(398f) Escape from Pinch-Off during Contraction of Low-Viscosity Liquid Sheets or 2D Drops.

Liquid sheets are omnipresent in many industrial applications such as spraying and polymer processing. The cross-sections of such sheets are rectangular in shape but with rounded ends, i.e. elongated 2D drops, such that the two ends contract towards each other due to surface tension forces. If sufficiently thin (of the order of a few tens of nanometers), sheets can rupture due to van der Waals (vdW) forces. Such intermolecular forces are not operational with much thicker films. However, regardless of the thickness of the film, it has been shown by Burton and Taborek (PoF, 2007) that a contracting inviscid liquid sheet can break even in the absence of vdW forces. Here, we demonstrate that in the presence of small yet finite viscosity, contracting liquid sheets can escape from pinch-off when vdW forces are absent. We investigate the problem using 2D free-surface flow simulations. That there are two distinct mechanisms for the escape will be demonstrated using scaling theory that relates the minimum sheet thickness when escape occurs to the Ohnesorge number (the ratio viscous stress to inertial and capillary stresses).