Temperature and concentration effects on supramolecular aggregation and phase behavior for poly(propylene oxide)-b-poly(ethylene oxide)-b-poly(propylene oxide) copolymers of different concentration in aqueous mixtures, 2

摘要

The micro- and mesoscopic structure of reverse Pluronic 25R4 in aqueous mixtures has been studied by SANS, SAXS and shear rheology. These techniques have been able to give a deep insight into the complex structure of the system phase diagram, that includes an isotropic water-rich liquid phase L_1, and liquid crystalline phases with hexagonal, E, or lamellar order, D.Particular attention has been paid to the isotropic water-rich phase L_1, which has a large stability region in the temperature-composition phase diagram. This region is crossed by a large " cloudy zone" Below it, namely at low temperature and composition, SANS data show the presence of polymer unimers in a gaussian coil conformation. Above the " cloudy zone", at higher temperature and composition, the L_1 phase is structured as a network of interconnected multimeric micelles. Rheology adds information about the structuring of the L_1 phase showing its incipient hexagonal pre-structuring. This technique is also able to highlight the defective structure of the E phase itself.In the temperature and concentration ranges in which a lamellar phase D is present, SANS and SAXS results are in complete agreement, showing how interlamellar distance is influenced by both polymer composition and temperature according to an " ideal deswelling" or a " not ideal swelling" mechanism. In addition, in the D phase rheology suggests the presence of densely packed vesicles.