Role of Gas Composition in Viscous Drop Splashing

Splashing occurs when a liquid drop impacts on a smooth, dry surface at high velocity. It has been discovered that the pressure of the surrounding air is important in causing a splash.\footnote{L. Xu, S. Nagel, and W. Zhang. Phys. Rev. Lett. 94, 184505 (2005).} Moreover, viscous splashing occurs at a much later time than the splashing of an inviscid liquid.\footnote{ L. Xu, Phys. Rev. E 75, 056316 (2007).} Here we investigate the relationship between the threshold pressure, $P_T$, and the impact velocity, $V_0$, for viscous splashes. $P_T$ demonstrates only a weak dependence on impact velocity above 2.0 m/s. Also, the composition of the gas in which splashing occurs is varied to gain insight on the role of gas molecular weight on $P_T$ in the viscous regime.