Caracterização eletroquímica de colóides magnéticos visando a aplicações nanotecnológicas nanobiotecnológicas

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Electric Double Layered Magnetic Fluids (EDL-MF) are stable colloidal dispersions of spinel ferrite type nanoparticles in water medium. The thermodynamic stability is achieved by balancing the van der Waals and magnetic dipolar attractions with the introduction of repulsive electrostatic interactions between particles in order to avoid the agglomeration phenomena. Recently, the Complex Fluids Group from University of Brasilia (GFC-UnB) proved by simultaneous potentiometric and conductimetric titrations, that EDL-MF particles behave like a diprotic acid/base system (Two-pK Model) in water medium, showing three types of surface sites. The positively charged sites are found in acid medium and the negatively charged in alkaline medium, occurring stability only in the following pH ranges: 3.5 pH 10.5. This study was feasible due to the determination of the particles surface charge density (SCD) and also the determination of those systems thermodynamic constants, both experimentally obtained through the simultaneous analysis of the curves. For physiologic buffering, it is necessary the synthesis of magnetic colloids that are stable in physiological medium. For this reason, functionalized magnetic fluids (F-MF) are produced from conventional EDL-MF through the chemoadsorsion of appropriate ligands in the particles acidic sites. In this work will be used colloidal dispersions of cobalt ferrite nanoparticles with tartrate-functionalized ions to implement the simultaneous potentiometric and conductimetric titrations in the monoprotic acid / base (One pK Model) system resolution. This work main goal is to describe, quantitatively, the pH dependency of SCD for the F-MF and compare these results to the new measures taken for the EDL-MF in order to, quantitatively, understand the empirical observations in terms of stability that were already published in the literature. To do this, will be presented the described methodology for the two used systems, pH dependency plots with the SCD, as well as speciation diagrams that reveal the existence or coexistence of stable species in dispersion within a certain range of pH.

ASSUNTO(S)

titulações potenciométricas e condutimétricas simultâneas quimica nanocolóides magnéticos densidade de carga superficial

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