Thermal hysteresis in wettability and the Leidenfrost phenomenon

The Leidenfrost temperature (T-L), at which the liquid drop lifetime peaks on a superheated surface, is believed to be wettability dependent. Here, we show that the wettability effect on T-L is subject to the history of the surface temperature. Observing a water drop evaporating on a polished stainless-steel surface heated from 100 to 400 degrees C in argon gas, we find T(L )265 degrees C. We then repeat the experiment along decreasing temperature and find a TL L increase by 10 K, i.e., T-L 275 degrees C. This thermal hysteresis is due to a reduced contact angle during heating. Once hydrophilized, the hysteresis disappears until the contact angle recovers. Similar observations are made in the air where oxidation is possible.