Figure 2. (a) Schematic illustration of directional freeze-casting of a CNC suspension. (b) Photographs of the CNCs-ice monolith and CNCs aerogel. Note that the shape and dimensions of the aerogel can be controlled by use of a mold. POM images of the CNC-ice monolith before sublimation: (c) freezing of a 3.0 wt% CNCs suspension, directional freezing of a 10 wt% CNCs liquid crystal, with the view directions parallel (d) and perpendicular (e) to the freezing directions.
Of particular interest was the fact that the freeze-thaw process induced reorganization of the CNCs into a highly anisotropic order, with a hydrogel-like character. Unidirectional freeze-casting of the 10 wt% CNCs aqueous suspension, followed by thawing, yielded a hydrogel-like CNC, lacking fluidity, which indicated the formation of interconnected network of CNCs (Figure 3). POM analysis revealed that the CNCs in the thawed hydrogel were well oriented with anisotropy and various kinds of birefringent textures. These observations confirm the fact that freezing could induce phase solidification of liquid crystalline CNCs networks, and that ordering can be preserved after thawing. In contrast, the freeze-thaw process had no effect on the fluidity and texture of the 3 wt% CNC suspension (Figure S4).