Manifestation of surfactant–carrier interaction in ferrofluids in temperature-dependent magnetic rheology

The present study investigates surfactant–carrier interactions in non-aqueous ferrofluids with magneto-rheology at different temperatures. To the authors’ knowledge, such a study has not yet been reported. For this purpose, three ferrofluids—A, B, and C—were procured from Ferrotec, which had identical particles but different surfactant–carrier combinations. The study also encompasses structural and magnetic techniques to elucidate these samples’ physicochemical nature. The results show that the average magnetic size of particles (10 nm) is the same for all the three fluids. The nominal value of the surfactant chain length (4.5 nm) was derived from dynamic light scattering measurements, and the Rosensweig viscosity model and the Shliomis theory were the same. The magneto-rheological properties, e.g., shear stress vs shear rate in zero field and relative increase in ferrofluid viscosity in the applied field at two different temperatures (300 and 313 K), were fitted with Rosensweig and Shliomis models. They showed some variations in surfactant chain lengths. The results suggested the presence of surfactant–carrier interactions in these colloids. This new investigation may be useful in characterizing the stability of a ferrofluid and its practical aspects.