Fast‐Response and Large‐Deformation Moisture‐Driven Janus Structured Fiber Actuator Composed of Multiscale Hydrophilic‐Hydrophobic Interfaces

Abstract Moisture‐driven actuators are the smart materials or devices that respond to changes in humidity by converting moisture fluctuations into mechanical motion, with versatile applications in soft robotics, bio‐inspired systems, smart textiles, and intelligent devices. In this work, a fast and large‐deformation moisture‐driven Janus fiber actuator with multiscale hydrophilic‐hydrophobic interfaces inside is fabricated. Specifically, the Janus fiber actuators are composed of hydrophilic side and hydrophobic side to create a macroscopic hydrophilic‐hydrophobic interface, while the highly hydrophilic polyethylene glycol segments in the hydrophilic side form island‐like phase domains inside polyurethane matrix and create the microscopic hydrophilic‐hydrophobic interfaces. These unique multiscale hydrophilic‐hydrophobic interfaces endow the Janus fiber with fast and reversible swelling–deswelling feature, thus enabling it with superior moisture‐driven performance. The actuator exhibits a maximum contraction rate of 96.68%, a contraction speed of 58.23% s −1 , a curvature of 33.33 cm −1 , and a maximum response speed of 14.2 cm −1 s −1 , outperforming all reported moisture‐driven fiber‐based actuators. Due to these exceptional properties, the actuators can be applied in bio‐inspired systems to mimic the contraction behaviors of natural actuators. More interestingly, the actuators can also be used as moisture‐sensitive smart wigs, which can reversibly switch between short curls and straight hair in response to changes in humidity.