Electrorheological responses of particulate suspensions and emulsions in a small-strain dynamic shear flow: Viscoelasticity and yielding phenomena

The dynamic rheological behavior of multiphase electrorheological (ER) fluids was considered, as continuation of a previous paper [Chin and Park, 2000]. Oil-in-oil emulsions, which differ in electrical conductivity and dielectric constant, were employed for an ER-active emulsion and also for a multiphase ER fluid with enhanced performance. The polyaniline particle suspension in an electric field showed viscoelastic behavior within a very limited range of strain amplitude, indicating the transition from viscoelasticity to viscoplasticity. Within the region of viscoelasticity, the linear region was restricted below the amplitude of 0.1%, whereas the ER-active emulsions showed a rather wide linear regime. Frequency dependence of the storage shear modulus in the linear viscoelastic region revealed the typical features of an elastic solid. When the fraction of emulsion drops (Phi) in multiphase ER fluids increased, the limiting strain for viscoelasticity showed a higher value.