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

The micro- and mesoscopic structure of reverse Pluronic 25R4 in aq. mixts. was studied by SANS, SAXS and shear rheol. These techniques were able to give a deep insight into the complex structure of the system phase diagram, that includes an isotropic water-rich liq. phase L1, and liq. cryst. phases with hexagonal, E, or lamellar order, D. Particular attention was paid to the isotropic water-rich phase L1, which has a large stability region in the temp.-compn. phase diagram. This region is crossed by a large cloudy zone. Below it, at low temp. and compn., SANS data show polymer unimers in a Gaussian coil conformation. Above the cloudy zone, at higher temp. and compn., the L1 phase is structured as a network of interconnected multimeric micelles. Rheol. adds information about the structuring of the L1 phase showing its incipient hexagonal pre-structuring. This technique is also able to highlight the defective structure of the E phase itself. In the temp. and concn. 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 compn. and temp. according to an ideal deswelling or a not ideal swelling mechanism. In the D phase rheol. suggests densely packed vesicles.