Fractal patterns, cluster dynamics, and elastic properties of magnetorheological suspensions

We study pattern formation and the aggregation processes in magnetorheological suspensions in the presence of a static magnetic field, and some of their associated physical properties. In particular, we analyze the elastic modes as a function of the intensity of the applied field and for several particle concentrations. We observe that the clusters formed in these systems have multifractal characteristics, which are the result of three well defined stages of the aggregation process. In these stages three generations of clusters are produced sequentially. The structure of the suspension can be well characterized by its mass fractal dimensions and the mass radial distribution. The size distribution of the second-generation clusters written in terms of their mass fractal dimension allows us to calculate the sound speed of the longitudinal modes in the large wavelength regime. This multifractal analysis applied to several kinds of aggregates reveals that the occurrence of at least three stages of aggregation is a common feature to several physical aggregation processes.