Effect of temperature and shear on phase separation in liquid crystalline polymer/polycarbonate blends.

摘要

The objective of this thesis is to obtain deeper understanding of phase separation in blends of liquid crystalline polymers (LCPs) and polycarbonate (PC) under the influence of temperature and shear (at low steady shear rates). The LCP selected for this work was a main-chain type copolyester exhibiting low solubility and high chemical resistance. Therefore, melt-blending was used to prepare blends. Polarized light microscopy, in conjunction with a heating/shearing stage, was employed to observe the evolution of the phase-separated structure in the blends.;The effects of low steady shear rate on the phase diagram and phase-separated morphology of the blends were examined. Compared to the phase diagram under quiescent conditions, phase separation temperatures were shifted to lower values at the corresponding concentrations. Also, the speed and extent of phase separation in the 50 wt.% blends increased, when shear was applied. Thus, the blend exhibited shear-induced phase separation behavior at low shear rates.;Phase separation in the blends was observed with increasing temperature. Two phase separation temperatures (Tsp1 and Tsp2) were determined for each LCP/PC blend composition. Thus, the phase diagram, obtained under quiescent conditions, exhibited three regions separated by two internal boundaries. Thermally induced phase separation in the blends at different positions of the phase diagram was investigated. A wide range of phase-separated morphologies was observed. Blends containing 20-30 wt.% LCP developed into interconnected structures, which is one of the characteristic of spinodal decomposition. Blends with other LCP contents (up to 60 wt.%) formed droplet-type structure. Coarsening of the phase-separated domains was also observed in the late stages of the phase separation.