Equilíbrio líquido-líquido de sistemas aquosos constituídos por copolímero tribloco e sal em diferentes temperaturas / Liquid-liquid equilibrium of aqueous systems consisting of triblock copolymer and salt at different temperatures

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

Phases diagrams of aqueous biphasic systems (ABS) formed by triblock copolymer+salt+H2O were construed at three temperatures: The ABS L64+Na2SO4+H2O and L64+Li2SO4+H2O at 5, 10 and 25 C and ABS L35+Na2CO3+H2O, F68+Na3C6H5O7+H2O, F68+Na2C4H4O6+H2O, F68+Na2CO3+H2O and F68+Na2C4H4O4+H2O at 10, 25 and 40 C. The effect of temperature on the position of the binodal curve was observed, thus demonstrating that there is an enthalpic contribution to the formation of two phases. The process of phases separation is exothermic for the system L64+Na2SO4+H2O and endothermic for all other systems. It was found that the increase in temperature promoted the increasing slope of tie line (STL). The ability of sodium to induce phases separation in systems containing L64 is higher than that of lithium. The ability of different anions to induce the formation of two-phase systems containing F68 followed the order: CO3 2- >C6H5O7 3- >C4H4O6 2- >C4H4O4 2-. The increase in molar mass of the copolymer resulted in the formation of phase which occurs at lower concentrations of salt and copolymer. In addition to these biphasic systems, an aqueous triphasic system (ATS) was obtained for the first time, formed by the triblock copolymer L64+Li2SO4+H2O. Phases equilibrium data were determined at 25 C. The formation of three phases occurs by a segregative process between the copolymer and salt. Measurements using the technique of small angle x-ray scattering (SAXS) have shown that the intermediate phase and upper phase have different nanostructures, and, possibly, the L64 macromolecules in the upper phase form structures which are similar to the liquid crystal, and in the intermediate phase the copolymer molecules are structured in the form of micelles.

ASSUNTO(S)

copolímero tribloco triblock copolymer quimica analitica biphasic aqueous system salt sal sistema aquoso bifásico

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