Direct Observation of Block Copolymer Micelle Fragmentation

Block copolymers (BCPs) self-assemble into various micellar nanostructures in block selective solvents, which can be applied in a host of diverse technologies including drug delivery, viscosity modification, and nanoreactor design. To fully realize these practical uses, the mechanisms for BCP micellization and equilibration must be elucidated. Micelle fragmentation, fusion, and chain exchange are all possible relaxation mechanisms. Fragmentation has not been studied in detail. We use temperature-jump dynamic light scattering (T-jump DLS), synchrotron small-angle X-ray scattering (SAXS), and liquid-phase transmission electron microscopy (LP-TEM) to develop a quantitative understanding of micelle fragmentation kinetics in ionic liquids (ILs). Fragmentation of 1,2-polybutadiene-b-poly(ethylene oxide) was observed for various molecular weights in one IL using LP-TEM. The fragmentation kinetics were studied with time-resolved SAXS and T-jump DLS. By combining these experimental techniques, a detailed analysis of micelle fragmentation kinetics, along with the direct observation of intermediate structures during fragmentation events, was conducted.