Improved rheological properties of dimorphic magnetorheological gels based on flower-like carbonyl iron particles

In this study, a new kind of dimorphic magnetorheological gels (MRGs) based on the conventional carbonyl iron particles (CIPs) and flower-like CIPs have been prepared for improving the yield stress and dynamic mechanical properties. The flower-like CIPs are synthesized by a simple and facile in situ reduction method. Characterization results indicate that the flower-like CIPs are synthesized successfully and a layer of uniform and continuous Fe nanosheets are grown on the surface of the raw microsphere CIPs. In addition, the flower-like CIPs exhibit excellent magnetic properties, which the saturated mass magnetization (Ms) can achieve 168.76 emu/g. In order to study the influence of mass fraction of flower-like CIPs on the rheological properties of this dimorphic MRGs, a series of polyurethane-based dimorphic MRGs are prepared by partial substitution of the CIPs with as-synthesized flower-like CIPs, and the MR properties of them are systematically investigated under both oscillatory and rotational shear modes. The experimental results indicate that, with 8 wt% flower-like CIPs, the maximum dynamic yield stresses and magneto-induced shear yield stress of dimorphic MRGs are 58.11 kPa and 54.53 kPa, similar to 1.39 and similar to 1.37 times of the MRG without flower-like CIPs at the same magnetic particle content. Moreover, the average loss factor and the loss factor under 1 T of the sample (flower-like CIPs weight content 8 wt%) are 0.36 and 0.07, which are approximately 1.71 and 2.71 times than that in the non-substitution sample. The increased loss factor is beneficial to improving the vibration reduction effect of MRGs of damping devices in the whole magnetic field region. Furthermore, the possible mechanism for the enhanced MR properties in dimorphic MRGs is proposed. In summary, this work is expected to promote the design and application of MRG devices. (C) 2017 Published by Elsevier B.V.