Formation of mesophase mono-domains and micro-structures in thin films of a series of copolyethers containing both odd-numbered methylene units

The structural and morphological evolution of mono-domains in thin films ha s been investigated for a series of liquid crystalline (LC) copolyethers. T he copolyethers studied were synthesized by the reaction of 1-(4-hydroxy-4 ' -biphenylyl)-2-(4-hydroxyl-phenyl)propane (TPP) with 1,7-dibromoheptane a nd 1,11-undecane at different compositions (coTPPs-7/11). In contrast to th e solution-cast thin films without annealing, which exhibit the isotropic h omogeneous molecular orientation, mono-domains with a homeotropic alignment were found in coTPP-7/11(5/5) after the thin films were annealed in the hi gh-temperature columnar phase (Phi '). Similar to the nucleation process in polymer crystallization, transmission electron microscopic observations sh ow that small mono-domains appear in the initial stage of annealing, where molecules form a uniaxial in-plane chain orientation. With increasing annea ling time, the molecular orientation gradually became tilted with respect t o the substrate surface, and finally, a uniaxial homeotropic molecular orie ntation was achieved after a prolonged annealing time. The lateral size of mono-domains was found to increase continuously with annealing time and gre w into a circular shape, indicating an isotropic lateral growth scheme whic h implies a hexagonal molecular packing proved by the electron diffraction experiments.