an RCBCP led to improvement of their properties compared to the homopolymers
due to enhanced ordering (Liang et al. 2007).
Using low M w oligo PV as the rod block and PI as the coil block with varying w
rod
(weight fraction of rod, 0.12–0.4), Li et al. reported L morphologies with bilayered
supramolecular structures within the OPV block (Li et al. 1999). Introducing
amphiphilic nature to these BCPs by using PEG instead of PI, Wang et al. observed
long cylindrical micelles (15–18 nm core diameter) with OPV core formed in water/
THF solvents and in thin films (Wang et al. 2000). Further changing the coil to
hydrophobic PPG led to the formation of well-oriented fiber patterns on mica
substrate (Wang et al. 2004). The orientation of these fibers was attributed to the
interactions between the coils and the substrate where longer coils led to better
oriented fibers.
In PS-b-PPQ system, Jenekhe et al. reported unique supramolecular phase structures such as hollow S, L, hollow C, vesicles, etc. depending upon the type of solvent
used and the rate of solvent evaporation (Fig. 9a) (Chen and Jenekhe 2000; Jenekhe
and Chen 1998, 1999). By changing the type of solvent, they were able to obtained
hollow hard spheres (rod core) and hollow soft spheres (coil core). At a macrolevel,
the hard spheres undergo self organization to form 2D hexagonally ordered arrays of
spherical holes formed due to the condensation of the solvent during annealing. The
nano hollow spheres were also used to encapsulate molecules such as fullerenes
(Chen and Jenekhe 1999). Sary et al. explored the relationship between χ and μ in
P4VP-b-PV RCBCP system (Sary et al. 2007a, b). The ratio μ/χ determined whether
the LC ordering or microphase separation dominated the overall morphology. In
their system (χN > 15–20 and μ/χ < 4), Sary et al. observed the domination of the
microphase separation and the PPV rods were confined into L, C, and S domains.
However, the C and S domains were highly distorted and exhibited poor long range
order. Within the L, annealed PPV domains showed SmC 2 (bilayered SmC) phase
with a tilt angle of ~52
. This SmC 2 -in-L transformed into L which further transformed into isotropic phase with increase in temperature. In the PPV hexagonal C
structure, the molecules were arranged radially, perpendicular to the C axis. In a PSb-PPV RCBCP with f
rod
= 0.17 which forms homogeneous isotropic structures,
blending with PPV homopolymers resulted in the formation of SmC 2 structures due
to the π–π conjugation between the homopolymer PPV and the rod block of the
RCBCP (Fig. 9b) (Sary et al. 2007a). These rods were tilted at an angle of 54
with
respect to the layer normal. Blending of up to 50 wt.% PPV did not result in any
macrophase separation. They attribute the increase in the Sm ordering upon blending
to the increased rod-rod interactions. By attaching a cyano substituted PV chromophore segment to the rod segment of their mushroom forming oligomeric system,
Stuppet al. observed the fluorescent properties of the molecules (Pralle et al. 2000).
The observation of strong polar ordering in layered mushroom structures of ~5 nm
diameter after conjugating indicates the high thermodynamic stability of the mushroom structures. Strong photoluminescence and piezoelectric behavior and mechanical adhesion were reported in these conjugated molecules.
7 Structure and Assembly of Liquid Crystalline Block Copolymers
191
due to enhanced ordering (Liang et al. 2007).
Using low M w oligo PV as the rod block and PI as the coil block with varying w
rod
(weight fraction of rod, 0.12–0.4), Li et al. reported L morphologies with bilayered
supramolecular structures within the OPV block (Li et al. 1999). Introducing
amphiphilic nature to these BCPs by using PEG instead of PI, Wang et al. observed
long cylindrical micelles (15–18 nm core diameter) with OPV core formed in water/
THF solvents and in thin films (Wang et al. 2000). Further changing the coil to
hydrophobic PPG led to the formation of well-oriented fiber patterns on mica
substrate (Wang et al. 2004). The orientation of these fibers was attributed to the
interactions between the coils and the substrate where longer coils led to better
oriented fibers.
In PS-b-PPQ system, Jenekhe et al. reported unique supramolecular phase structures such as hollow S, L, hollow C, vesicles, etc. depending upon the type of solvent
used and the rate of solvent evaporation (Fig. 9a) (Chen and Jenekhe 2000; Jenekhe
and Chen 1998, 1999). By changing the type of solvent, they were able to obtained
hollow hard spheres (rod core) and hollow soft spheres (coil core). At a macrolevel,
the hard spheres undergo self organization to form 2D hexagonally ordered arrays of
spherical holes formed due to the condensation of the solvent during annealing. The
nano hollow spheres were also used to encapsulate molecules such as fullerenes
(Chen and Jenekhe 1999). Sary et al. explored the relationship between χ and μ in
P4VP-b-PV RCBCP system (Sary et al. 2007a, b). The ratio μ/χ determined whether
the LC ordering or microphase separation dominated the overall morphology. In
their system (χN > 15–20 and μ/χ < 4), Sary et al. observed the domination of the
microphase separation and the PPV rods were confined into L, C, and S domains.
However, the C and S domains were highly distorted and exhibited poor long range
order. Within the L, annealed PPV domains showed SmC 2 (bilayered SmC) phase
with a tilt angle of ~52
. This SmC 2 -in-L transformed into L which further transformed into isotropic phase with increase in temperature. In the PPV hexagonal C
structure, the molecules were arranged radially, perpendicular to the C axis. In a PSb-PPV RCBCP with f
rod
= 0.17 which forms homogeneous isotropic structures,
blending with PPV homopolymers resulted in the formation of SmC 2 structures due
to the π–π conjugation between the homopolymer PPV and the rod block of the
RCBCP (Fig. 9b) (Sary et al. 2007a). These rods were tilted at an angle of 54
with
respect to the layer normal. Blending of up to 50 wt.% PPV did not result in any
macrophase separation. They attribute the increase in the Sm ordering upon blending
to the increased rod-rod interactions. By attaching a cyano substituted PV chromophore segment to the rod segment of their mushroom forming oligomeric system,
Stuppet al. observed the fluorescent properties of the molecules (Pralle et al. 2000).
The observation of strong polar ordering in layered mushroom structures of ~5 nm
diameter after conjugating indicates the high thermodynamic stability of the mushroom structures. Strong photoluminescence and piezoelectric behavior and mechanical adhesion were reported in these conjugated molecules.
7 Structure and Assembly of Liquid Crystalline Block Copolymers
191