Direct observation of director fields of disclinations in the nematic mesophase of a main chain thermotropic aromatic polyester by surface microcrackdecoration

For a main chain thermotropic aromatic polyester with a flexible spacer, Cr 194 N 245 I (degreesC), the director fields around disclinations in the ne matic mesophase can be decorated by both the solidification-induced band te xture and surface microcracks. Director fields of various types of disclina tions, including inversion walls, in the nematic mesophase of this semi-rig id polyester have been observed directly by polarizing optical microscopy. It was found that when the polymer was pre-sheared in the nematic state and then quenched to room temperature, a shear-induced band texture was observ ed, which relaxed slowly during annealing at 200 degreesC, and then on quen ching the solidification-induced band texture and surface microcracks appea red, displaying the pattern of the disclination fields. Pre-shearing is a n ecessary condition for the appearance of microcracks. On annealing, disclin ations of various types were generated, quite often connected by inversion walls in the direction of pre-shearing. In some areas of the specimen where the shear-induced bands had not been completely relaxed during annealing, the shear-induced band texture was shown by the birefringence and surface m icrocracks to have a supermolecular structure of sinusoidal chain fibrils.