RM010, the liquid crystal monomer HCM009, the liquid crystal monomer HCM008, the liquid crystal monomer HCM020, and the liquid crystal monomer HCM021.

2. The preparation method according to claim 1, wherein: The molar ratio of the liquid crystal monomer to 1,5-diaminopentane in step (1) is 1:0.2-1.5; The photothermal filler accounts for 0-10% of the mass ratio of the liquid crystal elastomer prepolymer; The volatile organic solvent accounts for 0-50% by mass of the liquid crystal elastomer prepolymer.

3. The preparation method according to claim 1, wherein: The photothermal filler in step (1) includes one or more of graphene and carbon nanotubes.

4. The preparation method according to claim 1, wherein: The volatile organic compound in step (1) includes one or more of dimethylformamide, tetrahydrofuran, dichloromethane and chloroform.

5. The preparation method according to claim 1, wherein: The 3D printer in step (2) includes: a printer based on fused deposition modeling technology, a printer based on selective laser sintering technology, a printer based on photo-stereolithography technology, and a printer based on thin-film lamination technology.

6. A liquid crystal elastomer plant bionic tendril prepared according to the preparation method according to any one of claims 1 to 5.

7. Use of the liquid crystal elastomer plant bionic tendril according to claim 6 in preparing an actuator.

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