The phenomenon of bubble entrapment during capsule formation

During the formation of polymer-based capsules, following the impact of poly-anion drops onto a pool of poly-cation solution, an air bubble is often trapped on the drop/capsule surface, affecting the membrane quality locally. This entrapment has been experimentally examined for a typical anion-cation pair through detailed imaging of the impact crater. Experiments show that the bubble entrapment is caused by the collapse of the impact crater above the top surface of the submerged-and-reacting drop.