Supramolecular Interactions in the Formation of Thermotropic Liquid Crystalline Polymers - Liquid Crystalline Functional Assemblies and Their Supramolecular Structures - page 136

Fig. 15 a The structure of the side chain SLC block copolymer 30 · 31 used by Ober and
Thomas to access temperature-dependant photonic band gap materials b ASchematicof
the proposed model for “free” mesogen formation believed to be important for the re-
orientationofblendsheatedbelowODTinanappliedACfield

of both the mesogens and microdomains with AC fields [98]. In this case,
a lower molecular weight polystyrene- block -acrylic acid (25 and 5.3 kg mol),

to enhance the mobility of the system, was used as the block copolymer. The
addition of the mesogen (0.8 molar ratio mesogen to acrylic acid repeat units)
to this system resulted in films which again formed lamellar morphologies
(6 nm thickness) in which one of the domains exhibits a smectic phase. SAXS
data indicated that the smectic phase destabilizes at 110 ◦ C and that the ma-
terial shows an order-disorder transition (ODT) occurring at ca. 170 ◦ C. It
should be noted that, from POM observations, the films do not go isotropic
until 135 ◦ C, suggesting the presence of an additional LC phase. The lamel-
lar morphologies formed run parallel to the (electrode) surface on account
of a shear-induced alignment that occurred during sample preparation. Sim-
ple heating of the film above the ODT resulted in complete loss of orientation
upon cooling. However, if the film is heated above the ODT and cooled under
an AC field (1

/

m -1 with a frequency of 10 Hz)alignmentofthelamellar
structure occurs normal to the electrode (perpendicular orientation). More
interestingly, the parallel orientation can be directly converted into the per-

∼ 2 V µ