A humidity-driven film with fast response and continuous rolling locomotion

The widespread availability and easy accessibility of humidity make it essential to explore simple and low-cost methods to prepare structurally and materially efficient humidity-driven actuators with spontaneous and continuous locomotion to facilitate the application of bionic devices, intelligent sensors, and soft robots. Herein, this paper reports a humidity-driven monolayer film actuator. It is self-assembled from agarose (AG) and graphene oxide (GO) modified with polyvinylpyrrolidone (PVP), referred to as PGO, using a simple casting method. The PGO/AG composite film actuator exhibits an ultra-fast humidity response time (124.58° s−1) and recovery time (18.87° s−1), enabling rapid rolling locomotion driven by water evaporation. Notably, the programmable surface patterning of the PGO/AG composite film actuator with graphite results in a shorter single rolling time (0.43 s) and a faster rolling speed (28.73 mm s−1). Based on these advantages, the PGO/AG film actuator can mimic the opening and closing of flowers, mimosas, and fast-crawling robot driven by periodic water vapor (9.9 body length min−1). This finding provides new insights into the design of multifunctional actuators based on humidity-driven films.