RHEO-OPTICS OF LIQUID-CRYSTALLINE POLYMERS IN COMPLEX GEOMETRIES

The flow of isotropic and liquid-crystalline hydroxypropylcellulose-wa ter solutions is studied in a transparent slit die with several geomet ries including divergent and convergent configurations. The flow is ob served between crossed polars. In addition to the two different flow r egimes that are known in shear (zones I and II), a new flow behavior i s observed (zone III). Zone I is characterized by a large macroscopic orientation, as seen between crossed polars. It is localized where eit her shear rates or elongation rates are large. The extinction angle is a function of the position in the die. It is similar to the flow-alig ning regime observed at high shear rates. Zone II is much less oriente d, due probably to a large density of defects. It is typical of the lo w shear rate region observed in simple shear. Zone III exhibits a pecu liar behavior with long-range orientation instabilities. It is always localized after a diverging zone. Flow around obstacles and colliding streams are also studied.