Synthesis and characterization of oleic acid coated maghemite nanoparticles to obtain insulating oil based magnetic fluids

Made available in DSpace on 2014-07-29T15:12:48Z (GMT). No. of bitstreams: 1 Dissertacao - Wesley Renato Viali.pdf: 3929545 bytes, checksum: b4e900de56f7f751a05beaeb0b326f0b (MD5) Previous issue date: 2009-03-18In this work maghemite nanoparticles were synthesized by co-precipitating Fe2+ and Fe3+ in alkaline medium. The freshly prepared magnetite was oxidized by two different routes: by bubbling O2 through an acid suspension of magnetite nanoparticles or by hydrothermal treatment of magnetite with ferric nitrate/nitric acid solution. After oxidation, the nanoparticles were covered with oleic acid and the grafting coefficient was evaluated according to the oxidation method and pH employed in the adsorption experiments. The covered particles were dispersed in mineral and vegetable insulating oils, resulting in magnetic fluids whose colloidal stability was investigated in regard to the following parameters: dilution, heating, water content, chemical composition of insulating oils and addition of oleic acid. The nanoparticles were characterized by X-ray diffratometry, thermogravimetric and differential thermal analyses and infrared spectroscopy. The Fe3+/Fe2+ molar ratio in the solids was determined by UV-Vis spectrometry. The magnetic fluids were characterized regarding the volume fraction of nanoparticles, the water content, and their colloidal stability was monitored by dynamic light scattering measurements and visual observations. The results obtained from the analyses indicated that the oxidized magnetite nanoparticles (5 to 10 nm) have inverse spinel structure and Fe3+/Fe2+ molar ratio varied from 20 to 70, depending on the oxidation method and employed conditions. The grafting coefficient varied from 2,1 to 4,8, reflecting the oleic acid adsorption conditions, and the further treatments. It was also observed that by controlling the experimental conditions, a grafting coefficient very close to a Langmuir s monolayer can be achieved, together with a decrease in the amount of physisorbed species which contribute negatively to the colloidal stability. The study of colloidal stability showed that dilution, heating and XVII water content have a great influence in the sedimentation of diluted magnetic fluids, when they are diluted with minerals insulating oils. It was verified that the magnetic fluids diluted with vegetable insulating oil showed very high colloidal stability in the accelerated thermal aging experimentNeste trabalho foram preparadas nanopartículas de maghemita pelo método da coprecipitação de íons Fe3+ e Fe2+ em meio básico. A magnetita inicialmente obtida foi oxidada utilizando-se gás oxigênio ou solução de nitrato férrico/ácido nítrico. Após a oxidação, as nanopartículas foram revestidas com ácido oleico e a eficiência deste processo foi avaliada em função do método de oxidação e do pH de adsorção. As partículas revestidas foram dispersas em óleos isolantes dos tipos naftênico, parafínico ou vegetal, resultando em fluidos magnéticos cujas estabilidades coloidais foram avaliadas em função dos seguintes parâmetros: diluição, aquecimento, teor de água, natureza do meio dispersante e adição de ácido oleico. As nanopartículas foram caracterizadas por difratometria de raios X, análise termogravimétrica e térmica diferencial e espectroscopia de infravermelho. A razão Fe3+/Fe2+ nos sólidos foi determinada por espectrofotometria no visível. Os fluidos magnéticos foram caracterizados quanto à fração volumétrica de nanopartículas e ao teor de água, e sua estabilidade coloidal foi acompanhada por espalhamento dinâmico de luz e por medidas visuais de turbidez. Os resultados das análises e experimentos indicaram que as nanopartículas de magnetita oxidada (5 a 10 nm) apresentaram estrutura espinélio inverso e razão Fe3+/Fe2+ desde 20 até 70, dependendo do método e condições de oxidação empregadas. O coeficiente de revestimento variou de 2,1 a 4,8, refletindo tanto as condições utilizadas nos procedimentos de adsorção do ácido oleico, como também os tratamentos subseqüentes. Demonstrou-se que através do controle das condições experimentais pode-se obter um revestimento muito próximo ao de uma monocamada de Langmuir, bem como reduzir a quantidade de XV espécies moleculares fisissorvidas que contribuem negativamente para a estabilidade coloidal. O estudo da estabilidade coloidal mostrou que a diluição, o aquecimento e o teor de água favorecem a sedimentação dos fluidos magnéticos quando estes são diluídos em óleos isolantes naftênico e parafínico. Verificou-se que os fluidos magnéticos em óleo vegetal quando em frações volumétricas baixas apresentaram alta estabilidade coloidal em experimentos de envelhecimento acelerad

Síntese e caractrização de nanopartículas magnéticas do tipo caroço@casca de 'CO'@'PD' com propriedades para aplicações tecnológicas

A proposta deste trabalho foi a síntese e caracterização de nanoestruturas caroço@casca de cobalto@paládio através do método de crescimento mediado por sementes. Foram utilizados como caroços magnéticos nanopartículas de cobalto obtidas pelo método da decomposição térmica assistida por redutores, utilizando alcanodiois e trietilborohidreto de lítio como redutores. Foram avaliados os efeitos do redutor utilizado para a síntese dos núcleos magnéticos, assim como os efeitos da taxa de aquecimento, concentração do precursor metálico, razão molar entre percussor metálico e agentes de superfície. O diâmetro médio das nanopartículas utilizando alcanodiol como redutor variou entre 9 e 12 nm, estas nanopartículas apresentam forte interação magnética e se mostraram não adequadas para a realização da etapa de crescimento da casca de metal nobre. O diâmetro médio das nanopartículas utilizando trietilborohidreto de lítio como redutor variou entre 3 e 7 nm. Neste método foi avaliada a influência da presença de precursor de metal nobre no meio reacional e crescimento do núcleo magnético através da metodologia de crescimento de sementes. As nanopartículas de cobalto obtidas por este método apresentaram comportamento superparamagnético em temperatura ambiente se mostrando adequadas para a etapa de formação da casca de metal nobre. Algumas nanoestruturas caroço@casca foram obtidas através da metodologia de crescimento via sementes, onde foram utilizados como sementes de nucleação as nanopartículas de cobalto e também nanoestruturas Co@Pd. A formação da casca de paládio foi avaliada em função da concentração de precursor de paládio no meio reacional. Também foi avaliada a obtenção de nanoestruturas caroço@casca utilizando etapas consecutivas para melhor ajuste do diâmetro final. Essas...The aim of this work was the synthesis and characterization of core@shell nanostructures through seed mediated growth, in which the magnetic cores were cobalt nanoparticle obtained by thermal decomposition of organometallic compounds in the presence of reductants, namely alkanediol and lithium triethylborohydride. The effects of reductant used in the magnetic cores were evaluated, as well as the effect of heating rate, the concentration of the metal precursor, the molar ratio between metal precursor and surfactants. The average diameter of the nanoparticles using alkanediol as reductant varied from 9 to 12 nm, these nanoparticles exhibit strong magnetic interactions and proved not suitable to carry out the formation of noble metal shell layer. The average diameter of nanoparticles using triethylborohydride as reductant varied from 3 to 7 nm. Using this synthetic route, the presence of noble metal compounds during the reduction step and the seed mediated grown of magnetic cores were evaluated. The cobalt nanoparticles synthetized showed superparmagnetic behavior at room temperature allowing its use as magnetic cores in the synthesis of noble metal shell. The core@shell nanostructures were synthetized by seed mediated route, using as seed the cobalt nanoparticles and other Co@Pd nanostructures. The palladium shell formation was evaluated as a function of concentration of palladium precursor in the reaction medium. The increase of palladium content of shell was evaluated repeating the step of formation of palladium layer, obtaining onion like structures. The nanostructures exhibited lower average diameters in comparison with their magnetic cores. Nonetheless the average diameter can be adjusted by tuning the experimental conditions, like increasing in palladium precursor contents. The average diameter of... (Complete abstract click electronic access below

Aqueous Nanofluids Based on Copper MPA: Synthesis and Characterization

<div><p>The application and use of efficient cooling fluids have become increasingly important due to the increasing industrial and energy demand associated with the miniaturization of various electronic devices. The search for high-efficiency heat exchanger fluids in the early 1990s led to the development of a new class of refrigerants called nanofluids. The use of nanofluids is linked to obtaining stable colloidal dispersions which exhibit high thermal conductivity. For this purpose, the efficiency of a nanofluid will depend on the type of fluid used and the dispersed nanomaterial. In this work, a stable aqueous nanofluid based on mercaptopropionic acid-coated copper sulfide nanoparticles (Cu2S/MPA), synthesized by the chemical reduction method, was developed. The nanofluid presented colloidal stability in alkaline medium and an average increase of 36% in thermal conductivity for a volumetric fraction of 0.05%.</p></div

PEGylation of SPIONs by polycondensation reactions: A new strategy to improve colloidal stability in biological media

In this study, we report on a new route of PEGylation of superparamagnetic iron oxide nanoparticles (SPIONs) by polycondensation reaction with carboxylate groups. Structural and magnetic characterizations were performed by X-ray diffractometry (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and vibrating sample magnetometry (VSM). The XRD confirmed the spinel structure with a crystallite average diameter in the range of 3.5-4.1 nm in good agreement with the average diameter obtained by TEM (4.60-4.97 nm). The TGA data indicate the presence of PEG attached onto the SPIONs' surface. The SPIONs were superparamagnetic at room temperature with saturation magnetization (M S) from 36.7 to 54.1 emu/g. The colloidal stability of citrate- and PEG-coated SPIONs was evaluated by means of dynamic light scattering measurements as a function of pH, ionic strength, and nature of dispersion media (phosphate buffer and cell culture media). Our findings demonstrated that the PEG polymer chain length plays a key role in the coagulation behavior of the Mag-PEG suspensions. The excellent colloidal stability under the extreme conditions we evaluated, such as high ionic strength, pH near the isoelectric point, and cell culture media, revealed that suspensions comprising PEG-coated SPION, with PEG of molecular weight 600 and above, present steric stabilization attributed to the polymer chains attached onto the surface of SPIONs. © 2013 Springer Science+Business Media Dordrecht