Oleic Acid Surface Modification in the Preparation of Magnetic Nanoparticles by a Chemically Induced Transition

Using a chemically induced transition method, magnetic nanoparticles of γ-Fe ₂ O ₃ coated by FeCl ₃ · 6H ₂ O (γ-Fe ₂ O ₃ /FeCl ₃ · 6H ₂ O nanoparticles) can be prepared. Surface modification is performed using oleic acid. By adding oleic acid during the synthesis, FeCl ₃ · 6H ₂ O can be replaced to produce nanoparticles of γ-Fe ₂ O ₃ coated by a monolayer of oleic acid (γ-Fe ₂ O ₃ /oleic acid nanoparticles). The amount of oleic acid added is sufficient, with the as-prepared sample single γ-Fe ₂ O ₃ /oleic acid nanoparticles, whereas the as-prepared sample is a mixture of both γ-Fe ₂ O ₃ /FeCl ₃ · 6H ₂ O and γ-Fe ₂ O ₃ /oleic acid nanoparticles. By chemical species analysis, the mass fraction of both the γ-Fe ₂ O ₃ phase and oleic acid adsorbed can be estimated. These magnetic nanoparticles coated by oleic acid can be considered as effective nanoparticles with an effective density ρ _p.e . The ρ _p.e reflects the amount of oleic acid chemisorbed on the nanoparticles. A kerosene-based suspension comprising the effective nanoparticles was synthesized. Results for the specific saturation magnetization σ _f.s and density ρ _f of the suspension confirm the effective particle structure, involving the mass fraction of oleic acid adsorbed and the effective density of the effective particles.