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

In this work, we report on flow-induced orientation in two low molecular weight polyesters, both containing the smectic diol 4,1′-bis (6-hydroxy hexoxy) biphenyl (BHHBP) and either isophthalic acid (IA) or terephthalic acid (TA). The polyester of BHHBP and IA 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 dicahroism of vibrational bands in the polarised infrared spectra.