Effect of drop-like aggregates on the viscous stress in magnetic suspensions

Abstract

Abstract.We present results of theoretical and experimental study of effect of dense drop-like aggregates on the magnetoviscous effects in suspensions of non-Brownian magnetizable particles. Unlike the previous works on this subject, we do not restrict ourselves by the limiting case of highly elongated drops. This allows us to reproduce the experimental rheological curve in wide region of the shear rate of the suspension flow.

Chain Formation and Phase Separation in Ferrofluids: The Influence on Viscous Properties

“…The main problem facing the microscopic analysis of the rheological effects in ferrofluids with drop-like aggregates is to understand the mechanisms of the drop’s destruction due to the hydrodynamic forces. Various models of the similar rupture effect with different mechanisms of the drops’ destruction have been suggested for magnetorheological suspensions of micron-sized magnetizable particles [ 120 , 121 , 122 , 123 ]. In these models, the total viscous stress in the suspension is presented as: where Φ is volume concentration of the aggregates and is the so-called Mason number, which is proportional to the ratio of the hydrodynamic forces to the magnetic forces acting on the drop-like aggregates.…”

“…The second term in the brackets represents the effect of the drops on the suspension viscosity. The magnitudes of the multiplier C and exponent p were determined differently in [ 120 , 121 , 122 , 123 ]: the model in [ 120 ] predicts Bingham-like behavior of the suspension with , the models in [ 121 , 122 ] give , whereas the approach in [ 123 ] predicts . A comparison of these models with experiments [ 123 , 124 ] does not allow us to choose the best of these models.…”

“…The models used in [ 120 , 121 , 122 , 123 ], as well as the interpretations of the experiments in [ 125 , 126 ] were based on the idea that the macroscopic rheological properties of the ferrofluids are determined by the internal dense spindle-like aggregates. Figure 13 demonstrates a high correspondence between the experimentally measured and theoretically predicted total shear stress σ in a ferrofluid under shear flow and the shear rate at two different magnetic field strengths.…”

“…Lines represent theoretical predictions and the dots represent experimental data: line 1 and open squares correspond to a field of 8.6 kA/m, while line 2 and filled squares correspond to a field of 5.7 kA/m. Adopted from [ 122 ]. Further details are given in [ 122 ].…”

Rheological investigation of magnetic sensitive biopolymer composites: effect of the ligand grafting of magnetic nanoparticles

“…7), structures induced by the magnetic field should consist of column-like arrangements constituted by a large number of those aggregates aligned along the field direction. Note that in response to the applied magnetic field, each of the aggregates would also deform, in order to minimize its free energy balanced by the bulk free energy due to the demagnetizing field, which would tend to stretch the aggregate in the direction of the applied field, and the energies associated to the surface tension and the role of the polymer that would tend to maintain a spherical shape for the aggregates (Lopez-Lopez et al 2014).…”