Breakdown in the directional transport of droplets on the peristome of pitcher plants

Over the centuries, scientists and engineers have been fascinated by the directional transport of water on the peristome of pitcher plant. Through experimental investigation and theoretical analysis, here we reveal the more complex picture of droplet transport on this peculiar natural surface. First, we demonstrate that in addition to the presence of the asymmetric arch-shaped microcavity with gradient wedge corners and sharp edges, the structural gradient in the first-tier microgroove of the pitcher's peristome also plays an important role in the regulation of the directional droplet transport. Moreover, the directional liquid transport only occurs in a limited condition. Without the intricate control of the interplay between its multiscale structures and multiscale sources of water, as well as the dynamic conditions of water, the preferential directional droplet transport will collapse. The new transport phenomenon and the mechanisms we reveal will provide important insights for the design of asymmetric morphologies for droplet manipulation.