Toroid Micelle Formation by Polyelectrolyte Triblock Copolymers Through the Ion-ion Interaction

摘要

Self assembly of amphiphilies in solution has received tremendous interest due to current and potential applications in the fields of materials science, electrical engineering, molecular biology and pharmaceutical industries. The associative behavior and aggregation structure of small molecular amphiphilies, such as surfactants and lipids, are fairly well understood experimentally and theoretically. Recently, the macromolecular analogues of conventional surfactants, block copolymers, have been recognized for their substantial advantages, such as low critical micelle concentration, more robust assemblies, highly tunable composition and chain architecture, micellization depending on selective solvents, and abilities to trap metastable structure due to slow kinetics. Amphiphilic block copolymers with a polyelectrolyte block have the structural features of surfactant, block copolymer and polyelectrolyte. The combined properties offer a great opportunity to construct materials with novel structure by manipulation of these factors. More importantly, due to the presence of polyelectrolyte block, the associative behavior and final assembled structure can be tuned by added counterions. In this context, we reported that the toroid, or ring, micelle morphology, which is theoretically predicted but rarely observed, has been produced by the self assembly of poly(acrylic acid)-block-poly(methyl acrylate)-block-polystyrene (PAA-b-PMA-b-PS) triblock copolymer in combination with an organic counterion and mixed THF/H2O solvent.