Synthesis and Characterization of Magnetic Colloids

Magnetic fluids which constitute a suspension of magnetic nanoparticles in a carrier liquid are termed ferrofluids. Ferrofluids are smart fluids exhibiting both magnetic and fluid like characteristics. In the present study, we report on ferrofluidswhich are suspensions of magnetite (Fe 3 O 4 ) nanoparticles in carrier fluids of varying viscosity. The magnetite nanoparticles have been synthesized by a chemical co‐precipitation method.X‐Raydiffraction of the as prepared sample revealsa single phase of magnetite.SEM characterisation reveals regular morphology and a narrow size distribution for the synthesized nanoparticles. These are dispersed in pure water and mixtures of water and glycerol using suitable surfactants and ultrasonicated. Our studies reveal that the stability of the ferrofluids have a strong dependence on the viscosity of the carrier fluid as well as the pH, with high viscosity and low pH yielding more stable ferrofluids. While low concentration of the magnetic component renders it impossible to see signatures of its presence in Raman spectroscopy, SQUID magnetometryreveals the presence of the magnetic component suggesting a distribution in size of the nanoparticles with a broad blocking temperature range. Further, a magnetic anomaly is seen at the freezing point of the carrier fluid in the ZFC‐FC measurements for the ferrofluid made with 50% v/v aqueous glycerol solution.