Preparation of Ultrafine Magnetic Particles Using Microemulsions and Vesicles

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In recent years there has an increasing demand for the preparation of ultrafine magnetic oxides of uniform size which are mainly used in computer data storage, audio and video recording, magnetic fluids and fabrication of certain microwave devices. The primary objective of the proposed research program is to synthesize nanoparticles of magnetic oxides using microemulsion processing and intravesicular precipitation. These are unique methods which can be used to produce ultrafine, microhomogeneous particles with a narrow size distribution, which cannot be achieved by conventional methods such as solid-state reaction, bulk precipitation, sol- gel processing and spray drying. Microemulsion processing consists of the precipitation of precursor hydroxides or carbonates of magnetic oxides within the aqueous cores (typically 10 - 50 nm in size) of water-in- oil microemulsions. These nanosize precursors would then be further processed and calcined to produce the magnetic oxides. Intravesicular precipitation consists of aqueous phase precipitation or reduction inside organically constrained microdomains defined by vesicles. Each vesicle becomes a submicroreactor of dimensions of the order of a few hundreds of angstroms. Cations trapped in the intravesicular spaces will react with anions permeating through the vesicle wall from the extravesicular region or be photolytically/chemically reduced to form the product. Intravesicular coprecipitation as well as precipitation upon encapsulated seed particles will be used to create nanocomposites, opening up the possibility of tailoring the functionality of products by manipulating both their morphology and composition at a near molecular scale. The results of the research would delineate the similarities as well as differences between the two processes (microemulsion processing and intravesicular precipitation) in relation to the mechanisms involved and the products formed in them.