Aplicação da microcalorimetria e do espalhamento de raios-x a baixos ângulos no estudo da interação poli (óxido de etileno) e dodecil sulfato de sódio: efeito de cosolutos iônicos

• Autor(a) principal: Mageste, Aparecida Barbosa
• Data de Publicação: 2009
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/2083
• topic: Interação intermolecular; Microcalorimetria; SAXS; Surfactante; Poli-(óxido de etileno); Intermolecular interaction; Microcalorimetry; SAXS; Surfactants; Poly-(ethylene oxide); CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::FISICO-QUIMICA

The influence of the ionic cosolutes NaCl, Na2SO4, Li2SO4, NaSCN, Na2[Fe(CN)5NO] and Na2[Co(NO2)6] in the interaction between poly(ethylene oxide) (PEO), of average molecular weight 35000, and ionic surfactants has been studied. Five parameters were analyzed: critical aggregation concentration (cac), the concentration of saturation (C2), the variation of Gibbs free energy of aggregation (ΔΔGagg), extent of binding and the integral enthalpy change for aggregate formation ΔHagg(int.). The analysis was performed using the isothermal titration calorimetry (ITC) technique and Small Angle X-Ray Scatterning (SAXS). The influence of ionic cosolutes depends on the nature of the electrolyte, since the thermodynamic parameters change depending on the characteristics of the interaction between PEO and each cosolute. The cosolutes NaCl, Na2SO4, Li2SO4, NaSCN at concentrations of 10 and 100 mmol L-1 cause a decrease of the cac and an increased of C2. This behavior indicates that the presence of the electrolyte decreases the interfacial tension between water and macromolecule and / or increases the chemical potential of surfactant. NPS at concentrations of 10 and 100 mM modifies the surfactant- polymer interaction to the point of the curve almost become athermanous, which suggests the absence of surfactant- polymer interaction. Nevertheless, the SAXS data show that the formation of aggregates still occurring. Interestingly, the stability of clusters formed along the polymer chain was not altered by the presence of cosolutes.