Snapping induced by controlled drying of polymer gels: from moving bonito flakes to jumping shells*

Dynamic changes in swelling states can induce life-like motions in bonito flakes placed on a hot Okonomiyaki. The shape transitions of these thin polypeptides films not only happen smoothly but also occur abruptly. Inspired by these generally occurring, but random events, we developed novel design principles for inducing self-repeating snapping motions during the drying process of swollen polymer disks that can persist until the depletion of the solvent. We demonstrate the ability to tune the system performance of these polymer devices to achieve either higher jumping kinetics (t ~ 2ms, Power ~ 370W/kg) or greater total energy output (Eout ~ 2J/kg) by controlling the geometry and boundary conditions. The performance of the snapping shells under different conditions was modeled with finite element analysis results. The systematic study on the snapping mechanism and its incorporation into engineered systems will bring great advantages for designing micro-scale, high-efficiency robots.