Direct Observation of Block Copolymer Micelle Fragmentation in Ionic Liquids

Recently, attention has been directed to quantifying the relaxation kinetics of block copolymer micelles, such as micelle fragmentation and fusion. Studies on block copolymer micelle fragmentation typically involve indirect techniques such as small angle scattering and ex-situ transmission electron microscopy. In this work, the direct observation of fragmentation in 1,2-polybutadiene-block-poly(ethylene oxide) (PB-PEO) micelles in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide was achieved using high-temperature liquid-phase transmission electron microscopy. The kinetics of PB-PEO fragmentation were also studied for various molecular weights in one ionic liquid using time-resolved small-angle X-ray scattering and dynamic light scattering. By combining these experimental techniques, a detailed analysis of the effect of molecular weight on micelle fragmentation kinetics, along with the observation of intermediate structures during fragmentation events, was conducted. These experiments provide further insights into the equilibration kinetics of block copolymer micelles via fragmentation and the mechanism of fragmentation itself.