Ferrofluids as a new kind of nano-functional material, possessing both magnetism of solid material and fluidity
of liquid material, thus, they have extensive scientific research and engineering application value. To avoid the
defects of conventional non- or single silane coupling agent in silicone oil-based ferrofluid preparation, TEOS
and KH-792 were introduced as surfactants to modify Fe3O4 magnetic nanoparticles (MNPs). Silicone oil modified
by carboxylic acid was used as based liquid because of improved compatibility with surfactants. Silicone
oil-based ferrofluid was prepared by high-energy ball milling method, and its rheological properties were studied.
The saturated magnetization of the silicon oil based ferrofluid was 142.71 Gs. When external magnetic field
was applied, the MNPs formed a chain structure in the microscope. The viscosity of ferrofluid increased with
magnetic field and the shear stress rose with shear rate. The viscosity decreased steeply with increasing temperature
and shear rate. The viscosity of silicone oil-based ferrofluid was 950 mPa·s at 25 °C and can vary from
2044 mPa·s at 5 °C to 465 mPa·s at 40 °C. The ferrofluid transformed from a Newtonian fluid at zero magnetic
field to a shear-thinning pseudoplastic Bingham fluid when an external magnetic field was applied. The
viscosity varied from 1.37 to 2.38 × 105 mPa·s at zero shear rate. While, when magnetic field varied from 0 kA/
rose to 160 kA/m, the viscosity increased obviously and this phenomenon became more pronounced as the
shear rate decreased. When magnetic field intensity was higher than 64 kA/m, the viscosity increased slowly
with increasing shear rates and viscosity curve was close to a straight line at 100 s-1. This study expands the idea
of exploring the synthesis of ferrofluids with mixed surfactants. Silicone oil-based ferrofluid is expected to have
unique application prospects in the aerospace field, especially in space damping, sealing and biomedicine.