The dependence of the yield stress on the rheological method and microstructure in soft materials

Yield stress is a key parameter in the study of soft materials, but its value depends on the experimental criterion used to define it. In this work, three representative systems are analyzed: a BBQ sauce as a low-strength colloidal dispersion, a hair gel as an intermediate polymer hydrogel, and a chitosan hydrogel as an example of a rigid polyelectrolyte network. The rheological results show that the obtained yield stress values vary depending on the method used. The comparison between systems shows that the concentration and type of polymer determine the magnitude of \:G^\: , \:G^\:\: and \:τ\:₀ with chitosan being the strongest material due to its rigid structure and stronger interactions. The determination of the yield stress should not be interpreted as an absolute value but rather as an interval, considering the point at which the material begins to change its structure until it becomes completely liquid.