Artificial muscle fiber for realizing large strain by utilizing thermally induced self-helix, preparation method and application

Abstract

The invention provides a fiber artificial muscle for realizing large strain by utilizing thermally induced self-helix and a preparation method thereof. The preparation method comprises the following steps: dissolving a liquid crystal monomer, a chain extender, a cross-linking agent and a photoinitiator in an organic solvent, and carrying out Michael addition reaction for 20-30 minutes to form an oligomer; preparing liquid crystal elastomer fibers by using a direct writing and printing method, and placing the obtained fibers at room temperature for 24 hours for later use; the fiber and a carbon nano tube fiber are stranded and twisted for a certain twist degree to form a winding fiber. After being electrified, the fiber artificial muscle can be heated to the highest temperature within a short time (4s), and the self-spiral behavior of the fiber can be rapidly completed after the fiber is heated. The output work density of the fiber reaches 55.74 J / kg. The preparation method is simple, efficient and low in cost, and has large output strain (60%) and electrothermal driving performance.

Description

Technical Field

[0001] The present invention relates to the field of robotics, specifically the field of artificial muscles, and in particular to an artificial muscle fiber that realizes large strain by utilizing thermally induced self-helicalization and a preparation method thereof. Background Art

[0002] Liquid crystal elastomer is a good thermal drive material with reversible driving ability. However, it has a slow response speed and low mechanical strength when driven only by light. The heat source of driving can be realized by Joule heat, which greatly improves its response speed. Compounding with conductive materials such as carbon nanotube particles and carbon black particles is a common means of introducing Joule heat, but the direct introduction of these materials will reduce the mechanical strength of liquid crystal elastomers and is not conducive to the formation of twisted fibers.

[0003] Carbon nanotube fibers have good flexibility, conductivity and high mechanical strength. There are also methods in the prior art for winding conductive fibers with liquid crystal elastomer fibers to make brake fibers. For example, US20210071649A1 discloses a kink-free artificial muscle, including a core fiber of a polymer arranged along the length of the core fiber, and a wire wound on the core fiber; the core fiber has a negative linear thermal expansion coefficient, wherein the core fiber has a radial thermal expansion coefficient higher than the bulk thermal expansion coefficient of the polymer. The core fiber is selected from fibers made of nylon, polyvinylidene fluoride (PVDF), polyetheretherketone (PEEK), liquid crystal polymer, aromatic polyamide, etc., and the wire is selected from carbon nanotube fibers, etc. The core fiber is arranged between two components, which prevent linear and torsional movement at the opposite ends of the core fiber, wherein each of the opposite ends of the core fiber is fixed to a corresponding one of the two components, and the two components prevent linear and torsional movement at the opposite ends of the core fiber; the wire prevents the radial expansion of the core fiber and converts the radial expansion into torsional actuation. However, this winding structure easily leads to the problem that the core fiber is tightened and damaged by the conductive fiber during braking. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides an artificial muscle fiber that realizes large strain by thermal self-helicalization, a preparation method and application. After being heated, the fiber can not only realize its own contraction, but also wind the straight fiber into a spiral fiber, thereby greatly improving the contraction strain and response speed of the fiber, and at the same time, avoiding the damage of the fiber caused by expansion in the corresponding process, and improving the repeatability of braking.

[0005] The present invention achieves the above technical objectives through the following technical means.

[0006] An artificial muscle fiber that uses thermally induced self-helix to achieve large strain, characterized in that it includes multiple elastomeric fibers and carbon nanotube fibers. The multiple elastomeric fibers are twisted and then wrapped around the outer surface of the carbon nanotube fibers in a spiral winding manner. The elastomeric fibers are made of a material with a thermally induced shape memory effect, and the carbon nanotube fibers can be connected to a driving power source.

[0007] Furthermore, the elastomeric fibers are liquid crystal elastomeric fibers, the number of which is three, and the twist is at least 15 turns / cm. Preferably, the elastomeric fibers have a pre-stretch of 5%-15%.

[0008] Further, the diameter of the elastomeric fiber is 0.1-0.35 mm, the diameter of the carbon nanotube fiber is 30-60 μm, preferably, the elastomeric fiber has a pre-stretch of 5%-15%, and preferably, the carbon nanotube fiber has a twist.

[0009] The method for preparing a fiber artificial muscle that uses thermally induced self-helicalization to achieve large strain is characterized in that it includes the following steps: taking multiple elastomeric fibers of the same length and evenly distributing them around a single carbon nanotube fiber, fixing one end of the elastomeric fiber and the carbon nanotube fiber, twisting the multiple elastomeric fibers at the other end using a stepper motor, and then wrapping them around the outside of the carbon nanotube by spiral winding to make parallel fibers.

[0010] Furthermore, the elastomeric fiber has a pre-stretching of 5%-15% after being twisted and wrapped, and the carbon nanotube fiber is twisted by a stepper motor and then spirally wrapped with a plurality of elastomeric fibers.

[0011] Furthermore, the preparation process of the elastomeric fiber is as follows:

[0012] (1) Preparing a precursor solution: adding a liquid crystal monomer, a chain extender, a crosslinking agent and a photoinitiator to an organic solvent, and subjecting the mixture to a Michael addition reaction at room temperature for 20-30 minutes to obtain a prepolymer as a precursor solution;

[0013] (2) 3D printing of liquid crystal elastomer fibers: The prepared precursor solution is placed in the syringe of a microfluidic pump for spinning, and ultraviolet light is used to solidify the fibers into shape.

[0014] Furthermore, the liquid crystal monomer is 1,4-bis-[4-(3-acryloxypropyl)benzoyloxy]-2-methylbenzene (RM257); the chain extender is 3,6-dioxa-1,8-octanedithiol (EDDET); the cross-linking agent is pentaerythritol tetrakis(3-mercaptopropionic acid) (PETMP); the catalyst is dipropylamine (DPA); the organic solvent is toluene; and the photoinitiator is 2-hydroxy-2-methylpropiophenone.

[0015] Furthermore, the molar ratio of the chain extender to the cross-linking agent is 2:1; and the content of the photoinitiator is 2%-5% of the liquid crystal monomer content.

[0016] Furthermore, in step (2), the syringe is perpendicular to the ground, and the fiber is collected by a roller located directly below the syringe. The height between the syringe needle and the collecting device is 8-12 cm, the printing speed is 0.5 mL / min, and the needle diameter is 0.3 mm to 0.5 mm. Fibers of different diameters are prepared by adjusting the height between the syringe needle and the collecting device. Preferably, the illumination intensity of the ultraviolet light in step (2) is 70-100 mW / cm 3 ; The collecting device is a drum with a diameter of 70 to 90 cm and a rotation speed of 50-80 rad / min.

[0017] The application of the artificial muscle fiber that realizes large strain by utilizing thermally induced self-helix is ​​characterized in that it is used for artificial muscle.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The preparation method of the artificial muscle fiber of the present invention, the liquid crystal elastomer fiber obtained by spinning straight writing, has a certain axial orientation, and the twisting behavior not only enhances the molecular orientation, but also gives it an orientation along the twisting direction. In this case, when the two ends of the fiber are restricted, the liquid crystal elastomer cannot untwist after thermal expansion, thereby converting the untwisting trend into a self-helical state, thereby achieving contraction drive.

[0020] In the artificial muscle fiber that utilizes thermally induced self-helicalization to achieve large strain as described in the present invention, the elastomeric fiber has an axial molecular orientation and an orientation along the twisting direction superimposed after twisting. As long as there is a slight twist, after being heated, the transformation from twisted straight fiber to self-helical fiber can be achieved in a short time. The generation of this action increases the contraction strain.

[0021] For liquid crystal elastomer fibers, the traditional mold molding technology is cumbersome to make and cannot be mass-produced. The preparation process of the artificial muscle fiber of the present invention is simple, the reaction conditions are easy to achieve, and it can be mass-produced, which greatly shortens the production cycle and provides an effective method for developing low-cost, high-driving performance actuators. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The principle and process flow chart of the liquid crystal elastomer fiber prepared by the present invention;

[0023] Figure 2 This is a SEM image of the raw silk of the liquid crystal elastomer fiber prepared by the present invention;

[0024] Figure 3 The differential scanning calorimetry diagram of the precursor of the liquid crystal elastomer fiber prepared by the present invention;

[0025] Figure 4 This is a driving performance diagram of the precursor of the liquid crystal elastomer fiber prepared in the present invention;

[0026] Figure 5 This is a schematic diagram of the principle of preparing self-helical fibers according to the present invention;

[0027] Figure 6 is a two-dimensional wide-angle diffraction pattern of the twisted fiber obtained in the embodiment;

[0028] Figure 7 This is a schematic diagram of the indirect heat drive of the fiber after power is applied in the embodiment;

[0029] Figure 8 This is a graph of the heating rate of the fiber obtained by an infrared camera in the embodiment;

[0030] Fig. 9 It is a comparison curve diagram of the shrinkage rate at different frequencies in the embodiment. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below. The specific implementation methods listed below only describe the principles and features of the present invention, and the examples are only used to explain the present invention and do not limit the scope of the present invention. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0032] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0033] like Figure 1 As shown, the method for preparing liquid crystal elastomer fibers comprises the following steps:

[0034] (1) Preparing a precursor solution: dissolving a liquid crystal monomer, a chain extender, a crosslinker and a photoinitiator into an organic solvent to carry out a Michael addition reaction, and continuing the reaction for 20-30 minutes to obtain a prepolymer. The liquid crystal monomer is 1,4-bis-[4-(3-acryloxypropyl)benzoyloxy]-2-methylbenzene; the chain extender is 3,6-dioxa-1,8-octanedithiol; the crosslinker is pentaerythritol tetrakis(3-mercaptopropionic acid); the catalyst is dipropylamine; the organic solvent is toluene; and the photoinitiator is 2-hydroxy-2-methylpropiophenone. The molar ratio of the chain extender to the crosslinker is 2:1; and the content of the photoinitiator is 2%-5% of the liquid crystal monomer content.

[0035] (2) Preparation of liquid crystal elastomer fibers LCE: The precursor solution is loaded into a syringe, and the syringe is placed vertically on the ground and on a microfluidic pump for spinning. A roller located directly below the syringe is used as a collecting device to collect the LCE fibers. During the spinning process, ultraviolet light is used to solidify the fibers and at the same time assists in the solidification and collection of the fibers. The diameter of the fiber is adjusted by adjusting the height between the syringe needle and the collecting device. Usually, the height between the syringe needle and the collecting device is 8-12 cm, the printing speed is 0.5 ml / min, and the needle diameter is 0.5 mm, 0.3 mm. The illumination intensity of the ultraviolet light is 70-100 mW / cm3; the collecting device is a roller with a diameter of 70-90 cm and a rotation speed of 50-80 rad / min. After printing, the obtained elastomer fiber is placed at room temperature for at least one day before use. The surface morphology of the obtained liquid crystal elastomer fiber is shown in the figure below. Figure 2 . And its crystal phase transition temperature was tested, such as Figure 3 As shown, it indicates that the transition temperature from anisotropy to isotropy of this fiber is around 72°C.

[0036] During the spinning process of LCE fibers, by adjusting the height between the syringe needle and the collecting device, i.e., the printing height, multiple liquid crystal elastomer fibers with different diameters ranging from 100 μm to 500 μm were obtained. As the diameter of the liquid crystal elastomer fibers decreased, the corresponding shrinkage rate of the liquid crystal elastomer fibers with different diameters also increased from 24% to 34%, such as Figure 4 shown.

[0037] The liquid crystal elastomer fiber obtained above is twisted with the carbon nanotube fiber, and the twisted fiber is spirally wound on the carbon nanotube fiber. The specific preparation method is as follows:

[0038] Three liquid crystal elastomer fibers of the same length are placed side by side on a plane and pre-stretched to a certain length so that the liquid crystal elastomer fibers have a certain driving effect after being heated. Taking a liquid crystal elastomer fiber with a diameter of 0.35 mm as an example, the pre-stretching amount is 15%. Take a carbon nanotube fiber with a diameter of 60 μm. The specific operation method is shown in Figure 5 .

[0039] One end of the liquid crystal elastomer fiber is fixed, and the other end is twisted by a stepper motor to a certain twist. For example, the twist of a liquid crystal elastomer fiber with a diameter of 0.35 mm needs to be at least 15 turns / cm. The carbon nanotube fiber is also twisted by a stepper motor to form a cluster, generally 450-500 turns. Then, multiple twisted elastomer fibers are wrapped around the outer surface of the carbon nanotube fiber by spiral winding to form a stranded fiber.

[0040] The twisting process of the liquid crystal elastomer fiber gives the liquid crystal elastomer fiber a certain rotational orientation, such as Figure 6 After twisting, the molecular orientation degree of the liquid crystal elastomer fiber increased from 0.144 to 0.171, which makes it not only driven in the axial direction during the thermally driven contraction, but also in a spiral contraction state, which can increase the shrinkage rate to 60%; this shows that the twisting behavior enhances the molecular orientation, so that it can achieve driving behavior under not too high voltage.

[0041] When the artificial muscle fiber is powered on, the carbon nanotube fiber heats up and causes the liquid crystal elastomer to contract. After the first bend appears, it can easily achieve a self-helical state. After the power is turned off, the fiber dissipates heat and returns to the vertical twisted fiber state. The principle and process of the entire contraction are as follows: Figure 7 When the diameter of the liquid crystal elastomer fiber is 0.1 mm, the diameter of the carbon nanotube fiber used is 30 μm.

[0042] Regarding the response speed of the artificial muscle fiber prepared by the present invention, Figure 8 As shown, because the diameter of the liquid crystal elastomer fiber is relatively small, it heats up quickly and reaches the highest temperature in 3.5 seconds after power is turned on. At the same time, after power is turned off, it can return to room temperature within 4 seconds. The heating and cooling rates are very fast.

[0043] The responses of the artificial muscle fibers prepared by the present invention at different contraction frequencies are as follows: Fig. 9 As shown in the figure, it can be seen that 0.025Hz is the frequency at which the maximum shrinkage rate (60%) is reached under this voltage. As the frequency increases, the shrinkage rate decreases, until at 0.25Hz, the shrinkage rate is only about 3%.

[0044] The embodiments are preferred implementations of the present invention, but the present invention is not limited to the above-mentioned implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essential content of the present invention belong to the protection scope of the present invention.

Claims

1. An artificial muscle fiber that achieves large strain by thermally induced self-helicalization, characterized in that: It comprises a plurality of elastomeric fibers and carbon nanotube fibers. The plurality of elastomeric fibers are twisted and then wrapped on the outer surface of the carbon nanotube fibers in a spiral winding manner. The elastomeric fibers are made of a material having a thermal shape memory effect. The carbon nanotube fibers can be connected to a driving power source.

2. The fiber artificial muscle that realizes large strain by utilizing thermally induced self-helix according to claim 1, characterized in that: The elastomeric fibers are liquid crystal elastomeric fibers, the number of which is three, and the twist degree is at least 15 turns / cm. Preferably, the elastomeric fibers have a pre-stretching of 5%-15%.

3. The fiber artificial muscle using thermally induced self-helical to achieve large strain according to claim 1, characterized in that: The diameter of the elastomer fiber is 0.1-0.35 mm, and the diameter of the carbon nanotube fiber is 30-60 μm. Preferably, the carbon nanotube fiber has twist.

4. The method for preparing a fiber artificial muscle that realizes large strain by utilizing thermally induced self-helical movement according to claim 1, characterized in that: The method comprises the following steps: taking a plurality of elastomeric fibers of the same length and evenly distributing them around a single carbon nanotube fiber, fixing one end of the elastomeric fiber and the carbon nanotube fiber, twisting the plurality of elastomeric fibers at the other end by using a stepper motor, and wrapping them around the outside of the carbon nanotube by spiral winding to make parallel stranded fibers.

5. The preparation method according to claim 4, characterized in that: The elastomeric fibers are pre-stretched by 5% to 15% after being twisted and wrapped. The carbon nanotube fibers are twisted by a stepper motor and then wrapped by a plurality of elastomeric fibers in a spiral manner.

6. The method for preparing a fiber artificial muscle that realizes large strain by utilizing thermally induced self-helical movement according to claim 4, characterized in that: The preparation process of the elastomeric fiber is as follows: (1) Preparing a precursor solution: adding a liquid crystal monomer, a chain extender, a crosslinking agent and a photoinitiator to an organic solvent, and subjecting the mixture to a Michael addition reaction at room temperature for 20-30 minutes to obtain a prepolymer as a precursor solution; (2) Preparation of liquid crystal elastomer fibers: The prepared precursor solution is placed in the syringe of a microfluidic pump for spinning, and ultraviolet light is used to solidify the fibers into shape.

7. The preparation method according to claim 6, characterized in that: The liquid crystal monomer is 1,4-bis-[4-(3-acryloxypropyl)benzoyloxy]-2-methylbenzene (RM257); the chain extender is 3,6-dioxa-1,8-octanedithiol (EDDET); the cross-linking agent is pentaerythritol tetrakis(3-mercaptopropionic acid) (PETMP); the catalyst is dipropylamine (DPA); the organic solvent is toluene; and the photoinitiator is 2-hydroxy-2-methylpropiophenone.

8. The preparation method according to claim 7, characterized in that: The molar ratio of the chain extender to the crosslinker is 2:1; the content of the photoinitiator is 2%-5% of the liquid crystal monomer content.

9. The preparation method according to claim 4, characterized in that: In the step (2), the syringe is perpendicular to the ground, and the fiber is collected by a roller located directly below the syringe. The height between the syringe needle and the collecting device is 8-12 cm, the printing speed is 0.5 mL / min, and the needle diameter is 0.3 mm to 0.5 mm. Fibers of different diameters are prepared by adjusting the height between the syringe needle and the collecting device. Preferably, the illumination intensity of the ultraviolet light in the step (2) is 70-100 mW / cm 3 ; The collecting device is a drum with a diameter of 70 to 90 cm and a rotation speed of 50-80 rad / min.

10. The use of artificial muscle fibers that achieve large strain by utilizing thermally induced self-helicalization according to claim 1, characterized in that: For artificial muscles.

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