mesogens is achieved by forcing the backbone to adopt an extended chain conformation due to steric hindrance of the mesogens. Thus macromolecular columns, with
characteristic rigid rod-like structure, are formed where the polymer backbone forms
the axis of the rod (Fig. 4c) (Zhou et al. 1987, 1988, 1989). Additionally, since the
mesogens are attached to their “gravity centers,” the motions of the backbone were
expected to have the least effect on the mesogen orientation and this decoupling was
achieved without using spacers. N LC phase structures were observed by Zhou et al.
both in monomers and polymers of 2,5-bis(p-methoxybenzoyl)oxy)styrene based
MJ-LCP system (Zhou et al. 1987, 1988, 1989).
Liquid Crystalline Block Copolymers
LCBCPs are formed by introducing LCPs into BCPs and since LC ordering occurs at
1-10 nm length scale which is an order of magnitude smaller than the dimensions of
ordered nanostructures formed due to BCP microphase separation (10–100 nm),
LCBCPs exhibit hierarchical structures with characteristic self-organization at multiple
length scales. The overall phase behavior of LCBCPs is influenced by two competing
interactions: BCP microphase separation and LC ordering. This results in unique phase
structures (not attainable in coil-coil BCP systems) depending upon which of the two
interactions dominates. In an LCBCP, the mesogens can be associated with the LC
block of the BCP using either covalent or non-covalent interactions (Chen et al. 2010;
Fischer and Poser 1996; Fischer et al. 1994; Mao and Ober 1998; Olsen and Segalman
2008; Walther and Finkelmann 1996; Yu 2014). Using MCLCPs or SCLCPs as one of
the combining blocks in a BCP results in covalently bonded LCBCPs whereas
noncovalently bonded LCBCPs consist of introducing the mesogen into the BCPs
using weaker secondary interactions such as hydrogen bonding, ionic interactions etc.
These two types of LCBCPs differ in the degree of rigidity of the LC block. Covalent
bonding imparts more rigidity compared to the noncovalent interactions, and within
the covalently bonded systems, MCLCPs possess more rigidity compared to SCLCPs.
The term “rod-coil” (RC) is often used to describe these systems, and it emphasizes the
difference in flexibility between the rigid LC block and the flexible coil block in a
covalent LCBCP system. The increased rigidity contrast results in well-defined BCP
nanodomains even in low M n systems. Consequently, the LCBCP ODT occurs at a
lower value of χN (higher temperature) compared to coil-coil systems. LCBCPs are a
very promising system both from a technological and scientific point of view. Due to
the different length scales of ordering, hierarchy in ordered structures can be obtained
and by incorporating various groups within each of the blocks, different functionalities
can be achieved at different length scales. From a scientific point of view, phase
behavior of these systems will be different compared to a coil-coil BCP system
because LCs are rigid and characterized by preferential orientation of the director.
Novel self-assembling materials with complex phase structures are possible due to the
competition between BCP microphase separation and LC ordering. In the following
sessions, we shall discuss phase behavior and assembly behaviors of LCBCPs with
covalent and noncovalent interactions.
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K. K. Tenneti et al.
characteristic rigid rod-like structure, are formed where the polymer backbone forms
the axis of the rod (Fig. 4c) (Zhou et al. 1987, 1988, 1989). Additionally, since the
mesogens are attached to their “gravity centers,” the motions of the backbone were
expected to have the least effect on the mesogen orientation and this decoupling was
achieved without using spacers. N LC phase structures were observed by Zhou et al.
both in monomers and polymers of 2,5-bis(p-methoxybenzoyl)oxy)styrene based
MJ-LCP system (Zhou et al. 1987, 1988, 1989).
Liquid Crystalline Block Copolymers
LCBCPs are formed by introducing LCPs into BCPs and since LC ordering occurs at
1-10 nm length scale which is an order of magnitude smaller than the dimensions of
ordered nanostructures formed due to BCP microphase separation (10–100 nm),
LCBCPs exhibit hierarchical structures with characteristic self-organization at multiple
length scales. The overall phase behavior of LCBCPs is influenced by two competing
interactions: BCP microphase separation and LC ordering. This results in unique phase
structures (not attainable in coil-coil BCP systems) depending upon which of the two
interactions dominates. In an LCBCP, the mesogens can be associated with the LC
block of the BCP using either covalent or non-covalent interactions (Chen et al. 2010;
Fischer and Poser 1996; Fischer et al. 1994; Mao and Ober 1998; Olsen and Segalman
2008; Walther and Finkelmann 1996; Yu 2014). Using MCLCPs or SCLCPs as one of
the combining blocks in a BCP results in covalently bonded LCBCPs whereas
noncovalently bonded LCBCPs consist of introducing the mesogen into the BCPs
using weaker secondary interactions such as hydrogen bonding, ionic interactions etc.
These two types of LCBCPs differ in the degree of rigidity of the LC block. Covalent
bonding imparts more rigidity compared to the noncovalent interactions, and within
the covalently bonded systems, MCLCPs possess more rigidity compared to SCLCPs.
The term “rod-coil” (RC) is often used to describe these systems, and it emphasizes the
difference in flexibility between the rigid LC block and the flexible coil block in a
covalent LCBCP system. The increased rigidity contrast results in well-defined BCP
nanodomains even in low M n systems. Consequently, the LCBCP ODT occurs at a
lower value of χN (higher temperature) compared to coil-coil systems. LCBCPs are a
very promising system both from a technological and scientific point of view. Due to
the different length scales of ordering, hierarchy in ordered structures can be obtained
and by incorporating various groups within each of the blocks, different functionalities
can be achieved at different length scales. From a scientific point of view, phase
behavior of these systems will be different compared to a coil-coil BCP system
because LCs are rigid and characterized by preferential orientation of the director.
Novel self-assembling materials with complex phase structures are possible due to the
competition between BCP microphase separation and LC ordering. In the following
sessions, we shall discuss phase behavior and assembly behaviors of LCBCPs with
covalent and noncovalent interactions.
182
K. K. Tenneti et al.