Coalescence-induced droplet spreading: Experiments aboard the International Space Station

Abstract

We report experiments of centimeter-sized sessile drop coalescence aboard the International Space Station, where microgravity conditions enable inertial-capillary spreading motions to be explored for a range of hydrophobic wetting conditions. Observations of the time traces of the coalescence event and projected areas compare favorably to numerical simulations, which employ the Davis–Hocking contact line (CL) condition with contact line mobility M parameter independently measured using the resonant-frequency scan technique of Xia and Steen [“Moving contact-line mobility measured,” J. Fluid Mech. 841, 767–783 (2018)]. This observation suggests that M is a material parameter, and that the Davis–Hocking model is an appropriate CL model for inertial-capillary spreading.