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CPP: Chemische Physik und Polymerphysik

CPP 11: POSTER Disperse Polymer Systems

CPP 11.18: Poster

Dienstag, 28. März 2006, 17:00–19:00, P3

Suspensions with plastic flow behavior - relation between shear stress and first normal stress difference — •Dimiter Hadjistamov — DECE GmbH, Helvetierstr.15, CH-4125 Riehen

Model suspensions with plastic flow behavior were rheologically investigated. The shear stress and simultaneously the first normal stress difference were measured during stressing experiments and follwing that a stress relaxation. We compared the flow and normal stress curves. The flow curve of a system with plastic flow behavior shows one or more yield stress regions, where the shear stress does not change with the shear rate. The shear stress rises continuously after the yield stress region with the shear rate. We found that the normal stress curve also exhibits a yield section - the yield normal stress region. The first normal stress decreases (contrary to the shear stress) at first after the yield normal stress region. The decrease of the normal stress can lead to negative values for the normal force. After them, the normal stress increases with the shear rate. It was established that it is possible to draw conclusion from the ratio between shear stress and normal stress about the strengthening of the structure of a suspension with plastic flow behavior.