Binary Superlattices from {Mo-132} Polyoxometalates and Maghemite Nanocrystals: Long-Range Ordering and Fine-Tuning of Dipole Interactions

摘要

In the present article, the successful coassembly of spherical 6.2 nm maghemite (gamma-Fe2O3) nanocrystals and giant polyoxometalates (POMs) such as 2.9 nm {Mo-132} is demonstrated. To do so, colloidal solutions of oleic acid-capped gamma-Fe2O3 and long-chain alkylammonium-encapsulated {Mo-132} dispersed in chloroform are mixed together and supported self-organized binary superlattices are obtained upon the solvent evaporation on immersed substrates. Both electronic microscopy and small angles X-ray scattering data reveal an AB-type structure and an enhanced structuration of the magnetic nanocrystals (MNCs) assembly with POMs in octahedral interstices. Therefore, {Mo-132} acts as an efficient binder constituent for improving the nanocrystals ordering in 3D films. Interestingly, in the case of didodecyldimethylammonium (C-12)-encapsulated POMs, the long-range ordered binary assemblies are obtained while preserving the nanocrystals magnetic properties due to weak POMs-MNCs interactions. On the other hand, POMs of larger effective diameter can be employed as spacer blocks for MNCs as shown by using {Mo-132} capped with dioctadecyldimethylammonium (C-18) displaying longer chains. In that case, it is shown that POMs can also be used for fine-tuning the dipolar interactions in gamma-Fe2O3 nanocrystal assemblies.