Magnetoviscosity of dilute suspensions of magnetic ellipsoids obtained through rotational Brownian dynamics simulations

The magnetic field dependent viscosity (magnetoviscosity) of dilute suspensions of magnetic tri-axial ellipsoidal particles suspended in a Newtonian fluid and under applied shear and magnetic fields was studied numerically. Brownian dynamics simulations were performed to compute the intrinsic magnetoviscosity of the suspension. Results are presented for the response of dilute suspensions of ellipsoidal particles to constant magnetic and shear flow fields. Suspensions of ellipsoidal particles show a significant effect of aspect ratio on the intrinsic magnetoviscosity of the suspension, and this effect is more pronounced as the aspect ratio becomes more extreme. The use of an effective rotational diffusion coefficient D-r,D-eff collapses the normalized intrinsic magnetoviscosity of all suspensions to a master curve as a function of Peclet number with the Langevin parameter alpha = (mu(0)mu H)/(k(B)T) as parameter, up to a critical value of a for which the results for suspensions of spherical particles deviate from those of suspensions of ellipsoids. This discrepancy is attributed to the action of the shear-torque on the ellipsoidal particles, which tends to orient these particles in the direction of maximum deformation of the simple shear flow, and which does not act on spherical particles. (C) 2008 Elsevier Inc. All rights reserved.