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organized in layers, where the terphenyl units and the lateral carbohydrate
units are incorporated in the layer and these sublayers are separated by layers
of alkyl chains. Increasing the space unit (oligo(ethylene glycol)) transformed
smectic mesophase into a hexagonal channeled layer phase (ChL
hex
). This
mesophase appears almost completely black between crossed polarizers and
shows a very high viscosity, indicating an optically uniaxial mesophase with
a 3D lattice. Small-angle X-ray diffraction pattern shows five spots that could
be indexed as a 3D hexagonal lattice (
P
6
mmm
). This mesophase consists
of alternating layers of aromatic units and aliphatic chains, penetrated at
right angles by columns with undulating profiles containing the polar lateral
groups. Accordingly, the structure consists of layers perforated by an array of
polar channels, which are arranged on a 2D hexagonal lattice.
When the space units were increased further, rod-coil molecules form
square columnar mesophases confirmed by optical polarized microscopy and
X-ray diffraction pattern. The polar column is located inside the square, pro-
viding strong attractive intermolecular interactions via hydrogen bonding
and the hydrophobic columns containing alkyl chains are at the corners in-
terconnecting the aromatic rods end-to-end. For the columnar mesophases,
the rigid-rod segments tend to restrict the side length of the polygons within
relatively narrow limits, giving rise to columns with a well-defined polygonal
shape. The lateral chains fill the interior of the polygons; the terminal chains
form the corners of these polygons and connect the rigid rods. Thus, the
number of sides of the polygons critically depends on the volume of the lateral
chain and the length of the molecule. Extending the hydrophilic chain, raising
the temperature, or reducing the alkyl chain length leads to a transition from
square to hexagonal columnar phases. Due to amphotropic characteristics of
rod-coil molecules, new types of laminated mesophases also were induced by
solvent (Fig. 18).
/
4
Multiblock Rod-Coil System
4.1
Main-Chain Rod-Coil Copolymers
The rod-coil approach as a means to manipulate supramolecular structure
as a function of rod volume fraction was reported to be extended to main
chain multiblock copolymer systems, which generate bicontinuous cubic and
hexagonal columnar mesophases depending on the rod-to-coil volume frac-
tion [95, 96]. For example, rod-coil multiblock copolymer (
28
)basedon
short length of coil (rod volume fraction,
f
rod
= 0.38) exhibits a bicontinuous
cubic mesophase, while copolymer (
29
) based on higher coil volume frac-
tion (
f
rod
= 0.29) shows a hexagonal columnar mesophase. A notable feature
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