Liquid spreading on cold surfaces: Solidification-induced stick-slip dynamics

We study the contact line dynamics of a liquid drop on a substrate at temperature T-s colder than the freezing temperature T-m. The purpose is to determine experimentally the criterion for a solidification-induced pinning of the liquid at its triple line. The substrate is driven at constant velocity, while the upper part of the drop is pinned to the injection pipe. Within a certain range of substrate velocity and temperature difference T-m - T-s, the solidification can induce contact-line pinning. This pinning occurs when the velocity of the substrate is slower than a critical value V-c and leads to a discontinuous stick-slip dynamics of the contact line, while at high enough velocity the contact-line motion remains continuous. Stick-slip dynamics appear when the solid front, showing dendritic structure, catches up the advancing contact line. We study the dynamics of the stick-slip regime at different substrate velocities V-s, T-m - T-s, and injection flow rate Q. We relate the dependence of V-c on T-m - T-s to the velocity of the solidification front V-f calculated and measured with an independent experiment. These results are consistent with a mechanism of kinetic undercooling where the front velocity follows a trend reminiscent to that measured and predicted in dendritic solidification front growth.