Preparation of Highly Anisotropic Cobalt Ferrite/Silica Microellipsoids Using an External Magnetic Field

Abstract

Magnetic cobalt ferrite/silica microparticles having both an original morphology and an anisotropic nanostructure are synthesized through the use of an external magnetic field and nanoparticles characterized by a high magnetic anisotropy. The association of these two factors implies that the ESE (emulsion and solvent evaporation) sol-gel method employed here allows the preparation of silica microellipsoids containing magnetic nanoparticles aggregated in large chains. It is clearly shown that without this combination, microspheres characterized by an isotropic distribution of the magnetic nanoparticles are obtained. While the chaining of the cobalt ferrite nanoparticles inside the silica matrix is related to the increase of their magnetic dipolar interactions, the ellipsoidal shape of the microparticles may be explained by the elongation of the sol droplets in the direction of the external magnetic field during the synthesis. Because of their highly anisotropic structure, these microparticles exhibit permanent magnetic moments, which are responsible, at a larger scale, for the existence of strong magnetic dipolar interactions. Therefore, when they are dispersed in water, the microellipsoids self-assemble into large and irregular chains. These interactions can be reinforced by the use of external magnetic field, allowing the preparation of very large permanent chains. This research illustrates how nanostructured particles exhibiting complex architectures can be elaborated through simple, fast, and low-cost methods, such as the use of external fields in combination with soft chemistry.

Particle Size Determines the Shape of Supraparticles in Self-Lubricating Ternary Droplets

“…Combining the effect of size on the supraparticle shape with the size-based stratification of colloids in a mixture of large and small particles, ,, we are able to obtain supraparticles with not only nonspherical or asymmetric shapes but also stratified distribution of the colloidal particles inside the supraparticle. These findings can be important in many areas where asymmetry and anisotropy are crucial for the performance of supraparticles, for example, in optics , and magnetics ,, and in directional propulsion …”

“…As a result of the assembly, the supraparticles gain additional functionality as compared to the colloidal building blocks they are made of. , In symmetric assemblies, the additional functionality is obtained by a collective response of the colloids, for instance, in optoelectronics, optics, and photonics, − catalysis, and drug delivery . Tuning the shape and introducing asymmetry and anisotropy in supraparticles can be important in applications where directionality is crucial. − Therefore, there is a need for the development of methods that are simple and scalable and that allow to precisely adjust the properties of the supraparticles. Here, we show that changing the size and composition of the colloidal building blocks can tune the shape and anisotropy of supraparticles, made through evaporating self-lubricating ouzo droplets as templates.…”

Supraparticles: Functionality from Uniform Structural Motifs

“…There are a few reports in literature on the change of magnetic properties that are caused by a specific arrangement of the magnetic nanoparticles in a supraparticle. Abramson et al found that when arranging magnetic nanoparticles to microellipsoidal supraparticles, the magnetic moments of the nanoparticles were all orientated and caused alignment of the supraparticles in fluids . An anisotropic chain-like supraparticle arrangement of magnetic nanocubes was reported to yield superior inductive heating properties .…”

Influence of magnetic fields on the morphology and pseudocapacitive properties of NiO on nickel foam

“…37 As a result, the magnetic force may play an important role in the growth on (111) along the [111] of the NiO nanoplates, and promoting to form multilayer nanoplate array structure. 33,38 From the change in the size of the nanoplates of MF-NiO-0A and MF-NiO-1.5A, it may be the kinetics which was inuenced by the magnetic eld. The detailed FE-SEM and HR-TEM analyses indicated that the weak magnetic eld had an inuence on the surface energy of Ni(OH) 2 , and therefore had a signicant impact on surface and cross-sectional structures of the NiO lms.…”