Rheology and microstructures of electrorheological fluids containing both dispersed particles and liquid drops in a continuous phase

The effects of dispersed drops in the electrorheological (ER) behavior of a polyaniline particle suspension were considered. Oil-in-oil emulsions, whi ch differ in the electrical conductivity and dielectric constant, were empl oyed for the liquid biphase. The yield stress behavior of ER suspension und er steady shear and electric held was examined. Only when the dispersed dro ps with a higher conductivity formed the dispersed liquid phases in the pre sence of dispersed polyaniline particles was a synergistic effect in the yi eld stress observed, giving a better ER performance and reduced current den sity. A direct microscopic observation demonstrated that such a synergistic effect is due to the unique microstructures in a complex composed of parti cles and deformed emulsion drops. Not only the magnitude but also the depen dence of the yield stresses on the electric field strength were strongly af fected by the change in relative composition of particulate and liquid drop phases. The associated mechanism of ER response in particle-drop bidispers ion was explained on the basis of the relationship between the microscopic change of structures and macroscopic rheological properties. (C) 2000 The S ociety of Rheology. [S0148-6055(00)00602-7].