Water-Evaporation-Powered Fast Actuators with Multimodal Motion Based on Robust Nacre-Mimetic Composite Film.

Water evaporation as a source of energy to trigger moisture-responsive soft materials is an emerging field in a variety of energy-harvesting devices, which has attracted widespread attention. Here, we design and fabricate bioinspired nacrelike composite film actuators consisting of graphene oxide and sodium alginate, which demonstrate an obvious shrinkage in volume when their state transfers from wet to dry and the contractile stress is up to 42.3 MPa. Based on these features, the film actuators can show rapid and continuous movements under the water gradient. The flipping frequency of the actuators can reach up to 76 rounds min, which is much faster than those in previous reports. The film can flap back and forth quickly on water vapor even after loading a cargo that is 9 times its own weight. Moreover, high mobility with multimodal motion including blooming, stretching, folding, and twisting can also be achieved by modulating the shapes of films. Thus, film actuators may hold great potential in many fields, such as microrobots, artificial muscles, and sensors on grounds of their rapid response speed and adjustable motion models.