Synthesis and Magnetorheology Study of Iron Oxide and Iron Cobalt Oxide Suspensions

This study investigates the magnetorheology (MR) of polydimethylsiloxane (PDMS) that contains magnetic powders of various compositions, shapes, and concentrations. Two magnetic powders, Fe3O4 and CoFe2O4, were synthesized. TEM images reveal that a powder of spherical particles was obtained at high temperature. A powder with nonspherical star shape was synthesized at low temperature. A rheological test confirmed a typical Bingham behavior for all the MR fluids prepared in this study. Experimental results demonstrated that the cobalt ferrite exhibited a more superior yield stress than the ferrite compound. A magnetic powder of larger particles was found to have higher yield stress. Moreover, the spherical particles yielded a higher yield stress than the star-shaped particles. The "saturated magnetic strength" increased with the loading of the magnetic powder. Finally, the results demonstrate that 12 wt% CoFe2O4 nanopowder (10 nm) dispersed in the PDMS liquid exhibited a large range of yield stresses (0 to 644 Pa).