Field-Induced Columnar and Bent-Wall-Like Patterns in a Ferrofluid Emulsion

Using optical microscopy, we studied magnetic-field-induced structures in a confined ferrofluid emulsion. Disks, "worms" and branch-like patterns are observed in 2-D, reflecting columnar, bent-wall-like and labyrinthine structures in 3-D. These structures are controlled by varying either the thickness of the cell used to confine the sample, the particle concentration, or the rate of the magnetic field application. The induced structures are characterized by both the ratio of "worms" vs. total aggregates and the average complexity of the aggregates. "Phase" diagrams are obtained between these tuning parameters to characterize columnar to bent-wall structural transitions.