Surface modifications of nanometer- and micron-sized particles and their applications

In this thesis, a generic method was developed for surface modification of nanoparticles (NP) with silica shell using Stober method. Nanoparticles synthesized from non-hydrolytic solvents such as various ethers were first surface activated with a silane-based poly(ethylene glycol) (PEG). Because of the amphiphilicity of PEG moiety, these nanoparticles could be easily transferred from hydrophobic to hydrophilic solutions including different biological buffers. After ligand exchange with this silane-based PEG, silica deposition could happen on the surface of these nanoparticles using ethanol and water as solvents, ammonium hydroxide as catalyst and tetraethyl orthosilicate (TEOS) as precursor. This method has been successfully used to nanoparticles such as iron oxide, silver and Pt iron oxide which were synthesized with oleic acid and/or oleylamine as capping agents.;Hollow MPEG-sil-SiO2 nanoparticles were made from NP MPEG-sil-SiO 2 core-shell nanostructures by removing the metal or metal oxide cores using acid. Both core-shell and hollow nanoparticles were used in the drug delivery study of penicillin in the inhibition of Streptococcus mutans. The inhibition zones show that hollow nanoparticles have larger loading capacity than core-shell ones.;A new method has been developed for the formation of Pt Fe2O 3 yolk-shell nanostructures from Pt Fe core-shell nanoparticles. Under the electron beam of TEM the oxidation of iron shells occurred and resulted in the formation of hollow structures because of the Kirkandall effect. The oxidation provided enough energy for Pt cores to hop, split and move in convective motion. This study demonstrates an approach of using nanostructures for the synthesis of nanoparticles inside. The size of Pt core and the thickness of iron shell are critical factors in the structural evolution of the nanoparticles. Besides nm-sized particles, a sol-gel method was developed for the surface modification of micron-sized carbonyl iron particles. Faceted ZrO2 nanoparticles were coated onto the surface for better protection of these particles from acid corrosion and oxidation. The thickness and morphology of the coating were controlled by changing either the reaction conditions or precursor concentrations. The coated carbonyl iron particles should be very useful in various applications that use magnetorheological fluids.