The Role of Suspension Structure in the Dynamic Response of Electrorheological Suspensions

Abstract

The dynamic response of electrorheological (ER) suspensions has received little attention relative to the effort devoted to the study of the steady shear response. We report on simulation and experimental investigations of the dynamic oscillatory response of ER suspensions, in particular focusing on the relationship between suspension structure and the rheological response. We consider the response of monodisperse and polydisperse suspensions under linear deformation, as well as the response in the nonlinear regime. Dimensional analysis of the equations of motion predict that the linear rheological response obeys a time-field strength superposition principle, which is confirmed by experiment. The response is found to exhibit a sharp dispersion that is only broadened slightly by polydispersity. Nonlinear deformation is found to significantly broaden the observed dispersion.

Relaxation of polydisperse electrorheological suspensions

“…The authors attributed this behavior to nonlinear deformation associated with yielding of the chain structure. Parthasarathy et al (1993) observed similar trends using the idealized model and computer simulation technique described here, as well as for experimental studies with alumina particles in poly(dimethylsiloxane). Computer simulations suggested that nonlinearity does not arise initially from macroscopic rupture of the particulate columns, but rather from slight rearrangements within clusters.…”

“…Otsubo et al (1992) experimentally observed a pronounced broadening of the dispersion as the oscillatory strain amplitude was increased from 1% to 20%, suggesting that nonlinearity may provide another mechanism for dispersion broadening. This has been supported by recent experiments and simulations that compared the frequency dependence of the shear moduli at various strain amplitudes [Parthasarathy et al (1993)].…”

Electro-Rheological Response of Liquid Crystals under Oscillatory Squeeze Flow

“…It thus seems that the relaxation phenomenon observed in the viscoelastic tests is closely related to the electric response time (t r ). The data collapse when the frequency dependence of the viscoelastic functions are re-plotted with ω·t r is similar to the collapse observed in particulate electrorheological fluids (14), (15) , although the relaxation mechanism is quite different (rearrangement of particles within the aggregates for the particulate systems).…”

Electrically Induced Microstructures in Micro- and Nano-Suspensions and Related Physical Properties

“…[97][98][99][104][105][106] However, a plateau region with a stress smaller than 10 À3 Pa was observed by Marshall et al 43 at shear rates below 10 À2 s À1 under no electric fields for a suspension of weakly flocculated non-Brownian particles with 0 ¼ 0:13. A slightly pseudoplastic flow was also observed by Otsubo et al 107 at lower shear rates under no electric fields for a suspension with sub-micrometer particles of monodispersed silica with 0 ¼ 0:4, while no elastic responses in the dynamic measurement were shown without electric fields.…”