Effect of polydispersity in concentrated magnetorheological fluids

Magnetorheological fluids (MRF) are smart materials of increasing interest due to their great versatility in mechanical and mechatronic systems. As main rheological features, MRFs must present low viscosity the absence a magnetic field (0.1 - 1.0 Pa.s) high yield stress (50 100 kPa) when magnetized, order optimize magnetorheological effect. Such properties, turn, directly influenced by composition, volume fraction, size, size distribution (polydispersity) particles, latter being an important piece improvement these properties. In this context, work aims analyze, through experiments simulations, influence polydispersity on maximum packing under (on-state), plastic (off-state) concentrated MRF (phi = 48.5 vol.%). Three blends carbonyl iron powder polyalphaolefin oil were prepared. These have same mode, but different indexes, ranging from 0.46 1.44. Separate simulations show that random close fraction increases about 68% 80% as index over range. The on-state stress, is raised 30 +/- 0.5 kPa 42 2 (B ~ 0.57 T) off-state viscosity, reduced 4.8 Pa.s Pa.s. Widening distributions, well known literature, efficiency reduces dispersions, beyond that, it proved be viable way increase effect MRF. Brouwers model, which considers void suspensions particles with lognormal distribution, was proposed possible hypothesis explain field.