Unusual Perpendicular Chain Orientation in a Smectic Liquid Crystal Polyester Subjected to Shear or Elongational Flow

Abstract

In this work, we report on flow-induced orientation in two low molecular weight polyesters, both containing the smectic diol 4,l'-bis (dhydroxy hexoxy) biphenyl (BHHBP) and either isophthalic acid (IA) or terephthalic acid (TA). The polyester of BHHBP and 1A has a mesophase, while the polyester of BHHBP crystallises on cooling from the isotropic melt without any mesophase formation. When the TA polyester was subjected to flow, the chains were aligned parallel to the flow direction. In contrast, when the IA polyester was sheared or subjected to elongational flow in the mesophase state, it was found that the chains were surprisingly oriented perpendicular to the flow direction or the fibre axis. However, when the IA polyester was sheared or elongated in the isotropic molten state, the normal orientation with the chain axis parallel to the flow direction was observed. Thus, perpendicular orientation appears to have an association with deformation in the mesophase state. The orientation information was deduced from studying the dichroism of vibrational bands in the polarised infrared spectra.

Parallel and Perpendicular Orientations Observed in Shear Aligned SCA Liquid Crystal of Main-Chain Polyester

“…Finally, we shall comment on the orientations observed in the uniaxially stretched fiber or film of main-chain polymer smectic liquid crystals. Most characteristic orientation is so-called “anomalous orientation” where the chain axis lies perpendicular to the fiber axis; in other words, the smectic layer arranges parallel to the stretching direction (i.e., flow direction) as has been reported by us 23,24 and other groups. − Comparing this orientation to the orientations observed in this study, one would notice that there are two mechanisms to produce the anomalous orientation since the anomalous orientation is apparently identical to the perpendicular and parallel orientations produced by shear flow. Thus, we reasonably speculate that when the fiber or film is stretched from the smectic melt at high temperature close to the isotropization temperature the anomalous orientation is caused by the internal flow of the mesogens within the layer.…”