Dynamic rheology of electrorheological suspensions.

摘要

Electrorheological (ER) fluids are fascinating materials that undergo dramatic reversible changes in their rheological properties upon the application of electric fields. In many proposed applications, the fluids will be subjected to a dynamic stimulus with finite deformation. A particle-level simulation method based on electrostatic polarization interactions between particles is used to investigate the dynamic rheological behavior of ER fluids. Experiments on model fluids are performed to confirm simulation results.;ER fluids are linear viscoelastic for only very small strain amplitudes. The linear response moduli are functions only of a dimensionless frequency (;At large strain amplitudes, the rheological behavior is viscoplastic and is well described by models with a dynamic yield stress (e.g., the Bingham equation). Plastic behavior is defined by the loss of elasticity and hence irreversible deformation. The critical strain marking tbe transition to viscoplastic deformation is a constant for small dimensionless frequencies and decreases slightly with increasing dimensionless frequency. At large dimensionless frequencies, the response is Newtonian for all strain amplitudes. Simulation results agree qualitatively with experiments.;The dependence of the flow behavior on the strain amplitude and dimensionless frequency is summarized in a Pipkin diagram.