In this work, a solution of poly(ethylene oxide)-block-polystyrene (PEO-b-PS) block copolymer in an organic solvent was dispersed in water to form an emulsion in the presence of poly(acrylic acid) (PAA), which upon solvent evaporation produced micelles, and the "emulsion and solvent evaporation" process was studied. It was found that PAA interacted with the PEO corona of the micelles to reduce the curvature, transforming the aggregates from cylinders into vesicles when 1,2-dichloroethane was the solvent. However, when a more volatile solvent, dichloromethane, was used instead, cylindrical micelles were obtained. Even from 1,2-dichloroethane, cylinders were the predominant species when the initial solution concentration was higher (i.e., shorter evaporation process) or when PAA with a much higher molecular weight was used. On the basis of these observations, the interplay between the solvent evaporation rate and the mass transport and chain reorganization at the inteface is discussed. In addition, some intermediate structures were observed, which provided insight into the assembly process.