A self-sensing material, its preparation method and application in artificial muscle fibers

Abstract

The present invention discloses a self-sensing material, a preparation method thereof, and an application in artificial muscle fibers, belonging to the technical field of flexible actuators. The structure of the self-sensing material from the inside to the outside is successively a helical insulating polymer-coated carbon nanotube fiber, a polydopamine layer, and a conductive strain sensing layer; the helical insulating polymer-coated carbon nanotube fiber, the polydopamine layer, and the conductive strain sensing layer are coaxial structures. The self-sensing material prepared by the present invention has high self-sensing signal accuracy, strong linear correlation, and good cyclic stability. The self-sensing material can be used to prepare artificial muscle fibers, which can exhibit different contraction amounts under different voltages, and the contraction amount linearly increases with the increase of the voltage. Through the signal of relative resistance change, the movement position and process of the artificial muscle fiber can be monitored at all times without a sensor.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible actuators, and particularly relates to a self-sensing material, a preparation method thereof, and an application in artificial muscle fibers. Background Art

[0002] Mammalian skeletal muscles can control bones through contraction and relaxation, thereby driving joint movement, and perform real-time sensing signal feedback through muscle spindle proprioceptors. Inspired by mammalian skeletal muscles, people are constantly working hard to develop muscle-like materials with self-sensing functions and explore their applications in fields such as soft robotics, biomedical engineering, and bionic devices. Among the developed muscle-like materials, artificial muscle fibers have recently attracted wide attention because they can provide a reversible contraction driving stroke with high energy density and can be bundled for high driving force scenarios. However, the currently developed high-performance artificial muscle fibers lack self-sensing functions.

[0003] The self-sensing function of artificial muscle fibers is very important for real-time monitoring of their motion states. Some film-like actuators have achieved self-sensing functions through the superposition of multi-layer structures. Due to the complexity of the fibrous artificial muscle structure, the development of artificial muscle fibers with self-sensing functions is still challenging. Recently, artificial muscle fibers composed of a polymer and silver nanowires developed through a thermal stretching process have achieved self-sensing functions under environmental temperature changes. However, self-sensing cannot be achieved under Joule heat stimulation, which limits its practical applications. Summary of the Invention

[0004] To solve the above problems, the present invention provides a self-sensing material, a preparation method thereof, and an application in artificial muscle fibers.

[0005] In the present invention, a sensing layer is adhered to a driving layer by constructing a coaxial structure to enable the driving and sensing units to work synchronously, thereby realizing the self-sensing function during the driving process. In the structural design, a carbon nanotube fiber is wrapped with a narrow band of an insulating polymer (such as polydimethylsiloxane, etc.) having a large thermal expansion coefficient and then twisted into a helical structure. A layer of dopamine is polymerized on the surface of the polymer layer, and then a conductive strain sensing layer (such as generated using a dispersion of MXene and single-walled carbon nanotubes) is adhered, enabling the fiber to have strain sensing functions during the active stimulation contraction process. The carbon nanotube fiber core has an electrothermal effect, the polymer layer serves as both a driving layer and an insulating layer, and polydopamine is used to adhere and capture the sensing material that deforms the driving layer. The smooth surface of polydimethylsiloxane cannot be coated with a carbon-based sensing material. As a sticky protein secreted by mussel-like organisms, polydopamine can form a strong adhesion on the smooth group surface and stably bridge between polydimethylsiloxane and the carbon-based conductive material. Compared with other adhesives, the artificial muscle fibers prepared using polydopamine have higher self-sensing stability.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention: Provide a self-sensing material, the structure of the self-sensing material from the inside to the outside is a carbon nanotube fiber wrapped with a helical insulating polymer, a polydopamine layer, and a conductive strain sensing layer in sequence; the helical insulating polymer wrapped carbon nanotube fiber, the polydopamine layer, and the conductive strain sensing layer are coaxial structures.

[0008] Preferably, the twist of the helical polymer-wrapped carbon nanotube fiber is 3000 turns / m.

[0009] Preferably, the thermal expansion coefficient of the insulating polymer is 1×10 -4 ~9.6×10 -4 / °C, such as polydimethylsiloxane, nylon, aramid, or polyimide, etc.

[0010] The conductive strain sensing layer of the present invention can complete the function of conductive sensing, and the material can be selected from conductive carbon-based materials, preferably MXene / single-walled carbon nanotube composites.

[0011] MXene in the present invention is a class of two-dimensional inorganic compounds in materials science, with hydroxyl groups or terminal oxygen on the material surface, and they have the metallic conductivity of transition metal carbides.

[0012] Another technical solution of the present invention: Provide a preparation method of the above self-sensing material, including the following steps:

[0013] Wrap carbon nanotube fibers with an insulating polymer and then twist them into a helix; then hydrophilize the surface of the insulating polymer; polymerize dopamine on the surface of the hydrophilized insulating polymer to generate a polydopamine layer; finally, generate a conductive strain sensing layer on the surface of the polydopamine layer.

[0014] Preferably, the method of hydrophilization treatment is oxygen plasma treatment, the purpose is to generate more hydrophilic functional groups on the surface of the insulating polymer, achieve the purpose of hydrophilic modification, and enable the insulating polymer to better combine with the polydopamine layer.

[0015] Another technical solution of the present invention: Provide an application of the above self-sensing material in the preparation of artificial muscle fibers.

[0016] The conductive strain sensing layer of the self-sensing material of the present invention is equivalent to the sheath layer of artificial muscle fibers. As the artificial muscle fibers contract, the resistance of the sheath layer changes accordingly, and the change in relative resistance can be used to track the movement position state of the fibers in real time.

[0017] The beneficial technical effects of the present invention are as follows:

[0018] The self-sensing material prepared by the present invention has high self-sensing signal accuracy, strong linear correlation, and good cycle stability. This self-sensing material can be used to prepare artificial muscle fibers, which can exhibit different contraction amounts at different voltages, and the contraction amount increases linearly with the increase of voltage. Through the signal of relative resistance change, the movement position and process of the artificial muscle fibers can be monitored at all times without a sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a preparation flow chart and a schematic cross-sectional view of the material of the artificial muscle fiber with self-sensing function in Example 1 of the present invention; wherein, a is the preparation flow chart; b is the schematic cross-sectional view of the material.

[0020] Figure 2 It is a structural characterization diagram of the artificial muscle fiber with self-sensing function prepared in Example 1 of the present invention.

[0021] Figure 3 It is a schematic diagram of the working mechanism of the artificial muscle fiber with self-sensing function prepared in Example 1 of the present invention.

[0022] Figure 4 It is a self-sensing performance diagram of the artificial muscle fiber with self-sensing function prepared in Example 1; wherein, a is the contraction amount of the artificial muscle fiber at different voltages; b is the relative resistance of the artificial muscle fiber under different driving amounts; c is the strain sensing characteristic of the artificial muscle fiber under different loads when the voltage is 10V; d is the relationship between temperature change and the contraction stroke of the artificial muscle fiber; e is the relationship between the contraction characteristic and time of the artificial muscle fiber under 10V voltage, 14g load, and three cycles; f is the power density of the artificial muscle fiber under different voltages and load amounts.

[0023] Figure 5 It is a cycle performance diagram of the artificial muscle fiber with self-sensing function prepared in Example 1.

[0024] Figure 6 It is a comparison diagram of the driving strain of the artificial muscle fiber with self-sensing function and the driving performance of the artificial muscle fiber without a self-sensing layer coated. DETAILED DESCRIPTION OF THE INVENTION

[0025] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention. It should be understood that the terms described in the present invention are only for describing specific implementation modes and are not used to limit the present invention.

[0026] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Intermediate values within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, are also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0027] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention.

[0028] Regarding "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0029] The preparation flow chart and the schematic cross-sectional view of the material of the artificial muscle fiber with self-sensing function in Example 1 of the present invention are shown in Figure 1 ; where a is the preparation flow chart; b is the schematic cross-sectional view of the material.

[0030] The schematic diagram of the working mechanism of the artificial muscle fiber with self-sensing function prepared in Example 1 is shown in Figure 3 , and while the artificial muscle fiber contracts, it is accompanied by a change in the resistance of the sheath structure. The relative resistance change of the MXene / single-walled carbon nanotube sensing layer can be used to track the movement position state of the fiber in real time.

[0031] Example 1

[0032] Preparation of artificial muscle fiber with self-sensing function:

[0033] After wrapping a 50-μm-thick, 5-mm-wide, and 27-cm-long polydimethylsiloxane film around a carbon nanotube fiber, one end was fixed to the tip of a motor, and the other end was fixed to a clip with a 10-g weight. The entire fiber was suspended between the motor and the clip for twisting, and the inserted twist was 3000 turns / m. The prepared fiber was fixed on a polytetrafluoroethylene template for pre-stretching and treated with oxygen plasma (power 150 W, treatment time 90 s) to make its surface hydrophilic for the polymerization of dopamine. Single-walled carbon nanotubes (0.1 wt%) and sodium dodecylbenzenesulfonate were uniformly dispersed in deionized water at a ratio of 1:1 by a cell disruptor, and then 0.2 g of MXene powder and 10 mL of the single-walled carbon nanotube dispersion were ultrasonically dispersed to obtain a uniform MXene / single-walled carbon nanotube dispersion. After the polymerization of dopamine, the fiber surface was coated with the MXene / single-walled carbon nanotube conductive dispersion. After the entire fiber surface was uniformly coated (thickness 20 μm), it was twisted again by a stepper motor to prepare an artificial muscle fiber with self-sensing function.

[0034] The structural characterization diagram of the artificial muscle fiber with self-sensing function prepared in Example 1 is shown in Figure 2 。

[0035] Example 2

[0036] Preparation of artificial muscle fiber with self-sensing function:

[0037] Compared with Example 1, other conductive dispersions can be used to prepare artificial muscle fibers with self-sensing function. Specifically, graphene (0.1 wt%) and sodium dodecylbenzenesulfonate were uniformly dispersed in deionized water at a ratio of 1:1 by a cell disruptor, and then 0.2 g of MXene powder and 10 mL of the graphene dispersion were ultrasonically dispersed to obtain a uniform MXene / graphene dispersion.

[0038] Comparative Example 1

[0039] Preparation of artificial muscle fiber with self-sensing function:

[0040] Compared with Example 1, the oxygen plasma treatment step was omitted. After omitting the oxygen plasma treatment step, dopamine could not polymerize in the composite fiber, and the conductive layer could not stably adhere to the fiber.

[0041] Comparative Example 2

[0042] Preparation of artificial muscle fiber with self-sensing function:

[0043] Compared with Example 1, polydopamine was replaced with a silicone adhesive Sil Poxy. The experimental results showed that the conductive layer could not stably adhere to the composite fiber, and the number of cycles of the entire artificial muscle fiber decreased to about 1000 times.

[0044] Comparative Example 3

[0045] Preparation of artificial muscle fibers with self-sensing function:

[0046] Compared with Example 1, poly-dopamine conductive layer is not coated.

[0047] Test results:

[0048] Measure the self-sensing performance of the artificial muscle fibers with self-sensing function prepared in each experimental group.

[0049] Figure 4 It is the self-sensing performance diagram of the artificial muscle fibers with self-sensing function prepared in Example 1; wherein, a is the contraction amount of the artificial muscle fibers under different voltages; b is the relative resistance of the artificial muscle fibers under different driving amounts; c is the strain sensing characteristics of the artificial muscle fibers under different loads when the voltage is 10V; d is the relationship between temperature change and the contraction stroke of the artificial muscle fibers; e is the relationship between the contraction characteristics and time of the artificial muscle fibers under 10V voltage, 14g load and three cycles; f is the work density of the artificial muscle fibers under different voltages and load amounts.

[0050] From Figure 4 it can be seen that the maximum contraction amount of the artificial neuromuscular fibers under 10V voltage is 17%, and different contraction amounts are shown under different voltages, and the contraction amount increases linearly with the increase of voltage ( Figure 4 in a)); the relative resistance of the artificial muscle fibers shows a linear change under different driving amounts ( Figure 4 in b). Through the signal of the relative resistance change, the movement position and process of the artificial muscle fibers can be monitored at all times without a sensor. The present invention also shows the strain sensing characteristics of the artificial muscle fibers under different loads at 10V voltage, and the relative change of its resistance is also linearly related to the contraction stroke of the artificial muscle fibers ( Figure 4 in c). As shown in Figure 4 d, the change of temperature is linearly related to the contraction stroke of the artificial muscle fibers. Therefore, the artificial muscle fibers with temperature sensing function will provide the possibility of measuring temperature change to obtain the contraction stroke. Figure 4 e shows the relationship between the contraction characteristics and time of the artificial muscle fibers under 10V voltage, 14g load and three cycles. In each cycle, the 10V voltage is turned on for 7s and turned off for 38s. When a 10V voltage is applied, with the increase of the load amount, the contraction force and the isometric force show a consistent increasing trend, up to 14g (~0.8MPa) at most, and then rapidly decrease. Finally, we calculated that when the voltage is 10V and the load is 16g, the maximum work density of the artificial muscle fibers is 134.5kJ·m -3 ( Figure 4In f), it is 17 times that of mammalian skeletal muscle (8 kJ·m -3 ).

[0051] Figure 5 It is the cyclic performance graph of the artificial muscle fiber with self-sensing function prepared in Example 1, Figure 5 showing that after 1000 cycles under a load of 14 g, the contraction of the artificial neuromuscular fiber did not change significantly. In each cycle, a 10 V voltage was turned on for 5 s and turned off for 25 s.

[0052] In Comparative Example 1, the fiber surface was not treated with oxygen plasma, and the amount of dopamine polymerized on the surface of polydimethylsiloxane was small, and uniform polymerization could not be achieved, so that the MXene / single-walled carbon nanotube dispersion could not be uniformly coated to form a stable conductive layer, and an artificial muscle fiber with self-sensing function could not be prepared.

[0053] Comparative Example 2 shows that replacing polydopamine with other adhesives will affect the stability of self-sensing. Polydopamine is thinner and has a better adhesion effect than other adhesives, and does not limit the driving effect.

[0054] The comparison graph of the driving strain of the artificial muscle fiber with self-sensing function in Example 1 and the driving performance of the artificial muscle fiber without the self-sensing layer coated is shown in Figure 6 , and it can be seen from Figure 6 that the coating of the self-sensing layer does not affect the output strain and output stress performance of the muscle driving layer.

[0055] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should fall within the protection scope determined by the claims of the present invention.

Claims

1. Application of self-sensing material in preparing artificial muscle fibers, Characterized in that, The structure of the self-sensing material from the inside to the outside is a helical insulating polymer-wrapped carbon nanotube fiber, a polydopamine layer, and a conductive strain sensing layer in sequence; the helical insulating polymer-wrapped carbon nanotube fiber, the polydopamine layer, and the conductive strain sensing layer are coaxial structures; The preparation method of the self-sensing material includes the following steps: wrapping carbon nanotube fibers with an insulating polymer and then twisting them into a helix; then hydrophilizing the surface of the insulating polymer; polymerizing dopamine on the surface of the hydrophilized insulating polymer to generate a polydopamine layer; and finally generating a conductive strain sensing layer on the surface of the polydopamine layer; The method of hydrophilization treatment is oxygen plasma treatment, the power of the oxygen plasma treatment is 150 W, and the treatment time is 90 s.

2. Application of the self-sensing material according to claim 1 in preparing artificial muscle fibers, Characterized in that, The twist of the helical insulating polymer-wrapped carbon nanotube fiber is 3000 turns / m.

3. Application of the self-sensing material according to claim 1 in preparing artificial muscle fibers, Characterized in that, The coefficient of thermal expansion of the insulating polymer is 1×10 -4 ~9.6×10 -4 / °C.

4. Application of the self-sensing material according to claim 3 in preparing artificial muscle fibers, Characterized in that, The insulating polymer is polydimethylsiloxane, nylon, aramid or polyimide.

5. Application of the self-sensing material according to claim 1 in preparing artificial muscle fibers, Characterized in that, The material of the conductive strain sensing layer is MXene / single-walled carbon nanotube composite.

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