First, there is a chemical effect: glass, unlike the vegetal wax that coats lotus leaves,
has a strong affinity for water. That is why a water drop spreads more easily on clear glass
than on greasy glass. Then, there is an additional physical effect : the surface of the lotus
leaf is covered with many microscopic bumps. The droplet does not touch the bottom of this
rough surface : it sits on the top of those micro-bumps like a fakir on nails.
We can mimic lotus leaf in our laboratory designing forests of micro-pillars by micro-fabrication techniques. Such substrates allow us to study the stability of those « fakir drops » and their subsequent properties: bouncing droplets, anti-adhesion, low-friction, anti-fogging…
When a water droplet meets a hot surface, it starts to boil and turns into vapor very quickly. But when the surface is clearly above the boiling temperature, the vapor forms quickly enough to create a thin layer between the surface and the drop, which is therefore levitating
This vapor film has two roles: