title: How coalescing droplets jump.
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.
authors.affiliation: Thermal Management Research Group, Efficient Energy Transfer (ηET) Department, Bell Laboratories Ireland, Alcatel-Lucent Ireland Ltd. , Blanchardstown Business & Technology Park, Snugborough Road. Dublin 15, Ireland.
authors.forename: Ryan
authors.initials: R
authors.lastname: Enright
authors.forename: Nenad
authors.initials: N
authors.lastname: Miljkovic
authors.forename: James
authors.initials: J
authors.lastname: Sprittles
authors.forename: Kevin
authors.initials: K
authors.lastname: Nolan
authors.forename: Robert
authors.initials: R
authors.lastname: Mitchell
authors.forename: Evelyn N
authors.initials: EN
authors.lastname: Wang
keywords: coalescence; condensation; droplet jumping; microfluidics; nanostructured surface design; superhydrophobic; wetting