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DRG: Deutsche Rheologische Gesellschaft

DRG 14: Mikrosymposium Lebensmittelrheologie

DRG 14.3: Talk

Tuesday, March 2, 1999, 10:40–11:00, HS 22

Influence of Particle Shape and Morphology on the Rheological Behavior of Concentrated Suspensions — •Erich J. Windhab, Jean Claude Eischen, and Peter Braun — Swiss Federal Institute of Technology Zurich (ETH), Food Process Engineering, CH-8092 Zurich, Switzerland

To study the effect of particle shape on the viscous properties of concentrated suspension systems, model suspensions have been used with Newtonian and Non-Newtonian continuous fluid phases and solid particles of different size, shape and morphology. To separate the influence of particle shape on the rheological suspension properties from the effects of particle size and morphology, the rheological behavior has been measured under large and small deformation conditions in steady and oscillatory shear experiments. Concentrated suspension systems show a lower Newtonian viscosity plateau in the low shear rate regime. If a specific critical shear stress is exceeded the flow forces dominate the structure forces and consequently particle orientation and/or deformation is induced. A maximum degree of orientation or deformation is often related to an upper shear rate regime where particle interaction is negligible. A further increase in shear rate/shear stress can lead to a collapse of the shear-induced structure or the built-up of a flow-induced superstructure, thus providing dilatant or rheopectic flow behavior.