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triblock molecule (
13
) with coil volume fraction,
f
coil
=0.47exhibitsabicon-
tinuous cubic phase instead of smectic phase [76, 77]. Similarly to diblock
rod-coil systems, increasing the volume fraction induces a hexagonal colum-
nar mesophase as in the case of
14
.
Remarkably, molecules with a longer length of coil (
15
) assemble into
discrete supramolecular aggregates that spontaneously organize into a 3D
tetragonal phase with a body-centered symmetry in the solid state and
mesophase as determined by small-angle X-ray scattering. Based on X-ray
data and density measurements, the inner core of the supramolecular ag-
gregate is composed of the discrete rod bundle with a cylindrical shape of
5 nm in diameter and 3 nm in length. It is encapsulated with phase-separated
PPO coils, which gives rise to the formation of non-spherical oblate aggre-
gate (Fig. 12). The supramolecular rod bundles subsequently organize into
a 3D body-centered tetragonal symmetry. The oblate shape of supramolecu-
lar aggregates is believed to be responsible for the formation of the unusual
3D tetragonal phase (M
tet
). This unique phase behavior mostly originates
from the anisotropic aggregation of rod segments with their long axes within
microphase-separated aromatic domains. Consequently, rod bundles with
puck-like cylindrical shape would give rise to oblate micelles, which can pack
more densely into an optically anisotropic 3D tetragonal lattice, rather than
an optically isotropic cubic lattice. These results demonstrate that the linear
combination of flexible coils in both terminals of rod segment leads to dis-
crete micellar aggregates that organize into a body-centered tetragonal liquid
crystalline phase above a certain coil volume fraction.
Another possible way to manipulate the liquid crystalline structure could
be provided by systematic variation of the rod length at constant rod-to-coil
Fig. 12
Mesophase structures of the ABA coil-rod-coil triblock molecules
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