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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 Ts colder than the freezing temperature Tm. 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 Tm − Ts, the solidification can induce contact-line pinning. This pinning occurs when the velocity of the substrate is slower than a critical value Vc 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 Vs, Tm − Ts, and injection flow rate Q. We relate the dependence of Vc on Tm − Ts to the velocity of the solidification front Vf 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.