Phase behaviour and structure of amphiphilic poly(ethylene oxide)-poly(propylene oxide)triblock copolymers((EO)_4(PO)_59(EO)_4and(EO)_17(PO)_59(EO)_17)in ternary mixtures with water and xylene

摘要

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 deg 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 mormal("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.