Functional Liquid-Crystalline Polymers for Ionic and Electronic Conduction - Liquid Crystalline Functional Assemblies and Their Supramolecular Structures - page 153

Fig. 2 Molecular structure of a columnar liquid crystal having a crown ether moiety

parallel to the column axis was expected because oligo(ethylene oxide) chains
themselves do not form a columnar structure.
The self-assembly of LC block molecules composed of two or more cova-
lently bonded immiscible molecular parts including an ion-conductive moiety
leads to the formation of well-defined nano-segregated structures such as layer
and columnar structures [4, 5, 26, 27, 30]. These anisotropic structures formed
for LC block molecules having PEO and ionic liquid moieties would be use-
ful for the anisotropic transportation of ions. Moreover, we considered that the
macroscopic orientation of the nano-segregated LC structures plays a key role
in the enhancement of the conductivities because the boundary in randomly
oriented polydomains disturbs the anisotropic transportation of ions.
A rod-coil-rod type of twin mesogenic molecule having oligo(ethylene
oxide) chains 2 (Fig. 3) was designed as a 2D ion conductor [44-47]. The
lithium salt complexes of these molecules showed smectic LC phases. The
lithium salts were incorporated into the oligo(ethylene oxide) layers of
phase-segregated layered structures. Ionic conductivities of the aligned LC
materials were measured by the alternating current impedance method.
Highly anisotropic ion conduction along the layer structures was observed
for complexes exhibiting LC smectic A and B phases aligned vertically on
a glass substrate. The ionic conductivities parallel to the smectic layer were
1.9 10 -4 Scm -1 in the

smectic A phase at 152 ◦ C. Then, perfluoroalkyl moieties were incorporated
into twin mesogenic moieties containing PEO chains in order to stabilize the
nano-segregated LC layered structures and to enhance the anisotropy of ion
conduction [47]. The triply layered structures of perfluorocarbon, aromatic
mesogen, and oligo(ethylene oxide) moieties led to the thermal stabilization
of mesophases and a slight increase in anisotropy of ionic conductivities.
A rod-coil molecule containing a tetra(ethylene oxide) chain was also pre-
pared for the design of a 2D ion conductor exhibiting a smectic A phase
at room-temperature [48]. The lithium triflate complex showed a smectic A
phase over a wide temperature range, including room temperature. Uniax-
ially parallel alignment of the LC smectic A samples on rubbed polyimide

10 -4 Scm -1 in the smectic B phase at 79 ◦ Cand5.5 × ×