Phase Behavior and Microstructure in Binary Block Copolymer/Selective Solvent Systems: Experiments and Theory

A combined experimental and theoretical study of phase behavior and structure in binary systems of block copolymers and a selective solvent is presented. The block copolymers used here consist of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), and the solvent is water, selective for the PEO block. The concentration−temperature phase diagrams of (EO)8(PO)47(EO)8 (Pluronic L92) and (EO)11(PO)70(EO)11 (Pluronic L122) in water have been determined experimentally. These two block copolymers are unique in that they form both normal (H1, “oil-in-water”) and reverse (H2, “water-in-oil”) hexagonal lyotropic liquid crystalline structures in binary systems with water over the same temperature range. This is the first time the H2 structure is reported in a binary PEO−PPO−PEO/water system. Thereafter, the predicted phase diagram of (EO)20(PO)69(EO)20 in water is given, employing a self-consistent mean-field lattice theory with internal degrees of freedom. The free energy for a number of possible microstruc...