Tough biomimetic films for harnessing natural evaporation for various self-powered devices

Natural water evaporation is a ubiquitous resource at the Earth's surface. Actuating materials that convert such evaporation energy into mechanical motions are highly desirable but challenging. Herein, tough nacre-mimetic films featuring excellent dry/wet tensile strength (294.4 MPa/182.3 MPa) are reported. Benefiting from this feature, the resultant film actuators can not only perform fast flipping motion and lasting oscillation driven by natural evaporation, but also undergo rapid turnover upon exposure to small humidity gradients on the palm of the hand. Importantly, the film actuators further exhibit exceptional actuation without fatigue when exposed to thermal water vapors. Furthermore, it is demonstrated that the stretch-induced oriented film could be used to construct a self-powered soft robot driven by water gradients. As a proof of concept, a natural evaporation-driven generator is assembled by connecting the actuators with a piezoelectric element to power a LED. These demonstrations clearly show that the biomimetic films are promising for harnessing natural evaporation to drive various self-powered devices.