On the biggest bubble formed in quasi-static conditions from a submerged orifice*

We present an experimental study on quasi-static bubble formation from a submerged orifice on a super-hydrophobic substrate. When injecting air in a quiescent liquid, bubbles grow until the surface tension forces cannot longer balance the buoyancy, and the detachment occurs. If the contact line is pinned to the injector, the maximum diameter, and therefore the volume of the bubble, is limited by the Rayleigh-Taylor instability. However, this limitation can be overcome if the contact line movement allows the bubble base expansion. The properties of the surface, in particular the contact angle θ, affect crucially this contact line dynamics. Thus, to determine how the surface wettability affects the dynamics of the bubble formation, we have performed experiments using a substrate whose contact angle is modified with a super-hydrophobic coating, reaching values of θ≈165^o, significantly higher than those previously studied. Our results show that the expansion of the base diameter in the early times, in addition to its retraction to the orifice scale prior to the detachment, results in the generation of bubbles with volumes substantially larger than those reported up to date.