Abstract
An experimental study is reported of the quiescent and flow birefringent characteristics of two liquid crystalline polymer solution systems, poly- p-phenylene terephthalamide (PPD-T) in sulfuric acid and hydroxypropyl cellulose (HPC) in water over a range of concentrations. It is shown that for the quiescent state the dilute solutions are optically isotropic while the concentrated solutions consists of negatively birefringent domains. During flow at low deformation rates, moving domains are still seen. At higher deformation rates, a homogeneous highly birefringet fluid is obtained. The birefringence increases with concentration at constant deformation rate and exhibits a major increase as the liquid crystalline state is formed. The source of the birefringence is due to (1) anisotropy of polarizability of oriented macromolecules, and (2) difference in refractive index of solvent and oriented macromolecules (form birefringence). The results are interpreted in terms of the level of polymer orientation which may be developed in flow for liquid crystalline polymer solutions as compared to solutions of flexible macromolecules.
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