RADIAL CREEPING FLOW OF ROD-LIKE NEMATIC LIQUID-CRYSTALS

Three solutions of the Leslie-Ericksen equations for low-molar mass rod-like nematic liquid crystals are obtained for pressure-driven radial outflow between concentric parallel disks. There are two competing hydrodynamic effects on the orientation: extensional flow (strongest in the centerline region) and shear (strongest near the bounding surfaces). At low pressure drops the in-plane orientation is stable; the centerline orientation is normal to the flow direction. For each radial distance there is a critical pressure drop at which the elongational torques twist the material out-of-plane of flow; left and right rotations are possible. The transition from in-plane mode to out-of-plane modes is analogous to the second order Frederiks transition. The two out-of-plane modes are characterized by a secondary azimuthal flow. At certain pressure drops all the stationary modes can coexist in the flow cell. The radius of the boundary between in- and out-of-plane modes increases with increasing pressure drops. There is a minimum pressure drop to observe the transition at the edge of the entrance hole, and there is also another minimum pressure drop at which the out-of-plane modes fill the whole flow cell. © 1990, The Society of Rheology. All righrs reserved.