Assembly of Reduced Graphene Oxide-Conducting Polymer Fibers in the Lyotropic Liquid Crystal Phase as Synthetic Muscle Actuators*

Soft actuators are known for their compliance, adaptivity and dexterity, however, at the cost of load bearing, bit rates and energy efficiency compared with rigid body counterparts. Very few have achieved performance comparable with biological muscles with fast response time, high elastic energy and power density at the same time. Meanwhile, among different stimulation methods, application of electric fields is highly desired for more forceful and faster responses.

Here, we create strong and ultrafast actuators through wet-spinning of graphene oxide (GO) into fibers coupled with conducting polymers, PEDTO:PSS, with enhanced toughness, followed by reduction. The composite fibers exhibit ultra-fast (80 ms) and reversible bending via electrostatic repulsion between the well-aligned, closely packed rGO sheets assembled in the lyotropic liquid crystal (LLC) phase. We investigate the importance of pre-assembly of GP in LLC phase, and their confinement in a fiber vs. in film. We also suggest different approaches to enhance the close-packing of GO sheets.  When the fiber actuators are plied with nylon yarns together, the artificial muscles outperform skeletal muscles in terms of work capacity and power density without diminishing the bending strain and efficiency up to 10,000 cycles. Further, we show integration of the yarn actuators to power flapping wings and fishtail structures both in air and in water.