Thermal properties of the γ-Fe2O3/poly(methyl methacrylate) core/shell nanoparticles

Thermal properties of γ-Fe2O3/poly(methyl methacrylate) (PMMA) core/shell particles with an average core size of 4 nm were studied through measurements of thermogravimetry, powder X-ray diffraction and magnetization. The thermal degradation of the PMMA shell in the air was found to occur at temperatures lower by about 60 °C than that of free PMMA. Random scission of the PMMA chains seemed to be catalyzed by the core oxide. The γ-Fe2O3 to α-Fe2O3 structural transformation took place at different temperatures depending upon the shell material. Namely, α-Fe2O3 was the only product for the caprylate-capped γ-Fe2O3 nanoparticles treated at 400 °C, whereas γ-Fe2O3 still remained for the γ-Fe2O3/PMMA composite treated at 500 °C. It is possible that some species containing silicon of the polymerization initiator origin were formed on the surface and prevented interparticle atomic diffusions needed for the γ-α transformation.