Model magnetorheology: A direct comparative study between theories, particle-level simulations and experiments, in steady and dynamic oscillatory shear

Abstract

We investigate model magnetorheological (MR) fluids (inverse ferrofluids) under both steady and dynamic oscillatory shear. Analytical theories, particle-level simulations, and magnetorheometry are used in an attempt to obtain universal master curves. Steady shear flow data can be collapsed when plotted as a function of a dimensionless Mason number. The critical Mason number associated with the transition from magnetostatic to hydrodynamic control of the suspension structure is demonstrated to linearly increase with particle concentration which is in good agreement with theories and our simulations. Experimental linear viscoelastic moduli are in good agreement with micromechanical and macroscopic models in the dilute regime. However, upon increasing particle concentration, theoretical predictions underestimate experimental data while particle-level simulations are in good agreement. The accordance with particle-level simulations suggests that the mean (average) magnetization approximation gives a good prediction and multibody and hydrodynamic forces are not expected to play a crucial role in the shear flow behavior of model MR fluids.