The influence of thixotropy on the magnetorheological property of oil-based ferrofluid

Abstract

A Fe3O4 hydrocarbon oil-based ferrofluid was synthesized and its magnetorheological behavior was investigated. The ferrofluid exhibits shear thinning behavior under different magnetic fields and a significant hysteresis effect was observed from the viscosity-shear rate flow curves due to the thixotropy of ferrofluid. The thixotropic behavior is induced by the presence and evolution of the microstructures in the ferrofluid. Moreover, the experimental results demonstrate that the viscosity of the ferrofluid decreases with increasing magnetic field when the magnetic field is below 81 mT. This is followed by an abrupt increase in the viscosity when the magnetic field increases to 124 mT. However, the viscosity again decreases as the magnetic field continue to increase beyond 124 mT. We reveal the negative correlations between viscosity and magnetic fields. The unusual magnetorheological behavior of the ferrofluid is due to the joint effect of thixotropy and magnetic fields. These findings provide a new perspective on the rheological behaviors of ferrofluids that takes the thixotropic effect into consideration.