Self-enhancement of droplet jumping velocity: the interaction of liquid bridge and surface texture

Abstract

Coalescence-induced droplet jumping on superhydrophobic surfaces (SHSs) has attracted considerable attention over recent years. Studies show that this jumping motion results from the impact of a liquid bridge on the substrate. However, quantitative experiments and mechanisms of the droplet jumping affected by a liquid bridge impingement are still very limited. In this paper, the effect of the liquid bridge impact on the droplet jumping is investigated experimentally and theoretically. Macrotextures (rectangular grooves and triangular prisms) are constructed on SHSs to regulate the impact position of the liquid bridge. The measured droplet jumping velocities in this work show that the impact of the liquid bridge will be delayed if the lower contour of the merging droplet falls into the gap of a rectangular groove, which results in a larger viscous dissipation that is not beneficial to the droplet jumping. In particular, we demonstrate that it is an alluring avenue to improve the droplet jumping velocity to break the jumping speed limit by making liquid bridge impacts on a triangular prism structure, which might be very significant for the design and fabrication of this kind of superhydrophobic material. The droplet hydrodynamics are altered, which accelerates the retraction of the droplet base area during the jumping process with the assistance of the additional structure.