Stability of magnetorheological fluids in ionic liquids

In this work, magnetorheological (MR) fluids using ionic liquids (ILs) as carrier were prepared. With this aim, two different ILs, with low and high electrical conductivity, and two kinds of iron particles, either with silica coating or without it, were used. The viscosity of the suspensions was measured, and the results compared with the theoretical predictions of Batchelor's equation. The deviations from Batchelor's equation were used to make inferences on the aggregation state of the suspensions. Contact angle measurements on iron powder pellets were also performed in order to analyze the wetting of the particles by the ILs employed as carriers. In addition, sedimentation and redispersion experiments were carried out and discussed in view of the aggregation degrees of the suspensions inferred from the previously mentioned experiments. From all these experiments, it could be concluded that the suspension consisting of silica coated iron particles dispersed in the low conductivity ionic liquid presents the best stability and redispersibility properties. Finally, microscopic observations of diluted suspensions, carried out upon magnetic field application, showed that the most regular field-induced structure was also obtained for this suspension.