The self-assembly of ABA triblock copolymers comprising
flexible amorphous poly(ethyl methacrylate) (PEMA, A block) and
semiflexible liquid crystal (LC) polyester (B block) was investigated for
amorphous block volume fractions (φ) ranging from 20% to 80%. Two
copolymer series with different LC block molecular weights (Mn,LC)
were examined. At φ < 55%, block copolymers with Mn,LC = 11 600
formed lamellar microdomains in which LC segments mostly extended
along the lamella normal but folded to fit in the lamellae. When φ was
augmented, the LC segment fold (Nfold) increased to enhance the
interface between the LC and amorphous segments and counterbalanced
the increase in amorphous lamella thickness by reducing the
LC lamella thickness. When φ > 68%, the LC lamellae were divided into cubes, transforming into spheres in the PEMA matrix.
When Mn,LC decreased to 6300, the copolymers showed similar morphology. However, the lamellae adopted zigzag
configurations showing a greater tilting angle between the lamella normal to the LC chain axis with increasing φ. Thus, the LC
and PEMA segments enhanced their interface by mutually sliding along the chain axis instead of increasing Nfold.
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