Droplet ski-jumping on an inclined macro-textured superhydrophobic surface

Abstract

Rapid shedding of impinging water drops is crucial in a cold habitat for diverse reasons spanning from self-cleaning to thermal regulation in most plants, animals, and industrial applications as well. It was shown recently that deploying linear millimetric ridges on a superhydrophobic surface can reduce the contact time (for drops crashing normally) up to 50% compared to a flat surface. However, the contact time rises for drops impacting at an increasing offset to the structure. Counter-intuitively, we demonstrate a ski-jumping mechanism occurring only over a range of offsets from the macro-structure with a remarkable reduction in contact time (∼65%) during oblique impacts. Theoretically, the reduction can be as high as 80%. The flow hydrodynamics is very similar to the oblique impacts on a flat surface. However, the architecture of ridge allows the drop to rapidly fly away from the surface. This work provides new insight which can be useful for the design of surfaces with high water repellency.