Kinetics of Block Copolymer Micelle Fragmentation in Ionic Liquids

Recently, more attention has been directed to quantifying the relaxation kinetics of block copolymer micelles. However, there are very few experimental studies quantifying the rates of fragmentation in block copolymer micelles. The micelle radius for poly(1,2-butadiene)-block-polyethylene oxide (BEO) in EO-selective ionic liquids (ILs) depends on the solution preparation method. When BEO is dissolved directly into an IL, the spherical aggregates are large and disperse in size. Upon high temperature annealing, these micelles equilibrate and decrease in size. Exploration of the equilibration kinetics for BEO in ILs is being conducted using temperature-jump light scattering, small-angle X-ray scattering, and liquid-phase transmission electron microscopy. The effects of solvent quality between the B block and the IL were explored in four different ILs. Equilibration occurs after annealing, and the relaxation times exhibit a significant dependence on concentration and solvent quality. SAXS and liquid-phase TEM demonstrate that the core radius decreases by 5 nm after annealing. These experiments demonstrate that relaxation mechanisms other than individual chain exchange dominates in these highly amphiphilic systems.