Polydomain model predictions of molecular orientation in isothermal channel flows of thermotropic liquid crystalline polymers

We report process simulations of molecular orientation of liquid crystalline polymers for isothermal channel flows in extrusion. The simulations use a "polydomain" model due to Larson and Dol (Larson and Dol, J. Rheol., 35, 539 (1991)), which is implemented by exploiting a nearly exact analogy with a fiber orientation model that is widely used for analysis of composites processing. Simulation results are compared to experimental data previously obtained using a customized X-ray capable extrusion die that allows a wide range of channel flow geometries to be explored. Competition between inhomogeneous shear and extension in these kinematically complex flows has a profound effect on the resulting molecular orientation distributions. We find that the Larson-Doi model successfully predicts most aspects of the experimental observations, demonstrating its utility for process modeling.