Single Ice Crystal Growth with Controlled Orientation during Directional Freezing

Ice
growth has attracted great attention for its capability of
fabricating hierarchically porous microstructure. However, the formation
of tilted lamellar microstructure during freezing needs to be reconsidered
due to the limited control of ice orientation with respect to the
thermal gradient during in situ observations, which can greatly enrich
our insight into architectural control of porous biomaterials. This
paper provides an in situ study of the solid/liquid interface morphology
evolution of directionally solidified single crystal ice with its C-axis (optical axis) perpendicular to directions of both
the thermal gradient and the incident light in poly­(vinyl alcohol,
PVA) solutions. Multifaceted morphology and V-shaped lamellar morphology
were clearly observed in situ for the first time. Quantitative characterizations
on lamellar spacing, tilt angle, and tip undercooling of lamellar
ice platelets provide a clearer insight into the inherent ice growth
habit in polymeric aqueous systems and are suggested to exert significant
impact on future design and optimization in porous biomaterials.