Particle size polydispersity of the rheological properties in magnetorheological fluids

Abstract

Dispersion of metal particles in fluids can be used to manufacture magnetorheologic fluids (MRF). Properties of these dispersion systems are mainly determined by the arrangements and contacts among particles. In this paper, particles with smaller sizes than those in the target dispersion system are added using iron particles dispersed in silicon oil as a model to control the arrangements and contacts. The result suggests that these small-sized particles have a significant effect on the viscoelastic properties of the dispersion. The maximum packing density and the fluid viscosity depend mainly on the adhesion of small particles, which is directly related to the fraction of small particles in the model dispersion system. Under a magnetic field, the yield stress of the dispersion system is proportional to the concentration of iron particles, suggesting that the yield stress relies directly on the presence of small particles. These small particles in the fluid determine the difference in stress of the magnetorheological fluid (MRF) with or without a magnetic field.