MAGNETIC ORIENTATION AND MICROSTRUCTURE OF MAIN-CHAIN THERMOTROPIC COPOLYESTERS

The structural response of a molten main-chain liquid crystal polymer to an applied magnetic field has been investigated microscopically, with the microstructure being characterized as a function of field strength, time in the field and molecular weight. The application of the field to a structure in which the director wandered gradually on a scale of about 100 mum resulted in the formation of domains delineated by well defined boundaries. The domains were elongated along the field axis to an aspect ratio of about 8 in the case of a 1.1 T field, although for the higher field strength of 5.6 T the domains were no longer visible. Evidence is presented that the domain boundaries correspond to a director reorientation of pi rad. Etched domain microstructure revealed a uniform distribution of crystallites, representing regions of local ordering in the material, on a scale of a few hundred nanometres. The crystallites had the form of platelets normal to the local director and acted as orientational markers across the domain boundaries.