SHG Active Fe(IO3)3 Particles: From Spherical Nanocrystals to Urchin-Like Microstructures through the Additive-Mediated Microemulsion Route

Spherical nanocrystals of iron iodate (Fe(IO 3 ) 3 ) as well as different hierarchically organized hybrid superstructures are synthesized at 80 °C from AOT-based water-in-oil microemulsions. For a fixed reaction time of 2 h, initial addition of PEG molecules and changes in the water/surfactant molar ratio w allow modification of the interactions between surfactant and PEG molecules at the surface of amorphous precursor particles. At low water content ( w = 5.8), adsorption of AOT molecules inhibits the formation of crystallized nanoparticles if the amount of added PEG is too low, whereas spherical nanocrystals are obtained otherwise. In contrast, at a high water content ( w = 12.2), SEM and TEM imaging reveal that the aggregation-induced crystallization of amorphous precursors induces the formation of higher-order complex forms. Aggregates of elongated cone-shaped bundles of nanofilaments and, subsequently, quasi-spherical urchin-like microstructures as long as the PEG amount is raised are observed. Significantly, lattice parameter refinements originally demonstrate the key role of AOT in the self-assembly and a homogeneous nucleation, leading to the formation of primary bouquet-like structures, is suggested before further self-assembly results in urchin-like structures. In terms of potential applications, spherical nanocrystals are promising exogenous labels for multiphoton microscopy, whereas higher-order architectures give perspectives in the morphogenesis of new functional materials.