Modeling of the phase behavior in Ternary triblock copolymer/water/oil systems

Ternary poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO−PPO−PEO)/water/oil systems have been studied theoretically with a lattice mean-field theory. Phase diagrams for three PEO−PPO−PEO block copolymers are presented, and the existence of the ordered cubic micellar, hexagonal, lamellar, reverse hexagonal, and reverse cubic micellar phases as well as disorded water-rich and water-poor phases was considered. It was found that the length of the EO blocks strongly affected the phase behavior. The lamellar phase was studied in more detail with respect to the domain spacing and interfacial area per PEO block at different compositions and to the polymer conformations. The degree of looplike conformations and of bridging conformations across the apolar domain (PO + oil) was found to be dependent on the apolar domain thickness. Comparison with experimentally determined phase diagrams and lamellar domain spacings was also made.