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gregate can be viewed as generating a barrel-like supramolecular structure in
which the rods are aligned axially with their preferred direction, and both the
interior and exterior of the barrel are filled by the coil segments (Fig. 17b).
These results indicate that a flat discrete ribbon-like aggregate transforms
into a curved barrel-like structure on crystal melting of the rod segments.
This transformation may be rationalized by considering end-to-end connec-
tion by rolling of the discrete ribbon [90]. With increasing temperature, space
crowding of coil segments would be larger because of greater thermal motion
of the flexible chains. A ribbon-like ordering of the rod segments would con-
fine flexible coil segments to a flat interface, forcing a strong deformation of
the flexible coils and making the system energetically unfavorable. To release
this deformation without sacrificing anisotropic order of the rod segments,
the flat ribbons would roll to form curved barrels.
Tschierske and coworkers reported on new complex liquid crystalline
phases of polyphilic block molecules or their metal complex [91-93]. These
triblock rod-coil molecules consist of a rod-like
p
-terphenylene unit, and two
hydrophobic alkyl chains at both ends of the rod, and oligo(ethylene glycol)
with a terminal carbohydrate unit at a lateral position of the rod [94]. De-
pending on the size of the hydrophilic and hydrophobic segments, a series of
unusual liquid crystalline phases were detected (Fig. 18). When the carbohy-
drate unit is directly conjugated to the rod building block, a simple smectic
(S
A
) phase was observed. In this liquid crystalline phase, the molecules are
Fig. 18
Supramolecular architectures from self-assembly of facial rod-coil molecules with
lateral hydrophilic groups as a function of the size of polar lateral and hydrophobic ter-
minal groups. Reprinted with permission from [94].
©
2005 American Chemical Society
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