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Phase Behavior of Amphiphilic Block Copolymers in Water−Oil Mixtures: The Pluronic 25R4−Water− p -Xylene System

1996; American Chemical Society; Volume: 100; Issue: 1 Linguagem: Inglês

10.1021/jp951626s

1541-5740

Paschalis Alexandridis, Ulf Olsson, Björn Lindman,

Block Copolymer Self-Assembly

A rich phase behavior with lamellar, normal hexagonal, reverse hexagonal, and bicontinuous cubic liquid crystalline regions, as well as water-rich (L1) and oil-rich (L2) solutions, was observed at 25 °C in a ternary system composed of water, p-xylene, and Pluronic 25R4, an amphiphilic block copolymer of ethylene oxide (EO) and propylene oxide (PO) with the structure (PO)19(EO)33(PO)19. The phase boundaries were identified using 2H-NMR and inspection under polarized light. Small angle X-ray scattering was employed to ascertain the structure of the various liquid crystalline phases formed and to determine the characteristic lengths involved. The sequence of L1, normal hexagonal, lamellar, reverse hexagonal, and L2 phases was observed when replacing water by oil at a constant polymer weight fraction of 0.5. The volume fraction of the apolar components (PPO + oil) can be identified as the major parameter governing the phase behavior. The ternary phase behavior of the PPO−PEO−PPO copolymer is similar to that of the opposite block sequence PEO−PPO−PEO copolymer (Pluronic L64) of comparable molecular weight to 25R4.