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 $400{}^{\circ }\mathrm{C}$ in argon gas, we find $T_L\approx 265{}^{\circ }\mathrm{C}$. We then repeat the experiment along decreasing temperature and find a $T_L$ increase by 10 K, i.e., $T_L\approx 275{}^{\circ }\mathrm{C}$. 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.