Please use this identifier to cite or link to this item: http://repositorio.unicamp.br/jspui/handle/REPOSIP/249997
Type: TESE
Title: Síntese de nanopartículas de fosfatos de cálcio em cristais líquidos liotrópicos
Title Alternative: Synthesis of calcium phosphates nanoparticles in liotropic liquid crystals
Author: Campos, Daniella Dias Palombino de
Advisor: Bertran, Celso Aparecido, 1951-
Abstract: Resumo: Sistemas auto-organizados, preparados com surfactantes nonilfenil etoxilados com diferentes tamanhos de cadeia etoxilada, foram utilizados para sintetizar nanopartículas de hidroxiapatita (HAP - Ca5(PO4)3OH), que é o fosfato de cálcio majoritariamente presente nos tecidos mineralizados dos vertebrados. O efeito do tamanho do grupo etoxilado do surfactante foi avaliado tanto na formação dos sistemas auto-organizados quanto nas propriedades das partículas de HAP precipitadas in situ nestes sistemas. Cristais líquidos hexagonal reverso, lamelar, hexagonal e cúbicos foram formados, nesta ordem, a medida que surfactantes com maiores grupos etoxilados foram empregados. Os fosfatos de cálcio sintetizados em todos os sistemas auto-organizados apresentaram-se na forma de nanohastes, de modo que as nanohastes formadas nas fases anisotrópicas (cristais líquidos hexagonais e lamelares) apresentaram diâmetros mais uniformes quando comparadas àquelas sintetizadas nos sistemas auto-organizados isotrópicos. O diâmetro das hastes de HAP comparado com as dimensões dos sistemas auto-organizados sugere que estas se formaram pela aglomeração orientada de partículas ainda menores de HAP, o que foi evidenciado por microscopia eletrônica de varredura (SEM-FEG). Estes resultados, em conjunto com medidas de tempo de relaxação transversal (T2) do hidrogênio das moléculas de água presentes nos sistemas auto-organizados, permitem propor que a limitação do tamanho das nanopartículas de HAP seja conseqüência da limitação da difusão iônica in situ e que a morfologia de hastes é resultante da autoorganização das fases.

Abstract: Self-assembled systems from nonylphenol ethoxylate surfactants were prepared using surfactants with different hydrophilic chain lengths. These systems were used to synthesize hydroxyapatite (HAP - Ca5(PO4)3OH) nanoparticles, the main constituent of vertebrates mineralized tissues. The surfactant hydrophilic length influence was evaluated both on the self-assembled systems formation and on the properties of HAP nanoparticles which were obtained by in situ precipitation in these systems. As the surfactant hydrophilic length increased different liquid crystals were formed in this sequence: reverse hexagonal, lamellar, normal hexagonal and cubic mesophases. HAP nanoparticles synthesized in all selfassembled systems had morphology of rods. Particles precipitated in the anisotropic systems (hexagonal and lamellar liquid crystals) had more uniform diameters compared to particles precipitated in the isotropic systems (cubic liquid crystals). The HAP nanorods diameters were bigger than the repetition distances of the self-assembled systems. This occurrence, evidenced by SEM-FEG micrographs of the HAP nanoparticles, suggests that the nanorods were formed by even smaller HAP particles which were previously confined in the hydrophilic domains of the phases, and after the surfactant removal they were neatly clustered as induced by the self-assembled systems. These results along with the transversal relaxation times measurements (T2) for hydrogen in water molecules belonging self-assembled systems, allow us to propose the following: there is a reduced ionic diffusion within the liquid crystals hydrophilic domains and it is the cause for the size particles limitation and the particles morphology is influenced by the self-assembling of the systems.
Subject: Cristais líquidos
Síntese de nanopartículas
Hidroxiapatita
Language: Português
Editor: [s.n.]
Date Issue: 2012
Appears in Collections:IQ - Tese e Dissertação

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