  Manipulating surface topography is one of the most promising strategies for
increasing the efficiency of numerous industrial processes involving droplet
contact with superheated surfaces. In such scenarios, the droplets may
immediately boil upon contact, splash and boil, or could levitate on their own
vapor in the Leidenfrost state. In this work, we report the outcomes of water
droplets coming in gentle contact with designed nano/micro-textured surfaces at
a wide range of temperatures as observed using high-speed optical and X-ray
imaging. We report a paradoxical increase in the Leidenfrost temperature (TLFP)
as the texture spacing is reduced below a critical value (~10 um). Although
droplets on such textured solids appear to boil upon contact, our studies
suggest that their behavior is dominated by hydrodynamic instabilities implying
that the increase in TLFP may not necessarily lead to enhanced heat transfer.
On such surfaces, the droplets display a new regime characterized by splashing
accompanied by a vapor jet penetrating through the droplets before they
transition to the Leidenfrost state. We provide a comprehensive map of boiling
behavior of droplets over a wide range of texture spacings that may have
significant implications towards applications such as electronics cooling,
spray cooling, nuclear reactor safety and containment of fire calamities.
