  Coalescence is an important hydrodynamic event that frequently takes place in
nature as well as in industry. Here we provide an experimental study on short
time dynamics of water coalescence, particularly when a water droplet comes in
contact with a flat water surface, by utilizing high-resolution
high-penetration ultrafast X-ray microscopy. Our results demonstrate a
possibility that an extreme curvature difference between a drop and a flat
surface can significantly modify the hydrodynamics of water coalescence, which
is unexpected in the existing theory. We suggest a plausible explanation for
why coalescence can be modified by an extreme curvature difference.

Fluid Dynamics;Soft Condensed Matter