On the Use of Unsteady Magnetic Fields in Magnetorheology

Abstract

The aggregation process in magnetorheological fluids is responsible for the shape and size of the generated aggregates; it strongly depends on the characteristics of the applied magnetic fields. In turn, aggregates control the change in physical properties of magnetorheological fluids. Magnetorheological fluids are typically characterised under the presence of steady uniaxial DC fields. However, unsteady magnetic fields introduce more notable changes in the system structure than steady fields. Despite this, a reduced number of studies on rheological behaviour under unsteady magnetic fields have been carried out. The most studied unsteady field configuration used in rheological measurement is the oscillating magnetic field which induces a waving movement in the chains, favouring lateral interactions, and therefore the formation of longer and thicker structures. This aggregation is remarkably more intense and faster than that produced by thermal fluctuations. When an oscillating magnetic field is used, it does not affect joint stability among the particles. Furthermore, the chains remain essentially oriented in the direction of the static magnetic field, and with this, the anisotropy of the system remains unchanged in direction.