Preparation and photo/chemical-activation of wormlike network micelles of core-shell quantum dots and block copolymer hybrids

Poly(styrene-b-4-vinylpyridine) diblock copolymers PS(404)-b-P4VP(76) and PS(317)-b-P4VP(76) (the subscripts indicate the degree of polymerization) self-assemble into spherical "crew-cut" micelles with a PS core and P4VP corona when prepared in a mixture of chloroform and 2-propanol. When the micelles are formed in the presence of quantum dots (QDs), the nature of the structures formed depends upon the polymer and the type of QDs. In our previous report [Macromolecules, 2010, 43, 5066-5074], PS(404)-b-P4VP(76) + CdSe QDs formed stable spherical hybrid micelles, but prolonged vigorous stirring of the solutions led to a rearrangement into wormlike networks and loss of photoluminescence (PL) from the QDs. Here we report that PS(317)-b-P4VP(76) + CdSe/ZnS core-shell QDs behave differently. Partial loss of PL intensity occurred upon addition of 2-propanol to the chloroform solution of the components, and the rearrangement to a network structure occurred spontaneously. We describe two strategies for recovery of the PL intensity for the QDs within the network, photo-activation and chemical activation with elemental sulfur.