Kinetic roughening transition of ice crystal and its implication during recrystallization.

Hypothesis: Roughening transitions at solid-liquid interfaces govern crystal morphology in diverse systems. In ice crystallization, these transitions control interfacial faceting and surface kinetics. Faceted morphologies are often associated with ice-active molecules, which inhibit recrystallization and are essential for cryopreservation. We hypothesize that kinetic roughening transitions can induce faceting even in the absence of ice-active agents, particularly at high solute concentrations with depressed melting points, potentially complicating the interpretation of crystal morphology as an indicator of ice activity.

Experiments: We investigated the kinetic roughening transition of ice in dimethyl sulfoxide (DMSO) and proline-water solutions using cryomicroscopy and real-time image analysis. Crystals grew in microdroplets, maintaining near-equilibrium conditions as solute concentration increased during growth due to conversion of liquid water to ice. Antifreeze protein type III (AFPIII) was applied to distinguish intrinsic roughening from adsorption-mediated effects.

Findings: A distinct kinetic roughening transition temperature (T = -16.0 ± 0.2 °C) was identified, marking a shift from rounded disks at higher temperatures to faceted hexagonal plates at lower temperatures, independent of solute type. Recrystallization below T revealed asymmetry between growth and melting interfaces. AFPIII promoted faceting even above T, consistent with stabilization of step edges and elevation of the roughening transition temperature. These results clarify the interplay between intrinsic interface kinetics and molecular adsorption, with implications for interpreting ice morphology, surface roughening, and cryopreservation design.