Breakup of thin films of micro-magnetic drops in perpendicular fields

New modes of striking drop breakup instabilities of a thin film of micro-magnetic drops are experimentally observed under a constant perpendicular field. These modes are shown to depend strongly on the initial sizes of drops. Three modes of well-ordered breakup instability patterns are recorded for drop sizes ranging from diameter d = 400 to 1400 mu m. Mode I instability (d <= 400 mu m) shows a fully evolved central droplet associated with numerous incompletely developed droplets in a formation of evenly distributed waves at a separated outer fluid annulus. These waves at the outer annulus are further destabilized and fully evolve into Mode II instability (500 mu m <= d <= 1000 mu m) which forms an additional outer circular array of droplets. A more vigorous Mode III instability with an additional array of droplets in the middle region and smaller secondary droplets in the outer array is observed for an even bigger initial drop size (1100 mu m <= d <= 1400 mu m). For drop sizes d >= 1500 mu m, a more complex Mode IV instability is recorded, which shows disorderly arrangements of numerous droplets in the middle region and derivative droplets at the outer array. Contrast to the first three modes of instabilities with the numbers of breakup droplets remaining almost constant before evolving into the next state, Mode IV instability has the number of breakup droplets increasing gradually. (C) 2006 Elsevier B.V. All rights reserved.