De-wetting of evaporating drops on regular patterns of triangular posts

Abstract

Directional wicking and spreading of liquids can be achieved by regular micro-patterns of specifically designed topographic features that break the reflection symmetry of the underlying pattern. The present study aims to understand the formation and stability of wetting films during the evaporation of volatile liquid drops on surfaces with a micro-pattern of triangular posts arranged in a rectangular lattice. Depending on the density and aspect ratio of the posts, we observe either spherical-cap shaped drops with a mobile three-phase contact line or the formation of circular or angular drops with a pinned three-phase contact line. Drops of the latter class eventually evolve into a liquid film extending to the initial footprint of the drop and a shrinking cap-shaped drop sitting on the film. The drop evolution is controlled by the density and aspect ratio of the posts, while no influence of the orientation of the triangular posts on the contact line mobility becomes evident. Our experiments corroborate previous results of systematic numerical energy minimization, predicting that conditions for a spontaneous retraction of a wicking liquid film depend weakly on the orientation of the film edge relative to the micro-pattern.

Chemical physics of controlled wettability and super surfaces

“…These simulations enable a comprehensive characterization of the droplet's dynamics and provide insights into the various mechanisms governing droplet mobility, particularly in the context of competing forces. Reference [3] reports an experimental study complemented by simulations to systematically study and describe the dynamics of evaporating drops on surfaces with micro-patterns of triangular posts.…”