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

Abstract

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) triblock copolymers, (EO)4(PO)59(EO)4 and (EO)17(PO)59(EO)17, at 25°C. The phase boundaries were identified using 2H 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.Key words: amphiphilic, triblock copolymers, poly(ethylene oxide), poly(propylene oxide), ternary mixtures, phase behaviour, lyotropic liquid crystals, SAXS, 2H NMR.