Hi, I'm new to rheology and viscosity study. I have emulsion samples containing clay, polymer, and emulsifier. The difference between the samples is just clay concentrations and oil constituents which give them different viscosity from low to medium viscosity (0.2 - 31 Pa.s). The current rheometer I have in the lab is Rheosys Merlin II (controlled shear rate rheometer). The goal of the rheometry analysis is to assess:

1. Apparent viscosity

2. Shear thinning (viscosity slope)

3. Yield stress

4. Thixotropy

For the preset, I can only use shear rate. I have the range of shear stress, viscosity, time, and torque results generated from shear rate of 1s-1 to 1000 s-1 (10 data points per decade; three decades; 10 seconds measuring duration per data). I found out that some medium viscosity samples experienced solvent evaporation, so maybe I will try 5 seconds instead of 10 seconds.

So, my question is:

I found that several references told me to not use curve fitting models for yield stress determination since those methods are only used for simple QC tests and not for modern RnD work. Can you recommend to me which yield stress method with the preset controlled shear rate that I can use instead of curve fitting models? I plan to use a single fitting line because it provides yield point of "reversible deformed" behavior that may benefit the next analysis: thixotropy. But the method can only be used for the preset controlled shear stress. Anyone can help me?