Phase behaviour and structure of amphiphilic poly(ethylene oxide)-poly(propylene oxide) triblock copolymers ((EO)(4)(PO)(59)(EO)(4) and (EO)(17)(PO)(59)(EO)(17)) in ternary mixtures with water and xylene

The isothermal ternary phase behaviour and structure of amphiphilic copolymer-water-xylene systems was investigated for two poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) triblo
k copolymers, (EO)(4)(PO)(59)(EO)(4) and (EO)(17)(PO)(59)(EO)(17), at 25degreesC. The phase boundaries were identified using H-2 NMR and inspection under polarized light. The microstructure and structural length scales in the lyotropic liquid crystalline phases were determined and characterized by small-angle X-ray scattering. The amounts and relative proportions of the selective solvents can modulate the resulting microstructures, although the phase sequence observed depends on the relative PEO-PPO block ratio. A variety of lyotropic liquid crystalline (LLC) phases are thermodynamically stable in the system with copolymer (EO)(17)(PO)(59)(EO)(17), both of the normal ("oil-in-water") and of the reverse ("water-in-oil") morphology. The high hydrophobic content of copolymer (EO)(4)(PO)(59)(EO)(4), however, favours reverse LLC structures with low interfacial curvature. No normal LLC phases are formed by this system.