Shear-driven and pressure-driven flow of a nematic liquid crystal in a slowly varying channel

Motivated by the industrially important processes of blade coating and cavity filling of liquid crystalline materials, we consider steady, two-dimensional shear-driven (Couette) and pressure-driven (plane Poiseuille) flow of a thin film of a nematic liquid crystal in the slowly varying channel formed between a fixed blade of prescribed shape and a planar substrate. Specifically, blade coating motivates the study of shear-driven flow due to the motion of the substrate parallel to itself with constant velocity, while cavity filling motivates the study of pressure-driven flow due to an imposed pressure drop. We use a combination of analytical and numerical techniques to analyze the Ericksen-Leslie equations governing the fluid velocity and pressure and the director orientation in cases when both the aspect ratio of the channel and the distortion of the director field are small. We demonstrate a variety of flow and director-orientation patterns occurring in different parameter regimes. In the limit of weak flow effects, flow alignment does not occur and the appropriate solution of the governing equations is found explicitly. In the limit of strong flow effects flow alignment occurs and orientational boundary layers exist near the substrate and near the blade, and, in addition, an orientational internal layer may also exist within which the director orientation changes from +theta(0) to -theta(0), where theta(0) is the flow-alignment angle. (c) 2006 American Institute of Physics.