Abstract
The impact of liquid drops on solid surfaces is ubiquitous in nature, and of practical importance in many industrial processes. A drop hitting a flat surface retains a circular symmetry throughout the impact process. Here we show that a drop impinging on Echevaria leaves exhibits asymmetric bouncing dynamics with distinct spreading and retraction along two perpendicular directions. This is a direct consequence of the cylindrical leaves that have a convex/concave architecture of size comparable to the drop. Systematic experimental investigations on mimetic surfaces and lattice Boltzmann simulations reveal that this novel phenomenon results from an asymmetric momentum and mass distribution that allows for preferential fluid pumping around the drop rim. The asymmetry of the bouncing leads to ∼40% reduction in contact time.
Highlights
The impact of liquid drops on solid surfaces is ubiquitous in nature, and of practical importance in many industrial processes
Since Worthington’s pioneering work studying the complex dynamics of liquid drops impacting on solid surfaces[1] in 1876, extensive progress has been made in understanding and controlling drop dynamics on various textured surfaces
Bird et al.[4] showed that drops impacting on surfaces where asymmetry is introduced with ridges, an order of magnitude smaller than the drop, leave the surface with shortened contact time
Summary
The impact of liquid drops on solid surfaces is ubiquitous in nature, and of practical importance in many industrial processes. We show that a drop impinging on Echevaria leaves exhibits asymmetric bouncing dynamics with distinct spreading and retraction along two perpendicular directions. This is a direct consequence of the cylindrical leaves that have a convex/concave architecture of size comparable to the drop. The left–right symmetry can be broken by imposing a surface gradient to induce a directional movement[32,33,34,35,36] or by considering impacts on a moving surface[37,38] In these studies, the reported surfaces are still macroscopically flat, with the feature size at the scale of microns or nanometres. Evidence from lattice Boltzmann simulations and analytical analysis reveals that the drop hydrodynamics is due to the anisotropic architecture, which engenders an asymmetric momentum distribution and flow coupling
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