Surfactant Effect on the Thermal and Electrical Behaviors of Sonochemically Synthesized Fe and Fe-PVP Nanofluids and Insight into the Magnetism of Their in Situ Oxidized α-Fe₂O₃ Analogues

Magnetic nanofluids are dispersions of magnetic nanoparticles in a diamagnetic base liquid, which display distinct physical properties that can be tuned easily by an external magnetic field, electric current, and temperature. Iron nanofluids were synthesized sonochemically in a one-step process and were observed to oxidize in situ over prolonged air exposure, forming α-Fe₂O₃ nanofluids. The thermal conductivity measurements on these single-step fabricated magnetic nanofluids were performed for the first time and showed enhanced thermal transport. Hence, we present a new one-pot synthesis approach to improve the heat transfer. The electrical properties of the iron and ferric oxide nanofluids in the presence and absence of a surfactant are also newly reported in this paper. The different electrical conductivities among the two sets of nanofluids are interpreted, and mechanisms are proposed to account for the observed deviation. The heat transport by Fe₂O₃ nanofluids with respect to the magnetic flux was investigated by subjecting the samples to an external magnetic field. The presence of a surfactant had a substantial effect on the magnetic field-dependent thermal conductivity. Magnetization data as a function of temperature and magnetic field were obtained using the Mössbauer and superconducting quantum interference device techniques, and the influence of the stabilizer is revealed. The present findings are significant for tailoring the properties of magnetic nanofluids for improved applications.