Super‐Flexible Water‐Proof Actuators

Abstract Humidity‐responsive materials hold broad application prospects in sensing, energy production, and other fields. Particularly, humidity‐sensitive, flexibility, and water resistance are pivotal factors in the development of optimized humidity‐responsive materials. In this study, hydrophobic linear polyurethane and hydrophilic 4‐vinylphenylboronic acid (4‐VPBA) form a semi‐intercross cross‐linking network. This copolymer of polyurethane exhibits excellent humidity‐sensitive, mechanical properties, and water resistance. Its maximum tensile strength and maximum elongation can reach 40.56 MPa and 543.47%, respectively. After being immersed in water at various temperatures for 15 days, it exhibited a swelling ratio of only 3.28% in water at 5 °C and 9.58% in water at 70 °C. While the presence of 4‐VPBA network imparts humidity‐sensitive, reversible, and multidirectional bending abilities, under the stimulus of water vapor, it can bend 43° within 1.4 s. The demonstrated material surpasses current bidirectional humidity actuators in actuating ability. Based on these characteristics, automatically opening waterproof umbrellas and windows, as well as bionic‐arms, crawling robots, and self‐propelled boats, are successfully developed.