Gravito-capillary trapping of pendant droplets under wet uneven surfaces

Pendant drops spontaneously appear on the underside of wet surfaces through the Rayleigh-Taylor instability. Here, I show that such pendant drops can get stuck on topographic defects, despite having no contact line. Unlike traditional pinning, the trapping force has a gravito-capillary origin: liquid has to move up or down and the interface has to deform for the drop the pass the defect. I model this topography induced force, demonstrate how to harness it to guide pendant drops, and expect it to be relevant to other contact line free systems.