Oscillation stress and strain sweeps provide easy-to-interpret information about the soft-solid rigidity and yield stress (gel strength) of even delicately-structured fluids such as fruit juices and thickened drinks, "light-touch" lotions and sedimentation-resistant suspensions.
The graphic here shows the clear zero-shear plateaux forming at the low-shear end of viscosity profiles of three coating products.
For shear-thinning products measuring viscosity at a single shear rate obviously only provides a tiny glimpse of the "full picture" - instead a flow curve of viscosity across a range of shear rates is far more meaningful, from which a viscosity value at a shear.
The test has two particular uses: To obtain a high quality zero-shear viscosity measurement - by the sustained application of a shear stress that is significantly within the linear viscoelastic limit for the material under test.If you would like some advice on how these test methods could be applied to your products please don't hesitate to ask us a question.Like to learn more? These powerful tests are easy to perform and yet provide a deep insight into the rigidity and strength of the soft-solid structures that impart critical quality attributes in many manufactured products. Popular models include: Bingham and Casson, power Law (Ostwald) and Herschel Bulkley.Viscosity Temperature Relationships, viscosity typically, but not always, exhibits an inverse relationship with temperature.The measurement results can be superposed to significant master curves.By far the most common form of non-Newtonian behaviour is shear-thinning where viscosity decreases with increasing applied shear rate.Sisko, cross and Carreau, the graphic shows a a simple Power Law model fit on a mayonnaise sample tested across the range 20 to 200s-1 shear rate. The viscosity at this point is the zero-shear viscosity. Note that at shear rates of 1 1/s and above the viscosities have converged and even crossed over!
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Rheology Model Fits for Pump-sizing and Process Design.