Polyoxyalkylene Block Copolymers in Formamide−Water Mixed Solvents: Micelle Formation and Structure Studied by Small-Angle Neutron Scattering

Abstract

We investigated the solution properties of an amphiphilic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO−PPO−PEO) block copolymer (Pluronic P105: EO37PO58EO37) in mixed solvents consisting of water and formamide (a nonaqueous polar solvent). The critical micellization concentration and temperature, the thermodynamic parameters of micellization, and the micelle structural parameters were obtained from small-angle neutron scattering (SANS) as a function of the formamide−water ratio, solution temperature, and block copolymer concentration. PEO−PPO−PEO block copolymers self-assemble in formamide−water mixed solvents with increasing temperature, indicating an endothermic micellization. Upon an increase of the formamide−water ratio, the enthalpy and entropy of micellization become smaller than the respective quantities in water. The micelle core and corona radii, the hard-sphere interaction distance of the micelles, the micelle association number, as well as the polymer volume fraction in...