Efeito de contra-íon em complexos poli(oxietileno)-dodecilsulfato :: determinação da concentração de contra íons aromáticos em micelas de cetiltrimetilamônio através da reação de decomposição de um sal de diazônio /

Tese (Doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas

Efeitos de micelas funcionais de decilfosfato de sodio sobre a hidrolise acida de acetais

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciencias Fisicas e MatematicasMicelas de dodecilsulfato de sódio aumentam a velocidade de hidrólise ácida dos acetais di-terc-butil benzaldeído e di-butil benzaldeído. A reação do di-terc-butil benzaldeído geralmente sofre catálise ácida e na presença de micelas mistas de dodecilsulfato de sódio e decilfosfato de sódio a constante de velocidade aumenta linearmente com o aumento de fração molar de decilfosfato de sódio, portanto o principal objetivo deste trabalho é verificar o efeito do decilfosfato sobre a hidrólise de acetais. Entretanto tal comportamento não é observado para o acetal de di-butil benzaldeído onde a constante de velocidade independe da fração molar de fosfato

Discrepancies over the onset of surfactant monomer aggregation interpreted by fluorescence, conductivity and surface tension methods

Molecular probe techniques have made important contributions to the determination of microstructure of surfactant assemblies such as size, stability, micropolarity and conformation. Conductivity and surface tension were used to determine the critical aggregation concentration (cac) of polymer-surfactant complexes and the critical micellar concentration (cmc) of aqueous micellar aggregates. The results are compared with those of fluorescent techniques. Several surfactant systems were examined, 1-butanol-sodium dodecylsulfate (SDS) mixtures, solutions containing poly(ethylene oxide)-SDS, poly(vinylpyrrolidone)-SDS and poly(acrylic acid)-alkyltrimethylammonium bromide complexes. We found differences between the cac and cmc values obtained by conductivity or surface tension and those obtained by techniques which use hydrophobic probe

New Evidence for an Episode of Accelerated Environmental Change in the Late Barremian: Geochemical and Paleontological Records from the Subbetic Basin (Western Tethys)

We investigate a new event of accelerated environmental change that was recorded during the late Barremian in the pelagic Subbetic Basin (Western Tethys). Two pelagic sections have been studied using a multi-proxy approach based on C-isotope stratigraphy and a high-resolution quantitative study of nannofossil assemblages, along with major and trace elements and biomarkers. Our results provide a detailed biostratigraphy and C-isotope stratigraphy, and outline the paleoenvironmental conditions recorded during the early stages of the Taxy Episode. A disturbance has been identified in the C-isotope record, called the IFeNE (Intra-Feradianus negative C-excursion), which is coeval with environmental and biotic changes that predate the well-known ISNE (Intra-Sarasini negative C-excursion). The combined analysis of nannofossil associations, C-isotopes, major and trace elements, and biomarker distributions indicates a separate episode of warming heralding the ISNE, resulting in the acceleration of the hydrological cycle and a consequent increase in continental inputs and the fertilization of surface waters. The origin of the Taxy Episode (the IFeNE and ISNE) has been related to orbital factors (high-eccentricity cycles), and to a global increase in volcanism, probably related to the early phases of the Ontong Java Plateau