Biomedical Engineering Reference
In-Depth Information
on their ionic self-assembly, that are useful for the preparation of new low-
dimensionally functional sot solid materials. h e fundamental phenom-
enon underlying the approach to electrical conductors is addressed in this
chapter using nanomaterials (such as carbon nanotubes) and ionic DLCs
that have great potential to orient the nanomaterials for anisotropic elec-
trical conduction. h e mesomorphic behavior of ionic DLCs (including
oligomers and polymers) is described with a particular focus directed to
the development of fundamental understanding of structural-mesophase
morphology relationship. Meticulous attention is given to the dependence
of mesomorphism on the inl uence of spacer length, counter ions, loca-
tion and types of the charged groups in determining the supramolecular
organization of these compounds. Finally, some concluding perspectives
are presented related to optical, electronic and other properties such as
use of them in certain biological functions, catalysis and templates for new
organic synthesis.
Ionic DLCs can be primarily categorized into two classes (as shown in
Figure 9.1); (a) lyotropic and (b) thermotropic [5]. Lyotropic mesophases
of ionic DLCs arguably belong to the class of chromonic liquid crystal con-
sisting of a disc-like polyaromatic core with polar groups at the periphery.
In both cases, mesophase formation is dictated by the formation of stacks
of multi-ring aromatic molecules, and these stacks lie in a l uid continuum.
In columnar phases this is a sea of l exible alkyl chains (that predominantly
consist of columnar structures, although lamellar and cubic phases have
also been reported) and in chromonics, it is water. A number of studies
with columnar mesophase formed by dendritic, wedge-shaped and many
polycatenar LCs have also been reported over the past decade; however,
we do not attempt to address those advances but rather refer the interested
reader to relevant literature [6-14].
Ionic Discotic Liquid Crystals
Lyotropic
(Chromonic)
Thermotropic
N
M
Sm
Col
Cub
Figure 9.1
Structural classii cation of ionic discotic liquid crystals (N = nematic phase,
Col = columnar phase, M = hexagonal phase, Sm = smectic phase, Cub = cubic phase).
