Optical microscopy of banded structures in oriented thermotropic polymers

Abstract

Banded structures apparent in thermotropic polymers are analysed by optical microscopy. The structures result from shear at elevated temperatures and are preserved by rapid cooling. The bands are shown to be the consequence of a periodic variation in the orientation of the principal optical vibration directions about the shear axis. It is possible that this variation may be directly related to a corresponding variation in the direction of the long axis of the molecule. The maximum divergence angle is measured for a range of copolyesters; the weakness or complete absence of the zero order reflection in the conoscopic image (optical diffraction pattern) in certain circumstances is explained in terms of a periodic alternation of phase as well as amplitude, which contributes to the image of the banded structure.