Dynamic Contact Angles in Splashing

Samantha Jones, Andrzej Latka, and Sidney R. Nagel

When a drop of liquid impacts a solid surface it will splash emitting tiny droplets. This phenomenon results from a variety of complex interactions between the liquid and the substrate. Surprisingly, when air pressure is reduced splashing is completely suppressed [1-3]. The mechanism by which air induces splashing is still unexplained and the question remains: where does the air matter? In this project we consider the air at the advancing edge of the spreading drop. This was done by studying the dynamic contact angle between the spreading liquid and the solid surface. Using high-speed videos of drop impacts, we measured the evolution of the dynamic contact angle for water/glycerol drops of different viscosities. We found that the contact angle increases as the edge of the drop decelerates. At late times, the liquid shows a pronounced overturning, that is the contact angle grows to be significantly greater than 90°, so that the spreading liquid is more likely to engulf air as it moves. This behavior was robust and was unaffected by the viscosity of the liquid. 

[1] L. Xu, W.W. Zhang, and S.R. Nagel, Phys. Rev. Lett. 94, 184505 (2005)

[2] M. M. Driscoll, C.S. Stevens, and S.R. Nagel, Phys. Rev. E 82, 036302 (2010)

[3] A. Latka, A. Strandburg-Peshkin, M.M. Driscoll, C.S. Stevens, and S.R. Nagel, Phys. Rev. Lett. 109, 054501 (2012)