Structural evolution of mixed micelles due to interchain complexation and segregation investigated by laser light scattering

Polystyrene-b-poly(acrylic acid) (PS-b-PAA) diblock copolymers form micelles in toluene with PAA as the core and PS as the corona. The introduction of poly(methyl methacrylate)-b-poly(ethylene oxide) (PMMA-b-PEO) solution in toluene leads to mixed micelles due to the hydrogen-bonding complexation between PAA and PEO. By using a combination of static and dynamic laser light scattering, we have investigated the evolution of the mixed micelles. Our results revealed that the complexation between PAA and PEO in the core and the segregation between PS and PMMA in the corona as a function of the molar ratio (r) of PEO to PAA manipulate the evolution. At r < approximately 1.0, the mixed micelles hold a spherical structure after a long-time standing. However, at r > approximately 1.0, the average radius of gyration Rg, the average hydrodynamic radius , and the ratio / of the mixed micelles increase with time, whereas the molar mass (Mw) does not change. The facts indicate that the mixed micelle has evolved from a spherical structure to a hyperbranched structure.