Omnidirectional droplet propulsion on surfaces with a Pac-Man coalescence mechanism

Abstract

Electrohydrodynamic (EHD) nanoprinting is used to demonstrate a novel open-atmosphere microfluidic platform, where femtoliter sessile droplets can be formed sustainably despite high volatility, manipulated, and made mobile in any planar direction on-demand, by a sequence of controlled coalescence events. By studying sessile droplet coalescence kinetics in a partially wetting regime, we found that, even for minute droplet sizes, contact line motion still dominates. Coalescing moving droplets were tasked to perform typical microfluidic operations like collecting, transporting, and merging solid materials on otherwise unpatterned substrates.