This is a slow-paced phase-contrast movie showing the formation of microbubbles in a cascade.
Microbubbles formed this way can be used to track thin film flows. The highly refractive surfactant
droplet first explodes into a less bright or even invisible film that spreads over a much larger
area than the size of the droplet. The film then contracts and bubbles form at the periphery of the
film. The film contraction proceeds and a second round of bubble formation takes place, resulting in
many bright air bubbles all over the area previously occupied by the film. The bubbles formed in the
end have a minimum diameter of ~1.0 μm and a maximum diameter of ~2.0 μm. See: Wu et al., PNAS
108(10): 4147-51.