Symmetry breaking in drop bouncing on curved surfaces

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.

Drops bouncing off macro-textured superhydrophobic surfaces

“…A spectacular reduction in contact time by factor of four was reported. Further experimental studies of similar macro-textures can be found in [12,18]. Although pancake bouncing was shown to reduce the contact time significantly, questions remain regarding the physics behind the phenomenon including the role played by surface energy, viscous dissipation and influence of air pockets that might be trapped between the droplet and the surface texture.…”

“…Minimization of contact time is a central point in a rational design of hierarchically structured surfaces and has been the focus of recent studies [6,7,12,18,19,32,37,38]. Richard, Clanet, and Quéré [32] found that the conventional mechanism of rebound on macroscopically flat superhydrophobic surfaces (impact-spread-recoil-rebound, [28, 31, 32, 43]) scales universally with the inertia-capillarity time,…”

“…For example, nanoand/or microscale roughening of a flat hydrophobic substrate yields a super-hydrophobic surface (contact angle above θ = 150 ○ and negligible contact angle hysteresis) through trapping gas. Drop repellence from hydrophobic and super-hydrophobic surfaces is an area of active research [6,8,12,14,18,19,28,29,32,38,41,46].…”

A solvable model of axisymmetric and non-axisymmetric droplet bouncing

“…Several authors have recently shown that the drop-substrate contact time is reduced if the bouncing is not axisymmetric [20][21][22][23] . Non-axisymmetric bouncing may result from an asymmetry in the initial conditions, such as different initial momenta along the a and b directions or a non-axisymmetric drop shape at the collision, or from anisotropy of the physical process of interaction of the drop with the substrate, such as anisotropic surface drag.…”

“…Examples include micro-scale ridges on a flat surface 20 , superhydrophobic stripes 21 , cylindrical substrates 22 , and wires laid upon surfaces 23 . These experiments and simulations showed that inducing non-axisymmetric bouncing modes reduces the contact time of a drop on a surface below that found for axisymmetric collisions.…”