Maximal air bubble entrainment at liquid-drop impact.
At impact of a liquid drop on a solid surface, an air bubble can be entrapped. Here, we show that two competing effects minimize the (relative) size of this entrained air bubble: for large drop impact velocity and large droplets, the inertia of the liquid flattens the entrained bubble, whereas for small impact velocity and small droplets, capillary forces minimize the entrained bubble. However, we demonstrate experimentally, theoretically, and numerically that in between there is an optimum, leading to maximal air bubble entrapment. For a 1.8 mm diameter ethanol droplet, this optimum is achieved at an impact velocity of 0.25  m/s. Our results have a strong bearing on various applications in printing technology, microelectronics, immersion lithography, diagnostics, or agriculture.
Physics of Fluids Group, Faculty of Science and Technology, MESA+ Institute, and Burgers Center for Fluid Dynamics, University of Twente, 7500AE Enschede, The Netherlands.
Wilco
W
Bouwhuis
Roeland C A
RC
van der Veen
Tuan
T
Tran
Diederik L
DL
Keij
Koen G
KG
Winkels
Ivo R
IR
Peters
Devaraj
D
van der Meer
Chao
C
Sun
Jacco H
JH
Snoeijer
Detlef
D
Lohse