Direct observation of a smectic bilayer microstructure in side-chain liquid crystalline diblock copolymers

TEM analyses enable a priori investigation of smectic bilayer structures in an amorphous-liquid crystalline (LC) diblock copolymer. A newly synthesized copolymer with 85 wt % LC phase segregates into a layered morphology in both bulk and thin film studies. The microstructure has a periodicity of similar to 70 Angstrom and forms highly ordered micron-size monodomains. SAXS, TEM, and AFM data suggest that the LC domains consist of smectic bilayers, and amorphous polystyrene domains are present as disklike domains that arrange hexagonally between smectic bilayers. Temperature-dependent SAXS experiments and quenched TEM micrographs indicate that a reversible change in microstructure occurs at the LC clearing point. These observations confirm that, at high LC volume fractions, side-group ordering has a greater affect on block copolymer microstructures. Our results are contrasted to recent theoretical predictions of block copolymer microstructures.