Divergent channel flow of a liquid crystalline polymer solution

The how of a 'model' lyotropic liquid crystal polymer, (hydroxypropyl)cellu lose in water, through a rectangular channel with a divergence in the chann el width, is studied by in situ light microscopy. Microscopic texture obser vations are related to measurements of the flow velocity field, in order to characterize the shear and elongational aspects of the flow and to examine the effects of the divergence from a narrow channel to a wide channel. A s trong dependence of flow-induced texture on position in the channel is obse rved and is related to the interplay of shear and elongational strain. The divergence generates both a perpendicular elongational strain due to the wi dening of the channel, and subsequently an elongational strain along the fl ow direction due to the change in flow pattern from quasi-radial to unidire ctional down the wide channel. Additionally side wall structure is observed to be more complex than a simple strong alignment, displaying a fine biref ringent texture. Finally there is a marked dependence of the macroscopic st ructure on the strain history of the fluid prior to entry into the channel, indicating that very different structures of, for instance, moulded parts, can result from differences in geometry and fluid treatment prior to entry into the mould itself.