Architecture-Driven Fast Droplet Transport without Mass Loss

Spontaneous droplet transport without mass loss has great potential applications in the fields of energy and biotechnology, but it remains challenging due to the difficulty in obtaining a sufficient driving force for the transport while suppressing droplet mass loss. Learning from the slippery peristome of Nepenthes alata and wedge topology of a shorebird beak that can spontaneously feed water against gravity, a combined system consisting of two face-to-face hydrophilic slippery liquid-infused porous surfaces (SLIPS) with variable beak-like opening and spacing was proposed to constrain the droplet in-between and initiate fast droplet transport over a long distance of 75 mm with a maximum speed of 12.2 mm·s–1 without mass loss by taking advantage of the Laplace pressure gradient induced by the asymmetric shape of the constrained droplet. The theoretical model based on the Navier–Stokes equation was developed to interpret the corresponding mechanism of the droplet transport process. In addition, in situ sophisticated droplet manipulations such as droplet mixing are readily feasible when applying flexible 304 stainless foil as the substrate of SLIPS. It is believed that extended research would contribute to new references for the precise and fast droplet motion control intended for energy harvest and water collection devices.