The effects of dispersed phase saturation magnetization and applied magnetic fields on the rheological properties of magnetorheological (MR) fluids are described. MR fluids based on two different grades of carbonyl iron powder with different average particle size, 7–9 μm (grade A) and 2 μm (grade B), were prepared. Vibrating sample magnetometer measurements showed that the saturation magnetization values were 2.03 and 1.89 T for grades A and B, respectively. Rheological measurements were conducted for 33 and 40 vol% grade A and grade B based MR fluids with a specially built double Couette strain rate controlled rheometer at flux densities ranging from 0.2 to ~0.8 T. The yield stresses of 33 and 40 vol% grade A were 100 ± 3 and 124 ± 3 kPa, respectively at 0.8 ± 0.1 T. The yield stress values of MR fluids based on finer particles (grade B) were consistently smaller. For example, the yield stresses for 33 and 40 vol% grade B based MR fluid were 80 ± 8 and 102 ± 2 kPa, respectively at 0.8 ± 0.1 T. The yield stresses at the flux density approaching magnetic saturation in particles (B ~ 0.8T) were found to increase quadratically with the saturation magnetization (μ0Ms) of the dispersed magnetic phase. This is in good agreement with the analytical models of uniformly saturated particle chains developed by Ginder and co-workers. The results presented here show that the decrease in yield stress for finer particle based MR fluids is due to the relatively smaller magnetization of the finer particles.

https://iopscience.iop.org/article/10.1088/0964-1726/11/1/316/pdf

Rheological properties of magnetorheological fluids

Synthesis of Fe3O4 magnetic fluid used for magnetic resonance imaging and hyperthermia

Synthesis of Fe3O4 nanoparticles without inert gas protection used as precursors of magnetic fluids

Rheological properties of water-based Fe3O4 ferrofluids

In this work, the magnetorheological properties of suspensions of micron-sized iron particles dispersed in magnetite ferrofluids were studied. With this aim, the flow properties of the suspensions in the steady-state regime were investigated using a commercial magnetorheometer with a parallel-plate measuring cell. The effect of both magnetite and iron concentration on the magnitude of the yield stress was studied for a broad range of magnetic fields. In addition, the experimental values of the yield stress were compared with the predictions from the chain model. With this purpose the values of the yield stress were obtained by means of finite element calculations. Interestingly, it was found that the experimental yield stress increases with the concentration of magnetite nanoparticles in the ferrofluid. Unfortunately, this behaviour is not obtained from calculations based on the chain model, which predict just the opposite trend.

/pdf/magnetorheology-for-suspensions-of-solid-particles-dispersed-4gfju685ep.pdf

Magnetorheology for suspensions of solid particles dispersed in ferrofluids

A pressure-driven apparatus was used to measure the yield stress of magnetorheological (MR) fluids as a function of the applied magnetic field, the carbonyl iron particle content, and the amount of surfactant used to stabilize the MR fluid. The yield stress was measured from the pressure difference necessary to initiate flow of a MR fluid in a straight tube present in a magnetic field. Yield stress measurements were made on MR fluids that contained up to 30 vol % carbonyl iron particles, up to 14 vol % surfactant oleic acid, and the remainder 100 cS silicone oil. In the absence of an applied magnetic field, the MR fluids did not have a yield stress and behaved as Newtonian fluids. In the presence of magnetic fields up to 2.2 kG, the MR fluids had yield stresses up to 1.9 kPa. An effect of the tube size on the yield stress was observed for MR fluids above 15 vol % carbonyl iron and magnetic fields above 1.0 kG.

Yield stress measurements of magnetorheological fluids in tubes

The adsorption of both random coil and α-helical poly l-arginine (PLA) on a surface templated by sodium dodecyl sulfate (SDS) hemicylindrical micelles is investigated and compared. Both secondary structures of PLA irreversibly adsorb on the SDS hemimicelles preserving the secondary conformation present in solution. However, the hemicylindrical SDS surface micelles induce aligned ordering of the α-helical PLA molecules by the adsorption of them into the grooves and at the top of the hemimicelles. For random coil PLA, ordering is not promoted by the surface hemimicelles. The surface concentration of the α-helical PLA is approximately 2 times larger than that for the random coil PLA although electrostatic attraction to the surface is largely screened by the presence of NaClO4 for the α-helical case. The results indicate that the adsorption process for α-helical PLA case is governed by a combination of electrostatic and van der Waals forces. Neutron reflectivity data show that the templated surface of surface...

Pieter Stroeve

Papers

Yield stress measurements of magnetorheological fluids in tubes

Templating polypeptides on self-assembled hemicylindrical surface micelles