Interações de sistemas nanoestruturados de zircônia/ácido oleico em diferentes solventes orgânicos
Ferreira, William Alberto Leonel
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The promising technologies to modify the future, demands materials with special properties. The functionalized nanocrystals represents the building blocks that can leverage these technologies. This project aims at the study of ZrO2 nanocrystals of oleic acid functionalized (AO) called NCf in dispersions in three different solvents, hexane, toluene and chloroform. In previous studies, it has been observed that the organic layer can modify the conformation of the molecules on the surface (the organic layer) depending on the solvent, the affinity allows it to swell, if it has high affinity or contracts, if the affinity is low. These studies were performed with transmission electron microscopy (TEM). However, the direct study in solutions is challenging due to the difficulty of the characterization of this system in relation to the nanometric size and the hybrid character of the nanomaterial. In order to overcome these difficulties, density and viscosity measurements of the NCf dispersions were used at concentrations. 1x10-3, 5x10-3, 1x10-2, 5x10-2 and 1x10-1 g.ml-1 in triplicate. The nucleus of the NCf was characterized by TEM as a spheroid of larger radius 2.5 + 1,1 nm and a smaller radius of 1.9 + 0,6 nm, X-ray diffraction with monoclinic phase and organic load of 35% identified by thermogravimetric analysis. From the viscosimetric measurements, the intrinsic viscosity of the NCf was obtained in the solvents cited using the empirical power equation. With the intrinsic viscosity it was possible to approximate the NCf to a molecule using the Einstein molecular viscosity model and find the hydrodynamic radius (Rh) with values of 4.2 + 0.1 nm for hexane, 4.1 + 0.2 nm for toluene and 4.0 ± 0.2 nm for chloroform. These Rh values were compared to nanostructure characterization techniques, low angle X-ray scattering (SAXS) and dynamic light scattering (DLS). The SAXS values were 4.2 ± 0.1 nm for the NCf in hexane and 4.0 ± 0.1 nm in toluene, not having counts in chloroform due to high X-ray absorption by the solvent. With DLS the values found were 7.0 ± 0.1 nm for the hexane dispersion, 4.9 ± 1.5 nm for the toluene and 3.5 ± 0.3 nm for the chloroform. There was excellent agreement of the data showing the success of the approach of the nanocrystal to a molecule and the viscosimetric characterization. It was observed the importance of the organic layer in the NCf behavior, which represents more than 85% of the volume and is responsible for the high dispersivity of nanocrystals even in high mass fractions (mixture of 80% by mass of NCf in dispersions using toluene). The one-step synthesis in oleic acid showed excellent reproducibility, which allowed the elaboration of this project that used more than 20 g of NCf, an amount considered as ultra-high scale for this type of nanomaterial. The unique properties of this NCf together with the detailed understanding of its behavior in solutions and high-scale synthesis denote a nanomaterial with potential for various industrial applications.