(641g) Effect of Elastic Sebs Beads As Additives on the Chain Formation of Iron Particles in Magnetorheological Fluids

Magnetorheological fluids (MRFs) are mixtures of magnetic particles in a liquid that transits from a liquid to a solid-like state due to the rapid formation of reversible chain-like structures upon the application of a magnetic field. The transition from a liquid to a solid-like state is usually measured by the increase in MRF viscosity, while the strength of the formed chains is measured by MRF yield stress. Greater viscosity and yield stress indicate stronger chain-like structures, which is usually desired for MRF applications such as vibrational dampers, and magnetic brakes in addition to surface finishing technologies and soft robotics. However, MRFs lack elastic properties that limit MRF recovery behavior with respect to applied load and subsequent energy dissipation. Limited MRF recovery after fluid impact results in irreversible MRF chain deformation, limiting long-term use of MRF liquids. Hence, this study developed elastic SEBS (Styrene-Ethylene-Butylene-Styrene) beads by mixing SEBS (a synthetic rubber) with water and a surfactant at a temperature of 70°C, with subsequent cooling once the droplets were formed. Optimal mixing parameters, surfactant, and polymer concentrations to achieve improved fluid viscosity were also determined. Size and viscosity of the developed SEBS beads were found to be a function of SEBS concentration, while the surfactant concentration had negligible effect. Bead size increased with increasing SEBS concentration, while the best viscosity was obtained at 40vol% SEBS and 30vol% surfactant. The elastic beads were then added as additives to silicone oil-based MRFs with iron as the dispersed phase. The rheology and microscopy of the resulting MRFs with SEBS beads as an additive was studied as a function of both bead and magnetic particle concentration. Subsequently, an in-depth microscopic study on the chain-formation properties like chain-length, formation speed, and chain disintegration speed was performed. Unique chain conformations and field response not previously seen in neat particle fluids were observed.