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

The dynamic rheological behavior of multiphase electrorheological (ER) flui ds was considered, as continuation of a previous paper [Chin and Park, 2000 ]. Oil-in-oil emulsions, which differ in electrical conductivity and dielec tric constant, were employed for an ER-active emulsion and also for a multi phase ER fluid with enhanced performance. The polyaniline particle suspensi on in an electric field showed viscoelastic behavior within a very limited range of strain amplitude, indicating the transition from viscoelasticity t o 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 sh ear modulus in the linear viscoelastic region revealed the typical features of an elastic solid. When the fraction of emulsion drops (Phi) in multipha se ER fluids increased, the limiting strain for viscoelasticity showed a hi gher value.