Fig. 1.

Displacement of a partially wetting liquid from a microcapillary tube. As the glycerol (white) is withdrawn from the right end of the tube with a constant flow rate $Q$, air (black) invades the tube from the left end at atmospheric pressure and entrains a thin film of the glycerol on the tube walls (the white stripe in the middle of the tube is due to light refraction; SI Appendix, section 1). The entrained liquid film then starts receding along the tube axis with a velocity $U_{\mathrm{c}\mathrm{l}}$, forming a growing dewetting rim ahead of the contact line, where the liquid, solid, and air meet at a nonzero apparent contact angle ${\theta }_{ap}$. As the liquid rim grows, the bubble neck diameter shrinks and ultimately leads to pinch-off and the formation of a bubble.