SELF-ASSEMBLY IN A MIXTURE OF 2 POLY(ETHYLENE OXIDE)-B-POLY(PROPYLENEOXIDE)-B-POLY(ETHYLENE OXIDE) COPOLYMERS IN WATER

The self-assembly behavior in water,of a mixture of two poly (ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) copolymers, (EO )(13)(PO)(30)(EO)(13) (L64) and (EO)(37)(PO)(58)(EO)(37) (P105), was e xplored at 25 degrees C. The phase boundaries were established using H -2-NMR and inspection under polarized light; the structure of the vari ous lyotropic liquid crystalline (LLC) phases was determined with smal l-angle X-ray scattering, while viscosity and differential scanning ca lorimetry measurements were used to probe the isotropic water-rich sol ution region. Isotropic regions, similar to the neat polymers, are sta ble at high polymer content. The addition of water induces structure i n the amphiphilic block copolymer system. An extended lamellar (D)LLC phase is formed at 20-25% water content; a hexagonal (E) and a cubic ( I) LLC phases supersede D at higher water contents. In addition to the above, a narrow isotropic region (L') is observed on the L64-water bi nary axis, in equilibrium with the E and the D phases. The hexagonal a nd lamellar LLC phases extended all the way from the L64-rich to the P 105-rich side of the ternary L64-P105-water phase diagram; the charact eristic hexagonal and lamellar structural dimensions varied linearly w ith P105 content in the L64-P105 mixture at a constant water concentra tion, An isotropic (micellar) solution phase (L(1)) dominates the high -water content corner of the ternary phase diagram, Viscosity measurem ents in this region provided evidence for increased interactions betwe en the micelles as the boundary to the LLC phases was approached. (C) 1996 Academic Press, Inc.