Influence of nanoparticles morphology in magnetic fluids

In this work magnetic fluids at two different volume concentrations (5 % and 10 %) of magnetite nanoparticles of different morphologies and sizes (octahedral, 38 +/- 5 nm; truncated octahedral, 10 +/- 1 nm; rod -like, 95 nm x 10 nm; spherical 33 +/- 20 and 90 +/- 10 nm) have been formulated (by using mineral oil as liquid carrier and Aerosil (R) 300 as viscosity-controller agent) and fabricated. The obtained results allow us to conclude that: a) the fluid with 10 %vol concentration spherical nanoparticles presents the highest magnetorheological response observed in this study, over a 4000 % change of yield stress with the maximum applied field strength. This is due both to their highest magnetic saturation and an effective nanoparticle clustering; b) the fluid based on octahedral particles shows a good balance between magnetorheological response (up to a 795 % change of yield stress) and reversibility (up to a 92 %), which indicates the competitiveness of these particles for the formulation of magnetic fluids. On the contrary, truncated octahedral nanoparticles, although maintaining that high reversibility capability, present a poor MR response (75-95 % change of yield stress for 5 and 10 %vol. concentrations); c) the poor magnetorheological response observed and non-expected reversibility behavior obtained for rod -like particles indicate that further deepening of the understanding of their dispersion and internal structuring is needed.