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 molecul ar weight polyesters, both containing the smectic diol 4,1'-bis (6-hyd roxy hexoxy) biphenyl (BHHBP) and either isophthalic acid (IA) or tere phthalic acid (TA). The polyester of BHHBP and IA has a mesophase, whi le the polyester of BHHBP crystallises on cooling from the isotropic m elt without any mesophase formation. When the TA polyester was subject ed to flow, the chains were aligned parallel to the flow direction. In contrast, when the IA polyester was sheared or subjected to elongatio nal flow in the mesophase stare, it was found that the chains were sur prisingly oriented perpendicular to the flow direction or the fibre ax is. However, when the IA polyester was sheared or elongated in the iso tropic molten state, the normal orientation with the chain axis parall el to the flow direction was observed. Thus, perpendicular orientation appears to have an association with deformation in the mesophase stat e. The orientation information was deduced from studying the dichroism of vibrational bands in the polarised infrared spectra.