Preparation And Actuation Properties Of Carbon Nanotube Yarn Artificial Muscles

Artificial muscles,as a kind of actuators,can be used in soft exoskeleton,prostheses,bionic robots,morphing aircraft,and energy harvesters and other fields due to their ability to convert external stimuli(such as light,heat,humidity)into mechanical energy.Carbon nanotube fibers,which integrate excellent properties such as good flexibility,high strength,high electrical conductivity,and low density,meet the overall requirements for artificial muscles and the study of carbon nanotube fibers artificial muscles is of great significance.However,the reported CNT fiber artificial muscles still existed some problems,for example,low-actuation,slow-response,and poor-cycling performance,which severely restrict their applications.A stable artificial muscle was prepared by Joule heating and self-plied CNT fiber,which was based on multi-stage assembly structure of CNT fiber.The actuations driven by organic solvents were investigated.The main research contents and results of this paper are as follows:1.Mechanical performance of coiled CNT fiber: Twist density is related to the diameters and twist angles.The spring index of coiled CNT fiber is effected by tensile stress.The coiled CNT yarns have high strength and low strain,and the elastic modulus lost much during the dynamic tensions.These are important for artificial muscles.2.Actuations of coiled CNT yarn muscles driven by organic solvent adsorption: We utilized different solvents to drive coiled CNT muscles.It is found that artificial muscles driven by acetone possess best actuation performance.Because acetone has low viscosity,high polarity,low surface tension,and low boiling point,and the adsorption volumes was maximum.Then CNT fibers were infiltrated in concentrated HNO3 and H2SO4 respectively to achieve surface treatment.The contractions of coiled CNT muscles which had been treated by HNO3 and H2SO4 were 1.4 and 1.6 times than the pristine muscles.Moreover,the energy density increased from 296.65 J/kg to 340.52 J/kg and 490.73 J/kg,respectively.3.Stabilize of coiled CNT yarns by Joule heating: After treated by 1500 °C,coiled CNT yarns are cured and we get a stable structure.Under a strain of 10%,the coiled CNT yarn could retain excellent cycling stability after 100 loading-unloading cycles.Infiltrated in acetone,the coiled CNT yarns could contract repeatedly.The method solved the instability of coiled yarns.4.A stable and high performance self-plied yarn muscles: Self-plied yarns were torque-balanced by plying two coiled CNT yarns,its torsional actuation was almost 0 °/mm.Self-plied muscles showed a contraction strain of about 13.3%,and the maximum specific work was about 847.2 J/kg which was 22 times than mammalian skeletal muscles.Additionally,the self-plied CNT muscles showed stable actuation performance after 400 cyclic absorption and desorption.5.Actuations of CNT yarn muscles driven by electro-thermal-solvent adsorption: Joule heating could reduce the desorption times of acetone and increased the response rate.When applied 60 m A,the desorption time is only 58% of the time at room temperature.By applying different currents,actuation modes could be adjusted.When the current was less than 80 m A,the muscle was driven by adsorption.With a current of 80 m A,the yarn was scarcely actuated.While the driving mode converted to electric thermal when the current exceed 80 m A.That indicated the actuation of CNT yarns driven by currents was mainly caused by temperature difference.