Viscous Drop Impact on a Dry Smooth Surface: Spreading and Splashing

The splashing of a liquid drop on a smooth dry surface is dependent on the pressure of the surrounding air.\footnote{L.\ Xu et al., Phys.Rev.\ Lett.\textbf{94}, 184505 (2005)} Recent findings suggest, however, that the pressure-dependent splashing of a viscous drop is by a different mechanism than that for an inviscid one. For example, unlike an inviscid liquid, a viscous liquid splashes only after the drop has spread to nearly its maximum extent.\footnote{L.\ Xu, Phys.\ Rev.\ E \textbf{75}, 056316 (2007)} Here we report on experiments with viscous silicone oil (10--1000 cSt) that examine the parameters affecting the spreading of a viscous drop upon impact, and the role of the surrounding gas in splashing. Of particular note is the strong effect of viscosity on spreading rate and behavior.