(495c) Polydomain Simulation Of Liquid Crystalline Polymer Orientation In Channel Flows

The ultimate properties of liquid crystalline polymers are strongly affected by the molecular orientation state induced by flow fields during processing. LCP orientation development under flow is quite complex, due to the propensity towards 'director tumbling' dynamics in rodlike nematics, and the complex 'polydomain' distributions of orientation that are typically observed. A wide range of models exist that can in principle describe the coupling between processing flows and the resulting fluid structure. Many of these begin with a detailed description of the molecular orientation state, possibly including a molecular-level description of distortional elastic effects. While well suited for simulations of fundamental rheological and structural phenomema in simple flows, application of these models to processing flows is still far out of reach. Conversely, the model of Larson & Doi, which treats distortional elasticity in polydomain LCPs in a phenomenological way, is sufficiently simple to allow for its application to process simulations. This is further facilitated by a nearly exact analogy between the Larson-Doi model and the Folger-Tucker model for predicting orientation in fiber dispersions, which is incorporated in commercial process simulation software. We use this available modeling infrastructure to test the ability of the Larson-Doi model to predict orientation distributions in kinematically complex but isothermal channel flows of liquid crystalline polymers, comparing simulation results orientation distribution data previously obtained using in situ x-ray scattering methods.