Block copolymer micelles enable the formation of widely tunable self-assembled structures in liquid phases, with applications ranging from drug delivery to personal care products to nanoreactors. In order to understand fundamental aspects of micelle assembly and dynamics, the structural properties and solvent uptake of biocompatible poly(ethylene oxide-b-ε-caprolactone) (PEO-PCL) diblock copolymers in deuterated water (D2O) / tetrahydrofuran (THFd8) mixtures were investigated with a combination of small-angle neutron scattering, nuclear magnetic resonance, and transmission electron microscopy. PEO-PCL block copolymers, of varying molecular weight yet constant block ratio, formed spherical micelles through a wide range of solvent compositions. Varying the solvent composition from 10 to 60 % by volume THFd8 in D2O / THFd8 mixtures was a convenient means of varying the core-corona interfacial tension in the micelle system. An increase in THFd8 content in the bulk solvent increased the solvent uptake within the micelle core, which was comparable for the two series, irrespective of the polymer molecular weight. Whereas the smaller molecular weight micelle series exhibited a decrease in aggregation number with increasing THFd8 content in the bulk solvent, as anticipated due to changes in the core-corona interfacial tension, the aggregation number of the larger molecular weight series was surprisingly invariant with bulk solvent composition. Differences in the dependencies of the micelle size parameters (core radius and overall micelle radius) on the solvent composition originated from the differing trends in aggregation number for the two micelle series. In summary, the two micelle series showed similar solvent uptake that was independent of the polymer molecular weight, yet significantly different dependencies of their aggregation number and size parameters on the solvent composition.

Tunable structural properties of block copolymer micelles

256th National Meeting (2018)

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