Ripening droplet: spontaneous movement of non-contact micro/nano droplets*

The rapid removal of condensates is highly desirable in condensation. Existing technologies are centered on jumping droplets, which can passively remove coalesced droplets on superhydrophobic surfaces. However, the jumping effect suffers from significant weaknesses. First, it is inefficient to jump off by waiting for the contact of multiple droplets. Second, once droplets jump off, they can not contribute to the removal of other droplets. Third, the jumping effect relies on the existence of air under droplets, but the air can be easily displaced by condensates at an elevated subcooling. To overcome those bottlenecks, we present the newly observed ripening effect: non-contact tiny droplets are propelled to coalesce with bigger droplets on a pinning-free liquid infused surface. Moreover, large droplets can easily form and sweep the remaining droplets on the surface. The ripening process can passively remove micro/nanoscale droplets by gradient vapor pressure and rapidly generate water-free area for further condensation. Our ripening droplet demonstrates the sustainable passive droplet removal of non-contact tiny droplets, outperforming the state-of-the-art jumping droplet condensation.