Flows and instabilities of ferrofluids at the microscale

In the present work we report on the behavior of ferrofluid microdrops in an immiscible nonmagnetic carrier fluid and vice versa subjected to the action of magnetic fields. Our experiments evidence previously unexplored instability and flow patterns. We investigated the instabilities initiated by constant magnetic field and by combined action of constant and rotating magnetic fields. The observed instabilities lead to the formation of various microdrop configurations such as star-like and comb-like shapes, bending deformation, ridges and crests, spiral arms and rings, etc. The reviled peculiarities of the microscopic drops behavior can be of interest in applications to the ferrofluid-based microfluidics.