Physicochemical properties of mixed oil-based and bilayer-stabilized magnetic fluids

A primary goal of the present work is to study the physicochemical properties of magnetic nanoparticles (magnetite) coated with identical primary surfactants but have different secondary surfactants. The properties studied are magnetic, rheological and magnetoviscous under different shear rates and magnetic fields. The bilayer surfactant thickness was determined using dynamic light scattering and magnetization measurements. Magnetoviscous data revealed that the magnetic field-induced change in viscosity was dominated by oversize particles only and that there was no pre-agglomerate present in the fluids. These results were compared to Rosensweig et al. prior model for viscosity change as well as with Shiliomis's theory of viscous behavior of dilute suspension of noninteracting particles. The presence of a secondary surfactant on the magnetic surface affects the carrier-surfactant interaction and the stability of the colloid. Two-surfactant system increases the chain length and reduces and weakens the dipolar interactions. Thus, in such a ferrofluid a minimum particle agglomeration can be expected. This work shows that it does not matter whether the fluid is manufactured with one surfactant/one carrier or two surfactants/two carriers; the fluid's stability is the most important parameter.

Automated summary

The aim of this study is to investigate the physicochemical properties of magnetic nanoparticles with different secondary surfactants while coated with identical primary surfactants. The properties studied include magnetic, rheological, and magnetoviscous characteristics under different shear rates and magnetic fields. The thickness of the bilayer surfactant was determined using dynamic light scattering and magnetization measurements. The results suggest that the presence of a secondary surfactant affects the carrier-surfactant interaction and the stability of the colloid, resulting in reduced particle agglomeration.