Perfectly monodisperse microbubbling by capillary flow focusing: an alternate physical description and universal scaling.

In a recent work [Phys. Rev. Lett. 87, 274501 (2001)], a method to produce monodisperse microbubbles was described. The physics of the phenomenon was explained in terms of the absolute instabilities of a gas microjet formed when a liquid stream which surrounds a coflowing gas stream is forced through a small orifice. Now, a much more consistent physical picture to describe the phenomenon which corrects prior assumptions is presented. Consequently, a much simpler and universal scaling law for the microbubble size is finally obtained which involves the orifice diameter and the gas/liquid flow rates ratio only. All data shown in prior works, together with newly obtained data sets, have been analyzed anew. These are in remarkable agreement with the here proposed scaling law.