Phase-separation processes and self-organization of textures in the biphase region of thermotropic liquid crystalline poly(4,4'-dioxy-2,2'-dimethylazoxybenzene-dodecanedioyl) .2. A study of the isothermal conditions

The isothermal phase-separation process and the self-organization of textures in the biphase region of a thermotropic liquid crystalline polyester were investigated in situ by using polarizing light microscopy. When the test temperature was rapidly raised from room temperature to the temperature corresponding to the biphase region (T-jump) or rapidly lowered from a temperature corresponding to the isotropic phase to that corresponding to the biphase region (T-drop), the phase separation occurs as a consequence of chain segregation according to the chain length: the chain species shorter than the average length gradually separate from the anisotropic phase to form the isotropic phase. The phase-separated textures transiently formed in the biphase region depend strongly on the thermal processes: in the case of the T-jump the coarsening of texture involves the diffusion-coalescence of isotropic drops in the anisotropic matrix, while in the case of the T-drop it involves the diffusion-coalescence of anisotropic drops in the isotropic matrix. For both cases growth of the radius of the drop R with the annealing time t obeys approximately the same power law, R(t) similar to t(1/3), over the time scale covered in this experiment. The coarsening mechanism is discussed in the text.