Droplet impact on superhydrophobic substrates

Electrowetting-controlled transition between bouncing and sticky droplets.

Superhydrophobic surfaces have a surface chemistry and topography tailored to synergistically reduce their wetting by fluids. A well-known example from nature is the lotus leaf. Dew or rain droplets do not spread on this leaf, but bounce back (bouncing droplet). In a student project, Karina van Beek and Florian Sterl (supervised by Jolet de Ruiter) are working with superhydrophobic substrates. By increasing the droplet velocity above a critical value, the droplet impales the superhydrophobic structure and remains stuck (sticky droplet). We make use of electrowetting to control this transition between bouncing and sticky droplets. The movie shows a 3D-animation (made by Florian Sterl) of the two regimes.

The movie can be viewed here.