Arrested dynamics of droplets on ice

Dynamics of droplets impacting a chilled icy substrate or fiber were studied using high-speed imaging. Two spreading regimes were observed for droplets impacting planar ice: (i) at low Weber numbers, the spreading diameter exhibited a capillary-inertial 1/2 power law before being arrested; (ii) at high Weber numbers, the 1/2 power law deviated to an unexpected inertio-viscous 1/6 power law.  The behavior of contact line arrest was also bimodal: (i) at low Weber numbers, the capillary-inertial spreading was halted as soon as the droplet’s bulk temperature cooled down to 0 °C, (ii) at high Weber numbers, the speed of a lateral non-equilibrium freeze front had to match the spreading velocity to arrest the inertial spreading.  For droplets impacting a chilled fiber, droplet capture was enabled by a temperature-induced viscous dissipation effect, with wicking also playing a role for frosted fibers.