I recently got a great question from our customers on how to measure zero shear viscosity with RheoSense viscometers. It is a fairly common misconception so I wanted to cover what zero shear viscosity.
Zero shear viscosity is often confused with the idea that viscosity is at a shear rate of 0 1/s. This is NOT the case. Zero shear viscosity refers to the viscosity plateau prior to the onset of shear thinning. What this means is that this could occur at very low shear rates but also for certain materials, it can still also occur at very high shear rates. This will depend on the sample type.
For Newtonian fluids, there is only one viscosity value at multiple shear rates. This means that zero shear viscosity would not be relevant or be available at such samples.