Artificial muscle fiber based on liquid crystal elastomer and its preparation method and application

Abstract

The present invention discloses an artificial muscle fiber based on liquid crystal elastomers that is electrically driven and heat-resistant. The fiber improves its overall mechanical strength without affecting its drive performance, enabling rapid and precise actuation and exhibiting rapid response characteristics. The electrically driven liquid crystal elastomer artificial muscle has high sensitivity, high drive capacity, and high output force, achieving 60% of its maximum drive capacity within 0.3 seconds. While meeting the requirements for a large drive capacity, it also possesses a high driving force, offering broad research prospects in the fields of flexible electronics, soft robotics, and rehabilitation medicine. The preparation method of the present invention is simple and easy to operate, enabling mass production.

Description

Technical Field

[0001] The present invention belongs to the technical field of artificial muscles, and in particular relates to artificial muscle fibers based on liquid crystal elastomers, and a preparation method and application thereof. Background Art

[0002] In the fields of materials science and intelligent robotics, the rapid development of flexible electronics has spawned a series of innovative materials with unprecedented performance, providing new impetus for the development of soft robotics. In-depth research has led to the emergence of a new type of composite fiber material that exhibits exceptional properties in human-robot interaction, deformation resilience, and mechanical properties. This composite fiber material is widely considered to be a key driving unit in soft robotics, namely artificial muscle fibers. They not only provide powerful power output but also operate in a low-noise environment, giving robots unprecedented freedom and flexibility. Furthermore, artificial muscle fibers can be combined with flexible electronics to achieve self-perception and feedback, which is crucial for building autonomous and dexterous soft robots.

[0003] Artificial muscle fibers have extremely high performance requirements, including fast actuation response, large actuation strain and stress, excellent flexibility, and controllability. These requirements have driven the research and development of liquid crystal elastomer (LCE) fibers. LCE fibers are composed of oriented liquid crystal polymers and have a high thermal contraction effect along the molecular chain direction. Therefore, they have high deformation capacity, excellent mechanical properties, and reversible deformation characteristics, making them an ideal material for manufacturing artificial muscles. Although LCE fibers have shown great potential in the manufacture of artificial muscles, the actuation mechanisms proposed in existing research often rely on external factors such as ambient heating, light, magnetism, or humidity, which limits the controllability of the robotic system. Electrothermal technology has particular application potential in artificial muscle fibers for soft robots. Artificial muscle fibers driven by electrothermal technology can achieve fast response and precise control, which is crucial for improving the performance of robots.

[0004] The advantages of electrothermally driven liquid crystal elastomer (LCE) artificial muscles lie in their rapid response, high power output, and excellent controllability. This actuation method directly converts electrical energy into heat, leveraging the thermal expansion or phase change of the material to achieve rapid contraction and relaxation of the artificial muscle. Compared to traditional methods such as photothermal, magnetothermal, and direct heating, electrothermal actuation avoids reliance on external light sources or magnetic fields, providing more stable and controllable power output. Electrothermally driven LCE artificial muscles also feature a simple structure and ease of integration. By adjusting the magnitude and direction of the current, the degree of contraction and movement pattern of the muscle can be precisely controlled, achieving a high degree of controllability and flexibility. Furthermore, electrothermal actuation offers a fast response speed, enabling material deformation in milliseconds, which is particularly important for applications requiring rapid response. Furthermore, electrothermally driven LCE artificial muscles exhibit excellent environmental adaptability. They can operate stably in a variety of environmental conditions, including extreme temperatures and humidity, opening up new possibilities for artificial muscle applications.

[0005] In exploring electrothermal actuation of liquid crystal elastomers (LCEs), researchers have developed a variety of strategies to achieve efficient and controllable actuation performance. For example, by combining liquid metals (such as mercury and gallium) with LCEs, the electrothermal effect of the liquid metal can be exploited to drive the deformation of the LCE. This approach has the advantage that the fluidity of the liquid metal does not restrict the deformation of the LCE. However, the presence of the liquid metal may reduce the mechanical strength of the LCE. Embedding serpentine metal wires in the LCE is also a common electrothermal actuation method. The metal wires generate heat when an electric current passes through them, causing the LCE to deform. However, the addition of metal wires may affect the uniformity of the LCE, thereby reducing its overall actuation performance. Composites of LCEs with nanocarbon materials: Nanocarbon materials such as graphene and carbon nanotubes are used in electrothermal actuation of LCEs due to their excellent electrical conductivity and thermal properties. Composites of these materials can improve electrothermal conversion efficiency, but their electrical conductivity is lower than that of metals, which may affect actuation performance. Summary of the Invention

[0006] Purpose of the invention: The purpose of the present invention is to provide an artificial muscle fiber based on liquid crystal elastomer and electrothermally driven, which improves the overall mechanical strength of the fiber without affecting its driving performance, and can achieve fast and precise driving.

[0007] Technical solution: The artificial muscle fiber based on liquid crystal elastomer described in the present invention is prepared from spring-shaped conductive fibers and liquid crystal elastomer oligomers.

[0008] Preferably, the conductive fiber is one of metal wire, nylon fiber, carbon fiber, conductive polymer, shape memory alloy wire or carbon nanotube wire.

[0009] The present invention also provides a method for preparing artificial muscle fibers based on liquid crystal elastomers, comprising the following steps:

[0010] 1) Preparation of spring-shaped conductive fibers;

[0011] 2) Preparation of liquid crystal elastomer oligomers;

[0012] 3) Preparation of artificial muscle fibers based on liquid crystal elastomers: The liquid crystal elastomer oligomer solution obtained in step 2) is perfused into a tetrafluoroethylene tube containing the conductive fibers prepared in step 1); after the cross-linking reaction, the tetrafluoroethylene tube is peeled off to obtain conductive liquid crystal elastomer fibers in a multi-domain state; after removing the solvent, the conductive liquid crystal elastomer fibers in the multi-domain state are stretched and secondary cross-linked to obtain the final artificial muscle fibers based on liquid crystal elastomers.

[0013] Preferably, the inner diameter of the tetrafluoroethylene tube is 1-6 mm.

[0014] Preferably, the stretching step is to mechanically stretch the multi-domain conductive liquid crystal elastomer fibers by 3 times using a mechanical stretching method.

[0015] Preferably, the preparation method of the spring-shaped conductive fiber is as follows: the conductive fiber is wound on a stainless steel core shaft, and after high-temperature heating and annealing, the core shaft is removed to obtain a densely wound spring-shaped conductive fiber.

[0016] Preferably, the diameter of the conductive fiber is 0.1-1.0 mm, the diameter of the stainless steel core shaft is 0.6-3.0 mm, and the temperature of the high-temperature heating annealing is 120-180° C., and the time is 1.5-3 hours.

[0017] Preferably, the liquid crystal elastomer oligomer is prepared by the aza-Michael addition method, and the specific process is as follows: the liquid crystal monomer, chain extender, cross-linker and photoinitiator are dissolved in a solvent, stirred and dissolved at 40-80°C to prepare a uniform solution, and then a catalyst is added and stirred continuously to obtain a liquid crystal elastomer oligomer solution.

[0018] Preferably, the liquid crystal monomer is any one or two of 1,4-bis[4-(3-acryloyloxypropoxy)benzoyl]-2-toluene or 2-methyl-1,4-phenylenebis(4-((6-(acryloyloxy)hexyl)oxy)benzoate); the chain extender is any one or more of 3,6-dioxa-1,8-octanedithiol, ethylene glycol bis(3-mercaptopropionate), 1,4-butanediol bis(thioglycolate), ethylene glycol bis(thioglycolate), bis(2-mercaptoethyl) ether, 1,3-propanediol, 1,6-hexanedithiol, and 1,10-decanedithiol.

[0019] Preferably, the solvent is selected from any one or more of dichloromethane, ethyl acetate, toluene or acetone; the crosslinking agent is pentaerythritol tetrakis(3-mercaptopropionate), the photoinitiator is 2,2-dimethoxy-2-phenylacetophenone, and the catalyst is di-n-propylamine.

[0020] The present invention also provides the application of artificial muscle fibers based on liquid crystal elastomers in the preparation of flexible electronics and soft robots.

[0021] Beneficial effects:

[0022] The electrothermally driven artificial muscle fiber based on liquid crystal elastomer provided by the present invention first constructs a conductive spring, and then uses a template method to coat the liquid crystal elastomer, wherein the conductive spring can play the role of supporting the skeleton and improving the mechanical output, and when the liquid crystal elastomer is deformed, the spring will not hinder its deformation effect; the present invention can improve the overall mechanical strength of the fiber without affecting its driving performance, and can achieve fast and precise driving, with the characteristics of fast response. The electrothermally driven liquid crystal elastomer artificial muscle has high sensitivity, high driving amount and high output force, and can achieve 60% of the maximum driving amount within 0.3 seconds. It has a large driving force while meeting the large driving amount, making it have broad research prospects in the fields of flexible electronics, soft robots and rehabilitation medicine. The preparation method of the present invention has a simple and easy-to-operate preparation process, and can achieve large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart for preparing the spring-shaped conductive fiber of the present invention.

[0024] Figure 2 This is a flow chart for preparing the artificial muscle fibers of the present invention.

[0025] Figure 3 This is an optical photograph of the artificial muscle fiber of the present invention.

[0026] Figure 4 It is the driving amount of the artificial muscle fiber of the present invention under different voltages when the frequency is 0.1 Hz (duty cycle is 5%).

[0027] Figure 5 It is the driving amount of the artificial muscle fiber of the present invention at different voltages when the frequency is 0.1 Hz (duty cycle is 10%).

[0028] Figure 6 This is a comparison of the driving performance of conductive liquid crystal elastomer fibers prepared from conductive nylon fibers with different diameters. DETAILED DESCRIPTION

[0029] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the embodiments and drawings. The embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention. Example 1

[0030] 1) Preparation of conductive spring: Conductive nylon fiber with a diameter of 0.1 mm is used as the conductive fiber and is evenly wound on a stainless steel core shaft with a diameter of 0.6 mm ( Figure 1 A), fix the two ends and anneal in an oven at 120℃ for 3 hours, take out the mandrel, and obtain a densely wound conductive nylon spring ( Figure 1 B), the conductive spring has excellent elasticity and can be stretched more than 500% ( Figure 1 C).

[0031] 2) Preparation of Liquid Crystalline Elastomer Oligomer: Liquid crystal elastomer oligomers were prepared using the aza-Michael addition method. The specific process is as follows: 2.0 mmol of liquid crystal monomer (RM257, 1,4-bis[4-(3-acryloyloxypropoxy)benzoyl]-2-toluene), 1.73 mmol of chain extender (EDDET, 3,6-dioxa-1,8-octanedithiol), 0.173 mmol of cross-linker (PETMP, pentaerythritol tetrakis(3-mercaptopropionate)), and 0.04 mmol of photoinitiator (IG-651, 2,2-dimethoxy-2-phenylacetophenone) were dissolved in 1.2 mL of dichloromethane. The mixture was stirred at 50°C for 20 minutes to prepare a homogeneous solution. Finally, 0.04 mmol of catalyst (DPA, di-n-propylamine) was added and stirring was continued for 1 minute to obtain a liquid crystal elastomer oligomer solution (transparent liquid) for later use.

[0032] 3) Preparation of conductive liquid crystal elastomer fibers: The conductive nylon spring prepared in (1) was placed in a tetrafluoroethylene tube with an inner diameter of 1.0 mm ( Figure 2 A and Figure 2 B), the liquid crystal elastomer oligomer solution obtained in (2) was injected into the tetrafluoroethylene tube containing the conductive nylon spring using a syringe ( Figure 2 C). After preliminary cross-linking for 24 hours in a dark environment, the tetrafluoroethylene tube was peeled off to obtain a multi-domain conductive liquid crystal elastomer fiber ( Figure 2 D), and placed it in an 80°C oven to remove excess solvent for 24 hours. The multi-domain conductive liquid crystal elastomer fibers were mechanically stretched 3 times ( Figure 2 E), and then secondary cross-linking is carried out under ultraviolet light for 15 minutes to obtain uniaxially oriented conductive liquid crystal elastomer fibers, that is, the final conductive liquid crystal elastomer fibers are obtained for standby use ( Figure 2 F).

[0033] Figure 3This is an optical photograph of a conductive liquid crystal elastomer fiber from this example, with a fiber diameter of 0.7 microns. When mechanically stretched, the conductive liquid crystal elastomer transforms the mesogen from a nematic phase to an isotropic phase, resulting in macroscopic deformation and, in turn, excellent driving performance. WAXS was used to characterize its internal orientation. Example 2

[0034] 1) Preparation of conductive springs: 0.1 mm diameter carbon fiber was used as the conductive fiber. It was first twisted to a certain twist (not twisted into a spiral state) and evenly wound around a 1.0 mm diameter stainless steel mandrel. After securing both ends, it was oven-annealed at 150°C for 2 hours. The mandrel was removed to obtain a densely wound conductive carbon fiber spring.

[0035] 2) Same as step (2) in Example 1.

[0036] 3) Preparation of conductive liquid crystal elastomer fibers: The conductive carbon fiber spring prepared in (1) was placed in a tetrafluoroethylene tube with an inner diameter of 1.0 mm. The liquid crystal elastomer oligomer solution obtained in (2) was injected into the tetrafluoroethylene tube containing the conductive carbon fiber spring using a syringe. After preliminary cross-linking for 24 hours in a dark environment, the tetrafluoroethylene tube was peeled off to obtain a multi-domain conductive liquid crystal elastomer fiber. The fiber was placed in a 60°C oven to remove excess solvent for 24 hours. The multi-domain conductive liquid crystal elastomer fiber was mechanically stretched 3 times by mechanical stretching and then secondary cross-linked under ultraviolet light for 15 minutes to obtain the final conductive liquid crystal elastomer fiber for use. Example 3

[0037] 1) Preparation of conductive spring: Conductive nylon fiber with a diameter of 0.1 mm is used as the conductive fiber and is evenly wound on a stainless steel core shaft with a diameter of 0.6 mm ( Figure 1 A), fix the two ends and anneal in an oven at 140℃ for 2.5 hours, take out the mandrel, and obtain a densely wound conductive nylon spring ( Figure 1 B), the conductive spring has excellent elasticity and can be stretched more than 500% ( Figure 1 C).

[0038] 2) Preparation of Liquid Crystalline Elastomer Oligomer: Liquid crystal elastomer oligomers were prepared using the aza-Michael addition method. The specific process is as follows: 2.0 mmol of liquid crystal monomer (RM257, 1,4-bis[4-(3-acryloyloxypropoxy)benzoyl]-2-toluene), 1.73 mmol of chain extender (DDT, 1,10-decanedithiol), 0.173 mmol of cross-linker (PETMP, pentaerythritol tetrakis(3-mercaptopropionate)), and 0.04 mmol of photoinitiator (IG-651, 2,2-dimethoxy-2-phenylacetophenone) were dissolved in 1.2 mL of ethyl acetate. The mixture was stirred at 50°C for 20 minutes to obtain a homogeneous solution. Finally, 0.04 mmol of catalyst (DPA, di-n-propylamine) was added and stirring was continued for 1 minute to obtain a liquid crystal elastomer oligomer solution (transparent liquid) for later use.

[0039] 3) Same as step (3) in Example 1. Example 4

[0040] 1) Same as step (1) in Example 1.

[0041] 2) Preparation of Liquid Crystalline Elastomer Oligomer: Liquid crystal elastomer oligomers were prepared using the aza-Michael addition method. The specific process is as follows: 2.0 mmol of liquid crystal monomer (RM257, 1,4-bis[4-(3-acryloyloxypropoxy)benzoyl]-2-toluene), 1.73 mmol of chain extender (HDT, 1,6-hexanedithiol), 0.173 mmol of cross-linker (PETMP, pentaerythritol tetrakis(3-mercaptopropionate)), and 0.04 mmol of photoinitiator (IG-651, 2,2-dimethoxy-2-phenylacetophenone) were dissolved in 1.2 mL of toluene. The mixture was stirred at 50°C for 20 minutes to prepare a homogeneous solution. Finally, 0.04 mmol of catalyst (DPA, di-n-propylamine) was added and stirring was continued for 1 minute to obtain a liquid crystal elastomer oligomer solution (transparent liquid) for later use.

[0042] 3) Same as step (3) in Example 1. Example 5

[0043] The conductive liquid crystal elastomer fiber prepared in Example 1 was used to test the driving performance. The driving performance of the conductive liquid crystal elastomer under different voltages was tested at a frequency of 0.1 Hz (duty cycle of 5%). Figure 4 At a voltage of 1.0 V / cm, the maximum driving amount can reach 65%. At the same time, the driving amount increases with the increase of voltage, indicating that the conductive liquid crystal elastomer fiber has the ability to work with a large driving amount. Example 6

[0044] The conductive liquid crystal elastomer fiber prepared in Example 1 was used to test the driving performance. The driving performance of the conductive liquid crystal elastomer under different voltages was tested at a frequency of 0.1 Hz (duty cycle of 10%). Figure 5 As shown in Figure 2, at a voltage of 1.0 V / cm, the maximum actuation reached 70%. The actuation increased with increasing voltage, demonstrating that the conductive liquid crystal elastomer fiber is capable of operating at high actuation levels. Compared to Example 2, the actuation level increased with increasing duty cycle and prolonged power-on time. Example 7

[0045] (1) Preparation of conductive spring: Conductive nylon fiber with a diameter of 0.2 mm was used as the conductive fiber. It was evenly wound on a stainless steel core shaft with a diameter of 0.6 mm. After fixing both ends, it was annealed in an oven at 120°C for 3 hours. The core shaft was taken out to obtain a densely wound conductive nylon spring.

[0046] (2) Same as step (2) in Example 1.

[0047] (3) Preparation of conductive liquid crystal elastomer fibers: The conductive nylon spring prepared in (1) was placed in a tetrafluoroethylene tube with an inner diameter of 1.2 mm. The remaining steps were the same as step (3) of Example 1. Example 8

[0048] (1) Preparation of conductive spring: Conductive nylon fiber with a diameter of 0.3 mm was used as the conductive fiber. It was evenly wound on a stainless steel core shaft with a diameter of 0.6 mm. After fixing both ends, it was annealed in an oven at 120°C for 3 hours. The core shaft was removed to obtain a densely wound conductive nylon spring.

[0049] (2) Same as step (2) in Example 1.

[0050] (3) Preparation of conductive liquid crystal elastomer fibers: The conductive nylon spring prepared in (1) was placed in a tetrafluoroethylene tube with an inner diameter of 1.4 mm. The remaining steps were the same as step (3) of Example 1. Example 9

[0051] (1) Preparation of conductive spring: Conductive nylon fiber with a diameter of 0.4 mm was used as the conductive fiber. It was evenly wound on a stainless steel core shaft with a diameter of 0.6 mm. After fixing both ends, it was annealed in an oven at 150°C for 2 hours. The core shaft was taken out to obtain a densely wound conductive nylon spring.

[0052] (2) Same as step (2) in Example 1.

[0053] (3) Preparation of conductive liquid crystal elastomer fibers: The conductive nylon spring prepared in (1) was placed in a tetrafluoroethylene tube with an inner diameter of 1.6 mm. The remaining steps were the same as step (3) of Example 1. Example 10

[0054] (1) Preparation of conductive spring: Conductive nylon fiber with a diameter of 0.5 mm was used as the conductive fiber. It was evenly wound on a stainless steel core shaft with a diameter of 0.6 mm. After fixing both ends, it was annealed in an oven at 120°C for 3 hours. The core shaft was taken out to obtain a densely wound conductive nylon spring.

[0055] (2) Same as step (2) in Example 1.

[0056] (3) Preparation of conductive liquid crystal elastomer fibers: The conductive nylon spring prepared in (1) was placed in a tetrafluoroethylene tube with an inner diameter of 1.8 mm. The remaining steps were the same as step (3) of Example 1.

[0057] The driving performance characteristics (driving amount and contraction force) of conductive liquid crystal elastomer fibers prepared from conductive nylon fibers with different diameters are compared, such as Figure 6 As shown. Figure 6 It can be seen that the conductive liquid crystal elastomer fiber greatly improves the driving force while meeting a large driving amount (>30%).

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An artificial muscle fiber based on liquid crystal elastomer, characterized in that: It is made of spring-shaped conductive fibers and liquid crystal elastomer oligomers; the conductive fibers are selected from metal wires, nylon fibers, carbon fibers, conductive polymers, shape memory alloy wires, or carbon nanotube wires; The method for preparing the artificial muscle fiber based on liquid crystal elastomer comprises the following steps: 1) Preparation of spring-shaped conductive fibers; 2) Preparation of liquid crystal elastomer oligomers; 3) Preparation of artificial muscle fibers based on liquid crystal elastomers: The liquid crystal elastomer oligomer solution obtained in step 2) is perfused into a tetrafluoroethylene tube containing the conductive fibers prepared in step 1); after the cross-linking reaction, the tetrafluoroethylene tube is peeled off to obtain conductive liquid crystal elastomer fibers in a multi-domain state; after removing the solvent, the conductive liquid crystal elastomer fibers in the multi-domain state are stretched and secondary cross-linked to obtain the final artificial muscle fibers based on liquid crystal elastomers.

2. The preparation method according to claim 1, characterized in that The inner diameter of the tetrafluoroethylene tube is 1-6 mm.

3. The preparation method according to claim 1, characterized in that The stretching step is to mechanically stretch the multi-domain conductive liquid crystal elastomer fibers by 3 times using a mechanical stretching method.

4. The preparation method according to claim 1, characterized in that The preparation method of the spring-shaped conductive fiber is as follows: the conductive fiber is wound on a stainless steel core shaft, and after high-temperature heating and annealing, the core shaft is removed to obtain a densely wound spring-shaped conductive fiber.

5. The preparation method according to any one of claim 4, characterized in that The diameter of the conductive fiber is 0.1-1.0 mm, the diameter of the stainless steel core shaft is 0.6-3.0 mm, the temperature of the high-temperature heating annealing is 120-180° C., and the time is 1.5-3 hours.

6. The preparation method according to claim 1, characterized in that The liquid crystal elastomer oligomer is prepared by the aza-Michael addition method, and the specific process is as follows: liquid crystal monomers, chain extenders, crosslinkers and photoinitiators are dissolved in a solvent, stirred and dissolved at 40-80°C to prepare a uniform solution, and then a catalyst is added and stirred continuously to obtain a liquid crystal elastomer oligomer solution.

7. The preparation method according to claim 6, characterized in that The liquid crystal monomer is any one or two of 1,4-bis[4-(3-acryloyloxypropoxy)benzoyl]-2-toluene or 2-methyl-1,4-phenylenebis(4-((6-(acryloyloxy)hexyl)oxy)benzoate); the chain extender is any one or more of 3,6-dioxa-1,8-octanedithiol, ethylene glycol bis(3-mercaptopropionate), 1,4-butanediol bis(thioglycolate), ethylene glycol bis(thioglycolate), bis(2-mercaptoethyl) ether, 1,3-propanediol, 1,6-hexanedithiol, and 1,10-decanedithiol.

8. The preparation method according to claim 6, characterized in that The solvent is selected from any one or more of dichloromethane, ethyl acetate, toluene or acetone; the crosslinking agent is pentaerythritol tetrakis(3-mercaptopropionate), the photoinitiator is 2,2-dimethoxy-2-phenylacetophenone, and the catalyst is di-n-propylamine.

9. Use of the artificial muscle fiber according to claims 1-8 in the preparation of flexible electronics and soft robots.

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