Dynamics and unsteady morphologies at ice interfaces driven by DO-HO exchange.

The growth dynamics of DO ice in liquid HO in a microfluidic device were investigated between the melting points of DO ice (3.8 °C) and HO ice (0 °C). As the temperature was decreased at rates between 0.002 °C/s and 0.1 °C/s, the ice front advanced but retreated immediately upon cessation of cooling, regardless of the temperature. This is a consequence of the competition between diffusion of HO into the DO ice, which favors melting of the interface, and the driving force for growth supplied by cooling. Raman microscopy tracked H/D exchange across the solid HO-solid DO interface, with diffusion coefficients consistent with transport of intact HO molecules at the DO ice interface. At fixed temperatures below 3 °C, the DO ice front melted continuously, but at temperatures near 0 °C a scalloped interface morphology appeared with convex and concave sections that cycled between growth and retreat. This behavior, not observed for DO ice in contact with DO liquid or HO ice in contact with HO liquid, reflects a complex set of cooperative phenomena, including H/D exchange across the solid-liquid interface, latent heat exchange, local thermal gradients, and the Gibbs-Thomson effect on the melting points of the convex and concave features.