Field-induced particle dispersion in extremely bidisperse magnetorheological fluids

Magnetorheological fluids (MRFs) are smart materials with controllable microstructural and mechanical properties, which are of interest for the fabrication of high-performance viscous dampers, energy dissipators, and fast response actuators. Despite their promising applications, achieving a stable, reversible, and homogeneous magnetic suspension remains a challenge due to the dipole-dipole interaction and high mass density of magnetic microparticles. Here, we report a simple strategy for synthesizing extremely bidisperse MRFs with a homogeneous particle distribution using precessing magnetic fields. Our findings reveal a quadratic experimental relationship between the magnetic field intensity and the precession angle, allowing a clear identification of the regions where homogeneous particle dispersion can be achieved. We also examined the effects of particle concentration and magnetic field strength on the 2D morphology and reversibility of particle microstructures. We demonstrate that by tuning the precessing magnetic field and particle concentration, a programmable and rich variety of self-organized 2D particle microstructures such as chains, fractal networks, cellular networks and island-like clusters can be obtained. Overall, the results of this work open the possibility of using precessing magnetic fields to disperse magnetic microparticles in order to obtain extremely bidisperse MRFs with stable and reversible properties, which provides a platform to design magnetic fluid devices with additional control parameters and long-term stability.