Fig. 1. Water drops on hot hydrophilic and superhydrophobic materials.
(A) Water drops (Ω = 4 μl) on a hydrophilic silicon wafer (blue frame) or on a superhydrophobic Glaco-treated wafer (red frame) brought to temperature T. Scale bar, 1 mm. While boiling occurs above 100°C in the hydrophilic case, neither boiling nor apparent change in shape is observed on the repellent solid. Both drops only become similar above 210°C, in a common Leidenfrost state. (B) Lifetime τ of water drops (Ω = 20 μl) as a function of the substrate temperature T on bare aluminum (blue data) and Glaco-treated aluminum (red data). Each point is an average over at least five measurements, and error bars represent standard deviations. The Leidenfrost transition is observed at TL ≈ 210°C on the hydrophilic substrate, whereas τ(T) monotonically decreases in the repellent situation. Beyond TL, both curves superimpose.