Preparation and rheological studies of uncoated and PVA-coated magnetite nanofluid

Experimental studies of rheological behavior of uncoated magnetite nanoparticles (MNPs)U and polyvinyl alcohol (PVA) coated magnetite nanoparticles (MNPs)C were performed. A Co-precipitation technique under N2 gas was used to prevent undesirable critical oxidation of Fe2+. The results showed that smaller particles can be synthesized in both cases by decreasing the NaOH concentration which in our case this corresponded to 35 nm and 7 nm using 0.9 M NaOH at 750 rpm for (MNPs)U and (MNPs)C. The stable magnetic fluid contained well-dispersed Fe3O4/PVA nanocomposites which indicated fast magnetic response. The rheological measurement of magnetic fluid indicated an apparent viscosity range (0.1–1.2) pa s at constant shear rate of 20 s−1 with a minimum value in the case of (MNPs)U at 0 T and a maximum value for (MNPs)C at 0.5 T. Also, as the shear rate increased from 20 s−1 to 150 s−1 at constant magnetic field, the apparent viscosity also decreased correspondingly. The water-based ferrofluid exhibited the non-Newtonian behavior of shear thinning under magnetic field.

► The stable water-based magnetic fluid with fast magnetic response was synthesized.
► The shear rate was increased from 20 S−1 to 150 S−1 at constant magnetic field.
► The viscosity of magnetic fluid decreased with increasing of shear rate.
► Viscosity range (0.1–1.2) pa s was measured for (MNPs)U and (MNPs)C.
► The ferrofluid was non-Newtonian (shear thinning) under magnetic field.