Analysis of the yielding behavior of electrorheological suspensions by controlled shear stress experiments

The yielding behavior of two model electrorheological suspensions of uncoated silica particles and silica coated with polyaniline base in silicone oil using controlled shear rate and controlled shear stress experiments has been analyzed. The results demonstrate that unlike the uncertain dynamic yield stress values estimated from the results obtained in the former mode by extrapolation of the unsteady shear stresses to zero shear rate, the controlled shear stress measurement permits to detect sensitively the region starting from the initial rupture of particle chain structure in the electric field at rest corresponding to a static yield stress τ_y and ending in total breakage of suspension structure at a breaking stress τ_b. The latter quantity can be detected with a good accuracy and proved to be a reliable criterion of the stiffness of ER structure.