How Coalescing Droplets Jump

TLDR

Surface engineering at the nanoscale is rapidly advancing, promising applications from energy to anti‑icing, and detailed insights into dynamic wetting—especially droplet coalescence on ultra‑low adhesion surfaces that can trigger droplet jumping—are increasingly needed. Our measurements and simulations show that droplet jumping during condensation is highly inefficient, converting less than 6 % of excess surface energy into kinetic energy, and reveal the internal fluid dynamics that must be considered to design systems that harness this phenomenon.

Abstract

Surface engineering at the nanoscale is a rapidly developing field that promises to impact a range of applications including energy production, water desalination, self-cleaning and anti-icing surfaces, thermal management of electronics, microfluidic platforms, and environmental pollution control. As the area advances, more detailed insights of dynamic wetting interactions on these surfaces are needed. In particular, the coalescence of two or more droplets on ultra-low adhesion surfaces leads to droplet jumping. Here we show, through detailed measurements of jumping droplets during water condensation coupled with numerical simulations of binary droplet coalescence, that this process is fundamentally inefficient with only a small fraction of the available excess surface energy (≲ 6%) convertible into translational kinetic energy. These findings clarify the role of internal fluid dynamics during the jumping droplet coalescence process and underpin the development of systems that can harness jumping droplets for a wide range of applications.