Interaction of impacting water drop with a heated surface and breakup into microdrops

Drop impact is important for numerous industrial processes. The recent progress in investigations of drop impact on heated solid surface covers the processes near and above the boiling temperature of the liquid. There is a gap in understanding of drop dynamics for the substrate temperature below the liquid boiling point. We conduct a detailed study of the interaction of the water drop of 10µl impacting on a heated sapphire plate with a temperature varied within a range of 23–135^◦C. Characteristic stages of drop interaction with a substrate at various temperatures are identified, namely impact, spreading, rollback, one liquid column splashing, microdrops detachment, formation, stabilization, breakup, boiling, and evaporation. We show that the spreading time and maximal spreading diameter of the droplet are dominated by inertia and practically independent of the temperature. The influence of the temperature on viscosity dissipation, which limits the maximum spreading diameter, is not significant. However, the temperature rise leads to a considerable decrease of the liquid column contact diameter and to an increase of the liquid column height at the splashing stage. It is revealed that the contact line velocity at the rollback stage depends on temperature. Microdrop detachment from the liquid column is observed for a substrate temperature of 60–100^◦C. Beginning from the substrate temperature of 100^◦C, the liquid column height is decreased again. The most important observation is the drop breakup into several sessile microdrops just after the spreading for 135^◦C, which prevents the rollback and rebound. We show the possible importance of the Marangoni force for thin liquid film breakup and detect the presence of microbubbles, which is also potentially important for breakup.