Phase diagram for droplet impact on superheated surfaces

We experimentally determine the phase diagram for impacting ethanol droplets on a smooth, sapphire surface in the parameter space of Weber number We versus surface temperature T. We observe two transitions, namely the one towards splashing (disintegration of the droplet) with increasing We, and the one towards the Leidenfrost state (no contact between the droplet and the plate due to a lasting vapour film) with increasing T. Consequently, there are four regimes: contact and no splashing (deposition regime), contact and splashing (contact-splash regime), neither contact nor splashing (bounce regime), and finally no contact, but splashing (film-splash regime). While the transition temperature T_L to the Leidenfrost state depends weakly, at most, on We in the parameter regime of the present study, the transition Weber number We_C towards splashing shows a strong dependence T on and a discontinuity at T_L. We quantitatively explain the splashing transition for T < T_L by incorporating the temperature dependence of the physical properties in the theory by Riboux & Gordillo (Phys. Rev. Lett., vol. 113(2), 2014, 024507; J. Fluid Mech., vol. 772, 2015, pp. 630-648).