(220g) Surface Modification of Magnetic Nanoparticles: Characterization and Colloidal Stability in Polar Solvents

The surface of monodisperse maghemite (Fe2O3) nanoparticles capped by oleic acid was modified to increase the stability of the suspension in polar solvents. The lyophobic surface coating of maghemite particles in ethanol was made to be more lyophilic by ozonolysis. The ozone oxidatively cleaved the double bond of oleic acid to form carbonyl and carboxyl groups on the surface of the nanoparticles which increased the stability of the maghemite particles in ethanol. Additionally, interfacial ligand exchange of the capping molecules was also done to make the particle surface more hydrophilic. The maghemite particles showed enhanced miscibility and short-term stability in water after interfacial ligand exchange. The structure changes of the capping molecules on the nanoparticle surfaces were investigated using Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). From these spectroscopy studies, the cleavage of the oleic acid and the formations of the carboxyl and carbonyl groups on the particle surface were confirmed. The shape and the magnetic properties of the maghemite particles were maintained after the surface modification. Ozonolysis is an effective method in modifying the lyophobic surface of the maghemite nanoparticles.