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We study both experimentally and theoretically the self-assembly of binary polycaprolactonepolyethyleneoxide (PCL-PEO) block copolymers in dilute solution, where self-assembly is triggered by changing the solvent from the common good solvent THF to the selective solvent water, and where the two species on their own in water form vesicles and spherical micelles respectively. We find that in water the inter-micellar exchange of these block copolymers is extremely slow so that the resultant selfassembled structures are in local but not global equilibrium (i.e., they are non-ergodic). This opens up the possibility of controlling micelle morphology both thermodynamically and kinetically. Specifically, when the two species are first molecularly dissolved in THF before mixing and self-assembly ('premixing') by dilution with water, the morphology of the formed structures is found to depend on the mixing ratio of the two species, going gradually on a route of decreasing surface curvature from vesicles via an intermediate regime of micelles in the shape of 'bulbed' rods, rings, Y-junctions finally to spherical micelles as we increase the proportion of the "sphere formers". On the other hand, if the two species are first partially self-assembled (by partial exchange of the solvent with water) before mixing and further self-assembly ('intermediate mixing'), novel metastable structures, including nanoscopic 'pouches', emerge. These experimental results are corroborated by self-consistent field theory
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