Micellar Structure of an Ethylene Oxide−Propylene Oxide Block Copolymer:  A Small-Angle Neutron Scattering Study

Abstract

Micellar solutions of a highly hydrophilic ethylene oxide−propylene oxide triblock copolymer, pluronic F88 (EO10 3PO39EO10 3), in aqueous solution are examined by small-angle neutron scattering (SANS) at different concentrations and temperatures and in the presence of different salts. At temperature less than 30 °C, F88 solution in water (5 wt %) showed unimers which are fully dissolved Gaussian chains. The unimer-to-micelle transition takes place when the temperature or concentration is increased. Added neutral salt favors micellization of the copolymer at lower concentration/temperature. At temperature close to ambient, block copolymer forms micelles that consist of a central core, presumably dominated by the propylene oxide blocks, surrounded by a corona of highly hydrated ethylene oxide subchains. SANS analysis shows that the size of hydrophobic core increases as a part of PEO adjacent to the PPO core loses water with increasing temperature or salt (KCl) concentration. The micellar volume fraction increases with increasing concentration of block copolymer. The salting out effect of different electrolytes on structure of micelles is in the order KCI > KBr > KI. The effect of temperature on micellar solutions in the presence of KCl is also examined. It has been observed that the effect of added salt on the structural phase behavior of block copolymer is analogous to that of temperature. In all the above study, micelles are found to be spherical.

Effect of Salts on the Micellization, Clouding, and Solubilization Behavior of Pluronic F127 Solutions

“…Jain et al (7) reported that salts did not change the aggregation number of F88 significantly; however, the size of the hydrophobic micellar core of Pluronic F88 was thought to increase as KCl was added, due to the greater loss of water from the PEO adjacent to the PPO core. In view of this, and since the cmt is lower in the presence of salts, we are led to the conclusion that more micelles with a larger hydrophobic volume are present in F127/salt solutions, explaining reduced excimer formation.…”

“…It is generally accepted (10,20) that the aggregation number of Pluronic micelles does not change with copolymer concentration, but increases with temperature. However, the effect of salts on aggregation number is not well-understood (4,7).…”

Development and characterization of thermosensitive pluronic-based metronidazole in situ gelling formulations for vaginal application

“…It has been shown that gel formation is a result of micellar enlargement and packing and that the gel is more entangled at higher PF-127 concentrations. As a result of these micelle entanglements, they cannot separate easily from each other, which accounts for the rigidity and high viscosity of gels containing high concentrations of pluronics (15,16). (F 6 ) and 20/15 (%) (F 8 ) showed 14.4-and 1.1-fold higher viscosity than the other formulations, respectively.…”

New micellar morphologies from amphiphilic block copolymers: disks, toroids and bicontinuous micelles

“…1 The most common structures formed by these amphiphilic macromolecules are spherical micelles, cylindrical micelles and vesicles (polymersomes). [2][3][4][5][6][7][8][9][10][11][12] The morphology of the aggregate depends upon the relative volume ratio of the different blocks and upon the packing parameter (p), where…”