Sphere-to-Wormlike Network Transition of Block Copolymer Micelles Containing CdSe Quantum Dots in the Corona

Poly(styrene-b-4-vinylpyridine) (PS404-b-P4VP(76), 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, PS404-b-P4VP(76) 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 T-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.