The aggregation behavior in solution of polystyrene-b-poly(acrylic acid) (PS-b-PAA) in dioxane-water mixtures has been characterized in the presence of sodium dodecyl sulfate (SDS) using turbidity and transmission electron microscopy studies. These aggregates were found to undergo morphological transformations at lower water contents in the presence of SDS than those normally required for the same transitions in the absence of any additives. It was confirmed from parallel studies carried out with sodium chloride and tridecanoic acid that SDS molecules interact with the copolymer aggregates in two ways. The sulfate and sodium ions screen the electrostatic charge generated by the partially charged PAA chains, while the hydrocarbon tails of the SDS molecules are able to partition into the core of the aggregates. Both of these factors promote architecture changes in the copolymer aggregates by altering the balance between the three forces (,hat have been identified as having a major influence on the morphology of the aggregates (i.e., the stretching of the core chains, the interfacial tension between the core and the solvent, and the intercorona interactions). A phase diagram was constructed, which contains the morphological phase boundaries for the copolymer aggregates in the presence of SDS at different solvent compositions. The effects of the copolymer concentration and the method of solution preparation on the morphological boundaries were also investigated.