Flow visualization and modeling of liquid crystalline polymers

To better understand the strong coupling between orientation and flow of liquid crystalline polymers, tracer experiments were performed on thermotropic Vectra A to visualize the flow field in a piston-driven, cylindrical capillary rheometer. Upstream of the contraction, in a region of approximately Poiseuille flow, the observed blunt displacement profiles were indicative of shear-thinning, and slow transient effects did not permit the fluid to achieve a Lagrangian steady state. The flow at the contraction exhibited asymmetric vortex formation and discolorations in the material which were most likely the result of complex orientational inhomogeneities. The profile near the piston tip, in a region of approximately wedge flow, did not qualitatively follow the profiles expected for Newtonian or power-law fluids.;Several new constitutive models were developed. The kinetic-domain theory and the mesoscopic-domain model presume the existence of polydomains, and interdomain elasticity is included through a generalized representation of Frank elasticity. The tumbling parameter in these models is directly related to the aspect ratio of the domain, which is an experimentally measurable quantity. The predictions of the order parameter and scaling of the shear and normal stresses in simple shear flow are in agreement with the experimental literature.;An extension of a finite aspect ratio molecular theory, which incorporates a generalized Frank expression based on a spatially varying order parameter tensor, was developed. This textured model is capable of predicting the formation and dynamics of texture without assuming the existence of polydomains a priori. Preliminary calculations for Couette flow suggest that this model can explain some of the rheological and orientational features observed in experiments.