The rheological response of carbonyl iron particles suspended in mineral oil solution of 12-hydroxy stearic acid

In this study, carbonyl iron based magnetorheological fluids (MRFs) with 12-hydroxy stearic acid (12-HSA) oil solutions as carrier were fabricated. Rheological performance of the magnetorheological fluid, including viscosity, yielding, magnetic hysteresis, dynamic modulus as well as thixotropic behavior, was investigated by using a rotational rheometer equipped with a magnetic device. It is found that the 12-HSA gave rise to an increase in the off-state viscosity and shear stress in the absence of magnetic field, indicating gel structure developed in the suspensions. This gel network associating with field-induced particle structure lead a substantial yield stress and dynamic modulus. The hysteresis test validated that the gel like network had a certain effect on maintaining the aggregation structure after removing the magnetic field. Dynamic oscillatory tests showed that 12-HSA solution based MRF exhibits solidlike property in the absence of magnetic field. The dependence of plateau value G′ on magnetic field showed relationship of natural logarithm. Regarding to the thixotropy, a longer recovery progress was observed in 12-HSA solution based MRF due to the restriction of gel network. The sedimentation measurements revealed that the strong flocculation could be formed by 12-HSA and enhances the stability of suspensions.