title: Suppression of instabilities in multiphase flow by geometric confinement.
abstract: We investigate the effect of confinement on drop formation in microfluidic devices. The presence or absence of drop formation is studied for two immiscible coflowing liquids in a microfluidic channel, where the channel width is considerably larger than the channel height. We show that stability of the inner fluid thread depends on the channel geometry: when the width of the inner fluid is comparable to or larger than the channel height, hydrodynamic instabilities are suppressed, and a stable jet that does not break into drops results; otherwise, the inner fluid breaks into drops, in either a dripping or jetting regime. We present a model that accounts for the data and experimentally exploit this effect of geometric confinement to induce the breakup of a jet at a spatially defined location.
authors.affiliation: Department of Physics, School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Katherine J
authors.initials: KJ
authors.lastname: Humphry
authors.forename: Armand
authors.initials: A
authors.lastname: Ajdari
authors.forename: Alberto
authors.initials: A
authors.lastname: Fernández-Nieves
authors.forename: Howard A
authors.initials: HA
authors.lastname: Stone
authors.forename: David A
authors.initials: DA
authors.lastname: Weitz