Physical Mechanisms of Magnetic Field Effects on the Dielectric Function of Hybrid Magnetorheological Suspensions

In this paper, we study the electrical properties of new hybrid magnetorheological suspensions (hMRSs) and propose a theoretical model to explain the dependence of the electric capacitance on the iron volumetric fraction, ΦFe, of the dopants and on the external magnetic field. The hMRSs, with dimensions of 30 mm×30 mm×2 mm, were manufactured based on impregnating cotton fabric, during heating, with three solutions of iron microparticles in silicone oil. Flat capacitors based on these hMRSs were then produced. The time variation of the electric capacitance of the capacitors was measured in the presence and absence of a magnetic field, B, in a time interval of 300 s, with Δt=1 s steps. It was shown that for specific values of ΦFe and B, the coupling coefficient between the cotton fibers and the magnetic dipoles had values corresponding to very stable electrical capacitance. Using magnetic dipole approximation, the mechanisms underlying the observed phenomena can be described if the hMRSs are considered continuous media.

Gelatine-Coated Carbonyl Iron Particles and Their Utilization in Magnetorheological Suspensions

This study demonstrates the formation of biocompatible magnetic particles into organized structures upon the application of an external magnetic field. The capability to create the structures was examined in silicone-oil suspensions and in a gelatine solution, which is commonly used as a blood plasma expander. Firstly, the carbonyl iron particles were successfully coated with gelatine, mixed with a liquid medium in order to form a magnetorheological suspension, and subsequently the possibility of controlling their rheological parameters via a magnetic field was observed using a rotational rheometer with an external magnetic cell. Scanning electron microscopy, infrared spectroscopy, and thermogravimetric analysis confirmed the successful coating process. The prepared magnetorheological suspensions exhibited a transition from pseudoplastic to Bingham behavior, which confirms their capability to create chain-like structures upon application of a magnetic field, which thus prevents the liquid medium from flowing. The observed dynamic yield stresses were calculated using Robertson–Stiff model, which fit the flow curves of the prepared magnetorheological suspensions well.

Surface-initiated mechano-ATRP as a convenient tool for tuning of bidisperse magnetorheological suspensions toward extreme kinetic stability

Magnetic NPs grafted via mechano-ATRP served as a powerful agent for enhancing performance and stability of magnetorheological suspensions.