|
Surfaces designed in such a way that liquid drops do not adhere to them but instead rebound off have received considerable attention because of a wide range of their applications including resist-icing, spray cooling and self-cleaning. A drop impacting on non-wetting surface will spread out to a maximum lateral deformation and then recoil in such a way that it completely rebounds and finally leaves the solid material. The amount of time that the drop stays in contact with the solid, namely “contact time” depends on the inertia and the capillarity of drop, internal dissipation and surface structures. It is often advantageous to minimize the contact time, since it controls mass, momentum and energy transfer between liquid and solid surface. Surfaces that are hydrophobic and patterned by a lattice of posts exhibit superhydrophobic behaviour which dramatically reduces the contact time between drop and solid material (Bird, James C., et al. Nature (2013), Liu, Yahua, et al. Nature Physics (2014).). Superhydrophobic surfaces exhibit extreme water-repellent properties. Drops impacting superhydrophobic surfaces normally spread, retract, and leave the surface in an approximately spherical shape, with little loss of energy. Recently, it was experimentally shown that drops can leave the substrate before retracting while still in an extended pancake-like form (Liu, Yahua, et al. Nature Physics (2014)). We use the Entropic Lattice Boltzmann Method to simulate a drop impacting on superhydrophobic surface decorated with a lattice of posts and compare simulation results with experimental data. Experiment and also our simulation show that such “pancake bouncing” occurs when impacting drop is slowed down and then ejected by capillary forces. Moreover, we present new finding of an optimized structure on the surface under which contact time is minimized.
|