  The formation and evolution of immersed surface micro- and nanobubbles are
essential in various practical applications, such as the usage of
superhydrophobic rematerials, drug delivery, and mineral flotation. In this
work, we investigate the entrapment of microbubbles on a hydrophobic surface,
structured with microwells, when water flow passes along, and the subsequent
microbubble dissolution. At entrapment, the microbubble is initially pinned at
the edge of the microwell. At some point, the three-phase contact line detaches
from one side of the edge and separates from the wall, after which it further
recedes. We systematically investigate the evolution of the footprint diameter
and the contact angle of the entrapped microbubbles, which reveals that the
dissolution process is in the constant contact angle mode. By varying the gas
undersaturation level, we quantify how a high gas undersaturation enhances the
dissolution process, and compare with simplified theoretical predictions for
dissolving bubbles on a plane surface. We find that geometric partial blockage
effects of the diffusive flux out of the microbubble trapped in the microwell
lead to reduced dissolution rates.
