Block copolymer micelles in selective solvents are of great interest across a range of technologies, including drug delivery, imaging, catalysis, lubrication, and extraction. While block copolymers generally adopt the morphologies familiar in small molecule surfactants and lipids, one key difference is that polymeric micelles are typically not at equilibrium. The primary reason is the large number of repeat units in the insoluble block, Ncore, which often makes the critical micelle concentration (CMC) too small to accessed experimentally; however, in the proximity of a critical micelle temperature (CMT), equilibration is possible. When micelles are significantly larger than the equilibrium size, fragmentation mechanisms become operative. We will describe measurements of fragmentation using dynamic light scattering, small-angle X-ray scattering, and liquid-phase TEM, on a series of polybutadiene-b-polyethylene oxide diblocks in ionic liquids. Micelles larger than the equilibrium size are prepared by a direct dissolution protocol; the distance to equilibrium can also be systematically tuned by changing the solvent after formation. The dependence of the fragmentation rate on molecular weight, interfacial tension, and distance to equilibrium, will all be described.

Fragmentation kinetics in block copolymer micelles

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