Spatial variation in viscosity in sheared polymer melts

Measurements have been performed using a Weissenberg Rheogoniometer equipped with parallel plates in order to investigate the rheological properties of a polymer melt, namely polystyrene, at very small plate separations. An appreciable gap dependent torque was observed which is indicative of an inhomogeneous viscosity through the sample thickness. The effect is associated with the macromolecular nature of the melt, as confirmed by subsequent measurements performed with polystyrenes of different molecular weight together with a low molecular weight silicone fluid. The results are discussed in relation to models of the molecular chain conformation at a solid-melt interface.