Drop impact

The resulting outcome depends on the properties of the drop, the surface, and the surrounding fluid, which is most commonly a gas.

Richard and Quéré showed that a small liquid drop was able to bounce off of a solid surface over 20 times before coming to rest.

[6] Of particular interest is the length of time that the drop remains in contact with the solid surface.

To find a relationship between drop size and contact time for low Weber number impacts (We << 1) on superhydrophobic surfaces (which experience little deformation), a simple balance between inertia (

[9] For large-deformation drops (We > 1), similar contact times are seen even though dynamics of impact are different, as discussed below.

[9] By creating tapered surfaces with large spacing, the impacting droplet will exhibit the counterintuitive pancake bouncing, characterized by the droplet bouncing off at the end of spreading without retraction, resulting in ~80% contact time reduction.

The drop deformation pattern can be split up into regimes based on the Weber number.

[3] If the velocity is below a critical value, the liquid will spread on the surface, similar to deposition described above.

[11][12] Splashing on thin fluid films occurs in the form of a corona, similar to that seen for dry solid surfaces.

Under proper conditions, droplet hitting a liquid interface can also display a superhydrophobic-like bouncing, characterized by the contact time, spreading dynamics and restitution coefficient independent of the underlying liquid properties.

Cleanliness of the liquid surface is reportedly very important in the ability of drops to float.

[14] If the drop is able to rupture a thin film of gas separating it from the liquid reservoir, it can coalesce.

Finally, higher Weber number drop impacts (with greater energy) produce splashing.

[14][16] If the impact energy is high enough, the jet rises to the point where it pinches off, sending one or more droplets upward out of the surface.