N-substituted poly(p-phenylene terephthalamide) film: surface characteristics and liquid-crystal alignment with high pretilt angles

Abstract

N-Substituted poly(p-phenylene terephthalamide)s (PPTA) with various substituents in their side chains have been synthesized, and the surface characteristics of their films studied. N-Substituted PPTA showed high thermal stability and solubility in organic solvents, and the thin films, prepared by a casting method, showed a smooth surface with surface free energies of 30–50 erg cm^–2. After rubbing with rayon fibres, the films easily aligned nematic liquid crystals at their surfaces. Pretilt angles induced at the surface of benzyl- and 4-methylbenzylsubstituted PPTAs with a high degree of substitution, were 4.6 and 8.1°, respectively. A rigid side-chain structure and a high degree of substitution are suggested as being more important than low surface free energy for inducing a high pretilt angle.