Bioinspired Superhydrophobic Papillae with Tunable Adhesive Force and Ultralarge Liquid Capacity for Microdroplet Manipulation

Template-free, highly efficient, and large-area construction of complex multiscale architectures is still a great challenge for microfabrications. Inspired by the hierarchical micropapillae on the superhydrophobic surface of natural rose petals, here, a facile 3D shrinking method is reported to build a graphene oxide (GO) papillae array. Circular GO speckles with a gradient of thickness are deposited on an inflated latex balloon through the water-evaporation-driven assembly of GO nanosheets, which then shrink into hierarchical papillae under compressive stresses upon deflation. The fluoroalkylsilane modified GO papillae array exhibits a combined performance of strong superhydrophobicity (CA > 170 degrees), tunable adhesive force (39.2-129.4 mu N), and ultralarge liquid capacity (25 mu L). The wetting states (Wenzel, Cassie-I, and Cassie-Baxter), the adhesive forces, and the liquid capacities all can be tuned by varying the buckling topography (microwrinkle or microfold), the papillae number (3, 4, 6, or 7), and the array arrangement (triangle, square, or hexagon). For one single papillae, the highest adhesive force and the highest liquid capacity incresed to a record breaking value of 26.5 mu N and 4.2 mu L, respectively, which are promising for programmable manipulations of microdroplets and relevant for multistep microreactions.