RELATIONSHIP BETWEEN MESOPHASE AND SEMICRYSTALLINE MORPHOLOGY IN SMECTIC LIQUID-CRYSTALLINE POLYMERS

The semicrystalline morphology of a semiflexible smectic polyester is investigated by high-resolution electron microscopy. Images combining diffraction and phase contrast allow simultaneous visualization of the mesomorphic and semicrystalline phases. A smectic C2 mesophase is confirmed by electron diffraction of quenched (noncrystalline) specimens. A new disordered-uniaxial model is developed to evaluate the molecular tilt in smectic mesophases in which the layers rather than the molecules are aligned. Biaxial symmetry for small selected areas (<200 nm) and uniaxial symmetry, about the layer normal, for larger areas requires extended polymer chains to be twisted and entangled around one another. These molecular entanglements, unique to polymeric smectic mesophases, are argued to limit crystal growth to very thin lamellae (8 nm) and low crystallinity (approximately 40%). In spite of the small thickness of the crystals, the coherence length normal to the lamellae is large.