The aggregate morphologies of the biamphiphilic triblock PAA(26)-b-PS(890)-b-P4VP(40) have been studied by TEM as a function of pH in DMF/THF/H(2)O mixtures. The outside surfaces of the aggregates were characterized by zeta potential measurements. Starting at the apparent pH (pH) of 1, and increasing gradually to pH14, the aggregate morphologies of this triblock change progressively from vesicles (pH1), to solid spherical or ellipsoidal aggregates (pH3 approximately 11), and finally back to vesicles (pH14). Vesicles prepared at pH1 contain P4VP chains on the outside and PAA chains on the inside, while those prepared from the same triblock at pH14 contain PAA outside and P4VP inside. The segregation is based on the difference in repulsive interactions within the PAA or P4VP corona under different pH conditions. At low pH, the curvature is stabilized through increased repulsive interactions between the P4VP chains on the outside relative to the less repulsive interactions between the PAA chains on the inside. At pH14, by contrast, the PAA is preferentially segregated to the outside and the P4VP to the inside because of the increased repulsive interaction between PAA chains and the decreased repulsive interaction between P4VP chains at high pH. Most importantly, vesicles with PAA on the outside can be inverted to P4VP on the outside by changing the pH while the vesicles have swollen cores and are under dynamic conditions. The conversion mechanism is suggested to involve a whole vesicle process because the CMC is far too low for single chain reassembly to be involved.

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Cadmium sulfide (CdS) quantum dots (QDs) are formed within poly(ethylene oxide)-block-polystyrene-block-poly (acrylic acid) (PEO-b-PS-b-PAA) triblock copolymer aggregates of different architectures. These structures are obtained starting with the same ionically cross-linked primary micelles consisting of a cadmium acrylate core, a PS shell, and a PEO corona. One morphology is a worm-shaped micelle prepared in tetrahydrofuran (THF) in which the CdS QDs are surrounded by the PAA and aligned as a loose necklace in the PS matrix. The PEO serves as a corona around the PS rod. Another structure is a multicore spherical (ca. 50 nm) water soluble PS micelle, surrounded by PEO chains. The CdS particles within these two latter structures are formed by the reaction of cadmium ions present in the acrylate cores with hydrogen sulfide. In a third structure, the CdS QDs are located on the surface of PS micelles. A fourth spherical single-core micelle structure is postulated to exist in dilute THF solutions. The dimensions in all the aggregates can be controlled by the block length.

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