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

Abstract

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.

Role of PPO–PEO–PPO triblock copolymers in phase transitions of a PEO–PPO–PEO triblock copolymer in aqueous solution

“…The single PEO-PPO-PEO triblock copolymers [1-9] and PPO-PEO-PPO triblock copolymers [44][45][46] have been studied extensively in the literature. Since PPO blocks in both PEO-PPO-PEO and PPO-PEO-PPO copolymers are of the same chemical structure, it is reasonable to infer that PPO blocks of PPO-PEO-PPO copolymers would be able to participate in the micellization of PEO-PPO-PEO copolymers, and then affect the gelation.…”

“…As the temperature further increases, G′ increases dramatically at 57G′ and G" reach to a plateau. Considering D'Errico's experimental results[45], we think that the increase in G′ and G" in the region II should be attributed to association of PPO blocks, while the formation of a lyotropic liquid crystal (LLC) phase at the higher temperatures contributes to the high elasticity (the region III). But the formation of LLC phase has a strong dependence on 25R4 concentration because a LLC phase was not observed in our previous experiments for the aqueous solutions of low 25R4 concentrations (13.2 and 17.1 wt%)[47,48].…”

“…In concentrated solutions (above 40 wt%), the two outer PPO blocks of a chain joined in the same micelle, so that the looping shaped micelles were formed. Recently, D'Errico et al [45] further studied the change in the microstructure of 25R4 (PPO 19 -PEO 33 -PPO 19 ) with increasing 25R4 concentration, which included the isotropic water-rich solution phase, hexagonal phase, lamellar phase and isotropic polymer-rich solution phase. Kell et al [46] studied 25R8 (PPO 15 -PEO 156 -PPO 15 ) and found that the formation of large domains of networks of copolymer strands interconnected randomly through the hydrophobic PPO end blocks for aqueous solutions of low 25R8 concentrations.…”

Gels with sense: supramolecular materials that respond to heat, light and sound

“…9), which exhibit lower polarity at higher temperatures due to increased conformational flexibility. 139,140 Heating therefore causes the fibres to become more hydrophobic, resulting in increased aggregation and expulsion of solvent beyond 70 o C. The swollen gel can be regenerated slowly by cooling or, more rapidly, through redox-induced sol-gel and gel-sol transitions.…”

Premicellar interaction of PEO–PPO–PEO triblock copolymers with partially hydrophobic alcohols: NMR study

“…Above the critical micellar temperature (CMT), the copolymers usually form micelles with a micellar core consisting mostly of PPO blocks and a corona in the outer part of the micelle made up of more hydrophilic PEO blocks, which render the associate its thermodynamic stability in water. The dynamics of micellization and macrophase separation of the (EO) 13 (PO) 30 (EO) 13 copolymer Pluronic L64 was studied using time‐resolved DLS, SANS, and time‐resolved fluorescence …”