title: Field-induced patterns in confined magnetorheological fluids.
abstract: We study the behavior of a magnetorheological fluid droplet confined to a Hele-Shaw cell in the presence of an applied radial magnetic field. Interfacial pattern formation is investigated by considering the competition among capillary, viscoelastic, and magnetic forces. The contribution of a magnetic field-dependent yield stress is taken into account. Linear stability analysis reveals the stabilizing role played by yield stress. On the other hand, a mode-coupling approach predicts that the resulting fingering structures should become less and less sharp as yield stress effects are increased. By employing a vortex-sheet formalism we have been able to identify a family of exact stationary solutions of the problem, unveiling the development of swollen polygonal patterns. A suggestive magnetically controlled shape transition in which the edges of the patterns change from convex to concave has been also identified.
authors.affiliation: Departamento de Física, LFTC, Universidade Federal de Pernambuco, Recife 50670-901, PE, Brazil.
authors.forename: Sérgio A
authors.initials: SA
authors.lastname: Lira
authors.forename: José A
authors.initials: JA
authors.lastname: Miranda
authors.forename: Rafael M
authors.initials: RM
authors.lastname: Oliveira