  Coalescence-jumping of condensation droplets is widely studied for
anti-icing, condensation heat transfer, water harvesting and self-cleaning.
Another phenomenon that is arousing interest for potential enhancements is the
individual droplet self-ejection. However, whether it is possible from
divergent structures without detachment from pinning sites remains unexplored.
Here we investigate the self-ejection of individual droplets from divergent,
uniformly hydrophobic structures. We designed, fabricated and tested arrays of
nanostructured truncated microcones arranged in a square pattern. The dynamics
of the single condensation droplet is revealed with high speed microscopy: it
self-ejects after cycles of growth and self-propulsion between four cones.
Adopting the conical pore for simplicity, we modelled the slow iso-pressure
growth phases and the surface energy release-driven rapid transients enabled
once a dynamic configuration is reached. In addition to easier fabrication,
microcones with uniform wettability have the potential to allow self-ejection
of almost all the droplets with a precise size while maintaining mechanical
resistance and thus promising great improvements in a plethora of applications.
