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

Thermal properties of gamma-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 degreesC than that of free PMMA. Random scission of the PMMA chains seemed to be catalyzed by the core oxide. The gamma-Fe2O3 to alpha-Fe2O3 structural transformation took place at different temperatures depending upon the shell material. Namely, alpha-Fe2O3 was the only product for the caprylate-capped gamma-Fe2O3 nanoparticles treated at 400 degreesC, whereas gamma-Fe2O3 still remained for the gamma-Fe2O3/PMMA composite treated at 500 degreesC. 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 gamma-alpha transformation. (C) 2004 Elsevier SAS. All rights reserved.