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).