Ordered structure of thermotropic liquid crystalline copolymers 2. Observation of annihilation kinetics of wedge disclinations

Abstract

The isothermal annihilation kinetics of wedge disclinations in the fully liquid crystalline state were investigated using thin film specimens of a thermotropic liquid crystalline copolyester prepared by a solution-cast method. The as-cast films which are vitrified, homogeneous and amorphous were first subjected to a temperature jump to appropriate temperatures and the coarsening of the liquid crystalline texture was observed in real-time and in situ by means of optical microscopy and laser light scattering. The experimental results obtained show that, in the early stages, the domain size, D, which is inversely proportional to the square root of the density of disclinations in the sample, approximately obeys a power law of D(t) ∼ t ^0.35 over the time scale covered in the experiment. In the later stages, anchoring of some of the disclination lines onto the glass surface and/or formation of crystallites from some sequences of the copolyester having a higher melting point suppress and then pin the annihilation process. The annihilation processes for pairs of wedge disclinations between s = + 1/2 and s = − 1/2 or between s = + 1 and s = − 1/2 were directly observed in situ by optical microscopy, and the distance between them was observed to decrease with time.