Plateau formation induced by salinity in freezing saline droplets

The freezing of saline droplets is important in marine icing, cryopreservation, and freeze desalination, yet the mechanisms governing salt-induced morphological evolution remain unclear. Here, combining controlled experiments, Molecular Dynamics (MD) simulations, and analytical modeling, we quantitatively investigate how salinity and substrate temperature regulate freezing dynamics and final droplet morphology. Experiments reveal that increasing salt concentration and decreasing temperature significantly affect freezing time, frozen height, and plateau radius. MD simulations demonstrate that salt ions are rejected by the advancing ice front and accumulate in the remaining liquid, forming a concentrated brine layer that delays solidification. We identify the lateral redistribution of this salt-rich brine layer near the droplet apex as the key mechanism responsible for plateau formation. An analytical model incorporating solute rejection, salt entrapment, and freezing-point depression reasonably predicts interface evolution and final morphology. This work establishes a quantitative framework linking salt transport, freezing kinetics, and droplet shape evolution.