Balanced Devil Triangle: A Satisfactory Comprehensive Performance Magnetorheological Fluids with Cross‐Scale Particles

Abstract Magnetorheological (MR) fluids are magnetic responsive smart materials that are widely used in real‐time damping adjustment devices. However, a major challenge for MR fluids is balancing the constraints relationship among various key performances. This study demonstrates that by utilizing home‐made high saturation magnetization (208.0 emu g −1 ) nanoparticles as the second component in the preparation of cross‐scale bidisperse MR fluids, the shortcomings of monodisperse micron particles performance can be compensated, effectively balancing the relationship between various performances. This is attributed to the fact that the addition of nanoparticles enhances the density of chain structures under an applied magnetic field, while reducing the overall particle density without a magnetic field. By replacing part of micron particles with nanoparticles, the phenomenon of significant increase in zero‐field viscosity caused by the direct introduction of nanoparticles is avoided. The optimal content of nanoparticles in MR fluids is preliminarily explored, and the results indicate that Micro‐Nano bidisperse MR fluids exhibit a high dynamic yield strength (58.3 kPa when 436 kA m −1 ), excellent sedimentation stability (82.6% when 7 days), suitable zero‐field viscosity (1.25 Pa s when 100 s −1 ), and ideal reversibility. Most importantly, the simple preparation method adds significant engineering application value to these MR fluids.