Actuation Behavior Study Of Carbon Nanotube/Liquid Crystal Polymer Composite Artificial Muscle Fibers

Smart materials represented by artificial muscle fibers have obtained widespread attention due to their excellent performance and muscle-like properties.The development of soft robots has enriched the application fields of artificial muscle fibers,and the self-adaptably smart fibers responding to the environment are the research direction of new materials in the future.The coiled artificial muscle fibers with large contractile stroke,high output power,and wide material sources are promising in new robotic applications.Although the coiled fiber has many advantages,it still suffers from several challenges:1.how to develop high-performance coiled fibers(large contractile stroke,high actuation force and fast response);2.how to endow coiled fibers with selfrecoverable properties;3.how to execute the application according to the function of coiled fibers.Therefore,the development of coiled fibers with high performance and self-recoverability is a challenge in the field of artificial muscle fibers.In this paper,the high-performance carbon nanotube/liquid crystal elastomer composite fibers are constructed,where the carbon nanotube(CNT)fiber acts as the backbone and the liquid crystal elastomer(LCE)acts as the guest material.We further investigate the actuation mechanism of the composite fibers and their possible application demonstrations.This paper mainly includes the following three aspects:1.In response to the problem of the slow response rate of artificial muscle fibers,inspired by the spring structure,supercoiled artificial muscle fiber was constructed.The composite fiber with a sheath-core structure was constructed based on CNT fibers and LCE.The structure of the supercoiled fiber is regulated by inserting an ultra-high twist,which provides more space for contraction.This structure reduces the specific surface area of the fiber,which allows more heat accumulation and enables ultrafast response.The maximum contraction rate of the fiber reached 452%/s in 0.1 s.This fiber works well in both air and water and exhibits good cycling stability.2.In response to the problem of insufficient actuation force and poor structure stability of supercoiled fibers.Inspired by commercial plied yarns,2-ply coiled fibers are prepared by twisting the fibers in parallel.A 2-ply coiled structure is more stable compared with supercoiled fiber.The actuation force of the coiled 2-ply fiber is more than twice that of the supercoiled fiber owing to the better orientation of the liquid crystal(LC)molecules on the surface by the extrusion and stretching of the adjacent coil fibers.Inspired by the biological muscle fibers,the actuation performance of fiber bundles was further investigated.The contraction reduces after bunching but remains above 30%,and the actuation force is greater than 0.5 N.Fiber bundles have more advantages in applications.3.In response to the poor work capacity of the above two fibers and the weak selfrecovery of most coiled fibers,a 2-ply coiled fiber with higher stiffness was constructed by adjusting the types of guest materials.The load resistance of the fiber is increased due to the improved stiffness.Therefore,the contraction of the fiber is higher under the same load,and the work capacity is increased by more than two times.In addition,the helical stress induces the oriented arrangement of LC molecules and the stably coiled structure fixes the aligned LC mesogens,imparting self-recoverability to the composite fibers.The self-recoverability and large explosive force of the fibers provide greater advantages for applications in soft robotics and biomedicine.