ABSTRACT: This presentation discusses unprecedented directional transport during the coalescence process on a pre-wetted cylindrical fiber, where either the coalesced droplets self-propel or the larger droplet is pulled toward the smaller one. The magnitude of the latter effect often exceeds that of the gravitational pull, allowing coalescing droplets to temporarily ascend a vertical fiber. This phenomenon occurs primarily because the viscous friction that a droplet experiences on a pre-wetted cylindrical fiber is negatively correlated with the size of the droplet, in contrast to the droplets coalescing on flat surfaces. We present a scaling relationship and a mass-spring-damper (MSD) model to explain the behavior of merging droplets. The numerical calculation results from our MSD model show qualitative agreement with the empirically measured directional migration of merged droplets. This research reveals an intriguing aspect of the coalescence dynamics of droplets, offering a fresh perspective on the interfacial phenomena in droplet-fiber systems.

BIOSKETCH: Dr. K.-C. Kenneth Park joined the Department of Mechanical Engineering as an Assistant Professor in 2017. He received his BS in mechanical and aerospace engineering from Seoul National University in 2008 and his MS and PhD in mechanical engineering from MIT in 2013. He then worked as a postdoctoral fellow in the Wyss Institute for Biologically Inspired Engineering at Harvard University in 2013-2016. He was selected as a recipient of the 2021 Hanwha Non-Tenured Faculty Award, the 2023 Micro Flow and Interfacial Phenomena Outstanding Early Career Award, and the 2023 Cole-Higgins Award for Excellence in Teaching. His research group works on bio-inspired surface engineering problems and interfacial transport phenomena.