Sphere-to-wormlike network transition of block copolymer micelles containing cdSe quantum dots in the corona

Poly(styrene-b-4-vinylpyridine) (PS₄₀₄-b-P4VP₇₆, where the subscripts refer to the number-averaged degree of polymerization) forms spherical crew-cut micelles with a PS core and a P4VP corona when 2-propanol is added to a solution of the polymer in chloroform. When the CHCl₃ solution also contains CdSe quantum dots, hybrid micelles form with the QDs bound to the corona. Here we report that vigorous magnetic stirring of a solution of these hybrid micelles in a solution containing 73 vol % 2-propanol leads to a morphology transformation to form three-dimensional wormlike networks that have structural features similar to that first reported by Jain and Bates [Science 2003, 300, 460-464] for a poly(butadiene-b-ethylene oxide) block copolymer in water. Under the influence of shear, PS ₄₀₄-b-P4VP₇₆ micelles appear to aggregate and then rearrange to form colloidally stable networks consisting of wormlike micelles, uniform in width, that are present as loops and tails connected by T- and Y-junctions. The wormlike micelles are similar in width to the original hybrid micelles, whereas the tails of the micelles have thicker bulbous end-caps. This morphology transition is extremely sensitive to solvent composition and is also affected by the stirring rate.