Role of surrounding gas in the outcome of droplet splashing

This study investigates the influence of the surrounding gas on a droplet impacting a smooth dry glass surface at high Weber and Reynolds numbers. It was performed using a flywheel experiment and different gases at ambient pressure. We analyzed the splashing outcome by measuring the size, velocity, and angle of the secondary droplets and by calculating the total volume ejected. We show that gas entrapment is not the mechanism responsible for splashing at high Weber and Reynolds numbers. We demonstrate that splashing is influenced by the density, followed by the viscosity, and last by the mean free path of the surrounding gas. Furthermore, the surrounding gas primarily affects the number of secondary droplets ejected and their ejection angle, whereas the droplet size and horizontal velocity are independent of the surrounding gas properties. We provide the first theoretical expression for the total volume ejected using the theory of Riboux and Gordillo [Phys. Rev. Lett. 113, 024507 (2014)], which attributes the secondary droplet generation to a lift force experienced by spreading lamella. The relationship between the ejected volume and the splashing parameter is described by a power function.