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.