Navegar por los elementos (1 total)
- Resumen es exacto "The structures whose dimensions are in the nanometric scale display chemical and physical properties closely related to their size, shape and morphology, which markedly differ from their bulk counterpart. This has entailed to the intensive study of these systems over the last decades, finding magnified and even unique properties that have led to important technological advances and the development of knowledge in an area that is on the boundary of quantum phenomena. An important direction in the synthesis of nanostructures was the expansion to hybrid nanostructures conformed by discrete domains of different materials arranged in a controlled fashion, also known as heterostructures, which have shown important advantages as multifunctionality or novel functions unavailable in single component nanostructures. Three families of nanoparticles formed by iron oxide single cores and silica shells were prepared by chemical methods. First, a ferrofluid composed of monodisperse nanoparticles covered with oleic acid was obtained by thermal decomposition of organic precursors. The organic layer in the particles surface was subsequently used to promote the ligand exchange in the inverse microemulsion process, as a result the particles are transferred to the polar phase where confined TEOS (Si(OC2H5)4) hydrolyzation and condensation takes place to form an amorphous SiO2 coating on each nanoparticle. The reaction parameters were varied to obtain different cores sizes and shell thicknesses. Solvent transfer of hydrophobic nanoparticles by the formation of a chemically and mechanically resistant shell is an interesting alternative as a first step of modification that allows the creation of more complex and functional structures taking advantage of the well-known versatility of the organosilane compounds. This method yields homogeneous morphologies and low hydrodynamic radii, providing a core-shell system that can be used as a model to study of basic phenomena of magnetism at the nanoscale. Nanoparticles with cores of radii ranging from 4 to 9 nm and shells from 1 to several nanometers were characterized through X-Ray diffraction (XRD) Scanning and Transmission Electron Microscopy (SEM/TEM), and Small Angle X-ray Scattering (SAXS) confirming the desired composition, morphology and stability. An intensive magnetic characterization was performed and the dependency of the main magnetic features with the sizes and interparticle distance was identified. All the variations of the obtained parameters from the magnetic characterization show a dependency that goes as the inverse of the distance cubed, according to the expression of dipolar interactions. Hence the effect is attributed to the increase of magnetic interactions with decreasing shell thickness. A frontier between interacting and non-interacting systems is observed and discussed."
Ordenar por: