In conventional dropwise condensation on a hydrophobic surface, the condensate drops must be removed by external forces for continuous operation. This Letter reports continuous dropwise condensation spontaneously occurring on a superhydrophobic surface without any external forces. The spontaneous drop removal results from the surface energy released upon drop coalescence, which leads to a surprising out-of-plane jumping motion of the coalesced drops at a speed as high as $1\mathrm{m}/\mathrm{s}$. The jumping follows an inertial-capillary scaling and gives rise to a micrometric average diameter at steady state.

• Received 25 May 2009

DOI:https://doi.org/10.1103/PhysRevLett.103.184501