On the interplay between hydrodynamic and dipolar particle interactions in suspensions

The long range nature of particle interactions in the framework of sedimenting suspensions of magnetic particles is discussed. We present new results on the topic, obtained by an in-house code named SIMS. This code solves simultaneously the equations of translational and rotational motion for each magnetic particle in colloidal and non-Brownian suspensions. We use a sophisticated technique of Ewald summations to compute both hydrodynamic and long-range dipolar interactions for force and torque. A brief discussion on the nature of the spatial decays of the sums used to model our multi-body system and the demand for a periodic geometrical representation of the suspension structure is presented. Examples on the calculation of transport properties of colloidal and non-Brownian suspensions of magnetic spheres are presented and validated. Moreover, we discuss how magnetic interactions affects classical transport properties of sedimenting suspensions and also how hydrodynamic interactions modify the micro-structural dynamics of magnetic colloidal suspensions and consenquently the equilibrium magnetization of the so called ferrofluids. The quantitative results are interpreted in terms of the suspension structure evolution in time.