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

We report experiments of centimeter-sized sessile drop coalescence aboard the International Space Station (ISS), 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 \& Steen (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.