Aromatic polyesters with flexible side chains. 10. studies on biaxiality in nematic liquid crystal of BC-n polyester

Abstract

This paper reports a possibility of biaxiality in the nematic liquid crystal formed from aromatic polyesters, BC-n, which are composed of 1,4-dialkyl ester of pyromellitic acid and 4,4′-biphenol. In these BC-n polyesters, as a general trend, the microsegregation of aromatic backbone and flexible side chains takes place and the nematic liquid crystal appears after these layered phases melt. X-Ray diffraction pattern from oriented nematic fiber shows unusual inner reflection with a large spacing around 20 Å in addition to normal outer reflection with a spacing of 4.5 Åon equatorial line, indicating that there are two types of packing correlation in a direction perpendicular to the director, n, in other words, there is a biaxiality. Optical microscopic textures exhibit exclusively the two-brush disclinations with |s| = 1/2, which also conforms to the biaxial nematic order. The spacing of inner equatorial reflection approximates to the layer spacing in the layered mesophase formed from the same homologues. This strongly suggests that the layered aggregation is still remained in the nematic liquid crystals, and its board-like shape is responsible for the biaxia-lity.