theoretical analysis of the phase behavior in SC-LCBCPs as a function of M n , rod
length, and f of the blocks using SCFT and is shown in Fig. 14c (Note: N in the figure
represents degree of polymerization and not N LC phase) (Shah et al. 2008). They
observed that the segregation strength for microphase separation is much weaker
than that for I to N (nematic) LC transition (in the figure, (χ 1 N) C < (χ 1 N) I-N )
indicating that microphase separated structures are necessary to obtain ordered LC
phases. C of coil in LC matrix was observed in samples with low f
coil in which the
mesogen axis was parallel to the C axis. This kind of orientation was facilitated by
the stretching of the polymer backbone away from the interface. Alternative arrangement of mesogens, oriented tangential to the C, would lead to defects in the structure.
L phases were observed at symmetric f values where the mesogens were aligned
parallel to the IMDS. Compared to the coil-coil phase diagram, theoretical
SC-LCBCP phase diagram is asymmetric. At higher f
coil , C of the LC phase, with
the mesogens aligned parallel to the C axis was the most favored morphology.
In a PS-b-PI system where PI is functionalized with an azobenzene-based mesogen, Ober and Thomas et al. reported the phase behavior as a function of f
PI-LC with
morphologies including L, PS C in PI-LC matrix and PI-LC cylinders in PS matrix
(Fig. 15) (Osuji et al. 1999, 2000). The LC block showed a T SmA-I at 171
C. In L
samples and C forming samples where PS is the majority phase, the authors observed
PI-LC forming SmA type of LC phase with homogeneously anchored mesogens. In
shear-oriented C forming samples where PI-LC formed the majority phase, the
authors observe a transformation of the orientation of the cylinders as a function
of shearing temperature. When sheared in the Sm LC temperature, the cylinders were
oriented with their long axis parallel to the neutral direction (perpendicular to the
shear direction and in the plane of shear, also known as transverse orientation) and
the Sm layers were oriented with their layer normal parallel to the neutral axis. The
cylinders reoriented to adopt a parallel orientation (preferred orientation for coil-coil
systems) when sheared in the T I . The authors propose four different possible models
that are possible in a C forming LCBCP system: (where the LC forms the matrix)
parallel-transverse, perpendicular-parallel, parallel-parallel, and transverse-perpendicular (Fig. 15). In this notation, the first word indicates the orientation of C axis
and the second word is the orientation of the Sm layers. Among these possible
orientations, the transverse-perpendicular orientation is the most favorable morphology compromise where both the Sm layers and the cylinders are not under strain and
this morphology also satisfies the homogeneous anchoring condition of the LCs.
Anthamatten et al. studied the room temperature and high temperature phase
behavior of PS-b-PMMA based SC-LCBCPs where the methacrylate contained a
chiral biphenyl benzoate mesogen attached using six and ten carbon alkyl spacers
(Anthamatten 2001; Anthamatten and Hammond 1999; Anthamatten et al. 1999,
2001). The phase diagram (shown in Fig. 16) for this system showed predominantly
L phase due to the layered nature of the Sm LC phase (Anthamatten et al. 1999). At
lower f
LC (<0.25), noncontinuous LC S were observed. As f
LC increased (<0.5), the
morphology changed to predominantly L in nature. At f
LC ~ 0.5, L phases coexisting
with C defects and possessing HPL correlation were observed. At higher f
LC (~0.79),
the morphology was hexagonally packed PS C in LC matrix. In the L samples, the
7 Structure and Assembly of Liquid Crystalline Block Copolymers
199
length, and f of the blocks using SCFT and is shown in Fig. 14c (Note: N in the figure
represents degree of polymerization and not N LC phase) (Shah et al. 2008). They
observed that the segregation strength for microphase separation is much weaker
than that for I to N (nematic) LC transition (in the figure, (χ 1 N) C < (χ 1 N) I-N )
indicating that microphase separated structures are necessary to obtain ordered LC
phases. C of coil in LC matrix was observed in samples with low f
coil in which the
mesogen axis was parallel to the C axis. This kind of orientation was facilitated by
the stretching of the polymer backbone away from the interface. Alternative arrangement of mesogens, oriented tangential to the C, would lead to defects in the structure.
L phases were observed at symmetric f values where the mesogens were aligned
parallel to the IMDS. Compared to the coil-coil phase diagram, theoretical
SC-LCBCP phase diagram is asymmetric. At higher f
coil , C of the LC phase, with
the mesogens aligned parallel to the C axis was the most favored morphology.
In a PS-b-PI system where PI is functionalized with an azobenzene-based mesogen, Ober and Thomas et al. reported the phase behavior as a function of f
PI-LC with
morphologies including L, PS C in PI-LC matrix and PI-LC cylinders in PS matrix
(Fig. 15) (Osuji et al. 1999, 2000). The LC block showed a T SmA-I at 171
C. In L
samples and C forming samples where PS is the majority phase, the authors observed
PI-LC forming SmA type of LC phase with homogeneously anchored mesogens. In
shear-oriented C forming samples where PI-LC formed the majority phase, the
authors observe a transformation of the orientation of the cylinders as a function
of shearing temperature. When sheared in the Sm LC temperature, the cylinders were
oriented with their long axis parallel to the neutral direction (perpendicular to the
shear direction and in the plane of shear, also known as transverse orientation) and
the Sm layers were oriented with their layer normal parallel to the neutral axis. The
cylinders reoriented to adopt a parallel orientation (preferred orientation for coil-coil
systems) when sheared in the T I . The authors propose four different possible models
that are possible in a C forming LCBCP system: (where the LC forms the matrix)
parallel-transverse, perpendicular-parallel, parallel-parallel, and transverse-perpendicular (Fig. 15). In this notation, the first word indicates the orientation of C axis
and the second word is the orientation of the Sm layers. Among these possible
orientations, the transverse-perpendicular orientation is the most favorable morphology compromise where both the Sm layers and the cylinders are not under strain and
this morphology also satisfies the homogeneous anchoring condition of the LCs.
Anthamatten et al. studied the room temperature and high temperature phase
behavior of PS-b-PMMA based SC-LCBCPs where the methacrylate contained a
chiral biphenyl benzoate mesogen attached using six and ten carbon alkyl spacers
(Anthamatten 2001; Anthamatten and Hammond 1999; Anthamatten et al. 1999,
2001). The phase diagram (shown in Fig. 16) for this system showed predominantly
L phase due to the layered nature of the Sm LC phase (Anthamatten et al. 1999). At
lower f
LC (<0.25), noncontinuous LC S were observed. As f
LC increased (<0.5), the
morphology changed to predominantly L in nature. At f
LC ~ 0.5, L phases coexisting
with C defects and possessing HPL correlation were observed. At higher f
LC (~0.79),
the morphology was hexagonally packed PS C in LC matrix. In the L samples, the
7 Structure and Assembly of Liquid Crystalline Block Copolymers
199