How Droplets Move on Surfaces with Directional Chemical Heterogeneities

The nature of adhesion of droplets to surfaces is a long pending scientific question. With the evolution of complex surfaces, quantification and prediction of these adhesion forces become intricate. Nevertheless, understanding these forces is highly relevant for explaining liquid transport in nature and establishing design guidelines for manmade interfaces. Here, it is shown that adhesion of droplets is highly sensitive to the direction of chemical heterogeneities, both in the static and dynamic regimes. This dependency is quantified by bending beam and droplet roll-off experiments. The shape of the fluid contact line on the microscale elucidates the origin of the direction-dependent adhesion. Namely, the droplet receding part pins to a higher number of patches when moving toward to the apex in comparison to the opposite direction. These findings improve the understanding of droplet adhesion to surfaces with chemical heterogeneities and directional transport phenomena.