Effect of the swelling degree on the formation of magnetite nanoparticles in hydrogels

TEM image of magnetite nanoparticles in polymer gel. Composites containing magnetite nanoparticles in poly(acrylamide-co-hydroxyethylacrylate) cross-linked using poly-ethylene–glycol-diacrylate were prepared and characterized. The magnetite was synthesized in situ in the polymer network by treatment with a water solution of Fe (II) and Fe (III). The salts were then coprecipitated by exposing the swollen gels to ammonia vapors and the obtained magnetic gels dried. The ratio acrylamide (AM)/hydroxyethylacrylate (HEA) was varied to compare matrices with different hydrophilicity. Moreover solutions with different concentration of iron salts were used to swell the gels. The effect of both the network composition and the concentration of iron salts in the swollen polymers on the final structure and properties of the dried magnetic polymers were studied. The investigation was carried out by means of electron diffraction, X-ray diffraction, vibrating sample magnetometry, small angle X-ray scattering and transmission electron microscopy. The coercivity of the magnetic composites prepared was close to zero and they provided super-paramagnetic properties. The decrease of the acrylamide content in the polymer gel and of the iron salts concentration in the swelling aqueous solution leads to the formation of amorphous particles of iron oxide. The average sizes of the magnetite nanoparticles obtained are compared.