SEDL / STP / STP1369-EB / STP14350S

Pitfalls in Measurement of non-Newtonian Materials—“It's a Line, Not a Point!”

Whittingstall, P
Technical Manager, TA Instruments Inc., New Castle, DE

Pages: 14    Published: Jan 2000

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Abstract

Isaac Newton in his “Principia” defined viscosity for simple liquids such as water and oils, which have a constant viscosity at a given temperature. As a result such liquids are labeled as “Newtonian” in his honor. Most materials of interest to the laboratory however are non-Newtonian, in that they do not have a single value for their viscosity at a given temperature. In fact, their viscosity is a function of applied shear stress or shear rate. The science of rheology examines the behavior of real, viscoelastic materials as they deform or flow under applied shear or extension, and an understanding of its concepts is necessary if complex fluids are to be successfully measured. This article highlights some of the anomalies that can be encountered when trying to measure the subtleties of such materials.