Liquid Crystalline Assembly of Rod–Coil Molecules - Liquid Crystalline Functional Assemblies and Their Supramolecular Structures - page 77

Fig. 9 Tetragonal perforated lamellar structure in an AB-BA sequence formed by tetra-
branched triblock molecule
between the rod and PEO coil segments. The 3D lattice is built up of two inter-
penetrating centered 3D lattices. In comparison with the phase behavior of
9 , the remarkable feature of 10 is that attachment of coil-rod-coil molecules
into a central point induces a perforated lamellar liquid crystalline phase with
a 3D tetragonal symmetry that is thermodynamically stable. Upon melting
of rod segments in 9 , there is adequate free volume for PEO to form a 2D
hexagonal columnar mesophase. Attachment of four PEO chains to a cen-
tral point, however, has the effect of reducing the freedom of movement for
the flexible chains, which in turn suppresses the ability of the rod segments
to form a columnar mesophase with a larger interfacial area. Consequently,
certain supramolecular structures with reduced interfacial area, such as a per-
forated lamellar structures, are preferred over the columnar phase exhibited
by the monomer.
Incorporation of a dendritic building block into the end of an incom-
patible linear chain gives rise to novel self-assembling systems because the
molecule shares certain general characteristics of both block copolymers and
small amphiphiles. Amphiphilic dendrimers containing an extended rigid rod
block represent another class of self-assembling systems that are increasingly
used for the construction of supramolecular architectures with well-defined
shape. The introduction of a hydrophobic docosyl chain and hydrophilic den-
drimer into each end of an extended rigid segment would give rise to a unique
amphiphilic ABC triblock system consisting of a hydrophilic dendritic block,