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Abstract:
Volatile drops deposited on a hot solid can levitate on a cushion of their own vapor, without contacting
the surface. We propose to understand the onset of this so-called Leidenfrost effect through an analogy to
nonequilibrium systems exhibiting a directed percolation phase transition. When performing impacts on
superheated solids, we observe a regime of spatiotemporal intermittency in which localized wet patches
coexist with dry regions on the substrate. We report a critical surface temperature, which marks the upper
bound of a large range of temperatures in which levitation and contact coexist. In this range, with
decreasing temperature, the equilibrium wet fraction increases continuously from zero to one. Also, the
statistical properties of the spatiotemporally intermittent regime are in agreement with that of the directed
percolation universality class. This analogy allows us to redefine the Leidenfrost temperature and shed light
on the physical mechanisms governing the transition to the Leidenfrost state.
