Lateral aggregation induced by magnetic perturbations in a magnetorheological fluid based on non-Brownian particles

A study of lateral aggregation, induced by an oscillatory field, in a magnetorheological fluid based on non-Brownian magnetic particles is presented. We investigate the behavior of chains formed by the particles, due to the simultaneous application of a static magnetic field and a sinusoidal magnetic field transverse to each other. We show that the effective oscillating field enhances the aggregation process. We discuss this result in terms of an effective particle concentration induced by the oscillating field when chains oscillate angularly and sweep the area around them. The oscillating field produces a lateral aggregation similar to that observed in systems composed of Brownian particles which is induced by thermal fluctuations. We study the effect of the oscillating field on the angular amplitude described by single chains. It is observed that the angular amplitude decreases as the frequency of the oscillating field increases; we discuss this behavior numerically in terms of a simple model for this system. Lateral aggregation is studied in detail in isolated pairs of chains of equal length at several conditions of separation and displacement. From the results, a phase diagram is obtained showing the conditions under which aggregation is possible.