  We report on the collision-coalescence dynamics of drops in Leidenfrost state
using liquids with different physicochemical properties. Drops of the same
liquid deposited on a hot concave surface coalesce practically at contact, but
when drops of different liquids collide, they can bounce several times before
finally coalescing when the one that evaporates faster reaches a critical size,
of the order of the capillary length. The bouncing dynamics is produced because
the drops are not only in Leidenfrost state with the substrate, they also
experience Leidenfrost effect between them at the moment of collision. This
happens due to their different boiling temperatures, and therefore, the hotter
drop works as a hot surface for the drop with lower boiling point, producing
three contact zones of Leidenfrost state simultaneously. We called this
scenario the triple Leidenfrost effect.
