Stokesian Dynamics Simulations of Ferromagnetic Colloidal Dispersions in a Sinusoidal Shear Flow. Non-Newtonian Viscosities and Viscoelastic Properties.

Abstract

We have conducted Stokesian dynamics simulations to investigate the dynamic properties of ferromagnetic colloidal dispersions subjected to a sinusoidal shear flow. Thick chainlike cluster formation is significantly influenced by an oscillatory shear flow even if the amplitude is relatively small, since the internal structures of thick chainlike clusters are highly sensitive to the change in the direction of the shear flow. The motions of thick chainlike clusters are out of phase to a sinusoidal shear rate, and this phase difference is strongly correlated with that of the viscosity and normal stress coefficients. The viscoelastic properties become more apparent with decreasing frequency of the oscillatory shear flow, since such properties have a strong relationship with thick chainlike cluster formation. In other words, since thick chainlike clusters are more stable for the case of a smaller frequency shear flow, such stable clusters induce significant viscoelastic properties of ferromagnetic colloidal dispersions in a strong applied magnetic field.