Stability behavior of composite magnetorheological fluids by an induction method

In this work, we study the stability behavior of composite magnetorheological fluids consisting of magnetic (iron) and non-magnetic (poly(methylmethacrylate)) particles dispersed in mineral oil. Because of the opacity of the suspensions, optical methods traditionally employed for evaluation of the gravitational settling in colloidal suspensions are not suitable for sedimentation follow-up in this case. For this reason, we use an alternative method based on the evaluation of the resonant frequency of the inductance of a thin coil surrounding the sample. The movement of the coil along the height of the container at specified steps and time intervals allows obtaining information about the local volume fraction of particles inside the tube. The obtained successive profiles for the multi-component suspensions show a decrease of the iron particle settling and of the initial rate of settling as the poly(methylmethacrylate) volume fraction is increased. Finally, the increase of the poly(methylmethacrylate) concentration gives rise to an improvement of the rheological properties upon magnetic field application for a given concentration of iron. Both a strong rheological response and a good colloidal stability are essential for practical applications.