Artificial muscle fiber based on liquid crystal elastomer, and preparation method therefor and use thereof

Abstract

An electrothermally driven artificial muscle fiber based on a liquid crystal elastomer. The overall mechanical strength of the fiber is improved without affecting the driving performance thereof, can be driven quickly and precisely, and has quick response characteristics. The electrothermally driven liquid crystal elastomer artificial muscle has high sensitivity, large actuation strain and high output force, can achieve a maximum actuation strain of 60% within 0.3s, and has a large driving force while satisfying a large actuation stroke, such that the electrothermally driven liquid crystal elastomer artificial muscle has broad research prospects in the fields of flexible electronics, soft robotics and rehabilitation therapy. The preparation method for the electrothermally driven artificial muscle fiber based on a liquid crystal elastomer involves a simple preparation process and easy operations, and can be mass-prepared.

Description

Liquid crystal elastomer-based artificial muscle fiber, and preparation method and application thereof TECHNICAL FIELD

[0001] The present application belongs to the technical field of artificial muscle, and particularly relates to a liquid crystal elastomer-based artificial muscle fiber, and a preparation method and application thereof. BACKGROUND

[0002] In the field of material science and intelligent robotics, the rapid development of flexible electronics has given birth to a series of innovative materials that possess unprecedented properties, providing new impetus for the development of soft robots. With further research, a new type of composite fiber material has emerged, which exhibits outstanding characteristics in human-machine interaction, deformation recovery, and mechanical properties. This composite fiber material is widely recognized as a key driving unit in soft robots, namely artificial muscle fiber. They not only provide powerful power output, but also work in a low-noise environment, giving robots unprecedented degrees of freedom and flexibility. In addition, artificial muscle fibers can be combined with flexible electronics to achieve self-sensing and feedback, which is crucial for building autonomous and agile soft robots.

[0003] Artificial muscle fibers have extremely high performance requirements, including fast driving response, large driving strain and stress, excellent flexibility and controllability. These requirements have driven the research and development of liquid crystal elastomer fibers (LCE). LCE fibers are composed of oriented liquid crystal polymers, which have high thermal shrinkage effect along the molecular chain direction, thus having high deformation capacity, excellent mechanical properties and reversible deformation characteristics, becoming an ideal material for manufacturing artificial muscles. Although LCE fibers have shown great potential in the manufacture of artificial muscles, the driving mechanisms proposed in existing research usually rely on external factors such as environmental heating, light, magnetism or humidity, which limits the controllability of the robot 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 electro-thermal driving of liquid crystal elastomer (LCE) artificial muscles include fast response, high power output, and excellent controllability. This driving method can directly convert electrical energy into thermal energy, using the thermal expansion or phase change of the material to achieve rapid contraction and relaxation of the artificial muscle. Compared with traditional methods such as photothermal, magnetic heating, and direct heating, electro-thermal driving avoids the dependence on external light sources or magnetic fields, providing more stable and controllable power output. Electro-thermal driven LCE artificial muscles also have the characteristics of simple structure and easy integration. By adjusting the size and direction of the current, the contraction degree and movement mode of the muscle can be accurately controlled, achieving high controllability and flexibility. In addition, electro-thermal driving has fast response speed, which can achieve material deformation in milliseconds, which is particularly important for applications that require fast response. In addition, electro-thermal driven LCE artificial muscles also have good environmental adaptability. They can work stably under different environmental conditions, including extreme temperature and humidity conditions, which provides more possibilities for the application of artificial muscles.

[0005] In the study of electro-thermal driving of liquid crystal elastomer (LCE), researchers have developed various strategies to achieve efficient and controllable driving performance. For example, by combining liquid metal (such as mercury and gallium) with LCE, the electro-thermal effect of liquid metal can be used to drive the deformation of LCE. The advantage of this method is that the fluidity of liquid metal does not limit the deformation of LCE, but at the same time, the presence of liquid metal may reduce the mechanical strength of LCE. Embedding a serpentine metal wire in LCE is also a common electro-thermal driving method. The metal wire generates heat when an electric current passes through, causing the LCE to deform. However, the addition of metal wires may affect the uniformity of LCE, thereby reducing its overall driving performance. LCE is compounded with nanocarbon materials: nanocarbon materials such as graphene and carbon nanotubes are used for electro-thermal driving of LCE due to their excellent electrical conductivity and thermal performance. The compounding of these materials can improve the electro-thermal conversion efficiency, but the electrical conductivity is not as good as metal, which may affect the driving performance. SUMMARY

[0006] The purpose of the present application is to provide an electro-thermal driven artificial muscle fiber based on liquid crystal elastomer, which improves the overall mechanical strength of the fiber without affecting its driving performance, and can achieve fast and accurate driving.

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

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

[0009] The application also provides a preparation method of artificial muscle fiber based on liquid crystal elastomer, comprising the following steps:

[0010] 1) preparation of spring-shaped conductive fiber;

[0011] 2) preparation of liquid crystal elastomer oligomer;

[0012] 3) preparation of artificial muscle fiber based on liquid crystal elastomer: the liquid crystal elastomer oligomer solution obtained in step 2) is infused into a tetrafluoroethylene tube containing the conductive fiber prepared in step 1); after cross-linking reaction, the tetrafluoroethylene tube is stripped to obtain a multi-domain conductive liquid crystal elastomer fiber, and after removing the solvent, the multi-domain conductive liquid crystal elastomer fiber is stretched and secondarily cross-linked to obtain the final artificial muscle fiber based on liquid crystal elastomer.

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

[0014] Preferably, the stretching step is mechanical stretching of the multi-domain conductive liquid crystal elastomer fiber by 3 times by mechanical drafting method.

[0015] Preferably, the preparation method of the spring-shaped conductive fiber is as follows: the conductive fiber is wound on a stainless steel mandrel, after high-temperature heating and annealing, the mandrel is taken out 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 mandrel is 0.6-3.0 mm, and the high-temperature heating and annealing temperature is 120-180℃, and the time is 1.5-3 hours.

[0017] Preferably, the liquid crystal elastomer oligomer is prepared by azomichael addition method, and the specific process is as follows: liquid crystal monomer, chain extender, crosslinking agent and photoinitiator are dissolved in a solvent, a uniform solution is prepared by stirring and dissolving at 40-80℃, then a catalyst is added and stirring is continued to obtain a liquid crystal elastomer oligomer solution.

[0018] Preferably, the liquid crystal monomer is any one or both of 1,4-bis[4-(3-acryloyloxypropoxy)benzoic acid]-2-methylbenzene or 2-methyl-1,4-phenylene bis(4-((6-(acryloyloxy)hexyl)oxy)benzoate); the chain extender is any one or several of 3,6-dioxa-1,8-octane dithiol, ethylene glycol bis(3-mercaptopropionate), 1,4-butanediol bis(mercaptouscinate), bis(mercaptouscinate) ethylene glycol, bis(2-mercaptoethyl) ether, 1,3-propanedithiol, 1,6-hexanedithiol, 1,10-decanedithiol.

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

[0020] The application also provides application of the liquid crystal elastomer-based artificial muscle fiber in preparing flexible electronics and soft robots.

[0021] Beneficial effects:

[0022] The liquid crystal elastomer-based artificial muscle fiber driven by electricity and heat provided by the application is constructed by first constructing a conductive spring and then coating the liquid crystal elastomer by using a template method, wherein the conductive spring can play a role of a supporting skeleton and improve the mechanical output, and the spring will not hinder the deformation effect of the liquid crystal elastomer when the liquid crystal elastomer deforms. The application can improve the overall mechanical strength of the fiber while not affecting the driving performance, can realize fast and accurate driving, and has the characteristics of fast response. The liquid crystal elastomer artificial muscle driven by electricity and heat has high sensitivity, high driving capacity and high output force, can realize 60% of the maximum driving capacity within 0.3 s, and has large driving force on the premise of meeting large driving capacity, so that it has broad research prospects in the fields of flexible electronics, soft robots and rehabilitation medicine. The preparation method of the application has a simple and easy-to-operate preparation process and can realize mass production. BRIEF DESCRIPTION OF DRAWINGS

[0023] Fig. 1 is a preparation flowchart of the spring-shaped conductive fiber of the application.

[0024] Fig. 2 is a preparation flowchart of the artificial muscle fiber of the application.

[0025] Fig. 3 is an optical photograph of the artificial muscle fiber of the application.

[0026] Fig. 4 is the driving capacity of the artificial muscle fiber of the application under different voltages when the frequency is 0.1 Hz (duty ratio is 5%).

[0027] Fig. 5 is the driving capacity of the artificial muscle fiber of the application under different voltages when the frequency is 0.1 Hz (duty ratio is 10%).

[0028] Fig. 6 is a comparison of the driving performance characterization of the conductive liquid crystal elastomer fibers prepared by using conductive nylon fibers with different diameters. DETAILED DESCRIPTION

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

[0030] 1) Preparation of conductive spring: Conductive nylon fiber with a diameter of 0.1 mm is used as conductive fiber and is evenly wound on a stainless steel mandrel with a diameter of 0.6 mm (Figure 1A). After fixing both ends, it is annealed in an oven at 120°C for 3 hours. The mandrel is then removed to obtain a tightly wound conductive nylon spring (Figure 1B). This conductive spring has excellent elasticity and can be stretched by more than 500% (Figure 1C).

[0031] 2) Preparation of liquid crystal elastomer oligomers: Liquid crystal elastomer oligomers were prepared by 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)benzoic acid]-2-toluene), 1.73 mmol of chain extender (EDDET, 3,6-dioxa-1,8-octanedithiol), 0.173 mmol of crosslinking agent (PETMP, pentaerythritol tetrakis(3-mercaptopropionic acid)), and 0.04 mmol of photoinitiator (IG-651, 2,2-dimethoxy-2-phenylacetophenone) were dissolved in 1.2 mL of dichloromethane. The solution 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 the mixture was stirred for another 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 1.0 mm inner diameter PTFE tube (Figures 2A and 2B). The liquid crystal elastomer oligomer solution obtained in (2) was injected into the PTFE tube containing the conductive nylon spring using a syringe (Figure 2C). After preliminary crosslinking for 24 hours in a light-protected state, the PTFE tube was peeled off to obtain multi-domain conductive liquid crystal elastomer fibers (Figure 2D). The fibers were placed 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 using a mechanical stretching method (Figure 2E). After secondary crosslinking for 15 minutes under ultraviolet light, uniaxially oriented conductive liquid crystal elastomer fibers were obtained, which were then used for the final conductive liquid crystal elastomer fibers (Figure 2F).

[0033] Figure 3 is an optical photograph of the conductive liquid crystal elastomer fiber in this embodiment, with a fiber diameter of 0.7 micrometers. During mechanical stretching, the conductive liquid crystal elastomer transforms the liquid crystal cells from a nematic phase to an isotropic phase, resulting in macroscopic deformation and thus excellent driving performance. Its internal orientation was characterized using WAXS. Example 2

[0034] 1) Preparation of conductive spring: Carbon fiber with a diameter of 0.1 mm is used as conductive fiber. First, it is twisted to a certain twist (not twisted to a spiral state), and then evenly wound on a stainless steel mandrel with a diameter of 1.0 mm. After fixing both ends, it is annealed in an oven at 150°C for 2 hours. The mandrel is then removed to obtain a closely 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 in the dark for 24 hours, the tetrafluoroethylene tube was peeled off to obtain multi-domain conductive liquid crystal elastomer fibers. The fibers were then placed in a 60°C oven to remove excess solvent for 24 hours. The multi-domain conductive liquid crystal elastomer fibers were mechanically stretched 3 times using a mechanical stretching method and then subjected to secondary cross-linking under ultraviolet light for 15 minutes to obtain the final conductive liquid crystal elastomer fibers for later use. Example 3

[0037] 1) Preparation of conductive spring: Conductive nylon fiber with a diameter of 0.1 mm is used as conductive fiber and is evenly wound on a stainless steel mandrel with a diameter of 0.6 mm (Figure 1A). After fixing both ends, it is annealed in an oven at 140℃ for 2.5 hours. The mandrel is then removed to obtain a tightly wound conductive nylon spring (Figure 1B). This conductive spring has excellent elasticity and can be stretched by more than 500% (Figure 1C).

[0038] 2) Preparation of liquid crystal elastomer oligomers: Liquid crystal elastomer oligomers were prepared by aza-Michael addition method. The specific process is as follows: 2.0 mmol of liquid crystal monomer (RM257, 1,4-bis[4-(3-acryloyloxypropoxy)benzoic acid]-2-toluene), 1.73 mmol of chain extender (DDT, 1,10-decanedithiol), 0.173 mmol of crosslinking agent (PETMP, pentaerythritol tetrakis(3-mercaptopropionic acid)), and 0.04 mmol of photoinitiator (IG-651, 2,2-dimethoxy-2-phenylacetophenone) were dissolved in 1.2 mL of ethyl acetate. The solution 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 the mixture was stirred for another 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 crystal elastomer oligomers: Liquid crystal elastomer oligomers were prepared by aza-Michael addition method. The specific process is as follows: 2.0 mmol of liquid crystal monomer (RM257, 1,4-bis[4-(3-acryloyloxypropoxy)benzoic acid]-2-toluene), 1.73 mmol of chain extender (HDT, 1,6-hexanedithiol), 0.173 mmol of crosslinking agent (PETMP, pentaerythritol tetrakis(3-mercaptopropionic acid)), and 0.04 mmol of photoinitiator (IG-651, 2,2-dimethoxy-2-phenylacetophenone) were dissolved in 1.2 mL of toluene. The solution 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 the mixture was stirred for another 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 driving performance of the conductive liquid crystal elastomer fiber prepared in Example 1 was tested. 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%), as shown in Figure 4. At a voltage of 1.0 V / cm, the maximum driving amount can reach 65%, and 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 driving performance of the conductive liquid crystal elastomer fiber prepared in Example 1 was tested. 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%), as shown in Figure 5. At a voltage of 1.0 V / cm, the maximum driving amount reached 70%, and the driving amount increased with increasing voltage, indicating that the conductive liquid crystal elastomer fiber has the ability to operate with a large driving amount. Compared with Example 2, the increased duty cycle and extended energizing time resulted in an increased driving amount. Example 7

[0045] (1) Preparation of conductive spring: Conductive nylon fiber with a diameter of 0.2 mm is used as conductive fiber. It is evenly wound on a stainless steel mandrel with a diameter of 0.6 mm. After fixing both ends, it is annealed in an oven at 120°C for 3 hours. The mandrel is then removed 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 fiber: The conductive nylon spring prepared in (1) is placed in a tetrafluoroethylene tube with an inner diameter of 1.2 mm, and the remaining steps are the same as step (3) in Example 1. Example 8

[0048] (1) Preparation of conductive spring: Conductive nylon fiber with a diameter of 0.3 mm is used as conductive fiber. It is evenly wound on a stainless steel mandrel with a diameter of 0.6 mm. After fixing both ends, it is annealed in an oven at 120°C for 3 hours. The mandrel is then 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 fiber: The conductive nylon spring prepared in (1) is placed in a tetrafluoroethylene tube with an inner diameter of 1.4 mm, and the remaining steps are the same as step (3) in Example 1. Example 9

[0051] (1) Preparation of conductive spring: Conductive nylon fiber with a diameter of 0.4 mm is used as conductive fiber. It is evenly wound on a stainless steel mandrel with a diameter of 0.6 mm. After fixing both ends, it is annealed in an oven at 150°C for 2 hours. The mandrel is then removed 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 fiber: The conductive nylon spring prepared in (1) is placed in a tetrafluoroethylene tube with an inner diameter of 1.6 mm, and the remaining steps are the same as step (3) in Example 1. Example 10

[0054] (1) Preparation of conductive spring: Conductive nylon fiber with a diameter of 0.5 mm is used as conductive fiber. It is evenly wound on a stainless steel mandrel with a diameter of 0.6 mm. After fixing both ends, it is annealed in an oven at 120°C for 3 hours. The mandrel is then removed 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 fiber: The conductive nylon spring prepared in (1) is placed in a tetrafluoroethylene tube with an inner diameter of 1.8 mm, and the remaining steps are the same as step (3) in Example 1.

[0057] The driving performance (driving amount and contraction force) of conductive liquid crystal elastomer fibers prepared from conductive nylon fibers of different diameters is characterized and compared, as shown in Figure 6. Figure 6 shows that the conductive liquid crystal elastomer fibers significantly improve the driving force while meeting the requirement of 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 within the protection scope of the present invention.

Claims

1. A liquid crystal elastomer-based artificial muscle fiber, characterized by, Prepared from spring-like conductive fibers and liquid crystal elastomer oligomers; the conductive fibers are one of metal wires, nylon fibers, carbon fibers, conductive polymers, shape memory alloy wires or carbon nanotube wires.

2. The method for producing an artificial muscle fiber based on a liquid crystal elastomer according to claim 1, wherein Comprising the following steps: 1) Preparation of spring-like conductive fibers; 2) Preparation of liquid crystal elastomer oligomers; 3) Preparation of liquid crystal elastomer-based artificial muscle fibers: perfuse the liquid crystal elastomer oligomer solution obtained in step 2) into a tetrafluoroethylene tube containing the conductive fibers prepared in step 1); after crosslinking reaction, the tetrafluoroethylene tube is stripped to obtain a multi-domain conductive liquid crystal elastomer fiber, and after removing the solvent, the multi-domain conductive liquid crystal elastomer fiber is stretched and secondarily crosslinked to obtain the final liquid crystal elastomer-based artificial muscle fiber.

3. The production method according to claim 2, characterized by, The inner diameter of the tetrafluoroethylene tube is 1-6 mm.

4. The production method according to claim 2, characterized by, The stretching step is mechanical stretching of the multi-domain conductive liquid crystal elastomer fiber by mechanical drafting method by 3 times.

5. The preparation method according to claim 2, characterized in that, The preparation method of the spring-like conductive fibers is as follows: winding the conductive fibers on a stainless steel mandrel, high temperature annealing, then taking out the mandrel to obtain densely wound spring-like conductive fibers.

6. The method of any one of claims 5, wherein, The diameter of the conductive fibers is 0.1-1.0 mm, the diameter of the stainless steel mandrel is 0.6-3.0 mm, and the high temperature annealing temperature is 120-180℃ for 1.5-3 hours.

7. The preparation method according to claim 2, characterized in that, The liquid crystal elastomer oligomers are prepared by azo-Michael addition method, and the specific process is as follows: dissolving liquid crystal monomers, chain extenders, crosslinking agents and photoinitiators in a solvent, stirring and dissolving at 40-80℃ to obtain a uniform solution, then adding a catalyst and continuing to stir to obtain a liquid crystal elastomer oligomer solution.

8. The method of claim 7, wherein, The liquid crystal monomer is any one or both of 1,4-bis[4-(3-acryloyloxypropoxy)benzoic acid]-2-methylbenzene or 2-methyl-1,4-phenylene bis(4-((6-(acryloyloxy)hexyl)oxy)benzoate); the chain extender is any one or several of 3,6-dioxa-1,8-octanedithiol, ethylene glycol bis(3-mercaptopropionate), 1,4-butanediol bis(mercaptouscinate), ethylene glycol bis(mercaptouscinate), bis(2-mercaptoethyl)ether, 1,3-propanedithiol, 1,6-hexanedithiol, 1,10-decanedithiol.

9. The preparation method according to claim 7, characterized in that, The solvent is selected from any one or several of dichloromethane, ethyl acetate, toluene or acetone; the crosslinking agent is pentaerythritol tetra(3-mercaptopropionate), and the photoinitiator is 2,2-dimethoxy-2-phenylphenylacetophenone, and the catalyst is di-n-propylamine.

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

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