Impact, spreading, and solidification of liquid droplets on supercooled surfaces*

The problem of liquid droplet spreading on surfaces below the liquid's freezing temperature is relevant in nature and in (e.g. aircraft, rapid manufacturing) technology. The competition between fast spreading dynamics and freezing is particularly intriguing. In the current work we give an overview on the studies we have performed on the impact of millimetric sized droplets on supercooled surfaces.

We visualize the impact of tin droplets from the side and from below at ultrafast time scale, providing us with unique views on the solidification patterns and their dynamics. To better understand the pattern formation, a novel method based on total internal reflection (TIR) is presented, which allows us to observe the formation and growth of solidification seeds and dendrites. We study the dependence of the phenomena on the control parameters, namely on impact velocity and surface temperature, both during the impact even and the competing solidification and on much longer time scales thereafter.