It is well known that the determination of the yield stress
depends on the procedure used for its estimation (Fig. 7). Therefore,
four different methods were used for this goal. First, the yield
stress was found by the cross point of quasi-Newtonian plateau and
falling part of the flow curve as shown in Fig. 6 by the dashed line
of the left graph (for Ccar = 0.05%, w/w). The second method was
based on measuring the dependence of elasticity on shear stress.
This method is based on the estimation of the boundary between
linear and nonlinear regions in the amplitude dependence of the
elastic modulus (as will be illustrated below in Fig. 8). The third
and the fourth methods were used in extrapolation of experimental
data to zero shear rate by presenting experimental data in the coordinates
of the Casson and Herschel–Bulkley models, consequently.
Both models are written as usual [45].
Casson model: