Akemi Nakai

Phase-separated structures formed in polymer mixtures containing a thermotropic liquid crystalline copolyester as one component

Abstract The phase-separated structures formed in polymer mixtures consisting of a thermotropic liquid crystalline copolyester and poly(ethylene terephthalate) (PET) are investigated. The 50 wt%/50 wt% mixtures isotropic, transparent and homogeneous were prepared by dissolution of the copolyester and PET in an organic solvent followed by rapid removal of the solvent. Their phase separation processes during isothermal annealing at various temperatures after rapidly heating the as-prepared thin films were investigated by real-time and in situ polarized light microscopy and light scattering. At the annealing temperature below the melting point of PET (Tm,PET), the vitrification and crystallization of the components strongly affect phase separation, giving rise to pinning of the coarsening process at the different stages of phase separation and hence leading to various phase-separated structures. Rapid phase separation via spinodal decomposition was observed at annealing temperatures above Tm,PET. The phase-separated structures were found to evolve via the following sequence of mechanisms: (1) self-similar growth of the percolated networks of the anisotropic and isotropic phases; (2) disruption of the percolated network and formation of anisotropic droplets in the isotropic matrix; and (3) coalescence of anisotropic droplets. Light scattering from the percolated network structure was further investigated in terms of the spatial distributions of the orientation and concentration fluctuations.

Mechanism and Kinetics of Phase Separation of a Semi-Rigid and Flexible Polymer Mixture

The mixture of a semi-rigid polymer and a flexible polymer undergoes phase separation via spinodal decomposition. The unmixing process of the polymer mixture can be divided into three characteristic regions depending on the difference in the growth behavior. In each region the growth of the wavelength of the concentration fluctuation obeys a scaling law.

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 an...