Orientational flipping and flow alignment of a model main-chain thermotropic LCP

A model thermotropic liquid crystalline polymer with low isotropization point, good optical transparency and thermal stability was synthesized and the evolution of orientation during flow was monitored using in situ wide angle X-ray diffraction. The polymer, a random copolyether of dihydroxymethylstilbene coupled with 7- and 9-methylene, showed a rich relationship between mesophase behavior, shear induced orientation and bulk flow properties. In the nematic phase, as DHMS-7,9 is flow-aligning, steady shear aligns its director to a fixed angle, giving rise to a nearly constant orientation parameter at different shear rates. In the x-phase, the polymer showed an interesting orientation flipping from parallel to perpendicular at low shear rates.