Rheological properties of electrorheological fluids : Silica, polyaniline, and polyaniline-coated silica suspensions

Abstract

Electrorheological (ER) fluids, typically composed of small particles dispersed in nonconducting liquids, are fascinating materials whose structure and rheological properties can be dramatically altered by external electric fields. In this study, three types of particles; silica, polyaniline, and polyaniline-coated silica were used as the dispersed phase and silicone oil as the medium. The effects of the weight fraction and size of particles and electric field strength were investigated by a modified cone and plate rheometer, connected to a high voltage generator under oscillatory shear. All of the ER fluid samples showed the linear viscoelastic behavior only at small strain amplitudes. The ER effect could be enhanced by increasing the weight fraction of the particles and the electric field strength. The effect in linear viscoelastic region was larger than that of nonlinear due to the less deformation of chain structures. Upon subsequent applications of the electric fields, the samples showed almost the same response. After the electric field was released, the samples recovered almost completely. However, at higher frequencies, the ER effect tended to diminish.