Preparation and Characterization of the Magnetic Fluid of Trimethoxyhexadecylsilane-Coated Fe₃O₄ Nanoparticles

A new magnetic fluid was prepared by colloidal dispersion of paramagnetic Fe 3 O 4 nanoparticles coated with monomolecular adsorbed monolayer films of long-chain trimethoxyhexadecylsilane (THS) in a nonpolar hydrocarbon oil. The magnetic Fe 3 O 4 nanoparticles were characterized by using TEM, XRD, FT-IR, and VSM. The silanization of the magnetic particle surface was conducted in methanol. The silanized films on the magnetic particles are characterized with FT-IR spectroscopy. The optical absorbance of the magnetic particle versus concentration of the solution was measured with a UV−vis spectrophotometer and shows a linear increase of absorbance. Langmuir behavior of the THS-coated Fe 3 O 4 nanoparticles at the air/water interface was characterized with pressure−area isotherms and Brewster Angle Microscopy. The collapse pressure of the Langmuir monomolecular films was determined as 62 mN/m. The stability of magnetic fluids of the THS-coated Fe 3 O 4 nanoparticles are comparatively studied with the conventional oleic acid-coated magnetic fluid of Fe 3 O 4 nanoparticle at the acidic condition of pH 4. The durability of the magnetic fluid of THS-coated Fe 3 O 4 nanoparticles is shown as it lasted longer than 60 days.