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

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.