Synthesis of Stable Magnetic Nanofluids of Different Particle Sizes

Highly stable suspensions of Fe₃O₄ nanoparticles are produced by simple co-precipitation approach, combined with dynamic coating of surfactant where the particle size is controlled by varying reaction temperature. The size, distribution and morphology of magnetite nanoparticles are measured by using the X-ray diffraction (XRD), Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM). The XRD patterns of particles prepared at incubation temperatures 30, 50, 60 and 70 C show the cubic crystal structure of magnetite. The particles size and saturation magnetization values are found to increase with increase in incubation temperature due to a decrease in supersaturation at elevated temperature. The average size of the particles obtained by light scattering are higher than the values obtained by XRD due to the adsorbed surfactant layer. The Mossbauer data shows an intensified central doublet due to the superparamagnetic nature of particles and two sextets due to the two structurally different iron sites in the material. The narrow size distribution of the particles and the long term stability of the dispersions are attributed to the presence of a monolayer of surfactant on individual particles, as confirmed by thermogravimetric analysis.