For a given temperature and test speed (strain rate), you will measure one viscosity. If your material is viscoelastic, your viscosity will change with temperature and rate of loading.

If the different solution conditions that you impose all result in solutions having Newtonian characteristics, then you can certainly measure a single viscosity for each of them. On the other hand, if the different solution conditions give solutions with non-Newtonian characteristics, then it would be difficult to stick with one single viscosity value and compare the behaviors of the various solutions. Hence, you will have to run at least one or two representative solutions over a range of shear rates at a fixed temperature to establish whether the solutions are going to be Newtonian or non-Newtonian. It is only then that you can take the decision of whether to use one single viscosity value for comparison or you need the entire rheogram. Single-point viscosity measurements are not uncommon, for example, melt-flow index is used in the polymer industry for quality control and quality assurance purposes. More details about it can be found in the book

A. V.Shenoy and D. R. Saini, Thermoplastic Melt Rheology and Processing, Marcel Dekker, New York (1996).

If your fluid is Newtonian, then yes. For non-Newtonian fluids, the viscosity changes with shear rate.

It depends on whether the fluid you're studying is Newtonian or not. If the rheometer-derived viscosity value depends on the shear rate, which would be the Non-Newtonian case, I suggest you perform some shear stress measurements at different shear rates and plot them. In the shear-rate vs. shear-stress space, you might have an idea of the constitutive law of the fluid you're analyzing, and if you fit an appropriated model, you'd be able to obtain some relevant parameters of it. Examples of them would be Bingham plastics, Herschel-Bulkley fluids, or power-law fluids. More can be found in Rao, M. A. (2014).

All that I've mentioned above assumes there's no relevant temporal variation on the rheology of your fluid. If there was, that's an even more interesting problem!

Rao, M. A. (2014). Flow and functional models for rheological properties of fluid foods. In Rheology of fluid, semisolid, and solid foods (pp. 27-61). Springer, Boston, MA.

The liquids are mainly divided into three categories:

• Newtonian.
• Time independent Non-Newtonian.
• Time dependent Non-Newtonian.

When the viscosity of a liquid remains constant and is independent of the applied shear stress (in the range that interests you); this liquid is Newtonian.

And so you will get your simple viscosity measurement.

For non-newtonian , you have to mention at X shear rate, Z temperature, the viscosity was Y . and if you compare different sample choose a single shear rate for all the sample, so that you can compare at a single value.

What do you mean by "single viscosity value". Do you mean the Newtonian viscosity? Or are you talking about a single value of apparent viscosity for a given shear rate? A single viscosity value is also a parameter of the Burgers mechanical model.