Magnetic field dependent viscoelasticity of a highly stable magnetorheological fluid under oscillatory shear

Abstract

In our previous works, a new kind of magnetorheological fluid (MRF) consisting of high viscosity linear polysiloxane (HVLP) as carrier and carbonyl iron particles (CIPs) as magnetoactive dispersions, i.e., HVLP MRF, was proposed. HVLP MRF is a promising candidate in the field of heavy equipment for its long-term suspension stability. In this study, we further investigate the viscoelastic properties of HVLP MRF under oscillatory shear in order to evaluate its work performance. HVLP MRFs with different CIP concentrations (0, 20, 40, 60, and 70 wt. %) were synthesized. SEM microstructure, visible MR effect, and magnetic properties were performed. The effects of magnetic flux density, CIP concentration, shear strain, and shear angular frequency on the viscoelastic moduli were examined by using a Physica MCR-301 rheometer. The results show that the viscoelastic moduli are magnetic field dependent. The storage modulus increases with increasing the magnetic flux density, while the loss modulus presents a tendency of rising up at the beginning and declining in late. A critical particle concentration threshold (∼70 wt. %) was found to maximize the magneto-storage modulus increment. Both the upper limit of linear viscoelastic region and the flow point increase as the magnetic flux density increases. It reveals that the field dependent viscoelasticity of HVLP MRF is the result of competition between the structure-enhancement of magneto-induced particle chains and structural deformation under oscillatory shear. Additionally, in the linear viscoelastic region, HVLP MRF shows little dependence on shear angular frequency, implying an excellent working stability in a complex environment.