On the stability of magnetic colloids

In this paper, the preparation of fluids belonging to ferrofluid (FF) and magnetorheological (MR) categories is described. Furthermore, the effect of different stabilizing additives (thixotropic agents, surfactants, magnetic nanoparticles) and carrier liquids on the sedimentation of these fluids is analyzed. These studies are conducted using: (i) optical and electromagnetic induction techniques for monitoring the stability of dilute and concentrated suspensions, respectively; (ii) contact angle and pendant drop measurements to explain the observed stability in different carriers. The results of these experiments are analyzed in detail and magnetic fluids with improved stability properties are prepared accordingly.