Controlled release of volatile fragrance molecules from PEO-b-PPO-b-PEO block copolymer micelles in ethanol-water mixtures.

Active materials that can solubilize in different compartments of a sample show release properties which might be of interest in some applications where a delayed release of solutes for instance is required. We studied perfume solutes in compartments of Pluronic block copolymers of different compositions and molecular weights over a range of ethanol-water mixtures. Phase diagrams were constructed to identify and map micellar phases, then dynamic light scattering was used to characterize the solute-swollen micelles; NMR provided with the partition of solutes between solvent and micelles, and equilibrium constants K(c) were estimated using headspace analysis. Finally solute-evaporation rates were measured by thermogravimetry. We focused on two typical behaviors: when solubilization in a micellar compartment occurs, delayed release increased with K(c). When solubilization was limited or absent, either because no micelles form or, in the presence of micelles, because solubilization was minor or absent, delayed release was correspondingly absent.