The role of polymer films on the oxidation of magnetite nanoparticles

A detailed investigation about the role of polymer films on the oxidation process of magnetite nanoparticles (∼7 nm diameter), under laser irradiation is performed employing micro Raman spectroscopy. To support this investigation, Fe₃O₄-np are synthesized by the co-precipitation method and assembled layer-by-layer with sodium sulfonated polystyrene (PSS). Polymer films (Fe₃O₄-np/PSS)_n with n=2,3,5,7,10 and 25 bilayers are employed as a model system to study the oxidation process under laser irradiation. Raman data are further processed by principal component analysis. Our findings suggest that PSS protects Fe₃O₄-np from oxidation when compared to powder samples, even for the sample with the greater number of bilayers. Further, the oxidation of magnetite to maghemite occurs preferably for thinner films up to 7 bilayers, while the onset for the formation of the hematite phase depends on the laser intensity for thicker films. Water takes part on the oxidation processes of magnetite, the oxidation/phase transformation of Fe₃O₄-np is intensified in films with more bilayers, since more water is included in those films. Encapsulation of Fe₃O₄-np by PSS in layer-by-layer films showed to be very efficient to avoid the oxidation process in nanosized magnetite. - Graphical abstract: Encapsulation of Fe₃O₄-np by PSS in layer-by-layer films avoids the oxidation and phase transformation of nanosized magnetite. - Highlights: • (Fe₃O₄-np/PSS)_n nanofilms, with n=2 up to 25, where layer-by-layer assembled. • The influence of film architecture on the Fe₃O₄-np oxidation was investigated through Raman spectroscopy. • Encapsulation of Fe₃O₄-np by PSS showed to be very efficient to avoid the Fe₃O₄-np oxidation.