Magnetorheological suspensions based on modified carbonyl iron particles with an extremely thin poly(n-butyl acrylate) layer and their enhanced stability properties

This study is focused on the modification of magnetic carbonyl iron (CI) particles with a thin polymer shell utilizing the atom-transfer radical polymerization (ATRP) technique, enabling control of the molecular weight and polydispersity of the final grafted polymer chains on the surface of CI particles and therefore also allowing tuning of the magnetorheological (MR) performance as well as stability properties (chemical, sedimentation). Hence, the bare CI particles were coated with a poly(butyl acrylate) (PBA) shell by the ATRP technique. The polymerization procedure of polymer grafting on the surface of the CI particles was characterized by gel permeation chromatography and nuclear magnetic resonance. The presence of the PBA chain on the CI particles was confirmed by Fourier infrared spectroscopy and energy dispersive spectroscopy. A saturation magnetization analysis using vibrating sample magnetometer proved that a thin polymer shell negligibly affects their magnetic properties, and data fit into the Jiles-Atherton model allowed the finite magnetization saturation for both bare CI and CI-PBA particles to be obtained. Furthermore, it was proved that a thin PBA coating provides sufficiently enhanced chemical and sedimentation stability properties for such a system, while the MR performance investigated using a rotational rheometer was affected negligibly. Finally it can be stated that a controllable coating performed via the ATRP technique is a useful tool to significantly improve stability properties, while the MR performance maintains values suitable for real-life applications.