Flow-induced transition from cylindrical to layered patterns in magnetorheological suspensions

A transition from a hexagonal to a layered pattern is observed when a magnetic suspension structured by a magnetic field is submitted to an oscillating shear flow. This transition occurs at a well-defined strain γₒ=0.15, which is found to be independent of the cell thickness, the intensity of the magnetic field, and the P\'eclet number. This layered pattern is stable in the absence of the flow if it has been formed at a P\'eclet number higher than unity. In this domain the period of the stripes increases with the intensity of the magnetic field and decreases with the initial volume fraction of magnetic particles. These features are explained by a model based on the minimization of the magnetic energy and on the equilibrium of osmotic, hydrodynamic, and magnetic pressures.