Preparo e modificação química de látex magnético à base de nanocompósitos de ferrita de cobalto e poliestireno
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2009-12-15
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Universidade Federal de Goiás
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In this work, magnetic nanocomposites based on cobalt ferrite/polystyrene with aproximately 30 % of encapsulated ferrite and average diameter of 100 nm were prepared through miniemulsion polymerization with poly(vinyl alcohol) (PVA) as emulsifying agent. The cobalt ferrite was synthesized through coprecipitation technique followed by the formation of hydrophobic gel constituted of nanoparticles surfactated with oleic acid. Ferrite gel was separated by simple filtration and directly dispersed in styrene monomer for encapsulation, even after drying and storage for several days. After ferrite gel dispersion in styrene, it was produced a miniemulsion in water through mechanical agitation with high speed in the presence of PVA. This system was polymerized at 70 oC with sodium persulfate as initiator. The grafting of PVA on polystyrene surface was investigated. The hydroxyl groups of PVA on the surface of cobalt ferrite/polystyrene nanocomposite were esterified in aqueous medium with stearic acid and dodecylbenzene sulfonic acid as catalyst and surfactant directly in polymerization reactor. Cobalt ferrite nanoparticles in the form of powder and gel, magnetic cobalt ferrite/polystyrene nanocomposites non-esterified and esterified were characterized by thermogravimetric analysis and differential thermal analysis (TG/DTA), infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy, X-ray diffraction, transmission electron microscopy (TEM) and dynamic light scattering. Dispersions in mineral oil of CoFe2O4 gel and CoFe2O4/polystyrene nanocomposite esterified with concentrations of 0,05%; 0,1%; 0,2%; 0,5% e 1,0% (w/v) were characterizated by particle size distribution and stability. The presence of NaCl in CoFe2O4 gel and in CoFe2O4/polystyrene nanocomposite esterified induced corrosion reactions of CoFe2O4 nanoparticles at high temperatures during TG/DTA analysis. NaCl contamination also prevented the correct determination of CoFe2O4 content in the gel and in the esterified nanocomposite. The nanofluid with 1% of CoFe2O4/polystyrene nanocomposite esterified was more stable than all nanofluids of ferrite gel. The presence of agglomerates in mineral oil dispersion of CoFe2O4 gel and CoFe2O4/polystyrene nanocomposite esterified can be due the presence of NaCl and the inefficiency of mechanical dispersion process
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CRUZ, Fábio Pereira da. Preparation and chemical modification of latex-based nanocomposite magnetic cobalt ferrite and polystyrene. 2009. 69 f. Dissertação (Mestrado em Educação em Química) - Universidade Federal de Goiás, Goiânia, 2009.