| With the final goal of identifying important factors for optimizing the design of superior electrorheological (ER) materials, we have performed new experimental studies on the ER effect. These experiments are based on considerations from several new physical perspectives and are designed to further advance our understanding on the underlying mechanisms of this phenomenon. The ER response of an emulsion system is first investigated and the response characteristics are compared with that of conventional ER suspensions. Radically different response behaviors are observed for phase-reversed emulsions in which the mismatch in electrical properties between the dispersed phase and the dispersing phase is also reversed. These differences can be qualitatively explained by the leaky dielectric liquid model which is in fact consistent with the Maxwell-Wagner polarization model. The viscoelastic properties and the material strength of an ER fluid of carbonaceous particles in silicone oil are then compared with those of a physical gel of untreated fumed silica in mineral oil. An anisotropic network microstructural model is proposed for ER materials to account for their material characteristics. Finally, simultaneous measurements of electrical conduction and viscoelasticity of the carbonaceous ER fluid are carried out under oscillatory shear to investigate the role of electrical conduction in ER response. The results indicate no correlation between the electrical conduction and the mechanical strength of ER materials. Surprisingly, after undergoing a large-amplitude shear the electrified suspension exhibits a significant increase in its overall conductivity. The concept of the homogeneity of the network of contact among particles is hence considered to be important to the material properties of ER suspensions. |
