(3-(triethoxysilyl)propyl isocyanate)) (PS-b-PIC) (DP
PS ~ 1900 and DP
PIC ~ 100)
and with f
PS
= 0.9, Park et al. observed anisotropic nanoscale objects in the shape of
parallelograms that form Sm ordering in solution cast films (Park and Thomas 2004).
Using theoretical calculations, it was shown that these parallelograms, with a side of
at least 45 nm, had a tilted bilayer arrangement of the PIC rods. The authors propose
that interdigitation of the rods is also possible. Within these nano-objects, the PIC
rods are oriented uniaxially and these nano-objects have a 25–45
angle between the
sides.
Rods made of mesogenic molecules also possess inherent rigidity as a result of
their molecular chemistry. A lot of interesting morphologies were observed in
RCBCPs containing mesogenic rods although most of the mesogens were based
on low M n molecules. Stupp’s group investigated the phase structures in mesogenic
oligomers (formed by attaching an azo dye to a rigid biphenyl carboxylic acid) of
length 6 nm attached to flexible polyisoprene (M w = 3200 g/mol). Good control over
the polydispersity of the rod molecule allowed the researchers to explore the subtle
competition between the microphase separation and LC ordering processes by
altering the chemistry and M n of the molecules (Radzilowski et al. 1993, 1997;
Radzilowski and Stupp 1994; Stupp 1998; Stupp et al. 1997). At f
rod
= 0.36, the
rigid mesogenic rods formed stripes arranged in layers inside the PI matrix. At
similar f values, hexagonally close packed C morphologies are observed in coil-coil
systems. In the present RCBCP case, although the stripes possess a hexagonal
symmetry, the nature of the orientation of the rods within the stripes was not clear
(Fig. 7a) (Lee et al. 2001). Qualitatively, these stripe-like patterns are similar to the
broken L phases as reported in the numerical calculations by Ganesan et al.
(Pryamitsyn and Ganesan 2004). As the f
rod decreased to 0.25, the morphology
transformed from stripes into super lattice aggregates (7 nm in diameter) that are
oriented parallel to the substrate (Fig. 7b)(Lee et al. 2001). These aggregates are
arranged with hexagonal in-plane symmetry in a PI matrix. Theoretical calculations
by Fredrickson et al. and Ganesan et al. also showed similar puck-like morphologies
(Pryamitsyn and Ganesan 2004; Williams and Fredrickson 1992). The authors claim
that the observation of a hexagonally packed lattice at such highly asymmetric
f suggests the nonuniformity in distribution of the coronal coils around the core.
The coils grafted to the edge of the core adopt a radial conformation whereas the
ones at the center are more elongated. The authors suggest that this resulted in
nonuniformity in space filling that manifests in the distortion of an otherwise BCC
lattice. In a triblock RC architecture with oligostyrene and oligoisoprene coils and
three biphenyl units as rods, Radzilowski et al. reported unique mushroom-shaped
nanostructures where an aggregated packet of rods form the stem and the oligomeric
coils splay forming the head of the mushroom. About 100 rod molecules aggregate
into a mushroom (the size is limited by the repulsive interactions of the oligomers
coils that form the head of the mushroom) (Fig. 7c) (Stupp et al. 1997). These
mushrooms further stack to form a layered structure. The rods orient normal to the
substrate leading to self-organized films with polar and nonpolar bottom and top
surfaces. Keeping the length of the rod constant, the authors observed a disruption of
the layered structures with an increase in the f
coil due to the steric repulsions between
7 Structure and Assembly of Liquid Crystalline Block Copolymers
187
PS ~ 1900 and DP
PIC ~ 100)
and with f
PS
= 0.9, Park et al. observed anisotropic nanoscale objects in the shape of
parallelograms that form Sm ordering in solution cast films (Park and Thomas 2004).
Using theoretical calculations, it was shown that these parallelograms, with a side of
at least 45 nm, had a tilted bilayer arrangement of the PIC rods. The authors propose
that interdigitation of the rods is also possible. Within these nano-objects, the PIC
rods are oriented uniaxially and these nano-objects have a 25–45
angle between the
sides.
Rods made of mesogenic molecules also possess inherent rigidity as a result of
their molecular chemistry. A lot of interesting morphologies were observed in
RCBCPs containing mesogenic rods although most of the mesogens were based
on low M n molecules. Stupp’s group investigated the phase structures in mesogenic
oligomers (formed by attaching an azo dye to a rigid biphenyl carboxylic acid) of
length 6 nm attached to flexible polyisoprene (M w = 3200 g/mol). Good control over
the polydispersity of the rod molecule allowed the researchers to explore the subtle
competition between the microphase separation and LC ordering processes by
altering the chemistry and M n of the molecules (Radzilowski et al. 1993, 1997;
Radzilowski and Stupp 1994; Stupp 1998; Stupp et al. 1997). At f
rod
= 0.36, the
rigid mesogenic rods formed stripes arranged in layers inside the PI matrix. At
similar f values, hexagonally close packed C morphologies are observed in coil-coil
systems. In the present RCBCP case, although the stripes possess a hexagonal
symmetry, the nature of the orientation of the rods within the stripes was not clear
(Fig. 7a) (Lee et al. 2001). Qualitatively, these stripe-like patterns are similar to the
broken L phases as reported in the numerical calculations by Ganesan et al.
(Pryamitsyn and Ganesan 2004). As the f
rod decreased to 0.25, the morphology
transformed from stripes into super lattice aggregates (7 nm in diameter) that are
oriented parallel to the substrate (Fig. 7b)(Lee et al. 2001). These aggregates are
arranged with hexagonal in-plane symmetry in a PI matrix. Theoretical calculations
by Fredrickson et al. and Ganesan et al. also showed similar puck-like morphologies
(Pryamitsyn and Ganesan 2004; Williams and Fredrickson 1992). The authors claim
that the observation of a hexagonally packed lattice at such highly asymmetric
f suggests the nonuniformity in distribution of the coronal coils around the core.
The coils grafted to the edge of the core adopt a radial conformation whereas the
ones at the center are more elongated. The authors suggest that this resulted in
nonuniformity in space filling that manifests in the distortion of an otherwise BCC
lattice. In a triblock RC architecture with oligostyrene and oligoisoprene coils and
three biphenyl units as rods, Radzilowski et al. reported unique mushroom-shaped
nanostructures where an aggregated packet of rods form the stem and the oligomeric
coils splay forming the head of the mushroom. About 100 rod molecules aggregate
into a mushroom (the size is limited by the repulsive interactions of the oligomers
coils that form the head of the mushroom) (Fig. 7c) (Stupp et al. 1997). These
mushrooms further stack to form a layered structure. The rods orient normal to the
substrate leading to self-organized films with polar and nonpolar bottom and top
surfaces. Keeping the length of the rod constant, the authors observed a disruption of
the layered structures with an increase in the f
coil due to the steric repulsions between
7 Structure and Assembly of Liquid Crystalline Block Copolymers
187