Chaining in magnetic colloids in the presence of flow

We discuss the effect of an homogeneous flow in the aggregation process of colloidal magnetic particles at moderate concentration. Situations in which the presence of flow acts in favor of the chaining process: particles asse mble into chains larger than the ones emerging in the absence of flow, unde r the only influence of an externally imposed field, have been analyzed. Th e results we obtain follow from the analysis of the pair correlation functi on which, owing to the potential character of the flow we consider, can be interpreted in terms of a Boltzmann-type stationary distribution function. To render the influence of the flow on the resulting structures explicit, w e study the particular cases of axisymmetric and planar elongational flows. (C) 2000 American Institute of Physics. [S0021-9606(00)50939-8].