Magnetorheological response of homogeneous and Janus iron-oxide coated silica particles

The flow behavior of magnetic suspensions made of nonmagnetic spherical particles surface-decorated by a magnetic shell is investigated in this study. Suspensions of SiO2@Fe3O4 homogeneous particles (HPs) (the so-called core/shell particles) and SiO2@Fe3O4 Janus particles (JPs) were compared in terms of their rheological properties. Particle surface characteristics and the contribution of anisotropic magnetization of JPs to interparticle interactions were investigated for the first time. Higher shear viscosity, shear stress, and viscoelastic modulus were obtained in magnetic HP suspensions. However, upon elimination of the saturation magnetization effect of particles, higher shear viscosity was achieved in magnetic JP suspensions due to the more significant contribution of the contact force in the JP systems. The dependence of the magnetorheological (MR) properties on the magnetic particle concentration and magnetic field strength was also evaluated for HP and JP suspensions. These two magnetic systems deviate from conventional MR fluids because the magnetization is generated by the magnetic shell instead of the core of the particles. These observations provide new insights and opportunities for designing MR fluids.