(273b) Magnetorheology of Multi-Component Magnetic Composites

Magnetorheological fluids (MRFs) are typically simple dispersions of magnetic particles in a non-magnetic carrier liquid, silicone oil being one of the most common due to its ease of manufacture and thermal stability. When MRFs are subject to a magnetic field, the formerly homogenous dispersion of magnetic particles aligns to the field creating chain-like structures that resist shear. The performance of the MRF is most commonly measured via the ratio of on-state to off-state viscosity or modulus (i.e., the stiffness of the material after and before application of the magnetic field) as well as the on-state yield stress (a measure of the force that the chains can withstand without breaking). While MRFs were first developed in the early 20^th century, significant problems remain such as colloidal instability, corrosion, and high energy requirements. Strategies to solve these challenges have thus far included coatings (which frequently reduce performance), improved magnetic particles (which increases cost), new device designs (which still rely on the poorly performing fluid), and new control algorithms (which have the same challenges as new device designs). In this work we take a different approach, specifically looking at the impact of rubber-based additives as well as new polymer framework, for improving the performance of MRFs. We have studied the impact of these additives on the rheological properties of the MRFs in the off state and the on state and investigated the changes in chain structure and alignment in the presence if additives as a function of additive particle size, concentration, and shape, field strength, and magnetic particle (iron) concentration. There was a significant difference between synthetic rubber beads manufactured in-house vs. ground rubber particles generated industrially. Both rubber populations caused increases in viscosity and enhanced viscoelasticity of the dispersions, including in the on-state particularly at lower magnetic fields. These results demonstrate a new formulation strategy for the implementation of MRFs and a path forward for low cost integration of MRFs to full scale earthquake dampers and prosthetic devices.