class of ionic (cationic or anionic) and non-ionic. The lyotropic LCPs are formed by
direct participation of amphiphilic molecules with water leading to the formation of
mesophases.
Non-amphiphilic LCPs: These can be referred to as the nonpolar or organic
polymers of less polarity possessing high anisotropy in its geometry due to the
inherent rod or disk-like structures. These LCPs generally form mesogenic phases
after melting defined as thermotropic LCPs.
According to Phase
LCPs can be classified into two main groups based on the liquid phase as thermotropic
and lyotropic. Thermotropic LCPs are generated by the application of heat when
structural ordering in pure molecules takes place, whereas in the case of lyotropic
LCPs, mesogenic ordering of phases is observed in the presence of suitable solvent
molecules. Thermotropic LCPs can again be subcategorized as enantiotropic and
mesotrophic phases. In the case of enantiotropic LCPs, the formation of a liquid
crystalline phase takes place during both heating and cooling cycles, whereas mesotrophic LCPs are formed from the isotropic liquid and are stable on a supercooled stage.
The mesotrophic LCPs can be subdivided into three more groups such as smectic,
nematic, and cholesteric as described earlier.
According to Nature of Mesogens
Depending on the nature of mesogenic groups, LCP structures may differ to a great
extent, and this can be the main-chain LCPs and side-chain LCPs. As the name suggests,
the main-chain LCPs are those materials, where the mesogenic units are itself a part of
the main chain of the polymer, whereas in case of side-chain LCPs, the mesogen units
are attached like a side chain or pendant with a flexible spacer molecule in the main
polymer backbone. Structurally, a main-chain LCP is formed when rigid groups are
attached to the comparatively flexible polymer chain. These can be formed from a rigid
and rod-like monomer molecule. In another case, the main-chain LCPs can be generated
due to the direct incorporation of mesogenic groups into the main polymer chain. The
mesogens so attached work just like some stiff areas inside the first group. The liquid
crystal behavior is observed due to the structural restriction imposed by the mesogenic
aromatic rings. The side-chain LCPs are composed of three main structural units,
namely, the backbone, spacer, and mesogen unit. The backbone provides the spine,
where the side chains are attached. The structure of the main chain also decides an
important role in determining the fact that whether the liquid crystalline structure will be
formed or not. The most important part has been played by the mesogen units attached
to LCPs, since the alignment of structural units generates the liquid crystal behavior. In
general, the mesogens are made of rigid core or two or more aromatic groups clubbed
with a functional group. Figure 6 represents some possible structural arrangements of
the main-chain, side-chain, and crosslinked LCPs formed from mesogenic units and
flexible spacers.
8
S. Banerjee and K. K. Kar
direct participation of amphiphilic molecules with water leading to the formation of
mesophases.
Non-amphiphilic LCPs: These can be referred to as the nonpolar or organic
polymers of less polarity possessing high anisotropy in its geometry due to the
inherent rod or disk-like structures. These LCPs generally form mesogenic phases
after melting defined as thermotropic LCPs.
According to Phase
LCPs can be classified into two main groups based on the liquid phase as thermotropic
and lyotropic. Thermotropic LCPs are generated by the application of heat when
structural ordering in pure molecules takes place, whereas in the case of lyotropic
LCPs, mesogenic ordering of phases is observed in the presence of suitable solvent
molecules. Thermotropic LCPs can again be subcategorized as enantiotropic and
mesotrophic phases. In the case of enantiotropic LCPs, the formation of a liquid
crystalline phase takes place during both heating and cooling cycles, whereas mesotrophic LCPs are formed from the isotropic liquid and are stable on a supercooled stage.
The mesotrophic LCPs can be subdivided into three more groups such as smectic,
nematic, and cholesteric as described earlier.
According to Nature of Mesogens
Depending on the nature of mesogenic groups, LCP structures may differ to a great
extent, and this can be the main-chain LCPs and side-chain LCPs. As the name suggests,
the main-chain LCPs are those materials, where the mesogenic units are itself a part of
the main chain of the polymer, whereas in case of side-chain LCPs, the mesogen units
are attached like a side chain or pendant with a flexible spacer molecule in the main
polymer backbone. Structurally, a main-chain LCP is formed when rigid groups are
attached to the comparatively flexible polymer chain. These can be formed from a rigid
and rod-like monomer molecule. In another case, the main-chain LCPs can be generated
due to the direct incorporation of mesogenic groups into the main polymer chain. The
mesogens so attached work just like some stiff areas inside the first group. The liquid
crystal behavior is observed due to the structural restriction imposed by the mesogenic
aromatic rings. The side-chain LCPs are composed of three main structural units,
namely, the backbone, spacer, and mesogen unit. The backbone provides the spine,
where the side chains are attached. The structure of the main chain also decides an
important role in determining the fact that whether the liquid crystalline structure will be
formed or not. The most important part has been played by the mesogen units attached
to LCPs, since the alignment of structural units generates the liquid crystal behavior. In
general, the mesogens are made of rigid core or two or more aromatic groups clubbed
with a functional group. Figure 6 represents some possible structural arrangements of
the main-chain, side-chain, and crosslinked LCPs formed from mesogenic units and
flexible spacers.
8
S. Banerjee and K. K. Kar