Measuring viscosity at a single and arbitrary shear rate provides limited information which can be difficult to interpret. A much more thorough understanding of a formulation is obtained by measuring the shear rate dependence. In addition to the practical relevance of predicting the behavior during application or processing, the details of a non-Newtonian response reflect the molecular interactions and resulting microstructure at therapeutic levels. Even protein solutions at moderate concentrations can exhibit a Newtonian plateau followed by a shear thinning region illustrating the importance of non-hydrodynamic forces and degree of structure formation.
Download the webinar to hear the full review of the non-Newtonian response of protein solutions under steady shear and discussion of options for interpretation.
Long story short, newtonian samples are materials that do not change in viscosity as it is exposed to various shear rates. non-Newtonian samples on the other hand, will change in viscosity as shear rate changes. Additional indepth detail can be found here: https://www.rheosense.com/applications/viscosity/newtonian-non-newtonian.
We recommend a minimum of three different shear rates when analyzing your samples to determine whether they are Newtonian or non-Newtonian. Separately, the shear rates should have a wide range. The reason for the wide range is because many are complex. Sometimes, your sample will not show shear thinning or shear thickening behavior at low shear rates but will at high shear rates.
Overall, there is just a lot to your sample that you may not know about until you actually test it. As a result, we recommend testing as much of a range as possible to ensure full knowledge of how your sample behaves.