In a newtonian fluid, the slope of the curve is constant and would be equivalent to the viscosity (shear stress vs shear rate) In all the rotational geometries discussed here, lower viscosity fluids have a smaller experimental window with limitations at high shear rate due to secondary flow. At low enough shear rates, shear thinning fluids will show a constant viscosity value, η0, termed the zero shear viscosity or zero shear viscosity plateau At a critical shear rate or shear stress, a large drop in viscosity is observed, which signifies the beginning of the shear thinning region. Viscosity and rheology significantly different concepts The viscosity of a fluid or suspension is an indication of its fluidity
Heavy or thick fluids such as heavy oils, or molasses, are recogniz d as those having high viscosity Water, many lubricating and cooking oils, cof ee, and tea have low viscosities In contrast, measuring with rheostream will provide shear stress and viscosity values across a range, making it possible to differentiate the three liquids clearly This section is dedicated to explaining the basic concepts of rheology, such as viscosity and shear thinning, discussing how process operating conditions, such as shear rate and temperature, and characteristics of the polymer affect rheological properties of the polymer. If a material is applied (coated) at the same velocity but with different film thicknesses, this results in different shear rates The lower the coating thickness, the higher the shear rate and vice versa.
