Communications: Wall free capillarity and pendant drop removal

Abstract

When a sessile drop encounters a pendant drop through a hole, it is generally anticipated that they will coalesce and flow downward due to gravity. However, like "wall-free" capillarity, we show that the pendant drop may be sucked up by a sliding drop instantaneously if the radius of the curvature of the former is smaller than that of the later. This phenomenon can be explained by Laplace-Young equation and convective Ostwald ripening. Our results indicate that superhydrophilic perforated surface can be used as an effective way for the removal of small droplets adhering to the inner walls of microchannel systems.

Wetting Behavior of a Drop Atop Holes

“…Counterintuitively, liquid flowing up against gravity results in droplet advancing on the upper plane and a more flat bottom interface. Evidently, the surface free energy contribution dominates over that of the gravitational energy, and a wall-free capillary phenomenon is thereby observed . It may be useful in extracting liquid from microfluidic devices spontaneously or explaining fluid leakage from small holes against gravity.…”