Dual color fluorescence cross-correlation spectroscopy was applied to measure the equilibrium chain exchange kinetics of amphiphilic diblock copolymer micelles. As a model system we choose the copolymer polystyrene-block-poly[oligo-(ethylene glycol) methyl ether methaxrylate] (PS-POEGMA) comprising a linear-brush architecture forming micelles with a thin and bulky corona [FIG. 1].
FIG. 1: Scheme of the dynamic equilibrium chain exchange of amphiphilic diblock copolymer micelles formed by PS-POEGMA.
The exchange was monitored in different solvents and at various temperatures showing the reliability of the method.[1] In methanol as a solvent, the exchange persists even at temperatures well below the nominal glass transition of the core forming PS suggesting that the methanol swells the micelle core. At the same temperatures no exchange could be observed when pure water is used as a solvent. Furthermore, even small changes in solvent quality can slow down or fasten the exchange by orders of magnitude. This tremendous impact of solvent quality allows extensive tuning of the exchange kinetics.
[1] Schaeffel et al., ACS Macro Lett. 2014, (doi: 10.1021/mz500169n)
