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 (EO103PO39EO103), 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 incre...