The interface dynamics of drops impacting onto a different liquid*

In this talk we explore drop impact onto a pool of another liquid, a scenario of relevance to many applications of interest, from inkjet printing to estimating environmental risks after oil spills. A combination of high-speed photography, high-resolution numerical simulations, and physical modelling has been used to disentangle the different roles that physical fluid properties play in determining the detailed dynamics in this multi-fluid system. Simple mechanistic models and experiments of drops impacting onto a pool of the same fluid have led to estimates of the penetration speed being half the impacting drop speed. However, this is only one small part in a rich and intricate behavior landscape once fluid properties are no longer identical - we uncover velocities between 10% and 90% of the reference initial drop velocity over a range of three orders of magnitude in density and viscosity ratios between the impacting drop and the pool, while also explaining these findings and summarizing them into one key compact predictive formula. In higher speed contexts we then shed light into changes to the splashing threshold within the more complex landscape of three-phase flows.