Hygroresponsive Torsional Yarns and Actuators Based on Cascade Amplification of the Deformation

Fiber‐based hygroresponsive torsional actuators provide desirable merits, such as light weight and shapeability, for developing smart systems to harvest energy from moisture which is a ubiquitous natural resource. A key challenge in this development is to realize moisture‐triggered actuation combining large actuation and rapid responses. Here, a multiscale design strategy is explored to create high‐performance hygroresponsive torsional actuators consisting of chitosan and multiwalled carbon nanotubes (MWCNTs). The superior actuation performance arises from the synergism of contributing factors at different scales, including 1) MWNCTs accelerate the water transport in primary twisted fibers (PTFs), fostering the rotation of PTFs upon moisture stimuli; 2) in situ‐formed hierarchically‐assembled twists realize cascade amplification of moisture‐triggered actuation. Specifically, PTFs are self‐twisted to generate secondary helical yarns, that are subsequently over‐twisted to yield tertiary coiled yarn. The resultant yarn actuator can reach a maximum rotation speed of 11 400 rpm in 5 s, output gravitational potential energy of 2.4 J kg−1 and gravitational potential power of 0.053 W kg−1 during contraction. This work represents the first design of fiber‐based actuators by virtue of moisture‐triggered in situ formation of yarns. The established principles of multiscale design will enable high‐performance fiber‐based hygroresponsive actuators toward advanced intelligent textile and soft robotics.