Liquid sheets are omnipresent in nature and applications. The cross sections of liquid sheets are elongated two-dimensional (2D) drops the two ends of which contract towards each other because of surface tension $\left(\sigma \right)$. If sufficiently thin, sheets can rupture due to van der Waals forces. Burton and Taborek, however, have shown that regardless of sheet thickness $2{\tilde{h}}_0$, a contracting inviscid liquid sheet can break even in their absence. Here we use 2D simulations and theory to show that for small yet finite viscosity $\mu$, contracting liquid sheets will escape from pinch-off when van der Waals forces are absent due surprisingly to two distinct mechanisms that depend on Ohnseorge number $\mathrm{Oh}=\mu /\sqrt{\rho \sigma {\tilde{h}}_0}$ ($\rho$: density). For $\mathrm{Oh}\to 0$, escape is shown to be due to viscous resistance, while for larger but yet still small Oh, it can be attributed to vorticity generation at the free surface. The distinct mechanisms yield different scaling laws relating minimum sheet thickness when escape occurs to Oh.

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• Thin fluid films
• Drops & bubbles