Morphing textures by dynamic polymorphic elastocapillarity

We present soft structures which switch their shapes or pattern textures via delicate external forces driven by hydrodynamics, capillarity, and elasticity. We fabricate an elastomeric fin between two parallel walls, and close to a drainage pore at the base on one side to break the symmetry. The drainage pore is used to secrete and drain liquid which interacts with the soft fin. We further break the symmetry of the device by adding an eccentricity such that the fin is closer to the wall on one side, that side without the drainage pore. Depending on the drain rates controlled by a syringe pump, the fins show bimorphic textures due to the interplay between hydrodynamics and capillarity. At the slow drainage, the flexible fin deforms to the narrow side due to the capillary pressure at the narrow spacing. However, the fin flaps to the wide side at fast drainage. This is mainly due to the suction pressure within the soft cell induced by drain dynamics We develop a theoretical model to provide a universal regime map for the texture style of the flapping fins. Further, we present a more complex polymorphism in the array of the flapping fins. This novel switchable texture system can pave the way for various practical implications such as reflective display and multimodal signaling system.