Crossover from lamellar to intersected ice morphologies within a single ice crystal during unidirectional freezing of an aqueous solution

Abstract

Ice growth from liquid phase has been extensively investigated in various conditions, especially for ice freely grown in undercooled water and aqueous solutions. Although unidirectional ice growth plays a significant role in various domains, the detailed pattern formation of unidirectionally grown ice in an aqueous solution remains elusive. For the first time, we in situ proved a crossover from lamellar to intersected ice morphologies of a single ice crystal via unidirectional freezing of an aqueous solution. It is revealed that the tilted lamellar morphology occurs within a single ice crystal and consists of two groups of tilted lamellar ice with different tilting directions with respect to basal plane of ice. Further observations also confirm a competition relation between the two groups of ice lamellae which are either “divergent” or “convergent”. This intersected morphology which originates from peculiar growth habit of ice is crystallographically different from the competitive growth of bi-crystal composed of two differently orientated grains which usually appears in directional solidification. These results are suggested to provide a more complete physical picture of unidirectionally grown ice from aqueous solution and are believed to promote our understanding of various pattern of ice in many relevant domains where pattern formation of ice crystal is vital.