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We study both experimentally and theoretically the self-assembly of binaryblock copolymers in dilute solution, where self-assembly is triggered bychanging the solvent from the common good solvent THF to the selective solventwater, and where the two species on their own in water form vesicles andspherical micelles respectively. We find that in water the inter-micellarexchange of these block copolymers is very slow so that the self-assembledstructures are in local but not global equilibrium (i.e., they arenon-ergodic). This opens up the possibility of controlling micelle morphologyboth thermodynamically and kinetically. Specifically, when the two species arefirst dissolved in THF before mixing and self-assembly (`premixing') bydilution with water, the morphology is found to depend on the mixing ratio ofthe two species, going gradually from vesicles via `bulbed' rods, rings,Y-junctions and finally to spherical micelles as we increase the proportion ofthe sphere-formers. On the other hand, if the two species are first partiallyself-assembled (by partial exchange of the solvent with water) before mixingand further self-assembly (`intermediate mixing'), novel metastable structures,including nanoscopic pouches, emerge. These experimental results arecorroborated by self-consistent field theory calculations (SCFT) whichreproduce the sequence of morphologies seen in the pre-mixing experiments. SCFTalso reveals a clear coupling between polymer composition and aggregatecurvature, with regions of positive and negative curvature being stabilized byan enrichment and depletion of sphere formers respectively. Our studydemonstrates that both thermodynamic and kinetic blending of block copolymersare effective design parameters to control the resulting structures and allowus to access a much richer range of nano-morphologies than is possible withmonomodal block copolymer solutions.

Controlling the micellar morphology of binary PEO-PCL block copolymers in water-THF through controlled blending