Morphological transition of droplets during evaporation driven self-assembly of colloidal dispersion of alumina particles has been investigated. It was found that a sphere to doughnut-like transition of the droplet morphology takes place even when the rate of drying remains moderate and is not extremely fast. Further, it has been seen that such transition is strongly dependent on the volume fraction of the colloids in the droplets. The transition proceeds via buckling of the initial spherical droplets, which occurs when the capillary forces driving the deformation overcomes the interparticle electrostatic forces. However, the transition is hindered and the buckling probability is reduced due to the inherent spatial constraint when the colloid volume fraction is increased. Mesoscopic structures of the assembled grains have been investigated by scanning electron microscopy, small-angle neutron scattering, and dynamic light scattering techniques. Interestingly, it has been observed that the functionality of photoluminescence spectrum of the dried nanoporous grains depends somewhat on the grain morphology.

Nanoparticles confined in droplets of less than a picoliter are forced to organize in submicronic dry grains through solvent evaporation. The evolution of structures of the grains and the constituent nanoparticles during the slow drying process are investigated in situ with small-angle X-ray scattering (SAXS) for the first time. The scattering results have been explained on the basis of the equilibrium thermodynamics of the droplets in the drying tube. We demonstrate that this technique is really efficient in describing the internal arrangement of the nanoparticles inside the drying droplets. Distinction between an almost homogeneous repartition of the nanoparticles in droplets and formation of core shell like particles even in strongly polydispersed droplets can be made using SAXS.

We report on the realization of particle size, morphology, and chemical composition controlled cobalt ferrite nanoparticles (CFO NPs) with tunable magnetic properties for application in electronic and electromagnetic devices. The effect of oleic acid concentration (0.0–0.1 M) on the structural, physical, chemical, electronic, and magnetic properties of solvothermally synthesized CFO NPs is investigated in detail by using the oleic acid (OA) based chemical method for synthesis. Crystalline, cubic, and chemically homogeneous CFO NPs (5–15 nm) can be obtained by controlling the OA concentration. Spectroscopic analyses revealed that the OA molecules form covalent bonds with CFO NPs. The particle-size control was achieved by bridging bidentate interactions between the OA molecules and CFO NPs. Detailed magnetic measurements revealed that the OA concentration helps to effectively control the magnetic behavior of particle-size-controlled CFO NPs. The interfacing between OA molecules and CFO surface atoms leads to modified magnetism which is the key to understand the underlying mechanisms and utilize magnetic nanoparticles in practical applications. The anisotropy constant variation directly with nanoparticle size indicates that the magnetocrystalline component governs the magnetic anisotropy in OA coated CFO. Removal of OA (after thermal treatment) induces enhanced magnetic anisotropy and exchange bias as consequence of surface component. The results and analyses suggest that the molecular coating of nanoparticles offers the most important and critical step to design novel nanostructured magnetic materials for current and emerging electronic device technologies.