Iron–chromium oxide nanoparticles self-assembling into smectic mesophases

Organic-coated iron–chromium oxide (chromite) nanoparticles have been prepared by using the thermal decomposition procedure. For this purpose, the substrate – bimetallic acetate – was treated with oleic acid and dodecylamine as co-ligands in trichloroacetic acid solvent at high temperature (320 °C). The main characteristics and behaviors of the obtained nanoparticles were investigated by combined techniques. The size of the obtained nanoparticles was around 11 nm, as estimated by TEM, WAXD and SAXS, which were in good agreement. The bimetallic nature of the nanoparticles was emphasized by X-ray energy dispersive spectrometry (EDX) and their structure was confirmed by WAXD. The Fourier transform infrared (FTIR) spectrum revealed the bands characteristic to metal oxides as well as to the organic components and confirmed the replacement of the acetate with long chain ligands. The co-existence of the organic coatings and metallic core induced a special behavior that was studied by thermogravimetric analysis, differential scanning calorimetry and polarized optical microscopy. The coated bimetallic nanoparticles proved to be thermostable up to 252 °C and thermotropic showing a highly organized crystalline smectic mesophase (3D plastic mesophase). The organic part alone, in the absence of the inorganic component, did not develop this self-assembly. The results of the magnetic measurements suggest superparamagnetic behavior of the iron–chromium oxide nanoparticles and a weak ferromagnetic behavior.