Formation of micelles with complex coacervate cores.

Micelles are commonly regarded as colloidal structures spontaneously formed by amphiphilic molecules, that is, molecules consisting of two distinct parts of which one is soluble and the other is insoluble. This definition is too restrictive: other kinds of molecules can also form micelles. We report on the formation of micelles from a mixture of a (water-soluble) polyanion and a diblock copolymer with two entirely water-soluble blocks: one cationic and one neutral. The cationic block forms a complex coacervate with poly(acrylic acid); the neutral block serves as a stablizing block, prohibiting the growth of the complex coacervate droplets to macroscopic sizes. The formation of these micelles upon mixing is preceded by a macroscopic phase separation. The polymer-rich phase which initially forms rearranges into a stable micellar solution.