SYNTHESIS OF SUPERPARAMAGNETIC POLYMER-FERRITE COMPOSITES USING SURFACTANT MICROSTRUCTURES

Superparamagnetic microspheres are prepared by incorporating nanometer -sized iron oxide crystals into micron-sized phenolic polymer particle s. The synthesis of ferrite particles is conducted in the structured e nvironment of water-in-oil microemulsions (reversed micelles). This is followed by the enzymatic polymerization of p-ethylphenol. The polyme r precipitates in spherical morphologies and during precipitation inco rporates ferrite nanocrystals into the polymeric matrix. SQUID (superc onducting quantum interference device) generated magnetic hysteresis l oops exhibit zero remanence and coercivity for the ferrite-polymer com posite at room temperature, indicating the superparamagnetic nature of the composite. At very low temperatures, hysteretic effects, nonzero remanence, and coercivity are seen. Spin glass behavior is apparent at low temperatures from de magnetic susceptibility measurements. Therma l and isothermal remanent magnetization measurements confirm the exist ence of the spin glass state. The composites exhibit blocking temperat ures in the range 12.0-27.0 K. TEM micrographs of sectioned composite particles show that the iron oxide component is uniformly distributed in the polymer matrix.