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 particles. The synthesis of ferrite particles is conducted in the structured environment of water-in-oil microemulsions (reversed micelles). This is followed by the enzymatic polymerization of p-ethylphenol. The polymer precipitates in spherical morphologies and during precipitation incorporates ferrite nanocrystals into the polymeric matrix. SQUID (superconducting quantum interference device) generated magnetic hysteresis loops exhibit zero remanence and coercivity for the ferrite−polymer composite 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 dc magnetic susceptibility measurements. Thermal and isothermal remanent magnetization measurements confirm the existence of the spin glass state. The composites exhibit blocking temperatures 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.