Study of viscoelastic properties of magnetic nanofluids: an insight into their internal structure

Three magnetic nanofluids were prepared as colloidal suspensions in ethylene glycol using two types of Fe3O4 ferrimagnetic nanoparticles (MGMFs)-one of them commercial (CMGMFs) and the other synthesized in our laboratory (SMGMFs)-and from one type of Fe2O3 nanoparticle (HMF). Using a shear stress controlling rheometer, they were characterized in order to comparatively analyze their viscoelastic behavior and structure. Effects of magnetic particle size and nature on elastic and viscous moduli were determined. The static yield stress and the percolation concentration were also obtained. The fractal dimension (D-f) was estimated from the suspension static yield-stress and volume fraction (phi) dependence, and was determined to be D-f approximate to 2.3 for SMGMFs and CMGMFs, and D-f approximate to 1.5 for HMFs. The corresponding aggregation models and structures were discussed. Finally, master curves were obtained for the magnetic fluids under study, which provide valuable information to estimate the material response for any concentration.